Pore Size Effect on Kinetics of Photoinduced Electron Transfer in the Quinone−Amine System on the Silica Surface Studied by Diffuse-Reflectance Laser Flash Photolysis

Abstract

Electron transfer (ET) quenching of duroquinone (DQ) triplet by triphenylamine (TPA) coadsorbed onto porous silicas with different average pore size (PS = 2.2, 4, 6, 14, and 100 nm) and back ET within corresponding geminate triplet radical ion pairs (RIPs) were studied at different temperatures by the diffuse-reflectance laser flash photolysis technique. The PS effects both on inter- and intracage molecular dynamics and on the distribution of adsorbed molecules are discussed in terms of fractal effects in restricted geometries. The PS effect on the static ET quenching of 3DQ by TPA (responsible for fast (≤10 ns) formation of RIPs) is well described by the Perrin model in appropriate fractal dimensions, df. The values of df ranging from 3 to 2.37 are PS dependent in a manner similar to that known for long-range Forster type energy transfer. The average and time-dependent behavior of kinetics of diffusion-controlled dynamic quenching of 3DQ by TPA and that of back geminate ET both are strongly dependent on ...