4,4′‐Bipyridine as a Unidirectional Switching Unit for a Molecular Pushing Motor

A chirality switch in which the intrinsic chirality of a 4,4′‐bipyridine is combined with a metal‐ion‐induced switching principle is described. In the uncomplexed state the 4,4′‐bipyridine unit, which is linked to an S,S,S,S‐configured cyclic imidazole peptide, is P‐configured. The addition of zinc ions leads to a rotation around the C?C bond axis of the 4,4′‐bipyridine and the M isomer of the metal complex is formed. By addition of a stronger complexing agent the metal ions are removed and the switch returns to its initial position. The combination of the chirality switch with a second switching unit allows the construction of a molecular pushing motor, which is driven chemically and by light.     

Light‐Gated Rotation in a Molecular Motor Functionalized with a Dithienylethene Switch

A multiphotochromic hybrid system is presented in which a light‐driven overcrowded alkene‐based molecular rotary motor is connected to a dithienylethene photoswitch. Ring closing of the dithienylethene moiety, using an irradiation wavelength different from the wavelength applied to operate the molecular motor, results in inhibition of the rotary motion as is demonstrated by detailed ¹H‐NMR and UV/Vis experiments. For the first time, a light‐gated molecular motor is thus obtained. Furthermore, the excitation wavelength of the molecular motor is red‐shifted from the UV into the visible‐light region upon attachment of the dithienylethene switch.     

Modulated molecular recognition by a temperature‐sensitive molecularly‐imprinted polymer

Modulated molecular recognition was achieved in a temperature‐sensitive molecularly‐imprinted polymer. Using PNIPA as the temperature‐sensitive element, the adenine‐imprinted polymer (i.e., MIP‐S) was prepared and characterized. The MIP‐S exhibited a temperature‐responsive molecular recognition behavior because of the thermal phase‐transition within the MIP‐S network. Specifically, below the transition temperature (e.g., 20 °C), the MIP‐S showed a highly specific recognition for the imprint species (adenine). However, the MIP‐S did not show any significant resolution for the imprint species (adenine) and its analogue (1‐methyladenine) above the transition temperature (e.g., 40 °C). Such temperature‐regulated recognition is comparable to a switch‐on and switch‐off process, thereby making tunable molecular recognition feasible. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2352–2360, 2009     

Cooperative Molecular Motion within a Self‐Assembled Liquid‐Crystalline Molecular Wire: The Case of a TEG‐Substituted Perylenediimide Disc

Always on the move : Molecular dynamics of perylene cores in columnar structures influences the processability and self‐healing of these materials. A combination of X‐ray scattering and advanced solid‐state NMR methods show that these systems have restricted angular mobility of the cores even in the frozen phase, and a cooperative spiral type of motion in the liquid crystalline phase (see picture).

     

Anion‐Induced Shuttling of a Naphthalimide Triazolium Rotaxane

The anion‐templated synthesis of a rotaxane structure, incorporating the new naphthalimide triazolium motif, is described and the interlocked host shown to exhibit selective, uni‐directional, anion‐induced shuttling. Initial pseudorotaxane investigations demonstrate the ability of a naphthalimide triazolium threading component to form interpenetrated assemblies with counter‐anion‐dependent co‐conformations. ¹H NMR studies reveal that the shuttling behaviour of the analogous rotaxane host system is controlled by selective anion binding and by the nature of the solvent conditions. Complete macrocycle translocation only occurs upon the recognition of the smaller halide anions (chloride and bromide). The rotaxane solid‐state crystal structure in the presence of chloride is in agreement with the solution‐phase co‐conformation. The sensitivity of the axle naphthalimide absorbance band to the position of the macrocycle component within the interlocked structure enabled the molecular motion to be observed by UV/Vis spectroscopy, and the chloride‐induced shuttling of the rotaxane was reversed upon silver hexafluorophosphate addition.     

Cooperative Self‐Assembly of a Quaternary Complex Formed by Two Cucurbit[7]uril Hosts,Cyclobis(paraquat‐p‐phenylene), and a “Designer” Guest

The self‐assembly in aqueous solution of the well‐known cyclophane, cyclobis(paraquat‐p‐phenylene) (BB⁴⁺), and two cucurbit[7]uril (CB7) hosts around a simple hydroquinol‐based, diamine guest (GH₂²⁺) was investigated by ¹H NMR and electronic absorption spectroscopies, electrospray mass spectrometry and DFT computations. The formation of a quaternary supramolecular assembly [GH₂²⁺?BB⁴⁺? (CB7)₂] was shown to be a very efficient process, which takes place not only because of the attractive forces between each of the hosts and the guest, but also because of the lateral interactions between the hosts in the final assembly. This complementary set of attractive interactions results in clear cooperative binding effects that help overcome the entropic barriers for multiple component assembly.     

Molecular Conductance through a Quadruple‐Hydrogen‐Bond‐Bridged Supramolecular Junction

A series of self‐complementary ureido pyrimidinedione (UPy) derivatives modified with different aurophilic anchoring groups were synthesized. Their electron transport properties through the quadruple hydrogen bonds in apolar solvent were probed employing the scanning tunneling microscopy break junction (STMBJ) technique. The molecule terminated with a thiol shows the optimal electron transport properties, with a statistical conductance value that approaches 10^?3 G₀. The ¹H NMR spectra and control experiments verify the formation of quadruple hydrogen bonds, which can be effectively modulated by the polarity of the solvent environment. These findings provide a new design strategy for supramolecular circuit elements in molecular electronics.     

