Supermolecular Assemblies Research Articles

Electrical transport measurements on self-assembled organic molecular wires

The electrical properties of supermolecular assemblies of oligo(p-phenylene vinylene) were studied. These materials self-assemble into well-defined cylindrical structures in solution with lengths in the range of 100 nm-10 microm and diameters between 5 and 200 nm. Atomic force microscopy showed that by adjusting the concentration, either individual molecular wires or a dense film could be deposited. The molecular wires showed poor electrical conduction. Several tests were performed that show that it was the molecular wires themselves, not the contacts, that limit the conductivity.

Preface [Hot Topic: Supermolecular Machines and Assemblies (Guest Editors: Katherine L.B. Borden & Paul S. Freemont)

Preface [Hot Topic: Supermolecular Machines and Assemblies (Guest Editors: Katherine L.B. Borden & Paul S. Freemont)

Superexchange Mechanism of Charge Transfer in Supermolecular Assemblies

Superexchange Mechanism of Charge Transfer in Supermolecular Assemblies

Structural properties of dilute aqueous solutions of dimethylformamide and acetone based on computer simulation

The Monte Carlo simulation of molecular configurations for aqueous solutions ofN,N-dimethylformamide and acetone was carried out. The atom-atom radial distribution functions were determined. The topological properties of the H-bond system were investigated. The concentrations of closed H-bond cycles and the radial distribution functions of their geometric centers were found. It was shown that the local arrangement of molecules and supermolecular assemblies typical of the H-bond network in neat water is retained in the solutions studied.

Optical activity measurements in solids 7. Polylactides and poly(β‐hydroxybutyrates)

AbstractThe optical activities of poly‐(R)‐lactide, poly‐(S)‐lactide, poly(β‐hydroxybutyrate) and two β‐hydroxyvalerate copolymers were measured in solution, as solid powders in suspension, and where possible, as films. Poly‐(+)‐3‐methyl‐1‐pentene was also reinvestigated. In some cases the specific rotation values of powder samples showed significant differences from the values of the solution measurements. The discrepancies of the data observed seem to reflect the local environment of the polymer chains in supermolecular assemblies and consequently the solid state structure(morphology)of the polymers.The circular dichroism (CD) spectra of the polymers were also measured in solution and in the form of their films. For comparison, the CD spectra of the naturally occurring protein casein and of the synthetic polypeptide poly‐(L)‐proline were also measured.

Optical activity measurements in solids 5. Optical rotation of natural polymers

AbstractThe optical activity of ten natural‐type polymers [poly(α‐aminoacids), polysaccharides, proteins and nucleic acids] was measured in solution, as solid powders in suspension, and where possible in the form of films. In some cases the specific rotation of powder samples showed significant differences to the values obtained from solution measurements. The discrepances seem to reflect the arrangements of polymer chains in supermolecular assemblies in the polymer solid state.

Environmental effects on redox potentials of viologen groups embedded in electroactive self-assembled monolayers

Abstract : The electrochemical behavior of a new class of redox surfactant capable of forming electroactive, self-assembled monolayers was described. These compounds have redox moieties derived from the well known viologens, which display two distinct, reversible, one-electron couples. Their well behaved electrochemistry has lead to their use in a variety of studies ranging from electron transfer mediation to redox proteins to surface enhanced Raman studies of adsorption at electrode surfaces to the behavior of supermolecular assemblies at electrode surfaces. Our interest in understanding the influence of ionic interactions and solvation processes on redox behavior in such supermolecular assemblies lead us to synthesize several of these compounds and study their redox behavior in such assemblies using both electrochemical (cyclic voltametric, CV) and quartz crystal microbalance (EQCM) techniques. In this report we describe the strong dependence of the redox potential of the viologen moiety on its exact position within the assembly (i.e. with respect to the monolayer/electrode and monolayer/solution interfaces) and expand on our previous report of the dependence of electrochemical behavior on the type of anion present within the monolayer assembly.

