Feng-Wei Gao

Two-electron/24-center (2e/24c) bonding in novel diradical π-dimers

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.

Charge transfer and first hyperpolarizability: cage-like radicals C59X and lithium encapsulated Li@C59X (X=B, N).

Very recently, two new cage-like radicals (C59B and C59N) formed by a boron or nitrogen atom substituting one carbon atom of C60 were synthesized and characterized. In order to explore the structure–property relationships of combination the cage-like radical and alkali metal, the endohedral Li@C59B and Li@C59N are designed by lithium (Li) atom encapsulated into the cage-like radicals C59B and C59N. Further, the structures, natural bond orbital (NBO) charges, and nonlinear optical (NLO) responses of C59B, C59N, Li@C59B, and Li@C59N were investigated by quantum chemical method. Three density functional methods (BHandHLYP, CAM-B3LYP, and M05-2X) were employed to estimate their first hyperpolarizabilities (βtot) and obtained the same trend in the βtot value. The βtot values by BHandHLYP functional of the pure cage-like radicals C59B (1.30 × 103 au) and C59N (1.70 × 103 au) are close to each other. Interestingly, when one Li atom encapsulated into the electron-rich radical C59N, the βtot value of the Li@C59N increases to 2.46 × 103 au. However, when one Li atom encapsulated into the electron-deficient radical C59B, the βtot value of the Li@C59B sharply decreases to 1.54 × 102 au. The natural bond orbital analysis indicates that the encapsulated Li atom leads to an obvious charge transfer and valence electrons distribution plays a significant role in the βtot value. Further, frontier molecular orbital explains that the interesting charge transfer between the encapsulated Li atom and cage-like radicals (C59B and C59N) leads to differences in the βtot value. It is our expectation that this work will provide useful information for the design of high-performance NLO materials.

Transition metals doped fullerenes: structures – NLO property relationships

ABSTRACT In this work, three complexes C59Co, C59Rh and C59Ir are devised by the transition metals (Co, Rh and Ir) doped into fullerenes to study the structure–property relationships of the heterofullerenes. Results show that the natural population analysis (NPA) revealed substituting one carbon atom arouse an apparent charge transfer, which can be proved by the strong electron density transfer from SOMO to LUMO. Significantly, the first hyperpolarisability (βtot) were investigated by BHandHLYP and CAM-B3LYP and got the same trend in βtot value: C59Ir > C59Rh > C59Co. Further, two-level expression was also provided to test the βtot values of C59Co, C59Rh and C59Ir. We hope our work can offer a new idea for designing high-performance NLO materials based on metal-doped fullerene. Density function theory can provide a precise calculation on the first hyperpolarisability of metal-doped fullerenes. In this work, compared to traditional fullerene, transition metal-doped fullerenes show spectacular NLO response, the three heterofullerenes: C59Co, C59Rh and C59Ir are designed to explore NLO materials. This article takes a look at initial reasons why they possess evident first hyperpolarisabilities and outlines a step to keep research on new NLO materials. GRAPHICAL ABSTRACT

Constructing Stable π-Dimers: Two Parallel Pancake π-π Bonds

Stable phenalenyl (PLY) radical π-dimers still play an important role for new multifunctional materials owing to their intriguing molecular structure and unusual pancake π-π bonding mode. Herein, we design a new biphenalenyl biradicaloid (1) consisting of two PLYs and one benzene ring linkage tethered by single bonds, which presents an open-shell character. Further, three π-dimers (a1, b1, and c1) combined with 1 and conventional biphenalenyl biradicaloid (a, b, and c), which are capable of forming two staggered PLY dimers, exhibiting a short interlayer distance between the monomers. Interestingly, the analysis of the frontier molecular orbital reveals that two bonding orbitals, namely, the two highest occupied molecular orbitals (HOMO and HOMO-1) are doubly occupied. The results reveal that three π-dimers display two parallel pancake bonds. Moreover, they have small diradical and tetraradical characters, large interaction energies, and strong aromaticity, which indicate the stability of these π-dimers. The present work creates a new class of strong pancake bonding and might be utilized in devising an array of materials.

The inner-induced effects of YCN in C76 on the structures and nonlinear optical properties

Very recently, an unprecedented novel monometallic cluster of fullerenes entrapping a yttrium cyanide (YCN) cluster inside a popular C82 cage YCN@Cs(6)-C82 was synthesized and characterized. Inspired by this investigation, four non-IPR YCN@C1(17459)-C76, YCN@C2v(19138)-C76, YCN@C2(17646)-C76, and YCN@C1(17894)-C76 (1, 2, 3, and 4) containing a pair of adjacent pentagons are designed to explore the encapsulated molecular effect on their interaction energies and nonlinear optical properties. The interaction energy (Eint) values of 1, 2, 3, and 4 are −481.35 (1), −477.91 (2), −482.04 (3), −482.69 (4) kcal mol−1, respectively, which shows that the Eint value of 4 is the largest. Furthermore, the electron-transfer is mainly from the YCN to C76 cage. When YCN is encapsulated into C76 cage, we can find that the α0 values of the four molecules are very close, ranging from 6.50 × 102 to 6.65 × 102 au. Significantly, the first hyperpolarizabilities are in relation to the encapsulated molecular: 1.63 × 103 (1) > 8.03 × 102 (2) > 7.76 × 102 (4) > 4.86 × 102 au (3), the results show that the βtot value of 1 is the largest. Besides this, the encapsulation of the YCN to C76 cage brings some distinctive changes in its UV–vis spectra along with its other electronic properties that might be used by the experimentalists to develop the potential nonlinear optical nanomaterials based on endohedral metallofullerenes.