Chlorinated BODIPYs: Surprisingly Efficient and Highly Photostable Laser Dyes

Abstract A series of mono‐ to hexachlorinated BODIPY dyes have been prepared in good to excellent yields through the use of N ‐chlorosuccinimide as an inexpensive halogenating reagent. This library of chlorinated dyes allowed analysis in detail, from the experimental and theoretical points of view, of the dependency of the photophysical and optical properties of the dyes on the number and positions of the chlorine substituents on their BODIPY cores. Quantum mechanical calculations predict the regioselectivity of the halogenation reaction and explain why some positions are less prone to chlorination. The new chlorinated BODIPYs exhibit enhanced laser action with respect to their non‐halogenated analogues, both in liquid solution and in the solid phase. In addition, chlorination is a facile and essentially costless protocol for overcoming important shortcomings exhibited by commercially available BODIPYs, which should favor their practical applications in optical and sensing fields.