DOI: 10.1002/anie.201004245
Nanostructures
Two-Dimensional Nanostructures from Positively Charged Polycyclic
Aromatic Hydrocarbons**
Dongqing Wu, Ruili Liu, Wojciech Pisula, Xinliang Feng,* and Klaus Mꢀllen*
Over the last years, the rapid development of graphene, an
ultrathin flat hexagonal lattice of carbon,[1] has led to
increased interest in two-dimensional (2D) nanomaterials.
These materials mainly refer to sheetlike structures that
possess a high degree of anisotropy with a thickness that is a
few orders of magnitude smaller than other dimensions.[2] The
self-assembly of organic amphiphiles allows for the bottom-
up fabrication of versatile nanostructures with controllable
morphology by modification of the molecular structures or
external conditions.[3] Thus this approach provides an appeal-
ing possibility for the template-free construction of novel 2D
Scheme 1. PQP14 complexes studied herein.
nanomaterials.[4] The organization of amphiphilic molecules
with functional moieties, such as large aromatic cores or ionic
species, into 2D nanostructures has been scarcely studied so
far. Such 2D nanostructures can provide pathways for the
transport of charges, ions, and energy.[5]
for the transport of ionic species dissolved within.[7] Recently,
we have made use of these advantages of PQPs to control
their self-assembly behavior in solution as well as in the bulk.
Nanostructures of alkylated PQPs with different morpholo-
gies such as fibers, ribbons, and tubes can be formed in
methanol depending on the length of the alkyl substituents
and the size of the inorganic anions.[8] On the other hand,
well-ordered 1D columnar superstructures of PQPs are
established in the bulk by the use of alkyl sulfonate anions
through a so-called ionic self-assembly (ISA)[9] process.[10]
Inspired by these results, we envision that the self-assembly
of PQP salts into nanostructures with diversified morpholo-
gies would be experimentally feasible by the selection of
different organic anions.
Herein we demonstrate that the amphiphilic tetradecyl-
substituted PQP (PQP14, Scheme 1) salts that contain alkyl
sulfonate anions or disulfonate anions, can spontaneously
organize into 2D nanostructures in solution. For PQP14
complexes with alkyl sulfonates, puckered 2D nanobelts with
regular morphology are formed with the increase in the alkyl
chain length of the anions, which can be ascribed to improved
amphiphilic interactions during the coassembly of the cations
and anions. By using a disulfonate anion, planar 2D aggre-
gates are obtained, thus indicating that the “double anion”
has a more profound impact on the 2D organization of PQP14
cations than the alkyl sulfonates. Notably, the different
morphologies of these 2D nanostructures significantly affect
the ionic conductivity of the mixture of PQP14 complexes and
lithium salts, for which the planar aggregates exhibit a
conductivity of two orders of magnitude higher than that of
the puckered ones.
Positively charged polycyclic aromatic hydrocarbons
(PAHs), like 9-phenyl-benzo[1,2]quinolizino[3,4,5,6-fed]phe-
nanthridinylium (PQP, Scheme 1) salts, are particularly
attractive building blocks for supramolecular chemistry
because: 1) their extended aromatic frameworks offer aro-
matic interactions to enhance the stacking of molecules in the
aggregated state;[6] 2) the introduction of hydrophobic alkyl
chains to the hydrophilic aromatic cores of PQPs provides
amphiphilic interactions, thus leading to molecules that form
well-defined arrays in solution; 3) the arrangement of PQPs
in superstructures can be controlled by choosing proper
anions; and more importantly, 4) such self-organized super-
structures of PQPs can serve as electrolytes to offer a channel
[*] Dr. D. Wu, Dr. R. Liu, Dr. W. Pisula,[+] Dr. X. Feng, Prof. Dr. K. Mꢀllen
Max Planck Institute for Polymer Research
Ackermannweg 10, 55128, Mainz (Germany)
Fax: (+49)6131-379-350
E-mail: feng@mpip-mainz.mpg.de
Dr. D. Wu
School of Chemistry and Chemical Engineering
Shanghai Jiao Tong University, Shanghai (P.R. China)
[+] Present address: Evonik Degussa GmbH, Process Technology &
Engineering, Process Technology—New Processes
Rodenbacher Chaussee 4, 63457 Hanau-Wolfgang (Germany)
[**] This work was financially supported by the Max Planck Society
through the program ENERCHEM, the German Science Foundation
(Korean-German IR TG), DFG Priority Program SPP 1355, DFG MU
334/32-1, DFG Priority Program SPP 1459, and ESF Project GOSPEL
(Ref Nr: 09-EuroGRAPHENE-FP-001). We also gratefully acknowl-
edge Long Wang for help with TEM measurements and Shuping
Pang for help with ionic conductivity measurements.
Ionic complexes 2–7 (Scheme 1) were prepared from
PQP14-Cl 1 and the sodium salts of the corresponding
sulfonate anions by an ion-exchange procedure described
previously (see the Supporting Information).[10] To investigate
their aggregation behavior, a phase transfer (PT) method with
a methanol/water 1:1 binary solvent system was adopted to
Supporting information for this article is available on the WWW
Angew. Chem. Int. Ed. 2011, 50, 2791 –2794
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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