Reactions of low work function metals Na, Al, and Ca on α,ω-diphenyltetradecaheptaene. Implications for metal/polymer interfaces

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Abstract
The interactions between different low work function metals aluminium, calcium and sodium, and α,ω-diphenyltetradecaheptaene, a model molecule for certain conjugated polymers, have been investigated using both x-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy. The spectra are interpreted with the help of the results of quantum chemical calculations performed within the local spin density (LSD) approximation methodology. The metals are found to interact with the conjugated system in very different ways. Aluminium forms a covalent bond, which strongly modifies the π-electronic structure of the conjugated molecule, while both the sodium and the calcium atoms act as doping agents, inducing new states in the otherwise forbidden bandgap. These new gap states can be viewed as a soliton–antisoliton pair for the Na/DP7 and a bipolaronic-like defect for Ca/DP7.