Pictet–Spengler synthesis of twisted quinoline-fused BODIPYs as heavy-atom-free photosensitizers

Abstract

Singly and doubly quinoline-fused BODIPYs were effectively synthesized through a reaction sequence consisting of the reduction of nitrophenyl-substituted BODIPYs and subsequent Pictet–Spengler cyclization. The combination of the BODIPY core and fused quinoline rings imposed significantly twisted conformations in the quinoline-fused BODIPYs (around 20.0° deviation from coplanarity obtained from X-ray crystal structure analysis). These twisted BODIPYs showed significantly reduced LUMO, redshifted absorption/emission bands, high molar extinction coefficients and satisfactory reactive oxygen species generation efficiency up to 0.56, indicating potential use as heavy-atom-free photosensitizers.