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Heteronuclear d-d and d-f Ru(II)/M complexes [M = Gd(III),Yb(III), Nd(III), Zn(II) or Mn(II)] of ligands combiningphenanthroline and aminocarboxylate binding sites:combined relaxivity, cell imaging and photophysicalstudiesDOI:10.1039/C9DT00954J

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Citation for published version (APA):Crowston, B., Shipp, J., Chekulaev, D., McKenzie, L., Jones, C., Weinstein, J., Meijer, A., Bryant, H., Natrajan, L.,Woodward, A., & Michael, W. (2019). Heteronuclear d-d and d-f Ru(II)/M complexes [M = Gd(III), Yb(III), Nd(III),Zn(II) or Mn(II)] of ligands combining phenanthroline and aminocarboxylate binding sites: combined relaxivity, cellimaging and photophysical studies. Dalton Transactions. https://doi.org/10.1039/C9DT00954JPublished in:Dalton Transactions

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Download date:14. Sep. 2020

1

Heteronucleard-dandd-fRu(II)/Mcomplexes[M=Gd(III),Yb(III),Nd(III),

Zn(II)orMn(II)]ofligandscombiningphenanthrolineandaminocarboxylate

bindingsites:combinedrelaxivity,cellimagingandphotophysicalstudies.

BethanyJ.Crowston,aJamesD.Shipp,aDimitriChekulaev,aLukeK.McKenzie,a,b

CallumJones,a,bJuliaA.Weinstein,aAnthonyJ.H.Meijer,aHelenE.Bryant,b

LouiseNatrajan,cAdamWoodward,candMichaelD.Warda,d,*

a DepartmentofChemistry,UniversityofSheffield,SheffieldS37HF,UK

b SheffieldInstituteforNucleicAcids(SInFoNiA),DepartmentofOncology,Medical

School,BeechHillRoad,SheffieldS102RX,UK

c DepartmentofChemistry,UniversityofManchester,OxfordRoad,ManchesterM13

9PL,UK

d DepartmentofChemistry,UniversityofWarwick,CoventryCV47AL,UK.Email:

m.d.ward@warwick.ac.uk

2

Abstract

Aligandskeletoncombininga1,10-phenantholine(phen)bindingsiteandoneortwo

heptadentateN3O4aminocarboxylatebindingsites,connectedviaalkynespacerstothe

phenC3orC3/C8positions,hasbeenusedtopreparearangeofheteronuclearRu•Mand

Ru•M2complexeswhichhavebeenevaluatedfortheircellimaging,relaxivity,and

photophysicalproperties.Inallcasesthephenunitisboundtoa{Ru(bipy)2}2+unittogivea

phosphorescent{Ru(bipy)2(phen)}2+luminophore,andthependantaminocarboxylatesites

areoccupiedbyasecondarymetalionMwhichiseitherlanthanide[Gd(III),Nd(III),Yb(III)]

oranotherd-blockion[Zn(II),Mn(II)].WhenM=Gd(III)orMn(II)theseionsprovidethe

complexeswithahighrelaxivityforwater;inthecaseofRu•GdandRu•Gd2the

combinationofhighwaterrelaxivityand3MLCTphosphorescencefromtheRu(II)unit

providethepossibilityoftwodifferenttypesofimagingmodalityinasinglemolecular

probe.InthecaseofRu•MnandRu•Mn2theRu(II)-basedphosphorescenceissubstantially

reducedcomparedtothecontrolcomplexesRu•ZnandRu•Zn2duetothequenchingeffect

oftheMn(II)centres.UltrafasttransientabsorptionspectroscopystudiesonRu•Mn(and

Ru•Znasanon-quenchedcontrol)revealtheoccurrenceoffast(<1ns)PETinRu•Mn,from

theMn(II)iontotheRu(II)-based3MLCTstate,i.e.MnII–(phen•–)–RuIII→MnIII–(phen•–)–RuII;

theresultingMnIII–(phen•–)statedecayswithτ≈5nsandisnon-luminescent.Thisoccursin

conformerswhenanETpathwayisfacilitatedbyaplanar,conjugatedbridgingligand

conformationconnectingthetwounitsacrossthealkynebridgebutdoesnotoccurin

conformerswherethetwounitsareelectronicallydecoupledbyatwistedconformationof

thebridgingligand.Computationalstudies(DFT)onRu•Mnconfirmedboththeoccurrence

ofthePETquenchingpathwayanditsdependenceonmolecularconformation.Inthe

complexesRu•LnandRu•Ln2(Ln=Nd,Yb),sensitisednear-infraredluminescencefrom

Nd(III)orYb(III)isobservedfollowingphotoinducedenergy-transferfromtheRu(II)core,

withRu→Ndenergy-transferbeingfasterthanRu→Ybenergy-transferduetothehigher

densityofenergy-acceptingstatesonNd(III).

3

Introduction

Thecombinationoftransitionmetalandlanthanideionsinasinglemolecular

complex(d/fcomplexes)hasprovidedinterestingopportunitiesarisingfromthe

combinationofmetalcentreswithsubstantiallydifferentstructural,photophysicaland

magneticproperties.1-4Particularpropertiesofd/fcomplexesthathaveattractedinterest

aretheabilitytocombineblue[fromIr(III)]andred[fromEu(III)]luminescencetogenerate

whitelight;2fundamentalstudiesofd→fphotoinducedenergy-transfer(PEnT)includingthe

useofd-blockchromophorestoactasantennaforsensitisationofnear-IRlanthanide

luminescence;3andthecombinationofaluminescentd-blockunitwithahighly

paramagneticlanthanide,usuallyGd(III),forpreparationofdual-modalimagingagents

whichpermitbothluminescence-basedvisualisationofcellsandmagneticresonance

imagingbasedanalysisonalargerlengthscaleusingasingleprobemolecule.4

Wehaverecentlyinvestigatedd/fcomplexesbasedonligandskeletonscombininga

diimine-typeunit[basedon2,2’-bipyridyl(bipy)or1,10-phenanthroline(phen)]coordinated

toad-blockcentretoenableabsorbanceinthevisiblerangeduetometal-to-ligandcharge-

transfertransitions,withapolyaminocarboxylateunitthatprovideshighkineticand

thermodynamicstabilitywhencomplexedtolanthanide(III)ions.5,6TheseIr/Lncomplexes

(Scheme1)demonstratedtheabilitytocombineeffectiveluminescenceimagingofHeLa

andMCF7cells,includingtwo-photonphosphorescencelifetimeimagingoflocalO2

concentration,withhighrelaxivityfortheGd(III)unitsassociatedwiththerigidityofthe

assemblywhichcomesfromtheliganddesign.6However,therewereclearlysolubility

limitationsarisingfromthehydrophobicityofthecentralIr(III)corewhichcarriesacharge

ofonly+1.

Inthispaperwedeveloptheworkusingthisligandsystemintwonewdirections.

FirstlywehaveusedaRu(II)tris-diimineunitasthed-blockluminophore,givenitsexcellent

promiseasacomponentofwater-soluble,non-toxicagentsforopticalmicroscopy,7andits

higherchargecomparedtothecyclometallatedIr(III)centre(+2vs.+1)whichshouldaid

watersolubility.WehavecombinedthiswitharangeoflanthanideionsincludingGd(III)(for

itsrelaxivityproperties)andYb(III)/Nd(III)(forthepossibilityofsensitisednear-IR

luminescence).Secondly,wehaveusedthependantheptadentatepolyaminocarboxylate

unitasaligandforcomplexingadditionaltransitionmetalionsaswellasjustlanthanide(III)

ions–creatingthepossibilitytoformd/daswellasd/fassemblies,inwhichultrafast

4

spectroscopystudieshavebeenusedtoinvestigateintramolecularphotoinducedelectron

transferfromMn(II)totheRu-based3MLCTstateintheRu/Mndyad.

ResultsandDiscussion

(i)Synthesisandcharacterisation.

MononuclearRu(II)complexes.

ThesyntheticstrategyissummarisedinSchemes2–4andissimilartotheapproach

weusedforthepreviously-reportedIr/Lncomplexes6exceptthatthekeySonogashira

couplingstep,connectingthepolyaminocarboxylateandphenanthrolineunits,was

performedwiththephenanthrolineunitalreadycoordinatedtotheRu(II)ion:thistypeof

‘chemistryonthecomplex’approachhasbeenusedbyothers.8Wefoundthatthecoupling

workedbetterifweexchangedthepositionsoftherelevantfunctionalgroupsfromthose

usedpreviously,6suchthatthereactiveBrsubstituentisattachedtotheRu(II)complexcore

asa3-Br-phenor3,8-Br2-phenligand,andtheterminalalkyneispendantfromthe

protectedpolyaminocarboxylateunit.

Thecomplex[Ru(bipy)2(Br-phen)](PF6)2,A(Scheme2),8awaspreparedbyreactionof

3-Br-phen9with[Ru(bipy)2Cl2]•2H2O.Thealkyne-containingcouplingpartnercompoundC

(Scheme3)requiredafive-stepsynthesis,someofthesebeingintheliterature.Atfirst,

commerciallyavailable4-hydroxy-2,6-dimethylpyridinewasbrominatedatthe4-position

usingPBr5.10Thetwomethylgroupswerethenconvertedto–CH2Brgroupsusingradical

brominationwithN-bromosuccinimidetogive4-bromo-2,6-bis(bromomethyl)pyridine.11

Installationofthetert-butylprotectedpendantarmsofthemetalchelatingfragmentsto

givetheknownintermediateB12wasachievedthroughasubstitutionreactionwithtwo

equivalentsofdi-(tert-butyl)-iminodiacetate,andthenastraightforwardSonogashira

reactionwithtrimethylsilylacetylene(TMSA)introducedthetrimethylsilyl-protectedalkyne

groupatthe4-positionofthepyridinering(compoundCSi,Scheme3).Deprotectionofthe

trimethylsilylgrouptorevealthefreealkyneCwascarriedoutinTHFusingtetra-n-

butylammoniumfluoride(TBAF),butasthisdeprotectionwasperformedinsitubefore

immediatefurtherreactionofcompoundC,nocharacterisationdatawererecordedforthis

5

intermediatespecies;attemptstoisolateanalyticallypureCwereunsuccessfulandtended

toaffordtheGlaser-coupleddi-alkynebridgeddimer.

ComponentsAandCwerethencombinedusingaSonogashiracouplingusingCu(I)/

Pd(dppf)Cl2ascatalystinanhydrousDMF/diisopropylamine(5:1,v/v)assolventunder

argon,affordingtheprotectedRu(II)complexRu•Ein50%yield(Scheme2;‘E’indicatesthe

presenceoftheesterprotectinggroupsatthesecondarybindingsite).Satisfactory

characterisationwasprovidedby1HNMRspectroscopyandhigh-resolutionelectrospray

massspectrometry(SI,Figs.S1andS2).Inparticularatlowerchemicalshiftsinthe1HNMR

spectrumtherearesingletpeaksat1.45ppm,3.49ppmand4.00ppmintegratingas36,8

and4protons,respectively,whichrepresentthealiphaticprotonsonthependantarmsof

theprotectedsecondarybindingsiteformedfromthetwoimino-diacetateunits.Finally,

removalofthetert-butylprotectinggroupswaseffectedbyprolongedstirringofRu•Ewith

excesstrifluoroaceticacidinCH2Cl2toaffordRu•L(where‘L’denotesthedeprotected

secondaryligandsite).Again,satisfactorycharacterisationwasprovidedby1HNMR

spectroscopyandahigh-resolutionESmassspectrum(SI,Figs.S3andS4),withthe1HNMR

spectrumconfirmingcompletelossoftheprotonsfromthetBugroups(previouslyat1.45

ppm).A500MHzCOSYspectrumwasusedtoconfirmthe1HNMRassignments.

Asimilarmethodwasusedtopreparethescaffoldforthepotentiallytrinuclear

complexesinwhichtheretwoaretwoidenticalaminocarboxylatebindingsitespendant

fromthephenligandonthecentralRu(II)unit(Scheme4).InthiscasetheRu(II)-based

startingcomplex[Ru(bipy)2(Br2-phen)](PF6)2(complexD)hasBrsubstituentsatboth

positionsC3andC8ofthephenligand.SonogashiracouplingofDwithtwoequivalentsofC,

undersimilarconditionstothosedescribedabovebutwithalongerreactiontime,afforded

complexRu•E2–withtwoester-protectedheptadentatebindingsitesoneithersideofthe

phenligand–in45%yield(SI,FigS5andS6).Thehigher(twofold)symmetrycomparedto

Ru•Eaffordsasimpler1HNMRspectrumwiththealiphaticsignalsarisingfromthe

protectedpolyaminocarboxylatearmsat1.45ppm,3.49ppmand3.99ppm(Fig.S5)having

integralsconsistentwiththeexpected72:16:8ratioofprotons.Removaloftheestergroups

usingthesamemethodasdescribedabove(TFAinCH2Cl2)affordedthedeprotected

complexligandRu•L2withtwopendantbindingsites.The1HNMRspectrumofthis

compoundinD2O(SI,Fig.S7)wasnoticeablybroaderandlesswelldefinedthanthe

protectedformRu•E2possiblyduetoacombinationofthesizeofthecomplex,theviscosity

6

ofthesolvent,andstronghydrogen-bondinginteractionsbetweensoluteandsolventwhich

resultsinslowtumblinginsolution.Thenumberofsignalsandtheirrelativeintegralsare

correct,andahigh-resolutionESmassspectrum(SI,Fig,S8)confirmsformulationofthe

complex.

HeteronuclearRu•LnandRu•Ln2complexes(Ln=Gd,Nd,Yb).

