Dansyl-anthracene dyads for ratiometric fluorescence recognition of Cu 2+

Article abstract of DOI:10.1039/c0dt01016b

Dansyl-anthracene dyads 1 and 2 in CH₃CN-H₂O (7:3) selectively recognize Cu²⁺ ions amongst alkali, alkaline earth and other heavy metal ions using both absorbance and fluorescence spectroscopy. In absorbance, the addition

Full text of DOI:10.1039/c0dt01016b

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Dansyl-anthracene dyads for ratiometric fluorescence recognition of Cu2+†
Kuljit Kaur and Subodh Kumar*
Received 15th August 2010, Accepted 13th December 2010
DOI: 10.1039/c0dt01016b
Dansyl-anthracene dyads 1 and 2 in CH3CN–H2O (7 : 3) selectively recognize Cu2+ ions amongst alkali,
alkaline earth and other heavy metal ions using both absorbance and fluorescence spectroscopy. In
absorbance, the addition of Cu2+ to the solution of dyads 1 or 2 results in appearance of broad
absorption band from 200 nm to 725 nm for dyad 1 and from 200 nm to 520 nm for dyad 2. This is
associated with color change from colorless to blue (for 1) and fluorescent green (for 2). This
bathochromic shift of the spectrum could be assigned to internal charge transfer from sulfonamide
nitrogen to anthracene moiety. In fluorescence, under similar conditions dyads 1 and 2 on addition of
Cu2+ selectively quench fluorescence due to dansyl moiety between 520–570 nm (for 1)/555–650 nm (for
2) with simultaneous fluorescence enhancement at 470 nm and 505 nm for dyads 1 and 2, respectively.
Hence these dyads provide opportunity for ratiometric analysis of 1–50 mM Cu2+. The other metal ions
viz. Fe3+, Co2+, Ni2+, Cd2+, Zn2+, Hg2+, Ag+, Pb2+, Li+, Na+, K+, Mg2+, Ca2+, Ba2+ do not interfere in the
estimation of Cu2+ except Cr3+ in case of dyad 1. The coordination of dimethylamino group of
dansyl unit with Cu2+ causes quenching of fluorescence due to dansyl moiety between 520–600 nm and
also restricts the photoinduced electron transfer from dimethylamino to anthracene moiety to release
fluorescence between 450–510 nm. This simultaneous quenching and release of fluorescence respectively
due to dansyl and anthracene moieties emulates into Cu2+ induced ratiometric change.
of the signal allows single reading based evaluation of species
Introduction
concentration. In particular, development of ratiometric probes
The development of chemosensors for heavy metal ions1 is a
demanding area of research due to their biological and environ-
mental relevance. Fluorescent sensors2 for cations are especially
attractive due to their high sensitivity and simple detection
methods.
for Cu2+ ions7 is a challenge due to its inherent paramagnetic
nature and hence complexation generally results in quenching of
fluorescence intensity of the probe.
In case of dual fluorophore-based chemosensors, the commu-
nication between two fluorophores present in a single molecular
probe can be decreased or increased by the presence of an analyte.
This is evident by the simultaneous decrease and increase in inten-
sity of the two fluorophore moieties in the presence of analyte. This
situation not only increases the sensitivity of the molecular system
towards an analyte but also provides opportunities for ratiometric
analysis of the analyte. Such communication between two fluo-
rophores could be miniaturized through different mechanisms, viz.
