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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. [ABSTRACT FROM AUTHOR]

Abstract Coronene as the smallest molecular approximation of polycyclic aromatic hydrocarbon (PAH) has large π-conjugated orbital. In the present work, under the action the external electric fields (E ext , perpendicular to molecular plane), the geometric structure of Coronene from plane to "bowl" and "curly". Interestingly, there is a redistribution of orbitals in E ext would give rise to significant effect on the NBO charge, which the main negative charge is gradually concentrated in the center-six-membered with the increasing E ext. The distinct charge transfer phenomenon brought about a remarkable nonlinear optical (NLO) property and changed the location of the main aromaticity. Surprisingly, the irregular phenomena of these properties would be happened in same E ext range: 5.00 × 10−2 to 6.00 × 10−2 au, which is respond to the structural change. We hope present work can provide a new strategy to design the high-performance electro-optical materials for large π-conjugated centrosymmetric system. Graphical abstract Image 1 Highlights • The geometry of Coronene under E ext is from plane to "bowl" and further to "curly". • Redistribution of orbitals in E ext would result in a negative charge that was gradually concentrated in center-six-membered. • The distinct charge transfer phenomenon brought a remarkable NLO property and changed the location of the main aromaticity. [ABSTRACT FROM AUTHOR]

[Display omitted] • Based on the π-conjugated DHTPs, four isomers (1 – 4) with D(–NH 2)-π(DHTPs)-A(–NO 2) framework are designed and characterized. • The change of hydrogen position on DHTPs bridge can affect their nonlinear optics (NLO) property. • The change of hydrogen position on DHTPs brings distinctive changes in NICS, NPA charge, UV–vis absorption spectrum, etc. The donor-π-conjugated bridge-acceptor (D-π-A) is a classical framework to design high-performance organic electro-optical materials. In this work, based on the π-conjugated dihydrotetraazapentacenes (DHTPs), four isomers (1 – 4) with D(–NH 2)-π(DHTPs)-A(–NO 2) framework are designed and characterized. The 2 and 3 originate from single-hydrogen migration of 1 , and 4 derives from double-hydrogen migration of 1. Significantly, the change of hydrogen position on DHTPs bridge can affect their nonlinear optics (NLO) property. Compared with the first hyperpolarizability (β tot) (4.08 × 103a.u.) of 1 , the 6.90 × 103-2.56 × 104 a.u. of 2 – 4 are enhanced. More interestingly, the 4 has largest β tot value of 2.56 × 104, which is approximately equal to the sum of 6.90 × 103 a.u. of 2 and 1.82 × 104 a.u. of 3. Furthermore, the change of hydrogen position on DHTPs brings some distinctive changes in their geometric structure, nucleus-independent chemical shifts (NICS) value, natural population analysis (NPA) charge, UV–vis absorption spectrum along with its other electronic property that might be beneficial to explore their structure–property relationships. [ABSTRACT FROM AUTHOR]

Molecular machines were attractive for scientists due to their excellent dynamical properties and potential applications. Inspired by the feature of molecular machine, we designed an ideal unscrewing process of double-chain sexipyridine complex with four conformations and explored the variation of stability and optical properties. As a result, we found the double helices where the fragments bound by only weak π-π interaction had poor stability. Thus the conformation with stronger π-π interaction was more stable than others. But this could be changed by adding alkali metals, and different alkali metal atoms such as Li and Na could control the stability order because of their different atomic radii. For Li-doped molecules, Li-1 with tightly coiled strands was the most stable conformation. While for Na-doped molecules, Na-4 with unscrewed fragments was the most stable one. This mainly resulted from the intra-molecular interaction potential energy especially the interaction between metal and ligand. At the same time, the charge distribution showed corresponding variation. In the aspect of optical properties, the unscrewing process was followed by the variation of absorption intensity at about 500 nm in the UV–Vis absorption spectra because of the conformation change. Meanwhile, the first-order static hyperpolarizability (β tot) showed zigzag variation due to the change of frontier molecular orbital energy gap in the unscrewing process. Image 1 • Double-strand pyridine helix was designed with different conformation. • The stability order of isomers related to the sizes of introduced Li and Na. • NLO property showed zigzag curve in the unscrewing process. • New peak appeared in UV–Vis absorption spectra in the unscrewing process. [ABSTRACT FROM AUTHOR]