Photophysical and theoretical studies on the solvatochromic effects and dipole moments evaluation of substituted 1-phenyl-3-naphthyl-5- (4-ethyl benzoate)-2-pyrazoline

The solvatochromic behavior of four 1-phenyl-3-naphthyl-5-(4-ethylbenzoate)-2-pyrazoline with various electron donating and withdrawing substituents on N1-phenyl group were investigated in nonpolar, polar aprotic and protic solvents experimentally and theoretically. The photophysical behavior of pyrazoline in solvents was attributed to the intramolecular charge transfer (ICT) of the compound along with the specific and non-specific interactions with the solvent molecules. On view of the effect of different types of interactions on the optical properties, the Stokes shift of each compound in various solvents was correlated to various parameters such as orientation polarity parameter (Δƒ), microscopic solvent polarity parameter (E_T 30), and linear solvation regression of the absorption and emission with specific and non-specific types of interaction. The dipole moments of these compounds in the ground and excited state were also explored and compared using different methods, and the results showed greater stabilization of the studied pyrazoline molecules in the excited state. The DFT and TDDFT calculations supported and explained the experimental data, by obtaining the absorption and emission energies, HOMO/LUMO energies and the dipole moments for each compound in various solvents. Analysis of electron-hole distribution suggests that the intense fluorescent of these molecules originates from a hybrid local excitation charge-transfer state (HLCT).