6. Plasmon-Enhanced Homogeneous and Heterogeneous Triplet-Triplet Annihilation

Triplet-triplet annihilation (TTA) process includes two categories, a homogeneous TTA occurring between two triplet excited molecules of the same type such as the homogeneous TTA upconversion (TTA-UC) and a heterogeneous TTA occurring between two triplet excited molecules of different types such as the heterogeneous TTA-UC, or between a triplet excited state and a triplet ground state such as the sensitized singlet oxygen generation. To the other front, noble metal nanostructures are known to exhibit an extraordinary capability to manipulate light through the collective oscillations of their conduction-band electrons, the so-called localized surface plasmon resonances (LSPR). Plasmonic nanostructures have been shown to be able to dramatically enhance the performances of many optical systems. In this book chapter, we will use a few examples to demonstrate that LSPR of noble metal nanoparticles can enhance the efficiency of both categories of TTA, and to discuss the conditions where such plasmonic enhancement would occur. The results shed light onto ways to improve the overall TTA efficiency, which would be relevant to the broad applications involving TTA-UC or sensitized singlet oxygen generation.