Showing papers by "Mark S. Wrighton published in 1994"

Functional Group Imaging by Chemical Force Microscopy

Abstract: Mapping the spatial arrangement of chemical functional groups and their interactions is of significant importance to problems ranging from lubrication and adhesion to recognition in biological systems. A force microscope has been used to measure the adhesive and friction forces between molecularly modified probe tips and organic monolayers terminating in a lithographically defined pattern of distinct functional groups. The adhesive interactions between simple CH(3)/CH(3), CH(3)/COOH, and COOH/COOH functional groups correlate directly with friction images of sample surfaces patterned with these groups. Thus, by monitoring the friction between a specifically functionalized tip and sample, one can produce friction images that display predictable contrast and correspond to the spatial distribution of functional groups on the sample surface. Applications of this chemically sensitive imaging technique are discussed.

Living Cyclopolymerization of 1,6-Heptadiyne Derivatives Using Well-Defined Alkylidene Complexes: Polymerization Mechanism, Polymer Structure, and Polymer Properties

Abstract: We report here the living cyclopolymerization of 1,6-heptadiyne derivatives (usually 4,4-disubstituted) using well-defined alkylidene complexes as initiators. Diethyl dipropargylmalonate (2a), di-tert-butyl dipropargylmalonate (2b), optically active di-(1R,2S,5R)-([minus])-menthyl dipropargylmalonate (2c([minus])), di-(1S,2R,5S)-(+)-menthyl dipropargylmalonate (2c(+)), di-(1R)-endo-(+)-fenchyl dipropargylmalonate (2d), 4,4-bis[[(p-tolylsulfonyl) oxy]methyl]-1,6-heptadiyne (3b), 4,4-bis[(trimethylsiloxy)methyl]-1,6-heptadiyne (3c), the cyclic silyl ether, PhEtSi(OCH[sub 2])[sub 2]C-(CH[sub 2]C[triple bond]CH)[sub 2] (3d), and N,N-dipropargyl-2,4,6-triisopropylbenzamide (5b) are polymerized to give soluble polymers in high yield using Mo(NAr)(CHCMe[sub 2]Ph)(OR[sub F6])[sub 2] (1a; Ar = 2,6-i-Pr[sub 2]C[sub 6]H[sub 3], OR[sub F6] = OCMe(CF[sub 3])[sub 2]) as the initiator in 1,2-dimethoxyethane (DME). The polymers show a high degree of conjugation ([lambda][sub max] > 500 nm) and have narrow molecular weight distributions. Poly(2a) is soluble in most organic solvents (THF, C[sub 6]H[sub 6], toluene, CH[sub 2]Cl[sub 2], CHCl[sub 3], DME, DMF, MeCN). The mechanism of the polymerization has been investigated by [sup 1]H NMR studies and by monomer, initiator, and solvent variations. Symmetric, diphenyl-capped polyenes, [open quotes]pull-pull[close quotes] polyenes containing p-cyanophenyl end groups, and [open quotes]push-push[close quotes] polyenes containing p-dimethylamino end groups have all been prepared. 93 refs., 12 figs., 11 tabs.

Flat Band Potential Measurements of Naked and Viologen-Modified n-WS2 Electrodes in Aqueous Iodide and Triiodide Solutions

Abstract: The flat band potentials, E[sub FB], of naked n-WS[sub 2] electrodes and cationic viologen polymer-modified n-WS[sub 2] electrodes have been determined in KI and KI[sub 3] solutions by differential capacitance measurements. The E[sub FB] values for naked n-WS[sub 2] electrodes are shifted negatively in electrolyte media containing I[sup [minus]] or I[sub 3][sup [minus]]. This negative shift is much larger in the I[sub 3][sup [minus]] solution than in the I[sup [minus]] solution. The magnitude of the shift depends on the concentration of I[sup [minus]] or I[sub 3][sup [minus]] in the solution, and this dependence can be modeled by Langmuir adsorption isotherms. The polymer-modified electrodes are formed by deposition of the polymer via hydrolysis of N,N[prime]-(bis(p-trimethoxysilyl)-benzyl)-4,4[prime]-bipyridinium. Because of the high concentration of anions in the cationic viologen polymer due to electrostatic forces, the polymer-modified n-WS[sub 2] surface is in contact with a high concentration of I[sup [minus]] or I[sub 3][sup [minus]] even in dilute I[sup [minus]] or I[sub 3][sup [minus]] solution. However, the E[sub FB] shifts are about the same for both naked and polymer-modified electrodes in a wide range of concentrations of I[sup [minus]] or I[sub 3][sup [minus]] solution, as expected form a thermodynamic analysis. 11 refs., 7 figs., 1 tab.