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
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