DOI: 10.1002/chem.201102851

A Charge-Transfer Challenge: Combining Fullerenes and Metalloporphyrinsin Aqueous Environments

Evangelos Krokos,[a] Fabian Sp�nig,[a] Michaela Ruppert,[b] Andreas Hirsch,*[b] andDirk. M. Guldi*[a]

Introduction

Charge transfer between redox pairs is undoubtedly of fun-damental importance in nature, and governs a number ofpivotal processes, such as photosynthesis and vision. Artifi-cial mimics that replicate ultrafast photoinduced chargetransfer present unique opportunities for a variety of tech-nological applications, which range from high-efficiency

solar cells[1] to emerging fields, such as molecular electron-ics.[2]

Following the discovery of fullerenes by Kroto et al.,[3]

C60, C70, etc. have attracted ample attention from scientistsin different fields, including physics, chemistry, medicine,and biology. Of exceptional interest are artificial photosyn-thetic systems that rely on fullerenes to convert solar tochemical energy.[4] These three-dimensional carbon allo-tropes demonstrate properties that render them well suitedfor charge-transfer systems. In particular, their readiness toaccept electrons[5] suggests them to be excellent buildingblocks for electron donor–acceptor conjugates and hybrids.Additionally, the chemistry of fullerenes, such as intramolec-ular nucleophilic addition reactions (Bingel–Hirsch reac-tion), 1,3-dipolar cycloadditions of azomethyne ylides (Pratoreaction), Diels–Alder cycloaddition reactions of ortho-qui-nodimethanes,[6] enables the linking of C60 to porphyrinsthrough a diverse collection of linkers.[6b, 7] Equally impor-tant is the rigidity of their structure, which leads to excep-tionally small reorganization energies of fullerenes[8] incharge-transfer reactions. Contemporary research on chargeseparation has focused predominantly on the investigationof C60/porphyrin electron donor–acceptor conjugates and hy-brids.[1b, c,9]

Abstract: A series of truly water-solu-ble C60/porphyrin electron donor–ac-ceptor conjugates has been synthesizedto serve as powerful mimics of photo-synthetic reaction centers. To this end,the overall water-solubility of the con-jugates was achieved by adding hydro-philic dendrimers of different genera-tions to the porphyrin moiety. An im-portant variable is the metal center ofthe porphyrin; we examined zinc(II),copper(II), cobalt(II), nickel(II), iron-ACHTUNGTRENNUNG(III), and manganese ACHTUNGTRENNUNG(III). The first in-sights into electronic communicationbetween the electron donors and theelectron acceptors came from electro-chemical assays, which clearly indicatethat the redox processes centeredeither on C60 or the porphyrins are mu-

tually affected. Absorption measure-ments, however, revealed that the elec-tronic communication in terms of, forexample, charge-transfer features, re-mains spectroscopically invisible. Thepolar environment that water providesis likely to be a cause of the lack of de-tection. Despite this, transient absorp-tion measurements confirm that intra-molecular charge separation processesin the excited state lead to rapid deac-tivation of the excited states and, inturn, afford the formation of radicalion pair states in all of the investigated

cases. Most importantly, the lifetimesof the radical ion pairs were found todepend strongly on several aspects.The nature of the coordinated metalcenter and the type of dendrimer havea profound impact on the lifetime. Ithas been revealed that the nature/elec-tronic configuration of the metal cen-ters is decisive in powering a charge re-combination that either reinstates theground state or any given multiplet ex-cited state. Conversely, the equilibriumof two opposing forces in the dendrim-ers, that is, the interactions betweentheir hydrophilic regions and the sol-vent and the electronic communicationbetween their hydrophobic regions andthe porphyrin and/or fullerene, is thekey to tuning the lifetimes.

Keywords: charge transfer · ful-lerenes · porphyrinoids · waterchemistry

[a] E. Krokos, Dr. F. Sp�nig, Prof. Dr. D. M. GuldiDepartment of Chemistry and Pharmacy andInterdisciplinary Center of Molecular Materials (ICMM)Friedrich-Alexander Universit�t Erlangen N�rnbergEgerlandstrasse 3, 91058 Erlangen (Germany)Fax: (+49) 9131-85-28307E-mail : guldi@chemie.uni-erlangen.de

[b] M. Ruppert, Prof. Dr. A. HirschDepartment of Chemistry and Pharmacy andInterdisciplinary Center of Molecular Materials (ICMM)Friedrich-Alexander Universit�t Erlangen N�rnbergHenkestrasse 42, 91054 Erlangen (Germany)Fax: (+49) 9131-85-26864E-mail : andreas.hirsch@chemie.uni-erlangen.de

Supporting information for this article is available on the WWWunder http://dx.doi.org/10.1002/chem.201102851.

� 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Chem. Eur. J. 2012, 18, 1328 – 13411328

According to the Marcus theory of non-adiabatic intramo-lecular electron transfer, the rate constants of charge separa-tion (kCS) and charge recombination (kCR) are a parabolicfunction of the free energy changes (�DG0

CS, �DG0CR) for

the corresponding reactions.[10] It follows that the parame-ters that control the rate constants are the electronic cou-pling (V) between the donor and acceptor and the reorgani-zation energy (l). As the thermodynamic driving force in-creases (�DG0<l), so does the rate constant. The reactionrate reaches its maximum value when the driving forceequals the reorganization energy (�DG0�l), at which pointit is essentially controlled by the measure of the electroniccoupling, that is, the overlap between the donor and accept-or orbitals. A further increase in the driving force (�DG0>

l) leads to a rather counterintuitive situation in which thereaction slows down and the highly exergonic range of theparabola is entered, commonly referred to as the Marcus in-verted region. The synthesis and subsequent characteriza-tion of C60/porphyrin conjugates and hybrids, in which bothconstituents are in close proximity with strong p–p stacking,have been reported on multiple occasions.[11] Ultrafastcharge transfer evolves at the expense of energy transfer inthese systems, provided that the center-to-center distancesdid not exceed 7.0 �. At larger distances, that is, greaterthan 7.0 �, the polarity of the solvent enables control overboth energy and charge transfer.[11j, 12]

The introduction of paramagnetic metal centers into theporphyrin ring, as opposed to just free-base porphyrins orzinc porphyrins, constitutes anappealing variation. Augmentedelectronic coupling is assumedto transcend the actual charge-transfer processes in the result-ing metalloporphyrins and theirelectron donor–acceptor sys-tems. Nevertheless, severalissues remain to be investigat-ed, especially regarding the be-havior under photoexcitation.The effect the localized positivecharge on the metal, as opposedto its delocalization on the por-phyrin macrocycle, has on theexcited charge separated stateis one of them. Furthermore,very strong spin-orbit couplingresults in extremely fast deacti-vation of the excited states inmetalloporphyrins, which inturn dictates that the charge-transfer reaction needs to beaccelerated to its maximumrate, namely the top of theMarcus parabola, at whichpoint the associated process be-comes a simple function of theelectronic coupling.[11h, j,13] In

fact, the rate constants of charge transfer may compete withthose of the intrinsic porphyrin deactivation. Such a compet-itive scenario is the motivation for the current work on ful-lerenes and metalloporphyrins.

Herein, we report on the synthesis of several truly water-soluble C60/porphyrin electron donor–acceptor conjugatesthat implement a redox-active architecture in addition totheir physicochemical properties. A key asset of these conju-gates is their solubility in water; not only is the toxicity ofmost commonly used organic solvents a significant factor,but for many applications water solubility is indispensable.For example, the implementation of artificial ensembles inhydrogen-producing photovoltaic cells is based on closeproximity of the active site relative to water. Likewise, thephotoinactivation of artificial photonucleases is another ex-ample that requires water solubility.

