Cholesterol-Appended Benzimidazolium Salts: Synthesis, Aggregation, Sensing, Dye Adsorption, and Semiconducting Properties

Article abstract of DOI:10.1021/acs.langmuir.7b01713

A series of cholesterol-appended benzimidazolium salts 1-9 have been designed and synthesized. They have been explored in gel chemistry. The gelation of the benzimidazolium salts is dependent on the nature of the counteranions. In addition, the gelation behavior of the gelators is linked with the presence of both π-stacking and cholesteryl motifs. Whereas bisbenzimidazolium salt 2 forms a gel in dimethylsulfoxide/H₂O (1:1, v/v) itself, under similar conditions, monobenzimidazolium salts 4 and 6 exhibit gelation in the presence of F^- ions and validate the visual sensing of F^-. As an application, the gel phase of 2 efficiently removes toxic dyes from waste water. Furthermore, all gels show thermally activated semiconducting property within a wide voltage window.

Full text of DOI:10.1021/acs.langmuir.7b01713

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Article
Cholesterol appended benzimidazolium salts: synthesis,
aggregation, sensing, dye adsorption and semiconducting properties
Santanu Panja, Subhratanu Bhattacharya, and Kumaresh Ghosh
Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.7b01713 • Publication Date (Web): 30 Jul 2017
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Cholesterol appended benzimidazolium salts: synthesis,
aggregation, sensing, dye adsorption and semiconducting
properties
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Santanu Panja, Subhratanu Bhattacharya and Kumaresh Ghosh*
Departments of Chemistry, University of Kalyani, Kalyani-741235, India
Structure - property
relationship
ABSTRACT: A series of cholesterol appended benzimidazolium salts 1-9 have
been designed and synthesized. They have been explored in gel chemistry. The
gelation of the benzimidazolium salts is dependent on the nature of the counter
anions. In addition, the gelation behavior of the gelators is linked with the pres-
ence of both π-stacking and cholesteryl motifs. While the bisbenzimidazolium
salt 2 forms gel in DMSO:H2O (1:1, v/v) itself, under similar conditions mono ben-
zimidazolium salts 4 and 6 exhibit gelation in the presence of F- ions and validate
the visual sensing of F-. As application, the gel phase of 2 efficiently removes toxic
dyes from waste water. Furthermore, all the gels show thermally activated semi-
conducting property within a wide voltage window.
Fꢀ sensing
N
N
Semiconducting
property
H
Aromatic
surface
Cholesteryl
unit
Hydrogen
bonding site
Fꢀ
Sol
Dye adsorption
Gel
Careful scrutiny of the literature reveals that a number of
synthetic receptors consisting of functionalised benzim-
idazoles are known in last few years to recognize analytes
by accomplishing considerable changes in their absorp-
tion and emission spectra during interaction in solution
states.7,30-35 However, the utilization of benzimidazolium
moiety in constructing functional gelators for anions is
relatively less in number.36-44 Apart from their use as sen-
sors, the investigation of benzimidazolium-based gelators
in dye adsorption process is almost unexplored and there-
fore, deserves attention.41-44 It is worthy to be mentioned
that dyes are widely used to colour the products in many
industries including textile, lather, cosmetics, paper,
printing, pharmaceuticals, foods etc. Removal of dyes
from waste water is vital as they are toxic to human body
and also affect the aquatic ecosystem.45,46
Our ongoing interest in the synthesis of stimuli respon-
sive cholesterol-based supramolecular gelators,36,47-51 has
inspired us to report herein the synthesis and gelation
behaviour of a series of structurally diversed cholesterol
appended benzimidazolium compounds 1-9 (Fig. 1). The
gelation of the benzimidazolium salts is dependent on the
nature of the counter anion. While the chloride salts ex-
hibit non gelation tendency, the hexafluorophosphate
analogues are self assembled either itself or in the pres-
ence of externally added anion. In addition, the gelation
behavior of the gelators is linked with the presence of
both π-stacking and cholesteryl motifs. While the bisben-
zimidazolium salt 2 forms gel in DMSO:H2O (1:1, v/v) it-
self, under similar conditions mono benzimidazolium
INTRODUCTION
Organic cations such as guanidinium, pyridinium, imid-
azolium and benzimidazolium etc., are considered to be
important binding motifs in devising molecular receptors
for recognition and sensing of anionic species.1-8 The
proper placement of these motifs in the designed struc-
tures sometime draws attention in supramolecular as-
semblies and molecules of this class find use in gel chem-
istry. Gels are considered as viscoelastic solid like materi-
als in which the solvent molecules are entrapped within
the gelator molecules to form a three dimensional cross-
linked network via self-assembly. Different non covalent
interactions such as electrostatic, van der Waals, π- stack-
ing and hydrogen bondings play decisive role in this re-
gard.9-18 Over the last few decades, the interest in supra-
molecular gels derived from the self-assembly of low mo-
lecular weight organic compounds has been increased
significantly not only to understand the structure-
gelation relationship but also to develop advanced mate-
rials with a number of applications in sensing, biomedi-
cine, drug delivery, tissue engineering, photophysics
etc.19-27 In recent years, the development of hydrogels ca-
pable of encapsulating pollutants including water soluble
toxic dyes has been a focus in material chemistry.23,28,29
Of the different charged receptor modules, benzimidazo-
lium-based compounds draw attention due to availability
of the polar C-H bond in benzimidazolium motif that
takes part in hydrogen bonding with anion and the com-
plex is further stabilized by charge-charge interaction.
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salts 4 and 6 exhibit gelation in the presence of F- ions
gave compound 15. Anion exchange of 1, 3, 5, 7 and 15 us-
and validate the visual sensing of F-. As application, the
gel phase of 2 efficiently removes toxic dyes from waste
water. Additionally, each gel shows thermally activated
semiconducting property within a wide range of applied
voltage.
ing NH4PF6 in aqueous CH3OH containing 2% DMF af-
forded the desired compounds 2, 4, 6, 8 and 9, respective-
ly in appreciable yields. Compounds 1-9 were character-
ized by usual spectroscopic techniques.
1
2
3
4
5
6
7
Gelation study, thermal stability and morphologies
of gels
8
9
N
In general, in compounds 1-8 the benzimidazolium ring
nitrogens are coupled with different substituents of which
cholesterol motif is common to all. The supramolecular
systems 1 and 2 have been designed based on the A(LS)2
type model in which aromatic benzene ring (A) is con-
nected to the benzimidazolium unit (L), capable of form-
ing hydrogen bonds.15 Subsequent connection of the cho-
lesterols (S) to the benzimidazoles is considered to main-
tain a hydrophobic/ hydrophilic balance in the designs.
Compounds 3-8 represent ALS-type architectures having
N
N
N
N
N
N
N
N
ꢀ
N
N
N
PF6
Xꢀ
Xꢀ
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Xꢀ
Xꢀ
O
Xꢀ
O
O
O
O
O
O
O
O
R
R
R
R
R
O
1; Xꢀ = Clꢀ
2; Xꢀ = PF6
3; Xꢀ = Clꢀ
4; Xꢀ = PF6
5; Xꢀ = Clꢀ
6; Xꢀ = PF6
7; Xꢀ = Clꢀ
8; Xꢀ = PF6
ꢀ
ꢀ
9
ꢀ
ꢀ
R =
Figure 1. Structures of compounds 1-9.
-
different counter anions (Cl- or PF6 ) associated with the
benzimidazolium functionality. Compounds 1 and 2 are
doubly charged whereas the rest of the compounds are
mono cationic in nature. The gelation abilities of the
compounds 1-9 were examined in different solvents and
solvent combinations of different polarities (Table 1S).
While compound 1 did not show any gelation ability,
compound 2 under similar conditions formed pale yellow
colored transparent gel from DMSO–H2O (1:1, v/v). Use of
more water content DMSO (e.g., 25% or 5% DMSO in
water) failed to gelate compound 2. Instead, precipitation
appeared due to poor solubility of 2 in such solvent com-
binations. However, mono cationic gelators 3-9 did not
form gel in any of the solvent tested without assistance of
any external stimuli. This indicates the key role of more
number of cholesterol and benzimidazolium motifs in 2
that trigger the self-aggregation involving hydrogen
bonding, π-stacking and hydrophobic interactions.
RESULTS AND DISCUSSION
Synthesis
Compounds 1-9 were obtained according to the Scheme 1.
Cholesterol was initially converted to the chloride 10.47
Reaction of benzimidazole separately with m-xylene di-
bromide, benzyl bromide, 9-chloromethyl anthracene and
n-butyl bromide in the presence of NaH in dry THF af-
forded compounds 11,52 12, 1353 and 14, respectively. Salt
formation reactions of 11-14 with the chloride compound
10 in dry DMF-CH3CN produced the chloride salts 1, 3, 5
and 7, respectively. On the other hand, treatment of com-
pound 13 with n-butyl bromide under similar conditions
(i)
O
R
OH
R
Cl
R =
O
10
(ii)
(iv)
(iii)
2
1
The hydrogel of 2 exhibited marked stability over four
months at room temperature and the gel to sol phase
transition temperature (Tgel) as determined by capillary
N
N
N
Br
Br
N
11
R1
R1
R1
0
N
insertion method was recorded as 72 C. The morphology
N
N
(ii)
(iv)
N
(iii)
R1 Br
of the gel was characterized by recording the SEM and
AFM images. SEM image shows flake like aggregates (Fig.
