S1. Experimental section: SE 1. Materials: All the solvents and the chemicals (puriss grade) were obtained from Fluka. tertButhylpyridine, acetonitril and varironitril were distilled before use. Guanidinium thiocyanate (Aldrich) and H2PtCl6 was used as received. Two kinds of TiO2 paste containing nanocrystalline (20 nm) TiO2 (paste A) and submicroparticle (400 nm) TiO2 (paste B) were prepared by a procedure previously reported.29
The
ruthenium
complexes
(Bu4N)2[Ru(dcbpyH)2(NCS)2]
N719
and
[Ru(dcbpyH)(tdbpy)(NCS)2] N621 (H2dcbpy = 4,4'-dicarboxy-2,2'-bipyridine, tdbpy = 4,4’-tridecyl2,2’-bipyridine) were available from our previous studies.30,31 SE 2. Analytical measurements: 1H and
13
C NMR spectra were measured on a Bruker 200 and 600
MHz spectrometer in CD3OD. The reported chemical shifts were against TMS. The FTIR spectra were measured using a Digilab 7000 FTIR spectrometer. The ATR data reported here was taken with the ‘Golden Gate’ diamond anvil ATR accessory (Graseby-Specac) using typically 64 scans at a resolution of 2 cm-1. UV-VIS and fluorescence spectra were recorded in a 1-cm path length quartz cell on a Cary 5 spectrophotometer and Spex Fluorolog 112 Spectrofluorometer, respectively. Electrochemical data were obtained by cyclic voltammetry in a conventional three-electrodes cell using an AUTOLAB system (PGSTAT 30). A glassy-carbon or a gold working electrode, glassy-carbon auxiliary electrode and silver rod used as a quasi reference electrode in a single-compartment-cell configuration. Cyclic voltammograms were obtained typically by dissolving 1 mM of in DMF containing 0.1 M tetrabutylammonium perchlorate salt. The solution was de-aerated by bubbling argon gas. After measurement, ferrocene cyclic voltammogram was recorded by adding at the end of the experiment and the reported potentials were against ferrocenium/ferrocene couple (Fc+/Fc). SE 3. Photovoltaic measurements: Photoelectrochemical data were measured using a 450W Xenon light source that was focused to give 1000 W/m2, the equivalent of one sun at AM1.5, at the surface of the test cell. The TiO2 electrodes of were heated at 450 °C for 20 minutes under an O2 atmosphere and allowed to cool to 100 °C before dipping them into the dye solution. The N719 and N621 dye solutions S1
were prepared in 1:1 acetonitrile and tert -butanol solvents. The typical concentrations were in the range of 5 X 10-4 M and the electrodes were left in the dye solutions for 18-20 hours. The monoprotonated dye solutions of 1.8 X 10-2 M were prepared in methoxypropionitrile or DMF solvent by mixing dye and tetrabutylammonium hydroxide 30-Hydrate in 1:1 molar ratio. The heated TiO2 electrodes were dipped into 1.8 X 10-2 M dye solution for 10 minutes. Alternatively, a measured volume of the concentrated solution was pipetted (5 µl for 0.25 cm2 TiO2 area) onto the surface of TiO2 electrode and the dye solution left for 10 minutes. The dye-coated electrodes were rinsed quickly with acetonitrile and used as such for photovoltaic measurements. A sandwich cell was prepared by using the dye anchored TiO2 film as a working electrode and a second conducting glass coated with chemically deposited platinum from 0.05M-hexachloroplatinic acid as a counter electrode. The two electrodes were superimposed with a thin transparent film of Surlyn polymer gasket (DuPont). The superimposed electrodes were