Dynamic control of Förster energy transfer in a photonic environment

In this study, the effect of modified optical density of states on the rate of Förster resonant energy transfer between two closely-spaced chromophores is investigated. A model based on a system of coupled rate equations is derived to predict the influence of the environment on the molecular system. Due to the near-field character of Förster transfer, the corresponding rate constant is shown to be nearly independent of the optical mode density. An optical resonator can, however, effectively modify the donor and acceptor populations, leading to a dramatic change in the Förster transfer rate. Single-molecule measurements on the autofluorescent protein DsRed using a λ/2-microresonator are presented and compared to the theoretical model's predictions. The observed resonator-induced dequenching of the donor subunit in DsRed is accurately reproduced by the model, allowing a direct measurement of the Förster transfer rate in this otherwise inseparable multichromophoric system. With this accurate yet simple theoretical framework, new experiments can be conceived to measure normally obscured energy transfer channels in complex coupled quantum systems, e.g. in photovoltaics or light harvesting complexes.