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Helical bilayer nanographenes (HBNGs) possess a unique structure and versatile properties, which are of great interest in experimental and theoretical research. This study applied an external electric field to regulate the electronic properties of the HBNG with a helicene moiety length of [9] ([9]HBNG). The direction of the external electric field (Fz) is the positive z-axis along the nanographenes. Intriguingly, the interplanar angle of [9]HBNG is regulated under the Fz. Furthermore, molecular electrostatic potential (ESP) maps demonstrate that the Fz regulates charge distribution effectively. Notably, when Fz = 100 × 10−4 a.u., the highest occupied molecular orbital (HOMO) is primarily located on the lower nanographene, while the lowest unoccupied molecular orbital (LUMO) is concentrated on the upper nanographene. Remarkably, the Fz induces a substantial increase in the βtot values, ranging from 6.53 × 102 (Fz = 0 a.u.) to 1.26 × 104 a.u. (Fz = 100 × 10−4 a.u.). This study presents an efficient approach for developing high-performance nonlinear optical (NLO) materials through the application of external electric fields, with potential applications in NLO switch devices. [ABSTRACT FROM AUTHOR]

The helical structure is a classical framework to design high-performance organic electro-optical materials. In this work, the structure-property's relationships of helical tetraspirobenzene (1) and its oxidation (12+) and reduction (12–) products are explored. The results show that the redox brings some distinctive changes in their geometric structure and electronic property, which regulate the first hyperpolarisability (βtot). Among these structures, the 12– has the largest βtot value of 4.2 × 104, which is greatly larger than 2.0 × 102 a.u. of. 12+. Therefore, the reduction effect is more obvious than the oxidation effect. Furthermore, the UV-Vis absorption spectrum also proves this phenomenon: the oxidation product has a new red-shifted absorption peak (571 nm) and the reduction product has two new red-shifted absorption peaks (577 and 797 nm). We hope the present work can provide theoretical guidance for the search for high-performance nonlinear optical materials by using the redox effect. [ABSTRACT FROM AUTHOR]

A series of triangular nanorings, denoted BnN3–n-CPLY3 (n = 0, 1, 2, and 3), are designed by incorporating boron-/nitrogen-doped phenalenyl (B/N-PLY) units into cycloparaphenylene. These nanorings exhibit appropriate cavity size and shape complementarity to encapsulate fullerene (C60), resulting in the formation of supramolecular complexes termed BnN3–n-CPLY3@C60 (n = 0, 1, 2, 3). The geometric and electronic structures of nanorings and supramolecular complexes are investigated by density functional theory. Importantly, the self-assembly strategy effectively enhances the second-order nonlinear optical (NLO) response of the supramolecular complexes. The findings demonstrate that the first hyperpolarizabilities of BnN3–n-CPLY3@C60 (n = 0, 1, 2) are higher compared to that of B3-CPLY3@C60, which is attributed to the intra- and intermolecular charge transfer (CT) regulated by adjusting the amount of the B/N-PLY unit. By absorption spectrum analysis, the absorption peaks of BnN3–n-CPLY3@C60 (n = 0, 1, 2) are attributed to the host–guest interaction between BnN3–n-CPLY3 and C60. Furthermore, CT spectroscopy, main electron transition, and CT properties are studied to gain insights into the optical properties of BnN3–n-CPLY3@C60. This work not only emphasizes the importance of the B/N-PLY unit in supramolecular complexes to improve NLO properties but also shows that the BnN3–n-CPLY3@C60 complexes are important materials for optoelectronic applications. [ABSTRACT FROM AUTHOR]

Carbon nanohoop compounds have attracted extensive attention recently due to their aesthetically pleasing structures and unique properties. In order to reveal the structure–property relationship between the size-dependent effect and the nonlinear optical (NLO) response, a series of carbon nanohoops consisting of zigzag carbon nanotubes (CNTs), named D-CM2PnP-A (n = 4, 6, 8, 10, and 12), are systematically designed and investigated using density functional theory (DFT). Significantly, the first hyperpolarizability (βtot) of the system increases with the increasing structure size, which is primarily the result of the charge transfer transition. Subsequently, the major electronic transition changes from local excitation to charge transfer as the size of the structure increases, indicating that charge transfer becomes stronger significantly. Furthermore, a two-level model and the absorption spectrum can well explain the trend of the βtot value. In addition, the unit sphere representation (USR) and hyper-Rayleigh scattering (HRS) are used to further explain the nature of the second-order NLO response. More importantly, adding a π-bridge as an effective strategy further enhances the second-order NLO responses of the system. The relevant results are expected to provide a new perspective on the structure–NLO property correlation of donor (D)–conjugated bridge (π)–acceptor (A) type carbon nanohoops and theoretical guidance for the rational design and synthesis of fascinating carbon nanohoops as NLO materials. [ABSTRACT FROM AUTHOR]

