Remarkable ESIPT induced NIR emission by a selective colorimetric dibenzimidazolo diimine sensor for acetate

Article abstract of DOI:10.1016/j.tetlet.2013.07.078

A new dibenzimidazolo diimine sensor (DDS) has been designed and synthesized for selective detection of acetate ion. Significant naked eye recognized color change of DDS solution from light yellow to pink upon addition of only acetate ion is accompanied with near infra red (NIR) emission exploiting excited state intramolecular proton transfer (ESIPT).

Full text of DOI:10.1016/j.tetlet.2013.07.078

Accepted Manuscript
Remarkable ESIPT induced NIR emission by a selective colorimetric dibenzi‐
midazolo diimine sensor for acetate
Shyamaprosad Goswami, Sibaprasad Maity, Avijit kumar Das, Annada C
Maity, Tarun Kanti Mandal, Siddhartha Samanta
PII:
S0040-4039(13)01227-6
DOI:
http://dx.doi.org/10.1016/j.tetlet.2013.07.078
TETL 43276
Reference:
To appear in:
Tetrahedron Letters
Received Date:
Revised Date:
Accepted Date:
11 May 2013
11 July 2013
12 July 2013
Please cite this article as: Goswami, S., Maity, S., Das, A.k., Maity, A.C., Mandal, T.K., Samanta, S., Remarkable
ESIPT induced NIR emission by a selective colorimetric dibenzimidazolo diimine sensor for acetate, Tetrahedron
Letters (2013), doi: http://dx.doi.org/10.1016/j.tetlet.2013.07.078
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Graphical Abstract
Remarkable ESIPT induced NIR emission
by a selective colorimetric dibenzimidazolo
diimine sensor for acetate
Leave this area blank for abstract info.
*a
a,b
a
a
b
Shyamaprosad Goswami , Sibaprasad Maity , Avijit kumar Das , Annada C Maity ,Tarun Kanti Mandal ,
Siddhartha Samanta
b

1
Tetrahedron Letters
journal homepage: www.elsevier.com
Remarkable ESIPT induced NIR emission by a selective colorimetric
dibenzimidazolo diimine sensor for acetate
*
a
a,b
a
a
Shyamaprosad Goswami , Sibaprasad Maity , Avijit kumar Das , Annada C Maity ,Tarun Kanti
b
b
Mandal , Siddhartha Samanta
a
Department of Chemistry, Bengal Engineering and Science University, Shibpur, Howrah-711103,West Bengal, India,
Fax: +91-3326682916.e-mail address: spgoswamical@yahoo.com
b
Haldia Institute ofTechnology, Hatiberia, Haldia, West Bengal-721657
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
A new dibenzimidazolo diimine sensor (DDS) has been designed and synthesized for selective
detection of acetate ion. Significant naked eye recognized color change of DDS solution from
light yellow to pink upon addition of only acetate ion is accompanied with near infra red (NIR)
emission exploiting excited state intramolecular proton transfer (ESIPT).
Available online
Keywords:
ESIPT
NIR
Naked eye
Acetate
DFT
Fluorescent sensors are indispensable tools for visualizing
ions at the molecular level without the need for special
instrumentation because of their simplicity, high selectivity and
sensitivity in fluorescence assays. With the help of
supramolecular chemistry, recognition and sensing of anionic
analyte has emerged as a major area of endeavor due to their
important role in many biological, industrial and environmental
processes. The design of receptors for anion complexing and
sensing has been a great challenge since anion complexation with
the receptor is quite different from that for metal cations mainly
because of the peculiar characters of anions with varying size,
shape and charge. Such receptor should have hydrogen-bond
donors toward the envisaged anion, giving rise to a complex that
is stable in solution. Besides mere electrostatic interactions,
hydrogen-bonds are directional, a feature which allows the design
of receptors capable of differentiating between anions with
consideration, the applications and importance of excited-state
intramolecular proton transfer (ESIPT) inspired molecules, herein
we describe the design and evaluation of fluorescent probe,
dibenzimidazolo diimine based sensor DDS, which exhibits near-
infrared (NIR) emission with a large Stokes shift arising from
ESIPT as well as exciting colorimetric response to biologically
appealing acetate ion and Time-Dependent Density Functional
Theory (TD-DFT) explorations. The DDS forms intramolecular
hydrogen bond with the nearby hydrogen bonding acceptor and
its acidity is weak enough to avoid direct deprotonation upon
interaction with the basic anions but sufficient to facilitate
ESIPT. The cavity of the DDS is designed so smartly to
differentiate acetate ion from other competing basic anions and
hence establishes its uniqueness.
1
different geometries and hydrogen-bonding requirements.
Among various important anionic analytes, acetate is one of the
most significant anions due to its specific biochemical functions.
In enzymes and antibodies, the functions of carboxylate attribute
to their specific biochemical behavior and make them the critical
2-5
components for numerous metabolic processes. The rate of
AcO- production and oxidation has been frequently used as an
6
indicator of organic decomposition in marine sediments and
7-9
transmetalation of tetrapyrroles. Therefore the search for a
chromophore whose changes in physicochemical properties can
be used to sense acetate both qualitatively and quantitatively in
the presence of several other co-existing anions is highly
desirable. We have recently reported simple naphthalene-based
Figure 1. Proposed possible ESIPT of DDS
10
colorimetric sensor selective for acetate.
Taking into

