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1 DOI: /NCHEM.1977 Directed assembly of optoelectronically active alkyl π-conjugated molecules by adding n-alkanes or π-conjugated species Martin J. Hollamby, 1,2 Maciej Karny, 3 Paul H. H. Bomans, 4 Nico A. J. M. Sommerdjik, 4 Akinori Saeki, 5 Shu Seki, 5 Hiroyuki Minamikawa, 6 Isabelle Grillo, 7 Brian R. Pauw, 1 Paul Brown, 8 Julian Eastoe, 8 Helmuth Möhwald, 9 Takashi Nakanishi 1,3 1 National Institute for Materials Science (NIMS), Sengen, Tsukuba , Japan 2 School of Physical and Geographical Sciences, Keele University, Keele, Staffordshire, ST55BG, UK 3 Warsaw University of Technology, Pl. Politechniki 1, Warsaw, Poland 4 Laboratory of Materials and Interface Chemistry & Soft Matter CryoTEM Research Unit, Department of Chemical Engineering and Chemistry and Institute of Complex Molecular Systems, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven, The Netherlands 5 Department of Applied Chemistry, Graduate School of Engineering, Osaka University, Osaka , Japan 6 National Institute of Advanced Industrial Science and Technology (AIST), Higashi, Tsukuba , Japan 7 Institut Max-von-Laue-Paul-Langevin, BP 156-X, F Grenoble, Cedex, France 8 School of Chemistry, University of Bristol, Bristol BS8 1TS, UK 9 Department of Interfaces, Max Planck Institute of Colloids and Interfaces, Research Campus Golm, Potsdam 14476, Germany NATURE CHEMISTRY 1

2 Index Supplementary Methods... 3 Chemicals... 3 Synthesis... 3 Molecule NMR discussion... 4 Molecule Molecule Techniques... 6 Cryogenic transmission electron microscopy (cryo-tem)... 7 Small angle scattering... 8 SAXS... 8 SANS... 9 Small-angle scattering: model fitting... 9 Micelle clusters... 9 Gel fibres Supplementary Figures Supplementary Figure Supplementary Figure Supplementary Figure Supplementary Figure Supplementary Figure Supplementary Figure Supplementary Figure Supplementary Figure Supplementary Figure Supplementary Figure Supplementary Figure Supplementary Figure Supplementary Tables Supplementary Table Supplementary Table Supplementary Table Supplementary Table Supplementary references NATURE CHEMISTRY 2

3 Supplementary Methods Chemicals 2-Decyl-1-tetradecanol, 2-octyl-1-dodecanol, C 60 (99.5%+), sarcosine, carbon tetrabromide, triphenylphosphine and sodium sulfate were purchased from Sigma-Aldrich. 4- Hydroxyazobenzene and p-toluenesulfonic acid (TsOH) were supplied by TCI chemicals. 3,5-Dihydroxybenzaldehyde, potassium carbonate, potassium iodine and [6,6]-phenyl-C 61 butyric acid methyl ester (PCBM) were obtained from Acros Organics, Fluka, Alfa Aesar and Luminescence Tech. respectively. The alcohol used as a precursor to molecule 2 (iso-stearyl alcohol fineoxocol-180) was obtained as a gift from Nissan chemicals. Solvents for reactions included THF, DMF, toluene and chlorobenzene (anhydrous, Sigma-Aldrich). For the aggregation studies, n-decane was purchased from Wako Chemicals, while n-hexane was acquired from Kanto Chemicals and n-hexane-d 14 (99% D) was purchased from Sigma- Aldrich. All chemicals were used as received. Synthesis Molecule 3 (Supplementary Fig. 8) was synthesized by reacting 3,5-bis(2- decyltetradecyloxy)benzaldehyde with C 70 via the Prato reaction 1 as follows: 3,5-bis(2- decyltetradecyloxy)benzaldehyde was first synthesized as described elsewhere. 2 Then, to a 300 ml two-neck flask, C 70 (0.1 g, 0.12 mmol) and sarcosine (0.036 g, 0.4 mmol) were added. After removing oxygen by repeated vacuum-argon cycles, 70 ml anhydrous chlorobenzene was injected and the mixture was stirred at around 80 C until the C 70 dissolved. Then 3,5-bis(2-decyltetradecyloxy)benzaldehyde (0.065 g, 0.08 mmol), predissolved in 20 ml anhydrous chlorobenzene, was injected and the mixture was refluxed in the dark for 22 hours. After the reaction was stopped and the mixture was cooled to room temperature, unreacted sarcosine was filtered off and the solvent was removed under reduced pressure. The crude product was then twice subjected to column chromatography (silica gel 60, mm, eluent: 1 part CHCl 3 to 1 part n-hexane) to remove most of the unreacted C 70. The solution was collected, and the solvent was removed under reduced NATURE CHEMISTRY 3