2a). AFM image also clearly depicts the uneven surface of
the gel (Fig. 2b).
N
ꢀ
N
Clꢀ
PF6
O
N
N
O
R
R
O
O
Brꢀ
(iv)
(iii)
R1
=
4
3
12
15
(iv)
(v)
(a)
(b)
(iv)
(iii)
(iii)
R1
=
5
7
6
N
13
14
N
ꢀ
PF6
(iv)
R1
=
8
9
Figure 2. (a) SEM (Scale bar 3 μm) and (b) AFM images of
xerogel of 2 from DMSO: H2O (1:1, v/v).
Scheme 1. ((i) chloroacetyl chloride, dry CHCl3, pyridine; (ii)
benzimidazole, NaH, dry THF, reflux, 4h; (iii) 10, dry CH3CN
and DMF, reflux, 3 days; (iv) DMF/CH3OH, aq. solution of
NH4PF6; (v) n-butyl bromide, dry CH3CN and DMF, reflux, 3
days.
The inability of 1 in gel formation in comparison to 2 is
attributed to the effect of the counter anion. We believe
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that the participation of benzimidazolium motif in hy-
the intensity is gradually decreased due to dilution effect
(Fig. 5S). In H NMR, the persistence of the C(2)-H signal
1
1
2
3
4
5
6
7
8
drogen bonding with the chloride ion involving C(2)-H
bond does not allow 1 to gelate solvent. Such situation is
expected to be absent in 2. In 1H NMR, the appearance of
the signal of benzimidazolium C(2)-H in 1 was noticed in
more downfield region compared to the case with 2 and
thereby confirmed the hydrogen bonding participation of
benzimidazolium motif (Fig. 3A). In FTIR, lowering of
stretching frequency of the ester carbonyl of 1 by 7 cm-1
with respect to 2 was observed. Beside this, no other char-
at 9.78 ppm in the presence of 1 to 2 equiv. amounts of
TBAOH suggested non deprotonation (Fig. 6S). In the
presence of excess concentration of TBAOH, the deproto-
1
nation occurs and it was difficult to interpret by H NMR
due to significant broadening of the signals.
9
1
10
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acteristic change in the IR spectra like in H NMR was
worthy to explain the different hydrogen bonding charac-
teristics of bezimidazolium moieties in 1 and 2 (Fig. 1S). In
reality, the hydrogen bonding feature of the benzimidaz-
ole group with halides is an established fact in the litera-
ture.54-57 Hence, we believe that the molecules of 2 may
assume the packing arrangement where interlinking of
the molecules produces hydrogen bonded network for
solvent trapping to form gel. To get insight in this regard,
FTIR spectra of 2 in its amorphous and gel states were
compared (Fig. 2S). The signal for ester carbonyl at 1752
cm-1 in the amorphous state of 2 underwent shifting to
1743 cm-1 in the gel state. This decrease in stretching fre-
quency of the ester carbonyl in 2 is attributed to its in-
volvement in the formation of intermolecular hydrogen
bonds during gelation. Moreover, weak π-stacking inter-
actions during aggregation between the aromatic surfaces
cannot be ruled out.36-44
Benzimidazolium moiety binds anions via hydrogen bond
involving the C(2)-H bond. In our earlier study, we re-
ported the anion binding behaviour of a similar type of
designed molecule in solution phase.30 To realize more
along this direction in gel phase, we explored the gel state
of 2 in anion binding by adding aqueous solution of dif-
ferent anions (taken as tetrabutylammonium salts) to the
gel of 2 in DMSO/H2O (1/1, v/v). Of the different anions,
only in the presence of NaOH solution, the gel started to
collapse and was completely ruptured within five minutes
(Fig. 3S). On further acidification, the solution gradually
became thick and transformed into gel (Fig. 4S) and
thereby indicated its pH responsive behaviour. This pH
responsive behaviour is attributed to the acidic nature of
the hydrogen in C(2)-H of benzimidazolium motif. In the
presence of OH-, this acidic proton may either be depro-
tonated or participate in hydrogen bonding due to which
the gel state is transformed into the sol state. It is men-
tionable that the gel is highly stable in the pH range of 2
to 7.8. At higher pH the gel is disintegrated. Fig. 4S repre-
sents the pH dependant change of the gel state of 2. It is
to be pointed out that the imidazoliums are unstable in
the presence of bases owing to the deprotonation of the
acidic C(2)-H to produce N-heterocyclic carbenes (NHC)
which undergoes ring-opening reactions in aqueous me-
dium. However, such reactions are highly dependent on
the substituents at C(4) and C(5) positions.58 To investi-
gate the stability of the benzimidazolium salt in the pre-
Figure 3. Photograph showing the dye adsorption of Uranine
(A→A'), Rhodamine B (B→B'), Rose Bengal (C→C'), Mala-
chite Green (D→D') and Crystal Violet (E→E') (c= 2 x 10-5 M)
dyes, respectively on keeping in contact with the gel of 2 [8
mg/ml in 1:1 DMSO–H2O (v/v)] for 24h.
In order to explore the application of gel state of 2, we
used it in dye adsorption. Recently, Thomas et al. report-
ed a clay-cross linked hydrogel which can adsorb dyes
with opposite charge selectively, and the selective adsorp-
tion is based on the electrostatic interaction between the
hydrogel and dyes.59 Experimental findings have intimat-
ed that benzimidazolium salts have unique property to
adsorb dye molecules from waste water. For such study,
both anionic (Uranine, Rhodamine B, Rose Bengal) as
well as cationic (Malachite Green, Crystal Violet) dyes
were used. The dye adsorption experiment was carried
out by monitoring the change in absorbance of the dye
solution after keeping in contact with the hydrogel of 2
for 24h. Figure 3 shows the change in color of the dye so-
lutions when they individually remain in contact with the
hydrogel of 2.
A time dependent UV-vis study was performed with 2 mL
of corresponding dye solution (in water) (Fig. 7S). As rep-
resentative example, Fig. 4A corroborates the time de-
pendant change in absorption spectra of the uranine dye
when remains in contact with the gel. With time, the ab-
sorption maxima of the uranine dye solution was gradual-
ly decreased and after 24h it became almost flat without
showing any other change in the absorption spectrum.
The resulting solution appeared as almost colourless
1
sent case, UV-vis and H NMR spectra of 2 were recorded
in the presence of tetrabutylammonium hydroxide
(TBAOH). UV-vis study in DMSO:H2O revealed no char-
acteristics change in the spectra except at 270 nm where
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whereas the gel state acquired the color of the respective hydrogel had almost alike adsorption efficiency towards
1
2
dye solutions (Fig. 8S).
dianionic dyes Uranine and Rose Bengal whereas it
showed relatively much lower adsorption in case of mono
3
4
(B)
(A)
Table 1. Adsorption data of gel 2 using various dyes.
5
1.2
1.0
0.8
0.6
0.4
0.2
0.0
Quantity
of
adsorbed
dye (mg
per gram
6
7
8
9
----- 0 hr
Dye
( λmax in
nm)
Initial conc.
of dye (Ci)
[mM] (mgL-1)
Equilibrium
conc. of dye
(Cf) [mM]
(mgL-1)
----- 2 hr
----- 4 hr
----- 6 hr
----- 12 hr
----- 24 hr
10
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of
the
gelator)
Uranine
(490)
2 x 10-2 (7.52)
2 x 10-2 (9.30)
2 x 10-2 (20.30)
2 x 10-2 (7.28)
2.94 x 10-3 (1.10)
8.01 x 10-3 (3.73)
1.29 x 10-3 (1.31)
2.80 x 10-3 (1.01)
1.60
300
400
500
600
700
Rhodamine B
(554)
1.39
4.74
1.56
Wavelength (nm)
Rose Bengal
(541)
Figure 4. (A) Time-dependent UV–vis spectra of Uranine (c
= 2 x 10-5 M) solution after keeping in contact with the hy-
drogel of 2 [8 mg/ml in 1:1 DMSO–H2O (v/v)]; (B) pictorial
representation of the color change of the uranine-adsorbed
gel on changing pH: (a) gel of the compound 2 (8 mg/ml) in
1:1 DMSO–H2O (v/v), (b) aqueous solution of uranine dye (c
= 8x10-4 M) at pH = 7.2, (c) uranine dye adsorbed hydrogel of
2 at pH = 7.2 and (d) removal of uranine dye from the hydro-
gel by adding aq. solution of NaOH.
Malachite
Green (617)
Crystal Violet
(590)
2 x 10-2 (8.14)
8.36 x 10-3 (3.40)
1.18
anionic Rhodamine B. This could be obvious on the basis
of the extent of electrostatic interaction between the dica-
tionic hydrogelator molecule and the anionic dyes. The
positively charged dyes such as Malachite Green and
Crystal Violet in the present study were also significantly
captured by the gel. This suggests that the hydrophobicity
and π-stacking forces interplay major role over the
charge-charge repulsion during dye adsorption. Thus the
gel state of 2 is considered to be useful as adsorbent for
both anionic and cationic dyes.