TherearetwoparticularreasonsforstudyingRu(II)/Ln(III)(‘Ln’=ageneric

lanthanide)complexesbasedonthisligandskeleton.ThefirstisthatincorporationofGd(III)

ionsallowspreparationofpotentialdual-modalimagingagentsbasedonthecombination

ofluminescenceplusmagneticresonanceimagingwiththesameprobe.4,6Thesecondis

thatincorporationofthenear-IRemittinglanthanideionsNd(III)andYb(III)allowsthestudy

ofsensitisedemissionarisingfromd→fPEnT.3Inbothcasesthefullyconjugated,

unsaturatedstructureofthebridgingligandfacilitatesthedesireduse;thestructuralrigidity

willhelptominimisetherotationalcorrelationtimeoftheGd(III)centreswhichcontributes

tohighrelaxivity,13andtheelectronicconjugatedpathwaydirectlyconnectingbothRu(II)

andLn(III)centreswillfacilitateDexter-typePEnTwhichrequiresthrough-bondelectronic

coupling.6Thevaryingsizesofthelanthanideionsusedmeanthattheheptadentateligand

willbesupplementedbymostlikely1or2watermoleculesdependingonionicradius.

DinuclearRu•Gdwaspreparedin84%yieldsimplybystirring1.1equivalentsof

GdCl3•6H2OwithRu•Linwater(pH5–6)for18h.Size-exclusionchromatographyon

SephadexLH-20inMeOH,followedbyanionmetathesisusingDowex1x2chlorideresinto

ensurethatallhexafluorophosphateanions(fromthestartingRu(II)complex)werereplaced

bychloride,affordedpureRu•Gdasitsmono-chloridesalt.TrinuclearRu•Gd2wasprepared

similarlyin69%yieldfromRu•L2and2.6equivalentsofGdCl3•6H2Oinaqueoussolution.

ThecomplexRu•Gd2isneutralsonoanion-exchangestepwasnecessary,butwaslikewise

purifiedusingSephadexLH-20elutingwithMeOH.Giventhatroutinecharacterisationby1H

NMRspectroscopywasnotfeasibleforthesecomplexesduetoextensiveparamagnetic

line-broadeningbytheGd(III)ions,werelyonacombinationofchromatographicpurityand

high-resolutionmassspectra(SI,Fig.S9andS10),whichforbothcomplexesgiveexcellent

agreementwithexpectedvaluesaswellasthecorrectisotopicpatterns.

TheheteronuclearcomplexesRu•Nd,Ru•Nd2,Ru•YbandRu•Yb2weresynthesised

inhighyieldsinthesamemannerastheanalogousRu/Gdcomplexes,byreactionofthe

7

starting‘complexligands’Ru•LandRu•L2withexcess(1.6equivalentsor2.8equivalents,

respectively)oftheappropriatelanthanidetriflatesaltinwateratpH5–6.Thedinuclear

complexesRu•NdandRu•Ybwereanion-exchangedtothechloridesaltsusingDowex®1x2

chlorideion-exchangeresinandfinallypurifiedbysize-exclusionchromatographyon

Sephadex®G-15inwater.ThetrinuclearcomplexesRu•Nd2andRu•Yb2areneutralso

requirednoion-exchange.AswiththeRu/Gdcomplexes,highresolutionESmass

spectrometryoftheseparamagneticcomplexesconfirmedtheirformulation(SI,FigsS11–

S14).

HeteronuclearRu•MandRu•M2complexes(M=Mn,Zn).

HavingusedGd(III)ionstoprepareRu•GdandRu•Gd2asdescribedabove,wewere

interestedtotryotherhighlyparamagneticionsinthesesitesforpossiblealternativedual-

modalimagingagents.Recently,interestinutilisinghigh-spinMn(II)ionsasalternative

paramagneticcentrestoGd(III)inT1-weightedMRIcontrastagentshasgrown,14,15dueto

increasingconcernfortheinvivotoxicityoffreeGd(III)ions.Newligandstructuresare

beginningtobeexploredtoincorporateMn(II)intoprobesusedforMRimagingpurposes.14

However,examplesofdual-modalluminescence/MRIprobescontainingMn(II)asthe

paramagneticcentresarerare,withonlyonerecentexampleofMnO2nanosheets

combinedwith[Ru(bipy)3](PF6)2unitsbeingreported.15Accordinglyourligandskeletons

werealsousedtoprepareRu(II)/Mn(II)complexestoexaminetheirluminescenceand

magneticrelaxivityproperties;theanalogousRu(II)/Zn(II)complexeswerealsopreparedfor

controlexperiments.

DinuclearcomplexesRu•MnandRu•ZnwerepreparedbyreactionofRu•Lwith1.3

–1.6equivalentsoftheappropriateM(II)chloridehydrate(M=Mn,Zn)for18hinwaterat

pH5–6.Theexcessmetalsaltwasremovedbysize-exclusionchromatographyon

Sephadex®G-15inwatertoproducethepure,neutralcompoundsingoodyields(80-95%).

AsZn(II)isdiamagnetic,thesuccessfulsynthesisandisolationofpureRu•Znwasconfirmed

by1HNMRspectroscopy(SI,Fig.S15).Thesignalsinthearomaticregionofthe1HNMR

spectrum(400MHz,D2O)integratetotheexpectedtwenty-fiveprotons,althoughthereare

foursingletsatδ=7.52ppm,7.54ppm,8.76ppmand8.79ppmthateachintegratetohalf

aproton.Atwo-dimensional1H-1HNMRcorrelationspectrumconfirmedthatthesepeaks

correspondtoeitherapyridylH3/H5pyridineproton(δ=7.52ppmand7.54ppm)andthe

8

H2phenanthrolineproton(δ=8.76ppmand8.79ppm).Thesehalf-integralvaluessuggest

thepresenceoftwoisomersinsolution,whichwerenotpresentinthe1HNMRspectrum

(d6-DMSO,500MHz)ofthestartingcomplexRu•L.Astheprotonsinquestionareonlysplit

intoinequivalent‘halves’inRu•Zn,itwouldsuggestthatthetwoisomersarebroughtabout

bythechelationoftheZn(II)ionatthepolyaminocarboxylatebindingsitetogeneratea

chiralcentre,andarethereforediastereoisomersarisingfromthepresenceoftwochiral

centresclosetogether–theotherchiralcentrebeingofcoursetheRu(II)tris-chelateunit.

Thissuggestionissupportedbytheappearanceofamultipletatδ=3.34-3.52ppminthe1H

NMRspectrumforRu•Zn,whichintegratesaseightprotons,andrepresentsthefourCH2

groupsadjacenttothecarboxylategroupsofthesecondarymetalchelatesite.Inthe1H

NMRspectrumofRu•Lthese8protonsareequivalent,occurringasasingletatδ=3.94

ppm.However,oncetheZn(II)ionisboundinRu•Zn,theybecomeinequivalentandappear

asamultipletduetothepresenceofthediastereoisomers.Theremainingsignalinthe

aliphaticregionofthe1HNMRspectrumisfromthetwoCH2groupsattachedtoC2andC6of

thepyridinering(δ=4.15ppm).Wecouldnotobtainmeaningful1HNMRspectrafor

Ru•Mn,butbothcomplexeswerecharacterisedbyhigh-resolutionESmassspectrometry

(SI,Figs.S16andS17).WenotethatsevencoordinationisknownforinsomeMn(II)

complexes,andissupportedbythecalculations(seelater).16Therearealsoafewexamples

ofZn(II)complexeswithseven-foldcoordinationdespitethesmallerionicradiusofZn(II):

thesegenerallyhavetwosmallbidentatenitrateligands.17

TrinuclearRu•Zn2andRu•Mn2werepreparedsimilarlyfromRu•L2andexcess(2.4–

4.8equivalents)oftheappropriateM(II)chloridehydrate(M=Mn,Zn),andwereobtained

ingoodyieldsof67–82%.ThesearedianioniccomplexeswithNa+asthecounter-cation.

Ru•Zn2couldbecharacterisedby1HNMRspectroscopy(SI,Fig.S18)andgivesthecorrect

numberofsignalsinthearomaticandaliphaticregionswhichintegratetotherequired

total:thespectrumisnoticeablybroaderthanthatofRu•Zn,likelyduetoslowertumbling

insolutionbecauseofitssizeandtheviscosityofD2O(similartothedifferencethatwe

observedbetweenRu•LandRu•L2).AswithRu•Znthereisevidencethatthepresenceof

diastereoisomersarisingfromthepresenceofthreechiralcentressplitssomesignalsinto

severalcomponents.Forexample,thesingletatδ=7.69ppmforthefourpyridylH3/H5

protonsinRu•L2issplitintotwobroadsingletsbetween7.50and7.70ppminthespectrum

9

ofRu•Zn2.HighresolutionESmassspectraconfirmedtheformulationsofRu•Zn2and

Ru•Mn2(Figs.S19,S20).

(ii)Photophysicalproperties.

MononuclearRu(II)complexes.

AllfourmononuclearcomplexesRu•E,Ru•L,Ru•E2andRu•L2werecharacterisedby

UV/Visandluminescencespectroscopy(Table1,Fig.1andS21).Themonosubstituted

complexesRu•EandRu•Lbothshow,inadditiontotheusualligand-centredabsorptionsin

theUVregion,1MLCTabsorptionsspanningthe375–550nmregionwithamaximumat

around440nmineachcase.TheseareassignedasRu→bipyandRu→phen1MLCT

transitionsbycomparisonwithpublishedspectra:18wemightexpecttheRu→phen

transitiontobeatlowerenergygiventhealkynesubstituentconjugatedwiththephencore

whichwillreducetheenergyoftheLUMO,butanysucheffectisnotclearlyresolvedin

thesespectra.However,forRu•E2andRu•L2theabsorptionspectradoclearlyshowthis

effect(Fig.S9):thesecondalkynesubstituentonthephenligandresultsinaRu→phen1MLCTtransitionthatisclearlyapparentasalow-energyshoulderatca.480nmwiththe

moreintense1MLCTRu→bipytransition(astherearetwobipyligands)remainingatca.440

nm.

Theluminescencespectrainfluidandfrozensolution,atRTand77Krespectively

(Fig.1),likewisereflectthegeneralbehaviourof[Ru(bipy)3]2+-typecores18where

modificationbythealkynesubstituentsslightlyreducesthe3MLCTexcitedstateenergies.19

ForRu•EandRu•Lthebroad,featureless3MLCTemissionbandoccursatca.650nm,

slightlylowerinenergythanwhathasbeenobservedfor[Ru(bipy)2(phen)]2+bearingno

alkynesubstituents.8aAt77K(frozenEtOH/MeOHglass)theusualrigidochromismresultsin

ablue-shiftofthemainemissionmaximumto611nm(hence,the3MLCTenergyis16,400

cm-1,measuredfromthe0-0transitionenergy)andresultsintheappearanceofclearfine-

structurewithtwolow-energyshouldersontheemissionprofilearisingfromvibronic

effects.ThepresenceoftheadditionalalkynesubstituentinRu•E2andRu•L2resultsinan

additionalred-shiftofboththesolutionluminescencemaximumtoca.690nm.The77K

emissionspectrum(frozenEtOH/MeOHglass)ofRu•E2islikewisered-shiftedto645nm

10

comparedtoRu•EandRu•L.Ru•L2wasnotsufficientlysolubleinEtOH/MeOHtopermita

77KspectrumbutitisclearfromcomparisonofRu•EandRu•Lthatthepresenceor

absenceoftheestergroupshasnosignificanteffectontheluminescenceenergy.Thisgives

a3MLCTexcited-stateenergyof15,500cm-1forbothRu•E2andRu•L2.Luminescence

lifetimesinair-equilibratedsolutionatRTforallfourcomplexesareintheregionof100–

300ns;thesebecomelonger(µstimescale)at77K(seeTable1).

HeteronuclearRu•MandRu•M2complexes(M=Gd,Nd,Yb).

UV/Visabsorptionspectrainwater(Table2)revealedthatcoordinationoftheGd(III)

centrehadlittleeffectonthemainspectralfeatureswhichareofcourseassociatedwiththe

Ru(II)tris-diiminecore.18ThustheabsorptionspectrumofRu•GdissimilartothatofRu•L.

However,wecanseethatforRu•Gd2thelowestenergy1MLCTabsorptionfeature–a

shoulderassociatedwiththeRu→phentransition–isslightlyred-shiftedbyabout10nm

comparedtoRu•L2.Thiscanbeascribedtotheelectroniceffectofa3+cationcoordinated

toeachofthetwopyridinegroupspendantfromthephenligand,whichwillreducethe

LUMOinenergyandcausered-shiftingoftheassociatedRu→phenabsorption.Excitation

intothe1MLCTabsorptionprofileaffordedthecharacteristicbroad,featureless(influid

solution)3MLCTluminescencebandineachcase,at664nmand700nmforRu•Gdand

Ru•Gd2,respectively(Fig.2).Theseareslightlyred-shiftedfromtheemissionmaximafor

Ru•LandRu•L2,sincecoordinationofthepyridylgroupspendantfromthephenligandto

the3+ionsreducestheLUMOenergyslightly,whichisalsowhyared-shiftwasobservedin

theabsorptionspectra.Photophysicaldataforthesecomplexes,includingluminescence

lifetimesandquantumyields,areincludedinTable2.

TheUV/VisabsorptionspectrafortheRu/YbandRu/Ndcomplexesinwaterare

identicalwithinexperimentalerrortothoseoftheanalogousRu/Gdcomplexesdescribed

earlier,astheelectroniceffectsoftheperipheralGd(III),Nd(III)andYb(III)ionsonthe

absorptionfeaturesoftheRu(II)tris-diiminecoreareessentiallyidenticalandthusrequire

nofurtherdiscussion.However,theeffectsofthedifferentlanthanideionsonthe

luminescencearesubstantialandaremosteasilydiscussedintermsofcomparisonwiththe

Ru/Gdcomplexes,asinthesecomplexesGd(III)isnon-luminescent:thelowestexcitedstate

fortheGd(III)ion(6P7/2≈32,000cm-1)isfartoohighinenergytobedirectlypopulatedby

Ru→GdPEnT.