2
Tetrahedron
In ESIPT system, protons in the excited state depart or join a
naked eye recognized exciting color change from light yellow to
pink, with an isosbestic point at 460 nm indicating the formation
of a new complex between the DDS and the acetate anion. In
addition, the characteristic structured absorption bands at 342 nm
and 409 nm disappear almost completely suggesting that
significant electronic perturbation occurred in the ground state of
molecule at different rate to that in the ground state. The ESIPT
process is easy to recognize in steady-state spectra, the
absorbance is generally similar to that of the parent chromophore
but the fluorescence is significantly different. An advantage of
the large Stokes shift is the almost complete lack of spectral
overlap between absorption and emission, which makes ESIPT
13
DDS .
11
dyes promising for use in fluorescent sensors.
The color change in presence of acetate ion is attributable
DDS was synthesized in one step by the facile Schiff’s base
condensation reaction of 2-hydroxy-5-methylbenzene-1,3-
dicarbaldehyde (2) with 1H-benzoimidazo-l,2-ylamine (3) in
towards the probable hydrogen bond formation between acetate
ion and the -NH proton of two benzimidazole ring moieties of
DDS (Scheme 2) resulting in a decrease in energy responsible for
electronic transition through improved delocalization. About
seven fold absorbance enhancement is observed on addition of 5
equivalent of TBOAc after which it gets saturated.
12
ethanol as yellowish precipitation with good yield (Scheme
1
).The yellow solid product was recrystallized in absolute
ethanol giving the yellow solid compound DDS in 80% yield. Its
molecular structure and purity were established from different
1
13
spectroscopic studies like H NMR, C NMR and MS(ESI) (Fig
0
0
.7
.6
S5- S
7
).
-
-
-
-
F ,Cl ,Br ,I ,
-
2-
BzO ,SO
,
3
i) NaOH/H O
0.5
0.4
0.3
-
-
2
MnO2
NO ,NO ,
2
3
3
-
CHCl
3
reflux, OHC
PO4 ,DHP,DDS
ii)HCHO
rt
CHO
OH
OH OH OH 18 hr
OH
-
AcO
0
0
.2
.1
N
EtOH
+
NH2
reflux,4hr
N
H
0.0
OHC
CHO
4
00
500
600
700
N
OH
N
N
OH
N
Wavelength(nm)
N
NH
H
2
3
DDS
Figure 3: UV-vis spectra of DDS upon addition of different anions
5 quiv.).
(
Scheme 1. Synthetic scheme for DDS
2
Job plot (Fig S , ESI) analysis confirms 1:1 stoichiometry for
complexation between DDS and acetate ion with association
Figure1 shows DDS exhibiting ESIPT. The enol isomer which is
lower in energy than the keto isomer (Table S -S ) in the
4
-1
constant 3×10 M (Fig S
1
, ESI). It is also revealed that minimum
-
6
7
7
.4 µM of AcO can be detected by using 10 µM of DDS solution
electronic ground state, undergoes the proton transfer reaction
