Binding energies of triplet excimers in poly(N-vinylcarbazole) solid films from laser-based kinetic spectroscopy between 15 and 55 K

Abstract

Time-resolved delayed luminescence spectra from solid films of poly(N-vinylcarbazole) have been recorded in the temperature interval between 15 and 55 K. Below 40 K the phosphorescence spectra are primarily nonexcimeric in character but become totally excimeric at 55 K. Rate constants for the phosphorescence decay in this same temperature interval yield linear Arrhenius plots but with a discontinuous change in slope at 40 K. The activation energy above 40 K is 2.0 kJ/mol and is associated with the trapping of nonexcimeric triplets. When combined with previous determinations of the activation energies for detrapping of triplet excimers, binding energies of 2.5 and 12.1 kJ/mol are found for the shallow and deep excimers relative to the energy of the limited free rotor, the energy of which corresponds to the top of the activation barrier.