Molecular structure, multipolar charge density study and nonlinear optical properties of 4-methyl-N-[(5-nitrothiophen-2-ylmethylidene)] aniline

Abstract

In this work we present a comparative structural study of the 4-methyl-N-[(5-nitrothiophen-2-ylmethylidene)] aniline molecule using X-ray diffraction and theoretical ab initio methods. The title compound is considered as a good candidate for non-linear optical applications. The experimental results were obtained from a high-resolution X-ray diffraction study using the multipolar charge density model of Hansen and Coppens (1978) in which the charge density around the atoms are described with their non-spherical parts. Where the theoretical investigations were performed using the Hartree–Fock (HF) Density Functional Theory (DFT) methods at B3LYP level of theory using 6-31G(d,p) basis set. The knowledge of the analytical function of the electron charge density distribution have led easily to the determination of the net atomic charges, molecular dipole moment and the electrostatic potential around the studied compound. The optimized geometry of the title compound was found to be coherent with the structure determined by X-ray diffraction. The calculated HOMO and LUMO energies show also the charge transfer within the molecule. The obtained molecular electrostatic potential from the two methods confirm the nature of the electron charge transfer and locate the electropositive and the electronegative parts. The theoretical predicted non-linear optical properties are much greater than ones of urea.