A luminescent ph-responsive ternary europium(Iii) complex of β-diketonates and terpyridine derivatives as sensitizing antennae – photophysical aspects, anion sensing, and biological interactions

Article abstract of DOI:10.1002/ejic.201701495

The highly luminescent stable Eu³⁺ complex [Eu(tta)3(naptpy)] [1, tta = 2-thenoyltrifluoroacetone, naptpy = 2-{4-[(2,2′:6′,2′′-terpyridin)-4′-yl]phenyl}-6-bromo-1H benzo-[de]isoquinoline-1,3(2H)-dione] was designed as a pH-responsive anion-sens

Full text of DOI:10.1002/ejic.201701495

A Journal of
Accepted Article
Title: A Luminescent pH-Responsive Ternary Eu3+ Complex of β-
diketonate and Terpyridine Derivative as Sensitizing Antenae:
Photophysical Aspects, Anion Sensing and Biological Interactions
Authors: Kritika Gupta and Ashis K. Patra
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Eur. J. Inorg. Chem. 10.1002/ejic.201701495
Link to VoR: http://dx.doi.org/10.1002/ejic.201701495

European Journal of Inorganic Chemistry
10.1002/ejic.201701495
FULL PAPER
3
+
A Luminescent pH-Responsive Ternary Eu Complex of β-
diketonate and Terpyridine Derivative as Sensitizing Antenae:
Photophysical Aspects, Anion Sensing and Biological
Interactions
[
a]
*[a]
Kritika Gupta and Ashis K. Patra
3
+
Abstract:
Eu(tta) (naptpy)] (1) [tta = 2-thenoyltrifluoroacetone, naptpy = 2-(4-
[2,2':6',2''-terpyridin]-4'-yl)phenyl)-6-bromo-1H benzo[de]isoquinoline
1,3(2H)-dione] was designed as pH-responsive anion sensing probe.
A
highly luminescent stable Eu
complex,
luminescent sensors with high sensitivities and specificities
have been reported previously.[5-7] Several multidentate
[
3
(
-
cyclen-based lanthanide complexes for selective detection of
various anions at Ln3+ centers in aqueous media were
reported.[6,7] Gunnlaugsson et al. have reported a cylen
based luminescent self-assembly of Eu3+ ternary complex
Complex
1
was synthesized and characterized using various
1
physicochemical and spectral methods like FT-IR, H-NMR, ESI-MS,
UV-vis and emission spectral studies.
A
photosensitization
and
assembly is highly pH dependent. Further, they employed
this probe as luminescent sensor for anions, where the

-diketonate in water where the ternary Eu3+ self-
mechanism with two antennae, viz. tta and naptpy for Eu-
[
7]
5
3+
luminescence by energy transfer to emissive
0
D states of Eu

-
through corresponding excited triplet states of the ligands are shown.
It displays strong luminescence properties, remarkable photostability,
diketonate antenna is displaced by anions with concomitant
changes in the Eu3+ emission intensity.
2
long luminescence lifetime ( = 0.365 ms) in H O and absence of any
Unique emission properties like longer excited state
coordinated inner-sphere water (q < 1). The pH-dependent study
showed that emission intensity of 1 was quenched or ‘switched off’
upon displacement of the β-diketonate antenna due to the acid
sensitivity of -proton in tta and subsequent ligand exchange reaction.
The anion sensitivity of the probe was evaluated using a series of
lifetime (
), large ligand-induced Stokes’ shift and sharp
emission bands corresponds to the characteristic f

f
3
+
transitions in the inner 4f shell of Ln . These transitions are
shielded from the influence of the chemical environment by
¯
¯
2
6
anions in aqueous DMF. Upon binding to citrate, F and HCO
3
,
the outer 5s 5p subshells which make optical properties of
luminescence quenching of complex 1 was demonstrated, while only
minor luminescence changes were observed in the presence of other
anions suggesting oxophillicity or stronger binding affinity with the
lanthanide complexes are rather more fascinating. The
radiative transition in Ln3+ is parity-forbidden thus inducing
only weak absorbance and ineffective direct excitation.[8] The
3+
hard oxoanions with hard Eu Lewis acid. The probe shows efficient
luminescence efficiency of the Ln3+ complex is mainly due to
4
-1
5
-1
b
DNA (K = 6.53 X 10 M ) and BSA (KBSA = 5.09 X 10 M ) binding
its strongly absorbing ligands, that absorbs light and
transfers its energy from 3T state to the emissive excited
state of the Ln3+ ion, which can then decay non-radiatively or
emit light. This phenomenon of indirect sensitization is
known as “antenna effect”.[8,9] The fascinating luminescence
and magnetic properties of lanthanides have diverse
applications in bioimaging, laser source, luminescent probes,
affinity under physiological condition. Quenching in luminescence
intensity upon interaction with CT-DNA suggests possible
luminescence-based sensing application.
Introduction
sensors, drug delivery, medical diagnosis, MRI, labels for
biomolecules and stains for cellular imaging.[10-15]
-
-
Recognition and sensing of different anions (e.g., F , CN ,
HCO
-, citrate, ascorbate, etc.) have aroused significant
3
We are interested in exploring such emissive lanthanide
attention due to their association in various biological and
metabolic processes as well as their detrimental effect on
certain organisms and the environment.[1-7] Sensitive
probes for sensing and recognition of bioanalytes and
cellular imaging.[
16,17]
Herein, we have designed
a
3+
luminescent Eu -probe based on 1,8-naphthalimide
appended planer terpyridine ligand (naptpy) and 2-
thenoyltrifluoroacetone (tta) as photosensitizing antennae
(Scheme 1). We have chosen 2-thenoyltrifluoroacetone
response requires specific reactive receptor composed of
organic fluorophores to monitor particular anions.[3,4]
3
+
Lanthanide (Ln ) complexes provide strong electrostatic
(
Htta) as -diketonate ligand to introduce pH-sensitivity and
interaction with such anions as they are oxophilic with higher
charge density (e/r).[5] Numerous lanthanide-based
potential anion sensing application via lanthanide based
displacement assay. Usually, tta is highly sensitive to pH
changes due to the presence of
-acidic proton. The three
tta ligands provide hard oxygen donor sites which forms a
[
a]
Department of Chemistry
Indian Institute of Technology Kanpur, Kanpur 208016
Uttar Pradesh, India
3+
thermodynamically stable Eu
complex and promote
3
+
effective energy-transfer to Eu for visible light emission by
serving as ‘’antenna’’ with enhancement in the Eu3+
E-mail: akpatra@iitk.ac.in
https://www.iitk.ac.in/new/ashis-k-patra
Supporting information for this article are available on the WWW
under http://dx.doi.org/10.1002/ejic.201701495.
luminescence.[18-20] Moreover, low energy C-F bonds helps
to reduce non-radiative quenching of lanthanide excited state
which consequently displays longer emissive lifetimes (),
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201701495
FULL PAPER
enhanced quantum yield (
5
→7
) Eu3+

) and higher luminescence
citrate, HCO
3
¯ and F¯, where characteristic ( D
0
F
2
intensity. However, often such lanthanide complexes have
coordinated water molecules or labile anion or solvents
which undergo undesirable inner-sphere water-exchange
reactions in aqueous media, resulting non-radiative
luminescence quenching via O-H oscillators which is
detrimental for an imaging probe. A second ligand could
provide a coordinatively saturated and structurally rigid
Eu-complex and acts as a chromophoric antenna. This
approach will ultimately avoid nonradiative luminescence
quenching through vibrational energy transfer (VET) to O–H,
N–H and C–H oscillators hence, enhancing desired optical
properties and making them ideal as imaging probes.[17-19]
The naptpy ligand provides tridentate binding site
emission was quenched or ‘switched off’ upon displacing
diketone antenna on recognition of these anions. Complex
also exhibit potential binding affinity with DNA and BSA in an
aqueous medium due to presence of planar naptpy ligand.

