A tale of two triplets: manipulating and harvesting triplet pairs with strong light-matter coupling (Conference Presentation)

The interaction of organic semiconductors with confined light fields offers one of the easiest means to tune their material properties. In the regime of strong light-matter coupling, the semiconductor exciton and cavity photon mode hybridize to form new 'polariton' states. In organic systems these light-matter hybrids are tuneably separated by as much as 100’s of meV from the parent exciton, enabling radical alteration of the energetic landscape. The effects of strong coupling can be profound, including reports of long-range energy transfer, enhanced carrier mobility and altered chemical reactivity. Theoretical work is now increasingly focused on the potential of polariton to manipulate electronic dynamics in the excited state, but experimental realisation has proved challenging. Here, we demonstrate the ability to manipulate triplet photophysics in singlet exciton fission materials in the strong coupling regime. Within microcavities, we dramatically enhance the emission lifetime and increase delayed fluorescence by >100%, which we explain through a shift in the thermodynamic equilibrium between dark states in the exciton reservoir and the bright polaritons. Indeed, with this approach we can create entirely new radiative pathways, turning completely dark states bright and opening new scope for microcavity-controlled materials.