Molecular rotors as a class of generally highly active ion transporters

We describe here a class of unconventional ion transporters,molecular rotors that transport ions through a rotating function rather than via traditional carrier or channel mechanisms.Mimicking macroscopic rotors,these molecular rotors consist of three modularly tunable components,i.e.,a membrane-anchoring stator,a crown ether-containing rotator for ion binding and transport,and a triple bond-based axle that allows the rotator to freely rotate around the stator in the lipid membrane.Lipid bilayer experiments reveal the generally high ability of all molecular rotors in promoting the highly efficient transmembrane K^(+)flux(EC50 values=0.49-1.37 mol%relative to lipid).While molecular rotors differing only in the ion-binding unit exhibit similar ion transport activities,those differing in the rotator’s length display activity differences by up to 174%.

Fluorescence lifetime imaging of molecular rotors to map microviscosity in cells

Fluorescence liftime imaging （FLIM） of modified hydrophobic bodipy dyes that act as fluorescent molecular rotors shows that the fluorescence lifetime of these probes is a function of the microviscosity of their environment. Incubating cells with these dyes, we find a punctate and continuous distribution of the dye in cells. The viscosity value obtained in what appears to be endocytotic vesicles in living cells is around 100 times higher than that of water and of cellular cytoplasm.Time-resolved fluorescence anisotropy measurements also yield rotational correlation times consistent with large microviscosity values. In this way, we successfully develop a practical and versatile approach to map the microviscosity in cells based on imaging fluorescent molecular rotors.

Manipulation and control of a single molecular rotor on Au(111) surface

Three different methods are used to manipulate and control phthalocyanine based single molecular rotors on Au （111） surface： （1） changing the molecular structure to alter the rotation potential; （2） using the tunnelling current of the scanning tunnelling microscope （STM） to change the thermal equilibrium of the molecular rotor; （3） artificial manipulation of the molecular rotor to switch the rotation on or off by an STM tip. Furthermore, a molecular ＇gear wheel＇ is successfully achieved with two neighbouring molecules.

Adsorption and rotational barrier for a single azobenzene molecule on Au(111)surface

The orientation switching of a single azobenzene molecule on Au(111)surface excited by tunneling electrons and/or photons has been demonstrated in recent experiments.Here we investigate the rotation behavior of this molecular rotor by first-principles density functional theory(DFT)calculation.The anchor phenyl ring prefers adsorption on top of the fcc hollow site,simulated by a benzene molecule on close packed atomic surface.The adsorption energy for an azobenzene molecule on Au(111)surface is calculated to be about 1.76 eV.The rotational energy profile has been mapped with one of the phenyl rings pivots around the fcc hollow site,illustrating a potential barrier about 50 meV.The results are consistent with experimental observations and valuable for exploring a broad spectrum of molecules on this noble metal surface.

Hierarchical Self-assembly of Atomically Precise Au Nanoclusters with Molecular Rotor-based Ligands

The hierarchical assemblies of precise nanoparticles(NPs)have created materials with emergent properties and functionalities.However,the complex assemblies remain unclear at a precise scale.Here,we show the hierarchical self-assembly of atomically precise gold nanoclusters(Au NCs)with molecular rotor-based ligands(MRL),featuring a double-layer surface.Compared to two other types of monolayer-protected(MLP)Au NCs,the significantly reduced surface density for MRL Au NCs profoundly influences their assembly behavior within the lattice.Furthermore,the long length of rotor-based ligands and the rotational freedom of the phenyl-rings of rotor-based ligands also facilitate the assembly of NCs.Our works elucidate the hierarchical assembly on a precise scale,suggesting that the rotor-based ligand’s strategy offers promising potential for designing well-defined and more complex structures in supercrystals.

Thermal-induced reversible ferroelastic phase transition in a new bromethyl-substituted molecular rotor

A new bromethyl-substituted molecular rotor, [Cu（dabcoCH2Br）（H2O）Br3] （dabcoCH2Br＋=1-（2-bromethyl）-1,4-diazoniabi- cyclo[2.2.2]octane cation）, which belongs to a family of balomethyl-substituted molecular rotors, was synthesized and struc- turally characterized. The reversible phase transition at ca. 250 K was well established for this molecular rotor by thermal analyses, variable-temperature X-ray diffraction, and variable temperature dielectric measurements. The order-disorder trans- formation of the rotator part （dabco moiety） causes ferroelastic phase transition with an Aizu notation of mmmF2/m from high- temperature orthorhombic phase （Pbnm） to low-temperature monoclinic phase （P21/n）. More important, in reference to the density functional theory calculations and structural analyses, the key factors to tune the phase transition behaviors were dis- cussed in detail for this family of halomethyl-substituted molecular rotors.

