Perylene diimides (PDIs) are one class of the most explored organic fluorescent materials due to their high luminescence efficiency, optoelectronic properties, and ready to form well-tailored supramolecular structures. However, heavy aggregation caused quenching (ACQ) effect in solid state has greatly limited their potential applications. We have easily solved this problem by chemical modification of the PDI core with only phenoxy moietie at one of the bay position. In this paper, we report two perylene bisimides with small rigid substituents, 1- phenol -N, N’-dicyclohexyl perylene-3,4,9,10-tetracarboxylic diimide (PDI 1) and 1- p-chlorophenol-N, N’-dicyclohexyl perylene-3,4,9,10-tetracarboxylic diimide (PDI 2) possess both well defined organic nanostructures and high fluorescence quantum yield in the solid state. In contrast, 1-propanol-N, N’-dicyclohexyl perylene-3,4,9,10-tetracarboxylic diimide (PDI 3) bearing a straight chain only shown weak orange fluorescence. In addition, morphological inspection demonstrated that PDI 3 molecules easily form well-organized microstructures despite the linkage of the PDI core with a straight chain. The present strategy could provide a generic route towards novel and advanced fluorescent materials and these materials may find various applications in high-tech fields.
Tannic acid (TA) is a polyphenol‐rich compound found in many natural plants. There are large numbers of phenolic hydroxyls at the terminal of the TA molecule, being capable of forming hydrogen bonds with hydrogen‐bonding donating polymers such as polyvinylpyrrolidone (PVP) and then engineering a hydrogel network. The reversible switch between phenolic hydroxyls and quinones tuned by pH affords the dynamic nature of the resultant hydrogen bonds. The gels exhibit excellent shear‐thinning and self‐recovery properties. Moreover, the polyphenols can form coordinates with Fe(III) that link different TAs to form a hydrogel network. Hence, adding Fe(III) solution to the TA‐PVP sol can form additional interactions inside the TA‐PVP gel. The easy preparation of the dual‐responsive gels with nontoxic raw materials may allow for its application in the biomedical field.
The ferromagnetic couplings were observed in an unpublished crystal that consists of binuclear copper(II) complexes, namely, [Cu(2)(μ(1,3)-SCN)(2)(PhenOH)(OCH(3))(2)(HOCH(3))(2)] (PhenOH = 2-hydroxy-1,10-phenanthroline), and in the binuclear complex Cu(ii) ion assumes a distorted octahedral geometry and thiocyanate anion functions as a μ(1,3)-SCN(-) equatorial-axial (EA) bridging ligand. The analysis for the crystal structure indicates that there are three types of magnetic coupling pathways, in which two pathways involve π-π stacking between the adjacent complexes and the third one is the μ(1,3)-SCN(-) bridged pathway. The fitting for the data of the variable-temperature magnetic susceptibilities shows that there is a ferromagnetic coupling between adjacent Cu(II) ions with J = 50.02 cm(-1). Theoretical calculations reveal that the two types of π-π stacking resulted in ferromagnetic couplings with J = 4.16 cm(-1) and J = 2.75 cm(-1), respectively, and the bridged thiocyanate anions pathway led to a weaker ferromagnetic interaction with J = 0.88 cm(-1). The theoretical calculations also indicate that the ferromagnetic coupling sign from the two types of π-π stacking does not accord with McConnell I spin-polarization mechanism. The analysis for the Wiberg bond indexes that originate from the π-π stacking atoms indicates that the Wiberg bond indexes are relevant to the associated magnetic coupling magnitude and the Wiberg bond index is one of the key factors that dominates the associated magnetic coupling magnitude.
The π-π stacking interaction, one of the main intermolecular forces, sometimes leads to amazing magnetic properties. Although the concept has been raised that spin density is one of the main factors that contribute to the magnetic coupling strength in intermolecular magnetic coupling systems, it has not been confirmed either experimentally or theoretically to date. Herein we present a study on the magnetostructural data of seven unpublished Cu(II) complexes and ten reported radicals. It is confirmed for the first time that the spin density on short contact atoms is a major factor that contributes to the π-π stacking magnetic coupling strength. Based on the reported data to date, when the short contact distance is larger than the default contact radius, medium or relatively strong magnetic coupling strength could be obtained only if the spin density on the short contact atoms is greater than 0.1350; when the C···C short contact is less than the default contact radius of 3.4 Å, but not less than 3.351 Å, and the spin density is less than 0.1, neither medium nor strong magnetic coupling strength could be observed. Further, when the short contact distance decreases with a temperature drop, the spin densities on the relevant short contact atoms increase. In the complexes reported the small spin densities on the relevant short contact atoms are the major factors that result in the weak π-π magnetic coupling strength.
We facilely synthesized a novel guest-free homochiral metal-organic framework, (Cu 4 L 4 ) n [H 2 L ¼ N-(2-hydroxybenzyl)-L-leucine] in space group P1. The (Cu 4 L 4 ) n nanocrystals exhibit high electrochemical activity for rapidly discriminating chiral a-methylbenzylamine enantiomers and quantitatively determining the enantiomeric excess in the chiral amine mixture.Many important molecules in the modern pharmaceutical and agrochemical industries, are chiral-that is, they are not superimposable on their mirror image, the pair of asymmetric molecules are known as enantiomers. The recognition and quantication of enantiomers is a major challenge particularly owing to their identical physical and chemical properties in an achiral environment.1 In many cases, one of the enantiomers exhibits the desired responses while the other is inactive or even toxic.2-4 The present technology depends largely upon nuclear magnetic resonance (NMR), gas chromatography (GC) and high performance liquid chromatography (HPLC) based on homochiral stationary phases (CSPs), which is of particular importance for laboratories and industries in the discovery and development of enantiomeric substances and quality control of corresponding products.5-7 However, these methods require high concentrations of analytes, sophisticated operation, relatively expensive instrumentation, and GC and HPLC are also typically time-consuming. 8,9 Molecularly imprinted polymers (MIPs) have more than 80 years of history, 10,11 considerable advances have been made on the fundamental study. 12,13Although the approach behaves special desired selectivity because the MIPs create three-dimensional cross-linked polymers with tailor-made memory of the shape, size and functional groups for a template or target molecule, 14,15 this sometimes also suffers from some problems, such as incomplete template removal, poor mass transfer, low binding capacity and slow binding kinetics, which restricts its applications in various aspects.16 In contrast, the electrochemical sensors can provide highly selective, low cost, fast speed, real time and on-line operation. Unlike chromatographic instruments, the technology can be easily adapted for detecting a wide range and low concentrations of analytes, while remaining inexpensive. 17However, there are only a handful of progress at the present chiral sensing using this approach.The key of the electrochemical chiral sensing is the material used to prepare the sensor's electroactive surface. The emerging chiral metal-organic framework (CMOFs) are the intriguing class of crystalline materials formed usually by the selfassembly of metal ions and chiral polydentate ligands. These materials are highly promising for electrochemical chiral sensors owing to ultrahigh surface area, precise network structures, ne-tuned chiral channels and pores, regularly ordered functionalities and host-guest interactions involved.18,19 At present, however, only a few achiral MOFs have been attempted as electrochemical sensors for detecting a few achiral analyte...
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