Temperature dependence of fluorescence from polymer-bound 2-(2′-hydroxyphenyl)-2H-benzotriazole photostabilizers

Abstract

The temperature dependence of fluorescence from films of polymer-bound o-hydroxy-phenylbenzotriazole derivatives was investigated. The films exhibit a temperature-dependent red fluorescence (λ max ≈ 570 nm) ascribed to emission from the proton-transferred tautomer formed following excited state intramolecular proton transfer (ESIPT) and a temperature-insensitive blue emission (λ max ≈ 400 nm) associated with molecules in which the intramolecular hydrogen bonding is disrupted. Analysis of the fluorescence data indicates that the activation energy for the ESIPT process is negligible, whilst the temperature dependence of the red fluorescence is attributed to vibronically assisted internal conversion in the proton-transferred species.