A Poly(2,7-anthrylene) with peri-Fused Porphyrin Edges

Anthracene has served as an important building block of conjugated polymers with the connecting positions playing a crucial role for the electronic structures. Herein, anthracene units have been coupled through their 2,7-carbons to develop an unprecedented, conjugated polymer, namely, poly(2,7-anthrylene) featuring additional peri-fused porphyrin edges. The synthesis starts from a 2,7-dibromo-9-nickel(II) porphyrinyl-anthracene as the pivotal precursor. Polymerization is achieved by an AA-type Yamamoto coupling, followed by a polymer-analogous oxidative cyclodehydrogenation to obtain a peri-fusion between porphyrin and anthracene moieties. Although further cyclodehydrogenation between the repeating units cannot be achieved in solution, the thermal treatment of the precursor polymer derived from 2,7-dibromo-9-porphyrinyl-anthracene on a metal surface realizes the full cyclodehydrogenation. The difference between solution and on-surface reactivity can be rationalized by the larger dihedral angle between repeat units in solution, which is reduced under the pronounced interaction with the metal surface. The peri-fusion in the title polymer gives rise to a narrow electronic band gap optical absorptions extending far into the near-infrared region. Oligomeric models are synthesized as well to support the analyses of the electronic and photophysical properties.