Phenalenyl (PLY) and its derivatives could form one-dimensional π-aggregates through pancake π–π bonding, which would lead to exotic optoelectronic properties. We will highlight the key aspects of the PLY derivatives from the design strategies to exploration of the electronic properties. Here, we primarily construct alternating boron (B)- and nitrogen (N)-doped PLY π-aggregates: dimer[12], trimer[12-1], trimer[12-2], tetramer[12]2, pentamer[12]2-1, pentamer[12]2-2, and hexamer[12]3. The geometric and electronic structures show that the short intermolecular distances of the π-aggregates drive the formation of pancake π–π bonding. Significantly, the molecular structures show periodic changes in the π-aggregates, but the first hyperpolarizabilities (βtot) present unexpected changes, which are found to increase sharply with increasing even layer thickness due to intermolecular charge transfer. The βtot value of hexamer[12]3 (5.72 × 104 a.u.) is 6.4 times that of tetramer[12]2 (8.95 × 103 a.u.), and is 22.4 times that of dimer[12] (2.55 × 103 a.u.). Thus, constructing π-aggregates can significantly improve the second-order NLO response, which is mainly due to intermolecular charge transfer through pancake π–π bonding of the interlayers. [ABSTRACT FROM AUTHOR]

• FeN 2 -GN, CoN 2 -GN and NiN 2 -GN are designed and explored as eNRR catalysts. • CoN 2 -GN is investigated as the most promising candidate. • The improvement of the catalytic activity of CoN 2 -GN can be contributed to its confinement effects and appropriate space. • The curvature of the junctions helps the promotion of the selectivity of eNRR, where the 'neck' C atoms act as the H-activator to N 2. Exploring efficient and highly selective ammonia synthesis electrocatalysts can advance the development of both modern agriculture and industry. Graphene nanobuds (GN) feature both fullerene and graphene characteristics which inspires new design ideas of electrocatalysts for N 2 reduction reaction (NRR) to ammonia based on the novel GN with traditional Fe-, Co-, Ni-N 2 sites. Among these structures, CoN 2 -GN is investigated as the most promising candidate with a limiting potential of -0.83 V through a distal pathway. The excellent activity and selectivity for the eNRR can be attributed to synergistic effects originated from both confinement space of buds (fullerene fragment) and curvature of the junctions. Especially, acting as an H-activator to N 2 , the 'neck' C atoms in the GNs improve the selectivity significantly for eNRR and facilitate the subsequent processes. This research would greatly contribute to develop the novel, efficient, multi-component graphene-based eNRR catalysts. First principles calculations show that Co-N 2 sites incorporating on the graphene nanobuds (CoN 2 -GN) could act as a promising eNRR catalyst on account of synergistic effects from confinement and curvature of the junctions, where the 'neck' C atoms can act as H-activators to N 2. [Display omitted] [ABSTRACT FROM AUTHOR]

Endohedral open-cage fullerenes are one of the attractive types of fullerenes due to their interesting electronic properties which make it potentially promising for applications in molecular electronics. In this paper, a novel structure of Na + ···Cl - @C 50 N 5 H 5 with Na + inside the cavity and Cl - at the opening of the open-cage fullerene is designed to explore the chemical bonding and interaction between the open-cage fullerene system C 50 N 5 H 5 and NaCl salt. Further, the directional migration of Na + was achieved by applying an external electric field (EEF) along the X -axis. Notably, when the EEF ranges from -85 to -86 × 10 -4 au, Na + sharply approaches Cl - to regain its ionic bonding character. In addition, the Wiberg bond index, electron localization function topological analysis, and interaction energy ( E int ) of the structure under the effect of the EEF also experienced a series of interesting changes. We hope that this work will provide a new strategy for the design of innovative materials for molecular electronics.