Fluorescence spectroscopic evidence for hydrogen bonding and deprotonation equilibrium between fluoride and a thiourea derivative

Article abstract of DOI:10.1002/chem.201000837

Interaction of anions with thiourea-linked acridinedione fluorophore was studied by absorption, ¹H NMR, steady-state and time-resolved fluorescence techniques. Addition of AcO^- and H₂PO ₄^- shows a gen

Full text of DOI:10.1002/chem.201000837

FULL PAPER
DOI: 10.1002/chem.201000837
Fluorescence Spectroscopic Evidence for Hydrogen Bonding and
Deprotonation Equilibrium between Fluoride and a Thiourea Derivative
Pichandi Ashokkumar, Vayalakkavoor T. Ramakrishnan, and Perumal Ramamurthy*[a]
Abstract: Interaction of anions with
thiourea-linked acridinedione fluoro-
phore was studied by absorption,
1H NMR, steady-state and time-re-
solved fluorescence techniques. Addi-
473 nm and the deprotonated 1 exhibits
an emission peak at 502 nm. Presence
of these three different emitting species
was probed by 3D emission spectro-
scopic studies. Equilibrium between
the free receptor 1, 1·Fꢀ H-bonded
complex and deprotonated 1 was con-
firmed by time-resolved fluorescence
studies. Time-resolved area normalised
emission spectra (TRANES) of 1 in
the presence of Fꢀ shows two isoemis-
sive points at 456 and 479 nm between
time delays of 0–0.5 ns and 1–20 ns, re-
spectively, due to the existence of three
emitting species in equilibrium. Obser-
vation of such an equilibrium based on
fluorescence spectroscopic studies fur-
ther proves the earlier reported absorp-
ꢀ
tion of AcOꢀ and H2PO4 shows a gen-
uine H-bonded complex with thiourea
receptor; whereas, Fꢀ shows stepwise
H-bonding and deprotonation of thio-
1
1
urea NH as confirmed by H NMR ti-
tion and H NMR spectroscopic studies
tration. Free receptor 1 shows emission
maximum at 418 nm; whereas, H-
bonded complex of 1·Fꢀ shows a new
redshifted emission maximum at
of H-bonding and deprotonation pro-
cesses and also illustrates the dynamics
of anion-receptor interactions.
Keywords: charge transfer · depro-
tonation · fluorescence spectrosco-
py · hydrogen bonds · thioureas
Introduction
If the basicity is high enough, it will induce deprotonation
prior to the hydrogen-bonding interaction [Eq. (2)].
Anion recognition and sensing has recently grown into a
subject of great interest in supramolecular and organic
chemistry.[1] Over the past decade, various examples of hy-
drogen-bond donors such as urea,[2] thiourea,[3] amine,[4]
amide,[5] pyrrole,[6] imidazole,[7] indole[8] moieties have been
shown to be particularly effective anion receptors in organic
solvents. Both hydrogen-bonding and deprotonation pro-
cesses are involved in anion interaction, which depends on
the basicity of the anion and acidity of the proton.[9] If the
basicity of an anion Aꢀ is insufficient to induce deprotona-
tion of the receptor RH, one observes a formation of hydro-
gen bonded complex R-H···Aꢀ [Eq. (1)].
RHþAꢀ Ð RꢀþAH
ð2Þ
In a borderline case, an anion initially forms the hydro-
gen-bonded complex. But with sufficiently excess of added
anions, deprotonation occurs due to formation of hydrogen-
bonded anion dimer A2Hꢀ [Eq. (3)].
