| Electronic Structure and Spectroscopy of Cadmium Sulfide Clusters |
12 FEB 96 |
41 pages |
| Authors:
Hui-Jean Liu; Joseph T. Hupp; Mark A. Ratner; NORTHWESTERN UNIV EVANSTON IL DEPT OF CHEMISTRY
|
 | There has been extensive study, both experimentally and theoretically, on how a semiconductor nanocrystal evolves to a bulk material and how its corresponding electronic properties change. Experimental observations show a close relationship between the size of nanocrystals, the lowest energy optical absorption peak and the highest energy band of the luminescence spectrum. These are usually assigned to the transition between the valence band and the conduction band or, in the ... |
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| Semiconductor Based Interfacial Electron Transfer Reactivity: Decoupling Kinetics from pH Dependent Band Energetics in a Dye-Sensitized Titanium Dioxide/ Aqueous Solution System |
26 OCT 95 |
17 pages |
| Authors:
Susan G. Yan; Joseph T. Hupp; NORTHWESTERN UNIV EVANSTON IL DEPT OF CHEMISTRY
|
| Hexaphosphonation of Ru(bpy)3(2+) provides a basis for surface attachment to nanocrystalline TiO2 in film (electrode) or colloidal form and for subsequent retention of the molecule over an extraordinarily wide pH range. Visible excitation of the surface attached complex leads to rapid injection of an electron into the semiconductor. Return electron transfer, monitored by transient absorbance spectroscopy, is biphasic with a slow component that can be reversibly eliminated by adjusting the ... |
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| Energetics of Semiconductor Electrode/Solution Interfaces: EQCM Evidence For Charge-Compensating Cation Adsorption and Intercalation During Accumulation Layer Formation in the Titanium Dioxide/Acetonitrile System |
31 MAY 95 |
15 pages |
| Authors:
L. A. Lynn; Joseph T. Hupp; NORTHWESTERN UNIV EVANSTON IL DEPT OF CHEMISTRY
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| Combined reflectance, electrochemical quartz crystal microbalance and conventional voltammetric measurements on high area titanium dioxide electrodes in dry, electrolyte-containing solutions of acetonitrile show that electron accumulation layer formation is coupled directly to irreversible intercalation (e.g. Li+ or Na+) or to quasi-reversible adsorption (tetraethylammonium ion) of charge compensating cations. Difficulty in achieving intercalation with these ions appears to account for the extreme negative shift of the flatband potential in acetonitrile, in ... |
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| Toward Molecular Selectivity with Chemically Modified Electrodes: Can Electroactivity and Permeability through an Overlaying Metallopolymer Film be Controlled via Rational Manipulation of Internal Architecture? |
30 NOV 94 |
26 pages |
| Authors:
Susan G. Yan; Joseph T. Hupp; NORTHWESTERN UNIV EVANSTON IL DEPT OF CHEMISTRY
|
| Metallopolymeric films featuring widely varying metal-to-metal linkage lengths have been prepared via a combination of oxidative and reductive electropolymerization schemes. Each of the film materials exhibits strong size selective permeability behavior towards molecular reactants - providing a primitive physical basis, therefore, for selectivity with respect to reactivity at an underlying electrode. Surprisingly, the observed molecular size cutoffs are essentially independent of film composition, implying that a uniform molecular cavity or ... |
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| Ion Modulated Electroactivity in Thin-Film Polymers Derived from Bipyridyl and Phenanthroline Complexes of Iron |
10 JUN 94 |
17 pages |
| Authors:
L. A. Lyon; Mark A. Ratner; Joseph T. Hupp; NORTHWESTERN UNIV EVANSTON IL DEPT OF CHEMISTRY
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| Profound changes in the metal-centered electroactivity of thin-film redox polymer/electrolyte systems accompany the replacement of a conventional electrolyte solution (aqueous tetraethylammonium perchlorate) by any of several aq. CH3(CH2)SO3-Na(+) solutions. For example for a poly-Fe(4-methyl-4'-vinyl-2, 2'-bipyridine)3m+ film in contact with an aq. sodium decanesulfonate solution: (a) the overall redox capacity decreases by roughly half an order of magnitude, (b) the rate of hopping-based electron transport during charging decreases by 20-fold, and ... |
