Supporting Information

Transcription

1 Supporting Information Proton Coupled Electron Transfer in a Strongly Coupled Photosystem II-Inspired Chromophore-Imidazole-Phenol Complex: Stepwise Oxidation and Concerted Reduction Gerald F. Manbeck*, Etsuko Fujita, and Javier J. Concepcion* Chemistry Division, Brookhaven National Laboratory, Upton, NY , United States. * gmanbeck@bnl.gov, jconcepc@bnl.gov Contents: Figures S1 15 NMR spectra S2 S9 Figure S16 Infrared spectra (KBr) S1 Figure S17 UV-vis absorption spectra S1 Figure S18 Emission spectra S11 Table S1 Photophysical data S11 Figure S19 Stern-Volmer quenching S12 Figure S2 Excited state transient absorption spectra S13 Figure S21 Transient absorption spectra and kinetic traces with 5 mm methyl S14 viologen Figure S22 Temperature dependence of the phenoxyl radical reduction by the methyl S15 viologen radical cation. Table S2 Kinetic data for intramolecular phenol oxidation S16 Table S3 Kinetic data for phenoxyl radical reduction by MV + S16 Figures S23 27 Cyclic voltammetry S17 19 Table S4 Summary of electrochemical data S2 Table S5 Calculated OH and NH + IR stretching frequencies S21 Figure S28 Spin density plots of Ru(III) and phenoxyl radicals before and after PCET S21 Tables S6 9 Cartesian coordinates of DFT structures S21 31 References S32 S1

2 Figure S1. 1 H NMR spectrum of (phen-im-phome) in CDCl 3. Figure S2. 13 C NMR spectrum of (phen-im-phome) in CDCl 3. S2

3 Figure S3. 13 C DEPT NMR spectrum of (phen-im-phome) in CDCl 3. Figure S4. 1 H NMR spectrum of (phen-im-phoh) in CDCl 3. S3

4 Figure S5. 13 C NMR spectrum of (phen-im-phoh) in CDCl 3. Figure S6. 13 C DEPT NMR spectrum of (phen-im-phoh) in CDCl 3. S4

5 Figure S7. 1 H NMR of [(bpy-d 8 ) 2 Ru(phen-Im-PhOMe)](PF 6 ) 2 in CD 3 CN. Figure S8. 1 H COSY NMR of [(bpy-d 8 ) 2 Ru(phen-Im-PhOMe)](PF 6 ) 2 in CD 3 CN. S5

6 Figure S9. 13 C NMR of [(bpy-d 8 ) 2 Ru(phen-Im-PhOMe)](PF 6 ) 2 in CD 3 CN. Figure S1. 13 C DEPT NMR of [(bpy-d 8 ) 2 Ru(phen-Im-PhOMe)](PF 6 ) 2 in CD 3 CN. S6

7 Figure S11. 1 H NMR of [(bpy-d 8 ) 2 Ru(phen-Im-PhOH)](PF 6 ) 2 in CD 3 CN. Figure S12. 1 H COSY NMR of [(bpy-d 8 ) 2 Ru(phen-Im-PhOH)](PF 6 ) 2 in CD 3 CN. S7

8 Figure S C NMR of [(bpy-d 8 ) 2 Ru(phen-Im-PhOH)](PF 6 ) 2 in CD 3 CN. Figure S C DEPT NMR of [(bpy-d 8 ) 2 Ru(phen-Im-PhOH)](PF 6 ) 2 in CD 3 CN. S8