RH ꢁ ꢁ ꢁ Aꢀ Ð RꢀþAHAꢀ
ð3Þ
The above stepwise changes are most often observed for thi-
ourea receptor with Fꢀ and also with AcOꢀ.[9a,c,d]
Fluorescence-based anion sensors are most attractive due
to the simplicity and high detection limit of fluorescence.[10]
Thus, the understanding of anion-receptor interactions from
fluorescence spectroscopic studies is vital; but until now
anion-receptor interactions, namely the H-bonding and de-
protonation and its equilibrium, are not clearly investigated
by fluorescence spectroscopic studies. Most of the reported
fluorescence based sensors utilize different kind of signaling
mechanism such as photoinduced electron transfer (PET),[11]
intramolecular charge transfer (ICT),[12] metal-to-ligand
charge transfer,[13] excimer/exciplex formation,[14] and tuning
RHþAꢀ Ð RH ꢁ ꢁ ꢁ Aꢀ
ð1Þ
[a] P. Ashokkumar, Prof. Dr. V. T. Ramakrishnan,
Prof. Dr. P. Ramamurthy
National Centre for Ultrafast Processes, University of Madras
Taramani Campus, Chennai 600 113 (India)
Fax : (+91)44-24546709)
E-mail: prm60@hotmail.com
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201000837.
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of proton transfer.[15] In classical PET-based anion sensors,
both H-bonding and deprotonation do not show any change
in the absorption spectrum and leads to the fluorescence
quenching without any spectroscopic shift. Whereas in ICT-
based sensors, H-bonding interaction shows a red shift in
the absorption maximum and the deprotonation leads to the
formation of a new absorption band at longer wavelength.
H-bonding and deprotonation processes are also observed
1
with H NMR spectroscopic studies; H-bonding interaction
Scheme 1. Synthesis of ADDTU (1).
shows downfield shift of the NH signals and the deprotona-
tion leads to the disappearance of NH signals with the for-
mation of new triplet around 16 ppm corresponding to an
FHFꢀ complex. Although the above equilibrium is observed
from absorption and 1H NMR spectroscopic studies,[9] the
detailed investigation from fluorescence spectroscopic stud-
ies has not yet been reported. Since the fluorescence-based
detection will offer additional advantages such as high sensi-
tivity of detection down to the single molecule, local obser-
vation by fluorescence imaging with subnanometer spatial
resolution and remote sensing by using optical fibers with a
molecular sensor immobilized at the tip,[16] the detailed in-
vestigation from fluorescence spectroscopy will further
expand the fluorescence based anion detection. Herein, we
have carried out steady-state and time-resolved fluorescence
studies to probe the H-bonding and deprotonation equilibri-
um of anions with thiourea linked acridinedione (ADD) de-
rivative 1 (ADDTU). Since both PET and ICT mechanisms
can operate in ADD, it will be good to use it as a signaling
unit in sensor molecules.[17] In the present sensor molecule
1, the thiourea receptor is linked through conjugation with
the ADD chromophore. Thus, any variation in the electron
density of the thiourea receptor will alter the ICT of the
chromophore and results in a shift in both absorption and
emission maxima. Interestingly, three different emission
maxima are observed with the addition of Fꢀ, which corre-
spond to free ADDTU 1, H-bonded complex of 1·Fꢀ and
deprotonated species of 1. In addition to the previous ab-
out electron donor OCH3 moiety at the nineth position
(ff =0.63ꢂ2% and tf =5.2ꢂ0.01 ns) are attributed to the
intramolecular PET process through space from the electron
rich OCH3 group to the relatively electron deficient excited
state of the ADD fluorophore.[18]
ꢀ
AcOꢀ and H2PO4 binding studies: Addition of AcOꢀ to
the acetonitrile solution of 1 shows a 6 nm redshifted ab-
sorption maximum with an isosbestic point at 366 nm as
shown in Figure 1a. The observed red shift in the absorption
maximum indicates the H-bonding interaction of AcOꢀ with
1:1 complexation, which is evident from the observed isos-
bestic point. The corresponding fluorescence spectrum,
when excited at its isosbestic point, shows the formation of
a new redshifted emission peak at 484 nm with fluorescence
enhancement (Figure 1b). The binding constant was estimat-
ed to be 3275mꢀ1 from the linear relationship obtained in
the Benesi–Hildebrand plot[19] (Figure 2).
