Synthesis, characterization and photophysical studies on novel benzofuran-3-acetic acid hydrazide derivatives by solvatochromic and computational methods

Abstract In the present studies, synthesis of two novel benzofuran-3-acetic acid hydrazide derivatives namely, (6-methyl-benzofuran-3-yl)-acetic acid hydrazide [6MLBH] and (6-methoxy-benzofuran-3-yl)-acetic acid hydrazide [6MOBH] are reported. The probes are characterized by IR, 1 H-NMR, 13 C-NMR and mass spectral methods. The absorption and fluorescence maxima of novel derivatives 6MLBH and 6MOBH are determined for different solvents of varying polarity and the solvatochromic behavior and dipole moments are investigated. Stoke's shift exhibits a red shift with increase in solvent polarity for both the probe molecules indicating a π→π* transition. The ground state dipole moment (μ g ) of both the molecules in gaseous phase is estimated from ab initio computations by using Gaussian 09 W software and also from solvatochromic method and the results are compared. Further, the ground state dipole moments of the probe molecules in different solvents were also estimated theoretically by using the integral equation formalism of polarizable continuum model (IEF-PCM). By using solvatochromic correlations like Lippert's, Bakhshiev's, Kawski-Chamma-Viallet's and solvent polarity parameter ( E T N ) , the excited state dipole moments (μ e ) are determined. Results show that, the excited state dipole moments (μ e ) are higher than the ground state dipole moments (μ g ) and suggest that, the probe molecules 6MLBH and 6MOBH are more polar in the excited state. The HOMO-LUMO energy gaps computed from density functional theory (DFT) and from absorption threshold wavelengths are found to be in agreement and also support intramolecular charge transfer (ICT). Using HOMO-LUMO energies, the chemical hardness (η) of the molecules are determined and the chemical stability is discussed. Further, using DFT molecular electrostatic potential (MESP) plots, the electrophilic site and nucleophilic site which are useful in photochemical reactions were identified. The various types of interactions present between the solute-solvent were analyzed by multiple linear regression analysis using Catalan parameters. The preliminary observations and results suggest that, the probe molecules 6MLBH and 6MOBH can be considered as potential candidates for luminescence materials, fluorescent probes and for designing non-linear optical materials in future.