Bisbenzothieno[b]-fused BODIPYs as efficient near-infrared heavy-atom-free photosensitizers

Abstract

Fusion thiophene to BODIPY endows the chromophore with more fundamental and special functions. Herein, novel symmetric bisbenzothieno[b]-fused BODIPYs (BTBs) were synthesized and developed. These newly prepared BTB dyes possessed absorption maxima in the range of 643–665 nm, and many outstanding properties including large molar extinction coefficients, and high singlet oxygen generation. Theoretical calculations affirmed that the smaller singlet-triplet energy gap and larger spin−orbit coupling result in efficient intersystem crossing, thus increasing the singlet oxygen generation yield. Notably, Me2NPh-substituted BTB displayed good reactive oxygen species generation efficiency up to 0.41, and a remarkable photo-cytotoxicity (IC50 = 83.5 nM) in HeLa cells, which shows potential in low-dose photodynamic therapy.