Correlation between structural features and optoelectronic properties in superhalogen doped hexaazakekulenes

Superhalogens, owing to their higher electron affinities than conventional halogens, possess exceptional electron-accepting capabilities, making them attractive candidates for tuning nonlinear optical (NLO) properties. In this study, we systematically investigated the NLO behavior of superhalogen-doped hexaazakekulene (M1) macrocycles using density functional theory (DFT) through both static and dynamic hyperpolarizability analyses. The electronic and thermodynamic stabilities of the doped systems are evaluated via interaction energies (E_int), vertical ionization energies (I), and frontier molecular orbital (FMO) analysis. Among the studied complexes, CaF₃–M1 exhibits the highest interaction energy (− 68.33 kcal mol⁻¹), indicating superior binding stability. Static and dynamic NLO analyses revealed substantial improvements in optical responses upon doping. Among the designed systems, MgF₃-M1 exhibited the highest static first hyperpolarizability (8.77 × 10⁴ au) and lowest excitation energy (0.90 eV), aligning with the two-level model predictions. Frequency-dependent studies at 532 nm and 1064 nm confirmed enhanced electro-optic Pockels effects and second harmonic generation (SHG), with BeF₃-M1 and CaF₃-M1 showing particularly strong responses. These variations are attributed to the atomic size and electronic characteristics of the dopant metals. Third-order NLO behavior was also analyzed, showing significant enhancements in second hyperpolarizability (γ) and nonlinear refractive index (n₂), especially for CaF₃-M1. UV–Vis spectral analysis revealed bathochromic shifts and dual absorption bands, confirming extended π-conjugation and distinct electronic transitions. Overall, superhalogen doping of M1 macrocycles results in remarkable improvements in NLO activity, stability, and optical tunability. These findings highlight their strong potential as advanced materials for photonic and optoelectronic applications.