Results and Discussion

Synthesis and structural characterization: Upon deprotec-tion of the tert-butyl groups by treatment of M-1, M-3, andM-5 with formic acid, hexa- and octadecacarboxylates M-2,M-4, and M-6 were obtained in very good yields and puri-fied by recrystallization from n-pentane (see Schemes 1 and2). In contrast to their precursors, these compounds aresoluble in water at pH values of 10 (M-4) and 7 (M-2, M-6),respectively.

Scheme 1. The synthesis of precursors M-1 (M=Cu, Co, Ni, Fe(Cl), Mn(Cl)) and M-3 is reported else-ACHTUNGTRENNUNGwhere.[11j, k] Yields of water-soluble conjugates M-2 and M-5 range from 85 to 98%.

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Electronic absorption spectra : It is clear when contrastingthe absorption spectra of the metalloporphyrin conjugateswith those of the references that a trend toward significantperturbation of the p–p transitions emerges. Possible aggre-gation of the reference systems and/or electron donor–ac-ceptor conjugates was, however, not observed; this findingcorrelates with the bulky dendritic groups as a potent meansto prevent p–p porphyrin and metal–metal interactions. Theunderlying changes are limited to the l=300 to 650 nmrange. Very short van der Waals distances between thecenter part of the metalloporphyrins and C60 are thought tobe responsible because they cause structural distortions,charge transfer interactions, etc. Note that the energies ofthe interactions vary with the nature of the metalloporphyr-in. In the l=650 to 700 nm range, the fundamental absorp-tion of C60, that is, the 0–*0 transition, emerges.[14]

In comparison with the absorption characteristics of theirnon-water-soluble counterparts, namely M-3 and M-5, inwhich a redistribution of the charge density from the por-phyrin to the fullerene in the ground state gave rise to newabsorptions in the near-infrared region of the spectrum,[11j]

the absorption spectra of M-4 and M-6 remain somewhatfeatureless beyond l=700 nm. However, the excitationspectra confirmed the presence of weak absorptions aroundl=820 nm for ZnII-4/ZnII-6 (Figure 1). Overall, it is likelythat the solvent polarity plays a decisive role in preventingthe formation of appreciable charge-transfer features.

Emission spectra : In contrast to the ZnP reference withfluorescence quantum yields as high as 0.04, none of the

metalloporphyrin references reveal significant emission inthe l=600 to 900 nm range.[15] However, in the correspond-ing electron donor–acceptor conjugates we note a ratherbroad and featureless emission that centers around l=

865 nm for ZnII-4/ZnII-6 (Figure 2). A comparison with

recent studies on 1) analogous H2P–C60 and ZnP–C60 sys-tems in aqueous media, which do show H2P- and ZnP-cen-tered fluorescence,[11k] and 2) the analogous MnIIIP–C60,CoIIP–C60, FeIIIP–C60, NiIIP–C60, CuIIP–C60 systems in organicsolvents,[11j] leads us to hypothesize a charge-transfer nature.This implies rather large electronic coupling elements(300 cm�1) between the face-to-face oriented electrondonors/electron acceptors and slow radiative decays. Consid-ering the charge-transfer features in the absorption andemission modes, we calculated the inner (lV = (labs +lem)/2)reorganization energy for ZnII-4/ZnII-6 to be 0.039 eV.

Electrochemistry : To gain insight into the energetics of elec-tron-transfer reactions, electrochemical studies were per-formed by using cyclic voltammetry (CV). The measure-

Scheme 2. Synthesis of dendronized water-soluble C60/porphyrin electrondonor–acceptor conjugates M-6 from precursor M-5.

Figure 1. Excitation spectrum at l= 940 nm of ZnII-6 in deaerated waterat pH 10.

Figure 2. Emission spectrum at l =830 nm of ZnII-6 in deaerated water atpH 10.

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D. M. Guldi, A. Hirsch et al.

ments were carried out in DMF as the solvent with 0.1 m

Bu4NPF6 as the supporting electrolyte. However, usingwater as the electrochemical solvent did not lead to any re-producible results due to the limited potential window and/or the limited stability of the reduced and oxidizedspecies. Representative examples for ZnII-4 andCuII-6 are given in Figures S1 and S2, respectively,in the Supporting Information.

The first oxidation potential of ZnII-4 manifestsat 0.31 V to give [ZnIIP]C+ , whereas the formationof its dication follows at 0.62 V. In the reductiveregion of the voltammogram, the peaks for ZnII-4at �1.09, �1.46, and �2.03 V were assigned to thereduction of C60 to give C60C

�, C602�, and C60

3�, re-spectively. In addition, the reduction of porphyrinto [ZnIIP]C� is discernible at �1.86 V. CompoundsCuII-4 and CuII-6 demonstrate two oxidative processes at0.51 and 0.45 V, respectively, that lead to the formation of[CuIIP]C+ and [CuIIP]2+ . On the reductive side, formation of[CuIIP]C�[16] is seen at �1.68 V for CuII-4 and at �1.75 V forCuII-6. C60-related reductions for CuII-4 occur at �0.92,�1.37, and �1.85 V, and analogous processes for CuII-6appear at �0.96 and �1.29 V. In the case of CoII-4, a singleoxidation that corresponds to the generation of [CoIIIP]arises at 0.64 V. C60-centered reductions appear at �0.84 and�1.33 V to give C60C

� and C602�, respectively, whereas the

porphyrin-associated reduction is detected at �1.80 V. Thefirst anodic redox process for FeIII-6 manifests at 0.50 V be-cause it relates to the creation of [FeIIIP]C+ ,[17] whereas theformation of [FeIIIP]2+ follows at 0.78 V. The reduction of[FeIIIP] to [FeIIP] transpires at �0.90 V. Additionally, the re-duction of [FeIIP], which leads to the formation of [FeIIP]C�

is observed at �1.81 V. Three C60 reductions involving C60C�,

C602�, and C60

3� are distinct at �1.13, �1.35, and �1.99 V, re-spectively. Complex NiII-4 exhibits two oxidations at 0.43and 0.86 V that correlate to the formation of [NiIIP]C+ and[NiIIP]2+ accordingly. When the reductive scans are consid-ered, the C60 reductions evolve at �0.87, �1.33, and�1.84 V, whereas [NiIIP]C�[18] formation takes place at�1.68 V. The voltamogram of MnIII-4 reveals a single oxida-tion at 0.88 V that gives [MnIIIP]C+ .[19] Of the four reductiveprocesses detected, the ones at �1.25 and �1.97 V are as-signed to C60-based reductions, whereas those at �0.77 and�1.82 V are thought to represent the reductions of [MnIIIP]to [MnIIP] and to [MnIP].

When comparing the electrochemistry of the water-solu-ble conjugates in DMF with that of the non-water-solubleconjugates in dichloromethane, a clear trend towards lowerenergies of the radical ions/radical ion pairs evolve.[11j] Over-all, the water-soluble conjugates exhibit oxidation potentialsthat are approximately 100 mV lower that the analogousnon-water-soluble conjugates. Likewise, their reduction be-comes easier. Here, the potentials are shifted between 100and 200 mV. Both trends are rationalized on the basis of amore polar environment (DMF), which assists in stabilizingradical ions/radical ion pairs. Notable exceptions are CoII-4and MnIII-4, which reveal oxidation potentials that are in-

creased by 100 and 200 mV, respectively, in comparison tothe analogous non-water-soluble conjugates in dichlorome-thane. A summary of the electrochemical potentials is pre-sented in Table 1.

Pulse radiolysis : To determine the corresponding character-istics of the one-electron-oxidized products of the metallo-porphyrins, that is, either the p-radical cations of the por-phyrin macrocycle or the higher oxidation states of themetal, we took our previous data from pulse-radiolysis ex-periments.[11j] As a general feature, broad transitions areseen to develop in the spectral regions and are bathochromi-cally shifted relative to the Q-band transitions, which impliesmacrocycle-centered rather than metal-centered oxidationprocesses.