4 pressure. The crude product was then subjected to GPC (Bio-Beads S-X1 Beads, mesh) using toluene as an eluent and finally purified by recycling preparative HPLC, using CHCl 3 as the eluent. Obtained 3 as a black, viscous liquid: g, yield: 39% (based on conversion of 3,5-bis(2-decyltetradecyloxy)benzaldehyde). 1 H NMR (600 MHz, CDCl 3 ), δ 6.99 (br), 6.61 (s), 6.46 (s), 6.31 (s), (d, J = 9.6 Hz), (d, J = 9.6 Hz), (d, J = 9.6 Hz), 4.12 (s), (d, J = 5.4 Hz), 3.94 (s), 3.73 (m), (d, J = 9.6 Hz), (d, J = 9.6 Hz), (d, J = 9.6 Hz), (d, J = 5.4 Hz), 2.51 (s), 1.89 (br), (m), (m). For more details of 1 H NMR assignment, including peak assignment, see the discussion below and Supplementary Fig C NMR (150 MHz, CDCl 3 ), δ , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , 83.63, 83.30, 80.42, 71.35, 71.08, 70.27, 69.75, 62.04, 60.36, 58.34, 39.66, 39.63, 39.58, 38.05, 37.93, 37.83, 32.00, 31.53, 31.45, 31.35, 30.25, 30.20, 30.12, 29.84, 29.79, 29.75, 29.45, 27.07, 27.03, 26.90, 26.87, 22.77, MALDI-TOF-MS (matrix-haba) calculated: , obtained: [M + ]. NMR discussion: Due to the asymmetric nature of C 70, attachment to different parts of the cage leads to structural isomers, which can be evidenced by the complex 1 H and 13 C NMR spectra. The 1 H NMR of 3 is shown in Supplementary Fig. 11, alongside an assigned spectrum of 1 for comparison. Five regions are highlighted; theoretically including 3, 7, 3, 80 and 12 hydrogen atoms (see assigned spectra for 1). Integrations for these regions were 2.7, 6.5, 2.7, 82.4, 12.0 [set] for 3, indicating that all of the peaks in the spectra derive from the various isomers. Comparing the spectra (e.g. looking at the signal from the e proton for NATURE CHEMISTRY 4

5 molecule 1 versus 3 singlets in the same region for molecule 3) indicates the presence of 3 isomers, in line with previous reports 3 in which C 70 derivatives were synthesized using the Prato reaction. The peak ratios are of order 30:30:40, suggesting that no substitution position is strongly favored. Molecule 4 (Supplementary Fig. 8) was synthesized as follows: First, 1-octyl-2-dodecyl bromide was synthesized from 2-octyl-1-dodecanol as described elsewhere. 2 Then, 4- hydroxyazobenzene (1 g, 5.1 mmol), 2-octy-1-dodecyl bromide (2 g, 5.5 mmol), potassium carbonate (2 g, 14.5 mmol), and potassium iodide (0.5 g, 3.0 mmol) were added to 5 ml of anhydrous DMF and the mixture was stirred at 80 C for 24 hours. The mixture was added into CHCl 3, and washed with water several times. The organic layer was collected, dried over anhydrous Na 2 SO 4, and concentrated under reduced pressure. The crude product was purified by silica gel column chromatography (eluent: n-hexane, then 3 parts n-hexane to 1 part CHCl 3 ) to yield a viscous orange oil (2.11 g, 86.4%). 1 H NMR (600 MHz, CDCl 3 ), δ 7.91 (m, 2H, Ar), 7.87 (m, 2H, Ar), 7.50 (m, 2H, Ar), 7.43 (m, 1H, Ar), 7.01 (d, 1H, Ar), 3.92 (d, J = 5.8, 2H, CH 2 ), 1.81 (m, 1H, CH), (m, 32H, -CH 2 -), 0.88 (m, 6H, CH 3 ). 13 C NMR (100 MHz, CDCl 3 ), δ , , , , , , , , 71.35, 38.06, 32.07, 31.46, 30.16, 29.81, 29.78,, 29.49, 26.99, MALDI-TOF-MS, (matrix-dithranol): calculated ; found [M + ]. T g (DSC), C. The PCBM derivative 5, [6,6]-phenyl-C 61 -butyric acid 2-decyl-1-tetradecyl ester, was synthesized by a procedure similar to that reported elsewhere. 4 In a 300 ml flask equipped with a Dean-Stark apparatus, PCBM (0.3 g, 0.33 mmol), 2-decyl-1-tetradecanol (11.7 g, 33 mmol), and TsOH H 2 O (0.06 g, 0.32 mmol) were mixed and placed under argon. Toluene (120 ml) was injected and the solution was refluxed for 24 hours with stirring, until the PCBM spot in the TLC (eluent: 1 part n-hexane to 1 part CH 2 Cl 2 ) was no longer visible. After cooling to room temperature, Na 2 CO 3 was added to neutralize the mixture, which was then NATURE CHEMISTRY 5