tightly held and applied heat (130°C) around the Surlyn gasket to seal the two electrodes. A thin layer of electrolyte solution containing 0.60 M butylmethylimidazolium iodide (BMII), 0.03 M I2, 0.10 M guanidinium thiocyanate and 0.50 M tertbuthylpyridine in a mixture of atetonitril and valeronitril volume ratio: 85:15 (A6141) was introduced into inter electrode space from the counter electrode side through a pre-drilled hole. Then, the drilled hole was sealed with microscope cover slide and Surlyn to avoid leakage of the electrolyte solution. SE 4. Purification on Sephadex LH-20: The N719 and N621 complexes were purified on a Sephadex LH-20 column using the following procedure. The N719 complex was dissolved in water containing two equivalents of tetrabutylammonium hydroxide. The concentrated solution was filtered through a sintered glass crucible and charged onto a Sephadex LH-20 column, which was prepared in water. The adsorbed complex was eluted using water. The main band was collected and the solution pH was lowered to 4.3 using 0.02 M HNO3 acid. The titration was carried out slowly over a period of three hours. Then, the solution was kept at –20 °C for 15 hours. After allowing flask to 25 °C, the precipitated complex was collected on a glass frit and air-dried. The same purification procedure was repeated three more times to get pure N-bonded isomer complex. S2
The purification method for N621 is similar to that of N719 except the N621 complex was dissolved in methanol containing two equivalents of tetrabutylammonium hydroxide and the column was prepared in methanol. The adsorbed complex was eluted using methanol. The main band was collected and the solution pH was lowered to 4.5 using 0.02 M HNO3 acid. Then, the solution was concentrated to 5 ml and to this concentrated solution 15 ml of water was added. The precipitated complex was collected on a glass frit and air-dried.
S2. Theoretical section Table S2.1: Calculated vertical excitation energies in eV and nm and oscillator strengths (f) for the N621(Na) dye. Band I EV
Nm
f
Character
2.0731 598.05
0.0238 89%(173 ->174); 5%(171 ->174)
2.3128 536.08
0.0269 82%(173 ->175); 10%(172 ->174);
2.4560 504.82
0.0974 64%(171 ->174); 13%(172 ->174); 6%(172 ->175); 5%(173 ->174)
2.6574 466.55
0.0468 55%(171 ->175); 25%(172 ->175); 6%(173 ->175)
(1) Band II EV Nm
f
Character
3.0031 412.85
0.0386 56%(173 ->177); 34%(173 ->176)
3.1345 395.54
0.0177 96%(170 ->174)
3.1731 390.73
0.0191 93%(172 ->176)
3.2291 383.96
0.0203 57%(173 ->178); 35%(171 ->176)
3.2533 381.10
0.0113 62%(172 ->177); 13%(171 ->176); 11%(173 ->178); 5%(173 ->179)
3.2777 378.26
0.0311 93%(171 ->177)
3.3962 365.07
0.0482 63%(173 ->179); 7%(170 ->175); 6%(172 ->178); 5%(173 ->184)
3.4549 358.86
0.0329 71%(172 ->178); 9%(168 ->174); 5%(173 ->179); 5%(171 ->178)
3.4767 356.62
0.0289 69%(169 ->174); 14%(168 ->174); 8%(171 ->178)
3.5412 350.12
0.0144 31%(168 ->174); 25%(171 ->178);9%(172 ->179); 6%(167 ->174); 5%(172 ->178); 4%(169 ->174); 3%(173 ->179) S3
3.6208 342.42
0.0125 43%(171 ->179); 11%(171 ->185); 10%(172 ->179); 4%(172 ->185); 4%(172 ->184); 3%(173 ->185)
3.6628 338.50
0.0362 43%(169 ->175); 38%(167 ->174); 4%(168 ->175)
3.6837 336.57
0.0269 29%(171 ->179); 25%(167 ->174); 9%(171 ->185); 8%(172 ->185); 6%(169 ->175); 3%(169 ->185)
3.7405 331.46
0.0138 39%(169 ->175); 12%(167 ->174); 9%(171 ->179); 5%(171 ->185); 5%(167 ->175): 3%(172 ->184)
