On-surface synthesis of ethynylene bridged anthracene polymers.

Engineering low band gap π-conjugated polymers is a burgeoning area in basic and applied research. The main synthetic challenge lies in the solubility of the materials during the chemical synthesis which precludes the advance of the field. Here, we report an unprecedented on-surface synthesis protocol to overcome such difficulties, being able to design poly(p-anthracene ethynylene) molecular wires on an Au(111) surface. To this aim, a quinoid anthracene precursor endowed with =CBr2 moieties is deposited and annealed to 400 K resulting in anthracene-based polymers, with a measured electronic bandgap of 1.5 eV. High-resolution non-contact atomic force microscopy with a CO functionalized tip unambiguously corroborates the nature of the ethynylene bridge bond between anthracene moieties. Complementary theoretical simulations of the reaction pathways illustrate the mechanism of the chemical reaction, highlighting three major steps: dehalogenation, diffusion of surface-stabilized carbenes, and homocoupling enabling the formation of an ethynylene bridge. Our results introduce a ground-breaking chemical protocol to design π-conjugated polymers based on oligoacene precursors and pave new avenues for advancing the emerging field of on-surface synthesis.