A novel colorimetric and fluorescent chemosensor for anions involving PET and ICT pathways

Article abstract of DOI:10.1021/ol047463k

(Chemical Equation Presented) A novel colorimetric and fluorescent chemosensor ADDTU-1 bearing dual receptor sites, which shows specific optical signaling for AcO^-, H₂PO₄^-, and F^- over other anions an

Full text of DOI:10.1021/ol047463k

ORGANIC
LETTERS
2005
Vol. 7, No. 4
657-660
A Novel Colorimetric and Fluorescent
Chemosensor for Anions Involving PET
and ICT Pathways
Viruthachalam Thiagarajan,† Perumal Ramamurthy,*,†
Dhakshanamurthy Thirumalai,‡ and Vayalakkavoor T. Ramakrishnan‡
National Centre for Ultrafast Processes, UniVersity of Madras, Taramani Campus,
Chennai - 600 113, India, and Department of Inorganic Chemistry and Department of
Organic Chemistry, UniVersity of Madras, Guindy Campus, Chennai - 600 025, India
prm60@hotmail.com
Received December 10, 2004
ABSTRACT
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A novel colorimetric and fluorescent chemosensor ADDTU-1 bearing dual receptor sites, which shows specific optical signaling for AcO ,
-
-
-
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H2PO4 , and F over other anions and dual response toward AcO and F via PET and ICT mechanisms, is described.
Anions play a fundamental role in a wide range of chemical
and biological processes, and numerous efforts have been
devoted to the development of abiotic receptors for anionic
species.1 Anion recognition in biological systems is very
often achieved via hydrogen bonding by highly preorganized
proteins with sterically well-defined complex sites in the
interior of proteins.2 Macrocyclic hosts with preorganized
binding sites can chemically mimic the complex properties
of such receptor proteins for anions.3 The sensors based on
anion-induced changes in fluorescence appear particularly
attractive because they offer the potential for high sensitivity
at low analyte concentration.4 Many fluorescence anion
sensors utilizing photoinduced electron transfer (PET),5
intramolecular charge transfer (ICT),6 excited-state proton
(3) (a) Rudkevich, D. M.; Verboom, W.; Brzozka, Z.; Palys, M. J.;
Stauthamer, W. P. R. V.; van Hummel, G. J.; Franken, S. M.; Harkema,
S.; Engbersen, J. F. J.; Rein-houdt, D. N. J. Am. Chem. Soc. 1994, 116,
4341-4351. (b) Alcazar, V.; Segura, M.; Prados, P.; de Mendoza, J.
Tetrahedron Lett. 1998, 39, 1033-1036. (c) Nikura, K.; Bisson, A. P.;
Anslyn, E. V. J. Chem. Soc., Perkin Trans. 2 1999, 1111-1114. (d) Davis,
A. P.; Perry, J. J.; Williams, R. P. J. Am. Chem. Soc. 1997, 119, 1793-
1794.
(4) de Silva, A. P.; Gunaratne, H. Q. N.; Gunnlaugsson, T.; Huxley, A.
J. M.; McCoy, C. P.; Rademacher, J. T.; Rice, T. E. Chem. ReV. 1997, 97,
1515-1566.
† National Centre for Ultrafast Processes and Department of Inorganic
Chemistry.
(5) (a) Kim, S. K.; Yoon, J. Chem. Commun. 2002, 770-771. (b)
Gunnlaugsson, T.; Davis, A. P.; Hussey, G. M.; Tierney, J.; Glynn, M.
Org. Biomol. Chem. 2004, 2, 1856-1863. (c) Gunnlaugsson, T.; Davis, A.
P.; O’Brien, J. E.; Glynn, M. Org. Lett. 2002, 4, 2449-2452. (d)
Gunnlaugsson, T.; Davis, A. P.; Glynn, M. Chem. Commun. 2001, 2556-
2557. (e) Nishizawa, S.; Kaneda, H.; Uchida, T.; Teramae, N. J. Chem.
Soc., Perkin Trans. 2 1998, 2325-2327. (f) Nishizawa, S.; Kato, Y.;
Teramae, N. J. Am. Chem. Soc. 1999, 121, 9463-9464. (g) Vance, D. H.;
Czarnik, A. W. J. Am. Chem. Soc. 1994, 116, 9397-9398.
‡ Department of Organic Chemistry.
(1) (a) Mart´ınez-Ma´n˜ez, R.; Sanceno´n, F. Chem. ReV. 2003, 103, 4419-
4476. (b) Gale, P. A. Coord. Chem. ReV. 2001, 213, 79-128. (c) Beer, P.
D.; Gale, P. A. Angew. Chem., Int. Ed. 2001, 40, 486-516. (d) Gale, P. A.
Coord. Chem. ReV. 2000, 199, 181-233. (e) Sessler, J. L.; Davis, J. M.
Acc. Chem. Res. 2001, 34, 989-997. (f) Snowden, T. S.; Anslyn, E. V.
Curr. Opin. Chem. Biol. 1999, 3, 740-746. (g) Schmidtchen, F. P.; Berger,
M. Chem. ReV. 1997, 97, 1609-1646.
(6) (a) Kovalchuk, A.; Bricks, J. L.; Reck, G.; Rurack, K.; Schulz, B.;
Szumna, A.; Weibhoff, H. Chem. Commun. 2004, 1946-1947. (b) Wu,
F.-Y.; Jiang, Y.-B. Chem. Phys. Lett. 2002, 355, 438-444.
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Luecke, H.; Quioncho, F. A. Nature 1990, 347, 402-406.
10.1021/ol047463k CCC: $30.25
© 2005 American Chemical Society
Published on Web 01/27/2005