1
-
Results and Discussion
Synthesis and general aspects
[
Eu(tta)
3
(naptpy)] (1) was synthesized in high yield (~71%) by
reacting [Eu(tta) (H O) ] with naptpy in THF (Scheme 2). The
3
2
2
1
naptpy ligand and the complex 1 were fully characterized by H-
NMR, ESI-MS, FT-IR, Job’s plot and UV-Vis spectroscopy. The
complex 1 was stable under ambient condition. The ESI-MS
analysis of complex 1 in DMF showed respective molecular ion
3
+
coordination for Eu . The terpyridine (tpy) is an excellent
3
+
3+
neutral ligand for Eu ; it offers efficient sensitization of Eu
centred luminescence by reducing non-radiative decay of the
excited states of the europium ion. The tpy moiety also acts
as a light harvesting photosensitizing antenna, making it
+
peak as [1-tta] with calculated isotopic distribution exhibiting it’s
structural integrity in solution (Fig. S2, SI). The FT-IR spectra
shows C=O at 1640 cm-1 of Htta shifted to 1611 cm-1 for complex
1 indicating strong interaction between the oxygen atoms from
[
21-
highly attractive for incorporation into single ligand design.
2
3]
Moreover, tpy and 1,8-naphthalimide derivatives were
Htta and Eu , C=N at 1423 cm-1 for complex 1 also shifted to
lower energy compared to the naptpy ligand at 1585 cm-1
suggesting possible coordination through N,N,N-donor naptpy
3+
extensively used due to their excellent fluorescence
properties, photostability and effective interactions with
biomolecules. The choice of naptpy as a ligand is based on
the fact that tpy with 1,8-naphthalimide moiety could act as
photosensitizer cum DNA binders. Moreover, the
photophysical properties of naphthalic anhydride derivatives
can be tuned through structural modification on either at the
nitrogen of the imide site or at the aromatic ‘naphthalene’
moiety itself.[24] These derivatives were extensively used as
strongly absorbing and colourful dyes, building block for
artificial light harvesting arrays, fluorescent chemosensors
for metal cations and anions in recent years.[24,25]
3
+
ligand to Ln . The presence of Ln−O and Ln−N vibrations also
confirms such coordination mode. A strong band at 1134 cm-1
3
assigned to C-F stretching mode of CF (Table 1).
-
1
Table 1. Selected FT-IR frequencies ( ̅ / cm , in KBr disc) and their
assignments for free naptpy, [Eu(tta) (naptpy)] (1) and Htta
3
-
1
(
̅ in cm )
[Eu(tta)
3
(naptpy)] (1)
naptpy
Htta




(C=O)
(C=N)
1611
1423
1184
1134
458
-
1640
1585
-
-
(C-N)
(C-F)
1223
-
-
-
1111

(Eu-O)
(Eu-N)

518
-
The UV-visible spectra of 1 in 5mM Tris-buffer showed two major
ligand based -* (S →S ) transitions ranging from ~260 to 400
0
1
nm. The absorption maxima at 339 nm for free Htta ligand were
blue-shifted to 349 nm in complex 1 due to electronic perturbation
induced by the coordinated Eu3 (Fig. 1a). The emissive nature of
complex 1 was also probed using fluorescence spectroscopy that
revealed a broad band ~350-550 nm due to the ligand-centred
+

