Supporting Information

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1 Supporting Information A Push Pull Porphyrin Dimer with Multiple Electron-donating Groups for Dye-sensitized Solar Cells: Excellent Light-harvesting in Near-infrared Region Tomohiro Higashino, 1 Kenichi Sugiura, 1 Yukihiro Tsuji, 1 Shimpei Nimura, 1 Seigo Ito, 2 and Hiroshi Imahori* 1,3 1 Department of Molecular Engineering, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto Department of Materials and Synchrotron Radiation Engineering, Graduate School of Engineering, University of Hyogo, 2167 Shosha, Himeji, Hyogo Institute for Integrated Cell-Material Sciences (WPI-iCeMS), Kyoto University, Nishikyo-ku, Kyoto (Received June 16, 2016; CL ; imahori@scl.kyoto-u.ac.jp) Copyright The Chemical Society of Japan

2 Contents 1. Experimental Section 2. Synthesis 3. High-Resolution Mass Spectra 4. NMR Spectra 5. Fluorescence Spectra 6. Electrochemical Properties 7. Molecular Orbital Diagrams 8. Device Optimization 9. EIS Nyquist Plots 10. References 2

3 1. Experimental Section Instrumentation and Materials. Commercially available solvents and reagents were used without further purification unless otherwise mentioned. Silica-gel column chromatography was performed with UltraPure Silica Gel ( mesh, SiliCycle) unless otherwise noted. Thin-layer chromatography (TLC) was performed with Silica gel 60 F 254 (Merck). Size exclusion gel permeation chromatography (GPC) was performed by Bio-beads S-X1 (Bio-rad). UV/Vis/NIR absorption spectra of solutions and films were measured with a Perkin-Elmer Lambda 900 UV/vis/NIR spectrometer. Steady-state fluorescence spectra were obtained by a HORIBA Nanolog spectrometer. 1 H and 13 C NMR spectra were recorded with a JEOL EX-400 spectrometer (operating at 400 MHz for 1 H and 100 MHz for 13 C) by using the residual solvent as the internal reference for 1 H (CDCl 3 : δ = 7.26 ppm, THF-d 8 : δ =1.72, 3.58 ppm) and 13 C (THF-d 8 : δ = 25.31, ppm). High-resolution mass spectra (HRMS) were measured on a Thermo Fischer Scientific EXACTIVE spectrometer for ESI and a Thermo Fischer Scientific MALDI-Duo-orbitrap XL spectrometer for MALDI by using trans-2-[3-(4-t-butylphenyl)-2-methyl-2- propenylidene]malononitrile (DCTB) as a matrix. Attenuated total reflectance-fourier transform infrared (ATR-FTIR) spectra were taken with the golden gate diamond anvil ATR accessory (NICOLET 6700, Thermo scientific), using typically 64 scans at a resolution of 2 cm 1. All samples were placed in contact with the diamond window using the same mechanical force. Electrochemical Measurements. Electrochemical measurements were made using an ALS 660a electrochemical analyzer. Redox potentials were determined by differential pulse voltammetry (DPV) in THF containing 0.1 M tetrabutylammonium hexafluorophosphate (Bu 4 NPF 6 ). A glassy carbon (3 mm diameter) working electrode, Ag/AgNO 3 reference electrode, and Pt wire counter electrode were employed. Ferrocene ( V vs NHE) was used as an external standard for the DPV measurements. Preparation of Porphyrin-Sensitized TiO 2 Electrode and Photovoltaic Measurements. The preparation of TiO 2 electrodes and the fabrication of the sealed cells for 3

