Polythiophenes

Polythiophene for chemical sensors

(in situ ESR/UV-Vis-NIR voltammetric study)

J. Tarábek^a, M. Wolter^b, P. Rapta^a, W. Plieth^b, M. Maumy^c, L. Dunsch^a*

^aIFW Dresden, Helmholtzstrasse 20, D - 01069 Dresden,Germany

^bDresden University of Technology, Mommsenstr. 13, D-01062 Dresden, Germany

^cLaboratoire de Recherche Organique, ESPCI, 10 rue Vauquelin,7505 Paris, France

Preparation of conducting polymers on electrode surfaces for applications such as chemical sensors, electrocatalysts or electronic and optical devices still remains an active field of research and it is of great significance to clarify their detailed optical, electrochemical and ESR characteristics. The results will provide a better understanding of the processes occurring with additional charge transfer into the polymer. We are currently engaged in the design and spectroelectrochemical characterization of new conducting polymer architectures containing salen complexes with transition metals and their copolymers with polythiophenes containing complexing substituents . The main point is to prepare all-solid-state sensors that allows selective recognition of the ions and transduction of the chemical signal into an electric signal in the solid state .

The redox and optical properties of various newly prepared well defined polymer and copolymer films containing  thiophene units were studied using an in situ technique for simultaneous recording of responses from cyclic voltammetry, ESR and UV-VIS-NIR spectroscopy. Investigated polymers and copolymers were deposited on the optically transparent indium-tin-oxide (ITO) electrodes electrochemically or by a special chemical procedure using adhesion promoter. The redox behavior of chemically deposited polythiophene on ITO was compared with the redox behavior of the electrochemically prepared one on the same substrate.

In Fig.1 a summary of the spectroelectrochemical studies on chemically prepared polythiophene (Fig.1A) and electrochemically prepared one (Fig.1B) are presented.

Fig.1. A (a) Schematic structure of chemically deposited polythiophene on ITO,  corresponding cyclic voltammogram(0.2-1.15 V vs. Ag/AgCl) (b) and UV-VIS-NIR spectra (c). B Cyclic voltammogram(0.5-1.45 V vs. Ag/AgCl) (a) and UV-VIS-NIR spectra (b) of electrochemiccally prepared polythiophene on ITO. Carried out in acetonitrile / 0.1 M TBABF₄ solution at 5 mV/s.

The ESR/UV-VIS-NIR cyclovoltammogram of polythiophene deposited on ITO by the anodic oxidation measured in 0.1 M TBABF₄ acetonitrile  (Fig.1 B) exhibits similar characteristics as previously observed for PPy and polyaniline. The results can be interpreted assuming neutral, mono-charged and di-charged states, where the mono-charged units exhibit well known polaronic single ESR line (g = 2.0027, DH_pp = 0.2 mT) with the corresponding visible band at 1.4 eV. In fully oxidized state double-charged ESR silent segments (bands at 2.9 eV, 1.7 eV and 1.2 eV) dominate. Very similar behavior was observed in the case of chemically prepared polythiophene on ITO (Fig.1 A) indicating analogous electrochemical and optical  properties as founded for electrochemically prepared films. This implies that the special chemical procedure used (as described above) is suitable for the preparation of thin well defined polymer layers with the same characteristics as can be obtained in the electrochemical way.

Contact

Prof. Lothar Dunsch