10 Abstract 11 The poly(o-aminophenol) (POAP) redox process has been studied in aqueous acid solution using spectroscopic and optic in situ 12 techniques. The redox transition of the POAP from its completely oxidized state to its completely reduced state occurs through two 13 consecutive reactions in which a charged intermediate species takes part. UV-Vis and Raman signals agree with an increase of the 14 concentration of an intermediate species until the potential of the maximum redox peak, which later diminishes with the potential. 15 The results of in situ FTIR spectroscopy agrees with Raman measurements. Probe beam deflection (PBD) suggests that during its 16 oxidation, the polymer incorporates anions in a first process and thenexpels protons in a second one. 17 © 2004 Published by Elsevier B.V. 18 Keywords: Poly(o-aminophenol); In situ Raman spectroscopy; Probe beam deflection 19 20 1. Introduction 21 Since the discovery of conducting polymers there 22 have been many studies dealing with the synthesis, char-23 acterization and properties of these polymers [1-5]. 24 Polyaniline (PANI) and derivatives have been studied 25 extensively, the electrochemical behavior being one of 26 the more studied properties [6,7], 27 On other hand, the polymerization of derivatives of 28 aniline such as aminophenols is interesting since, unlike 29 aniline [8] and other substituted anilines [9], they have 30 two groups which could be oxidized. o-Aminophenol 31 (OAP) is the only isomer that produces an electroactive 32 polymer during its oxidation [10-14], At the present 33 time, it is agreed that poly(o-aminophenol) (POAP) is 34 a ladder polymer formed by phenoxazine-type units. 35 The voltammetric response of POAP is characteristic (E. Morallon).