Quantum chemical engineering of enhanced nonlinear optical responses in alkali metal-doped diazadioxacirculenes for...

The pursuit of high-performance nonlinear optical (NLO) materials remains central to advancing optical communication, photonic circuitry, and laser-based technologies. In this study, we theoretically designed and evaluated a new class of alkali metal-doped diazadioxa[8]circulene complexes, denoted as M@C8 (M = Li, Na, K), using density functional theory. Metal doping induces profound structural and electronic reorganization, with interaction energies ranging from -0.25 to -11.21 kcal mol^-1, affirming both favorable metal binding and thermodynamic stability. Remarkably, these modifications lead to dramatic enhancements in NLO performance. The pristine C8 molecule exhibits a negligible static first hyperpolarizability (β₀) of just 0.03 au; however, upon doping, β₀ surges to an exceptional 470074.83 au for 3-Li@C8, an increase of nearly 1.57 × 10⁷-fold. Under dynamic conditions (λ = 1064 nm), the first-order hyperpolarizability β(-ω, ω, 0) reaches 104948.80 au for 3-Na@C8, while the hyper-Rayleigh scattering hyperpolarizability (β_HRS) peaks at 2837379.65 au for 5-K@C8, showcasing outstanding frequency-dependent NLO activity. Complementary UV-Vis analysis reveals pronounced redshifts in absorption (from 199.39 nm for C8 to 773.60 nm for 6-K@C8), indicating enhanced π-electron delocalization and efficient intramolecular charge transfer. Taken together, these findings position M@C8 complexes as compelling molecular platforms for next-generation NLO materials with exceptional static and dynamic optical responses.