English

• Welcome to this virtual special issue, which focuses on supramolecular/macrocyclic Chemistry. The beginnings of supramolecular chemistry can be traced back to 1967 with the identification of crown ethers by Pedersen [1], and being acknowledgement by the 1987 Nobel Prize to Lehn, Cram, and Pedersen for their leading discoveries in the host - guest systems [2]. Since these landmarks, supramolecular chemistry has developed into a highly cross-disciplinary field, promoting the development of numerous supramolecular systems for applications in functional materials, nano-medicine, electronic devices, sensors, catalysis, and so on [3]. Perhaps not surprisingly, as a result Sauvage, Stoddart, with Feringa were jointly awarded the 2016 Nobel Prize for their pioneering efforts in the design and synthesis of molecular machines. Currently, the goal of supramolecular chemistry isto gainprogressive controlof the structural and dynamic features of architectures through selforganization in the development of highlycomplicated and adaptive chemical systems. The purpose of this special issue is to provide an efficient communication platform for supramolecular chemists to promote the rapid development of supramolecular chemistry, sufficiently unlock our full potential to narrow the gap between theory and practical application, and finally realize the real functionalization of supramolecular systems.

  This special issue includes totally 29 original research papers and 6 reviews, and it covers various research areas that related with supramolecular/macrocyclic chemistry, including host-guest chemistry, molecular recognition, self-assembly, supramolecular polymers, supramolecular catalysis, functional supramolecular materials and so on.

  In the field of host-guest chemistry, Shi-Guo Sun and colleagues reported the formation of a host–guest inclusion complex between N-phenyloxypropyl-N′-ethyl-4,4′-bipyridium (1) and CB[n] (n = 6–8), and the bromination of compound 1 could efficiently perform by using CB[8] as a molecular reactor [4]. Keming Wang and colleagues developed a simple and sensitive method for the detection of APE1 activity based on host-guest interaction of β-cyclodextrin polymer and pyrene [5]. Yu Liu and colleagues constructed an interesting redox-responsive diphenylalanine aggregate mediated by cyclodextrin-based host-guest interaction, which showed a reversible morphological conversion by the chemical redox of ferrocenyl moiety [6]. Qing-Dao Zeng and colleagues summarized the recent advances in the study of the host-guest interaction by using coronene as the guest molecule [7].

  For the molecular recognition-based studies, Dong-Sheng Guo and colleagues reported the investigation of molecular recognition of sulfonatocalixarene at self-assembled interface by means of microcalorimetry [8]. Ying Zhou and colleagues developed a rhodamine-based sensor for the detection of chromium ions, this sensor showed low toxic and it was successfully used for bioimaging [9]. Wei Jiang and colleagues found that aromatic hydrocarbons can be selectively recognized by four endofunctionalized molecular tubes through C/N-H…π interactions in nonpolar media [10]. Very recently, Simin Liu and colleagues reviewed the research progresses of CB [10]-based chemistry, involving its purification and applications in fields such as molecular recognition and molecular assembly [11].

  Regarding the supramolecular self-assembly and its applications, Tolbin and colleagues reported the formation of thermally stable metal-free slipped-cofacial J-type phthalocyanine dimer, which stands for an unusual self-assembled nanoaggregation [12]. Ling Chen and colleagues reported the synthesis of pyridazine-containing tetracationic cyclophane for fabricating [2]rotaxane based on the template- directed self-assembly process [13]. Using a model functional amyloid, Chao Zhong and colleagues described the interesting self-assembly and morphologies of two-component functional amyloid proteins [14]. Shiyong Liu and colleagues reported the supramolecular self-assembly of the triblock copolymers and developed a method for precisely installing the gold nanoparticles at the core/shell interface of the micelles [15]. Fei Zeng and colleagues reported a new strategy for the one-pot synthesis of well-organized heteropolyrotaxane via self-sorting assembly [16]. Xin-Long Ni and colleagues developed a pH-switchable fluorescent molecular shuttle based on the selfassembly of cucurbit[7]uril with bispyridinium ethylene derivatives [17].

