C. Michael Elliott

Near‐IR Absorption Spectra for the Buckminsterfullerene Anions: an Experimental and Theoretical Study

Abstract : C60 can exist in a number of oxidation states including C60(1-), C60(2-) and C60(3-). Ultraviolet-visible absorption data have been described. Near-infrared absorption data have not been presented for any of the oxidation states of C60. we have discovered that this is a serious oversight, because near-IR absorption peaks which are unique to C60(1-) C60(2-) and C60(3-) are observed upon one, two and three electron electrochemical reductions of C60. We have rationalized the energies and intensities of these electronic absorptions based on modifications of the known molecular orbital diagram for C60. The near-IR absorptions reported here should provide a clear and unambiguous route for determining the oxidation state of C60 in solution.

Realization of organic pn-homojunction using a novel n-type doping technique

We present a novel n-type doping technique for organic semiconductors using the metal complex bis(terpyridine)ruthenium as a strong donor. Owing to its low oxidation potential, the reduced neutral form of the donor complex allows an electron transfer to the matrix. This enables n-type conduction that has been seldom reported in metallophthalocyanine systems doped with organic compounds. The n-type zinc-phthalocyanine layers are characterized by the conductivity and the field-effect measurements. By sequential coevaporation of p- and n-doped layers, we have prepared the first stable and reproducible organic homojunction of zinc-phthalocyanine. The diode exhibits surprisingly high built-in voltage attractive e.g. for organic solar cell applications. The temperature dependence of the current-voltage characteristics does not follow the standard Shockley theory of pn-junctions. We explain the behavior of the ideality factor and the saturation current by deviations from the classical Einstein relation at low temperatures.

Aqueous and non-aqueous electrochemistry in thick-film nafion/mercury modified electrodes

Abstract Thick films (0.013 cm) of insoluble bulk Nafion can be brought into intimate electrochemical contact with liquid mercury. Electroactive exchanged into these films exhibit redox chemistry similar to the observed in solution. The fact that bulk Nafion is insoluble in most solvents allows these modified electrodes to be examined in non-aqueous solution. Consideration is also given to the problem of diffusion within permselective membranes under electrochemical conditions.

Switchable gate membranes. Conducting polymer films for the selective transport of neutral solution species

Abstract The conductive polymers poly(3-methylthiophene) and poly(N-methylpyrrole) have been explored for their use as “gate” for the separation of neutral solutes. The diffusion of a few common solvents through the films is found to depend on the oxidation state of the polymers and the dopant anion. Scanning electron micrographs show significant macroscopic morphological differences between the oxidized and reduced polymers which may be linked to the transport properties of the films.

Dye-sensitized solar cells: Out with both baby and bathwater

After two decades of research, the efficiency of dye-sensitized solar cells seems to have reached a plateau. Now, changing both electrolyte and dye opens up new opportunities that offer the hope that the efficiency ceiling can be broken.

Stability and response studies of multicolor electrochromic polymer modified electrodes prepared from tris(5,5′-dicarboxyester-2,2′-bipyridine)ruthenium(II)

Abstract A monomeric metal complex, tris(5,5′-dicarbo(3-acrylatoprop-1-oxy)-2,2′-bipyridine)ruthenium(II) as its p-toluene sulfonate salt, can be spin coated onto optically transparent SnO2 and thermally polymerized to yield a polymer modified electrode with multicolor (7 color) electrochromic properties. The polymer shows rapid electrochemical response (as short as 250 ms for total conversion through seven oxidation states) and good stability. The response and stability characteristics of the polymer have been examined with respect to polymerization conditions, electrode substrate pretreatment, solvent, supporting electrolyte, and potential excitation vs. time program

Photoinduced Multistep Charge Separation in a Heteroleptic Cu(I) Bis(phenanthroline)-Based Donor–Chromophore–Acceptor Triad

A molecular triad assembly consisting of an electron donor, a bis(phenanthroline)copper(I) chromophore, and an electron acceptor has been prepared. Under visible-light excitation, this assembly undergoes efficient (ca. 50%) photoinduced, multistep formation of a diradical cation charge-separated state that has a lifetime of >100 ns and stores >1.0 eV of energy. This system constitutes an earth-abundant functional analogue of related Ru(bpy)(3) triad systems.

Synthesis and Catalytic Activity of Transition Metal Polymers Containing Alkane‐Linked Bipyridine and Terpyridine Ligands

Transition metal polymers containing alkane-linked bi- and ter-pyridine ligands have been prepared and studied as thin films deposited on electrode surfaces. The cobalt and iron containing polymers exhibit electrochemical behavior similar to that of the corresponding monomers and to polymers formed by reductive polymerization of vinyl-containing monomers (in cases where such polymers exist). Despite these similarities, in several instances the present polymers exhibit distinctly different behavior with regard to their ability to catalyze the reduction of CO 2 and O 2 when compared to soluble monomers and other supposedly similar polymers. Consideration is given to potential structural differences that may give rise to differences in catalytic activity

Spatially Resolved Current-Voltage Measurements-Evidence for Nonuniform Photocurrents in Dye-Sensitized Solar Cells

Spatial current distributions of dye-sensitized TiO 2 solar cells (DSSCs) mediated with a cobalt polypyridine complex are described. By rastering a laser over the surface of a DSSC while measuring the short-circuit current, a spatial current image is obtained. Experiments that highlight the potential uses of this technique are discussed. First, intentional damage inflicted on the photoanode and cathode of the DSSC are visualized with the scanning technique and second, the effects of increased pressure of the cell holder clamps are discussed and shown to warrant further investigation. Finally, other variations of the scanning technique are suggested.

Electron hopping in immobilized polyvalent and/or multicouple redox systems

Abstract A general equation is derived which accounts for both diffusive and (electric) field-assisted electron hopping through a matrix comprising any number of simple or polyvalent redox couples (a simple redox couple has two valence states interconverted by the transfer of one electron; a polyvalent redox couple has three or more valence states with one-electron interconversions). The derivation evolves from a fundamental equation derived separately by Saveant and by Buck describing electron transport through a matrix comprising a single redox couple . Of particular interest is the trivalent system where the three valence states are related by A + e − ⇋ B and B + e − ⇋ C. Vectorial electron hopping can occur between appropriately positioned pairs of redox moieties: A-B ⇋ B-A; B-C ⇋ C-B; and A-C ⇋ B-B. Expressions for the electronic flux are discussed for four experimental cases: Case 1, the instantaneous electronic flux with a large excess of mobile counter ions; Case 2, the steady-state electronic flux with a large excess of mobile counterions; Case 3, the electronic flux with no counterions (i.e., the concentrations and charges of species A, B, and C sustain electroneutrality); Case 4, the electronic flux with immobile counterions. Only small (interfacial) perturbations and limiting (time independent) conditions are considered. A basis for the analysis of the electronic flux in a generalized system comprising immobilized polyvalent or multi-couple redox coupless is also presented.