Poonam et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 152 (2016) 304–310
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scientific flash 2000 elemental analyzer, 1H NMR spectra were
recorded on Bruker Avance II 400 spectrometer (400 MHz) using
dimethylsulfoxide (DMSO) as solvent, IR spectra (4000–
400 cmꢂ1) were recorded at resolution 4 cmꢂ1 on Perkin Elmer
spectrum 400 FT-IR spectrometer with KBr pellets.
Thermogravimetric analysis was carried on a SDT Q600 V20.9
Build 20 thermal analyzer from 20 to 1200 °C at heating rate of
10 °C/min under nitrogen atmosphere. Photoluminescence excita-
tion (PLE), emission (PL) spectra and fluorescence lifetime decay
were conducted by using Hitachi F-7000 fluorescence spectropho-
tometer equipped with Xe-lamp at room temperature in solid
state. Antimicrobial and antioxidant activities were determined
by tube dilution method and DPPH method respectively.
1. Introduction
In recent 20 years, the interest of the scientific community
regarding optical properties of organolanthanide complexes has
been increased because of their intriguing applications in elec-
tronic technological field especially in flat panel displays and
organic light emitting diodes (OLEDs) [1–3]. The emission in these
complexes originates from electronic transitions within the inner
f-orbital of the central ion [4,5]. These lanthanide complexes exhi-
bit unique photoluminescent properties such as large stokes shifts,
high luminescence efficiencies, long fluorescence decay time and
extremely sharp emission spectra [6]. On account of their excellent
photoluminescent properties these complexes have also been uti-
lised in luminescent solar concentration [7], optical fibres for data
transmission [8], pH sensing [9] and UV dosimeters [10]. Moreover,
it is worth to mention that some of these complexes find extensive
use in medical diagnosis for instance as magnetic resonance imag-
ing (MRI) contrast agents [11].
2.2. Synthesis
The synthetic routes of ligand HDAP and complexes 1–3 are
shown in Scheme 1, which were synthesized from the reaction of
the ligand HDAP, ancillary ligand and Tb(NO3)3ꢁ5H2O in ethanol
solution.
Among the lanthanide ions, trivalent Eu3+ and Tb3+ ions have
attracted more attention due to their high luminescence intensity
as well as high colour purity [12–14]. The organolanthanide com-
plexes have very bright luminescence and their intensity depends
upon radiative and non-radiative process with in a complex [15–
17] and energy transfer from organic ligand to central metal ion
by ‘‘antenna effect’’, which can increase the luminescence effi-
ciency [5,18–21]. The b-hydroxyketone ligand is one of the major
antenna ligand which is found to sensitise Tb3+ ion luminescence
magnificently. The luminescence is further enhanced by the intro-
duction of ancillary ligand in Tb(III) complexes. The literature
study reveals that many lanthanide complexes also exhibited
interesting antimicrobial and antioxidant activities [22,23].
Therefore, with an aim to develop new photoluminescent materi-
als and potent antimicrobial and antioxidant agents, we success-
fully synthesized Tb(III) complexes by incorporating nitrogen
containing heterocyclic ancillary ligand.
2.2.1. Synthesis of ligand (HDAP)
The hydroxyketone ligand (HDAP) was synthesized by follow-
ing Houben–Hoesch reaction mechanism between phloroglucinol
and acetonitrile according to the method cited in literature [24].
White powder with 85% yield was obtained. The elemental analysis
data of HDAP (C10H12O4) is found (calculated)% C, 61.14 (61.22); H,
6.18 (6.16); O, 32.48 (32.62). IR (KBr) cmꢂ1 3430 (b), 3009 (w),
2943 (w), 2847 (w), 1630 (s), 1457 (m), 1422 (m), 1366 (s), 1324
(m), 1270 (s), 1221 (s), 1207 (s), 1154 (s), 1112 (m), 1079 (m),
1045 (w), 896 (m), 835 (m), 658 (m), 606 (w). 1H NMR
(400 MHz, DMSO): d 2.52 (s, 3H, CH3), 3.83 (s, 6H, OCH3), 6.02 (s,
2H, Ar–H), 13.84 (s, 1H, OH).
