Synthesis of [24]azacyclacene Via a Nitrogen-Doped Macrocycle
Polyaromatic hydrocarbons (PAHs), particularly acene-derived materials, have been studied as organic semiconductive materials for low-cost electronics due to their unique optoelectronic properties. Cyclacene, a conjugated macrocycle consisting of laterally fused benzene rings, is a theoretical aromatic belt that would be the shortest zigzag carbon nanotube (CNT) with unique predicted electronic properties. It was first proposed in 1954 and while many attempts have been made, cyclacene has yet to be synthesized. An analogous heterocyclacene could be synthesized as a doped semiconductor and precursor for hetero-CNTs. One such heterocyclacene would be [24]azacyclacene, a nitrogen-doped acene macrocycle, which might be used as an n-type organic semiconductor since nitrogens would lower the energy of the lowest unoccupied molecular orbital of the pi-system. As a never-before-synthesized aromatic belt, the synthesis of [24]azacyclacene would allow for investigation of its predicted electronic and physical properties. We plan to synthesize [24]azacyclacene through a nitrogen-doped macrocyclic precursor assembled from curved macromolecular building blocks via palladium-catalyzed Buchwald-Hartwig amination. Through a chiral assisted synthesis (CAS) strategy, using enantiopure starting material, we hope to promote a selective macrocyclic formation by directing chain growth towards a macrocycle. Via a double decarbonylative irreversible conjugation event, the macrocycle will be converted to the target azacyclacene.