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.