1
sorption and H NMR spectroscopic studies on the discrimi-
nation of the H-bonding and deprotonation processes, the
present fluorescence studies clearly illustrates the dynamics
of anion-receptor interactions.
Results and Discussion
Synthesis: The thiourea-linked ADD derivative (1) was syn-
thesized by refluxing tetraketone 1a with thiosemicarbazide
in acetic acid as shown in Scheme 1.
Photophysical studies of 1: Compound 1 shows the absorp-
tion and emission maxima at 363 and 418 nm, respectively,
in acetonitrile, which are assigned to the ICT from the ring
nitrogen atom to the ring carbonyl center within the ADD
moiety. Fluorescence quantum yield and lifetime were
found to be 0.03 (ꢂ2%) and 0.35 ns (ꢂ0.02), respectively,
in acetonitirile. Lower fluorescence quantum yield and life-
time of 1 compared with the constituent fluorophore with-
Figure 1. a) Absorption and b) emission spectroscopic changes of
1
(12 mm) upon addition of AcOꢀ in acetonitrile; lex =366 nm.
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Hydrogen Bonding
FULL PAPER
ꢀ
Addition of H2PO4
also
shows a similar behavior with a
5 nm redshifted absorption
maximum and a new redshifted
emission peak at 436 nm with
fluorescence enhancement (Fig-
ꢀ
Figure 2. Benesi–Hildebrand
plot for 1 (12 mm) upon addi-
tion of AcOꢀ in acetonitrile;
lex =366 nm; lem monitored at
484 nm.
ure S3). H2PO4 shows (Fig-
ure S4) a lower binding con-
stant (1678mꢀ1) than AcOꢀ. Ad-
ꢀ
dition of AcOꢀ and H2PO4 re-
sults in the hydrogen-bonding
interaction with the thiourea
NH, thereby increasing the
electron density of the donor group of the ICT chromo-
phore. This increase in the charge density leads to the red-
shift of absorption and the formation of the new redshifted
emission peak together with an increase in the intensity. The
extent of redshift depends on the charge density of anions,
which accounts for the observed redshift for AcOꢀ and
ꢀ
H2PO4 .
Fꢀ-binding studies: In contrast to the results obtained with
AcOꢀ and H2PO4 , addition of Fꢀ shows two stepwise
ꢀ
Figure 3. a) Absorption, b) emission spectroscopic changes of 1 (12 mm)
upon addition of Fꢀ in acetonitrile; lex =315 nm; inset of b) normalised
changes in the absorption spectrum of 1 as shown in Fig-
ure 3a. At lower concentration of Fꢀ (up to 0.1 mm), a
12 nm red shifted absorption maximum with isosbestic
points at 315 and 385 nm is observed; whereas at higher
concentration, a new absorption peak at 459 nm is formed
with isosbestic points at 315 and 401 nm. Similar to AcOꢀ
emission intensity at three different wavelengths versus concentration of
ꢀ
~
&
*
F : l: 502, 472, 418 nm.
ꢀ
and H2PO4 , H-bonded complex of Fꢀ shows the red shift in
the absorption maximum, but the deprotonation of the thio-
urea NH leads to the formation of a new peak, which is con-
firmed by observing similar peak on the addition of HOꢀ
(Figure S5a).
After observing a different response of H-bonded and de-
protonated species from absorption spectroscopic studies,
we carried out fluorescence spectroscopic studies (Fig-
ure 3b) by excitation at its isosbestic point. Addition of Fꢀ
results in the formation of a new peak at 473 nm followed
by a peak at 502 nm. At higher concentration of Fꢀ, the in-
tensity of 502 nm peak increases at the expense of 473 nm
peak. H-bonded complex of 1·Fꢀ shows a peak at 473 nm;
whereas, the deprotonation leads to the formation of anoth-
er new emission peak at 502 nm. To confirm this observa-
tion, we carried out similar experiment with the addition of
HOꢀ, which also shows a new emission peak at 502 nm at
the expense of 418 nm peak (Figure S5b). HOꢀ is a well
known deprotonating agent, which can deprotonate the thio-
urea NH without a hydrogen-bonding complex as shown in
Equation (2). Absence of 473 nm peak with the addition of
HOꢀ confirms that this peak is originated from the 1·Fꢀ H-
bonded complex. To probe the origin of the excitation of
these emitting species, we have carried out excitation spec-
troscopic studies of 1 in the presence of Fꢀ. Figure 4 presents
the excitation spectra of 1 in the presence of 0.30 mm of Fꢀ.
