Communications
illustrate the specific properties that directly result from the
incorporation of s3,l3-phosphole moieties into the conjugated
backbone. Owing to its intimate coupling with the p system,
the P moiety has the capacity to influence the overall
properties of the conductive material in a cooperative way.
Moreover, its versatile reactivity allows for the detection of
elemental chalcogens, thus representing a novel development
in the field of molecular recognition by conjugated polymers.
The optimization of this P-based material, in terms of
selectivity, reversibility, and sensitivity, to obtain an applica-
ble chemosensor is under active investigation.
Scheme 2. Chemical modification of polymer 4 with S8 or Se yielding
5a,b and 6a1–3
Received: May 10, 2006
Published online: August 14, 2006
.
Keywords: chalcogens · cyclic voltammetry ·
.
electropolymerization · phosphorus heterocycles · sensors
230 mV, Figure 2) and 2) a bathochromic shift of the UV/Vis
band (Dlonset = 38 nm).[9] Hence, this quantitative chemical
=
transformation of the P centers (P!P S) induces significant
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modifications of the conjugated polymer properties. Note that
4 can display a real-time response to elemental sulfur
(1 minute) upon addition of a small amount of NEt3 (acting
as an S8 activator) to the toluene solution. In the same way,
material 4 also reacts with a suspension of selenium (gray or
red) in CH2Cl2 to yield 5b (Scheme 2). This reaction is rather
slowbecause of the poor solubility of selenium, and is
accompanied by a significant anodic shift (about 110 mVafter
5 hours). Indeed, phosphole-modified polythiophene 4 is the
first conjugated polymer which can detect elemental chalc-
ogens. The ability of s3-P centers to react with elemental
sulphur and selenium is trivial in molecular phosphorus
chemistry. However, transposed to the field of conjugated
polymers, this reaction is the key to affording unprecedented
sensing properties since these chemical postmodifications
result in easily measurable macroscopic responses.
Intriguingly, when a Pt electrode that is modified with the
polymer 4 is submerged in a solution of S8 (0.3m) for just
2.5 minutes, a 60-mV positive offset shifting of the oxidation
wave of the resulting material 6a1 is observed (CV in green,
Figure 2). It is important to recall that the complete trans-
formation 4!5a (Scheme 2) requires 20 minutes. Further
similar sequential exposures of 6a1 to the S8 solution resulted
in a gradual shift of the oxidation peak (6a1!6a2!6a3,
Figure 2) until a signal similar to that of 5a was recorded.
Having fully characterized the final adduct 5a, it is obvious
that increasing the contact time involves a progressive
sulfurization of the s3,l3-P centers of 4 (m(6a1) < m(6a2) <
m(6a3), Scheme 2).[11] Despite the fact that 6a1–3 feature both
s3- and s4-P centers, cyclovoltammetric measurements show
just one collective response (Figure 2). Hence, the modifica-
tion of a collective system response (shift in Epa) upon gradual
binding of the s3,l3-P sites of polymer 4 shows that these
recognition sites act in a cooperative fashion. This behavior,
which is also observed upon treating 4 with [(tht)AuCl],[9] is
an essential prerequisite for the design of sensors that show
signal amplification.[5a,b]
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In conclusion, these results showthat molecular P chem-
istry (coordination chemistry, P derivatization, NMR analysis,
etc.) can be extended to conjugated polymers, and they
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Angew. Chem. Int. Ed. 2006, 45, 6152 –6155