Transient spectroscopy of tetracene single crystals

Ultrafast dynamics of photoexcitations in ultrapure tetracene crystals were studied using transient photomodulation spectroscopy. We measured characteristic transient absorption and stimulated emission bands of Frenkel excitons and found that efficient internal conversion to the lowest exciton and subsequent vibronic relaxation occurs within 200 and 500 fs, respectively. Exciton relaxation to the ground state proceeds by direct radiative and nonradiative decays, as well as via intermediate long-lived excited states. We measure the transient absorption and dynamics of these states and discuss their possible origin. (C) 2001 Elsevier Science B.V. All rights reserved.