Unusual spectroscopic and photophysical properties of solvatochromic BODIPY analogues of Prodan

Here, we report the synthesis of two isomeric BODIPY-based fluorescent molecules with a diethylamino donor group and an acetyl acceptor group at positions 5 and 2 (or 3), respectively, on the boron dipyrromethene core. The structure of the new BODIPY dyes is similar to Prodan, probably the most widely used solvatochromic probe, but with the donor and acceptor groups attached to an electron-poor heteroaromatic core. Interestingly, these BODIPY dyes exhibit unusual spectroscopic and photophysical properties, involving inverse solvatochromic behavior. An in-depth study of the solvent effects and quantum-chemical calculations have been performed to assess the basis for such spectroscopic properties and the effect of the position of the substitution. This work points towards a rational design of new fluorescent probes, based on understanding their spectroscopic and photophysical behavior. • New BODIPY dyes analogues of Prodan are synthesized. • These dyes exhibit unusual spectroscopic features. • In-depth solvatochromic and computational studies allow understanding excited-state dynamics. • This information is essential for the rational design of new dyes.