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.