6 washed with Na 2 CO 3(aq) (5 wt% solution) and dried over anhydrous MgSO 4. After filtration and solvent evaporation, the crude product was purified by silica gel column chromatography (eluent: 3 parts n-hexane to 1 part CH 2 Cl 2 ), and recycling preparative HPLC (eluent: CHCl 3 ), to yield 5 as a black, viscous liquid: g (0.31 mmol), yield: 94%. 1 H NMR (400 MHz, CDCl 3 ), δ 7.93 (Ar, d, J = 6.0 Hz, 2H), (Ar, m, 3H), 3.97 (CO 2 CH 2, d, J = 5.9 Hz, 2H), 2.91 (CH 2 CO 2, m, 2H), 2.52 (ArCCH 2, t, J = 8.0 Hz, 2H), 2.20 (m, 2H), 1.60 (m, 1H), 1.25 (m, 40H), 0.88 (CH 3, t, J = 8.0 Hz, 6H). 13 C NMR (100 MHz, CDCl 3 ), δ , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , 79.85, 67.47, 51.88, 37.25, 34.18, 33.65, 31.91, 31.25, 30.00, 29.69, 29.65, 29.36, 26.72, 22.69, 22.45, MALDI-TOF-MS (matrix-haba) calculated: , obtained: [M + ]. T melting (DSC), 9.7 C. The complex viscosity η* at 25 C is 146 Pa s at strain amplitude (1.0%). Higher loss modulus G values than storage modulus G were observed throughout the entire applied angular frequency (ω) range ( Hz), indicating viscoelastic liquid-like behavior. Techniques Visible absorption spectroscopy measurements (Fig. 1b, Supplementary Fig. 1) were carried out on a Jasco V660 spectrophotometer, using absorption cells with a 1 mm pathlength. Optical microscopy images were obtained under polarized (POM) and normal light conditions using an Olympus BX51 optical microscopy system equipped with a Linkam temperature-controlled heating/cooling stage. XRD measurements on the gel fibers (Fig. 3a, Supplementary Fig. 7) were performed in transmission mode using a Rigaku diffractometer (type 4037) using graded d-space elliptical side-by-side multlayer optics, monochromated Cu-Kα radiation (40 kv, 30 ma) and an imaging plate detector (R-Axis IV). This was equipped with temperature control (Mettler Toledo Central Processor FP90 with heating and cooling options). The exposure time was 30 min, with a camera length of 280 nm. XRD NATURE CHEMISTRY 6

