Cheng-Hui Li

A highly stretchable autonomous self-healing elastomer

It is a challenge to synthesize materials that possess the properties of biological muscles-strong, elastic and capable of self-healing. Herein we report a network of poly(dimethylsiloxane) polymer chains crosslinked by coordination complexes that combines high stretchability, high dielectric strength, autonomous self-healing and mechanical actuation. The healing process can take place at a temperature as low as -20 °C and is not significantly affected by surface ageing and moisture. The crosslinking complexes used consist of 2,6-pyridinedicarboxamide ligands that coordinate to Fe(III) centres through three different interactions: a strong pyridyl-iron one, and two weaker carboxamido-iron ones through both the nitrogen and oxygen atoms of the carboxamide groups. As a result, the iron-ligand bonds can readily break and re-form while the iron centres still remain attached to the ligands through the stronger interaction with the pyridyl ring, which enables reversible unfolding and refolding of the chains. We hypothesize that this behaviour supports the high stretchability and self-healing capability of the material.

Distinct magnetic dynamic behavior for two polymorphs of the same Dy(III) complex

Two polymorphs of the same Dy(III) complex show distinct slow magnetic relaxation behaviors due to the different local environments of Dy(III) in the crystal. This work represents the first example where the magnetic dynamic property of neutral rare earth complexes could be tuned by growing polymorphic crystals without changing the ligand.

Solvent-Induced Single-Crystal-to-Single-Crystal Transformation in Multifunctional Chiral Dysprosium(III) Compounds

Two new enantiomeric ionic chiral dysprosium(III) compounds were designed and synthesized. These compounds show simultaneously the optical activity, ferroelectric effects, nonlinear-optical effects, and slow magnetic relaxation behavior. More interestingly, these compounds exhibit reversible single-crystal-to-single-crystal transformations associated with the release or absorption of solvent molecules. The structure transformations are accompanied by distinct changes in the physical properties.

A Stiff and Healable Polymer Based on Dynamic-Covalent Boroxine Bonds

A stiff and healable polymer is obtained by using the dynamic-covalent boroxine bond to crosslink PDMS chain into 3D networks. The as-prepared polymer is very strong and stiff, and can bear a load of more than 450 times its weight. When damaged, it can be completely healed upon heating after wetting.

Mechano-induced luminescent and chiroptical switching in chiral cyclometalated platinum(II) complexes

A couple of enantiomeric chiral cyclometalated platinum(II) complexes [Pt((−)-L1)(Dmpi)]Cl ((−)-1) and [Pt((+)-L1) (Dmpi)]Cl ((+)-1) [(−)-L1 = (−)-4,5-pinene-6′-phenyl-2,2′-bipyridine, (+)-L1 = (+)-4,5-pinene-6′-phenyl-2,2′-bipyridine, Dmpi = 2,6-dimethylphenylisocyanide] were synthesized. Two polymorphs (Form-Y and Form-R) of the complex (−)-1 were obtained. The crystallographic studies of both forms revealed that the emission and electronic circular dichroism (ECD) spectra of these complexes at solid state were sensitive to the intermolecular effects and to the molecular surrounding environments. The yellow forms (Form-Y) of the complexes (−)-1 and (+)-1 were found to undergo crystal-to-amorphous transformation upon mechanical grinding, resulting in luminescent and chiroptical switching behaviours as evidenced by emission and ECD spectra. The mechanochromic process can be reversed repeatedly by the addition of a few drops of dichloromethane. When the counteranion Cl− in 1 was replaced with trifluoromethanesulfonate (OTf−), complexes [Pt((−)-L1)(Dmpi)]OTf ((−)-2) and [Pt((+)-L1)(Dmpi)]OTf ((+)-2) were obtained. Complexes (−)-2 and (+)-2 showed a more pronounced luminescent switching behaviour, suggesting that the switching properties can be tuned by the counteranions.

Coordination polymers based on the octamolybdate and flexible bis(triazole) ligands with different spacer lengths

By using the in situ generated octamolybdate as an inorganic building block and tuning the spacer length of the flexible bis(triazole) ligands, three coordination polymers with different architectures, [CuII(btp)2(H2O)(β-Mo8O26)0.5]·H2O (1) (btp = 1,3-bis(1,2,4-triazol-1-yl)propane), [CuII2(btb)3(H2O)2(ζ-Mo8O26)]·3H2O (2) (btb = 1,4-bis(1,2,4-triazol-1-yl)butane), and [CuII(bth)2(θ-Mo8O26)0.5]·H2O (3) (bth = 1,6-bis(1,2,4-triazol-1-yl)hexane) were synthesized and structurally characterized. Compound 1 displays 2-fold interpenetration architecture, in which the [β-Mo8O26]4−polyanions act as pillars between the stagger-packed [Cu(btp)2]2+ sheets. Compound 2 exhibits parallel-packed 2D layers with the [ζ-Mo8O26]4−polyanions encircled by chair-type [Cu(btb)2]2+ rings. For compound 3, there exist quadrangular channels in the 3D network constructed from the [Cu(bth)2]2+ cations. The [θ-Mo8O26]4−polyanions are incorporated into the channels, resulting in a novel interpenetrated 3D architecture with (42·611·82)(42·64)(44·610·8) topology. Thermogravimetric analyses and electrochemical measurements for all the compounds were also performed.