Transient absorption measurements : In light of the unusualphotophysics of the metalloporphyrin references, theyshould be discussed in more detail. Upon photoexcitation,the closed-shell electronic nature of the ZnP reference(ZnII-2) results in a sequence of short-lived singlet (S1) andlong-lived triplet (T1) excited states with lifetimes of around10.0/2.0 ns and 380/44 ms, respectively (Figure 3).

In CuII-2,[20] a fast intersystem crossing[21] gives rise to thetriplet excited state, the features of which[21, 22] (minima atl=538 and 620 nm, maxima at l=565, 640, and 735 nm) areformed in less than 0.4 ps (Figure 4). The decay of the fore-most singdoublet to the tripdoublet and tripquartetstates[23]* is also characterized by an absorption in the infra-red region that is centered around l=900 nm.[21,22] Still, aredshift of approximately 50 nm is observed in our case. Thedynamics of the tripmultiplet state are primarily a functionof solvent coordination. In essence, the presence of coordi-nating solvents appears to accelerate the return to theground state.[21,24] The deactivation was measured as 180 ps,which correlates well with the lifetimes of the non-water-soluble counterpart in less polar solvents in our previouswork.[11j]

In the CoIIP reference (CoII-2), interactions of the d-orbi-tal electrons with the singlet and triplet states of the porphy-rin macrocycle induces the formation of doublet and quartet

Table 1. Redox potentials of water-soluble M-4 and M-6 vs. Fc+/Fc.

Ered5 [V] Ered4 [V] Ered3 [V] Rred2 [V] Ered1 [V] Eox1 [V] Eox2 [V]

Zn ZnII-4 �2.03 �1.86 �1.46 �1.09 0.31 0.62Cu CuII-4 �-1.85 �1.68 �1.39 �0.92 0.51 0.83

CuII-6 �1.75 �1.29 �0.96 0.45 0.76Co CoII-4 �1.80 �1.33 �0.84 0.64Fe FeIII-6 �1.99 �1.81 �1.35 �1.13 �0.90 0.50 0.78Ni NiII-4 �1.84 �1.68 �1.33 �0.87 0.43 0.86Mn MnIII-4 �1.97 �1.82 �1.25 �0.77 0.88

[*] These terms describe the splitting of the spin states. The first part(e.g., sing, trip) indicates the spin state and the second part (e.g, dou-blet, quartet) indicates the splitting.

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states.[25] In fact, the ground state is a doublet, whereas thelower excited states are a singdoublet (2Q1), a tripdoublet(2T1), and a tripquartet (4T1), from the highest to thelowest.[25,26] The instantaneously formed spectroscopic fea-tures in the l= 430 to 700 nm range (transient bleaching atl=535 nm and maxima at l=575 and 635 nm; seeFigure 5), correlate with the tripdoublet (2T1) excitedstate.[27] This state then disappears over 10 ps and we ob-serve a new excited state characterized by a minimum at l=

525 nm and a maximum at l=560 nm. Note that the newspectrum, which is due to a charge-transfer state, disap-peared completely about 50 ps after the pulse. Also, no re-sidual transient features were registered on the nano- andmicrosecond timescale. The kinetic data can be fitted with adouble exponential decay with lifetimes of 2 and 30 ps. It isworth nothing that, depending on the pH, CoII-2 is hexa-coordinated as [CoIIP ACHTUNGTRENNUNG(OH�)2]

2�, [CoIIPACHTUNGTRENNUNG(H2O) ACHTUNGTRENNUNG(OH�)]� , or[CoIIPACHTUNGTRENNUNG(H2O)2]. Importantly, rapid nonradiative decays to theground state are favored and dominate over ligand release.In line with the assumption of low yields for the ligand re-lease, we see no firm evidence for dissociation followed byrapid recombination during or after the excitation. Never-

theless, a contribution from this process cannot be complete-ly ruled out.

For the MnIIIP reference (MnIII-2), the nature of theground state, that is, 5S0,

[28] has strong implications. Figure 6shows that the instantaneously formed minima at l= 470,565, and 605 nm, which closely mirror the ground-state ab-sorption, and maxima in the l=485 to 550 nm and beyondl=610 nm ranges as assigned to the tripquintet (5T1) excitedstate. Considering that the 5S1 to 5T1 conversion happenswithin the detection limit of our instrumental resolution, theinitially formed 5S1 state was invisible to us. 5T1 is subject toeither an indirect deactivation via a transient tripheptet(7T1) excited state or a direct deactivation to the 5S0 groundstate. The indirect pathway necessitates a spin conversionand, in turn, is slow (70 ps), whereas the direct pathway isspin-allowed and faster (30 ps). For the tripheptet (7T1) ex-cited state,[29] sharp maxima at l= 490 and 630 nm emergeduring our experiments. The kinetic control is augmented byvery good overlaps between the porphyrin (p, p*) and themanganese (d, d*) orbitals and by interactions with severalcharge transfer states.[27,28] Changes in the absorption spec-trum in form of shifts in the ground-state bleaching reflectthe different ligation of the complexes as the pH is changed.

Figure 3. Top: Differential absorption spectra (visible and near-infrared)obtained upon femtosecond flash photolysis (l =387 nm, 150 nJ) of ZnII-2 (�10�6

m) in argon-saturated H2O (pH 10, RT) at time delays of 1.1,6.4, 24.0, 67.0, 167.0, 432.0, and 632.0 ps (from darkest line to lightestline). Bottom: Time absorption profile at l =900 nm of the spectrashown above, monitoring the excited-state dynamics.

Figure 4. Top: Differential absorption spectra (visible and near-infrared)obtained upon femtosecond flash photolysis (l =387 nm, 150 nJ) of CuII-2 (�10�6

m) in argon-saturated H2O (pH 10, RT) at time delays of 0.1,2.4, 10.4, 44.0, 117.0, 167.0, and 232.0 ps (from darkest line to lightestline). Bottom: Time absorption profile at l =460 nm of the spectrashown above, monitoring the excited-state dynamics.

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D. M. Guldi, A. Hirsch et al.

In particular, [MnIIIPACHTUNGTRENNUNG(OH�)2]� , [MnIIIP ACHTUNGTRENNUNG(H2O) ACHTUNGTRENNUNG(OH�)], and

[MnIIIP ACHTUNGTRENNUNG(H2O)2]+ are dominant at pH 12, 10, and 7, respec-

tively. A possible ligand release is, however, hampered by arapid intersystem crossing/deactivation by CT states, a sce-nario that resembles CoII-2. Again, in accordance with thisassumption is the lack of evidence for ligand release fol-lowed by rapid recombination. Still, possible contributionsevolving from this pathway cannot be completely excluded.

The 6S0 ground state of the [FeIIIP(OH)2]� reference

(FeIII-2) undergoes an ultrafast transformation via an inter-mediate singhexet (6S1) excited state to the correspondingtriphexet (6T1) excited state. Characteristics of the latterstate include maxima in the visible region at wavelengths of>490, 541, 595, and 634 nm that go together with groundstate bleaching around l= 570 and 610 nm (Figure 7).[29] Inthe near-infrared region, a maximum discernable around l =

800 nm directly after laser excitation resembles the generaltriplet markers of metalloporphyrins. Following its forma-tion, the recombination of the triphexet (6T1) excited statecompetes with internal conversions to other tripmultiplets,including the tripoctet (8T1) excited state and ligand release(i.e., OHC) that is accompanied by one-electron reduction ofthe iron center. This all occurs on a timescale of up to 6 ps.

Beyond 6 ps, only the characteristics of FeII (minima at l=

450 and 620 nm, maxima at l=545 and 590 nm)[30] and aweakly bound OH� or OH2 species (minimum at l=

565 nm) remain. These convert within 1.2 ns to reinstate theground state quantitatively.

