C O M M U N I C A T I O N S
and methanol solvate molecules are located in the channels between
the columns. Interestingly, three methanol molecules are bound by
hydrogen bonds to only one of the two anions in the dimer (Figure
S2b). We ascribe the dissimilar stacking behaviors of 1 and 2 to
the different sizes of their anions. The small BF4- anions are located
next to the cations, allowing the formation of a condensed layered
structure. In contrast, the large benzenesulfonate anions require more
space, leading to a better separation between the rigid aromatic
cores. To the best of our knowledge, 2 is the first example of a
single-crystal structure in which a columnar stacking of PAHs with
charged aromatic cores has been observed.
controlled.1 In our present case, the intracolumnar staggered
organization remains unchanged for 3, 4, and 5, although the
thermotropic properties of the compounds differ significantly. As
expected, long chains result in the formation of discotic mesophases
for 4 and 5 even at ambient temperatures. Each compound shows
only one phase transition directly to the isotropic melt, at 180 °C
for 4 and 210 °C for 5. Images from polarized optical microscopy
(POM) reveal that both compounds exhibit typical birefringent
mesophase textures that are shearable as thin films (Figure 2b),
confirming the soft mesophase character.10 On the other hand,
compound 3 shows only a crystalline state, as indicated by the
highly optically anisotropic needles in the POM picture (Figure
2d) and the reflections in the 2D pattern with mixed indices in the
first layer line (Figure 2c). A hexagonal unit cell with ahex ) 2.78
nm was determined for 3.
In conclusion, an unprecedented columnar organization of ionic
complexes based on PQP has been achieved via ionic self-assembly.
These complexes represent the first family of PAHs containing a
charged aromatic core with controllable columnar organization in the
bulk state. Since the supramolecular organization of PAHs with charged
aromatic cores can be easily tuned by their counterions, future work
should include the use of more elaborate counterions that can
incorporate hydrogen bonding, metal coordination, or chirality to further
adjust their phase behavior. The influence of the charges of the aromatic
cores could be investigated by the selection of charged PAHs with
different core sizes, charges, or heteroatoms. The combination of their
charged nature and well-organized columnar superstructure makes these
materials promising for 1D anisotropic ion transport or construction
of novel charge-transfer complexes.11
Figure 2. 2D WAXS patterns for (a) 5 and (c) 3 recorded at 30 °C [white
arrows indicate the fiber orientation, and the dashed layer lines in (a) are
assigned using Miller indices]. POM images with cross-polarizers recorded
at 30 °C for (b) 5 and (d) 3 as each cooled from the isotropic phase at 1
°C/min.
Acknowledgment. This work was financially supported by the
Max Planck Society through the program ENERCHEM, the German
Science Foundation (Korean-German IRTG), DFG Priority Pro-
gram SPP 1355, and DFG Grant AN 680/1-1.
Inspired by the single-crystal results, one may expect that the
columnar superstructures of PQP complexes should be even
established in the liquid-crystalline phase. Therefore, the behavior
of LCs of PQP complexes 3, 4, and 5 containing sulfonate anions
with long alkyl tails was subsequently investigated. Fiber wide-
angle X-ray scattering (WAXS) experiments performed at 30 °C
on both 5 (Figure 2a) and 4 (Figure S4) revealed 2D patterns typical
of columnar discotics. The equatorial plane of the pattern, assigned
as the hk0 layer line, indicates the intercolumnar arrangement
whereby the columnar stacks are oriented along the fiber direction.
