Exciton–phonon coupling for the lowest Davydov component of quaterthiophene

The temperature dependence of the 0–0 absorption transition to the lower Davydov exciton band in quaterthiophene single crystals is reported and examined in terms of exciton–phonon interactions. Below an activation temperature, a Lorentzian lineshape is found as a consequence of exciton coherence in a bath of both acoustic and optical phonons, the latter giving only a phonon-absorption broadening. At higher temperatures, a modification of position, intensity, shape, and width of the exciton band is observed due to exciton scattering. From the experimental data, the activation temperature, the average phonon energy, the exciton–phonon stabilization energy are deduced.