Three different excitation maximum at 364, 387 and 458 nm
are observed when they were monitored at emission maxi-
Figure 4. Excitation spectra of 1 (12 mm) with Fꢀ (0.30 mm) in aceto-
AHCTUNTGERGnNNUN itrile; lem at a) 418 nm, b) 473 nm, c) 502 nm.
mum of 418, 473 and 502 nm, respectively. The 364 nm exci-
tation maximum matches with the absorption maximum of
free ADDTU 1; excitation maximum at 458 nm is similar
with the absorption maximum of deprotonated 1. Whereas,
the 1·Fꢀ H-bonded complex shows redshifted excitation
maximum compared to its absorption maximum. Since the
absorption of both the H-bonded and deprotonated species
are overlapping in that region, a clear absorption maximum
could not be observed. Existence of above three emitting
species and their excitation wavelength are further con-
firmed by 3D emission spectroscopic studies as shown in
Figure 5.
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P. Ramamurthy et al.
remains unchanged. When the decay was monitored at
502 nm, compound 1 shows similar biexponential behaviour
with the lifetime of 0.35 ns (84.7%) and 2.81 ns (15.3%).
Up to 0.22 mm of Fꢀ, the fluorescence decay profile of 1
show a similar behavior as observed at the wavelength of
473 nm; whereas at higher concentrations, the new longer
lifetime is further increased to 8.12 ns (Figure 6b, inset). Ad-
dition of HOꢀ also shows a longer lifetime of 8.12 ns (Fig-
ure S8), which confirms that this lifetime, is corresponding
to the deprotonated 1.
Figure 5. 3D emission spectroscopic contour plot of a) 1 alone (12 mm), b)
1 + Fꢀ (0.10 mm), c) 1 + Fꢀ (0.40 mm) & d) 1 + Fꢀ (0.80 mm) in aceto-
nitrile.
Compound 1 shows a contour at an excitation wavelength
of 365 nm and emission wavelength of 420 nm. Addition of
0.10 mm of Fꢀ shows three contours centered at excitation,
emission wavelength of 365, 420 nm; 386, 473 nm and 450,
501 nm. The presence of above three contours confirms the
existence three different emitting species namely free
ADDTU 1, H-bonded complex of 1·Fꢀ and deprotonated 1,
respectively. Further increase in the concentration of Fꢀ
(0.40 mm), shows the disappearance of contour of free 1
with increase in the intensity of the other two contours. At
higher concentration of Fꢀ (0.80 mm), only one contour of
deprotonated 1 is observed with higher intensity. This clear-
ly shows that at lower concentration of Fꢀ, H-bonded com-
plex is formed from the free receptor 1; and at higher con-
centration, deprotonated species is formed from the H-
bonded complex of 1·Fꢀ. Addition of other anions like Clꢀ,
Brꢀ, Iꢀ, HSO4 , ClO4 did not show any such changes in
both absorption and emission spectra.
ꢀ
ꢀ
Figure 6. Fluorescence decay profiles of 1 (12 mm) with the addition of Fꢀ
in acetonitrile; lex =393 nm; a) lem at 473 nm; i) lamp profile, ii) 0, iii)
0.013, iv) 0.020, v) 0.030, vi) 0.043, vii) 0.097, viii) 0.151, ix) 0.224 and x)
0.820 mm of Fꢀ; b) lem at 502 nm; i) lamp profile, ii) 0, iii) 0.020, iv) 0.030,
v) 0.043, vi) 0.097, vii) 0.151, viii) 0.224, ix) 0.452 and x) 0.820 mm of Fꢀ.
