Ultralong‐Range Polariton‐Assisted Energy Transfer in Organic Microcavities

Non‐radiative energy transfer between spatially‐separated molecules in a microcavity can occur when an excitonic state on both molecules are strongly‐coupled to the same optical mode, forming so‐called “hybrid” polaritons. Such energy transfer has previously been explored when thin‐films of different molecules are relatively closely spaced (≈100 nm). In this manuscript, we explore strong‐coupled microcavities in which thin‐films of two J‐aggregated molecular dyes were separated by a spacer layer having a thickness of up to 2 μm. Here, strong light‐matter coupling and hybridisation between the excitonic transition is identified using white‐light reflectivity and photoluminescence emission. We use steady‐state spectroscopy to demonstrate polariton‐mediated energy transfer between such coupled states over “mesoscopic distances”, with this process being enhanced compared to non‐cavity control structures. Ultralong‐range polariton‐assisted energy transfer was achieved in a microcavity containing two J‐aggregate cyanine dyes. The two dyes were separated by a distance of up to 2 μm using a polymeric spacer layer. Here, it was confirmed that hybrid middle polariton (MP) states, composed of a mixture between the cavity photon modes and the different exciton states, act as a route for efficient ultralong‐range energy transfer to energetically lower‐lying states.