9 CD 3 CN CH 3 OD Figure S15. 1 H NMR spectrum of [(bpy-d 8 ) 2 Ru(phen-Im-PhOD)](PF 6 ) 2 in CD 3 CN. S9

10 absorbance absorbance wavenumber / cm wavenumber / cm Figure S16. Infrared spectra of [(bpy) 2 Ru II (phen-im-phoh)] 2+ (black, bottom) and [(bpy) 2 Ru II (phen-im- PhOMe)] 2+ (blue, top) in KBr. Inset: expansion of the region 1 to 17 cm 1. The weak OH stretch is not evident due to its hydrogen bonded nature. Spectra of the PhOH and PhOMe complexes are virtually identical with the exception of the stretch at 14 cm 1 which can be assigned as a CO stretch of the PhO CH 3 by comparison to the analogous mode in anisole (139 cm 1 ). 1 8 ε / M 1 cm 1 x PhOMe PhOH Wavelength / nm 6 7 Figure S17. Absorption spectra of [(bpy-d 8 ) 2 Ru(phen-Im-PhOMe)](PF 6 ) 2 and [(bpy-d 8 ) 2 Ru(phen-Im- PhOH)](PF 6 ) 2 and in CH 3 CN. S1

11 Normalized Intensity 1.5 phen-im-ph-ome phen-im-ph-oh phen-im-ph-od Ru(bpy) Wavelength / nm 8 9 Figure S18. Steady state emission spectra of [(bpy-d 8 ) 2 Ru(phen-Im-PhOMe)](PF 6 ) 2, [(bpy-d 8 ) 2 Ru(phen- Im-PhOH)](PF 6 ) 2, [(bpy-d 8 ) 2 Ru(phen-Im-PhOD)](PF 6 ) 2, and [Ru(bpy) 3 ] 2+ in deoxygenated CH 3 CN. The intensities are normalized with respect to quantum yields of emission relative to [Ru(bpy) 3 ] 2+ (Φ em =.62). The Ru III/II standard potential relative to both phenol couples indicates that Ru III can oxidize the PhOH via PCET or ET-PT pathways, given assignments of waves 1 and 2 (see text and Figure S24) as the PhOH/PhO and PhOH +/ couples. The absence of excited state intramolecular quenching as shown by the identical steady state emission intensities and lifetimes of Ru-phen-Im-PhOH/OMe are understood by analysis of the excited state Ru II*/I potential: E o (Ru II*/I ) = E oo + E o (Ru II/I ) The emission energy of Ru-phen-Im-PhOH is identical to [Ru(bpy) 3 ] 2+ for which E oo is 2.1 ev. 2 Thus, E o (Ru II*/I ) =.82 V and the free energy change, ΔE, for excited state oxidation of the phenol, (E o (Ru II*/I ) E o (PhOH/PhO ), is minimally.31 ev using the peak potential of the PhOH/PhO couple. This is not an exact value because the analysis does not consider the effect of the excited state on the measured ground state PhOH/PhO potential which should be significant in the strongly coupled system. Nevertheless, with ΔG o = -nfe, it is significantly uphill. Table S1. Summary of photophysical data in acetonitrile. τ / μs Φ em k r k nr [(bpy-d 8 ) 2 Ru(phen-Im-PhOMe)](PF 6 ) s s 1 [(bpy-d 8 ) 2 Ru(phen-Im-PhOH)](PF 6 ) s s 1 [(bpy-d 8 ) 2 Ru(phen-Im-PhOD)](PF 6 ) s s 1 S11

12 V V V A -1 6 τ /τ x x1-3 [MV 2+ ] / M 2 4 time / μs 6 B -1 τ /τ x x1-3 [MV 2+ ] / M C 2 4 time / μs τ /τ x x1-3 [MV 2+ ] / M 2 4 time / μs 6 Figure S19. Stern-Volmer quenching of [(bpy-d 8 ) 2 Ru(phen-Im-PhOMe)](PF 6 ) 2 (A), [(bpy-d 8 ) 2 Ru(phen- Im-PhOH)](PF 6 ) 2 (B) and [(bpy-d 8 ) 2 Ru(phen-Im-PhOD)](PF 6 ) 2 (C) with methyl viologen in deoxygenated CH 3 CN. The quenching constants, k Q, are M 1 s 1, M 1 s 1, and M 1 s 1, respectively. S12

