Fang Ma

Theoretical investigation on nonlinear optical properties of carbon nanotubes with Stone–Wales defect rings

Based on (6, 0) zigzag carbon nanotubes (ZCNTs), a Stone–Wales defect ring ([5.7]3) is constructed at one end of the ZCNTs, forming a novel nanostructure [5.7]3ZCNT. The introduction of [5.7]3 breaks the centrosymmetry of the nanotube and remarkably changes electronic and magnetic properties of the nanotube. Unlike the (6, 0)ZCNT which has an open-shell singlet ground state, the [5.7]3ZCNT has a closed-shell singlet ground state with a large dipole moment, polarizability, and first hyperpolarizability. Interestingly, the [5.7]3ZCNT itself has a donor–π–acceptor framework, in which the Stone–Wales defect ring serves as an electron donor (D) while the zigzag nanotube works as an electron acceptor (A) and a conjugated bridge (π). Moreover, increasing both the tube diameter and tube length could enhance second-order nonlinear optical (NLO) responses, with the former being more effective than the latter.

Li2 trapped inside tubiform [n] boron nitride clusters (n=4-8): structures and first hyperpolarizability.

The geometries and electronic properties of tubiform [n] boron nitride clusters entrapping Li(2) (Li(2)@BN-cluster(n,0); n=4-8), obtained by doping BN-cluster(n,0) with Li(2) molecules, are investigated by means of DFT. The effects of tube diameter n on the dipole moment μ(0), static polarizability α(0), and first hyperpolarizability β(0) are elucidated. Both the dipole moment and polarizability increase with increasing tube diameter, whereas variation of the static first hyperpolarizability with tube diameter is not monotonic; β(0) follows the order 1612 (n=4)<3112 (n=5)<5534 (n=7)<8244 (n=6)<12,282 a.u. (n=8). In addition, the natural bond orbital (NBO) charges show that charge transfer takes place from the Li(2) molecule to the BN cluster, except for BN-cluster(8,0) with larger tube diameter. Since the large-diameter tubular BN-cluster(8,0) can trap the excess electrons of the Li(2) molecule, Li(2)@BN-cluster(8,0) can be considered to be a novel electride compound.

Theoretical investigation of boron-doped lithium clusters, BLin (n = 3–6), activating CO2: an example of the carboxylation of C–H bonds

This work reports the first example of boron-doped lithium clusters, BLin, activating CO2. The investigation shows that a kind of novel BLin–CO2 (n = 2–6) complex (In) with bidentate double oxygen M(η2-O2C) coordination is obtained through the bimetal 2Li of BLin clusters binding to the two O atoms of CO2, and the structural integrities of BLin clusters are not destroyed. We find that the partial negative charge transfer from BLin to the π* orbital of CO2 leads to weakening of the CO bonds of CO2 and an active CO2 moiety, except for when n = 2. Further, we perform reactions between In (n = 3–6) and benzene to elucidate a novel alternative approach to direct carboxylation by inserting CO2 into C–H bonds. We find that the carboxylation of the C–H bond of benzene can be achieved through the transition states (TS) of C–C bond formation and H-atom-transfer from C to O via two H2O molecules acting as a H-transfer tunnel. Comparing the transition states of H-direct transfer and one H2O molecule assisting H transfer, two H2O molecules assisting H-transfer as a tunnel is shown to lower the barrier, due to this long H-bond bridge effectively easing the rotation of the dihedral angle between the C6H6 and CO2 moiety planes. Considering the whole free energy profile, BLi5 and BLi6 clusters are more feasible for the carboxylation of C–H bonds.

