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

Synthetic Metals (Impact Factor: 2.11). 05/2011; 161(9-10):680-691. DOI: 10.1016/j.synthmet.2011.01.014

ABSTRACT 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