MIGRATION OF CT TRIPLET EXCITONS IN TCNB-BIPHENYL AND TCNB-HMB CRYSTALS

Delayed fluorescence decay curves of charge transfer (CT) crystals of tetracyanobenzene with biphenyl (TCNB-B) and with hexamethylbenzene (T CNB-HMB) have been studied over a wide temperature range (5-200 K). Th e decay curves have been adequately described by decay expressions der ived for different mechanisms of triplet-triplet annihilation. This an alysis points to one-dimensional, thermally activated motion of CT tri plet excitons. The estimated activation energies for the exciton hoppi ng are 360+/-60 and 650+/-100 cm(-1) (or 550+/-150 cm(-1) depending on the applied model) for the TCNB-B and TCNB-HMB crystals, respectively . The results seem to confirm the self-trapping of triplet CT excitons .