Electron transfer reactions in ternary systems on silica gel surfaces: evidence for radical cation diffusion

Electron transfer reactions have been studied between 9-anthracenecarboxylic acid co-adsorbed with perylene on silica gel surfaces employing azulene as a molecular shuttle in order to facilitate hole transfer. In this paper we present for the first time a ternary system that unambiguously demonstrates an appreciable mobility of radical cations on the silica gel surface. Rates of hole transfer from the 9-anthracenecarboxylic acid radical cation to perylene via azulene have been studied using diffuse reflectance laser flash photolysis spectroscopy. Azulene has been shown to enhance the rate of electron transfer in the ternary system, proving significant mobility of the azulene and its radical cation species on silica gel surfaces. The data shows that the azulene radical cation can diffuse at an appreciable rate on the silica gel surface.