For the NiIIP reference (NiII-2), the transient absorption ischaracterized by excited-state bleaching at l= 520 nm andexcited-state absorption in the l=430–500 nm region andabove l=540 nm (see Figure 8). The latter relates to thevery fast (1 ps) intersystem crossing between the singlet (S1)and the hot triplet (T1) states.[31] Subsequently, the transientfeature narrows and undergoes a blueshift within the next20 ps to form the relaxed (T1) excited state prior to deacti-vation to the ground state within 200 ps. Notably, NiII-2exists predominantly as a diamagnetic tetracoordinated spe-cies with minor contributions from the hexacoordinatedform. Evidence for the latter comes from ground-statebleaching at l=565 and 610 nm. In fact, lifetimes of 30 and15 ps for first- and second-generation dendron, respectively,mirrors the equilibration time of the ensembles.

In line with our previous work, excitation of ZnII-6 revealsan absorption from l=580 to 790 nm and bleaching at l=

560 nm (Figure 9).[11k] These features fully develop 0.8 ps

Figure 5. Top: Differential absorption spectra (visible and near-infrared)obtained upon femtosecond flash photolysis (l =387 nm, 150 nJ) of CoII-2 (�10�6

m) in argon-saturated H2O (pH 10, RT) at time delays of 1.1,1.6, 4.4, 8.8, 10.8, 16.0, and 26.0 ps (from darkest line to lightest line).Bottom: Time absorption profiles at l=460 (*) and 528 nm (*) of thespectra shown above, monitoring the excited-state dynamics.

Figure 6. Top: Differential absorption spectra (visible and near-infrared)obtained upon femtosecond flash photolysis (l =387 nm, 150 nJ) ofMnIII-2 (�10�6

m) in argon-saturated H2O (pH 10, RT) at time delays of1.1, 2.4, 4.4, 8.4, 14.0, 24.0, and 38.0 ps (from darkest line to lightest line).Bottom: Time absorption profiles at l=450 (*) and 465 nm (*) of thespectra shown above, monitoring the excited-state dynamics.

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after excitation.[32] Maxima at l=630 and 680 nm in the visi-ble region and at l=900 nm in the near-infrared regionappear about 1 ps after excitation and are assigned to ZnPC+

and C60C�, respectively.[33] The corresponding radical ion pair

state exhibits a lifetime of 275 ps.[11k] A similar pictureemerges for ZnII-4. In particular, from the transient absorp-tion measurements we derive that the radical ion pair stateis formed within 1 ps following the initial excitation. Thelifetime of the radical ion pair state itself extends up to50 ps.[11k]

Upon photoexcitation of CuII-6, the radical ion pair stateemerges after 0.6 ps (Figure 10). It is characterized by an ab-sorption maximum at l =660 nm and a minimum at l=

540 nm, which both relate to CuPC+ .[11j] These transients areaccompanied by a broad absorption around l=900 nm,which verifies the presence of C60C

�. The lifetime of the radi-cal ion pair state was gauged at 900 ps. Likewise, the photo-physics of CuII-4 is also characterized by a fast charge sepa-ration at 0.7 ps. As an example, the transient absorption fea-tures reveal a very broad absorption at l= 900 nm that lin-gers for more than 3 ns.

The tripdoublet (2T1) excited-state maxima were recordedfor CoII-2 after a time delay. However, the transient in the

visible spectrum of CoII-6 at pH 7 is replaced after 0.8 ps bya very broad absorption that covers most of the l=450–525and 550–750 nm regions and exhibits maxima at l= 455 and600 nm, respectively. In fact, the spectrum in Figure 11 bearsclose resemblance to a one-electron-oxidized ligand product,that is, the p-radical cation of CoIIP.[34] Further in the red, ataround l= 900 nm, a maximum was observed that resemblesC60C

� found in a typical trans-2 adduct.[31a] Thus, we concludethat the energetically low-lying radical ion pair state is con-stituted by CoIIPC+–C60C

� as a product of an ultrafast photo-induced electron transfer. Both fingerprints were employedas reliable probes to determine the lifetime of the associatedCoIIPC+–C60C

� radical ion pair state. The decay curves werewell fitted by a single exponential decay component. In par-ticular, lifetimes that are of the order of 58 ps were derivedfrom the decays of the oxidized donor and reduced acceptorabsorption at l=600 and 900 nm, respectively. In the caseof CoII-4, a similar spectrum emerges 0.7 ps after excitation,with the only difference being a redshift of the second maxi-mum by 30 nm. Fitting of the decay profiles reveals that thedeactivation occurs with a lifetime of 93 ps.

Particularly important for MnIII-6 (pH 7) is the near-infra-red region, in which a broad transition that extends from

Figure 7. Top: Differential absorption spectra (visible and near-infrared)obtained upon femtosecond flash photolysis (l=387 nm, 150 nJ) of FeIII-2 (�10�6

m) in argon-saturated H2O (pH 10, RT) at time delays of 0.6,1.1, 1.6, 2.4, 6.4, 10.4, and 24.0 ps (from darkest line to lightest line). Bot-tom: Time absorption profiles at l=450 (*) and 565 nm (*) of the spec-tra shown above, monitoring the excited-state dynamics.

Figure 8. Top: Differential absorption spectra (visible and near-infrared)obtained upon femtosecond flash photolysis (l =387 nm, 150 nJ) of NiII-2(�10�6

m) in argon-saturated H2O (pH 10, RT) at time delays of 1.1, 1.6,4.4, 8.4, 10.4, 14.0, and 24.0 ps (from darkest line to lightest line). Bot-tom: Time absorption profile at l =475 nm of the spectra shown above,monitoring the excited-state dynamics.

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l=800 to 1200 nm is seen to emerge 0.8 ps after photoexci-tation. A closer look at Figure 12 again reveals the signatureof C60C

� at l=880 nm.[33c] Interactions with MnIIIP arethought to be responsible for the small blueshift. In the visi-ble region, on the other hand, the ground-state absorptionin form of minima at l=480, 525, 576, and 610 nm is notice-able, together with maxima at l= 450, 510, 545, and above630 nm. Overall, a good spectral resemblance to the featuresseen during the pulse radiolysis study, that is, the one-elec-tron oxidation and one-electron reduction of MnIIIP (i.e.,MnIIIPC+) and C60 (i.e. , C60C

�), respectively, confirms that acharge-transfer mechanism is operative to form MnIIIPC+

–C60C�. Charge recombination populates the ground state

and takes place within 84 ps. A likely ligand release withinthe pentacoordinated species is prevented by the fast chargeseparation. Turning to MnIII-4, the corresponding radical ionpair state is formed 0.9 ps after excitation. The lifetime ofthe radical ion pair state was appreciably longer when com-pared with MnIII-6, which has a value of 114 ps.

In FeIII-6 (pH 7), the triphexet (6T1) excited state featurestransform into a new transient when excitation commences

(Figure 13). The spectral features of this newly formed tran-sient, namely, a broad band redshifted with regard to thelong wavelength absorption (i.e., l= 550–800 nm) withmaxima at l=565, 615, 660, and 730 nm, are a good matchto those detected upon the pulse radiolytically formed FePp-radical cation. Importantly, the bleaching at l=510 nmcorrelates with the 6S0 ground-state absorption. From theabovementioned findings, we postulate a rapid intramolecu-lar charge transfer that oxidizes FeIIIP, while detection of thefingerprint of the C60 p-radical anion at around l=900 nmapproximately 0.8 ps after excitation also completes thecharacterization of the FeIIIPC+–C60C

� radical ion pair state inthis case. Beyond the timescale of the charge recombination(48 ps) only the features of the tripoctet (8T1) excited stateremain. The different ligation of FeIIIP and FeIIIP–C60 shouldbe considered. Unlike FeIII-2, which exists as a hexacoordi-nated species, the only possible form for FeIII-6 is a penta-coordinated species. Pentacoordinated high-spin FeIII-6, withan aqua or hydroxy ligand, deactivates faster to the charge-separated state, undergoing the ligand ejection as discussedfor the reference system. Examination of the transients ofFeIII-4 reveals a blueshifted absorption spectrum in the visi-

Figure 9. Top: Differential absorption spectra (visible and near-infrared)obtained upon femtosecond flash photolysis (l =420 nm, 150 nJ) of ZnII-6 (�10�6

m) in argon-saturated H2O (pH 7, RT) at time delays of 1.1, 4.4,8.4, 14.0, 24.0, 34.0, and 54.0 ps (from darkest line to lightest line). Bot-tom: Time absorption profiles at l=555 (*) and 640 nm (*) of the spec-tra shown above, monitoring the charge-separation and charge-recombi-nation dynamics.

