Ultrafast Non-Förster Intramolecular Donor–Acceptor Excitation Energy Transfer

Abstract

Ultrafast intramolecular electronic energy transfer in a conjugated donor-acceptor system is simulated using nonadiabatic excited-state molecular dynamics. After initial site-selective photoexcitation of the donor, transition density localization is monitored throughout the S → S internal conversion process, revealing an efficient unidirectional donor → acceptor energy-transfer process. Detailed analysis of the excited-state trajectories uncovers several salient features of the energy-transfer dynamics. While a weak temperature dependence is observed during the entire electronic energy relaxation, an ultrafast initially temperature-independent process allows the molecular system to approach the S-S potential energy crossing seam within the first ten femtoseconds. Efficient energy transfer occurs in the absence of spectral overlap between the donor and acceptor units and is assisted by a transient delocalization phenomenon of the excited-state wave function acquiring Frenkel-exciton character at the moment of quantum transition.

Vibrational energy redistribution during donor–acceptor electronic energy transfer: criteria to identify subsets of active normal modes

“…As we have reported previously 59 , immediately after photoexcitation to the S 2 state, the molecule experiences an ultrafast S 2 S 1 internal conversion process (see Figure 2(a)) leading to an excitation transfer between donor and acceptor segments. This intramolecular electronic energy redistribution is confirmed by monitoring the time evolution of the fraction of electronic transition density localized on either the donor, , or the acceptor, during the δ α donor ( ) δ α acceptor ( ) S 2 S 1 electronic energy relaxation, see Figure 2(b).…”

“…In a previous publication, we reported an ultrafast donoracceptor intramolecular electronic energy transfer in the molecular dyad system comprising a ladder-type poly(paraphenylene) oligomer donor unit (LPPP5) covalently linked with a perylenemonoimide acceptor unit (PMI) (see Figure 1a) 59,54 . In this contribution, we shall characterize the role of vibrational energy redistribution during the internal conversion process of the model LPPP5-PMI dyad system using atomistic non-adiabatic excited-state molecular dynamics (NEXMD) simulations.…”

Molecular excitonic seesaws

“…In closing, we note that the presence of two competing energy-transfer pathways within a molecule should lead to coherent quantum interference effects manifested either in time-domain spectroscopy or in the yields of relaxation pathways (55). Such asymmetric seesaw molecules should therefore offer a unique materials basis to explore the interplay of electronic quantum coherence and vibrational modes (56).…”

Unraveling the Fate of Host Excitons in Host–Guest Phosphorescent Organic Light-Emitting Diodes

“…It has been shown that efficient energy transfer can take place even in the absence of spectral overlap, which often results from intramolecular through-bond interactions and electronic delocalization. [57][58][59] However, only intermolecular interactions exist in our system. Therefore, we expect the energy transfer between such non-overlapping states to be significantly slower than the fluorescence rate of BTDF.…”