Relaxation dynamics of excitons in thin quaterthiophene films on different substrates

We compare picosecond time-resolved photoluminescence spectra of thin polycrystalline films of quaterthiophene (4T) vapour deposited on two different substrates: highly oriented pyrolytic graphite (HOPG) and glass. At zero time delay, both films show the same highly resolved vibrational fine structure as isolated 4T molecules. The fine structure remains over time on HOPG, but vanishes within the first 100 ps on glass and is replaced by emission from two luminescent traps. The results explain the line broadening in time-integrated (cw) spectra and yield information on the luminescence quenching in polycrystalline organic films.