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.
An interesting biphenalenyl biradicaloid (IDPL) dimer consisting of both-middle superimposed phenalenyls and both-end nonsuperimposed phenalenyls has been synthesized, and has attracted intensive research interest due to its intra- and intermolecular interactions and semiconductive characteristics. It is significant that under regulation of the external electric field the directional charge transfer (CT) can produce attractive properties. In the present work, the structure and electronic properties of the IDPL dimer under an external electric field (along the horizontal Fx or the vertical Fz directions) are explored, and the following properties determined: (i) as the horizontal Fx increases, the intramolecular CT becomes larger, which induces the intermolecular CT of the IDPL dimer. (ii) In contrast, as the vertical Fz increases, the large intermolecular CT gives rise to the intramolecular CT of the IDPL dimer. (iii) More importantly, the external electric field effectively regulates and controls the first hyperpolarizability (βtot) of the IDPL dimer. Compared with the vertical Fz, the horizontal Fx induces a larger first hyperpolarizability (βtot = 5.48 × 105 a.u.). Furthermore, the application of a uniform external electric field (Fx,y,z) to the IDPL dimer was investigated to define the external electric field direction of the material application. The βtot values were increased with increasing of the uniform Fx,y,z. Our study provides an effective strategy for developing high-performance NLO materials by tuning the external electric field, and could be of significance for application in switch devices.
Phenalenyl π-dimer (PLY 2 ) has recently attracted intensive research interest due to its unique structure and binding characteristics (two-electron/12-center bonding). The directional transfer of electron or electron pair under the external electric field can produce a new structure with interesting properties. In the present work, we investigate for the first time the effect of the external electric field along the main molecule axis on PLY 2 . Two unpaired electrons between two layers are gradually shifted to the upper layer with increasing of the external electric field strength (F ext): the weaker the two-electron/12-center bonding, the stronger the electrostatic interaction between two layers. Significantly, a small increment of F ext makes a big difference: the interlayer distance in the PLY 2 is sharply elongated from 3.241 Å (F ext = 203 × 10–4 au) to 3.485 Å (F ext = 204 × 10–4 au), which leads to the two-electron/12-center bonding breaking at 204 × 10–4 au. Therefore, the F ext = 204 × 10–4 au is regarded as the critical electric field. In this case, the interaction between two layers in PLY 2 is exclusively governed by the electrostatic interaction. Besides this, the effect of the external electric field brings some distinctive changes in its diradical character (y 0), the Wiberg bond index (WBI), the interaction energy (E int), and the frontier molecular orbital (FMO) that can be used to explore the conversion between bonding and electrostatic interactions. This study can deepen the understanding for the effect of the external electric field on structures and electric properties for molecule and be an open a door for the discovery and development of new switching devices.
Based on s-indaceno [1,2,3-cd;5,6,7-c′d′]diphenalene (1) consisting of two phenalenyl moieties, the monomer 2 and its dimer 2 2 are designed by boron and nitrogen atoms substituting the central carbon atoms of phenalenyl moieties. Calculated energy decompose analysis (EDA) shows that the orbital interaction for 2 2 possesses a large attractive contribution of −18.31 kcal mol −1 , which is dominated by the π−π stacking interaction between the upper and the lower π-conjugated units. Interestingly, the natural population analysis (NPA) charge and the transition density matrix (TDM) show that both intramolecular charge transfer and intermolecular charge transfer (CT) exist in 2 2 . Further, the first hyperpolarizability (β tot = 4.56 × 10 4 au) of 2 with intramolecular CT is greatly larger than that of reported molecule 3 (5.45 × 10 3 au) with intermolecular CT. Significantly, 2 2 exhibits the largest β tot value to be 1.42 × 10 5 au, which is caused by combining the intra-and intermolecular CT transitions (β x = 1.40 × 10 5 au and β z = 2.27 × 10 4 au). Correspondingly, highest occupied molecular orbital (HOMO) → lowest unoccupied molecular orbital (LUMO) (intramolecular CT) in the low-energy electronic transition of 2 2 is 68%, while HOMO → LUMO + 1 (intermolecular CT) is 18%, which demonstrates that the intramolecular CT effect on the β tot value is stronger than the case of the intermolecular CT effect. The present work might provide rich insight into designing and developing potential second-order optical nonlinearity materials with inter-and intramolecular CT characters.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.