title: Molecular architecture: construction of self-assembled organophosphonate duplexes and their electrochemical characterization.
abstract: Self-assembled monolayers of phosphonates (SAMPs) of 11-hydroxyundecylphosphonic acid, 2,6-diphosphonoanthracene, 9,10-diphenyl-2,6-diphosphonoanthracene, and 10,10'-diphosphono-9,9'-bianthracene and a novel self-assembled organophosphonate duplex ensemble were synthesized on nanometer-thick SiO(2)-coated, highly doped silicon electrodes. The duplex ensemble was synthesized by first treating the SAMP prepared from an aromatic diphosphonic acid to form a titanium complex-terminated one; this was followed by addition of a second equivalent of the aromatic diphosphonic acid. SAMP homogeneity, roughness, and thickness were evaluated by AFM; SAMP film thickness and the structural contributions of each unit in the duplex were measured by X-ray reflection (XRR). The duplex was compared with the aliphatic and aromatic monolayer SAMPs to determine the effect of stacking on electrochemical properties; these were measured by impedance spectroscopy using aqueous electrolytes in the frequency range 20 Hz to 100 kHz, and data were analyzed using resistance-capacitance network based equivalent circuits. For the 11-hydroxyundecylphosphonate SAMP, C(SAMP) = 2.6 ± 0.2 μF/cm(2), consistent with its measured layer thickness (ca. 1.1 nm). For the anthracene-based SAMPs, C(SAMP) = 6-10 μF/cm(2), which is attributed primarily to a higher effective dielectric constant for the aromatic moieties (ε = 5-10) compared to the aliphatic one; impedance spectroscopy measured the additional capacitance of the second aromatic monolayer in the duplex (2ndSAMP) to be C(Ti/2ndSAMP) = 6.8 ± 0.7 μF/cm(2), in series with the first.
authors.affiliation: Walter Schottky Institut, Technische Universität München, München, Germany.
authors.forename: Anna
authors.initials: A
authors.lastname: Cattani-Scholz
authors.forename: Kung-Ching
authors.initials: KC
authors.lastname: Liao
authors.forename: Achyut
authors.initials: A
authors.lastname: Bora
authors.forename: Anshuma
authors.initials: A
authors.lastname: Pathak
authors.forename: Christian
authors.initials: C
authors.lastname: Hundschell
authors.forename: Bert
authors.initials: B
authors.lastname: Nickel
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Schwartz
authors.forename: Gerhard
authors.initials: G
authors.lastname: Abstreiter
authors.forename: Marc
authors.initials: M
authors.lastname: Tornow
mesh_terms: D000873:Anthracenes / Q000737:chemistry; D004563:Electrochemistry; D018625:Microscopy, Atomic Force; D063065:Organophosphonates / Q000737:chemistry*; D014961:X-Ray Diffraction
chemical_list: D000873:Anthracenes; D063065:Organophosphonates; C034020:anthracene