Spectroscopy of a terthiophene–vinylbenzoate

Abstract

A new terthiophene–vinylbenzoate compound has been synthesized for applications in molecular optoelectronic devices. The photophysical properties of the compound have been studied in a series of solvents. The compound is characterized by a high emission yield (43% in cyclohexane) and a large solvent-dependent Stokes shift (90–120 nm). The shift is attributed to a considerable change in the dipole moment in the excited state as compared to that in the ground state. The emission spectra have been analyzed in the frame of semi-classic charge-transfer theory. This gave estimates for the emitting state free energy, the solvent and internal reorganization energies, and the vibrational frequency. Fast dynamics of the emitting state have been studied by using femtosecond pump–probe and up-conversion methods. In polar solvents, the intramolecular vibrational energy redistribution in the excited state takes place in a sub-picosecond time domain and may result in a molecular configuration different from the all-trans conformer in the ground state. The conformational difference between the excited and ground states makes it possible to use the compound for light amplification. The amplification coefficient can be greater than 2 cm⁻¹, as demonstrated by preliminary experiments.