Carbazole-benzimidazole based dyes for acid responsive ratiometric emissive switches

Article abstract of DOI:10.1039/c6nj00063k

Three carbazole based benzimidazole derivatives exhibiting the effect of intramolecular charge transfer (ICT) caused by the donor-acceptor interaction between their carbazole and benzimidazole units were synthesized. Their photophysical properties were systematically investigated in various solvents with different polarities. Positive solvatofluorochromic effects were observed with the change of solvent from non-polar to polar for all of the three dyes. The synthesized compounds presented proton-induced absorption as well as ratiometric emission changes, indicating that these compounds might be used as proton sensors. The dyes in their solid state are also able to detect acid vapours. The optimized structures of the dyes and their protonated forms were calculated by density functional theory calculations.

Full text of DOI:10.1039/c6nj00063k

View Article Online
View Journal
NJC
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: S. Goswami, K.
Aich, S. Das, C. K. Quah, D. Sarkar, T. K. Mondal and H. K. Fun, New J. Chem., 2016, DOI:
10.1039/C6NJ00063K.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the Ethical guidelines still
apply. In no event shall the Royal Society of Chemistry be held
responsible for any errors or omissions in this Accepted Manuscript
or any consequences arising from the use of any information it
contains.
www.rsc.org/njc

Please do not adjust margins
New Journal of Chemistry
Page 1 of 10
View Article Online
DOI: 10.1039/C6NJ00063K
Journal Name
ARTICLE
Carbazole-benzimidazole based dyes for acid responsive
ratiometric emissive switches
Krishnendu Aich,a,c Sangita Das,a Shyamaprosad Goswami,*a Ching Kheng Quah,b Deblina Sarkar,c
Received 00th January 20xx,
Accepted 00th January 20xx
Tapan Kumar Mondal c and Hoong-Kun Funb
DOI: 10.1039/x0xx00000x
Three carbazole based benzimidazole derivatives exhibit the effect of intramolecular charge transfer
(ICT) caused by the donor-acceptor interaction between its carbazole and benzimidazole units were
synthesized. Their photophysical properties were systematically investigated in various solvents with
different polarities. Positive solvatofluorochromic effects were observed with change the solvent from
non-polar to polar for all of the three dyes. The synthesized compounds, presented proton-induced
absorptions as well as ratiometric emissions changes, indicating that these compounds might be used
as proton sensors. The dyes in their solid state are also able to detect acid vapours. The optimized
structures of the dyes and their protonated forms were calculated by density functional theory
calculations.
www.rsc.org/
fluorescent probes and they have important implications in
biological chemistry.5 Ratiometric proton-induced sensors are
Introduction
Small organic molecules possessing bright fluorescence in both
solid and solution states are gaining importance recently
because of their wide-spread applications in the field of
optoelectronic materials, sensor design, electroluminescent
devices and fluorescence bioimaging.1 In this regard, many
strategies such as the aggregation-induced enhanced emission,2
and intra-molecular charge transfer transition3 have been
developed to achieve intense emitters in the solid state. A
number of organic dyes with strong fluorescence in the solution
state have been reported. But most of them remain non-
emissive in the solid state mainly because of the aggregation.
Thus, the development of new organic dyes with intense
fluorescence in solid state as well as in solution state is very
important. On the other hand fluorogenic sensory devices
which can detect selectively and specifically volatile acid and
base (amine) vapours have gained considerable interest in
recent years due to the practical application in the field of
environmental and medicinal purpose.4 There are many
fluorescent compounds that are sensitive to changes in pH and
can be used as chemical sensors to measure pH. Many
fluorescent derivatives have been extensively employed as pH
in high demand, because ratiometric sensors usually allow
measuring the emission intensity at two different wavelengths
which is beneficial for the evaluation of analytes with better
accuracy. This is because of the independency of ratiometric
probe on the local probe concentration, photo bleaching and
experimental condition such as optical path length etc.
Solvatochromic probes have emerged as powerful tools for
identifying and characterizing microenvironments created by
macromolecules and molecular assemblies. In this regard,
organic materials possessing extended π-conjugation have
received immense attention in recent years owing to their
unique photophysical and charge transport properties. One
important factor involved in displaying such properties is the
presence and nature of electron-donating and electron-
accepting groups. In continuation of our work,6 herein, we have
synthesized and characterized three benzimidazole conjugated
carbazole dyes for fluorescence ratiometric proton sensing. The
first one without spacer (CBIM1), second one with p-styryl
spacer (CBIM2) and the last one with intervening phenyl moiety
between carbazole and benzimidazole system (CBIM3). All of
them showed bright fluorescence in their solution as well as
solid state. Based on the investigation of these compounds in
mixed aqueous system, the trio exhibit acid-dependent
absorption and emission properties and thus might be used as
efficient proton sensors. These dyes also have been examined
to observe the change of solvatofluorochromism with increase
the solvent polarity from n-hexane to DMSO.
a.Department of Chemistry, Indian Institute of Engineering Science and Technology,
Shibpur, Howrah-711 103, INDIA. Fax: +91 33 2668 2916; Tel:+91 33 2668 2961-3;
E-mail: spgoswamical@yahoo.com.
b.X-ray Crystallography Unit, School of Physics, Universiti Sains Malaysia, 11800
USM, Penang, Malaysia
c. Department of Chemistry, Jadavpur University, Kolkata- 700032, India.
† Electronic Supplementary Information (ESI) available: [Computational data, 1
H
NMR, 13C NMR, MS spectroscopy, X-ray data etc. CCDC number of compound 4 is
CCDC 995262 and CCDC number of compound 6 is CCDC 1445812]. See
DOI: 10.1039/x0xx00000x
Results and discussion
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
Please do not adjust margins

Please do not adjust margins
New Journal of Chemistry
Page 2 of 10
ARTICLE
Journal Name
Synthesis of the dyes (CBIM1, CBIM2 and CBIM3)
C14=C15 double bond. In molecule A, the benzene ring is also
View Article Online
roughly coplanar with the carbazoleDOriIn: 1g0.1s0y3s9t/eCm6NJ0[r0.0m6.3sK.