  With respect to the construction of supramolecular polymers, Juli Jiang and colleagues developed a novel method for modulating the properties of quadruple hydrogen bonded supramolecular polymers by photo-crosslinking between the coumarin moieties [18]. Xin Zhao and colleagues reported the construction of a supramolecular bottlebrush polymer in water through cucurbit[8]uril-mediated self-assembly [19]. Xiang Ma and colleagues described the formation of a linear supramolecular polymer based on host-guest recognition and metal-ligand coordination [20]. Da-Hui Qu and colleagues developed a new type of strategy for photo-induced supramolecular polymerization based on host-guest interaction [21]. Myonghoon Lee and colleagues reported supramolecular conducting microfibers from amphiphilic tetrathiafulvalenebased organogelator [22].

  Supramolecular catalysis as a burgeoning research field has attracted wide attention. Gill and colleagues developed an efficient method for the synthesis of 2H-indazolo[2,1-b]-phthalazine-trione derivatives in water by using β-cyclodextrin as a supramolecular catalyst [23]. Cheng Yang and colleagues successfully achieved mediating the enantiodifferentiating [4 + 4] photocyclodimerization of 2-anthracenecarboxylic acid by using a series of 6^A, 6^X-diguanidio-γ-cyclodextrins (CDs) as chiral hosts [24]. Chuanfeng Chen and colleagues reported the efficient proline-catalyzed asymmetric List-Lerner-Barbas aldol reactions of bulky aldehyde substrates by employing tetrahydrobenzo[5]-helicenediol derivatives as additives [25]. Qiaochun Wang and colleagues described the cucurbit[7]uril/CuCl-promoted decomposition of 4-nitrobenzenediazonium in aqueous solution [26].

  To realize the functionalization of supramolecular systems, various functional supramolecular materials have been successfully fabricated. For the construction of drug delivery systems (DDSs), Zhan-Ting Li and colleagues reported the in situ-preparation of homogeneous supramolecular organic framework drug delivery systems (sof-DDSs) for overcoming cancer multidrug resistance and controlled release [27]. They also achieved the construction of loading-free sof-DDSs for the delivery and release of doxorubicin [28]. Ying-Wei Yang and colleagues reviewed the applications of covalent organic frameworks (COFs) from gas storage and separation to drug delivery [29]. Xingyi Li and colleagues summarized the recent advances of constructing various stimuli-responsive hydrogels by using self-assembled prodrugs as building unit [30]. Yu Liu and colleagues reported the construction of cyclodextrin/polyethylenimine-based supramolecular nanoparticles for loading and sustained release of ATP [31]. Moreover, they also achieved the fabrication of luminescent and injectable functional supramolecular hydrogel through the non-covalent cross-linking of polymers mediated by tetraphenylethylene-bridged cyclodextrin oligomers [32]. Wei Jiang and colleagues developed a bis-urea, phase-selective functional organogelator with a curved bis-naphthalene core, which can be used to recover oil spill in water when applied in the powder form [33]. Very recently, Tangxin Xiao and colleagues reviewed the recent progress on artificial light-harvesting systems (LHSs) fabricated by supramolecular host-guest interaction, and these varied examples have greatly enriched the field of artificial LHSs [34]. They also summarized the research process of dynamic functional supramolecular materials fabricated from water-soluble pillar[n]arenes with triethylene oxide groups [35].

  In addition, some excellent examples about the synthesis of novel macrocycles and their interesting properties and applications have also been reported. For example, Jianxin Song and colleagues reported the one-pot synthesis of β to β terpyridylenebridged porphyrin nanorings through Suzuki-Miyaura crossing coupling reaction [36]. Xinghai Shen and colleagues obtained a novel single crystal of Th(Ⅳ) with cucurbit[6]uril [37]. Wei Sun et al. reported a novel nonheme manganese(Ⅲ)-peroxo complex bearing a proline-derived pentadentate aminobenzimidazole ligand, which showed good reactivity in aldehyde deformylation [38].

  We wish this virtual special issue would provide a useful platform for readers to get an over view of the versatile research fields of supramolecular chemistry. We should also clearly know that the development of supramolecular chemistry, especially the functionalization of supramolecular systems, is still in its infancy period, and we are still far away from the ultimate goal. In the future, we anticipate that more and more highly functionalized supramolecular materials will be reported and the field as a whole will have a 'bright' future.

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