Reversible Photochromic Coordination Polymer by Phototriggered Subtle Molecular Conformation Variations.

Photochromic materials are constructed with molecules accompanied by structural change after triggering by light, which are of great importance and necessity for various applications. However, because of space-confinement effects, molecule stacking of these photoresponsive chromophores within coordination polymers (CPs) always results in an efficiency decrement and a response delay, and this phenomenon will lead to a poor photochromic property. Herein, a CP (named CIT-E) with a 3-fold-interpenetrating network structure, which was prepared with (Z)-1,2-diphenyl-1,2-bis[4-(pyridin-3-ylmethoxy)phenyl]ethene (1Z) and a CuI cluster, showed fast reversible photochromic behavior. Under UV-light illumination, the color of CIT-Z changed from pale yellow to reddish brown. With the illumination of green light, the polymer could return to its initial color within 10 s. To reveal the mechanism of reversible photochromic behavior of CIT-Z, single-crystal structures of each color state were fully studied, and other scientific study methods were also used, such as time-dependent density functional theory calculation and control experiments. It was found that, with light illumination, this behavior of CIT-Z was the result of a ligand-to-metal charge-transfer process, and this process was triggered by subtle molecular conformation variation of tetraphenylethylene. It should be noted that CIT-Z has high thermal and chemical stability, which are excellent advantages as smart photoresponsive materials. As a proof of concept, a uniform thin film with such a fascinating photochromic property allows applications in invisible anticounterfeiting and dynamic optical data storage. Overall, the present study opens up a new avenue toward reversible photochromic materials.

Three Silver Coordination Polymers with Diverse Architectures Constructed from Pyridine Carboxylic Hydrazide Ligands.

A series of silver coordination polymers (CPs) have been synthesized through self-assembly of three pyridinecarboxylic acid hydrazide (p-, m-, o-position) ligands with silver clusters (named Ag1-iah, Ag2-iah, and Ag3-iah). These silver CPs show different one- and two-dimensional topologies including cross-helical chains, planar network, and parallel helical chains for Ag1-iah, Ag2-iah, and Ag3-iah, respectively. The combination of experimental and computational results reveals the critical role in the space distribution of the coordination site of silver clusters and ligands in controlling the silver CPs' dimensionality and packing arrangement and modulating the optical properties and stability. Luminescent investigations reveal that Ag3-iah can selectively detect dichloromethane or trichloromethane in tetrachloromethane. These silver CPs provide a good model to study the influence of the space distribution of the coordination site of ligands on their packing arrangement and properties.

Solvent-Driven Reversible Phase Transition of a Pillared Metal-Organic Framework.

Over the last decade, the controllable reversible phase transition of functional materials has received growing interest as it shows unique suitability for various technological applications. Although many metal-organic frameworks (MOFs) possess a lamellar structure, the reversible structural transformation of MOFs between their three-dimensional (3D) phase and two-dimensional (2D) phase remains a largely unexplored area. Herein, we report for the first time a europium MOF with unprecedented reversible morphology in different solvents at room temperature. This europium MOF displayed a 3D nanorod morphology in organic solvent and a 2D nanobelt architecture in water. As a proof of concept for potential applications of this reversible-phase-transition MOF, we were able to use a delamination recovery method to load dye molecules that previously could not be loaded into europium MOFs.

Arterial wall remodeling under sustained axial twisting in rats.

Blood vessels often experience torsion along their axes and it is essential to understand their biological responses and wall remodeling under torsion. To this end, a rat model was developed to investigate the arterial wall remodeling under sustained axial twisting in vivo. Rat carotid arteries were twisted at 180° along the longitudinal axis through a surgical procedure and maintained for different durations up to 4weeks. The wall remodeling in these twisted arteries was examined using histology, immunohistochemistry and fluorescent microscopy. Our data showed that arteries remodeled under twisting in a time-dependent manner during the 4weeks post-surgery. Cell proliferation, MMP-2 and MMP-9 expressions, medial wall thickness and lumen diameter increased while collagen to elastin ratio decreased. The size and number of internal elastic lamina fenestrae increased with elongated shapes, while the endothelial cells elongated and aligned towards the blood flow direction gradually. These results demonstrated that sustained axial twisting results in artery remodeling in vivo. The rat carotid artery twisting model is an effective in vivo model for studying arterial wall remodeling under long-term torsion. These results enrich our understanding of vascular biology and arterial wall remodeling under mechanical stresses.