11

Fig.2showstheemissionspectrainthevisibleregionofallsixRu•LnandRu•Ln2

complexes(Ln=Gd,Nd,Yb)inwater,recordedonsamplespreparedtohavethesame

opticaldensityattheexcitationwavelengthof430nm,suchthatcomparisonsofemission

intensitiesareameaningfulindicationofquantumyieldvariations.Itisimmediatelyclear

that(i)theemissionmaximaforallthreeRu•Ln2complexesisatlongerwavelength(700

nm)thantheemissionmaximaforallthreeRu•Lncomplexes(662–664nm),forreasons

discussedearlier,and(ii)theintensityofRu(II)-basedemissionwithineachsetofthree

complexesdecreasesintheorderGd>Yb>Nd.Thus,comparedtoRu•Gd,thequenching

arisingfromthepresenceofYb(III)andthenNd(III)is10%and45%,respectively:and

comparedtoRu•Gd2,thequenchingarisingfromthepresenceofYb(III)andthenNd(III)is

45%and90%,respectively(Table3).

ThisquenchingofRu(II)-basedemissionbyYb(III)andNd(III)isaconsequenceof

PEnTfromtheRu(II)-based3MLCTstatetolower-lyingf-fexcitedstatesoftherelevant

Ln(III)ions.Thedifferentdegreesofquenching,arisingfromdifferentextentsofRu→Ln

PEnT,canbereadilyunderstoodintermsofthespectroscopicoverlapbetweendonorand

acceptorstates.1a,20Yb(III)hasasinglef-fexcitedstateatca.10,200cm-1(absorptionat980

nm)whichoverlapsonlywiththelow-energytailoftheRu(II)-basedemissionprofilethat

hasvanishinglysmallintensityat980nm.IncontrastNd(III)hasalargenumberofclosely-

spacedf-fexcitedstatesbetween10,000cm-1and15,000cm-1,intheregioncoveredbythe

Ru(II)-basedemissionspectrum,sodonor/acceptoroverlapwillbemuchbetter.Indeed,it

isgenerallytruethatforexcitedstatesofdonorsinthevisibleregionofthespectrum,

Nd(III)isafarbetterenergyacceptorthanYb(III)forthisreason,1a,20andweseethisinboth

seriesofcomplexesRu•LnandRu•Ln2.

Time-resolvedmeasurementsontheRu(II)-basedluminescenceallowstheRu→Ln

PEnTratestobequantified.ForRu•GdtheRu(II)-basedluminescenceinair-equilibrated

wateratRTis350ns;inRu•YbandRu•Ndtheluminescencedecayisdominatedbyshorter-

livedcomponentswithτ=73nsand22nsrespectively(Table3),confirmingthegreater

abilityoftheNd(III)iontoactasaquencheroftheRu(II)-basedexcitedstate.Averysmall

contributiontotheluminescencedecayfromalong-liveddecaycomponentwithτ≈300ns

(<5%)isascribedtoatraceoffreeRu•L.

12

kPEnT=1/τq–1/τu (2)

Usingequation2[whereτuisthe‘unquenched’lifetimeofRu•Gd,andτqisthepartially

quenchedlifetimeoftheRu•Lncomplexes(Ln=Yb,Nd)]theRu→YbandRu→Ndenergy-

transferratesof1.1x107s-1and4.2x107s-1,respectively,wereestimated.Thesevalues

arebroadlycomparabletowhatweobservedintheIr/Lncomplexesbasedonthesame

ligandskeleton,6aandtheserelativelyhighPEnTratesareaconsequenceofthefully

conjugatedpathwayconnectingthetwometalcomplexcomponentswithineachmolecule.

ThedecayoftheRu(II)-basedemissioninRu•Gd2showedtwocomponents:alonger

lifetimeofτ1=402ns(20%oftotal)andadominantshortercomponentofτ2=164ns(80%

oftotalemissionintensity).Wetentativelyascribedthepresenceofasecondlonger-lived

componenttothepresenceofdifferentconformersofthecomplexarisingfromthe

presenceofmultiplediastereoisomers(seesectionsonthe1HNMRspectraofthe

analogousRu/Zncomplexes,andconformationalflexibilityofdinuclearcomplexesstudied

computationally).InRu•Yb2andRu•Nd2theluminescencedecayprofilesaredominatedby

short-livedcomponentswithτ=88nsand18nsforRu•Yb2andRu•Nd2respectively,with

(again)asmallamountofalong-livedcomponentlikelycorrespondingtotracesoffree

Ru•L2.Applicationofeq.2(takingτu=164ns,thedominantcomponentofemissionfrom

Ru•Gd2)yieldsenergy-transferratesof5.3x106s-1(forRu→YbPEnT)and4.9x107s-1(for

Ru→NdPEnT),againconfirmingthatNd(III)isabetterenergy-acceptorthanYb(III)inthese

complexesduetoitshigherdensityofexcitedstatesintherelevantspectralregion.1a,20

FinalproofthatRu→LnPEnThasoccurredintheYb(III)andNd(III)complexesisshownby

theappearanceofsensitisedLn(III)-basedluminescencefollowingexcitationintotheRu(II)-

based1MLCTabsorptionbandofthecomplexesinD2O(thedeuteratedsolventisusedto

minimisesolvent-basedquenchingofthelowenergylanthanideluminescence).21Fig.3

showsthespectraofRu•Yb2andRu•Nd2;thoseofRu•YbandRu•Ndaresimilar.Both

Yb(III)-containingcomplexesdisplayacharacteristicYb(III)-basedemissionfeaturecentred

at980nmarisingfromthe2F5/2→2F7/2transition.Time-resolvedmeasurementsafforded

Yb(III)-basedluminescencelifetimesof13µsforRu•Yband11µsforRu•Yb2(Table3).

LifetimesinthisregionaretypicalofYb(III)-basedluminescenceinfluidsolutionwherethe

effectofthesolventisminimisedbyencapsulationofthemetalioninapolydentateligand,

13

and/orbydeuteriationofthesolvent(ashere).22ThetwoNd(III)-containingcomplexes

showluminescencebandsat1060nmand1380nm,arisingfromthe4F3/2→4IJtransitions(J

=11/2and13/2),respectively.Time-resolvedmeasurementsonthe1060nmsignal

affordedNd(III)-basedemissionlifetimesof0.8µsforRu•Ndand0.7µsforRu•Nd2.Again,

thesearetypicalvaluesforNd(III)-basedemissioninfluidsolutionwhentherearenoOH

oscillatorsinthesolvent,22withthemuchshorterluminescencefromNd(III)centres

comparedtoYb(III)arisingfromthelowerenergyassociatedwithluminescencewhichis

morereadilyquenchedbymolecular(orsolvent)vibrations.Finally,excitationspectra–

monitoringtheLn(III)-basedemissionintensityasafunctionofexcitationwavelength–

revealedareasofabsorbancebetween400and500nmassociatedwiththeRu(II)-based1MLCTtransitions,confirmingtheoccurrenceofRu→LnPEnTinallcases(seeSI,Fig.S22for

examples).

HeteronuclearRu•MandRu•M2complexes(M=Mn,Zn).

UV/VisabsorptionspectraforthesetoffourRu/MnandRu/Zncomplexes(Table2)

followthesamepatternthatwesawwiththeRu/Lncomplexes,i.e.theabsorptionspectra

areessentiallythesameasthecomplexesRu•GdandRu•Gd2withnosignificant

contributionsfromtheMn(II)orZn(II)ions,aswouldbeexpectedgiventheirhigh-spind5

andd10electronicconfigurations.Toconfirmthatthelowluminescenceintensityfromthe

Ru/MncomplexesisspecificallyassociatedwiththepresenceoftheMn(II)ions,we

comparedtheluminescencepropertiesoftheRu/MncomplexestotheRu/Znanalogues

Ru•ZnandRu•Zn2(seeFig.5).ThesubstantialadditionalquenchingcausedbyMn(II)ions

overZn(II)ions–asshownbyreductioninemissionintensitybyapproximately80%–

confirmstheroleofMn(II)inthequenching.

Thisquenchingcouldhavetwopossibleorigins:(i)photoinducedelectron-transfer

(PET)fromMn(II)totheRu(III)centrethatisphoto-generatedinthe[Ru3+–phen•–]3MLCT

state;23or(ii)photoinducedenergy-transferfromthe3MLCTstatetoMn(II),generatingad-

dexcitedstateofMn(II)thatcannotbepopulatedbydirectabsorptionfromtheground

stateasitisspin-forbidden,butcouldbegeneratedbyenergy-transferfromtheRu-based3MLCTstateactingasasensitiser.24AssembliesbasedonRu(II)chromophoresconnectedto

mononuclearorpolynuclearMn(II)unitshavebeenextensivelystudiedbecauseoftheir

relevancetothePETpropertiesofphotosystemIIingreenplants.Indeed,Hammarström,

14

Åkermarkandco-workershavedemonstratedthatMn(II)→Ru(III)PEToccursinaseriesof

Ru(III)/Mn(II)dyadsinwhichtheRu(III)centrehasbeengeneratedbyphoto-oxidationofa

Ru(II)unit,providedthemetalcentresareclosetogether.23a-c

Time-resolvedluminescencemeasurementsonRu•ZnandRu•Zn2(inair-

equilibratedaqueoussolution)revealed3MLCTemissionlifetimesthataresimilartothose

ofRu•GdandRu•Gd2.ForRu•Znasingle-exponentialluminescencedecayof329nswas

observed;forRu•Zn2thedecayprofilefittedtotwocomponentswithτ1=301ns(55%)and

τ2=117ns(45%),verysimilartowhatwealsoobservedforRu•Gd2.Wethereforepropose

–forthesamereasonassuggestedearlier–thatthetwolifetimesarisefromamixtureof

diastereoisomerswithdifferentconformations.Wenotethatinthiscaseindividuallifetimes

maynothavespecificphysicalmeaning,asitisadistributionoflifetimes(multiexponential

decay)whichhasbeenfittedsatisfactorilywithatwo-exponentialmodel.Incontrastthe

partialquenchinginRu•MnandRu•Mn2leadstoashortercomponentdominatingthe3MLCTemissiondecayprofiles,withlifetimesof91nsforRu•Mnand21nsforRu•Mn2.In

bothcasessmallcontributionsfromalonger-livedcomponentwerealsopresent,consistent

withtracesoffreeRu•LandRu•L2beingpresentduetolossofMn(II)ionsfromthebinding

sitesofRu•MnandRu•Mn2inthecompetitivesolvent.However,thedominantshort-lived

componentsindicatequenchingoftheRu(II)excitedstatebytheMn(II)ions:theseemission

lifetimesdidnotchangesignificantlyoverarangeofconcentrationsfrom4µMto90µM,

i.e.thequenchingprocessesinRu•MnandRu•Mn2areintramolecular.

Thedecreasedluminescencelifetimes(tensofns)arenotthewholestoryhowever,

sincethelimitationofourluminescencelifetimespectrometer(ca.1nstimeresolution)

meansthatanyfasterdecayprocessesassociatedwithe.g.rapidPETarenotdetectableon

thisinstrument.Toinvestigatewhetheranyultrafastprocesseswereoccurringonthe

timescalefasterthan1ns,theexcitedstatedynamicbehaviourofRu•ZnandRu•Mnwas

investigatedusingfemtosecondtransientabsorptionspectroscopy(TA).Here,Ru•Znacts

asacontrolsinceanyinter-metalPETorPEnTprocessesthatoccurinRu•Mncannotoccur

inRu•Zn.Excitation(λexc=400nm,40fspulse,3mW)ofasolutionofeitherRu•Znor

Ru•Mninaeratedwater,followedbymeasurementoftheabsorptionspectraataseriesof

timedelaysupto5ns,producedsimilarlyshapeddifferentialTAspectraforbothcomplexes

(Fig.5a,6a).Therearenegativesignals(bleaches)oftheMLCTtransitionsat442/480nm,

andpositivesignalsthathavemaximaat367nmand456nmpresentinbothspectra,as

15

wellasabroadabsorptionintherange500-700nmwithamaximumat620nm.These

transientspectralfeaturesapproximatelyresemblethoseofthe[phen]•–radicalanionin

otherreducedmetalcomplexessuchas[ReICl(CO)3(phen•–)]–.25Thusthetransient

absorptionspectraareinagreementwiththeinitialpopulationofanMLCTstateinboth

cases.

Analysisofthedynamicsofthetransientsignalsforeachoftheheteronuclear

complexesrevealsdifferentdecaykineticsforRu•ZnandRu•Mn.Thedynamicbehaviourof

Ru•Zn(Fig.5b)isdescribedbytwolifetimecomponents;along-livedcomponent(bluetrace

inthefigure)thatdoesnotcompletelydecayoverthepump-probedelayperiod,anda

muchshorter-livedcomponent(redtrace)withalifetimeof6ps.Decay-associatedspectra

forthedifferentlifetimecomponentsareinSI(Fig.S23).Theshorter-livedcomponentcan

beascribedtofastvibrationalcoolingwithinthecomplex,whereasthelonger-lived

componentcanbeascribedtotheRu-based3MLCTstate,forwhichanemissionlifetimewas

measuredas329nsinaeratedwater(seeearlier).Anaccuratelifetimeforthe3MLCTstate

couldnotbedeterminedbyfemtosecondTAasitismuchlongerthanthemaximum

possibletimedelayoftheexperiment.

