The chemical and electronic properties of a phenyl-capped 3,4-(ethylenedioxy)thiophene trimer (EDOT trimer) and its interface formation with aluminum have been studied. Thin EDOT trimer films were prepared on clean gold substrates through in-situ vapor deposition. Aluminum was deposited stepwise on top of the EDOT trimer, and the initial stages of interface formation were investigated by photoelectron spectroscopy. The organic/metal interface formed was not completely abrupt; some degree of diffusion of aluminum into the EDOT trimer film occurred. The aluminum atoms preferentially react with the alpha-position of the trimer (C-S carbon atoms) forming covalent bonds. The formation of these covalent bonds causes a break in the pi-conjugation of the system due to the introduction of sp(3) defects. The charge density also is somewhat redistributed within the oligomer as a whole, mainly affecting the neighboring atoms: sulfur and beta-position of the trimer (C=C-O carbon atoms). Once the C-S carbon sites are saturated, the aluminum instead reacts with the less favorable carbon atom of the ethylene bridge (C-O-C carbons). Worth noting is the decrease in work function from 5.2 eV for sputter cleaned gold to 4.1 eV upon deposition of the EDOT trimer. Our results have several implications for organic electronics. The sp(3) defects introduced by the aluminum-EDOT contacting will influence the charge injection into the material across the EDOT trimer/aluminum interface negatively. The change in work function could potentially be used to modify gold contacts for electron injection into molecules with low electron affinity.