Synthesis, Optical Investigation and Biological Properties of Europium(III) Complexes with 2-(4-Chlorophenyl)-1-(2-Hydroxy-4-Methoxyphenyl)Ethan-1-one and Ancillary Ligands

Article abstract of DOI:10.1007/s10895-016-1930-0

Synthesis and photoluminescence behaviour of six novel europium complexes with novel β-hydroxyketone ligand, 2-(4-chlorophenyl)-1-(2-hydroxy-4-methoxyphenyl)ethan-1-one (CHME) and 2,2′-bipyridine (bipy) or neocuproine (neo) or 1,10-phenanthroline (phen) o

Full text of DOI:10.1007/s10895-016-1930-0

J Fluoresc
DOI 10.1007/s10895-016-1930-0
ORIGINAL ARTICLE
Synthesis, Optical Investigation and Biological Properties
of Europium(III) Complexes with 2-(4-Chlorophenyl)
-
1-(2-Hydroxy-4-Methoxyphenyl)Ethan-1-one
and Ancillary Ligands
1
1
2
2
1
Poonam Nandal & S. P. Khatkar & Rajesh Kumar & Avni Khatkar & V. B. Taxak
Received: 14 May 2016 /Accepted: 7 September 2016
#
Springer Science+Business Media New York 2016
. .
Keywords Eu(III) complexes Photoluminescence
Abstract Synthesis and photoluminescence behaviour of
six novel europium complexes with novel β-
hydroxyketone ligand, 2-(4-chlorophenyl)-1-(2-hydroxy-
.
.
Quantum efficiency Judd-Ofelt intensity parameters
.
Antimicrobial activity Antioxidant activity
4
-methoxyphenyl)ethan-1-one (CHME) and 2,2′-
bipyridine (bipy) or neocuproine (neo) or 1,10-
phenanthroline (phen) or 5,6-dimethyl-1,10-
phenanthroline (dmphen) or bathophenanthroline
Introduction
(
bathophen) were reported in solid state. The free ligand
The lanthanide complexes with organic ligand have been
widely studied from last few decades due to their potential
applications in full color flat-panel displays [1–3], organic
light emitting diodes (OLEDs) [4, 5], optical telecommunica-
tions [6–8] and medical applications [9, 10]. As a result lot of
attention have been paid on the synthesis and
photoluminescent investigation of novel lanthanide com-
plexes with organic ligand possessing excellent luminescent
properties [11–13]. Most of the lanthanide ions emit in entire
CHME and europium complexes, Eu(CHME) .2H O [1]
E u ( C H M E ) . b i p y [ 2 ] , E u ( C H M E ) . n e o [ 3 ] ,
Eu(CHME) .phen [4], Eu(CHME) .dmphen [5] and
Eu(CHME) .bathophen [6]were characterized by elemen-
tal analysis, FT-IR and H-NMR. The photoluminescence
emission spectra exhibited four characteristic peaks aris-
ing from the D0
europium ion in the solid state on monitoring excitation
at λex = 395 nm. The luminescence decay curves of these
europium complexes possess single exponential behav-
iour indicating the presence of a single luminescent spe-
cies and having only one site symmetry in the com-
plexes. The luminescence quantum efficiency (η) and
the experimental intensity parameters, Ω and Ω of eu-
ropium complexes have also been calculated on the basis
of emission spectra and luminescence decay curves. In
addition, the antimicrobial and antioxidant activities were
also studied of the investigated complexes.
3
2
3
3
3
3
3
1
5
7
→ FJ (J = 1–4) transitions of the
3
+
3+
spectroscopic region from UV (Gd ) to visible (blue, Tm ;
3
+
3+
3+
3+
white, Dy ; green, Tb ; orange, Sm and red, Eu ) and
3
+
3+
3+
3+
NIR (Pr , Yb , Nd and Er ) [14]. Among these lantha-
3
+
nide ions, Eu ion has large energy gap between the lowest
luminescent energy state to highest non-luminescent energy
state; thus gives rise to tremendously sharp and strong emis-
2
4
3
+
sion in the visible region. The Eu offers four characteristic
5
7
5
7
emission lines at 593 nm ( D → F ), 616 nm ( D → F ),
0
1
0
2
5
7
5
7
650 nm ( D → F ) and 685 nm ( D → F ). Out of these
0
5
3
7
0
4
transitions D → F being intense is responsible for the
0
2
bright red color of complexes. However, direct excitation of
lanthanide ions is extremely difficult because trivalent lantha-
nide cations have low molar extinction coefficient
−1
−1
(
ɛ < 1 M cm ) due to Laporte forbidden 4f-4f electronic
*
V. B. Taxak
v_taxak@yahoo.com
transitions of lanthanide ions [15–17]. To overcome this draw-
back, we must incorporate organic ligands having high ab-
sorption coefficient which can act as photosensitizer. The che-
lating organic ligand efficiently absorbs and transfer energy to
trivalent lanthanide ions through Bantenna effect^ [18–21],
1
2
Department of Chemistry, Maharshi Dayanand University,
Rohtak 124001, India
UIET, Maharshi Dayanand University, Rohtak 124001, India

J Fluoresc
resulting in intense lanthanide ion emission. Therefore, the
design of efficient ligands has become an important goal for
research. It is well known that O,O- or O,N- or N,N- chelate
group with extended conjugated system including β-
diketones, aromatic carboxylic acids, pyridine derivatives,
nuclic acids, quinoline derivatives, cryptends and several oth-
er macrocyclic ligands [22–24] have received considerable
interest and have been extensively applied in the synthesis
of luminescent lanthanide complexes. But little attention has
been paid for the synthesis of lanthanide complexes with β-
hydroxyketones. Our previous research results indicate that β-
hydroxyketones have strong absorption coefficient and effi-
broth medium, dimethyl sulfoxide (DMSO) were purchased
f r o m H i - M e d i a P v t . L t d . 1 , 1 - D i p h e n y l - 2 -
picrylhydrazylradical (DPPH) were purchased from Sigma-
Aldrich.
