Kinetic characteristics of the photoreduction of benzophenone in solid polymers in the presence of 4-halophenols

Abstract

Benzophenone photoreduction in the presence of 4-halophenols (RC6H4OH; R = Cl, Br, and I) in a polymer glass is studied in terms of steady-state and nanosecond laser photolysis. The experimental data on the kinetics of the decay of the ketone triplet state are treated using a polychronous kinetic model in the assumption that two concurrent processes (hydrogen atom abstraction from the polymer and from the phenol) occur. The proton transfer rate constants averaged over the distribution and the parameter n that characterizes the distribution width were determined. The value of kav for the halophenols is shown to be more than an order of magnitude higher. No heavy atom effect is observed. The reaction product composition is demonstrated to change upon addition of a halophenol. The photoreduction in glass polymers is controlled by hydrogen atom abstraction from the respective donor by triplet ketone molecules. The reaction occurs predominantly in a polymer cage, a kind of polymer nanoreactor.