Reversible piezochromism in a molecular wine-rack

SUPPLEMENTARY INFORMATION

Elena L. Harty,1 Alex R. Ha,1 Mark R. Warren,2 Amber L. Thompson,1

David R. Allan,2 Andrew L. Goodwin,1 and Nicholas P. Funnell1∗

1Department of Chemistry, University of Oxford, Inorganic Chemistry Laboratory,

South Parks Road, Oxford OX1 3QR, U.K.

2Diamond Light Source, Harwell Campus, Didcot, Oxfordshire OX11 0DE, U.K.

∗To whom correspondence should be addressed; E-mail: nicholas.funnell@chem.ox.ac.uk.

Submitted to Chemical Communications

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Electronic Supplementary Material (ESI) for ChemComm.This journal is © The Royal Society of Chemistry 2015

Contents

1 Experimental Methods 31.1 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31.2 Variable-Pressure Single-Crystal X-ray Diffraction . . . . . . . . . . . . . . . . . . . . . . . 31.3 Variable-Pressure Single-Crystal Data Processing and Refinement Procedure . . . . . . . 31.4 Low-Temperature Single-Crystal Data Processing and Refinement Procedure . . . . . . . 31.5 Variable-Pressure UV–Vis Absorption Spectroscopy . . . . . . . . . . . . . . . . . . . . . 5

2 Crystal Structure Refinement Tables 6

3 Variable-Pressure Crystal Photographs 9

4 Intermolecular interactions 10

5 References 14

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1 Experimental Methods

1.1 Materials

ROY was purchased from TCI Chemicals in the OP (orange plate) form. Recrystallisation from dichloro-methane yielded a mixture of differently-coloured polymorphs. Among these were yellow crystals ofsuitable size for diffraction — a handful of these were confirmed to be Y (yellow) polymorphs via SXRDmeasurements.

1.2 Variable-Pressure Single-Crystal X-ray Diffraction

High-pressure, single-crystal, X-ray diffraction data were collected using a Merrill-Bassett diamondanvil cell (DAC), equipped with a steel gasket, a ruby chip to act as a pressure marker, and a 4:1methanol:ethanol pressure-transmitting medium.S1–3 Data collection over the full pressure range ofambient–5.2 GPa proceeded in two stages. The structure of a small, well-diffracting, yellow crystalwas determined by X-ray diffraction (confirming it as a Y-form polymorph) and then loaded into the DACwhere data were collected at pressures of 0, 0.25, 0.54, 0.99 and 1.49 GPa. Above the last pressurepoint, the steel gasket failed — the crystal was recovered from the cell and another ambient data setwas recorded on this sample. A second Y-form crystal, also confirmed by ambient X-ray diffraction, wascompressed directly to 1.89 GPa. Data were collected at this pressure and then at 1.89, 2.84, 4.03 and5.20 GPa, above which pressure, the diffraction quality deteriorated.

1.3 Variable-Pressure Single-Crystal Data Processing and Refinement Proce-

dure

All data were collected on an Agilent Technologies SuperNova diffractometer (Mo Kα radiation, λ =0.71073 A) and integrated using CrysAlisPro.S4 Reflections arising from the diamond anvils were omit-ted as part of the data processing. Although the crystal structure could be solved using SIR92 at allpressure points investigated, to ensure consistency, the atomic coordinates of the preceding pressurepoint were used as a starting model for each refinement.S5 The models were refined against F 2 usingCRYSTALS.S6 In all cases a poor data-to-parameter ratio, caused by shading of reciprocal space by theDAC body, precluded anisotropic refinement of the model; only the relatively electron-rich sulfur atomwas refined anisotropically. It was also necessary to place distance, angle and thermal similarity re-straints on the model — full details of these are given in the CIFs supplied. Following initial refinement ofthe non-hydrogen atoms, the hydrogen atom positions were refined with restraints (available in the CIFs)using the procedure described in ref. 7. The hydrogen atoms were then constrained to ride on their hostatoms for subsequent cycles of refinement. Refined cell parameters and a third order Birch-Murnaghanequation of state are shown in Figure S1.S8, S9