emission possibly due to the ligand based  excited state (Fig.
1b).
3
Scheme 1. (a) Design strategy for luminescent [Eu(tta) (naptpy)] (1) probe
highlighting various photophysical parameters. (b) Time-delayed luminescence
spectra of Eu(III) complex in aq. DMF at 298 K with corresponding assignments
5
7
of D  F transitions [ex= 349 nm, delay and gate time = 0.1 ms, Ex. and Em.
0 J
slit width = 5 nm] (top) and photographs Eu(III) complex under ambient light and
UV-light exposure (bottom).
With the aim mentioned above of pH dependent
quenching process, we have developed
a
stable
coordinatively saturated photosensitized luminescent
complex, [Eu(tta) (naptpy)] (1) which inhibits binding of H O
3 2
to Ln3+ and prevent non-radiative quenching by vibrational
energy transfer (VET) and later on can be used as a platform
Figure 1. (a) UV-visible absorption spectral traces of complex 1, tta and naptpy
ligands in 5 mM Tris-buffer (with 2% DMF) at pH 7.2 (T = 298 K), [1] = 10 μM.
(b) Steady state emission spectra for complex 1 recorded in fluorescence in 5
for sensing anions (Scheme 1). Complex
1 act as a
luminescent sensor for the detection of anions such as
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201701495
FULL PAPER
−
1 [28,29]
mM Tris-buffer (with 2% DMF) (T = 298 K). ex = 349 nm, Ex. and Em. slit width
cm .
[
Time-delayed
luminescence
spectra
of
=
5 nm.
Eu(tta) (naptpy)] (1) shows characteristic europium based red
3
luminescence at ex = 349 nm attributed to the 5
7
0
J
D → F f–f
transitions of Eu3 (J = 0-4). The most intense band at 614 nm
+
The Job’s plot analysis and luminescence titrations were
3
+
5
performed to evaluate the stoichiometry between Eu and the
respective ligands and speciation of complex 1 in aqueous
solution at pH 7.2. As shown in Fig. 2a, the Job’s plot exhibited
maxima at 0.5 mole fraction, indicating 1:1 stoichiometry of
originated from electric dipole (ED) induced hypersensitive
→ F transition.
2
D
0
7
[30,31]
[
Eu(tta)
3
(H
2
O)
2
]
and naptpy. Subsequently, the binding
3
+
stoichiometry between tta and Eu was also evaluated (Fig. S3,
SI). The Job’s plot displayed a maximum at 0.75 molar fraction,
indicating 1:3 stoichiometry between Eu3+ and tta. Moreover, the
naptpy to [Eu(tta)
luminescence titrations of naptpy (10 μM) with varying
concentration of [Eu(tta) (H O) ] in 5 mM Tris-buffer at pH 7.2.
3 2 2
(H O) ] ratio was also calculated by
3
2
2
The resulting titration curve exhibit best fitting with a 1:1
stoichiometry (Fig. 2b). These results unambiguously proved that
[
3
Eu(tta) (naptpy)] as the sole major species in aqueous solution
at physiological pH.
Figure 3. Schematic energy transfer diagram for [Eu(tta)
and naptpy ligands is non-radiative transition,
transition, S = singlet, T = triplet, ET = energy transfer).
3
(naptpy)] (1) from tta
(
is radiative
-1
The electronic energy levels of tta were at 25,164 cm (S
1
1
) and
8,954 cm-1 (T
). Density functional theory (DFT) was applied
1
[28]
Figure 2. (a) Job's plot of the reaction between [Eu(tta)
mM Tris-buffer (pH 7.2) (the total concentration of [Eu(tta)
3
(H
2
O)
(H
was kept at 20 M). (b) Luminescence titration of naptpy with varying
concentration of [Eu(tta) (H O) ] in 5 mM Tris-buffer at pH 7.2. The resulting
2
] and naptpy in 5
to the naptpy ligand for calculating it’s energy levels which justifies
3
2
O) ] and naptpy
2
the plausible energy transfer mechanism from corresponding
3
+ [32]
3
2
2
ligand to Eu . The calculated singlet (S
1 1
) and triplet (T ) energy
luminescence titration curve was analyzed by a non-linear regression based on
a 1:1 binding isotherm model (T = 298 K, ex = 349 nm, em = 614 nm, Ex. and
Em. slit width = 5 nm).
levels of the naptpy by DFT and TD-DFT analysis were located at
-1
-1
28,025 cm (3.48 eV) and 22,987 cm (2.85 eV), as
schematically shown in Fig. 3. Both ligands thereby can effectively
transfer the energy from their T states to the 5
Eu .
3
0
D state of the
Time-dependent absorption spectra of 1 in 5 mM Tris-buffer was
recorded for 4 h at 298 K do not show any observable changes
suggesting it’s appreciable stability in solution and unlikely any
ligand-exchange reactions occurring at neutral pH. Further,
emission/luminescence spectra were also recorded at regular
time interval upon irradiation with complex 1 (Fig. S5, SI). The
steady-state fluorescence and luminescence intensity of complex
3+ [33]
3
Therefore, in luminescent [Eu(tta) (naptpy)], the ET-
process is more facile from dual antennae to Eu because of
efficient intersystem crossing (ISC) and optimal energy gap from
excited state of Eu . The effective
sensitization effect of ancillary ligand ‘naptpy’ on Eu emission
3+
ligand triplet states to 5
3+
D
0
3+
can also be seen on luminescence spectra of [Eu(tta)
which increases upon the addition of naptpy. Moreover, we also
observed enhancement of luminescence spectra of
[Eu(naptpy)(NO ) ] upon gradual increment of ‘tta’. These results
3 2
.2H O)]
1
show no notable changes (only 8% reduction) in its
luminescence intensity. These observations strongly indicate
3
3
remarkable photostability of complex 1 in solution (Fig. S5, SI).
further underscores the effect of sensitization by both the ligands
in complex 1 (Fig. S4, SI).
Photophysical Properties
(
b) Photoluminescence excited state lifetimes and effect of
solvents. The excited state lifetime of complex 1 was measured
Lanthanide complexes are well-known for their intense
luminescence based applications ranging from biomedical
imaging to sensing anions and bioanalytes based on their narrow
emission bands, large Stokes’ shift and long-lived excited state
5
7
at 298 K by monitoring the most intense emission line ( D
at em = 614 nm under excitation at ex = 349 nm (Fig. 4a, Table
). The exhibited monoexponential decay is indicative of the
0
2
 F )
2
3
+
presence of a single chemical environment around the Eu ion.
The measured data were fitted with single exponential functions
[
26,27]
lifetimes (µs-ms).
The detailed photophysical studies were
performed for complex 1 as discussed here.
−
풕
given by the equation: 푰(풕) = 푰 + 푨 풆풙풑 , where A
1
is the
ퟎ
ퟏ
흉
(
a) Energy Transfer Mechanism. The energy transfer pathway
scalar quantity obtained from the curve fitting, I = 0 is the offset
0
3
+
in luminescent Eu -complex comprise of photoexcitation of the
value, t is the time in ms and t is the decay time for the exponential
ligand energy to the Eu3+ through their corresponding triplet (T
)
[34]
1
component. The effect of solvent types on the emissive lifetime
3
+
states via intersystem crossing (ISC); finally, the Eu ion emits
when the electronic transition from D
(
the D
(
were studied using a variety of solvents (Table 2 and Fig. S6, SI).
5
7
0
to F
J
ground state occurs
The lifetimes decreased in the order of CHCl > DCM > THF >
3
[
28]
3
5
Fig. 3). Ideally, the T level of ligands should be higher than
DMF > H O. Overall, the primary process that quenches the D
excited state of Eu in solution is non-radiative relaxation via a
Presence of C-H, N-H, and O-H groups
from solvents in close vicinity to the central Eu favours
2
0
5
3+
−1
3+
0
level of Eu (17,200 cm ) for effective energy transfer
vibronic coupling.[
34-36]
ET) and hydration number, q = 0. Moreover, the difference of
3
3+
optimal energy gap (ΔE) between the ligand T states to the
emissive excited state of Eu3+ ( D
5
) ideally should ~2500–3000
0
quenching of the luminescence. The longer lifetime in CHCl and
3
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201701495
FULL PAPER
DCM are because of the frequency of C–H vibrational oscillators
is lower than that of O–H.
5
Figure 4. Luminescence decay profile of D
0
excited state at 614 nm in H
(naptpy)] (1) from at T = 298 K, ex
49 nm, [1] = 3 M, delay and gate time = 0.1 ms, total decay time = 10 ms, Ex.
and Em. slit width = 5 nm. Red and blue curves are single exponential fitting
2
O and
D
2
O under ambient condition for [Eu(tta)
3
=
Figure 5. Proposed schematic representation and visible color changes of the
luminescent complex 1 at pH 7.2 showing red Eu3+ emission (self-assembly)
and the dissociation of complex 1 in acidic and alkaline solution at pH 2 and pH
11 respectively. Photographs of complex 1 in different conditions under ambient
(left) and UV light exposure (right) respectively.
3
2 2
O and D
O respectively. (b) The changes in Eu3 emission of
+
curve in H
Eu(tta) (naptpy)] (1) in 5 mM Tris-buffer as a function of pH, showing switched
off-on-off’ upon basification, ex = 349 nm. Inset: the change in 5
emission intensity of [Eu(tta) (naptpy)] (1) monitored at 614 nm as a function of
pH (blue traces = basic pH, red traces = acidic pH).
[
3
7
0 2
D  F
‘
3
The pH-sensing mechanism of [Eu(tta)
that characteristic luminescence intensity of Eu ( D
(naptpy)] (1) demonstrate
3
3+
5
7
0
2
 F ) would
+
be reduced immediately as H can break the six-membered
3
+
To gain an appreciation of the solution state speciation of complex
in aqueous media, excited state lifetimes in H O and D O were
chelate ring built by tta and Eu , which deteriorate the
1
2
2
sensitization mechanism of -diketonate and consequently
3
+
recorded that allows determination of hydration number (q) of the
complex via modified Horrock’s equation ignoring any alternative
deactivation pathway (Fig. 4a).[34] The determined q < 1 for the
results in poor energy transfer to Eu (Fig. 4b). Thus at lower
acidic pH the ternary complex 1 dissociate to form a solvent
bound complex with mostly significant quenching by VET (Fig. 5,
S7). In addition, the response rate to the pH changes must be
considered for the luminescence-based pH detecting systems. As
both protonation and deprotonation are instantaneous reversible
chemical processes, the luminescence change occurs
immediately, thus considered as a real-time measurement. The
reversibility of a pH probe is a very important and necessary criterion.
To test this reversible response for probe 1, the pH of the solution was
3
+
complex 1 confirms absence of any bound H
2
O to Eu in solution.
This coordinnative saturation restricts the energy dissipation by
3
+
VET from Eu to the O−H oscillator and enhances the emissive
lifetime of the probe.
Table 2. Selected photophysical data of [Eu(tta)3(naptpy)] (1)
[ms] (b)