The target compounds were prepared by adapting the synthetic deviation = 0.0428 Å] with a dihedral angle of 5.5 (2)º. The
route outlined in the scheme 1. N-butylation of carbazole, corresponding r.m.s. deviation and dihedral angle for molecule
followed by mono formylation afforded CA1 (9-butyl-9H- B are 0.0408 Å and 3.2 (2)º, respectively.
carbazole-3-carbaldehyde). Finally, the condensation of CA1
with o-phenylenediamine gives the probe CBIM1 [3-(1H-
benzo[d]imidazol-2-yl)-9-butyl-9H-carbazole] as a white solid.
Upon
Wittig
condensation
of
CA1
with
methyltriphenylphosphoniumbromide salt, the vinyl derivative
(9-butyl-3-vinyl-9H-carbazole) was produced in 72% yield. The
Heck cross coupling reaction of the vinyl derivative with p-
bromo benzaldehyde afforded CA2 [(E)-4-{2-(9-butyl-9H-
carbazole-3-yl)vinyl}benzaldehyde] with 80% yield. Finally,
CBIM2 [(E)-3-{4-(1H-benzo[d]imidazol-2-yl)styryl}-9-butyl-9H-
carbazole] was obtained from the condensation reaction of CA2
with o-phenylenediamine as a yellow solid. CBIM3 [3-(4-(1H-
benzo[d]imidazol-2-yl)phenyl)-9-butyl-9H-carbazole]
was
synthesized from the Suzuki coupling of compound 5 with 4-
formylphenylboronic acid followed by the condensation with o-
phenylenediamine. The detailed synthetic procedures of the
probes are given in supporting information. All the new
1
compounds are characterized by H NMR, 13C NMR and HRMS
(Figure S10 – S30, Supporting Information).
Figure 1: (a) The molecular structure of compound 4, showing 30% probability
displacement ellipsoids for non-H atoms and the atom-numbering scheme. Open
bonds show the minor component. (b) The crystal packing of the major
components of compound 4 viewed down the a-axis. H atoms not involved in the
hydrogen bond interactions (dashed lines) have been omitted for clarity.
In the crystal, the two independent molecules are linked into
pairs, viz. A-B, by intermolecular C24A—H24A···O1B hydrogen
bonds (Table S7, ESI). These pairs are stacked along the a axis
(Figure 1b) by way of weak aromatic π···π stacking interactions
between
(N1B/C3B/C4B/C9B/C10B) [centroid-centroid separation
3.654(3) Å] and benzene(C15B-C20B)/benzene(C1B—
the
benzene
(C15B-C20B)/pyrrole
=
C3B/C10B—C12B) [centroid-centroid separation = 3.631(3) Å]
rings of adjacent molecules. The crystal structure is further
stabilized by C—H···π and Van Der Waals interactions.
Compound 6 crystallizes in monoclinic space group P21/c and it
also consists of two molecules (A and B) of each species in the
asymmetric unit, with comparable geometries. The molecular
structure of compound 6 is depicted in Figure 2. In molecule A,
the benzene ring deviates slightly from plane parallel to the
carbazole ring system [r.m.s. deviation = 0.040 Å] with a
dihedral angle of 18.25 (9)º. The corresponding r.m.s. deviation
and dihedral angle for molecule B are 0.040 Å and 2.77 (6)º,
respectively. Atoms C21 and C22 for molecules A and B are
disordered over two sites with a refined occupancy ratio of
0.564(8): 0.436(8) and 0.785(7): 0.215(7), respectively. No
Scheme 1: Synthesis of CBIM1 and CBIM2. (i) n-butyl bromide, 30% aqueous NaOH
solution, DMSO, 700C-800C, 16 h, 95%; (ii) DMF/POCl3, 500C-600C, 12 h, 87%; (iii)
o-phenylenediamine,
p-TSA,
DMF,
reflux,
5
h,
76%;
(iv)
Methyltriphenylphosphonium bromide, tBuOK, THF, 00C to rt, 12 h, 72%; (v) p-
bromo benzaldehyde, Pd(OAc)2, KOAc, PPh3, DMF, 800C-900C, 12 h, 80%; (vi) o-
phenylenediamine, p-TSA, DMF, reflux, 8 h, 58%
X-ray crystallographic study
Compound 4, crystallizes in triclinic space group P-1 and
consists two molecules (A and B) of each species in the
asymmetric unit, with similar geometries as shown in Figure 1a.
The molecules exist in the E configuration with respect to the
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 3 of 10
New Journal of Chemistry
Please do not adjust margins
Journal Name
ARTICLE
hydrogen-bonding interactions were observed for the structure nm) to DMSO (473 nm). The above findings (solvatochromatic
View Article Online
compound 6.
effects) could be attributed to solvenDt OsIt: a10b.i1l0iz3a9t/iCo6nNJo0f00t6h3eK
internal charge-transfer (ICT) in the excited state.7 Noteworthy
the polarized excited state with large dipole moment got
stabilized by a solvent with high polarity keeping the ground
state is relatively untouched. As a result, we get a positive
solvatochromic effect (bathochromic shifts or red shift) in the
emission spectra.8
Figure 2: ORTEP view of compound 6, showing 30% probability displacement
ellipsoids for non-H atoms and the atom-numbering scheme. Open bonds show
the minor component.
Figure 4: Solvent dependent emission photos of the (i) CBIM2 and (ii) CBIM3
solutions under UV light. Concentrations of all dyes were in the order of 1 × 10-5
M.
Solvatofluorochromic study
The result also indicates that the excited state of CBIM2 is
consistent with higher dipole moment than its ground state and
the intramolecular charge transfer (ICT) transition is the
responsible factor for the red shift. CBIM3 also bears the same
electron acceptor and donor group with a different linker site
and shows charge transfer (CT) transition in excited state. The
CT process is expected to strongly increase the dipole moment
in the excited state, explaining the positive fluorescence
solvatochromism in this compound. In here also using the above
mentioned solvents the emission maxima exhibit a regular red
shift with increasing solvent polarity (n-hexane to DMSO),
consequently the fluorescence color changes from fluorescence
‘off’ to intense blue (Figure 4). A red shift of approximately 30
nm was observed (n-hexane: 393 nm and DMSO: 422 nm)
(Figure 3c). CBIM1 also showed same type of
solvatofluorochromism but the effect was not so prominent
because of the absence of extended π-conjugation (Figure 3a).