Fluorescence Resonance Energy Transfer (FRET) between two
fluorophores, Photoinduced Electron Transfer (PET) mechanism
or through Internal Charge Transfer (ICT) mechanism. The FRET
has been quite commonly used for devising dyads for Cu2+, Zn2+,
Hg2+, Pb2+ and Cr3+.8
In design of such fluorescence-based probes, the selection of
fluorophore plays a significant role in selectivity and sensitivity
of the molecular sensor. Amongst commonly used fluorescent
moieties like naphthalene7d,9 anthracene, pyrene,7f,7i quinoline,
benzimidazole, dansyl, naphthalimide,7e,7k etc., the dansyl group
has been quite generously used because of its characteristic
spectroscopic properties like absorbance in near UV-region, fluo-
rescence band in visible region with relatively large Stokes shift,
Because copper is an essential trace element in biological
systems at low concentration but acts as a pollutant when its
concentration is high, as it can cause oxidative stress and disorders
associated with neurodegenerative diseases such as Alzheimer’s
disease,3 there is particular attention on the design of new
fluorescent probes for the detection of copper ion.4 However,
many of the reported Cu2+ fluorescent chemosensors undergo
fluorescence quenching5 upon the addition of Cu2+, although
there are some probes that show fluorescence enhancement.6
Compared to fluorescence quenching and enhancement, a ratio-
metric fluorescent response due to ON-OFF-ON process at two
different acquisition wavelengths provides advantage over ON-
OFF and OFF-ON based chemosensors and is considered to be
more efficient, not only because of its higher sensitivity but also
because of its better resistance to background fluorescence and
variation of fluorescent probe concentration. Further rationing
Department of Chemistry, Guru Nanak Dev University, Amritsar, India.
E-mail: subodh_gndu@yahoo.co.in
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c0dt01016b
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sensitivity of emission spectrum to chemical environment and is
also the smallest available fluorophore. Dansyl has been commonly
used as a fluorescent tag with biomolecules like proteins, lipids,
peptides, DNA, etc. for understanding molecular interactions.
In recent years, the dansyl-based synthetic probes10 have gained
attention for designing molecular probes for anions and cations.
Fluorescent chemosensors based on calixarene scaffold utilizing
dansyl as fluorescent tag have found use for detection of various
metal ions like Pb2+, Hg2+, Cu2+ etc., but small molecular probes
are well suited for quick detection of various metal ions and for
in vivo studies in biological systems.
Conspicuously, dansyl amide of alkyl amine8b or p-
toluenesulfonamide of fluorescent pyrenemethylamine,7i even in
the absence of any other coordination site, have been found
to form 1 : 2 complexes selectively with Cu2+. In the case of
p-toluenesulfonamide of pyrenemethylamine, the selective static
fluorescence due to excimer formation between pyrenyl groups
of two chemosensor molecules enables ratiometric estimation of
Cu2+.
In the present work, we have synthesized two new dyads 1
and 2 based on dansyl and anthracene fluorophores and three
model compounds 3–5 for comparison and have investigated their
photophysical behavior towards various monovalent and divalent
metal ions. The dyads 1 and 2 bind selectively with Cu2+ ions as
compared to other metal ions and signal the binding event through
simultaneous increase in fluorescence between 450–500 nm and
decrease in fluorescence between 515–600 nm. This simultaneous
increase and decrease at two acquisition wavelengths could be
used for ratiometric detection of Cu2+ and indicates their potential
use as sensitive fluorescence ratiometric probes for the selective
recognition of Cu2+ ions. The poor response of model compounds
3–5, lacking either dansyl or the anthracene unit, towards Cu2+
and other metal ions under the conditions studied here further
highlights the significance of dyad structural architect in probes 1
and 2 for ratiometric analysis of Cu2+.
Scheme 1 Synthesis of dyads 1–5.
Results and discussion
Synthesis of dyads 1–5
The probes 1–5 have been synthesized by stirring the solution of
respective 1-anthracenamine (7)/2-anthracenamine (8)/aniline (9)
and triethylamine in dichloromethane with dansyl chloride (6)/p-
toluenesulfonyl chloride (10) at room temperature (Scheme 1). The
structures of the probes were characterized by 1H - 1H decoupling,
13C NMR, HRMS and elemental analysis.
Fig. 1 Effect of addition of different metal ions on the UV-vis. spectrum
of dyad 1 (25 mM, CH3CN : H2O (7 : 3), HEPES (0.01 M), pH 7.0 0.1)
[Different metal ions are Cr3+, Fe3+, Co2+, Ni2+, Cu2+, Cd2+, Zn2+, Hg2+
Ag+, Pb2+, Li+, Na+, K+, Mg2+, Ca2+, Ba2+].
