Modulating spectroelectrochemical properties of [Ni(salen)] polymeric films at molecular level

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 π 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 calculated 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 polymeric materials; the extent to which such modelling can be used to optimise synthetic effort is discussed.