Remarkable static and dynamic nonlinear optical responses of Al13-TCNQ/F4-TCNQ complexes: a quantum chemical study

Abstract

The electronic and nonlinear optical (NLO) properties of Al₁₃-TCNQ/F4-TCNQ were systematically investigated using density functional theory methods. The Al₁₃-TCNQ/F4-TCNQ complex has a high ionization potential of 7.51/6.71 eV and a strong binding energy of 1.93/2.39 eV, indicating its high structural stability. The stability of the complexes is confirmed through atom-centered density matrix propagation simulation at different temperatures up to 2000 fs. TCNQ/F4-TCNQ (electron donor) interacts with Al₁₃ to form a charge-transfer framework, and F4-TCNQ is a stronger electron acceptor. A1₁₃-TCNQ and A1₁₃-F4-TCNQ complexes exhibit excellent NLO responses [static first and second hyperpolarizability (β₀ and γ₀), hyper-Rayleigh scattering coefficient (β_HRS), frequency-dependent first hyperpolarizability β(−2ω; ω, ω) and β(−ω; ω, 0)], which are crucial evaluation indexes for designing NLO materials. The static and dynamic hyperpolarizability increases with the enhancement of the electron-acceptor capacity, for example, the β₀ value of Al₁₃-F4-TCNQ (92 275 au) is larger than that of Al₁₃-TCNQ (76 720 au). The absorption spectrum reveals that these molecules have deep ultraviolet (UV) and infrared (IR) transparent regions, and hence are new UV and IR NLO molecules. Therefore, linking an Al₁₃ cluster with TCNQ/F4-TCNQ is an effective strategy to design stable potential candidates for high-performance NLO molecules.