2.2.2. Synthesis of complex Tb(HDAP)3ꢁbiq (1)
The complex Tb(HDAP)3ꢁbiq was prepared by mixing ethanolic
solutions of HDAP (0.58 g, 3 mmol) and biq (1 mmol) with an aque-
ous solution of Tb(NO3)3ꢁ5H2O (1 mmol) with constant stirring on
magnetic stirrer. The pH of mixture was adjusted to 7–8 with
0.05 M NaOH solution. This resulted into formation of white pre-
cipitates. These precipitates were stirred for 3 h at 35 °C and then
allowed to stand for 1 h. The precipitates were filtered, washed
with water, ethanol, dried in air and then in vacuum desiccators
to obtain complex Tb(HDAP)3ꢁbiq (1). White powder with 86%
yield was obtained. The elemental analysis data of Tb(HDAP)3ꢁbiq
(C48H45O12N2Tb) is found (calculated)% C, 57.56 (57.60); H, 4.54
(4.50); N, 2.78 (2.80). IR (KBr):cmꢂ1 3008 (m), 2947 (m), 1616
(s), 1593 (s), 1534 (s), 1516 (s), 1496 (s), 1418 (m), 1384 (s),
1328 (m),1263 (m), 1220 (s), 1212 (m), 1159 (m), 1128 (s), 1057
(m), 1013 (w), 936 (m), 869 (m), 839 (m), 829 (s), 787 (m), 738
(s), 625 (m), 538 (w), 471 (w). 1H NMR (400 MHz, DMSO): d 2.67
(bs, 9H, CH3), 3.52 (bs, 18H, OCH3), 6.31 (bs, 6H, Ar–H), 7.63 (d,
2H, biq), 7.84 (d, 2H, biq), 8.02 (d, 2H, biq), 8.21 (d, 2H, biq), 8.49
(d, 2H, biq), 8.83 (d, 2H, biq).
In present work, a b-hydroxyketone ligand 2-hydroxy-4,6-dime
thoxyacetophenone (HDAP) was synthesized. With this
b-hydroxyketone as the first ligand and 2,2-biquinoline (biq) or
5,6-dimethyl-1,10-phenanthroline (dmph) or bathophenanthro-
line (bathophen) as an ancillary ligand, three new
terbium(III)complexes [Tb(HDAP)3ꢁbiq], [Tb(HDAP)3ꢁdmph] and
[Tb(HDAP)3ꢁbathophen] were synthesized. The compositions of
these complexes were ascertained by elemental analysis, IR, 1H
NMR spectra and thermal behaviour was perceived by TG–DTA
curves. The photoluminescent properties were investigated by
excitation spectra, emission spectra and luminescence decay
curves. The photoluminescent (PL) studies demonstrate that
Tb(III) complexes exhibit bright green colour in solid state at room
temperature. The excellent bright green luminescence of these
Tb(III) complexes suggest their potential application in display
devices. We have also explicated in vitro antimicrobial activities
and antioxidant activities of ligand and its corresponding Tb(III)
complexes employing tube dilution method and DPPH method
respectively in detail.
2.2.3. Synthesis of complex Tb(HDAP)3ꢁdmph (2)
2. Experimental
Same procedure as for Tb(HDAP)3ꢁbiq (1) but the mixture with
HDAP (3 mmol) and dmph (1 mmol) and 1 mmol Tb(NO3)3ꢁ5H2O.
The complexes Tb(HDAP)3ꢁdmph (2) was obtained as a white pow-
der with 85% yield. The elemental analysis data of
Tb(HDAP)3ꢁdmph (C44H45O12N2Tb) is found (calculated)% C, 55.42
(55.46); H, 4.70 (4.72); N, 2.93 (2.94).
2.1. Materials and methods
2,2-Biquinoline, 5,6-dimethyl-1,10-phenanthroline, batho-
phenanthroline and terbium nitrate pentahydrate were purchased
from Sigma–Aldrich. Other reagents were of analytical grade, and
used without any further purification.
IR (KBr):cmꢂ1 3006 (m), 2965 (m), 2939 (m), 1615 (s), 1573 (s),
1533 (s), 1495 (s) 1450 (m), 1417 (m), 1364 (s), 1329 (m), 1262 (s),
1220 (s), 1206 (s), 1159 (s), 1119 (s), 1076 (s), 1040 (w), 963 (m),
830 (s), 690 (m), 595 (m), 538 (w), 448 (w); 1H NMR (400 MHz,
The elemental analysis (C, H, N) for the synthesized ligand
HDAP and the Tb3+ complexes were carried out using thermo