Electroactive polymer films based on [Ni(salen)]-type complexes were fabricated and their electronic
properties characterized using in situ UV–visible spectroelectrochemistry. The extent of electronic
delocalisation and electronic asymmetry were manipulated by introduction of different conjugated imine
bridges. Measured electronic spectra were interpreted in terms of polaronic states in the band gap
and metal-oxidized ligand charge transfer bands. Density functional theory (DFT) calculations for the
monomers showed that the HOMO orbital (which governs oxidation potential) is ligand-dominated, and
that substituents with greater electronic delocalisation in the diimine bridge decrease the HOMO–LUMO
energy gap. Replacement of methyl by methoxyl substituents in the aldehyde moiety increases the cal-
culated dipole moment. Substitution-driven variations in EHOMO –ELUMO for the monomers were reflected
in the corresponding polymer band gaps, demonstrating that monomer electronic properties can be
used predictively in the manipulation of polymer electronic properties. An important strategic aspect
is the correlation of DFT predictions with the observed electronic properties of monomeric and poly-
meric materials; the extent to which such modelling can be used to optimise synthetic effort is
[Show abstract][Hide abstract] ABSTRACT: A series of electroactive films based on the Cu(salen) motif was produced on Pt electrodes by potentiodynamic polymerization of [Cu(3-MeOsalen)] (1), [Cu(3-MeOsaltMe)] (2), [Cu(3-MeOsalpd)] (3) and [Cu(3-MeOsalophen)] (4). Coulometric assay showed coverages to be in the range Γ ∼ 90-530 nmol cm -2. During polymerization and subsequent redox cycling, the films had distinct i-E signatures, despite the fact that the imine bridge is notionally outside the site of electroactivity (the conjugated polymer spine). A combination of DFT and XAS was used to explore underlying structural reasons for the differing electrochemical signatures and the facility of the films to complex solution phase Ba 2+ (a model for metal ion sensing). DFT was able to provide finer details, notably between the N- and O-donors in the Cu local environment, but its application was restricted to monomeric entities. The most significant structural effect of the nature of the imine bridge involvement was the extent of distortion from planarity of the salen moiety. This in turn alters the size of the pseudo-crown pocket formed by the two O-donors shared by the Cu and the two O-donors of the methoxy groups, such that the Ba 2+ ion can only lie within the molecular plane in the cases of 1 and 2. XANES shows the Cu to be invariably present in an essentially square planar environment, irrespective of imine bridge, monomer or polymer environment, or Ba 2+ complexation. The relevance of these outcomes to design criteria for materials of relevance to metal ion sensing is discussed.
[Show abstract][Hide abstract] ABSTRACT: Metal complexes based on the salen ligand are highly versatile compounds that have many interesting properties, including magnetism, catalysis, and reversible oxygen binding. The marriage of complexes of salen with porous materials is a promising way to combine the attractive properties of the salen complex with those of the porous structure. In this Microreview, we discuss several recent examples of published research that illustrate the power of combining these two disparate areas of research. Approaches based on supramolecular chemistry are emphasized.
Berichte der deutschen chemischen Gesellschaft 01/2012; 2012(1). DOI:10.1002/ejic.201100786 · 2.94 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Polymer complexes of nickel with SalEn-type ligands (SalEn = N,N′-bis (salicylidene) ethylenediamine) possess a number of unique properties, such as high redox conductivity, electrochromic behavior and selective catalytic activity in heterogeneous reactions. However, the mechanism of their redox transformation is still not clear. To understand this mechanism, we have performed a combined study of electrochemical and spectral properties of polymers derived from nickel complexes with various SalEn-type ligands containing methoxy substituents in phenyl rings, and methyl substituents in imino bridges. Experimental data were correlated with the results of density functional theory (DFT) calculations for model chains consisting of one to four monomer units. We found that, in acetonitrile-based supporting electrolyte, oxidation of such complexes, regardless of ligand substituents, proceeds via two routes, leading to formation of two oxidized forms: for the first one, a good correlation between experimental and computation results was observed. It has been demonstrated that positive charge in this form is delocalized in the phenyl moieties of ligand. The second oxidized form is stable only in coordinating solvents at high electrode polarizations and is likely to have the charge localized on the central metal atom, stabilized by axial coordination of solvent molecules. The complicated electrochemical response of each of the polymers that we have studied can be explained in the scope of this model without any additional assumptions by taking into account conversion of one oxidized form into another. Understanding the solvent effect on the oxidation route of the complexes will enable controlling their catalytic properties and stability.
Journal of Solid State Electrochemistry 02/2015; 19(2):453-468. DOI:10.1007/s10008-014-2619-4 · 2.45 Impact Factor
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