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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]

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]

Nonlinear optical (NLO) switches, especially multi-state NLO switches, have attracted much attention because of their applications in optical memory with multiple storage and nondestructive capacity. However, it is still a challenge to design new second-order NLO switch molecules with high first hyperpolarizability (β) contrasts. In this study, we theoretically investigated the second-order NLO property and second-order NLO switch effect of dimethyldihydropyrene photoswitch derivatives with a push–pull electronic structure during protonation. Remarkably, the quinoxaline acceptor-based systems have a larger β ratio contrast, demonstrating a simple "ON"–"OFF" NLO switch. Interestingly, the system with a pyridine acceptor and aniline donor showed a multi-state "ON"–"OFF"–"ON" NLO switch under light-triggered and pH-triggered transformations. Furthermore, the DFT and TDDFT calculations provided meaningful insights into their structure–property relationship. Specifically, a large second-order NLO response was displayed in the protonation of the acceptor, resulting from the production of a stronger electron push–pull structure, larger π-conjugation, and more obvious CT transition. However, a weak NLO response was observed upon the protonation of the donor because of inhibiting electron-donating ability, reducing the degree of π-conjugation and producing a predominant LE transition. We hope that the present work will provide a theoretical guide for the design of multifunctional organic materials based on the DHP core. [ABSTRACT FROM AUTHOR]

The electro-optical properties (nonlinear optical (NLO) and thermally activated delayed fluorescence (TADF) properties) of a negative T-type dihydropyrene (DHP)-cyclophanediene (CPD) photoswitch were studied systematically in this work. An interesting "seesaw" phenomenon between the two properties was revealed during the reversible process of configuration transformation between DHP and CPD derivatives. The DHP derivative "declines" due to a larger first hyperpolarizability β, while the CPD derivative "rises" because of a smaller singlet–triplet energy gap (ΔEST). The DHP derivative displays excellent NLO properties due to the extended π-conjugation, more planar molecular structure, lower transition energy and larger separate distributions of the first hyperpolarizability density. The CPD derivative has a smaller singlet–triplet energy gap (ΔEST) because of the obvious spatial separation of HOMO and LUMO. Notably, the CPD derivative shows potential TADF properties (vertical ΔEST < 0.1 eV) in a solid-state environment, which can be attributed to the fact that the dominant LE characteristics in the gas phase were switched to 1CT and 3CT in the polarizable environment. In addition, the substituents at positions (2, 7) of the DHP derivative are conducive to obtaining a greater NLO response. The substituents at positions (4, 9) of the CPD derivative can obtain a smaller ΔEST value. Introducing a polarizable environment is an effective method to improve electro-optical properties. Overall, we hope that the present work can provide a route towards the rational design of such a D–A system for novel functional electro-optical 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]

Density functional theory (DFT) calculations have been carried out to investigate two synthesized iridium(III) complexes with substituted Phbd (1-phenyl-2-(pyridin-2-yl)-1H-benzo[d]imidazole) and Crbd (9-(4-(2-(pyridin-2-yl)-1H-benzo[d]imidazol-1-yl)phenyl)-9H-carbazole) as ancillary ligands. The aim of this paper is to study the effect of the substituent on the geometrical structures, electronic and second-order nonlinear optical (NLO) properties, and UV-vis absorption spectra. It is found that the first hyperpolarizabilities can be easily modulated by the introduction of Phbd and Crbd units. The complex with Phbd possesses larger first hyperpolarizability values compared to the complex with Crbd as an ancillary ligand. Significantly, the changes in the first hyperpolarizabilities can be qualitatively explained by means of the charge transfer pattern. It is anticipated that the theoretical investigation of these iridium(III) complexes will be helpful for designing high performance and versatile NLO materials. [ABSTRACT FROM AUTHOR]

An external electric field (EEF), as a metal-free catalyst, catalyzing the Markovnikov hydrosilylation of styrene was studied for the first time. As compared to the field-free situation, the barrier height was almost halved upon the application of EEF with a field strength of 180 × 10−4 a.u. in the direction perpendicular to the "bond axis". Therefore, the use of EEF not only resolved the questions of the separation of homogeneous catalysts from the reaction mixture, but also facilitated the reaction by decreasing its barriers. Furthermore, we found that the lower the energy of the transition state (TSX) and the higher the energy of the HOMO of the reactant (R1′), the lower the barrier height of hydrosilylation. Hopefully, this study can provide guidance toward experiments involving an external electric field. [ABSTRACT FROM AUTHOR]

