Supporting Information for: Tetramethoxybenzene is a Good Building Block for Molecular Wires: Insights from Photoinduced Electron Transfer

Transcription

1 Supporting Information for: Tetramethoxybenzene is a Good Building Block for Molecular Wires: Insights from Photoinduced Electron Transfer Luisa G. Heinz, Oleksandr Yushchenko, Markus Neuburger, Eric Vauthey,*, and Oliver S. Wenger,* Department of Chemistry, University of Basel, St. Johanns-Ring 19, 4056 Basel, Switzerland Department of Physical Chemistry, University of Geneva, 30 quai Ernest Ansermet, 1211 Geneva, Switzerland *Corresponding authors. s: eric.vauthey@unige.ch, oliver.wenger@unibas.ch Table of contents Methods and equipment Synthesis and product characterization data X-ray crystallography Additional transient absorption data References S2 S3 S12 S13 S15 S1

2 Methods and equipment 1 H NMR spectra were measured on a Bruker Avance III instrument operating at 400 MHz frequency. The instrument was equipped with a direct observe 5-mm BBFO smart probe. Mass spectra were recorded on a Bruker esquire 3000 plus or on a Bruker maxis 4G QTOF ESI spectrometer. Elemental analysis was measured by Ms. Sylvie Mittelheisser (Department of Chemistry, University of Basel) with a Varia Micro Cube instrument from Elementar. Optical absorption spectroscopy was performed on a Cary 5000 UV-Vis-NIR spectrophotometer from Varian. The nanosecond transient absorption data in Figure 4 were acquired on an LP920-KS spectrometer from Edinburgh Instruments, using the frequency-doubled output of a Quantel Brilliant b Nd:YAG laser for excitation. The laser pulse duration was approximately 10 ns, the pulse frequency was 10 Hz. Detection occurred either an iccd camera from Andor. Transient difference spectra were time-averaged over the duration of 200 ns. The transient absorption experiments from Figures 5, S1 were performed on a fs/ps TA described recently, using an excitation wavelength of 400 nm. 1 The transient absorption data in Figures 7, S3 were acquired on a sub-ns/ s TA setup described recently, using an excitation wavelength of 355 nm. 2 The sample solutions for TA measurements were located in a 1 mm quartz cell and were continuously stirred by N2 bubbling. Their absorbance at the excitation wavelengths was around Cyclic voltammetry was performed in a conventional setup with three electrodes using a Versastat3-200 potentiostat from Princeton Applied Research. A glassy carbon disk was employed as a working electrode, and two silver wires served as counter and quasi-reference electrodes, respectively. Internal voltage calibration occurred by addition of small amounts of ferrocene. Spectroelectrochemistry occurred with a Pt grid electrode immersed into a suitable cuvette. S2

3 Synthesis and product characterization data 2,5-Dimethoxy-1,4-benzoquinone (2). Following a previously published method, 3 2,5- dihydroxy-1,4-benzoquinone (1) (5.00 g, 35.7 mmol) was suspended in dry MeOH (75 ml). BF3 Et2O was added (12.5 ml, 98.6 mmol), and the mixture was heated to reflux for 2 hours. After cooling to room temperature, the precipitate was filtered and washed with cold MeOH until the washing solution stayed clear and colorless. The solvents were evaporated and the product was obtained as beige needles (5.25 g, 31.2 mmol, 87%). 1 H NMR (400 MHz, CDCl3): [ppm] 5.87 (s, 2 H), 3.85 (s, 6 H). 1,4-Dimethoxy-2,5-dihydroxybenzene (3). Following a previously published method, 4 2,5- dimethoxy-1,4-benzoquinone (2) (2.00 g, 11.9 mmol) in dry EtOH (30 ml) was cooled to 0 C, and NaBH4 (1.62 g, 42.8 mmol) was added in small portions over 20 minutes. After removal of the ice bath, the slurry mixture was stirred at room temperature for 4 hours. 1 M aqueous HCl solution was added (50 ml), and the clear brown solution was extracted with CH2Cl2 and Et2O. The combined organic phases were dried over anhydrous Na2SO4, and then the solvents were evaporated. The product was obtained as a pale brownish solid (1.67 g, 9.8 mmol, 82%). 1 H NMR (400 MHz, CDCl3): [ppm] 6.57 (s, 2 H), 3.82 (s, 6 H). 1,2,4,5-Tetramethoxybenzene (4). Following a previously published method, 4 to 1,4- dimethoxy-2,5-dihydroxybenzene (3) (3.86 g, 22.7 mmol) in EtOH (50 ml) at 0 C, (CH3)2SO4 (9.68 ml, mmol) was added dropwise via syringe. Then, NaHSO3 (0.708 g, 6.80 mmol) and KOH (8.91 g, mmol) dissolved in H2O (20 ml) were added, and the reaction mixture was stirred at 0 C for 30 minutes before heating to reflux for 40 hours. After addition of aqueous S3