n-hexane
Toluene
THF
n-hexane
toluene
THF
DCM
CH CN
3
1.0
0.8
0.6
0.4
0.2
0.0
1.0
0.8
0.6
0.4
0.2
0.0
(a)
(b)
DCM
CH CN
3
DMSO
DMSO
MeOH/H
O
2
MeOH/ H
O
2
(1/1)
(1/1)
400 450 500 550 600 650
Wavelength (nm)
350
400
450
500
Wavelength (nm)
n-hexane
toluene
THF
DCM
CH CN
3
1.0
0.8
0.6
0.4
0.2
0.0
(c)
DMSO
Acid induced fluorescence study in solid state
350
400
450
500
550
Wavelength (nm)
In order to investigate the solid state emissive property of the
probes, we recorded emission spectra using their solid
powders. As shown in Figure 5, all the dyes CBIM1, CBIM2 and
CBIM3 showed intense fluorescence in their solid form and
exhibit excellent high contrast emission change after bubbling
with TFA vapour (their protonated forms). CBIM1 displayed
bluish-violet fluorescence with the emission maximum at 417
nm upon excitation at 350 nm. In case of CBIM2 the emission
maximum appeared at 520 nm upon excitation at 390 nm and
an intense green fluorescence was observed under the UV light.
CBIM3 exhibits emission maximum centred at 475 nm upon
excitation at 380 nm.
Presence of basic benzimidazole moieties in the probes, leads
us to investigate their acidochromic as well as vapochromic
behaviour in the solid state. Upon exposure to volatile acid
vapours (TFA), a bathochromic shift in the emission maximum
is observed. However, the probe once exposed with acid
vapours, further gets exposed with volatile base (NH3 or Et3N)
Figure 3: Solvent dependent emission spectra of (a) CBIM1, (b) CBIM2 and (c)
CBIM3. Concentrations of all dyes were in the order of 1 × 10-5 M.
Owing to, having a push-pull motif, our probes are examined for
solvatochromic effect and monitored the absorption and
emission properties in different solvents with altered polarity.
In case of CBIM2 a slight red shift of absorption maxima is
observed in the polar (DMSO) solvent compared to the non-
polar one (n-hexane). In the emission spectra, the
solvatofluorochromic property of CBIM2 is more prominent
than the other two. As shown in Figure 3b, from n-hexane to
DMSO the emission maxima gradually red shifted with
increasing the solvent polarity. Accordingly, the apparent
fluorescence color change is observed from violet to blue to
cyan and finally green (Figure 3b). A remarkable red shift (~ 54
nm) of emission maximum is also noticed from n-hexane (419
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
New Journal of Chemistry
Page 4 of 10
ARTICLE
Journal Name
vapours restores the original emission and indicates a reversible (TFA) CBIM1, CBIM2 and CBIM3 get protonated in their
View Article Online
1
sensing nature of the probes towards acid/base vapours. The respective benzimidazole moieties (SchDemOIe: 102.1)0. 3T9h/Ce6NHJ00N0M63RK
original emission of CBIM1 is stimulated via TFA vapour from titration experiments of the probes and their respective
417 nm to 428 nm with a concomitant fluorescence color protonated forms also suggests the following mechanism takes
change from bluish-violet to cyan. Whereas CBIM2 shows a place (ESI, Figure S31-S33). Consequently colours of the
prominent change in fluorescence color, a green emission fluorescence of the solutions dramatically changed which are
becomes yellow upon exposure to fumed TFA. The third probe observable through naked eyes after illumination under UV
CBIM3 exhibits a red shift from 475 nm to 525 nm; accordingly light. CBIM1 solution turns colourless to purple, CBIM2 changes
a color change was noticed from cyan to bright green after cyan to yellow and CBIM3 turns blue to green under UV light
bubbling with TFA vapour. The Stokes shifts for the dyes were after protonation.
found to be 11 nm, 55 nm (from 520 nm to 575 nm) and 50 nm
for CBIM1, CBIM2 and CBIM3 respectively. The TFA vapours can
cause such type of changes in a closed container within 30
seconds for all the cases.
Figure 5: Solid state emission spectra of (a) CBIM1, (b) CBIM2 and (c) CBIM3 before
and after exposure to TFA vapour. Inset: The corresponding photographs of
CBIM1, CBIM2 and CBIM3 after exposure to TFA vapour, taken under UV-light (ex
Scheme 2: Probable sensing mechanism of the dyes towards H+ (acid) and their
= 365 nm).
corresponding photograph after illumination under UV light (ex = 365 nm).
The UV-vis titration experiment was exemplified by increasing
acid concentration. The solution of the dyes were prepared in
MeOH/H2O (1/1, v/v) solutions. CBIM1 (10 µM) itself exhibits a
prominent peak at 302 nm, upon increasing concentration of
TFA this peak gradually decreases and a new peak at 346 nm
regularly increases with a well defined isosbestic point at 335
nm (Figure 6a). This spectral red-shift might be the result of
protonation at the benzimidazol nitrogen (CBIM1-H+), thereby
enhancing the intramolecular charge transfer (ICT). In case of
CBIM2, the dye itself demonstrates a peak at 343 nm, which was
gradually quenched with increasing amount of TFA (Figure 6b).
Meanwhile, a new peak centred at 395 nm resultant to a red
shift of 52 nm. This large stokes shift is indicative of the strong
ICT with the formation of new chemical species (CBIM2-H+). An
isosbestic point was found at 379 nm corresponding to change
of color from colorless to light yellow. CBIM3 showed a peak at
333 nm in absence of any proton. In here also after addition of
TFA, the peak at 333 nm decreases rapidly, whereas a new peak
generated at 368 nm with an isosbestic point at 359 nm. A red
shift about 35 nm was found after addition of TFA (Figure 6c).
All the dyes act as good reversible solid state sensors in their
respective solid states; it was observed that after exposure in
NH3 vapours, the protonated forms of the dyes revert back to
their original spectrum suggesting that the transformation of
the protonation and deprotonation could be completely
reversible, and essentially non-destructive.
Carbazole systems are planer in nature, the restriction in
rotation ultimately help the probe to emit in solid state. The
compactness of the carbazole systems interrupt the rotational
freedom along with the incorporation of imidazole groups
restricts the intramolecular rotation. This restriction of
intramolecular vibration suppresses radiationless excited state
deactivation which may leads to exhibit a prominent
fluorescence in solvents or/ and in the solid state.
