Ultrafast excited state relaxation in long-chain polyenes

We present a comprehensive study, by femtosecond pump-probe spectroscopy, of excited state dynamics in a polyene that approaches the infinite chain limit. By excitation with sub-10-fs pulses resonant with the 0-0 S0 → S2 transition, we observe rapid loss of stimulated emission from the bright excited state S2, followed by population of the hot S1 state within 150 fs. Vibrational cooling of S1 takes place within 500 fs and is followed by decay back to S0 with 1 ps time constant. By excitation with excess vibrational energy we also observe the ultrafast formation of a long-living absorption, that is assigned to the triplet state generated by singlet fission.

Excited state dynamics of a long-chain polyene studied by femtosecond pump-probe spectroscopy.