4 NH3 solution and extraction with CH2Cl2, the organic phase was dried over anhydrous Na2SO4. After solvent evaporation the brown solid was washed with a small amount of cold MeOH. This afforded the product as an off-white crystalline solid (4.00 g, 20.2 mmol, 89%). 1 H NMR (400 MHz, CDCl3): [ppm] 6.61 (s, 2 H), 3.85 (s, 12 H). 1,4-Diiodo-2,3,5,6-tetramethoxybenzene (5). Following a previously published protocol, 5 to 1,2,4,5-tetramethoxybenzene (4) (4.00 g, 20.2 mmol) in dry Et2O with TMEDA (7.22 ml, 48.4 mmol) at 0 C was added 2.5 M n-butyllithium in hexane (19.4 ml, 48.4 mmol). The reaction mixture was stirred at room temperature for 1 hour. After cooling to 0 C, iodine (12.29 g, 48.4 mmol) was added, and the reaction mixture was stirred at room temperature overnight. Saturated aqueous Na2S2O3 solution was added, and the product was extracted with ethyl acetate. The combined organic phases were dried over anhydrous Na2SO4. After solvent evaporation, the crude product was purified by chromatography on a silica gel column with CH2Cl2 as the eluent. The product was washed with cold MeOH, yielding a white solid (6.21 g, 13.8 mmol, 68%). 1 H NMR (400 MHz, CDCl3): [ppm] 3.85 (s, 12 H). Compound 6. A de-oxygenated mixture of 1,4-diiodo-2,3,5,6-tetramethoxybenzene (5) (1.00 g, 2.22 mmol), 2-methyl-3-butyn-2-ol (0.5 ml, 4.89 mmol), CuI (17 mg, 89 mol), and PdCl2(PPh3)2 (31 mg, 44 mol) in Et3N (25 ml) was heated to reflux until the reaction was completed. Progress was monitored by thin layer chromatography. After cooling to room temperature, ethyl acetate was added, and the mixture was washed with saturated aqueous NH4Cl solution and with brine. The combined organic phases were dried over anhydrous Na2SO4, and the solvents were evaporated. The solid residue was dissolved in a minimal amount of ethyl acetate, and then pentane was added slowly until a precipitate formed. This afforded the product S4

5 as an off-white crystalline solid (660 mg, 1.82 mmol, 82%). 1 H NMR (400 MHz, acetone-d6): [ppm] 4.51 (s, 2 H), 3.85 (s, 12 H), 1.58 (s, 12 H). 1,4-Diethynyl-2,3,5,6-tetramethoxybenzene (7). Compound 6 (2.30 g, 6.35 mmol) was dissolved in toluene (50 ml). NaH (127 mg, 3.17 mmol) was added and the reaction mixture was heated to reflux until the reaction was completed; progress was monitored by thin layer chromatography. The crude product was collected by filtration of the cooled toluene solution and subsequent evaporation of the solvent. The solid residue was purified on silica gel column with a 4:1 (v:v) mixture of pentane and ethyl acetate as the eluent. This yielded the product as an offwhite solid (1.33 g, 5.40 mmol, 85%). 1 H NMR (400 MHz, CDCl3): [ppm] 3.92 (s, 12 H), 3.56 (s, 2 H). Compound 9. Following a previously published protocol, 6 1,4-diiodobenzene (8) (5.00 g, 15.2 mmol), 2-methyl-3-butyn-2-ol (3.25 ml, 33.3 mmol), CuI (116 mg, 0.61 mmol), and PdCl2(PPh3)2 (211 mg, 0.30 mmol) were dissolved in dry Et3N (75 ml). The mixture was deoxygenated and then heated to reflux for 2 hours. After cooling to room temperature, ethyl acetate was added, and the mixture was washed with saturated aqueous NH4Cl solution and with brine. The organic phase was dried over anhydrous Na2SO4, and the solvents were evaporated. Column chromatography on silica gel occurred with a mixture of pentane and ethyl acetate as the eluent, first in 5:1 (v:v) and then in 1:1 (v:v) ratio. The product was obtained as a pale yellow solid (3.67 g, 15.1 mmol, 99%). 1 H NMR (400 MHz, acetone-d6): [ppm] 7.36 (s, 4 H), 1.53 (s, 12 H). S5

