The exciton dynamics in tetracene thin films

Tetracene thin films are investigated by time-resolved photoluminescence on picosecond to nanosecond time-scales. The picosecond luminescence decay dynamics is confirmed to be independent of temperature, but the nanosecond timescale luminescence dynamics is highly temperature dependent. This is interpretted in terms of motion along an intermolecular coordinate which couples the S-1 state to the multiexciton (ME) state, arising from frustrated photodimerization, and giving rise to exciton dimming through adiabatic coupling. Dull excitons persist at low temperatures, but can thermally access separated triplet states at higher temperatures, quenching the delayed fluorescence. The effects of exciton density on both the picosecond and nanosecond luminescence dynamics are investigated, and a rate constant of (1.70 +/- 0.08) x 10(-8) cm(3) s(-1) is determined for singlet-singlet annihilation.