,
of broad range absorption band is associated with change in
color of the solution from colorless to blue and points to the
deprotonation of sulfonamide NH and delocalization of negative
charge on both sulfonamide and anthracene moieties. Therefore,
probe 1 shows selective complexation towards Cu2+ with unique
absorption behavior. The spectral fitting of the absorption data
obtained by titration of 1 with Cu2+ (Fig. 2) shows the formation
of 1 : 1 stoichiometric 1-Cu2+ complex (log b = 5.1 0.1) with
lowest detection limit of Cu2+ 2.5 mM.
Similarly, dyad 2 (25 mM, CH3CN–H2O (7 : 3), HEPES buffer
pH 7.0 0.1), having dansyl group placed at position 2 of anthra-
cenamine moiety, displayed an absorption spectrum (Fig. 3) with
a structured band having lmax at 338 nm (e = 13 284 l mol-1 cm-1)
UV-Vis absorption studies of dyads 1–5
Dyad 1 (25 mM, CH3CN–H2O (7 : 3), HEPES buffer pH 7.0
0.1) displayed an absorption spectrum with a structured band
having lmax at 365 nm (e = 8800 l mol-1 cm-1), 345 nm (e = 9200
l mol-1 cm-1) and 385 nm (e = 7000 l mol-1 cm-1). On addition
of different metal ions, viz. Li+, Na+, K+, Mg2+, Ca2+, Ba2+, Cr3+,
Fe2+, Co2+, Ni2+, Zn2+, Hg2+, Cd2+, Ag+ and Pb2+, to solution of
1, there is no significant change in its UV-vis spectrum except
in case of addition of Cu2+ ions. On addition of Cu2+ to the
solution of 1, a new broad absorption band with absorption
in the range of 400–725 nm appeared (Fig. 1). The appearance
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Fig. 2 Effect of gradual addition of Cu2+ ions on the UV-vis. spectrum
of dyad 1 (25 mM, CH3CN : H2O (7 : 3), HEPES (0.01 M), pH 7.0 0.1).
The inset shows the increase in absorbance at 612 nm on gradual addition
of Cu2+ ions to the solution of 1. The points refer to experimental values
and line shows the spectral fit.
Fig. 4 Effect of gradual addition of Cu2+ ions on the UV-vis. spectrum of
dyad 2 (25 mM, CH3CN : H2O (7 : 3), HEPES (0.01 M) pH 7.0 0.1). The
inset shows the increase in absorbance at 335 nm and 464 nm on gradual
addition of Cu2+ ions to the solution of 2. The points refer to experimental
values and line shows the spectral fit.
1 and 2 on interaction with Cu2+ has been further confirmed
by analysing pH induced changes in absorbance behaviour of
probes 1 and 2 and their Cu2+ complexes through spectral fitting.
These titration data show that probes 1 and 2, between pH 4–9
remain as neutral molecule but at pH < 4 undergo protonation at
dimethylamino group to form monocation species and at pH > 9,
undergo deprotonation at sulfonamide group to give monoanion
species (Fig. S3, ESI†). However, 1 : 1 1-Cu2+ solution between
pH 6.5–8.5 remains as 1(anion)-Cu2+ complex which at higher pH
is converted to hydroxide complex [1(anion)-Cu2+ (OH-)] and at
lower pH values is converted to 1-Cu2+ complex (Fig. S4 and S5†).
Similar trend is shown by dyad 2. Therefore, dyads 1 and 2 which
exist as neutral molecule at pH 7, on addition of Cu2+ ions undergo
deprotonation to form 1/2(anion)-Cu2+ complex.
Fig. 3 Effect of addition of different metal ions on the UV-vis. spectrum
of dyad 2 (25 mM, CH3CN : H2O (7 : 3), HEPES (0.01 M) pH 7.0 0.1)
[Different metal ions are Cr3+, Fe3+, Co2+, Ni2+, Cu2+, Cd2+, Zn2+, Hg2+
Ag+, Pb2+, Li+, Na+, K+, Mg2+, Ca2+, Ba2+].
