Hidden triplet states at hybrid organic–inorganic interfaces

Triplet states have been widely studied in phosphorescent molecules, lanthanide complexes and triplet–triplet annihilation systems, in which they have a critical role in energy transfer processes. However, advances have also shed light on their importance in organic–inorganic hybrid materials, wherein they can be used for decoding energy transfer mechanisms, enhancing interfacial energy transfer and attaining new properties. In this Review, we provide an overview of triplet properties, activation strategies and regulatory approaches. Our focus is on their crucial contribution to organic–inorganic hybrids, including inorganic semiconductor-sensitized triplet–triplet annihilation, the utilization of triplet reservoirs for thermally activated delayed photoluminescence, singlet exciton fission-induced silicon sensitization, dye-triplet-mediated upconversion nanoparticles, and other triplet systems. We discuss potential applications, exciting challenges, and opportunities for the advancement of triplet-mediated organic–inorganic hybrid materials.