To be confirmed with the adsorption, we further recorded
the FTIR spectrum of the gel 2 before and after the ad-
sorption of uranine dye. Adsorption of uranine into the
gel matrix resulted in change in stretching frequency of
the ester carbonyl groups (Fig. 9S). During adsorption,
the morphology of the gel including gel melting tempera-
ture (Tg) was changed. The morphology of uranine dye
adsorbed gel was observed to be more aggregated in na-
ture than the normal gel (Fig. 9S) and Tg was decreased
O
Cl
Cl
Cl
N
N
O
0
N
O
N
Clꢀ
by 8 C. In the event the volume of the gel was merely
O
ꢀ
Cl
O
I
I
changed.
+ꢀOOC
Oꢀ
Na+
ꢀO
Na+
Na
O
O
Oꢀ
Na+
The pH responsive nature of the dye-adsorbed gel was
investigated. Figure 4B represents the effect of aq. NaOH
on the uranine dye adsorbed gel of 2 and the associated
color changes under ordinary light and UV exposure.
While the uranine dye-adsorbed gel shows orange color
in ordinary light, the same is viewed as deep yellow under
UV illumination. In presence of OH-, the gel state (pH is
checked to be 7.2) is ruptured (pH >8.0) and the original
color of dye is retained.
Analysis of dye adsorption experimental findings reveals
that the hydrogel of 2 is convincingly capable of removing
water pollutant dyes from their aqueous solutions and the
dye adsorption capacity of the hydrogel was determined
to be 85.3%, 59.9%, 93.6%, 86.0% and 58.2% for Uranine,
Rhodamine B, Rose Bengal, Malachite Green and Crystal
Violet, respectively (Fig. 5). Table 1 and Fig. 10S represents
the details along this direction. It is mentionable that the
dye-adsorbed gels were stable over a month. As the ad-
sorption processes and mechanisms are complex, some-
time it is difficult to infer proper explanation. However,
here we believe that hydrophobic surface as provided by
the cholesterol, aromatic surface of the m-xylene spacer
and the positively charged benzimidazolium motifs alto-
gether play the role in adsorption of the anionic dyes. The
Na+
Clꢀ
I
I
O
Uranine
Rhodamine B
Malachite Green
Rose Bengal
N
N
N
Crystal Violet
Figure 5. Plot of % of dye removal efficiency (RE) of gel 2 (c
= 8 mg/mL) after keeping in contact with the dyes (A =
Uranine, B = Rhodamine B, C = Rose Bengal, D = Malachite
Green and E = Crystal Violet; [dye] = 2 x 10-5 M) for 24h.
In comparison to 2, mono cationic structures 3-8 behaved
differently in gelation. All the compounds 3-8 behaved as
nongelator in a number of tested solvents including
DMSO: H2O (1:1, v/v) (Table 1S). However, upon addition
of F- ions, the DMSO: H2O (1:1, v/v) solutions of 4 and 6
became thick to form pale brown and yellow colored gels,
respectively. Under similar conditions, rest of the com-
pounds either resulted in precipitation or exhibited par-
tial gelation. Interestingly, the chloride salt analogues of 4
and 6, i.e. compounds 3 and 5, respectively, did not exhib-
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intermolecular aggregation during gelation. The aggrega-
it gelation. This was most likely due to intramolecular
1
2
3
4
hydrogen bonding of the imidazolium moiety with the
closely spaced Cl- ions that prevents the intermolecular
association with the added F- ions to set up a cross-linked
tion is further stabilized by the hydrophobic interactions
exerted by the cholesterol units. The quenching of emis-
sion in the gel state is attributed to the ‘aggregation-
caused quenching’ (ACQ) phenomena.60
1
network in solution. In H-NMR, more downfield chemi-
5
6
7
8
cal shift of the signals for C(2)-Hs of benzimidazolium
moieties in 3 and 5 compared to their hexafluorophos-
phate analogues 4 and 6, undoubtedly supports this
To examine the role of cholesterol unit in the designs, we
introduced butyl chain instead of cholesterol in com-
pound 9. Non gelation behaviour of compound 9 in com-
parison to 6 strappingly corroborated the crucial role of
hydrophobic surface during gelation.
proposition (Fig. 11S). To our opinion, F-/HF2 (HF2 comes
from the interaction of F- with water) ions bind with the
benzimidazolium motifs of 4 and 6 in solution involving
C(2)-H in the mode as shown in Fig. 12S to set up an ag-
gregation for entrapping solvent.
-
-
9
10
11
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The anion responsive nature of the gelators 4 and 6 was
also examined with other anions in details. Except F-,
other anions taken in the study were nonresponsive in
bringing sol-gel conversion (Fig. 7a,b). Compounds 4 and
6 at minimum concentrations of 16 mg/mL and 15 mg/mL,
respectively, in the presence of 4 equiv. amounts of F- ions
resulted in instant gelation. Use of less than 4 equiv.
amounts of F- ions caused partial gelation in both cases.
The fluoride gels of 4 and 6 exhibited thermal induced gel
to sol reversible transition and at mgc the gel melting
temperatures were recorded to be 58 oC and 62 oC, respec-
tively. The surface morphologies of the gels were studied
by SEM images which intimated flake like porous struc-
tures (Fig. 7c,d).
The hydrogen bonding interaction of F- with the com-
1
pounds 4 and 6 was understood from H NMR, recorded
in CDCl3. As can be seen from Fig. 6, with increase in con-
centration of F- ion, the signal for C(2)Ha underwent
downfield chemical shift. Moreover, the benzyl protons
Hc, in both cases, exhibited downfield chemical shift dur-
ing interaction (for Hc: ∆δ4 = 0.19 ppm and ∆δ6 = 0.29
ppm). In this regard, FTIR study of 4 and 6 as shown in
Fig. 13S was not informative to interpret the F- ion interac-
tion.
Hb
Hb
Hc
(a)
Hd
Hc
(b)
(B)
(A)
N
N
N
N
Ha
ꢀ
Ha
R =
ꢀ
PF6
PF6
O
O
4
R
R
O
6
O
(d)
(c)
1
Figure 6. Partial H NMR (400 MHz, CDCl3) of compounds
(A) 4 (c = 5.50 x 10-3 M) and (B) 6 (c = 3.72 x 10-3 M) with F-
ion; (a) compound, (b) compound with TBAF (0.5 equiv) and
(c) compound with TBAF (1:1).
When the gelation abilities of 7 and 8 in the presence of F-
were examined and compared to that of compounds 4
and 6 under similar conditions, compound 7 resulted in
precipitation and 8 showed partial gelation. This observa-
tion undoubtedly suggested the subtle role of aromatic
stacking in the gel matrices of 4 and 6. In this regard, for
example, absorption and emission spectra of 6 were rec-
orded in solution and gel states to understand the stack-
ing interaction (Fig. 14S). In UV-vis, compound 6 exhibit-
ed 3 nm red shifted absorption in gel state. In fluores-
cence, the broad emission at 498 nm with reduced inten-
sity in the gel state demonstrated the formation of inter-
molecular excimer/exciplex between anthracenes or an-
thracene/benzimidazolium moieties. The possible inter-
molecular hydrogen bonded network as suggested in Fig.
11S gives the emission at longer wavelength due to exten-
sive π-stacking interaction that enhances the scope of
Figure 7. Photographs showing the phase changes of (a) 4
and (b) 6 in DMSO: H2O (1:1, v/v; 16 mg/ml) upon addition of
4 equiv. amounts of each anion of tetrabutyl ammonium salt
(c = 6.2 x 10-2 M); SEM images of the xerogels of 4 (c) [Scale
bar 2 μm] and 6 (d) [Scale bar 1 μm].
To enquire any role of counter cation during gelation of 4
and 6 with TBAF in DMSO: H2O (1:1, v/v), similar experi-
ments under identical conditions were performed with KF
and CsF. Indeed, all of them induced gelation (Fig. 15S)
and hence demonstrated the key role of F- ion in gelation
rather than the counter cation.
To demonstrate the solution phase interactions of 4 and 6
with F- and other anions in details, fluorescence and UV-
vis studies were performed in DMSO-H2O solvent combi-
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Page 6 of 13
nation. In the experiment, compounds were taken in charge delocalization within the gel matrix, enabling the
1
2
3
4
5
6
7
8
DMSO and aqueous solutions of anionic guests were add-
ed to these solutions in different amounts to record the
spectra. Although no significant change in the emission
of 4 was observed with F- ions, the absorption spectra
reflected significant increase near 340 nm with a clear
isosbestic point at 307 nm (Fig. 16S). On the other hand,
compound 6 that contains anthracene unit, a well known
fluorophore with good quantum yield, exhibited dramatic
change in the emission with F- ions over the other anions
taken in the study (Fig. 17S). Initially, on excitation at 370
nm, DMSO solution of 6 showed strong emissions at 400
nm, 422 nm and 448 nm, the characteristic triplet emis-
sion of anthracene. On addition of different anionic solu-
tions (in H2O), small change in emission of 6 was ob-
served except the case with AcO- and F- ions. While AcO-
ion resulted in moderate quenching of emission of 6, un-
der identical conditions F- ions caused almost complete
quenching without producing any other change in emis-
sion spectra (Fig. 8a). Fig. 8b in this purpose, represents
the change in fluorescence ratio of 6 in the presence of 15
equiv. amounts of different anions. The formation of 1:1
complex of 6 with F- ion in solution was determined by
Benesi-Hildebrand plot61 from which the association con-
stant value was calculated to be (7.50 ± 0.55) x 103 M-1 (Fig.
