Synthesis, characterization and applications of imidazolium ionic liquid-tagged zinc(II) complex

Article abstract of DOI:10.1016/j.ica.2018.04.001

A multi-functional zinc(II) complex of an imidazolium ionic liquid-tagged ligand was synthesized and characterized. The DSC and TGA analysis showed the thermal stability of the complex. The complex showed emission λ_max at 368–467 nm with quantu

Full text of DOI:10.1016/j.ica.2018.04.001

Accepted Manuscript
Research paper
Synthesis, Characterization and Applications of Imidazolium Ionic Liquid-tag-
ged Zinc(II) Complex
Pankaj Nehra, Bharti Khungar, Rajnish P. Singh, S.C. Sivasubramanian, Prabhat
N. Jha, Vaishali Saini
PII:
S0020-1693(17)31800-5
https://doi.org/10.1016/j.ica.2018.04.001
ICA 18192
DOI:
Reference:
Inorganica Chimica Acta
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Received Date:
Revised Date:
Accepted Date:
15 December 2017
1 April 2018
2 April 2018
Please cite this article as: P. Nehra, B. Khungar, R.P. Singh, S.C. Sivasubramanian, P.N. Jha, V. Saini, Synthesis,
Characterization and Applications of Imidazolium Ionic Liquid-tagged Zinc(II) Complex, Inorganica Chimica
Acta (2018), doi: https://doi.org/10.1016/j.ica.2018.04.001
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Synthesis, Characterization and Applications of Imidazolium Ionic
Liquid-tagged Zinc(II) Complex
Pankaj Nehraa, Bharti Khungara*, Rajnish P. Singhb, S. C. Sivasubramaniana, Prabhat N. Jhab, Vaishali
Sainia
aDepartment of Chemistry, Birla Institute of Technology and Science Pilani, Pilani Campus, Rajasthan-
333031, India
bDepartment of Biological Sciences, Birla Institute of Technology and Science Pilani, Pilani Campus,
Rajasthan-333031, India, email: bhartikh@gmail.com
Keywords Ionic liquid, antimicrobial activity, DNA cleavage, catalyst, recycling.
Abstract
A multi-functional zinc(II) complex of an imidazolium ionic liquid-tagged ligand was
synthesized and characterized. The DSC and TGA analysis showed the thermal stability of the
complex. The complex showed emission max at 368-467 nm with quantum yields up to 0.06.
The time-resolved fluorescence study revealed enhancement in lifetime on complexation with
zinc(II) ion indicating conformational rigidity. The complex showed good DNA cleavage,
antifungal and antibacterial activities against Gram +ve and Gram –ve bacteria. The complex
was found to be a good catalyst for the reaction of aromatic aldehydes and indole substrates in
water to synthesize bis(indolyl)methanes.
1. Introduction

Zinc has an important role [1] in many biological activities and zinc(II) complexes are
extensively investigated due to their thermal stability and structural diversity. Zinc(II)
complexes are known for applications in luminescent materials [2], biosensors and as drugs.
Emission spectroscopy of the zinc(II) complexes can be studied easily due to the change in the
fluorescence intensity of organic fluorophores [3-6]. Various zinc(II) complexes have been
screened for their biological applications [7, 8]. The DNA cleavage activities of cis and trans
forms of the azobenzene-linked dizinc complex were studied and the cis form exhibited
hydrolytic DNA cleavage activity, whereas the trans form was negligibly active [9]. Salophen
Zn(II) complexes were studied for their interaction with plasmid DNA. The Lewis acid
character of the complexes and the presence of electron-withdrawing substituents increased the
electrophilic character of the metal center that generated the strongest substituent effect on DNA
interaction [10]. (E)-N-(pyridin-2-ylmethylene)arylamine ligands based water-soluble Zn(II)
complexes largely interacted with DNA and ceased the growth of tumour cells [11].
Functionalized salphen zinc(II) complexes were determined towards their DNA interaction
studies with the help of linear dichroism, gel electrophoresis and PCR techniques [12]. A series
of water-soluble Zn(II) complexes, prepared from [N, Nʹ-bis{5-[(triphenyl phosphonium
chloride)-methyl]salicylidine}-3,4- diaminopyridine] ligand, was found highly efficient towards
DNA binding and cleavage activity [13]. An acetato-bridged trinuclear zinc(II) complex was
synthesized and screened towards its DNA cleavage activity. The complex was found to be
effective towards the cleavage of double-stranded DNA. The complex also showed significant
cytotoxicity against a human hepatocarcinoma cell line [14]. Schiff bases form an important
group of ligands and are widely used for complexation with several transition elements [15, 16].
They are studied for their electronic properties [17, 18], catalytic activity [19, 20] and biological

