Attachment of -Bu groups to aza-BODIPY core at 3,5-sites with ultra-large Stokes shift to enhance photothermal therapy through apoptosis mechanism.

By the introduction of the -Bu groups into aza-BODIPY core, di--butyl-substituted aza-BODIPYs at 3,5-sites (s) were prepared for the first time. Based on the X-ray analysis of , this molecular structure is twisted. Near-infrared dye has the ultra-large Stokes shift (152 ​nm) in aza-BODIPY system, combining with the twisted intramolecular charge transfer and the free rotation of the Bu groups at 3,5-sites. Although the barrier-free rotors of the distal Bu groups in result in low fluorescence quantum yield, the photothermal conversion efficiency is markedly enhanced. nanoparticles with low power laser irradiation were proven to block cancer cell cycle, inhibit cancer cell proliferation, and induce cancer cell apoptosis in photothermal therapy (PTT). The strategy of "direct attachment of Bu groups to aza-BODIPY core" gives a new design platform for a photothermal therapy agent.