,
The dansyl amide of aniline, i.e. probe 3 (25 mM, CH3CN–H2O
(7 : 3), HEPES buffer pH 7.0 + 0.1), on addition of Cu2+ (Fig. S6,
ESI†) and other metal ions did not show any discernible spectral or
color change and highlights the significance of anthracene moiety
in dyads 1 and 2 in the recognition of Cu2+.
and 352 nm (e = 13 328 l mol-1 cm-1). On addition of different metal
ions to the solution of 2, only addition of Cu2+ ions caused the
formation of a red shifted structured absorption band with lmax
at 432 nm, 464 nm and 494 nm associated with change in color
of the solution from colorless to fluorescent green. The spectral
fitting of the absorption data obtained by titration of 2 with Cu2+
(Fig. 4) shows the formation of 1 : 1 stoichiometric complex with
log b = 4.03 0.1 with lowest detection limit of 10 mM. The lower
red shift of absorption band on addition of Cu2+ to dyad 2 than
that observed in case of dyad 1 shows the significance of position
of dansyl amide moiety at anthracene moiety in its sensitivity to
metal ions.
The appearance of similar UV-vis. spectra in case of 1 + Cu2+ and
4 + Cu2+ solutions and that of 2 + Cu2+ and 5 + Cu2+ solutions
in CH3CN: H2O (7 : 3), HEPES 0.01 M, pH 7.0 (Fig. 5) points
The addition of Cu2+ ions to the solution of dyads 1 and 2 in
pure CH3CN showed significantly lower absorption changes (Fig.
S1 and S2, ESI†) as compared to that observed in CH3CN–H2O
(7 : 3) mixture. The spectral fitting of the titration data shows the
formation of relatively weaker complex (log b = 3.72 0.2) of 1
with Cu2+ in pure acetonitrile than that observed in CH3CN–H2O
(log b = 5.1 0.1). This points to the deprotonation of dyads 1
and 2 in presence of Cu2+ and formation of ionic complexes of
these dyads with Cu2+ in aqueous medium. The presence of water
is essential for appearance of blue or green colors on addition
of Cu2+ to dyads 1 and 2. The deprotonation of the probes
Fig. 5 Effect of addition of Cu2+ on the UV-vis. spectra of probes 4 and
5 (25 mM, CH3CN : H2O (7 : 3), HEPES 0.01 M, pH 7.0 0.1).
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that in the ground state these molecules interact with Cu2+ in a
similar manner. The similar association constants for coordination
of Cu2+ with probes 4 (log b = 4.8 0.1) and 5 (log b = 4.0 0.1) with
that of dyads 1 ((log b = 5.1 0.1) and dyad 2 (log b = 4.03 0.1)
clearly point the dansyl or p-toluene moieties have insignificant
effect in absorbance based estimation of Cu2+.
Fluorescence studies of dyads 1–5
Dyad 1 (2 mM, CH3CN, U = 0.033), on excitation at 335 nm, dis-
played emission bands at 440 nm, 470 nm (anthracene moiety) and
516 nm (typical of dansyl moiety) which underwent fluorescence
quenching on addition of Cu2+ (Fig. 6). Therefore on excitation
at 335 nm both anthracene and dansyl moieties are excited and
exhibit respective fluorescence bands. The spectral fitting of the
titration data of dyad 1 (2 mM, CH3CN) with Cu2+ shows the
formation of ML (log b = 9.6 0.2), M2L (log b = 17.9 0.3)
and M3L (log b = 23.4 0.3) species. The careful examination of
the fluorescence quenching on addition of Cu2+ ions to the solution
of 1 shows that emission intensity due to dansyl moiety at 516 nm
is quenched by >90% on addition of 5 mM Cu2+ ions, whereas the
complete quenching of fluorescence due to anthracene moiety is
delayed to the addition of 10 mM Cu2+ ions. Therefore, anthracene
and dansyl moieties in CH3CN solution of dyad 1 respond to Cu2+
in a different manner.
