In situ conductance and in situ ATR-FTIR study of poly(N-methylaniline) in aqueous solution Di Wei a,b , Pamela Espindola c , Tom Lindfors a , Carita Kvarnstro ¨m a, * , Ju ¨ rgen Heinze c , Ari Ivaska a a Process Chemistry Centre, c/o Laboratory of Analytical Chemistry, A ˚ bo Akademi University, Biskopsgatan 8, 20500 A ˚ bo/Turku, Finland b Graduate School of Materials Research (GSMR), A ˚ bo Akademi University, 20500 A ˚ bo/Turku, Finland c Institut fu ¨ r Physikalische Chemie, FMF, Universita ¨ t Freiburg, Albertstr. 21a, D-79104 Freiburg i. Br, Germany Received 19 July 2006; received in revised form 14 December 2006; accepted 20 December 2006 Available online 12 January 2007 Abstract In situ attenuated total reflection Fourier transform infrared spectroscopy, ATR-FTIR and in situ conductance measurements offer information on structure, electronic, and conductance changes during doping and electropolymerization of conducting polymers. In this paper, we report the in situ recording of the conductance changes during cyclic voltammetry measurements (electropolymerization and the subsequent doping) of N-methylaniline (NMA). The vibrational spectra of poly(N-methylaniline) (PNMA) show specific and char- acteristic features not only related to its chemical structure, but also to the existence of free charge carriers delocalized along the p-elec- tron network. Results from both in situ conductance and in situ ATR-FTIR have brought us a better understanding of electronic properties and the nature of charge carriers of PNMA film synthesized in acidic aqueous solutions. Ó 2007 Elsevier B.V. All rights reserved. Keywords: Poly(N-methylaniline); Electropolymerization; In situ ATR-FTIR; In situ conductance 1. Introduction Conductance is an essential parameter when construct- ing polyaniline-based microelectronic devices as diodes and transistors [1–3]. New organic electronics can be designed by functionalizing polyaniline (PANI) at the nitrogen atom. N-grafting of PANI is also expected to affect the electrical conductivity. Recently, Yasuda et al. prepared N-substituted PANI with oligo-ether side chains using ring-opening graft copolymerization of epoxide [4]. The resulting copolymers showed both electrochemical and electrochromic activity during redox switching. The mechanism of charge transport in conducting poly- mers has been intensively studied since the report of an insulator to metal transition in polyacetylene [5]. Many non-degenerate ground state polymers such as polythioph- ene (PT) and polypyrrole (PPy) have also been studied in this aspect [6,7]. PANI is different from these well known conducting polymers in the following important aspects. First, the Fermi level and the band gap of PANI are not formed in the center of the band, resulting in asymmetric valence and conduction bands. A single broad polaron band appears deep in the gap instead of two, and another very narrow band appears near the conduction-band edge in PANI [8]. Second, in contrast to PPy, which nitrogen atoms do not contribute significantly to the conjugation [9], both carbon rings and nitrogen atoms are within the conjugation path in PANI. Third, the electronic state of PANI can be altered through variation of either the num- ber of electrons or the number of protons. Monkman et al. [10] concluded that the conduction mechanism in PANI is mainly inter and intra chain hopping between localized charge sites on the polymer backbone. One big difference between PNMA and PANI is that PNMA is 0022-0728/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jelechem.2006.12.017 * Corresponding author. Tel.: +358 2 215 4419; fax: +358 2 215 4479. E-mail addresses: carita.kvarnstrom@abo.fi, ckvarnst@abo.fi (C. Kvarnstro ¨m). www.elsevier.com/locate/jelechem Journal of Electroanalytical Chemistry 602 (2007) 203–209 Journal of Electroanalytical Chemistry