C. Photochemistry of adsorbed species. Photochemistry of adsorbed species

Abstract

A survey is given of photochemical reactions of weakly adsorbed species. First, the changes in the absorption spectra of molecules induced by adsorption are discussed. An extension of the spectral absorbance to longer wavelength is found for dye molecules adsorbed on noble metals, which is interpreted as an indication of a charge transfer interaction in the excited state. Fluorescence and energy transfer from adsorbed molecules are briefly reviewed.Secondly, electron transfer between the excited adsorbate and the adsorbent is discussed as the prominent photochemical reaction of weakly adsorbed species. The fundamental relations for the redox properties of excited molecules adsorbed at the interface between a solid and a solution are derived and correlated for the discussion of electron transfer with various types of solids according to their electronic properties. Some typical examples for charge injection into solids from excited adsorbed molecules are given.Finally, a few examples of other photochemical reactions in the adsorbed state are taken from the literature.