The europium content of the complexes was estimated by
complexometric titration with EDTA using xylenol orange as
an indicator. Elemental analysis (C, H and N) was performed
using thermo scientific flash 2000 elemental analyzer. FT-IR
spectra were obtained on Perkin Elmer spectrum 400 FT-IR
spectrometer by using KBr disks in the range of 4000–
−1
1
400 cm . The H-NMR spectra were recorded on Bruker
Avance II 400 spectrometer (400 MHZ) in dimethylsulfoxide
3
+
3+
3+
13
ciently sensitize the luminescence of Eu , Tb and Sm ions.
Moreover nitrogen containing non charged heterocyclic li-
gands like 2,2′-bipyridine (bipy) or neocuproine (neo), or
solution. The C-NMR spectra were measured on Jeol: JNM-
EXCP 400; 400 MHz FT-NMR spectrometer. The excitation
and emission spectra of complexes in the UV-Visible region
and decay curves under time scan mode were measured on
Hitachi F-7000 fluorescence spectrophotometer equipped
with Xe-lamp at room temperature in solid state. The life time
values of the complexes were calculated with the help of soft-
ware of the spectrophotometer (FL solution for F-7000). The
UV-Visible absorption spectra were measured on Shimadzu-
2450 UV-Vis spectrophotometer.
1
,10-phenanthroline (phen) or 5,6-dimethyl-1,10-
phenanthroline (dmphen) or bathophenanthroline
bathophen) serves synergistic effect and enhance the
(
photoluminescent intensity by transfer of the energy from li-
gand to central metal ion through antenna effect.
In present section focus is on the synthesis of β-
hydroxyketone, 2-(4-chlorophenyl)-1-(2-hydroxy-4-
methoxyphenyl)ethan-1-one (CHME). With the CHME as
the main ligand and 2,2′-bipyridine (bipy) or neocuproine
(
neo), or 1,10-phenanthroline (phen) or 5,6-dimethyl-1,10-
phenanthroline (dmphen) or bathophenanthroline
bathophen) as ancillary ligand six novel europium complexes
Synthesis
(
Synthesis of Ligand 2-(4-Chlorophenyl)
were synthesized in order to achieve effective luminescence
performance.
-1-(2-Hydroxy-4-Methoxyphenyl)Ethan-1-one (CHME)
The ligand was synthesized in two steps by using Houben-
Hoesch reaction mechanism between resorcinol and 4-
chlorobenzylcyanide. The first step involves the preparation
of 2-(4-chlorophenyl)-1-(2,4-dihydroxyphenyl)ethan-1-one
(CDHPE) and the second step involves the preparation of
Experimental Details
Materials and Instrumentation
2-(4-chlorophenyl)-1-(2-hydroxy-4-methoxyphenyl)ethan-1-
Europium nitrate hydrate [Eu(NO ) . H2O], 2,2′-bipyridine,
one (CHME) which are described as follows:
3
3
neocuproine, 1,10-phenanthroline, 5,6-dimethyl-1,10-
phenanthroline and bathophenanthroline were purchased from
Sigma-Aldrich. Resorcinol, 4-chlorobenzylcyanide, anhy-
drous zinc chloride, potassium carbonate, dimethyl sulphate
were purchased from Hi-Media Pvt. Ltd. The reagent
employed were of analytical grade and used without any fur-
ther purification. Solvents were freshly distilled with standard
methods. Synthesized ligand CHME was recrystalized three
times with methanol before the synthesis of complexes.
Microbial strains Gram-positive bacteria: Staphylococcus
aureus (MTCC 3160), Bacillus subtilis (MTCC 441), and
Gram-negative bacterium: Escherichia coli (MTCC 443)
and fungal strains: Candida albicans (MTCC 227)
Aspergillus niger (MTCC 281) were purchased from
Institute of microbial Technology, Sector 39-A, Chandigarh,
India. Nutrient broth medium, nutrient agar medium,
subourand dextrose agar medium and subourand dextrose
Step 1. Synthesis of 2-(4-chlorophenyl)-1-(2,4-
dihydroxyphenyl)ethan-1-one (CDHPE)
A mixture of resorcinol (10 g), 4-chlorobenzylcyanide (7 g)
and powered anhydrous ZnCl were added in dry ether
2
(100 mL). The mixture was cooled at 0 °C and rapid HCl gas
was passed for 5 h. After leaving over night in ice chest, the
orange yellow precipitate of ketimine hydrochloride was sepa-
rated by decanting ether and washed twice with dry ether
(20 mL). The solid was refluxed with water (200 mL) for 1 h.
On cooling 2-(4-chlorophenyl)-1-(2,4-dihydroxyphenyl)ethan-
1-one (CDHPE) was separated as pale yellow needles, which
were filtered and dried at 120 °C.
Step 2. Synthesis of 2-(4-chlorophenyl)-1-(2-hydroxy-4-
methoxyphenyl)ethan-1-one (CHME)

J Fluoresc
A solution of CDHPE (5 g) in dry acetone (50 mL) was
then in vacuum desiccators. Finally the complex was dried at
50 °C in hot air oven to obtain the complex. The obtained
complex Eu(CHME) .2H O was white power with 86 %
refluxed with dimethyl sulphate (7.3 mL) and freshly ignited
potassium carbonate (25 g) for 2 h. The inorganic salt was
filtered and washed with hot acetone. Acetone was distilled
off from filtrate and ice cold water was added to oily residue
when colorless solid separated out. Solid was filtered, washed
with water and recrystalized three times with methanol to give
CHME. The progress of the reaction was monitored by thin
layer chromatography. CHME was obtained as white crystals
with 78 % yield, m.pt. 219-220 °C. The synthetic route of
ligand CHME is given in Scheme 1. The elemental analysis
data for CHME (C H O Cl) was found (calc.) % C, 65.18
3
2
yield. The elemental analysis data for Eu(CHME) .2H O
3
2
(C H O Cl Eu) was found (calc.) % C, 53.21 (53.24); H,
4
5
40 11
3
4.06 (3.97); Eu, 14.92 (14.97).
