Investigation of the electronic and optical activity of halogen-substituted 2-nitrotoulene by density functional theory

The enhancement of Nonlinear optical (NLO) activity of the 2-nitrotoulene (2NT) after the substitution of the halogens (F, Cl, Br, and I) at the para position of the benzene ring was reported in the paper. All the computational details were mentioned using density functional theory with B3LYP/6-311++G(d,p) basis set. The engagement of the electrophilic and nucleophilic regions in molecules was established using contour plots. Mulliken charge analysis and frontier molecular orbital parameters laid the high chemical reactivity of 2NT molecule after the substitution of F, Cl, Br, and I. Using time-dependent density functional theory, electronic properties were analyzed by computing absorption and emission spectra. The higher Raman intensity modes and higher absorbance intensity curve for iodine-substituted 2NT (2NT-I) highlighted the highest reactivity. The lowest band gap was reported for 2NT-I (4.02 eV) which better correlates with the charge and spectral findings. The polarizability parameters set a fair comparison between the NLO activities of the molecules. 2NT-I has the highest values of polarizability parameters among the other molecules.