Acetone‐Induced Graphene Oxide Film Formation at the Water–Air Interface

Graphene oxide (GO) is an amphiphilic soft material, which can accumulate at the water–air interface. However, GO sheets diffuse slowly in the aqueous phase because of their large size. It is still challenging to form high quality GO films in a controllable and simple way. In this study, we showed that GO sheets can quickly migrate to the water–air interface and form thin films when a suitable amount of acetone is directly mixed with a GO aqueous dispersion. The film formation rate and surface coverage of GO sheets depend on the volume of acetone added, GO dispersion concentration, and formation time. Among several organic solvents, acetone has its advantage for GO film formation owing to its three properties: a nonsolvent to GO aqueous dispersions, miscible with a GO aqueous dispersion, and fast evaporation. Furthermore, we have found that the film formation also is governed by the size of GO sheets and their oxygen content. Although smaller GO sheets could migrate to the water–air interface faster, the overlapping of small GO sheets and the increase in contact resistance is not desirable. A higher oxygen content in GO sheets could also result in smaller GO sheets. Multilayer GO films can be obtained through layer‐by‐layer dip‐coating. These findings open opportunities in developing simple scalable GO film fabrication processes.     

Supersonic molecular beam growth of thin films of organic materials: A novel approach to controlling the structure,morphology, and functional properties

Thin films of semiconducting molecular materials can be grown with a seeded supersonic molecular beam epitaxy (SuMBE), which provides unprecedented control over structural, morphological, and, therefore, functional properties. This novel technique of deposition takes full advantage of its ability to regulate the initial state of the molecular precursors in the beams and, in particular, the kinetic energy, to control the morphology, structure, and functional properties of growing films. This article reviews the state of the art of SuMBE, discussing the basic aspects of the technique and the major achievements so far. The major results obtained with respect to growth on dielectrics and metal substrates of films of oligothiophenes and pentacene and with respect to the codeposition of phthalocyanines and fullerenes are discussed and compared with the state of the art of more conventional organic molecular beam deposition. The potential impact of SuMBE in the field of π‐conjugated materials and devices is also examined. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2501–2521, 2003     

Influence of imidazole‐based acidity control of PEDOT:PSS on its electrical properties and environmental stability

Poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) has been studied for a wide range of applications due to its potential as a transparent electrode. Herein, the use of imidazole and its derivatives as a neutralizing additive for PEDOT:PSS dispersion and in‐depth studies of their effects in terms of electrical properties and stability is reported. Although the neutralization in general reduces the electrical conductivity of PEDOT:PSS, the conductivity after imidazole treatment (685.2 S cm^?1) is higher than that after treatment of other derivatives. Spectroscopic and thermoelectric studies show that the de‐doping effect resulted in the conductivity reduction. As a trade‐off of the conductivity reduction, greatly enhanced long‐term stability and noncorrosive characteristics are obtained after neutralization. The change in sheet resistance of imidazole‐treated PEDOT:PSS after 500 h under harsh conditions (85 °C and 85% humidity) is half that of the untreated samples, demonstrating the great enhancement of the stability. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1530–1536     

Organic–Organic Heterostructures: Concepts and Applications

We review basic concepts as well as recent examples and applications of organic–organic heterostructures. We organize the different types of heterostructures according to material A deposited on material B (A/B), A co‐deposited with B (A:B), heterostructures in the monolayer regime including nanostructuring concepts and systems involving self‐assembled monolayers, as well as various other architectures, including superlattices. While most examples are related to small‐molecule organic semiconductors, many of the ideas can be applied to other systems. The central theme is growth and structure as well as optical and electronic properties. Finally, we comment on implications for device applications.     

Synthesis and Transistor Properties of Asymmetric Oligothiophenes: Relationship between Molecular Structure and Device Performance

A series of three thiophene–naphthalene‐based asymmetric oligomers—5‐decyl‐2,2′:5′,2′′:5′′,2′′′‐quaterthiophene (DtT), 5‐decyl‐5′′‐(naphthalen‐2‐yl)‐2,2′:5′,2′′‐terthiophene (D3TN), and 5‐(4‐decylphenyl)‐5′‐(naphthalen‐2‐yl)‐2,2′‐bithiophene (DP2TN)—was synthesized by Suzuki cross‐coupling reactions. The long alkyl side chains improved both the solubility of the oligomers in solvents and their tendency to self‐assemble. UV/Vis absorption measurements suggested that DtT, D3TN, and DP2TN form H‐type aggregates with a face‐to‐face packing structure. In addition, the three oligomers were found to adopt vertically aligned crystalline structures in films deposited on substrates, as revealed by grazing‐incidence wide‐angle X‐ray scattering. These oligomers were used as the active layers of p‐type organic field‐effect transistors, and the resulting devices showed field‐effect mobilities of 3.3×10^?3 cm² V^?1 s^?1 for DtT, 1.6×10^?2 cm² V^?1 s^?1 for D3TN, and 3.7×10^?2 cm² V^?1 s^?1 for DP2TN. The differences in transistor performances were attributed to the degree of π overlap and the morphological differences determined by the molecular structures.     

