Jian-Ke Sun

Reversible luminescence switch in a photochromic metal-organic framework.

Eu(III) ions have been introduced into a photoactive viologen system to yield a polyrotaxane-like metal-organic framework, which exhibits reversible photochromism and luminescence modulation with a non-destructive readout capability in the solid state.

Solvent- and anion-controlled photochromism of viologen-based metal–organic hybrid materials

Research on the tunable photosensitive properties of soft metal organic hybrid materials via environmental stimulation is presented. A supramolecular coordination polymer accommodating guest water molecules and anions is synthesized in aqueous solution. The original photochemically inert framework exhibits thermochromism, and can be transferred into a photochromic state via dehydration treatment. Furthermore, the interlayer ClO4− ions can be exchanged by halide and pseudohalide anions in a crystal to crystal manner. Although the favorable geometry for electron transfer from the carboxylate group to the bipyridinium moiety is created in transformed structures, the introduction of halide or pseudohalide anions leads to the formation of different charge transfer interactions with electron-accepting bipyridinium units in the ground state, which improves the light absorption of the compounds in the visible region and greatly affects the photoreduction efficiency of the bipyridinium unit. Consequently, the transformed crystals exhibit multicolor photochromic properties in solid states.

Supramolecular isomer-dependent photochromism and emission color tuning of bipyridinium salts

A study of the supramolecular isomer-dependent photoresponse and emission behaviors of a carboxybenzyl-substituted bipyridinium salt in the solid state is presented. Two supramolecular isomers (A1 and A2) are obtained by self-assembly with the same starting materials at different concentrations. The flexible conformation of the bipyridinium molecule results in different crystal packing geometries, which further influence and alter their photochromic behaviors owing to the crucial differences in the distance and orientation between the donor and acceptor moieties. Remarkably, the introduction of carboxyl groups into the bipyridinium molecule leads to intramolecular charge transfer (ICT) emissions in the visible region. A strong fluorescence emission can be detected in A1, and reversible on/off and multicolor (yellow, olivine and green) fluorescence switching, via photo-irradiation in the solid state, has been observed. Considering the easy chemical modification and the intriguing multicolor photoswitching properties, the present system shows great potential for use in solid photonic devices.

Structural diversity of the mixed-ligand system Mn-cpdba-2,2′-bpy controlled by temperature

A series of Mn-cpdba-2,2′-bpy complexes, {[Mn(cpdba)(2,2′-bpy)]}n1, {[Mn2(cpdba)2(2,2′-bpy)(H2O)2]·3H2O}n2, {[Mn2(cpdba)2(2,2′-bpy)2(H2O)2]·H2O}n3, {[Mn(cpdba)(2,2′-bpy)]·1.5H2O}n4, {[Mn4(cpdba)4(2,2′-bpy)3(H2O)2]}n5 (H2cpdba = 4-(4-carboxyphenylamino)-3,5-dinitrobenzoic acid; 2,2′-bpy = 2,2′-bipyridine) have been synthesized at different temperatures under hydrothermal conditions. Complex 1 has a 2D (4,4) network with alternate left and right-handed helical chains. With increasing temperature to 150 °C, complex 2, which has a complicated 3D framework constructed by a unique building block Mn3(cpdba)6(2,2′-bpy)2, can be obtained. Complex 3 that has been reported previously was obtained at 160 °C. This complex exhibits a 1D chain structure which is extended into a 3D supermolecular framework by π–π stacking interactions. Complex 4 was detected as a by-product in the synthesis of 3. X-Ray single crystal diffraction analysis reveals the formation of 2D layer network containing [Mn(CO2) + Mn(CO2)]n double-helices. With continuing increase to 170 °C, complex 5 featuring 3D framework similar to 2, with the decrease in the coordinated water and lattice water molecules as well as increase in the regularity of the framework, was formed. Influence of the 2,2′-bpy co-ligand on the coordination configuration of the cpdba2− ligand has been discussed. The magnetic susceptibility measurements of 1 and 5 reveal that two complexes exhibit antiferromagnetic coupling interactions.