Fig. 7 Effect of different metal ions on the fluorescence spectrum of dyad
1 (3 mM, CH3CN : H2O (7 : 3), HEPES 0.01 M, pH 7.0 0.1. (lex : 335 nm).
Fig. 6 Effect of gradual addition of Cu2+ ions on the fluorescence
spectrum of dyad 1 (2 mM, CH3CN). Inset shows the spectral fitting of the
titration curve (lex 335 nm).
Dyad 1 (1 mM, CH3CN : H2O (7 : 3), HEPES 0.1 mM, pH 7.0
0.1, U = 0.026), on addition of different alkali, alkaline earth and
heavy metal ions, viz. Cr3+, Fe2+, Co2+, Ni2+, Zn2+, Hg2+, Cd2+, Ag+
and Pb2+, displayed no significant change in the emission spectrum
(Fig. 7) except on addition of Cu2+. On gradual addition of Cu2+
ions, the fluorescence spectrum of dyad 1 (Fig. 8a) showed gradual
quenching of emission band at 515 nm with a small hypsochromic
shift which is associated with concomitant increase in fluorescence
intensity at 470 nm. The spectral fitting of the data shows the
formation of ML (log b = 7.0 0.3), M2L (log b = 12.0 0.6)
and M3L (log b = 18.2 0.3) stoichiometric species.
The decrease in log b values in CH3CN–H2O mixture in com-
parison to that observed in pure CH3CN is in general agreement
with the lower complexation due to higher solvation of metal ions
and ligand sites in presence of water. The simultaneous decrease
and increase in emission intensity respectively at 560 nm and
470 nm, arising on addition of Cu2+ to aqueous solution of dyad 1
provides opportunities for elaboration of ratiometric approach for
Fig. 8 (a) Effect of different concentrations of Cu2+ on emission spectrum
of 1 (1 mM, CH3CN: H2O (7 : 3) HEPES buffer, 0.01 M, pH 7. (b)
Fluorescence ratiometric response (I470/I560) of 1 (1 mM) on addition of
Cu2+ ions (lex : 335 nm).
the estimation of Cu2+ using rationing of fluorescence intensities
at I470/I560 for sensing of 0.5–5 mM Cu2+ (Fig. 8b).
The bar graph between ratio of emission intensities at 470 nm
and 560 nm versus different metal ions (Fig. S7, ESI†) shows
the selective recognition of Cu2+. To check the practical applica-
bility of dyad 1 as Cu2+ selective fluorescent probe, competition
experiments were performed. The addition of different metal ions,
viz. Ni2+, Hg2+, Co2+, Cd2+, Ag+, Zn2+ (50 mM), to solution of
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1 + Cu2+ (5 mM) did not affect the ratio of emission intensity
obtained for 1+Cu2+ solution. The decrease in emission ratio of
1+Cu2+ on addition of Cr3+ shows its interference in estimation
of Cu2+ (Fig. S8, ESI†). Hence, 1 is acting as selective ratiometric
probe for Cu2+.
In case of dyad 2 (0.5 mM, CH3CN), the gradual addition of Cu2+
ions caused gradual decrease in emission intensity at 544 nm with
hypsochromic shift of the emission band to 475 nm (Fig. 9). The
spectral fitting analysis of the titration data shows the formation
of M3L species (log b = 18.71 0.1).
Fig. 9 Effect of gradual addition of Cu2+ on the fluorescence spectrum
of dyad 2 (0.5 mM, CH3CN, lex 335 nm). Inset shows the spectral fitting of
the titration curve at 520 and 475 nm.
