Keli Zhong

Synthesis and self-assembly of amphiphilic bent-shaped molecules based on dibenzo[a,c]phenazine and poly(ethylene oxide) units

Bent-shaped amphiphilic molecules 1–5, consisting of a dibenzo[a,c]phenazine unit and phenyl groups linked together as a rigid segment, and poly(ethylene oxide) (PEO) with a degree of polymerization (DP) of 6, 8 and 12 as flexible chains were synthesized and characterized. Their aggregation behavior was investigated using DSC, POM, SAXS, CD, TEM, and AFM in the bulk and aqueous solutions. Molecules 1–4 with various PEO coil chains self-organize into oblique columnar structures in the solid state. In aqueous solution, molecule 1 (with a DP of 6) self-assembles into spherical aggregates, whereas molecules 2, 3, and 5 (with coil chains longer than those of molecule 1) exhibit a self-organizing capacity to form cylindrical micelles or diverse lengths of fibers, depending on the PEO chain lengths. Interestingly, CD experiments, together with TEM investigations of molecules 4–5 incorporating lateral methyl groups at the interface of the rod and coil domains, showed that these molecules self-assemble into helical fibers. This indicates that lateral methyl groups lead to the formation of helical arrangement of the rod segments.

A Phenylbenzothiazole Derived Fluorescent Sensor for Zn(II) Recognition in Aqueous Solution Through “Turn-On” Excited-State Intramolecular Proton Transfer Emission

AbstractA highly selective and sensitive fluorescent Zn2+ sensor N-(2-(benzo[d]thiazol-2-yl)phenyl)-2-((pyridin-2-ylmethyl)amino)acetamide (1) that derived from 2-(2′-aminophenyl)benzothiazole has been developed. In aqueous solution (HEPES/CH3CN=4/6, v/v, HEPES 20xa0mM, pHu2009=u20097.4), sensor 1 displays highly selective recognition to Zn2+ over other metal ions with a distinct longer-wavelength emission enhancement. Sensor 1 binds Zn2+ through its amide form with a 1:1 binding stoichiometry, which switched on the excited-state intramolecular proton transfer (ESIPT).n Graphical AbstractA simple 2-(2′-aminophenyl)benzothiazole-based fluorescent “off-on” sensor for Zn2+ recognition in HEPES/CH3CN(4/6, v/v, HEPES 20xa0mM, pHu2009=u20097.4) solution through switching on ESIPT has been developed.

Ordered nanostructures from self-assembly of rod–coil oligomers with n-shaped rod and dendritic poly(ethylene oxide) coil segment

The n-shaped rod–coil molecules consisting of an anthracene unit and two biphenyl groups connected by acetylenyl bonds as a conjugated rod segment and dendritic poly(ethylene oxide)s with different cross-sectional areas were synthesised. These new molecular structures were characterised by using 1H NMR and MALDI-TOF-MS. The self-assembly of these molecules in the bulk state and in aqueous solution was investigated using differential scanning calorimetry, X-ray diffraction and transmission electron microscopy (TEM). In the bulk state, molecule 1a with a linear coil segment, self-organised into lamellar crystalline structures, whereas molecules 1b and 1c with di- and tetra-branched dendritic wedges did not solidify at room temperature. Dynamic light scattering and TEM experiments reveal that in aqueous solution, the molecules exhibit a strong tendency to organise into the thread-like fibres along the axial direction of cylindrical micelles or into the wide fibroid bundles via the aggregation of cylindrical micelles as the cross-sectional area of the dendritic coil segments increases.

Liquid Crystalline Assembly of Coil-Rod-Coil Molecules with Lateral Methyl Groups into 3-D Hexagonal and Tetragonal Assemblies

In this paper, we report the synthesis and self-assembly behavior of coil-rod-coil molecules, consisting of three biphenyls linked through a vinylene unit as a conjugated rod segment and poly(ethylene oxide) (PEO) with a degree of polymerization (DP) of 7, 12 and 17, incorporating lateral methyl groups between the rod and coil segments as the coil segment. Self-organized investigation of these molecules by means of differential scanning calorimetry (DSC), thermal polarized optical microscopy (POM) and X-ray diffraction (XRD) reveals that the lateral methyl groups attached to the surface of rod and coil segments, dramatically influence the self-assembling behavior in the liquid-crystalline mesophase. Molecule 1 with a relatively short PEO coil length (DP = 7) self-assembles into rectangular and oblique 2-dimensional columnar assemblies, whereas molecules 2 and 3 with DP of 12 and 17 respectively, spontaneously self-organize into unusual 3-dimensional hexagonal close-packed or body-centered tetragonal assemblies.

Self-assembly of amphiphilic linear diblock rod-coil molecules by hydrogen bond and π-π stacking interactions

Aromatic amphiphilic molecules (1) consisting of three biphenyl groups linked together with ether bonds as a rigid rod segment and poly(ethylene oxide) with the number of repeating units of 17 as a coil segment were synthesized, and their self-assembly behavior in the bulk state and aqueous solution was investigated. In bulk, molecules 1 self-assembled into 1-D lamellar structure in the solid state or smectic A phase in the liquid crystalline phase via the cooperative effects of π-π stacking, micro-phase separation and hydrogen bond interactions. In dilute aqueous solutions, molecules 1 were observed to self-assemble into cylindrical micelles owned uniform diameter and length of hundreds of nanometers.

Morphological Control of Coil–Rod–Coil Molecules Containing m-Terphenyl Group: Construction of Helical Fibers and Helical Nanorings in Aqueous Solution

Rod-coil molecules, composed of rigid segments and flexible coil chains, have a strong intrinsic ability to self-assemble into diverse supramolecular nanostructures. Herein, we report the synthesis and the morphological control of a new series of amphiphilic coil-rod-coil molecular isomers 1-2 containing flexible oligoether chains. These molecules are comprised of m-terphenyl and biphenyl groups, along with triple bonds, and possess lateral methyl or butyl groups at the coil or rod segments. The results of this study suggest that the morphology of supramolecular aggregates is significantly influenced by the lateral alkyl groups and by the sequence of the rigid fragments in the bulk and in aqueous solution. The molecules with different coils self-assemble into lamellar or oblique columnar structures in the bulk state. In aqueous solution, molecule 1a, with a lack of lateral groups, self-assembled into large strips of sheets, whereas exquisite nanostructures of helical fibers were obtained from molecule 1b, which incorporated lateral methyl groups between the rod and coil segments. Interestingly, molecule 1c with lateral butyl and methyl groups exhibited a strong self-organizing capacity to form helical nanorings. Nanoribbons, helical fibers, and small nanorings were simultaneously formed from the 2a-2c, which are structural isomers of 1a, 1b, and 1c. Accurate control of these supramolecular nanostructures can be achieved by tuning the synergistic interactions of the noncovalent driving force with hydrophilic-hydrophobic interactions in aqueous solution.