A Crown-Ether Loop-Derivatized Oligothiophene Doubly Attached on Gold Surface as Cation-Binding Switchable Molecular Junction

electronic properties. [ 9–11 ] The interplay of the cation-binding properties of crown-ether and conformational changes has already been investigated. Thus, Shinkai used the photoisomerization of azobenzene units inserted in crown ether systems to modulate the cation binding properties of the cavity. [ 12 ] From a different viewpoint, we have shown that the cation-binding ability of a polyether loop attached at two fi xed points of an oligothiophene chain can serve as driving force to generate changes in the geometry and hence electronic properties of the conjugated system. [ 13 ] A related approach has been also used for the synthesis of polythiophene-based sensors [ 14 ] and more recently for the control of the intramolecular photoinduced electron transfer in crown ether bridged oligothiophenes. [ 15 ] In this context, we now report on the surface immobilization by double fi xation on gold surface of a dithiol quaterthiophene derivatized with a polyether loop 1-SH ( Scheme 1 ). In recent years we have extensively studied the structural conditions and synthetic approaches allowing the horizontal double fi xation of conjugated oligothiophenes as monolayers on gold surface. [ 16 ] After an analysis of the cation complexation properties of the related acetyl-protected dithiol molecule 1 in solution by UV-vis spectroscopy and cyclic voltammetry, the preparation of monolayers by double fi xation of the oligothiophene chain on gold surface will be described, the structure and properties of these monolayers will be investigated using cyclic voltammetry, ellipsometry, water contact angle measurement, XPS and their electrical properties will be assessed by contacting the monolayer with a conducting eutectic GaIn drop. Finally, preliminary results on the cation binding properties of the monolayer and investigations on the use of the immobilized molecule as a switchable molecular junction will be presented and possible transport mechanisms will be discussed. Compound 1 has been synthesized by deprotection/functionalization of the appropriately protected thiolate groups according to the already published method. [ 16b ] The detailed synthesis of this molecule and of some parent compounds will