Optical studies of triplet excitations in poly(p-phenylene vinylene)

We have studied energy states in the triplet manifold in films of poly(p-phenylene vinylene) (PPV) using a multitude of optical spectroscopies including photoinduced absorption, photoluminescence, phosphorescence, their optically detected magnetic resonances, as well as their photogeneration action spectra. We found that singlet fission into two triplets with opposite spins is an efficient route for triplet generation in PPV, similar in strength to the intersystem crossing process. From the threshold energy for singlet fission we deduced that the lowest-lying, odd-parity triplet excitonic state, 1³B_u, is located at 1.55 eV from the ground state, which is about 0.9 eV lower than the lowest-lying, odd-parity singlet state 1¹B_u.