Acid-induced spectroscopic studies of the dyes in solution
state
Interestingly, all the dyes (CBIM1, CBIM2 and CBIM3) are
sensitive towards acid. With increasing proton concentration
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 5 of 10
New Journal of Chemistry
Please do not adjust margins
Journal Name
ARTICLE
of TFA a new peak grew at 570 nm and it increased rapidly with
incremental addition of TFA. Consequently, a ratiometric
View Article Online
DOI: 10.1039/C6NJ00063K
0.8
0.6
0.4
0.2
0.0
(a)
0.4
0.3
0.2
0.1
0.0
(b)
spectrum was obtained with an isoemmision point at 526 nm
and a red-shift of emission maximum about 90 nm was noticed
(Figure 7b). A clear fluorescence color change from cyan to
yellow was observed, after illumination under UV light (Scheme
2). The same type of observation was found for CBIM3 also. This
probe itself showed a peak at 440 nm after excitation at 340 nm.
Proton induced emission titration of CBIM3 exhibited a
beautiful ratiometric spectrum. The peak at 440 nm gradually
decreased whereas a new one which appeared at 532 nm
readily increases and the corresponding stokes shift of 92 nm
was found with an isoemissive point at 509 nm (Figure 7c). In
this case, the strong blue fluorescence turns to green after
protonation.
250
300
350
400
450
250
300
350
400
Wavelength (nm)
Wavelength (nm)
1.2
0.8
0.4
0.0
(c)
Sensing of acid/base vapours using TLC plate
250
300
350
400
450
Wavelength (nm)
Efforts were made to examine the sensing of acid/amine
vapours with the dyes CBIM1, CBIM2 and CBIM3 in the solid
state (using TLC plates). It is a simple but important experiment
because it gives instant qualitative information without
resorting to the instrumental analysis. In order to perform this
experiment, we prepared TLC plates which were immersed into
the solution of the probes (1 × 10-4 M) in methanol solution, and
then dried the plates by evaporating the solvent in open air. The
TLC plates were then exposed to trifluoroacetic acid (TFA)
vapours for 1 minute and their photographs were taken (Figure
8). Again the TLC plates which were exposed with TFA vapors
were further exposed to triethyl amine vapors and the restored
color were observed in each case. This experiment evokes a real
time monitoring and it is devoid of using any instrumental
analysis. Just by naked-eye detection and use of TLC plates we
can easily investigate a qualitative instant detection of acid /
amine vapors.
Figure 6: Acid-induced UV-vis absorption changes of (a) CBIM1, (b) CBIM2 and (c)
CBIM3 in MeOH/H2O (1/1, v/v) solution. Concentrations of all the dyes were 10
μM.
We have also elaborated the emission signalling behaviour of
the probes upon addition of TFA. As shown in Figure 7, upon
excitation at 330 nm, the free probe CBIM1 (10 μM) shows a
strong emission band centred at 384 nm. With increasing
proton concentration the peak at 384 nm decreases, whereas a
new peak gradually appeared at 440 nm which increased
regularly and a good ratiometric spectrum is obtained with a
well defined isoemission point at 410 nm (Figure 7a).
1000
800
600
400
200
0
1000
800
600
400
200
0
(a)
(b)
450 500 550 600 650 700
Wavelength (nm)
350
400
450
500
550
Wavelength (nm)
CBIM1 CBIM2 CBIM3
900
750
600
450
300
150
0
(c)
Figure 8: TLC plates immersed with CBIM1 or CBIM2 or CBIM3 (a) and after
exposure to TFA vapours (b). The photographs were taken under the hand-held
UV light (λex = 365 nm).
Computational study
A theoretical calculation is performed to clarify the sensing
mechanism of the probes in the ground state as well as to look
insight into the optimized geometries of the probes before and
after protonation (Figure 9). The optimized geometries, HOMO
and LUMO of CBIM1, CBIM2 and CBIM3 calculated by
DFT/B3LYP/6-31+G(d) method are shown in Figure S1 - S9 (ESI).
The HOMO-LUMO energy gap in the protonated species
(CBIM1-H+, CBIM2-H+ and CBIM3-H+) gets significantly reduced
350 400 450 500 550 600 650
Wavelength (nm)
Figure 7: Acid-induced fluorescence changes of the dyes (a) CBIM1 (λex = 330 nm),
(b) CBIM2 (λex = 390 nm) and (c) CBIM3 (λex = 340 nm) in MeOH/water (1/1, v/v)
solution. Concentrations of all the dyes were 10 μM.
However, in case of CBIM2 (10 μM), the probe itself exhibited a
peak centered at 480 nm when excited at 390 nm. With addition
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins

Please do not adjust margins
New Journal of Chemistry
Page 6 of 10
ARTICLE
Journal Name
by 0.87 eV, 1.36 eV and 1.62 eV compared to the respective
non-protonated neutral species CBIM1, CBIM2 and CBIM3.
These significant changes in HOMO-LUMO energy gap are also
reflected in the calculated electronic transitions by
TDDFT/B3LYP method. The calculated HOMO to LUMO vertical
electronic transition has been observed at 330, 407 and 358 nm
for CBIM1, CBIM2 and CBIM3 respectively, which has been
shifted to longer wavelengths at 372 nm, 451 nm and 454 nm in
CBIM1-H+, CBIM2-H+ and CBIM3-H+ respectively (Table S4).
View Article Online
DOI: 10.1039/C6NJ00063K
Figure 10: Life time decay profile of CBIM2 () and CBIM2-H+ () in MeOH (ex
= 370 nm).
Conclusions
In summary, we have designed and synthesised three
carbazole-benzimidazole conjugated solid state emitters, which
recognize the volatile acid vapours in the solid state with high
sensitivity. The reversibility of the probes is also established
upon exposure to volatile amine vapors. In addition, the dyes
display significant spectroscopic responses when protonated,
clearly suggesting that they can function as “naked-eye” dual
mode probes for protons. DFT and TDDFT theoretical studies
are conducted to support the experimental findings.
Experimental
General
Unless otherwise mentioned, materials were obtained from
commercial suppliers and were used without further
purification. Thin layer chromatography (TLC) was carried out
1
using Merck 60 F254 plates with a thickness of 0.25 mm. H and
13C NMR spectra were recorded on JEOL 400 MHz and 125 MHz
instruments respectively. For NMR spectra, CDCl3 and d6-DMSO
Figure 9: Energy diagrams of HOMO and LUMO orbitals of CBIM2 and CBIM2-H+ were used as solvents using TMS as an internal standard.
calculated at the DFT level using a B3LYP/6-31+G(d) basis set.
