Small asymmetric halogenated Phenylene–Naphthalimide molecules for organic field-effect transistors

Abstract

A series of polycyclic aromatic hydrocarbons (PAH) based on phenylene-naphthalimide assemblies, in which both the phenylene unit and the electron-withdrawing moiety of naphthalimide are directly conjugated through rigid inverted amidine (NAI) bonds, are synthesized and characterized. Different halogen atoms (F and Cl) are introduced into the phenylene unit to modulate the electron-accepting and charge-transport properties of the new systems. A physicochemical study is performed in which the neutral and charged species are analyzed together with the electronic properties of the naphthalimide derivatives, switching from ambipolar mobility in phenylene-naphthalimide to n-type mobility in the halogenated derivatives. Maximum n-type field effect mobilities of 0.1 cm2V-1s-1 and 0.2 cm2V-1s-1 were measured for the halogenated compounds, NAI-Ph-F and NAIPh- Cl, respectively. It has been demonstrated that halogenation at the phenylene unit is a convenient strategy to facilitate charge injection, due to the lowering of the frontier energy levels and reduction potentials, without sacrificing molecular planarity, and thus maximizing charge stabilization and transport.