A chromogenic macrocycle exhibiting cation-selective and anion-controlled color change: An approach to understanding structure-color relationships

Article abstract of DOI:10.1021/ol0602405

A N-azo-coupled macrocycle (1) with a NO₂S₂ donor set was synthesized as a chromoionophore and shown to exhibit Hg²⁺ selectivity; anion control of the color of the Hg²⁺ complex was observed. As a first approach,

Full text of DOI:10.1021/ol0602405

ORGANIC
LETTERS
2006
Vol. 8, No. 8
1641-1643
A Chromogenic Macrocycle Exhibiting
Cation-Selective and Anion-Controlled
Color Change: An Approach to
Understanding Structure−Color
Relationships
Soo Jin Lee,† Jong Hwa Jung,*,† Joobeom Seo,† Il Yoon,† Ki-Min Park,†
Leonard F. Lindoy,‡ and Shim Sung Lee*,†
Department of Chemistry and Research Institute of Natural Sciences, Gyeongsang
National UniVersity, Chinju 660-701, Korea, and Centre for HeaVy Metal Research,
School of Chemistry, F11, The UniVersity of Sydney, NSW 2006, Australia
sslee@gsnu.ac.kr
Received January 27, 2006
ABSTRACT
+
A N-azo-coupled macrocycle (1) with a NO2S2 donor set was synthesized as a chromoionophore and shown to exhibit Hg2 selectivity; anion
+
control of the color of the Hg2 complex was observed. As a first approach, the nature of the color generation process was probed by
determining the crystal structures of the two different colored species obtained with perchlorate and iodide anions. The results can be explained
in terms of a “Push-n-Pull Process”, which serves to illustrate how the coordinating ability of the anion controls the color change through
formation of endo- or exo-metal complexes. The use of “simple” salts to induce color-switching of the above complex species was also
reported.
Chromogenic receptors as chemosensors are especially
attractive because guest determination can be carried out
without the use of instrumentation.1-5 Such systems are
basically composed of two parts: binding (recognition) and
color-changing (signaling) units which are covalently linked.
N-azo-coupled macrocycles,1,3,6 the protypical type in this
(4) (a) Inoue, Y.; Liu, Y.; Hakushi, T. In Cation Binding by Macrocycles;
Inoue, Y., Gokel, G. W., Eds.; Dekker: New York, 1990; Chapter 1. (b)
Descalzo, A. B.; Mart´ınez-Ma´n˜ez, R.; Radeglia, R.; Rurack, K.; Soto, J. J.
Am. Chem. Soc. 2003, 125, 3418. (c) Kim, S. K.; Lee, S. H.; Lee, J. Y.;
Bartsch, R. A.; Kim, J. S. J. Am. Chem. Soc. 2004, 126, 16499. (d) Lee, J.
Y.; Kim, S. K.; Jung, J. H.; Kim, J. S. J. Org. Chem. 2005, 70, 1463.
(5) (a) Sanceno´n, F.; Descalzo, A. B.; Mart´ınez-Ma´n˜ez, R.; Miranda,
M. A.; Soto, J. Angew. Chem., Int. Ed. 2001, 40, 2640. (b) Kim Y.-H.;
Hong, J.-I. Angew. Chem., Int. Ed. 2002, 41, 2947. (c) Lee, D. H.; Im, J.
H.; Son, S. U.; Chung, Y. K.; Hong, J.-I. J. Am. Chem. Soc. 2003, 125,
7752.
† Gyeongsang National University.
‡ The University of Sydney.
(1) (a) Dix, J. P.; Vo¨gtle, F. Chem. Ber. 1980, 113, 457. (b) Dix, J. P.;
Vo¨gtle, F. Chem. Ber. 1981, 114, 638.
(2) (a) Izatt, R. M.; Pawlak, K.; Bradshaw, J. S. Chem. ReV. 1991, 91,
1721. (b) Beer, P. D.; Gale, P. A. Angew. Chem., Int. Ed. 2001, 40, 486.
(c) Lavigne, J. J.; Anslyn, E. V. Angew. Chem., Int. Ed. 2001, 40, 3118.
(3) Sanceno´n, F.; Mart´ınez-Ma´n˜ez, R.; Soto, J. Angew. Chem., Int. Ed.
2002, 41, 1416.
10.1021/ol0602405 CCC: $33.50
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Published on Web 03/15/2006