1
1
Chemical shifts are expressed in δ units and H–1H and H–C
coupling constants in Hz. UV-vis spectra were recorded on a
JASCO V-630 spectrometer. Fluorescence spectra were
recorded on Perkin Elmer LS 55 fluorescence spectrometer.
Fluorescence lifetimes were measured using a time-resolved
spectrofluorometer from IBH, UK. The instrument uses a
picoseconds diode laser (NanoLed-07, 370 nm) as the excitation
source and works on the principle of time-correlated single
Fluorescence lifetime decay
In order to examine the excited state behaviour, nano second
time-resolved fluorescence technique has been adapted for
CBIM2 and CBIM2-H+ (Figure 10). The fluorescence decay curves
of compounds were fitted by utilizing the mono-exponential
functions with the acceptable ϰ2 values (Table S5). According to
the equations τ-1 = kr + knr, where kr = Φf /τ, the radiative rate
constant kr and the total non-radiative rate constant knr of
CBIM2 and CBIM2-H+ species were calculated. For CBIM2, τ =
0.776 ns (ϰ2 = 1.005) and CBIM2-H+, τ = 2.036 ns (ϰ2 = 1.123).
photon counting. The goodness of fit was evaluated by
criterion and visual inspection of the residuals of the fitted
function to the data.
2
General method of UV-vis and fluorescence titration
UV-vis method
For UV-vis titrations, stock solution of the receptor (10 μM) was
prepared in [(CH3OH / water), 1/1, v/v] (at 25°C) mixed aqueous
solution. UV-vis spectra were recorded on a JASCO V-630
6 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 7 of 10
New Journal of Chemistry
Please do not adjust margins
Journal Name
ARTICLE
spectrometer. Solutions of various concentrations containing To a solution of methyltriphenylphosphonium bromide (3.5 g,
View Article Online
t
the sensor and increasing concentrations of acid were prepared 9.79 mmol) in dry THF (20 ml) was addDeOdI: 1B0u.1O03K9/(C26.2NJg0,010693.6K
separately. The spectra of these solutions were recorded by mmol) at 0°C under N2—atmosphere. The resulting yellowish-
means of UV-vis method.
Fluorescence method
orange solution was stirred for 30 min at that temperature. THF
(10 ml) solution of compound 2 (2 g, 7.96 mmol) was added to
For fluorescence titrations, stock solution of the sensor (10 μM, the reaction mixture and ice bath was removed to allow to
CH3OH / water, 1/1, v/v, at 25°C) used was the same as that warm to room temperature. After continuous stirring of 6
used for UV-vis titration. Fluorescence spectra were recorded hours, the reaction mixture was quenched with the addition of
on a Perkin Elmer LS 55 fluorescence spectrometer.
saturated ammonium chloride solution. The organic layer was
extracted with dichloromethane (3 × 30 ml) and the combined
organic layer was dried over anhydrous sodium sulphate. After
Determination of fluorescence quantum yield
To determine the quantum yields of the dyes and their evaporation of the solvent under reduced pressure, the crude
protonated forms, we recorded their absorbance in methanol product was subjected to column chromatography (silica gel,
solution. The emission spectra were recorded using the 100-200 mesh) using 5% EtOAc in petroleum ether as eluent to
maximal excitation wavelengths, and the integrated areas of get the title compound as colourless gummy liquid. Yield = 1.42
the fluorescence-corrected spectra were measured. The g (72 %).
quantum yields were then calculated by comparison with
fluorescein (Φs = 0.97 in basic ethanol) as reference using the 1H NMR (400 MHz, CDCl3): δ 0.89 (t, J = 4Hz, 3H), 1.33 (m, 2H),
following equation:
Φx = Φs
(Ix/Is) × (As/Ax) × (nx/ns)2
1.79 (m, 2H), 4.21 (t, J = 4 Hz, 2H), 5.17 (d, J = 8 Hz, 1H), 5.75 (d,
J = 8 Hz, 1H), 6.89 (m, 1H), 7.19 (m, 1H), 7.29 (d, J = 4 Hz, 1H),
×
Where, x & s indicate the unknown and standard solutions 7.34 (d, J = 8 Hz, 1H), 7.42 (t, J = 8 Hz, 1H), 7.53 (d, J = 8 Hz, 1H),
respectively, Φ is the quantum yield, I is the integrated area 8.07 (t, J = 8 Hz, 2H)
under the fluorescence spectra, A is the absorbance and n is the 13C NMR (100 MHz, CDCl3): δ 13.97, 20.58, 30.50, 42.99, 108.78,
refractive index of the solvent.
108.93, 111.01, 118.54, 119.02, 120.50, 123.03, 123.11, 124.06,
125.82, 128.96, 137.70, 140.44, 140.96
HRMS (ESI, positive): Calculated for C18H20N (M + H)+ (m/z):
Preparations of the compounds
Synthetic method for the preparation of the dyes (CBIM1, 250.1596; found: 250.5050.
CBIM2 and CBIM3)
Synthesis
of
(E)-4-{2-(9-butyl-9H-carbazole-3-
Synthesis of 9-butyl-9H-carbazole-3-carbaldehyde (2)
yl)vinyl}benzaldehyde (4)
To a stirred solution of DMF (4 ml, 51.9 mmol), POCl3 (2 ml, A mixture of KOAc (0.59 g, 6.02 mmol) and n-Bu4NBr (1.5 g, 4.65
21.82 mmol) was added dropwise over five minutes at 00C mmol) in DMF (15 ml) was stirred for 15 min in a double necked
under N2-atmosphere. After complete addition, the reaction round-bottomed flask under nitrogen atmosphere at room
mixture was left to stir for 1 hour at room temperature. 9-butyl- temperature. To this reaction mixture, p-bromo benzaldehyde
9H-carbazole (0.5 g, 2.24 mmol) was added to the reaction (0.75 g, 4.05 mmol), PPh3 (0.1 g, 0.038 mmol) and 9-butyl-3-
mixture and then heated at 500-600C for 6 hours, when the TLC vinyl-9H-carbazole (1 g, 4.01 mmol) were added simultaneously
showed the full conversion of starting material to product. The and stirred for another 15 min. Catalytic amount of Pd(OAc)2
whole reaction mixture was poured into ice-water (50 ml) and (0.05 g) was added and heated for 12 hours at 800 900C. The
̶
extracted the organic layer using dichlorometane (3 × 30 ml). mixture was cooled to room temperature and extracted with
The solvent was dried under reduced pressure and the crude dichloromethane (50 ml). The organic layer was washed with
was subjected to column chromatography using 10% EtOAc in water (3 × 10 ml), brine (10 ml), and dried over anhydrous
petroleum ether as eluent to get the pure compound 2 as Na2SO4. Solvent was removed under reduced pressure and the
gummy liquid which solidified on standing. Yield = 0.48 g (87%). crude product was purified through column chromatography
(silica gel, 100-200 mesh) using 10% ethyl acetate in petroleum
1H NMR (400 MHz, CDCl3): δ 0.95 (t, J = 4 Hz, 3H), 1.39 (m, 2H), ether to yield compound 4 as yellow solid. Yield = 1.12 g, (80 %).
