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

Abstract

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 (CTEhigh), low energy charge-transfer (CTElow), and excimer exciton states. The thermal activation energy (Δact) of CTElow in PTCDI-C8 thin film was evaluated as 25 meV, which is 1/5 of that of FE, indicating that CTElow 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-C8/QT thin film at 30 K, and demonstrated that lFE = 9.9 nm, lCTElow = 4.2 nm, lCTEhigh = 4.3 nm, and lexcimer = 11.9 nm. To elucidate the difference in l among these excitons, the activation energies (Ea) for quenching at the heteromolecular interface were investigated. Ea values were estimated to be 13.1 meV for CTElow and 18.6 meV for CTEhigh. 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.