max [nm],[a]
3
switched back and forth between 7.5 and 2.5 by using HCl and Et N
q(c)
 [M−1cm−1])
CHCl
3
THF
DMF
DCM
H
2
O
D
2
O
(Fig. S8, SI). Results clearly show that the probe exhibited a highly
reversible response to pH and the response time is instantaneous.
The switching between the luminescence ON/OFF states could thus
be repeated for multiple cycles. The luminescence response of 1
(
2
3
85 (56,820),
49 (64,200)
0.26
0.652
0.528
0.498
0.599
0.365
0.440
[
a] UV-vis spectrum in aq. DMF. [b] Luminescence lifetimes (  15%). [c]
[34]
Hydration number (q  10%) determined using modified Horrock’s equation.
3
can be recovered completely after exposure to the Et N due to the
formation of complex 1 by self-assembly in solution.
In neutral pH 7.2, complex 1 shows strong red emission
while in either acidic (pH < 4) or alkaline solution (pH > 9)
luminescence is quenched as the tta moiety get dissociated from
ternary complex 1. It might be possible that on dissociation of
complex some solvent molecules or anions were displacing -
pH response on Photoluminescence
Luminescence properties of Eu(III)-β-diketonate complex 1 was
expected to be very sensitive to pH changes due to the presence
of -acidic proton in tta ligand. Generally acidic sites are
3
+
diketone moiety which results in quenching of Eu -emission via
nonradiative vibrational energy transfer (VET). Moreover, a
decrease in Eu3 emission intensity was also evident under UV
lamp as directly seen in Fig. 5. The changes in absorption spectra
+
responsible for quenching of luminescence intensity of lanthanide
complexes.[
37,38]
This leads us to expect that complex 1 having
3
of [Eu(tta) (naptpy)] (1) as a function of pH also displayed
significant changes suggesting a possible dissociation of tta
ligands and scope of further ligand-exchange reactions (Fig. S9,
SI).
three -diketonate moieties could also be used as pH measuring
probe. To further evaluate the potential sensing applications of
complex 1 as pH probe, the changes in emission intensity at
various pH ranges were examined. The emission intensity of 1
(

ex = 349 nm) was quenched with changes in pH due to the
protonation of the -proton of tta.
Displacement based anion sensing
Reversible displacement of tta in complex 1 in the presence of
competitive coordinating ligands, especially anions could be
[
38-40]
applied as a potential sensing strategy.
This can be termed
as lanthanide based 'displacement assays’ where Eu3 emission
+
was anticipated to be quenched as energy transfer from antenna
[
41]
would be prevented upon displacement of -diketonate moiety.
Thus, the binding of anions to the inner-sphere of Eu3+ brings
5
significant changes in the intensity of the hypersensitive
D
0
3
+
emissive peak of Eu . This hallmark makes the complex 1 ideal
for the development of luminescent sensor for coordinating
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201701495
FULL PAPER
anions. Quantitative titrations in the presence of various anions
DNA binding studies
with [Eu(tta)
3
(naptpy)] at pH 7.2 were performed to assess this
assumption. The result illustrates that luminescence intensity of
Eu at 614 nm does not affect much upon addition of anions such
DNA is the vital pharmacological target for various metal-based
chemotherapeutic drugs like cisplatin, carboplatin or oxaliplatin
where they mainly bind with the nitrogen of nucleobases of DNA
and trigger cell-death pathways. The non-covalent DNA binding
agents are either intercalators or groove binders. The presence of
planar naptpy moiety encouraged us to study the DNA-binding
3
+
¯
¯
¯
¯
¯
as Br , ClO
4 6 3 2
and PF to [Eu(tta) (naptpy)] (1) while NO and I
3
+
offers only small changes in Eu emission intensity at 614 nm
Fig. S10 and S11, SI). In contrast, the presence of citrate, F ,
¯
(
¯
3 ,
acetate, tartaric acid, HCO and ascorbate results in significant
decrease in luminescent intensity of Eu3+ at 614 nm as shown in
Fig. 6 and Fig. 7.
propensity of the complex
1 using various spectroscopic
techniques.[
42,43]
Figure 8. (a) Absorption spectral traces of [Eu(tta)
mM Tris-buffer (pH 7.2) with increasing [CT- DNA] at 298 K. Inset: af/bf vs.
DNA] plot for complex 1. (b) Emission spectral traces of EB-bound CT-DNA
with increasing [1] in 5 mM Tris-buffer (pH 7.2) at 298 K. ex= 546 nm, em = 603
nm, [EB] = 13.5 M. Inset: plot of I/I vs. [complex].
3
(naptpy)] (1) (15 µM) in 5
[
0
Absorption spectroscopy. The binding propensity of complex 1
with CT-DNA was studied by UV-vis spectral titrations. The
intercalation results in a bathochromic shift and hypochromism
¯,
Figure 6. Luminescence spectral changes of complex 1 with tartarate, HCO
3
¯
¯
ascorbate, CH
3
COO , citrate and F (as their sodium or TBA salt). ex = 349 nm;
1] = 10 M; [Anions] = 20 M; Ex. and Em. slit width = 5.0 nm, T = 298 K. Inset
shows digital photographs of complex 1 under UV lamp (= 365 nm) showing
due to possible perturbation of the -orbitals of DNA base pairs
[
[42]
with the -orbitals of the intercalated ligand.
The absorption
spectral traces of complex 1 with increasing concentration of CT-
DNA is shown in Fig. 8a. The intrinsic DNA binding constant (K
of the complex 1 was obtained by monitoring the changes in
absorbance of the complex with increasing DNA
concentrations. The calculated K value for complex 1 in the
intensity changes for corresponding anions.
b
)
Furthermore, these changes are clearly visible by the naked eye
under UV lamp (Fig. 6). Detailed quantitaive anion titration using
[43]
-1
b
sodium citrate, tartaric acid and NaHCO
3
were also performed at
4
range of 10 M suggests groove binding or partial intercalation
through naptpy and tta moiety with the DNA (Table 3).
pH 7.2 which clearly confirms that Eu3+ emission decresed
gradually via displacement of tta (Fig. S12, SI). These
observations indicates oxophillicity and stronger binding affinity of
oxoanions with hard Eu3+ centre. The present probe although lack
Emission quenching method. Ethidium bromide (EB) is a well-
known intercalating dye used as a fluorescent tag which shows
intense emission upon binding to duplex-DNA. The displacement
of EB by competitive titration with 1 leads to decrease in the
emission intensity of EB at 603 nm suggesting intercalative or
minor groove binding modes for 1 (Fig. 8b). The extent of
decrease in fluorescence intensity gives a measure of the relative
very high specificity to a particular anion, which could be achieved
via appropriate modification of the ligand framework. This system
and current strategy although proves itself as potential platform
for luminescent Ln-based displacement assay for various anions.
6
-1
binding affinity of the complex. The calculated Kapp of 10 M for
the probe indicates it’s strong binding affinity with DNA.
Serum protein binding studies
Serum albumins are the major (~55%) and most extensively
studied transport proteins present in circulatory system. BSA is a
model protein for physicochemical and biophysical studies as it
serves as a transporter of many organic molecules, steroids, fatty
acids, thyroid hormones, and many drugs to their target. The
binding interaction of Eu3 complex with BSA was monitored using
quenching of tryptophan (Trp-134 and Trp-212) emission
intensity.[ With gradual increase in concentration of complex 1
the fluorescence intensity at 345 nm gets quenched steadily
indicating a binding interaction between complex 1 and BSA (Fig.
+
44]
3
Figure 7. The emission intensity contrast bars of [Eu(tta) (naptpy)] (1) (10 M,
¯
¯
3 3
ex = 349 nm) upon addition of anions (tartrate, HCO , ascorbate, CH COO ,

