Ultrafast electron injection processes for a serties of Ru-based dyes bound to the TiO2 nanoparticles have been studied. The Ru-based chromophores with spacers of different length (up to 24 Ĺ) have been synthesized in order to study the effect of separation between the chromophore-bearing group and the semiconductor surface onto the rate of electron injection. Also, the effect of spacer conjugation on the rate of electron injection has been investigated by interrupting the spacer conjugation with bicyclooctane unit. Furthermore, sensitizers with different number of binding groups (bipods and tripods) were synthesized to study the effect of binding geometry to the semiconductor surface. It was found that electron injection is mostly complete within a sub-picosecond timescale. This behavior suggests that spacers work as molecular wires. The kinetics of electron injection turns out to be mostly biexponential that can be caused by the competition between the “hot” electron injection on one side and vibrational cooling and intersystem crossing on the other hand. The resolution of these competing processes is now being thoroughly studied and will be reported as well.
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