Optical properties and photoluminescence of tetrahexyl-sexithiophene allotropes

The optical absorption, Raman scattering and photoluminescence of two phase s of tetrahexyl-sexithiophene (4HT6) display properties coherently related to the different molecular conformations imposed by the chain packing. We a nalyse the temperature dependence of the optical properties of a sample in which the two phases coexist. In the photoluminescence the lower energy emi ssion from the phase possessing planar molecules is thermally activated at room temperature, while the emission from the phase possessing less planar molecules becomes dominant at low temperature due to effective excitation c onfinement. The time resolved photoluminescence study indicates that excito n migration processes within the inhomogeneous density of states of the two phases sample introduce relevant non-radiative quenching effects. (C) 2001 Elsevier Science B.V. All rights reserved.