Efficient intersystem crossing using singly halogenated carbomethoxyphenyl porphyrins measured using delayed fluorescence, chemical quenching, and singlet oxygen emission

Abstract

Sensitizers with high triplet quantum yields are useful for generating photovoltaics, photocatalysts and photodynamic therapy agents with increased efficiency. In this study, the heavy atom effect was used to optimize the triplet and singlet oxygen quantum yields of 5,10,15,20-tetrakis(4-carbomethoxyphenyl)porphyrin (1-TCM₄PP). The triplet quantum yields, determined using delayed fluorescence, was calculated as 0.35 for 1-TCM₄PP, 0.75 for 5,10,15-tris(4-carbomethoxyphenyl)-20-(4-bromophenyl)porphyrin (2-TBCM₃PP) and 0.88 for 5,10,15-tris(4-carbomethoxyphenyl)-20-(4-iodophenyl)porphyrin (3-TCM₃IPP). Chemical quenching of 1,3-diphenylisobenzofuran and singlet oxygen emission studies rendered an average singlet oxygen quantum yield of 0.51, 0.75, and 0.90 for TCM₄PP, TBCM₃PP and TCM₃IPP respectively. These photophysical properties indicate that a single halogen atom is capable of transforming TCM₄PP into a sensitizer with strong triplet character. This is useful for generating singlet oxygen for photodynamic therapy, creating a long lasting reactive species for catalysis and for extending diffusion lengths in photovoltaic applications while retaining three molecular modification points for further functionalization.