Alkali metal-induced modifications in the electronic and NLO properties of triselenasumanene complexes through DFT study

In this study, the optimized structure, electronic properties and nonlinear optical response (NLO) of TSSUM nanostructure and its complexes with alkali metals (M = Li, Na, and K) in the gas phase and solvent medium were investigated using density functional theory. The interaction energy of the complexes in the gas phase was calculated between − 10.20 to -10.75 kcal/mol, and in solvent medium as Li: -15.68 to − 24.30 kcal/mol, indicating higher stability of the complexes in the presence of solvent. QTAIM and NBO analysis also showed that the highest electron density and charge transfer to the metal occur in Li/TSSUM and the effective force in this system is higher than Na and K. UV–Vis spectral analysis and TD-DFT calculations showed that the main absorption of TSSUM in the gas phase is around 320 nm. The addition of alkali metals caused the absorption to shift to longer wavelengths (between 614 and 704 nm); indicating a decrease in excitation energy and an increase in charge transfer capability. Hyperpolarizability (β₀) values increased notably, with higher values in the solvent than in the gas phase, showing the medium’s effect on stability and charge distribution. For Li/TSSUM, Na/TSSUM, and K/TSSUM, β₀ ranged from 2242 to 4260 a.u in gas and 8246–12,032 a.u in solvent. The decrease in the energy gap Eg and the increase in β₀ indicate that the M/TSSUM complexes have significantly higher nonlinear optical response than pristineTSSUM and can be considered as suitable candidates for optoelectronic and photonic applications.