| Abstract
| - The electron injection dynamics of RuII(4,4‘-dicarboxy-2,2‘-bipyridine)2(SCN)2 (the so-called N3-dye) adsorbedon colloidal ZrO2 particles in room-temperature solution have been studied using time-resolved absorptionpolarization spectroscopy. The solvents used are acetonitrile and methanol. Electron injection is evidencedby the transient absorption anisotropy and/or the wavelength-dependent unpolarized absorption intensity. Theresults indicate that 630 nm excitation results in no N3* to ZrO2 electron transfer in both acetonitrile andmethanol solvents, 515 nm excitation results in electron injection in acetonitrile, and 495 nm excitation resultsin electron injection in both acetonitrile and methanol. These results may be understood in terms of simpleenergetic considerations: 630 nm excitation produces N3* with insufficient energy for electron injectionwhile 495 nm excitation produces N3* with an energy just sufficient for electron injection. In all cases whereelectron injection is energetically favorable, it occurs very rapidly, <200 fs. There is no indication of rapid(<5 ps) electron injection into deep trap states on the ZrO2 surface; however, the possibility of rapid injectioninto shallow trap states cannot be excluded. The observed kinetics also indicate that, following photoexcitationof the adsorbed N3, the ZrO2 surface relaxes on the 5−10 ps time scale.
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