Impact of the Keto-Enol Tautomeric Equilibrium on the BODIPY Chromophore.

An intramolecular tautomeric fluorescent BODIPY sensor has been designed and synthesized. The obtained BODIPY dye is a combination of the 4-bora- 3a, 4a-diaza- s-indacene core and a diketone fragment. The study of conformational equilibria in the ground and excited states has been completed for a broad range of solvent polarity by steady state and NMR methods as well as by DFT and TD-DFT calculations. The interpretation of the unique emission observed in hydrogen bond accepting solvents upon the excitation of the fluorescent dye in the S0-S2 transition has been accomplished. The Jablonski diagram has been analyzed for the observed processes in the BODIPY dye studied on the basis of DFT and TD-DFT calculations.