Higher Triplet Excited States of Oligo(p-phenylenevinylene)s

Abstract

Properties of the higher excited triplet states (T n ) of oligo(p-phenylenevinylene)s (OPVn, n denotes the number of phenyl rings, n = 3, 4) were investigated with use of the ns-ps and ns-ns two-color two-laser flash photolysis techniques. The lowest triplet excited states of OPVn were generated through the triplet energy transfer (ENT) process by the first 355-nm laser irradiation to the triplet sensitizer. With the delay time of 4 μs after the first laser irradiation, OPVn(T 1 ) was selectively excited with the second 532-nm laser. Bleaching of the absorption of OPVn(T 1 ) was observed during the second ps laser irradiation, indicating the generation of OPVn(T n ). The bleaching completely recovered at a few tens of picoseconds after the second picosecond laser irradiation, because of the internal conversion from OPVn(T n ) to OPVn(T 1 ). The lifetimes of T n were estimated to be 35 and 30 ps for OPV3 and OPV4, respectively. In the presence of the triplet energy acceptor (Q), the quenching and recovery of the T 1 -absorption bands of OPVn were observed because of ENT from OPVn(T n ) to Q and Q(T 1 ) to OPVn, respectively. On the basis of the ENT from OPVn(T n ) to a series of Q, the T 2 -T 1 energy gaps of OPV3 and OPV4 were estimated to be 1.3 and 1.1 eV, respectively.