Four bridged bis(b-cyclodextrin) s tethered by different lengths of oligo(ethylenediamine)s have been synthesized and their inclusion complexation behavior with selected substrates elucidated by circular dichroism spectroscopy and fluorescence decay. In order to study their binding ability quantitatively, inclusion complexation stability constants with four dye guests, that is, brilliant green (BG), methyl orange (MO), ammonium 8-anilino-1-naphthalenesulfonic acid (ANS), and sodium 6-(p-toluidino)-2-naphthalenesulfonate (TNS), have been determined in aqueous solution at 25 8C with spectrophotometric, spectropolarimetric, or spectrofluorometric titrations. The results obtained indicate that the two tethered cyclodextrin units might cooperatively bind to a guest, and the molecular binding ability toward model substrates, especially linear guests such as TNS and MO, could be extended. The tether length plays a crucial role in the molecular recognition, the binding constants for ANS and TNS decrease linearly with an increase in the tether length of dimeric cyclodextrin. The Gibbs free energy changes (

Nanometer-sized supramolecular assemblies created by the simple inclusion complexation of host cyclodextrins (CDs) and guest molecules have attracted more and more attention in recent years because of their potential to serve as molecular devices and molecular machines, as well as functional materials. [1-4] Indeed, CDs can be threaded on a polymer chain to form a polyrotaxane and extended to molecular tubes through the cross-linking of adjacent CD units in a polyrotaxane.[5] Furthermore, b- and g-cyclodextrins can also be constructed into nanometer-sized molecular tubes linked by diphenylhexatrienes,[6] and conjugated polyrotaxanes can be used as building blocks to form insulated molecular wires on which a- or b-CDs are threaded.[7] We recently showed that the resulting complex formed from an organoseleniumbridged b-CD dimer and a platinum ion could be fabricated into bis(molecular tube)s through formation of a pesudorotaxane with poly(propylene glycol), and the bridged bis(bcyclodextrin) s and calix[4]arene derivatives could also form nanometer-sized linear aggregations by simple host-guest inclusion complexation.[8-10] Molecular semiconductors can also be exploited for organic electronics and single molecules can be manipulated and incorporated into nano-engineered devices at a supramolecular level by threading a chargetransport macromolecule.[11-15] However, higher order polymeric rotaxanes fabricated by metal-ion binding to the inclusion complexes formed between CDs and aromatic molecules have not been investigated so far. Dipyridine-metal complexes have very interesting photochemical and other properties, and therefore many studies have been devoted to this topic.[16] Herein we report our investigations on two uncommon supramolecular aggregations: assembly 1, formed from the reaction of b-CD with 4,4'-dipyridine (DPD), and polymeric rotaxane 2, which was synthesized by coordination of 1 with NiII ions. The binding behavior of 1 and 2 was examined, both in solution and in the solid state, by 1H NMR spectroscopy, X-ray crystallography, induced circular dichroism, powder X-ray diffraction studies, thermogravimetric (TG) and differential thermal analysis (DTA), scanning tunneling microscopy (STM), and transmission electron microscopy (TEM). The binding behavior of the supramolecular assembly formed by the molecular recognition of the host and guest in solution and in the solid state is of particular interest, since the inclusion complex and the polymeric rotaxane display different photophysical behavior. The present investigations have revealed that the resulting complex of CDs with guest molecules is the first step in the formation of a polymeric rotaxane, which provides access to coordination polymeric supramolecules with CDs, and will serve to further our understanding of this developing, but less investigated, area of electroactive organic materials that contain CDs and a coordination linkage.

To investigate quantitatively the cooperative binding ability of β-cyclodextrin dimers, a series ofbridged bis(β-cyclodextrin)s with 2,2'-diselenobis(benzoyl) spacer connected by different lengths of oligo(ethylenediamine)s (2-5) and their platinum(Ⅳ) complexes (6-9) have been synthesized and their inclusion complexation behavior with selected substrates, such as Acridine Red, Neutral Red, Brilliant Green, Rhodamine B, ammonium 8-anilino-1-naphthalenesulfonate, and 6-p-toluidino-2-naphthalenesulfonic acid, were investigated by means of ultraviolet, fluorescence, fluorescence lifetime, circular dichroism, and 2D-NMR spectroscopy. The spectral titrations have been performed in aqueous phosphate buffer solution (pH 7.20) at 25°C to give the complex stability constants (KS) and Gibbs free energy changes (-△G°) for the inclusion complexation of hosts 2-9 with organic dyes and other thermodynamic parameters (△H°and T△S°) for the inclusion complexation of 2-5 with fluorescent dyes ANS and TNS. The results obtained indicate that β-cyclodextrin dimers 2-5 can coordinate with one or two platinum(Ⅳ) ions to form 1:1 or 1:2 stoichiometry metallobridged bis(β-cyclodextrin)s. As compared with parent β-cyclodextrin (1) and bis(β-cyclodextrin)s 2-5, metallobridged bis(β-cyclodextrin)s 6-9 can further switch the original molecular binding ability through the coordinating metal to orientate two β-cyclodextrin cavities and an additional binding site upon the inclusion complexation with model substrates, giving the enhanced binding constants KS for both ANS and TNS. The tether length between two cyclodextrin units plays a crucial role in the molecular recognition with guest dyes. The binding constants for TNS decrease linearly with an increase in the tether length of dimeric β-cyclodextrins. The Gibbs free energy change (-△G°) for the unit increment per ethylene is 0.32kJ•mol-1 for TNS. Thermodynamically, the higher complex stabilities of both ANS and TNS upon the inclusion complexation with 2-5 are mainly contributed to the favorable enthalpic gain (-△H°) by the cooperative binding of one guest molecule in the closely located two β-cyclodextrin cavities as compared with parent β-cyclodextrin. The molecular binding ability and selectivity of organic dyes by hosts 1-9 are discussed from the viewpoints of the multiple recognition mechanism and the size/shape-fitting relationship between host and guest.

Two channel-type supramolecular aggregations 1 and 2 were prepared by the inclusion complex of β-cyclodextrin with 2,2'-dipyridine and 4,4'-dipyridine, respectively, and their binding ability and assembly behavior were investigated comprehensively by X-ray crystallography, 1H NMR, circular dichroism spectra, and microcalorimetric titration in solution and the solid state. The obtained results revealed that the hydrogen bonds and π-πstacking interactions are crucial factors for the formation of the molecular aggregations containing β-cyclodextrin and dipyridines. The disparity of nitrogen atom position in dipyridines leads not only to the distinct crystal system and space group, i.e., monoclinic system (C2) for 1 and triclinic system (P-1) for 2, but also different binding modes and thermodynamical parameters upon complexation of 2,2'-dipyridine and 4,4'-dipyridine with β-cyclodextrin in aqueous solution.

he obtained results indicate that watersoluble cyclodextrin–fullerene complexes show unique photophysical and biological properties. Recently, our studies indicated that the resultant complexes of bis-cyclodextrins and pharmacy molecules significantly enhance both water solubility and biological activity of fullerene derivatives.[21] Herein, we report a simple way to prepare a water-soluble fullerene assembly with a coordinated metal center through end-to-end intermolecular inclusion complexation of a dimeric cyclodextrin with a fullerene. Furthermore, the assembly behavior of this complex has been comprehensively investigated by UV/Vis absorption, FTIR, 1H NMR, and 13C NMR spectroscopies, elemental analysis, thermogravimetric analysis (TGA), scanning tunneling microscopy (STM), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The biological activity of the assembly was assayed under visible light irradiation and another in dark as a control, which indicates that the assembly may serve as an effective photodriven DNA cleaver.