posted on 2021-08-09, 14:15authored byDaniel
C. Lee, Kathryn N. Guye, Rajan K. Paranji, Kacper Lachowski, Lilo D. Pozzo, David S. Ginger, Suzie H. Pun
We synthesize and characterize a
triblock polymer with asymmetric
tetramethoxyazobenzene (TMAB) and β-cyclodextrin functionalization,
taking advantage of the well-characterized azobenzene derivative-cyclodextrin
inclusion complex to promote photoresponsive, self-contained folding
of the polymer in an aqueous system. We use 1H NMR to show
the reversibility of (E)-to-(Z)
and (Z)-to-(E) TMAB photoisomerization,
and evaluate the thermal stability of (Z)-TMAB and
the comparatively rapid acid-catalyzed thermal (Z)-to-(E) isomerization. Important for its potential
use as a functional material, we show the photoisomerization cyclability
of the polymeric TMAB chromophore and calculate isomerization quantum
yields by extinction spectroscopy. To verify self-inclusion of the
polymeric TMAB and cyclodextrin, we use two-dimensional 1H NOESY NMR data to show proximity of TMAB and cyclodextrin in the
(E)-state only; however, (Z)-TMAB
is not locally correlated with cyclodextrin. Finally, the observed
decrease in photoisomerization quantum yield for the dual-functionalized
polymer compared to the isolated chromophore in an aqueous solution
confirms TMAB and β-cyclodextrin not only are in proximity to
one another, but also form the inclusion complex.