category, have been extensively investigated for the detection
of cations,2,3 anions,4,5 and organic species.2b,5c In this
category of chromophore, photoexcitation causes a net
electronic charge transfer from the donor end (bridgehead
nitrogen) to the acceptor end within the chromophore.
However, contrary to our expectation, neither the preparation
nor crystal structure of an N-azo-coupled macrocyclic
complex has been reported previously in relation to their
chromophoric function. Further, the complexity of such
chromophoric systems frequently results in the co-occurrence
of multiple phenomena, some of which may involve both
cations and anions.3,6
We recently reported two NO2S2 macrocycles7 showing
affinity for Hg2+, with the latter being bound in an exo-8 or
endo-coordination manner. More recently, we synthesized
the N-azo-coupled analogue 1, which shows Hg2+ selectivity;
the color of the Hg2+ complex is controlled by anions as
outlined in the Abstract. This result prompted a structure-
function analysis in terms of the use of 1 for sensing. From
this approach, we were able to elucidate the nature of the
color-generation process. As a first approach, the latter was
probed in two ways. The crystal structures of the two
different colored species were obtained and simple salt-
induced color-switching in solution was investigated.
Ligand 1 (see Abstract) was synthesized by the reaction
of the diazonium salt of p-nitroaniline with the N-phenylated
macrocycle 4 (Schemes 1 and S1 (Supporting Information)).
Figure 1. (a) UV/vis spectra of 1 (0.30 mM) in the presence of
metal nitrates (5.0 equiv) in acetonitrile and (b) UV/vis titrations
of 1 (0.30 mM) with Hg(NO3)2 (0-5.0 equiv) in acetonitrile; (inset)
Job’s plot.
a change from red to pale-yellow (Figures 1a and S1
(Supporting Information)), whereas no significant color
change was observed upon addition of other selected metal
ions. The titration of 1 with Hg(NO3)2 resulted in the 480
nm absorption gradually decreasing whereas the 368 nm
absorption gradually increased to give an isosbestic point at
407 nm (Figure 1b). In addition, a 1:1 (1 to Hg2+)
stoichiometry for complexation was demonstrated by means
of a Job’s plot. From the titration data the log K values for
the (1:1) complexes were calculated to be 6.02, 5.12, and
5.08 for Hg2+, Cu2+, and Fe3+, respectively (Figures S2 and
S3, Supporting Information). Thus 1 forms its strongest
complex with Hg2+ among the metal ions investigated.
More interestingly, we found that the color change for 1
with Hg2+ may change with the anion. For instance, the
Scheme 1. Synthesis of 1
-
-
addition of NO3 or ClO4 resulted in hypochromic shifts
to 367 and 350 nm (pale-yellow), respectively (Figures 2
and S4 (Supporting Information)). However, no color
changes were observed upon addition of Cl-, Br-, I-,
CH3COO-, SCN-, or SO42-. This is attributed to the
First, the binding properties of 1 were examined with respect
to color changes (Figure 1a). Species 1 exhibits an intense
absorption at 480 nm (red, ꢀ 29 700). Interestingly, the large
cation-induced hypochromic shift for Hg2+ (∆λ ) 133 nm)
and Cu2+ or Fe3+ (∆λ ) 74 nm) (all as nitrates) resulted in
(6) Kim, J. S.; Shon, O. J.; Lee, J. K.; Lee, S. H.; Kim, J. Y.; Park,
K.-M.; Lee, S. S. J. Org. Chem. 2002, 67, 1372.
(7) Jin, Y.; Yoon, I.; Seo, J.; Lee, J.-E.; Moon, S.-T.; Kim, J.; Han, S.
W.; Park, K.-M.; Lindoy, L. F.; Lee, S. S. Dalton Trans. 2005, 788.
(8) (a) Hill, S. E.; Feller, D. J. Phys. Chem. A 2000, 104, 652. (b) Wolf,
R. E., Jr.; Hartman, J. R.; Storey, J. M. E.; Foxman B. M.; Cooper, S. R.
J. Am. Chem. Soc. 1987, 109, 4328. (c) Yoon, I.; Seo, J.; Lee, J.-E.; Song,
M. R.; Lee, S. Y.; Choi, K. S.; Jung, O.-S.; Park, K.-M.; Lee, S. S. Dalton
Trans. 2005, 2352. (d) Park, K.-M.; Yoon, I.; Seo, J.; Lee, J.-E.; Kim, J.;
Choi, K. S.; Jung, O.-S.; Lee, S. S. Cryst. Growth Des. 2005, 5, 1707. (e)
Seo, J.; Yoon, I.; Lee, J.-E.; Song, M. R.; Lee, S. Y.; Park, S. H.; Kim, T.
H.; Park, K.-M.; Kim, B. G.; Lee, S. S. Inorg. Chem. Commun. 2005, 8,
916.
Figure 2. Anion-dependent shift in the spectrum of 1 for
mercury(II) salts in acetonitrile.
1642
Org. Lett., Vol. 8, No. 8, 2006

