Molecular structure and solvent effects on the dipole moments and polarizabilities of some aniline derivatives

This work presents the quantum chemical studies of the effects of substituents and solvents on the ground state molecular geometry, dipole moments, polarizabilities and frontier orbital energies of aniline (A), N-methylaniline (NMA), N-ethylaniline (NEA), N,N-dimethylaniline (DMA) and N,N-diethylaniline (DEA) towards understanding their structure–property relationship. The ground state molecular geometry, dipole moments, polarizabilities and frontier orbital energies of A, NMA, NEA, DMA and DEA were computed by use of the ab initio restricted HF–DFT self-consistent field method (B3LYP) with 6-31G* basis set in vacuum, ethanol and tetrahydrofuran. The results of the B3LYP/6-31G* calculations revealed that these properties are enhanced upon successive substitution with size and number of alkyl groups at the amino group of the molecules, and as the dielectric constant of the solvents decrease. It was also found that for all the molecules, the enhanced ground state molecular geometry, dipole moments and polarizabilities upon substitution or solvent effect are associated with a decrease in the EHOMO − ELUMO (optical) gap. The lower optical gap, higher dipole moments and polarizabilities with increased size and planarity illustrates increased reactivity and ground state electro-optic (non-linear optical) activity of the molecules upon substitution, and as the dielectric constant of the solvents decreased. Of the studied molecules, DEA was found to exhibit the most electro-optic activity and reactivity.