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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]

Carbon-boron-nitride heteronanotubes have attracted much interest owing to their adjustable properties and wide applications in many fields. In this work, the structures and first hyperpolarizabilities ( β0) of a series of HA- n and isoelectronic PA- n heteronanotubes are investigated, in which HA- n is composed of a helical C segment and BN segment, and PA- n is composed of an arc C segment and BN segment. Interestingly, the helix C segment in HA-9 leads to a fascinating long-range charge-transfer character. As a result, the β0 value of HA-9 is 1.80×104 a.u., which is much larger than that of PA-9 (4.99×103 a.u.). Significantly, the β0 value of the C segment in HA-9 is 1.72×104 a.u., whereas that of the BN segment in HA-9 is much smaller (7.48×102 a.u.). In this context, the larger β0 value of HA-9 is essentially induced by the helix topological effect of the C segment. It is our expectation that this new knowledge about heteronanotubes might provide more ideas for further exploration of sp2-hybridized carbon segments with special topologies. [ABSTRACT FROM AUTHOR]

In this work, we add different strength of external electric field ( Eext) along molecule axis (Z-axis) to investigate the electric field induced effect on HArF structure. The H-Ar bond is the shortest at Eext = −189 × 10−4 and the Ar-F bond show shortest value at Eext = 185 × 10−4 au. Furthermore, the wiberg bond index analyses show that with the variation of HArF structure, the covalent bond H-Ar shows downtrend (ranging from0.79 to 0.69) and ionic bond Ar-F shows uptrend (ranging from 0.04 to 0.17). Interestingly, the natural bond orbital analyses show that the charges of F atom range from −0.961 to −0.771 and the charges of H atoms range from 0.402 to 0.246. Due to weakened charge transfer, the first hyperpolarizability (βtot) can be modulated from 4078 to 1087 au. On the other hand, make our results more useful to experimentalists, the frequency-dependent first hyperpolarizabilities were investigated by the coupled perturbed Hartree-Fork method. We hope that this work may offer a new idea for application of noble-gas hydrides. © 2013 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

The unusual properties of species with excess electrons have attracted a lot of interest in recent years due to their wide applications in many promising fields. In this work, we find that the excess electron could be effectively bound by the B atoms of boron nitride nanotube (BNNT), which is inverted pyramidally distributed from B-rich edge to N-rich edge. Further, Li@ B-BNNT and Li@ N-BNNT are designed by doping the Li atom to the two edges of BNNT, respectively. Because of the interaction between the Li atom and BNNT, the 2s valence electron of Li becomes a loosely bound excess electron. Interestingly, the distribution of the excess electron in Li@ N-BNNT is more diffuse and pyramidal from B-rich edge to N-rich edge, which is fascinating compared with Li@ B-BNNT. Correspondingly, the transition energy of Li@ N-BNNT is 0.99 eV, which is obviously smaller than 2.65 eV of Li@ B-BNNT. As a result, the first hyperpolarizability (3.40×104 a.u.) of Li@ N-BNNT is dramatically larger (25 times) than 1.35×103 a.u. of Li@ B-BNNT. Significantly, we find that the pyramidal distribution of the excess electron is the key factor to determine the first hyperpolarizability, which reveals useful information for scientists to develop new electro-optic applications of BNNTs. [ABSTRACT FROM AUTHOR]

Significant alkali-metal-doped effects on the structure and the first hyperpolarizability ( β) of effective multi-nitrogen complexant tris[(2-imidazolyl)methyl]amine (TIMA) are investigated. Three imidazoles of TIMA like three blades of propeller connect with methyls by the C-C single bonds. Because of the three C-C single-bond cooperative rotations, the TIMA behaves with great flexibility, and it is a high-performance multi-nitrogen complexant for the alkali metal doping. Thus, the new complexes A-TIMA (A = Li, Na, and K) with electride characteristic have diffuse excess electron than the reported electride-type system due to the strong interaction between the complexant TIMA and alkali metal. For the first hyperpolarizability, three engaging electrides A-TIMA with the diffuse excess electrons exhibit considerably large β values using the MP2 (full) method and the β values of new electrides are greatly larger (3,464-29,705 times) than that (338 au) of TIMA. Surprisingly, the K-TIMA sets a new record β value to be 1.00 × 10 au which far exceeds than that (3,694-76,978 au) of the reported electride-type system Li@calix[4]pyrrole (J Am Chem Soc 127:10977-10981, ) and Li−H−(CF−CH)−H ( n = 1, 2) (J Am Chem Soc 129:2967-2970, ) and 31,123 au of the organometallic system (J Am Chem Soc 121:4047-4053, ) Ru(trans-4,4′-diethylaminostyryl-2,2′-bipyridine), as well as 1.23 × 10 au of the large donor-CNT systems (Nano Lett 8:2814-2818, ). Clearly, the alkali-metal-doped effect on the first hyperpolarizability is very dramatic for the high-performance multi-nitrogen complexant TIMA. Considering simple possibility from molecule to material, the β values of optimized Li-TIMA-dimer and Li-TIMA-tetramer are investigated by BHandHLYP method. Interestingly, results show that the order of β value is Li-TIMA-monomer < Li-TIMA-dimer < Li-TIMA-tetramer. So the new three-propeller-blade-shaped electrides can be considered as candidates for high-performance nonlinear optical materials. [ABSTRACT FROM AUTHOR]