Tuning the electronic and nonlinear optical properties of black phosphorus quantum dots by introducing electron-donating/withdrawing molecules (TTF/TCNQ)

Two novel complexes were constructed by adsorption of two typical organic molecules, including one electron-donating molecule (TTF = tetrathiafulvalene) and one electron-withdrawing molecule (TCNQ = tetracyanoquinodimethane), on the surface of black phosphorus quantum dots (BPQDs). There exist considerable charge transfer and strong non-covalent interaction between organic molecules and BPQDs. The results of density functional theory (DFT) calculations show that the static first and second hyperpolarizabilities can be significantly enhanced by introducing TTF/TCNQ groups on BPQDs. Apart from static nonlinearity, hyper-Rayleigh scattering (HRS) first hyperpolarizability shows a remarkable value at a dispersion frequency of 1907 nm. Besides, the frequency-dependent first hyperpolarizability increases significantly while going from the gas to solvent phase. BPQDs-TTF presents a strong dipolar character, whereas BPQDs-TCNQ presents a relatively larger octupolar behavior. Compared with BPQDs-TTF, BPQDs-TCNQ exhibits better stability and larger first hyperpolarizability. This work highlights the superiority of combining TCNQ and BPQDs to construct high-performance nonlinear optical (NLO) molecules.

Automated summary

Two novel complexes were constructed by adsorbing electron-donating molecule TTF and electron-withdrawing molecule TCNQ on black phosphorus quantum dots (BPQDs), showing considerable charge transfer and strong non-covalent interaction. Density functional theory calculations revealed that introducing TTF/TCNQ groups on BPQDs can significantly enhance hyperpolarizabilities, with BPQDs-TCNQ displaying better stability and larger first hyperpolarizability compared to BPQDs-TTF. This work highlights the potential of combining TCNQ and BPQDs for high-performance nonlinear optical molecules.