Photon upconversion (UC) is a photophysical process where low energy photons are combined into one of higher energy. Among mechanisms of UC, triplet-triplet annihilation (TTA) UC has received widespread attention as it can occur efficiently even at sub-solar incident flux. This enables a wide scope of applications, ranging from enhancing photovoltaic efficiency, to anti-counterfeiting, to improved 3D printing, among many others.
TTA upconversion requires two species, a sensitizer which absorbs low energy photons, and an annihilator which emits high energy photons. Despite the breadth of applications of TTA upconversion, few families of TTA-UC annihilators have been explored, with most work focusing on unstable acene-based annihilators.
Here, I will discuss our work in developing design rules for TTA-UC annihilators. By focusing on novel families of annihilators based on well-studied organic semiconductors, we can develop libraries of molecules that are easily derivatized. This allows the development of structure-function relationships, to synthesize optimized annihilators with enhanced efficiencies compared to the commonly used acene-based annihilators. Furthermore, we can develop design-rules for optimized TTA-UC in the solid state, which will be crucial for the widespread application of TTA-UC.