1.4 Low-Temperature Single-Crystal Data Processing and Refinement Proce-

dure

Low-temperature single-crystal data were collected on beamline I19 at the Diamond Light Source,λ = 0.6889 A. The sample was cooled to 30 K using an Oxford CryoSystems Helix and the data wereintegrated using CrysAlisPro.S4 The coordinates of the refined ambient-pressure structure were used asa starting model for the refinement and were refined against F 2 using CRYSTALS.S6 All non-hydrogen

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atoms were refined anisotropically. Restrained refinement of the hydrogen atoms was carried out ac-cording to the procedure described in ref. 7

Figure S1: Unit cell parameters as a function of pressure. Triangular data points (all occurring at 0 GPa)

denote the ambient-pressure crystal recovered from the DAC at 1.49 GPa. Standard deviations are

within the size of the data points.

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1.5 Variable-Pressure UV–Vis Absorption Spectroscopy

High-pressure UV–Vis absorption spectroscopy measurements were carried out using an Andor Sham-rock SR-303i spectrometer (wavelength resolution and accuracy, 0.1 and 0.04 nm, respectively), equippedwith a NewtonEM detector and an Ocean Optics UV–Vis DH-2000 deuterium tungsten halogen lightsource. The DAC was loaded as described in §1.1 and high-pressure absorption spectroscopic mea-surements were taken between 280.25 and 826.96 nm at 0.74, 1.32, 2.09 and 3.01 GPa. The experimentwas complicated by slight dissolution of the crystal in the methanol:ethanol hydrostatic medium, colour-ing the solution and thus raising the level of background noise considerably. The data were rebinnedover larger intervals, in order to give prominence to the signal over the background noise, and then nor-malised against the most intense absorption peak at each pressure. In order to extract a quantitativelymeaningful absorption dependence on pressure, we used the leading edge of the most intense absorp-tion peaks, rather than the peak maximum, since this feature was more clearly represented in the data.The midpoint of each leading edge was identified by fitting a Gaussian function to the first derivative ofthe leading edge, shown in Figure S2.

Figure S2: First derivatives of the UV–Vis absorption spectra (black line), calculated over the wavelength

range of the leading peak edges. Gaussian fits are shown in red, with peak positions indicated in blue.

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2 Crystal Structure Refinement Tables

Refinement details for variable-pressure single-crystal X-ray diffraction measurements are given in TableS1. Low-temperature refinement details are given in Table S2. Additional details are available in the CIFssupplied.

Table S1: Variable-pressure crystal structure refinement details for ROY Y-form (continued on next page)

Radiation Mo Kα, λ= 0.71 A

Formula, weight C12H9N3O2S1, 259.29 g mol−1

Symmetry Monoclinic, P21/n, Z = 4

Pressure (GPa) Ambient 0.25 0.54 0.99 1.49

a (A) 8.5322(17) 8.412(3) 8.337(3) 8.2031(15) 8.116(2)

b (A) 16.412(3) 15.9905(15) 15.8027(14) 15.4235(10) 15.1210(10)

c (A) 8.4958(17) 8.469(2) 8.4626(19) 8.4569(14) 8.4699(16)

β (◦) 91.78(3) 91.55(3) 91.44(3) 90.851(14) 90.38(3)

V (A3) 1189.1(4) 1138.7(5) 1114.6(5) 1069.9(3) 1039.4(4)

Density (g cm−3) 1.448 1.512 1.545 1.610 1.657

θSCNC (◦) 104.7(2) 105.7(13) 108.7(11) 112.2(9) 117.1(9)

