Michael O. Wolf

Transition-Metal–Polythiophene Hybrid Materials

Electropolymerization of monomers containing both transition metals and thiophene, and the properties of the resulting materials are reviewed. Polymers with metal centers linked to the backbone via a saturated linker (Type I), closely coupled to the conjugated backbone (Type II), and directly in the backbone (Type III) are described.

Direct C–F Bond Formation Using Photoredox Catalysis

We have developed the first example of a photoredox catalytic method for the formation of carbon-fluorine (C-F) bonds. The mechanism has been studied using transient absorption spectroscopy and involves a key single-electron transfer from the (3)MLCT (triplet metal-to-ligand charge transfer) state of Ru(bpy)3(2+) to Selectfluor. Not only does this represent a new reaction for photoredox catalysis, but the mild reaction conditions and use of visible light also make it a practical improvement over previously developed UV-mediated decarboxylative fluorinations.

Luminescent molecular sensors based on analyte coordination to transition-metal complexes

Abstract Recent research towards luminescent molecular chemosensors in which sensing is achieved via binding of analytes as ligands to metal-based receptors is described. In some cases, the metal complex acts both as receptor and lumophore; in others, a pendant lumophore is coordinated to the metal receptor. Analyte binding can occur at a vacant coordination site on the metal chemosensor, or alternatively by displacement of a weakly bound ligand. In the latter case, hemilabile ligands, in which the displaced ligand remains attached to the complex upon analyte binding, have also been used. Examples of each of these approaches to metal-based chemosensors are discussed.

Electronic interactions in metallated polythiophenes: what can be learned from model complexes

Conjugated polymers containing metal centers are an important class of new materials due to the coupling of the chemical, optical, and electronic properties of the metal moiety to those of the polymer. Conjugated polythiophene derivatives have been extensively explored due to their chemical stability and synthetic accessibility. Bimetallic model complexes in which the two metals are bridged by a conjugated oligothiophene provide an approach to understanding the properties of these materials. The electronic interactions between the metals in these complexes can be examined, and provide insight into coupling between analogous complexes tethered to polythiophenes. In this review such model systems are surveyed, along with some of the metal-containing polythiophene derivatives that have been prepared.

Successful Bifunctional Photoswitching and Electronic Communication of Two Platinum(II) Acetylide Bridged Dithienylethenes

Coordinating two dithienylethenes to a platinum center results in the reversible ring closure of both photochromic units in a model for a photoresponsive pi-conjugated polymer. This system demonstrates how metal-sensitized photochemistry, from a triplet excited state, circumvents the problems associated with other multicomponent photochromic systems, where significant electronic interactions in the ground state and singlet excited state prevent full photoswitching. Changes in charge-transfer behavior based upon conversion of both dithienylethenes to their ring-closed forms illustrate how photomodulation of conductivity through a conjugated polymer might be achieved using Pt-bis(acetylide)s.

Supercapacitive properties of PEDOT and carbon colloidal microspheres.

The synthesis and characterization of a new PEDOT-carbon composite prepared using a microporous carbon template are described. The electrochemical behavior of this composite, as well as that of three other colloidal materials-PEDOT-silica, PEDOT, and microporous carbon particles-is investigated with respect to their suitability as electrode materials in supercapacitors. This was accomplished by a combination of cyclic voltammetry and galvanostatic charge/discharge cycles. It was found that the PEDOT-silica composite had the lowest specific capacitance of the four materials (ca. 60 F g(-1)) and also the worst retention of the capacitance at high scan rates. In the case of pure PEDOT, microporous carbon, or PEDOT-carbon microspheres, the specific capacitances of the materials were dramatically higher (C(M) = 115, 109, and 106 F g(-1), respectively). These values are higher than those of either unstructured electropolymerized PEDOT or commercially available high-surface-area carbon. The pure PEDOT materials retained this high capacitive behavior even at faster scan rates, although the capacitance of the carbon and PEDOT-carbon microspheres dropped substantially. These results are interpreted in the context of the local microstructure of the individual colloidal particles, as well as the overall film morphology. The morphologies of both the individual particles and the electrode films were investigated by field-emission scanning electron microscopy. Due to the monodisperse nature of the microspheres, films composed of these materials necessarily possess an interconnected network of interstitial pores that allow for facile ionic diffusion. This allows for more penetration of the conjugated polymer by the ionic electrolyte and therefore higher capacitances relative to the bulk materials. These results demonstrate the feasibility of utilizing monodisperse colloidal microparticles containing conjugated polymers as electrode materials for high-energy and high-power-density supercapacitors.

Template approaches to conjugated polymer micro- and nanoparticles

The control of nanostructure and morphology in conjugated polymers is of increasing importance to organic electronics and photonics. This tutorial review discusses template-based approaches to colloidal conjugated polymer particles having diameters in the 1-1000 nm range. Both soft and hard template approaches are covered, and particular emphasis is placed on those methodologies capable of producing spherical, monodisperse particles with good colloidal stability. Factors affecting the size and morphology of the conjugated polymer microspheres are discussed. Finally, emerging applications for particles of this type are highlighted, including those in the field of photonic crystals.

Metal nanoparticle—conjugated polymer nanocomposites

Recent literature describing nanocomposites of metal nanoparticles and conjugated polymers and oligomers are reviewed. Preparation of these nanocomposites by chemical and electrochemical methods are described, and the electronic and optical properties of these materials are discussed. Some initial applications that have been investigated for such nanocomposites are covered.

Linker-Dependent Metal-Sensitized Photoswitching of Dithienylethenes

Intramolecular energy-transfer results in sensitized ring closing of a pendant dithienylethene from a platinum terpyridyl complex only when the two components are connected with a short pi-conjugated linker.

Enhanced Photoluminescence of Sulfur-Bridged Organic Chromophores

A general approach to enhancing the emission quantum yield of several widely studied organic chromophores is presented. The luminescence properties of a series of symmetrical sulfur-bridged chromophores are reported as a function of the oxidation state of the bridging sulfur atom. The photoluminescence quantum yield is significantly enhanced by successively oxidizing the sulfur bridge from sulfide (S), to sulfoxide (SO), to sulfone (SO2).