Self-assembled pyrazinacene nanotubes

Abstract

Nanotubes of a pentacene derivative, 6,13-bis(1-n-dodecyl)-[a,c,l,n]-tetrabenzo-5,6,7,12,13,14-hexaazapentacene, have been prepared by a hierarchical self-assembly mechanism. The oligoazaacenes 1–3, referred to as pyrazinacenes due to their structures of linearly fused pyrazine heterocycles, can also be considered as two azatriphenylenes fused through a reduced pyrazine ring. Dissolution of 6,13-bis(1-n-dodecyl)-[a,c,l,n]-tetrabenzo-5,6,7,12,13,14-hexaaza pentacene in nearly boiling toluene followed by standing of the solution at room temperature yields self-assembled (sa) pyrazinacene (Pa) nanotubes (NT's), or sa-PaNTs. Self-assembled-PaNTs are formed after initial aggregation of the pyrazinacene giving a 130-nm-wide 2-dimensional tape followed by helical twisting of this tape into a hollow cylindrical form of 150–200 nm diameter which can exceed 10 μm in length. The morphologies of the tape and nanotube structures were investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), powder X-ray diffraction (XRD) and electron absorption spectroscopy (UV/Vis). The latter indicates that the tubes may be formed by chromophore J-aggregation. Also, high resolution TEM of the tubes reveals that they can be composed of several tapes while powder X-ray diffraction revealed the lamellar structure of the tapes composing the tubes.