Figure 10. Top: Differential absorption spectra (visible and near-infrared)obtained upon femtosecond flash photolysis (l =420 nm, 150 nJ) of CuII-6 (�10�6

m) in argon-saturated H2O (pH 7, RT) at time delays of 1.1, 1.6,2.4, 6.4, 10.4, 24.0, and 34.0 ps (from darkest line to lightest line). Bot-tom: Time absorption profiles at l=460 (*) and 900 nm (*) of the spec-tra shown above, monitoring the charge-separation and charge-recombi-nation dynamics.

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FULL PAPERFullerenes and Metalloporphyrins in Aqueous Environments

ble region by approximately 20 nm. Moreover, the chargeseparation and charge recombination were found to be 0.9and 586 ps, respectively. The participation of the one-elec-tron-reduced iron center is different; although this species isclearly seen at approximately 30 ps for FeIII-4, FeIII-6 lacksany similar formation. The slower charge separation in FeIII-4 is responsible for this finding because it allows a signifi-cant fraction to enter this reaction pathway.

In NiII-6 (pH 7), the very fast intersystem crossing be-tween the singlet (S1) and the hot triplet (T1) states, whichdominates the excited state of NiII-2, competes with chargeseparation. In fact, after about 2 ps features in the visibleand in the near-infrared regions (see Figure 14) develop thatare in perfect agreement with the pulse radiolytically gener-ated spectra of the NiIIP p-radical cation and the C60 p-radi-cal anion, respectively. The maxima in the differential ab-sorption spectra at l=450, 640, and 735 nm are clear finger-prints of the NiIIP centered oxidation, whereas the maxi-mum at l=900 nm is due to reduction of C60.

[33c] Kinetically,0.8 and 127 ps were determined to be the charge separationand charge recombination, respectively. Notably, charge re-combination from NiIIPC+–C60C

� leads to the population of

the relaxed T1 excited state and then the ground state.[21,31a]

Minima at l=575 and 610 nm, which are observed in minoryields, reflect the presence of a pentacoordinated species.Owing to the fact that these are discernable at any givendelay time, we conclude that the tetracoordinated and pen-tacoordinated species reveal a similar reactivity pattern.Upon excitation of NiII-4 at l=387 nm, the features of theradical ion pair state, as seen in the case of NiII-6, are fullyformed after 0.7 ps. The return to the ground state was de-termined to take place with a lifetime of 252 ps. Table 2summarizes these results for the M-4 and M-6 conjugates.

Conclusion

We wish to emphasize the impact that the different genera-tions of dendritic groups and the different transition metalsexert on the photophysics of water-soluble compounds M-4and M-6 in terms of charge-transfer dynamics, that is, chargeseparation and charge recombination. Overall, all of themshow fast and efficient charge separation upon photoexcita-tion and slow charge recombination.

Figure 11. Top: Differential absorption spectra (visible and near-infrared)obtained upon femtosecond flash photolysis (l =420 nm, 150 nJ) of CoII-6 (�10�6

m) in argon-saturated H2O (pH 7, RT) at time delays of 1.1, 1.6,2.8, 6.4, 10.4, 14.0, and 24.0 ps (from darkest line to lightest line). Bot-tom: Time absorption profiles at l=460 (*) and 900 nm (*) of the spec-tra shown above, monitoring the charge-separation and charge-recombi-nation dynamics.

Figure 12. Top: Differential absorption spectra (visible and near-infrared)obtained upon femtosecond flash photolysis (l =420 nm, 150 nJ) ofMnIII-6 (�10�6

m) in argon-saturated H2O (pH 7, RT) at time delays of1.1, 1.6, 2.4, 6.4, 8.4, 14.0, and 34.0 ps (from darkest line to lightest line).Bottom: Time absorption profiles at l=460 (*) and 482 nm (*) of thespectra shown above, monitoring the charge-separation and charge-re-combination dynamics.

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A closer look at the charge recombination of non-water-soluble conjugates M-3 and M-5 to recover the ground state(i.e., direct or via an excited state) shows no distinct genera-tion dependence. In fact, only the incorporated metal centerand the solvent, in which increased polarity leads to a de-creased lifetime of the radical ion pair states, are decisive.In contrast, the dynamics in water-soluble conjugates M-4and M-6 is dependent on the generation. It is, however, thefirst-generation dendron that leads to slower charge recom-bination. Interestingly, the electrochemical data suggest thatM-4 and M-6 have similar free energies for the charge sepa-ration/charge recombination processes (see Table 3). Thus,not only first- and second-generation dendrons but also non-water-soluble and water-soluble conjugates should revealcomparable radical ion pair state lifetimes. Nonetheless, thisperspective is incomplete because it overlooks the stabiliz-ing effect of the dendrimers, or the lack of it. Quantumchemical calculations revealed that different conformerspresent different shielding effects on the electroactive moie-ties.[11k] Importantly, although the hydrophilic part of thedendrons provides water-solubility, the hydrophobic part ofthe Newkome-type dendron interacts with the hydrophobic

porphyrin and/or the fullerene. Apparently, the right bal-ance between these two forces is decisive and leads to short-er charge-separated-state lifetimes in the M-6 series.

Finally, to assess the dynamics of the charge transfer ofthe water-soluble conjugates we correlated the free energy

Figure 13. Top: Differential absorption spectra (visible and near-infrared)obtained upon femtosecond flash photolysis (l=420 nm, 150 nJ) of FeIII-6 (�10�6

m) in argon-saturated H2O (pH 7, RT) at time delays of 1.1, 1.6,2.4, 4.4, 6.4, 14.0, and 34.0 ps (from darkest line to lightest line). Bottom:Time absorption profiles at l=470 (*) and 528 nm (*) of the spectrashown above, monitoring the charge-separation and charge-recombina-tion dynamics.

Figure 14. Top: Differential absorption spectra (visible and near-infrared)obtained upon femtosecond flash photolysis (l =420 nm, 150 nJ) of NiII-4(�10�6

m) in argon-saturated H2O (pH 10, RT) at time delays 1.1, 2.4,6.4, 10.4, 24.0, 34.0, and 44.0 ps (from darkest line to lightest line). Bot-tom: Time absorption profiles at l=455 (*) and 528 nm (*) of the spec-tra shown above, monitoring the charge-separation and charge-recombi-nation dynamics.

Table 2. Charge separation and charge-separation dynamics in water-soluble conjugates M-4 and M-6.

