Towards efficient solid-state triplet-triplet annihilation based photon upconversion: Supramolecular, macromolecular and self-assembled systems

Photon upconversion through sensitized Triplet-Triplet Annihilation (TTA-UC) has regained a lot of interest during the last decade mainly due to its potential for significantly increased solar energy harvesting. Other applications such as anti-Stokes fluorescence labels for bio-imaging and drug-targeting have also emerged. Considering practical large scale use of TTA-UC, solid state materials are required. The TTA-UC process depends on a sequence of energy transfer processes and it is a great challenge to maintain high efficiencies while solidifying these diffusion limited energy transfer steps. This review covers the basic, fundamental aspects of TTA-UC, but focuses on the current state of the art of the many attempts to develop solid state based TTA-UC systems. In particular, work aiming at overcoming the diffusion limit though supramolecular, macromolecular or self-assembly approaches are highlighted.