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To facilitate the formation of efficient fluorescent pyrene excimers in solids, sulfide-, sulfoxide-, and sulfone-substituted pyrenes (Py–S, Py–SO, and Py–SOO) showing different oxidation degrees were designed and synthesized. All molecules possess side groups oriented perpendicular to the pyrene plane, which promote the formation of an antiparallelly stacked π–π pyrene dimer and the resulting excimer. Analysis of the photophysical properties measured in solutions, crystals, and films reveals that the resulting excimer species for these three molecules have similar emission wavelengths. However, the excimer of Py–SOO demonstrates the highest photoluminescence quantum efficiency due to molecular rigidity of its crystal and evaporated film. Non-doped organic light-emitting diodes were fabricated using these materials as emitters, and Py–SOO exhibits the best electroluminescence performance with a stable excimer emission, an external quantum efficiency of 2.53%, and a maximum luminance of 21 428 cd m−2. These findings show that the introduction of a sulfone group can improve the luminescence efficiency of the pyrene-based excimers and present a valuable guideline for designing high-performance solid-state pyrene excimers. [ABSTRACT FROM AUTHOR]

Plastic waste is globally ubiquitous and ecologically harmful, but it can be recycled as an abundant carbon source to alleviate worldwide heavy dependence on fossil resources and reduce CO2 emissions. Therefore, research into the chemical recycling of plastic waste has become a critical and pressing area. Compared with polyolefins, polyesters, as represented by PET and PLA, can easily achieve selective depolymerization to their corresponding monomers due to the presence of weaker ester bonds, thus favoring their closed-loop recycling and upcycling. However, comprehensive reviews on this important topic remain scarce, especially from the standpoint of re/upcycling. In this review, we present significant progress in the catalytic depolymerization of different polyesters, including biodegradable polyesters and nonbiodegradable polyesters, and discuss the key factors that limit the efficacies of the different methods and formidable challenges towards closed-loop recycling and upcycling. Such insightful discussion may benefit the further development of advanced strategies to address the problems with the increasing polyester plastic wastes and stimulate their efficient recycling to value-added chemicals and materials. [ABSTRACT FROM AUTHOR]

The structure–property relationship is always the focus when organic light-emitting materials are used mainly in the aggregated state in some fields, such as optoelectronic devices, sensors, and bioimaging. To clarify a clear structure–property relationship between the aggregate structure and the luminescent property, the intermolecular dimer, which represents the smallest aggregate in a number, is selected as an ideal research model. However, how to achieve an intermolecular dimer by a rational molecular design is rarely found in previous papers in this field. Here, we design and synthesize three pyrene derivatives, aiming at achieving the pyrene-based dimer in a solid state, by bridging pyrene and benzo[d]thiazole (BZT) in a different position on a phenylene. The pyrene and BZT groups are connected with each other in the ortho-, meta-, and para-positions of the phenylene to construct three molecules Py-oBZT, Py-mBZT, and Py-pBZT. Experimental and theoretical investigations demonstrate that only Py-oBZT shows pyrene-based dimer stacking with a discrete feature due to the large steric hindrance provided by the BZT group. Compared to individual pyrenes in the crystal, the pyrene-based dimer in the Py-oBZT crystal exhibits a different molecular orientation, which is verified by the presence of multiple potential wells of the pyrene dimer using a theoretical simulation of the potential energy surface. This work not only examines the effect of steric hindrance on the formation of the pyrene dimer packing, but also provides an understanding of the multiplicity of the pyrene dimer structures. [ABSTRACT FROM AUTHOR]

Piperidine is an important cyclic amine with versatile applications. However, its commercial process is not green and depends mainly on the hydrogenation of fossil resource-based pyridine. Here, we report a novel one-pot approach to the sustainable synthesis of piperidine from bio-renewable tetrahydrofurfurylamine (THFAM) via its hydrogenolysis to 5-amino-1-pentanol (APO) and the subsequent intramolecular amination of APO. SiO2-supported Rh–ReOx catalysts exhibited high efficiency and stability in the THFAM reaction to piperidine, providing a high yield of 91.5% at 200 °C and 2.0 MPa H2 in water. Such high efficiency of Rh–ReOx/SiO2 was found to be related to the synergistic effect between the Rh nanoparticles and ReOx species on the kinetically-relevant cleavage of the C–O bond neighboring the C–NH2 group in THFAM, involving the strong adsorption of the C–NH2 group on ReOx and the heterolytic dissociation of H2 on Rh. This work provides an efficient strategy for the selective cleavage of the C–O bonds neighboring the C–NH2 groups, irrespective of their presence in amino ethers or amino alcohols, and the green production of piperidine and its derivatives from biomass resources. [ABSTRACT FROM AUTHOR]

The wide application of excimer materials in the OLED field is mainly based on the regulation of their stacking structure. Therefore, based on whether anthracene groups can form excimers, three anthracene derivative molecules with sterically hindered substituents were designed and their crystals with different aggregating structures were prepared to study the relationship between their structures and properties. Under high pressures, these anthracene groups exhibit enhanced fluorescence during the formation of excimers (in the pressure range of 2.3 to 4.2 GPa) while the anthracene groups that have already formed excimers under ambient conditions exhibit a wider red-shift range. Their abundant piezochromic fluorescence behavior indicate that regulating the aggregation mode of anthracene groups can meet different application requirements and provide guidance for the expansion of the application of excimer materials. [ABSTRACT FROM AUTHOR]

