Regulating 1O2 generation from heavy-atom-free triplet photosensitizers based on thiophene-fused BODIPY

Abstract

Triplet photosensitizers (PSs) used in photodynamic therapy (PDT) exhibit a strong relationship between the intersystem crossing (ISC) and generation of singlet oxygen (1O2). However, the effective design of PS molecules, particularly, heavy-atom-free PS, remains challenging due to limited understanding of the correlation between ISC rate (kISC) and the quantum yield of 1O2 generation (ΦΔ). We present a case study for designing heavy-atom-free PSs (R–SB) via a combination of experimental and theoretical investigations. Electron-donating groups were introduced to the thiophene-fused BODIPY core. The measured ΦΔ increased as the calculated kISC increased. The remarkable agreement between the experimental and theoretical findings improved our understanding of the ISC process in R–SB structures and established a framework for the potential future molecular design of heavy-atom-free PSs based on the BODIPY core. Among the various R–SB structures synthesized, carbazolyl benzene (Cbz) -SB exhibited fluorescence emission and was the most effective for 1O2 generation. Cbz-SB was further utilized for mitochondria-targeted fluorescence bioimaging and the PDT of HeLa cells, demonstrating its potential applicability in the respective areas. © 2023 Elsevier Ltd