In recent past years, investigation of hierarchical self-assembly for constructing artificial functional materials has attracted considerable attention. Discrete metallacycles based on coordination bonds have proven to be valid scaffolds to fabricate various supramolecular polymers or smart soft matter through hierarchical self-assembly. Here, we present the first example of the hierarchical self-assembly of discrete metallacycles by taking advantage of the positive charges of the organoplatinum(II) metallacycle skeleton through multiple electrostatic interactions. Heparin, a sulfated glycosaminoglycan polymer that has been widely used as an anticoagulant drug, was selected to induce hierarchical self-assembly because of the existence of multiple negative charges. To investigate the hierarchical self-assembly process, an aggregation-induced emission (AIE) active moiety, tetra-phenylethylene (TPE), was introduced onto the metallacycle via coordination-driven self-assembly. Photophysical studies revealed that the addition of heparin to the tris-TPE metallacycles solution resulted in dramatic fluorescence enhancement, which supported the aggregation between metallacycle and heparin driven by multiple electrostatic interactions. Moreover, the entangled pearl-necklace networks were obtained through hierarchical self-assembly as detected by SEM, TEM, and LSCM experiments. In particular, single bead-like chains were observed in the AFM and TEM images, which provided direct, visual evidence for the aggregation of positively charged metallacycles and negatively charged heparin. More interestingly, further optical study demonstrated that this TPE-decorated metallacycle could function as a turn-on fluorescent probe for heparin detection with high sensitivity and selectivity. Thus, this research presents the first example of counter polyanion-induced hierarchical self-assembly of discrete metallacycles and provides a "proof-of-principle" method for heparin sensing and binding.

Cyclic processes involving medium-sized rings show low rates because internal strains-torsions and transannular interactions-are created during the reactions. High dilution is often used to slow the competing bi- and higher-molecular processes but cannot accelerate the desired cyclization reaction. Here we apply cavitands to the formation of medium- to large-sized rings through conversion of long-chain diisocyanates to cyclic ureas. The reactions take place in aqueous (D2O) solution, where hydrophobic forces drive the starting materials into the cavitands in folded conformations. The guest assumes the shape to fill the space properly, which brings the reacting ends closer together than they are in bulk solvent. Complexation overcomes some of the internal strains involved in precyclization shapes of the guest molecules and accelerates the cyclization. The results augur well for applications of water-soluble cavitands to related processes such as remote functionalization reactions.

Described herein is the behavior of a,w-dienes sequestered within cavitands in aqueous (D 2 O) solution. Hydrophobic forces drive the dienes into the cavitands in conformations that best fill the available space.Shorter dienes (C9 and C10) bind in compressed conformations that tumble rapidly in the cavitands.L onger dienes induce capsule formation between cavitands with self-complementary hydrogen bonding sites,w here the dienes exist in extended conformations.Incavitands unable to form capsules,longer dienes adopt folded structures.T he wider open ends allowt he synthesis of medium-sized cycloalkenes by ring-closing metathesis reactions with the Hoveyda-Grubbs-II catalyst. Yields of cycloheptene and cyclooctene were enhanced by the chaperones in water when compared with reactions of the free dienes in either aqueous media or chloroform, and even cyclononene could be prepared within the cavitand.Molecularcontainerhostshavereceivedmuchattentionfor their ability to confine guest molecules and affect their reactivity.T he use of self-assembly has expanded the use of these containers for the promotion of reactions in small spaces. [1] We recently reported the synthesis and characterization of the deep cavitand 1a [2] (Figure 1). Thes elfcomplementary pattern of hydrogen bond donors and acceptors on the upper rim was devised by de Mendoza, [3] who showed that dimerization to host capsules occurs with suitable guests in organic solvents.W ef ound that pyridinium or methylimidazolium "feet" provided good solubility in water, and the formation of capsules occurs even in aqueous solutions when large hydrophobic guests are present. [4] To prevent such dimerization, we exhaustively N-methylated the benzimidazolones of the upper rim to form the octamethyl urea 1b (Supporting Information). Thec avitand 1b showed good solubility in water (D 2 O), where it exists as avelcrand [5] dimer in the absence of guests.H erein we report the complexation of symmetrical aliphatic a,w-dienes (C9-C14) with cavitands 1a and 1b,a nd their applications for olefin metathesis in otherwise reluctant cyclizations.Alkenes bound inside synthetic host structures are not often reported [6] because the NMR signals of the olefinic protons are rarely observed given the overlap with the signals of the cavitands. [7] We used commercially available a,w-dienes:C 91 ,8-nonadiene (2a), C10 1,9-decadiene (2b), C11 1,10-undecadiene (2c), C12 1,11-dodecadiene (2d), and C14 1,13-tetradecadiene (2f). TheC13 1,12-tridecadiene (2e) was synthesized by reaction of 10-bromo-1-decene with allylmagnesium bromide. [8] Brief sonication of these a,w-dienes (0.5 mm)w ith 1a (0.5 mm)i nw ater (D 2 O) gave host-guest complexes with 1 HNMR signals of the guest characteristically upfield-shifted by the shielding of the aromatic panels of the host structure (Figure 2; Supporting Information). Thelonger a,w-dienes 2c, 2d, 2e,and 2fshow signals that are spread out between d = 1.5 and À2.0 ppm (Figure 2). Thes ignals for terminal vinyl hydrogen of C11 appears at d = 0.05 ppm (Dd = À...

The design and self-assembly of novel multipyrene hexagonal metallacycles via coordination-driven selfassembly is described. By employing newly designed 120°d ipyridine donor and di-Pt(II) acceptor linkers substituted with pyrene, a variety of tris-and hexakis(pyrene) hexagonal metallacycles with well-defined shape and size were prepared via [3 + 3] and [6 + 6] self-assembly, respectively, under mild conditions in high yields. The structures of these novel metallacycles were well characterized by multinuclear NMR ( 31 P and 1 H) spectroscopy, cold-spray ionization time-of-flight mass spectrometry (CSI-TOF-MS), electrospray ionization timeof-flight mass spectrometry (ESI-TOF-MS), and elemental analysis. The shape and size of all hexagonal metallacycles were investigated by the PM6 semiempirical molecular orbital method. The preliminary study of their spectroscopic behavior was also carried out. It was found that these pyrene-modified metallacycles displayed different optical behaviors, which might be caused by the structural effects.

A discrete hexagonal metallacycle decorated with multiple amide groups and long hydrophobic alkyl chains was constructed via [3+3] coordination-driven self-assembly, from which the ordered nanofibers and stimuli-responsive supramolecular gels were successfully obtained via hierarchical self-assembly.