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| Some Perspectives on Solution-Phase Electron-Transfer Processes |
18 APR 94 |
56 pages |
| Authors:
Joseph T. Hupp; Michael J. Weaver; NORTHWESTERN UNIV EVANSTON IL DEPT OF CHEMISTRY
|
| This article presents a selective summary of pertinent issues and a review of experimental inquiries into solution-phase electron transfer processes, with illustrations taken in part from our own laboratories. Appreciable emphasis is placed on solvent effects. We preface the review with a short outline of relevant conceptual and theoretical material. Electron transfer, Electrode processes, Redox kinetics. |
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| Ion Modulated Electroactivity in Thin Film Metallopolymers |
18 APR 94 |
11 pages |
| Authors:
Joseph T. Hupp; L. A. Lyon; Mark A. Ratner; NORTHWESTERN UNIV EVANSTON IL DEPT OF CHEMISTRY
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| Electroactivity in thin-film redox polymers derived from Fe(2, 2'bipyridine)3(3+/2+) and Fe(phenanthroline)3(3+/2+) can be tremendously modulated by replacing conventional counter ions (such as perchlorate) with alkylsulfonates (CH3(CH2) nSO3, n=0-11). With large n species, the amount of charge passed during metal oxidation decreases (reversibly) by nearly an order of magnitude, while the rate of charge flow (as measured transiently by chronocoulometry) similarly decreases, again reversibly. Redox thermodynamic effects (systematic shifts in film-based ... |
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| Some Perspectives on Solution-Phase Electron-Transfer Processes |
FEB 94 |
56 pages |
| Authors:
Joseph T. Hupp; Michael J. Weaver; PURDUE UNIV LAFAYETTE IN DEPT OF CHEMISTRY
|
| The kinetics of electron-transfer (ET) process is a subject graced by a remarkable diversity as well as importance in chemistry and biology. Of the manifold types of chemical ET reactions, those occuring in solution and at electrode-solution interfaces have been the subject of a notably concerted and fruitful research effort. This activity was in large part spawned, and subsequently spurred, by the development of the theoretical treatments by Rudy Marcus ... |
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| Solvational Barriers to Interfacial Electron Transfer: Minimization via Valence Delocalization |
27 JUL 93 |
11 pages |
| Authors:
Joseph T. Hupp; Xiao L. Zhang; NORTHWESTERN UNIV EVANSTON IL DEPT OF CHEMISTRY
|
| Standard rate constants (k sub s) for interfacial electron transfer (ET) have been obtained for several redox couples featuring very small internal activation barriers. To render these ordinarily fast rates measurable, we have employed low-defect-density, highly ordered pyrolytic graphite (HOPG) as an electrode material (see: Allred and McCreery, Anal. Chem., 1992, 64, 444). At the HOPG/aqueous solution interface, we observe - for the first time - the systematic (exponential) increase ... |
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| High-Valent Oxo, Methoxorhenium Complexes: Models for Intermediates and Transition States in Proton-Coupled Multi-Electron Transfer Reactions |
30 MAY 93 |
59 pages |
| Authors:
M. S. Ram; Lisa M. Skeens-Jones; Christopher S. Johnson; Xiao L. Zhang; Joseph T. Hupp; NORTHWESTERN UNIV EVANSTON IL DEPT OF CHEMISTRY
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| Dioxorhenium(V) tetrapyridyl species are currently under active investigation as model systems for interfacial two-electron, two-proton transfer reaction sequences We now find that the corresponding oxo, methoxo complexes can be prepared from dioxo species and methyl trifluoromethanesulfonate. The new complexes behave nearly identically to the analogous oxo, hydroxo complexes-with one important exception: CH3(+), unlike H(+), does not dissociate from the oxo ligand. As a direct consequence, the usually elusive rhenium oxidation ... |
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| Structural Effects in Electron Transfer Reactions: Comparative Interfacial Electrochemical Kinetics for cis- Versus trans-Dioxorhenium(V)(bi) pyridine Oxidation |
