Transient hot-phonon-to-exciton spectroscopy in organic molecular semiconductors

The interaction dynamics between excitons and intramolecular vibrations is investigated in $\alpha$-sexithiophene crystals using transient pump-probe spectroscopy. The ultrafast fission of vibrons, i.e., exciton states bound to intramolecular vibrations, predicted in the 1960s by Davydov and Rasbha, is observed. The fission process is monitored by stimulating the optical transitions from the outgoing scattered states, the hot ground state C-C stretching vibrations, to the lowest exciton bands. The vibrational energy is dissipated in $1.5\pm 0.3$ ps.