ThedynamicbehaviourofthetransientabsorptionspectraforRu•Mnismore

complicatedthanforRu•Zn(Fig.6b),andrequiresthreelifetimecomponentstofitthe

decayprofilesatisfactorily.Ashort-livedcomponentwithalifetimeof2ps(greentrace)is

ascribedtofastvibrationalcoolingwithinthecomplex.Afurtherdecayprocesswitha

lifetimeof584ps(redtrace)issynchronouswiththegrow-inforasecondstatewhichthen

decaysmoreslowly,withanestimatedlifetimeof4.7ns(bluetrace).Astheprocesseson

thesetimescalesarenotpresentinRu•Zn,wesuggestthattheyareaconsequenceoffast

processesoccurringbetweenmetalcentresintheexcitedstateofRu•Mn,withone

componentdecayingatthesamerateastheothergrows,inaPETorPEnTprocess.Again,

decay-associatedspectraforthedifferentlifetimecomponentsareinSI(Fig.S23),andthe

evolution-associatedspectra(experimentalTAatdifferenttimedelays)forbothRu•Znand

Ru•MnareinFig.S24.

Ifthe584psdecayprocesswerePEnTfromtheRu(II)-based3MLCTstatetothe

Mn(II)centre,wewouldseedecayoftheintense(phen•–)transientsignalwithτ=584psas

the3MLCTstateconvertedtoa[Mn(II)]*state.However,thisisclearlynotthecase.There

isasmallchangeinshapeofthe(phen•–)transientsignalonthistimescale,butitonly

16

decaysonthelongertimescaleofτ=4.7ns.Thisisconsistentwiththe584psprocessbeing

Mn(II)→Ru(III)PETinwhichthebridging(phen•–)ispreserved,i.e.theprocesscanbe

writtenasMnII–(phen•–)–RuIII→MnIII–(phen•–)–RuII,generatinganewandlower-energy

MnIII/(phen•–)MLCTstatewhichthendecayswithτ=4.7ns(andisnotvisibleby

luminescencespectroscopy).

TheoccurrenceofMn(II)→Ru(III)PETintotheRu-based3MLCTstateisinagreement

withpreviousreportsofthebehaviourof[Ru(bipy)3]2+/Mn(II)dyadsfollowing

photochemicaloxidationofRu(II)toRu(III),23a-cwhichsimplyrequiresthattheMn(II)/Mn(III)

redoxpotentialislesspositivethantheRu(II)/Ru(III)redoxpotential.Attemptsto

determinetheMn(II)/Mn(III)redoxpotentialofRu•Mnbycyclicvoltammetryinwaterwere

unsuccessfulpossiblybecausethelargeexcessofelectrolyteused(NaCl)resultedinthe

Mn(II)ionbeingstrippedoutofthecomplex.Similarissueshaveoccasionallyprevented

detectionofMn(II)/Mn(III)couplesinotherRu/Mncomplexesrecordedincompetitive

media.23cRu•MnisnotsufficientlysolubleinpolarorganicsolventssuchasMeCNorDMF

toallowelectrochemicalmeasurementstobemade.Howeverwenotethat(i)theharder

N/O-donoranionicliganddonorsetaroundtheMn(II)ionsinRu•MnandRu•Mn2,

comparedtotheall-nitrogendonorsetsusedintheHammarström/Åkermarkcomplexes,

willreducetheMn(II)/Mn(III)redoxpotentialwhichwillfacilitatethePETprocess;and(ii)

thecomputationalstudies(nextsection)confirmthattheMn(II)centreoxidisesbeforethe

Ru(II)centre,asrequired.

AssumingthatthelifetimeofthePETprocessinRu•Mnis584ps,therateofETcan

beestimatedasket=1.7x109s-1.ThisPETrateismuchfasterthanwaspreviouslyobserved

byHammarström,Åkermarkandco-workerswhoreportedPETratesintherangeket=2x

105–2x106s-1;23a-cindeeditisfasterthantheradiativedecayrateoftheRu(II)

chromophore.Thus,theMn(II)→Ru(III)processoccursrapidlyintheMnII–(phen•–)–RuIII

excitedstate,anddoesnotrequirephoto-oxidationofthisstatetogeneratealong-lived

MnII–(phen)–RuIIIspeciesbeforetheMn(II)→Ru(III)ETcanoccur.ThishighETratecanbe

ascribedtothepresenceofafavourablepathwaythroughtheconjugatedbridgingligandin

Ru•Mn,whichprovidesa“conductive”bridgefortheETprocesstooccur,incontrasttothe

saturatedbridgingligandsdescribedpreviously.23a-c

17

GiventhatthisPETprocessdetectedbyTAspectroscopyisfast(sub-nanosecond

timescale)thefinalquestionarisesastowhyitdoesnotalwaysoccur,asshownbythe

observationofsignificantresidualluminescence(seeFig.4;τ=91nsforRu•Mnand21ns

forRu•Mn2).Thiscanbeascribedtothepresenceofamixtureofconformers,asimpliedby

someoftheNMRstudies(Ru/Zncomplexes)andotherluminescencemeasurements(Ru/Gd

complexes.Rotationofthepyridylgroupanditspendantaminocarboxylateunitsaboutthe

C-CsinglebondatthepyridylC4positioncouldleadthepyridineringtoadopta

conformationperpendiculartothephenunit,whichwouldelectronicallydecouplethe

Mn(II)ionfromthe{Ru(bipy)2(phen)}2+core.Inthisarrangement,through-bondPETwould

bemuchslower.Ifweassumethistobethecase,wearriveatMn(II)→[Ru(III)]*PETrate

constantskPET(usingeq.2)ofca.8x106s-1inRu•Mnand4x107s-1inRu•Mn2forthose

decoupledconformersinwhichPETisslow,whichisstillfastcomparedtothetimescaleof

Mn(II)→Ru(III)ETacrosssaturatedspacersinseveraldyads.23a-cToinvestigatethisfurther,

computationalstudieswereperformedonRu•Mnusingdensityfunctionaltheory.

ComputationalstudiesontheRu•Mndyad.

Allcalculationswereperformedusingtheproceduresoutlinedintheexperimental

detailssection.ThestructureofthelowestsextetstateofRu•MnisgiveninFig.7(a).Fora

Mn(II)ioninthisN/O-donorweak-fieldcoordinationenvironmentweexpectahigh-spin

configuration,whichiswhatthespindensityshows[Fig.7(b)].TheMn(II)ionisseven

coordinate16withanapproximatelypentagonalbipyramidalcoordinationgeometry.16dThe

threeN-donoratomsare2.5ÅfromMn(II),whereasthefourMn–Odistancesareshorterat

ca.2.2Å,reflectingthepartialnegativechargesonthecarboxylateOatomsThepyridineN-

donorisapproximatelyco-planarwithtwoofthecarboxylateO-donors:oneoftheamine

donorsisslightlybelowthisplanewiththeotheraminedonorasimilardistanceaboveit.

However,toafirstapproximation,theMn(II)ionispentagonalbipyramidal.

Giventhepossibilityforconformationalflexibilitywhichmightaffecttheelectronic

couplingbetweenthetwometalcomplexunits,asdiscussedabove,welookedatthe

barriertorotationoftheMn(II)unitwithrespecttotheRu(II)core,aroundtheC-Csingle

bondbetweenthealkynelinkerandthependantpyridylring.Calculationsonthisrotation

showthatanarrangementwiththependantpyridineunitperpendiculartothe

phenanthrolineunitisnotalocalminimum.However,theenergyofthis‘perpendicular’

18

arrangementisonly4.6kJmol-1(or1.8kT)abovetheenergyoftheco-planarorientation

[Fig.7(a)].ThissmallenergydifferencemeansthatrotationaroundtheC–Cbondisquite

facilesuchthatalargepartofthetorsionalspacewillbesampledinsolutionatRT.This

includestorsionalconformationsinwhichthepyridyl[coordinatedtoMn(II)]andphen

[coordinatedtoRu(II)]unitsareorthogonaltoeachotherandsubstantiallyelectronically

decoupled,inagreementwithourexplanationofthetwoobservedPETratesforRu•Mn.

TheoverlayinFig.8(a)showsthatrotationaroundthisbondhaslittlestructuraleffecton

theRu(II)moiety.

TD-DFTcalculationsonthestructurewithaplanarorientationofthebridgingligand

[Fig.7(a)]showthatthereareonlyasmallnumberofstrongelectronictransitions(Fig.9).

Inspectionofthemajorcomponentsofthesetransitions(seecomputationalSIdocument)

showsthatallstrongtransitionsatwavelengthslongerthan450nmareessentially

Ru→phenMLCTstates,inagreementwithawealthofprecedent,18generatingalocal

Ru(III)/phen•–moietyinatripletexcitedstate.Dependingontheinteractionbetweenthis

complexunitinits3MLCTexcitedstate,andthesextetstateoftheMn(II)ion,overalleither

aquartetoranoctetstatecanarisefollowingphoto-excitationoftheRu(II)centre.Our

calculationsshowthatthequartetstateisthelowerofthetwopossibilities,indicatingweak

antiferromagneticcouplingbetweentheRu(III)/phen•–(triplet)andMn(II)(sextet)moieties.

Ifthisquartetstateisoptimized,thentheresultingelectrondistributionwillreflectthe

relaxationbyPETfromMn(II)totheshort-livedRu(III)centre,andthestructuredepictedin

Fig.7(c)isobtained.Theassociatedspindensityshowsthatthemoleculeinthisstatehas

nospindensityonRu,i.e.theRucentreisnowRu(II),andthereisβ−spindensityonthe

phenligand,indicatingaphen•–species.Asaresult,theformalchargeonMnshouldbe3+:

thisisalsoevidentfromourinspectionofthecoordinationgeometryaroundthisionwhich

revealssubstantialshorteningofalloftheMn-ligandbonddistances[cf.theoverlayofthe

ground-statesextetgeometryofRu•Mnandthisquartetexcitedstate,Fig.8(b)].The

equatorialmetal-ligandbonddistancesreduceby0.1Å(allamineandoxygendonors)orby

0.2Å(pyridineNdonor).Theaxialbonddistancesreduceby0.4Å.ThusaMnII–(phen•–)–

RuIIIstateisshowntobethelowest-energystatefollowingphoto-excitation,confirmingthe

occurrenceofthePETprocessthatwasimpliedbytheTAmeasurements:thisisthespecies

thathasalifetimeof4.7nsaccordingtotransientabsorptiondata.

19

RotationofthepyridylunitaroundtheC–Cbondseparatingitfromthealkynelinker

togivethe‘perpendicular’orientationmentionedearlierincreasestheenergyofthequartet

excitedstateby25.1kJmol-1(or10.1kT)comparedtotheco-planararrangement–a

considerablylargerdifferencethatwasfoundforthegroundstate.Thissuggeststhatinthe

quartetMnII–(phen•–)–RuIIIexcitedstatethereislesstorsionalmotionofthepyridylunit

withrespecttothephenanthrolineunit,suchthattheperpendiculararrangementinthe

quartetstatecanonlybeaccessedfromthesamearrangementinthesextetstate.

FurtherconfirmationoftheoccurrenceoftheintramolecularPETprocessisprovided

byexaminationofthelocalisationofredoxprocessesinground-stateRu•Mn.Fig.8(c)and

9(d)showtheoverlaybetweenRu•Mn,Ru•Mn+andRu•Mn–,respectively.Bothoxidised

andreducedspeciesweregeometry-optimizedinthequintetstate.Theoverlaybetween

Ru•MnandRu•Mn+showsasimilarstructuralchangetothatseenintheoverlaybetween

thesextetandquartetstatesofRu•Mn,asshowninFig.8(b).Thisindicatesthatone-

electronoxidationdoesindeedhappenattheMncentre,yieldingaformalchargeof3+,and

thatthisisthereforethesiteofthefirstoxidation.Thislocalisationforthefirstoxidation

processisalsoevidentifoneconsidersthedifferenceinthetotalelectrondensitybetween

Ru•Mn+(atthegeometryofRu•Mn)andRu•Mnasdepictedin7(e):thereisadecreasein

electrondensityontheMnmoietyconsistentwithformationofMn(III),buttheelectron

densityoftheRu(II)centredoesnotchangeuponone-electronoxidationofthecomplex.

Incontrast,uponreductionofRu•MntoRu•Mn–thereisalmostnostructural

change,asisclearfromtheoverlayinFig.8(d).ThedifferenceelectrondensityshowninFig.

7(f)(betweenRu•Mn–andRu•MnattheRu•Mn–geometry)confirmsthattheone-electron

reductionisassociatedwiththephenligand.Theseobservationsfromcomputational

studiessupportourexperimentalfindings.

(iii)Applicationsforimaging:relaxivitypropertiesandluminescenceimagingstudies

Ru/Gdcomplexes.

RelaxivitymeasurementsforRu•GdandRu•Gd2wereperformedat400MHzand

298KinD2Obytheinversion-recoverytechnique,alongsidethecommercialcontrastagent

Magnevist®forcomparisonpurposes.Solutionsofeachcomplexwerepreparedatfive

differentconcentrations(0–2.0mM)andthelongitudinalrelaxationtime(T1)forthe

20

residualH2Opeakineachsamplewasmeasuredusingastandardinversion-recoverypulse

sequence.Theconcentration-normalisedlongitudinalrelaxivityvalue(r1)foreachcomplex

wasthendeterminedfromalinearplotoflongitudinalrelaxationtimeagainstcontrast

agentconcentration(SI,Fig.S25)inaccordancewitheq.1:

1/T1obs=1/T10+r1[M] (1)

wherer1istherelaxivityvalue,[M]isthecomplexconcentration,T1obsistheobservedT1

valueinthepresenceofcomplex,andT10isthevalueofT1intheabsenceofanycomplex.

