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charged arms show rather slow decrease of w and even the
opposite. Interestingly, the decrease of w strongly correlates
with the number of charges per layer Nc (equal to NL times
charge on the monomer) given in Table 2. A prominent de-
crease of w was observed for P-7-3 with Nc =7.74, whereas
only a moderate decrease was observed for P-8-3, with Nc =
6.36. For even small Nc, w either decreases only slightly or fluc-
tuates as concentration goes up. With the lowest Nc of less
than six, either an increase in w or broadening with concentra-
tion instead is observed for P-7-2-C.
generating correspondingly weaker repulsion. Consequently,
the growth of the correlation length with concentration is
gradually depressed following the same sequence, and peak
broadening behaves differently (weak decline, fluctuation, and
increase as concentration increases, respectively, for the three
molecules) even with similar change of bG/b. Nevertheless, the
behavior of P-7-3 and P-8-3 is distinct from that of P-6-2-C
and P-7-2-C in terms of clustering, which is also demonstrated
by the difference in POM in Figure S2 in the Supporting Infor-
mation for the two types of BTA molecules. The apparent
stripes observed for P-7-3 and P-8-3 indicate well-defined col-
umnar packing, the absence of which in the solutions of P-6-2-
C and P-7-2-C suggests less well ordered columnar arrange-
ments. The contrast between BTA molecules with different
numbers of ionic groups demonstrates the subtle influence of
surface charge density on the long-range ordering and ar-
rangements of highly charged supramolecular columns.
The width of scattering peaks in liquid crystals is usually re-
lated to the long-range ordering of the packing units or corre-
lation length. Generally speaking, the correlation length in-
creases with concentration of the packing units and narrowing
of peak width is expected, which is indeed observed for the
most charged P-7-3 assemblies and also for P-8-3, albeit to
a lesser extent. Then the broadening of the peaks for P-7-2-C
becomes intriguing. Similar disordering at higher densities was
also discovered in DNA packing, which has been attributed to
increasing frustration of the molecules.[16] However, this argu-
ment may not apply in our case for two reasons. First, the sep-
aration between the supramolecular nanotubes of approxi-
mately 10 nm is larger than that between DNA molecules, with
an axle–axle distance approximately 3.5 nm. Second, the supra-
molecular nanotubes are not as rigid as DNA helices and could
accommodate a larger number of defects inside the nanotubes
while maintaining the long-range positional ordering. The ar-
gument that distortion may not account for the broadening
observed in this study is further supported by quantitative
analysis of the broadening of the principle peak. As an exten-
sion of the Voigt function, the Pearson function also allows
double Voigt analysis to separate the broadening due to crys-
talline size (correlation length) and micro-strain (lattice imper-
fection). The contribution of lattice distortion to the peak
broadening (bG/b) can be estimated by calculating 2w/b of the
principle peak, which gives the value of bG/b according to re-
ported data.[15] Here, b stands for integral breadth of the peak
and is given in the Supporting Information (Figure S9). As
shown in Figure 6b, bG/b of all lyotropic solutions tend to de-
crease with molecular concentration after going up slightly at
lower concentrations. For asymmetric molecules, the total de-
crease of bG/b is of roughly the same magnitude. However the
behavior with respect to peak widths is completely different,
indicating that peak broadening is not dominated by lattice
distortion. Instead, line broadening due to correlation length
could be responsible for the distinctive behavior of w.
Conclusion
BTA molecules are more structurally versatile because of the
various repeating linkages between the central cores and the
peripheral functional groups. Directionality of hydrogen bonds
and p–p interactions between the fully rigid BTA molecules co-
operating solvophobic effects and electrostatic repulsive inter-
action[17] contributes to the stability of the lyotropic liquid-crys-
tal phases. Here, we demonstrate the robustness of supra-
molecular hierarchical structures with similar stacking architec-
ture and packing behavior for fully rigid ionic BTA molecules
with structural versatility along one arm. The mode of molecu-
lar stacking, such as the number of molecules per stacking
layer, is determined jointly by rigid arm length and the ionic
terminals in a way that mesoscopic parameters, including di-
ameters and internanotube distances, can be maintained
almost constant for different BTA molecules. The only nuance
of long-range ordering is found in terms of correlation length
depending on the charge distribution along the nanotubes.
The similarity in the dimensions and ordering of the nanotubes
assembled by the BTA molecules reflects the robust architec-
ture imparted by synergetic multiple noncovalent interactions.
In contrast to the assembly of molecules with flexible chains,
which show sensitivity to the geometry and component of the
arm,[18] fully rigid ionic BTA molecules can self-assemble into hi-
erarchical structures with excellent control over geometry and
symmetry on the nanometer scale. As a result, it is possible to
regulate supramolecular structures for new functional materials
by modulating the functional group distribution, hydrophobic
arm numbers, and arm length without losing the hierarchical
architecture of the assembly. In addition, the sensitivity of ag-
gregation to the chemical and geometrical structures of the
BTA molecules demonstrated here can help understand the
subtleties involved in hierarchical supramolecular assembly.
This knowledge can be used for the design and construction
of more complex lyotropic mesogenic structures.
For the highly charged systems, the driving force for long-
range ordered packing could be strong electrostatic repul-
sion.[7b] It is not surprising that the correlation length in that
case will be dominated by the strength of repulsion. The rapid
reduction in peak width w for nanotubes assembled by P-7-3
could be explained by the promoted long-range ordering with
concentration due to stronger repulsion between the nano-
tubes with the largest number of charged groups. The dramat-
ic suppression of bG/b also contributes to the peak narrowing
for P-7-3. Number of charges along the supramolecular nano-
tubes decreases progressively for P-8-3, P-6-2-C, and P-7-2-C,
Chem. Eur. J. 2015, 21, 15388 – 15394
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