¯
citrate and F ) at em = 614 nm at pH 7.2. The tertiary complex 1 is shown for
comparison.
9).
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201701495
FULL PAPER
vibrational
quenching.[30]
3
Figure 9. (a) The effect of addition of [Eu(tta) (naptpy)] (1) on fluorescence
3
Figure 10. (a) Time-delayed luminescence spectra of [Eu(tta) (naptpy)] (1)
showing luminescence intensity quenching with increasing concentration of CT-
quenching of BSA in 5 mM Tris-buffer (pH 7.2) at 298 K. The inset shows the
plot of I /I vs. [complex] for complex 1. ex = 295 nm, em= 345 nm, [BSA] = 2
M. (b). Scatchard plots of log[(I - I)/I] vs. log[complex] to determine the binding
0
DNA in 5 mM Tris buffer (pH=7.2) at 298 K [delay time = gate time = 0.1 ms, ex

0
=
349 nm, Ex. and Em. slit width = 5 nm]. (b) Luminescence emission intensity
q
constant (K), quenching rate constant (k ) and number of binding site (n) for
of complex 1 at 614 nm vs. the [CT-DNA]/[1] ratio.
BSA to complex interaction.
The remarkable quenching may be attributed to the various
changes in the BSA secondary structure, such as ground state Conclusions
complex formation, collision between fluorophores and
a
quenchers, protein denaturation, or conformational changes of
the protein induced by these quenchers.[45] The Stern-Volmer
equation and Scatchard plots were used to dtermine the Stern-
In summary,
a
highly stable luminescent complex
sensitized light absorbing
[
Eu(tta) (naptpy)] (1) with
3
a
Volmer quenching constant for BSA fluorescence (KBSA) for
chromophores viz. tta and naptpy, have been prepared and their
solution state behavior have been thoroughly characterized using
a combination of 1H-NMR, IR, ESI-MS, UV/Vis and emission
44]
[
Eu(tta)
3
(naptpy)] (1).[ The plots were shown in Fig. 9 and
5
-1
values are listed in Table 3. The KBSA value (10 M ) indicate the
strong affinity of complex 1 to serum proteins.
spectroscopy. Complex
1 shows characteristic strong red
luminescence both in solution and solid state, which suggests
efficient excited state energy transfer from the antenna moieties
3
Table 3. Binding interaction parameters for the [Eu(tta) (naptpy)] (1) complex
with CT-DNA and BSA
to the Eu3+ or 5D
state with long excited state lifetime in
0
K
b
/M-1(a)
K
app/M-1(b)
K
BSA/M-1(c)
k
q
/M-1(d)
K/M-1(e)
milliseconds. We have shown that the ternary complex 1 is highly
pH sensitive and further it can be used as a luminescent sensor
for anions at physiological pH, where tta (-diketone) moiety is
displaced by oxyanions with gradual decreases in the Eu3+
emission. Furthermore, complex 1 shows effective binding
tendency with CT-DNA via groove binding or partial intercalation
through naptpy and tta moiety. It also strongly binds with BSA as
determined through emission quenching studies and may be
suitable to transport the Eu3+ probe to the pathological site for its
delivery. The remarkable photostability, the absence of inner-
sphere water (q < 1), and longer excited-state lifetimes (ms) and
high luminescence under biological pH window of the complex
make them an ideal platform for intracellular pH measurement
probes.
[
Eu(tta)
3
(naptpy)]
(1)
6
.53 X 104 2.21 x 106 5.09 X 105 5.09 X 1013 1.93 X 106
b
[a] K intrinsic DNA binding constant with calf-thymus DNA. [b] Kapp apparent
DNA binding constant. [c] KBSA Stern-Volmer quenching constant for BSA
fluorescence. [d] kq quenching rate constant. [e] K binding constant with BSA.
Number of binding sites (n) are 2.03.
DNA sensing studies
Due to unrivalled optical properties originating from the ff
3
+
transitions in the inner 4f shell of Ln , lanthanide complexes are
ideal luminescent probes for an array of numerous applications in
sensing and detection of various analytes and biological
targets.[
16,36]
To investigate the sensing ability of complex 1 towards DNA,
the time-delayed luminescence spectra was recorded in presence
of CT-DNA. The significant quenching of the Eu-centered
Experimental Section
5
7
luminescence ( D
0
J
 F transitions) was obeserved on addition of
Materials and methods
CT-DNA to the complex 1 (Fig. 10). The notable quenching of
hypersensitive peak (J =2) of Eu3+ at 614 nm indicates the
possible alteration of direct bonding in the primary coordination
All the chemicals and reagents were purchased from Sigma-
Aldrich, Alfa Aesar and used without further purification unless
otherwise stated. The naptpy ligand was prepared using 4-bromo-
3
+
sphere of Eu . The luminescence quenching of complex 1 by
DNA indicated that complex had a strong interaction with DNA
possibly through the binding of negatively charged oxygen atoms
1,8-naphthalic anhydride and 4’-(4-aminophenyl)-2,2’:6’,2’’-
3
-
terpyridine (Tpy-NH ). Solvents used were either HPLC grade or
2
of phosphate (PO
4
) and displacement of tta as antenna which
were purified by standard procedures.
leads to poor sensitization of the probe by static or nonradiative
The FTIR spectra were collected with a Perkin-Elmer Model 1320
FT-IR spectrometer. Electronic spectra were measured at 298 K
1
using a Perkin-Elmer Lambda 25 UV-Vis spectrophotometer. H-
NMR spectra were recorded at 298 K on a JEOL-ECX 500 FT
(
400 MHz) instrument with chemical shift-referenced to
tetramethylsilane (TMS). ESI-MS measurements were carried out
