Migration of electronic excitation energy in the charge-transfer crystal of pyromellitic dianhydride-phenanthrene

Singlet and triplet exciton energy migration in the charge-transfer crystal of pyromellitic dianhydride-phenanthrene, undoped and doped with anthracene (10−4−10−2M/M), have been studied in the 5–300 K temperature range. At low temperatures singlet and triplet excitons are self-trapped. They become mobile with increasing temperature with activation energies of 380 ± 70 and 400 ± 80 cm−1 for singlet and triplet excitons, respectively. The motion of triplet excitons in the temperature range 50–100 K can be described by one-dimensional hopping within cages, limited by structural defects of the host crystal. Mobile singlet excitons are observed for temperatures above 100 K and their motion is well described by a time-independent excitation transfer rate constant.