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The combination of molecular recognition [1] and selfassembly processes [2] offers a powerful route to the development of nanoscale systems that have technological applications as sensors, devices, and switches. [3] Macrocyclic ligands continue to attract widespread attention, [4] especially when complexation of a neutral or ionic guest at one site in the molecule induces a change in the optical [5] or redox properties [6] of the system.The recent incorporation of the electroactive tetrathiafulvalene (TTF) unit into metal-binding macrocyclic structures has demonstrated that they can function as metal-cation sensors in organic media. [7] The presence of a metal cation imposes an inductive effect on the polarizable TTF system, resulting in an anodic shift of the first oxidation potential as indicated by cyclic voltammetry experiments (e.g., for compound 1, a maximum shift of DE 1,1/2 = 80 mV for Na + complexation has been observed); [7] the second oxidation potential is essentially unchanged, consistent with the expulsion of the metal cation after the first oxidation. There is current interest in electrochemically active self-assembled monolayers (SAMs), [8] and the recent observation of stable redox chemistry of TTF derivatives 2 in self-assembled monolayers [8b] prompted us to investigate thin-film electrochemical sensors based on the cation-sensitive redox-active molecules 6 and 9 immobilized on a metal surface. SAMs represent an attractive method for device fabrication, having the advantages of straightforward preparation and being generally very robust (stable to solvents, acids, and bases). The key starting reagent in our syntheses of compounds 6 and 9 (Scheme 1) is compound 3, [9] the hydrolysis of which under basic conditions (1 M sodium hydroxide in dioxane) yielded, after acidic work-up, the acid derivative 4 (75 % yield). Treatment of acid 4 with either 12-bromo-1-dodecanol or 6-bromo-1-hexanol in the presence of dicyclohexylcarbodiimide (DCC) and N,N-dimethylaminopyridine (DMAP) afforded ester derivatives 5a and 5b, respectively (75 and 85 % yield, respectively) with subsequent conversion of the bromide into a thiol being achieved by treatment with thiourea followed by basic hydrolysis of the intermediate isothiouronium salt to afford the target derivatives 6a and 6b (42 and 33 % yield, respectively). In both cases, this last step gave a complex reaction mixture; consequently, the purified yields for compounds 6a and 6b were reduced as a result of repeated chromatography. The byproducts could not be obtained pure and their structures are unknown. Reduction of compound 3 to afford the methanol derivative 7 occurred in dichloromethane at ±78 C using diisobutylaluminum hydride (DIBAL-H) [10] (85 % yield). Using a modification [11] of the Mitsunobu reaction [12] we successfully converted alcohol 7 into sulfanylmethyl derivative 9:[13] a mixture of compound 7 and thioacetic acid in tetrahydrofuran was added to a stirred mixture of diisopropyl azodicarboxylate (DIAD) and triphenylphosphine in tetrahydrofur...

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Production of smooth, defect-free silicon surfaces is essential for the fabrication of precise three-dimensional devices. Micromachining usually involves anisot ropic etching in alkaline media such as potassium hydroxide-isopropanol mixtures (KOHIIPA). The quality of the etched surfaces is highly dependent on the etching conditions and surface inhomogeneities such as micropyramids or pits can present major problems. In the present investigation, the purity of the reagents used in the etchant and the effects of dissolved gases, such as oxygen and nitrogen, on surface finish have been evaluated for KOHIIPA baths. The purity of both the water and KOH used was found to be extremely important; the best surfaces were obtained with baths prepared with the lowest impurity content. Dissolved gases had marked effects on surface finish. Pyramid-free surfaces were obtained in oxygen-saturated etchants; this is attributed to the rapid reaction of oxygen with hydrogen produced at the surface during etching, thereby decreasing hydrogen bubble formation. The opposite was seen in solutions saturated with nitrogen where pyramid formation increased. The presence of IPA in the nitrogen-saturated bath improved the sudace finish but did not prevent pyramid formation whereas with oxygen and IPA, defects were completely eliminated and surfaces with a roughness of less than 5 nm were obtained.

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