upon excitation. The binding and recognition abilities of DDS
towards various anions were studied by UV-vis as well as
fluorescence spectroscopy. The titration was carried out in
in UV-vis titration (Fig S
4
(a), ESI). To evaluate the selectivity of
the DDS for acetate ion, we monitored the titration of various
-
-
-
-
-
anions like F , Br , Cl , I , PhCOO as their tetrabutyl ammonium
3-
-
-
-
2-
salts and PO
4
, H
2
PO
4
, NO
3
, NO
2
and SO
3
as their sodium
-
5
CH
3
CN at 1×10 M concentration of DDS upon the successive
salts but no significant change was observed in the UV-vis
spectrum (Fig 3).
-4
addition of tetrabutylammonium acetate (TBOAc) (C =2 × 10
M) and other competing anions. The UV-vis spectrum of the
DDS is characterized by two bands centered at 342 nm and 409
nm (Fig 2).
To gain more insight into the chemosensing properties of DDS
towards acetate ion, fluorescence titration was also carried out.
The DDS contains an acidic -OH group at the 2-position with
respect to diimine moiety. The location of acidic -OH group and
=N- groups is such that there is an existence of the intramolecular
hydrogen bonding in the ground state. Absorption of radiation
causes excitation of the ground state enol (I) to the excited state
0
.70
.56
.42
.28
.14
.00
409
0.25
342
0.20
0.15
0.10
0.05
0.00
0
*
*
0
enol (I ) (Fig 1). This I form either undergoes ESIPT to form the
566
*
excited keto (II ) or emits radiation and returns to the enol form
(I). The keto form (II ) emits radiation and comes to the keto
form (II) . On excitation the =N- moiety of diimine becomes
strongly basic and -OH becomes strongly acidic as shown by the
changes in the Mulliken charge distribution (Table S4). This
0
10 20 30 40 50 60
*
0
-
[
AcO ]/µΜ
14
4
60
0
*
*
0
favors conversion of enol form (I ) to keto form (II ) through
300
400
500
600
700
ESIPT (Fig 1).
Wavelength (nm)
In this way upon excitation at 409 nm, DDS exhibits
Figure 2: UV-vis absorption spectra of DDS upon titration with
TBOAc in CH CN. Inset: Binding isotherm recorded at 566 nm.
3
fluorescenc spectrum (Fig 4) recorded in CH CN (C=1×10-5 M)
having dual emission peaks, one weak band at 550 nm originated
from excited enol (I*) and another NIR strong emission at 638
nm which can be attributed to the excited state keto (II*)
originating from the excited state enol (I*). Upon the gradual
addition of the TBOAc upto 5 equivalents, 10 fold fluorescence
enhancement at 638 nm with 20-fold increase of fluorescence
3
Upon gradual addition of the acetate ion, the bands at 342 nm
and 409 nm gradually diminish accompanied with a new band
with increasing intensity which appears at 566 nm causing a

