Tuning the inter-molecular charge transfer, second-order nonlinear optical and absorption spectra properties of a π-dimer under an external electric field

Abstract

In this work, we applied an external electric field (F) to a biphenalenyl derivative (BN-PLY) in the direction of the negative z-axis (F) and the positive z-axis (F), respectively. The influence of the two directions of F on the molecular structures and electronic properties is investigated, which gives interesting results. Density functional theory (DFT) calculations show that the application of F (F = 0 to -190 × 10) is an advantage toward improving π-dimer stability, which is attributed to an increase in bonding and attractive electrostatic interactions. Interestingly, a large amount of negative charge is induced by applying F to the upper layer, resulting in an increase in the electron density in the upper layer, which is the main factor for the formation of a symmetric highest occupied molecular orbital (HOMO) at F = -180 × 10 au (-9.26 × 10 V m). Moreover, when F is applied, the HOMO and HOMO-1 undergo orbital interchange in the π-dimer at F = 100/110 × 10 au. Significantly, the effect of the external electric field effectively regulates the first hyperpolarizabilities (β). When the F ranges from 0 to 140 × 10 au, the β values slightly decrease to 0 au. Note that, upon increasing F, the β values sharply increase to 6.67 × 10 au (F = 190 × 10 au). Furthermore, the evolutions of the absorption spectra under F might well explain the trend of β values. When the F ranges from 0 to 140 × 10 au, the broad absorption spikes with a low-energy are significantly blue-shifted, while only absorption spikes with a high-energy are significantly red-shifted (F = 140 to 190 × 10 au). The present work not only provides a deeper understanding of the relationships between the molecular structure and the electronic properties of a π-dimer system, but can also be developed for designing highly efficient nonlinear optical materials through the influence of an external electric field.

Long-Range Charge Transfer Driven by External Electric Field in Alkalides M–LCaL–M (M = Li or Na, L = All-cis 1,2,3,4,5,6-Hexafluorocyclohexane): Facially Polarized Janus-Type Second Order Nonlinear Molecular Optical Switches

“…M06-2X not only exhibits good performance for calculating electronic structures, but it is also broadly used to calculate electric properties, , that is, dipole moment, polarizability, and hyper-polarizabilities. In order to certify the reliability of M06-2X for calculating electronic contribution of the hyperpolarizabilities (β 0 ), Gu’s results display that the difference of β 0 values between MP2 and M06-2X is within 1.8% for C 6 F 6 H 6 (L), and therefore, M06-2X/6-311++G­(2d,2p) was chosen to calculate the β 0 values of alkalide L–M–L–M′ and superalkalide L–M–L–M 3 ′ O (M = Li and K, M′ = Li and Na).…”

“…Geometrical structures of these studied systems under different EEFs were fully optimized, and the frequency calculations confirmed that these geometrical structures lie on their minima of potential energy surfaces of ground states because frequency calculations display no imaginary values. M06-2X not only exhibits good performance for calculating electronic structures, but it is also broadly used to calculate electric properties, 55,56 that is, dipole moment, polarizability, and hyper-polarizabilities. In order to certify the reliability of M06-2X for calculating electronic contribution of the hyperpolarizabilities (β 0 ), Gu's results 47 display that the difference of β 0 values between MP2 and M06-2X is within 1.8% for C 6 F 6 H 6 (L), and therefore, M06-2X/6-311++G(2d,2p) was chosen to calculate the β 0 values of alkalide L−M−L−M′ and superalkalide L−M−L−M 3 ′O (M = Li and K, M′ = Li and Na).…”

Facially Polarized Molecule for Alkalides and Superalkalides with Considerable Nonlinear Optical Response

“…The first hyperpolarizability density and the natural transition orbital maps were also plotted by the Multiwfn. M06‐2X not only exhibits good performance for calculating electronic structures, but also broadly used to calculate electric properties,,, i.e . dipole moment, polarizability, hyperpolarizabilities.…”

Nonlinear Migration Dynamics of Excess Electrons along Linear Oligopeptides Controlled by an Applied Electric Field

“…In fact, a number of studies have revealed that E ex can effectively modify the electronic structures and transport properties of low‐dimensional systems . For examples, Song and co‐authors revealed a charge separation and further transport process under the influence of E ex in solar cell materials .…”

“…[59] Gao et al reported that the E ex with different directions and strengths could control the molecular structure, inter-molecular charge transfer and nonlinear optical properties of π-dimers. [60] Also, researchers have demonstrated that, an E ex can be utilized not only to influence the adsorption energy of small molecule but also to control the charge transfer between the small molecule and adsorbent. [61] Conceivably, E ex is one of the important elements that should not be ignored in the charge transfer process.…”