Alec Moradpour

Excited-state electron-transfer quenching by a series of water photoreduction mediators

Rate constants kq for the quenching of the excited state of Ru(bipy)32+ by a series of viologen salts having different redox potential E12 have been determined in deaerated aqueous solutions at pH = 5 by laser flash photolysis. The kq values are found to decrease with increasing —E12 and to correlate with the reaction free-energy change ΔG. Such a correlation is shown to be consistent with the Rehm—Weller model for electron-transfer reactions.

Ruthenium dioxide: a redox catalyst for the generation of hydrogen from water

Ruthenium dioxide, already known to be a catalyst for the oxidation of water to oxygen, has been shown to mediate effectively the generation of hydrogen from water in Ru(bipy)2+3, methyl viologen and EDTA model systems, with efficiencies even higher (pH > 5) than those of previously investigated platinum catalysts. The main factor limiting the evolution of hydrogen is found to be the destruction of the organic electron-transfer relay, and this side-reaction is attributed to H˙(ads) species formed on the particles of catalyst.

Low-temperature structural effects in the (TMTSF)2PF6 and AsF6 Bechgaard salts

We present a detailed low-temperature investigation of the statics and dynamics of the anions and methyl groups in the organic conductors (TMTSF)2PF6 and (TMTSF)2AsF6 (TMTSF: tetramethyl-tetraselenafulvalene). The 4 K neutron-scattering structure refinement of the fully deuterated (TMTSF)2PF6-D12 salt allows locating precisely the methyl groups at 4 K. This structure is compared to the one of the fully hydrogenated (TMTSF)2PF6-H12 salt previously determined at the same temperature. Surprisingly, it is found that deuteration corresponds to the application of a negative pressure of 5 × 10 2 MPa to the H12 salt. Accurate measurements of the Bragg intensity show anomalous thermal variations at low temperature both in the deuterated PF6 and AsF6 salts. Two different thermal behaviors have been distinguished. Small Bragg-angle measurements reflect the presence of low-frequency modes at characteristic energies θE = 8.3 K and θE = 6.7 K for the PF6-D12 and AsF6-D12 salts, respectively. These modes correspond to the low-temperature methyl group motion. Large Bragg-angle measurements evidence an unexpected structural change around 55 K, which probably corresponds to the linkage of the anions to the methyl groups via the formation of F ... D-CD2 bonds observed in the 4 K structural refinement. Finally we show that the thermal expansion coefficient of (TMTSF)2PF6 is dominated by the librational motion of the PF6 units. We quantitatively analyze the low-temperature variation of the lattice expansion via the contribution of Einstein oscillators, which allows us to determine for the first time the characteristic frequency of the PF6 librations: θE ≈ 50 K and θE = 76 K for the PF6-D12 and PF6-H12 salts, respectively.

Exploring the charge-ordering transition in (TMTTF)2X via thermal expansion measurements

Abstract We report results of high-resolution measurements of the c * ‐axis expansivity ( α c * ) at the charge-ordering (CO) transition for the quasi-1D (TMTTF) 2 X compounds with X = SbF 6 and Br and make a comparison with previous results for the X = PF 6 and AsF 6 salts. For X = SbF 6 , due to the screening of the long-range Coulomb forces, a sharp λ -type anomaly is observed at T CO , which contrasts with the step-like mean-field anomaly at T CO for PF 6 and AsF 6 , where CO occurs in the Mott–Hubbard charge-localized regime. For the latter two salts, a negative contribution to α c * is observed above T CO . This feature is assigned to the anions’ rigid-unit modes, which become inactive for T T CO . Our α c * results for the X = Br salt, where such rigid-unit modes are absent, reveal no traces of such negative contribution, confirming the model based on the anions’ rigid-unit modes for the X = PF 6 and AsF 6 salts.

Microwave dielectric study of spin-Peierls and charge-ordering transitions in ( TMTTF ) 2 PF 6 salts

We report a study of the 16.5 GHz dielectric function of hydrogenated and deuterated organic salts (TMTTF)

Light-induced hydrogen generation from water catalysed by ruthenium dioxide

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Magnetoelastic coupling in the spin-Peierls ground state of hydrogenated and deuterated (TMTTF)2PF6salts

PF

Does non-planarity obstruct low-dimensional conducting polyarene cation radical salts?

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Evidence for Lattice Effects at the Charge-Ordering Transition in (TMTTF)2X

. The temperature behavior of the dielectric function is consistent with short-range polar order whose relaxation time decreases rapidly below the charge ordering temperature. If this transition has more a relaxor character in the hydrogenated salt, charge ordering is strengthened in the deuterated one where the transition temperature has increased by more than thirty percent. Anomalies in the dielectric function are also observed in the spin-Peierls ground state revealing some intricate lattice effects in a temperature range where both phases coexist. The variation of the spin-Peierls ordering temperature under magnetic field appears to follow a mean-field prediction despite the presence of spin-Peierls fluctuations over a very wide temperature range in the charge ordered state of these salts.

Ring-strain-modified properties of substituted perylene radical cation salts. A solid-state carbon-13 CPMAS NMR study

Ruthenium dioxide, which is known to be a catalyst for the oxidation of water to oxygen, has been observed to mediate hydrogen formation from water in a model system containing Ru(2,2′-bipyridyl)32+, methyl viologen, and ethylenediaminetetra-acetic acid with higher efficiency above pH = 5 than that previously observed with colloidal platinum as catalyst.