Photo-induced proton transfer reaction in pentacene-doped benzoic acid crystals

Abstract

ABSTRACT Optical excitation at low temperature ofpentacene guest molecules in benzoic acid crystals leads to the appearance of a great variety of defect structures. The reaction mechanism proposed is thetransfer of a proton from the matrix to the dye forming a very unstable hydrogenated complex of pentacene which relaxes to ground state pentacene and a proton in a defect position of matrix. These results may serve as model for the study of spectral holeburning and spectral diffusion processes in amorphous solids.Keywords: proton transfer, pentacene, benzoic acid, photoinduced site, deuteration, holeburning.1. INTRODUCTIONSeveral phototransformations in condensed molecular phases at low temperatures are based onhydrogen photoinduced motions. Beyond its potential use for optical memories, the hydrogen motion inorganic solids at low temperature has become an important topic over the past decade in holeburningspectroscopy1 . Carboxylic acid crystals doped with dye molecules offer model systems for studies ofhydrogen motions. Previously, optical studies has led to the measurement ofthe tunnelig tautomerisationreaction of individual benzoic acid dimers coupled to neighbouring dye molecules2. Here, we presentsome results on laser induced proton transftr reaction in benzoic acid crystals doped with pentacene