Generally, the hydroboration of benzonitrile produces B–N containing compounds. However, an unprecedented B–C bond may be formed in the presence of a suitable external electric field (EEF). In reactions of benzonitrile with borane, when the EEF is oriented parallel to the positive direction (N → C) of the N≡C bond, the barriers to Markovnikov hydroboration are decreased gradually, meaning the pathway for generating B–C bonds becomes more favorable. Accordingly, hydroboration could be influenced and its selectivity could be controlled by changing the magnitude and direction of an applied EEF. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Usually, the NICS values at 1.0 Å above the center serve as the NICS probe to estimate the aromaticity of planar or nearly planar π-conjugated molecules. How does one judge the aromaticity of hoop-shaped π-conjugated molecules? In this work, [6]8cyclacene and [16]trannulene are used as representative molecules to further study the aromaticity from a new research perspective by using the NICS values scan in three-dimensional space methodology. A huge difference of aromaticity has been observed in three-dimensional space through the method. The main ring current of [6]8cyclacene has been located on the stacked [16]trannulene, the distance of which is 0.8 Å to the edge. The main ring current of [16]trannulene has been located on the center cross-section, the distance of which is 1.4 Å to the edge. This demonstrates that the detailed NICS values scan method is more reasonable to describe the aromaticity than a single NICS value. The method is not only helpful in understanding the internal magnetic field structure of hoop-shaped π-conjugated molecules but also of other planar or spherical aromatic structures. In addition to this, the methodology successfully helps us to clearly understand the aromaticity of any point in three-dimensional space and confirm the main ring current position inside a molecule. [ABSTRACT FROM AUTHOR]

In this work, we applied an external electric field (F) to a biphenalenyl derivative (BN-PLY2) in the direction of the negative z-axis (F−z) and the positive z-axis (F+z), 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−z (F−z = 0 to −190 × 10−4) 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−z 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−z = −180 × 10−4 au (−9.26 × 109 V m−1). Moreover, when F+z is applied, the HOMO and HOMO−1 undergo orbital interchange in the π-dimer at F+z = 100/110 × 10−4 au. Significantly, the effect of the external electric field effectively regulates the first hyperpolarizabilities (βtot). When the F+z ranges from 0 to 140 × 10−4 au, the βtot values slightly decrease to 0 au. Note that, upon increasing F+z, the βtot values sharply increase to 6.67 × 103 au (F+z = 190 × 10−4 au). Furthermore, the evolutions of the absorption spectra under F might well explain the trend of βtot values. When the F+z ranges from 0 to 140 × 10−4 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+z = 140 to 190 × 10−4 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. [ABSTRACT FROM AUTHOR]

A series of diradical π-dimers 2 with interesting pancake-shaped 2e/24c π–π bonding character were designed and investigated based on the famous phenalenyl (PLY) π-dimer with 2e/12c π–π bonding character. The position of stronger interaction between two layers of radicals was found by the Wiberg bond index (WBI) maximum component. Further, the different contributions of the interaction energy were analyzed quantitatively by energy decomposition analysis (EDA). Among these new diradical π-dimers, 2180 has the smallest layer distance and the largest interaction between two layers of radicals. The unusual PLY analogues can provide new insights into the unique features of two-electron/multicenter (2e/mc) π–π bonding. [ABSTRACT FROM AUTHOR]

In the current work, a series of bithiopheneimide (BTI)-based D–A copolymers were investigated based on the reported PDTSBTI (1) to screen excellent molecules toward organic photovoltaic (OPV) donor materials. It is found that the PCE based on the proposed derivative 4, where the silicon atom is replaced with vinyl and cyano groups on the DTS unit, shows a 70 percent improvement by Scharber diagrams compared with its prototype 1. Then, the charge transfer dynamics of 1/PC71BM and 4/PC71BM were investigated, including the intermolecular charge transfer (inter-CT) and recombination (inter-CR) rates. The theoretical data demonstrate that the ratio kinter-CT/kinter-CR of 4/PC71BM heterojunction is about 1 × 105 times higher than that of 1/PC71BM. These results clearly reveal that the designed donor molecule 4 will be a promising candidate for high-performance OPV device. We expect that this work from electron processing at the D/A interface may provide a theoretical guideline for further optimization and design of organic copolymer donor materials. [ABSTRACT FROM AUTHOR]