UndertheconditionsusedthereferencecompoundMagnevist®hasr1=4.6mM-1s-1,and

ournewcompoundsRu•GdandRu•Gd2haver1=6.2and13.6mM-1s-1,respectively.The

increaseinrelaxivitybetweenMagnevist®andbothRu/Gdcomplexescanbeascribedtoa

combinationofgreatercomplexbulk(andhenceslowertumblinginsolution)forRu•Gdand

Ru•Gd2,andpossiblyalsothefactthattheGd(III)ionbindingsiteinbothRu/Gdcomplexes

isheptadentate,whichleavesroomforpotentiallytwowatermolecules(q=2),whereas

Magnevist®hasq=1.InfacttheqvalueforaEu(III)complexwiththesame

aminocarboxylatedonorsetwaspreviouslydeterminedas1.6±0.5,6aimplyingamixtureof

mono-anddi-aquacoordinationinsolution.Theser1valuescomparefavourablywiththose

forotheroligonuclearcomplexes.4a

GiventhepromisingrelaxivitypropertiesofRu•GdandRu•Gd2wewerealso

interestedtoseeiftheRu(II)-basedluminescencecouldbeusedasthebasisofcellular

imaging.LiveHeLacellswereinitiallyincubatedwitheitherofthesecomplexesat

concentrationsof25μM,50μMand75μMforsixorsixteenhours.Cellsstainedwith

eitheroftheprobesforthelongerincubationperiod(16h)atallconcentrationswere

visuallyunhealthywhenviewedunderthemicroscope,andcellsstainedwiththelowest

concentrationoftheprobes(25μM)demonstratedonlyweakRu(II)-basedemissionevenat

thelongerincubationtimes.Theseresultssuggested,therefore,thatshorterincubation

timesandhigherconcentrationswouldprovidetheoptimumimagingconditionsforboth

complexes.Accordingly,furthercellularstainingwasconductedwithliveHeLacells

incubatedwithprobeconcentrationsof50μM,75μMand100μMforfourhours,orwith

anincreasedprobeconcentration(75μM,100μMand150μM)overashorterincubation

period(twohours).Inthisinstanceallofthecellsstainedforeachincubationtimeandat

21

eachconcentrationforbothprobeswerevisuallyhealthywhenviewedunderthe

microscope,apartfromthecellsincubatedwithaprobeconcentrationof150μM,which

werebeginningtodetachfromthesterilecoverslip.

Ru(II)-basedemissionwasobservedfromallofthehealthycellswhenimagedwitha

confocalmicroscope(λexc=405nm,λem=570-620nm):however,theemissionfromthecells

incubatedforonly2h(witheithercomplex)wasweak,suggestinglowercellularuptake.The

optimumimagingconditionsforeachcomplexwerefoundtobeanincubationtimeof4h

usingaconcentrationof50μM,whichallowedforreasonablecellularuptakewithouthigh

levelsofcytotoxicitybeingobserved.ExampleemissionimagesofHeLacellsincubatedwith

Ru•GdandRu•Gd2(Fig.10)showpunctatecytoplasmicstaining,suggestingthatbothofthe

probeslocaliseinaspecificorganellewithintheHeLacells,suchasthelysosomesorthe

mitochondria.Co-localisationstudieswiththecommerciallysosomalandmitochondrial

stainsLysoTracker®RedandMitoTracker®Redwerenotsuccessfulassomeabsorbanceof

thesestainsattheexcitationwavelengthused(405nm)producedredluminescencewhich

interferedwiththatoftheRu(II)complexes.

ThecytotoxicityofRu•GdandRu•Gd2towardsHeLacellsundertheoptimum

imagingconditions(50μM,4h)andalsoatanincreasedprobeconcentration(200μM,4h)

wasassessedbyclonogenicassay(SI,Fig.S26).Bothofthecomplexesexhibitedlowtoxicity

undertheconditionsusedtoimagethecells,withsurvivalfractionsof>0.85being

observedinbothcases.Increasingtheprobeconcentrationfour-foldto200μMhadthe

expectedeffectofloweringthecellsurvivalfractionincomparisontothelower

concentration,butgoodsurvivallevelswerestillobservedforbothprobes(>0.8).The

trinuclearprobeRu•Gd2causeslowercellsurvivalfractionsatbothprobeconcentrations

whencomparedtodinuclearRu•Gd.Overall,theabilityofthesecomplexestoactasstains

inluminescenceimaging–inadditiontoprovidinghighrelaxivityforwaterprotons–is

clear.

Ru/Mncomplexes

ToseehowtheMn(II)centresfaredforrelaxivitypurposescomparedtoGd(III),

relaxivityexperimentsonRu•MnandRu•Mn2werecarriedoutinD2Oat400MHzand298

K,alongsidethecommercialGd(III)-basedcontrastagentMagnevist®forcomparison

purposes(SI,Fig.S27).ExactlythesamemethodologywasusedasfortheRu/Gd

22

complexes,affordingrelaxivityvaluesofr1=3.7mM-1s-1and4.8mM-1

s-1forRu•Mnand

Ru•Mn2respectively,whichcomparefavourablytoarangeofmononuclearMn(II)

complexesinasimilarN/O-donorcoordinationenvironmentbasedpredominantlyonamine

andcarboxylateligands.14cUnderthesameexperimentalconditions,Magnevist®hasa

relaxivityvalueofr1=4.6mM-1s-1.WerecallthatRu•GdandRu•Gd2havelargerrelaxivity

values(r1=6.2mM-1s-1and13.6mM-1

s-1,respectively).Thesmallerrelaxivityvaluesforthe

Ru/MncomplexescomparedtotheRu/Gdanaloguesareofcourseprincipallyattributable

tothesmallermagneticmomentofMn(II)comparedtoGd(III),butthesmallernumberof

watermoleculescoordinatedtothemetalcentreinsolutionwillbesignificanttoo.In

Magnevist®theGd(III)ionis9-coordinatefromanoctadentateDTPAligandandonewater

molecule,whereasthesmallerMn(II)ioninthesameligandiscoordinativelysaturatedby

theligand(q=0).14dWeobservedahydrationnumberof1.6±0.5forEu(III)ionsinthe

heptadentatebindingsiteusedinthesecomplexes,6aandbyanalogywiththeDTPA

complexesthisvaluewillbesmallerwhenMn(II)iscoordinatedatthesamebindingsitedue

toitssmallersizeandpreferenceforlowercoordinationnumbers.AlthoughRu•Mn2does

showrelaxivitysimilartothatofMagnevist®,itsuseasadualmagneticresonance/

luminescenceimagingagentisinhibitedbythefactthattheRu(II)-based3MLCT

luminescenceispartlyquenchedbytheMn(II)ions;thesameistrueforRu•Mn.

Conclusion

Theligandskeletoncontainingaphenanthrolineunit(forcoordinationtoa

photosensitisingcomplexcore)withoneortwopendantpyridyl/aminodicarboxylateunits

connectedviaalkynelinkageshasbeenusedtoprepareavarietyofd/dandd/f

heterodinuclearandheterotrinuclearcomplexes.Thecentralphotosensitisingunitis

{Ru(bipy)2(phen)}2+inallcases.Thesecondarymetalionsatthependantsitesareeither

fromthef-block[Gd(III)foritsrelaxivity;Nd(III)orYb(III)fortheirnear-infrared

luminescence]orthed-block[Mn(II)foritsrelaxivityandabilitytoeffectPETtotheexcited

stateoftheRu(II)unit;andZn(II)asacontrolforcomparisonwiththeMn(II)complexes].

Arangeofinterestingbehaviourshasemerged.ThecomplexesRu•GdandRu•Gd2

showrelaxivityofwaterprotonsthatishighforthenumberofGd(III)ionsthattheycontain

becauseoftheirsizeand,therefore,slowrotationinsolution;inadditiontheyretainthe

characteristicphosphorescenceofthe{Ru(bipy)2(phen)}2+corewhichcanbeusedfor

23

luminescenceimagingofcellssuchthattheyhavepotentialasdual(luminescenceandMRI

relaxivity)imagingagents.TheanalogousRu/YbandRu/NdcomplexesdisplayRu→Yband

Ru→Nd(respectively)photoinducedenergy-transfer,leadingtopartialquenchingofthe

Ru(II)-basedemissionandsensitisednear-infraredluminescencefromthelanthanideunit.

Theenergy-transfertoNd(III)ismuchfasterthantoYb(III)becauseofthehigherdensityof

f-fexcitedstatesinthecorrectspectralregiononNd(III),whichcanactasenergyacceptors.

IntheRu/MncomplexesRu•MnandRu•Mn2thepresenceoftheMn(II)ions

likewiseprovideabasisforrelaxivityofwaterprotons,withrelaxivityvaluescompetitive

withotherMn(II)-basedcomplexes.Inthiscasehoweverthephosphorescenceofthe

{Ru(bipy)2(phen)}2+coreissubstantiallyquenchedbytheMn(II)ions–similarquenching

doesnotoccurwhenMn(II)isreplacedbyZn(II).Ultrafasttransientabsorptionexperiments

onRu•Mn(andRu•Znasacontrol)revealthepresenceoffast(<1ns)PETfromtheMn(II)

iontotheRu(II)-based3MLCTstate,i.e.MnII–(phen•–)–RuIII→MnIII–(phen•–)–RuII.The

resultingMnIII–(phen•–)statedecayswithτ≈5nsandisnon-luminescent.Thisfast

quenchingmechanismdoesnotalwaysoccur,asshownbythepresenceofresidualRu(II)-

basedluminescenceinRu•MnandRu•Mn2(tensofnslifetime),whichweascribetothe

presenceofaconformerinwhichthecentralandperipheralmetalcomplexcentresare

decoupledbyrotationofthepyridylunitssuchthattheyareperpendiculartothephenunit.

24

Experimental

Generaldetails.

Allreagents,unlessotherwisestated,werepurchasedfromcommercialsources

(Sigma-Aldrich,AlfaAesar,Fluorochem)andusedasreceived.AllsolventswereofHPLC

gradequalityandobtainedfromFisher,excludingdeuteratedsolvents(Sigma-Aldrich,Acros

Organics,VWR).DrysolventswereobtainedfromtheGrubbsdrysolventsystematthe

UniversityofSheffield.Thefollowingmaterialswerepreparedusingliteratureprocedures:

4-bromo-2,6-bis[N,N-bis(tert-butoxycarbonylmethyl)aminomethyl]pyridine(compoundB),12

3-bromo-1,10-phenanthroline,93,8-dibromo-1,10-phenanthroline,9[Ru(bipy)2Cl2]•2H2O.26

Instrumentation.

One-dimensional1Hand13CNMRspectraandtwo-dimensionalCOSYspectrawere

recordedusingeitheraBrukerAvanceIIIHD400spectrometeroraBrukerAvanceIIIHD

500spectrometer.Electrosprayionisation(ES)massspectrawererecordedonanAgilent

Technologies6530Accurate-MassQ-TOFLC/MSinstrument(UniversityofSheffield).High-

resolutionspectrawererecordedonaBrukerMaXisplusinstrument(Universityof

Warwick).UV/VisspectraweremeasuredonaVarianCary50BioUV-Visible

Spectrophotometer.

PhotoluminescencespectrawererecordedonaHoribaJobinYvonFluoromax-4-

Spectrofluorimeterandwerecorrectedusingcorrectionfilesincludedwithinthe

FluorEssenceTMsoftware.Near-IRemissionandexcitationspectraoftheYb(III)andNd(III)

complexeswererecordedonanEdinburghInstrumentFP920PhosphorescenceLifetime

Spectrometerequippedwitha450wattsteadystatexenonlamp;a5wattmicrosecond

pulsedxenonflashlamp(withsingle300mmfocallengthexcitationandemission

monochromatorsinCzernyTurnerconfiguration);aredsensitivephotomultiplierinaPeltier

(aircooled)housing(HamamatsuR928P);andaliquidnitrogencooledNIRphotomultiplier

(Hamamatsu),andwerecorrectedusingcorrectionfilesincludedwithinthesoftware.Near-

IRemissionspectrawererecordedusinga645nmlongpassfilter.Low-temperature

emissionspectrainthevisibleregionweremeasuredinfrozen(77K)glassesof

ethanol/methanol(4:1,v:v).Decaycurvesgeneratedbysinglephotoncounting(SPC)were

25

fittedusingOrigin®softwareandthequalityoffitjudgedbyminimizationofreducedchi-

squaredandsum-of-residualssquaredvalues.

NMRrelaxivitymeasurements.

RelaxivitymeasurementsforRu•Gd,Ru•Gd2,Ru•Mn,Ru•Mn2andthecommercial

contrastagentgadopenteticacid(‘Magnevist®’)wereperformedonaBrukerAvanceIII400

spectrometerat298K.EachcompoundunderinvestigationwasdissolvedinD2Oatfive

differentconcentrations(0–2.0mM)andthespin-latticerelaxationtime(T1)forthe

residualH2Opeakineachsamplemeasuredusingastandardinversion-recoverypulse

sequencewith12recoverytimesvaryingbetween0.001-60secondsforgadopenteticacid

and15recoverytimesvaryingbetween0.001-15secondsforthefournewcomplexes.

Relaxivityvaluesweredeterminedfromalinearplotofspin-latticerelaxationtime(T1)

againstcontrastagentconcentration(0–2.0mM)inaccordancewitheq.1.

Cellimagingstudies.

HeLacellswereculturedinDulbecco’smodifiedeaglemedium(DMEM,highglucose

withL-glutamine)purchasedfromLonza(500mL)andsupplementedwith10%(v/v)foetal

bovineserum(FBS).CulturesweregrownasmonolayersinT-75flasksat37°Cina5%CO2/

95%air(v/v)environment.Onceat75-80%confluency,cellsweresubculturedusing

trypsin-EDTA(2mL).Subculturesforlivecellstainingwereseededontosterilecoverslips

(15mmx15mm)in6-wellplates(100,000/well)andthoseforclonogenicassayswere

seededdirectlyinto6-wellplates(200-400/well).AllsubcultureswereincubatedinDMEM

at37°Cina5%CO2/95%air(v/v)environmentovernighttoallowforadhesiontothe

well-plateorcoverslip.

