Photophysics and photochemistry of singlet fission materials in microcavities

Singlet fission (SF) is a process in organic semiconductors where a singlet exciton state generates two triplet excitons, which provides a way of enhancing power conversion efficiency in organic photovoltaics. An important intermediate step in SF is the formation of a spin-entangled triplet-pair state (TT), whose properties are critical in mediating both the generation of free triplets and the reverse process of triplet-triplet annihilation. We systematically examine formation of the TT state and its properties in functionalized acenes depending on the derivative and film morphology, as well as external parameters such as temperature, magnetic field, and excitation energy. By placing the films in optical microcavities we further show that strong exciton-photon coupling (resulting in formation of exciton-polaritons) can manipulate SF yields by altering the energy relaxation dynamics of the system. We establish the effects of intermolecular interactions on the polariton properties and report on polariton-controlled dynamics depending on cavity design and detuning. Additionally, a major concern in the applications of organic semiconductors is their photostability. By manipulating SF yields and interactions between excitons and cavity photons we explore the possibility of tuning photodegradation processes mediated by excited states to increase stability.