Reversible luminescence switching between single and dual emissions of bipyridinium-type organic crystals

An excitation-wavelength-dependent luminescence behavior of a bipyridinium derivative, together with its luminescence switching between single- and dual-emissions upon reversible solid state structural transformation, has been presented.

Polycatenation‐Driven Self‐Assembly of Nanoporous Frameworks Based on a 1D Ribbon of Rings: Regular Structural Evolution, Interpenetration Transformation, and Photochemical Modification

A series of nanoporous frameworks constructed by a polycatenated isoreticular 1D ribbon of rings have been developed. The orientation of catenated ribbons can be fine tuned by varying counter anions, which allows both pore size and shape to be systematically adjusted in a pre-synthetic process. Distinct from conventional pore construction modes in which the organic linkers are alternately connected by metal nodes into a 3D periodic arrangement, the present polycatenation approach represents an alternative for constructing soft porous materials with tunable pore metrics and functions. Furthermore, these porous structures can interconvert into each other based on an anion-exchange process, accompanied by the transformation of the interpenetrating structures in different dimensional networks, which is unusual in porous frameworks. In addition, such a porous framework can be post-synthetically modified by a photoinduced [2+2] cycloaddition reaction, which not only achieves the surface modification (from conjugated to non-conjugated inner surface), but also triggers the structural transformation from low dimension to high dimension. Such a post-modification process reinforces the pore architecture through a covalent locking effect and has a great impact on the adsorption properties.

Thermally triggered reversible transformation between parallel staggered stacking and plywood-like stacking of 1D coordination polymer chains.

An unusual example showing reversible interconversion of chain-like isomers under controlled experimental settings is reported, which illustrates the key role of assembly conditions for the target packing architecture with related properties. The reaction of Mn(II) ions with an organic ligand 2-hydroxypyrimidine-4,6-dicarboxylic acid (H(3)hpdc) at room temperature gives a coordination polymer {[Mn(3)(hpdc)(2)(H(2)O)(6)] x 2 H(2)O}(n) containing parallel staggered stacking, whereas the reaction under hydrothermal conditions at 150 degrees C affords a compound {[Mn(3)(hpdc)(2)(H(2)O)(6)] x H(2)O}(n) possessing plywood-like stacking. Interestingly, two compounds contain similar one-dimensional chain components with different orientations that can be controlled by thermodynamic factors. Thermally triggered reversible interconversion of the two compounds was verified by X-ray powder, IR, and element analysis. The spin-canted antiferromagnetic behaviors are observed in as-synthesized samples, and the influence of chain orientations on magnetic properties has been detected.

Tunable solid-state photoluminescence based on proton-triggered structural transformation of 4,4′-bipyridinium derivative

An organic molecular system with proton-tunable photoluminescence properties based on a mono-substituted bipyridinium derivative 1-(3-carboxybenzyl)-4,4′-bipyridinium chloride, which possesses both pyridine and carboxylic acid groups as proton-responsive units, has been developed. Through controlling the pH value of the self-assembled systems, three compounds with different degrees of protonation have been obtained. These compounds display distinctly different luminescence behaviors and undergo solid-state structural conversion in response to changes in pH values. In particular, luminescence switching triggered by acid–base vapor can be realized.

2D self-catenated coordination polymer constructed by triple- and double-helical chains

The hydrothermal reaction of the prochiral amine-containing ligand 4-(4-carboxyphenylamino)-3,5-dinitrobenzoic acid, 1,3-bis(4-pyridyl)propane, zinc nitrate and NaOH results in an unprecedented 2D self-catenated network consisting of triple and double helical chains. The chirality of the stereo-chemically labile amine core can be locked via coordination interactions and transferred to the coordination polymer, facilitating the integration of the N-chirality and helicity in the 2D sheet. An unusual trefoil-type molecular knot is firstly observed in this coordination polymer.