Delayed fluorescence of a poly (p-phenylenevinylene) derivative:: Triplet-triplet annihilation versus geminate pair recombination

The question of the origin of delayed fluorescence from a phenyl-substituted poly(p-phenylenevinylene)-type copolymer (Ph-PPV) is addressed. Two origins have to be considered, i.e., triplet-triplet annihilation and recombination of geminate electron-hole pairs. Ph-PPV is investigated in the form of two different samples, namely diluted in 2-methyltetrahydrofuran (MTHF) glass at 80 K and as a thin film of optical density of 0.6. It will be shown that in the diluted solution, delayed fluorescence is due to triplet-triplet annihilation and in the thin film, it is due to geminate pair recombination. The assignment of delayed fluorescence to geminate pair recombination in the thin film could be made due to delayed fluorescence experiments under applying an electric field of 2x10(6) V/cm. The delayed fluorescence is strongly influenced by the electric field which is a sign that charged species, i.e., geminate electron-hole pairs, are involved in the process of delayed fluorescence. (C) 2002 American Institute of Physics.