1.84 (m, 2H), 4.27 (t, J = 4 Hz, 2 H), 7.31 (t, J = 8 Hz, 1 H), 7.42
(m, 2H), 7.97 (d, J = 4 Hz, 1H), 8.12 (d, J = 8 Hz, 1 H), 8.56 (s, 1 1H NMR (500 MHz, CDCl3): δ 0.96 (t, J = 4Hz, 3H), 1.41 (m, 2H),
H), 10.07 (s, 1H)
1.87 (m, 2H), 4.31 (t, J = 4 Hz, 2H), 7.24 (m, 3H), 7.46 (m, 4H),
13C NMR (100 MHz, CDCl3): δ 13.87, 20.54, 31.07, 43.17, 108.95, 7.68 (d, J = 8 Hz, 3H), 7.87 (d, J = 8 Hz, 2H), 8.13 (d, J = 8 Hz, 1H),
109.45, 120.32, 120.75, 123.01, 123.07, 123.94, 126.74, 127.13, 8.26 (s, 1H), 9.99 (s, 1H)
128.53, 141.21, 144.08, 191.74
HRMS (ESI, positive): Calculated for C17H18NO (M + H)+ (m/z): 109.14, 109.18, 119.47, 120.44, 120.58, 121.13, 122.95, 124.88,
13C NMR (100 MHz, CDCl3): δ 13.99, 20.68, 31.28, 43.14, 108.63,
252.1388; found: 252.4609
126.16, 126.93, 127.85, 129.87, 130.42, 133.50, 134.07, 134.97,
140.89, 141.08, 144.40, 191.91
HRMS: Calculated for C25H23NONa (M + Na)+ (m/z): 376.1677;
found: 376.1680.
Synthesis of 9-butyl-3-vinyl-9H-carbazole (3)
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 7
Please do not adjust margins

Please do not adjust margins
New Journal of Chemistry
Page 8 of 10
ARTICLE
Journal Name
anhydrous Na2SO4. The solvent was removed under reduced
View Article Online
Synthesis
of
3-(1H-benzo[d]imidazol-2-yl)-9-butyl-9H- pressure and the residue was puDriOfiIe:d10.10u3s9in/Cg6NJc0o0lu0m63nK
carbazole (CBIM1)
chromatography using ethyl acetate/petroleum ether (1/9, v/v)
A mixture of 2 (0.1 g, 0.39 mmol) and o-phenylenediamine (0.1 as eluent afforded the compound 6 (0.12 g, 65%) as white solid.
g, 0.92 mmol) was dissolved in DMF (5 ml) solution and a 1H NMR (400 MHz, CDCl3): δ 0.97 (t, J = 7.4 Hz, 3H), 1.44 (m, 2H),
catalytic amount of p-TSA (20 mg) was added to it. The whole 1.88 (m, 2H), 4.32 (t, J = 7.2 Hz, 2H), 7.29 (t, J = 7.2 Hz, 1H), 7.50
reaction mixture was stirred under reflux for 5 hours at N2-atm. (m, 3H), 7.75 (d, J = 6.8 Hz, 1H), 7.87 (d, J = 8.0 Hz, 2H), 7.96 (d,
After cooling the reaction mixture to room temperature, it was J = 8.0 Hz, 2H), 8.17 (d, J = 7.6 Hz, 1H), 8.38 (s, 1H), 10.06 (s, 1H).
poured into ice-water (20 ml) when an off-white precipitate 13C NMR (100 MHz, CDCl3): δ 13.98, 20.67, 31.25, 43.12, 109.15,
formed which was filtered. Then the crude product was purified 109.30, 119.38, 120.58, 122.99, 123.66, 125.24, 126.24, 127.61,
through column chromatography using neutral alumina and 130.44, 130.57, 134.58, 140.75, 141.13, 148.33, 192.03.
20% EtOAc in petroleum ether as eluent to give the product as HRMS: Calculated for C23H22NO (M + H)+ (m/z): 328.1701;
a white compound with 76% (0.98 g) yield.
found:328.2006.
1H NMR (400 MHz, CDCl3): δ 0.86 (t, J = 4 Hz, 3H), 1.18 (m, 2H), Synthesis of 3-(4-(1H-benzo[d]imidazol-2-yl)phenyl)-9-butyl-
1.73 (m, 2H), 4.16 (m, 2H), 7.14 (m, 3H), 7.34 (m, 3H), 7. 53 (m, 9H-carbazole (CBIM3)
3H), 8.02 (dd, 2H), 8.71 (s, 1H)
13C NMR (100 MHz, CDCl3): δ 13.71, 20.44, 31.02, 42.90, 109.01, A mixture of compound 6 (0.1 g, 0.30 mmol) and o-
109.07, 114.54, 119.01, 119.39, 120.36, 120.45, 122.30, 122.81, phenylenediamine (0.05 g, 0.46 mmol) was stirred in DMF (5 ml)
123.12, 124.50, 126.15, 139.06, 140.94, 141.42, 153.43.
HRMS: Calculated for C23H22N3 (M + H)+ (m/z): 340.1814; found: and stirred in refluxing condition for 6 h under N2- atmosphere.