3.9142 316.76 (2) Band III eV Nm
0.0166 83%(167 ->175)
f
Character
4.0599 305.39
0.2760 77%(166 ->174)
4.1402 299.47
0.0212 93%(163 ->174)
4.3036 288.09
0.0244 46%(168 ->176); 37%(169 ->176); 3%(168 ->177)
4.3163 287.25
0.0573 49%(166 ->175);21%(170 ->179); 18%(169 ->177);12%(168 ->176); 6%(163 ->175); 3%(169 ->178)
4.3371 285.87
0.0180 38%(166 ->175); 19%(163 ->175); 18%(169 ->176); 12%(168 ->176); 4%(169 ->177)
4.3479 285.16
0.0105 43%(169 ->177);26%( 169 ->176); 11%(168 ->176); 5%(166 ->175)
S4
Table S2.2: Calculated vertical excitation energies in eV and nm and oscillator strengths (f) for the N719 dye. Molecule
Band
Character of the main transitions
Band I eV
nm
f
Character
1.9704
629.24
0.0570
87%(187->188); 4%(185->188);
2.0356
609.06
0.0195
71%(187->189); 13%(185->189); 10%(186->188)
2.2481
551.50
0.1169
53%(185->188);36%(186->189); 6%(187->188)
2.3915
518.43
0.0567
56%(185->189); 17%(187->189); 13%(186->188); 6%(187->191) Band IIa
eV
nm
f
Character
2.7555
449.95
0.0477
95%(187->190)
2.8674
432.40
0.0826
71%(187 ->191); 10%(184 ->188); 9%(186 ->190)
2.8947
428.32
0.0358
97%(184 ->189)
2.9631
418.43
0.0108
87%(186 ->190); 6%(187 ->191)
2.9878
414.97
0.0491
49%(185 ->190); 47%(186 ->191)
3.0747
403.25
0.0190
95%(187 ->192) Band IIb
eV
nm
f
Character
3.2124
385.95
0.0316
91%(183 ->188); 4%(182 ->189)
3.2563
380.75
0.0100
46%(182 ->188); 26%(186 ->192); 24%(183 ->189)
3.3305
372.27
0.0436
60%(185 ->192); 32%(182 ->189);
3.4293
361.54
0.0997
87%(181 ->188); 6%(186 ->193)
3.6395
340.67
0.0200
56%(181 ->189); 11(185 ->197); 4%(186 ->196); 3%(186 ->192); 3%(183 ->197); 3%(187 ->197); 3%(185 ->193); 3%(182 ->188)
(2) Band III eV nm
f
Character
3.8562
321.52
0.0523
67%(178 ->188); 22%(184 ->192)
3.8673
320.60
0.0125
78%(184 ->192); 19%(178 ->188)
3.9072
317.32
0.2239
77%(177 ->188); 5%(181 ->190); 3%(184 ->193); 3%(178 ->189)
3.9699
312.31
0.0430
65%(178 ->189); 17%(184 ->193); 9%(177 ->188)
3.9788
311.61
0.0173
45%(183 ->190); 40%(184 ->193); 5%(182 ->191); 5%(178 ->189)
3.9886
310.85
0.0639
35%(184 ->193); 34%(183 ->190); 12%(178 ->189); 6%(180 ->189); 4%(179 S5 >188); 3%(180 ->188)
4.0078
309.36
0.0415
81%(177 ->189); 3%( 182 ->190); 3%(178 ->188); 3%(175 ->189)
N621
N719 a
N719 b
N719 c
N719 av.(ac)
E I =2.49 (2.41) II =3.46 (3.32) III=4.29 (4.00 4.19) E I =2.24 (2.35) IIa=2.96 (3.22) IIb=3.37 (3.22) III=3.92 (3.97) E I =2.31 (2.35) II =3.27 (3.22) III=3.98 (3.97) E I =2.62 (2.35) II =3.26 (3.22) III=4.01 (3.97) E I =2.30 (2.35) II =3.29 (3.22) III=3.94 (3.97)
R 1.0 (1.0) 1.6 (1.1) 3.9 (2.7-3.9) R 1.0 (1.0) 1.3 (0.9) 1.2 (0.9 2.4 (3.5) R 1.0 (1.0) 1.8 (0.9) 3.4 (3.5) R 1.0 (1.0) 1.1 (0.9) 3.1 (3.5) R 1.0 (1.0) 1.4 (0.9) 3.2 (3.5)
Ru(t2g)+SCN-> π*(B-B’) Ru(t2g )+SCN-> π* (A-A’)(B-B’) π (B-B’)-> π* (B-B’) Ru(t2g)+SCN-> π*(A-A’) Ru(t2g)+SCN-> π* (A-A’)(B-B’) Ru(t2g)+SCN-> π* (A-A’) π (A-A’)(B-B’)-> π* (A-A’) Ru(t2g)+SCN-> π*(A-A’) Ru(t2g)+SCN-> π* (A-A’)/(A-A’)(B-B’) π (A-A’)(B-B’)-> π* (A-A’) Ru(t2g)+SCN-> π*(A-A’)/ π*(B-B’) Ru(t2g)+SCN-> π*(A-A’) π (A-A’)(B-B’)-> π* (A-A’)
Table S2.3: Summary of the main calculated spectral features for the [N621(0H-2Na)](0) model of the non-protonated N621 dye and for the [N3(2H-2Na)] models of the di-protonated N719 dye. E is the absorption maximum energy (eV) and R is the band intensity relative to band I. Experimental data are reported in parenthesis.