Nonlinear optical (NLO) materials are the smartest materials of the era, and have the ability to generate new electromagnetic fields with changed frequencies, phases, and other physical properties. Recently, many cutting edge research reports have been focused on NLO materials especially on those which are composed of sp2 hybridized carbon nanostructures. As the carbon nanostructures are composed of abundant π-electrons and have significant delocalization, these are potential candidates for modern NLO materials. Generally, sp2 hybridized carbon nanostructures can be divided into zero-dimensional fullerenes, one-dimensional nanotubes and two-dimensional graphene nanoribbons and quantum dots etc. These dimensionally different carbon nanomaterials are promising candidates for a wide range of applications in next-generation nanotechnologies. In present feature article, we first briefly explain a theoretical structure–NLO property relationship based on perturbation theory and then elucidate the crucial factors to control the NLO responses. We put together the different random investigations of sp2 hybridized carbon nanostructures for NLO application by highlighting the importance of their several structural designs to tune NLO amplitudes. Furthermore, we make a comparative and updated analysis of the NLO properties of dimensionally different sp2 hybridized carbon nanomaterials i.e. fullerenes, carbon nanotubes, and graphene nanoribbons and quantum dots. Finally, we make a brief discussion about different aspects and opportunities to use the sp2 hybridized carbon nanomaterials as high performance NLO materials of the future. This review is a focused perspective based on different updated quantum chemical investigations about fullerenes, nanotubes and graphene nanoribbons and quantum dots for their possible use in nonlinear optical applications. [ABSTRACT FROM AUTHOR]

The anti-Markovnikov hydroamination reaction is considered to be a particular challenge, and one of the reactants, parent hydrazine, is also regarded as a troubling reagent. In this study, we first studied the hydrohydrazination of parent hydrazine via an effective and green catalyst-external electric field (EEF). The calculation results demonstrated that the anti-Markovnikov and Markovnikov pathways are competitive when there was no catalyst. EEF oriented along the negative direction of the X axis (F x ) accelerated the anti-Markovnikov addition reaction. Moreover, it lowered the barrier height of the first step by 16.0 kcal mol -1 (from 27.8 to 11.8 kcal mol -1 ) when the field strength was 180 (×10 -4 ) au. Under the same conditions, the Markovnikov reaction pathway was inhibited, which means that EEF achieved the specificity of hydrohydrazination. The solvents are favorable for the first step addition reaction, particularly the synergy between solvents and F x lowered the barrier heights by 8.3 (C 6 H 6 ) and 10.7 (DMSO) kcal mol -1 for an F x = -60 (×10 -4 ) au. Besides, the introduction of the electron-withdrawing substituent (trifluoromethyl) is also a good strategy to catalyze hydrohydrazination, while the electron-donating group (methoxy) is unfavorable., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Generally, the hydroboration of benzonitrile produces B-N containing compounds. However, an unprecedented B-C bond may be formed in the presence of a suitable external electric field (EEF). In reactions of benzonitrile with borane, when the EEF is oriented parallel to the positive direction (N → C) of the N[triple bond, length as m-dash]C bond, the barriers to Markovnikov hydroboration are decreased gradually, meaning the pathway for generating B-C bonds becomes more favorable. Accordingly, hydroboration could be influenced and its selectivity could be controlled by changing the magnitude and direction of an applied EEF.

Carbon-boron-nitride heteronanotubes (BNCNT) have attracted a lot of attention because of their adjustable properties and potential applications in many fields. In this work, a series of CA, PA and HA armchair BNCNT models were designed to explore their nonlinear optical (NLO) properties and provide physical insight into the structure-property relationships; CA, PA and HA represent the models that are obtained by doping the carbon segment into pristine boron nitride nanotube (BNNT) fragments circularly around the tube axis, parallel to the tube axis and helically to the tube axis, respectively. Results show that the first hyperpolarizability (β0) of an armchair BNCNT model is dramatically dependent on the connecting patterns of carbon with the boron nitride fragment. Significantly, the β0 value of PA-6 is 2.00 × 10(4) au, which is almost two orders of magnitude larger than those (6.07 × 10(2) and 1.55 × 10(2) au) of HA-6 and CA-6. In addition, the β0 values of PA and CA models increase with the increase in carbon proportion, whereas those of HA models show a different tendency. Further investigations on transition properties show that the curved charge transfer from N-connecting carbon atoms to B-connecting carbon atoms of PA models is essentially the origin of the big difference among these models. This new knowledge about armchair BNCNTs may provide important information for the design and preparation of advanced NLO nano-materials.