A molecular brake hoop for the motion of metal atoms inside fullerene cage

Molecular machines have attracted extensive attention due to their fancy concept and their potential to influence the science and technology.The dynamic motion of encapsulated metallic clusters is a distinctive character for endohedral metallofullerenes.For the development of molecular rotors based on metallofullerenes,the most challenging issue is how to control the motion of untouchable metallic cluster inside fullerene cage.In this work,we report a molecular brake hoop for the motion of metal atoms inside fullerene cage.A cycloparaphenylene of[12]CPP was employed to hoop the metallofullerene and produce two supramolecular complexes of Sc_(3)N@C_(80)⊂[12]CPP and Sc_(2)C_(2)@C_(82)⊂[12]CPP.Moreover,the temperature-dependent ^(45)Sc nuclear magnetic resonance spectroscopy(NMR)was employed to detect the motion of internal Sc_(3)N and Sc_(2)C_(2) clusters.^(45)Sc NMR results reveal that the[12]CPP can slow down the rotation of internal metallic cluster through host-guest interaction,and thus the[12]CPP can be considered as a molecular brake hoop for the internal metal motion of metallofullerenes.Furthermore,by means of this molecular brake hoop,the motion of metal atoms inside fullerene cage have expanded range of velocity.In addition,theoretical calculations on Sc_(3)N@C_(80)⊂[12]CPP were executed to illustrate the molecular orientation as well as internal Sc_(3)N rotation.This study would promote the research of endohedral metallofullerene as a molecular rotor.

A Crystalline Supramolecular Rotor Functioned by Dual Ultrasmall Polar Rotators

As an extended model of conventional molecular rotors,a conceived construction of novel crystalline molecular rotor that simultaneously contains two discrete polar rotators is presented here.The supramolecular self-assembly of 18-crown-6 host and two rotator-containing ion-pair guests affords a three-in-one cocrystal,(2-NH_(3)-iBuOH)(18-crown-6)[ZnBr_(3)(H_(2)O)],in which the hydroxyl group and aqua ligand both function as ultrasmall polar rotators.On the basis of the variable-temperature single-crystal X-ray diffraction,variable-temperature/frequency dielectric response,density functional theory calculations,and molecular dynamics simulations,it is found that such dual polar rotators experience a gradually enhanced rotation with increasing temperature,and more importantly,could be controlled by a reversible polar-to-polar structural phase transition,i.e.,from a“single-(polar rotator)”state at low-temperature phase to a“mixed-dual-(polar rotator)”state in the vicinity of transition,and to an unusual“synchronized-dual-(polar rotator)”state at high-temperature phase.

Julolidine-labelled fluorinated block copolymers for the development of two-layer films with highly sensitive vapochromic response

Fluorinated block copolymers composed of a polystyrene(Sx) first block and a polyacrylate second block carrying hydrophobic/lipophobic perfluorohexyl side chains(AF) were prepared by atom transfer radical polymerization(ATRP). Fluorescence emission properties were imparted to the copolymers by incorporation in the second block of a julolidine-based fluorescent molecular rotor(JCBF). The synthesized block copolymers were used as the fluorescent low-surface energy thin top-layer onto a polystyrene bottom-layer to produce novel two-layer film vapochromic sensors. Contact angle and X-ray photoelectron spectroscopy(XPS) measurements revealed that the two-layer film surfaces were hydrophobic and lipophobic at the same time and highly enriched in fluorine content as a result of the effective segregation of the perfluorinated tails to the polymer-air interface.The fluorescence intensity of the two-layer films decreased significantly when they were exposed to vapours of organic solvents,including tetrahydrofurane, chloroform, and trifluorotoluene. However, an AF content-dependent sensing behaviour was also observed, with the two-layer films containing the copolymer with the shorter fluorinated block giving a more rapid and almost quantitative decrease in fluorescence variation. Fluorescence emission of the films was also proved to vary with temperature.Both the vapochromic and thermochromic responses were reversible after successive solicitation cycles. The fluorescence variation of the two-layer films was much more marked than that of the corresponding PS/JCBF blend, thus providing a system potentially applicable as highly sensitive volatile organic compound(VOC) sensor, thanks to the active role of the fluorinated block in promoting the migration of the fluorophore to the outermost surface layers.