Efficient and tunable photochemical charge transfer via long-lived Bloch surface wave polaritons

Hybrid light-matter molecular exciton-polariton states have been proposed as a strategy to directly modify the efficiency and rate of photoinduced molecular charge transfer reactions. However, the efficacy of polariton-driven photochemistry remains an open question owing to the experimental challenges to tease out this effect. Here we demonstrate conditions under which photoinduced polaritonic charge transfer can be achieved and visualized using momentum-resolved ultrafast spectroscopy. Key conditions for charge transfer are satisfied using Bloch surface wave polaritons, which exhibit favourable dispersion characteristics that permit the selective pumping of hybrid states with long lifetimes (100-400 fs) that permit vibrationally assisted charge transfer between a donor and an acceptor molecule dispersed in a polymer matrix. Using this approach, we tune the energetic driving force for charge separation, reducing it by as much as 0.5 eV compared with the bare exciton pumping with an internal quantum efficiency of 0.77. These results corroborate the notion that tunable and efficient polariton-driven molecular charge transfer is indeed possible using carefully constructed photonic systems.