A pyrene-based non-covalent dimer in a crystal showed a strengthened π–π interaction, which was robust enough against external disturbances. Such a strong π–π interaction made the pyrene-based dimer easily form in the amorphous film, indicating that the dimer could potentially work as the monomer. [ABSTRACT FROM AUTHOR]

Red and deep-red fluorescent materials are broadly applied in many fields, such as organic light emitting diodes (OLEDs), biological imaging and night-vision devices. In this work, we designed and synthesized two orange to red emissive donor–acceptor (D–A) materials, DMAC-NZP and DMAC-NZC, in which DMAC-NZC possesses an extra cyano group. The DMAC-NZC aggregate demonstrates a large red-shift of 60 nm compared with DMAC-NZP, which can be assigned to the formation of discrete dimer and excimer emissions in its single crystal and neat films, respectively, upon cyano-substitution. Both DMAC-NZC and DMAC-NZP exhibit a maximum external quantum efficiency (EQEmax) of over 4% and a very small efficiency roll-off in doped OLEDs. More importantly, the non-doped OLEDs of DMAC-NZC show deep-red electrofluorescence at 688 nm with a considerably high exciton utilization efficiency (EUE) of 55%–82%. This work not only gives a new functional group for the construction of deep-red pure organic efficient excimer materials, but also further verifies that the "hot exciton" theory can also be effective in the excimer-based OLEDs. [ABSTRACT FROM AUTHOR]

Sheet-liked organic semiconductor crystals with two-dimensional (2D) packed structures play an essential role in practical applications of high-property optoelectronic devices. Here, we report a practical example in combination with chemical structures and crystallization engineering to construct a balanced 2D network for organic thin sheet-shaped crystals. The introduction of the cyano group enabled the formation of hydrogen bonds, promoting the in-plane 2D network construction both in strength and direction with π⋯π (or C–H⋯π) interactions. Through changing the chamber pressure and growth temperature, we realized a macroscopic morphology adjustment from rods to sheets with the same single crystal structure, ascribed to the relative strength changes of different facet energies. Such a macroscopic dimension control combined with supramolecular chemistry and crystal engineering offers a new perspective for boosting further developments for 2D stacked organic semiconductor crystals. [ABSTRACT FROM AUTHOR]

Citric acid is an important biomass-derived platform chemical for the synthesis of high-value organic acids, such as itaconic acid (ICA), 2-methylsuccinic acid (MSA) and tricarballylic acid (TCA). However, these reactions frequently encounter low efficiency and severe leaching of catalysts imposed by the acidity of citric acid under hydrothermal conditions, limiting their practical applications. Here, we report that highly acid- and etching-resistant monoclinic zirconium dioxide (m-ZrO2) exhibited high catalytic efficiency in the conversion of citric acid to ICA via sequential dehydration and decarboxylation steps, providing a high yield of 70.3% at 180 °C on m-ZrO2 (calcined at 300 °C). The correlation between the activity of the m-ZrO2 catalysts and their acid-basicity demonstrates that the synergistic effect of acidic and basic sites facilitates the rate-determining dehydration step for the citric acid conversion to ICA. On the bifunctional catalysts, Pt and Pd nanoparticles supported on P25 and anatase TiO2, citric acid can be selectively converted to MSA and TCA, respectively, with yields as high as 83.1% and 64.9%. The hydrogenation activity of the bifunctional catalysts was found to be crucial for regulating the relative rates of the decarboxylation and hydrogenation steps involved in the selective conversion of citric acid to MSA and TCA. These catalysts showed excellent stability and recyclability in acidic aqueous solutions. This study provides a rationale for tuning catalytic functions required for the green production of important carboxylic acids from citric acid and other biomass-derived feedstocks. [ABSTRACT FROM AUTHOR]

In this work, we found that the pressure-induced emission enhancement (PIEE) phenomenon can be produced by the restriction of intramolecular chemical bond vibration, which differs from the mechanism of restricting intramolecular motion (RIM). Dibenzo[b,d]thiophene 5,5-dioxide (DBTS) is an aggregation-induced emission enhancement (AIEE) material. In the crystal state of DBTS, the high pressure strengthens intermolecular C–H⋯O＝S hydrogen bonds, which greatly restricts the vibration of C–H and S＝O bonds and then rigidifies the molecular skeleton, thereby suppressing the non-radiative process and promoting emission enhancement. In situ high-pressure infrared spectroscopy and angle-dispersive X-ray diffraction analysis combined with reorganization energy and Hirshfeld surface theory calculation provide clear evidence that the restriction of the deformation vibration C–H bonds plays an essential role in PIEE, and S＝O bonds can act as the powerful controller that enhances intermolecular C–H⋯O＝S hydrogen bonds. This study introduces a new AIEE and PIEE fluorophore and provides deep insights into the influence of intermolecular interactions on intramolecular chemical bond vibration and luminescence, which will play an important role in the development of precision optical sensors. [ABSTRACT FROM AUTHOR]