applications [21]. Furthermore, Schiff base ligands, commonly containing a π-conjugated
system can coordinate to various metal ions, thereby altering the properties [22, 23]. Schiff base
metal complexes are also known for their wide spectrum antimicrobial [24, 25] and DNA
cleaving activities [26, 27].
Indole fragments such as bis(indolyl)methanes (BIMs) are an important class of compounds,
which have a wide range of biological and pharmaceutical applications [28, 29]. Condensation
of indole derivatives with carbonyl compounds leads to the formation of BIMs and a variety of
reports are accessible where a range of catalysts viz. CuBr2, I2, CAN, NBS, InCl3, In(OTf)3 and
BF3 are employed [30, 31]. Few limitations are associated with these methodologies including,
the use of volatile organic solvents, toxic reagents, tedious workup, poor yields etc. and
therefore advanced and improved methods to synthesize (BIMs) in laboratories are being
developed [32, 33]. A cis-Dioxomolybdenum (VI) complex and a magnetic nanoparticles-
supported Cu-isatin Schiff base were found to be efficient and recyclable catalysts in the
synthesis of bis(indolyl) methanes [34, 35]. Adding together to this work and in continuation of
our efforts in aqueous catalysis [36], the synthesized zinc complex was used as a catalyst for the
synthesis of bis(indolyl)methanes in water.
Experimental section
Materials and methods
All the reagents (reagent grade) and solvents (analytical grade) were purchased from
Spectrochem, Avra, Himedia, Sigma-Aldrich and Merck India. The reagents were used without
additional purification and the solvents were dried and distilled before use. The melting points
were obtained in open capillary tubes on an MPA120 automated melting point apparatus and are

uncorrected. The IR spectra were recorded on ABB Bomen MB 3000 FTIR spectrophotometer
using KBr pellets and the electronic spectra were recorded on U.V-vis Shimadzu U.V-2450
spectrometer. The mass spectra were recorded on AB SCIEX TOF/TOF 5800 spectrometer. The
13
1H and C NMR spectra were recorded on a Bruker Ascend TM 400 MHz spectrometer using
CDCl3 and DMSO-d6 as solvents and the chemical shifts are expressed in ppm. Powder X-ray
diffraction (XRD) data with Cu Kα radiation, were obtained on a Rigaku Miniflex II
diffractometer and the diffraction patterns were recorded over a range of 2θ angles from 10 to
50°. DSC was recorded on Perkin Elmer DSC 4000 at a heating rate of 10C min-1 using
nitrogen as the carrier gas in the range 30C to 400C. Thermogravimetric analysis was
performed on Perkin Elmer TGA 4000 in the presence of nitrogen flow at a linear heating of
10C min-1 starting from 30°C to 400C. Steady-state fluorescence measurements were
executed on Horiba Jobin Yvon Fluoromax-4 scanning spectrofluorimeter. The quartz cuvettes
of 1 cm path length, excitation and emission slit widths of 3 nm were used for the spectral
measurements. Fluorescence quantum yields of the zinc(II) complex were estimated at room
temperature for a variety of solvents by a relative method using quinine sulfate ( = 0.55 in 0.1
N H2SO4), as the secondary standard using the following equation:
Where I is the area under the curve, Φ is the fluorescence quantum yield, is the refractive
index of the medium, OD denotes absorbance at the wavelength of exciting light and the
subscripts S and R stand for the parameters of studied sample and reference, respectively.

