Solid-State Photopolymerization of a Shape-Persistent Macrocycle with Two 1,8-Diazaanthracene Units in a Single Crystal

A macrocyclic monomer with two opposing 1,8-diazaanthracene units is polymerized in a single crystal by a photochemically induced [4 + 4] cycloaddition reaction between neighboring monomers in which the anthracene units are stacked face-to-face at the critical Schmidt distance. The severe structural changes associated with this are minimized by the monomer design, wherein the linkers between the two opposing photoreactive 1,8-diazaanthracene units are connected to the 4 and 5 positions of the latter, whose spatial positioning is changed the least during dimerization. This helps to keep the monomer’s overall shape basically unchanged during the polymerization. The resulting new rigid-rod polymer is soluble in its protonated form, and after counterion exchange with a surfactant, it can be depolymerized back into monomer upon relatively mild thermal treatment (120 °C) in an organic solvent.