Synthesis of platinum(II)-complex end-tethered polymers: spectroscopic properties and nanostructured particles.

Although metal-containing polymers have been widely studied as a novel class of functional soft materials, the microphase separation between polymeric segments and metal-ligand complexes has been less addressed, which is critical to control their structures and functions. To do this, short-chain polystyrenes (PSs) have been end-functionalized with nanosized square-planar platinum(II) complexes. The platinum(II)-comprising polymers were found to show significant luminescence enhancement in chloroform/methanol solvent mixtures upon increasing the methanol composition. By modulating both the PS length and solvent quality, various self-assembled morphologies formed controllably in the mixed solvents and typical examples include nanofibers, nanoellipsoids, and nanospheres. More interestingly, the inside structures of these polymer particles are shown to be lamellar with sub-10 nm spacings, wherein the PS blocks are alternatively aligned with the platinum(II) units. Such a luminescence enhancement and hierarchical nanostructured particles originate from a subtle combination of directional Pt(II)⋯Pt(II) and/or π-π stacking interactions between the platinum(II) units and the solvophobic effect between the PS blocks. This work suggests that by microphase separating polymer chains with nanosized metal-ligand complexes, metal-containing polymers can self-assemble to form sub-10 nm scale nanostructures showcasing desired properties and functions.

Supramolecular Assembly Mediated by Metal Ions in Aqueous Solution and Its Application in Their Analysis.

A water-soluble fluorescent sensor based on the interaction of twisted cucurbit[14]uril (tQ[14]) and thiazole orange (TO) in aqueous solution was developed. Formation of the tQ[14]/TO complex gives rise to stronger fluorescence in both neutral and acidic aqueous solutions compared with that of free TO. Further experiments on the interaction of the tQ[14]/TO complex with metal ions revealed that, from a series of nineteen selected common metal ions, 1) only Hg2+ can lead to fluorescence enhancement and then quenching of the tQ[14]/TO (2:1) complex in neutral aqueous solution; 2) only Ba2+ can induce fluorescence quenching of the tQ[14]/TO (2:1) complex in aqueous HCl solution (pH 2); furthermore, the tQ[14]/TO/Ba2+ systems exhibit reversible changes in fluorescent intensity on successively adding SO42- and Ba2+ ; and 3) only Ba2+ or Pb2+ can induce fluorescence quenching of the tQ[14]/TO (15:1) complex in aqueous HCl solution (pH 2). Thus, the tQ[14]/TO complex can act as a supramolecular fluorescence-based sensor for the determination of Hg2+ , Ba2+ , and Pb2+ ions.

A New Member of the Inverted Cucurbit[n]uril Family.

A new inverted cucurbituril, namely inverted hexamethylcucurbit[3,3]uril (iMe6 Q[3,3]), has been isolated and characterized. It incorporates a single inverted un-substituted glycoluril unit oriented towards the interior of the cavity, shows good solubility in water and organic solvents (DMSO), and exhibits different selectivity for guests to those of iQ[6] and other known Q[6]s.

Synthesis of Platinum(II)-Containing Block Copolymers: Luminescence Enhancement and Controllable Self-Assembly.

In this work, a novel class of diblock polymer ligands, poly(ethylene oxide)-block-polystyrenes end-functionalized with 2,6-bis(benzimidazol-2'-yl)pyridine (bzimpy), have been synthesized and their coordination reactions with K2PtCl4 have created platinum(II)-containing diblock copolymers. They emit red phosphorescence in both THF-water and 1,4-dioxane-n-hexane mixed solvents, arising from Pt(II)···Pt(II) and/or π-π stacking interactions between the planar [Pt(bzimpy)Cl]+ units. Correspondingly, the block copolymers demonstrate a solvent-tunable self-assembly behavior to controllably generate vesicles and worms with core-shell-corona architectures. In these hierarchical nanostructures, the planar [Pt(bzimpy)Cl]+ blocks are associated together to form cores driven by Pt(II)···Pt(II) and/or π-π stacking interactions. Such cores are completely isolated by PS shells, which are further encapsulated by PEO coronas. It should be highlighted here that diblock polymers as polymeric ligands are coupled with phosphorescence platinum(II) complexes, representing a novel approach to create functional metal-containing polymer materials with hierarchical architectures.

Encapsulation of alkyldiammonium ions within two different cavities of twisted cucurbit[14]uril.

Binding interactions between twisted cucurbit[14]uril (tQ[14]) and a series of alkyldiammonium ions both in aqueous solution and DMSO media were investigated by NMR spectroscopy and ITC. Experimental data indicate that tQ[14] possesses two kinds of cavities with different space environments, which can encapsulate two or even three guest molecules with suitable shape and size.

Twisted Cucurbit[n]urils.

Two new twisted cucurbiturils, cucurbit[13]uril (tQ[13]) and cucurbit[15]uril (tQ[15]), have been synthesized and separated, and their structures have been confirmed by NMR spectroscopy and MALDI-TOF mass spectrometry together with the X-ray structures of two new complexes, {Dy(H2O)4Cd(H2O)4tQ[13]}·2.5[CdCl4]·65H2O and {Cd0.5(H2O)2tQ[15]}·[CdCl4]·47H2O. tQ[15] is the largest cucurbit[n]uril (Q[n]) in the Q[n] family reported to date. The X-ray diffraction studies of both complexes indicated that these large tQ[n]s effectively exhibit two different cavities-a central cavity and two side cavities. Preliminary host-guest behavior by each of the new systems was investigated by NMR studies.