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Title

Controlling the structural and electrical properties of diacid oligo(phenylene ethynylene) Langmuir-Blodgett films

AuthorsBallesteros, Luz M.; Martín, Santiago; Low, Paul J.; Cea, Pilar
KeywordsOligo(phenylene ethynylene)s
Scanning probe microsco
Langmuir–Blodgett films
Conducting materials
Carboxylic acids
Issue Date2013
PublisherWiley-VCH
CitationChemistry - A European Journal 19(17): 5352-5363 (2013)
AbstractThe preparation, characterization and electrical properties of Langmuir–Blodgett (LB) films composed of a symmetrically substituted oligomeric phenylene ethynylene derivative, namely, 4,4′-[1,4-phenylenebis(ethyne-2,1-diyl)]dibenzoic acid (OPE2A), are described. Analysis of the surface pressure versus area per molecule isotherms and Brewster angle microscopy reveal that good-quality Langmuir (L) films can be formed both on pure water and a basic subphase. Monolayer L films were transferred onto solid substrates with a transfer ratio of unity to obtain LB films. Both L and LB films prepared on or from a pure water subphase show a red shift in the UV/Vis spectrum of about 14 nm, in contrast to L and LB films prepared from a basic subphase, which show a hypsochromic shift of 15 nm. This result, together with X-ray photoelectron spectroscopic and quartz crystal microbalance experiments, conclusively demonstrate formation of one-layer LB films in which OPE2A molecules are chemisorbed onto gold substrates and consequently COOAu junctions are formed. In LB films prepared on a basic subphase the other terminal acid group is also deprotonated and associates with an Na+ counterion. In contrast, LB films prepared from a pure water subphase preserve the protonated acid group, and lateral H-bonds with neighbouring molecules give rise to a supramolecular structure. STM-based conductance studies revealed that films prepared from a basic subphase are more conductive than the analogous films prepared from pure water, and the electrical conductance of the deprotonated films also coincides more closely with single-molecule conductance measurements. This result was interpreted not only in terms of better electron transmission in COOAu molecular junctions, but also in terms of the presence of lateral H-bonds in the films formed from pure water, which lead to reduced conductance of the molecular junctions.
Descriptionet al.
Publisher version (URL)http://dx.doi.org/10.1002/chem.201203261
URIhttp://hdl.handle.net/10261/117513
DOI10.1002/chem.201203261
Identifiersdoi: 10.1002/chem.201203261
issn: 0947-6539
e-issn: 1521-3765
Appears in Collections:(ICMA) Artículos
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