Synthesis, Characterization, and Thin-Film Properties of Post-Functionalized N,N-Dimethylanilinoethynyl-Substituted Cyclobutenofullerenes.

A π-extended cyclobutenofullerene containing an N,N-dimethylanilinoethynyl group was synthesized via a one-pot cascade reaction of C60 with the corresponding propargylic phosphate. The cyclobutenofullerene was further modified using either one-pot or sequential post-functionalization methods, yielding derivatives containing altered addend structures. During one-pot post-functionalization, hydration reaction of the alkyne moiety continued after the formation of cyclobutenofullerenes. The sequential post-functionalization approach involved introducing the tetracyanobutadiene structure through formal [2 + 2] cycloaddition and a subsequent retroelectrocyclization reaction with tetracyanoethylene. The electronic and optical properties of the derivatives in solution, as well as their field-effect transistor behavior in thin films, were thoroughly assessed to elucidate the optoelectronic differences arising from various addend structures. The properties of the three characteristic cyclobutenofullerene derivatives in the solution and thin films significantly varied depending on the addends. Among the three derivatives studied, only cyclobutenofullerene, featuring a folded structure induced by the hydration of the alkyne moiety, exhibited n-type semiconductor behavior in the thin films. The findings of this study present a novel methodology for synthesizing and functionalizing fullerene derivatives, together with a conceptual framework for tailoring molecular properties.