−1
IR (KBr)cm : 3447 (b), 3063 (w), 2944 (m), 2427 (w),
1706 (s), 1630 (s), 1560 (s), 1493 (m), 1422 (s), 1384 (s), 1338
(s), 1285 (m), 1223 (s), 1155 (s), 1084 (m), 1032 (s), 993 (w),
1
944 (w), 813 (m), 783 (m), 733 (m), 640 (m), 497 (m). H-
NMR (400 MHz, DMSO, δ, ppm): 3.47 (s, 9H, OCH ), 4.26
3
(s, 6H, CH ), 6.45 (bd, 6H, Ar-H), 7.29 (d, 6H, Ar-H), 7.91 (d,
15
13
3
2
1
3
(
65.10); H, 4.76 (4.73).
6H, Ar-H), 8.09 (s, 3H, Ar-H). C-NMR (400 MHz, DMSO,
δ, ppm): 197.4, 166.6, 158.3, 133.2, 131.2, 131.0, 129.9,
129.3, 110.7, 106.8, 101.2, 55.8, 38.4.
−1
IR (KBr)cm : 3429 (b), 3055 (m), 3022 (w), 2940 (w),
842 (w), 1650 (s), 1633 (s), 1596 (s), 1567 (s), 1494 (s), 1439
2
(
1
5
s), 1351 (s), 1310 (m), 1291 (s), 1229 (s), 1207 (s), 1197 (s),
Ternary Eu(III) complexes 2–6 were also prepared using
same procedure as adopted in the synthesis of complex 1,
taking the mixture of 3 mmol CHME, 1 mmol corresponding
ancillary ligand and 1 mmol europium nitrate. The synthetic
route and the structure of Eu(III) binary and ternary complexes
1–6 are given in Scheme 2.
084 (s), 1028 (s), 994 (s), 822 (s), 810 (s), 777 (s), 600 (s),
1
81 (s). H-NMR (400 MHz, DMSO, δ, ppm): 3.83 (s, 3H,
OCH ), 4.18 (s, 2H, CH ), 6.42 (s, 1H, Ar-H), 6.43 (s, 1H, Ar-
H), 7.24 (d, 2H, Ar-H), 7.30 (d, 2H, Ar-H), 7.57 (s, 1H, Ar-H),
1
2
1
3
2
1
3
2.61 (s, 1H, OH). C-NMR (400 MHz, DMSO, δ, ppm):
01.7, 166.6, 165.5, 133.2, 131.2, 131.0, 129.9, 129.3, 112.8,
06.8, 103.2, 55.8, 40.2.
Eu(CHME) . Bipy [2] The obtained complex was white
3
power with 78 % yield. The elemental analysis data for
Eu(CHME) .bipy (C H O Cl N Eu) was found (calc.) %
Synthesis of Complexes
3
55 44
9
3 2
C, 58.21 (58.18); H, 3.86 (3.90); N, 2.42 (2.46); Eu, 13.31
(13.38).
Eu(CHME) . 2H O [1] In a ethanolic solution of CHME
3
2
−1
(
0.82 g, 3 mmol) add an aqueous solution of Eu(NO ) .
IR (KBr)cm : 3084 (w), 3010 (w), 2942 (m), 2843 (m),
1706 (s), 1606 (s), 1589 (s), 1525 (s), 1493 (s), 1468 (s), 1456
(s), 1415 (s), 1384 (s), 1292 (s), 1229 (s), 1206 (s), 1154 (s),
1126 (s), 1084 (s), 1030 (m), 992 (m), 944 (m), 868 (m), 812
(s), 782 (m), 734 (s), 664 (m), 640 (m), 586 (m), 539 (w), 496
3
3
H2O (0.33 g, 1 mmol) was added with constant stirring on
magnetic stirrer. The solution was neutralized with 0.05 M
NaOH solution and adjusted pH of mixture 7 8. The mixture
was stirred for 3 h at 35 °C and then allowed to stand for 1 h.
During stirring white precipitates appeared, which were fil-
tered and washed with doubly distilled water and then with
ethanol to remove the free ligand, after that dried in air and
1
(m). H-NMR (400 MHz, DMSO, δ, ppm): 3.80 (s, 9H,
OCH ), 4.29 (s, 6H, CH ), 6.45 (bd, 6H, Ar-H), 7.13–7.38
3
2
(bs, 14H,12 Ar-H and 2H bipy), 8.14 (s, 3H, Ar-H), 8.59 (d,
Scheme 1 The synthetic route of
ligand CHME

J Fluoresc
Scheme 2 The synthetic route
and structure of Eu(III) binary and
ternary complexes 1–6 with
CHME
1
3
2
(
1
1
H, bipy), 8.71 (d, 2H, bipy), 9.21 (d, 2H, bipy). C-NMR
ppm): 198.3, 166.6, 162.2, 158.2, 144.3, 135.6, 133.2,
131.2, 131.0, 129.9, 129.3, 128.1, 126.8, 124.2, 110.2,
106.8, 99.8, 55.8, 38.4, 25.2.
400 MHz, DMSO, δ, ppm): 195.4, 166.6, 162.2, 155.3,
48.2, 137.2, 133.2, 131.2, 131.0, 129.9, 129.3, 123.6,
21.4, 109.6, 106.8, 98.4, 55.8, 37.2.
Eu(CHME) . Phen [4] The obtained complex was white
3
Eu(CHME) . Neo [3] The complex Eu(CHME) .neo was
power with 92 % yield. The elemental analysis data for
Eu(CHME) .phen (C H O Cl N Eu) was found (calc.) %
3
3
obtained as white power with 81 % yield. The elemental anal-
ysis data for Eu(CHME) .neo (C H O Cl N Eu) was found
3
57 44
9
3 2
C, 59.13 (59.05); H, 3.79 (3.82); N, 2.44 (2.41); Eu, 13.08
(13.10).