6 1,4-Diethynylbenzene (10). Compound 9 (1.00 g, 4.11 mmol) was dissolved in toluene (20 ml), and freshly powdered KOH (0.57 g, 10.3 mmol) was added. After heating to reflux for 3 hours, the precipitate was filtered off, and the solvent was removed on a rotary evaporator. Purification on a silica gel column with pentane resulted in a white solid (0.40 g, 3.17 mmol, 77%). 1 H NMR (400 MHz, acetone-d6): [ppm] 7.50 (s, 4 H), 3.81 (s, 2 H). 5-Bromo-2,2 -bipyridine (13). Following a previously published protocol, 7 commercial 5- bromo-2-iodopyridine (11) (1.42 g, 5.00 mmol) and Pd(PPh3)4 (116 mg, 0.10 mmol) were dissolved in dry THF (15 ml) and the solution was de-oxygenated. Then, commercial 0.5 M 2- pyridylzinc bromide (12) solution in THF (15 ml, 7.50 mmol) was added slowly via syringe. The reaction mixture was stirred for 24 hours at room temperature, and then aqueous EDTA/Na2CO3 solution was added until the precipitate dissolved. After extraction with Et2O, the combined organic phases were dried over anhydrous Na2SO4, and the solvents were evaporated. The beige residue was purified on silica gel column. First, the eluent was a 2:1 (v:v) mixture of pentane and Et2O, and then 1% of triethylamine was added to this eluent mixture. This afforded the pure product as a white crystalline solid (1.12 g, 4.76 mmol, 95%). 1 H NMR (400 MHz, acetone-d6): [ppm] 8.76 (d, J = 2.4 Hz, 1 H), (m, 1 H), 8.44 (d, J = 9.1 Hz, 2 H), 8.13 (dd, J = 8.5, 2.4 Hz, 1 H), 7.94 (td, J = 7.8, 1.8 Hz, 1 H), (m, 1 H). Compound Bromo-2,2 -bipyridine (13) (1.00 g, 4.25 mmol), 4- (trimethylsilyl)phenylboronic acid (14) (1.04 g, 4.68 mmol), 8 and Na2CO3 (1.35 g, 12.8 mmol) were dissolved in a 1:1 (v:v) mixture of THF and H2O (20 ml). After de-oxygenating, Pd(PPh3)4 (246 mg, 0.21 mmol) was added, and the mixture was reacted at reflux during 2 days. After cooling to room temperature, CH2Cl2 was added and the phases were separated. The organic S6

7 phase was dried over Na2SO4 and the solvents were evaporated. The brown oily residue was purified by column chromatography on a silica gel stationary phase. At first, the eluent was a 2:1 (v:v) mixture of pentane and Et2O, and then 1% triethylamine was added to this eluent mixture. This afforded the pure product as a white crystalline solid (1.21 g, 3.64 mmol, 86%). 1 H NMR (400 MHz, acetone-d6): [ppm] 8.70 (d, J = 4.8 Hz, 1 H), 8.65 (d, J = 2.3 Hz, 1 H), (m, 2 H), (m, 2 H), (m, 2 H), 7.13 (s, 1 H), 2.48 (s, 3 H), 2.30 (s, 3 H), 0.37 (s, 9 H). Compound 16. To a solution of compound 15 (1.37 g, 4.14 mmol) in CH2Cl2 (5 ml) and CH3CN (20 ml) at 0 C was added ICl (0.65 ml, 12.4 mmol) in CH3CN. The mixture was stirred at 0 C for 5 minutes and then at room temperature overnight. After addition of saturated aqueous Na2S2O3 solution, the phases were separated. The organic phase was dried over anhydrous Na2SO4, and the solvents were evaporated. The crude product was purified by column chromatography on silica gel. At first, pure pentane was the eluent, then a 2:1 (v:v) mixture of pentane and Et2O, and finally a 2:1 (v:v) mixture of pentane and Et2O with 1% triethylamine was used. The pure product was obtained as an off-white crystalline solid (1.46 g, 3.78 mmol, 91%). 1 H NMR (400 MHz, acetone-d6): [ppm] 8.70 (d, J = 5.6 Hz, 1 H), 8.65 (d, J = 2.3 Hz, 1 H), (m, 2 H), (m, 2 H), 7.84 (s, 1 H), 7.43 (dd, J = 8.1, 5.4 Hz, 1 H), 7.27 (s, 1 H), 2.44 (s, 3 H), 2.28 (s, 3 H). N,N-bis(4-methoxyphenyl)aniline (19). Following a previously published method, 9 bis(panisyl)amine (17) (2.00 g, 8.7 mmol), 1-bromobenzene (18) (1.1 ml, 10.5 mmol), NaO t Bu (16.76 g, mmol), Pd(dba)2 (0.25 g, 0.44 mmol), and (HP t Bu3)BF4 (0.127 g, 0.44 mmol) were dissolved in dry toluene (150 ml). After de-oxygenating, the reaction mixture was heated to S7

