Making the Brightest Ones Dim: Maximizing the Photothermal Conversion Efficiency of BODIPY‐Based Photothermal Agents

Abstract The successful implementation of photothermal therapy (PTT) in cancer treatment hinges on the development of highly effective photothermal agents (PTAs). Boron dipyrromethene (BODIPY) dyes, being well known for their high brightness and quantum efficiencies, are the antithesis of PTAs. Nonetheless, a systematic exploration of the photophysics and photothermal characteristics of a series of π‐extended BODIPY dyes with high absorptivity in the near‐infrared (NIR) region has achieved superior photothermal conversion efficiencies (>90%), in both monomeric state and nanoparticles after encapsulation in a biocompatible polyethyleneglycol 1,2‐distearoyl‐ sn ‐glycero‐3‐phosphoethanolamine‐N‐methoxy‐(polyethylene glycol)‐2000. Optimal PTA candidates combine strong NIR absorption provided by extended donor–acceptor conjugation and an optimization of the electronic and steric effects of meso ‐substituents to maximize photothermal conversion performance. The PTT‐optimized meso ‐CF 3 ‐BODIPY, T CF 3 P En exhibits exceptional efficacy in inducing cancer cell apoptosis and in vivo tumor ablation using low‐power NIR laser irradiation (0.3 W cm −2 , 808 nm) as well as excellent biological safety, underscoring its potential for advancing light‐induced cancer therapies.