Towards a DNA Nanoprocessor: Reusable Tile‐Integrated DNA Circuits

Modern electronic microprocessors use semiconductor logic gates organized on a silicon chip to enable efficient inter‐gate communication. Here, arrays of communicating DNA logic gates integrated on a single DNA tile were designed and used to process nucleic acid inputs in a reusable format. Our results lay the foundation for the development of a DNA nanoprocessor, a small and biocompatible device capable of performing complex analyses of DNA and RNA inputs.     

NMR Structure of a Triangulenium‐Based Long‐Lived Fluorescence Probe Bound to a G‐Quadruplex

An NMR structural study of the interaction between a small‐molecule optical probe (DAOTA‐M2) and a G‐quadruplex from the promoter region of the c‐myc oncogene revealed that they interact at 1:2 binding stoichiometry. NMR‐restrained structural calculations show that binding of DAOTA‐M2 occurs mainly through π–π stacking between the polyaromatic core of the ligand and guanine residues of the outer G‐quartets. Interestingly, the binding affinities of DAOTA‐M2 differ by a factor of two for the outer G‐quartets of the unimolecular parallel G‐quadruplex under study. Unrestrained MD calculations indicate that DAOTA‐M2 displays significant dynamic behavior when stacked on a G‐quartet plane. These studies provide molecular guidelines for the design of triangulenium derivatives that can be used as optical probes for G‐quadruplexes.     

Solution‐Processed Bulk‐Heterojunction Photovoltaic Cells Based on Dendritic and Star‐Shaped D‐π‐A Organic Dyes

A series of D ‐π‐A organic dendritic and star‐shaped molecules based on three various chromophores (i.e., the truxene nodes, triphenylamine moieties as the donor, and benzothiadiazole chromophore as the acceptor) and their corresponding model compounds are facilely developed. Their photophysical and electrochemical properties are investigated in detail by UV/Vis absorption and photoluminescent spectroscopy, and cyclic voltammetry. By changing the various conjugated spacers (i.e., single bond, double bond, and triple bond) among the three chromophores of dendritic series, their photophysical properties (that is, the one‐photon absorption range and two‐photon absorption cross‐section values) are effectively modulated. All D ‐π‐A conjugated oligomers show a broad and strong absorption band from 250 to 700 nm in thin films. Solution‐processed bulk‐heterojunction photovoltaic devices using our oligomer as donor and PCBM as acceptor are fabricated and measured. The power conversion efficiency of the devices based on our oligomers continuously increases from DBTTr to TRTD2A as a result of an increasing relative absorption intensity in longer wavelength region by changing the donor‐acceptor ratio and conjugated spacers between the donor and acceptor. The power conversion efficiency of the devices based on TRTD2A was 0.54 % under the illumination of AM 1.5 and 100 mW cm^?2, which is the highest value recorded based on D ‐π‐A conjugated oligomers containing triphenylamine moieties and benzothiadiazole chromophores with truxene to date.     

Internal‐to‐Cartesian back transformation of molecular geometry steps using high‐order geometric derivatives

In geometry optimizations and molecular dynamics calculations, it is often necessary to transform a geometry step that has been determined in internal coordinates to Cartesian coordinates. A new method for performing such transformations, the high‐order path‐expansion (HOPE) method, is here presented. The new method treats the nonlinear relation between internal and Cartesian coordinates by means of automatic differentiation. The method is reliable, applicable to any system of internal coordinates, and computationally more efficient than the traditional method of iterative back transformations. As a bonus, the HOPE method determines not just the Cartesian step vector but also a continuous step path expressed in the form of a polynomial, which is useful for determining reaction coordinates, for integrating trajectories, and for visualization. © 2013 Wiley Periodicals, Inc.     

Supramolecular Interaction of Fullerenes with a Curved π‐Surface of a Monomeric Quadruply Ring‐Fused Porphyrin

Molecular binding of fullerenes, C₆₀ and C₇₀, with the Zn^II complex of a monomeric ring‐fused porphyrin derivative ( 2 ‐py) as a host molecule, which has a concave π‐conjugated surface, has been confirmed spectroscopically. The structures of associated complexes composed of fullerenes and 2 ‐py were explicitly established by X‐ray diffraction analysis. The fullerenes in the 2:1 complexes, which consist of two 2 ‐py molecules and one fullerene molecule, are fully covered by the concave surfaces of the two 2 ‐py molecules in the crystal structure. In contrast, in the crystal structure of the 1:1 complex consisting of one 2 ‐py molecule and one C₆₀ molecule, the C₆₀ molecule formed a π–π stacked pair with a C₆₀ molecule in the neighboring complex using a partial surface, which was uncovered by the 2 ‐py molecule. Additionally, the molecular size of fullerene adopted significantly affects the ¹H NMR spectral changes and the redox properties of 2 ‐py upon the molecular binding.