3
59 50
9
3 2
(
calc.) % C, 59.49 (59.58); H, 4.19 (4.23); N, 2.31 (2.35); Eu,
−
1
1
2.73 (12.77).
IR (KBr)cm : 3063 (w), 2925 (w), 2493 (w), 2298
(w), 1765 (w), 1626 (m), 1592 (m), 1577 (m), 1474 (s),
1424 (s), 1384 (s), 1344 (m), 1306 (s), 1221 (s), 1141
(m), 1103 (s), 1031 (s), 991 (w), 863 (m), 842 (s), 814
(m), 765 (m), 736 (m), 725 (s), 638 (m), 553 (w), 511 (w),
−1
IR (KBr)cm : 3094 (w), 2927 (w), 2495 (w), 2317 (w),
975 (w), 1767 (w), 1607 (s), 1583 (s), 1543 (s), 1495 (s),
384 (s), 1342 (m), 1300 (s), 1218 (s), 1191 (m), 1167 (s),
1
1
1
123 (m), 1080 (s), 1030 (s), 949 (m), 812 (s), 734 (s), 689
1
1
(m), 640 (m), 620 (m), 549 (w), 427 (w). H-NMR (400 MHz,
DMSO, δ, ppm): 2.53 (s, 6H, neoCH ), 3.39 (s, 9H, OCH ),
475 (w). H-NMR (400 MHz, DMSO, δ, ppm): 3.84 (s,
9H, OCH ), 4.19 (s, 6H, CH ), 6.43 (d, 6H, Ar-H), 7.19
3
3
3
2
4
1
.21 (s, 6H, CH ), 6.41–6.56 (bd, 6H, Ar-H), 7.30–7.76 (bs,
(d, 6H, Ar-H), 7.21 (d, 6H, Ar-H) 7.26 (d, 2H, phen), 7.32
(d, 2H, phen), 7.70 (d, 2H, phen), 7.73 (d, 2H, phen), 8.30
(s, 3H, Ar-H). C-NMR (400 MHz, DMSO, δ, ppm):
2
2H, Ar-H), 7.88 (d, 2H, neo) 8.30 (s, 3H, Ar-H), 8.61 (d, 2H,
1
3
13
neo), 9.15 (d, 2H, neo). C-NMR (400 MHz, DMSO, δ,

J Fluoresc
1
1
1
95.8, 166.6, 158.4, 148.8, 146.2, 136.4, 133.2, 131.2,
31.0, 129.9, 129.3, 129.2, 127.6, 121.5, 110.5, 106.8,
01.9, 55.8, 38.4.
(antifungal) were the standard drug as references. The stan-
dard drug, CHME and the Eu(III) complexes were dissolved
in DMSO to prepare a stock solution of the concentration of
100 μg/mL. Dilutions of test samples and standard drugs were
Eu(CHME) . Dmphen [5] Eu(CHME) .dmphen was obtain-
prepared in double strength nutrient broth I.P. (bacteria) or
sabouraud dextrose broth I.P. ( fungi). The test samples were
incubated at and 7 days at respectively.
3
3
ed as white power with 89 % yield. The elemental analysis
data for Eu(CHME) .dmphen (C H O Cl N Eu) was found
3
59 50
9
3 2
(
1
calc.) % C, 59.61 (59.58); H, 4.21 (4.23); N, 2.38 (2.35); Eu,
MIC values were evaluated for four different concentra-
tions (50, 25, 12.5 and 6.25) for each test samples and the
standard drugs. These different concentrations were obtained
by tube dilution in autoclaved nutrient broth in assay tubes.
2.79 (12.77).
−1
IR (KBr)cm : 3095 (w), 2927 (w), 2495 (w), 2318 (w),
976 (w), 1767 (w), 1608 (s), 1584 (s), 1542 (s), 1484 (s),
433 (s), 1384 (s), 1343 (m), 1300 (s), 1222 (w), 1191 (m),
1
1
5
0.1 mL of normal saline suspension of strains (1.0 × 10 c.f.u./
1
168 (s), 1124 (m), 1080 (s), 1031 (s), 950 (m), 812 (s), 735
mL of microorganism) was added to each test tubes. The test
samples were incubated at 37 °C for 24 h (bacteria), at 37 °C
for 48 h (Candida albicans) and at 25 °C for 7 days
(Aspergillus niger). The results were recorded in terms of
MIC (the lowest concentration of test substance which
inhibited the growth of microorganisms) by observing turbid-
ity in assay tubes.
1
(
s), 689 (m), 641 (m), 621 (m), 550 (w), 427 (w). H-NMR
(
400 MHz, DMSO, δ, ppm): 2.53 (s, 6H, dmphenCH ), 3.38
3
(
s, 9H, OCH ), 4.19 (s, 6H, CH ), 6.41–6.56 (b, 6H, Ar-H),
3
2
7
.24–7.78 (b, 12H, Ar-H), 7.92 (d, 2H, dmphen), 8.11 (s, 3H,
1
3
Ar-H), 8.51 (d, 2H, dmphen), 9.20 (d, 2H, dmphen). C-
NMR (400 MHz, DMSO, δ, ppm): 195.6, 166.6, 158.2,
1
1
48.2, 143.9, 134.0, 133.2, 131.2, 131.0, 129.9, 129.7,
29.3, 129.1, 121.1, 110.6, 106.8, 101.6, 55.8, 38.2, 21.1.
