“…Aza-BODIPY derivatives are known to be extensively employed in fluorescence imaging, phototherapy, photocatalysis, and others. [37][38][39][40][41] For blocking fluorescence, inducing intersystem crossing (ISC), and enhancing photothermal conversion, the skillful structural design of aza-BODIPYs is required, including photoinduced electron transfer (PET), 42,43 intramolecular charge transfer (ICT), 44,45 twisted intramolecular charge transfer (TICT), [46][47][48] or a rotor with the freely rotating groups. 49 Our group recently discovered that aza-BODIPY with tert-butyl groups at 1,7-or 3,5-sites is a novel molecule, and the rotating tert-butyl group caused non-radiative heat production in excited states, which is an intriguing approach for designing photothermal reagents (Fig.…”