Photon-, electron-, and proton-induced isomerization behavior of ferrocenylazobenzenes

3-, 4-, and 2-ferrocenylazobenzenes, 1, 2, and 3, respectively, and several derivatives of 1 were synthesized, and their photoisomerization behaviors were examined. The molecular structures of 1 and its derivatives, 2-chloro-5-ferrocenylazobenzene (5) and 3-ferrocenyl-4'-hydroxylazobenzene (11), were determined by X-ray diffraction analysis. 3-Ferrocenyl compound 1 undergoes reversible trans-to-cis isomerization with a single green light source and the Fe(III)/Fe(II) redox change. 4- and 2-Ferrocenyl compounds, 2 and 3, also respond to green light in addition to UV light, exciting the pi-pi* transition, but the cis molar ratio in the photostationary state (PSS) is lower than that of 1. The response to green light in 2 and 3 is caused by the MLCT (from Fe d orbital to azo pi* orbital) band excitation, while the character of the MLCT band, as estimated by time-dependent density functional theory calculations, differs between 1 and 2. The oxidized form of 2 undergoes facile cis-to-trans thermal isomerization. Both 1 and 2 undergo facile protonation and show proton-catalyzed cis-to-trans isomerization. Among the derivatives of 1, 2-chloro-5-ferrocenylazobenzene (5) exhibits the highest cis molar ratio (47%) in the PSS of green light irradiation.     

十二烷基硫酸根复合物的制备及电子转移催化剂应用

制备了三种聚烷基紫精-十二烷基硫酸根复合物(PRV-LS), 用紫外光谱、顺磁共振波谱研究了复合物的氧化、还原行为, 将复合物用作电子转移催化剂于异相体系(CH2Cl2-H2O; 1:1, 20mL)考察了其透导的偶氮苯还原。结果表明: 复合物在异相条件被还原时, 聚烷基紫精自由基(PRV^+)在LS成份的作用下发生相转移, 复合物具有良好的诱导偶氮苯还原的能力。     

Exciplex emission from electroluminescent ladder-type pentaphenylene oligomers bearing both electron- and hole-accepting substituents

We examine the photophysical properties of ladder-type pentaphenylenes, which have been prepared as prototypical "all-in-one" emissive materials bearing both electron-accepting (diaryloxadiazole) and electron-donating (triphenylamine) units. We find that donor-acceptor interactions are very dependent on the nature of the connectivity of these groups to the main pentaphenylene chain. When the oxadiazole and triphenylamine units were substituted on opposite sides of the pi-conjugated pentaphenylene chromophore, photoluminescence with long lifetimes typical of exciplex-like species was observed, while being significantly quenched by intermolecular charge separation between the substituents. By contrast, when the triphenylamine units were attached at the ends of the chromophore, no such effects were observed and a blue/green photoluminescence was obtained with very high quantum efficiency. In this latter configuration, evidence of ambipolar charge transport and a blue/green electroluminescence were additionally observed.     

Soluble electroluminescent poly(phenylene vinylene)s with balanced electron- and hole injections.

We report a new route for the design of efficient soluble electroluminescent PPV-based copolymers bearing electron-deficient oxadiazole (OXD) moieties on side chains. The introduction of OXD through a long alkylene spacer with PPV backbone provides a molecular dispersion of OXD in the film; both the side chain OXD and the main chain PPV do retain their own electron-transport and emissive properties, respectively. The use of phenylene vinylene derivatives with asymmetric and branched substituents and a long spacer provides solubility for ease of device fabrication as well as amorphous structure to allow a well-mixing of OXD groups with the main chains. By properly adjusting the OXD content through copolymerization, we can tailor the chemical structure of electroluminescent material to give a balance of hole- and electron injections for various metal cathodes, such that the quantum efficiency is significantly improved and the turn-on voltage is reduced for the devices with aluminum and calcium. For the device with calcium fabricated in open air, a maximum brightness of 15000 cd/m(2) at 15 V/100 nm and a maximum luminance efficiency of 2.27 cd/A can be obtained, respectively, about 30 times brighter and 9.4 times more efficient than those with the corresponding homopolymer, poly[2-methoxy-5-(2'-ethylhexyloxy)-p-phenylenevinylene] (MEH-PPV). The use of physical blends to simulate the copolymers provides no significant improvement, since phase-separation structures appear, causing an inefficient utilization of OXD and sometimes voltage-dependent emission spectra. The present route permits a fabrication of single layer PLED with high brightness, high efficiency, and low turn-on voltage.     

