A series of π-expanded coplanar BODIPY dyes with deep-red emission: Synthesis, optical properties, and application in amplified spontaneous emission

Abstract

Boron dipyrromethene (BODIPY)-derived dyes are a class of superior emitters, and a classic BODIPY structure has absorption and emission at ∼500 nm. To meet the practical application requirements, this work was dedicated to the design and synthesis of BODIPY emitters covering the deep-red region with a high emission quantum yield. Aromatic rings and a well-known electron-withdrawing group, –CF₃, were introduced into a π-expanded BODIPY structure. These BODIPY emitters were discussed in detail, including their thermal stability and optical parameters, as well as their photodynamic therapy performance. The correlation between the BODIPY photophysical performance and their substituents was discussed. It was found that the formation of a π-expanded coplanar conjugation chain successfully shifted BODIPY emission to the deep-red region (626 nm) with a high quantum yield (0.99). The –CF₃ modification on the BODIPY meso-C, however, quenched its emission. A threshold energy for the ASE (amplified spontaneous emission) effect of 980 μJ was exhibited with an efficiency of 5.5%. The cell viability was decreased to 9.0 ± 4.6% using these BODIPY dyes as a photosensitizer.