Near IR to red up-conversion in tetracene/pentacene host/guest cocrystals enhanced by energy transfer from host to guest

Solid-state materials with up-conversion activity at low power excitation are highly desirable for several optoelectronic applications. In this work we show that a host/guest cocrystal of tetracene/pentacene (Tc/Pc) exhibits a near-infrared (NIR) excited up-conversion process. Förster resonant energy transfer (FRET) from Tc to Pc is enhanced by NIR excitation with respect to visible excitation. A triplet-triplet annihilation mechanism activated by the pentacene molecules acting as traps in the host crystal is proposed and confirmed by time-resolved fluorescence spectra. TDDFT calculations on model molecular clusters support this hypothesis, highlighting the existence of strong excitonic interactions which is a necessary prerequisite for good transport of photogenerated excitons in Pc-doped Tc crystals.