Angewandte
Chemie
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addition of more than 1.2 equivalents can readily transform
the gel matrix into a sol phase (Figure 6). Therefore,this
organogel-based approach becomes quite attractive,consid-
ering that conventional colorimetric sensors that operate in
Org. Biomol. Chem. 2003, 1,895 – 899; b) M. Shirakawa,S.-i.
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Figure 6. Photograph of organogel 1 (5.0 mm in cyclohexane): A) with-
out 3 f; B) with 0.2 equivalents of 3 f; C) with 1.0 equivalent of 3 f, and
D) with 1.2 equivalents of 3 f.
J. K. M. Sanders, J. Am. Chem. Soc. 1998, 120,1096 – 1097;
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solution require 10–100 equivalents of the analyte for sensing
with the naked eye.[14] Although the present organogel matrix
can detect analytes on the milligram scale,an improved
design could lead to attractive systems that operate on the
ppm scale. This development would make organogels attrac-
tive for future applications to determine environmental
pollutants.
In summary,we have found a rare example of an
organogel in which a multiple set of noncovalent interactions
confers hostlike character to the gel matrix[15],and by virtue
of this character,the organogel can perform several exciting
functions. It can differentiate different classes of electron-rich
naphthalene compounds such as dihydroxynaphthalenes from
alkoxy- and hydroxynaphthalenes. Naked-eye differentiation
of several positional isomers of dihydroxynaphthalene
becomes possible as a result of an unprecedented coerced
H-bonding-driven recognition that significantly amplifies the
binding in the gel state.
Iijima,H.-R. Tseng,J. K. M. Sanders,J. F. Stoddart,
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[6] See the Supporting Information.
[7] Our work differs conceptually from the donor–acceptor-assisted
gelation processes in that our work focuses on utilizing the 1D
gel matrix to study the novel recognition processes. For donor–
acceptor-induced gel formation,see: a) U. Maitra,P. V. Kumar,
N. Chandra,L. J. DꢀSouza,M. D. Prasanna,A. R. Raju, Chem.
Commun. 1999,595 – 596; b) A. Friggeri,O. Gronwald,K. J. C.
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Lee,T.-S. Bae,S. S. Lee,S. Shinkai, Chem. Mater. 2005, 17,459 –
462.
[8] A charge-transfer band due to this well-known donor–acceptor
interaction has been observed by various groups: P. Talukdar,G.
Bollot,J. Mareda,N. Sakai,S. Matile, J. Am. Chem. Soc. 2005,
127,6528 – 6529.
[9] The recognition studies in the gel matrix of 1 were carried out in
cyclohexane or decalin. Dichloromethane and chloroform,
which are common solvents for studying donor–acceptor com-
plexes,could not be used because of the inability of 1 to form a
gel in these solvent. However,we had to use the mixed solvent
cyclohexane/chloroform for 2·3a, 2·3d,and 2·3 f to maintain the
solubility of the complexes and overcome precipitation.
[10] Naphthalenediimide–pyrene complexes are well known both in
solution and in the solid state. For a recent example that employs
this motif,see: H. M. Colquhoun,Z. Zhu,D. J. Williams, Org.
Lett. 2003, 5,4353 – 4356.
Experimental Section
Organogelator 1 and the nongelling reference compound 2 were
synthesized from 1,4,5,8-naphthalenetetracarboxylic dianhydride. See
the Supporting Information for experimental details on the synthesis,
gelation tests, 1H NMR,ATR-FTIR,and UV/Vis spectrometry,
MALDI TOF mass spectrometry,and SEM/TEM measurements.
Received: September 6,2005
[11] For donor–acceptor interactions of 2,6-dihydroxynaphthalenes
in aqueous solution,see: a) H.-J. Kim,J. Heo,W. S. Jeon,E. Lee,
J. Kim,S. Sakamoto,K. Yamaguchi,K. Kim, Angew. Chem. 2001,
113,1574 – 1577; Angew. Chem. Int. Ed. 2001, 40,1526 – 1529;
b) J. W. Lee,K. Kim,S. W. Choi,Y. H. Ko,S. Sakamoto,K.
Yamaguchi,K. Kim, Chem. Commun. 2002,2692 – 2693.
Keywords: donor–acceptor systems · host–guest systems ·
molecular recognition · sensors · supramolecular chemistry
.
=
[12] ATR-IR observations show that the peaks due to C O
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vibrations shifted gradually with the addition of small amounts
of 3 f from 1706 and 1665 cmÀ1 to 1700 and 1659 cmÀ1
,
respectively,until a 1:1 stoichiometry was achieved. No further
=
changes in the C O vibrations were observed with the addition
of excess 3 f.
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[13] One of the referees has suggested that a solvophobic effect could
be the major driving force for the observed interaction.
[14] R. M. Martinez,F. Sansenon Chem. Rev. 2003, 103,4419,4476.
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