Assessment of alkali and alkaline earth metals doped cubanes as high-performance nonlinear optical materials by first-principles study

Novel organic materials have played a tremendous role in developing high-performance nonlinear optical materials. Herein, the geometric, electronic and nonlinear optical properties of designed alkali (Li, Na, and K) and alkaline earth metals (Be, Mg, and Ca) doped cubane (C8H8) complexes have been explored by using density functional theory. Excess electrons generated by doping alkali/alkaline earth metals have significantly enhanced the NLO properties by reducing the crucial excitation energy of the cubane. The HOMO–LUMO energy gap of doped complexes is reduced up to 4.43 eV. It is revealed that the reduction in the HOMO–LUMO energy gap results from the development of the new highest occupied molecular orbital, which is confirmed by the density of state (DOS) analysis. The NBO analysis is carried out to confirm the charge transfer between metal atoms and the cubane ring. Further, the NCI and QTAIM analyses confirmed the nature of intramolecular interaction. The remarkable first hyperpolarizability (βo) of 3.01 × 104 au is observed for K@Cubane. Moreover, frequency dependent first hyperpolarizability (β (ω)), second harmonic generation β (-2ω; ω,ω), electro-optic Pockel's effect β (-ω; ω,0), hyper-Rayleigh scattering coefficient (βHRS), second hyperpolarizability (γ (ω)), electric field-induced second harmonic generation γ(-2ω; ω, ω,0) electro-optic Kerr effect γ(-ω; ω,0,0), and nonlinear refractive indices (n2) were also studied. The highest dc-Kerr (2.69 × 1010 au) and EFISHG (3.69 × 109 au) values observed for K@Cubane along with large n2 (1.73 × 10−9 au) justify the large NLO response. These intriguing outcomes will be advantageous for promoting the possible utilization of designed complexes in the field of high-performance NLO materials.