Computationally empowered design of emerging earth-abundant electrocatalysts toward electron- /proton-transferring energy conversion

Affordable and sustainable, also often quoted as Pt-free or metal-free, electrocatalysts have a pivotal role in various electrochemical energy conversion systems, which are attracting huge demands in the 21st century. Recent technological development enables us to perform computationally empowered experimental design or discovery of materials constituted of abundant elements (e.g. carbon, nitrogen, boron, etc.) with desirable electrochemical properties. These works indicate that nontraditional candidates, such as insulators being believed to unfavorable, are indeed found to be applicable as active electrocatalysts. This review summarizes state-of-the-art cooperative experimental/theoretical works devoted to understand fundamental aspects of electron- /proton-transferring surface electrochemical reactions from the point of materials. These works are expected to accelerate material research to find out optimal Pt- or metal-free electrocatalysts, even based on material classes which were previously rejected as candidates, toward electrochemical energy conversion devices.     

Haloacetaldehyde polymers and macromolecular asymmetry

Polyhaloaldehydes play a special role in aldehyde polymerization. The most prominent trihaloacetaldehyde polymer, polytrichloroacetaldehyde, opened the door to new concepts in polymer chemistry: first, cryotachensic polymerization, the separation of the initiation step from the propagation steps with the ceiling temperature principle for the fabrication of insoluble and infusible polymers, and second, the concept of macromolecular asymmetry and stereospecific and conformationally specific polymerization. Trichloroacetaldhyde could be readily polymerized with a wide range of anionic (and also some cationic) initiators. When the anionic polymerization was initiated with chiral anions, it gave polychloral of one helix sense. To understand the genesis of the polymerization, the oligomerization was investigated to learn how the stereochemistry of the polymerization was established, also in chiral form. All 10 fluoro‐, chloro‐, and bromo‐substituted trihaloacetaldehydes were synthesized as necessary and polymerized, and the polymers were investigated. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2623–2634, 2000     

Organogels of 8-quinolinol/metal(II)-chelate derivatives that show electron- and light-emitting properties

8-quinolinol/copper(II)-, palladium(II)-, and platinum(II)-chelate-based organogelators (1 M) and their nongelling reference compounds (2 M) were synthesized. Complexes 1 M could gelate various organic solvents at very low concentrations. Electron microscope measurements gave visual images of well-developed fibrous structures characteristic of low-molecular-weight organogels. UV/Vis and FTIR spectroscopy revealed that the good gelation ability of 1 M arises from the pi-pi interactions of the chelate moieties and the hydrogen-bond interactions among the amide groups. Very interestingly, field emission performances of the nanofibers prepared from the 1 M gels are evidently different depending on the electronic states of the three kinds of central metals. In addition, the 1 Pt gel shows unique thermo- and solvatochromism of visible and phosphorescent color in response to a sol-gel phase transition. Furthermore, the 1 Pt gel possesses an attractive ability to inhibit dioxygen quenching of excited triplet states, which increases the phosphorescence quantum yield of this gel. This effect is attributed to the isolation effect of the phosphorescent chelate moiety from the dioxygen-containing solution phase.     

Evaluating molecular asymmetry

A method for calculating the asymmetry parameters of molecules based on Avnir’s CSM approach combined with the “dissymmetry function” method is suggested. The performance of the approach is demonstrated on various geometrical models — high-symmetry antiprisms of S₁₀ and D₅ symmetry groups, helices, and molecular objects. It is shown that the MCSM method unambiguously determines the symmetry element or estimates the degree of asymmetry for molecules from different structural classes. A. V. Bogatskii Physiocochemical Institute, Ukrainian Academy of Sciences. Odessa State University. Translated fromZhurnal Strukturnoi Khimii, Vol. 39, No. 3, pp. 547–552, May–June, 1998.     

Organoiron activation combined with electron- and proton transfer: implications in biology, organic synthesis, catalysis and nanosciences

This Account summarizes the results obtained in our research group on the intra- and intermolecular organoiron activation of substrates by combining the coordination of arenes by CpFe^+/0 and electron and/or proton transfer. The concepts involved are those of electron and proton reservoirs, activation of O₂ by single electron transfer in solution, mimic and inhibition of the reactivity of superoxide radical anion, materials synthesis (for instance fullerene anions), electronic communication between two metals connected by a hydrocarbon bridge, activation of arene ligands for multiple functionalization, giant dendrimer synthesis and electron transfer in catalysis (redox and electron-transfer-chain).     

Spectroscopic and electronic structure studies of a dimethyl sulfoxide reductase catalytic intermediate: implications for electron- and atom-transfer reactivity

The electronic structure of a genuine paramagnetic des-oxo Mo(V) catalytic intermediate in the reaction of dimethyl sulfoxide reductase (DMSOR) with (CH(3))(3)NO has been probed by electron paramagnetic resonance (EPR), electronic absorption, and magnetic circular dichroism (MCD) spectroscopies. EPR spectroscopy reveals rhombic g- and A-tensors that indicate a low-symmetry geometry for this intermediate and a singly occupied molecular orbital that is dominantly metal centered. The excited-state spectroscopic data were interpreted in the context of electronic structure calculations, and this has resulted in a full assignment of the observed MCD and electronic absorption bands, a detailed understanding of the metal-ligand bonding scheme, and an evaluation of the Mo(V) coordination geometry and Mo(V)-S(dithiolene) covalency as it pertains to the stability of the intermediate and electron-transfer regeneration. Finally, the relationship between des-oxo Mo(V) and des-oxo Mo(IV) geometric and electronic structures is discussed relative to the reaction coordinate in members of the DMSOR enzyme family.     