In Vitro Antioxidant Activity
Eu(CHME) . Bathophen [6] This complex was obtained as
3
Free radical scavenging activity of ligand 2-(4-chlorophenyl)-
white power with 90 % yield. The elemental analysis data for
Eu(CHME) .bathophen (C H O Cl N Eu) was found
1-(2-hydroxy-4-methoxyphenyl)ethan-1-one (CHME) and its
3
69 55
9
3
2
corresponding Eu(III) complexes against nitrogen centered
most familiarly used stable free radical 2, 2-diphenyl-2-
picrylhydrazyl hydrate (DPPH), was most employed used to
determine antioxidant activity spectrophotometrically based
on the fact that odd electron present in the DPPH free radical
reacts with antioxidant complex, its deep violet colour in
methanol bleaches to yellow, gives a strong absorbance,
which maximises at λ = 517 nm. Stock solution of various
concentrations (25, 50, 75, and 100) μg/ml of the complexes
dissolved in methanol was added to 5 ml of a 0.004 % meth-
anol solution of DPPH. The mixtures were vigorously shaken
and allowed to stand for 30 min in the dark at room tempera-
ture for incubation. Tests were carried out in triplicate. By
using UV-Visible spectrophotometer, absorbance value was
measured at λ = 517 nm. The DPPH scavenging activity
was expressed as IC , whose concentration is sufficient to
(
calc.) % C, 63.09 (63.04); H, 4.23 (4.21); N, 2.17 (2.13);
Eu, 11.52 (11.56).
−1
IR (KBr)cm : 3010 (m), 2941 (m), 2845 (m), 1706 (s),
605 (s), 1589 (m), 1522 (m), 1492 (s), 1468 (s), 1414 (s),
384 (s), 1340 (m), 1224 (s), 1206 (s), 1183 (m), 1154 (s),
1
1
1
127 (s), 1085 (s), 1032 (m), 1015 (m), 993 (m), 834 (s), 813
m), 740 (m), 703 (m), 640 (w), 574 (w), 544 (w), 496 (w).
(
1
H-NMR (400 MHz, DMSO, δ, ppm): 3.83 (s, 9H, OCH3),
.19 (s, 6H, CH ), 6.45–6.58 (d, 6H, Ar-H), 7.53 (b, 12H, Ar-
4
2
H), 7.82–7.96 (b, 14H, bathophen), 8.12 (s, 3H, Ar-H), 9.23
(
1
1
1
1
3
d, 2H, bathophen). C-NMR (400 MHz, DMSO, δ, ppm):
97.2, 166.6, 158.4, 151.4, 149.4, 145.1, 140.3, 133.2, 131.2,
31.0, 129.9, 129.3, 129.2, 127.3, 123.1, 120.3, 111.3, 109.8,
06.8, 101.8, 55.8, 38.3.
5
0
Biological Evaluation of Synthesized Complexes
obtain 50 % of maximum scavenging activity. Standard curve
was plotted for different concentration of ascorbic acid and
complexes. Scavenging of DPPH free radical was calculated
as:
Antimicrobial Activity
Antibacterial activity of newly synthesized 2-(4-
chlorophenyl)-1-(2-hydroxy-4-methoxyphenyl)ethan-1-one
ðA0‐AsÞ
DPPH scavenging activityð%Þ ¼ 100
(
CHME) and its corresponding six new Eu(III) complexes
A0
were performed against Gram-positive bacteria:
Staphylococcus aureus (MTCC 3160), Bacillus subtilis
Where, A is the absorbance of the control reaction (con-
0
(
(
2
MTCC 441), and Gram-negative bacterium: Escherichia coli
MTCC 443) and fungal strains: Candida albicans (MTCC
27) and Aspergillus niger (MTCC 281) using tube dilution
taining all reagents except test complexes) and A is the ab-
s
sorbance of the test complexes. The observed results were
compared with the activity of ascorbic acid, which was used
as the standard.
method. Ciprofloxacin (antibacterial) and fluconazole

J Fluoresc
Results And Discussion
phenolic OH group. The strong absorption band in the region
−1
1
630–1605 cm due to C = O stretching vibrations [25, 26]
−1
Elemental Analysis and Solubility
were red shifted 3–28 cm with respect to those of free ligand
CHME due to extended conjugation present in the complexes,
confirming the coordination of the carbonyl oxygen atom with
the metal ion. A new absorption band in the complexes 2–6
appeared at 1592–1583 cm assigned to C = N stretching
vibration of ancillary ligand [27], indicated that nitrogen atom
of ancillary ligands can also participate in the coordination. In
The elemental analysis data for the synthesized ligand CHME
and its corresponding Eu(III) binary and ternary complexes 1–
−1
6
are tabulated in Table 1. The results revealed that the ligand
CHME and its corresponding Eu(III) complexes were suc-
cessfully synthesized. The ternary complexes 2–6 were found
in the ratio 1:3:1 i.e. europium metal to ligand CHME to
ancillary ligand. The complexes were white powder, stable
under atmospheric condition and soluble in DMSO, chloro-
form, dichloromethane, acetone, methanol and ethanol but
insoluble in benzene and hexane.
−1
the complexes 2–6, weak absorption band at 539 cm and
−
1
497–427 cm shows the presence of Eu-N and Eu-O
stretching vibrations [28, 29] respectively, which was not ob-
served in the spectra of binary complex 1 and ligand, this
indicated that in the ternary complexes nitrogen atom of the
3
+
ancillary ligand also coordinated with the Eu ion. All these
3
+
changes in the spectra confirmed that Eu ion coordinated
with the ligand through phenolic and carbonyl oxygen atom
of the ligand CHME and nitrogen atoms of respective ancil-
NMR and IR Spectra
1
13
3+
The assignments of H-NMR and C-NMR spectra of Eu(III)
complexes disclose some afferent changes as compared to the
free ligand CHME due to paramagnetism of metal ion. The
lary ligand, while in case of complex 1, Eu ion coordinated
with the phenolic and carbonyl oxygen atom of the ligand and
two oxygen atoms of water molecules. The elemental analy-
1
1
13
H-NMR spectrum of free ligand CHME exhibits a singlet of
sis, H-NMR, C-NMR spectra and FT-IR spectra of ligand
and its Eu(III) complexes 1–6, all were in well agreement with
Scheme 2.