Inset of b): Decay of 1 with 0.820 mm of Fꢀ when monitored at different
emission wavelengths.
Time-resolved fluorescence studies: Time-resolved emission
spectroscopy (TRES) provides information on the excited
state kinetics and heterogeneity of different emissive species
in a system.[20] The H-bonding complexation and deprotona-
tion have been investigated by time resolved fluorescence
studies to understand the excited state behavior of these
species. Figure 6a and b present the fluorescence decay of 1
with different concentrations of Fꢀ monitored at 473 and
502 nm, respectively. When the decay was monitored at
473 nm, compound 1 shows a biexponential behaviour with
lifetime of 0.35 ns (88.5%) and 2.81 ns (11.5%). During the
addition of Fꢀ, both the components disappear gradually,
with the formation of a new longer lifetime component
(6.93 ns) along with an increase in the amplitude. When the
concentration of Fꢀ reaches 0.22 mm, the decay was found
to be single exponential with longer lifetime component
(6.93 ns), and at the higher concentration of Fꢀ the lifetime
To get further insight into the presence of three emission
species, we have constructed TRES and TRANES as report-
ed earlier.[20a] Figure 7 shows the emission spectra of 1 in the
presence of 0.20 mm of Fꢀ at different time delays. Immedi-
ately after the excitation (0 ns delay), TRES shows a maxi-
mum at 473 nm, which correspond to 1·Fꢀ H-bonded com-
plex. In addition to this, higher intensity is also seen in the
region 400–440 nm, which is due to the free receptor 1. The
above observations indicate the presence of free 1 and 1·Fꢀ
H-bonded complex. After 0.75 ns delay, the intensity around
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Hydrogen Bonding
FULL PAPER
another isoemissive point at 479 nm, which is due to the ex-
istence of 1·Fꢀ H-bonded complex and deprotonated 1.
Thus the heterogeneity in the excited state is clearly proved
from TRES and TRANES studies, which is in good agree-
ment with the results obtained in the steady state fluores-
cence studies.
Addition of AcOꢀ also shows the similar kind of lifetime
decay profile as observed in 1·Fꢀ (monitored at 473 nm). On
complete complexation of 1 with AcOꢀ shows a single expo-
nential decay with the lifetime of 5.68 ns (Figure S9).
ꢀ
Whereas in the presence of H2PO4 , such a complete com-
plexation is not observed. Even after the addition of higher
concentrations of H2PO4 , the fluorescence decay was found
Figure 7. Emission spectra of 1 (12 mm) in the presence of 0.20 mm of Fꢀ
at different time delays in acetonitrile; lex =393 nm.
ꢀ
to be triexponential with the lifetime of 0.35 ns (6.0%),
2.81 ns (7.8%) and 4.67 ns (86.2%) (Figure S10). This clear-
ꢀ
400–440 nm decreases and a new peak is observed at 502 nm
(in addition to the peak at 473 nm), which is due to the de-
protonated 1. Whereas after 10 ns delay, intensity at 400–
440 nm is reduced almost to zero; and the intensity of
473 nm peak is also lower than 502 nm peak. The difference
in the lifetime of the above three species, leads to the time
dependent peak maximum in the TRES studies. This clearly
shows the presence of free 1, 1·Fꢀ H-bonded complex and
deprotonated 1. TRANES of 1 in the presence of Fꢀ also
supports the existence of three emission species. Figure 8a
and 8b show the TRANES between the time intervals of 0–
0.5 and 1–20 ns, respectively. Figure 8a shows an isoemissive
point at 456 nm, which is due to the existence of free
ADDTU 1 and 1·Fꢀ H-bonded complex. Figure 8b shows
ly indicates that the H-bonding interaction of H2PO4 with
the thiourea receptor is relatively weak, when compared to
Fꢀ and AcOꢀ. Therefore the free ADDTU 1 exists in the
ꢀ
system in addition to the H-bonded complex of 1.H2PO4 .