8 reflux under N2 overnight. After cooling to room temperature, H2O was added and the product was extracted with CH2Cl2. The combined organic phases were dried over anhydrous Na2SO4 prior to solvent evaporation. The crude product was purified on silica gel column using first pure pentane, then a 5:1 (v:v) mixture of pentane and CH2Cl2, and finally a 1:1 (v:v) mixture of pentane and CH2Cl2 as the eluent. The pure product was obtained as light beige crystals (2.45 g, 8.0 mmol, 92%). 1 H NMR (400 MHz, acetone-d6): [ppm] 7.17 (dd, J = 8.9, 7.1 Hz, 2 H), 7.02 (d, J = 9.1 Hz, 4 H), 6.89 (d, J = 9.1 Hz, 4 H), 6.85 (d, J = 7.7 Hz, 2 H), 6.82 (s, 1 H), 3.78 (s, 6 H). 4-Iodo-N,N-bis(4-methoxyphenyl)aniline (20). Following a previously published method, 10 [bis(trifluoroacetoxy)iodo]benzene (1.87 g, 4.36 mmol) and I2 (1.10 g, 4.36 mmol) were stirred in dry CH2Cl2 (15 ml) for 1 hour at room temperature. Then, N,N-bis(4-methoxyphenyl)aniline (19) (1.33 g, 4.36 mmol) was added, and the reaction mixture was refluxed for 1 hour. Meanwhile a second solution of [bis(trifluoroacetoxy)iodo]benzene (0.94 g, 2.18 mmol) and I2 (0.55, 2.18 mmol) in dry CH2Cl2 (10 ml) was stirred for 1 hour at room temperature before adding it to the reaction mixture. Then the reaction mixture was refluxed for another hour. After cooling to room temperature, saturated aqueous Na2S2O3 solution was added. After phase separation, the organic phase was dried over anhydrous Na2SO4, and the solvent was evaporated. The green oily residue was purified on silica gel column using first pure pentane and then a 1:1 (v:v) mixture of pentane and CH2Cl2 as the eluent. This afforded the pure product as off-white crystals (1.50 g, 3.47 mmol, 80%). 1 H NMR (400 MHz, acetone-d6): [ppm] 7.46 (d, J = 9.0 Hz, 2 H), 7.06 (d, J = 9.0 Hz, 4 H), 6.91 (d, J = 9.0 Hz, 4 H), 6.63 (d, J = 9.0 Hz, 2 H), 3.79 (s, 6 H). S8