R[F 2 > 2σ(F 2)] 0.0427 0.1048 0.0925 0.0800 0.0759

wR(F 2) 0.1074 0.2212 0.1813 0.1526 0.1667

S 0.9671 0.9588 0.9407 0.9879 0.9781

Measured reflections 5816 7186 6766 6483 6322

Independent reflections 2826 966 907 862 861

Reflections [I/σ > 2.0] 2174 668 646 651 654

∆ρmax,∆ρmin (e A−3) 0.33, −0.30 0.79, −0.79 0.80, −0.88 0.69, −0.65 0.78, −0.75

Completeness at 0.85 (A) 99.8% 50.4% 48.3% 47.8% 49.1%

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Pressure (GPa) 1.89 2.84 4.03 5.20 Ambient (recovered)

a (A) 8.0755(16) 8.0025(16) 7.9246(16) 7.8626(16) 8.5460(17)

b (A) 14.874(3) 14.448(3) 14.028(3) 13.721(3) 16.420(3)

c (A) 8.4734(17) 8.4923(17) 8.4897(17) 8.4707(17) 8.5053(17)

β (◦) 89.76(3) 89.15(3) 88.75(3) 88.55(3) 91.78(3)

V (A3) 1017.7(4) 981.8(3) 943.5(3) 913.5(3) 1193.0(4)

Density (g cm−3) 1.692 1.754 1.825 1.885 1.444

θSCNC (◦) 119.0(11) 123.1(6) 127.9(5) 131.6(6) 104.8(4)

R[F 2 > 2σ(F 2)] 0.0950 0.0664 0.0557 0.0692 0.0464

wR(F 2) 0.2159 0.1844 0.1161 0.1644 0.0899

S 0.9791 0.9946 0.9767 0.9690 1.0366

Measured reflections 5263 5974 5729 5470 5266

Independent reflections 943 1041 975 931 2695

Reflections [I/σ > 2.0] 563 803 759 668 1846

∆ρmax,∆ρmin (e A−3) 1.18, −0.99 0.67, −0.70 0.61, −0.66 0.75, −0.70 0.44, −0.55

Completeness at 0.85 (A) 54.7% 62.6% 61.0% 60.4% 100%

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Table S2: 30 K crystal structure refinement details for ROY Y-form

Radiation λ= 0.6889 A

Formula, weight C12H9N3O2S1, 259.29 g mol−1

Symmetry Monoclinic, P21/n, Z = 4

Temperature (K) 30

a (A) 8.45062(16)

b (A) 15.9403(3)

c (A) 8.46555(13)

β (◦) 91.0663(17)

V (A3) 1140.16(3)

Density (g cm−3) 1.510

θSCNC (◦) 106.7(1)

R[F 2 > 2σ(F 2)] 0.042

wR(F 2) 0.0962

S 0.9081

Measured reflections 15136

Independent reflections 3890

Reflections [I/σ > 2.0] 3291

∆ρmax,∆ρmin (e A−3) 0.55, −0.47

Completeness at 0.85 (A) 99.6%

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3 Variable-Pressure Crystal Photographs

Figure S3: Variable-pressure microscopic photographs. The sample recovered from 1.49 GPa to ambi-

ent pressure is not surrounded by the DAC body and thus is illuminated differently to the other images

shown here. Note that the pressure increase between images is not constant — it is generally much

larger across the bottom row. Images are not shown on the same scale.

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4 Intermolecular interactions

The origin of the piezochromism has largely been explained in terms of molecular conformation, howevernot much has been said so far about intermolecular geometry/packing. Obvious intermolecular candi-dates for the change in crystal colour are the π · · · π stacking distances that exist between nitrophenyl–thiophene and nitrophenyl–nitrophenyl groups, in the Y form. The distance between the former de-creases from 5.0375(16) to 4.160(3) A, while the latter increases from 3.7600(15) to 4.250(5) A — thenet effect being that the π · · · π stacks become more evenly spaced. The increasing distance betweenthe nitrophenyl groups is due to ring slippage, which becomes more prominent as pressure is increased(see lower panels in Figure).

