New electroactive 2-n-octyloxy-5,6,11,12- tetrathiotetracene dodecylsulfate cation radical salt: Formation at the air-water interface and characteristic properties of Langmuir-Blodgett films

Abstract The formation and characteristic properties of the new electroactive 2- n -octyloxy-5,6,11,12-tetrathiotetracene dodecylsulfate cation radical salt 1 are described. The salt is prepared in monomolecular layers at the air-water interface according to the following steps: (a) neutral donor molecules of 2- n -octyloxy-5,6,11,12-tetrathiotetracene 2 are spread on an aqueous sodium dodecylsulfate solution, (b) the monolayer of 2 thus prepared is gradually oxidized by air under formation of cation radicals, while (c) the dodecylsulfate ions 3 present in the subphase are inserted in the monolayer as counterions of the cation radicals. This insertion is accompanied by an expansion of the monolayer by about 70% of the original area. The oxidized monolayers can be easily deposited on different substrates by the Langmuir-Blodgett (LB) technique. Characterization of the LB films by various spectroscopic methods such as UV-visible, IR and ESR spectroscopies indicates that the films consist exclusively of the cation radical salt 1 . Electron spin resonance spectroscopy studies suggest that the tetrathiotetracene molecular plane is oriented perpendicular to the substrate plane. It is demonstrated by conductivity measurements and cyclic voltammetry that the LB films are poorly conducting but can be reversibly oxidized and reduced electrochemically.