A theoretical investigation of one-dimensional lithium-bonded chain: enhanced first hyperpolarizability and little red-shift

AbstractWe present a theoretical investigation of the electric properties of two kinds of one-dimensional lithium bonded chains: (NC-Li)n and (NC-CC-Li)n (n = 1–8). The resulting (NC-Li)n and (NC-CC-Li)n were found to exhibit enhanced first hyperpolarizabilities (β0) with increasing n, and a slight change in the absorption maximum wavelength λmax at the crucial transition. Comparing with (NC-Li)n, (NC-CC-Li)n exhibited particularly drastically enhanced β0 values due to clearly enhanced coupled oscillators and double-degenerated charge transitions. β0 is known to be the microscopic origin of the second-order non-linear optical (NLO) property, and λmax is an approximate measure of the transparency achievable, thus both are important indices of high-performance NLO molecules. Therefore, our investigations into one-dimensional lithium bond chains will be beneficial to understanding the relationship between β0 and λmax, thus aiding the design of one-dimensional NLO materials with excellent transparence-efficiency. Graphical abstractOne-dimensional lithium bond complexes (NC-Li)n and (NC-CC-Li)n showing the π-Li-bond-π interactions investigated. The resulting (NC-Li)n and (NC-CC-Li)n exhibited enhanced first hyperpolarizabilities (β0) with increasing n, and a slight change in the absorption maximum wavelength λmax at the crucial transition.

Excess-electron-induced C–C bond formation in transformation of carbon dioxide

This study presents a new fixation method of CO2 through excess-electron-induced C–C bond formation using quantum chemical method. Because of active CO2−˙ with a distinct radical character at the carbon center, two divalent anion complexes [O2C–C6H6–CO2]2− (cis-II and trans-II) are obtained via C–C bond formation between the carbon atom of C6H6 and the carbon atom of CO2 in the process of CO2−˙ radical attacking on benzene molecule. Furthermore, the transformations of cis-II and trans-II are predicted. We found that the more favorable transformation is for cis-II. It can produce terephthalic and one H2 molecule via two H-atom elimination with the energy barrier of 35.70 kcal mol−1. Furthermore, we found that the formed hydrogen bond complex CO2–HCN did not reduce the energy barrier; however, it could reduce the energy of the transition state with respect to that of the reactant, due to it dispersing the charge of benzene ring.

Designing nonlinear optical molecule by incorporating the planar tetracoordinate unit NAl4- or CAl42- into decaborane B10H14

Molecular Incorporation is an important approach of providing novel compounds with fascinating structures. In this paper, we theoretically described the incorporation of the central planar tetracoordinate molecules NAl4- or CAl42- into borane cluster B10H14. By molecular orbital analysis, a novel four-fold Al–H bonding interaction was found, and it contributes to the molecular incorporation. In addition, we found that the counterion Li+ is critical for the neutral incorporation species, due to its small atomic radii and little positive charge. To measure the nonlinear optical (NLO) response, the static first hyperpolarizabilities (β0) were evaluated at the second-order Moller–Plesset (MP2) level. The β0 values are 1708 a.u and 8682 a.u for [B10H14⋯NAl4]- and [B10H14⋯CAl4]2-, respectively, which indicates that the charge plays a significant role on deciding the value of β0. Moreover, it is different for the change of β0 value brought by counterion Li+. Li+ decreases the β0 value of [B10H14⋯CAl4]2-, while it increases the β0 value of [B10H14⋯NAl4]-, therein, the sandwich-like B10H14–Li–NAl4(I) exhibits considerable β0 value (31,253 a.u.). This reveals that it is possible to explore high-performance NLO materials based on suitable molecular incorporation. Besides, the present study is also expected to enrich the knowledge of the planar tetracoordinate carbon chemistry and boron chemistry.

Hydrogen-bond-directed-linking solving transparence-efficiency tradeoff in nonlinear optical molecule.

It is well known that settling transparency-efficiency tradeoff is important to design nonlinear optical (NLO) materials. In this work, we constructed one-dimensional polymeric cyanoacetylene (NCCCH)n by hydrogen-bond-directed-linking to understand this tradeoff from molecular level. Results show that the first hyperpolarizability of (NCCCH)n (n=2-8) gradually increased with the increase of n, and what is more important is that the red-shifts, associated with the increase of n, were very little. It is proposed that these polymeric structures possess double-degenerated charge transitions, which contribute to the hyperpolarizability in an additive fashion, and that the coupled oscillators are gradually improved, which lead to the increase of the first hyperpolarizability. Therefore, we propose the hydrogen-bond-directed-linking idea is helpful to develop the potential high-performance NLO materials.