Controlling the structural and electrical properties of diacid oligo(phenylene ethynylene) Langmuir-Blodgett films.
Controlling the structural and electrical properties of diacid oligo(phenylene ethynylene) Langmuir-Blodgett films.
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DOI：
10.1002/chem.201203261
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发表时间：
2013-04
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通讯作者：
L. Ballesteros;S. Martín;Javier Cortés;Santiago Marqués-González;S. Higgins;R. Nichols;P. Low;P. Cea
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作者：
L. Ballesteros;S. Martín;Javier Cortés;Santiago Marqués-González;S. Higgins;R. Nichols;P. Low;P. Cea
本文报道了一种对称取代的低聚亚苯基乙炔衍生物4，4 ′-[1，4-亚苯基双（乙炔-2，1-二基）]二苯甲酸（OPE 2A）的LB膜的制备、表征和电学性质。分析表面压力与每分子面积的等温线和布鲁斯特角显微镜表明，高质量的朗缪尔（L）膜可以形成在纯水和碱性亚相。将单层L膜转移到固体基底上，转移比为1，以获得LB膜。在纯水亚相上或从纯水亚相制备的L和LB膜在UV/维斯光谱中显示出约14 nm的红移，与从碱性亚相制备的L和LB膜相反，其显示出15 nm的蓝移。这一结果，连同X射线光电子能谱和石英晶体微量天平实验，最终证明形成的一层LB膜，其中OPE 2A分子被化学吸附到金基板上，并因此形成-COO-Au结。在LB膜上制备的碱性亚相的其他终端酸基团也去质子化，并与Na（+）抗衡。与此相反，LB膜制备从纯水亚相保留质子化的酸基团，和横向H-键与相邻的分子产生超分子结构。基于STM的电导研究表明，从一个基本的亚相制备的薄膜比从纯水制备的类似的薄膜更导电，和去质子化的薄膜的电导也符合更密切地与单分子电导测量。这一结果被解释不仅在更好的电子传输在-COO-Au分子结，但也在横向H-键的存在下形成的膜从纯水中，这导致降低电导的分子结。
The 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 -COO-Au 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 -COO-Au 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.