29 MAY 93 |
26 pages |
| Authors:
Xiao L. Zhang; Joseph T. Hupp; Gerald D. Danzer; NORTHWESTERN UNIV EVANSTON IL DEPT OF CHEMISTRY
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| We have been exploring the proton-coupled reductions of various dioxorhenium(V) species because of the more general insights they provide into the kinetics and thermodynamics of multielectron transfer processes. The rhenium (V) complexes are also amenable, however, to proton-decoupled one-electron oxidation-both optically (via metal-to-ligand charge-transfer excitation; Our prior studies of electron transfer (ET) thermodynamics revealed a strong dependence of the Re (VI/V) formal potential on ligand substituent characteristics (most notably, substituent ... |
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| Fast Interfacial Electron Transfer: Evidence for Inverted Region Kinetic Behavior |
19 FEB 1993 |
14 pages |
| Authors:
Hong Lu; Janice N. Preiskorn; Joseph T. Hupp; NORTHWESTERN UNIV EVANSTON IL DEPT OF CHEMISTRY
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| Interfacial electron transfer (ET) in a prototypical semiconductor- liquid junction system (aq. Fe(CN)64-/3- with TiO2) can be initiated by directly pumping a molecule to surface charge transfer transition (max = 430nm). The return electron transfer(ET) kinetics, which can be monitored by visible-region transient-absorbance spectroscopy, reveal a well-defined fast component (r = 270ns) and a less well defined slow component (us -> ms). Detailed studies in the shorter time regime show ... |
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| Multielectron Transfer Kinetics for Cis versus Trans Dioxorhenium(V) species: Isoelectronic Modeling with Osmium(VI/V) and Control of Interfacial Reactivity by Rhenium(IV) Accessibility |
29 MAY 92 |
14 pages |
| Authors:
Lisa M. Jones-Skeens; Ziao L. Zhang; Joseph T. Hupp; NORTHWESTERN UNIV EVANSTON IL DEPT OF CHEMISTRY
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| Steady-state microelectrode voltammetry experiments show that the electrochemical exchange kinetics for the two-electron, two-proton reduction of cis-(O)2(Rev(py)2(bpy)+ (py = pyridine, bpy = 2,2' bipyridine) at pH* = 6, exceed by more than a factor of 100 the kinetics for trans(0)2Rev(py)4+ reduction under identical conditions. Mechanistic studies indicate that both reactions proceed via rate-limiting Re(V yields IV) steps. Comparisons with isoelectronic (and nearly isostructural) osmium redox couples, reveal that the key ... |
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| Unexpected Redox Rectification by an Electrochemically Prepared Iridium Oxide Electrode/Aqueous Acid Interface |
27 MAY 92 |
26 pages |
| Authors:
Christopher S. Johnson; Joseph T. Hupp; NORTHWESTERN UNIV EVANSTON IL DEPT OF CHEMISTRY
|
| In highly acidic aqueous solutions, electrochemically prepared iridium oxide films behave as steady-state insulators and transient rectifiers towards the Ru(NH3)6 3+/2+ redox couple. In less acidic solutions the films show only partial transient rectification or else fully reversible transient behavior, together with Koutecky-Levich type steady-state behavior. Experimental studies as a function of Ru(NH3)6 3+ concentration, solution pH, film thickness, voltammetric sweep rate and electrode rotation rate show that these unusual ... |
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| Resonance Raman Spectroscopic Studies of trans-Dioxorhenium(V) tetrapyridyl Species |
28 APR 92 |
16 pages |
| Authors:
Christopher S. Johnson; Carolyn Mottley; Joseph T. Hupp; NORTHWESTERN UNIV EVANSTON IL DEPT OF CHEMISTRY
|
| Resonance Raman spectra for several trans-dioxorhenium(V)tetrapyridyl species have been obtained. Excitation in the visible region (ligand-field (L-F) absorption) leads to modest enhancement of Raman scattering, chiefly for metal- oxo modes. The observations are qualitatively, consistent with an earlier luminescence study (Winkler, Gray, J. Am. Chem. Soc. 1985, 24, 346) which clearly demonstrated that L-F excitation induces displacements in O=Re=O coordinates. Excitation in the near LTV leads to much stronger scattering, ... |
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| Ultrafast Measurements on Direct Photoinduced Electron Transfer in a Mixed Valence Complex |