phenolic OH proton at δ 12.61 ppm which was not observed
in the complexes, indicating that the ligand was involved in
3
+
the coordination with the Eu through the phenolic oxygen
1
3
atom of CHME. In the C-NMR spectra, the carbon values in
free ligand appeared at 201.7 (C = O), 165.5 (C–O), 112.8
Photoluminescent Properties
(
=C–), 103.3 (−C=) and 40.2 (−CH –) which shifted upfield
2
in the corresponding complexes 1–6 (198.3–195.4 (C = O),
Figure 1 depicts the photoluminescence excitation spectra of
complexes 1–6 in solid state at room temperature on monitor-
ing emission at λem = 617 nm. The inset depicts the broad
excitation band of ligand CHME at about 382 nm with low
intensity due to π-π* transition in the ligand. The excitation
band in the complexes 1–6 stay in a wide range 300–425 nm,
centred at 395 nm with remarkable increase in intensity. As a
1
3
62.2–158.2 (C–O), 110.7–109.6 (=C–), 109.6–98.4 (=C–),
8.4–37.2 (−CH2).
The formation of complexes 1–6 were also observed by
FT-IR absorption spectra. The FT-IR absorption spectra of
complexes 1–6 exhibited some observable changes in com-
parison with the free ligand CHME which are summarized in
Table 2 along with their characteristic assignments. In the FT-
IR spectra of free ligand CHME a broad absorption band
comparison, the complex Eu(CHME) .bathophen shows
3
higher intensity due to the formation of a bigger π-
conjugation present in the complex.
−1
appeared at 3429 cm due to ν(O-H) which was red shifted
−1
1
8 cm in case of binary complex 1,while disappeared in the
Figure 2 shows the photoluminescence emission spectra of
ternary complexes 2–6 implying that the ligand CHME was
complexes 1–6 on monitoring excitation at λ = 395 nm. The
ex
coordinated with the metal ion in a mode of deprotonated
emission spectra of all the complexes exhibited four
Table 1 Elemental analysis data
for ligand CHME and its
corresponding Eu(III) complexes
Complexes
C (%) found
(calc.)
H (%) found
(calc.)
N (%) found
(calc.)
Eu (%) found
(calc.)
1–6
CHME
65.18 (65.10)
53.21 (53.24)
58.21 (58.18)
59.49 (59.58)
59.13 (59.05)
59.61 (59.58)
63.09 (63.04)
4.76 (4.73)
4.06 (3.97)
3.86 (3.90)
4.19 (4.23)
3.79 (3.82)
4.21 (4.23)
4.23 (4.21)
—
—
1
2
3
4
5
6
—
14.92 (14.97)
13.31 (13.38)
12.73 (12.77)
13.08 (13.10)
12.79 (12.77)
11.52 (11.56)
2.42 (2.46)
2.31 (2.35)
2.44 (2.41)
2.38 (2.35)
2.17 (2.13)

J Fluoresc
Table 2 The characteristic IR
−1
Complexes
ν(O-H)
ν(C = O)
ν(C = N)
ν(C = C)
ν(Ph-O)
ν(Eu-N)
ν(Eu-O)
bands (cm ) of the free ligand
CHME and its corresponding
Eu(III) complexes 1–6
CHME
3429 (b)
3447 (b)
—
1633 (s)
1630 (s)
1606 (s)
1607 (s)
1626 (m)
1608 (s)
1605 (s)
—
1567 (s)
1560 (s)
1525 (s)
1543 (s)
1577 (s)
1542 (s)
1522 (m)
1229 (s)
1223 (s)
1292 (s)
1218 (s)
1221 (s)
1222 (s)
1224 (s)
—
—
1
2
3
4
5
6
—
—
497 (m)
496 (m)
427 (m)
475 (m)
427 (m)
496 (m)
1589 (s)
1583 (s)
1592 (m)
1584 (s)
1589 (m)
539 (w)
549 (m)
511 (m)
550 (w)
544 (m)
—
—
—
—
b = broad, s = strong, m = medium, w = weak
5
7
characteristic peaks for the D → F (J = 1–4) transitions
solid state are depicted in Fig. 3. The luminescence decay time
is affected by luminescent centres, energy transfer, defects and
impurities present in the complexes. The time resolved
0
J
5
7
5
7
assigned to D → F (593 nm), D → F (617 nm),
D → F (650 nm) and D → F (684 nm). The
D → F (617 nm) transition is an electric dipole-allowed
0
1
0
7
2
5
7
5
0
3
0
4
5
7
5
7
D → F transition of all synthesized complexes obey single
0 2
0
2
transition and is extremely sensitive to site symmetry of the
exponential curve which can be calculated by applying the eq.
3
+
Eu ion [30, 31] whereas the magnetic dipole transition
I = I exp. (−t/τ), where τ is the radiative decay time I and I
o
o
5
7
D → F (593 nm) is insensitive to site symmetry [32].
are the luminescence intensities at time t and 0, respectively.
The luminescence decay curves of these europium complexes
possess single exponential behaviour indicating the presence
of a single luminescent species and having only one site sym-
metry in the complexes 1–6 [35–37]. The lifetime values cal-
culated for complexes 1–6 were found to be 0.493 ms [1],
0.632 (2), 0.842 (3), 0.867 (4), 0.896 (5) and 0.912 ms [6]
respectively as tabulated in Table 3. The relative shorter life-
time value observed for complex Eu(CHME) .2H O [1] may
0
1
5
7
The D → F transition is approximately 3–6 times stronger
than D → F transition, indicating a highly polarisable
0
2
7
5
0
1
3
+
chemical environment around the central Eu ion responsible
for the bright red color of these complexes. Moreover, after the
introduction of ancillary ligands, the emission intensity of
complexes 2–6 was greatly enhanced as compared to the bi-
nary complex [33], due to the synergetic effect of N,N-donor
ancillary ligands which causes an efficient energy transfer
3
2
3
+
from the ligands to central Eu ion [34]. The complex
be due to the dominant nonradiative decay pathway because
of the presence of water molecules in this complex, as report-
ed in many binary europium complexes [38]. The much lon-
ger lifetime value for complex 6 has been observed as com-
pared to complexes 1–5, which may be due to extended con-
jugation present in the complex 6.
