Abstract
Most non-metalized Salen-type ligands form passivation thin films on electrode surfaces upon electrochemical oxidation. In contrast, the H2(3-MeOSalen) forms electroactive polymer films similarly to the corresponding nickel complex. There are no details of electrochemistry, doping mechanism and charge transfer pathways in the polymers of pristine Salen-type ligands. We studied a previously uncharacterized electrochemically active polymer of a Salen-type ligand H2(3-MeOSalen) by a combination of cyclic voltammetry, in situ ultraviolet–visible (UV–VIS) spectroelectrochemistry, in situ electrochemical quartz crystal microbalance and Fourier Transform infrared spectroscopy (FTIR) spectroscopy. By directly comparing it with the polymer of a Salen-type nickel complex poly-Ni(3-MeOSalen) we elucidate the effect of the central metal atom on the structure and charge transport properties of the electrochemically doped polymer films. We have shown that the mechanism of charge transfer in the polymeric ligand poly-H2(3-MeOSalen) are markedly different from the corresponding polymeric nickel complex. Due to deviation from planarity of N2O2 sphere for the ligand H2(3-MeOSalen), the main pathway of electron transfer in the polymer film poly-H2(3-MeOSalen) is between π-stacked structures (the π-electronic systems of phenyl rings are packed face-to-face) and C-C bonded phenyl rings. The main way of electron transfer in the polymer film poly-Ni(3-MeOSalen) is along the polymer chain, while redox processes are ligand-based.
Highlights
Published: 4 February 2022Conducting polymers are widely used as electrode materials in sensors, electronic and optical devices, and batteries [1,2,3,4,5,6]
There are no details of electrochemistry, doping mechanism and charge transfer pathways in the polymers of pristine Salen-type ligands in the literature, while polymers of unmetallated Salen-type ligands with polymerizable side-groups have been explored [35,36]
The monomeric complex and the corresponding ligand as well as the polymer films deposited on the electrode surface were investigated by cyclic voltammetry, Electrochemical Quartz Crystal Microbalance (EQCM), in situ UV–VIS spectroscopy, Fourier Transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM)
Summary
Conducting polymers are widely used as electrode materials in sensors, electronic and optical devices, and batteries [1,2,3,4,5,6]. Salen-type Schiff base ligands are widely studied as promising materials for many different applications [7,8,9,10,11,12,13,14,15,16,17,18,19,20,21] The properties of these materials largely depend on substituents in the ligand environment and the metal center, special attention has been given to polymeric nickel(II) complexes with Salen-type ligands. Noncovalent π−π interactions between π-electronic systems of neighboring molecules are possible In this case, π-stacks formed within the polymer film can be part of the charge transfer pathway [30,31,32]. The monomeric complex and the corresponding ligand as well as the polymer films deposited on the electrode surface were investigated by cyclic voltammetry, EQCM, in situ UV–VIS spectroscopy, FTIR and scanning electron microscopy (SEM)
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