In the current work, a series of bithiopheneimide (BTI)-based D-A copolymers were investigated based on the reported PDTSBTI (1) to screen excellent molecules toward organic photovoltaic (OPV) donor materials. It is found that the PCE based on the proposed derivative 4, where the silicon atom is replaced with vinyl and cyano groups on the DTS unit, shows a 70 percent improvement by Scharber diagrams compared with its prototype 1. Then, the charge transfer dynamics of 1/PC71BM and 4/PC71BM were investigated, including the intermolecular charge transfer (inter-CT) and recombination (inter-CR) rates. The theoretical data demonstrate that the ratio kinter-CT/kinter-CR of 4/PC71BM heterojunction is about 1 × 10(5) times higher than that of 1/PC71BM. These results clearly reveal that the designed donor molecule 4 will be a promising candidate for high-performance OPV device. We expect that this work from electron processing at the D/A interface may provide a theoretical guideline for further optimization and design of organic copolymer donor materials.

Recently, the well-known phenalenyl radical π-dimer with its fascinating 2-electron/12-center (2e/12c) bond has attracted our attention. In this work, we designed two molecules, Li3OC13H9 () and BeF3C13H9 (). Interestingly, owing to the inductive effect of superatoms, an electron is transferred from Li3O to phenalenyl in , while an electron is transferred from phenalenyl to BeF3 in . Further, we employed and as building blocks to assemble two novel molecules with 2e/12c bonds: Li3O(C13H9)2BeF3 () and Li3O(C13H9)2BeF3 (). Remarkably, and with novel 2e/12c bonds exhibit a dramatic interlayer charge-transfer character, which results in a significant difference of dipole moments (Δμ: 2.6804 for and 3.8019 Debye for ) between the ground state and the crucial excited state. As a result, the static first hyperpolarizabilities (β0: 5154 for and 12 500 au for ) are considerably larger than the values of 347 for and 328 au for . It is our expectation that the results of the present work might provide beneficial information for further theoretical and experimental studies on the fascinating properties of molecules with interlayer charge-transfer character.

Recently, a new sulfide cluster fullerene, Sc2S@Cs (10528)-C72 containing two pairs of fused pentagons has been isolated and characterized (Chen et al., J. Am. Chem. Soc., 2012, 134, 7851). Inspired by this investigation, we propose a question: what properties will be influenced by the interaction between the encapsulated V-shaped polar molecule and C72? To answer this question, four encapsulated metallic fullerenes (EMFs) M2N@C72 (M = Sc or Y, N = S or O) along with pristine Cs-C72 (10528) were investigated by quantum chemistry methods. The results show that the Egap (3.01-3.14 eV) of M2N@C72 are significantly greater than that of pristine Cs-C72 (10528) (2.34 eV). This indicates that the stabilities of these EMFs increase by encapsulating the V-shaped polar molecule into the fullerene. Furthermore, the natural bond orbital (NBO) charge analysis indicates electron transfer from M2N to C72 cage, which plays a crucial role in enhancing first hyperpolarizability (βtot). The βtot follows the order of 1174 au (Y2O@C72) ≈ 1179 au (Sc2O@C72) > 886 au (Y2S@C72) ≈ 864 au (Sc2S@C72) > 355 au (C72). This indicates that the βtot of M2N@C72 is more remarkable than that of pristine Cs-C72 (10528) due to the induction effect of the encapsulated molecule. Compared with sulfide cluster fullerenes (Y2S@C72 and Sc2S@C72), oxide cluster fullerenes (Sc2O@C72 and Y2O@C72) show much larger βtot due to the small ionic radius and the large electronegativity of oxygen. In contrast, the metal element (scandium and yttrium) has a slight influence on the βtot. Thus, oxide cluster fullerenes are candidates to become promising nonlinear optical materials with higher performance.

