7‑Hydroxyflavone Revisited. 2. Substitution Effect on Spectral and Acid–Base Properties in the Ground and Excited States

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 2015-12, Vol.119 (51), p.12672-12685
• Main Authors: Serdiuk, Illia E, Roshal, Alexander D
• Format: Article
• Language: English
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/acs.jpca.5b09185

Three derivatives of 7-hydroxy-2-phenyl-4H-chromen-4-one (7-hydroxyflavone), containing chloro, methoxy, and dimethylamino substituents at position 4′, were synthesized and investigated from the view of their ground-state and electronically excited-state behavior. Spectral and fluorescent properties in a wide range of pH/H 0, thermodynamics of the ground and S1 states, and kinetics of the excited-state deactivation of the compounds were investigated by means of steady-state electronic absorption, steady-state, and time-resolved fluorescent spectroscopies as well as by computational methods. The results are rationalized from the point of view of the substituent effect. In spite of a similar structure and the same acid–base centers, the compounds strongly differ in fluorescence characteristics as well as in the dependence of fluorescent properties on pH/H 0 of the media. Various protolytic/tautomeric forms of the compounds investigated absorb light in the 300–500 nm range and fluoresce in the whole visible range of spectra. The electron-releasing substituents at position 4′ of 7-hydroxyflavone immensely affect spectral properties as well as the excited-state thermodynamics and kinetics, whereas the electron-withdrawing ones cause minimal effect.