RU-505

Photoinduced electron injection dynamics from Ru(dcbpy)(2)(X)(2) (dcbpy = 4,4'-dicarboxy-2,2'-bipyridine; X(2) = 2SCN(-), 2CN(-), and dcbpy; referenced as RuN3, Ru505, and Ru470) to In(2)O(3) nanocrystalline thin films were studied using ultrafast transient IR absorption spectroscopy. After 532 nm excitation of the adsorbates, the dynamics of electron injection from their excited states to In(2)O(3) were studied by monitoring the IR absorption of the injected electrons in the semiconductor. The injection kinetics were non-single-exponential. For samples exposed to air, the half rise times, defined as the time of 50% injection yield, were 5 +/- 0.8, 85 +/- 20, and >200 ps for RuN3, Ru505, and Ru470, respectively. For samples in pH 2 buffer, the corresponding half time for injection from these complexes became 6 +/- 1, 105 +/- 20, and 18 +/- 5 ps. The injection kinetics from RuN3 to In(2)O(3) was found to be similar to that to SnO(2). These kinetics traces showed a negligible <100 fs injection component and were very different from those to TiO(2). The dependences of the injection kinetics on adsorbate energetics and the nature of the semiconductors are discussed.

Ultrafast infrared spectroscopy was utilized to investigate the electron-transfer dynamics from Ru(dcbpy)(2)(X)(2) complexes (dcbpy = 4,4'-dicarboxy-2,2'-bipyridine; X(2) = SCN(-), 2CN(-), and dcbpy; referenced as RuN3, Ru505, and Ru470, respectively) to nanocrystalline SnO(2) films. For both films exposed to air (dry) and submerged in a pH 2 buffer solution, all traces show biphasic dynamics with a small ultrafast component (less than 10%) and nonexponential slow component, indicating that most injection occurs from thermalized excited state of the dye. In the dry film, the injection rate becomes slower, comparing RuN3, Ru505, and Ru470, correlating with decreasing excited-state oxidation potentials in these dyes. However, the variation of injection rate with dye potential is less noticeable at pH 2. The possible reason for the different injection dynamics in these dyes and under different environments are discussed. These injection dynamics are also compared with those on TiO(2) and ZnO.