Chargeseparation [ps]

Chargerecombination [ps]

Zn ZnII-6 1 275ZnII-4 1 50

Cu CuII-6 0.6 900CuII-4 0.7 3000

Co CoII-6 0.8 58CoII-4 0.7 93

Mn MnIII-6 0.8 84MnIII-4 0.9 114

Fe FeIII-6 0.8 48FeIII-4 0.9 586

Ni NiII-6 0.8 127NiII-4 0.7 252

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FULL PAPERFullerenes and Metalloporphyrins in Aqueous Environments

changes of the different electron-transfer processes with thedynamics. In this regard, we achieved the characteristic bell-shape dependence known from the Marcus theory on elec-tron transfer (Figure 15).[11j] In fact, the latter constitutes

one of the rare cases of the derivation of reorganization en-ergies in a very polar environment, such as water. However,the actual value of 0.65 eV, which is based on the drivingforces determined in DMF, is remarkably small and is indi-cative of the efficient shielding of the two photo- and elec-troactive constituents from the polar environment (waterand/or DMF). Notably, the electronic coupling matrix ele-ment with a value of 91 cm�1 is well in line with previous in-vestigations that were performed in non-aqueous media.

Experimental Section

General remarks : All chemicals were purchased from chemical suppliersand used without further purification. All analytical reagent-grade sol-vents were purified by distillation.

Thin-layer chromatography (TLC): Merck silica gel 60 F254 was used. AUV-lamp and KMnO4-bath were used for detection.

Column chromatography : Merck silica gel 60 (230–400 mesh, 0.04–0.063 nm) was used.

IR spectroscopy: A Bruker FT-IR Vector 22 spectrometer equipped withan ATR RFS 100/S unit was used; substances were measured as solids.

UV/Vis spectroscopy: An Analytik Jena Specord S 600 spectrometer wasused; absorption maxima lmax given in nm.

Mass spectroscopy : A Micromass Zabspec spectrometer in FAB(LSIMS) mode (matrix: 3-nitrobenzyl alcohol (NBA)) or a ShimadzuAXIMA Confidence with time-of-flight mass spectrometer with a l=

337 nm nitrogen laser (matrix: sinapic acid (SIN), 2,5-dihydroxybenzoicacid (DHB), or dithranole (DITH)) were used.

NMR spectroscopy: JEOL Alpha500, JEOL JNM EX 400, JEOL JNMGX 400, and Bruker Avance 300 spectrometers were used. Chemicalshifts are given in ppm relative to TMS. Resonance multiplicities are in-dicated as s (singlet), d (doublet), t (triplet) and m (multiplet). Broad sig-nals are indicated as br.

Steady-state fluorescence spectroscopy: A Horiba–Jobin–Yvon Fluoro-max 3 spectrophotometer was used; spectra were recorded in deaeratedsolutions at RT (298 K) in a 1 cm quartz cuvette. All spectra were cor-rected for the instrument response. The monitoring wavelength corre-sponded to the maximum of the emission band. For excitation wave-lengths below l= 450 nm, a cutoff filter (l=450 nm) was inserted.

Femtosecond transient absorption spectroscopy: Femtosecond transientabsorption studies were performed with l= 387 nm laser pulses (1 kHz,150 fs pulse width) from an amplified Ti/sapphire laser system (ModelCPA 2101, Clark-MXR; output l=775 nm). For an excitation wavelengthof l=420 nm, a nonlinear optical parametric converter (NOPA) wasused to generate ultra-short tunable visible pulses from the pump pulses.The transient absorption pump probe spectrometer (TAPPS) is referredto as a two-beam setup, where the pump pulse is used as excitationsource for transient species and the delay of the probe pulse is exactlycontrolled by an optical delay rail. As a probe (white-light continuum), asmall fraction of pulses stemming from the CPA laser system was focusedby a 50 mm lens into a 2-mm-thick sapphire disc. The transient spectrawere recorded by using fresh oxygen-free solutions in each laser excita-tion. M-4 dyads were measured in pH 10 phosphate buffer solution(Sigma–Aldrich), whereas M-6 was recorded at pH 07. All experimentswere performed at 298 K in a 2 mm quartz cuvette.

Nanosecond transient absorption spectroscopy : Transient absorption ex-periments, based on nanosecond laser photolysis, were performed withthe output of the third harmonics (l= 355 nm) from a Nd/YAG laser(Brilliant, Quantel). Moreover, pulse widths of <5 ns with an energy of10 mJ were selected. The optical detection was based on a pulsed Xenonlamp (XBO 450, Osram), a monochromator (Spectra Pro 2300i, ActonResearch), a R928 photomultiplier tube (Hamamatsu Photonics), or afast InGaAs photodiode (Nano 5, Coherent) with 500 MHz amplificationand a 1 GHz digital oscilloscope (WavePro7100, LeCroy). The laserpower of every laser pulse was registered by using a bypath with a fastsilicon photodiode. The solvents were always of spectroscopic grade. Thens-laser photolysis experiments were performed by using 1 cm quartzcells and the solutions were saturated with argon if no other gas satura-tion is indicated.

Pulse radiolysis : Pulse radiolysis experiments were performed by using50 ns pulses of 15 MeV electrons from a linear electron accelerator(LINAC). Dosimetry was based on the oxidation of SCN� to (SCN)2C

�,which in saturated aqueous N2O takes place with G�6 (G denotes thenumber of species per 100 eV, or the approximate mm concentration per10 J of absorbed energy). The radical concentration generated per pulsewas varied between 1–3 � 10�6

m.

Electrochemistry : Electrochemical measurements were undertaken byusing a Metrohm mAutolab Type III/FRA 2 instrument. Cyclic voltamme-try and differential pulse voltammetry were performed in a cell in whicha glassy carbon electrode, a platinum counter electrode and a silver refer-ence electrode were used. Ferrocene was applied as internal reference

Table 3. Driving forces for charge separation and charge-separation pro-cesses in water-soluble M-4 and M-6.[a]

�DG0CS [eV] �DG0

CR [eV][b]

Zn ZnII-6 0.62 1.38ZnII-4 0.62 1.38

Cu CuII-6 0.67 1.46CuII-4 0.67 1.46

Co CoII-6 0.27 0.14[c]

CoII-4 0.22 0.19[c]

Mn MnIII-6 0.32 0.08[c]

MnIII-4 0.32 0.08[c]

Fe FeIII-6 0.64 0.02[c]

FeIII-4 0.64 0.02[c]

Ni NiII-6 1.07 0.93NiII-4 1.11 0.89

[a] Driving forces were extrapolated from previously published values.[11j]

[b] Charge recombination to give the ground state. [c] Charge recombina-tion to give lower-lying porphyrin excited states.

Figure 15. Driving-force (�DG0ET) dependence of the rate constant for

charge separation (filled symbols) and charge recombination (open sym-bols) in MnIII-4/MnIII-6 (orange symbols), FeIII-4/FeIII-6 (blue symbols),CoII-4/CoII-6 (grey symbols), NiII-4/NiII-6 (green symbols), CuII-4/CuII-6(red symbols), ZnII-4/ZnII-6 (black symbols).

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D. M. Guldi, A. Hirsch et al.

and Bu4NPF6 at 0.1m was used as supporting electrolyte. All measure-ments were performed under argon atmosphere.

Synthesis : The syntheses of the dendronized porphyrins M-1 and the cor-responding dendronized porphyrin-fullerene dyads M-3 and M-5 (M=

Cu, Co, Ni, Fe(Cl), Mn(Cl)) are reported elsewhere.[11j, k]

General procedure for the synthesis of water-soluble porphyrins M-2 andporphyrin–fullerene dyads M-4 and M-6 : Porphyrins M-1 and dyads M-3and M-5 (M=Cu, Co, Ni, Fe(Cl), Mn(Cl)) were dissolved in formic acidand stirred for 24–36 h. After the solvent was evaporated the compoundswere dissolved in THF and DMF respectively and recrystallized from n-pentane.

Data for CuII-2 : Obtained as a pink solid in 90 % yield. 1H NMR(400 MHz, RT, CD3OD): d= 1.32–2.04 (br s, CH2), 3.71 ppm (br s,OCH3); 13C NMR (100.5 MHz, RT, CD3OD): d=30.2, 31.9, 32.1 (CH2),58.6, 59.4 (qC), 170.6, 175.3, 177.1 ppm (C=O); IR (ATR): nmax =718, 798,889, 1003, 1071, 1097, 1179, 1256, 1279, 1341, 1417, 1482, 1538, 1575,1604, 1704, 2546, 2926 cm�1; UV/Vis (H2O): l =412, 538 nm; MS(MALDI-TOF, SIN): m/z : 2978 [M]+ .