18S).
gel to show semiconducting behaviour. Therefore, we
were keen to observe the semiconducting properties of
the gels, in addition. This was understood by measuring
their temperature dependent current (I)–voltage (V)
characteristics as shown in Fig. 9a to Fig. 9c, respectively.
Observed symmetric, nonlinear increase in current with
increasing voltage in either side clearly demonstrates the
semiconducting nature of the gels within the applied
voltage range. Moreover, the current gradually increases
with temperature showing thermally activated charge
transport. The observed semiconducting nature of the gel
of 2 presumably arises due to the π- π stacking interaction
within the matrix. The gels of 4 and 6 in the presence of F-
show the considerable increase in current (Fig. 9d). This
is presumably due to occupancy of anions (either F- or
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
-
HF2 ) in the interstitial positions of the gel networks
through hydrogen bonding interactions as shown in Fig.
9. Thus, we believe that the anion doping reinforces the
semiconducting property of the gels apparently either by
inducing subtle arrangement of the gelators or by increas-
ing charge transfer domains within the gel matrix. As we
are aware about the binding of F- ions involving the imid-
azolium C(2)-H of compounds 4 and 6 in solution, we
believe that such unconventional hydrogen bonding
In presence of F-
In absence of F-
(a)
N
N
N
H
N
N
N
-
HF2
H
F-
electron defficient
centre
small charge delocalization
Hydrogen bonding followed by deprotonation
enhances charge delocalization
(b)
(a)
6.0x106
4.0x106
2.0x106
0.0
400
450
500
550
Wavelength (nm)
Figure 8. (a) Change in fluorescence ratio of 6 (c = 1.0 x 10-5
M in DMSO) at 423nm upon addition of 15 equiv. amounts of
anions (c = 4.0 x 10-4 M in H2O); (b) Change in emission of 6
(c = 1.0 x 10-5 M) upon addition of 15 equiv. amounts of F- ion
(c = 4.0 x 10-4 M).
In ground state, initially 6 displayed structured absorp-
tion at 370 nm which gradually increased upon addition
of F- ions. A concomitant decrease in the absorption at
280 nm was recorded (Fig. 19S). Such ratiometric change
in the absorption spectra gave isosbestic point at 309 nm.
In case of other anions, no significant change was noticed
in the absorption spectra of 6 during titration (Fig. 19S).
Figure 9. Temperature dependent I–V characteristics of the
gels (a) 2, (b) 4 and (c) 6 (temperature range 233–303 K); (d)
Comparison of I-V characteristics of gels 2, 4 and 6 at room
temperature (303 K).
offers the formation of more electronically rich charge
centres within the gel phase in comparison to the case of
the gel derived from 2, which intern remarkably enhances
the electrical conductivity.
Current (I)-Voltage (V) characteristics
It has been observed earlier62,63 that the self-organization
of a gelator with π-surface may establish a long-range
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Langmuir
Chloro-acetic
acid
17-(1,5-dimethyl-hexyl)-10,13-
CONCLUSION
1
dimethyl-2,3,4,7,8,9,10,11,12,13,14,15,16,17-
In summary, we have designed and synthesized a series of
benzimidazolium salts 1-9 that exhibit unique gelation
behaviour under different conditions. The gelation of the
benzimidazolium salts is dependent on the nature of the
counter anions. While the chloride salts exhibit non gela-
tion tendency, the hexafluorophosphate analogues are self
assembled either itself or in the presence of externally
added anion. Of the different salts, compound 2 itself
forms gel in DMSO:H2O (1:1, v/v), whereas F- as external
anion under similar conditions stimulates the self aggre-
gation of 4 and 6 in aqueous DMSO solvent. This vali-
dates the visual sensing of F-. Rest of the salts behaved as
nongelators even in presence of F- ion. In the designs, the
necessity of the aromatic π-stacking and hydrophobic
interaction exerted by cholesteryl group has been under-
stood from the structures 8 and 9.
As application, hydrogelator 2 that possesses more resid-
ual charge as well as extensive hydrophobicity due to
more cholesterol units was successfully applied as adsor-
bent of different anionic and cationic dyes. It is experi-
mentally established that the hydrogel of 2 is capable to
remove water pollutant dyes from their aqueous solutions
and the dye adsorption capacity of the hydrogel has been
noted to be 85.3%, 59.9%, 93.6%, 86.0% and 58.2% for
Uranine, Rhodamine B, Rose Bengal, Malachite green and
Crystal violet, respectively. The dye-adsorbed gels were
stable over a month. In addition, all the gels as obtained
through different processes, exhibit suitable environment
for electron conduction and the observed semiconducting
property are thermally activated in nature.
2
3
4
5
6
7
8
9
tetradecahydro-1H-cyclopenta[a]phenanthren-3-yl
ester (10):47
To a stirred solution of cholesterol (0.5 g, 1.29 mmol) in
20 mL dry CH2Cl2 was added chloroacetyl chloride (0.16
mL, 1.93mmol) and pyridine (0.05 mL, 0.65 mmol) under
nitrogenous atmosphere. The mixture was allowed to stir
for 10 h at room temperature. After completion of reac-
tion, the solvent was evaporated and the crude was ex-
tracted with CHCl3 (3 × 30 mL). The organic layer was
washed several times with water and separated and dried
over Na2SO4. Evaporation of the solvent gave white solid
compound. Recrystallization from petroleum ether af-
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
1
forded pure product 10 (0.58 g, yield 96%), mp 148 °C. H
NMR (400 MHz, CDCl3 ) δ 5.37 (m, 1H), 4.72 (m, 1H), 4.03
(s, 2H), 2.36 (m, 2H), 2.02–0.85 (m, 38H), 0.67 (s, 3H);
FTIR (KBr, cm−1 ): 2939, 2907, 2821, 1753, 1620, 1195.
1, 3-bis ((1H-benzo[d]imdazol-1-yl) methyl) benzene
(11):52
To a solution of benzimidazole (0.6 g, 5.08 mmol) in dry
THF (20 ml), NaH (0.122 g, 5.08 mmol) was added at
room temperature. Then the solution was refluxed for 1h.
The solution was cooled to room temperature. Then 1, 3-
bisbromomethyl benzene (0.67 g, 2.54 mmol) was added
to the solution and the reaction mixture was further re-
fluxed for 5h. The solvent was removed under vacuum.
Then the reaction mixture was extracted with 50 x 3 ml
chloroform containing 2% methanol. The organic solvent
was dried over Na2SO4 and concentrated under vacuum.
The residue was purified by flash column chromatography
(ethyl acetate/petroleum ether 80:20, v/v) to afford white
crystalline solid compound 11 (0.6 g, yield: 69%), mp 118
0C. 1H NMR (400 MHz, d6-DMSO) δ 8.37 (2H, s), 7.66 (2H,
d, J = 8 Hz), 7.43 (2H, m), 7.26 (1H, t, J = 8 Hz), 7.19-7.15
(7H, m), 5.46 (4H, s); 13C NMR (100 MHz, d6-DMSO) δ
144.1, 143.5, 137.3, 133.5, 129.1, 126.9, 126.8, 122.3, 121.6, 119.4,
110.6, 47.5; FT-IR: ν cm-1 (KBr): 3088, 1612, 1496, 1440.
EXPERIMENTAL
Materials
Cholesterol, Chloroacetyl chloride, 9-anthraldehyde, ben-
zyl bromide, butyl bromide and benzimidazole were pur-
chased from Spectrochem. Tetrabutylammonium salts of
anions used in the study were purchased from Sigma-
Aldrich and were carefully handled. All solvents used in
the synthesis were purified, dried and distilled as re-
quired. Solvents used in NMR experiments were obtained
from Aldrich. Thin layer chromatography was performed
1-(anthracen-9-ylmethyl)-1H-benzo[d]imidazole
(13):53
To a solution of benzimidazole (0.65 g, 5.50 mmol) in dry
THF (25 ml), NaH (0.19 g, 8.26 mmol) was added at room
temperature. Then the solution was refluxed for 1h. The
solution was cooled to room temperature and 9-
chloromethyl anthracene (2.15 g, 9.53 mmol) in 20 mL of
dry THF was added to the solution and the reaction mix-
ture was further refluxed for 8h. The solvent was removed
under vacuum. Then the reaction mixture was extracted
with 5% MeOH in chloroform solution. The organic sol-
vent was dried over anhydrous Na2SO4 and concentrated
under vacuum. The residue was purified by column
chromatography using 30% ethyl acetate in petroleum
ether as eluent to afford yellow colored compound 13 in
64% yield (0.79 g). 1H NMR in CDCl3 (400 MHz) δ 8.61 (s,
2H), 8.10 (d, 4H, J = 8 Hz), 7.82 (d, 1H, J = 8 Hz), 7.71 (d,
1H, J = 8 Hz), 7.51 (m, 4H), 7.42 (t, 1H, J = 8 Hz), 7.35(t, 1H,
J = 8 Hz), 6.19 (s, 2H); 13C NMR (CDCl3, 100 MHz) δ 144.0,
1
on Merck precoated silica gel 60-F254 plates. H and 13C
NMR spectra were recorded using Bruker 400 MHz in-
strument using TMS as internal standard. High resolution
mass data were acquired by the electron spray ionization
(ESI) technique on XEVO GS-2 QTOf Waters mass spec-
trometer. FTIR measurements of all the compounds and
dried gels (xerogels) were carried out using a Perkin-
Elmer L120-00A spectrometer (νmax in cm-1) using KBr cell
and KBr pellets, respectively. Scanning electron micros-
copy (SEM) images were obtained on EVO LS-10 ZEISS
instrument. Fluorescence and UV-Vis studies were per-
formed using Horiba Fluoromax 4C spectrofluorimeter
and Perkin-Elmer LS-55 instruments, respectively.
