Influence of solvents on the spectra of benzylidene malonitrile derivative and DFT calculations

The spectroscopic behavior of benzylidene malonitrile (BZM), a donor-π-conjugate-electron acceptor compound, is reported in various solvents. Kamlet–Taft and Catalan models were used to evaluate specific and non-specific solute-solvent interactions. Solvent polarizability (SP) was found to be the dominant factor affecting the absorption and fluorescence spectral shifts. The π →π* transitions was assigned between HOMO and LUMO, based on time-dependent density functional theoretical calculations. The dipole moment of BZM in the ground and excited states were calculated using Stokes shift and solvent polarity functions. The experimental ground state dipole moment (μ_g = 1.7 D) was found to be lower than that in the excited state (μ_e = 5.5 D). In binary solvent mixtures, BZM showed both ideal (DMSO/ethanol) and non-ideal (DMSO/acetone and DMSO/dioxane) behaviors. The formation constants in DMSO/ethanol was much lower as compared to the other two mixtures. BZM also exhibited self-quenching fluorescence which is attributed to the primary inner filter effect.