The chemical and electronic structure of the interface between aluminum and several prototypical conjugated systems is investigated with a combined experimental and theoretical approach. The experiments consist of following the evolution of the polymer surface during the early stages of aluminum deposition, with X-ray and Ultraviolet Photoelectron Spectroscopies (XPS, UPS). In parallel, quantum chemical calculations are performed on model oligomer systems interacting with isolated Al atoms. Aluminum is found to interact strongly with the polymer chain. New covalent Al-carbon bonds are formed along the polymer backbone; the chain geometry is deeply modified and the pi electron conjugation can be dramatically reduced.