Optical-Phase Relaxation at Low Temperature in the Lowest 1B2u ← 1A1g Transition of Tetracene and Pentacene in p-Terphenyl

Temperature dependent optical absorption experiments on the lowest 1B1u ← 1A1g transition of tetracene in a p-terphenyl mixed crystal show that the loss of optical coherence is due to photon emission of the excited state and phonon scattering of the ground state. The resonant phonon that induces the optical phase relaxation process is shown to be of u-symmetry and its lifetime is obtained from the previously reported photon-echo relaxation results. For pentacene in p-terphenyl it is concluded that phonon scattering in both the ground and excited state contributes to optical phase relaxation