Determination of the ground and excited state dipole moments of ferulic and sinapic acids by solvatochromic effects and density function theory method

Ferulic acid (FA) and sinapic acid (SA) are groups of phenolic acids that belong to the class of hydroxycinnamic acid. Due to their molecular structure and functional groups, these compounds exhibit a wide range of biological activities. In this research, we have determined the dipole moments of these compounds in gas and solvent phases using spectroscopic and computational methods. The change in the dipole moments of FA and SA was calculated by Bakhshiev’s, Kawski–Chamma–Viallet’s, Lippert–Mataga’s, and microscopic solvent polarity functions. The results show that the change in the dipole moment calculated using Lippert–Mataga’s method is higher than that using other methods. This is due to the fact that this method ignores the specific interactions of the solute and solvent as well as the polarizability of the solute molecule. Similarly, the ground and excited-state dipole moments were determined by theoretical quantum chemical calculations using density functional theory (DFT); the results are found to be similar to the experimental ones. In both approaches, the excited dipole moment is greater than the ground state, indicating a significant redistribution of electron densities and being more sensitive to the solvent in the excited state for both molecules. The HOMO-LUMO energy bandgaps calculated in the gas phase for FA and SA are 4.001 and 4.055 eV, respectively. In addition, electron charge density maps, UV–Vis absorption spectra, and oscillator strengths were calculated using the DFT method to obtain general information about the compounds.