Mechanism of the magnetic field dependence for the liquid phase photoreaction in the nanotube of MCM-41

Abstract

Photochemical reduction of xanthone in an alcoholic solution flowing in a column packed with MCM-41, a mesoporous silica, was dependent on the magnetic field. The free radical intermediates were detected by the spin trapping method and the yield of spin adducts was also dependent on the magnetic field. In addition, a radical-quenching experiment was made to analyze the bulk concentrations of the free radical intermediates as functions of the magnetic field. Although these magnetic field dependencies were different from those observed in the micelle, we concluded that these observations are explained with the “relaxation mechanism” of the radical pair model: i.e. the intermediate radical pair in a cage has a life span comparable to or longer than the spin lattice relaxation times of these radical intermediates. The mechanism and characteristics of this cage effect in the nanotube, which is opened at the both ends, are discussed.