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201701495
FULL PAPER
using a WATERS Q-TOF Premier mass spectrometer. The
steady-state fluorescence and time-delayed luminescence
spectra were recorded using Agilent Cary eclipse fluorescence
spectrophotometer at 298 K.
was then added dropwise to the reaction mixture and refluxed for
5 h. The resulting solution was then filtered over celite or cotton
wool, and the catalyst was washed with dichloromethane (200
mL). The organic phase was washed with water (4 X 100 mL).
Lifetime measurements were achieved under ambient conditions
2 4
The organic phase was then dried over Na SO and solvent was
in pure DMF, H
2
O, D
2
O (contains 1% DMF), CHCl
3
, DCM and
removed in vacuo to yield 4’-(4-aminophenyl)-2,2’,6,2’’-terpyridine
THF using a pulsed Xenon lamp at ex = 349 nm and em = 614
as yellow crystals. (Yield: 514 mg, 79%), 1H-NMR (400 MHz,
3
+
nm for Eu complex 1 with a delay and gate time of 0.1 ms. Decay
3
CDCl ) d (ppm): 8.73 (2H, d), 8.69 (2H, s), 8.66 (2H, d), 7.87 (2H,
curves were fitted by non-linear least square method. Lifetime
m), 7.79 (2H, d), 7.34 (2H, m), 6.80 (2H, d), ESI-MS (m/z) (%):
+
data for [Eu(tta)
shown in Fig. 4a and Fig. S6, SI. The excited state lifetime
measurements in water and D O allowed the determination of the
number of water molecules (q) directly coordinated to the Eu
3
(naptpy)] (1) under various conditions were
[M+H] calcd for C21
H
17
4
N : 325.1453, Found, 325.1459.
2-(4-([2,2':6',2''-terpyridin]-4'-yl)phenyl)-6-bromo-1H
benzo[de]isoquinoline-1,3(2H)-dione (naptpy).
4-Bromo-1,8-napthalic anhydride (277 mg, 1.0 mmol) and
2
3
+
3
+ [34]
using the following modified Horrocks’ equations for Eu .
2
TpyNH (324 mg, 1.0 mmol) in 30 mL ethanol were heated to
reflux for 24 h. Solvent was removed in vaccuo then washed with
water. A yellow coloured product was obtained, which was further
recrystallized from hot glacial acetic acid to afford the target
compound as a yellow powder. The yellow solid was then filtered
ퟏ
ퟏ
풒퐄퐮 = ퟏ. ퟐ ꢀ
ꢁ
ꢁ ퟎ. ퟐퟓꢂ
훕퐇ퟐ퐎 훕퐃ퟐ퐎
and washed with cold water and finally dried in vacuum over P
4
1
O
10
.
-
-
All the theoretical calculations were done using Gaussian 09 and
applying density functional theory (DFT). Ligand structure was
optimized using B3LYP/6-31G level of theory in the gas phase.[32]
(Yield: 532 mg, 91 %). UV/Vis (DMF, 298 K): max, nm, (ε, LM cm
1
): 282 (62,150), 329 (53,500), 1H-NMR (400 MHz, CDCl
3
) d
(ppm): 8.79 (2H, d), 8.77 (2H, s), 8.75 (1H, d), 8.68 (3H, m), 8.66
(1H, d), 8.48 (1H, d), 8.42 (t, 1H), 8.11 (2H, dd), 8.09 (m, 2H),
7.91 (2H, dd), 7.88 (2H, m), ESI-MS in DMF (m/z) (%): [M+H] ,
0 1
Ground states of both the singlet (S ) and first triplet state (T )
+
were optimized using their respective spin multiplicities. Excited
states of both singlet and triplet state were calculated using time-
dependent density functional theory (TD-DFT) method with the
pre-optimized ligand structure using B3LYP/6-31G level of theory
1 4 2
Calcd for C33H20Br N O : 583.077, Found: 583.077.
Synthesis of [Eu(tta)
To a stirred solution of naptpy (70 mg, 0.12 mmol) in 15 mL THF,
[Eu(tta) (H O) ] (85.19 mg, 0.1 mmol) was added. The reaction
3
(naptpy)] (1)
[32],
and simulated absorbance spectra are generated (Fig. S13
and Fig. S14, SI).
3
2
2
mixture was stirred overnight at RT. The resulting solution was
evaporated in vaccuo. The residue was re-dissolved in minimum
amount of THF and addition of n-hexane led to the precipitation
of brown-yellow microcrystalline powder as the target compound
Synthesis and characterization
4
’-(4-Nitrophenyl)-2,2’,6,2’’-terpyridine
Eu(tta) (H O) were prepared according to the reported
procedure in the literature (Scheme 2).
(Tpy-NO
2
)
and
3
2
2
]
[
46,47]
3
[Eu(tta) (naptpy)] (1). (Yield: 100 mg, 72 %), UV/Vis (aqueous-
-1
-1
DMF, 298 K): max, nm, (ε, LM cm ): 285 (56,820), 349 (64,200),
ESI-MS in DMF; (m/z) (%): Calcd for
([M-tta]+
Eu : 1176.97 (100), 1174.97 (43), 1175.97
C
49
H27Br
1
F
6
N
4
O
6
S
2
1
(
(
24), 1177.97 (54), 1178.97 (70), 1179.97 (34). Found: 1176.9730
100), 1174.9711 (46), 1175.9727 (25), 1177.9750 (53),
1178.9740 (75), 1179.9760 (37).
DNA binding experiment
DNA binding experiment was done in Tris–HCl/NaCl buffer (5 mM
Tris–HCl/NaCl, pH 7.2) using complex 1 in DMF solution. CT-DNA
in the buffer medium gave the ratio of 1.9:1 of absorbance in UV
region at wavelength 260 and 280 nm which showed that DNA is
free from protein. The DNA concentration was obtained using 260
-1
-1 [48]
=
6600 M cm . Absorption spectral titrations were performed
by varying the concentration of CT-DNA while keeping the
complex concentration constant. Due to the corrections made for
the absorbance of CT-DNA itself (Fig. 8a). The equilibrium binding
Scheme 2. General synthetic scheme for naptpy ligand and [Eu(tta)
1).
3
(naptpy]
b
constant (K ) of the complex 1 was determined by the following
(
equation.[
43]
4
2
’-(4-aminophenyl)-2,2’,6,2’’-terpyridine (Tpy-NH ).
[
DNA]/(
a
- 
f
) = [DNA]/(
b
- 
f
) + 1/K
b
(
b
- 
f
)
A solution of 4’-(4-nitrophenyl)-2,2’,6,2’’-terpyridine (708 mg, 2.0
mmol) in the presence of 10% Pd/Charcoal catalyst (300 mg) in
absolute ethanol (100 mL) was refluxed for 1.5 h. Hydrazine
monohydrate (3.2 mL, 56.4 mmol) in absolute ethanol (40 mL)
Where [DNA] is the concentration of CT-DNA in base pairs, 