Synthesis
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Page 8 of 13
142.2, 134.2, 131.4, 131.0, 129.7, 129.5, 127.5, 125.4, 123.6, 123.1, 7.43-7.36 (m, 3H), 5.82 (s, 2H), 5.70 (d, 2H, J = 4 Hz), 5.40
1
2
3
123.0, 122.5, 120.6, 109.5, 41.3; m/z (ES+): 308.9 [M].
(d, 1H, J = 4 Hz), 4.75-4.72 (m, 1H ), 2.40–0.67 (m, 43H);
FTIR (KBr) ν cm-1: 1733, 1564, 1456, 1374.
Compound 1:
4
5
6
7
8
9
Compounds 10 (0.41 g, 0.87 mmol) and 11 (0.1 g, 0.29
mmol) were taken in dry CH3CN (30 mL) containing 1%
DMF and the mixture was refluxed for 3 days. The precip-
itate was filtered off and washed with hot CH3CN fol-
lowed by diethyl ether to have the pure dichloride salt 1 in
85% yield (0.32 g), mp 162 C. H NMR (d6-DMSO, 400
MHz): δ 9.88 (s, 2H), 8.01 (d, 2H, J = 8Hz), 7.78 (d, 2H, J =
8Hz), 7.65 (t, 2H, J = 8 Hz), 7.54-7.51 (m, 5H), 7.38 (s, 1H),
5.83 (s, 4H), 5.57 (s, 4H), 5.33 (s, 2H), 4.59-4.58 (m, 2H),
2.34-0.67 (m, 86H); FTIR (KBr) ν cm-1: 2936, 1745, 1627,
1564; MALDI-TOF-MS: 1192.120 (M-2Cl)+, 1230.944 (M-
H+K)+.
Compound 4:
Compound 3 (0.2 g, 0.29 mmol) was dissolved in MeOH
(8 mL) containing 1% DMF and an aqueous solution of
NH4PF6 (0.09 g, 0.58 mmol) was added under hot condi-
tion. After stirring the mixture for 30 min, the precipitate
was filtered and washed well with diethyl ether to afford
pure compound 4 in 84% yield (0.19 g), mp 172 C. H
NMR (CDCl3, 400 MHz): δ 9.34 (s, 1H), 7.67-7.60 (m, 4H),
7.45-7.43 (m, 5H), 5.64 (s, 2H), 5.40 (s, 1H), 5.29 (s, 2H),
4.77-4.72 (m, 1H), 2.39-0.67 (m, 43H); 13C NMR (CDCl3, 100
MHz): 164.9, 142.5, 138.9, 131.8, 131.7, 130.7, 129.5, 129.4,
128.1, 127.6, 127.4, 123.2, 113.7, 113.0, 76.7, 56.6, 56.1, 51.7,
49.9, 47.8, 42.3, 39.7, 39.5, 37.6, 36.8, 36.4, 36.1, 35.8, 31.8,
31.7, 28.2, 28.0, 27.4, 24.2, 23.8, 22.8, 22.5, 21.0, 19.2, 18.7,
11.8; FTIR (KBr) ν cm-1: 2951, 1753, 1570, 1483; HRMS (TOF
MS ES+): calcd. 635.4571 (M-PF6)+, found 635.4576 (M-
PF6)+.
0
1
0
1
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Compound 2:
The dichloride salt 1 (0.2 g, 0.15 mmol) was dissolved in
MeOH (8 mL) containing 2% DMF and an aqueous solu-
tion of NH4PF6 (0.05 g, 0.3 mmol) was added under hot
condition. After stirring the mixture for 30 min, the pre-
cipitate was filtered. Repeated crystallization of the pre-
cipitate by diethyl ether afforded pure compound 2 in
Compound 5:
Compounds 10 (0.22 g, 0.48 mmol) and 13 (0.1 g, 0.32
mmol) were mixed in dry CH3CN (30 mL) containing 5%
DMF and the mixture was refluxed for 3 days. Then the
solvent was evaporated under reduced pressure and com-
pound 5 was purified by preparative TLC (0.19 g, 77%
0
1
85% yield (0.2 g), mp 186 C. H NMR (d6-DMSO, 400
MHz): δ 9.71 (s, 2H), 7.97-7.95 (m, 2H), 7.71 (d, 2H, J =
8Hz), 7.61 (m, 1H), 7.59 (t, 2H, J = 8 Hz), 7.47 (t, 2H, J = 8
Hz), 7.42 (s, 2H), 7.31 (s, 1H), 5.77 (s, 4H), 5.49 (s, 4H),
5.27 (s, 2H), 4.54-4.52 (m, 2H), 2.26-0.67 (m, 86H); 13C
NMR (d6-DMSO, 100 MHz): 166.4, 143.9, 139.4, 135.1, 132.0,
130.6, 130.3, 129.0, 127.8, 127.4, 127.2, 122.9, 114.4, 114.1, 76.1,
56.6, 56.1, 50.2, 49.8, 48.0, 42.3, 38.0, 36.8, 36.5, 36.2, 35.7,
31.7, 28.2, 27.8, 27.7, 24.3, 23.8, 23.0, 22.8, 21.0, 19.3, 18.9,
12.0 (two carbons of the cholesteryl part in the aliphatic
region are buried under the signal of d6-DMSO); FTIR
(KBr) ν cm-1: 2951, 1752, 1666, 1571; Mass (HRMS): Calcd.
1192.8673 for (M-2PF6)+ found 1192.8738 (M-2PF6 )+.
0
1
yield), mp 176 C. H NMR (CDCl3, 400 MHz): δ 11.56 (s,
1H), 8.56 (s, 1H), 8.38 (d, 2H, J = 8 Hz), 8.03 (d, 2H, J = 8
Hz), 7.65 (t, 2H, J = 8 Hz)), 7.53-7.46 (m, 4H), 7.38 (d, 2H,
J = 4 Hz), 6.77 (s, 2H), 5.57 (d, 1H, J = 8 Hz), 5.50 (d, 1H, J =
8 Hz), 5.29 (d, 1H, J = 4 Hz), 4.63 (m, 1H ), 2.29-0.60 (m,
43H); FTIR (KBr) ν cm-1: 2935, 1740, 1623, 1562, 1446;
HRMS (TOF MS ES+): calcd. 735.4884 (M-Cl-)+, found
735.4890 (M-Cl-)+.
Compound 6:
Compound 3:
The chloride salt 5 (0.2 g, 0.25 mmol) was dissolved in
MeOH (8 mL) containing 3% DMF and an aqueous solu-
tion of NH4PF6 (0.08 g, 0.5 mmol) was added under hot
condition. After stirring the mixture for 30 min, the pre-
cipitate was filtered and washed well with diethyl ether to
afforded pure compound 6 (0.18 g) in 81% yield, mp 158
To a solution of benzimidazole (0.75 g, 6.35 mmol) in dry
THF (25 ml), NaH (0.22 g, 9.53 mmol) was added at room
temperature. Then the solution was refluxed for 1h. The
solution was cooled to room temperature. Then benzyl
bromide (1.61 g, 9.53 mmol) in 10 mL of dry THF was add-
ed to the solution and the reaction mixture was further
refluxed for 2h. The solvent was removed under vacuum.
Then the reaction mixture was extracted with chloroform.
The organic solvent was dried over anhydrous Na2SO4 and
concentrated under vacuum. The residue was purified by
column chromatography using 25% ethyl acetate in petro-
leum ether as eluent to afford compound 12 in 84% yield
(1.11 g). Compound 12 was used directly in the next step.
Compounds 10 (0.33 g, 0.72 mmol) and 12 (0.1 g, 0.48
mmol) were taken in dry CH3CN (30 mL) containing 1%
DMF and the mixture was refluxed for 3 days. The precip-
itate appeared was filtered off and washed with diethyl
ether to have pure chloride salt 3 in 87% yield (0.28 g),
1
0C. H NMR (CDCl3, 400 MHz): δ 8.73 (s, 1H), 8.61 (s, 1H),
8.16 (d, 2H, J = 8 Hz), 8.05 (d, 2H, J = 8H), 7.63 (t, 2H, J =
8Hz), 7.57-7.45 (m, 6H), 6.50 (s, 2H), 5.30 (d, 1H, J = 8
Hz), 5.24 (d, 1H, J = 8 Hz), 5.08 (s, 1H), 4.54-4.52 (m, 1H),
2.89-0.59 (m, 43H); 13C NMR (CDCl3, 100 MHz): 164.7,
142.1, 138.8, 131.9, 131.2, 131.0, 129.7, 129.5, 128.7, 128.4, 127.6,
127.5, 125.7, 123.2, 122.2, 120.0, 113.6, 113.0, 76.7, 56.6, 56.1,
49.9, 47.8, 44.8, 42.2, 39.6, 39.5, 37.6, 36.7, 36.4, 36.1, 35.7,
31.8, 31.7, 28.2, 28.0, 27.3, 24.2, 23.8, 22.8, 22.5, 20.9, 19.2,
18.7, 11.8; FTIR (KBr) ν cm-1: 2952, 1752, 1668, 1559, 1483;
HRMS (TOF MS ES+): calcd. 735.4884 (M-PF6)+, found
735.4890 (M-PF6)+.
