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.

High-yield metal transfer printing on alkyl bis-phosphonate monolayers

“…In particular, SAMs of aliphatic organophosphonic acids on metal and semiconductor oxide surfaces are of interest due to their ability to tune the electronic properties of the substrate and to their relative robustness under ambient conditions [2], [3]. α,ω-Bisphosphonic acids (bisPA), which feature a distal phosphonic acid terminating group, have found application for growing three-dimensional structures such as stacked duplex layers [4], [5]. We recently demonstrated that SAMs of aliphatic bisPAs can act as strong tunneling current attenuators -an appealing property for applications as gate dielectric modifiers in organic transistor devices [6].…”

How reliable is the ReaxFF potential for describing the structure of alkanethiols on gold? A molecular dynamics study

“…The Au(111) surface was modeled using five atomic layers, the bottom two being kept fixed and the remaining three layers being mobile. Each layer comprised 36 atoms with lateral dimensions of 15 the alkanethiols are bounded to the surface through the S atom on-top binding-sites, and form a densely packed layer arranged into a (…”

“…15 A detailed knowledge of the structure of the molecule metal interface is needed to understand the growth mechanism 16 and the electrostatic properties 17 of this kind of materials. However, the structural features of thiols absorbed on the gold(111) crystal surface are still under debate.…”

Surface‐directed molecular assembly of pentacene on aromatic organophosphonate self‐assembled monolayers explored by polarized Raman spectroscopy

“…In this regard, organophosphonates are preferable to siloxanes for modifying inorganic surfaces ( e . g ., SiO 2 ), thanks to their superior monolayer properties . Indeed, aromatic organophosphonate monolayers (SAMPs) find applications in functionalizing surfaces because of their high stability and excellent passivating properties.…”

“…In this regard, organophosphonates are preferable to siloxanes for modifying inorganic surfaces (e.g., SiO 2 ), thanks to their superior monolayer properties. [3][4][5][6][7][8][9][10] Indeed, aromatic organophosphonate monolayers (SAMPs) find applications in functionalizing surfaces because of their high stability and excellent passivating properties. High-quality organophosphonate monolayers have shown excellent dielectric and interfacial properties in high-performance OFETs.…”