S6
LUMO+4
LUMO+2
LUMO
LUMO+5
LUMO+3
LUMO+1
Figure S2.1: Frontier molecular orbitals of the N621 dye. S7
LUMO+4 (LUMO+5)
HOMO-4
LUMO+2 (LUMO+3)
HOMO-3
LUMO (LUMO+1)
HOMO
Figure S2.2: Frontier molecular orbitals of the N719 dye.
S8
Figure S2.3: Comparison between calculated (blue line) and experimental (red points) spectra of the [N621(0H-2Na)(0) model of the N621 complex. Blue vertical lines correspond to calculated excitation energies and oscillator strengths. Energy in eV. The calculated spectrum has been obtained by a gaussian convolution with σ=0.20 and 0.12 eV for the transitions below and above 4.0 eV, respectively. The presence of band III substructure is evident. The experimental (calculated) absorption maxima of bands I-III are at: 2.41 (2.49), 3.32 (3.46) and 4.00-4.19 (4.09-4.37) eV.
S9
Figure S2.3: Optimized molecular structure of the Ti38O76 cluster representing the model of the TiO2 nanoparticle, together with main geometrical parameters (Å).The structure was optimized, as described in reference 37. by the Car-Parrinello method. The electronic structure and TDDFT excitation energy discussed in the text have been obtained using the Gaussian03 package, at the B3LYP/3-21g* level in water solution (C-PCM).
S10
Complete Reference 33: Gaussian 03, Revision B.05, Frisch, M.J.; Trucks, G.W.; Schlegel, H.B.; Scuseria, G.E.; Robb, M.A.; Cheeseman, J.R.; Montgomery, Jr., J.A.; Vreven, T.; Kudin, K.N.; Burant, J.C.; Millam, J.M.; Iyengar, S.S.; Tomasi, J.; Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G.A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li, X.; Knox, J.E.; Hratchian, H.P.; Cross, J.B.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R.E.; Yazyev, O.; Austin, A.J.; Cammi, R.; Pomelli, C.; Ochterski, J.W.; Ayala, P.Y.; Morokuma, K.; Voth, G.A.; Salvador, P.; Dannenberg, J.J.; Zakrzewski, V.G.; Dapprich, S.; Daniels, A.D.; Strain, M. C.; Farkas, O.; Malick, D.K.; Rabuck, A.D.; Raghavachari, K.; Foresman, J.B.; Ortiz, J.V.; Cui, Q.; Baboul, A.G.; Clifford, S.; Cioslowski, J.; Stefanov, B.B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R.L.; Fox, D.J.; Keith, T.; Al-Laham, M.A.; Peng, C.Y.; Nanayakkara, A.; Challacombe, M.; Gill, P.M. W.; Johnson, B.; Chen, W.; Wong, M.W.; Gonzalez, C.; and Pople, J. A.; Gaussian, Inc., Pittsburgh PA, 2003.
S11