3
quantum yield (Ф/ Ф0= 0.164/0.008) was observed but the
emission at 550 nm was hardly affected by acetate ion i.e.
presence of acetate ion facilitates the formation of keto tautomer
which causes such type of emission enhancement. The
association constant of DDS for acetate was calculated on the
To recognize the nature of interaction of acetate ion with DDS,
1
we performed H NMR titration in d
6) that on gradual addition of TBOAc upto 4 equivalents into the
solution of DDS the signal of –OH proton (H ) at 12.81 ppm
disappeared. Slight up field chemical shift of aldimine -CH=N-
(H ) proton and phenyl ring protons, specially noticeable up field
chemical shift of the proton(H ), which is ortho with respect to –
CH group, from 8.03 ppm to 7.83 ppm owing to through bond
6
-DMSO. It was found (Fig
a
15
basis of Benesi-Hildebrand plot (Fig S
3
, ESI) and it was found
b
4
-1
to be 1.7 × 10 M . The detection limit of DDS as a fluorescent
sensor for the acetate was determined to be 6.3 µM using 10 µM
c
3
4
of DDS (Fig S (b), ESI).
electron delocalization, affirms the substantial hydrogen bonding
between -NH proton of benzimidazole ring moiety and acetate
ion. It helps to bring the -OH
nitrogen closure together in such a fashion to facilitate the proton
transfer (H to Ha') through six member cyclic intra-molecular
hydrogen bonding from I (enol form) to II(keto form) which is
supported by the new signal at 6.18 ppm as well as by
computational study.
a
proton and aldimine (-CH=N-)
-
638
4
3
2
1
00 AcO
4
00
a
300
00
00
00
0
200
100
1
Figure 6: Partial H NMR spectrum of DDS in d6-DMSO with
0
0
10
20
30
40
50
addition of different equiv. of TBOAC.
-
[
AcO]/µΜ
5
50
5
00
600
700
800
Wavelength(nm)
Figure 4: Changes in the fluorescence spectrum of DDS upon
successive addition of TBOAc upto 5 equiv. in CH CN. Inset:
Fluorescence intensity change at 638 nm with addition of AcO .
3
-
-
4
-
-
-
-
Addition of other interfering anions (C= 2 × 10 M) like F ,Br ,Cl , I
-
3-
-
,
PhCOO as their tetrabutyl ammonium salts and PO
NO , NO , SO as their sodium salts showed no significant change
3 2 3
4
,
H
2
PO
4
,
-
-
2-
in fluorescence intensity (Fig 5).
4
3
2
1
00
00
00
00
0
-
AcO
-
DDS,F ,
-
-
Cl , Br ,
-
I , ATP,
-3
16-17
KDHP, PO
,
DFT
study reveals that enol(I), lower in energy than the
4
-
-
NO-22 , NO
,
3
-
keto(II) in their the electronic ground state, undergoes the proton
transfer reaction upon excitation. The driving force behind the
proton transfer is the associated intrinsic extra stabilization of the
II* (Table S6-S7, ESI).
S0 , BzO
3
4
50 500 550 600 650 700 750 800
W avelength(nm)
Figure 5: Fluorescence spectra of DDS upon addition of different
guest anions (5 equiv.) in CH CN.
3
This affirms that the DDS is highly selective in its response to
acetate ion in comparison to other anions. The reason for the high
-
selectivity of AcO over other competing anions may be related
-
to the configuration of the AcO matching with the cavity of DDS
as well as the acidity of two -NH protons of the benzimidazole
ring moiety. Acetate anion is a Y-shaped oxyanion and planar
o
triangular and the angle of O-C-O is about 120 , the distance of
the two oxygen atoms may fit to two hydrogen atoms on
recognition sites of the DDS. This increases its binding affinity
than the fluoride ion though the latter has smaller size and higher
basicity.
AcO-
N
O
N
N
N
O
N
N
N
H
N
O
N
N
N
H
N
H
N
H
N
H
NH
NH
N
H
-
NH
[II]
O
O
[I]
Figure 7: HOMO-LUMO of keto-enol tautomers of DDS.
Scheme 2. Probable DDS-Acetate ion binding in solution phase.

