Experimental and theoretical interpretations of spectral behavior of 6-methoxyflavone

Abstract

The present work emphasizes on the experimental and computational analysis of the solvatochromic behavior of 6-methoxyflavone (6MF). The steady-state absorption and fluorescence spectra were observed in certain polar protic, polar aprotic and non-polar/weakly polar solvents to examine their solvatochromism and determine the electrical dipole moment. Bathochromic shift in fluorescence spectra with solvent polarity was ascribed to intramolecular charge transfer (ICT) interaction. Calculations based on various solvent correlation techniques denote that the excited singlet-state dipole moment value is higher than the ground-state counterpart, hence indicates substantial redistribution of π-electron density in the excited state. Quantum chemical investigations were performed using density functional theory (DFT) and time-dependent density functional theory (TD-DFT), respectively, in vacuum and solvents. The vertical transitions, along with the bright singlet states and HOMO-LUMO, were obtained from the DFT/TD-DFT calculations. The experimentally calculated ground and excited state dipole moments and different photophysical parameters adequately reflect the values obtained from computational methods. Multiple linear regression (MLR) method based on Kamlet-Taft and Catalan solvent parameters demonstrate that the photophysical behavior of 6MF is attributed to both specific and non-specific solute-solvent interactions. Thus, the study helps to demonstrate the sensing ability of 6MF towards organic solvents and the charge transfer/hydrogen donor/acceptor properties of complex systems.