4 photovoltaic measurements were performed according to literature. S1,S2 We used two types of TiO 2 pastes, one composed of nanocrystalline TiO 2 particles (20 nm, CCIC:PST18NR, JGC-CCIC) and another containing submicrocrystalline TiO 2 particles (400 nm, CCIC:PST400C, JGC-CCIC), to form the transparent and the light-scattering layers of the photoanode, respectively. To prepare the working electrodes, FTO glasses (solar 4mm thickness, 10 Ω/o, Nippon Sheet Glass) were first cleaned in a detergent solution using an ultrasonic bath for 10 min and then rinsed with distilled water and ethanol. After UV-O 3 irradiation for 18 min, the FTO glass plates were immersed into a 40 mm aqueous TiCl 4 solution at 70 C for 30 min and washed with distilled water and ethanol. A layer of the nanocrystalline TiO 2 paste was coated on the FTO glass plate by a screen-printing method, kept in a clean box for a few minutes, and then dried over 6 min at 125 C. This screen-printing procedure with the nanocrystalline TiO 2 paste was repeated to reach a thickness of 7.5 µm. After drying the films at 125 C, a layer of the submicrocrystalline TiO 2 paste was further deposited by screen-printing in the same method as the fabrication of the nanocrystalline TiO 2 layer, resulting in formation of a light-scattering TiO 2 film of 4 µm on the transparent TiO 2 film of 7.5 µm. Finally, the electrodes coated with the TiO 2 pastes were gradually heated under an airflow at 325 C for 5 min, at 375 C for 5 min, at 450 C for 15 min, and at 500 C for 15 min. The thickness of the films was determined using a surface profiler (SURFCOM 130A, ACCRETECH). The size of the TiO 2 film was 0.16 cm 2 (4 4 mm). The TiO 2 electrode was treated again with 40 mm TiCl 4 solution at 70 C for 25 min and then rinsed with distilled water and ethanol, sintered at 500 C for 30 min, and cooled to 70 C before dipping into the dye solution. The TiO 2 electrode was immersed into an ethanol solution of the sensitizers (0.15 mm) containing chenodeoxycholic acid (CDCA) with various concentration at 25 C. The counter electrode was prepared by drilling a small hole in an FTO glass (solar 1 mm thickness, 10 Ω/o, Nippon Sheet Glass), rinsing with distilled water and ethanol followed by treatment with 0.1 M HCl solution in 2-propanol using an ultrasonic bath for 15 min. After heating in air for 15 min at 400 C, the platinum was deposited on the FTO glass by coating with a drop of H 2 PtCl 6 solution (2 mg in 1 ml of ethanol) twice. Finally, the FTO glass was heated at 400 C for 15 min to obtain the counter Pt-electrode. 4

5 A sandwich cell was prepared by using the dye-anchored TiO 2 film as a working electrode and a counter Pt-electrode, which were assembled with a hotmelt-ionomer film Surlyn polymer gasket (DuPont, 50 µm), and the superimposed electrodes were tightly held and heated at 110 C to seal the two electrodes. The aperture of the Surlyn frame was 2 mm larger than that of the area of the TiO 2 film, and its width was 1 mm. The hole in the counter Pt-electrode was sealed by a film of Surlyn. A hole was then made in the film of Surlyn covering the hole with a needle. A drop of an electrolyte was put on the hole in the back of the counter Pt-electrode. It was introduced into the cell via vacuum backfilling. Finally, the hole was sealed using Surlyn film and a cover glass ( mm thickness). A solder was applied on each edge of the FTO electrodes. The electrolyte solution used was 1.0 M 1-methyl-3-propylimidazolium iodide, 0.15 M I 2, 0.30 M LiI and 0.50 M 4-tert-butylpyridine in 85:15 mixture of acetonitrile and valeronitrile. Incident photon-to-current efficiency (IPCE) and photocurrent-voltage (I-V) performance were measured on an action spectrum measurement setup (CEP-2000RR, BUNKOUKEIKI) and a solar simulator (PEC-L10, Peccell Technologies) with a simulated sunlight of AM 1.5 (100 mw cm 2 ), respectively: IPCE (%) = i/(w in λ), where i is the photocurrent density (A cm 2 ) W in is the incident light intensity (W cm 2 ), and λ is the excitation wavelength (nm). During the photovoltaic measurements, a black mask was attached on the back of the TiO 2 electrode except for the TiO 2 film region to avoid scattering light. 5

