Abstract

We show exciting research opportunities when the concept of molecular self-assembly meets photon upconversion (UC) based on triplet-triplet annihilation (TTA). TTA -UC has attracted much attention for enhancing solar energy harvesting devices such as photovoltaics and photocatalysis. Previous examples of TTA -UC utilized the diffusion and collision of sensitizer and emitter molecules in solution or polymers, however, there are limitations such as quenching by oxygen and low diffusion rate in the solventfree state. In this context, we’re proposing a paradigm shift from the molecular diffusion in dispersed systems to the energy migration in condensed systems (Figure 1). In dense dye assemblies, triplet excitons can effectively migrate and annihilate. For the proof of concept, we show the first examples of TTA -UC in a solvent-free molecular liquid, ionic liquid, supramolecular assembly, gel, liquid crystal, and metal-organic frameworks (MOFs) (Figure 2). This approach allowed us to maximize UC quantum yield even at extremely low excitation power density such as solar irradiance.