The excited singlet state lifetimes were measured from intensity decays using a Horiba Jobin
Yvon Fluorocube-01-NL picosecond time-correlated single-photon counting (TCSPC)
experimental setup. A picosecond diode laser of 400 nm (NanoLED 400L, IBH, UK) was used
as an excitation light source. A TBX photon detection module (TBX-07C) was used for the
detection of fluorescence signals at magic angle (54.7°) polarization. The decays were analyzed
using IBH DAS-6 decay analysis software. The fineness of the fits was judged by the
criterion. Average fluorescence lifetime for the multi exponential decay curve was obtained
from the decay time constants and pre-exponential factors using the following equation:
Where is the pre-exponential factor corresponding to the ith decay time constant τi.
Synthesis of imidazolium ionic liquid-tagged ligand (1). Imidazolium ionic liquid-tagged
Schiff base ligand 1 was synthesized according to our previously reported method [36, 37]. A
100 mL round bottom flask was charged with 1, 3-dibromopropane (8.0 mmol), 2,4-
dihydroxybenzaldehyde (6.0 mmol) and sodium bicarbonate (6.0 mmol) in acetone (50 mL) and
was heated at 60C for 60 h. The product 4-(3-bromopropoxy)-2-hydroxybenzaldehyde was
isolated in 65% yield. This synthesized product (3.5 mmol) was treated with 1-methylimidazole
(3.5 mmol) and was stirred at 80C for 10 h. This viscous liquid obtained was washed with a
diethyl ether-ethyl acetate mixture to give the imidazolium ionic liquid-tagged aldehyde in
almost quantitative yield. The product obtained (3.0 mmol) was reacted with p-methoxy aniline
(4.0 mmol) in ethanol (15 mL) and refluxed for 4 h. After the completion of the reaction, the
solid product formed was filtered off and washed with cold ethanol. The crude product was
purified by recrystallization from ethanol-ethyl acetate (3:1 v/v) with 85% yield.

Synthesis of imidazolium ionic liquid-tagged zinc(II) complex (2). The ligand 1 (600 mg, 2.0
mmol) was stirred with ethanol in a 25 mL round bottom flask for 15 minutes, zinc acetate
tetrahydrate (148 mg, 1.0 mmol) was added to the resultant solution, and the mixture was
refluxed for 4 hours until the product precipitated completely. After cooling for 20 minutes the
product 2 was separated by simple filtration and recrystallized from a mixture of petroleum
ether (5 mL) and methanol (20 mL).
General procedure for the synthesis of bis(indolyl)methanes
A mixture of indole derivative (2.0 mmol), aromatic aldehyde (1.0 mmol) and 2 (3 mol%) as a
catalyst in water (5 mL) was stirred at 85C temperature for 6-8 h. The progress of the reaction
was continuously monitored by TLC. After completion of the reaction, the product was
extracted in ethyl acetate and purified by column chromatography over silica gel (mesh
100−200) using n-hexane/ethyl acetate as an eluent. The isolated products were analyzed by 1H
and 13C NMR spectroscopy.
Biological activity
In vitro antibacterial assay of 2 was evaluated by agar-well diffusion method following the
standard protocol [38]. The cultures of Gram-positive bacteria Staphylococcus aureus, Bacillus
cereus and Gram-negative bacteria Escherichia coli, Klebsiella pneumoniae were freshly
inoculated into sterile LB broth and suspension was adjusted to 1.5 × 108 CFU/mL. Autoclaved
Muller–Hilton agar medium was poured into glass petri plates and swabbed with 100 µl
inoculum of each organism. After the adsorption, well of 9 mm diameter was made by the
sterile metallic borer. 2 was dissolved in DMSO and added to well at 50 and 100 µg/mL
concentration using sterile pipettes. All the plates were incubated at 37C for 18-24 h.
Antibacterial activity of 2 was evaluated by measuring the zone of inhibition with zone reader

