Spectral and Acid−Base Features of 3,7-Dihydroxy-2,8-diphenyl-4H,6H-pyrano[3,2-g]chromene-4,6-dione (Diflavonol)A Potential Probe for Monitoring the Properties of Liquid Phases

Abstract

Diflavonol is a molecule that can exist in neutral or anionic form and in several tautomeric forms in ground and excited states. Absorption and emission spectroscopy combined with theoretical calculations have shown that only one tautomer of neutral diflavonol exists in the ground state, but two exist in the excited state. In the latter case, one is the tautomer originating from the ground state tautomer, which exists in strongly protic solvents, the other is the phototautomer occurring in weakly protic or aprotic solvents as a result of the intramolecular transfer of one proton. The OH groups present in diflavonol and involved in weak intramolecular hydrogen bonds exhibit a proton-donating ability reflected by the experimental values of acidity constants or theoretical enthalpies and free energies of proton detachment. The electronically excited molecule is a relatively strong acid when it loses one proton. With increasing basicity of the medium, monoanionic and dianionic forms occur which exhibit spectral characteristics and an emission ability different from those of neutral diflavonol. These interesting features of diflavonol open up possibilities for the analytical use of the compound and its application as a spectral probe sensitive to the properties of liquid phases.

3-Hydroxy-2-(4-hydroxyphenyl)-4H-chromen-4-one

“…In flavonols this phenomenon is strongly affected by molecules from their environment, which makes the compounds interesting fluorescent sensors for analytical applications in chemistry, biology, biochemistry, ecology and medicine (Klymchenko & Demchenko, 2003;Demchenko, 2009;Choulier et al, 2010). Continuing our investigations into the physical chemistry of flavonols (Bader et al, 2003;Roshal et al, 2003;Pivovarenko et al, 2004), we present the crystal structure of 3-hydroxy-2-(4-hydroxyphenyl)-4H-chromen-4-one in the hope that its structural and fluorescent features will appear interesting and helpful in its practical applications.…”

“…For general background to the properties of flavones (derivatives of 2-phenyl-4H-chromen-4-one) and fluorescence of flavonols (derivatives of 3-hydroxy-2-phenyl-4H-chromen-4-one), see: Bader et al (2003); Choulier et al (2010); Demchenko (2009); Klymchenko & Demchenko (2003); Nijveldt et al (2001); Pivovarenko et al (2004); Roshal et al (2003); Sengupta & Kasha (1979). For related structures, see: Etter et al (1986); Kumar et al (1998); Waller et al (2003).…”

2-(4-Fluorophenyl)-3-hydroxy-4H-chromen-4-one

“…For general background to fluorescence in flavanol (3-hydroxy-2-phenyl-4H-chromen-4-one) and its derivatives, see: Demchenko et al (2002); Pivovarenko et al (2005); Roshal et al (2003); Sengupta & Kasha (1979). For related structures, see: Cantrell & Stalzer (1982); Etter et al (1986); Waller et al (2003).…”

“…Since the fluorescence of flavonols depends strongly on the properties of the medium, the compounds can be applied as analytical probes in chemistry, biochemistry, biology and medicine (Demchenko et al, 2002). Continuing our investigations into this group of compounds (Roshal et al, 2003;Pivovarenko et al, 2005) we now present the crystal structure of a flavonol derivative -2-(4-fluorophenyl)-3-hydroxy-4H-chromen-4-one.…”

Characterization of Coupled Ground State and Excited State Equilibria by Fluorescence Spectral Deconvolution

“…Solutions of 3HC dyes in toluene in the presence of an amine show three emission bands corresponding to the N*, T* and anionic forms [30]. The information content of such a response can be increased by using dyes containing two ESIPT sites [31]. …”