Resonant confinement of an excitonic polariton and ultra-efficient light harvest in artificial photosynthesis*

We uncover a novel phenomenon from a recent artificial light-harvesting experiment [Angewandte Chemie Intl. Ed. 55, 2759 (2016)] on organic nanocrystals of self-assembled difluoroboron chromophores.

A resonant confinement of polariton under strong photon-exciton coupling is predicted to exist within the microcavity of the crystals own natural bound-aries. Moreover, the radiative energy of a localized exciton falls into the spectrum of the confinement.

The spontaneous emission of an excited pigment would undergo a two-step process. It should first decay to an excitonic polariton trapped by the cavity resonance. The captive intermediate could then funnel the energy directly to doped acceptors, leading to the observed over 90% transfer efficiency at less than 1/1000 acceptor-donor ratio.

The proposed mechanism is supported by parameter-free analyses entirely based on experiment data. Our finding may imply possible polariton-mediated pathways for energy transfers in biological photosynthesis.