06 MAY 91 |
23 pages |
| Authors:
Gilbert C. Walker; Paul F. Barbara; Stephen K. Doorn; Yuhua Dong; Joseph T. Hupp; MINNESOTA UNIV MINNEAPOLIS DEPT OF CHEMISTRY
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| In this paper, we report the first direct kinetic measurement of a MMCT optically induced et reaction, and compare the experimental results to theoretical predictions using experimentally estimated parameters. Our work is oriented, in part, toward evaluating contemporary theoretical models that explicitly consider the dramatic effect of solvation dynamics on et rates. In the last decade it has been established that et rates can be directly proportional to the time ... |
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| Experimental Assessment of Dynamic Structural Parameters for Homogeneous and Interfacial Charge-Transfer Reactions: Case Studies Based on Time-Dependent Raman Scattering Methods |
19 APR 91 |
45 pages |
| Authors:
Steven K. Doorn; Robert L. Blackbourn; Christopher S. Johnson; Joseph T. Hupp; NORTHWESTERN UNIV EVANSTON IL DEPT OF CHEMISTRY
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| The application of time-dependent scattering methodologies to dynamic structural problems involving charge transfer reactions is described. We show experimentally that a time-dependent analysis of resonance-enhanced Raman scattering can lead to a complete mode-by-mode description of the vibrational structural changes accompanying charge transfer and, therefore, a complete description of the vibrational activation barrier to charge transfer. (In other words, all force constants, all mode displacements, al bond length displacements, and all ... |
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| Sym-cis-Dioxo(2,2' -bipyridine)bis(pyridine)rhenium(V) hexafluorophosphate, Sym-cis-((0)(2)Re(bpy)(py)(2))(PF(6)) |
27 JUN 90 |
8 pages |
| Authors:
M. S. Ram; Joseph T. Hupp; NORTHWESTERN UNIV EVANSTON IL DEPT OF CHEMISTRY
|
| The complex sym-cis-(Dioxo(2,2'-bipyridine)bis(pyridine)rhenium (v) has recently been synthesized and its structure has been determined. The complex represents the first confirmed hexacoordinate cis-dioxo complex of rhenium and is one of only a handful of d2 metal complexes known to possess the cis-dioxo ligand configuration. The dioxo complexes of rhenium (V) are of interest in general because of their multielectron electrochemical behavior, persistent (in some instances) photophysical activity, and possible redox catalytic ... |
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| Molecular Structure of ((O)2Re(Bipyridine)(Pyridine)2)(clO4): An Unusual Example of a d2 Metal Complex with a cis-Dioxo Ligand Configuration |
30 MAR 90 |
9 pages |
| Authors:
Robert L. Blackbourn; Lisa M. Jones; M. S. Ram; Michal Sabat; Joseph T. Hupp; NORTHWESTERN UNIV EVANSTON IL DEPT OF CHEMISTRY
|
| An x-ray crystal structure investigation has revealed that the stable octahedral complex ((O)2Re(2,2'bipyridine)(pyridine)2) . (CLO4) exists in a cis- dioxo ligand configuration. The new complex represents only the second confirmed example of the cis-dioxo structure in hexacoordinate d2 transition-metal chemistry. The cis assignment provides an explanation for the marked electrochemical and spectral differences between the bipyridyl complex and the previously known trans-dioxo rhenium tetrapyridine complex. (aw) |
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| Linear Free Energy Relations for Multielectron Transfer Kinetics: A brief Look at the Bronsted/Tafel Analogy |
NOV 89 |
16 pages |
| Authors:
M. S. Ram; Joseph T. Hupp; NORTHWESTERN UNIV EVANSTON IL DEPT OF CHEMISTRY
|
| A comparison is made between electrochemical and homogeneous redox reactivity for species involving the transfer of multiple electrons at a single thermodynamic potential. In the electrochemical case the co-reactant is the electrode; in the homogeneous case it is any of several members of a homologous series of one-electron reagents. In the latter case it is shown that the slope of a plot of the observed pseudo first order rate constant ... |
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| Synthesis and Electrochemistry of 2,2'-Bipyridyl Complexes of Dioxorhenium(V). Revision |