(Antibiotic zone scale). DMSO was used as a negative control to evaluate the solvent effect on
the tested pathogens, whereas chloramphenicol (16 µg/mL) was used as a positive control. MIC
values were evaluated at 6.25, 12.5, 25, 50, 100, and 200 µg/mL concentration using broth
microdilution method. A set of tubes containing Luria-Burtani broth medium with different
concentrations of 2 were prepared. The tubes were inoculated with bacterial cultures 1.5 × 108
CFU/mL and incubated on a rotary shaker (180 rpm) at 37C for 18-24 h.
In vitro antifungal assay of 2 was determined by agar-well diffusion method against Fusarium
oxysporum, Fusarium graminearum, Fusarium moniliforme and Penicillium citrinum at varying
concentrations [39]. For the experimental work, potato dextrose agar was freshly prepared and
autoclaved at 121C at 15 psi for 15 min. After cooling to room temperature, 100 µL of fungal
inoculum was uniformly spread on the plate. Following the adsorption of inoculum, well of 9
mm diameter was prepared by the sterile metallic borer and the solution of 2 at 50 and 100
µg/mL concentration was added to the wells. Plates were incubated at 28C for 4 days under
dark conditions. The experiments were performed in duplicates.
MIC assay of 2 was performed at 6.25, 12.5, 25, 50, 100, and 200 µg/mL concentrations. Tubes
containing 10 mL of sterilized czapekdox broth medium was inoculated with 100 µl of freshly
grown culture. An appropriate amount of 2 was added to achieve the desired concentrations.
The tubes were incubated at 28°C for 4 days under dark conditions and observed for the
presence of visible turbidity. Broth without 2 was used as control [39].
The DNA cleavage activity of 2 was studied using 1% agarose gel electrophoresis. Supercoiled
plasmid pUC19 DNA (2 µL) was mixed with varying concentrations of 2 (10 - 100 µM) and the
total volume was maintained up to 18 µL with 50 mM Tris buffer (pH 7.4). The mixture was
incubated at 37°C. Similarly, another set of the mixture was incubated at different time intervals

from 1-4 h using DMSO as a solvent. Before performing the gel electrophoresis, the samples
were mixed with loading buffer containing 25% bromophenol blue, 0.25% xylene cyanol and
30% glycerol. Each sample (4 µL) was loaded into 1 w/v% agarose gel for 40 min at 60 V in
Tris-acetate-EDTA buffer (TAE) buffer. The gel was stained with ethidium bromide for 5 min
after electrophoresis and then photographed under UV light in Gel doc system (Bio-rad) [40].
Results and Discussion
Synthesis and Characterization
Imidazolium ionic liquid-tagged Schiff base 1 (Scheme 1) was synthesized in almost
quantitative yield as reported earlier by our group [37]. For the synthesis of 2, the Schiff base
obtained was mixed with zinc acetate tetrahydrate and refluxed in ethanol for 4 h.
Scheme 1: Synthesis of 2
The structures of 1 and 2 were confirmed by IR, NMR spectroscopy and mass spectrometry.
The FT-IR spectrum of 1 exhibited absorption bands at 1612 cm−1 (C=N stretch) and 3466 cm−1
1
(O-H stretch). In the H NMR spectrum of 1, a signal representing the azomethine proton
(CH=N) appeared at δ 8.87, and the hydroxyl proton resonated at δ 13.86. Signals
13
corresponding to other protons and C NMR were also revealing the structure of 1. In the IR
spectra of 2, the azomethine peak shifted towards lower frequency (1598 cm-1) and O-H peak
disappeared from the spectrum. The azomethine proton signal of 2 appeared at δ 8.37 and there

