Calculation of Electronic Properties of Some 4-Nitroaniline Derivatives: Molecular Structure and Solvent Effects

The effects of substituents and solvents on the ground state molecular geometry, dipole moments (µ), polarisabilities (α) and frontier molecular orbital energies (EHOMO, ELUMO) and optical gap (ΔE) of 4-nitroaniline and its N-substituted alkyl derivatives were studied by the ab initio restricted HF-DFT self-consistent field method (B3LYP) using the 6-31G* basis set in vacuum, tetrahydrofuran and ethanol. The result revealed that 4-nitroaniline is non-planar but its µ, α and molecular size are enhanced upon successive perturbative substitution with size and number of alkyl group(s) at the amino nitrogen. The µ and α are found to increase as the solvents become more polar. Furthermore, it was found that the enhancement of these properties is associated with decrease in the optical gap of the molecules and/or increase in molecular radius. The findings imply an enhanced reactivity and ground state electro-optic susceptibility of the molecules. N,N-diethyl-4-nitroaniline exhibits the most reactivity and ground state electro-optic susceptibility.