It has also been highlighted that the crystal topology varies significantly between the different ROYpolymorphs, when the molecular centres of mass are considered — see Figure 2 in Ref. 10. To demon-strate that there is no drastic change in packing, an analogous Figure is presented here (Figure S5),showing the radial distribution functions (RDFs) for Y-form ROY at each pressure point measured here.While small changes in the intermolecular environment clearly occur as pressure is increased, the his-tograms for the higher pressure structures do not appear strongly reminiscent of any of the other poly-morphs.

A question outstanding is whether the hydrogen bond between the carbonitrile group and the bridgingamine hydrogen is influential — it has been suggested on the basis of carbonitrile stretching frequencies,that this may be the case.S10, S11 As our crystallographic data are highly incomplete — owing to shadingof reciprocal space by the DAC — it was necessary to restrain bond distances within the molecule(details available in the CIFs), including geometric placement of hydrogen atoms, and so it is not possibleto draw any firm conclusions from our data regarding the carbonitrile bond length. However, a plot ofN· · ·N distances across the hydrogen bond (Figure S6) suggests that there is no smoothly varying trendas pressure is increased. A modest overall decrease in distance of ca. 0.14 A is observed.

It is the variation in topology and intermolecular interactions, but a consistency in molecular con-formational behaviour, across the ROY polymorphs and within the pressure series measured here thatleads us to conclude that intramolecular electronic conjugation between the nitrophenyl and thiophenegroups is predominantly responsible for the piezochromic effect. Given that the geometries of π · · · πstacking vary quite considerably across all the known polymorphs of ROY, this would suggest they playa lesser role in influencing crystal colour. As we are unable to disentangle changes in intermolecu-lar and intramolecular structure completely within our pressure series, we cannot say with a certaintythat intermolecular interactions are completely unimportant, but in light of the structures of other ROYpolymorphs, this would appear to be the case.

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Figure S4: Aromatic centroid· · ·centroid distances (d1 and d2) as a function of pressure (left). The

centre and right-hand panels show specific π · · · π interactions at ambient pressure and 5.20 GPa. The

lower panels show that the increasing distance between nitrophenyl groups (d2) can be explained by

ring slippage.

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Figure S5: Radial distribution functions for molecular centres of mass at each pressure point, for com-

parison with Figure 2 in Ref. 10. Centroids have been calculated without hydrogen atoms and frequen-

cies are shown using a bin width of 0.2 A. Histograms are coloured red and blue alternately, to aid visual

clarity.

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Figure S6: Distance between hydrogen bond donor and acceptor nitrogen atoms. Error bars for the

ambient pressure distance are within the size of the data point.

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5 References

(S1) L. Merrill, W. A. Bassett, Rev. Sci. Instrum. 45, 290 (1974).(S2) S. A. Moggach, D. R. Allan, S. Parsons, J. E. Warren, J. Appl. Crystallogr. 41, 249 (2008).(S3) G. J. Piermarini, S. Block, J. D. Barnett, R. A. Forman, J. Appl. Phys. 46, 2774 (1975).(S4) CrysAlis PRO. Agilent Technologies UK Ltd, Yarnton, UK (2011).(S5) A. Altomare, et al., J. Appl. Crystallogr. 27, 435 (1994).(S6) P. Betteridge, J. Carruthers, R. Cooper, K. Prout, D. Watkin, J. Appl. Crystallogr. 36 (2003).(S7) R. I. Cooper, A. L. Thompson, D. J. Watkin, J. Appl. Crystallogr. 43, 1100 (2010).(S8) F. Birch, Phys. Rev. 71, 809 (1947).(S9) M. J. Cliffe, A. L. Goodwin, J. Appl. Crystallogr. 45, 1321 (2012).

(S10) L. Yu, Accounts Chem. Res. 43, 1257 (2010).(S11) J. R. Smith, W. Xu, D. Raftery, J. Phys. Chem. B 110, 7766 (2006).

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