Conjugated polymers are intriguing materials that have potential practical applications in diverse interdisciplinary subjects. Among them, polydiacetylenes (PDAs) have been extensively studied due to their interesting structural, spectral, and optical features. In particular, the unique colorimetric and fluorescent transition of PDAs in response to different external stimuli makes them a novel class of sensing materials, and numerous applications of PDAs as bio-or chemosensors have been explored in the past few decades. In this review, we summarize the latest developments with regard to the applications of PDAs as a class of sensing materials presented in the literature since 2014. This review is sorted into categories based on the structural differences of diacetylene monomers, from which PDAs are generated. In addition, different forms of PDAs and various methods for improving the sensing performance of PDAs are also emphasized.

A luminescent cadmium-pamoate metal-organic framework, [Cd2 (PAM)2 (dpe)2 (H2 O)2 ]⋅0.5(dpe) (1), has been synthesized under hydrothermal conditions by using π-electron-rich ligands 4,4'-methylenebis(3-hydroxy-2-naphthalenecarboxylic acid) (H2 PAM) and 1,2-di(4-pyridyl)ethylene (dpe). Its structure is composed of both mononuclear and dinuclear Cd(II) building units, which are linked by the PAM and dpe ligands, resulting in a (4,8)-connected 3D framework. The π-conjugated dpe guests are located in a 1D channel of 1. The strong emission of 1 could be quenched efficiently by trace amounts of 2,4,6-trinitrophenol (TNP), even in the presence of other competing analogues such as 4-nitrophenol, 2,6-dinitrotoluene, 2,4-dinitrotoluene, nitrobenzene, 1,3-dinitrobenzene, hydroquinone, dimethylbenzene, and bromobenzene. The high sensitivity and selectivity of the fluorescence response of 1 to TNP shows that this framework could be used as an excellent sensor for identifying and quantifying TNP. In the same manner, 1 also exhibits superior selectivity and sensitivity towards Cu(2+) compared with other metal ions such as Zn(2+) , Mn(2+) , Mg(2+) , K(+) , Na(+) , Ni(2+) , Co(2+) , and Ca(2+) . This is the first MOF that can serve as a dual functional fluorescent sensor for selectively detecting trace amounts of TNP and Cu(2+) .

A series of side-chain constrained tyrosine derivatives, 2′,6′-dimethyl-β-methyltyrosines (TMT), has been designed and incorporated into position 1 of the highly selective δ opioid agonists DPDPE (Tyr-D-Pen 2 -Gly-Phe-D-Pen 5 -OH) and deltorphin I (DELT I, Tyr-D-Ala-Phe-Asp-Val-Val-Gly-NH 2 ). Molecular mechanics calculations on isolated TMT residues and nuclear magnetic resonance (NMR) studies of the TMT 1 -containing peptides in DMSO showed that each of the four stereoisomers of TMT favors one particular rotamer of the side-chain χ 1 torsional angle. Therefore, substitution of four TMT isomers for Tyr 1 allows us to perform a systematic conformational scan through three staggered rotamers of the aromatic side chain, gauche (-), trans, and gauche (+), and to explore specific binding requirements of the receptor in relation to the side chain conformation. The potency and selectivity of four isomers of [TMT 1 ]DPDPE and four isomers of [TMT 1 ]DELT I were evaluated by radioreceptor binding assays in the rat brain using µ-and δ-selective radiolabeled ligands and by bioassays with guinea pig ileum (GPI, µ receptor) and mouse vas deferens (MVD, δ receptor). In the DPDPE series only one isomer, [(2S,3R)-TMT 1 ]-DPDPE showed high potency and selectivity for the δ opioid receptors. The favorable side-chain rotamers found for this analogue, i.e., the trans rotamer of TMT 1 and the gauche (-) rotamer of Phe 4 , were proposed as the most probable δ receptor-binding conformations of DPDPE analogues. Two [TMT 1 ]DELT I isomers possessed considerable δ receptor potencies. The (2S,3R)-TMT 1 isomer appeared to be a superpotent, but moderately δ-selective agonist, while the (2S,3S)-TMT 1 isomer showed the highest selectivity for the δ receptors in this series. Surprisingly, [(2R,3R)-TMT 1 ]DELT I also was moderately potent at the δ receptor. These results suggest that the δ receptor requirements for the linear DELT I analogues may be satisfied with two different modes of binding of the (2S,3S)-and (2S,3R)-TMT 1 isomers. This study provides important guidance for the design of peptide and non-peptide ligands selective for the δ opioid receptor. conformation of the 14-membered disulfide ring of DPDPE.

Nested concentric structures widely exist in nature and designed systems with circles, polygons, polyhedra, and spheres sharing the same center or axis. It still remains challenging to construct discrete nested architecture at (supra)molecular level. Herein, three generations (G2−G4) of giant nested supramolecules, or Kandinsky circles, have been designed and assembled with molecular weight 17,964, 27,713 and 38,352 Da, respectively. In the ligand preparation, consecutive condensation between precursors with primary amines and pyrylium salts is applied to modularize the synthesis. These discrete nested supramolecules are prone to assemble into tubular nanostructures through hierarchical self-assembly. Furthermore, nested supramolecules display high antimicrobial activity against Gram-positive pathogen methicillin-resistant Staphylococcus aureus (MRSA), and negligible toxicity to eukaryotic cells, while the corresponding ligands do not show potent antimicrobial activity.