Forcellstaining,Ru•GdandRu•Gd2weredissolvedinsterile,double-distilledwater

toformstocksolutionswithaconcentrationof1mM.Furtherdilutiontogenerateworking

solutionsof50-200μMwasachievedusingDMEMsupplementedwith10%(v/v)FBS.After

removalofthegrowthmedia,cellswerewashedwithsterilisedphosphate-bufferedsaline

(PBS,3x2mL/well)beforebeingtreatedwithasolutionoftheappropriateRu/Gdcomplex

atconcentrationsof50–200μM(2mL/well).Cellswereincubatedfor2hor4hat37°Cin

DMEMina5%CO2/95%air(v/v)environment.Afterthedesiredincubationtimethe

growthmediumwasremovedandthecellswerewashedwithPBS(3x2mL/well)to

removeexcessmetalcomplex.Thecellswerethentreatedwithparaformaldehydesolution

26

(4%inPBS,1mL/well)for20minutes,beforebeingwashedagainwithPBS(3x2mL/well).

Thecoverslipsweremountedontomicroscopeslides(Immu-MountTM,ThermoScientific)

andlefttodryforaminimumof30minutesbeforeimaging.ConfocalimagesoffixedHeLa

cellswererecordedusinganinvertedNikonA1confocalmicroscopewitha60xlens(CFI

PlanApochromatVC60xoil,NA1.4).Adiodelaser(405nm)wasusedforexcitationofthe

Ru/Gdcomplexesanda570-620nmemissionfilterwasused.

Toxicityassay

Afterremovalofthegrowthmedia,liveHeLacellsweretreatedwithasolutionof

Ru•GdorRu•Gd2complexinmediaatboth50μMand200μM(1mL/well).Cellsinfour

controlwellswereleftuntreatedandimmersedinDMEM(2mL/well).Cellswereincubated

for4hat37°Cina5%CO2/95%air(v/v)environment.Followingincubation,the

treatmentsolutionwasremoved,andthecellsimmersedinfreshDMEM(2mL/well)and

incubatedforseventotendaysat37°Cina5%CO2/95%air(v/v)environmentuntil

visiblecellcolonieshadformed.Thegrowthmediumwasremoved,andthecellswerefixed

andstainedwithmethyleneblueinmethanol(4 g/L)foraminimumof30minutes.The

stainingsolutionwasremoved,andthenumberofcoloniescounted,witheachcolony

representingasurvivingcell.The‘survivalfraction’forcellstreatedwiththeRu/Gd

complexesisthenumberofcoloniesformedaftertreatmentwithRu/Gdcomplexes

comparedtocontrolsintheabsenceofcomplex.Experimentswereconductedinduplicate

forseedingdensitiesof200and400cells/wellandrepeatedonthreeseparateoccasions.

Survivalfractionsquotedareaveragesofthethreerepeats.

Transientabsorptionspectroscopymeasurements

ATi:Sapphireregenerativeamplifier(SpitfireACEPA-40,Spectra-Physics)provided

800nmpulses(40fsfwhm,10kHz,1.2mJ);400nmforsampleexcitationwasprovidedby

doublingaportionofthe800nmoutput,inaβ-bariumboratecrystalwithinacommercially

availabledoubler/tripler(TimePlate,PhotopTechnologies).Whitelight,supercontinuum,

probepulsesweregeneratedinsitubyusingaportionoftheTi:sapphireamplifieroutput,

focusedontoaCaF2crystal,allowingforthegenerationoflightspanning340–790nm.

Detectionwasachievedusingacommercialtransientabsorptionspectrometer(Helios,

UltrafastSystems)andwasperformedbyaCMOSsensorfortheUV/Visspectralrange.The

27

relativepolarisationofthepumpandprobepulseswassettothemagicangleof54.7˚for

anisotropy-freemeasurements.Sampleswereheldin1mmpathlengthquartzcells.The

opticaldensityattheexcitationwavelengthwaskeptatapproximately0.5.Theoptical

densityacrosstheproberangewaskeptbelow0.8.

Excitedstatedynamicswereelucidatedbygloballifetimeanalysis,performedin

Glotaran.27Differencespectrawerebaselinecorrectedthroughsubtractionofanaverageof

thepre-excitationspectra.Sequentialkineticmodelswerethenappliedtoeachdatasetto

modeltheexcitedstatedynamics.Apolynomialcurvewasfittothedatatoaccountforthe

groupvelocitydispersionoftheprobelightinthekineticmodel.Thenumberoflifetime

componentswassystematicallyvariedinordertominimisetheresidualintensitybetween

theexperimentalandmodeldata,wheretheminimumχ2valuehadbeenobtained.

Synthesis

4-(Trimethylsilyl)ethynyl-2,6-bis[N,N-bis(tert-butoxycarbonylmethyl)-

aminomethyl]pyridine(compoundCSi).Amixtureof4-bromo-2,6-bis[N,N-bis(tert-

butoxycarbonylmethyl)-aminomethyl]pyridine(compoundB;6.89g,10.2mmol),

Pd(PPh3)2Cl2(0.50g,0.712mmol),CuI(0.30g,1.58mmol)andPPh3(0.10g,0.381mmol)

wereaddedtoanhydrousiPr2NH(30cm3)andthemixturedeoxygenatedwithargongasfor

30minutes.Trimethylsilyl-acetylene(15cm3,108mmol)wasaddedwithvigorousstirring

andtheresultingmixtureheatedat83°Cfor24hours.Oncecooled,thereactionwas

filteredthroughcelite®andwashedwithCH2Cl2untilthewashingsranclear.Thesolvent

wasthenremovedunderreducedpressuretoaffordablackresidue,whichwasflash-

filteredthroughsilicagel(200-300mesh)withCH2Cl2aseluent.Thecrudeproductwasthen

purifiedfurtherusingcolumnchromatographyonsilicagel(200-300mesh)withpetroleum

ether/ethylacetate(9:1to8:2,v:v)astheeluenttoafford4-(trimethylsilyl)ethynyl-2,6-

bis[N,N-bis(tert-butoxy-carbonylmethyl)aminomethyl]pyridine(CSi:4.25g,60%)asadark

yellowoil.1HNMR(400MHz,CDCl3):δ=0.18(s,9H,SiMe3);1.42(s,36H,tBu);3.43(s,8H,

NCH2–ester);3.96(s,4H,NCH2–pyridyl);7.48(s,2H,pyridylH3/H5).ESMS:m/z=690.4[M+

H]+,712.4[M+Na]+.

4-Ethynyl-2,6-bis[N,N-bis(tert-butoxycarbonylmethyl)-aminomethyl]pyridine

(compoundC).ProtectedcompoundCSi(0.75g,1.09mmol)andtetra-n-butylammonium

fluoride(0.43g,1.63mmol)weredissolvedinTHF(45mL)andstirredatRTfor16hours.

28

Thesolventwasthenremovedunderreducedpressureandtheresultingresiduedissolved

inCH2Cl2(30cm3),washedwithwater(2x30cm3)anddried(MgSO4).Thesolventwas

removedunderreducedpressuretoaffordcompoundC(0.62g,92%)asadarkyellowoil.

Duetothereactivityofthealkynesubstituentthiscompoundwasusedimmediatelyafter

preparationwithoutfurthercharacterisation.

[Ru(bipy)2(Br-phen)](PF6)2(compoundA).Amixtureof3-bromo-1,10-

phenanthroline(0.95g,3.68mmol)andcis-[Ru(bipy)2Cl2]•2H2O(1.90g,3.65mmol)in

CH3OH(30cm3)washeatedtorefluxfor16hours.Oncecooled,thesolutionwas

concentratedunderreducedpressureandanexcessofsaturatedKPF6(aq)solution(20cm3)

wasadded.Thesolutionwasleftat4°Cfor16hoursandtheresultingprecipitatedissolved

inCH2Cl2(30cm3)andwashedwithwater(3x25cm3).Thecombinedaqueouslayerswere

thenre-extractedwithfurtherportionsofCH2Cl2(2x25cm3)andtheresultingorganic

extractscombinedanddried(MgSO4).Thesolventwasremovedunderreducedpressureto

affordcompoundA(3.51g)asaredsolidinquantitativeyield.1HNMR(400MHz,d6-

acetone):δ=7.36-7.42(m,2H,bipy);7.60-7.66(m,2H,bipy);7.85(dd,1H,J=1.5and5.6

Hz,bipy);7.94(dd,1H,J=5.2and8.2Hz,phen);8.04(dd,1H,J=1.5and5.6Hz,bipy);8.10

(dd,1H,J=1.5andHz,bipy);8.12-8.18(m,2H,bipy);8.19(dd,1H,J=1.5and5.6Hz,bipy);

8.25(tt,2H,J=1.5and7.9Hz,bipy);8.35(d,1H,J=8.9Hz,phen);8.44(dd,1H,J=1.2and

5.2Hz,phen);8.45(d,1H,J=8.9Hz,phen);8.47(d,1H,J=1.9Hz,phen);8.78–8.87(m,

5H,4xbipy,1xphen);9.06(d,1H,J=1.9Hz,phen).ESMS:m/z=337[M–2PF6]2+.High

resolutionESMS:m/z=337.0101(calculatedfor[C32H23N6BrRu]2+,337.0099).

[Ru(bipy)2(Br2-phen)](PF6)2(compoundD).Thiswaspreparedfrom3,8-dibromo-

1,10-phenanthroline(0.33g,0.98mmol)andcis-[Ru(bipy)2Cl2]•2H2O(0.51g,0.98mmol)

exactlyasdescribedaboveforcomplexA,toaffordcompoundD(1.02g)asaredsolidin

quantitativeyield.1HNMR(400MHz,d6-acetone):δ=7.40(ddd,2H,J=1.2,5.6and7.9Hz,

bipy);7.63(ddd,2H,J=1.2,5.6and7.9Hz,bipy);8.01(dd,2H,J=1.5and5.6Hz,bipy);8.12

(dd,2H,J=1.5and5.6Hz,bipy);8.16(td,2H,J=1.5and7.9Hz,bipy);8.25(td,2H,J=1.5

and7.9Hz,bipy);8.40(s,2H,phen);8.48(d,2H,J=1.9Hz,phen);8.79(d,2H,J=7.9Hz,

bipy);8.83(d,2H,J=7.9Hz,bipy);9.07(d,2H,J=1.9Hz,phen).ESMS:m/z=376.0[M–

2PF6]2+.HighresolutionESMS:m/z=375.9650(calculatedfor[C32H22N6Br2Ru]2+,375.9648).

CompoundRu•E.AmixtureofcompoundA(0.53g,0.55mmol),(dppf)PdCl2.CH2Cl2

(0.05g,0.06mmol)andCuI(0.01g,0.05mmol)inanhydrousDMF/iPr2NH(6cm3,5:1,v:v)

29

wasdeoxygenatedwithargonfor30minutes.Tothiswasaddeddropwiseasolutionof

compoundC(0.62g,1.00mmol)indeoxygenatedanhydrousDMF/iPr2NH(3cm3,5:1,v:v).

Thesolutionwasstirredatroomtemperaturefor16hoursunderargon,beforeremovalof

thesolventunderreducedpressure.Theresultingbrownsolidwaspurifiedbycolumn

chromatographyonsilicagel(200-300mesh)withCH3CN/H2O/sat.KNO3(aq)(100:0:0to

100:4:2,v:v:v)astheeluent.Thesolventwasthenremovedunderreducedpressureandthe

soliddissolvedinCH2Cl2(30cm3),washedwithanexcessofsaturatedKPF6(aq)solution(20

cm3)andseparated.TheaqueouslayerwasextractedwithfurtherportionsofCH2Cl2(2x15

cm3)andthecombinedorganiclayersthenwashedwithwater(2x15cm3)anddried

(MgSO4).ThesolventwasremovedunderreducedpressuretoaffordcomplexRu•E(0.41g,

50%)asadarkredsolid.1HNMR(400MHz,d6-acetone):δ=1.45(s,36H,tBu);3.49(s,8H,

N–CH2–ester);4.00(s,4H,CH2–pyridyl);7.37-7.45(m,2H,bipy);7.61(s,2H,pyridylH3/H5);

7.62-7.67(m,2H,bipy);7.88(d,1H,J=5.6Hz,bipy);7.96(dd,1H,J=5.2and8.2Hz,phen);

8.09(d,1H,J=5.6Hz,bipy);8.13(d,1H,J=5.6Hz,bipy);8.14-8.20(m,2H,bipy);8.21(d,

1H,J=5.6Hz,bipy);8.26(t,2H,J=7.9Hz,bipy);8.40-8.50(m,3H,phen);8.67(d,1H,J=1.9

Hz,phen);8.79-8.88(m,5H,4xbipy,1xphen);9.04(d,1H,J=1.9Hz,phen).ESMS:m/z=

604.7[M–2PF6]2+.HighresolutionESMS:m/z=604.7318(calculatedfor[C65H73N9O8Ru]2+,

604.7316).

CompoundRu•L.AsolutionofRu•E(73mg,0.049mmol)inCH2Cl2(3cm3)and

trifluoroaceticacid(TFA,3cm3)wasstirredatroomtemperaturefor18hours.Thesolvent

wasthenremovedunderreducedpressuretoyieldaredsolid.ToremoveanyresidualTFA

thesolidwasdissolvedinCH2Cl2(10cm3)andthenevaporatedtodrynessinvacuo.This

processwasrepeatedtentimes.ThesolidwasthenwashedwithCH3OH(10x10cm3)

followingthesameprocedure.Finally,theredsolidwasdissolvedintheminimumamount

ofCH3OHandprecipitatedwithanexcessofdiethylether.Thesolidwascollectedby

centrifugationanddriedunderastreamofN2toyieldRu•L(61mg,98%)asaredsolid.1H

NMR(500MHz,d6-DMSO,303K):δ=3.46(s,8H,N–CH2–acid);3.94(s,4H,CH2–pyridyl);

7.33-7.38(m,2H,bipy);7.53(d,1H,J=5.3Hz,bipy);7.56(s,2H,pyridylH3/H5);7.56-7.62

(m,2H,bipy);7.75(d,2H,J=5.3Hz,bipy);7.87(d,1H,J=5.3Hz,bipy);7.90(dd,1H,J=5.2

and8.2Hz,phen);8.07-8.16(m,3H,2xbipy,1xphen);8.21(t,2H,J=7.8Hz,bipy);8.29(d,

1H,J=1.0Hz,phen);8.35(d,1H,J=8.8Hz,phen);8.44(d,1H,J=8.8Hz,phen);8.78-8.90

(m,5H,4xbipy,1xphen);9.16(d,1H,J=1.0Hz,phen).ESMS:m/z=492.6[M–2PF6]2+,

30

328.7[M–2PF6+H]3+.HighresolutionESMS:m/z=492.6056(calculatedfor

[C49H41N9O8Ru]2+,492.6055).

