Quantum chemical studies of molecular structure, vibrational spectra and nonlinear optical properties of p-iodoaniline and p-bromoaniline

Abstract

Quantum chemical computations of monomer and dimer molecules of para-Iodoaniline (p-IA) and para-Bromoaniline (p-BA) were performed at best suitable DFT/WB97XD levels of theory using LANL2DZ basis set through Gaussian 09 program in addition to experimental z-scan and spectroscopic characterization. Molecular structure analysis reveals halogen/ hydrogen bonded interactions such as NH…X, CX…N and CH…N as well as π- π stacked intermolecular interactions to form the dimer with high binding energy (28.2979 kJ/mol) and stability. The order of planarity p-IA> p-BA is also identified. NBO predicts that the strength of intermolecular interaction in p-IA >p-BA and intramolecular interaction in p-BA >p-IA. The FT-IR and FT-Raman spectra also supports greater planarity and intermolecular interactions in p-IA compared to p-BA. The presence of higher π*(C15C16) → π*(C2C3) stacked intermolecular interaction energy (20.18 kJ/mol) enhances the NLO activity of p-IA. The FMO's and NBO analyses predict the delocalization of electrons within the phenyl ring of the molecules due to the strong ICT interaction between the lone pair of N and π*(CC) orbitals at high stabilization energy. Hirshfeld surface map and 2D fingerprint plot analysis confirm the stability and interactions within the compounds. First order hyperpolarizability values corresponding to p-IA and p-BA were computed which are 5.1 and 3.6 times that of urea. Third order optical nonlinearity was measured by the means of the open aperture z-scan technique .The calculated values of 2PA coefficient β =4.3 × 10−11 m/W in p-IA and β =2.4 × 10−11 m/W in p-BA reveal that the p-IA is a better optical limiter than p-BA crystal.