Photophysical Study of Perylene/TiO2 and Perylene/ZnO Varying Interfacial Couplings and the Chemical Environment

The impact of the chemical environment on heterogeneous electron transfer processes of two perylene derivatives chemically bound to ZnO or TiO2 colloids in a film was investigated by means of absorption and fluorescence spectroscopy. The perylene molecules varied in their electronic coupling between the perylene moiety and a carboxylic acid group, which also bound the perylene dyes to the semiconductor surface. Significantly different excited state dipole moments for the two perylene derivatives were found for certain perylene-solvent interactions and were attributed to different intramolecular charge transfer characters of the excited state. It is concluded that lifetime broadening due to ultrafast electron injection plays only a minor role in explaining the observed strong broadening of the absorption spectra for the hybrid systems with strong electronic coupling. Rather, a strong environmental effect of the colloidal semiconductor has to be taken into account for the hybrid systems with strong interfacial couplings.