Interface-Confined Triplet Sensitization and Photon Upconversion in Pyrene-Tetracyanobenzene Charge-Transfer Cocrystals.

Micro-cocrystals of the intermolecular charge-transfer (CT) complex formed from pyrene and tetracyanobenzene can be fabricated via a solution-based method. Intersystem crossing of the directly excited CT exciton in the cocrystal is observed, yielding a CT triplet exciton that undergoes efficient triplet-triplet energy transfer to a diphenylanthracence (DPA)-based triplet acceptor. For the first time, we demonstrate that these micro-cocrystals can act as triplet sensitizers to upconvert the emission of liquid-state DPA triplet acceptors, enabling highly efficient triplet-triplet annihilation photon upconversion (TTA-UC) from 532 to 430 nm. This work demonstrates the utilization of CT excitons as triplet sensitizers in a TTA-UC process, providing a novel approach for efficient and heavy-atom-free UC systems.