Polarization energies,transport gap and charge transfer states of organic molecular crystals

A self-consistent calculation of electronic polarization in organic molecular crystals and thin films is presented in terms of charge redistribution in nonoverlapping molecules in a lattice. The polarization energies P₊ and P₋ of a molecular cation and anion are found for anthracene and perelynetetracarboxylic dianhydride (PTCDA), together with binding energies of ion pairs and transport gaps of PTCDA films on metallic substrates. The 500 meV variation of P₊+P₋ with film thickness agrees with experiment, as do calculated dielectric tensors. Comparisons are made to submolecular calculations in crystals.     

Liquid-crystalline rigid-core semiconductor oligothiophenes: influence of molecular structure on phase behaviour and thin-film properties

The design, synthesis and properties of liquid-crystalline semiconducting oligothiophenes containing dithienothiophene (DTT), benzothiadiazole (BTZ) and carbazole (CBZ) rigid cores are described. The effect of molecular structure (shape, size and substitution) on their thermal behaviour and electrical properties has been investigated. Polarised optical microscopy (POM) and differential scanning calorimetry (DSC) analyses have revealed highly ordered smectic mesophases for most of the newly synthesised compounds. X-ray diffraction (XRD) studies performed at various temperatures have shown that the smectic order is retained in the crystalline state upon cooling across the transition temperature, affording cast films with a more favourable morphology for FET applications.     

Aqueous Foams: A Field of Investigation at the Frontier Between Chemistry and Physics

This paper reviews the properties of aqueous foams. The current state of knowledge is summarized briefly and the interdisciplinary aspects of this field of investigation are emphasized. Many phenomena are controlled by physical laws, but they are highly dependent upon the chemicals used as foam stabilizers: surfactants, polymers, particles. Most of the existing work is related to surfactants and polymer foams, and little is known yet for particle foams although research in this field is becoming popular. This article presents the general concepts used to describe the monolayers and the films and also some of the recent advances being made in this area.     

Molecular and Electronic‐Structure Basis of the Ambipolar Behavior of Naphthalimide–Terthiophene Derivatives: Implementation in Organic Field‐Effect Transistors

A new family of naphthalimide‐fused thienopyrazine derivatives for ambipolar charge transport in organic field‐effect transistors is presented. Their electronic and molecular structures were elucidated through optical and vibrational spectroscopy aided by DFT calculations. The results indicate that these compounds have completely planar molecular skeletons which promote good film crystallinity and low reorganization energies for both electron and hole transport. Their performance in organic field‐effect transistors is compared with twisted and planar naphthaleneamidine monoimide‐fused terthiophenes in order to understand the origin of ambipolarity in this new series of molecular semiconductors.     

SuFEx Click: New Materials from SOxF and Silyl Ethers

New forms of click chemistry present new opportunities in materials science. Sulfur(VI) fluoride exchange (SuFEx) is a recently discovered click reaction between molecules containing SO_xF groups and silyl ethers, two functionalities that are orthogonal to all other known click chemistries, that generates sulfate or sulfonate connections upon the addition of certain organobases or fluoride sources. SuFEx also has several important advantages over other click reactions in that it is insensitive to ambient oxygen and water, and its precursor materials, especially SO_xF, are chemically, UV, and thermally inert. This Concept article focuses on the unique reactivity of SuFEx and its relation to building high molecular weight polymers and surface coatings, both of which make it a powerful new tool for materials science.     

Theoretical investigation of the interactions between the π‐systems of molecular organic semiconductors and an analysis of the contributions of repulsion and electrostatics

A concept for the interactions between π‐systems is necessary to understand a number of phenomena in modern material sciences such as supramolecular properties and self‐assembly. In the present article, we investigate the intermolecular interaction energies between organic semiconductors with extended π‐systems using SAPT (symmetry‐adapted perturbation theory), LMO‐EDA (localized molecular orbital energy decomposition analysis), DFT‐D (density functional theory including dispersion corrections), and force‐field approaches. Both apolar organic molecules such as acenes and highly polarized π‐systems of merocyanines and squaraines were used to probe the influence of electrostatics on the shape of the potential energy surfaces (PES) governing the geometric structures of aggregates. Our results reveal that the shapes of the PESs result from variations in the short‐range, highly specific repulsion forces even for highly polar molecules. Using distributed quadrupoles, we show that it is nevertheless possible to mimic the intermolecular potentials with electrostatics. This is also possible with van‐der‐Waals potentials and a simple overlap‐based force‐field ansatz based on the overlap between p‐orbitals. © 2016 Wiley Periodicals, Inc.     

π‐Conjugated Dendrimers as Stable Pure‐Blue Emissive Materials: Photophysical,Electrochemical, and Electroluminescent Properties

Bigger, stronger, better : A family of giant π‐conjugated dendrimers has been developed as pure‐blue active materials for organic light‐emitting diodes. The dendrimer‐generation number has little effect on the photophysical, electrochemical, and EL properties, and device efficiency of G0 and G1 . The preliminary OLED devices achieve pure‐blue color with stable CIE chromaticity coordinates (0.16, 0.08) for both G0 and G1 .