Naphthalene bisimides asymmetrically and symmetrically N-substituted with triarylamine – comparison of spectroscopic, electrochemical, electronic and self-assembly properties

Two semiconducting naphthalene bisimides were comparatively studied: NBI–(TAA)2, symmetrically N-substituted with triaryl amine and asymmetric NBI–TAA–Oc with triaryl amine and octyl N-substituents. Both compounds show very similar spectroscopic and redox properties but differ in their supramolecular organization. As evidenced by STM, in monolayers on HOPG they form ordered 2D structures, however of different packing patterns. NBI–(TAA)2 does not form ordered 3D structures, yielding amorphous thin films whereas films of NBI–TAA–Oc are highly crystalline. DFT calculations predict the ionization potential (IP) of 5.22 eV and 5.18 eV for NBI–TAA–Oc and NBI–(TAA)2, respectively, as well as the electron affinity values (EA) of −3.25 eV and −3.22 eV. These results are consistent with the cyclic voltammetry data which yield similar values of IP (5.20 eV and 5.19 eV) and somehow different values of EA (−3.80 eV and −3.83 eV). As judged from these data, both semiconductors should exhibit ambipolar behavior. Indeed, NBI–TAA–Oc is ambipolar, showing hole and electron mobilities of 4.5 × 10−5 cm2/(V s) and of 2.6 × 10−4 cm2/(V s), respectively, in the field effect transistor configuration. NBI–(TAA)2 is not ambipolar and yields field effect only in the p-channel configuration. This different behavior is rationalized on the basis of structural factors.