Cyclobutane-linked Nanothreads through Thermal and Photochemically Mediated Polymerization of Cyclohexadiene

Abstract

Carbon nanothreads are a rapidly growing class of 1D nanomaterials with sp³-hybridized diamond-like backbones. They are typically synthesized through pressure-induced polymerizations of aromatics, resulting in diverse structures and functionalities. Aside from precursor selection, there are limited means to control reaction pathway or polymerization outcome. Analogous to selection rules that govern outcomes in molecular chemistry, we investigated thermally and photochemically mediated pressure-induced polymerizations of 1,4-cyclohexadiene and explored the resultant products. Thermally mediated polymerization of 1,4-cyclohexadiene yields a crystalline product; yet identification of the backbone architecture is consistent with multiple reaction pathways being accessed. While support for cyclobutane structures is present, comparison to simulated structures suggests multiple products are obtained. In contrast, the recovered product obtained from the photochemically mediated polymerization exhibits different d-spacings and is consistent with simulations that support a single pathway toward cyclobutane-linked nanothreads. These results suggest that photochemistry can enable reaction selectivity in nanothread synthesis.