was no signal nearby δ 13-14. These spectral inferences indicated the complexation of 1 with
the zinc metal (supporting information Figure 1, 2 and 3).
The MALDI mass spectrum of 2
showed a peak at 793.35 corresponding to [M - H -2Br]+
ion. The presence of zinc ion was indicated in terms of M (793.35), M+2 (795.34) and
M+4 (797.35) isotopic peaks and their intensities; also M+1, M+3 and M+5 isotopic peak
corresponding to the number of carbon atoms of the complex were evident. (supporting
information Figure 4). The powder XRD patterns indicated crystalline nature for both 1 and 2.
In the XRD pattern of 2, the appearance of new peaks indicated the presence of zinc(II). No
significant changes were observed in the powder XRD of 2 after heating at 200°C for 2 hours,
showing its stability (supporting information Figure 5). The thermal stabilities of 1 and 2 were
determined by DSC and thermogravimetric analysis (TGA) under a nitrogen atmosphere. In the
DSC scan of 1, a sharp endothermic peak corresponding to the melting point was observed at
151°C. In case of 2, the melting peak was observed at 322°C suggesting good thermal stability
in contrast to 1. The TGA of 2 did not show any specific loss in weight up to 200°C, indicating
the absence of both crystal and coordinated water molecules (supporting information Figure 6).
The single crystal could not be obtained in spite of our repeated efforts, also in literature single
crystal X-ray studies are not reported for large size ionic liquid-based complexes [41, 42].
Based on the characterization reported above, the proposed structure can be confirmed by the
following facts. Hydroxyl peak shown in the IR spectra of the ligand is missing in the complex
1
indicating complexation of zinc ion through oxygen atom. In the H NMR spectra of complex,
the disappearance of OH signal indicates the same. Moreover, the absence of extra proton
signals indicates non-existence of any other ligand around Zn centre. From the MALDI mass
spectrum, the presence of zinc ion and number of carbon atoms of the complex is evident. From

the above-stated facts, we are not able to justify a coordination number more than four for zinc.
The geometry is expected to be tetrahedral as shown by similar systems [43-45]. The distorted
tetrahedral geometry may be undergoing a transition five coordinated state during the catalytic
cycle.
Photophysical properties
The photophysical properties of 1 and 2 were thoroughly studied by UV/vis, steady state and
time-resolved fluorescence spectroscopy. The electronic spectra of 1 and 2 in distilled DMSO
exhibited two absorption bands at 305 nm and 380 nm due to the π–π* and n–π* transitions
respectively. In solid state, these bands appeared at 426 nm and 335 nm. The solution state U.V.
spectra was monitored while taking a 10µmolar concentration of each sample at room
temperature. On complexation with zinc metal hypsochromic shift was observed, resulting in
the appearance of bands at 275 nm and 343 nm in DMSO and at 403 nm and 318 nm in the
solid state (supporting information Figure 7).
Metal ion competition studies
To investigate the fluorescent selectivity of the imidazolium ionic liquid-tagged Schiff base
ligand 1 for various transition metal ions the fluorescence spectra of 1 with some metal salts
[Cu(II), Co(II), Ni(II) and Zn(II)] were recorded in acetonitrile at a concentration of 0.1µM and
by excitation at 380 nm. It can be seen clearly from Figure 1 that the Zn(II) ion enhances the
fluorescence intensity significantly as compared to the other metal ions.

Figure 1. Steady-state fluorescence of 1 and 2
The absorption and emission spectra of 2 were recorded in different solvents (Figure 2). The
quantum yields of 2 in various solvents and at different excitations are summarized in Table 1.
Table 1. Photophysical data of 2a
S. No. Solvent
λmax, abs, nm (ɛ, 1 x 10-5 M-1 cm-1)
λex, nm
λem,
nm
425
430
Quantum yield,
Φem (solution, r.t.)a
0.05
1.
2.
DMSO
Water
348 (0.34), 284 (0.21)
280
350
0.003
410 (0.10), 322 (0.11), 280 (0.17)
400
325
280
467
368
420
0.05
0.008
0.02
3.
4.
Ethanol
343 ( 0.32), 280 (0.24)
350
344
0.006
Acetonitrile 385 (0.33), 294(0.11)
350
380
446
430
0.06
0.02
aQuantum yields were measured relative to quinine sulfate in 0.1 N H2SO4 (Φem = 0.55). All
data were measured at 298 K.

