| Abstract
| - Reverse electron transfer from TiO2 to I2 in nanocrystalline TiO2 films with coadsorbed [NBu4]2[cis-Ru(Hdcbiq)2(NCS)2] (1; [NBu4]+ = tetrabutylammonium cation; H2dcbiq = 4,4‘-dicarboxy-2,2‘-biquinoline)and [NBu4]2[cis-Ru(Hdcbpy)2(NCS)2] (2; H2dcbpy = 4,4‘-dicarboxy-2,2‘-bipyridine) was investigated. Theapparent electron lifetime decreased when 1 was coadsorbed with 2 on TiO2. The incident monochromaticphoton-to-current conversion efficiency and the open-circuit photovoltage decreased substantially even whena small amount of 1 was coadsorbed with 2 on TiO2. The reduction of 1 on TiO2 was spectroelectrochemicallyobserved at a potential that was more positive than the energy of the conduction band edge of the TiO2 films.These results suggest that the injected electron from photoexcited complex 2 reacted with I2 through 1. Reverseelectron transfer from TiO2 to I2 depended not only on the electron density but also on the amount of 1adsorbed on TiO2. Therefore, we assumed that the injected electron was trapped by 1 on TiO2 and thenreacted with I2. If an injected electron diffused randomly in TiO2, the relative cross-section (σtrap) of electrontrapping by 1 on TiO2 would be expected to be 1 and to be the same as that of trapping by 2. However, theσtrap value was much larger than expected, which indicates that the electron in TiO2 predominantly reactedwith I2 through 1.
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