Superhalogen doping of aromatic heterocycles; effective approach for the enhancement of static and dynamic NLO response

In this study, for the first time, static and dynamic NLO responses of pure and superhalogen doped aromatic heterocyclic monomers have been investigated by using density functional theory (DFT) calculations. The thermal, electronic, linear, and nonlinear optical properties are computed at the omega B97XD/6-31+G(d,p) method. The thermodynamic stabilities of reported complexes are estimated based on interaction energies, which are in the range of -28.06 to -83.20 kcal/mol. The lowest interaction energies are observed for AlF4@X (X = C4H4NH, C4H4O, C4H4S, and C5H5N) complexes, which correspond to their higher stabilities. The appreciable decrease in the HOMO-LUMO energy gap (Egap) is an indicative of the increase in reactivity after doping with superhalogens. The decrease in Egap is further demonstrated with the help of density of state (DOS) analysis. The significant nonlinear optical responses of the superhalogen doped aromatic heterocyclic monomers are due to the strong electron-withdrawing nature of the fluorine atom. Overall, the results indicate the high NLO response for the AlF4@X complexes due to the presence of four electron-withdrawing fluorine atoms in AlF4. The NLO results are further analyzed through the two-level model.