Figure 2. Absorption and emission spectra of 2
The lifetime was measured by time-correlated single photon counting of 1 and 2. The increase
in a lifetime from 0.3 ns for 1 to 0.8 ns for 2 (Figure 3) indicated an enhancement in
conformational rigidity on complexation with Zn(II).
Figure 3. Time-resolved fluorescence decay of 1 and 2, fluorescence was monitored at 385 nm.
Biological evaluation
The zone of inhibition (ZIC) and minimum inhibitory concentration (MIC) values were
measured to evaluate the antibacterial and antifungal efficiency of 2. It exhibited moderate to
good antibacterial activity against the tested bacterial strains and is comparable to a standard
drug. The maximum zone of inhibition was 18 mm in case of Gram +ve bacteria (MIC value of

12.5 µg/mL), whereas it was 19 mm against the tested Gram –ve bacterial strains (MIC value in
the range of 12.5 to 6.25 µg/mL) (Table 2, Figure 4). It was observed that 2 was active in the
range of 25-50 µg/mL to inhibit the mycelial growth of tested fungal strains, comparable to
standard drug Amphotericin B (Table 3, Figure 4). Therefore 2 was found be potentially active
against fungi and both Gram +ve and Gram -ve bacteria.
Table 2. Zone of inhibition and minimum inhibitory concentration (MIC) values of 2 against
bacteria
Gram +ve
Gram –ve
K. pneumoniae
Zone of MIC
inhibition (µg/mL
Compound
S. aureus
Zone of
inhibition
(mm)
B. cereus
E.coli
Zone of
inhibition (µg/mL
Zone of MIC
inhibition(µg/mL
MIC
MIC
(µg/mL)
(mm)
)
(mm)
)
(mm)
)
13 18
>25
14 18
50
16 19
27 31
25
16 18
>25
2
Chloram-
phenicol
>12.
5
28 33 12.5
29 35 12.5
30 34 >6.25
Table 3. Zone of inhibition and minimum inhibitory concentration (MIC) values of 2 against
fungi
F. oxysporum
Zone of
F.graminearum
Zone of MIC
inhibition(µg/mL
F. moniliforme
P. citrinum
Zone of MIC
inhibition (µg/mL
Compound
Zone of
MIC
MIC
inhibition
(mm)
inhibition (µg/mL
(µg/mL)
(mm)
)
(mm)
)
(mm)
)
14 19
25 28
50
25
13 18 >25
24 27 25
14 18
25 30
50
13 19
25
2
Ampho-
tericin B
>25
24 28 >12.5

Figure 4. Zone of inhibition values of 2 against bacteria and fungi
Agarose gel electrophoresis was used to detect the molecular weight of DNA as well as to
confirm the conformational changes upon cleavage. DNA cleavage activity of the 2 was
examined using pUC19 plasmid as a target. When circular plasmid DNA was run on gel
electrophoresis, the fastest migration was observed for the supercoiled (Form I). While after
cleavage of one strand, the supercoil form relaxed and formed a slower moving nicked form
(Form II). It was observed that amount of cleaved DNA increases as the concentration of 2
increases from 10-40 µg (Figure 5).
Figure 5. Concentration-dependent DNA cleavage. Lane 1 control DNA,
Lane 2, 3, 4, 5, 6 at concentration 10, 20, 30, 40, 50 µg respectively

