Effects of the Atomic Number of Alkali Atom and Pore Size of Graphyne on the Second Order Nonlinear Optical Response of Superalkali Salts of Graphynes OM3+@GYs– (M = Li, Na, and K)

Abstract

Based on the combination of novel carbon material graphynes (GYs) and superalkalis (OM 3), a class of graphyne superalkali complexes, OM 3 + @(GY/GDY/GTY)-(M = Li, Na, and K), have been designed and investigated by density functional theory method. Computational results reveal that these complexes with high stability can be regarded as novel superalkali salts of graphynes due to electron transfer from OM 3 to GYs. For second order nonlinear optical response, these superalkali salts exhibit large first hyperpolarizabilities (β 0). Two important effects on β 0 values are found, namely the atomic number of alkali atom in superalkali and the pore size of graphyne. Integrating the two effects, the selected combination of OLi3 with large pore size GTY can bring the considerable β 0 value (6.5×10 5 au), which is a new record for superatom-doped graphynes. In the resulting complex, the OLi 3 molecule is located at the center of the pore of GTY, forming a planar structure with the highest stability among these salts. Besides large β 0 values, these superalkali salts of graphynes have deep-ultraviolet working region, hence can be considered as a new kind of high-performance deep-ultraviolet NLO molecules.

Influence of Alkali Metal Doping and BN Substitution on the Second-Order Nonlinear Optical Properties of Graphyne: A Theoretical Perspective

“…The total dipole moment (μ 0 ), static mean polarizability (α 0 ), and mean first hyperpolarizability (β 0 ) are given by where The projection of β on the dipole moment vector can be obtained as The static α 0 and β 0 values were analyzed using analytical derivatives of the system energy (coupled-perturbed Kohn–Sham method) at the CAM-B3LYP/6-31+G­(d) level of theory. The combination of CAM-B3LYP functional and 6-31+G­(d) basis set can provide a qualitative trend to extract the valuable NLO prediction for various complexes. , The time-dependent density functional theory (TD-DFT) is a common method for calculating the properties of excited states due to its efficiency and accuracy. , Hence, the transition energy (Δ E ) and oscillator strength ( f 0 ) were evaluated by employing the TD-CAM-B3LYP functional with the 6-31+G­(d) basis set.…”

“…The tunable direct band gap of GDY is about 0.46 eV, , which reveals its great potential in photonic fields. − In recent years, great efforts have been devoted to exploring the NLO properties of graphyne/graphdiyne-based compounds . Especially, the graphyne structure is very advisable for the design of novel NLO materials because it has a delocalized π-conjugated surface that can accommodate dopants to enhance the NLO response. − Li et al ,, introduced (super)­alkali metals into GDY, confirming that the (super)­alkali metal doping effect significantly improved the first hyperpolarizability (β 0 ) of GDY. We found that the β 0 value of the OM 3 + @GYs – (M = Li, Na, and K) depends on the atomic number of the alkali atom and the pore size of GY .…”

“…Especially, the graphyne structure is very advisable for the design of novel NLO materials because it has a delocalized π-conjugated surface that can accommodate dopants to enhance the NLO response. − Li et al ,, introduced (super)­alkali metals into GDY, confirming that the (super)­alkali metal doping effect significantly improved the first hyperpolarizability (β 0 ) of GDY. We found that the β 0 value of the OM 3 + @GYs – (M = Li, Na, and K) depends on the atomic number of the alkali atom and the pore size of GY . Additionally, functional modification on the edge of graphyne is also an effective strategy to increase its static β 0 value. − In our previous study, replacing carbon atoms in the graphdiyne analog with boron or nitrogen atoms can improve the second-order NLO response, where N atom substitution has the best effect …”