Data for CoII-2 : Obtained as a red solid in 95 % yield. 1H NMR(400 MHz, RT, [D8]THF): d=1.76–2.19 (m, 96H; CH2), 3.62 (br s, 4 H;CH2), 3.75 (br s, 6H; OCH3), 4.38–4.58 (m, 8H; CH2), 5.01 (m, 4H;CH2), 6.20 (m, 6 H; NH ACHTUNGTRENNUNG(C=O)), 7.33–8.02 (br s, 14 H; Ar-H), 8.81 ppm(br s, 8H; b-H); 13C NMR (100.5 MHz, RT, CD3OD): d=29.7, 30.3, 32.2(CH2), 53.0 (OCH3), 58.8 (qC), 64.7, 65.1, 67.8 (CH2), 105.1, 129.0, 129.0,135.1, 135.2, 145.6, 145.8, 157.7 (Ar-C), 168.3, 168.7, 169.6, 175.3 ppm (C=

O); IR (ATR): nmax = 794, 888, 1007, 1096, 1179, 1222, 1259, 1405, 1452,1540, 1699, 2341, 2360, 2854, 2924 cm�1; UV/Vis (H2O): l= 426, 540 nm;MS (MALDI-TOF, DHB): m/z : 2973 [M]+ .

Data for NiII-2 : Isolated as a red solid in 90% yield. 1H NMR(400 MHz, RT, [D8]THF): d =1.77–2.19 (m, 96 H; CH2), 3.77 (m, 6 H;OCH3), 4.35 (m, 8 H; CH2), 5.01 (m, 4H; CH2), 6.15 (m, 6H; NH ACHTUNGTRENNUNG(C=O)),7.31–7.64 (m, 16 H; Ar-H), 8.78 ppm (m, 8H; b-H); 13C NMR(100.5 MHz, RT, [D8]THF): d=28.5, 30.5 (CH2), 41.6 (CH2), 57.7 (qC),99.8, 104.4, 128.5 (Ar-C), 132.6 (b-C), 143.6 (Ar-C), 172.6, 174.3,174.7 ppm (C=O); UV/Vis (H2O): l= 413, 526 nm; IR (ATR): nmax =785,1008, 1096, 1170, 1222, 1259, 1405, 1538, 1698, 2923, 2978 cm�1.

Data for FeIII-2 : Obtained as a brown solid in 85% yield. 1H NMR(400 MHz, RT, CD3OD/[D8]THF): d=1.80–2.47 (m, 96H; CH2), 3.26 (m,4H; CH2), 4.42–5.00 (m, 12H; CH2), 6.20 (br s, 6H; NH ACHTUNGTRENNUNG(C=O)), 7.09–7.53 (m, 8 H; Ar-H), 10.36 (br s, 2H; Ar-H), 11.24 (br s, 2 H; Ar-H), 12.42(br s, 2H; Ar-H), 79.08 (br s, 4 H; b-H), 81.63 ppm (br s, 4H; b-H);13C NMR (100.5 MHz, RT, CD3OD): d=30.7, 31.7, 32.2 (CH2), 66.9(CH2), 169.0, 177.1 ppm (C=O); IR (ATR): nmax =722, 797, 865, 1003,1021, 1092, 1179, 1222, 1258, 1422, 1543, 1577, 1640, 1703, 2853,2923 cm�1; UV/Vis (H2O): l=410, 527 nm; MS (MALDI-TOF, SIN): m/z : 3003 [M]+ .

Data for MnIII-2 : Obtained as a green solid in 96 % yield. 1H NMR(400 MHz, RT, CD3OD): d =�30.82 (br s, 8 H; b-H), 1.80–2.81 (m, 96 H;CH2), 3.60 (br s, 4 H; CH2), 3.79 (br s, 6H; OCH3), 7.28–8.01 ppm (br s,16H; Ar-H); 13C NMR (100.5 MHz, RT, CD3OD): d= 30.6, 31.6 (CH2),67.7 ppm (CH2); IR (ATR): nmax =717, 803, 891, 1010, 1032, 1069, 1097,1181, 1222, 1256, 1279, 1407, 1481, 1539, 1576, 1605, 1644, 1701, 2341,2358, 2924 cm�1; UV/Vis (H2O): l=381, 401, 417 (sh), 467, 566, 600 nm.MS (MALDI-TOF, DHB): m/z : 2970 [M�Cl]+ .

Data for CuII-4 : Isolated as a red solid in 98 % yield. 1H NMR(400 MHz, RT, [D8]THF): d=2.03 (br s, 12H; CH2), 2.22 (br s, 12H;CH2), 3.94 (br s, 6 H; OCH3), 4.19–5.11 (br s, 12H; CH2), 6.87 (br s, 2H;NH ACHTUNGTRENNUNG(C=O)), 7.34–7.91 ppm (br s, 16H; Ar-H); 13C NMR (100.5 MHz, RT,[D8]THF): d=28.5, 30.5 (CH2), 54.1 (OCH3), 58.1 (qC), 71.7, 72.2 (C60-sp3), 115.3, 129.1 (Ar-C), 138.2, 138.3, 138.5, 139.8, 140.2, 140.4, 140.8,141.4, 142.8, 143,9, 144.8, 145.6, 146.4, 149.9 (C60-sp2), 156.6, 157.0 (Ar-C),163.9, 167.2, 167.5, 174.5 ppm (C=O); IR (ATR): nmax =735, 798, 931,1006, 1035, 1069, 1109, 1216, 1228, 1366, 1433, 1540, 1578, 1738, 2341,2360, 2941, 2970, 3015 cm�1; UV/Vis (H2O): l (log e) =261 (5.02), 321(4.70), 423 (5.18), 544 nm (4.16); MS (FAB, NBA): m/z : 2319 [M]+ , 720[C60]

+ .

Data for CoII-4 : Obtained as a red-brown solid in 97 % yield. 1H NMR(400 MHz, RT, [D8]THF): d=2.04–2.62 (br s, 24 H; CH2), 3.81 (br s, 6H;OCH3), 4.21–5.32 (br s, 12H; CH2), 7.19–8.73 (br s, 12 H; Ar-H),13.58 ppm (br s, 2H; Ar-H); 13C NMR (100.5 MHz, RT, [D8]THF): d=

28.5, 30.5 (CH2), 53.6 (OCH3), 174.5 ppm (C=O); IR (ATR): nmax =796,888, 1005, 1058, 1093, 1216, 1228, 1365, 1434, 1540, 1576, 1738, 2341,2360, 2970, 3015 cm�1; UV/Vis (H2O): l (log e)=260 (4.93), 320 (4.64),424 (4.88), 534 nm (3.84); MS (FAB, NBA): m/z : 2314 [M]+ , 720 [C60]

+ .

