Structure-property relationship of N-substituted triazolonitroindazoles: A comprehensive study on linear and non-linear optics, as a function of quantum parameters employing density function theory

[Display omitted] •Theoretical calculations of N-substituted triazolonitroindazoles were performed.•GIAO Approach was used and CDFT reactivity indices were defined.•Fukui functions and relative nucleophilicity indices were calculated.•MEP Surface was investigated.•Potential application of N-substituted triazolonitroindazoles in optoelectronics and photonics. The reaction of 5-nitroindazole with 1,2-dibromoethane gave N-bromoethyl-5-nitroindazole and N-vinyl-5-nitroindazole. N-Bromoethyl-5-nitroindazole was used as a precursor to synthesize N-substituted triazolonitroindazoles (NST1-NST4) through copper-catalyzed azide-alkyne cycloaddition (CuAAC). In this study, we investigated the reactivity indices of N-substituted triazolonitroindazoles defined within the conceptual DFT framework: chemical hardness, electronic affinity, ionization potential, and electronic chemical potential. Fukui functions as well as relative nucleophilicity indices were calculated using Mulliken calculation methods. The 1H NMR chemical shifts of NST1-NST4 were computed and compared to the experimental values. The theoretical UV visible spectroscopic and Fourier transform infrared studies were performed to define the absorption band and the functional groups for each compound. Nonlinear optical descriptors (NLO) specifically dipole moment, polarizability, first-order and second-order hyperpolarizability were also defined. According to the results, NST4 has the lowest hyperpolarizability, making it the most stable and exhibiting a weak NLO response. In contrast, NST3 displays the uppermost hyperpolarizability, making it the least stable with a high NLO response being a promising candidate for NLO-devices.