Abstract

Ultrafast dynamics of conjugated polymers such as polydiacetylens (PDA) has been attracting many scientists because they are model systems of quasi-one dimensional semiconductors with a strong electron-phonon coupling. From our extensive studies¹ the initial kinetics after photo-excitation can be explained by a relaxation of a free exciton (FE) to a self-trapped exciton (STE) within 150 fs. The recent achievement of sub-5-fs visible pulse generation based on a novel noncollinear optical parametric amplification (NOPA)² has enabled the real-time observation of the formation of a STE in a PDA for the first time. The stretching mode vibration (C=C, 23 fs and C≡C, 16 fs) coupled with the excitoninc transition drives the coherent relaxation of the backbone structure from an acetylene (A)-like (=CR–C≡C–CR′=)_n to a butatriene (B)-like (–CR=C=C=CR′-)_n configuration.

© 1999 Optical Society of America