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 (3.40×10(4) a.u.) of Li@N-BNNT is dramatically larger (25 times) than 1.35×10(3) 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.

A facile synthesis of cyclic aminodiborane (NH2B2H5, ADB) from ammonia borane (NH3·BH3, AB) and THF·BH3 has made it possible to determine its important characteristics. Ammonia diborane (NH3BH2(μ-H)BH3, AaDB) and aminoborane (NH2BH2, AoB) were identified as key intermediates in the formation of ADB. Elimination of molecular hydrogen occurred from an ion pair, [H2B(NH3) (THF)](+)[BH4](-). Protic-hydridic hydrogen scrambling was proved on the basis of analysis of the molecular hydrogen products, ADB and other reagents through (2)H NMR and MS, and it was proposed that the scrambling occurred as the ion pair reversibly formed a BH5-like intermediate, [(THF)BH2NH2](η(2)-H2)BH3. Loss of molecular hydrogen from the ion pair led to the formation of AoB, most of which was trapped by BH3 to form ADB with a small amount oligomerizing to (NH2BH2)n. Theoretical calculations showed the thermodynamic feasibility of the proposed intermediates and the activation processes. The structure of the ADB·THF complex was found from X-ray single crystal analysis to be a three-dimensional array of zigzag chains of ADB and THF, maintained by hydrogen and dihydrogen bonding. Room temperature exchange of terminal and bridge hydrogens in ADB was observed in THF solution, while such exchange was not observed in diethyl ether or toluene. Both experimental and theoretical results confirm that the B-H-B bridge in ADB is stronger than that in diborane (B2H6, DB). The B-H-B bridge is opened when ADB and NaH react to form sodium aminodiboronate, Na[NH2(BH3)2]. The structure of the sodium salt as its 18-crown-6 ether adduct was determined by X-ray single crystal analysis.

The studies of geometrical structures, thermal stabilities, redox properties, nonlinear responses and optoelectronic properties have been carried out on a series of novel ferrocenyl (Fc) chromophores with the view of assessing their switchable and tailorable second order nonlinear optics (NLO). The use of a constant Fc donor and a 4,4'-bipyridinium acceptor and varied conjugated bridges makes it possible to systematically determine the contribution of organic connectors to chromophore nonlinear optical activities. The structures reveal that both the reduction reactions and organic connectors have a significant influence on 4,4'-bipyridinium. The potential energy surface maps along with plots of reduced density gradient mirror the thermal stabilities of the Fc-based chromophores. The first and second reductions take place preferentially at the 4,4'-bipyridinium moieties. Significantly, the reduction processes result in the molecular switches with large NLO contrast varying from zero or very small to a large value. Moreover, time-dependent density functional theory results indicate that the absorption peaks are mainly attributed to Fc to 4,4'-bipyridinium charge transfer and the mixture of intramolecular charge transfer within the two respective 4,4'-bipyridinium moieties coupled with interlayer charge transfer between the two 4,4'-bipyridinium moieties. This provides us with comprehensive information on the effect of organic connectors on the NLO properties.

Organic molecules consisting of electron donor (D) and electron acceptor (A) subunits linked by π-conjugated bridge are promising building blocks for the thermally activated delayed fluorescence (TADF) and nonlinear optical...

An increasing number of scientists have focused on carbon−boron-nitride heteronanotubes because of their particularly adjustable properties, as shown in many fields. In this work, four isoelectronic models (BN-n, n = 1−4) were systematically investigated to explore the crucial factor for enhancing the static first hyperpolarizibility by doping the BN segment into the carbon nanotube (CNT) with differently connecting patterns. Theoretical results show that the N-connecting pattern might increase the contribution of the BN segment to the crucial transition states, which obviously increases the occupied orbital energy while the unoccupied orbital energy is slightly influenced. Correspondingly, the transition energy of BN-1 is smaller than that of BN-2. As a result, the static first hyperpolarizability of BN-1 is 1.05 × 10 4 au, which is remarkably larger than the 4.37 × 10 2 au of BN-2. The results indicate that, compared to the B-connecting pattern, the N-connecting pattern of the BN segment linking to the conjugated CNT segment is a more efficient way to enhance the first hyperpolarizability of heteronanotubes. It is our expectation that the new knowledge about the carbon−boron-nitride heteronanotubes could provide valuable information for scientists to develop the potential nonlinear optical nanomaterials by introducing BN segments into suitable positions of CNTs.