Semiempirical studies of the interaction between metals and π‐conjugated polymers: Sodium on diphenylpolyenes and aluminum on poly (p‐phenylenevinylene) and derivatives

We report some of our recent results from theoretical modeling of the interaction between metals and π‐conjugated molecules. We apply the semiempirical Austin Model 1 method for the investigation of two fundamentally different systems: sodium interacting with diphenylpolyenes and aluminum interacting with poly (p‐phenylenevinylene) and derivatives. In the former case, electronic‐structure calculations are also performed using the nonempirical pseudopotential Valence Effective Hamiltonian (VEH) technique. For sodium interacting with diphenylpolyenes, we investigate the geometric and electronic structure modifications that are induced upon charge transfer in a series of diphenylpolyenes with an even number of carbons (from stilbene to α,ω‐diphenyltetradecaheptaene, i.e., one to seven double bonds in the polyene part of the molecule). Densities of valence states generated from the VEH calculations are directly compared to experimental ultraviolet photoelectron spectroscopy valence band spectra; these are recorded during successive sodium exposure of the molecular solids. The charge‐storage states in the series are discussed in terms of soliton‐antisoliton‐pairs and polaron‐like states induced upon doping (reduction). Introducing aluminum atoms onto poly (p‐phenylenevinylene) systems allows us to study the initial stages of interface formation. We find that aluminum atoms preferentially react with the vinylene linkages in both poly (p‐phenylenevinylene) and poly (2,5‐dimethoxy‐p‐phenylenevinylene). When carbonyl groups appear on the side of the chains, as in poly (2,5‐dialdehyde‐p‐phenylenevinylene), new reactive sites are induced, leading to structures with stabilities comparable to those in the most stable configurations involving a single vinylene group. In all three systems investigated, the interaction with aluminum induces major modifications of the polymer chains with interruptions of the π‐system caused by formation of sp³‐like defects. © 1994 John Wiley & Sons, Inc.