Neuropeptides, neuropeptidases and brain asymmetry

Brain asymmetry is understood as an anatomical, functional or neurochemical difference between the two hemispheres. It is not a static but rather a dynamic phenomenon in which both environmental and endogenous factors act as modulators. Aging modifies brain asymmetry, and an imbalance in specific asymmetries characterizes some brain disorders such as schizophrenia, depression, infantile autism or Alzheimer's disease. However, it is not clear whether these changes are a cause or a consequence of these disorders. Although this phenomenon has been extensively studied, its functional significance is not yet clear, and the neurochemical basis underlying anatomical or functional asymmetries in the brain is still poorly understood. In recent decades intensive research on the behaviour of neuropeptides has revealed asymmetries in their distribution in the brain, and there is evidence that the lateralized patterns of distribution are involved in the regulatory control of some neuropeptidase activities. Therefore, if these enzymatic activities are distributed asymmetrically, their endogenous substrates would presumably be affected in an asymmetrical way, as would the functions they are involved in. Here we review the most significant literature regarding human and animal brain asymmetry involving neuropeptides such as corticotropin-releasing hormone, cholecystokinin, luteinizing hormone-releasing hormone, thyrotropin-releasing hormone and angiotensin II, as well as their neuropeptidases.     

Condensed phase photoelectron asymmetry

Large directional asymmetries were observed in photoelectron distributions from core and valence levels in metals and adsorbate atoms. Intensities varied by factors up to 25 as the angle between A and p was varied. The energy dependence of asymmetry showed atomic behavior similar to that expected for free atoms, modified for the tendency p∥A.     

Steric and magnetic asymmetry distinguished by encapsulation

Guests in an achiral cavity experience asymmetric magnetic environments induced by chiral centers outside the cavity.     

Charge asymmetry in HD+

Expanding the wave functions of the ground and excited states of HD(+) (or pde) in terms of spherically symmetric explicitly correlated Gaussian functions with preexponential multipliers consisting of powers of the internuclear distance, and using the variational method, we performed very accurate nonadiabatic calculations of all bound states of this system corresponding to the zero total angular momentum quantum number (vibrational states; v=0-22). The total and the transition energies obtained agree with the best available calculations. For each state we computed the expectation values of the d-p, d-e, and p-e interparticle distances. This is the first time these quantities were computed for HD(+) using rigorous nonadiabatic wave functions. While up to the v=20 state some asymmetry is showing in the d-e and p-e distances, for v=21 and v=22 we observe a complete breakdown of the Born-Oppenheimer approximation and localization of the electron almost entirely at the deuteron.     

Electrostatic induction of lipid asymmetry

The asymmetric arrangement of phospholipids between the two leaflets of the plasma membrane of eukaryotic cells is an integral part of cellular function. ATP-dependent translocases capable of selective lipid transport across the membrane are believed to play a role in this lipid asymmetry, but our understanding of this process is incomplete. Here we show the first direct and quantitative experiments demonstrating the induction of phosphatidylserine asymmetry in a membrane by electrostatic association of poly-l-lysine in an attempt to elucidate the complex factors which govern the establishment and maintenance of lipid compositional asymmetry in the plasma membrane on a fundamental level. The attractive electrostatic interactions between the charged surface-associated polylysine and phosphatidylserine are sufficient to both induce and maintain an asymmetric arrangement of phosphatidylserine in a planar supported membrane, as measured by sum-frequency vibrational spectroscopy. These studies provide a glimpse of the physical and chemical underpinnings of lipid asymmetry in the eukaryotic plasma membrane.     

Internal asymmetry in complex compounds

Summary The equilibrium spatial configuration of ligands around a central ion in six-coordinated high-spin (ionic) complexes with electron configurations dⁿ (n=1,2,...10) in the approximation of the crystal field theory has been determined theoretically. Formulas have been derived for all cases whereby it is possible to determine the deviations of the ligand positions from a regular octahedron (internal asymmetry), and formulas for additional splitting of electronic terms due to internal asymmetry. The results of applications of the theory so investigations of the physicochemical properties of complexes will be given in future communications.Translated from Zhurnal Strukturnoi Khimii, Vol. 2, No. 3, pp. 350–360, May–June, 1961