13 ΔA / mo.d. ΔA / mo.d. ΔA / mo.d. ΔA / mo.d. 2 A time / μs ns 15 ns 4 ns 25 ns 8 ns 1 ns Wavelength / nm B time / μs ns 15 ns 4 ns 25 ns 8 ns 1 ns Wavelength / nm Figure S2. Excited state transient absorption spectra of [(bpy-d 8 ) 2 Ru(phen-Im-PhOMe)](PF 6 ) 2 (A) and [(bpy-d 8 ) 2 Ru(phen-Im-PhOH)](PF 6 ) 2 (B) in CH 3 CN. 7 8 S13

14 A B D C [(bpy-d8)2ru(phen-im-phome)] 2 [(bpy-d8)2ru(phen-im-phoh)] 2+ ΔA / mo.d. ΔA / mo.d. [(bpy-d8)2ru(phen-im-phome)] 6 5 [(bpy-d8)2ru(phen-im-phoh)] time / μs time / μs 3 Figure S21. Transient absorption spectra for [(bpy-d8)2ru(phen-im-phome)](pf6)2 (A) and [(bpyd8)2ru(phen-im-phoh)](pf6)2 (B) in the presence of 5 mm methyl viologen. The data in C and D are the kinetic traces at 39 nm showing the growth (C) and disappearance (D) of the methyl viologen radical. In the presence of 5 mm methyl viologen (MV2+), the 3MLCT state is quenched oxidatively as shown by loss of the 35 nm absorbance and growth of methyl viologen radical cation (MV+ ) signals at 39 and 61 nm. The flash/quench experiment yielded different results for the PhOMe and PhOH complexes. Spectra of the PhOMe complex evolve from the 3MLCT excited state spectrum at 4 ns to a spectrum at 3 ns with methyl viologen radical cation (MV+ ) absorptions at 39 and 61 nm and the 3MLCT bleach of the oxidized RuIII at 46 nm. These signals decay over several hundred μs according to equal concentration second order kinetics due to the recombination of (MV + ) and RuIII (Scheme 1 kbet_1). Clear isosbestic points are present during the quenching and recombination reactions. In contrast, the spectra of Ru-phen-Im-PhOH evolve without isosbestic points from the 4 ns excited state to spectra after 3 ns which contain MV+ absorptions but not the 46 nm bleach associated with the [Ru]3+. The MV+ signals again decay according to second order kinetics but more slowly than the recombination with the RuIII of the PhOMe complex. The disappearance of the RuIII bleach following oxidation by methyl viologen is consistent with intramolecular oxidation of the phenol by Ru III. The kinetics of the RuIII bleach disappearance (at 5 mm MV2+) match the growth of the MV+ absorptions indicating that the quenching reaction is rate limiting. The slower kinetics for MV+ disappearance are consistent with a lower driving force for recombination with the phenoxyl radical (Scheme 1 kbet_2). S14

15 Figure S22. Temperature dependence of the recombination reaction between methyl viologen radicals and [(bpy-d 8 ) 2 Ru III (phen-im-phome)] 3+ or [(bpy-d 8 ) 2 Ru II (phen-im(h/d)-pho )] 3+ in CH 3 CN. S15

16 Table S2. Kinetic data for intramolecular phenol oxidation obtained from decay of the 46 nm bleach in transient absorption data. Temperature, ºC k ET Ru-phen-Im-PhOH, s 1 k ET Ru-phen-Im-PhOD, s E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E+7 Table S3. Kinetic data for phenoxyl radical reduction by MV +. The data are k obs not converted to k BET_1 (see text). Temperature ºC k ET Ru-phen-Im-PhOH M 1 s 1 k ET Ru-phen-Im-PhOD M 1 s 1 k ET Ru-phen-Im-PhOMe M 1 s E E+9 1.2E E E E E E E E E E E+1 6.2E E E+9 6.4E E+1 S16

17 current / μa current / μa current / μa.12 V V V E / V vs SCE Figure S23. Cyclic voltammograms of phen-im-phoh in CH 2 Cl 2..7 V E 1/ V V E 1/ V E 1/2 1.8 V E 1/ V V E / V vs SCE E / V vs SCE Figure S24. Cyclic voltammograms of [(bpy) 2 Ru II (phen-im-phoh)] 2+ in CH 3 CN. S17

