Synthesis and preliminary testing of molecular wires and devices.

Presented here are several convergent synthetic routes to conjugated oligo(phenylene ethynylene)s. Some of these oligomers are free of functional groups, while others possess donor groups, acceptor groups, porphyrin interiors, and other heterocyclic interiors for various potential transmission and digital device applications. The syntheses of oligo(phenylene ethynylene)s with a variety of end groups for attachment to numerous metal probes and surfaces are presented. Some of the functionalized molecular systems showed linear, wire-like, current versus voltage (I(V)) responses, while others exhibited nonlinear I(V) curves for negative differential resistance (NDR) and molecular random access memory effects. Finally, the syntheses of functionalized oligomers are described that can form self-assembled monolayers on metallic electrodes that reduce the Schottky barriers. Information from the Schottky barrier studies can provide useful insight into molecular alligator clip optimizations for molecular electronics.

An ion-selective electrode for acetate based on a urea-functionalized porphyrin as a hydrogen-bonding ionophore.

An ion-selective electrode for acetate based on (α,α,α,α)-5,10,15,20-tetrakis[2-(4-fluorophenylureylene)phenyl]porphyrin as an ionophore that has no metal center and forms hydrogen bonds to the analyte is described. At pH 7.0 (0.1 M HEPES-NaOH buffer), the electrode based on this ionophore and cationic sites (50 mol % relative to the ionophore) responds to acetate in a linear range from 1.58 × 10(-)(4) to 1.58 × 10(-)(2) M with a slope of -54.8 ± 0.8 mV/decade and a detection limit of (3.06 ± 1.15) × 10(-)(5) M. Selectivity coefficients determined with the separate solution method (SSM) indicate that interferences of hydrophobic inorganic anions are relatively small (log[Formula: see text] (SSM): NO(3)(-), +0.68; SCN(-), +0.60; NO(2)(-), +0.22; I(-), +0.20; ClO(4)(-), +0.12; Br(-), -0.13). Responses to anions that are good hydrogen bond acceptors, i.e., Cl(-), HSO(3)(-), and HCO(3)(-), were Nernstian and were weaker than the response to acetate (log[Formula: see text] (SSM): -0.54, -0.56, and -1.34, respectively). Negligibly small responses were observed for very hydrophilic anions, i.e., F(-), SO(4)(2)(-), and H(2)PO(4)(-)/HPO(4)(2)(-). While aliphatic carboxylates such as formate, propanoate, pyruvate, and lactate gave Nernstian responses similar to acetate, interferences of salicylate and benzoate were considerably decreased in comparison with electrodes based on cationic sites only. Concentrations of acetic acid in vinegar samples were determined by direct potentiometry and agreed with values determined by a standard enzymatic method.