340.1820. After cooling to room temperature, the mixture was poured
Synthesis of (E)-3-{4-(1H-benzo[d]imidazol-2-yl)styryl}-9- into ice-water. Yellow precipitate appeared which was filtered
solution. A catalytic amount of p-TSA (10 mg) was added to it
butyl-9Hcarbazole (CBIM2)
and subjected to column chromatography using neutral
alumina and chloroform as eluent to afford the pure product as
To a stirred solution of 4 (0.1 g, 0.28 mmol) and o- light yellow solid with 52% (0.07 g) yield.
phenylenediamine (0.05 g, 0.46 mmol) in DMF (5 ml), p-TSA (20
mg) was added and the reaction mixture was refluxed under N2- 1H NMR (500 MHz, CDCl3): δ 0.88 (t, J = 5.2 Hz, 3H), 1.32 (m, 2H),
atm for 8 hours. After cooling to room temperature, the mixture 1.78 (t, J = 7 Hz, 2H), 4.21 (t, J = 6.5 Hz, 2H), 7.16 (m, 4H), 7.33
was poured into ice-water. A yellow precipitate separated out (d, J = 8.5 Hz, 2H), 7.40 (t, J = 7.5 Hz, 1H), 7.61 (d, J = 8 Hz, 2H),
which was filtered and subjected to column chromatography 7.71 (d, J = 7.5 Hz, 3H), 8.06 (dd, J1 = 7.5 Hz , J2 = 8 Hz, 3H), 8.23
using neutral alumina and chloroform as eluent to afford the (s, 1H).
pure product as a yellow solid with 58% (0.07 g) yield.
13C NMR (125 MHz, CDCl3): δ 14.00, 20.69, 31.27, 43.10, 109.04,
109.17, 118.97, 119.21, 120.60, 123.07, 123.19, 123.57, 125.08,
1H NMR (400 MHz, d6-DMSO): δ 0.88 (t, J = 4 Hz, 3H), 1.31 (m, 126.06, 127.25, 127.78, 131.00, 140.44, 141.09, 144.19, 151.85.
+
2H), 1.76 (m, 2H), 4.40 (t, J = 4 Hz, 2H), 7.23 (m, 3H), 7.35 (d, J = HRMS: Calculated for C29H26N3 (M + H) (m/z): 416.2127; found:
12 Hz, 1H), 7.46 (t, J = 8 Hz, 1H), 7.54 (t, J = 4 Hz, 2H), 7.65 (d, J 416.2680.
= 8 Hz, 1H), 7.79 (t, J = 4 Hz, 3H), 8.19 (t, J = 8 Hz, 3H), 8.44 (s,
1H), 12.89 (s, 1H)
Computational details
13C NMR (100 MHz, d6-DMSO): δ 13.67, 19.73, 30.61, 42.10, Full geometry optimizations were carried out using the density
9-11
109.47, 109.56, 111.17, 118.71, 118.95, 120.31, 121.60, 122.07, functional theory (DFT) method at the B3LYP
level for the
122.42, 124.78, 125.89, 126.46, 126.75, 127.94, 128.40, 130.71, compounds. All elements were assigned 6-31+G(d) basis set.
135.00, 139.16, 139.95, 140.44, 143.91, 151.12 The vibrational frequency calculations were performed to
HRMS: Calculated for C31H28N3 (M + H)+ (m/z): 442.2283; found: ensure that the optimized geometries represent the local
442.2287.
minima and there were only positive eigen values. Vertical
electronic excitations based on B3LYP optimized geometries
were computed using the time-dependent density functional
theory (TDDFT) formalism12-14 in methanol using conductor like
Synthesis of 4-(9-butyl-9H-carbazole-3-yl)benzaldehyde (6)
A mixture of 9-butyl-3-iodo-9H-carbazole (5) (0.2 g, 0.57 mmol) polarizable continuum model (CPCM) 15-17. All calculations were
and 4-formylphenylboronic acid (0.1 g, 0.66 mmol) were performed with Gaussian09 program package18 with the aid of
dissolved in toluene (10 ml) under nitrogen atmosphere. the GaussView visualization program.
Aqueous solution of K2CO3 (2 ml, 2 M), tricaprylylmethyl
ammoniumchloride (Aliquat® 336) (3 drops) and Pd(PPh3)4 (10
mg) was added to the mixture. The reaction mixture was heated
at 900 C for 12 h. After being cooled to room temperature,
distilled water (5 ml) was added and extracted with
dichloromethane (3×10 ml). Organic layer was dried over
Acknowledgements
Authors thank CSIR and DST, Govt. of India for financial
supports. K.A, S.D and D.S acknowledge CSIR for providing them
fellowships.
8 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 9 of 10
New Journal of Chemistry
Please do not adjust margins
Journal Name
ARTICLE
12 R. Bauernschmitt, R. Ahlrichs, Chem. Phys. Lett., 1996, 256
13 R. E. Stratmann, G. E. Scuseria, M. J. DFOriIs:c1h0,.10J.39C/hCe6mNJ.0P0h06y3s.K,
1998, 109, 8218-8224.
14 M. E. Casida, C. Jamorski, K. C. Casida, D. R. Salahub, J. Chem.
Phys., 1998, 108, 4439.
15 V. Barone, M. Cossi, J. Phys. Chem. A, 1998, 102, 1995 –2001.
16 M. Cossi, V. Barone, J. Chem. Phys., 2001, 115, 4708–4717.
17 M. Cossi, N. Rega, G. Scalmani, V. Barone, J. Comput. Chem.,
2003, 24, 669-681.
18 Gaussian 09, Revision D.01, M. J. Frisch, G. W. Trucks, H. B.
Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, G.
Scalmani, V. Barone, B. Mennucci, G. A. Petersson, H.
Nakatsuji, M. Caricato, X. Li, H. P. Hratchian, A. F. Izmaylov, J.
Bloino, G. Zheng, J. L. Sonnenberg, M. Hada, M. Ehara, K.
Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y.
Honda, O. Kitao, H. Nakai, T. Vreven, J. A. Montgomery, Jr., J.
E. Peralta, F. Ogliaro, M. Bearpark, J. J. Heyd, E. Brothers, K. N.
Kudin, V. N. Staroverov, R. Kobayashi, J. Normand, K.
Raghavachari, A. Rendell, J. C. Burant, S. S. Iyengar, J. Tomasi,
M. Cossi, N. Rega, J. M. Millam, M. Klene, J. E. Knox, J. B. Cross,
V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E.
Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W.
Ochterski, R. L. Martin, K. Morokuma, V. G. Zakrzewski, G. A.
Voth, P. Salvador, J. J. Dannenberg, S. Dapprich, A. D. Daniels,
Ö. Farkas, J. B. Foresman, J. V. Ortiz, J. Cioslowski, and D. J.
Fox, Gaussian, Inc., Wallingford CT, 2009.
,
Notes and references
View Article Online
454-464.
