7 research outputs found
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Electron transfer in weakly interacting systems
A recently proposed semiclassical model, in which an electronic transmission coefficient and a nuclear tunneling factor are introduced as corrections to the classical activated-complex expression, is described. The nuclear tunneling corrections are shown to be important only at low temperatures or when the electron transfer is very exothermic. By contrast, corrections for nonadiabaticity may be significant for most outer-sphere reactions of metal complexes. The rate constants for the Fe(H/sub 2/O)/sub 6//sup 2 +/-Fe(H/sub 2/O)/sub 6//sup 3 +/, Ru(NH/sub 3/)/sub 6//sup 2 +/-Ru(NH/sub 3/)/sub 6//sup 3 +/ and Ru(bpy)/sub 3//sup 2 +/-Ru(bpy)/sub 3//sup 3 +/ electron exchange reactions predicted by the semiclassical model are in very good agreement with the observed values. The implications of the model for optically-induced electron transfer in mixed-valence systems are noted
trans-4-[(4-Dimethylaminophenyl)ethenyl]-N-methylquinolinium p-toluenesulfonate monohydrate
In the title salt, C20H21N2+ 路 C7H7SO3- 路 H2O, the quinolinium cation exhibits a large molecular non- linear optical ( NLO) response, as determined by Stark spectroscopy, but crystallization in the centrosymmetric space group P (1) over bar precludes significant bulk NLO effects. Intermolecular O - H ... O and weak C - H ... O hydrogen bonding links the constituent molecules into a three- dimensional network
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Photochemical carbon dioxide reduction with metal complexes: Differences between cobalt and nickel macrocycles
Problems related to increases of green house gases in the atmosphere and the depletion of fossil fuels have made the conversion of CO{sub 2} into useful chemicals and fuels an important area of research. However, CO{sub 2} reduction poses many scientific challenges. Despite intense interest in photochemical and electrochemical CO{sub 2} reduction, the kinetics and mechanism of the reduction remain unclear in many systems. This research focuses on mechanistic and kinetic studies of photochemical and electrochemical CO{sub 2} reduction that involves metal complexes as catalysts. This work makes use of UV-vis, NMR, and FTIR spectroscopy, flash photolysis, pulse radiolysis, X-ray diffraction, XANES (X-ray absorption near-edge spectroscopy) and EXAFS (extended X-ray absorption fine structure). Here the authors summarize their research on photochemical carbon dioxide reduction with metal macrocycles
Syntheses and quadratic nonlinear optical properties of salts containing benzothiazolium electron-acceptor groups
A series of chromophoric salts has been prepared in which electron-rich 4-(dimethylamino) phenyl groups are connected via polyenyl chains to electron-accepting N-methylpyridinium or 3-methylbenzothiazolium units. These compounds have been characterized by using various techniques, including electronic absorption spectroscopy and cyclic voltammetry. Single-crystal X-ray structures have been determined for several salts, all of which crystallize centrosymmetrically. Molecular quadratic nonlinear optical (NLO) responses have been determined using femtosecond hyper-Rayleigh scattering (HRS) at 1300 and 800 nm and via Stark (electroabsorption) spectroscopic studies on the intense, visible pi ->pi* intramolecular charge-transfer (ICT) bands. Large red shifts in the ICT transitions on replacing a pyridinium with a benzothiazolium unit indicate that the latter acts as a more effective electron acceptor. Both HRS and Stark measurements show that the static first hyperpolarizability, beta(0) increases with polyene chain extension in both types of chromophore, and the benzothiazolium salts have larger NLO responses than their pyridinium analogues. The results of time-dependent density functional theory calculations using a polarizable solvent continuum model agree with the observation that, beta(0) increases with chain lengthening, but the observed superiority of the benzothiazolium acceptor is not predicted either in the ICT energies or, beta(0) values. Coupled perturbed Hartree-Fock and semiempirical INDO/S calculations similarly fail to reproduce this principal conclusion from the experimental studies
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