Theoretical-experimental study of solvents’ effects on the spectroscopic properties of organic molecules

Abstract

The research focuses on the photochemical and spectroscopic properties of conjugated organic molecules. The study was based on exploring the effect of different solvents on the optical properties. The fluorescence analysis from PY-RES solutions varying the polarity allowed us to observe the solvatochromic effect. The Stokes shift analysis revealed a variation in the molecular dipole moment of 4.57 D after excitation with the 450 nm laser, consistent with the literature values for similar compounds. The behavior of PY-RES solutions as the temperature increased indicated a decrease in emission intensity, especially in less polar solvents. The sensitivity of PYRES to solvent polarity highlights its potential as a physicochemical probe for detecting solvent adulteration, evidenced by the ratiometric emission changes in ethanol-methanol mixtures. Monocarbonyl Curcumin (1E,4E-1,5-bis(4-(dimethylamino)phenyl)penta-1,4-dien-3-one) was examined for its electronic absorption and fluorescence spectra across various solvents. Experimental results, supported by Time-Dependent Density Functional Theory (TDDFT) simulations, indicated strong solvent polarity effects on fluorescence spectra. Absorption maxima ranged from 400 nm to 460 nm, with a bathochromic shift observed in more polar solvents, peaking at 458 nm in methanol. Computational studies with the B3LYP functional revealed a HOMO-LUMO gap of 2.8 eV and a theoretical absorption peak near the experimental value in methanol. Monocarbonyl Curcumin exhibited a high Stokes shift in methanol (175.6 nm), increasing with solvent polarity, suggesting significant changes in charge distribution upon excitation. Spectral decomposition and intensity decay analysis confirmed solvent-dependent emission properties and the impact of temperature on emission intensity without altering spectral shape. These findings highlight the potential of curcumin monocarbonyl as an environment-sensitive probe. The chalconoid (E)-1-(4-aminophenyl)-3-(4-(dimethylamino)phenyl)prop-2-en-1-one was investigated through UV-vis spectroscopy and theoretical calculations. The compound exhibited two main absorption bands corresponding to π − π ∗ and n − π ∗ transitions, with significant solvent-dependent shifts. A bathochromic shift was particularly notable in less polar solvents like heptane and toluene. Theoretical analyses using the CAM-B3LYP functional and the 6- 311+G(d,p) basis set corroborated experimental findings, detailing a HOMO–LUMO transition energy gap of 5.406 eV in acetonitrile and an n − π ∗ transition gap of 6.5 eV. Fluorescence studies revealed a substantial Stokes shift in nonpolar solvents, reinforcing the compound’s sensitivity to the solvent environment and its potential in optoelectronic and pharmaceutical applications.