Synthesis of Anthracene-Based Cyclic π-Clusters and Elucidation of their Properties Originating from Congested Aromatic Planes

Synthesis and properties of anthracene-based cyclic pi-clusters which possess two and four anthracene units are discussed. The optimal cyclization conditions were determined based on a nickel(0)-mediated reaction that afforded a cyclic anthracene dimer as the major product. Bringing two anthracene planes in close proximity in a face-to-face manner resulted in red-shifted absorption owing to the narrowing of the HOMO-LUMO gap. The cyclic anthracene dimer exhibits multi-stimuli responsiveness due to high pi-congestion. For example, photoirradiation on the anthracene dimer affords its photoisomer having C-C bonds that are longer than 1.65 angstrom, which can undergo thermal reversion under gentle heating. This enabled mechanochromism of the photoisomer (colorless) to the original anthracene dimer (red). Photoisomerization was also observed in the crystalline state, accompanied by crystal jumping or collapsing, that is, the photosalient effect.

Automated summary

This study discusses the synthesis and properties of anthracene-based cyclic pi-clusters with two and four anthracene units. The optimal cyclization conditions were determined through a nickel-mediated reaction, resulting in a cyclic anthracene dimer as the major product. The cyclic anthracene dimer showed red-shifted absorption and multi-stimuli responsiveness, such as photoisomerization and mechanochromism.