X-ray photoelectron spectroscopy characterization of poly(2,3-diaminophenazine) films electrosynthesised on platinum
Abstract
Films of poly(2,3-diaminophenazine) (PDAPh) were obtained on platinum substrates by electropolymerization (cyclic voltammetry, CV) of the monomer in acidic solutions. Limited investigations were performed by cyclic voltammetry and quartz crystal microbalance (QCM). CV showed that phenazine units are present along the polymer chains and exhibit their peculiar electrochemistry. QCM measurements confirmed the deposition of a film on the electrode surface during cyclic voltammetry on 2,3-diaminophenazine (DAPh) solutions. Film structures were thoroughly investigated by X-ray photoelectron spectroscopy (XPS) analysis both through curve fitting of C1s and N1s signals. XPS was also performed following chemical derivatization of samples for NH2, C
O, COOH and OH groups with fluorinated markers. As a result, the presence of NH2 groups could be excluded, COOH and CO groups were found to be minor defects, whereas OH groups, more abundant, were assigned partly to oximic groups (–CN–OH). The possible presence of other structural defects involving nitrogen (N–N and N+–O−groups) was also suggested by XPS. Finally, theoretical calculations on electron spin densities of 2,3-diaminophenazine radicals seem to support a 1,2 coupling mechanism for 2,3-diaminophenazine electrochemical polymerization.
Introduction
Polymer materials obtained from aromatic amines electropolymerization have stimulated a great deal of interest since the preparation of polyaniline [1]. Several possible applications of these materials in the field of batteries, analytical sensors, corrosion inhibitors, detectors and gas separation membranes have been recently reviewed [2]. Among them, polymers of o-phenylenediamine (OPD) have been thoroughly studied and a ladder structure has been proposed (see, e.g., Refs. [3], [4], [5], [6], [7], [8]) for those prepared under particular electrosynthesis conditions (low pH), although the point is still controversial.
It is worth noting that ladder polymers, due to their extended conjugation, can behave as “intrinsical conducting polymers” [9], [10], i.e., materials characterised by high electronic conductivity in the undoped state. Among aromatic amines, 2,3-diaminophenazine (DAPh) seems to be a better precursor than OPD for the electrosynthesis of a ladder polymer, due to the presence of the phenazine ring already in the monomer structure.
Indeed, interest in possible applications of phenazine-based polymers has increased in the past decade. As an example, phenazine and phenoxazine-like polymers, that exhibit a charge density higher than polyaniline, were applied to the development of ligthweight battery electrodes [11].
Phenazinic polymers could be also advantageously employed in oxygen-independent amperometric biosensors due to mediator capability of the phenazine systems.
On the other hand, few works have been devoted to the investigation of DAPh polymerization. Sazou et al. [12], [13] investigated electropolymerization of DAPh on Pt and glassy carbon electrodes and proposed a mechanism of growth producing a ladder structure.
A more recently published paper [14] compares the behaviour of OPD and its polymer (poly(orthophenylenediamine), PPD) and DAPh/(poly(2,3-diaminophenazine), PDAPh) in presence of light and oxygen. The differences observed are explained considering different coupling positions between monomer units during polymerization, also on the basis of theoretical calculations.
We have recently studied the correlation between structure and properties for PPD electrosynthesised at different pH values, using a combination of electrochemical and spectroscopical techniques [15], which proved to be very effective in elucidating fundamental aspects of PPD structure, like the degree of conjugation.
A similar approach has been then adopted to shed light on electrosynthesised poly(2,3-diaminophenazine), with a particular attention to the presence of ladder structures.
In the present paper, the results of electrochemical, quartz crystal microbalance (QCM) and, mostly, X-ray photoelectron spectroscopy (XPS) characterizations of PDAPh electrosynthesised on platinum are reported. Results of XPS following chemical derivatization of samples (see Ref. [16] for a review) are also presented for elucidating the actual structure of PDAPh and evidentiating the occurrence of structural defects.
Section snippets
Materials
2,3-Diaminophenazine was synthesised by oxidation of 1,2-diaminobenzene with FeCl3, according to the procedure reported elsewhere [17]. The product was characterized by means of elemental analysis, Fourier Transform Infrared Spectroscopy, mass spectrometry and XPS analysis (accomplished on the DAPh powder pressed on conducting adhesive tape).
o-Phenylenediamine was purified by sublimation at 80 °C under reduced pressure (200 Torr). Trifluoroacetic anhydride (TFAA), p-trifluoromethyl-benzaldehyde
Electrochemical data
The first and the last cycle of a typical voltammogram (23 cycles) obtained during polymerization of DAPh on a platinum substrate are shown in Fig. 1, in which the voltammogram relevant to the substrate cycled in the monomer-free electrolyte is reported for a comparison. The main features are in agreement with those already reported by Sazou et al. [12], [13] in the same conditions. In particular, while scanning from starting potential in anodic direction, firstly, an oxidation peak (A) is
Polymerization mechanism
Different mechanisms have been proposed for DAPh polymerization [12], [14]. In any case, the first step is believed to be the oxidation of monomer at amino group (contributing to peak C in CV):
Radical coupling, followed by deprotonation, generally then occurs. Two alternative schemes (1,2 coupling [14] or 2,6 coupling [12], [33]) have been devised:
2,6-Coupling is generally proposed due to resemblance with polymerisation of OPD [3], [8]. Recently, other authors have proposed, on the base of
Conclusions
CV, quartz crystal microbalance and, mainly, XPS were applied to the characterization of the poly(2,3-diaminophenazine) (PDAPh) films arising from the oxidation of 2,3-diaminophenazine on platinum substrates.
Electrochemical data suggested the presence of phenazine groups within the material structure, as expected. QCM data were correlated to measurements performed by a profilometer on PDAPh films deposited on ITO-covered glass substrates, showing that the polymer growth rate is not constant
Acknowledgements
This work is part of “Tesi di laurea” of I.D.B. L.Sabbatini (Bari) is gratefully acknowledged for many helpful discussions. XPS measurements were performed at Centro Interdipartimentale Spettroscopie (Università di Bari). Financial support by MIUR is gratefully acknowledged.
References (34)
- et al.
J. Electroanal. Chem.
(1980) - et al.
J. Electroanal. Chem.
(1987) - et al.
J. Electroanal. Chem.
(1987) - et al.
Synth. Met.
(1989) - et al.
J. Electroanal. Chem.
(2001) - et al.
J. Electroanal. Chem.
(1994) - et al.
J. Electroanal. Chem.
(1989) - et al.
Chem. Rev.
(2002) - et al.
Bull. Korean Chem. Soc.
(1995)
Rapid Commun. Mass Spectrom.
J. Polym. Sci., Pol. Chem.
J. Chem. Phys.
J. Electrochem. Soc.
Synth. Met.
J. Mater. Chem.
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