7 measurements on the blends of C 60 and 1 (Fig. 4h), and C 60 or PCBM and 5 (Supplementary Fig. 10), were performed in reflection mode using a Rigaku RINT Ultima+ diffractometer. The samples were spread onto glass slides for the measurement. The rheology experiments were carried out using an Anton Paar Physica MCR301 rheometer at 25 C, using the parallel plate geometry (10 mm diameter) and a measuring sample tickness of 0.4 mm for 1 alone and 1:10 C 60 :1 and 0.65 mm for 1:2 C 60 :1 blends. Before the measurements shown in Fig. 4, strain amplitude scans were performed to determine the linear-viscoelastic region. For all samples the strain amplitude of 0.1% was within this region. The flash-photolysis time resolved microwave conductivity (FP-TRMC) measurement was carried out using a X-band (9 GHz) microwave circuit at low power (approximately 20 mw) and a nanosecond laser irradiation at 355 nm with photon density of 9.1 x photons cm -2 pulse -1. FP-TRMC samples were prepared by pasting the samples on a quartz plate. The obtained transient conductivity (Δσ in S m -1 ) was converted to the product of the quantum yield: φ and the sum of charge carrier mobilities: Σμ (= μ + + μ ), by φσμ = Δσ (e I 0 F Light ) -1, where e, I 0, and F Light are respectively the unit charge of a single electron (in C), the incident photon density of laser excitation (in m -2 ), and a correction (or filling) factor (in m -1 ). F Light was calculated by taking into consideration the geometry and optical properties of the sample such as the size, laser cross-section, and absorption of the excitation laser. Cryogenic transmission electron microscopy (cryo-tem) For cryo-tem, 200 mesh Cu grids with Quantifoil R 2/2 holey carbon films (Quantifoil Micro Tools GmbH) were used. Sample preparation was performed using an automated vitrification robot (FEI Vitrobot Mark III) for plunging in liquid nitrogen. To prevent the evaporation of hexane, the chamber of the vitrobot was saturated with hexane vapor using a special designed humidifier for organic solvents. For TEM of the 1:10 mol:mol mixture of C 60 and 1, samples were prepared by dissolving a small amount of the blended material in toluene and dropping this solution onto grids. NATURE CHEMISTRY 7

8 Excess solution was removed using tissue paper and the grids were left overnight under vacuum to remove the solvent. All TEM specimens were studied on the TU/e cryotitan (FEI, operated at 300 kv, equipped with a field emission gun (FEG), a post-column Gatan Energy Filter (GIF) and a post-gif 2k x 2k Gatan CCD camera. FFT of the images were carried out on rectangular areas (as noted in figure captions) using Image-J. Small-angle scattering The majority of SAXS measurements (Fig. 1d and 2c, Supplementary Fig. 3 and 8c) were carried out on BL40B2 at SPring8, with λ = 1.01 Å and camera length = m and a 3000 x 3000 pixel IP detector, giving a detectable Q range of order Å -1. Sample temperature was controlled by a hot and cold stage (HCS302, Instec Inc., CO). Collected data were corrected for natural background radiation, transmission, sample thickness, measurement time, primary beam flux, parasitic background, polarisation and detector solid angle coverage using in-house developed data reduction software written in the Python language. 5 Sample transmission was established through comparison of ion chamber currents before and after the sample position, which were calibrated by a measurement with no sample in place. Average capillary thickness (1.5 mm capillary), based on the beam width of 8 mm x 4 mm, was calculated to be 1.42 mm. The intensity is subsequently binned using 200 linear bins spanning the aforementioned Q range, and scaled to absolute units using a calibrated glassy carbon standard provided by Jan Ilavsky. 6 The result was three-column data with Q, and I(Q) in absolute units, in addition to calculated error. In general, these errors were << 1%, which is unphysical, especially considering the known variability in SAXS capillary width. As such, the statistical error values were subjected to futher treatment and the greater of the calculated value or [0.02 x I(Q)] was used for the error in the chi squared calculations for the model fits. SAXS data for molecule 4 (Supplementary Fig. 8b) were taken at 25 C using an in-house pinhole collimated instrument, Rigaku Nano-viewer, with a Mo target and a PILATUS NATURE CHEMISTRY 8

9 detector, calibrated using AgBh. Two sample-to-detector distances, 136 cm and 34.7 cm respectively were used, giving a total Q range of order Å -1. Measurements, with individually measured sample thicknesses in the region 1.5 mm, were corrected as above. Deadtime correction is unnecessary at the count rates encountered in this study, 7 and deadpixel and flatfield corrections are performed by the detector acquisition software prior to ingestion by the data reduction software. 8 The SANS measurements were carried out at 25 C on the D11 beamline at Institut Laue Langevin, France. The sample was contained in a 1 mm pathlength Hellma cell and thermostated at 25 C. Two detector distances were used, at 1.2 m and 8 m, with respective distances from the collimator at 4 m and 8 m. The incident wavelength was 10 Å and the detectable Q range was of order Å -1. Absolute intensities for I(Q) (cm -1 ) were determined by calibrating the received signal for water and correcting for sample transmission and solvent background. Please note that raw data for all small-angle scattering measurements reported are freely available on request from Martin Hollamby (m.hollamby@keele.ac.uk). Small-angle scattering: model fitting To model the data the following approaches were used. In all cases, except those where references are given, equations are based on those found in the comprehensive SASfit documentation, which is available as part of the SASfit package written by Kohlbrecher and Bressler that can be freely downloaded from the PSI website. For both the micelles and gelled samples, a breakdown of how each component of the model contributes to the overall fit is shown in Supplementary Fig. 12. Micelle clusters. The clusters of molecules 1-4 were modeled as spheres. The equation for the form factor of a sphere with radius, R and scattering contrast with relation to the solvent, Δη is as follows: NATURE CHEMISTRY 9

