  We study the electronic structure of an ordered array of poly(para-phenylene)
chains produced by surface-catalyzed dehalogenative polymerization of
1,4-dibromobenzene on copper (110). The quantization of unoccupied molecular
states is measured as a function of oligomer length by scanning tunneling
spectroscopy, with Fermi level crossings observed for chains longer than ten
phenyl rings. Angle-resolved photoelectron spectroscopy reveals a graphene-like
quasi one-dimensional valence band as well as a direct gap of 1.15 eV, as the
conduction band is partially filled through adsorption on the surface.
Tight-binding modelling and ab initio density functional theory calculations
lead to a full description of the organic band-structure, including the k
dispersion, the gap size and electron charge transfer mechanisms which drive
the system into metallic behaviour. Therefore the entire band structure of a
carbon-based conducting wire has been fully determined. This may be taken as a
fingerprint of {\pi}-conjugation of surface organic frameworks.
