Choi et al.
Figure 1. Generalized formulations of the dipyrrolic species presented herein. n ) 2 or 3. R ) thienyl or phenyl. A. Research questions: (i) Is clean sulfur
oxidation achievable? (ii) Is stepwise dipyrrin bromination observable? B. (iii) Can meso-thienyl mediate metal ion recognition, and (iv) does sulfur oxidation
precede metal oxidation? C. Question (i) and (v) can aryl groups devoid of heteroatoms mediate metal ion recogntion?
There is a growing number of reports that feature thienyl
polypyrrole substrates as light absorbing materials and ligand
frameworks. Aside from an initial report on the photochemi-
cal preparation of 2-thienyl-dipyrromethane by D’auria and
systems, a third thiophene becomes incorporated at the
3-position, leading to “scorpionate”-like derivatives bearing
[SSS] binding sites.
Our general design parameters involve (i) having meso-
aryl groups whose sterics are modifiable and affect fluores-
2
2
co-workers, this laboratory has reported on 5-thienyl
2
3,24
11,25
5
dipyrromethanes
and -dipyrrins.
In addition to the
cence and (ii) substituting F’s with heterocycles that
n+
2
4
efforts of this laboratory, there is a growing number of reports
selectively revive latent fluorescence upon M binding.
on meso-tetrathienyl polypyrrole porphyrins from many
We are now seeking to test our thienyl-dipyrrin systems for
notable changes with neutral, yet reactive, small molecules.
26-36
different laboratories as well,
underscoring the growing
interest in substrates with this substitution.
Herein, we study three different meso-thienyl species with
The Ziessel research group has reported the synthesis and
photophysical properties of boron-dipyrromethene species
2+
2
three types of external stimulants (m-CPBA, Br , and M )
with five questions in mind (Figure 1).
37
bearing aryl substituents at boron. This inspired our interest
(i) Sulfoxidations are an important class of oxidative
2
4
in preparing boron thienyl-substituted analogues. In our
transformations that occur in chemistry and biology. Thus,
a substrate that can gauge the extent of such thienyl oxidation
would be of great interest to the molecular probes com-
munity. Fluorogenic derivatives containing thiophenes which
give rise to distinct photophysical changes upon oxidizing
may be suitable as metal and element-based catalytic or
biological probes alike. Specifically, these probes may be
considered for instance, in oxidative sulfur removal which
continues to be an essential and central theme in researching
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8,39
means to achieve cleaner fossil fuels.
ii) While the 8-position and boron substituents may contain
(
an oxidizable sulfur, we were also interested at the same time
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11072 Inorganic Chemistry, Vol. 47, No. 23, 2008