Effect of halogenated substituent on the properties of aza-octacenes

Abstract We systematically designed and developed three novel halogenated aza-octacene derivatives, which have the same π-conjugated backbone with different terminal halogen groups (F, Cl, Br). These aza-octacene derivatives are synthesized by acid-catalyzed condensation of naphthalene-bisisatin with 4,5-dihalo-1,2-phenylenediamine. The in-depth experimental and theoretical analyses on these molecules, using the non-halogenated system as a reference, allowed us to understand the impact of halogenation on electronic and optical properties. Both electronic affinity (EA) and ionization potential (IP) are increased through peripheral halogen substitution. Chlorination enhances the EA more effectively compared with fluorination and bromination. Micro-crystal devices based on the bromine substituted aza-octacene derivative show only p-type charge transport behavior. In contrast, the chlorinated and the fluorinated aza-octacene derivatives exhibit ambipolar charge transport.