1
(a) T. M. Figueira-Duarte and K. Müllen, Chem. Rev., 2011,
111, 7260–7314; (b) Z. M. Hudson and S. Wang, Acc. Chem.
Res., 2009, 42, 1584–1596; (c) Z. Chi, X. Zhang, B. Xu, X. Zhou,
C. Ma, Y. Zhang, S. Liu and J. Xu, Chem. Soc. Rev., 2012, 41
,
3878-3896.
2
3
Y. Hong, J. W. Y. Lam and B. Z. Tang, Chem. Soc. Rev., 2011, 40
,
5361-5388 .
(a) P. Xue, P. Chen, J. Jia, Q. Xu, J. Sun, B. Yao, Z. Zhang and R.
Lu, Chem. Commun., 2014, 50, 2569-2571 ; (b) C.-H. Zhao, E.
Sakuda, A. Wakamiya and S. Yamaguchi, Chem.–Eur. J., 2009,
15, 10603-10612.
4
5
(a) S. W. Thomas, G. D. Joly and T. M. Swager, Chem. Rev.,
2007, 107, 1339-1386; (b) E. L. Holthoff and F. V. Bright, Acc.
Chem. Res., 2007, 40, 756-767; (c) B.-P. Jiang, D.-S. Guo and Y.
Liu, J. Org. Chem., 2011, 76, 6101-6107; (d) X. Zhang, X. Liu, R.
Lu, H. Zhang and P. J. Gong, J. Mater. Chem., 2012, 22, 1167-
1172.
(a) J. Han and K. Burgess, Chem. Rev., 2010, 110, 2709-2728;
(b) M. H. Lee, J. H. Han, J. H. Lee, N. Park, R. Kumar, C. Kang
and J. S. Kim, Angew. Chem. Int. Ed., 2013, 52, 6206-6209; (c)
H. J. Kim, C. H Heo and H. M. Kim, J. Am. Chem. Soc., 2013,
135, 17969-17977; (d) S. Chen, Y. Hong, Y. Liu, J. Liu, C. W. T.
Leung, M. Li, R. T. K. Kwok, E. Zhao, J. W. Y. Lam, Y. Yu, B. Z.
Tang, J. Am. Chem. Soc., 2013, 135, 4926-4929.
6
(a) S. Goswami, S. Das, K. Aich, B. Pakhira, S. Panja, S. K.
Mukherjee and S. Sarkar, Org. Lett., 2013, 15, 5412-5415; (b)
S. Goswami, K. Aich, S. Das, A. K. Das, D. Sarkar, S. Panja, T. K.
Mondal and S. K. Mukhopadhyay, Chem. Commun.
10739-10741; (c) S. Goswami, K. Aich, A. K. Das, A. Manna and
S. Das, RSC Adv. 2013, 3, 2412-2416; (d) S. Goswami, S. Das,
K. Aich, D. Sarkar and T. K. Mondal, Tetrahedron Lett 2013,
, 2013, 49,
,
.
54, 6892-6896; (e) S. Goswami, K. Aich, S. Das, S. B. Roy, B.
Pakhira and S. Sarkar, RSC Advances, 2014, 4, 14210-14214;
(f) S. Goswami, K. Aich, S. Das, B. Pakhira, K. Ghoshal, C. K.
Quah, M. Bhattacharyya, H.-K. Fun and S. Sarkar, Chem. Asian
J., 2015, 10, 694-700; (g) S. Das, S. Goswami, K. Aich, K.
Ghoshal, C. K. Quah, M. Bhattacharyya and H.-K. Fun, New J.
Chem, New J. Chem., 2015, 39, 8582-8587; (h) K. Aich, S.
Goswami, S. Das, C. D. Mukhopadhyay, C. K. Quah and H.-K.
Fun, Inorg. Chem., 2015, 54, 7309–7315 (i) S. Goswami, K.
Aich, S. Das, C. D. Mukhopadhyay, D. Sarkar and T. K. Mondal,
Dalton Trans., 2015, 44, 5763-5770 (j) S. Goswami, S. Das and
K. Aich, RSC Adv., 2015, 5, 28996-29001 , (k) S. Goswami, S.
Das, K. Aich, P. K. Nandi, K. Ghoshal, C. K. Quah, M.
Bhattacharyya, H.-K. Fun and H. A. Abdel-Aziz, RSC Adv., 2014,
4
, 24881-24886; (l) S. Goswami, K. Aich, A. K. Das, A. Manna
and S. Das, RSC Adv., 2013, 3, 2412–2416, (m) S. Goswami, K.
Aich, S. Das, A. K. Das, A. Manna and S. Halder, Analyst, 2013,
138, 1903–1907; (n) K. Aich, S. Goswami, S. Das and C. D.
Mukhopadhyay, RSC Adv., 2015,
5, 31189-31194. (o) S.
Goswami, S. Das, K. Aich, Tetrahedron Letters, 2013, 54, 4620–
4623; (p) S. Goswami, S. Das, K. Aich, D. Sarkar, T. K. Mondal,
Tetrahedron Letters, 2014, 55, 2695–2699.
7
8
E. L. Spitler, L. D. Shirtcliff, M. M. Haley, J. Org. Chem. 2007,
72, 86– 96.
(a) J. Seo, S. Kim, S. Y. Park, J. Am. Chem. Soc., 2004, 126
,
11154 – 11155; b) V. W.-W. Yam, K. M.-C. Wong, N. Zhu, J. Am.
Chem. Soc., 2002, 124, 6506 –6507; c) J. W. Hong, H. Y. Woo,
B. Liu, G. C. Bazan, J. Am. Chem. Soc., 2005, 127, 7435 –7443;
d) S. Spange, S. Prause, E. Vilsmeier, W. R. Thiel, J. Phys. Chem.
B, 2005, 109, 7280 –7289.
9
A. D. Becke, J. Chem. Phys., 1993, 98, 5648-5652.
10 C. Lee, W. Yang, R. G. Parr, Phys. Rev. B, 1988, 37, 785-789.
11 D. Andrae, U. Haeussermann, M. Dolg, H. Stoll and H. Preuss,
Theor. Chim. Acta, 1990, 77, 123-141.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 9
Please do not adjust margins

New Journal of Chemistry
Page 10 of 10
View Article Online
DOI: 10.1039/C6NJ00063K
Graphical Abstract
Three carbazole conjugated benzimidazole dyes has been synthesized and their acid/base
induced photophysical properties has been studied.