Scheme 1. Structures of ADD Dyes
Scheme 2
transfer,7 excimer/exciplex formation,5e,f competitive bind-
ing,8 and metal-to-ligand charge transfer9 mechanisms have
been developed. We are particularly interested in developing
fluorescent chemosensors where the ion recognition takes
place at the receptor sites with concomitant changes in the
photophysical properties of a acridinedione (ADD) fluoro-
phore by modulation of PET and ICT processes.10 ADD dyes
have been reported as a new class of laser dyes with lasing
efficiency comparable to that of coumarin-102.11 Interest-
ingly, these dyes have been shown to mimic the NADH
analogues to a greater extent because of their tricyclic
structure, which is capable of protecting the enamine
moiety.12 The photophysical and photochemical properties
of ADD dyes in solution and PMMA matrix were extensively
studied.13 In this paper, we report the fluorescent chemosen-
sor ADDTU-1 with two different anion receptor sites
operated by both PET and ICT mechanisms. This molecule
of aminoacridinedione and phenyl isothiocyanate in dichlo-
romethane, on stirring at room temperature, afforded the
thiourea derivatives (ADDTU).
The anion-binding ability of ADDTU-1 and its analogues
(ADDTU-2, ADD-1, and ADD-2) with the anions F-, Cl-,
-
-
-
-
Br-, I-, HSO4 , ClO4 , AcO-, H2PO4 , and BF4 (as their
tetrabutylammounium salts) in acetonitrile were investigated
using UV-vis, steady-state, and time-resolved emission
techniques. The absorption and emission spectra of AD-
DTU-1 in acetonitrile display a maximum at 360 and 420
nm, respectively, which are assigned to the ICT from the
ring nitrogen to ring carbonyl oxygen center within the ADD
moiety.
-
exhibits excellent specificity toward AcO-, H2PO4 , and F-
over other anions and shows dual response toward AcO-
and F-, which is the first of its kind (Scheme 1).
The synthesis of ADDTU derivatives is outlined in Scheme
2. Refluxing a mixture of nitroacridinedione with Zn and
CaCl2 (catalytic amount) in ethanol afforded the ami-
noacridinedione (AADD) derivatives. An equimolar mixture
No significant change was observed in the longer wave-
length absorption band of ADDTU-1 (16 µM) even after the
addition of AcO- (<0.2 mM) and F- (<0.4 mM) in
acetonitrile. This indicates that there is no interaction between
these anions and ADD moiety within this concentration range
in the ground state. On the other hand, the corresponding
fluorescence spectra showed fluorescence quenching in the
presence of AcO- and F- as depicted in Figures 1 and 2,
respectively. The hydrogen-bonding interaction of these
anions with thiourea (TU) brings out a decrease in the
oxidation potential of TU receptor which triggers the PET
from TU to the relatively electron deficient ADD moiety,5b,5c
and this causes the fluorescence to be “Switched off”. To
further confirm the hydrogen bonding interactions between
(7) (a) Zhang, X.; Guo, L.; Wu, F.-Y.; Jiang, Y.-B. Org. Lett. 2003, 5,
2667-2670. (b) Choi, K.; Hamilton, A. D. Angew. Chem., Int. Ed. 2001,
40, 3912-3915.
(8) (a) Niikura, K.; Metzger, A.; Anslyn, E. V. J. Am. Chem. Soc. 1998,
120, 8533-8534. (b) Metzger, A.; Anslyn, E. V. Angew. Chem., Int. Ed.
1998, 37, 649-652. (c) Wiskur, S. L.; Ait-Haddou, H.; Lavigne, J. J.;
Anslyn, E. V. Acc. Chem. Res. 2001, 34, 963-972. (d) Fabbrizzi, L.;
Marcotte, N.; Stomeo, F.; Taglietti, A. Angew. Chem., Int. Ed. 2002, 41,
3811-3814.
(9) Beer, P. D. Acc. Chem. Res. 1998, 31, 71-80.
(10) Thiagarajan, V.; Selvaraju, C.; PadmaMalar, E. J.; Ramamurthy,
P. ChemPhysChem 2004, 5, 1200-1209.
(11) (a) Shanmugasundaram, P.; Murugan, P.; Ramakrishnan, V. T.;
Srividya, N.; Ramamurthy, P. Heteroatom Chem. 1996, 7, 17-22. (b)
Srividya, N.; Ramamurthy, P.; Shanmugasundaram, P.; Ramakrishnan, V.
T. J. Org. Chem. 1996, 61, 5083-5089.
(12) (a) Selvaraju, C.; Ramamurthy, P. Chem. Eur. J. 2004, 10, 2253-
2262. (b) Singh, S.; Chhina, S.; Sharma, V. K.; Sachdev, S. S. J. Chem.
Soc., Chem. Commun. 1982, 453-454.
(13) (a) Srividya, N.; Ramamurthy, P.; Ramakrishnan, V. T. Spectrochim.
Acta A 1998, 54, 245-253. (b) Srividya, N.; Ramamurthy, P.; Ramakrish-
nan, V. T. Phys. Chem. Chem. Phys. 2000, 2, 5120-5126. (c) Thiagarajan,
V.; Selvaraju, C.; Ramamurthy, P. J. Photochem. Photobiol. A; Chem. 2003,
157, 23-31.
1
the AcO- and TU moiety, we also carried out H NMR
titration experiments in CDCl3 + DMSO-d6. In the presence
of 25 equiv of AcO-, the complete disappearance of the
amide -NH proton signal was observed similar to that of
the earlier investigation.14
Addition of F- beyond 0.4 mM to ADDTU-1 shows a
color change which is perceptible to the naked eye, from
(14) (a) Lee, J. Y.; Cho, E. J.; Mukamel, S.; Nam, K. C. J. Org. Chem.
2004, 69, 943-950. (b) Jose, D. A.; Kumar, D. K.; Ganguly, B.; Das, A.
Org. Lett. 2004, 6, 3445-3448.
658
Org. Lett., Vol. 7, No. 4, 2005

