Electronic energy transfer in the charge-transfer crystal of 2,3-dimethylnaphthalene-tetracyanobenzene

Abstract

Optical, spectroscopic and kinetic studies of mixed-stack charge-transfer crystals of 2,3-dimethylnaphthalene with tetracyanobenzene (DMN-TCNB), undoped and doped with anthracene (concentrations 10 −5 − 2 × 10 −3 M/M), were performed between 5 and 300 K. The kinetic analysis of fluorescence and delayed fluorescence confirmed that excitons are self-trapped at low temperatures and they become mobile at higher temperatures. The obtained activation energies of mobility of singlet and triplet excitons are (380 ± 50) and (165 ± 30) cm −1, respectively. Triplet exciton motion (50–80 K range) is well described by the one-dimensional hopping model. Above 80 K, the intersystem crossing transition, T 1 → S 1, with the activation energy of (1450 ± 100) cm −1, becomes an efficient deactivation channel for triplet excitons. The experiments point to a possibility of structural disorder in DMN-TCNB crystals.