DOI: 10.1002/adfm.200800304 Electropolymerized Self-Assembled Monolayers of a 3,4-Ethylenedioxythiophene-Thiophene Hybrid System** By Maite´na Oc ¸afrain, Truong Khoa Tran, Philippe Blanchard, Ste´phane Lenfant, Sylvie Godey, Dominique Vuillaume, and Jean Roncali* 1. Introduction The immobilization of electroactive p-conjugated systems on gold surfaces by formation of self-assembled monolayers (SAMs) [1–17] has recently become a focus of high interest motivated by their potential applications in the field of functionalized surfaces, [1] sensors, [2] molecular electronics, [3] or molecular heterojunctions for photovoltaic conversion. [4] On the other hand, several groups have reported the use of surface-immobilized electropolymerizable systems as starting point for the deposition of electrogenerated electroactive conducting polymers. [5–12] Wrighton and coworkers used pyrrole attached on silicon by a silane group to promote the adhesion of subsequently electropolymerized poly(pyrrole). [6] More recently, this method has been extended to other systems such as pyrrole-containing dendrimers, [7] aniline, [8] carba- zole, [9] thiophene, and oligothiophenes derivatives. [5,10] From a different viewpoint, several groups have investigated the possibility to electrochemically polymerize p-conjugated systems after their surface immobilization in monolayers. Electrochemical coupling of pyrrole anchored on gold surface by alkanethiols was initially claimed in 1994, [11] but these results became controversial. [12] Electrooxidation of SAMs of terthiophene–hexanethiols has been investigated by Garnier and coworkers who proposed the electrochemically induced formation of covalent b–b 0 linkages between adjacent terthiophenes. [13] In an investigation of the electrochemical behavior of terthiophene–alkanethiols on gold, Liedberg et al. concluded that electrooxidation is accompanied with deso- rption of the molecules. [14] Berlin et al. have analyzed the influence of molecular geometry on the electrochemical coupling of carboxyl terminated bi- and ter-thiophene adsorbed on ITO and they have shown that SAMs of cyclopentabithiophenes in which the conjugated system lies parallel to the surface can be electro- chemically trimerized into sexithiophene. [15] More recently, Ju ¨ ttner and coworkers have reported the preparation of monolayers of thiophene and bithiophene immobilized on iron surface by means of phosphonic acid head groups and concluded that only bithiophene could undergo electropolymerization. [16] An important conclusion arising from these previous studies is that besides a proper orientation of the immobilized polymerizable system, its oxidation potential plays a determin- ing role by limiting possible competitive oxidation of the substrate electrode. In this context, we report here on the preparation and characterization of monolayers of a bithiophenic-conjugated FULL PAPER [*] Dr. J. Roncali, Dr. M. Oc ¸afrain, Dr. T. K. Tran, Dr. P. Blanchard University of Angers, CNRS, CIMA, Group Linear Conjugated Systems 2 Bd Lavoisier, Angers 49045 (France) E-mail: jean.roncali@univ-angers.fr Dr. S. Lenfant, Dr. S. Godey, Dr. D. Vuillaume Groupe Nanostructures et Composants Mole ´culaires, IEMN, UMR CNRS 8520 Avenue Poincare ´, Villeneuve d’Ascq 59652 (France) [**] The work done at IEMN was partly supported by IRCICA. The Ministe `re de la Recherche is acknowledged for the Ph.D. grant for T. K. Tran. Supporting Information is available online from Wiley InterScience or from the author. Self-assembled monolayers (SAMs) of a conjugated bithiophenic system connected to an alkanethiol chain have been deposited on gold surface. The electroactive bithiophenic system involves a 3,4-ethylenedioxythiophene (EDOT) unit and a thiophene ring on which an alkanethiol is attached at the internal b-position via a sulfide linkage. The analysis of the structure of the SAMs by IR spectroscopy, ellipsometry, contact angle measurement and X-ray photoelectron spectroscopy (XPS) provides consistent results indicating compact monolayers in which the alkyl linkers are arranged in an almost vertical fashion while the bithiophenic- conjugated systems are essentially parallel to the surface. Cyclic voltammetry shows that application of a few potential scans to SAMs immersed in a medium containing only a supporting electrolyte leads to the typical electropolymerization curves while the CV of the electrooxized monolayer exhibits a reversible cyclic voltammogram characteristic of a stable electroactive extended conjugated system. The characterization of the electropolymerized monolayers by IR spectroscopy, ellipsometry, contact angle measurement, and XPS indicates compact monolayers. The analysis of the current voltage characteristics of the monolayers by conducting AFM before and after electrooxidation shows that the enhancement of the effective conjugation resulting from electropolymerization leads to a significant increase of the transport properties. Adv. Funct. Mater. 2008, 18, 2163–2171 ß 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 2163