Dyad 2 (1 mM, CH3CN : H2O (7 : 3) HEPES 0.01 M, pH 7.0)
on excitation at 375 nm, displayed an emission spectrum with lem
at 544 nm. The addition of alkali, alkaline earth and heavy metal
ions, viz. Cr3+, Fe2+, Co2+, Ni2+, Zn2+, Hg2+, Cd2+, Ag+ and Pb2+,
displayed no significant change in the emission spectrum of dyad
2 (Fig. S9, ESI†). The gradual addition of Cu2+ to the solution of
dyad 2, caused decrease in emission intensity between 555–650 nm
with concomitant increase in intensity at 505 nm (Fig. 10a). The
spectral fitting of the data shows the formation of M2L (log b =
12.17 0.4) and M3L (log b = 16.59 0.4). This situation provides
an opportunity of ratiometric sensing of Cu2+ in 1–40 mM range.
(Fig. 10b). In this range, the increase in ratio of intensities shows
linear increase.
Fig. 10 (a) Effect of gradual addition of Cu2+ on emission spectrum
of 2 (1 mM, CH3CN: H2O (7 : 3) HEPES buffer, 0.01 M, pH 7). Inset
shows the spectral fitting of the titration curve at 505 nm and 590 nm.
(b) Fluorescence ratiometric response (I505/I590) of 2 (1 mM) towards Cu2+
ions (lex: 375 nm).
The analysis of species distribution diagram for complexation
of Cu2+ with dyad 2 both in absorbance and fluorescence based
titrations shows that in the ground state only one Cu2+ ion binds
with dyad 2 but in the excited state two more Cu2+ ions bind with
dyad 2 resulting in formation of M2L and M3L species (Fig. 11).
Both these species cause simultaneous decrease and increase in
fluorescence respectively due to dansyl and anthracene moieties
but this change is remarkably higher in case of M3L than observed
in case of M2L.
The bar diagrams (Fig. 12) between ratio of emission intensities
at 505 nm and 590 nm versus different metal ions and effect of
presence of interfering metal ions show the selective recognition
of Cu2+ and practical applicability of dyad 2 as ratiometric probe
in the presence of other metal ions.
The solution of probe 3, in CH3CN : H2O (7 : 3), HEPES
0.01 M, pH 7.0, on excitation at 335 nm gave lem at 525 nm
typical of dansyl group but emission remains unaffected by the
presence of metal ions even in large excess (Fig. S11, ESI†). Probes
4 and 5 in CH3CN : H2O (7 : 3), HEPES 0.01 M, pH 7.0, on
Fig. 11 Species distribution curve from fluorescence titration of dyad 2
with Cu2+
.
excitation at 335 nm gave lem at 425 nm typical of anthracene
moiety. The solution of probe 4 on keeping for more than
3 h undergoes lem shift from 423 nm to 480 nm. Probably 4
undergoes aggregation under these conditions and lem arises due
to excimer formation of anthracene moieties. The fluorescence of
probes 4 and 5 remains unaffected by the addition of metal ions
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Scheme 2 Proposed mechanism for fluorescence enhancement.
Cu2+ became effective due to conversion of monomer emission
in free probe to excimer emission in case of its Cu2+ complex,
but in the present case the variation in communication between
two fluorophores (anthracene and dansyl moieties) enables the
ratiometric evaluation of Cu2+ through Cu2+ mediated restriction
of PET from dansyl moiety to anthracene moiety.
Conclusions
Dyads 1 and 2 in the ground state interact with only one Cu2+
to generate ICT induced color changes. In excited state, the
coordination of dimethylamino group of dansyl unit with Cu2+
causes quenching of fluorescence due to dansyl moiety and also
restricts the photoinduced electron transfer from dimethylamino
to anthracene moiety to release its fluorescence. This simultaneous
quenching and release of fluorescence respectively due to dansyl
and anthracene moieties allows ratiometric estimation of Cu2+ ions
(1–50 mM) in CH3CN–H2O (7 : 3) under physiological condition.