significant coordinating ability of these latter anions to the
Hg2+ ion. The results indicate that 1 cannot only be useful
as an efficient chromogenic reagent for cation sensing, but
-
-
it also shows promise as a reagent for ClO4 and NO3
sensing in the presence of a range of other anions.
The behavior observed undoubtedly reflects the structures
of the respective complexes generated. Thus, we decided to
undertake the preparation and crystal structure of each
colored species. We have successfully isolated pale-yellow
(2) and red (3) complexes as single crystals suitable for X-ray
analysis from solutions of 1 with Hg(ClO4)2 and HgI2,
respectively.
The crystal structure of pale-yellow 2 revealed a 1:1
complex of formula [Hg(1)2(ClO4)]ClO4 (Figure 3). Hg2+ is
Figure 4. Exo-coordinated dimer structure of 3, [Hg2(1)2I4] (red
crystals).
This result can be explained in terms of the strong coordina-
tion (“Pull”, see Scheme 2) of the iodides acting to prevent
Hg-N bond formation, resulting in no color change. Once
again, the “Push-n-Pull Process” serves to illustrate how the
coordinating ability of anions can control the color change
through formation of endo- or exo-metal complexes.
On the basis of the crystal structures of 2 and 3, we
anticipated that the anion-induced color change might also
be switchable by the addition of simple salts. In fact, the
pale-yellow solution of 1 in the presence of Hg(ClO4)2 returns
to its original red color upon addition of KI or NaCl (Scheme
3). A reversible color change from red to pale-yellow occurs
Figure 3. Endo-coordinated structure of 2, [Hg(1)(ClO4)]ClO4
(pale-yellow crystals).
in a square planar environment with its coordination sites
occupied by two S and one N atom from 1 arranged in an
endo-fashion. One ClO4- is weakly bound to Hg2+ at a fourth
binding site while the other is not coordinated. The presence
of direct Hg-N [2.672(11) Å] bond formation appears to
be reflected by the color change to pale-yellow. That is, it
Scheme 3. Color-Switching of 1 by Addition of Salts in
Acetonitrile
-
suggests that the presence of the less coordinating ClO4
allows (“Push”, see Scheme 2) the Hg2+ to engage the N
Scheme 2. Push-n-Pull Process of Anion-Induced Color
Change
on addition of AgClO4 (a precipitate of AgI is formed). Such
phenomena correspond to “ON-OFF” switching of the
chromogenic system driven by the Push-n-Pull process
illustrated and involve simple addition of the chosen cation
and anion pair.
In this study, conclusive evidence for cation-selective and
anion-controlled color changes for the N-azo-coupled host
system 1 are presented. The investigation corresponds to the
first systematic study of the relationship between structure
and color change for chromogenic host molecules.
lone pair and thereby results in direct Hg-N bonding in the
endo-mode, resulting in the observed color change. This also
agrees with the results from the UV/vis experiments.
X-ray analysis of 3 confirms that this red product has a
dimeric structure with a formula of [Hg2(1)2I4)] (Figure 4).
The structure contains a rhomboidal Hg-I2-Hg core bridg-
ing two macrocycles through Hg-S bonds. The Hg2+ is four-
coordinated with one S and three I- in an exo-fashion. It
unequivocally shows that the N donor of 1 is not bound to
Hg2+, and hence the Hg2+ is located outside of the cavity.
Acknowledgment. This work was supported by a Korea
Research Foundation Grant (KRF-2004-015-C00250).
Supporting Information Available: Syntheses of 1, 2
and 3; UV/vis titrations, and X-ray crystallographic files
(CIF). This material is available free of charge via the Internet
at http://pubs.acs.org.
OL0602405
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