of hydroxide ions, such as the Grotthuss mechanisms, diffusion
and migration, and convection, were reported.18 The Grotthuss
mechanism was considered as a contributing mechanism in high
water-content membranes, where hydroxide ions will switch
hydrogen and covalent bonds, and then perform surface hopping
between the cation side chains. The distance between the two N
atoms in DDP was reduced when the closed-ring isomer formed,
which may facilitate the jumping of hydroxide ions between
the cation groups. This could be considered as one reason that
caused the increase in HC.
In conclusion, DDP groups were tethered onto the FPAEO
backbone to yield optically active AEMs. The DDP groups
served both as the cations and as the in situ optical switches. The
resultant membrane was thermally stable. The in situ switch
could be activated by irradiating the membrane with UV-vis
light; exposure to UV resulted in the formation of the closed-ring
form of the DDP, while exposing this closed-ring form to vis
reversed the process. The side-chain effects were investigated
using a same membrane sample, which made even trivial
difference in the properties reliable. The closed-ring isomer of
the membrane offered slightly higher HC because of the
reduction in the side-chain length, which facilitates the
Grotthuss mechanism of hydroxide transportation; however,
the open-ring isomer offered an enhanced mechanical stability
(20.7% vs. 14.1% elongation at break) because of the decrease in
the delocalized π-system. The change in the membrane structure
between the open-ring and closed-ring forms was verified by
AFM tests and DFT calculations. This study provided a new
pathway to evaluate the structural effects on AEMs, which could
avoid errors by using different membrane samples; it also
suggested a new strategy to elevate the HC of AEMs.
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G. Couture, A. Alaaeddine, F. Boschet, B. Ameduri, Prog.
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M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone, B.
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Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda,
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H. Nakai, T. Vreven, J. A. Montgomery, Jr., J. E. Peralta,
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Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene, J. E.
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Foresman, J. V. Ortiz, J. Cioslowski, D. J. Fox, Gaussian 09
(Revision D.01), Gaussian, Inc., Wallingford CT, USA, 2009.
The work was funded by the National High Technology
R&D Program of China (Nos. 2012AA051201 and
2012AA053401), Natural Science Foundation of China
(No. 21176140), and State Key Laboratory of Automobile
Safety and Energy (No. KF14162). Vijay Ramani would like
to acknowledge the Hyosung S. R. Cho Endowed Professorship
for partly funding the collaboration with Tsinghua University.
Supporting Information is available electronically on J-STAGE.
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© 2014 The Chemical Society of Japan | 1495