CompoundRu•E2.AmixtureofcompoundD(1.02g,0.98mmol),(dppf)PdCl2.CH2Cl2

(0.05g,0.06mmol)andCuI(0.01g,0.05mmol)dissolvedinanhydrousDMF/iPr2NH(6cm3,

5:1,v:v)wasdeoxygenatedwithargonfor30minutes.Tothiswasaddeddropwisea

solutionofC(1.28g,2.07mmol)indeoxygenatedanhydrousDMF/iPr2NH(3cm3,5:1,v:v).

Thesolutionwasstirredatroomtemperaturefor16hoursunderargonbeforetheaddition

ofanadditionalportionofC(1.28g,2.07mmol)inthesamedeoxygenatedsolventmixture.

Thereactionwasstirredunderargonfor24hoursbeforethesolventwasremovedunder

reducedpressure.Theresultingbrownsolidwaspurifiedbycolumnchromatographyon

silicagel(200-300mesh)withCH3CN/H2O/sat.KNO3(aq)(100:0:0to100:4:2,v:v:v)asthe

eluent.Thesolventwasthenremovedunderreducedpressureandthesoliddissolvedin

CH2Cl2(30cm3),washedwithanexcessofsaturatedKPF6(aq)solution(20cm3)and

separated.TheaqueouslayerwasextractedwithfurtherportionsofCH2Cl2(2x15cm3)and

thecombinedorganiclayersthenwashedwithwater(2x15cm3),dried(MgSO4)andthe

solventremovedunderreducedpressure.Furtherpurificationwasthenachievedbysize

exclusionchromatographyonSephadex®LH-20inCH3OH.Thesolventwasremovedunder

reducedpressuretoaffordRu•E2(0.94g,45%)asadarkredsolid.1HNMR(400MHz,d6-

acetone):δ=1.45(brs,72H,tBu);3.49(brs,16H,N–CH2–ester);3.99(brs,8H,CH2-pyridyl);

7.40-7.45(m,2H,bipy);7.56(s,4H,pyridylH3/H5);7.60-7.66(m,2H,bipy);8.05(d,2H,J=

5.6Hz,bipy);8.12-8.21(m,4H,bipy);8.25(t,2H,J=7.9Hz,bipy);8.48(s,2H,phen);8.67(d,

2H,J=1.9Hz,phen);8.85(m,4H,bipy);9.05(d,2H,J=1.9Hz,phen).ESMS:m/z=912.4[M

–2PF6]2+,608.6[M–2PF6+H]3+.HighresolutionESMS:m/z=912.4073(calculatedfor

[C98H122N12O16Ru]2+,912.4067).

CompoundRu•L2.AsolutionofRu•E2(92mg,0.044mmol)inCH2Cl2(3cm3)andTFA

(3cm3)wasstirredatroomtemperaturefor18hours.Thesolventwasthenremovedunder

reducedpressuretoyieldaredsolid.Thiswaspurifiedandisolatedexactlyasdescribedfor

Ru•L(above)anddriedunderastreamofN2toyieldRu•L2(71mg,98%)asaredsolid.1H

NMR(400MHz,D2O):δ=4.16(brs,16H,N–CH2–acid);4.74(brs,8H,CH2-pyridyl);7.17-

7.31(brm,2H,bipy)7.37-7.48(brm,2H,bipy);7.65(brd,2H,J=4.0Hz,bipy);7.69(brs,

4H,pyridylH3/H5);7.90(brd,2H,J=4.8Hz,bipy);7.98-8.06(brm,2H,bipy);8.06-8.16(br

m,2H,bipy);8.25(brs,2H,phen);8.35(brs,2H,phen);8.51-8.63(brm,4H,bipy);8.74(br

31

s,2H,phen).ESMS:m/z=688.2[M–2PF6]2+.HighresolutionESMS:m/z=688.1568

(calculatedfor[C66H58N12O16Ru]2+,688.1563).

CompoundRu•Gd.ToasolutionofRu•L(45mg,0.035mmol)inwater(3cm3)at0

°CwasaddeddropwiseasolutionofGdCl3.6H2O(14mg,0.038mmol)inwater(0.5cm3);

themixturewasstirredandallowedtoreachroomtemperature.After1hourthesolution

wasadjustedtopH5-6usingasolutionofNaOH(aq)(1M)andwasthenlefttostiratroom

temperatureforafurther18hours.SaturatedKPF6(aq)solutionwasthenaddedtoproducea

redprecipitate(hexafluorophosphatesaltofmono-cationicRu•Gd)whichwasfilteredand

washedwithwater.ThisredsolidwasdissolvedintheminimumamountofCH3OHand

precipitatedwithanexcessofdiethylether.Theprecipitatewascollectedbycentrifugation

andpurifiedfurtherusingSephadex®LH-20withCH3OH.Thesolventwasremovedunder

reducedpressureandtheresultingredsoliddriedunderastreamofN2.Counterion

exchangewasthenachievedusingDowex®1x2chlorideform(100-200mesh)inwater.The

aqueoussolutionwasfiltered,thewaterremovedunderreducedpressure,andthe

resultingsoliddriedunderastreamofN2toyieldRu•Gd(chloridesalt;35mg,84%)asared

solid.ESMS:m/z=570.1[M–Cl+H]2+,380.4[M–Cl+2H]3+.HighresolutionESMS:m/z=

570.0562(calculatedfor[C49H37N9O8RuGd+H]2+,570.0558).

CompoundRu•Gd2waspreparedusingthesamemethodasdescribedabovefor

Ru•Gd,fromRu•L2(100mg,0.060mmol)andGdCl3.6H2O(59mg,0.159mmol)inwater,

butwithoutthecounter-ionexchangestepasRu•Gd2isneutral.Attheendofthereaction

thesolutionwaspurifiedbychromatographyonSephadex®LH-20withwater.Evaporation

ofthesolventaffordedRu•Gd2(70mg,69%yield)asaredsolid.ESMS:m/z=842.1[M+

2H]2+,852.5[M+Na+H]2+,864.6[M+2Na]2+.HighresolutionESMS:m/z=842.5664

(calculatedfor[C66H50N12O16RuGd2+2H]2+,842.5530).

CompoundRu•Nd.AsolutionofRu•L(15mg,0.012mmol)inwater(3cm3)was

adjustedtopH5-6usingNaOH(aq)(0.1M).Withstirring,asolutionofNd(OTf)3(11mg,0.019

mmol)inwater(0.5cm3)wasaddeddropwise.Themixturewasstirredatroom

temperatureandthepHreadjustedto5-6usingNaOH(aq)(0.1M)whennecessary.After18

hours,asmallportionofDowex®1x2chlorideform(100-200mesh)wasaddedandthe

mixturestirredatroomtemperatureforafurther24hours.Thesolutionwasthenfiltered,

concentratedunderreducedpressureandpurifiedonSephadex®G-15elutingwithwater.

Thesolventwasremovedunderreducedpressureandtheresultingsoliddriedundera

32

streamofN2toyieldRu•Nd(chloridesalt;13mg,95%)asaredsolid.ESMS:m/z=563.0[M

–Cl+H]2+,375.7[M–Cl+2H]3+.HighresolutionESMS:m/z=563.0497(calculatedfor

[C49H37N9O8102Ru144Nd+H]2+,563.0488).

CompoundRu•YbwaspreparedinexactlythesamewayasRu•Nd,withRu•L(18

mg,0.014mmol)andYb(OTf)3(14mg,0.023mmol)affording14mg(83%yield)ofRu•Ybas

aredsolid.ESMS:m/z=578.1[M–Cl+H]2+.HighresolutionESMS:m/z=578.0632

(calculatedfor[C49H37N9O8102Ru173Yb+H]2+,578.0632).

CompoundRu•Nd2waspreparedinthesamewayasforRu•Gd2,withRu•L2(11.4

mg,0.007mmol)andNd(OTf)3(10mg,0.017mmol)affording11mg(97%yield)ofRu•Nd2

asaredsolidafterpurificationonSephadex®G-15elutingwithwater.ESMS:m/z=829.0

[M+2H]2+,553.0[M+3H]3+,415.0[M+4H]4+.HighresolutionESMS:m/z=829.0404

(calculatedfor[C66H50N12O16102Ru144Nd2+2H]2+,829.0429).

CompoundRu•Yb2waspreparedinthesamewayasforRu•Gd2,withRu•L2(7.4

mg,0.004mmol)andYb(OTf)3(7mg,0.011mmol)affording7.5mg(99%yield)ofRu•Yb2

afterpurificationonSephadex®G-15elutingwithwater.ESMS:m/z=858.1[M+2H]2+,

572.4[M+3H]3+,429.5[M+4H]4+.HighresolutionESMS:m/z=858.0683(calculatedfor

[C66H50N12O16102Ru173Yb2+2H]2+,858.0710).

CompoundRu•Mn.ToastirredsolutionofRu•L(130mg,0.102mmol)inwater(3

cm3),adjustedtopH5–6withNaOH(aq),wasaddeddropwiseasolutionofMnCl2.4H2O(26

mg,0.131mmol)inwater(0.5cm3).Themixturewasstirredatroomtemperatureandthe

pHre-adjustedto5–6ifnecessary.After18hoursthereactionmixturewasconcentrated

underreducedpressureandpurifiedonSephadex®G-15,elutingwithwater.Thesolvent

wasremovedunderreducedpressureandtheresultingredsoliddriedunderastreamofN2

toyieldRu•Mn(100mg,95%)asaredsolid.ESMS:m/z=519.1[M+2H]2+.Highresolution

ESMS:m/z=519.0658(calculatedfor[C49H37N9O8RuMn+2H]2+,519.0674).

CompoundRu•Zn.ThiswaspreparedinexactlythesamewayasRu•Mn,fromRu•L

(38mg,0.03mmol)andZnCl2.xH2O(10mg,ca.0.049mmol)togiveRu•Zn(25mg,80%)as

aredsolid.1HNMR(400MHz,D2O):δ=3.34-3.52(m,8H,NCH2-CO2);4.15(s,4H,NCH2-

pyridyl);7.16-7.26(m,2H,bipy);7.39-7.46(m,2H,bipy);7.48(s,1H,pyridylH3orH5);7.52

(s,0.5H,pyridylH3orH5);7.54(s,0.5H,pyridylH3orH5);7.58(d,1H,J=5.3Hz,bipy);7.68

(d,1H,J=5.3Hz,bipy);7.73(t,1H,J=6.5Hz,phen);7.91(d,1H,J=5.3Hz,bipy);7.94(d,

1H,J=5.3Hz,bipy);7.99(t,2H,J=7.5Hz,bipy);8.09(t,2H,J=7.5Hz,bipy);8.18(d,1H,J=

33

4.8Hz,phen);8.19-8.29(m,2H,phen);8.35(d,1H,J=4.5Hz,phen);8.50-8.64(m,5H,4x

bipy,1xphen);8.76(s,0.5H,phen);8.79(s,0.5H,phen).ESMS:m/z=523.6[M+2H]2+.

HighresolutionESMS:m/z=523.5632(calculatedfor[C49H37N9O8RuMn+2H]2+,523.5626).

CompoundRu•Mn2.ThiswaspreparedinthesamewayasRu•Mn,fromRu•L2(41

mg,0.025mmol)andMnCl2•4H2O(12mg,0.061mmol),affordingafterpurification

(Sephadex®G-15,elutingwithwater)pureRu•Mn2asitsdisodiumsalt(25mg,67%).ESMS:

m/z=739.1[M–2Na]2–.HighresolutionESMS:m/z=739.0598(calculatedfor

[C66H50N12O16102RuMn2]2–,739.0631).

CompoundRu•Zn2.ThiswaspreparedinthesamewayasRu•Zn,fromRu•L2(9mg,

5.2µmol)andZnCl2•xH2O(10mg,ca.49µmol),affordingafterpurification(Sephadex®G-

15,elutingwithwater)pureRu•Zn2asitsdisodiumsalt(7mg,82%).ESMS:m/z=748.1[M

–2Na]2–.HighresolutionESMS:m/z=748.0532(calculatedfor[C66H50N12O16102Ru64Zn2]2–,

748.0553).

ComputationalDetails

AllcalculationswereperformedwithGaussian09v.D.0128usingdensity-functional

theory.ThefunctionalusedwasB3LYP29withempiricaldispersioncorrectionsthroughthe

GD3BJkeyword.30ThebasissetusedconsistedofSDD31onRuorlanthanideatoms,and6-

311G(d,p)32,33onallotheratoms.AllbulksolventwasdescribedusingthePCMmethod34,35

asimplementedinGaussianusingtheprovidedparametersforwater.Noadditionalwater

moleculeswereincludedtosimulatehydrogenbonding.