Data for NiII-4 : Obtained as a red-brown solid in 99% yield. 1H NMR(400 MHz, RT, [D8]THF): d=2.04 (br s, 12H; CH2), 2.22 (br s, 12H;CH2), 3.91 (s, 6H; OCH3), 4.56 (m, 8H; CH2), 4.77 (m, 2 H; CH2), 5.16(m, 2 H; CH2), 6.90 (br s, 2 H; NH ACHTUNGTRENNUNG(C=O)), 7.11 (m, 8H; Ar-H), 7.35 (m,4H; Ar-H), 7.79 (t, 3J=7.93 Hz, 2 H; Ar-H), 8.21 (d, 3J= 7.32 Hz, 2 H),8.69 ppm (m, 8H; b-H); 13C NMR (100.5 MHz, RT, [D8]THF): d=28.5,30.5 (CH2), 51.0 (CH2), 54.0 (OCH3), 58.1 (CH2), 67.9 (CH2), 71.5, 72.16(C60-sp3), 114.5 (Ar-C), 119.6, 119.8 (meso-C), 121.7, 124.8, 125.9, 127.7,128.5 (Ar-C), 132.6 (b-C), 138.7, 139.1, 139.6, 141.1, 141.3, 142.0, 142.2,142.7, 142.97, 143.01, 143.1, 143.26, 143.33, 143.5, 143.7, 144.3, 144.6 (C60-sp2), 143.8, 144.0 (Ar-C), 145.0, 145.3, 146.0, 146.1, 149.1 (C60-sp2), 157.3,158.2 (Ar-C), 162.1, 163.9, 167.5, 174.5 ppm (C=O); IR (ATR): nmax =796,900, 1009, 1092, 1216, 1228, 1365, 1435, 1508, 1738, 2342, 2361, 2959,2970, 3015 cm�1; UV/Vis (H2O): l (log e)=260 (5.02), 321 (4.69), 421(5.05), 530 nm (4.10); MS (FAB, NBA): m/z : 2313 [M]+ , 720 [C60]

+ .

Data for FeIII-4 : Isolated as a brown solid in 99% yield. 1H NMR(400 MHz, RT, [D8]THF): d=2.27–2.48 (br s, 24 H; CH2), 4.00 (br s, 6H;OCH3), 6.48 (br s, 2 H; NH ACHTUNGTRENNUNG(C=O)), 7.27–7.91 (br s, 8H; Ar-H), 11.11 (br s,4H; Ar-H), 12.00 (br s, 2H; Ar-H), 79.27 (br s, 4 H; b-H), 82.17 ppm (br s,4H; b-H); 13C NMR (100.5 MHz, RT, [D8]THF): d =29.9, 30.8 (CH2),54.9 (OCH3), 59.7 (CH2), 174.7 ppm (C=O); IR (ATR): nmax =736, 758,803, 883, 1003, 1051, 1179, 1334, 1433, 1578, 1602, 1724, 2328, 2342, 2955,3406 cm�1; UV/Vis (H2O): l (log e)=260 (4.78), 322 (4.57), 421 nm(4.62); MS (FAB, NBA): m/z : 2311 [M�Cl]+ , 720 [C60]

+.

Data for MnIII-4 : Obtained as a green solid in 97 % yield. 1H NMR(400 MHz, RT, D2O): d =2.03–2.45 (br s, 24H; CH2), 6.94–8.09 ppm (br s,18H; Ar-H); 13C NMR (100.5 MHz, RT, D2O): d=166.8 ppm (C=O); IR(ATR): nmax =797, 864, 1016, 1090, 1216, 1228, 1259, 1366, 1408, 1437,1738, 2341, 2360, 2969, 3015 cm�1; UV/Vis (H2O): l (log e) =261 (5.00),323 (4.77), 387 (4.65), 408 (sh, 4.59), 481 (4.70), 578 (3.99), 613 nm (3.90);MS (FAB, NBA): m/z : 2310 [M�Cl]+ , 720 [C60]

+ .

Data for CuII-6 : Obtained as a red-brown solid in 99 % yield. 1H NMR(400 MHz, RT, D2O): d=1.95–3.22 (br s, 102 H; CH2), 8.09–8.53 ppm(br s, 16H; Ar-H); 13C NMR (100.5 MHz, RT, D2O): d= 31.3 (CH2), 58.7(CH2), 171.3 ppm (C=O); IR (ATR): nmax =735, 797, 900, 1005, 1106,1216, 1228, 1365, 1421, 1541, 1615, 1738, 2341, 2361, 2945, 2970,3016 cm�1; UV/Vis (H2O): l (log e) =260 (5.11), 324 (4.60), 423 (5.12),543 nm (4.10); MS (MALDI-TOF, SIN): m/z : 3696 [M]+ .

Data for CoII-6 : Isolated as a red-brown solid in 97% yield. 1H NMR(400 MHz, RT, D2O): d=1.24–2.82 (br s, 96H; CH2), 3.98 (br s, 6 H;OCH3), 7.29–9.15 ppm (br s, 12H; Ar-H); 13C NMR (100.5 MHz, RT,D2O): d =31.2, 31.7, 32.1 (CH2), 58.7 (CH2), 164.2, 175.4 ppm (C=O); IR(ATR): nmax =736, 787, 899, 1092, 1216, 1228, 1365, 1435, 1508, 1738,2341, 2361, 2945, 2970, 3015 cm�1; UV/Vis (H2O): l (log e) =260 (5.03),322 (4.67), 426 (4.98), 538 nm (4.04); MS (MALDI-TOF, SIN): m/z : 3690[M]+ .

Data for NiII-6 : Obtained as a red-brown solid in 98% yield. 1H NMR(400 MHz, RT, D2O): d=1.81–2.12 (br s, 96H; CH2), 3.93 (br s, 6 H;OCH3), 4.04–4.54 (br s, 8 H; CH2), 5.22 (br s, 4 H; CH2), 7.26–9.35 ppm(br s, 24 H; Ar-H); 13C NMR (100.5 MHz, RT, D2O): d =31.2, 32.1 (CH2),50.2 (CH2), 58.7 (CH2), 128.4 (Ar-C), 130.6, 131.6 (b-C), 140.1–145.6 (br s,C60-sp2), 163.8, 171.6 ppm (C=O); IR (ATR): nmax =782, 838, 1009, 1092,1216, 1228, 1365, 1455, 1558, 1647, 1737, 2341, 2360, 2970, 3016,3312 cm�1; UV/Vis (H2O): l (log e) =263 (5.54), 327 (sh, 4.38), 418 (4.88),528 nm (3.93); MS (MALDI-TOF, DITH): m/z : 3689 [M]+

.

Data for FeIII-6 : Obtained as a brown solid in 99% yield. 1H NMR(400 MHz, D2O, RT): d=1.30–3.00 (br s, 96H; CH2), 3.72 (br s, 6H;OCH3), 5.00–12.02 ppm (br s, 38 H; CH2, Ar-H); 13C NMR (100.5 MHz,RT, D2O): d =31.3, 31.9 (CH2), 160.6 ppm (C=O); IR (ATR): nmax =789,845, 1093, 1216, 1228, 1367, 1455, 1559, 1650, 1737, 2341, 2360, 2945,

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2976, 3015, 2239 cm�1; UV/Vis (H2O): l (log e)=260 (5.06), 321 (4.76),421 (4.88), 499 (sh, 4.02), 635 nm (sh, 3.65); MS (MALDI-TOF, nomatrix): m/z : 3688 [M�Cl]+ .

Data for MnIII-6 : Isolated as a green solid in 97 % yield. 1H NMR(400 MHz, RT, D2O): d=1.88–2.40 (br s, 96H; CH2), 3.80 (br s, 6 H;OCH3), 7.27–8.42 ppm (br s, 18H; Ar-H); 13C NMR (100.5 MHz, RT,D2O): d=31.5 (CH2), 164.3 ppm (C=O); IR (ATR): nmax =783, 839, 1093,1216, 1228, 1365, 1455, 1558, 1738, 2341, 2360, 2946, 2970, 3016,3327 cm�1; UV/Vis (H2O): l (log e) =263 (5.19), 319 (4.69), 386 (4.56),410 (sh, 4.49), 480 (4.55), 576 (3.89), 609 nm (3.80); MS (MALDI-TOF,SIN): m/z : 3687 [M�Cl]+ .

Acknowledgements

Financial support by the Deutsche Forschungsgemeinschaft throughgrant no. SFB583 is gratefully acknowledged.

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Received: September 13, 2011Published online: December 30, 2011

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