Similarly, time course of pUC19 DNA cleavage (Figure 6) reveals the more transformation from
form (I) to form (II). However, the absence of linear form (III) of DNA agreed with the result
observed by Mao et al.[40] using Zn2+ complexes.
Figure 6. Time-dependent DNA cleavage. Lane 1. Control DNA,
Lane 2, 3, 4, 5 with the incubation time 1/2h, 1h, 1.5h, 2h respectively
Catalytic application
2 was used as a catalyst for the synthesis of bis(indolyl)methanes by the reaction of aromatic
aldehydes and indole substrates. A varied mol% of 2 and variety of solvents were tested for the
reaction. 3 mol% of 2 and water gave the best results (Table 4, entry 4).
Table 4. Optimization of reaction conditions for the synthesis of bis(indolyl)methanes catalysed
by 2a
Entry
Solvent
THF
2 (mol%)
Time (h)
Yieldb (%)
1.
2.
3.
3
5
5
6
6
6
80
80
80
Water
Ethanol

4.
5.
6.
7.
Water
CAN
3
3
3
3
6
6
7
6
80
80
65
75
DCM
MeOH
aReaction conditions: indole derivative (2.0 mmol), aromatic aldehyde (1.0 mmol) and 2 (x
mol%) as a catalyst in solvent (5 mL). bIsolated yield.
To inflate the scope of the methodology, other kinds of indoles and aldehydes were tested for
the same reaction and good to excellent yields were achieved in all cases (Table 5).
Table 5. Formation of bis(indolyl)methanes, catalyzed by 2a
Entry
Product
5
Time/h
Yield (%)
1
5a
6
80
2
3
5b
5c
6
6
85
80

4
5
5d
7
65
5e
5f
7
8
70
75
6
aReaction conditions: indole derivative (2.0 mmol), aromatic aldehyde (1.0 mmol) and 2 (3
mol%) as a catalyst in water (5 mL). bIsolated yield.
Recycling of 2
In Figure 7, it is mentioned that the catalyst could be effectively used up to six repeated cycles
without much loss in catalytic activity. The gradual decrease in the yield of the product during
recycling may be due to the leaching of the catalyst during extraction.
80%
78%
76%
75%
72%
70%
80
60
40
20
0
1
2
3
4
5
6
Run
Figure 7. Reusability of 2 for the synthesis of bis(indolyl)methanes
Conclusion
In conclusion, a fluorescent imidazolium ionic liquid-tagged zinc(II) complex was synthesized
and well characterized. The steady-state fluorescence reflected enhancement in fluorescence,

while increment in the excited singlet state lifetime indicated conformational rigidity of the
complex. The complex showed good antifungal and antibacterial activity against Gram +ve and
Gram –ve bacteria. It was also found to have good DNA cleaving ability. The complex also
showed good catalytic activity for the reaction of aromatic aldehydes and indoles to synthesize
bis(indolyl)methanes in water.
Acknowledgements
We gratefully acknowledge the UGC, New Delhi [F. No. 42-288/2013 (SR)] for financial
support, DST-FIST and UGC-SAP for instrumental facilities in the Chemistry Department. We
also acknowledge DST-FIST supported X-ray diffraction facility of the Physics Department.
We thank the Advanced Instrumentation Research Facility (AIRF), JNU, New Delhi for spectral
analysis. PN thanks BITS Pilani and UGC BSR for the research fellowship.
Associated Content
Supporting Information
1
13
The Supporting Information encloses DSC, TGA, IR, UV-vis, Powder XRD, H & C NMR
and mass spectrometry data of 1 and 2 and 1H & 13C data for 5.
Author Information
Corresponding Author
Email: bhartikh@gmail.com
Notes: The authors declare no competing financial interest
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 Synthesis, characterization and photophysical studies of fluorescent imidazolium ionic
liquid-tagged zinc(II) complex are reported.
 The complex showed good DNA cleavage, antifungal and antibacterial activities.
 The complex is used as catalyst in water to synthesize bis(indolyl)methanes.