Theoretical Study On Nonlinear Optical Properties Of Modified Graphdyne And Black Phosphorus Quantum Dots

Nowadays,in the new era of abundant material,convenient life and technology-based,the design and research of nonlinear optical（NLO）materials have attracted the attention of researchers.Researchers have been committed to the exploration and research of new high-performance nonlinear optical materials.In this work,a series of modification of graphyne/black phosphorus quantum dots are mainly carried out,and their geometrical structure,electrical properties and nonlinear optical properties are systematically studied by using quantum chemical methods.According to the theoretical calculation and analysis,the introduction of donor/acceptor groups on the edge of graphyne and the surface of black phosphorus quantum dots can effectively improve the NLO response of the system,providing valuable theoretical clues for the design of new high-performance NLO materials.The main contents of this work are as follows:1.Based on the donor-acceptor framework of graphdiyne-triphenylamine（GDY-TPA）,eight GDY-π-TPA molecules were designed by introducing aπ-conjugated bridges,including electron-excessive heterocycles,electron-deficient heterocycles,and unsaturated hydrocarbons.Their geometrical structure,electronic properties,static and dynamic first hyperpolarizabilities were investigated using the density functional theory（DFT）method.Charge analysis shows that the first hyperpolarizability（β₀）of GDY-π-TPA（with exceptions）can be significantly increased when electron-rich heterocycles and unsaturated hydrocarbons are used as donors or electron-deficient heterocycles are regarded as acceptors.The compound containing vinyl units is the best NLO model of all systems.The first hyperpolarizability density analysis shows that A-1,B-1 and C-1 complexes have larger region of positiveβdensity in the TPA moiety compared to GDY-TPA,thus showing largerβ_xxx values.2.Density functional theory（DFT）was employed to calculate the second-order nonlinear optical（NLO）properties of a series of–（CH═CH）_m–NH₂/NO₂-modified graphynes（GY[n]）（n=1–3;m=1–6,9,12）.This modification can produce significant electron transfer between the graphyne and the conjugated chain,and also reduce the transition energy,which leads to these systems exhibiting large staticβ₀ values.Theβ₀ values of the systems crucially depend on the length of the–（CH═CH）_m–chain,the substituent groups at the end of the chain,and the size of the graphyne.The–（CH═CH）_m–NH₂/NO₂ co-modified GY[1]systems have better NLO responses than the single-modified GY[1].3.Two novel complexes were formed by adsorbing an electron-donating molecule（TTF=tetrathiafulvalene）andanelectron-withdrawingmolecule（TCNQ=tetracyanoquinodimethane）on the surface of black phosphorus quantum dots BPQDs.The results of density functional theory calculations reveal that the introduction of TTF/TCNQ groups on BPQDs can significantly increase the static first hyperpolarizability（β₀）and the second hyperpolarizability（γ₀）.Hyper-Rayleigh scattering（HRS）first hyperpolarizability exhibits a significant value at the dispersion frequency of 1907 nm.Furthermore,the frequency-dependent first hyperpolarizability increases remarkedly from the gas phase to the solvent phase.BPQDs-TCNQ has better stability and largerβ₀andγ₀ than BPQDs-TTF.