Exciton dynamics at the heteromolecular interface between N,N′-dioctyl-3,4,9,10-perylenedicarboximide and quaterrylene, studied using time-resolved photoluminescence

To elucidate the exciton dynamics at the heteromolecular interface, the temperature dependence of time-resolved photoluminescence (TRPL) spectra of neat-N,N′-dioctyl-3,4,9,10-perylenedicarboximide (PTCDI-C₈) and PTCDI-C₈/Quaterrylene (QT) heteromolecular thin films was investigated. The lifetimes of excitons were evaluated to identify the Frenkel (FE), high energy charge-transfer (CTE_high), low energy charge-transfer (CTE_low), and excimer exciton states. The thermal activation energy (Δ_act) of CTE_low in PTCDI-C ₈ thin film was evaluated as 25 meV, which is 1/5 of that of FE, indicating that CTE_low is more thermally sensitive than FE in PTCDI-C₈ thin film. We investigated the exciton transport length (l) along the vertical direction against the substrate surface in PTCDI-C ₈/QT thin film at 30 K, and demonstrated that l_FE = 9.9 nm, l_CTElow = 4.2 nm, l_CTEhigh = 4.3 nm, and l _excimer = 11.9 nm. To elucidate the difference in l among these excitons, the activation energies (E_a) for quenching at the heteromolecular interface were investigated. E_a values were estimated to be 13.1 meV for CTE_low and 18.6 meV for CTE_high. These values agree with the thermal sensitivity of CTEs as reported in a previous static PL study. This latter situation is different from the case of FE and excimer excitons, which are transported via a resonant process and have no temperature dependence. The small Ea values of CTEs suggest that exciton transport takes place via a thermal hopping process in CTEs. The present experimental study provides information on nano-scaled exciton dynamics in a well-defined PTCDI-C₈ (2 ML)/QT (2 ML) system.