In the case of both 4 and 5, the X-ray scattering results did not
allow one to distinguish clearly between a rectangular and a larger
hexagonal unit cell (Figure S3). The broad, high-intensity wide-
angle meridional reflection in the 2D pattern for each of three
compounds 3, 4, and 5 is related to the π-stacking distance of 0.35
nm between individual molecules packed in the columns. Remark-
ably, the three compounds also showed additional reflections on
the hk1 layer line corresponding to a spacing of 0.70 nm along the
stacking axis, which is twice the π-stacking distance.9 This
intracolumnar correlation between every second molecule in the
bulk confirms the above-described staggered arrangement of the
PQP cations already observed in the single crystal. It should be
noted that the intracolumnar staggered arrangement of the PQP
cations is independent of the degree of steric demand of the
substituents and remains unchanged in the mesophase and crystal-
line phase. Hence, the introduction of sulfonate anions with long
alkyl tails through the ISA process allows one to control the thermal
behavior in a relatively facile but efficient way while at the same
time maintaining the columnar organization. This is a great
advantage in comparison with systems in which substituents are
covalently linked to the PAH core, where variation is often
synthetically challenging and the molecular organization is less
Supporting Information Available: Preparation and characteriza-
tion of ionic complexes, WAXS experiments, and single-crystal data
(CIF). This material is available free of charge via the Internet at http://
pubs.acs.org.
References
(1) (a) Laschat, S.; Baro, A.; Steinke, N.; Giesselmann, F.; Hagele, C.; Scalia,
G.; Judele, R.; Kapatsina, E.; Sauer, S.; Schreivogel, A.; Tosoni, M. Angew.
Chem., Int. Ed. 2007, 46, 4832–4887. (b) Wu, J. S.; Pisula, W.; Mu¨llen,
K. Chem. ReV. 2007, 107, 718–747. (c) Sergeyev, S.; Pisula, W.; Geerts,
Y. H. Chem. Soc. ReV. 2007, 36, 1902–1929. (d) Feng, X.; Marcon, V.;
Pisula, W.; Hansen, M.; Kirkpatrick, J.; Grozema, F.; Andrienko, D.;
Kremer, K.; Mu¨llen, K. Nat. Mater. 2009, 8, 421–426.
(2) Gearba, R. I.; Lehmann, M.; Levin, J.; Ivanov, D. A.; Koch, M. H. J.;
Barbera, J.; Debije, M. G.; Piris, J.; Geerts, Y. H. AdV. Mater. 2003, 15,
1614–1618.
(3) (a) Percec, V.; Glodde, M.; Peterca, M.; Rapp, A.; Schnell, I.; Spiess, H. W.;
Bera, T. K.; Miura, Y.; Balagurusamy, V. S. K.; Aqad, E.; Heiney, P. A.
Chem.sEur. J. 2006, 12, 6298–6314. (b) Lee, M.; Kim, J. W.; Peleshanko,
S.; Larson, K.; Yoo, Y. S.; Vaknin, D.; Markutsya, S.; Tsukruk, V. V.
J. Am. Chem. Soc. 2002, 124, 9121–9128.
(4) van Herrikhuyzen, J.; Syamakumari, A.; Schenning, A.; Meijer, E. W. J. Am.
Chem. Soc. 2004, 126, 10021–10027.
(5) (a) Thunemann, A. F.; Kubowicz, S.; Burger, C.; Watson, M. D.;
Tchebotareva, N.; Mu¨llen, K. J. Am. Chem. Soc. 2003, 125, 352–356. (b)
Faul, C. F. J.; Antonietti, M. AdV. Mater. 2003, 15, 673–683.
(6) Kumar, S.; Pal, S. K. Tetrahedron Lett. 2005, 46, 4127–4130.
(7) Guan, Y.; Yu, S. H.; Antonietti, M.; Bottcher, C.; Faul, C. F. J. Chem.sEur.
J. 2005, 11, 1305–1311.
(8) Wu, D. Q.; Zhi, L. J.; Bodwell, G. J.; Cui, G. L.; Tsao, N.; Mu¨llen, K.
Angew. Chem., Int. Ed. 2007, 46, 5417–5420.
(9) Feng, X.; Pisula, W.; Mu¨llen, K. J. Am. Chem. Soc. 2007, 129, 14116–
14117.
(10) Lehmann, M.; Gearba, R. I.; Koch, M. H. J.; Ivanov, D. A. Chem. Mater.
2004, 16, 374–376.
(11) (a) Kato, T. Science 2002, 295, 2414–2418. (b) Sun, D. L.; Rosokha, S. V.;
Kochi, J. K. Angew. Chem., Int. Ed. 2005, 44, 5133–5136.
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