Insights from computational approach into dynamic NLO and electronic properties of N’-(4-X-3,5-dimethoxybenzylidene)-1 H-indole-3-carbohydrazides

The electronic structure, nonlinear optical (NLO) behavior, and solvent-dependent properties of two indole-based Schiff bases were systematically explored using density functional theory (DFT) and time-dependent DFT (TD-DFT). Key quantum chemical and reactivity descriptors were calculated to evaluate their optoelectronic potential. Urea was employed as a benchmark NLO prototype. Remarkably, both Schiff bases demonstrated significantly higher NLO responses than urea, with first hyperpolarizabilities indicative of efficient second harmonic generation (SHG). Furthermore, solvation studies revealed a pronounced enhancement in LHE (~ 90%) in polar media, underscoring the strong solvent dependence of their photophysical behavior. The HOMO–LUMO energy gaps (4.04–4.32 eV) and elevated hyperpolarizabilities highlight the compounds’ promise as tunable organic NLO materials. These findings establish a structure-property framework for advancing Schiff base derivatives in optoelectronic applications.