AllRu•Mncomplexes(andtheirreduced/oxidizedforms)wereassumedtobeinthe

high-spinconfigurationforMn,whererelevant.Duringthecalculationsitwasfoundthat

thereisalargemanifoldofpotentialsextetstatesforRu•Mn.Differentstartinggeometries

willleadtodifferentfinalelectronicstatesforasimilarfinalgeometrywiththepyridine

fragmentoftheMn(II)moietyco-planarwiththephenfragmentoftheRu(II)moiety.Infact,

thelowestsextetenergieswereobtainedbystartingfromageometryinwhichthepyridine

fragmentoftheMn(II)moietyisperpendiculartothephenfragmentoftheRu(II)fragment,

i.e.throughrestrictingthesizeoftheconjugatedsystem.Couplingbetweentheexcited-

state(3MLCT)Ru(II)andground-stateMn(II)moietieswasassumedtobeweaklyanti-

ferromagneticuponexcitation:preliminarycalculationsontheoctetstate(whichwould

arisefromferromagneticcoupling)ofphoto-excitedRu•Mnallshowahigherenergythan

34

thecorrespondingquartetstates.Foralloptimisedstructuresfrequencieswerecalculated

intheharmonicapproximation.Onlysmallimaginaryfrequencies(<15cm−1)werefound.

Thesemoleculeswereconsideredtobetrueminima,sincesuchsmallimaginaryvaluesare

commonlyassociatedwitherrorsintheintegrationgridsused.

AllabsorptionspectrawerecalculatedwiththeTD-DFTmethod36asimplementedin

G09.Allimageswerecreatedwithin-housedevelopedsoftware,whichisavailableupon

request.TheoverlayswerecreatedusingROCS.37,38Finally,thecomputationalESIwas

createdusingin-housedevelopedsoftwarebasedontheOpenEyeToolkit.39

Acknowledgements.WethanktheUniversityofSheffield(Ph.DstudentshipstoBJC,AJA);

theEPSRCCapitalEquipmentawardfortheLordPorterlaserlaboratoryinSheffield

(EP/L022613/1),theGranthamCenterforSustainableFutures(Ph.DstudentshiptoJDS)and

TheRosetreesTrust(Ph.DstudentshiptoCJ).Wealsogratefullyacknowledge(i)theuseof

theWolfsonLightMicroscopyFacilityattheUniversityofSheffield,and(ii)alicenseforthe

OpenEyetools,obtainedviathefreeacademiclicensingprogram.

35

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36 G.Scalmani,M.J.Frisch,B.Mennucci,J.Tomasi,R.Cammi,andV.Barone,J.Chem.

Phys.,2006,124,094107

37 P.C.D.Hawkins,A.G.Skillman,A.Nicholls,J.Med.Chem.,2007,50,74.

39

38 ROCS3.2.2.2:OpenEyeScientificSoftware,SantaFe,NM.

http://www.eyesopen.com.

39 OpenEyetoolkits2018.feb.1,OpenEyeScientificsoftware,SantaFe,NM.

http://www.eyesopen.com.

40

Scheme1:Previously-reportedIr(III)/Ln(III)complexesbasedonabridgingligandskeleton

combiningphenanthrolineandpolyaminocarboxylatebindingsitesfortheIr(III)andLn(III)

metalcentres,respectively,connectedbyanalkynespacer(seeref.6).

NNN

N

N

O

O

Ln

O

O

O

OO

ON

N

N

O

O

Ln

O

O

O

OO

O

–

IrN N

F

F F

F

NNN

N

N

O

O

Ln

O

O

O

OO

O

IrN N

F

F F

F

41

Scheme2.PreparationofRu•E,Ru•LandheterodinuclearcomplexesRu•M.

NN

RuN

N

N

N

Br

A

[2+]

N NN CO2tBu

CO2tButBuO2C

tBuO2C

Cu(I) / Pd(dppf)Cl2DMF / iPr2NH

C

NN

RuN

N

N

N

N

N

N

CO2tBu

CO2tBu

CO2tBu

CO2tBu

[2+]

NN

RuN

N

N

N

N

N

N

O

O

M

O

O

O

O O

O

[(n–2)+]Mn+ salt / water

Ru•E

Ru•M

CF3CO2H / DCM

NN

RuN

N

N

N

N

N

N

CO2H

CO2H

CO2H

CO2H

[2+]

Ru•L

42

Scheme3.Preparationofester-protectedalkyneintermediateC(usedinSchemes2and4)

N NN CO2tBu

CO2tButBuO2C

tBuO2C

C

N NN CO2tBu

CO2tButBuO2C

tBuO2C

CSi

SiMe3

N

Br

NN CO2tBu

CO2tButBuO2C

tBuO2C

BTMS-CCH / Pd(PPh3)2Cl2 /CuI / iPr2NH

Bu4NF / THF

43

Scheme4.PreparationofRu•E2,Ru•L2andheterotrinuclearcomplexesRu•M2.

NN

RuN

N

N

N

Br

D

[2+]

N NN CO2tBu

CO2tButBuO2C

tBuO2C

Cu(I) / Pd(dppf)Cl2DMF / iPr2NH

C

NN

RuN

N

N

N

N

N

N

CO2tBu

CO2tBu

CO2tBu

CO2tBu

[2+]

NN

RuN

N

N

N

N

N

N

O

O

M

O

O

O

O O

O

[(2n–6)+]Mn+ salt / water

Ru•E2

Ru•M2

CF3CO2H / DCM

Br

N

N

N

tBuO2C

tBuO2C

tBuO2CtBuO2C

NN

RuN

N

N

N

N

N

N

CO2H

CO2H

CO2H

CO2H

[2+]

Ru•L2

N

N

N

HO2C

HO2C

HO2C

HO2C

N

N

N

O

O

M

O

O

O

OO

O

44

Table1.UV/VisabsorptionandluminescencedataforthenewmononuclearRu(II)

complexes.

λabsRT/nm

[103ε /M-1cm-1]a

λemRT/nm

[τ /ns]a

λem77K/nm

[τ /µs]b

Ru•E 286[88],321(sh)[39],444

(br)[14]

647[240] 611,660(sh),711(sh)[6.2]

Ru•L 285[120],325(sh)[55],

442(br)[16]

661[340] 611,662(sh),706(sh)

[5.8]

Ru•E2 351[56],437[14],476(sh)

[10].

683[271] 645,701(sh)[3.8]

Ru•L2 349[46],434[6.5],485

(sh)[3.7]

697[209,102] Notsoluble

a AbsorptionandemissionspectraatRTmeasuredinMeCN(Ru•EandRu•E2)or

water(Ru•LandRu•L2).Estimateduncertaintyinlifetimesis±10%forsingle

componentdecays.

b Emissionspectraat77KmeasuredinEtOH/MeOH(4:1,v/v)glass

45

Table2.UV/VisabsorptionandluminescencedatafortheRu/Mheterometalliccomplexes

(M=Gd,Mn,Zn).

λabsRT/nm

[103ε /M-1cm-1]a

λemRT/nm

[τ /ns]a

λem77K/nm

[τ /µs]b

Ru•Gd 286[56],326(sh)[25],443

(br)[7.5]

664[351] 612,662(sh),706

(sh)[5.3]

Ru•Gd2 286[99],350[74],435[11],

486(sh)[5.9]

699[402,104] notsoluble

Ru•Mn 285[80],325(sh)[34],441

(br)[10]

657[410,91] 612,660,709[1.8,

0.45]

Ru•Mn2 286[86],350[59],435[7.9],

481(sh)[4.4]

700[456,164,21] notsoluble

Ru•Zn 285[80],326(sh)[34],440

(br)[10]

666[329] 617,668,720[5.6]

Ru•Zn2 285[88],348[55],435[9.2],

478(sh)[5.3]

695[301,117] notsoluble

a AbsorptionandemissionspectraatRTmeasuredinwater.Estimateduncertaintyin

lifetimesis±10%forsinglecomponentdecays.

b Emissionspectraat77KmeasuredinEtOH/MeOH(4:1,v/v)glass.

46

Table3.LuminescencedatafortheRu/YbandRu/Ndheterometalliccomplexes.

λemRT/nm[τ /ns]inH2O

forRu(II)emissiona

λemRT/nm[τ /µs]inD2O

forLn(III)emission

Ru•Yb 663[242,73] 980[13]

Ru•Yb2 700[223,88] 980[10.5,0.3]b

Ru•Nd 662[358,22] 1060,1380[0.8]

Ru•Nd2 703[408,18] 1060,1380[0.7]

a TwoRu(II)-basedluminescencecomponents:theshorteroneisassumedtobeassociated

withmaximumquenchingbythelanthanide(seemaintext).

b Theshorterluminescencecomponentdetectedat980nmisfromthetailofunquenched

Ru(II)-basedemissionwhichoverlapswiththeYb(III)-basedemission.

47

Fig.1. Normalised,correctedluminescencespectraofthefourmononuclearRu(II)

complexesinaeratedEtOH/MeOH(4:1,v/v)at298Kandinaglassat77K,

excitationwavelength435nm.

48

Fig.2. CorrectedluminescencespectrainwateratRTshowingtheRu(II)-based

luminescenceofthethreedinuclearRu•LnandthreetrinuclearRu•Ln2complexes

(Ln=Gd,Yb,Nd);allsolutionswereisoabsorbingattheexcitationwavelength(λexc

=430nm).

49

Fig.3. CorrectedluminescencespectrainD2Oat298Kinthenear-infraredregion,

showingthesensitisedlanthanide-basedluminescencefromthecomplexesRu•Yb2

andRu•Nd2complexes(λexc=440nmforbothspectra).

50

Fig.4. Correctedluminescencespectrainwaterat298KforthefourRu/MnandRu/Zn

complexes;allsolutionswereisoabsorbingattheexcitationwavelength(λexc=435

nm).

51

Fig.5. Top:differentialtransientabsorptionspectrainair-equilibratedwaterofRu•Znat

arangeofdifferenttimedelaysfollowingexcitation(λexc=400nm,40fs,3mW

pulse).Bottom:dynamicsofthetransientsignalsovera5nsperiod.

52

Fig.6. Top:differentialtransientabsorptionspectrainair-equilibratedwaterofRu•Mnat

arangeofdifferenttimedelaysfollowingexcitation(λexc=400nm,40fs,3mW

pulse).Thesmallsharpfeatureat400nmisscatteringofthepumplight.Bottom:

dynamicsofthetransientsignalsovera5nsperiod.

53

Fig.7. ResultsofcomputationalstudiesonRu•Mn.(a)OptimizedstructureforRu•Mnin

itssextetgroundstate.(b)SpindensityforRu•Mninitsgroundstatesextetstate

(isosurfaceatdensity=0.0004;blue=α-spin,red=β-spin).(c)Spindensityfor

Ru•Mninitslowestexcitedquartetstate(isosurfaceatdensity=0.0004,blue=α-

spin,green=β-spin).(d)SpindensityforRu•Mninlowestexcitedquartetstate

(isosurfaceatdensity=0.0004,blue=α-spin,red=β-spin)withrotatedpyridylunit

at90°tothephenanthrolineunit.(e)DifferencedensityforRu•Mnbetween

neutralandmono-oxidisedform(isosurfaceatdensity=0.0004,green=increase,

purple=decrease).(f)DifferencedensityforRu•Mnbetweenmono-reducedand

neutralform(isosurfaceatdensity=0.0004,green=increase,purple=decrease)

withrotatedpyridylunitat90°tothephenanthrolineunit.

54

Fig.8 OverlaysoftheneutralformofRu•Mnwithotherformsaccessedinthe

computationalexperiments.Inallpanels,theneutralformofRu•Mnisshownin

themajoritygreycolour,theotherformbeingcomparedtoisshowningreen.(a)

OverlayofRu•Mninits‘planar’form,withthe‘perpendicular’formarisingfrom

twistingthepyridylgroupwithrespecttothephengroup.(b)OverlayofRu•Mn(6A

groundstate)withRu•Mn(4Aexcitedstate):thesignificantchangeingeometry

aroundtheMncentreindicatesitstransientoxidationtoMn(III).(c)Overlayof

[Ru•Mn]0(6A)with[Ru•Mn]+(5A):thesignificantchangeingeometryaroundthe

MncentreindicatesitsoxidationtoMn(III).(d)Overlayof[Ru•Mn]0(6A)with

[Ru•Mn]–(5A):thelackofsignificantchangesincoordinationgeometryaround

eithermetalionisconsistentwithaphen-basedreduction.

55

Fig.9 SimulatedUV-VISspectrumforRu•Mn.Thestickspectrum(greenlines)indicates

thetransitionsascalculatedbyTD-DFTwiththeircalculatedoscillatorstrengths.

ThesimulatedfullspectrumisgeneratedusingGaussianshapeswithaFWHMof

1500cm-1;thismaybecomparedwiththerealspectruminSI.

56

Fig.10. ConfocalmicroscopyimagesofHeLacellsincubatedwith(a)Ru•Gdor(b)Ru•Gd2

(50µM,4hincubationineachcase).λexc=405nm;λem=570–620nm.Scalebars

=20µm.

57

Heteronucleard-dandd-fRu(II)/Mcomplexes[M=Gd(III),Yb(III),Nd(III),

Zn(II)orMn(II)]ofligandscombiningphenanthrolineandaminocarboxylate

bindingsites:combinedrelaxivity,cellimagingandphotophysicalstudies.

TableofContentsentry

Aseriesofcomplexesinwhichaphosphorescent[Ru(NN)3]2+coreisattachedtooneortwo

pendantf-block[Gd(III),Nd(III),Yb(III)]ord-block[Mn(II),Zn(II)]ionshavebeenstudiedfor

theirrelaxivityandcellimagingproperties,andphotophysicalpropertieswhichincludeRu-

to-lanthanidephotoinducedenergy-transferandMn-to-Ruphotoinducedelectrontransfer.

NN

RuN

N

N

N

N

N

N

O

O

M

O

O

O

O O

ON

N

N

O

O

M

O

O

O

OO

O

M = Gd(III), Nd(III), Yb(III), Mn(II), Zn(II)