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Figure 16.8 The non-fluorescent compound 28 reacted with Pd
2+
to form the fully
conjugated, fluorescent intermediate 29. This O-Pd-P complex re-
arranged to the more stable N-Pd-P complex 30.
Adapted from Ref. 50.
Figure 16.9
Structures of polymer-based palladium sensors developed by Bai's group.
Adapted from Refs 51, 52 and 53.
Figure 16.10
Structure of the palladium sensor developed by Mukherjee et al.
Adapted from Ref. 55.
fluorescent than the starting material. The same group reported the second-
generation sensor 32.
53
As the final step in the preparation of these sensors
was a palladium-catalyzed Sonogashira coupling, the sensors were pre-
sumably contaminated with palladium. Another polymer-based fluorescent
sensor for palladium was reported by Wang and Liao.
54
Although the
chemical structures of the palladium complexes were not well defined, it was
reported that poly(o-phenylenediamine) bound selectively to Pd
2+
and
emitted signals at 304 nm as the l
max
.
Mukherjee's group developed another on-off fluorescent chemosensor
(Figure 16.10).
55
Blue fluorescent hydrazone 33 became less fluorescent
upon binding to Pd
2+
. Using this hydrazine as a palladium chelator, Pd
2+
in
water could be selectively extracted into an organic layer and visualized by
the blue color.
Another fluorescent chemosensor for palladium(II) was developed by Tae
and co-workers (Figure 16.11).
56
The rhodamine derivative 34 was shown to
bind to 2 equiv. of Pd
2+
in water to form the fluorescent complex 35. This
complex formation was selective for Pd
2+
.
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