10 ,, Δ Δ (S1) For fits to both SAXS and SANS data, a log-normal distribution of core radii, R was assumed. This distribution is described as follows, with μ and σ the mean and width parameter of the number weighted distribution:,, (S2) For SAXS data, the aggregates were modeled as log-normal distribution of spheres. In that case, the following equation applies, in which R core is the core radius, which is distributed as above:,,,,,, Δ (S3) For all distributed cores, this becomes:,,,,, (S4) Additionally the contributions from monomers were modeled using a delta distribution of spheres. Without this contribution, the data could not be fit within error. Monomers are highly likely to exist in solution given the relatively low forces driving aggregation (cf. conventional nonionic surfactant aggregation in n-alkanes). They were modeled by simply multiplying the form factor for a sphere (R monomer, set to 0.51 nm) by a constant factor of N delta. For higher wt% samples of 1 and 3 an effective structure factor, S(Q) was required to fit the SAXS data (Supplementary Tables 1 and 4). This contribution arises from a broad peak in the SAXS, which becomes clearer at higher concentrations and is probably indicative of the diminishing distance between aggregate cores. A similar peak was not observed in the SANS, perhaps reflecting the relatively low contrast difference between core and solvent, as well as substantial solvent interpenetration into the shell. The peak was modeled using a hard sphere S(Q) of the type previously used by Vrij 9 and Kotlarchyk et al. 10 Fitted parameters are effective hard sphere radius R S(Q) and volume fraction φ S(Q). The monodisperse approach was used, in which the form factor contribution from aggregates is multiplied by the S(Q): NATURE CHEMISTRY 10

11 ,,,,, (S9) In all of the cases described above, fit results are summarized in Supplementary Tables 1 and 4. For SANS data, a log-normal distribution of core-shell particles with total radius R total and core radius R core and shell thickness dr was assumed. The shell thickness, dr was held constant at 0.72 nm. This is described below, in which Δη 1 and Δη 2 are core scattering contrasts relative to the solvent for the core and shell respectively:,,, Δ, Δ,, Δ,, Δ Δ (S8) As the densities of core and shell were not known, the ratio between Δη 1 and Δη 2 was held constant at 12. This ratio is reasonable, as the scattering constant from the shell should be much greater than that from the core, due to the contrast of deuterated solvent with normal (hydrogen-based) alkyl chains. Additionally, C 60 and deuterated alkanes have similar neutron scattering length densities (for C 60 with density = 1.7 g cm -3, sld sans = 5.7 x 10-6 Å -2, for n- hexane-d 14 [99% D], 6.12 x 10-6 Å -2 ). If the core is assumed to consist mainly of C 60 with some interpenetrated solvent and taking into account the effect of the (H-containing) monomer population on the solvent contrast, the value of Δη 1 should be low, at < 0.5 x 10-6 Å -2. The alkyl chains in the shell, without taking into account solvent penetration, would be expected to have sld sans of order -0.5 x With some solvent penetration, Δη 2 < 6.0 x 10-6 Å -2 would not be difficult to reach. To better verify this, further contrast variation experiments would be necessary. 11 However, the numbers used are reasonable and do not strongly affect the overall conclusions. Fit parameters are summarized in Supplementary Table 2. It is important to note that while SAXS and SANS data were both fit using spherical models, a relatively high polydispersity in core radii was noted in all cases. This is to be expected, given the large size of C 60 and C 70 : even a slight polydispersity in aggregation number will lead to a large polydispersity in radii. Another explanation for the high polydispersity could be NATURE CHEMISTRY 11