Photochromism of spiropyran on supermolecular assemblies

The monolayer characteristics and photochromic behaviours of 1′-hexadecyl-(SP16) and 1′-octadecyl-3′,3′-dimethyl-6-nitrospiro [2H-1-benzopyran-2,2′-indoline] (SP18) were observed on supermolecular assemblies with phenylalanine (Phe) by the LB method. Photomerocyanine forms on supermolecular assemblies were stable for several days in the dark. The half decay periods were much longer than the films spread on pure water. The supermolecular systems based on LB methods suggest a very useful approach for improving the characteristics of photochromic materials.

Molecular Engineering at the Air-Water Interface: Building up Designed Supermolecular Assemblies with Amphiphilic Porphyrins

Abstract Designed supermolecular assemblies can be built up by the Langmuir-Blodgett technique, through the vectorial control of chemical interactions occurring at the air/water interface between adjacent amphiphilic molecules.

ChemInform Abstract: Interfaces Between Molecular and Polymeric “Metals”: Electrically Conductive, Structure‐Enforced Assemblies of Metallomacrocycles

The design, synthesis, characterization, and understanding of new molecular and macro-molecular substances with “metal-like” electrical properties represents an active research area at the interface of chemistry, physics, and materials science. An important, long-range goal in this field of “materials by design” is to construct supermolecular assemblies which exhibit preordained collective phenomena by virtue of “engineered” interactions between molecular building blocks. In this review, such a class of designed materials is discussed which, in addition, bridges the gap between molecular and polymeric conductors: assemblies of electrically conductive metallomacrocycles. It is seen that efforts to rationally construct stacked metal-like molecular arrays lead logically to structure-enforced macromolecular assemblies of covalently linked molecular subunits. Typical building blocks are robust, chemically versatile metallophthalocyanines. The electrical optical, and magnetic properties of these metallomacrocyclic assemblies and the fragments thereof, provide fundamental information on the connections between local atomic-scale architecture, electronic structure, and the macroscopic collective properties of the bulk solid.

Interfaces between Molecular and Polymeric “Metals”: Electrically Conductive, Structure‐Enforced Assemblies of Metallomacrocycles

AbstractThe design, synthesis, characterization, and understanding of new molecular and macro‐molecular substances with “metal‐like” electrical properties represents an active research area at the interface of chemistry, physics, and materials science. An important, long‐range goal in this field of “materials by design” is to construct supermolecular assemblies which exhibit preordained collective phenomena by virtue of “engineered” interactions between molecular building blocks. In this review, such a class of designed materials is discussed which, in addition, bridges the gap between molecular and polymeric conductors: assemblies of electrically conductive metallomacrocycles. It is seen that efforts to rationally construct stacked metal‐like molecular arrays lead logically to structure‐enforced macromolecular assemblies of covalently linked molecular subunits. Typical building blocks are robust, chemically versatile metallophthalocyanines. The electrical optical, and magnetic properties of these metallomacrocyclic assemblies and the fragments thereof, provide fundamental information on the connections between local atomic‐scale architecture, electronic structure, and the macroscopic collective properties of the bulk solid.

Polar Langmuir-Blodgett thin film layers for non-linear optical and pyroelectric applications

Abstract Advances in the synthesis of non-centrosymmetric molecules coupled with the recently acquired ability to incorporate them into stable three dimensional arrays with a high degree of order, holds out exciting possibilities for the development of high quality, low cost organic materials for a variety of applications. Langmuir-Blodgett (LB) films possessing a unique polar axis can be fabricated by depositing head to tail sequences of a specially designed molecule or better still by forming organic superlattices (alternate layers of different molecules) using purpose built equipment. Two device areas of particular interest that capitalize on this ability to form supermolecular assemblies are optoelectronics and pyroelectricity. This paper reviews the efforts that have been made in engineering molecules so as to optimize their non-linear properties. In the optics field, most attention has been placed on materials designed specifically for second harmonic generation applications. For thermal imaging pur...

Past and future impact of electroactive polymers on the electronics sector

AbstractA broad review of the field of applications of electroactive polymers, defined as inherently conductive, charged, piezoelectric and pyroelectric, and systems made electroactive by addition of conductive additives, in the field of electronics and microelectronics. Applications mentioned include the use of polymers for electrodes for rechargeable batteries, electret microphones, hydrophones, vidicons, EMI and ESD protection, and conductor and resistor tracks as thick films on printed circuit boards. Future trends as the development of supermolecular assemblies for parallel processing are also highlighted.