Fig. 12 : Fluorescence ratiometric response (I505/I590) of dyad 2 (1 mM,
CH3CN–H2O (7 : 3) HEPES 0.01 M, pH 7.0 0.1 (lex: 375 nm)) (a) on
addition of different metal ions (100 mM), (b) on addition of Cu2+ (50 mM)
with different metal ions (100 mM).
including Cu2+ (Fig. S12, ESI†). These results unambiguously
point to the role of communication between anthracene and
dansyl fluorophores in dyads 1 and 2 responsible for characteristic
ratiometric fluorescence changes arising on addition of Cu2+.
Therefore, in the ground state dyads 1 and 2 complex with only
one Cu2+ to cause bathochromically shifted UV-Vis spectrum.
This change remains unaffected even when the dansyl moieties
are replaced by p-toluenesulfonamide groups in probes 4 and 5.
However, in the excited state dansyl moiety of dyads 1 and 2
binds with two more Cu2+ ions to form M2L and M3L species. In
excited state, the coordination of dimethylamino group of dan-
syl unit with Cu2+ causes quenching of fluorescence between 520-
600 nm due to dansyl moiety and also restricts the photoinduced
electron transfer from dimethylamino to anthracene moiety to
release its fluorescence between 450–510 nm. This simultaneous
quenching and release of fluorescence respectively due to dansyl
and anthracene moieties emulates into Cu2+ induced ratiometric
change (Scheme 2). The optimisation of structures for dyads
Experimental
General comments
Melting points were determined in open capillaries and are
1
uncorrected. JEOL A1 spectrometer was used for recording H
NMR spectra at 300 MHz and 13C NMR spectra at 75 MHz.
All chemical shifts are reported in ppm relative to the TMS
as an internal reference. The assignments of the NMR signals
1
were carried out under using decoupling experiments and H-
1H COSY. UV-Vis spectroscopy analysis was carried out on
a Shimadzu UV-2450 PC UV-Vis Spectrophotometer by using
slit widths of 1.0 nm and matched quartz cells. Fluorescence
spectra were measured on a Varian Cary Eclipse fluorescence
spectrophotometer. For measurements in CH3CN : H2O (7 : 3)
at pH 7.0 0.1 (10 mM HEPES buffer), the fluorescence titrations
were carried out in measuring flasks as the complete change was
not instantaneous. The prepared solutions were kept for 8–12 h
before recording their fluorescence spectra and showed enhanced
accuracy. All absorption and fluorescence scans were saved as
ACS II files and further processed in ExcelTM to produce all
graphs shown. Spectral data has been evaluated using Specfit 32
˚
1 and 2 at B3LYP/6-31G level shows average distance 6–7 A
between two fluorophores (Fig. S13, ESI†) and is sufficiently
small for communication between two fluorophores. Therefore, in
comparison to earlier reported single fluorophore based pyrenyl-
methylsulfonamide probe where the ratiometric estimation of
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analysis to get the formation constants and the species distribution
diagrams.
126.01, 127.0, 127.22, 127.37, 127.46, 127.82, 128.45, 129.56,
131.35, 131.65, 131.74, 132.11, 136.47, 143.86. HRMS (ESI) found
370.0878 (M+Na); calcd for C21H17NO2S+Na 370.0880.
General procedure for synthesis of dyads 1–5
Probe 5. (75%) as a light yellow solid, mp 175 ◦C (from
CH2Cl2), dH (300 MHz; CDCl3; Me4Si) 2.33 (3 H, s, CH3), 6.75 (1
H, br s, NH exchanges with D2O), 7.18–7.23 (3 H, m, ArH), 7.45
(2 H, quintet, ArH), 7.65 (1 H, s, ArH), 7.70 (2 H,d, J 8.4, ArH),
7.87–7.97 (3 H, m, ArH), 8.28 (1 H, s, ArH), 8.34 (1 H, s, ArH); dC
(75.5 MHz; CDCl3; Me4Si) 21.47, 117.21, 121.29, 125.33, 125.63,
125.81, 126.20, 127.27, 127.84, 128.14, 129.33, 129.69, 129.85,
131.32, 131.43, 132.11, 133.46, 135.98, 143.98. HRMS (ESI) found
370.0878 (M+Na); calcd for C21H17NO2S+Na 370.0880.