1H NMR titration with Fꢀ: Further insights into the two-
step process and nature of receptor–anion interactions were
provided by H NMR titration studies. Figure 9 displays the
1
1
Figure 9. Stack plot of H NMR spectra of 1 (8.0 mm) with a) 0, b) 0.5, c)
1.0, d) 1.5 and e) 2.0 equivalents of Fꢀ in [D6]DMSO.
NMR titration spectra of 1 with Fꢀ at 248C. Addition of one
equivalent of Fꢀ results in the broadening and downfield
shift (Dd=0.52 ppm) of the thiourea NH proton from d
9.21 ppm due to the H-bonding complexation with the thio-
urea receptor. Addition of second equivalent of Fꢀ shows
disappearance of the NH signal with the formation of a
characteristic triplet around 16.1 ppm due to the formation
of FHFꢀ.[21]
Addition of one equivalent of AcOꢀ (Figure 10) also
shows similar downfield shift (Dd=0.48 ppm) of thiourea
NH proton; whereas, the addition of excess amount of
AcOꢀ did not show any further change in the spectrum.
This clearly proves that the addition of Fꢀ causes initial H-
bonding followed by the deprotonation of thiourea NH.
Figure 8. TRANES of 1 (12 mm) in the presence of 0.30 mm of Fꢀ a) be-
tween 0-0.5 ns, b) 1-20 ns time delay in acetonitrile; lex =393 nm.
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P. Ramamurthy et al.
Presence of three different emission species was probed by
3D emission spectra, TRES and TRANES studies. The ob-
served spectroscopic changes and its interpretation were fur-
1
ther confirmed by H NMR titration. The present investiga-
tion from fluorescence studies clearly supports the earlier
1
report of absorption and H NMR studies for the differen-
tiation of H-bonding and deprotonation processes. Further,
it explains the equilibrium of these species hitherto unravel-
led in the fluorescent anion sensor. If the binding is high
enough, fluorescent sensor can detect guest species down to
the femtomolar concentration range. Thus future anion rec-
ognition chemistry should use more fluorescence-based de-
tection compared with other techniques.
1
Figure 10. Stack plot of H NMR spectra of 1 (8.0 mm) with a) 0, b) 1 and
c) 2.0 equivalents of AcOꢀ in [D6]DMSO.
While AcOꢀ results in the pure H-bonding without any de-
protonation due to its lower basicity compared to Fꢀ.
Binding mode of anions: From all of the above studies, it is
ꢀ
clear that addition of AcOꢀ and H2PO4 shows H-bonding
Experimental Section
interaction with thiourea receptor; whereas, addition of Fꢀ
shows stepwise H-bonding and deprotonation as shown in
Scheme 2. Substitution of H instead of thiourea group in the
General procedures and materials: Dimedone was purchased from Alfa
Aesar Pvt. Ltd.; thiosemicarbazide and all anions, as their tetrabutylam-
monium salts, were purchased from Sigma Aldrich Chemicals Pvt. Ltd.,
and were used as received. All the solvents used in the present study
were of HPLC grade and purchased from Qualigens India Ltd. Absorp-
tion spectra were recorded on Agilent 8453 diode array spectrophotome-
ter. Emission, excitation and 3D emission spectra were recorded on
HORIBA JOBIN YVON Fluoromax 4P spectrophotometer. Fluores-
cence quantum yield was determined by exciting the sample at 366 nm
with the use of quinine sulphate as the standard (ff =0.546 in 0.1n
H2SO4). Fluorescence decays were recorded by using an IBH time-corre-
lated single-photon counting technique as reported elsewhere.[17b] NMR
spectra were recorded on Bruker Avance III 500 MHz and JEOL
500 MHz instruments in deuterated solvents as indicated; the residual
solvent peaks were used as internal standards. Chemical shifts are report-
ed in ppm and coupling constants (JX–X’) are reported in Hz. ESI-MS
were performed on an ECA LCQ Thermo system with ion-trap detection
in positive and negative mode. Elemental analyses (C, H and N) were
taken on a Euro EA Elemental analyzer.
