Long-lifetime charged photo-excitations in polydiacetylenes: strongly localised bipolarons

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Abstract
The authors report photo-induced infrared absorption and photo-induced electron spin resonance measurements on crystalline powders of polydiacetylenes (PDAS). The results imply long-lived, localised, charged, spinless photo-excitations. They have observed metastable photo-induced absorption from the vibrational modes of the PDA backbone and an associated overlapping broad electronic transition. The authors conclude that bipolarons are created through inter-chain charge transfer and coexist with the intra-chain singlet and triplet (neutral) excitons. Weak inter-chain hopping inhibits recombination and leads to metastable bipolarons (with lifetimes of the order of 30 minutes) at low temperatures.