To the stirred solution of 1-anthracenamine (7) (293 mg, 1 mmol)
and Et3N (1 mmol) in dry CH2Cl2 (20 ml) at RT, the solution of
dansyl chloride (6) (324 mg, 1.2 mmol) in dry CH2Cl2 (10 ml)
was added during 5 min and stirring of the reaction mixture
was continued for 8 h. The reaction mixture was washed with
water, the solvent was removed under vacuum and the residue was
column chromatographed on silica gel and was recrystallized from
CH2Cl2 to get pure 5-dimethylamino-naphthalene-1-sulfonic acid
anthracen-1-yl-amide (1). Similarly reaction of 2-anthracenamine
(8)/aniline (9) with dansyl chloride (6) gave dyad 2/3. And the
reaction of (7) and (8) with p-toluenesulfonyl chloride (10) gave
(4) and (5), respectively.
Acknowledgements
We thank DST, New Delhi, for Rammana fellowship to SK and
FIST programme and IISc Bangalore for HRMS.
◦
Dyad 1. (65%) as a yellow solid, mp 220 C (from CH2Cl2),
dH (300 MHz; CDCl3; Me4Si) 2.76 (6 H, s, N(CH3)2), 7.09 (1
H, br s, NH exchanges with D2O), 7.23 (1 H, t, J 7.8, ArH),
7.28–7.44 (6 H, m, ArH), 7.67 (1 H, t, J 7.5, Dan-H), 7.79–7.87
(2 H, m, ArH), 7.99 (1 H, s, ArH), 8.02 (1 H, d, J 6.0, ArH),
8.28 (1 H, s, Dan-H), 8.33 (1 H, d, J 8.1, ArH), 8.63 (1 H, d, J
8.1, ArH); dC (75.5 MHz; CDCl3; Me4Si) 45.29, 115.23, 118.70,
120.38, 123.03, 123.28, 124.55, 125.61, 125.83, 126.71, 127.66,
127.75, 128.36, 128.61, 129.98, 130.20, 130.68, 131.48, 131.91,
134.39, 152.18; HRMS (ESI) found 449.1300 (M+Na), calcd for
C26H22N2O2S+Na 449.1302
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Dyad 2. (65%) as a yellow solid, mp 178 ◦C (from CH2Cl2), dH
(300 MHz; CDCl3; Me4Si) 2.85 (6 H, s, N(CH3)2), 6.92 (1H, br s,
NH exchanges with D2O), 7.05 (1 H, dd, J1,2 9.0, J1,3 1.8, AnthH-
3), 7.19 (1 H, d, J 7.2, Dan-H6), 7.36–7.46 (3 H, m, AnthH-
6,7, Dan-H3), 7.52 (1 H, d, J1,3 1.8, AnthH-1), 7.61 (1 H, dd, J
8.4 and 7.5, Dan-H7), 7.78 (1 H, d, J 9.0, AnthH-4), 7.91(1 H,
d, J 9.1, AnthH-5/8), 7.93 (1 H, d, J 9.0, AnthH-5/8), 8.18 (1
H, s, AnthH-9/10), 8.23 (1 H, dd, J1,2 7.5 and J1,3 1.2, DanH-4),
8.27 (1 H, s, AnthH-9/10), 8.40 (1 H, d, J 9.0, DanH-8), 8.45 (1
H, d, J 8.4, DanH-2/4); dC (75.5 MHz; CDCl3; Me4Si) 45.34,
115.23, 117.26, 118.38, 121.20, 123.09, 125.25, 125.55, 125.72,
126.08, 127.79, 128.08, 128.72, 129.22, 129.65, 129.79, 130.41,
130.94, 131.21, 131.27, 131.99, 133.29, 134.03; HRMS (ESI) found
449.1300 (M+Na), calcd for C26H22N2O2S+Na 449.1302.
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◦
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2458 | Dalton Trans., 2011, 40, 2451–2458
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