0
1
mp 184 C. H NMR (CDCl3, 400 MHz): δ 11.88 (s, 1H),
Compound 7:
7.65-7.60 (m, 1H), 7.59-7.54 (m, 3H), 7.48-7.46 (m, 2H),
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Langmuir
0.44 mmol) was added under hot condition. After stirring
To a solution of benzimidazole (0.58 g, 0.49 mmol) in dry
1
2
3
4
5
6
7
8
THF (25 ml), NaH (0.17 g, 7.37 mmol) was added at room
temperature. Then the solution was refluxed for 1h. The
solution was cooled to room temperature and butyl bro-
mide (0.99 g, 7.37 mmol) was added to it. The reaction
mixture was further refluxed for 4h. The solvent was re-
moved under vacuum. Then the reaction mixture was
extracted with ethyl acetate. The organic solvent was
dried over anhydrous Na2SO4 and concentrated under
vacuum. The residue mass was purified by column chro-
matography using 20% ethyl acetate in petroleum ether as
eluent to afford liquid compound 14 in 78% yield (0.67 g).
Compound 14 was used directly in the next step.
the mixture for 30 min, the precipitate was filtered and
washed well with diethyl ether to afford pure compound 9
0
1
(0.09 g) in 84% yield, mp 184 C. H NMR (d6-DMSO, 400
MHz): δ 9.02 (s, 1H), 8.92 (s, 1H), 8.35 (d, 2H, J = 8 Hz),
8.31-8.25 (m, 3H), 8.11 (d, 1H, J = 8Hz), 7.82-7.73 (m, 2H),
7.66-7.60 (m, 4H), 6.71 (s, 2H), 4.32 (t, 2H, J = 8 Hz), 1.68-
1.63 (m, 2H), 1.12-1.07 (m, 2H), 0.75 (t, 3H, J = 8 Hz); 13C
NMR (d6-DMSO, 100 MHz): 141.6, 132.2, 131.69, 131.63, 131.4,
130.9, 129.9, 128.8, 127.3, 127.4, 126.1, 123.8, 122.4, 114.7, 114.3,
46.8, 43.8, 31.1, 19.2, 13.6; Mass m/z (ES+): 365.3 [M-PF6]+;
Anal Calcd for C26H25F6N2P: C, 61.18; H, 4.94; N, 5.49,
Found: C, 61.22; H, 4.98; N, 5.51.
9
10
11
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13
14
15
16
17
18
19
20
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23
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25
26
27
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31
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35
36
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40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Compounds 10 (0.39 g, 0.85 mmol) and 14 (0.1 g, 0.57
mmol) were taken in dry CH3CN (30 mL) containing 1%
DMF and the mixture was refluxed for 3 days. Then the
solvent was evaporated under reduced pressure and
washed well with diethyl ether to have pure chloride salt
Gelation test and SEM imaging
The respective amounts of compounds 1-9 were dissolved
in desired solvents (1 mL) forming a homogeneous solu-
tion, slightly warmed and then allowed to cool slowly to
room temperature to form a gel. To study the effect of
anions, required amount of anionic solutions (in water)
were added to the DMSO solution of compounds 1-9. All
the gels were tested by an inversion of vial method. Sam-
ples of gels for SEM imaging were dried under vacuum
and then coated with a thin layer of gold metal.
0
1
7 in 86% yield (0.31 g), mp 208 C. H NMR (CDCl3, 400
MHz): δ 11.52 (s, 1H), 7.63-7.57 (m, 3H), 7.51-7.48 (m, 1H),
5.65 (d, 2H, J = 8 Hz), 5.31 (d, 1H, J = 4 Hz), 4.66-4.61 (m,
1H ), 4.49 (t, 2H, J = 8 Hz), 2.32-0.60 (m, 50H); FTIR (KBr)
ν cm-1: 2937, 1747, 1620, 1565, 1226.
Compound 8:
AFM measurements:
The chloride salt 7 (0.2 g, 0.31 mmol) was dissolved in
MeOH (8 mL) and an aqueous solution of NH4PF6 (0.1 g,
0.62 mmol) was added under hot condition. After stirring
the mixture for 30 min, the precipitate was filtered. Re-
peated crystallization of the precipitate by diethyl ether
afforded pure compound 8 (0.2 g) in 85% yield, mp 162 0C.
1H NMR (CDCl3, 400 MHz): δ 9.27 (s, 1H), 7.77-7.62 (m,
4H), 5.40 (d, 1H, J = 4 Hz), 5.28 (s, 2H), 4.75-4.72 (m, 1H ),
4.49 (t, 2H, J = 8 Hz), 2.42-0.69 (m, 50H); 13C NMR
(CDCl3, 100 MHz): 165.0, 142.2, 138.9, 131.7, 130.9, 127.6,
127.4, 123.2, 113.1, 76.7, 56.6, 56.1, 49.9, 47.77, 47.70, 42.3,
39.6, 39.5, 37.7, 36.8, 36.5, 36.1, 35.8, 31.8, 31.7, 30.7, 28.2,
28.0, 27.4, 24.2, 23.8, 22.8, 22.5, 21.0, 19.6, 19.2, 18.7, 13.3,
11.8 (one carbon in the aromatic region is unresolved);
FTIR (KBr) ν cm-1: 2945, 1749, 1621, 1573, 1231; HRMS (TOF
MS ES+): calcd. 601.4728 (M-PF6)+, found 601.4733 (M-
PF6)+.
Atomic Force Microscopy images were recorded under
ambient conditions using AFM (Veeco, Innova) operating
in the tapping mode. AFM samples were prepared by drop
casting a dilute solution of hydro gels on freshly cleaved
mica (Ted Pella) and dried cover slip was then put in a
vacuum desiccator overnight and the image then ana-
lyzed by Veeco SPM Lab Analysis software.
Dye adsorption experiment:
For this study, the gel of 2 [8 mg/ml] was prepared in 1:1
DMSO–H2O (v/v) solvent. On the top of the gel, 2 mL of
aqueous solutions of different dyes (c = 2 x 10-5 M) were
placed and the solutions were kept undisturbed for 24 h
at room temperature. The adsorption of dye during 24 h
with various time intervals was monitored by UV-vis
study. The removal efficiency (RE) of a dye64 from its
aqueous solution was estimated using UV-vis spectrosco-
py. The final concentration of the dye in solution was cal-
culated according to the Beer-Lambert law (A = εcl, A is
the absorbance of the dye at a certain absorption wave-
length in solution, ε is the molar extinction coefficient
and l is the path length of the incident light). The molar
extinction coefficients of Uranine, Rhodamine B, Rose
Bengal, Malachite Green and Crystal Violet dyes in their
aqueous solutions were calculated with l = 1.0 cm as 5.97 x
104, 9.22 x 104, 6.24 x 104, 1.27 x 104 and 3.12 x 104 respective-
ly. The final concentration of the dye in solution could be
obtained by the Beer-Lambert equation, which ultimately
determined the removal efficiency of the dye via the
equation as: RE = (Ci – Cf)/Ci, in which Ci represents the
initial concentration of the dye in solution; Cf is the final
concentration of the dye in the presence of adsorbing gel.
Compound 9:
Compound 13 (0.1 g, 0.32 mmol) was dissolved in dry
CH3CN (30 mL) containing 2% DMF and n-butyl bromide
(0.66 g, 0.48 mmol) was added to it. Then the reaction
mixture was refluxed for 3 days. During the course of the
reaction, n-butyl bromide was added at the time interval
of 1 day. After completion of the reaction precipitate ap-
peared was filtered off and washed with hexane to get
pure bromide salt 15 in 80% yield (0.11 g). 1H NMR (CDCl3,
400 MHz): δ 11.73 (s, 1H), 8.59 (s, 1H), 8.55 (d, 2H, J = 8
Hz), 8.08 (d, 2H, J = 8 Hz), 7.72-7.68 (m, 2H), 7.57-7.52
(m, 3H), 7.42 (t, 1H, J = 8Hz), 7.17 (t, 1H, J = 8 Hz), 6.98 (d,
1H, J = 8 Hz), 6.93 (s, 2H), 4.59 (t, 2H, J = 8 Hz), 2.05-2.00
(m, 2H), 1.46-1.40 (m, 2H), 1.25 (t, 3H, J = 8 Hz).
The bromide salt 15 (0.1 g, 0.22 mmol) was dissolved in
MeOH (8 mL) and an aqueous solution of NH4PF6 (0.03 g,
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Page 10 of 13
(7) Molina, P.; Tárraga, A.; Otón, F. Imidazole derivatives: A
General procedure for fluorescence and UV-vis titra-
tions
1
2
3
4
5
6
7
8
comprehensive survey of their recognition properties. Org.
