Abstract
The nature of photoexcitations in conducting polymers has been elucidated by the absorption-detected magnetic resonance (ADMR) technique. In this technique we measure changes in the photoinduced absorption (PA) spectrum due to changes in spin-dependent recombination rates induced by resonant absorption of μ-waves in magnetic fields. We have used the ADMR technique at 3 GHz to study spin states in trans-(CH) x , oriented poly( para-phenylene vinylene) (PPV), polythiophene (PT) and polydiethynylsilane (PDES). We have verified that the charged excitations are solitons (S ∓) in trans-(CH) x and PDES, and polarons (P ∓) and bipolarons (BP 2∓) in other nondegenerate ground state polymers. The long-lived neutral excitations, on the other hand, are self-trapped triplet excitons in all polymers, except for trans-(CH) x and PDES in which the triplets dissociate into neutral soliton (S 0) pairs due to their backbone degenerate ground state structure.
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