4
Tetrahedron
Computed vertical excitation of DDS, which exists exclusively
Acknowledgements:
as the enol-I form is supposed to show a prominent and intense
absorption at 424 nm. Comparatively weak absorption at 362 nm
DST and CSIR (Govt. of India) are gratefully acknowledged
by the authors for financial support and fellowships.
(
Table-S5, ESI) in acetonitrile showed absorptions
experimentally at 409 nm and 342 nm respectively. The
difference between the energies of the optimized geometries at
the first singlet excited state and the ground state predicts
emission at 533 nm (Table S6, ESI) and that for excited state
keto and ground state keto form causes emission at 637 nm
References:
1
.
Jiang, Y. B.; Li, A. F.; Wang, J. H.; Wang, F. Chem. Soc.
Rev. 2010, 39, 3729–3745.
(
Table S7, ESI) which are very close to our experimental
emission at 550 nm and 638 nm.
2. Martinez, R. M.; Sancenon, F.; Coord. Chem. Rev. 2006
50, 3081.
2
3
4
5
6
.
.
.
.
Gunnlaugsson, T.; Glynn, M.; Tocci, M. G.; Kruger, E. P.;
Pfeffer, M. F.; Coord. Chem. Rev. 2006, 250, 3094.
Gale, P. A.; García-Garrido, S. E.; Garric, J.; Chem. Soc.
Rev. 2008, 37, 151-190.
Gupta, K. V.; Goyal, N. R.; Sharma, R. A. Talanta. 2008,
7
6, 859.
Ho, T. Y.; Scranton, M. I.; Taylor, G. T.; Thunell, R. C.;
Varela, R.; Muller- Karger, F. Limnol Oceanogr. 2002, 47,
1
119-28.
7
8
9
1
1
1
.
.
.
Orzeł, L.; Fiedor, L.; Wolak. M.; Kania, A.; van Eldik, R.;
Stochel, G. Chem Eur J. 2008, 14, 9419-30.
Vishnuvardhan , V.; Kala, R.; Prasada Rao T. Anal Chim
Acta. 2008, 623, 53-58.
Shao, J.; Lin, H.; Yu, M.; Cai, Z.; Lin, H.; Talanta 2008, 75,
551-55.
0. Goswami,S.; Das, K. A.; Sen, D; Aich, K; Fun, H-K; Quah,
C. K.; Tetrahedron Lett. 2012, 53, 4819-23.
1. Jiasheng, W.; Weimin, L.; Jiechao, G.; Hongyan, Z.;
Pengfei, W. Chem. Soc Rev. 2011, 40, 3483-95.
2. Gagne, R. R.; Spiro, L. C.; Smith, J. T.; Hamann, A. C.;
Thies, R. W.; Shiemke, K. A.; J. Am. Chem. Soc. 1981, 103,
4073-81.
1
1
3. Qinghui, C.; Doug, A. M.; Pang, Y.; Chem. Mater. 2007,
Figure 8: B3LYP optimized structure of DDS
19, 6421-29.
4. Dlng, K.; Courtney, J. S; Strandjord, J. A.; Flom, S.;
Frledrich, D.; Barbara, F. P.; J. Phys. Chem. 1983, 87,
1184-88.
Molecular planarity which is mostly attained at I* form (Table
S4), is the major factor necessary for ESIPT from O17 (Fig-8) to
N18. As seen in the Table S4, elongation of the O17-H48 bond
and shortening of O17-N18 distance with concomitant
enlargement of O17-H48-N18 angle following photo-excitation
are some structural modifications in accord with translocation of
the proton from -O17H48 functional moiety to the aldimine -N18
atom in the excited-state. A close inspection of the modulation of
electronic charge density distribution over the atoms (particularly
the atoms constituting the ESIPT site) on photo excitation
precisely provides another window towards examining the proton
transfer process. The increase of the negative charge distribution
on -N18 atom (Table S4, ESI) also predicts favorable
translocation of the proton in the excited surface.
1
1
5. Benesi, H.; Hildebrand, H. J. Am. Chem. Soc. 1949, 71,
703-07
6. Treutler, O.; Ahlrichs, R. J. Chem. Phys. 1995, 102, 346-54.
2
17. M.J. Frisch et al. Gaussian, Inc., Wallingford, CT, 2009.
In presence of acetate, the charge of H48 increases and the
N18-H48 bond distance decreases compared to I. So in presence
of acetate the H48 atom approaches nearer to N18 and facilitates
proton transfer and hence more II* form. Thus in presence of
acetate the ESIPT phenomenon is improved.
In conclusion, we have synthesized a new dibenzimidazolo
diimine based sensor for acetate ion and through investigation of
its binding properties we have screened a wide range of
competing anions by the absorption and fluorescence methods.
The absorption and emission wave lengths were computed using
TD-DFT and they are in good agreement with the experimental
results. In view of the high selectivity and sensitivity and quick
Click here to remove instruction text...
synthetic accessibility, DDS may be useful as
colorimetric as well as fluorimetric acetate sensor.
a novel
Supporting Information Available: Experimental, synthetic,
spectroscopic and theoretical computation data.

5
Remarkable ESIPT induced NIR
Emission by a Selective Colorimetric
Dibenzimidazolo Diimine Sensor for
Acetate
*
a
a,b
Shyamaprosad Goswami , Sibaprasad Maity , Avijit
a
a
b
kumar Das , Annada C Maity ,Tarun Kanti Mandal ,
b
Siddhartha Samanta