We present the fabrication of acenes (polycyclic hydrocarbons formed by the linear fusion of several benzene rings) on metallic surfaces. In particular, scanning tunneling microscopy and spectroscopy of single hexacene molecules is performed to directly visualize the frontier orbital resonances and to capture their narrow energy gap. Due to the high reactivity of hexacene under ambient conditions, scanning probe investigations at the single molecule level could not be obtained so far. In this work, we proof the scalability of a recently introduced on-surface reaction [1] to generate and stabilize hexacene directly on Au(111) by making use of oxygen-containing precursors. In the last part of this talk, we analyze the electronic resonances of long acenes on Au(111) as function of their length.