Biomol. Chem., 2012, 10, 1711-1724.
(8) Sessler, J. L.; Gale, P. A.; Cho, W. S. Anion Receptor Chem-
istry, The Royel Society of Chemistry, Cambridge, UK,
2006.
(9) Fages, F. Low Molecular Mass Gelators, Topics in Current
Chemistry, Springer-Verlag, Berlin, 2005, vol. 256, pp. 283.
(10) Smith, D. K. Molecular Gels-Nanostructured Soft Materi-
als, in Organic Nanostructures, ed. J. L. Atwood, J.W.
Steed, Wiley-VCH, Weinheim, 2008.
(11) Jones, C. D.; Steed, J. W. Gels with sense: supramolecular
materials that respond to heat, light and sound. Chem. Soc.
Rev., 2016, 45, 6546-6596.
(12) van Esch, J. H.; Feringa, B. L. New Functional Materials
Based on Self-Assembling Organogels: From Serendipity
towards Design. Angew. Chem. Int. Ed. 2000, 39, 2263-
2266.
(13) Gale, P. A.; Busschaert, N.; Haynes, C. J. E.; Karagiannidis,
L. E.; Kirby, I. L. Anion receptor chemistry: highlights from
2011 and 2012. Chem. Soc. Rev., 2014, 43, 205-241.
(14) Babu, S. S.; Praveen, V. K.; Ajayaghosh, A. Functional π-
Gelators and Their Applications. Chem. Rev. 2014, 114, 1973-
2129.
(15) Svobodova, H.; N.oponen, V.; Kolehmainen, E.; Sievanen,
E. Recent advances in steroidal supramolecular gels. RSC
Adv. 2012, 2, 4985-5007.
(16) Vedhanarayanan, B.; Babu, B.; Shaijumon, M. M.;
Ajayaghosh, A. Exfoliation of Reduced Graphene Oxide
with Self-Assembled π-Gelators for Improved Electrochem-
ical Performance. ACS Appl. Mater. Interfaces, 2016,
DOI: 10.1021/acsami.6b09418.
Stock solution of the compounds 4 and 6 were prepared
in DMSO in the concentration of 1.0 x 10-5 M. Stock solu-
tions of anions were prepared in H2O in the concentration
of 4.0 x 10-4 M. Solution of respective compounds (2 mL)
were taken in the cuvette and to this solution different
anions were individually added in different amounts. Up-
on addition, the change in emission of the compounds
was recorded. The same stock solutions were used to per-
form the UV-vis titration experiment in the same way.
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I-V measurements
The gel was drop casted on separate cupper electrodes of
a cell having gap of 50 µm between them and then al-
lowed to dry in air overnight. The I-V measurement of the
cell containing the dried gel was performed under dynam-
ic vacuum by adopting the two probe 4-wire measure-
ment (as shown below) using a Keithely 2400 source me-
ter.
Supporting Information
Gelation results, Time-dependent UV–vis spectra of dyes,
1
emission and absorption spectra, FTIR and H NMR spec-
1
tra, Job plot, binding curves, and copies of H, 13C NMR
and HRMS.
AUTHOR INFORMATION
Corresponding Author
(17) Geiger, C.; Stanescu, M.; Chen, L.; Whitten, D. G. Organo-
gels Resulting from Competing Self-Assembly Units in the
Gelator:ꢀ Structure, Dynamics, and Photophysical Behavior
of Gels Formed from Cholesterol−Stilbene and Cholester-
ol−Squaraine Gelators. Langmuir 1999, 15, 2241-2245.
(18) Wang, R.; Geiger, C.; Chen, L.; Swanson, B.; Whitten, D. G.
Direct Observation of Sol−Gel Conversion:ꢀ The Role of the
Solvent in Organogel Formation. J. Am. Chem. Soc. 2000,
122, 2399-2400.
(19) Manouras, T.; Vamvakaki, M. Field responsive materials:
photo-, electro-, magnetic- and ultrasound-sensitive poly-
mers. Polym. Chem., 2017, 8, 74-96.
(20) Functional Hybrid Materials, ed. P. G. Romero, C. Sanchez,
Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim, 2004.
(21) Tam, A. Y. Y.; Yam, V. W. W. Recent advances in metallo-
gels. Chem. Soc. Rev., 2013, 42, 1540-1567.
(22) Sangeetha, N. M.; Maitra, U. Supramolecular gels: Func-
tions and uses. Chem. Soc. Rev., 2005, 34, 821-836.
(23) Bhattacharya, S.; Samanta, S. K. Soft-Nanocomposites of
Nanoparticles and Nanocarbons with Supramolecular and
Polymer Gels and Their Applications. Chem. Rev. 2016, 116,
11967-12028.
(24) Busschaert, N.; Caltagirone, C.; Rossomand, W.V.; Gale, P.
A. Applications of Supramolecular Anion Recognition.
Chem. Rev., 2015, 115, 8038-8155.
(25) Zhang, Y.; Kuang, Y.; Gao, Y.; Xu, B. Versatile Small-
Molecule Motifs for Self-Assembly in Water and the For-
mation of Biofunctional Supramolecular Hydrogels. Lang-
muir, 2011, 27, 529-537.
(26) Li, Y.; Rodrigues, J.; Toma´s, H. Injectable and biodegrada-
ble hydrogels: gelation, biodegradation and biomedical ap-
plications. Chem. Soc. Rev., 2012, 41, 2193-2221.
* Email: ghosh_k2003@yahoo.co.in
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENT
We thank DST, West Bengal, for financial support under
the project (sanc. No. 755(Sanc.)/ST/P/S&T/4G-3/2014
dated 27.11.2014). SP thanks CSIR, New Delhi, India for a
fellowship.
REFERENCES
(1) Blondeau, P.; Segura, M.; Fernandez, R. P.; de Mendoza, J.
Molecular recognition of oxoanions based on guanidinium
receptors. Chem. Soc. Rev., 2007, 36, 198-210.
(2) Schrader, T.; Maue, M. Ammonium, Amidinium, Guani-
dinium, and Pyridinium Cation from Functional Synthetic
Receptors, Wiley-VCH Verlag GmbH & Co. KGaA, 2005,
pp: 111–164.
(3) Conley, M. P.; Valero, J.; de Mendoza, J. Guanidinium-
Based Receptors for Oxoanions. Supramolecular Chemistry:
From Molecules to Nanomaterials, John Wiley & Sons, 2012.
(4) Kubik, S. Anion recognition in water. Chem. Soc. Rev.,
2010, 39, 3648-3663.
(5) Ghosh, K.; Sarkar, A. R.; Sarkar, T.; Panja, S.; Kar, D. Pro-
gress of 3-aminopyridinium-based synthetic receptors in
anion recognition. RSC Adv. 2014, 4, 20114-20130.
(6) Gilday, L. C.; Robinson, S. W.; Barendt, T. A.; Langton, M.
J.; Mullaney, B. R.; Beer, P. D. Halogen Bonding in Supra-
molecular Chemistry. Chem. Rev. 2015, 115, 7118-7195.
(27) Busseron, E.; Ruff, Y.; Moulin, E.; Giuseppone, N. Supramo-
lecular self-assemblies as functional nanomaterials. Na-
noscale, 2013, 5, 7098-7140.
ACS Paragon Plus Environment

Page 11 of 13
Langmuir
(28) Shen, X.; Zhu, L.; Wang, N.; Y, Lei.; H, Tang. Molecular
en by squaric acid: synthesis, characterization and dye ad-
1
2
3
4
5
6
7
8
imprinting for removing highly toxic organic pollutants.
Chem. Commun., 2012, 48, 788-798.
(29) Okesola, B. O.; Smith, D. K. Applying low-molecular
weight supramolecular gelators in an environmental set-
ting–self-assembled gels as smart materials for pollutant
removal. Chem. Soc. Rev., 2016, 45, 4226-4251.
sorption. J Porous Mater, 2016, 23, 663-669.
(45) Adhikari, B.; Palui, G.; Banerjee, A. Self-assembling tripep-
tide based hydrogels and their use in removal of dyes from
waste-water. Soft Matter, 2009, 5, 3452-3460.
(46) Chakraborty, P.; Roy, B.; Bairi, P.; Nandi, A. K. Improved
mechanical and photophysical properties of chitosan in-
corporated folic acid gel possessing the characteristics of
dye and metal ion absorption. J. Mater. Chem., 2012, 22,
20291-20298.
(47) Ghosh, K.; Panja, S. Cholesterol–based Bisamides on Bi-
phenyl Backbone: A Case of Selective Visual Sensing of F−
and H2PO4− through Breaking and Making of Gels. Chemis-
try Select, 2016, 1, 3667-3674.
(30) Ghosh, K.; Kar, D.; Sahu, D.; Ganguly, B. Benzimidazolium-
−
based chemosensors: selective recognition of H2PO4 ,
HP2O73−, F− and ATP through fluorescence and gelation
studies. RSC Adv. 2015, 5, 46608-46616.
9
(31) Kumari, N.; Jha, S.; Bhattacharya, S. olorimetric Probes
Based on Anthraimidazolediones for Selective Sensing of
Fluoride and Cyanide Ion via Intramolecular Charge Trans-
fer. J. Org. Chem., 2011, 76, 8215-8222.
