Physical Chemistry Chemical Physics

doi: 10.1039/c3cp90058dpmid: N/A

doi: 10.1039/c3cp90059bpmid: N/A

doi: 10.1039/c3cp90061dpmid: N/A

Liu, Chuan; Li, Yun; Lee, Michael V.; Kumatani, Akichika; Tsukagoshi, Kazuhito

doi: 10.1039/c3cp44715dpmid: 23546448

Self-assembly of interfaces is of great interest in physical and chemical domains. One of the most challenging targets is to obtain an optimal interface structure showing good electronic properties by solution-processing. Interfaces of semiconductor/semiconductor, semiconductor/insulator and insulator/insulator have been successfully manipulated to obtain high-performance devices. In this review we discuss a special class of interface, semiconductor/insulator interface, formed by vertical phase separation during spin-coating and focus on the versatile applications in organic field-effect transistors (OFETs). The formation of such an interface can be finished within tens of seconds and its mechanism is related to the materials, surfaces and dynamics. Fascinatingly, such self-assembly could be used to simplify the fabrication procedure, improve film spreading, change interfacial properties, modify semiconductor morphology, and encapsulate thin films. These merits lead to OFETs with high performance and good reliability. Also, the method is very suitable for combining with other solution-processed techniques such as patterning and post-annealing, which leads to facile paper electronics, in situ purification and single crystal formation. Research on this topic not only provides an in-depth understanding of self-assembly in solution processing, but also opens new paths towards flexible organic electronics.

Hoffmann, Armin; Neupane, Krishna; Woodside, Michael T.

doi: 10.1039/c3cp44564jpmid: 23612887

Protein misfolding and aggregation are relevant to many fields. Recently, their investigation has experienced a revival as a central topic in the research of numerous human diseases, including Parkinson's and Alzheimer's. Much has been learned from ensemble biochemical approaches, but the inherently heterogeneous nature of the underlying processes has obscured many important details. Single-molecule techniques offer unique capabilities to study heterogeneous systems, while providing high temporal and structural resolution to characterize them. In this Perspective, we give an overview of the single-molecule assays that have been applied to protein misfolding and aggregation, which are mainly based on fluorescence and force spectroscopy. We describe some of the technical challenges involved in studying aggregation at the single-molecule level and discuss what has been learned about aggregation mechanisms from the different approaches.

Yoo, Choong-Shik

doi: 10.1039/c3cp50761kpmid: 23615853

Carbon dioxide exhibits a richness of high-pressure polymorphs with a great diversity in intermolecular interaction, chemical bonding, and crystal structures. It ranges from typical molecular solids to fully extended covalent solids with crystal structures similar to those of SiO2. These extended solids of carbon dioxide are fundamentally new materials exhibiting interesting optical nonlinearity, low compressibility and high energy density. Furthermore, the large disparity in chemical bonding between the extended network and molecular structures results in a broad metastability domain for these phases to room temperature and almost to ambient pressure and thereby offers enhanced opportunities for novel materials developments. Broadly speaking, these molecular-to-non-molecular transitions occur due to electron delocalization manifested as a rapid increase in electron kinetic energy at high density. The detailed mechanisms, however, are more complex with phase metastabilities, path-dependent phases and phase boundaries, and large lattice strains and structural distortions – all of which are controlled by well beyond thermodynamic constraints to chemical kinetics associated with the governing phases and transitions. As a result, the equilibrium phase boundary is difficult to locate precisely (experimentally or theoretically) and is often obscured by the presence of metastable phases (ordered or disordered). This paper will review the pressure-induced transformations observed in highly compressed carbon dioxide and present chemistry perspectives on those molecular-to-non-molecular transformations that can be applied to other low-Z molecular solids at Mbar pressures where the compression energy rivals the chemical bond energies.

