No abstract

Primary processes of photoexcited states in an R-sexithienyl film are investigated by femtosecond transient absorption spectroscopy and picosecond time resolved fluorescence spectroscopy. Four species are observed in the transient absorption measurement. A broad absorption that shows a very rapid relaxation (within a few picoseconds) is ascribed to a singlet Frenkel exciton state. An oscillating structure is also apparent immediately after excitation and is ascribed to the Stark effect induced by a charged species (ion pair state). The latter state decays within 200 ps and is replaced by a different oscillating structure that is due to a thermal effect induced by a dissipation of excess energy. Another band owing to a triplet state appears via a very rapid conversion from a higher singlet exciton state. Fluorescence decay curves are well fitted with lifetimes of the charged state, which indicates that most of the emission is brought about by the charge recombination process, and furthermore, a charge-transfer (CT) emission band that has not been reported is observed.

We study a quasicontinuum system for which there exists a sparse dressed state composed of the ground state and a single state of the true continuum. In general, the loss of population from the ground state to a true continuum via the quasicontinuum is total. In a special case, however, population is trapped in the ground state and the sparse dressed state is replaced by a trapping state containing no contribution from the true continuum.

No abstract

Relaxation dynamics from a higher triplet excited state in R-sexithienyl (hereafter abbreviated as 6T) film was investigated by double-pulse excitation spectroscopy. Very rapid formation (within 1 ps) of the lowest singlet excited state and an intermolecular ion-pair state were observed. The mechanism of this rapid conversion process from a higher electronic excited state was discussed.