(32) R. Li,; S. Wang, Li, Q.; Lan, H.; Xiao, S.; Li, Y.; Tan, R.; Yi,
T. A fluorescent non-conventional organogelator with ge-
lation-assisted piezochromic and fluoride-sensing proper-
ties. Dyes and Pigments, 2017, 137,111-116.
(33) Lee, D. Y.; Singh, N.; Kim, M. J.; Jang, D. O. Chromogenic
and Fluorescent Recognition of Iodide with a Benzimidaz-
ole-Based Tripodal Receptor. Org. lett., 2011, 13, 3024-3027.
(34) Yan, G.; Wu, G.; Qu, W.; Shi, B.; Lin, Q.; Yao, H.; Zhang, Y.;
Wei, Taibao, W. A reversible dual-channel chemosensor
for fluoride anion. Supramol. Chem., 2015, 27, 552–558.
(35) Kaur, N.; Dhaka, G.; Singh, J. Hg2+-induced deprotonation
of an anthracene-based chemosensor: set–reset flip-flop at
the molecular level using Hg2+ and I- ions. New J. Chem.,
2015, 39, 6125-6129.
(36) Ma, X.; Zhang, J.; Tang, N.; Wu, J. A thermo-responsive
supramolecular organogel: dual luminescence properties
and luminescence conversion induced by Cd2+. Dalton
Trans., 2014, 43, 17236-17239.
(37) Dhinakaran, M. K.; Soundarajan, K.; Das, T. M. Synthesis of
novel benzimidazole-carbazole-N-glycosylamines and their
self-assembly into nanofibers. New J. Chem., 2014, 38, 4371-
4379.
(38) Weng, W.; Beck, J. B.; Jamieson, A. M.; Rowan, S. J. Under-
standing the Mechanism of Gelation and Stimuli-
Responsive Nature of a Class of Metallo-Supramolecular
Gels. J. Am. Chem. Soc. 2006, 128, 11663-11672.
(39) Yao, H.; Wu, H. P.; Chang, J.; Lin, Q.; Wei, T. B.; Zhang, Y.
M. A carboxylic acid functionalized benzimidazole-based
supramolecular gel with multi-stimuli responsive proper-
ties. New J. Chem., 2016, 40, 4940-4944.
(40) Ganta, S.; Chand, D. K. Nanoscale metallogel via self-
assembly of self-assembled trinuclear coordination rings:
multi-stimuli-responsive soft materials. Dalton Trans.,
2015, 44, 15181-15188.
(41) Yao, H.; You, X. M.; Lin, Q.; Li, J. J.; Guo, Y.; Wei, T. B.;
Zhang, Y. M. Multi-stimuli responsive metal-organic gel of
benzimidazol-based ligands with lead nitrate and their use
in removal of dyes from waste-water. Chinese Chem. Lett.,
2013, 24, 703-706.
(42) Dey, A.; Mandal, S. K.; Biradha, K. Metal–organic gels and
coordination networks of pyridine-3,5-bis(1-methyl-
benzimidazole-2-yl) and metal halides: self sustainability,
mechano, chemical responsiveness and gas and dye sorp-
tions. Cryst. Eng. Comm, 2013, 15, 9769-9778.
(43) Zhang, Y. M.; You, X. M.; Yao, H.; Guo, Y.; Zhang, P.; Shi,
B. B.; Liu, J.; Lin, Q.; Wei, T. B. A silver-induced metal-
organic gel based on biscarboxyl-functionalised benzimid-
azole derivative: stimuli responsive and dye sorption. Su-
pramol. Chem., 2014, 26, 39-47.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(48) Ghosh, K.; Panja, S. Coumarin-based supramolecular gela-
tor: a case of selective detection of F− and HP2O7 RSC
3−
Adv., 2015, 5, 12094-12099.
(49) Ghosh, K.; Panja, A.; Panja, S. Cholesterol appended bis-
1,2,3-triazoles as simple supramolecular gelators for the
naked eye detection of Ag+, Cu2+ and Hg2+ ions. New. J.
Chem., 2016, 40, 3476-3483.
(50) Ghosh, K.; Panja, S. Naphthalene-cholesterol conjugate as
simple gelator for selective sensing of CN– ion. Supramol.
Chem. 2017, 29, 350-359.
(51) Ghosh, K.; Kar, D.; Panja, S.; Bhattacharya, S. Ion conduct-
ing cholesterol appended pyridinium bisamide-based gel
for the selective detection of Ag+ and Cl− ions. RSC Adv.,
2014, 4, 3798-3803.
(52) Ghosh, K.; Kar, D.; Panja, A.; Petsalakis, I. D.; Theodora-
kopoulos, G. Benzimidazolium-based new simple rati-
ometric fluorescent sensor for selective detection of Dihy-
drogenphosphate. Supramol. Chem., 2014, 26, 856-863.
(53) Ghosh, K.; Saha, I.; Frohlich, R.; Patra, A. Selective Sensing
of Fumarate Over Maleate by Benzimidazolium – Based
Fluororeceptors. Mini-Rev.Org. Chem. 2011, 8, 31-37.
(54) Yoon, J.; Kim, S. K.; Singh, N. J.; Kim, K. S. Imidazolium
receptors for the recognition of anions. Chem. Soc. Rev.,
2006, 35, 355-360.
(55) Vickers, M. S.; Beer, P. D. Anion templated assembly of
mechanically interlocked structures. Chem. Soc. Rev., 2007,
36, 211-225.
(56) Hess, A. E.; Beer, P. D. Chelated charge assisted halogen
bonding enhanced halide recognition by a pyridinium-
iodotriazolium axle containing [2]rotaxane. Org. Biomol.
Chem., 2016, 14, 10193-10200.
(57) Caballero, A.; Bennett, S.; Serpella, C. J.; Beer, P. D. Iodo-
imidazolium salts: halogen bonding in crystals and anion-
templated pseudorotaxanes. CrystEngComm, 2013, 15,
3076-3081.
(58) Wang, B.; Qin, L.; Mu, T.; Xue∥, Z.; Gao, G. Chem. Rev.,
2017, DOI:10.1021/acs.chemrev.6b00594.
(59) Thomas, P. C.; Cipriano, B. H.; Raghavan, S. R. Nanoparti-
cle-crosslinked hydrogels as a class of efficient materials
for separation and ion exchange. Soft Matter, 2011, 7, 8192-
8197.
(60) Wei, T. –B.; W. –T. Li.; Li, Q.; Su, J. –X.; Qu, W. –J.; Lin, Q.;
Yao, H.; Zhang, Y. –M. A turn-on fluorescent chemosensor
selectively detects cyanide in pure water and food sample.
Tetrahedron Lett., 2016, 57, 2767-2771.
(61) Chou, P. T.; Wu, G. R.; Wei, C. Y.; Cheng, C. C.; Chang, C.
P.; Hung, F. T. Excited-State Amine−Imine Double Proton
Transfer in 7-Azaindoline. J. Phys. Chem B. 2000, 104, 7818-
7829.
(62) Ghosh, K.; Panja, S.; Bhattacharya, S. Naphthalene linked
pyridyl urea as a supramolecular gelator: a new insight into
naked eye detection of I- in the gel state with semiconduct-
ing behaviour. RSC Adv., 2015, 5, 72772-72779.
(44) Hu, A. B.; Zhou, H.; Pan, Z. Q.; Cheng, Q. R. Hybrid gels of
Bis(benzimidazole)-base ligand with perchlorate salts driv-
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(63) Ghosh, K.; Kar, D.; Bhattacharya, S. Fluoride – responsive
1
2
3
4
5
6
7
hydrogel of cholesterol appended pyridinium urea and its
metal detecting ability and semi conducting behavior. Su-
pramol. Chem. 2014, 26, 313-320.
(64) Zhang, X.; Song, J.; Ji, W.; Xu, Ning.; Gao, N.; Zhang, X.; Yu,
H. Phase-selective gelators based on closed-chain glucose
derivatives: their applications in the removal of dissolved
aniline/nitrobenzene, and toxic dyes from contaminated
water. J. Mater. Chem. A, 2015, 3, 18953 – 18962.
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Langmuir
GRAPHICAL ABSTRACT
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Cholesterol appended benzimidazolium salts: synthesis, aggregation,
sensing, dye adsorption and semiconducting properties
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Santanu Panja, Subhratanu Bhattacharya and Kumaresh Ghosh*
Structure - property
relationship
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We report the design, synthesis and gelation behavior of a series of cholesterol
linked benzimidazolium salts 1-9. While the bisbenzimidazolium salt 2 forms gel
Fꢀ sensing
N
N
in DMSO:H2O (1:1, v/v) itself, under similar conditions mono benzimidazolium
salts 4 and 6 exhibit gelation in the presence of F- ions and validate the visual
sensing of F-. As application, the gel phase of 2 efficiently removes toxic dyes from
waste water. Furthermore, all the gels show thermally activated semiconducting
property within a wide voltage window.
Semiconducting
property
H
Aromatic
surface
Cholesteryl
unit
Hydrogen
bonding site
Fꢀ
Sol
Dye adsorption
Gel
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13
ACS Paragon Plus Environment