9 Ligand 21. 1,4-Diethynyl-2,3,5,6-tetramethoxybenzene (7) (100 mg, 0.4 mmol), compound 16 (157 mg, 0.4 mmol), and 4-iodo-N,N-bis(4-methoxyphenyl)aniline (20) (175 mg, 0.4 mmol) were dissolved in dry de-oxygenated triethylamine (10 ml). CuI (3 mg, 16 mol) and PdCl2(PPh3)2 (5.6 mg, 8 mol) were added, and the mixture was de-oxygenated once more before refluxing under N2 overnight. After cooling to room temperature, ethyl acetate was added, and the mixture was washed with aqueous NH4Cl solution and with brine. The organic phase was dried over anhydrous Na2SO4, and the solvents were evaporated. The crude product was purified on silica gel column using first pure CH2Cl2, then a 3:1 (v:v) mixture of pentane and ethyl acetate as the eluent. The pure product was obtained as a yellow solid (90 mg, 0.11 mmol, 28%). 1 H NMR (400 MHz, acetone-d6): [ppm] 8.69 (d, J = 3.7 Hz, 2 H), 8.54 (dd, J = 12.9, 8.1 Hz, 2 H), (m, 2 H), 7.51 (s, 1 H), (m, 3 H), 7.27 (s, 1 H), 7.11 (d, J = 9.0 Hz, 4 H), 6.93 (d, J = 9.0 Hz, 4 H), 6.81 (d, J = 8.8 Hz, 2 H), 3.98 (d, J = 8.3 Hz, 12 H) 3.79 (s, 6 H), 2.59 (s, 3 H), 2.32 (s, 3 H). MS (ESI TOF) m/z: [M]+H + Calcd for C52H45N3O6+H ; Found Ligand 22. 1,4-Diethynylbenzene (10) (100 mg, 0.79 mmol), compound 16 (306 mg, 0.79 mmol), and 4-iodo-N,N-bis(4-methoxyphenyl)aniline (20) (342 mg, 0.79 mmol) were dissolved in dry de-oxygenated triethylamine (10 ml). CuI (6 mg, 31.6 mol) and PdCl2(PPh3)2 (11 mg, 15.8 mol) were added and after de-oxygenating once more, the reaction mixture was heated to reflux under N2 overnight. After cooling to room temperature, ethyl acetate was added. The mixture was washed with saturated aqueous NH4Cl solution and with brine. Then the organic phases were dried over anhydrous Na2SO4, and the solvents were evaporated. The crude product was purified on silica gel column using first pure CH2Cl2 and then a 3:1 (v:v) mixture of pentane and ethyl acetate with 1% of triethylamine as the eluent. This afforded the pure product as a pale yellow solid (270 mg, 0.39 mmol, 49%). 1 H NMR (400 MHz, acetone-d6): (m, 2 H), S9

10 (m, 2 H), 7.95 (ddt, J = 7.8, 4.2, 1.9 Hz, 2 H), (m, 5 H), 7.44 (ddd, J = 7.5, 4.8, 1.2, 1 H), (m, 3 H), (m, 4 H), (m, 4 H), 6.79 (d, J = 8.9 Hz, 2 H), 3.81 (s, 6 H), 2.55 (s, 3 H), 2.33 (s, 3 H). MS (ESI TOF) m/z: [M]+H + Calcd for C48H37N3O2+H ; Found Dyad TAA-tmb-Ru 2+. Ligand 21 (155 mg, 0.17 mmol) and Ru(bpy)2Cl2 (80 mg, 0.17 mmol) were refluxed in a mixture of CHCl3 (5 ml) and CH3OH (16 ml) overnight. After cooling to room temperature, the solvent was removed under reduced pressure. The raw product was purified on silica gel column using first pure acetone, then a 10:1 (v:v) mixture of acetone and de-ionized water, and finally a 100:10:1 (v:v:v) mixture of acetone, de-ionized water and saturated aqueous KNO3 solution as the eluent. The solvents were removed from the desired chromatography fractions, and acetone was added to the solid residue. After filtration, the solvent was evaporated and the residue was re-dissolved in a minimal amount of acetone. This concentrated solution was dropped into diethyl ether, leading to precipitation of the product in the form of its nitrate salt. After filtration, the precipitate was washed with water and diethyl ether. The precipitate was redissolved in a minimal amount of acetone and dropped into a saturated aqueous KPF6 solution. The resulting precipitate was filtered, washed with water and pentane, and then dried in vacuum. The product was obtained as an orange solid (130 mg, mmol, 51%). 1 H NMR (400 MHz, acetone-d6): [ppm] (m, 6 H), (m, 7 H), (m, 4 H), 7.97 (d, J = 1.8 Hz, 1 H), (m, 5 H), 7.38 (d, J = 9.0 Hz, 3 H), (m, 5 H), 6.95 (d, J = 9.0 Hz, 4 H), 6.81 (d, J = 8.9 Hz, 2 H), 3.95 (d, J = 2.0 Hz, 12 H) 3.81 (s, 6 H), 2.50 (s, 3 H), 2.01 (s, 3 H). HRMS (ESI TOF) m/z: [M] 2+ Calcd for C72H61N7O6Ru ; Found Anal. Calcd for C72H61N7O6F12P2Ru 2C5H12: C, 59.49; H, 5.17; N, Found: 59.24; H, 5.47; N, S10