Potential switchable circularly polarized luminescence from chiral cyclometalated platinum(II) complexes.

A series of chiral cyclometalated platinum(II) complexes, [Pt((−)-L1)(Dmpi)]Cl ((−)-1), [Pt((+)-L1)(Dmpi)]Cl ((+)-1), [Pt((−)-L2)(Dmpi)]Cl ((−)-2), [Pt((+)-L2)(Dmpi)]Cl ((+)-2), [Pt3((−)-L2)2(Dmpi)4](ClO4)4 ((−)-3), and [Pt3((+)-L2)2(Dmpi)4](ClO4)4 ((+)-3) [(−)-L1 = (−)-4,5-pinene-6′-phenyl-2,2′-bipyridine, (+)-L1 = (+)-4,5-pinene-6′-phenyl-2,2′-bipyridine), (−)-L2 = (−)-1,3-bis(2-(4,5-pinene)pyridyl)benzene, (+)-L2 = (+)-1,3-bis(2-(4,5-pinene)pyridyl)benzene, Dmpi = 2,6-dimethylphenyl isocyanide], have been designed and synthesized. In aqueous solutions, (−)-1 and (+)-1 aggregate into one-dimensional helical chain structures through Pt···Pt, π–π, and hydrophobic–hydrophobic interactions. (−)-3 and (+)-3 represent a novel helical structure with Pt–Pt bonds. The formation of helical structures results in enhanced and distinct chiroptical properties as evidenced by circular dichroism spectra. Circularly polarized luminescence (CPL) was observed from the aggregates of (−)-1 and (+)-1 in water, as well as (−)-3 and (+)-3 in dichloromethane. The CPL activity can be switched reversibly (for (−)-1 and (+)-1) or irreversibly (for (−)-3 and (+)-3) by varying the temperature.

Vibrational and electronic circular dichroism monitoring of copper(II) coordination with a chiral ligand.

Novel copper(II) coordination compounds with chiral macrocyclic imine ligands derived from R-/S-camphor were asymmetrically synthesized and characterized with the aid of chiroptical spectroscopies. Crystal structures of both enantiomers were determined by single crystal X-ray diffraction analysis. Circular dichroism (CD) spectra were analyzed using a simplified exciton model as well as quantum chemical computations. The absolute configuration of the copper(II) coordination compounds determined from CD was found consistent with the crystal data. The copper(II) complexes were further investigated by vibrational CD (VCD) measurement combined with density functional theory calculation. The complex formation was evidenced by spectral shifts of the characteristic bands in the CD and VCD spectra.

Asymmetric Donor–π-Acceptor-Type Benzo-Fused Aza-BODIPYs: Facile Synthesis and Colorimetric Properties†

Novel aza-diisoindolylmethene and their BF2 -chelating complexes (benzo-fused aza-BODIPYs) were synthesized on a large scale and in a facile manner from phthalonitrile in tBuOK-DMF solution. The unique asymmetric donor-π-acceptor structure facilitates B-N bond detachment in the presence of trifluoroacetic acid (TFA) in dichloromethane, resulting in sharp color change from red to colorless, with over 250 nm hypsochromic shift in the absorption maximum. This colorimetric process can be reversed by adding a very small amount of proton-accepting solvents or compounds. A (1) H and (11) B NMR spectroscopy study and also density functional theory (DFT) calculations suggest that TFA-induced B-N bond cleavage may disrupt the whole π-conjugation of the BODIPY molecule, resulting in significant colorimetric behavior.

A noncentrosymmetric 3D coordination polymer of metallocalix[4]arene

Sequential reaction of a lower-rim functionalized calix[4]arene, 25,27-bis(hydroxycarbonylmethoxy)-26,28-dimethoxy-p-tert-butylcalix[4]arene (H(2)L(C4)), with K(2)CO(3) and CoCl(2).6H(2)O in ethanol afforded a 3D coordination polymer [K(3)Co(2)(L(C4))(3)(EtOH)(6)]Cl (1). X-ray crystal analysis revealed that 1 features a noninterpenetrated (10,3)-a net structure wherein octahedral Co(2+) ions serve as the three-connecting nodes and [K(L(C4))](-) units function as the bridges between the Co(2+) ions. The calixarene ligands in 1 adopt a 1,3-alternate conformation, and there are considerable cation-pi interactions between the K(+) ion and the phenyl rings within each [K(L(C4))](-) unit.