The term aerogel is used for unique solid-state structures composed of three-dimensional (3D) interconnected networks filled with a huge amount of air. These air-filled pores enhance the physicochemical properties and the structural characteristics in macroscale as well as integrate typical characteristics of aerogels, e.g., low density, high porosity and some specific properties of their constituents. These characteristics equip aerogels for highly sensitive and highly selective sensing and energy materials, e.g., biosensors, gas sensors, pressure and strain sensors, supercapacitors, catalysts and ion batteries, etc. In recent years, considerable research efforts are devoted towards the applications of aerogels and promising results have been achieved and reported. In this thematic issue, ground-breaking and recent advances in the field of biomedical, energy and sensing are presented and discussed in detail. In addition, some other perspectives and recent challenges for the synthesis of high performance and low-cost aerogels and their applications are also summarized.

In this paper, we present the use of a disubstituted polyacetylene with high thermal stability and quantum yield as a fluorescence label for the identification, tracing, recycling, and eventually anti-counterfeiting applications of thermoplastics. A new method was developed for the dispersion of poly[1-phenyl-2-[p-(trimethylsilyl)phenyl]acetylene] (PTMSDPA) into polymer blends. For such purposes, four representative commodity plastics were selected, i.e., polypropylene, low-density polyethylene, poly(methyl methacrylate), and polylactide. Polymer recycling was mimicked by two reprocessing cycles of the material, which imparted intensive luminescence to the labelled polymer blends when excited by proper illumination. The concentration of the labelling polymer in the matrices was approximately a few tens ppm by weight. Luminescence was visible to the naked eye and survived the simulated recycling successfully. In addition, luminescence emission maxima were correlated with polymer polarity and glass transition temperature, showing a marked blueshift in luminescence emission maxima with the increase in processing temperature and time. This blueshift results from the dispersion of the labelling polymer into the labelled polymer matrix. During processing, the polyacetylene chains disentangled, thereby suppressing their intermolecular interactions. Moreover, shear forces imposed during viscous polymer melt mixing enforced conformational changes, which shortened the average conjugation length of PTMSDPA chain segments. Combined, these two mechanisms shift the luminescence of the probe from a solid- to a more solution-like state. Thus, PTMSDPA can be used as a luminescent probe for dispersion quality, polymer blend homogeneity, and processing history, in addition to the identification, tracing, and recycling of thermoplastics.

Supporting Information Experimental proceduresCopies of NMR, IR and Raman spectra X-Ray structure data EXPERIMENTAL Measurements. NMR spectra were recorded on Varian SYSTEM 300 and Bruker Avance-III 600 instruments and referenced to residual solvent signal. IR spectra were recorded on Nicolet Avatar 370 FT-IR and Thermo Nicolet 7600 FTIR spectrometer equipped with a Spectra Tech InspectIR Plus microscopic accessory using KBr-diluted samples and diffuse reflectance technique (DRIFT) (128 or more scans at resolution 4 cm -1 ). Raman spectra of solid samples were recorded on a DXR Raman microscope (Thermo Scientific) using excitations at 532 and 780 nm and the laser power at sample from 2 to 5 mW. Mass spectra were recorded with Q-Tof micro (Waters) instrument. Crystallographic data for aldehydes 1, 2 and dihydropyrazine 11 were collected on Nonius Kappa CCD diffractometer equipped with Bruker APEX-II CCD detector, using monochromatic MoKα radiation (λ = 0.71073 Å). The structures were solved by direct methods (SHELXS) [1] and refined by full matrix least squares based on F 2 (SHELXL97). [1] The hydrogen atoms on carbon were fixed into idealized positions (riding model) and assigned temperature factors either H iso (H) = 1.2 U eq (pivot atom) or H iso (H) = 1.5 U eq for methyl moiety. Melting points were measured on Büchi Melting Point B-545 (± 0.2 °C).Materials. Solvents were dried by standard procedures. Silica gel (Merck, 0.040-0.063 mm) was used for column chromatography. A radial-layer chromatograph (Chromatotron) was used for purification of crude products as well. All starting compounds, reagents and solvents were purchased from commercial suppliers. Anhydrous zinc chloride was dried using thionyl chloride. [2] Dimethyl pyrazine-2,5-dicarboxylate, [3] 2,5-bis(chloromethyl)pyrazine [4] and N,N,N´,N´-tetramethyl(benzene-1,2-diamine)-N-oxide [5] were prepared according to the published protocols. Dimethyl pyrazine-2,6-dicarboxylate was prepared by adopting the literature protocol for 2,5-isomer. Both dimethyl pyrazinedicarboxylates were purified by recrystallization/vacuum sublimation (white solids) for further use.

Novel nickel(ii) complexes [Ni(P,P)X2] = [Ni{tBuN(PPh2)2-κ2P}X2], X = Cl, Br, I, are prepared, characterized by IR and NMR spectroscopy, mass spectrometry and X-ray crystallography, and tested as catalysts in the Kumada cross-coupling reaction.

The chain coordination polymerization of (ethynylarene)carbaldehydes with unprotected carbaldehyde groups, namely ethynylbenzaldehydes, 1-ethynylbenzene-3,5-dicarboxaldehyde, and 3-[(4-ethynylphenyl)ethynyl]benzaldehyde, is reported for the first time. Polymerization is catalyzed with various Rh(I) catalysts and yields poly(arylacetylene)s with one or two pendant carbaldehyde groups per monomeric unit. Surprisingly, the carbaldehyde groups of the monomers do not inhibit the polymerization unlike the carbaldehyde group of unsubstituted benzaldehyde that acts as a strong inhibitor of Rh(I) catalyzed polymerization of arylacetylenes. The inhibition ability of carbaldehyde groups in (ethynylarene)carbaldehydes seems to be eliminated owing to a simultaneous presence of unsaturated ethynyl groups in (ethynylarene)carbaldehydes. The reactive carbaldehyde groups make poly[(ethynylarene)carbaldehyde]s promising for functional appreciation via various postpolymerization modifications. The introduction of photoluminescence or chirality to poly(ethynylbenzaldehyde)s via quantitative modification of their carbaldehyde groups in reaction with either photoluminescent or chiral primary amines under formation of the polymers with Schiff-base-type pendant groups is given as an example.