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Quantum Mechanics of Graphene
Published in Andre U. Sokolnikov, Graphene for Defense and Security, 2017
There are two wavefunctions and φ=0 is at a dimer position. The origin φ is shifted in the middle of the distance between two carbon atoms by the angle of 30°. A “dimer” is oligomer that consists of two monomers similar in structure. A dimer can be weak, strong, covalent or intermolecular. Oligomer is term that describes a molecular complex that consists of a few monomers. Oligomer is a counterpart of a polymer, for which the number of monomers (as constituents) is not limited.
Control of Magnetism and Conduction in Organic Materials by Light
Published in Toshio Naito, Functional Materials, 2019
The conductivity and magnetic susceptibility of [Ru(bpy)3] [Ni(dmit)2]2 shown in Fig. 1.3 depend on temperature. Note that every two [Ni(dmit)2]− anions are particularly close to each other and face each other in Fig. 1.3. There is an unpaired electron on each of the [Ni(dmit)2]− anions. Yet, due to strong antiferromagnetic interaction between them, unpaired electrons on the neighboring [Ni(dmit)2]− anions make a pair as if they have formed a weak covalent bond between them. This kind of intermolecular interaction leads to a molecular pair often called a dimer in the research fields of molecular conductors and magnets. Note that the term “dimer” in general chemistry formally means a single molecule comprising originally two independent molecules covalently bonded with each other. In other words, the unpaired electrons cannot move as carriers in this solid state. In their ground state, that is, at ~0 K, all the [Ni(dmit)2]− dimers practically possess no unpaired electrons. Neither do the [Ru(bpy)3]2+ cations at any temperature. At a finite temperature, the unpaired electrons receive energy as heat from their surroundings and some are excited to behave like unpaired electrons. With increasing temperature, an increasing number of pairs break into unpaired electrons. The resultant unpaired electrons still cannot move so freely but can serve as carriers to produce semiconducting properties. They have also magnetic moments called spins, which exhibit magnetism. In this way, [Ru(bpy)3][Ni(dmit)2]2 exhibits temperature-dependent conducting and magnetic properties and behaves as a diamagnetic insulator in the ground state.
Chemical bond analysis for the entire periodic table: energy decomposition and natural orbitals for chemical valence in the four-component relativistic framework
Published in Molecular Physics, 2023
Diego Sorbelli, Paola Belanzoni, Loriano Storchi, Olivia Bizzarri, Beatrice Bizzarri, Edoardo Mosconi, Leonardo Belpassi
As we have mentioned above, we have tested the validity of our new implementation on two simple cases: (i) hydrogen bond in water dimer and (ii) coordination bond in the Ag-alkyne system, where relativity effects (and in particular the spin-orbit coupling) are assumed to play a negligible or marginal role. After giving all relevant computational details in Section 3.1, we will present our results in comparison with those obtained using the ADF Modelling Suite [83]. We then apply the EDA-NOCV scheme on a series of complexes of group 6 elements, namely (CO)TM-CH, with TM =Cr, Mo, W, Sg, where the relativistic effects play an increasingly important role going down the group.
Synthesis and phase behavior of Y-shaped Schiff base liquid crystal oligomers
Published in Liquid Crystals, 2023
Zi-Yun Zhang, Jiang-Tao Sun, Yi-Min Wang, Zhong-Xin Ge, Ying-Gang Jia, Mei Tian, Dan-Shu Yao
In order to further determine the liquid crystal phase, the X-ray diffraction test was performed and the representative XRD pattern of MeOYP is shown in Figure 4. The XRD pattern of MeOYP obtained from the quenched sample at 150.0°C, confirming the existence of smectic phase. The pattern showed sharp and diffuse Bragg reflections in the low-angle and wide-angle regions (around 2θ = 2.9° and 2θ = 20.5°), respectively, indicating smectic phase arrangement. The XRD pattern of MeOYP obtained on cooling at 115°C only showed a diffuse wide-angle peak (around 2θ = 19.5°), with no diffraction peaks in the low-angle. In general, hydrogen bond made the carboxylic acid exist as the dimer [44,45]. It stabilised the behaviour of liquid crystals, had strong intermolecular force between molecules, and promoted the orderly arrangement of molecules. The texture change and XRD pattern of ClYP was similar to that of MeOYP. Combined with POM and X-ray diffraction, MeOYP and ClYP showed smectic phase at heating and nematic phase at cooling, respectively. Observation of MeYP from POM showed that when the sample was heated up to 176.7°C, the sample changed directly from melting to isotropic state. When the sample was cooled down to 96.1°C, it crystallised immediately. This indicated that MeYP did not belong to liquid crystal.
The influence of the structure of terminal groups and cores on the properties of schiff base star-shaped liquid crystals
Published in Liquid Crystals, 2021
Qing-Qing He, Yue Lan, Yuan-Yuan Quan, Chun-Yang Li, Ya-Ping Liu, Xin-Jiao Wang, Ying-Gang Jia, Mei Tian, Dan-Shu Yao
MeOSBAA, for example, when MeOSBAA was heat to that melting temperature, mosaic texture appeared. The texture did not disappear until the isotropic change of the sample occurred at 160.0°C. On cooling, the schlieren texture appeared at 107.4°C and disappeared at 100.9°C. The XRD patterns of MeOSBAA showed sharp and diffuse Bragg reflections in the low angle and wide-angle regions, respectively, suggesting smectic phase arrangement. In general, hydrogen bond made the carboxylic acid exist as the dimer [15]. The representative XRD pattern is shown in Figure 5. It stabilised the behaviour of the liquid crystal. There was a strong intermolecular force between molecules, which promotes the orderly arrangement of molecules. Combined with POM and X-ray diffraction, it was found that MeOSBAA and ClSBAA exhibited smectic phase at heating and nematic phase at cooling, respectively. Observation of MeSBAA from POM showed that when the sample was heated up to 176.7 oC, the sample changed directly from melting to isotropy. When the sample was cooled down to 95.3 oC, it crystallised immediately. This indicated that MeSBAA had no liquid crystal properties consistent with DSC transformation.