6 2. Synthesis Scheme S1. Synthesis of ZnPTD. 5,15-Bis(triisopropylsilylethynyl)porphyrin (1), S3 porphyrin 3 S4, and LDD1 S4 were prepared according to literatures. Porphyrin 2: To a solution of zinc porphyrin 1 (465 mg, mmol), and N,N -bis(4-methylphenyl)amine (1.56 g, 7.88 mmol) in CH 2 Cl 2 (110 ml), PhI(OAc) 2 (356 mg, 1.10 mmol), and FeCl 3 6H 2 O (523 mg, 1.31 mmol) were added. The reaction mixture was stirred at room temperature for 70 min under argon atmosphere. Then a saturated Na 2 S 2 O 3 aq. (70 ml) was added. After being stirred for 10 min, the reaction mixture was washed with water three times. The organic layer was dried over anhydrous MgSO 4 and the solvent was removed under reduced pressure. The residue was purified by column chromatography (silica gel) using hexane/ch 2 Cl 2 (v/v=3/1) as eluent to give porphyrin 2 (168 mg, mmol, 25.1% yield) as a green solid. 1 H NMR (400 MHz, CDCl 3 ): δ = 9.54 (d, J = 4.4 Hz, 4H), 9.21 (d, J = 4.7 Hz, 4H), 7.16 (d, J = 8.3 Hz, 8H), 6.99 (d, J = 8.3 Hz, 8H), 2.25 (s, 12H), (m, 42H) ppm; HR-MS 6

7 (ESI-TOF, positive) m/z calcd for C 70 H 78 N 6 Si 2 Zn [M+H] + : , found ; FT-IR (ATR): ν max 2940, 2889, 2862, 2135, 1609, 1504, 1461, 1431, 1338, 1316, 1293, 1253, 1214, 1165, 1061, 1004, 882, 794, 714 cm 1 ; m.p.: > 300 C. Porphyrin dimer 4: To a solution of porphyrin 2 (272.1 mg, µmol) in dry THF (60 ml) was added TBAF (720 µl, 1 M in THF). The solution was stirred at 23 C for 30 min under argon atmosphere. The mixture was quenched with H 2 O and then extracted with CH 2 Cl 2. The organic layer was dried over anhydrous MgSO 4 and the solvent was removed under reduced pressure. The residue was purified by column chromatography (silica gel) using hexane/thf (v/v = 2/1) and reprecipitation (THF/acetonitrile) as eluent to give the deprotected porphyrin (165.5 mg, µmol, 84.2% yield) as a dark brown solid. Into a solution of the deprotected porphyrin (114.2mg, µmol) in dry THF (80 ml) and NEt 3 (8.0 ml) argon was bubbled for 20 min. Porphyrin 3 (216.7 mg, µmol), 4-iodo-N,N -dimethylaniline (32.0 mg, 130 µmol), Pd(PPh 3 ) 4 (162.1 mg, µmol), and CuI (2.4 mg, 13 µmol) were added to the mixture. The solution was stirred at 45 C for 16.5 h under argon atmosphere. The solvent was removed under reduced pressure. The residue was purified by GPC (toluene) and column chromatography (silica gel) using THF/hexane (v/v=3/1) and as eluent to give porphyrin dimer 4 (27.5 mg, 11.7 µmol, 8.3%) as a dark brown solid. 1 H NMR (400 MHz, THF-d 8 ): δ = (d, J = 4.4 Hz, 2H), (d, J = 4.4 Hz, 2H), 9.62 (d, J = 4.9 Hz, 2H), 9.48 (d, J = 4.4 Hz, 2H), 9.32 (d, J = 4.4 Hz, 2H), 9.13 (d, J = 4.4 Hz, 2H), 8.91 (d, J = 4.4 Hz, 2H), 8.82 (d, J = 4.4 Hz, 2H), 8.22 (d, J = 7.8 Hz, 2H), 8.13 (d, J = 8.3 Hz, 2H), 7.82 (d, J = 8.3 Hz, 2H), 7.74 (t, J = 8.3 Hz, 2H), 7.27 (d, J = 8.8 Hz, 8H), 7.11 (d, J = 8.8 Hz, 4H), 7.02 (d, J = 8.3 Hz, 8H), 6.89 (d, J = 9.3 Hz, 2H), 3.93 (m, 11H), 3.08 (s, 6H), 2.25 (s, 12H), (m, 92H) ppm; HR-MS (MALDI-MS) m/z calcd for C 150 H 167 N 11 O 6 Zn 2 [M] + : , found ; FT-IR (ATR): ν max 2955, 2924, 2852, 2187, 1724, 1604, 1506, 1456, 1338, 1315, 1293, 1260, 1206, 1100, 998, 794 cm 1 ; m.p.: > 300 C. Porphyrin dimer ZnPTD: Porphyrin dimer 4 (24.0 mg, 10.2 µmol) was dissolved in THF (70 ml) and MeOH (20 7