18 current / μa current / μa E / V vs SCE Figure S25. Square wave voltammograms of [(bpy) 2 Ru II (phen-im-phoh)] 2+ in CH 3 CN V V E / V vs SCE Figure S26. Cyclic voltammograms of phen-im-phome in CH 2 Cl 2. S18

19 current / μa current / μa 2 E 1/ V E / V vs SCE Figure S27. Cyclic voltammograms of [(bpy) 2 Ru II (phen-im-phome)] 2+ in CH 3 CN E 1/ V -1.2 E 1/ V E / V vs SCE E 1/ V -1.8 S19

20 Table S4. Summary of redox potentials in volts vs SCE. The ligands were analyzed in CH 2 Cl 2 and complexes were measured in CH 3 CN. Phenol redox couples are shown in bold font. Compound Oxidations Potential / V vs SCE Reductions 1.19 a, 1.58, a.12 b 1.13 a, 1.27, a , b 1.37, 1.55, a, 1.86 a , 1.56, 1.76 a Anodic peak potential for an irreversible wave. b Cathodic peak potential for an irreversible wave. S2

21 Table S5. Predicted stretching O H and O D frequencies from DFT calculations for the Ru III complex obtained immediately after oxidative quenching with methyl viologen and stretching N H and N D frequencies for the phenoxyl radicals generated after intramolecular proton coupled electron transfer. a [(bpy) 2 Ru III (phen-im-phoh)] 3+ [(bpy) 2 Ru II (phen-im(h)-pho )] 3+ N---H OPh 3392 cm 1 N H---OPh 3454 cm 1 [(bpy) 2 Ru III (phen-im-phod)] 3+ [(bpy) 2 Ru II (phen-im(d)-pho )] 3+ N---D OPh 2472 cm 1 N D---OPh 2542 cm 1 A Figure S28. DFT calculated spin densities for the Ru III complex obtained immediately after oxidative quenching with methyl viologen (A) and the phenoxyl radicals observed after intramolecular proton coupled electron transfer (B). B Table S6. Calculated XYZ coordinates of [(bpy) 2 Ru II (phen-im-phoh)] 2+ Atom X Y Z H C H C N C C C H C C C C H S21

22 H C H N Ru H C H C N C C C H C C C C H H C H N H H H H H C H C N C C C C H C C C C C S22

23 H H C H N N N C C C C C C C H H O H C H H H C C H H H C H H H C H H H C C H H H C H S23

24 H H C H H H Table S7. Calculated XYZ coordinates of [(bpy) 2 Ru III (phen-im-phoh)] 3+ Atom X Y Z H C H C N C C C H C C C C H H C H N Ru H C H C N C C C H C C C C S24

25 H H C H N H H H H H C H C N C C C C H C C C C C H H C H N N N C C C C C C C H H O H S25

26 C H H H C C H H H C H H H C H H H C C H H H C H H H C H H H Table S8. Calculated XYZ coordinates of [(bpy) 2 Ru II (phen-im-phoh + )] 3+ Atom X Y Z H C H C N C C S26

27 C H C C C C H H C H N Ru H C H C N C C C H C C C C H H C H N H H H H H C H C N C C S27

28 C C H C C C C C H H C H N N N C C C C C C C H H O H C H H H C C H H H C H H H C H S28

29 H H C C H H H C H H H C H H H Table S9. Calculated XYZ coordinates of [(bpy) 2 Ru II (phen-im(h)-pho )] 3+ Atom X Y Z H C H C N C C C H C C C C H H C H N Ru H C H C S29

30 N C C C H C C C C H H C H N H H H H H C H C N C C C C H C C C C C H H C H N N N C S3

31 C C C C C C H H O H C H H H C C H H H C H H H C H H H C C H H H C H H H C H H H S31

32 References (1) Balfour, W. J. Spectrochim. Acta. A. 1983, 39, (2) Alstrum-Acevedo, J. H.; Brennaman, M. K.; Meyer, T. J. Inorg. Chem. 25, 44, S32