Non‐Radiative Energy Transfer Mediated by Hybrid Light‐Matter States

Abstract

We present direct evidence of enhanced non-radiative energy transfer between two J-aggregated cyanine dyes strongly coupled to the vacuum field of ac avity.E xcitation spectroscopya nd femtosecond pump-probe measurements show that the energy transfer is highly efficient when both the donor and acceptor form light-matter hybrid states with the vacuum field. The rate of energy transfer is increased by af actor of seven under those conditions as compared to the normal situation outside the cavity,w ith ac orresponding effect on the energy transfer efficiency.T he delocalized hybrid states connect the donor and acceptor molecules and clearly play the role of abridge to enhance the rate of energy transfer.T his finding has fundamental implications for coherent energy transport and light-energy harvesting.When an exciton transition and aresonant optical mode exchange energy faster than any competing dissipation process,itcan lead to light-matter strong coupling and the generation of two new hybrid (polaritonic) eigenstates,P + and PÀ,s eparated by the so-called Rabi splitting ( Figure 1a). This brings about interesting properties possessed by neither the original exciton or the optical mode, [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] and leads to new possibilities,such as modified chemical reactivity, [5,6] and enhanced conductivity of organic semiconductors. [9] In the latter case,the enhancement stems from the delocalized nature of the hybrid states over the spatial extent of the optical mode [10,11] which is expected to affect energy transport according to recent theoretical studies. [12,13] In this context, it is interesting to consider how such hybrid states would affect energy transfer between donor and acceptor molecules.Energy transfer is anon-radiative process which has been extensively studied over the last century and typically involves either Coulombic interactions (Fçrster) or electronic exchange (Dexter). [20] Ak ey confirmation of energy transfer is of course ar eduction in the lifetime of the donor concomitant with the rise of the acceptor excited state population. Other factors that affect energy transfer include molecular aggregation, the presence of bridges between the donor and acceptor,a nd the density of optical states. [20][21][22][23][24][25] Strong coupling could provide an alternate effective path for energy transfer in analogy with chemically bridged donors and acceptors where the linker mediates the interactions by an effective overlap between the wave functions of both the donor and the acceptor.I nt he strong coupling case,i ti st he polaritonic states which are by construction either donor or acceptor-like that mediates the interactions in the system due to their delocalized nature.R ecently,e nergy transfer under strong coupling based on steady-state fluorescence excitation spectroscopy of the acceptor was studied. [17] However no Figure 1. a) Schematic representation of strong coupling successively with the donor resonant with acavity mode " hw c ,and then the a...

Energy transfer and correlations in cavity-embedded donor-acceptor configurations

“…This is the focus of this manuscript. On the other hand, experiments with many organic molecules in bad cavities have decay rates of the order of tens to hundreds THz, 5,6 such that the strong coupling regime is very close to the ultra-strong coupling regime. Just as in the case of experiments involving superconducting artificial atoms coupled to on-chip cavities, the simple Jaynes-Cummings model is then insufficient to properly describe the dynamics.…”

Control over Energy Transfer between Fluorescent BODIPY Dyes in a Strongly Coupled Microcavity

“…Hybridization of Frenkel excitons through strong coupling and polariton mediated energy transfer between different excitons has been demonstrated in microcavities containing J-aggregated cyanine dyes. [11][12][13][14] Such molecular aggregates have relatively narrow absorption linewidths (10s of meV) 15,16 , allowing different materials to be selected whose excitonic transitions are separated by an energy commensurate with the typical Rabi-splitting energy of a molecular material in a microcavity (~ 100 meV). 1,2,17 However many J-aggregated molecular dyes have low fluorescence quantum efficiency 18 as a result of competing non-radiative pathways; a property that has so-far precluded polaritons in J-aggregate microcavities undergoing condensation and lasing.…”

Generation of Anti-Stokes Fluorescence in a Strongly Coupled Organic Semiconductor Microcavity

“…8 By coupling molecular materials with light, it is possible to engineer fascinating processes, such as polariton condensation, [9][10][11] superfluidity, 6 changes in the rate of chemical reactions 12,13 and a modification of energy transfer pathways. [14][15][16][17] The first microscopic models used to describe the strong-coupling of molecules to light treated the molecules in the cavity as an ideal two-level system and neglected rotational or vibrational degrees of freedom. 18 Recently however, there has been growing interest in understanding the role that the vibrational landscape plays in modifying basic processes in strongly-coupled microcavities.…”