Ultrafast spectroscopy of sexithiophene single crystals

Summary form only given. Recent utilization of organic materials as light emitting devices and thin film transistors stimulated studies of their electronic structure and basic optical properties. Particular attention was given to oligothiophenes, due to their high electronic mobilities and ability to form single crystals. Recent measurements of absorption and emission in /spl alpha/-sexithiophene (/spl alpha/6T) crystals provided many insights into their electronic structure. However, non-linear optical measurements and particularly, ultrafast spectroscopy were not thoroughly used to study these materials. Yet, understanding of photophysical processes without such studies is incomplete. We studied photoexcitation dynamics in /spl alpha/6T single crystals using fsec transient photomodulation (PM) spectroscopy. We show that whereas steady state photoluminescence (PL) may generally contain contributions from a variety of excitations, including trap-states and aggregates, psec PM spectra are not affected by the latter and exclusively characterize the lowest excitons.