Near-infrared absorbing aza-BODIPYs with 1,7-di-tert-butyl groups by low-barrier rotation for photothermal application

Abstract

Near-infrared absorbing aza-BODIPYs with 1,7-di-tert-butyl groups (tBuazaBDP) were successfully synthesized. Based on X-ray crystal analysis, S-tBuazaBDP is found to be more twisted than the reported dye tetraphenyl aza-BODIPY. tBuazaBDPs possess excellent optical properties such as high molar extinction coefficients, broad full width at half maxima, and large Stokes shifts. Experimental results and theoretical calculations proved that the distal –tBu groups in S-tBuazaBDP can undergo a low-barrier rotation. Although this low-barrier rotation of the distal –tBu groups in tBuazaBDP leads to a low quantum yield, the photothermal conversion efficiency and the singlet oxygen generation ability of S-tBuazaBDP-NPs are obviously enhanced, which are highly desirable for a photothermal therapy agent.