8 ml). After addition of saturated NaOH aq. (10 ml), the solution was stirred at 50 C for 4 h. Upon completion, the solvent was removed under reduced pressure. The residue was dissolved again in CH 2 Cl 2 for washing with NH 4 Cl aq. The organic layer was dried over anhydrous MgSO 4 and the solvent was removed under reduced pressure. The residue was purified by column chromatography (silica gel) using a CH 2 Cl 2 /methanol (v/v=15/1) and reprecipitation (THF/acetonitrile) to give porphyrin dimer ZnPTD (15.8 mg, 6.8 µmol, 66 %) as a dark brown solid. 1 H NMR (400 MHz, THF-d 8 ): δ = (d, J = 4.4 Hz, 2H), (d, J = 4.4 Hz, 2H), 9.51 (d, J = 4.9 Hz, 2H), 9.36 (d, J = 4.4 Hz, 2H), 9.20 (d, J = 4.9 Hz, 2H), 9.02 (d, J = 4.4 Hz, 2H), 8.80 (d, J = 4.9 Hz, 2H), 8.71 (d, J = 4.4 Hz, 2H), 8.12 (d, J = 8.3 Hz, 2H), 8.00 (d, J = 8.3 Hz, 2H), 7.70 (d, J = 8.8 Hz, 2H), 7.62 (t, J = 8.8 Hz, 2H), 7.16 (d, J = 8.8 Hz, 8H), 6.99 (d, J = 8.3 Hz, 4H), 6.91 (d, J = 8.3 Hz, 8H), 6.78 (d, J = 9.3 Hz, 2H), 3.81 (t, J = 6.6 Hz, 8H), 2.97 (s, 6H), 2.14 (s, 12H), (m, 92H) ppm; 13 C NMR (400 MHz, THF-d 8 ): δ =160.2, 152.4, 151.9, 151.7, 151.1, 150.8, 150.7, 150.6, 132.5, 131.8, 131.7, 131.3, 131.2, 131.0, 130.7, 130.5, 129.9, 129.8, 129.6, 129.5, 128.8, 125.1, 122.2, 120.9, 115.9, 112.0, 110.9, 104.7, 39.4, 31.8, 29.7, 29.5, 29.4, 29.3, 29.2, 29.0, 28.9, 28.5, 22.5, 19.8, 13.4.; HR-MS (MALDI-MS) m/z calcd for C 149 H 165 N 11 O 6 Zn 2 [M] + : , found ; FT-IR (ATR): ν max 2953, 2920, 2851, 1685, 1602, 1504, 1455, 1339, 1313, 1293, 1261, 1248, 1207, 1095, 1014, 1000, 807, 791, 730, 706 cm 1 ; UV/Vis (ethanol/toluene: v/v=1/1): λ (ε, 10 3 M 1 cm 1 ) = 442 (159.0), 504 (250.3), 589 (19.0), 647 (21.3), 775 (101.0) nm; m.p.: > 300 C. 8

9 3. High-Resolution Mass Spectra Figure S1. Observed (top) and simulated (bottom) high-resolution ESI-MS of (a) 2 and MALDI-MS of (b) 4 and (c) ZnPTD. 9

10 4. NMR Spectra Figure S2. 1 H NMR spectrum of 2 at 25 C in CDCl 3. Peaks marked with are due to residual solvents. Figure S3. 1 H NMR spectrum of 4 at 25 C in THF-d 8. Peaks marked with are due to residual solvents. 10

11 Figure S4. 1 H and 13 C NMR spectra of ZnPTD at 25 C in THF-d 8. Peaks marked with are due to residual solvents. 11

12 5. Fluorescence Spectra Figure S5. Normalized steady-state fluorescence spectra of ZnPTD (red) and LDD1 (green) in ethanol/toluene (v/v=1/1). The samples were excited at Soret-bands. 12

