Metal/conjugated polymer interfaces: A theoretical investigation of the interaction between aluminum and trans-polyacetylene oligomers

Molecular model systems are used to quantum chemically investigate the interface between aluminum and trans-polyacetylene. Modifications to the chemical and electronic structure of trans-polyacetylene oligomers upon interaction with a submonolayer of aluminum are studied at the semiempirical and ab initio Hartree-Fock levels. An aluminum atom is found to react strongly with a carbon atom of the trans-polyacetylene chain to form a heteropolar covalent bond. In this process, the binding carbon evolves from an sp²- to an sp³-hybridized electronic structure. Significant contributions from A1 3s and 3p atomic orbitals are found in the frontier molecular orbitals in aluminum/polyene complexes. This results in the fact that despite the presence of sp³ sites due to A1-C bonds, which reduces π conjugation along the chain, a large degree of delocalization in π levels is maintained. Our calculations are discussed in relation to experimental ultraviolet photoelectron spectra (UPS) taken during initial stages of aluminum deposition on oxygen-free films of trans-polyacetylene oligomers.