Communications
[2] a) H. Miyaji, J. L. Sessler, Angew. Chem. 2001, 113, 158; Angew.
Chem. Int. Ed. 2001, 40, 154.
[3] a) J. J. Lavigne, E. V. Anslyn, Angew. Chem. 1999, 111, 3903;
Angew. Chem. Int. Ed. 1999, 38, 3666.
[4] S. Yamaguchi, S. Akiyama, K. Tamao, J. Am. Chem. Soc. 2001,
123, 11372.
[5] a) Q. Zhou, T. M. Swager, J. Am. Chem. Soc. 1995, 117, 12593;
b) J.-S. Yang, T. M. Swager, J. Am. Chem. Soc. 1998, 120, 5321;
c) J.-S. Yang, T. M. Swager, J. Am. Chem. Soc. 1998, 120, 11864;
d) T. M. Swager, Acc. Chem. Res. 1998, 31, 201; e) D. T.
McQuade, A. E. Pullen, T. M. Swager, Chem. Rev. 2000, 100,
2537; f) for a recent review, see: T. M. Swager, J. H. Wosnick,
MRS Bull. 2002, 27, 446.
[6] D. T. McQuade, A. H. Hegedus, T. M. Swager,J. Am. Chem. Soc.
2000, 122, 12389.
[7] For another sensor approach that used the affinity of fluoride to
silicon see: S. Yamaguchi, S. Akiyama, K. Tamao, J. Am. Chem.
Soc. 2000, 122, 6793.
possible in the same way as for the small molecule 2, because
the fluorescence quantum yield of the polymer varies as a
function of conversion and at low conversion we observe less
efficient emission. Nevertheless, it is clear that the polymer 4
has a faster response to fluoride ion (Figure 1b). The
enhanced fluoride sensitivity of 4 relative to 2 is clearly
evident when one considers that exposure of 4 (1.5 10À6
m
based upon the repeating group) to fluoride (1.6 10À7 m,
TBAF in THF) results in a complete transformation of the
fluorescence intensity maximum of 4 in 2 h, whereas 2
required a 100-fold higher fluoride concentration to achieve
a complete fluorescence transformation over the same time
with all other conditions the same (Figure 1). Hence we
conclude that 4 is approximately 100-times more sensitive
than its small-molecule-based counterpart 2. This amplifica-
tion factor is in accord with our previous determination of
exciton diffusion in isolated polymers.[5a] We further note that
energy migration within isolated polymers (i.e. dilute solu-
tions) is inherently inefficient owing to the one-dimensional
exciton diffusion.[17] Thin films that display two- and three-
dimensional transport characteristics exhibit more favorable
transport statistics and also benefit from improved Förster
energy-transfer process between polymer chains. Unfortu-
nately 4 is strongly quenched in thin films, however, it should
be possible to generate related indicator materials with
desirable solid-state properties and much larger amplification
factors in the future.
[8] K. D. Drexhage in Dye Lasers, Vol. 1 (Ed.: F. P. Schäfer),
Springer, New York, 1977.
[9] a) W. Lehnert, Tetrahedron Lett. 1970, 4723; b) M. Black, J. I. G.
Cadogan, H. McNab, A. D. MacPherson, V. P. Roddam, C.
Smith, H. R. Swenson, J. Chem. Soc. Perkin Trans. 1 1997, 2483.
[10] A. Rose, C. G. Lugmair, T. M. Swager, J. Am. Chem. Soc. 2001,
123, 11298.
[11] T. M. Swager, C. J. Gil, M. S. Wrighton, J. Phys. Chem. 1995, 99,
4886.
[12] The alternative approach to develop PPE based on the 3,6-
diethynyl-2-hydroxy-benzaldehyde was not pursued, as o-phe-
noxyacetylenes could undergo tandem cyclization to the corre-
sponding benzofuran by use of TBAF or CsF, for example, see:
A. Sakai, T. Aoyama, T. Shioiri,Heterocycles 2000, 52, 643.
[13] See Supporting Information for details.
[14] 2-Hydroxy-4-(trifluoromethanesulfonyl) benzaldehyde (9) was
obtained by treating 4-hydroxy-2-methoxybenzaldehyde with
triflic anhydride in pyridine (95%), followed by demethylation
involving BBr3 in CH2Cl2 at À408C (79%). See also Supporting
Information.
[15] Triisopropylsilyl group (TIPS) was used instead oftert-butyldi-
methylsilyl (TBS) as the thermal polymerization conditions
required a more stable protecting group for phenol.
[16] 1,4-Diiodobenzene with ortho-dialkoxy side-chains 13 was
chosen as a comonomer to produce a sensory polymer with
higher frequencies (blue-shifted). Z. Zhu, T. M. Swager, Org.
Lett. 2001, 3, 3471.
In summary, we have introduced a new system for the
detection of fluoride ion and successfully amplified the
response using exciton migration in a semiconducting organic
polymer. In contrast to most semiconductive-polymer sensor
schemes that rely on changes in emission intensity, this
sensory system utilizes a new fluorescence signal. The
approach of directly interconnecting the indicator electroni-
cally with the polymer's band structure is a promising
alternative to FRETschemes and we intend to apply this
approach to other analytes of interest.
Received: June 6, 2003 [Z52075]
Published Online: September 23, 2003
[17] I. A. Levitsky, J. Kim, T. M. Swager,J. Am. Chem. Soc. 1999, 121,
1466.
Keywords: fluorescence · fluorides · materials science ·
.
polymers · sensors
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4806 ꢀ 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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