Linear acenes, a category of polycyclic aromatic hydrocarbons, are of great interest for organic materials and electronics due to their extended p-conjugation and optoelectronic properties. Nitrogen-embedded acene congeners, azaacenes, are a resurgent class of acene materials. Replacing [n]benzenoid rings with [n]pyrazine rings in an acene backbone modulates acene properties. Furthermore, this modification opens additional synthetic routes to the targets unavailable to all-carbon acenes. Azaacenes have increased electron affinity, making them robust n-type semiconductors in thin-film transistors and emitters for organic diodes Already several motifs dominate the literature, but continued innovation calls for novel acene structures and expanding existing synthetic techniques. In azaacene materials, insolubility and photodegradation become problems as conjugation extends in the acene backbones. To overcome these challenges, bulky edge groups or nonlinear fused benzenoid rings are added, forming “pseudo” acenes. . We report a new synthetic approach towards extended linear [n]azaacenes of varying acene lengths (n = 5, 7, 9), nitrogen count, and edge-group functionalization via a one-pot oxidation/condensation reaction. In our approach, we construct an azaacene precursor that has a carbonate-containing two carbon bridge over the central ring. This bridge gives the intermediates solubility and enables light-mediated decarbonylative aromatization at a late stage in the synthesis. Oxidative Schiff-base coupling between diamines and hydroquinones form the desired pyrazine rings. The choice of diamine sets the acene length, edge-groups, and nitrogen count. We will present synthesis of new azaacene materials through our route. Future work will include studying their optoelectronic properties and uses as materials for organic electronics.

One-pot oxidative cyclocondensation route to azaacenes and their soluble precursors

ACS Spring 2022

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