Regulation of Crystal Structures and Solid-State Photoreactivity of Diolefin Coordination Polymers by Carboxylate Ligands

Olefinic coordination polymers (CPs) have recently drawn more attention, owing to the many possibilities in conformational conversions and photochemical reactivity that olefin molecules offer. In the presence of different carboxylic acids, we utilize one diolefin ligand 4,4'-((1E,1'E)-(2,5-dimethoxyl-1,4-phenylene)bis(ethene-2,1-diyl))dipyridine (OCH3-bpeb) and Cd(II) to assemble six different crystalline CPs (1-6). By fine-tuning the substituent size, carboxyl group number, and geometrical configuration of carboxylate ligands, these diolefin CPs show quite different crystal architecture models, from one-dimensional intersecting stacking to one-dimensional parallel stacking to three-dimensional interpenetrated structure. Of these, four kinds of CPs (1, 2, 5, and 6) are demonstrated to be photoreactive for [2 + 2] cycloaddition reactions, as confirmed by proton nuclear magnetic resonance and single-crystal X-ray diffraction. Both 2 and 5 can be dimerized into different cyclobutane products in a single-crystal-to-single-crystal manner under visible light, and remarkably, the photocycloaddition reaction of 5 involves a rare phase transition with structural symmetry enhancement from P1̅ to P2/n. This work demonstrates the power of carboxylate ligands in tuning single crystal structures and photocycloaddition reactions of CPs, which provides important references for the further exploration of other physicochemical properties of functionalized olefin-containing complexes.

Fabrication of porous polymer coating layers with selective wettability on filter papers via the breath figure method and their applications in oil/water separation

A comb-like amphiphilic polymer (PBTF), composed of hydrophobic backbones and hydrophilic side chains, was employed to grow honeycomb coating layers in situ on a filter paper via directly casting a polymer solution and by the subsequent dynamic breath figure (BF) method. Through regulating the hydrophilic polymer side chain density and the solution concentration, a continuous honeycomb coating layer contouring to the filter paper surface profile, in addition to possessing a water contact angle (WCA) as high as 146°, was successfully fabricated. The present study also finds that increasing the hydrophilic side chain density will turn PBTF into a surfactant-like polymer, and thus, endow the PBTF solution with the capacity of numerous micro-nano-sized water droplets, rather than simply stabilizing the ordered water droplet arrays on the surface of the solution. With vast nano-sized water droplets in it, the once transparent PBTF solution changed into a translucent nano-emulsion, which demonstrates a strong Tyndall effect. While casting such nano-emulsion on a filter paper and then subjecting to the BF process, the polymeric solute takes both nano-emulsion intrinsic nano-sized water droplets and solvent evaporation-induced water droplets as templates and self-assembles into a bird-nest-like three-dimensional porous microstructure, which possesses micro-nano-sized communicating pores. By regulating the water content in the nano-emulsion, the bird-nest-like structure can be uniformly formed on the surface of the filter paper, which revealed a WCA of 152°. The coated filter papers possess selective wettability, and meanwhile, maintain the inherent permeability of the substrates, which therefore can be directly utilized as oil/water separation materials.

An Ultrasensitive Fluorescent Paper-Based CO2 Sensor

We demonstrate a versatile and easily fabricated paper-based CO₂ sensor. The sensor consists of a specially designed fluorescent color-shift chromophore infused into standard filter paper. The emission color of the resulting fluorescent paper changes upon exposure to CO₂ due to the formation of carbonic acid, which underlies the sensing mechanism. By using a ratiometric method, the undesirable effects of photobleaching can be eliminated, leading to a stable and repeatable sensor performance. These multiuse sensors have a response time on the order of 1 min and feature low detection limits for a paper-based CO₂ gas sensor, suggesting possible low-cost applications in smart buildings or other facilities in which CO₂ levels are required to be continuously monitored.

Tailored honeycomb-like polymeric films based on amphiphilic poly(urea/malonamide) dendrons

A series of hydrogen bond-rich poly(urea/malonamide) dendrons were utilized as surfactants to facilitate the formation of honeycomb-like porous structures from the breath figure (BF) process.

Self-assembly and hierarchical patterning of aligned organic nanowire arrays by solvent evaporation on substrates with patterned wettability

The controlled growth and alignment of one-dimensional organic nanostructures at well-defined locations considerably hinders the integration of nanostructures for electronic and optoelectronic applications. Here, we demonstrate a simple process to achieve the growth, alignment, and hierarchical patterning of organic nanowires on substrates with controlled patterns of surface wettability. The first-level pattern is confined by the substrate patterns of wettability. Organic nanostructures are preferentially grown on solvent wettable regions. The second-level pattern is the patterning of aligned organic nanowires deposited by controlling the shape and movement of the solution contact lines during evaporation on the wettable regions. This process is controlled by the cover-hat-controlled method or vertical evaportation method. Therefore, various new patterns of organic nanostructures can be obtained by combing these two levels of patterns. This simple method proves to be a general approach that can be applied to other organic nanostructure systems. Using the as-prepared patterned nanowire arrays, an optoelectronic device (photodetector) is easily fabricated. Hence, the proposed simple, large-scale, low-cost method of preparing patterns of highly ordered organic nanostructures has high potential applications in various electronic and optoelectronic devices.

Fabrication of microlens arrays by localized hydrolysis in water droplet microreactors

We report a facile self-assembly strategy for fabricating TiO2 microlens arrays by localized hydrolysis of TiCl4 precursor in water droplets. Microcontact printing was used to define hydrophilic areas on a substrate for space resolved hydrolytic reaction. The water droplets served as the templates, reactant, and microreactors. Highly ordered TiO2 microlens arrays could be produced, which exhibit excellent ability to focus light. Because both size and shape of the final TiO2 microlens can be controlled by the printed chemical pattern and the precursor concentration, it is possible to define TiO2 microlens arrays with different imaging properties. This new method shows attractive features of simplicity, low cost, and requires no heating process, hence is suitable for a range of applications.