Preparation, optical properties and photodynamic activity of <i>p-tert</i>-butylphenyl-substituted boron subphthalocyanine

Boron subphthalocyanine with bulky p-tert-butylphenyl functional groups was tested as a fluorophore and photosensitizer. Initial 1,2-dicyano-4,5-di([Formula: see text]-(tert-butyl)phenyl)benzene was prepared using a new synthetic strategy starting from butadiene sulfone. Template cyclization conditions were improved to achieve a high yield of the target subphthalocyanine. Bright fluorescence ([Formula: see text] 0.27) and moderate singlet oxygen quantum yield ([Formula: see text] 0.35) were demonstrated. The possibility of generating singlet oxygen was supported using flash photolysis measurements. The formation of triplet states with a lifetime [Formula: see text] 1.6 ms was detected. Boron subphthalocyanine substituted with [Formula: see text]-tert-butylphenyl showed low dark cytotoxicity and micromolar photocytotoxicity against an epidermoid carcinoma cell line (A431).