Eu(CHME) .bathophen showed prominent photoluminescent
3
intensity may be due to extended conjugation of π electrons in
the presence of ancillary ligand bathophenanthroline.
Luminescence Lifetime and Quantum Efficiency
The Commission Internationale de Eclairage (CIE)
coordinate of the photoluminescence spectra of these eu-
ropium complexes 1–6 has been analyzed with the help
PL decay curves for complexes 1–6 corresponding to
5
7
D → F transition (616 nm) under excitation at 395 nm in
0
2
Fig. 1 Photoluminescence excitation spectra of complexes 1–6,
monitored at λem = 617 nm in solid state at room temperature and inset
shows the excitation spectrum of ligand CHME
Fig. 2 Photoluminescence emission spectra of complexes 1–6 in solid
state at room temperature, monitored at λex = 395 nm

J Fluoresc
50 s− and A0J was obtained by using the following
1
≈
relation in equation (2) [40, 41]:
I υ
0
J
01
A0J¼ A01
ð2Þ
I υ
0
1
0J
5
7
Where I and I are the integrated intensities of D → F
0
1
0J
0
1
5
7
and D → F transition (J = 2 and 4) and the energy
0
J
barycenteres of these transitions are expressed by υ01 andυoJ
respectively. The reciprocal of life time is the total decay rate
which was determined from the calculated Arad rates and the
experimental decay rates by following equation (3) [42]:
1
¼
AradþAnrad
ð3Þ
5
7
τ
Fig. 3 Luminescence decay curves of the D
Eu(III) complexes 1–6 in solid state at room temperature, monitored at
ex = 395 nm
0 2
→ F transition for
From Table 3 it can be concluded that the complex 1 ex-
λ
hibited the lowest luminescent quantum efficiency (14.94)
due to presence of two water molecules in the coordination
sphere of complex. The O-H oscillator effectively quenches
the luminescence of the Eu ion. On the other hand, com-
plexes 2–6 exhibited high quantum efficiency as the ancillary
ligand displaced the water molecules from the coordination
sphere of the complexes, thereby making an efficient energy
transfer from ligands to emitting center [1]. The complexes 3–
of CIE chromaticity coordinate diagram. The CIE color
coordinates (x, y) of the complexes 1–6 are located at
3
+
(
(
0.5925, 0.4063), (0.6237, 0.3643), (0.6016, 0.3715),
0.6348, 0.3425), (0.6551, 0.3444) and (0.6570, 0.3235)
as shown in Fig. 4, which fall in deep red spectral re-
gion. These Eu(III) complexes might exhibit promising
applications in display devices.
The emission spectra and lifetimes values of the complexes
have been exploited for the determination of the luminescent
quantum efficiency (η) using the equation (1) [39]:
6
exhibited better quantum efficiency than that of complex 2
because of the presence of additional aromatic chromophore
moieties in the ancillary ligand 3–6 which can be improve the
3
+
radiative properties of the Eu complexes. Moreover, com-
plex 6 exhibited highest quantum efficiency due to extended
conjugation induced by two phenyl rings in the 4,7-positions
of the bathophenanthroline [38].
Arad
η ¼
ð1Þ
A þA
rad
nrad
Where Arad is the radiative transition rate and Anrad is
the non radiative transition rate. The obtained radiative
decay rates Arad, non radiative decay rates Anrad and
luminescence quantum efficiency (η) of these europium
complexes 1–6 are tabulated in Table 3 which were de-
termined in solid state at room temperature. The Arad can
be calculated by summing over the radiative rates A for
Judd-Ofelt Intensity Parameters
The Judd-Ofelt intensity parameter (J-O) is very useful to tell
about the possible chemical environment around the europium
ion. In the standard Judd-Ofelt theory of 4f-4f intensities, Ωt
intensity parameters contain the contributions from the forced
electric dipole and dynamic coupling mechanisms [43].
According to J-O theory, electronic transition state
0
J
5
7
5
7
each D → F transition. The transition D → F was
0
J
0
1
5
7
used as references because it was independent of local
ligand field and the value of A01 was estimated to be
D → F levels with J = 0, 3 or 5 are electrically as well as
0 J
magnificently forbidden [44]. Therefore, in order to examine
Table 3 Photoluminescence data
of Eu(III) complexes 1–6 in solid
−
1
−1
−1
nrad(s )
(10−20 cm2)
(10−20 cm2)
Complexes
τ (ms)
A
tot(s )
A
rad(s )
A
Ω
2
Ω
4
η(%)
state
1
2
3
4
5
6
0.493
0.632
0.842
0.867
0.896
0.912
2331.58
1916.81
1527.62
1496.04
1471.59
1468.31
303.19
334.54
339.98
342.64
355.52
371.82
2028.39
1582.27
1187.64
1153.40
1116.07
1096.49
9.98
0.26
0.21
0.24
0.26
0.23
0.89
14.94
21.14
28.62
29.70
31.85
34.43
11.04
11.21
11.29
11.73
11.78

J Fluoresc
Table 4 Minimum inhibitory concentration of HDMPE and its
corresponding Eu(III) complexes [1–6]
Compound Minimum Inhibitory Concentration (μM/mL)
B. subtillis S.aureus E.coli C.albicans A.niger
CHME
22.5
1.99
0.74
1.73
0.74
0.46
12.3
11.0
10.5
10.7
10.5
9.50
22.5
1.99
1.49
0.86
1.49
0.93
6.15
5.50
5.25
5.39
5.25
4.75
22.5
1.99
1.49
1.73
1.49
0.93
6.15
5.50
5.25
5.39
5.25
4.75
45.2
1.99
1.49
1.73
0.74
0.46
12.4
11.0
10.5
10.7
10.5
9.50
45.2
1.99
1.49
1.73
0.74
0.46
6.15
5.50
5.50
5.39
5.50
4.75
10.09
bipy
neo
phen
dmphen
bathophen
1
2
3
4
5
6
a
a
a
b
b
Std.
