On-surface synthesis is becoming an increasingly popular approach for the synthesis of novel organic materials. Performed on well-defined surfaces and under ultra-high-vacuum conditions, it has been shown to allow for the synthesis of materials unachievable by conventional solution chemistry alone. One such example are higher acenes, whose open-shell character increases as the number of fused benzene rings grows. This compromises their stability and makes their synthesis challenging. One way to overcome this stability limitation is an inert environment such as an ultra-high-vacuum, which has indeed allowed the synthesis of the longest acenes to date. However, the synthesis of even longer acenes still remains an open challenge in spite of its notable interest from both fundamental and application oriented viewpoints, the limiting case being the narrowest possible zigzag-edge graphene nanoribbons. In addition to the infinite polyacene, other linear acene-based polymers display similarly interesting properties, which can range e.g. from ultra-low band gaps to spin-polarized bands. In fact, also acenebased molecules attract great interest, as for example in the case of starphenes. All of the aforementioned structures may potentially be obtained by on-surface synthesis from the reactant m1 displayed in Fig. (see supplementary information note 1 and Figs. S1-S5 for synthesis details). It includes two halogen atoms and two methyl groups on either side of the anthracene backbone. Both types of functionalization are included among the first groups whose thermal activation was demonstrated to work in "on-surface synthesis" experiments, leading to the controlled and reproducible covalent coupling of reactants. On-surface, the ortho-dibromo moiety could afford an aryne (named as head, Fig. ), while the vicinal dimethyl groups could lead to an ortho-quinodimethane (named as tail, Fig. ), therefore forming intermediate i1. We expected that this intermediate could polymerize on surface to obtain polyacene by means of Diels-Alder cycloaddition (head-to-tail polymerization) followed by dehydrogenation.