the apparent extinction coefficient,  and  refers to the extinction
a
is
f
b
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201701495
FULL PAPER
coefficients of the complex in its free and fully bound form. The K
b
[4]
[5]
a) S. J. Butler, D. Parker, Chem. Soc. Rev. 2013, 42, 1652– 1666; b) L.
J. Charbonniere, R. Ziessel, M. Montalti, L. Prodi, N. Zaccheroni, C.
Boehme, G. Wipff, J. Am. Chem. Soc. 2002, 124, 7779.
values are obtained from the [DNA]/(
a
f
- ) vs. [DNA] plots.
Protein binding experiments
a) H. Tsukube, S. Shinoda, Chem. Rev. 2002, 102, 2389; b) T. Yamada,
S. Shinoda, H. Tsukube, Chem. Commun. 2002, 1218-1219; c) H.
Tsukube, T. Yamada, S. J. Shinoda, Alloys Compd. 2004, 374, 40; d) M.
D. Best, E. V. Anslyn, Chem. sEur. J. 2003, 9, 51; e) M. Montalti, L. Prodi,
N. Zaccheroni, L. J. Charbonnie`re, L. Douce, R. Ziessel, J. Am. Chem.
Soc. 2001, 123, 12694.
The interaction of the complex 1 with bovine serum albumin (BSA)
has been studied from tryptophan emission quenching
experiments. The quenching of the emission signals at 340 nm
(ex= 295 nm) were recorded by increasing concentration of
complex 1 in DMF solution to the solution of BSA (2 M) in 5 mM
[
6]
a) D. Parker, Coord. Chem. Rev. 2000, 205, 109–130; b) J. I. Bruce, R.
S. Dickins, L. J. Govenlock, T. Gunnlaugsson, S. Lopinski, M. P. Lowe,
D. Parker, R. D. Peacock, J. J. B. Perry, S. Aime, M. Bott., J. Am. Chem.
Soc. 2000, 122, 9674–9684; c) J. Yu, D. Parker, Eur. J. Org. Chem. 2005,
Tris-HCl-NaCl buffer (pH 7.2) Fig. 9a. The quenching constant
(KBSA) has been determined quantitatively by using Stern–Volmer
[
44]
equation (Fig. 9).
Stern–Volmer I /I vs. [complex] plots were made using the
4249–4252.
0
[7]
a) J. P. Leonard, C. M. G. dos Santos, S. E. Plush, T. McCabe, T.
Gunnlaugsson, Chem. Commun. 2007, 129-131; b) A. B. Aletti, D. M.
Gillen, T. Gunnlaugsson, Coord. Chem. Rev. 2018, 354, 98-120.
a) J.-C. G. Bꢀnzli, S. V. Eliseeva, Basics of Lanthanide Photophysics. In
Lanthanide Luminescence: Photophysical, Analytical, and Biological
Aspects; b) P. Hꢁnninen, H. H. Hꢁrmꢁ, Eds.; Springer Series on
Fluorescence, Springer-Verlag: Berlin, 2011, 7, 1−45.
corrected fluorescence data taking into account the effect of
dilution. Linear fit of the data using the equation:
[
8]
I
0
/I = 1 + KBSA[Q]
where, I
0
and I are the emission intensities of BSA in the absence
of quencher and in the presence of quencher of concentration [Q],
gave the quenching constants (KBSA).
[9]
a) G. A. Crosby, R. E. Whan, R. M. Alire, J. Chem. Phys. 1961, 3,
7
43−748; b) S. Comby, J.-C. G. Bꢀnzli, In Handbook on the Physics and
pH Titration
Chemistry of Rare Earths, vol. 37; c) K. A. Gschneidner, J.-C. G. Bꢀnzli,
V. K. Pecharsky, Elsevier, North Holland, 2007.
The luminescence titration of complex 1 (1 mM) have been
examined at different pH in 5 mM Tris–HCl/NaCl buffer by
performing acid–alkali (1M HCl and 1M NaOH) titration
experiment through both absorption and emission luminescence
[
[
[
10] a) J.-C. G. Bꢀnzli, C. Piguet, Chem. Soc. Rev. 2005, 34, 1048-1077; b)
e) H. Tsukube, S. Shinoda, H. Tamiaki, Coord. Chem. Rev. 2002, 226,
227.
11] a) R. Pal, D. Parker, Chem. Commun. 2007, 474-476; b) R. Pal, D.
Parker, Org. Biomol. Chem. 2008, 6, 1020-1033; b) B. S. Murray, E. J.
New, R. Pal, D. Parker, Org. Biomol. Chem. 2008, 6, 2085-2094.
spectroscopy. To observe the changes in luminescence emission
5
7F transition of Eu3+ complex 1 was monitored with
intensity, D
0
2
12]
a) C. P. McCoy, Chem. Mater. 2006, 18, 4336-4343; b) H. Tsukube, S.
Shinoda, Chem. Rev. 2002, 102, 2389.
gradual changes in pH.
Anion Sensing
[13] a) D. G. Smith, B. K. Mcmahon, R. Pal, D. Parker, Chem. Commun. 2012,
8, 8520-8522; b) E. J. New, D. Parker, D. G. Smith, J. W. Walton, Curr.
4
Luminescence spectroscopy is valuable tool to illustrate the
nature of anion binding to the Eu . The titrations with various
anions with complex 1 were done by adding aqueous solution of
Opin. Chem. Biol. 2010, 14, 238-246.
3
+
[14] a) S. Gupta, S. Mondal, A. Mhamane, A. Datta, Inorg. Chem. 2013, 52,
12314-12316; b) A. Datta, J. M. Hooker, M. Botta, M. B. Francis, S. Aime,
K. N. Raymond, J. Am. Chem. Soc. 2008, 130, 2546-2552.
anions in 2 mL aliquots to a solution of complex 1 in DMF:H
2
O
[
[
[
[
15] a) S. I. Klink, G. A. Hebbink, L. Grave, P. G. B. Oude, F. C. J. M. van
Veggel, M. H. V. Werts, J. Phys. Chem. A, 2002, 106, 3681; b) P. Sutar,
V. M. Suresha, T. K. Maji, Chem. Commun. 2015, 51, 9876-9879; c) S.
Roy, A. Chakraborty, T. K. Maji, Coord. Chem. Rev. 2014, 273, 139-164.
16] a) A. Chandra, K. Singh, S. Singh, S. Sivakumar, A. K. Patra, Dalton
Trans. 2016, 44, 19844-19855; b) K. Singh, S. Banerjee and A. K. Patra,
RSC Adv. 2015, 5, 107503-107513; c) K. Singh, S. Singh, P. Srivastava,
S. Sivakumar, A. K. Patra, Chem. Commun. 2017, 53, 6144-6147.
(
70%). To avoid pH changes upon addition to the anions, the
anion stock solutions were adjusted to pH 7.2 prior to addition to
the complex 1.
Acknowledgements
17] a) S. Dasari, A. K. Patra, Dalton Trans. 2015, 44, 19844-19855; b) S.
Dasari, S. Singh, S. Sivakumar, A. K. Patra Chem. Eur. J. 2016, 22,
17387-7396; (c) Z. Abbas, S. Dasari, A. K. Patra, RSC Adv. 2017, 7,
We thank Science and Engineering Research Board (SERB)
(EMR/2016/000521), Government of India for financial support. KG thanks