Figure 3. Fluorescence enhancement of ADDTU-1 (16 µM) in
Figure 1. Emission spectra of ADDTU-1 (16 µM) in acetonitrile
upon titration with AcO- (0 f 7.8 mM); λexc ) 370 nm.
-
the presence of H2PO4 (0 f 3.0 mM) in acetonitrile; λexc ) 363
nm.
colorless to an intense fluorescent green. In particular,
titration spectra of fluoride anion are found to show a new
peak in both absorption and emission spectra in acetonitrile.
This new longer wavelength absorption (460 nm) and
emission (500 nm) beyond 0.4 mM of F- is due to the
deprotonation of the ADD amino hydrogen with associated
enhancement in the push-pull character of the ICT transition,
which is reflected in the new red shifted absorption and
emission. A similar result with OH- ion confirms the
deprotonation of ADD amino hydrogen providing evidence
for the above observation.
The addition of AcO- beyond 0.2 mM to ADDTU-1 in
acetonitrile shows a red shift of 13 nm (360 to 373 nm) along
with a clear isosbestic point at 370 nm in the absorption
spectrum. The red shift has resulted because of the hydrogen-
bonding interaction of AcO- with the amino hydrogen of
the ADD moiety. However, the fluorescence spectrum
presented in Figure 1 shows the formation of a new emission
band at 490 nm beyond 0.2 mM of AcO-.
-
On the other hand, the addition of H2PO4 to the
ADDTU-1 in acetonitrile leads to a red shift (360-376 nm)
in the absorption spectrum with an isosbestic point at 363
nm as witnessed in the case of AcO- (>0.2 mM). Figure 3
shows the fluorescence spectra of ADDTU-1 as a function
-
of H2PO4 concentration. Increase in the concentration of
H2PO4- caused an enhancement in the fluorescence intensity
along with 20 nm red shift in the emission maximum.
The anion hydrogen bonding with the donor or acceptor
moiety changes the photophysical properties of ICT fluoro-
phore due to its effect on the efficiency of charge transfer.
-
Addition of AcO- (beyond 0.2 mM) and H2PO4 to
ADDTU-1 in acetonitrile brings in hydrogen-bonding inter-
action with the ADD amino hydrogen, thereby increasing
the electron density in the donor group (ADD amino group).
This increase in charge density results in the red shift of the
absorption and emission together with an increase in the
fluorescence intensity. The different optical signal response
-
obtained for AcO- and H2PO4 (490 and 440 nm) is due to
the difference in the charge density and size of the anions.
On the other hand, no such changes were observed upon
-
-
-
the addition of Br-, Cl-, I-, HSO4 , ClO4 , and BF4 to
ADDTU-1 in acetonitrile.
Evidence for 1:1 complex formation is provided by linear
relationship obtained in the Benesi-Hildebrand plot.15 The
binding constant was obtained from the variation in the
fluorescence intensity at the appropriate wavelength [AcO-
-
(419 nm); F- (419 nm); H2PO4 (440 nm)] by plotting the
ratio of 1/(I0 - I) against [anion]-1. The binding constants
-
for ADDTU-1 with AcO-, F-, and H2PO4 (1:1) were
determined to be 17 400, 16 275, and 380 M-1, respectively,
and the same for the 1:2 complex formation between
ADDTU-1 and AcO- (490 nm) was determined to be 13.56
M-1.
Figure 2. Emission spectra of ADDTU-1 (16 µM) in acetonitrile
upon titration with F- (0 f 3.4 mM); λexc ) 363 nm.
(15) (a) Benesi, H. A.; Hildebrand, J. H. J. Am. Chem. Soc. 1949, 71,
2703-2707. (b) Indirapriyadharshini, V. K.; Karunanithi, P.; Ramamurthy,
P. Langmuir 2001, 17, 4056-4060.
Org. Lett., Vol. 7, No. 4, 2005
659

