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Understanding the Effect of Metal Centers on Charge Transport and Delocalization in Conducting Metallopolymers

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journal contribution
posted on 23.01.2017, 19:33 by Minh T. Nguyen, Richard A. Jones, Bradley J. Holliday
A series of conducting polymers, formed from an electropolymerizable Schiff-base ligand, N,N′-((2,2′-dimethyl)­propyl)­bis­(2-thiophenyl)­salcylidenimine, and the corresponding metal complexes (i.e., Ni­(II), Cu­(II), V­(IV)O, Co­(II), and Zn­(II)) have been prepared, characterized, and studied in detail. Our successful synthesis of the ligand polymer helps to make a direct comparison between the properties of metal-free conducting polymers and the corresponding metallopolymers. This enables the role of metal centers in these Schiff-base conducting metallopolymers (CMPs) in particular, and in Wolf type III CMPs in general, to be unambiguously elucidated. Vis–NIR absorption spectroelectrochemical studies show that longer distances for charge delocalization were found in the CMPs when compared to the metal-free counterpart, an indication of the contribution of the metal centers in extending the effective conjugation length of these electroactive polymers. The systematic use of both redox-active and redox-inactive first row transition metals helps to better understand the nature of charge transport and the specific role of the metal centers in these systems. Cyclic voltammetry and in situ conductivity show superior charge transport in the CMPs compared to the ligand polymer, especially in systems containing redox-active metal centers with redox potentials higher than, but similar to, that of the conjugated organic backbone. Our results indicate that inner-sphere charge transport within the organic backbone, which is serving as a hopping station, is the dominant mechanism of conductivity enhancement and favorable for efficient charge transport in Schiff-base CMPs.