Photoinduced intramolecular proton transfer in 2- and 4-(2,4-dinitrobenzyl)pyridine

Abstract

Photoinduced absorption changes and thermal bleaching of the absorption were measured at different temperatures in 2- and 4-(2,4-dinitrobenzyl)pyridine ( α- and γ-DNBP) dispersed in polymer films in order to elucidate the mechanism of the photoinduced intramolecular proton transfer (PIPT) in DNBP. Three photoinduced absorption bands which correspond to the NH, anion and OH forms emerge in the visible light region after UV light irradiation. The efficiency of the PIPT to the NH form in γ-DNBP is much lower than that in α-DNBP. The thermal conversion from the OH to the anion/NH forms in γ-DNBP is faster, while the conversion from the NH to the stable form is slower than that in α-DNBP. Based on molecular-orbital calculations and the potential-energy diagram of the PIPT reaction by taking into account the different distances of the reaction pathway between α- and γ-DNBP, the observed differences in the PIPT reaction between α- and γ-DNBP are discussed.