The complexation between anions and ADDTU-1 has also
been investigated by the time-resolved fluorescence tech-
nique. Figure 4 presents the fluorescence decay of ADDTU-1
at different concentrations of AcO-. In the absence of anion,
ADDTU-1 exhibited a single-exponential lifetime (τ ) 1.04
( 0.03 ns) in acetonitrile, whereas in the presence of anions,
the fluorescence decay of ADDTU-1 is biexponential. This
suggests that there are two distinct species, consisting of
anion bound or deprotonated form [AcO- (5.81 ( 0.03 ns),
H2PO4- (4.13 ( 0.03 ns), and F- (6.20( 0.03 ns)] and free
ADDTU-1. The shorter component amplitude decreases
gradually in the presence of anions and the new longer
component amplitude increases. We observe single expo-
nential decay with longer lifetime component only on
complete complex formation between the anion and AD-
DTU-1.
We conclude that the chemosensor ADDTU-1 has two
different anion receptor sites which play a key role in specific
and dual optical output in anion sensing. At low concentra-
tions of AcO- and F-, selective binding with the TU moiety
of ADDTU-1, results in the fluorescence quenching by PET
mechanism. Higher concentrations of F- and AcO- leads to
a new CT state emission which is due to the deprotonation
and hydrogen bonding interaction with the amino hydrogen
Figure 4. Fluorescence decay profiles of ADDTU-1(16 µM) at
different concentrations of AcO- in acetonitrile; λexc ) 375 nm
and λem ) 490 nm: (a) laser profile; (b) ADDTU-1 alone; (c) 0.02;
(d) 0.03; (e) 0.07; (f) 0.17; (g) 0.42; (h) 5.50 mM of AcO-.
We have also carried out a blank experiment with ADD-2
(where both the receptor sites are absent) for all the anions
in acetonitrile. In this case we did not observe any change
in the absorption and emission spectra. This result indicates
that the fluorescence signaling of ADDTU-1 is not caused
directly by the interaction of the ADD group and the added
anions. Similar studies were also carried out using ADDTU-2
(the methyl group in the ADD ring blocks the ICT pathway),
which showed fluorescence quenching in the presence of
-
of ADD moiety, respectively. The sensing action for H2PO4
ion occurs through the hydrogen bonding interaction with
ADD amino hydrogen, which result in the fluorescence
enhancement. This observation is first of its kind where both
PET and ICT processes lead to different optical output within
the same molecule.
-
AcO-, F-, and H2PO4 , but it is insensitive toward other
anions. The fact that TU is the only receptor available for
anions in chemosensor ADDTU-2 indicates that the anion
hydrogen-bonding interaction with TU results in the fluo-
rescence quenching by PET mode of action. In ADD-1,
absence of TU receptor (blocks the PET mechanism) results
in the normal ICT pathway sensing action by the hydrogen-
bonding interactions of the anions with the amino nitrogen
in the 10th position. The specific optical signaling of ADD-1
is due to the formation of new distinct ICT emitting states
Acknowledgment. We acknowledge DST-IRHPA and
CSIR, India, for financial support.
Supporting Information Available: Experimental pro-
cedures and characterization for compounds ADDTU-1 and
ADDTU-2, UV-vis spectra of receptor ADDTU-1with
1
different anions, color change, H NMR spectra, Benesi-
Hildebrand plot, 3D contour plot and binding mode of anions
with ADDTU-1. This material is available free of charge
via the Internet at http://pubs.acs.org.
-
in the presence of AcO- (490 nm), H2PO4 (440 nm), and
a deprotonated state in the presence of F- (510 nm) over
other anions.
OL047463K
660
Org. Lett., Vol. 7, No. 4, 2005