Ehrenfreund, Eitan; Valy Vardeny, Z.

doi: 10.1039/c3cp50639hpmid: 23615781

We review the recent advances in both unipolar and bipolar organic spin valves. We discuss mechanisms that dominate the spin relaxation of injected spin aligned carriers and limit their spin diffusion length. A space charge limited current model with ferromagnetic electrodes is used to describe the bipolar organic spin valve operation. For unipolar spin valves we take into account finite spin diffusion length and obtain a general expression that is valid for devices with thick organic interlayers. For bipolar spin valves where the injected spin aligned electrons and holes selectively form polaron pairs having singlet or triplet spin configurations, we obtain modified expressions for the magneto-resistance and magneto-electroluminescence and show that they are proportional to the difference in singlet–triplet generation rates and the spin injection polarization degree of the ferromagnetic electrodes.

Duay, Jonathon; Gillette, Eleanor; Hu, Junkai; Lee, Sang Bok

doi: 10.1039/c3cp50724fpmid: 23624670

A review of electrochemically synthesized nanomaterials with different controllable architectures for electrochemical energy storage devices is shown. It is demonstrated that these nano-architectures can be created either by electrodeposition or by the electrochemical transformation of materials. Electrochemical synthesis is presented here as it provides intimate contact between the electrode and current collector and also promotes an electronic pathway for all materials to be connected to the circuit. Although still in their infancy, electrosynthesized nano-architectures show promise to be used in future electrochemical energy storage devices as utilization of this method bypasses the need for bulky conductive additives and electrochemically inactive binders. Furthermore, electrochemical transformations can be used to create additional architectural features or change the chemical make-up of the electrode. This review is meant to show the creativity of current science when it comes to these nano-architectured electrodes. It is organized by technique used for synthesis including hard template, soft template, and template-free synthesis along with electrochemical transformation techniques.

Krishna, Rajamani; van Baten, Jasper M.

doi: 10.1039/c3cp50449bpmid: 23628965

Published experimental data, underpinned by molecular simulations, are used to highlight the strong influence of adsorption thermodynamics on diffusivities of guest molecules inside ordered nanoporous crystalline materials such as zeolites, metal–organic frameworks (MOFs), and zeolitic imidazolate frameworks (ZIFs). For cage-type structures (e.g. LTA, CHA, DDR, and ZIF-8), the variation of the free energy barrier for inter-cage hopping across the narrow windows, −δFi, provides a rationalization of the observed strong influence of pore concentrations, ci, on diffusivities. In open structures with large pore volumes (e.g. FAU, IRMOF-1, CuBTC) and within channels (MFI, BEA, MgMOF-74, MIL-47, MIL-53), the pore concentration (ci) dependence of the self- (Di,self), Maxwell–Stefan (Đi), and Fick (Di) diffusivities are often strongly dictated by the inverse thermodynamic correction factor, 1/Γi ≡ ∂ln ci/∂ln pi; the magnitudes of the diffusivities are dictated by the binding energies for adsorption. For many guest–host combinations Đi−ci dependence is directly related to the 1/Γivs. ci variation. When molecular clustering occurs, we get 1/Γi > 1, causing unusual Đivs. ci dependencies. The match, or mis-match, between the periodicity of the pore landscape and the conformations of adsorbed chain molecules often leads to non-monotonic variation of diffusivities with chain lengths.

Ye, Shengfa; Geng, Cai-Yun; Shaik, Sason; Neese, Frank

doi: 10.1039/c3cp00080jpmid: 23632340

This perspective discusses the principles of the multistate scenario often encountered in transition metal catalyzed reactions, and is organized as follows. First, several important theoretical concepts (physical versus formal oxidation states, orbital interactions, use of (spin) natural and corresponding orbitals, exchange enhanced reactivity and the connection between valence bond and molecular orbital based electronic structure analysis) are presented. These concepts are then used to analyze the electronic structure changes occurring in the reaction of C–H bond oxidation by FeIVoxo species. The analysis reveals that the energy separation and the overlap between the electron donating orbitals and electron accepting orbitals of the FeIVoxo complexes dictate the reaction stereochemistry, and that the manner in which the exchange interaction changes depends on the identity of these orbitals. The electronic reorganization of the FeIVoxo species during the reaction is thoroughly analyzed and it is shown that the FeIVoxo reactant develops oxyl radical character, which interacts effectively with the σCH orbital of the alkane. The factors that determine the energy barrier for the reaction are discussed in terms of molecular orbital and valence bond concepts.