Impact of the Keto–Enol Tautomeric Equilibrium on the BODIPY Chromophore

Abstract

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 S-S 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.

Intramolecular Hydrogen Bonds in Selected Aromatic Compounds: Recent Developments

“…The growing popularity of fluorescent dyes rests upon the possibility of chemical modification of both the chromophore core and its substituents, which can manifest in a variety of spectroscopic properties [70][71][72][73][74][75][76][77][78][79][80][81][82][83]. The main objective of fluorescent BODIPY (4,4′-difluoro-4-boron-3a,4a-diaza-s-indacene) dye studies has been to explore the influence of the tautomeric equilibrium sensor on the spectroscopic parameters of the dye [84][85][86][87][88]. Below, we present a summary of our studies on BODIPY dyes with tautomeric sensors.…”

“…Refs. [87,88] present syntheses and studies of the BODIPY dyes with substituents sensitive to protonation The subsequent studies of fluorescent dyes in Refs. [84][85][86][87][88] successfully used the spectral parameters' dependences on the parameters defining the polarity of the environment for the detection and description of processes occurring in the electronic ground and excited states.…”

“…Refs. [87,88] present syntheses and studies of the BODIPY dyes with substituents sensitive to protonation and deprotonation, as well as to conformational equilibria in BODIPY-Schiff (X) and BODIPY-diketone dyes (XI), as seen in Figure 19. These studies were performed by experimental methods and DFT calculations in electronic ground and excited states.…”

“…These substituents feature keto-enol equilibrium (diketone moiety) and intramolecular proton transfer (ortho-hydroxy aldimine moiety), as well as isomerization around the imine bond conditioned by the polarity of the environment and specific interactions such as intermolecular hydrogen bonding ( Figure 19). The fluorescent BODIPY-Schiff and BODIPY-diketone dyes were studied in a wide range of solvent polarities in electronic ground and excited states [87,88]. The effects of the solvent polarity and specific interactions on the keto-enol equilibrium, isomerization of the imine bond, and intramolecular versus intermolecular hydrogen bond equilibrium on the spectroscopic characteristics of the BODIPY-chromophore were investigated.…”

“…The selected absorption (A,C) and emission (B,D) spectra of BODIPY-Schiff and BODIPY-diketone dyes, respectively, in variations of solvents. The list of solvents is presented in Refs [87,88]…”