47 J. Electroanal. Chem, zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDC 242 (1988) 47-62 Elsevier Sequoia S.A., Lausanne - Printed in The Netherlands zyxwvutsrqponmlkjihgfedcbaZYXWVUTSR AN IN-SITU INFRARED STUDY OF POLY THIOPHENR GROWTH P.A. CHRISTENSEN and A. I-IAMNETT Inorganic Chemisty Luboratoty, South Parks R& Oxford OXI 3QR (Great Britain) A.R. HILLMAN School of Chemistry, University of Bristol, Cantock’s Close, Bristol (Great Britain) (Received 2nd October 1987; in revised form 28th October 1987) ABSTRACI The growth of polythiophene has been studied by in situ PT-IR spectroscopy in order to understand in more detail the molecular processes that occur during fihn formation and cycling. It is shown that thiophene adsorbs at edge sites on the polished platinum electrodes used, and that growth is accompa- nied by gross changes in the IR spectrum from that of the thiophene monomer in solution. Oxidation of the film gives rise to additional bands corre-sponding to the “quinonoid” form of the chain, and to a reduction in the frequency of the ring deformation modes compared to the neutral form. A broad electronic absorption band corresponding to bipolaronic excitation is also seen. INTRODUCTION The electropolymerisation of simple organic heterocyclic derivatives has been a major area of electrochemical investigation in the last few years. The advantages of electropolymerisation are evident in terms of control over the thickness of the film and its localisation at the desired growth points. In addition, the properties of the films, once grown, are of great interest: in their oxidised form, such films show semiconductor or metallic type conductivity, and have potential applications in electrochromic devices, shielding and energy storage. For all these reasons, the study of the formation of these films and their behaviour under potential cycling has attracted considerable attention. In addition to often very sophisticated electro- chemical experiments, that have helped to clarify the rate-limiting processes in, for example, the reduction of Fe(II1) by polythionine films [l], a whole battery of spectra-electrochemical techniques has been brought into service to help provide an insight into the molecular transformations that take place in such films. The use of such techniques has provided a wealth of information, particularly about the dynamics of growth and change. However, much of the molecular jigsaw is still 0022-0728/88/$03.50 0 1988 Elsevier Sequoia S.A.