MIGRATION OF ELECTRONIC EXCITATION-ENERGY IN THE CHARGE-TRANSFER CRYSTAL OF PYROMELLITIC DIANHYDRIDE-PHENANTHRENE

Singlet and triplet exciton energy migration in the charge-transfer cr ystal of pyromellitic dianhydride-phenanthrene, undoped and doped with anthracene (10(-4)-10(-2) M/M), have been studied in the 5-300 K temp erature range. At low temperatures singlet and triplet excitons are se lf-trapped. They become mobile with increasing temperature with activa tion energies of 380 +/- 70 and 400 +/- 80 cm(-1) for singlet and trip let excitons, respectively. The motion of triplet excitons in the temp erature range 50-100 K can be described by one-dimensional hopping wit hin cages, limited by structural defects of the host crystal. Mobile s inglet excitons are observed for temperatures above 100 K and their mo tion is well described by a time-independent excitation transfer rate constant.