12 the presence of elongated (ellipsoidal or cylindrical) micelles. However, given that SAXS and SANS cannot significantly distinguish between polydisperse spheres and short ellipsoids/cylinders, and that elongated species are not clearly observed by cryo-tem, the simpler spherical model is used here. Gel fibres. To fit the SAXS data for the fibres, a model incorporating contributions arising from the form of the cylindrical C 60 columns (modelled as monodisperse cylinders), Bragg peaks arising from their hexagonal packing and the fractal structure of the network was used. The use of this relatively complex model is justified by data from the other techniques: POM images clearly indicate a branched network of nanosized ordered fibres, XRD clearly points to a hexagonally packed assembly and FP-TRMC data indicates a columnar structure through which charge may be carried. It should be noted that despite some approximations (e.g. monodispersity) and assuming a (low) error on each of the SAXS data points of 2%, a chi squared value of 1.4 was obtained. This is a good indication that the fit is a good description of the data. In this section, fitted parameters are highlighted in bold. The total scattering, I(Q) is given as follows: (S10) Here, I monomer is the same as used above for the micelles of 1 (again with a radius of 0.51 nm) and its use is justified in the same way. I bkg is the background scattering, taken as a low constant value ( in this case). The scattering from the columns, I cyl was modelled using an approximation for monodisperse cylinders taken from the SASfit documentation as follows: (S11) Where N is a scaling parameter, J 1 (x) is a first order Bessel function of the first kind. In this equation, R is the radius of the cylinder (Fitted as 1.6 nm ± 0.1 nm), L is the length (Fitted as 3.7 nm ± 0.2 nm) and Δη is the difference in scattering length density between the C 60 NATURE CHEMISTRY 12

13 core and the surrounding alkyl chains and alkane solvent. In this case, the length L is likely to be representative of a length scale at which the flexible, worm-like fibres can be approximated as rigid rods. Because Δη cannot easily be approximated due to a lack of knowledge about the density of either part, it was held as equal to 1x10-6 Å -2. In this case, N (Fitted as 2.27 x 10 3 ) is essentially equal to N Δη 2 rel where N is an approximation of the number of scatterers in a given volume (equal to N x cm -3 ). Approximating Δη rel to 5.5, which can be obtained if the C 60 -rich core density is 1.4 g cm -3 and the alkyl chains + n- alkane solvent are approximated as n-hexane, gives N = 7.5 x Assuming the cylinder dimensions above and the volume taken up by the C 60 part of each molecule of 2 to be 0.91 nm 3 (based on a radius of 0.6 nm, calculated by 1.65 / 1.4 * 0.51 where 1.65 is the density of C 60 in the bulk crystalline state and 0.51 is the van der Waals radius of C 60 in nm), there are around 31 molecules of 2 per cylinder, so the number of molecules involved in the scattering from the gel fibres is around 2.3 x cm -3 or 40 mm. This is lower than the concentration of the solution for this sample (100 mm), reflecting the large error in this calculation, but also indicating the strong likelihood of monomers of 2 (i.e. molecules not involved in the fibres) coexisting in solution. The fractal structure factor S fractal was modeled by a mass fractal with an exponential cut off, which is given as follows: (S12) where r 0 is the characteristic dimension of the scatterers making up the fractal (in this case the cylindrical components of the C 60 wires and found to be 3.28 nm), ξ is a cut-off length for fractal correlations (set as 500 nm, which is above the range detectable by SAXS in this experiment), and thereby approximating an infinite cut-off, D is the fractal dimension (Fitted as 2.7) and Г(x) is the gamma function. Because of the relatively small Q-range in which the fractal behavior is apparent, the error of all parameters is reasonably high. However, given NATURE CHEMISTRY 13

14 information from other techniques this treatment is reasonable. Future experiments using contrast-variation SANS alongside USAXS will probe the structure and low-q regions respectively in more detail. Finally, the contribution from the hexagonal packing was modelled by four peaks, using Lorentzian functions f(q,q 0,σ,A) as follows: (S13) where Q 0 is the peak position, σ is the half width at half maximum and A is the amplitude of each peak. To fit the data effectively, initially the values Q 0 and σ were fixed, but these were permitted to float in the final fitting routine. The values obtained for the peak positions were 0.11, 0.20, 0.26 and 0.37 Å -1, with corresponding amplitudes of 1.28, 0.57, and and corresponding widths of 0.010, 0.013, and respectively. NATURE CHEMISTRY 14

15 Supplementary Figure 1. (a, b, c) Absorption spectra for 1 in n-decane, n-octane and toluene for concentrations of 1 as indicated. (d) Shift in the position of the dominant maxima (around 704 nm) with concentration for the different solvents as indicated. NATURE CHEMISTRY 15

