Highly enantioselective construction of tertiary thioethers and alcohols via phosphine-catalyzed asymmetric γ-addition reactions of 5H-thiazol-4-ones and 5H-oxazol-4-ones: scope and mechanistic understandings

Phosphine-catalyzed highly enantioselective γ-additions of 5H-thiazol-4-ones and 5H-oxazol-4-ones to allenoates have been developed for the first time. With the employment of amino-acid derived bifunctional phosphines, a wide range of substituted 5H-thiazol-4-one and 5H-oxazol-4-one derivatives bearing heteroatom (S or O)-containing tertiary chiral centers were constructed in high yields and excellent enantioselectivities. The reported method provides facile access to enantioenriched tertiary thioethers/alcohols. The mechanism of the γ-addition reaction was investigated by performing DFT calculations, and the hydrogen bonding interactions between the Brønsted acid moiety of the phosphine catalysts and the “CO” unit of the donor molecules were shown to be crucial in asymmetric induction.     

Computational analysis of liquid crystalline elastomer membranes: Changing Gaussian curvature without stretch energy

Liquid crystalline elastomers (LCEs) can undergo extremely large reversible shape changes when exposed to external stimuli, such as mechanical deformations, heating or illumination. The deformation of LCEs result from a combination of directional reorientation of the nematic director and entropic elasticity. In this paper, we study the energetics of initially flat, thin LCE membranes by stress driven reorientation of the nematic director. The energy functional used in the variational formulation includes contributions depending on the deformation gradient and the second gradient of the deformation. The deformation gradient models the in-plane stretching of the membrane. The second gradient regularises the non-convex membrane energy functional so that infinitely fine in-plane microstructures and infinitely fine out-of-plane membrane wrinkling are penalised. For a specific example, our computational results show that a non-developable surface can be generated from an initially flat sheet at cost of only energy terms resulting from the second gradients. That is, Gaussian curvature can be generated in LCE membranes without the cost of stretch energy in contrast to conventional materials.     

Multiple‐Stimulus‐Responsive Supramolecular Gels of Two Components and Dual Chiroptical Switches

A new class of L ‐glutamic gelators, LG₁₂(CH₂)_nCOOH, containing different lengths of methylene spacer were synthesized. It was found that the gelation ability of these compounds themselves was very weak. However, when another compound, p‐xylylenediamine (XEA), was introduced, the gelation ability was improved greatly. In particular, LG₁₂(CH₂)₁₀COOH showed super‐gelation ability in the presence of XEA, which could immobilize almost all of the solvents except methanol. Moreover, the formed supramolecular gels even could be molded. Interestingly, some supramolecular gels of LG₁₂(CH₂)_nCOOH and XEA could respond to multiple stimuli, such as heating, shaking, sonication, and acid/base. The studies of CD spectra suggested that the supramolecular chirality induced by self‐assembled chiral gelator molecules in gels could be tuned by the length of methylene spacer. In addition, the supramolecular chirality could be regulated as on/off by heating–cooling or external NH₃/HCl. This would facilitate the development of dual chiroptical switches by temperature and acid/base.     

Visible-Light-Induced Vicinal Dichlorination of Alkenes through LMCT Excitation of CuCl2

This work demonstrates photoredox vicinal dichlorination of alkenes, based on the homolysis of CuCl₂ in response to irradiation with visible light. This catalysis proceeds via a ligand to metal charge transfer process and provides an exciting opportunity for the synthesis of 1,2-dichloride compounds using an inexpensive, low-molecular-weight chlorine source. This new process exhibits a wide substrate scope, excellent functional group tolerance, extraordinarily mild conditions and does not require external ligands. Mechanistic studies show that the ready formation of chlorine atom radicals is responsible for the facile formation of C−Cl bonds in this synthetic process.     

Ultra-high Tg and ultra-low coefficient of thermal expansion polyimide films based on hydrogen bond interaction

To tolerate high processing temperature during the fabrication of low-temperature polycrystalline silicon thin-film transistors (LTPS–TFT) in flexible OLED devices, the polyimide (PI) films, which are used as substrate, should have ultra-high glass transition temperature (T_g > 450°C) and ultra-low coefficient of thermal expansion (CTE at 0–5 ppm K⁻¹). In this paper, two novel heterocyclic monomers, namely, N,N'-(xanthone-2,7-diyl)bis(4-aminobenzamide) (p-DAXBA) and N,N'-(xanthone-2,7-diyl)bis(3-aminobenzamide) (m-DAXBA), which contain a xanthone moiety, are prepared and polycondensed with pyromellitic dianhydride (PMDA), respectively. PI films (PIa and PIb) with intrinsic high T_g and low CTE are designed from the perspective of rigid conjugate xanthone structure and hydrogen bonding interaction. It is found that the PIa films prepared by p-DAXBA have better linear structure of molecular chains and show relatively higher T_g and lower CTE. The T_g of PIa-40 is greater than 450°C, and CTE can reach as low as 2.7 ppm K⁻¹, tensile strength of 179 MPa, modulus of 5.67 GPa, indicating potential application prospect as a flexible OLED substrate.     

Twisted bounded-dilation group C*-algebras as C*-metric algebras

We construct a class of C~*-metric algebras. We prove that for a discrete group Γ with a 2-cocycle σ,the closure of the seminorm ||[M?, ·]|| on Cc(Γ, σ) is a Leibniz Lip-norm on the twisted reduced group C~*-algebra C*r(Γ, σ) for the pointwise multiplication operator M?on ?2(Γ), induced by a proper length function ? on Γ with the property of bounded θ-dilation. Moreover, the compact quantum metric space structures depend only on the cohomology class of 2-cocycles in the Lipschitz isometric sense.