Observation of photoinduced electron transfer in dye/semiconductor colloidal systems with different coupling strengths

Investigations on the ultrafast electron injection and recombination mechanism from the dyes alizarin and coumarin 343 to wide band gap semiconductor colloids in solution are presented, combined with detailed studies on population, depopulation and relaxation phenomena. We discuss transient absorption measurements on time scales from 100 fs to >1 ns throughout the visible spectral range (350–650 nm), allowing the simultaneous time resolved observation of signals assigned to ground state, cation and injected electron in the conduction band of the semiconductor. Analysis of transient absorption changes in the near UV region, where cation absorption is dominant, allows unambiguous assignment of the various kinetic components. This facilitates the distinction between the different contributions of the various absorbing species also in the congested visible spectral range. Comparison between the two dyes with respect to their different electron transfer parameters provides a direct way to analyze the influence of the electronic coupling element V on the injection and recombination process. Detailed inspection of the decay related spectra for both samples yields information on the environmental response succeeding the cation formation.