13 6. Electrochemical Properties Figure S6. DPV curves of ZnPTD. Redox potentials were determined by DPV. Solvent: THF; scan rate: 0.05 V s 1 ; working electrode: glassy carbon; reference electrode: Ag/AgNO 3 ; electrolyte: Bu 4 NPF 6. Table S1. Optical, electrochemical, and electron transfer properties of ZnPTD and ZnPBAT. E a ox / V E a red / V E b 0 0 / ev E ox *,c / V ΔG d inj / ev ΔG e reg / ev ZnPTD LDD a First oxidation and reduction potentials (versus the normal hydrogen electrode, NHE). b Determined from the intersection of normalized absorption and emission spectra. c Determined by adding E 0 0 to E ox (vs. NHE). d Driving force for electron injection from the porphyrin singlet excited-state to the CB of TiO 2 ( 0.5 V vs. NHE) (ΔG inj = E ox * ( 0.5)). e Driving force for the dye regeneration by I /I 3 redox shuttle (+0.4 V vs. NHE) (ΔG reg = 0.4 E ox ). 13

14 7. Molecular Orbital Diagrams (a) (b) LUMO 2.57 ev 2.39 ev 4.41 ev 4.30 ev HOMO Figure S7. Selected molecular orbital diagrams for (a) ZnPTD and (b) LDD1 obtained by DFT calculations with B3LYP/6-31G(d). To simplify the calculations, alkyl chains on the diarylamino groups were replaced with methyl ones, and dodecyloxy groups on the phenyl groups were replaced with methoxy ones. 14

15 8. Device Optimization Figure S8. Plots of the η-value as a function of immersion time for DSSCs based on ZnPTD (red) and LDD1 (green). The sensitizers were adsorbed on the TiO 2 electrodes by immersing them into ethanol solutions of the sensitizers without CDCA. Figure S9. Plots of the power conversion efficiency (η) as a function of the amount of CDCA for the DSSCs based on ZnPTD (red) and LDD1 (green). The immersion times of 0.5 h for ZnPTD and of 3 h for LDD1 were used for the experiments. 15

16 Figure S10. Absorption spectra of the TiO 2 electrodes sensitized by ZnPTD (red) and LDD1 (green) under the optimized conditions. The light scattering layers were not applied to the electrodes to measure absorbance accurately. Table S2. Photovoltaic parameters of the DSSCs based on ZnPTD and LDD1. a dye J SC / ma cm 2 V OC / V ff η / % ZnPTD 14.7 (13.7±1.0) (0.595±0.004) (0.712±0.018) 6.22 (5.81±0.40) LDD (19.2±0.2) (0.628±0.015) (0.677±0.012) 8.17 (8.12±0.11) a Values represent the photovoltaic parameters exhibiting the highest η-value. The average value from three independent experiments is shown in parenthesis in each case. 16

17 9. EIS Nyquist Plots Figure S11. EIS Nyquist Plots of DSSCs based on ZnPTD (red) and LDD1 (green) under AM 1.5 illumination at open-circuit conditions. The inset is an equivalent Randles circuit impedance model. R s is the series resistance accounting for transport resistance of transparent conducting oxide (TCO); R p is the charge transfer resistance for charge recombination at the FTO/TiO 2 /electrolyte interfaces; CPE is the constant phase element representing capacitance at the TiO 2 /electrolyte/interface. The R p values at the TiO 2 /dye/electrolyte interface were determined as 14.8 Ω for ZnPTD and 18.2 Ω for LDD1. 17

18 10. References [S1] K. Kurotobi, Y. Toude, K. Kawamoto, Y. Fujimori, S. Ito, P. Chabera, V. Sundström, H. Imahori, Chem. Eur. J. 2013, 19, [S2] S. Ito, T. N. Murakami, P. Comte, P. Liska, C. Grätzel, M. K. Nazeeruddin, M. Grätzel, Thin Solid Films 2008, 516, [S3] T. E. O. Screen, K. B. Lawton, G. S. Wilson, N. Dolney, R. Ispasoiu, T. Goodson III, S. J. Martin, D. D. C. Bradley, H. L. Anderson, J. Mater. Chem. 2001, 11, 312. [S4] J.-W. Shiu, Y.-C. Chang, C.-Y. Chan, H.-P. Wu, H.-Y. Hsu, C.-L. Wang, C.-Y. Lin, E. W.-G. Diau, J. Mater. Chem. A 2015, 3,