16 Supplementary Figure 2. (a, b) Cryo-TEM image and corresponding Fast Fourier transform (FFT) of a pure n-decane film (defocus = 2 μm). (c, d) Cryo-TEM image and corresponding Fast Fourier transform (FFT) of a film of 1 in n-decane ([1] = 20 wt%, defocus = 2 μm). In both (b) and (d), the FFT has been enlarged by a factor of 4. The dashed box in (c) indicates the region shown in Fig. 1c of the main paper. The average size of micelles (N = 100) was 2.5 ± 0.3 nm. The darker region corresponds to a crystal of n-decane, containing C 60 -rich micelles and the lighter blotches are likely to be due to a small amount of beam damage. NATURE CHEMISTRY 16

17 Supplementary Figure 3. (a, c) Fitted SAXS data for solutions of 1 as a function of (a) concentration, for samples of 1 in n-hexane at 25 C, (c) solvent, for samples of 1 at 25 C. [1] = 22.0 wt% (n-hexane), 20.4 wt% (n-decane), 17.5 wt% (toluene). In both panels (a) & (c), lines are fits to the data. (b, d) Volume-weighted size distributions of the C 60 -rich core radii as determined by model fitting. NATURE CHEMISTRY 17

18 Supplementary Figure 4. (a) Example data for the normalized change in absorption at λ = 900 nm with increasing temperature for 19.8 wt% 2 with n-hexane. This occurs due to the transition from the gel phase (strongly scatters λ = 900 nm light) to the isotropic phase (transparent to λ = 900 nm light). Taking the 1 st derivative of the transition curve (dotted line) yields T trans at the minimum, which in this case is 32.9 C. (b) Plot of T trans versus concentration of 2 in wt% for both n-hexane and n-decane. The region above the curves is the isotropic phase, while below the curves the samples are gelled. NATURE CHEMISTRY 18

19 Supplementary Figure 5. Full size POM images for the isotropic and gel states formed on the addition of n-hexane, [2] = 19.8 wt%. Images of the isotropic and gel phases were taken with and without crossed polarizers at 50 C (isotropic) and 10 C (gel). NATURE CHEMISTRY 19

20 Supplementary Figure 6. (a) XRD data for the gelled state of 2 in various solvents as indicated, taken at 0 C. The noted wt% of 2 in n-hexane and n-decane correspond to similar vol% 2 in either solvent (see Methods section). However, the wt% of 2 in n-octane corresponds to a lower vol% and is approximately 60% of the vol% of 2 in n-decane or n- hexane. (b) XRD data for the gelled state of 2 in at 26.5 and 42.2 wt% in n-decane, taken at 0 C. A peak list with corresponding d-spacing values for all samples is given in Supplementary Table 4. (c) Schematic diagram of the hexagonally ordered columns within gel fibers of 2 in n-hexane, highlighting the d-spacings that give rise to major peaks i and ii. (d) Schematic diagram of a situation in which the hexagonally ordered columns compress in a uniaxial manner, which might occur if solvent were to be partially excluded from the gel fibers. Peak ii remains unchanged, but peak i shifts to higher 2θ (smaller d-spacing), would initially broaden and eventually split into two peaks (as i' i"). This possibility will be probed in future experiments. NATURE CHEMISTRY 20

21 Supplementary Figure 7. (a) Cryo-TEM image of a sample of 2 in n-decane during the early stages of gel formation. In the image, two regions can clearly be separated containing micelles and more ordered structures that are likely to be growing gel fibers. (b) FFT of the boxed ordered region as indicated, in which spots corresponding to 2 different repeat distances, d 1 = 4.7 nm and d 2 = 3.0 nm, can be observed. (c) FFT of the boxed region comprising micelles as indicated. In this region, the average diameter of the clusters (N = 25) is 1.6 ± 0.2 nm. Unfortunately, difficulties in sample preparation meant it was not possible to obtain images of a fully gelled sample. NATURE CHEMISTRY 21

22 Supplementary Figure 8. (a) Chemical structures of 3 and 4. (b) Fitted SAXS data for 4 ([4] = 20 wt%) in different solvents as specified in the legend, at 25 C. (c) Fitted SAXS data for 3 in n-decane at 25 C, at different [3] as indicated. (d) Volume-weighted size distributions of the C 70 -rich core radii as determined by model fitting. In (b) and (c), solid lines represent fits to the data using the same models used to fit the data from the clusters of 1 with n-hexane. Fitting parameters for both systems are summarized in Supplementary Table 4. NATURE CHEMISTRY 22

