Thermostimulated luminescence of poly(diphenylenephthalide) films. Kinetics and mechanistic steps of irradiative processes

Abstract

Kinetics of thermostimulated luminescence (TSL) of poly(diphenylenephthalide) (PDPh) films has been studied using mathematical modelling and DFT approximation. TSL of PDPh-film was considered to be arising from irradiative deactivation of diphenylene (DP) fragment of polymer chain in excited state formed upon recombination of the spatial separated ion-radical pairs generated by photoexcitation. Two parallel monomolecular transformations leading to excited DP have been revealed: the first path is characterized by the activation parameters of the kinetic rate constant k1 which equal to A1 ≈ 105 sec−1 and Ea1 ≈ 70 kJ mol−1. This path may be interpreted in terms of mechanical relaxation theory by segmental polymer mobility as electron transfer (ET) from phthalide (Ph) anion-to DP cation-radical. The second channel is supposed to be consist of two consecutive ET from triarylmethyl anion-radical to phthalide neutral (A2 ≈ 1 sec−1, Ea2 ≈ 20 kJ mol−1), and then to DP cation-radical (A3 ≈ 104 sec−1, Ea3 ≈ 40 kJ mol−1) of the polymer chain indicating γ- and β-relaxation, respectively. The revealed mechanistic steps and electron retention efficiency estimated in B97-2/6-311 + G(d,p) approximation for the most probable anion-radicals may point out the key role of domino quantum tunneling in transfer and recombination of charges in PDPh films.