Photophysics of Phosphorus Corroles and Application of the Compounds in Triplet-Triplet Annihilation Upconversion

Abstract

Triplet-triplet annihilation upconversion (TTA-UC) is in particular of interest, due to the strong absorption of the excitation light and the high upconversion quantum yields.[1,2] For TTA-UC, a proper triplet photosensitizer and a triplet acceptor are combined to perform the cascade photophysical processes to convert the photons with lower energy to photons with higher energy. Triplet photosensitizers are crucial for TTA-UC. The conventional triplet photosensitizers used for TTA-UC are transition metal complexes or organic compounds containing iodine or bromine atoms.[3] The rationales to use the heavy atoms are to employ the heavy atom effect to facilitate the ISC for triplet state formation upon photoexcitation. Heavy atom-free organic compounds were rarely used as triplet photosensitizers because the ISC is almost unpredictable without the heavy atom effect.[4] Free base corrole is tetrapyrrolic macrocycle with one meso carbon less than porphyrins. Corrole compounds usually show strong absorption of visible light and high photo-stability, as well as efficient ISC. However, corroles were rarely used as triplet photosensitizers for TTA-UC. Herein we studied the photophysical properties of series of corroles with steady state and time-resolved spectroscopies. The corroles were used as triplet photosensitizers for TTA-UC, with perylenebisimide (PBI) as the triplet acceptor. Upon 589 nm cw-laser excitation, upconversion emission at 520 nm was observed. The upconversion quantum yield was determined as 1%.