Phenolic deprotonation triggered NIR emission and large Stokes shifts of BODIPY dyes

Abstract

Boron-dipyrromethene (BODIPY) derivatives are well-known for their high brightness, and those that emit in the near-infrared (NIR) region with moderate to large Stokes shifts are particularly sought after. Different from the conventional approach of expanding the π-conjugation by fusing aromatic rings, this work introduces a spontaneous deprotonation strategy. By incorporating one or two functional phenol groups onto the BODIPY core, a series of BODIPY derivatives with NIR emission (up to λ_em = 791 nm) and significantly enlarged Stokes shifts (up to 225 nm) were synthesized. DFT calculations revealed that the redshift in both absorption and emission, along with the enlarged Stokes shift, can be attributed to the deprotonation of the phenolic hydroxyl group. This deprotonation not only prompts intramolecular charge transfer but also disrupts the planar structure of the BODIPY core. The resultant BODIPYs demonstrated strong singlet oxygen photogeneration efficiency and high photo penetration capabilities.