0D, 1D and 2D Nanostructured
Electronic Materials

Low-dimensional organic nanostructures such as 1D nanowires and nanotubes represent attractive building blocks for nanoscale electronic and photonic devices. Based on the design and synthesis of novel donors and acceptors, we aim to fabricate phase-separated nanostructures from orderly arranged discotic molecules, which are distinct from the bulk supramolecular blends. Networks of n- or p-type nanowires or nanotubes are among the targets to be fabricated by controlling temperature, the solvent compositions, and core and substituent structures. Recently, easily accessible, symmetrically substituted
TP derivatives were assembled (Figure a) into single molecular thick 2D nanosheets, which stacked further to give multilayered nanofibers through a convenient solution process. The formation of such nanostructures was both solvent specific and side chain dependent, as acetonitrile was the only solvent that was found to effectively promote the nanostructure formation for TP with linear alkyl side chains. Detailed information on molecular arrangement was probed by AFM, SEM, TEM and X-ray diffraction (XRD). As shown in Figure a, features composed of single-layer, double-layer and triple-layer nanosheets, with step size around 2.3 nm were clearly identified by AFM. The ordered assembly of HAT molecules in the nanosheets was facilitated in two dimensions by parallel stacking of the aromatic planes along the long axis as a result of π-π interactions, and side-by-side packing of adjacent HAT molecules through alkyl chain interdigitation along the other axis (Figure b). The formation of nanosheets composed of single molecular layer is reminiscent of the graphene and can be of fundamental importance in directing the self-assembly of functional organic semiconductor nanostructures.

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(a) SEM, TEM, AFM image and cross-section analysis showing the formation of multilayered nanofibers.
(b) Proposed stacking of
TP molecules in nanosheets. [Click to enlarge]

Koshkakaryan, G.; Jiang, P.; Cao, D.; Klivansky, L. M.; Altoe, V.; Zhang, Y.; Ma, B.; Salmeron, M.; Aloni, S.;
Liu, Y.* “Multi-Layered Nanofibers from Stacks of Single-Molecular Thick Hexakis(alkoxyl)triphenylenes”, Chem. Commun. 2010, 46, 8579-8581 (Editor’s choice as “Hot Paper”).

Dr. Shaul Aloni and Virginia Altoe, Imaging Facility, Molecular Foundry
Prof. Miquel Salmeron and Dr. Peng Jiang, UCB