AUG 89 |
35 pages |
| Authors:
M. S. Ram; Christopher S. Johnson; Robert L. Blackbourn; Joseph T. Hupp; NORTHWESTERN UNIV EVANSTON IL DEPT OF CHEMISTRY
|
| The rhenium(V) bipyridyl(bpy) complexes (BPY) (PY)2Re(O)2CLO4 and (bpy) (3 - pySO3)2Re(O)2(Na).2H2O have been prepared by reaction of 2,2' - bipyridine with trans -(PY)4Re(O)2CL and trans-(3-PYSO3)4Re(O)2 (Na)3 in methanol or methanol/water solutions (py = pyridine, 3-pySO3 = 3 pyridinesulfonate). Despite the seemingly trivial change in coordination environment the bpy-containing complexes were found to behave very differently than the corresponding tetrapyridyl complexes. For example, the pH-independent formal potential for reduction of Re ... |
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| The Frequency Factor for Outer-Sphere Electrochemical Reactions |
FEB 1983 |
|
| Authors:
Joseph T. Hupp; Michael J. Weaver; PURDUE UNIV LAFAYETTE IN DEPT OF CHEMISTRY
|
 | The conventional formulation of the frequency factor (A sub (n)(e) for outer-sphere electrochemical reactions based on a 'collisional' model is compared with an alternative 'encounter preequilibrium' treatment whereby An is determined by the effective frequency of surmounting the free energy barrier within a previously assembled precursor state. The latter model is shown to provide a more appropriate description for electrochemical reactions under most conditions, in harmony with analogous considerations for ... |
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| The Significance of Electrochemical Activation Parameters for Surface- Attached Reactants |
18 NOV 1982 |
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| Authors:
Joseph T. Hupp; Michael J. Weaver; PURDUE UNIV LAFAYETTE IN DEPT OF CHEMISTRY
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| The interpretation of activation parameters for electrochemical reactions involving surface-attached or adsorbed reactants is considered, and compared with the corresponding experimental quantities for solution-phase reactants. The relation between the experimental activation parameters and the theoretically relevant quantities describing the energetics of heterogeneous electron transfer is summarized; this relationship is shown to be especially straightforward for surface-attached reactants. (Author) |
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| Specific Adsorption of Halide and Pseudohalide Ions at Electrochemically Roughened Versus Smooth Silver-Aqueous Interfaces |
NOV 1982 |
43 pages |
| Authors:
Joseph T. Hupp; D. Larkin; Michael J. Weaver; PURDUE UNIV LAFAYETTE IN DEPT OF CHEMISTRY
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| The differential capacitance of electrochemically roughened silver surfaces in mixed perchlorate electrolytes containing chloride, bromide, iodide, thiocyanate, or azide anions has been measured as a function of electrode potential and anion concentration. These results are compared with corresponding data for electropolished of the silver in order to ascertain the influence of surface roughening on the double-layer structure and composition of polycrystalline silver-aqueous interfaces. The surface concentrations of specifically adsorbed anions ... |
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| Some Comparisons between the Energetics of Electrochemical and Homogeneous Electron-Transfer Reactions |
23 NOV 1981 |
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| Authors:
Michael J. Weaver; Joseph T. Hupp; MICHIGAN STATE UNIV EAST LANSING DEPT OF CHEMISTRY
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| Some conceptual relationships between the kinetics of corresponding electrochemical and homogeneous redox processes are discussed and applied to experimental data for suitable outer-sphere reactions in order to illustrate the utility of electrochemical kinetics for gaining some fundamental insights into the energetics of electron-transfer processes. It is pointed out that electrochemical kinetics and thermodynamics measurements as a function of temperature and electrode potential yield direct information on the shapes of the ... |
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Reports by Author
