because no azopyridinium was formed in this case. This
indicated that the hydrophilic azopyridinium was one of the
most important factors in the fabrication of nanofibers and
their hybrids.
this robust hybrid method. It is expected that more variations
of hybrid nanofibers with multi-components such as various
organic and inorganic compounds can be created via this
simple method, which would advance their future applications
in conductive nanomaterials.2
Besides, two other compounds such as sodium lauryl sulfate
without the aromatic ring and p-toluenesulfonic acid mono-
hydrate (TSAM) with a short alkyl chain were also utilized for
fabrication of hybrid nanofibers. Although the same reactive
conditions were used, neither of them showed nanofiber
formation (Fig. S11, ESIw). For TSAM, solids preferably
precipitated from the solution upon addition of excess HCl.
These indicate that both p–p stacking interactions of aromatic
rings and a long alkyl chain in benzenesulfonic groups are
necessary for fabrication of the hybrid nanofibers.
We thank Dr. M. Masuda in AIST and Dr. Y. Hoshino in
Yokohama National University for helpful discussions.
Notes and references
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Then, electrical conductivity of the fabricated nanofibers
was evaluated via a standard four-probe method. All the
nanofiber films were prepared with a thickness of about
0.4–0.5 mm, but two contrary results were obtained. The
nanofibers with 2 had no electrical conductivity, whereas the
hybrid nanofibers with a mixture of 4 and 5 (or 4, 5 plus NaCl)
showed an electrical conductivity of 1.1 ꢁ 10ꢀ7 S cmꢀ1 (or 1.3 ꢁ
10ꢀ7 S cmꢀ1). Undoubtedly, this additional conductive property
should be achieved from the hybridizing process.
In the UV-vis absorption spectrum of a mixture of 4, 5 plus
NaCl in the solid state (Fig. 2c), lmax was obtained at 417 nm.
In its solution, lmax appeared at 357 nm (Fig. S12, ESIw),
almost the same as that of Fig. 2a, indicating that p–p stacking
interactions existed in the solid state of the hybrid nanofibers.
Moreover, lmax in Fig. 2c showed a remarkable red shift of
46 nm compared with that in Fig. 2b. This demonstrates that
the p–p stacking interactions were strongly enhanced in the
hybrid nanofibers than that without a hybrid, which might be
responsible for the obtained conductivity.
XRD of the obtained hybrid nanofibers is shown in Fig. S5b
(ESIw). Two broad peaks at 2y 4 201 and 151 o 2y o 201
were observed. The former was attributed to p–p stacking
interactions among the azopyridine chromophores, similarly
to that of Fig. S5a (ESIw). The latter is an additional peak,
originated from the hybridization process by introduction of
DBSA or its salt, which should be responsible for the
enhancement of p–p stacking interactions. The sharp peak at
0.28 nm was ascribed to NaCl (Fig. S5b, ESIw). Therefore, a
possible schematic illustration of the enhanced p–p stacking in
the hybrid nanofibers is given in Fig. S13b (ESIw). It is the
strong p–p stacking interactions improved by the hybrid
method that resulted in the additional electrical conductivity.
In summary, hybrid organic nanofibers were successfully
fabricated with LMW amphiphilic azopyridinium and DBSA
or its salt by a simple self-assembled process. The formation of
azopyridinium salts played an important role in the fabrication
of nanofibers and their hybrids. Interestingly, electrical conductivity
was obtained by the enhanced p–p stacking interactions using
c
12770 Chem. Commun., 2011, 47, 12768–12770
This journal is The Royal Society of Chemistry 2011