11 Dyad TAA-ph-Ru 2+. Ligand 22 (214 mg, 0.31 mmol) and Ru(bpy)2Cl2 (150 mg, 0.31 mmol) were refluxed in a mixture of CHCl3 (3 ml) and CH3OH (10 ml) overnight. After cooling to room temperature, the solvent was removed under reduced pressure. The crude product was subjected to column chromatography on a silica gel stationary phase using first pure acetone, then a 10:1 (v:v) mixture of acetone and de-ionized H2O, and finally a 100:10:1 (v:v:v) mixture of acetone, de-ionized H2O, and saturated aqueous KNO3 solution as the eluent. The solvents were evaporated from the desired chromatography fractions, and acetone was added to the solid residue. After filtration the solvent was removed. After re-dissolving in a minimal amount of CH3CN, the concentrated solution was dropped into diethyl ether. The precipitate was filtered and washed with H2O and diethyl ether. After drying in vacuum, the pure product was obtained as an orange solid (75 mg, 0.06 mmol, 19%) in the form of a nitrate salt. 1 H NMR (400 MHz, acetone-d6): [ppm] (m, 6 H), (m, 11 H), 7.95 (d, J = 1.8 Hz, 1 H), (m, 9 H), (m, 3 H), (m, 5 H), 6.96 (d, J = 9.0 Hz, 4 H), 6.79 (d, J = 8.9 Hz, 2 H), 3.81 (s, 6 H), 2.44 (s, 3 H), 2.00 (s, 3 H). HRMS (ESI TOF) m/z: [M] 2+ Calcd for C68H53N7O2Ru ; Found Anal. Calcd for C68H53N9O8Ru CH3CN 5H2O: C, 61.98; H, 4.90; N, Found: 62.17; H, 4.85; N, S11

12 X-ray crystallography Formula C52H45N3O6, M = , F(000) = 1704, yellow block, size mm 3, triclinic, space group P-1, Z = 4, a = (9) Å, b = (12) Å, c = (2) Å, = (3), = (3), = (3), V = (6) Å 3, Dcalc. = g cm -3. The crystal was measured on a Bruker Kappa Apex2 diffractometer at 123 K using Cu K -radiation with = Å, max = Minimal/maximal transmission 0.92/0.95, = mm -1. The Apex2 suite has been used for data collection and integration. 11 From a total of reflections, were independent (merging r = 0.035). From these, were considered as observed (I > 2.0 (I)) and were used to refine 1099 parameters. The structure was solved by the charge flipping method using the program Superflip. 12 Least-squares refinement against F was carried out on all non-hydrogen atoms using the program CRYSTALS. 13 R = (observed data), wr = (all data), GOF = Minimal/maximal residual electron density = -0.38/0.75 e Å -3. Chebychev polynomial weights were used to complete the refinement. 14 Plots were produced using Mercury. 15 Crystallographic data (excluding structure factors) for the structure in this paper have been deposited with the Cambridge Crystallographic Data Center, the deposition number is Copies of the data can be obtained, free of charge, on application to the CCDC, 12 Union Road, Cambridge CB2 1EZ, UK [fax: or deposit@ccdc.cam.ac.uk]. S12

13 Additional transient absorption data Figure S1. Transient absorption spectra measured after excitation of TAA-ph-Ru 2+ in CH3CN at 400 nm using a fs/ps TA setup. 1 Analogous data for the TAA-tmb-Ru 2+ dyad are reported in the main paper (Figure 5). Figure S2. Species-associated difference spectra (SADS) extracted from the data for TAA-ph- Ru 2+ in Figure S1. Analogous SADS for TAA-tmb-Ru 2+ are reported in the main paper (Figure 6). S13

14 Figure S3. Transient difference spectra measured after excitation of TAA-ph-Ru 2+ in CH3CN at 355 nm using a sub-ns/ s TA setup. 2 Analogous data for the TAA-tmb-Ru 2+ dyad are reported in the main paper (Figure 7). Figure S4. Species-associated difference spectra (SADS) extracted from the data for TAA-ph- Ru 2+ in Figure S3. Analogous SADS for TAA-tmb-Ru 2+ are reported in the main paper (Figure 8). S14

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16 (15) Macrae, C. F.; Bruno, I. J.; Chisholm, J. A.; Edgington, P. R.; McCabe, P.; Pidcock, E.; Rodriguez-Monge, L.; Taylor, R.; van de Streek, J.; Wood, P. A., J. Appl. Crystallogr. 2008, 41, 466. S16