Scheme 2. Binding mode of Fꢀ with ADDTU (1).
ring nitrogen shows the deprotonation of ring amino hydro-
gen without any H-bonding complex [Eq. (2)] in the pres-
ence of Fꢀ, which clearly reveals the importance of thiourea
receptor in the formation of stable H-bonding complex at
the lower concentration of Fꢀ. The formation of 1·Fꢀ H-
bonded complex is observed even in highly polar solvent
like DMSO, which also shows similar trend as observed in
acetonitrile. ADDTU 1, H-bonded complex 1·Fꢀ and depro-
tonated 1 will have different charge density on N atom (ICT
donor), which causes red shift in the emission maximum to
different extent.
4-Methoxybenzylidene bisdimedone (1a): To a solution of dimedone (4 g,
28.5 mmol) in aq. methanol (20 mL) was added 4-methoxybenzaldehyde
(1.75 mL, 14.4 mmol) and warmed until the solution became cloudy. Bis-
dimedone 1a started to separate. The reaction mixture was diluted with
water (100 mL) and allowed to stand overnight; the tetraketone 1a was
collected by filtration, dried and recrystallized from methanol to yield
pure 1a (5.36 g, 94%). M.p. 186–1878C.
N-[9-(4-Methoxyphenyl)-3,3,6,6-tetramethyl-3,4,6,7,9,10-hexahydro-1,8-
AHCTUNGERTG(NNUN 2H,5H)acridinedione-10-yl]thiourea (1): A mixture of the tetraketone
1a (1 g, 2.5 mmol) and thiosemicarbazide (0.23 g, 2.5 mmol) was kept
reflux in acetic acid (15 mL) for 14 h. The reaction mixture was cooled
and poured into crushed ice. The solid obtained was purified by column
chromatography over silica gel and eluted with CHCl3: MeOH (96:4, v/v)
to isolate the pure ADDTU 1 (0.83 g, 73%) as a brown powder. M.p.
208–2108C; 1H NMR (500 MHz, [D6]DMSO, 248C): d=9.26 (s, 1H, ex-
changed with D2O; NH), 7.05 (d, J=8.5 Hz, 2H; ArH), 6.71 (d, J=
8.5 Hz, 2H; ArH), 4.74 (s, 1H; CH(9)), 3.91 (s, 2H, exchanged with
Conclusion
D2O; NH2), 3.66 (s, 3H; CH3), 2.29–2.45 (2d, J=17 Hz, 4H; CH
2A
2CH3); 13C NMR (125 MHz, [D6]DMSO, 248C): d=194.9 (CO), 181.1
(CS), 157.5 (C(Ar)), 149.5 (C=C), 140.0 (C(Ar)), 129.0 (CH(Ar)), 113.4
CHTUNGTRENNUNG(2&7)),
A detailed steady-state and time-resolved fluorescence stud-
ies of anion–receptor interactions were carried out to under-
stand the fluorescence response of different species present
ꢀ
in the system. H-bonding complex of AcOꢀ and H2PO4
(CH(Ar)), 112.2 (C=C), 55.3 (CH3), 50.7 (CH2ACTHNUGRTNENUG(2&7)), 40.4 (CH2ACHTUNGTRENNUNG(4&5)),
32.6 (CH(9)), 32.3 (C), 29.6 & 26.9 cmꢀ1 (CH3); IR (KBr): n˜ =3467
(-NH2), 1626 (conj. C=O), 1367 (conj. C=C) cmꢀ1; ESI-MS: m/z: 454.3
[M+H]+; elemental analysis calcd (%) for C25H31N3O3S1: C 66.20, H
8.48, N 6.89; found: C 66.31, H 8.46, N 6.85.
show a new emission peak at the red shifted region depend-
ing on their basicity. Whereas Fꢀ shows two new emission
peaks due to the stepwise H-bonding and deprotonation.
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Received: April 2, 2010
Published online: October 4, 2010
Chem. Eur. J. 2010, 16, 13271 – 13277
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