23 Supplementary Figure 9. Absorption spectra of blends of 1 and C 60 in toluene solution at molar ratios of C 60 :1 of 1:2 and 1:10, compared to the spectrum of 1 alone in toluene. Data have been normalized for comparison to the peak at 705 nm. NATURE CHEMISTRY 23

24 Supplementary Figure 10. (a) Chemical structure of 5. (b) XRD data for blends of C , PCBM + 5 (molar ratio for both of 1:10) and 5 alone, at room temperature. Data for crystalline C 60 is included alongside these for reference. Data are consistent with a lamellar structure and, where possible, tentative peak assignments have been made. The 001 peak, indicative of the inter-lamellar spacing is located at 2θ = 2.44 (d = 3.6 nm) and 2.78 (d = 3.2 nm) for blends of C and PCBM + 5 respectively. (c) POM image of the C blend (molar ratio 1:10) at room temperature. (d) POM image of the PCBM + 5 blend (molar ratio 1:10) at room temperature. NATURE CHEMISTRY 24

25 Supplementary Figure H NMR spectra of 1 and 3 in CDCl 3. Assignment of shifts is provided for molecule 1, inset. NATURE CHEMISTRY 25

26 Supplementary Figure 12. (a) Breakdown of the contributions of the models representing micelles and monomers to the overall fit for the SAXS data of 1 with n-hexane, [1] = 22 wt%. (b) Breakdown of the various model contributions as indicated to the overall fit for the SAXS data of the gel fibers formed by 2 in n-hexane, [2] = 20 wt%, taken at 5 C. NATURE CHEMISTRY 26

27 Supplementary Tables Supplementary Table 1. Fitted parameters for SAXS data of 1 under different conditions as noted. Key values are highlighted in bold. See above for details of the models used to obtain these parameters. R core is the volume-weighted average radius of the C 60 -rich core. [1] / wt% solvent T / C N LogNorm / μ / Å σ R core / nm cm -3 N delta cm -3 R S(Q) / Å φ S(Q) χ n-hexane n-hexane n-hexane n-hexane n-decane toluene NATURE CHEMISTRY 27

28 Supplementary Table 2. Fitting parameters for SANS data of 22.0 wt% 1 in n-hexane at 25 C. Key values are highlighted in bold. See above for details of the models used to obtain the parameters. R core+shell is the volume-weighted average radius of the micelle. [1] / wt% solvent N LogNorm / μ / Å σ cm -3 R core+shell / nm 22.0 n-hexane χ 2 NATURE CHEMISTRY 28

29 Supplementary Table 3. XRD peak list (2θ < 10 ) for samples of 2 in different solvents and at different wt% as noted, at 0 C. [2] / wt% solvent visible peaks (2θ / degrees) d-spacing / nm 42.0 n-decane 1.96, 3.06, 3.96, 4.60, 6.07, 9.11, , 2.88, 2.23, 1.92, 1.45, 0.97, n-decane 1.92, 3.06, (3.96), (4.60), 6.04, 9.08, , 2.88, 2.23, 1.92, 1.46, 0.97, n-hexane 1.77, 3.04, (3.60), (4.47), 6.00, 9.08, , 2.90, 2.45, 1.97, 1.47, 0.97, n-octane 1.80, 3.09, (4.69), (6.00), 9.20, , 2.86, 1.88, 1.47, 0.96, 0.92 NOTE: The slight difference in the position of peaks i and ii determined by SAXS and XRD may be due to their proximity to the limit of detection (2θ 1.6 ) for our XRD setup or the difference in concentration. The latter point is discussed in more detail in the main text. NATURE CHEMISTRY 29

30 Supplementary Table 4. Model fitting parameters for SAXS data of 3 and 4 under different conditions as noted. Key values are highlighted in bold. See above for details of the models used to obtain these parameters. R core is the volume-weighted average core radius. N LogNorm Sample details / cm -3 μ / R core / σ Å nm N delta cm -3 R S(Q) / φ S(Q) χ 2 Å 3, 20.2 wt%, n-decane , 10.4 wt%, n-decane , 5.3 wt%, n-decane , 2.1 wt%, n-decane , 1.1 wt%, n-decane , 20 wt%, n-hexane , 20 wt%, n-decane , 20 wt%, toluene NATURE CHEMISTRY 30

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