Guest-Controlled Topochemical Polymerization and Dimerization of Macrocyclic Pillar[5]arene

Topochemical polymerization enables precise control over polymer structure by confining reactive sites within a preorganized crystal packing. However, accessing a different product generally requires redesign of the monomer. Here, we report a host-guest strategy that regulates the outcome of a photoinduced topochemical reaction without altering the monomer structure. We synthesized a macrocyclic pillar[5]arene monomer bearing polymerizable 1,3-diene groups. In the crystalline state, this monomer formed one-dimensional columns, and its packing mode was found to vary depending on the length of the encapsulated guest molecules. When 1,2-dichloroethane was encapsulated in the monomer cavity, its short length allowed the reactive 1,3-diene groups to align closely within the column. As a result, topochemical polymerization proceeded through a single-crystal-to-single-crystal transformation, affording a covalently linked one-dimensional polymer. By contrast, when the monomer cavity was occupied by the longer guest adiponitrile, the packing mode was altered, leading to preferential intercolumn dimerization. These results demonstrate that host-guest chemistry provides a distinct strategy for controlling the products of topochemical reactions.