8.71
8.71
8.71
10.09
a
Ciprofloxacin
Fluconazole
b
Fig. 4 CIE coordinate diagram of Eu(III) complexes 1–6
microorganisms tested are presented in Table 4. The antibac-
terial activity results indicated that the synthesized ligand
CHME was found to be inactive, whereas all the complexes
showed more active than the standard drug against S. aureus
and E. coli bacteria. In case of antifungal activity all the com-
plexes exhibited excellent activity than the standard drug flu-
conazole against A. niger, whereas moderate activity showed
by all the complexes against C. albicans.
Finally it can be concluded that all the complexes are potent
antimicrobial agent due to increase π-conjugation present in
the complexes. Moreover, it was interesting to note that all the
complexes proved to be better than the standard references
3
+
the possible structural changes around the Eu ion, the inten-
sities parameters Ω and Ω were calculated from the emission
spectra (Fig. 2) using the D → F and D → F as per
2
4
5
7
5
7
0
2
0
4
equation [45]:
3
3
ℏc AoJ
Ωt ¼
ð4Þ
ꢀ
ꢁ
2
2
3
5
ðtÞ
7
4
e ω χ D ∥U ∥ F
0
J
Where Ω is the angular frequency of the transition,
À
Á
χ ¼ n n þ 2 2=9 is a Lorentz local field correction and
2
0
2
0
an average index of refraction equal to 1.5 was used. The
squared reduced matrix element is independent of the chemi-
(
ciprofloxacin and fluconazole) in case of the microbes
3
+
5
cal environment of the Eu ion and is 0.0032 for 〈 D ∥
U ∥ F 〉 and 0.0023 for〈 D ∥ U ∥ F 〉 . The experimental
0
S. aureus, E. coli and A. niger. This may be occurs due to
the complexatation of trivalent europium ion with β-
hydroxyketone ligand 2-(4-chlorophenyl)-1-(2-hydroxy-4-
(2)
7
2
5
(4)
7
2
2
0
4
value of J-O intensities parameters Ω and Ω are tabulated in
2
4
Table 3, which reflect the local structure and bonding in the
environment of Eu ion. The value of Ω parameter indicates
the hypersensitive behaviour of the D → F transition,
which reflects that the Eu ions are located in a higher
polarisable chemical environment.
3
+
2
100
5
7
0
2
9
0
0
0
0
3
+
8
7
6
CHME
Antimicrobial Activity
50
5
4
3
2
1
0
0
0
0
6
The synthesized ligand CHME and its corresponding Eu(III)
complexes 1–6 were evaluated for their in vitro antibacterial
activity against Gram-positive bacteria: S. aureus, B. subtilis
and Gram-negative bacterium: E. coli and fungal strains:
C. albicans and A. niger using tube dilution method using
ciprofloxacin (antibacterial) and fluconazole (antifungal) as
reference standard drugs. The values of the MIC against
Std.
0
0
20
40
60
80
100
120
Fig. 5 Percentage inhibition values of CHME, Eu(III) complexes 5 and 6
with respect to standard ascorbic acid

J Fluoresc
Table 5 Percentage inhibition and IC50 values of DPPH radical
scavenging activity of synthesized CHME and its corresponding Eu(III)
complexes 1–6
properties such as excitation spectra, emission spectra as well
as decay curves have also been investigated in solid state. The
emission spectra of all the complexes exhibited four charac-
5
7
5
7
Compound
Concentration (μg/mL)
teristic transitions assigned to D → F (593 nm), D → F
0 1 0 2
5
7
5
7
(
617 nm), D → F (650 nm) and D → F (684 nm). The
0
3
0
4
2
5
50
75
100
IC50
5
7
D → F transition is approximately 3–6 times stronger than
0
2
5
7
D → F transition, indicating a highly polarisable chemical
CHME
21.56
25.68
23.78
22.46
28.67
31.68
32.68
34.02
40.21
42.65
42.72
46.74
47.62
49.43
52.68
56.22
58.23
61.54
64.56
64.25
63.58
68.78
68.54
76.12
73.46
81.74
78.46
80.67
83.24
81.37
92.37
92.01
64.84
58.62
59.32
57.94
54.47
50.98
47.74
43.78
0
1
3
+
environment around the central Eu ion responsible for the
bright red color of these complexes. These complexes might
be promising photoluminescent materials for the fabrication of
display devices. The photoluminescence analysis of the radi-
ative decay rate Arad, nonradiative rates Anrad, the lifetime
values (τ) and the luminescence quantum yield (η) confirmed
that ancillary ligands could enhanced the photoluminescence
properties of the Eu(III) complexes with the β-hydroxyketone
1
2
3
4
5
6
Std.
2-(4-chlorophenyl)-1-(2-hydroxy-4-methoxyphenyl)ethan-1-
methoxyphenyl)ethan-1-one. In the complexes Eu(III) ion co-
ordinated with the donor oxygen and nitrogen atoms of the
ligand CHME and ancillary ligands respectively which leads
to the π-electron delocalization over the chelate ring [46].
Furthermore, it was noticed that the antimicrobial activity of
the synthesized complexes increases with the increasing π-
conjugation system present in the complexes.
one. Moreover, it was interesting to note that all the complexes
proved to be having better antimicrobial activity than the stan-
dard references (ciprofloxacin and fluconazole) in case of the
microbes S. aureus, E. coli and C. albicans.
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