Recently, two isomeric thiophene-fused benzocarborane derivatives Tb1 and Tb2 with different locations of sulfur atoms, labeled as 1, 4 and 6, 9 of the thiophene were synthesized by Morisaki (Chem.-Eur. J., 2012, 18, 11251-11257) and Barrere (Macromolecules, 2009, 42, 2981-2987), respectively. In the present work, natural bond orbital (NBO) analysis shows that after doping one lithium atom into the isomeric structures Tb1 and Tb2, the electrons transfer to different regions in Tb1 and Tb2. For Tb1-Li, the transferred electrons mainly locate at S1, C2, C3, and S4, but for Tb2-Li, the transferred electrons mainly locate at C2, C3, C7, and C8. Significantly, the charge distribution is a crucial factor influencing the static first hyperpolarizabilities for Tb1-Li and Tb2-Li. Furthermore, the βtot value of Tb1-Li is 6222 au, which is about 160 times larger than that of Tb1 (39 au). However, the βtot value of Tb2-Li (498 au) is only about 5 times larger than that of the corresponding Tb2 (91 au). It is our expectation that this work could provide useful information for the development of nonlinear optical materials based on carboranes.

Very recently, two novel Sc(3)NC-based cluster fullerenes Sc(3)NC@C(80) (Wang et. al. J. Am. Chem. Soc. 2010, 132, 16362) and Sc(3)NC@C(78) (Wu et. al. J. Phys. Chem. C 2011, 115, 23755) were prepared and characterized, respectively. Inspired by these findings, the possibility of encapsulating Sc(3)NC cluster in the C(84) fullerene is performed using density functional theory (DFT). Firstly, the isolated pentagon rule (IPR) D(2d) (23) C(84) fullerene is employed to encase the Sc(3)NC cluster: four possible endohedral metallofullerene isomers a-d are designed. The large binding energies (ranging from 163.7 to 210.0 kcal mol(-1)) indicate that the planar quinary cluster Sc(3)NC can be stably encapsulated in the C(84) (isomer 23) cage. Further, we consider the incorporation of Sc(3)NC into the non-IPR C(s) (51365) C(84) cage leading to isomer e and show the high stability of isomer e, which has a larger binding energy, larger HOMO-LUMO gap, higher adiabatic (vertical) ionization potential, and lower adiabatic (vertical) electron affinity than the former four Sc(3)NC@C(84) (isomer 23). Significantly, the predicted binding energy (294.2 kcal mol(-1)) of isomer e is even larger than that (289.2 and 277.7 kcal mol(-1), respectively) of the synthesized Sc(3)NC@C(80) and Sc(3)NC@C(78,) suggesting a considerable possibility for experimental realization. The (13)C NMR chemical shifts and Raman spectra of this a new endofullerene have been explored to assist future experimental characterization.

The interesting radical ion pair salts M(2)*(+)TCNQ*(-) (M=Li, Na, K) are a particular class of charge transfer complexes with excess electron. The ground states of these complexes are triplet. The C(2v) symmetry geometrical structures of the M(2)*(+)TCNQ*(-) (M=Li, Na, K) with all-real frequencies are obtained at the density functional theory (DFT) B3LYP/6-31+G(d) level. All calculations of electric properties in this paper have been carried out at the restricted open-shell second order Møller-Plesset perturbation theory (ROMP2) level. Owing to existing excess electron (from the polarized alkali metal atoms) these charge transfer complexes exhibit large nonlinear optical (NLO) responses dominated by excess electron transitions.For these radical ion pair salts M(2)*(+)TCNQ*(-), the static first hyperpolarizabilities (beta(0)) are large. The order of beta(0) values is 19 203 (M=Li)<24 140 (M=Na) < 29 065 a.u. (M=K). Specially, the second hyperpolarizability (gamma(0)) of the complexes with excess electron is obtained for the first time. These static second hyperpolarizabilities are also large. The order of gamma(0) values is 2,213,006 (M=Li)<3,136,754 (M=Na)<7,905,623 a.u. (M = K). Among the three structures, K(2)*(+)TCNQ*(-) has the largest gamma(0) value to be 7.9 x 10(6) a.u. (3982 x 10(-36) esu), which is about 9 times larger than that of the intramolecular charge transfer complex sigma-arylvinylidene trans-[Ru(4-C[double bond, length as m-dash]CHC(6)H(4)C[triple bond, length as m-dash]CC(6)H(4)NO(2))Cl(dppm)(2)]PF(6) [Hurst et al., Organometallics, 2001, 20, 4664]. The present investigation provides a new kind of candidates for the high-performance NLO materials.