4
4272-44281
18] a) N. S. Baek, M. K. Nah, Y. H. Kim, H. K. Kim, J. Lumin. 2007, 127, 707–
12; b) R. K. Mahajan, I. Kaur, R. Kaur, S. Uchida, A. Onimaru, S.
the University Grant Commission (UGC) for research fellowship. We thank
Amitosh Sharma for helping in DFT calculations.
7
Shinoda, H. Tsukube, Chem. Commun. 2003, 2238-2239; c) J. Lehr, P.
D. Beer, S. Faulkner, J. J. Davis., Chem. Commun. 2014, 50, 5678—
Keywords: Lanthanide• luminescence • europium • pH sensing
5
687; d) C. S. Bonnet, J. Massue, S. J. Quinn, T. Gunnlaugsson, Org.
•
anion sensing
Biomol. Chem. 2009, 7, 3074.
[
[
19] a) C. Yang, J. Xu, J. Ma, D. Zhu, Y. Zhang, L. Lianga, M. Lu, Polym.
Chem., 2012, 3, 2640; b) Z. Li, P. Li, Q. Xu, H. Li., Chem. Commun.,
[
1]
a) P. A. Gale, R. Quesada, Coord. Chem. Rev. 2006, 250, 3219–3244;
b) S. Shinoda, H. Tsukube, Analyst, 2011, 136, 431–435; c) D. Parker,
Chem. Soc. Rev. 2004, 33, 156-165.
2015, 51, 10644-10647. c) H.-Y. Wong, W.-S. Lo, W. T. K. Chan, G.-L.
Law Inorg. Chem. 2017, 56, 5135−5140; d) J. Li, L. Wang, X. Liu, X.
Jiang, Y. Cheng, C. Zhu, Polym. Chem., 2012, 3, 2578–2582.
[
2]
U. Reddy, G., R. Lo, S. Roy, T. Banerjee, B. Ganguly, A. Das, Chem.
Commun. 2013, 49, 9818–9820.
20] a) D. Ghosha, M. N. Luwang, RSC Adv., 2015, 5, 47131–47139; b) X. Li,
D. Zhang, J. Li., Spectrochimica Acta Part A: Molecular and Biomolecular
Spectroscopy, 2014, 127, 1–9. c) C. Yang, J. Xu, J. Ma, D. Zhu, Y. Zhang,
L. Lianga, M. Lu, Photochem. Photobiol. Sci., 2013, 12, 330–338. d) D.
[
3]
a) Y. Bretonniere, M. J. Cann, D. Parker, R. Slater, Org. Biomol. Chem.
2004, 2, 1624-1632; b) A. Thibon, V. C. Pierre, J. Am. Chem. Soc. 2009,
131, 434-435; c) R. Pal, D. Parker, L. C. Costello, Org. Biomol. Chem.
2009, 7, 1525-1528; d) S. J. Butler, B. K. McMahon, R. Pal, D. Parker, J.
W. Walton, Chem. Eur. J. 2013, 19, 9511-9517.
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201701495
FULL PAPER
V. Kazakov, F. E. Safarov, Photochem. Photobiol. Sci., 2014, 13, 1646–
[36] D. Costa, H. D. Burrows, M. da Gracüa, Langmuir, 2005, 21, 10492–
10496.
1649.
[
21] a) O. Kotova, R. Daly, C. M. G. dos Santos, M. Boese, P. E. Kruger, J. J.
[37] a) K. Binnemans, Chem. Rev. 2009, 109, 4283; b) X. Zhang, Y. Jiao, X.
Jing, H. Wu, G. He, C. Duan, Dalton Trans. 2011, 40, 2522-2527; c) Y.
Lu, B. Yan, Chem. Commun. 2014, 50, 13323-13326.
Boland and T. Gunnlaugsson, Angew. Chem., Int. Ed., 2012, 51, 7208–
7212; b) A. Wild, A. Winter, F. Schlutter, U. S. Schubert, Chem. Soc. Rev.
2
011, 40, 1459; c) U. S. Schubert, H. Hofmieier, G. R. Newkome, Modern
[38] (a) T. Gunnlaugsson, A. Harte, J. P. Leonard, M. Nieuwenhuyzen,
Supramol. Chem., 2003, 15, 505; (b) T. Gunnlaugsson, A. Harte, J. P.
Leonard, M. Nieuwenhuyzen, Chem. Commun., 2002, 2134-2135.
[39] a) S. J. A. Pope, B. P. Burton-Pye, R. Berridge, T. Khan, P. J. Skabara,
S. Faulkner, Dalton Trans. 2006, 2907-2912; b) R. S. Dickins, T.
Gunnlaugsson, D. Parker, R. D. Peacock, Chem. Commun. 1998, 1643-
1650; c) C. Li, W.-T. Wong, Chem. Commun. 2002, 2034-2035.
[40] a) P. A. Gale, Acc. Chem. Res., 2006, 39, 465-475; P. A. Gale, Chem.
Commun. 2005, 3761-3772; b) T. Gunnlaugsson, P. E. Kruger, P.
Jensen, J. Tierney, H. D. P. Ali, G. M. Hussey, J. Org. Chem. 2005, 70,
10875-10878.
Terpyridine Chemistry, Wiley-VCH, Weinheim, 2006.
[
22] a) W. S. Lo, W. M. Kwok, G. L. Law, C. T. Yeung, C. T. L. Chan, H. L.
Yeung, H. K. Kong, C. H. Chen, M. B. Murphy, K. L. Wong and W. T.
Wong, Inorg. Chem., 2011, 50, 5309– 5311; b) R. Shunmugam and G.
N. Tew, J. Am. Chem. Soc., 2005, 127, 13567–13572; c) B. Song, G. L.
Wang, M. Q. Tan and J. L. Yuan, J. Am. Chem. Soc., 2006, 128, 13442–
13450.
[
[
23] a) J. Costa, R. Ruloff, L. Burai, L. Helm and A. E. Merbach, J. Am. Chem.
Soc., 2005, 127, 5147–5157; b) N. Chandrasekhar and R. Chandrasekar,
J. Org. Chem., 2010, 75, 4852–4855; c) C. L. Yang, J. Xu, Y. F. Zhang,
Y. W. Li, J. Zheng, L. Y. Liang and M. G. Lu, J. Mater. Chem. C, 2013, 1,
[41] a) A. T. Wright, E. V. Anslyn, Chem. Soc. Rev. 2006, 35, 14-28; b) S. L.
Wiskur, H. Ait-Haddou, J. J. Lavigne, E. V. Anslyn, Acc. Chem. Res.
2001, 34, 963-972.
4885–4901.
24] a) I. Grabchev, P. Meallier, T. Konstantmova, M. Popova, Dyes Pigm.
1
995, 28, 41– 46; b) Z. Cao, P. Nandhikonda, M.D. Heagy, J. Org. Chem.
009, 74, 3544–3546; c) C. S. Bonnet, M. Devocelle and T.
[42] a) T. M. Kelly, A. B. Tossi, D. J. McConnell, T. C. Strekas, Nucleic Acids
Res. 1985, 13, 6017-6034; b) A. M. Pyle, J. P. Rehamann, R. Meshoyrer,
C. V. Kumar, N. J. Turro, J. K. Barton, J. Am. Chem. Soc. 1989, 111,
3051-3058; c) V. A. Bloomfield, D. M. Crothers, I. Tinocoo Jr, Physical
Chemistry of Nucleic Acids, Harper & Row, New York, 1974.
[43] a) A. Wolfe, G. H. Shimer, T. Meehan Jr, Biochemistry, 1987, 26, 6392-
6396; b) A. Pyle, J. K. Barton, S. J. Lippard (Ed.), Progress in Inorganic
Chemistry, 1990, 38, 413-475; c) P. J Dandliker, R. E Holmlin, J. K Barton,
Science, 1997, 275, 1465-1468; d) R. Palchaudhuri, P. J. Hergenrother,
Curr. Opin. Biotechnol. 2007, 18, 497-503.
2
Gunnlaugsson, Chem. Commun., 2008, 4552; d) D. R. Kauffman, C. M.
Shade, H. Uh, S. Petoud and A. Star, Nat. Chem., 2009, 1, 500; e) M. de
Sousa, M. Kluciar, S. Abad, M. A. Miranda, B. de Castro and U. Pischel,
Photochem. Photobiol. Sci., 2004, 3, 639-642; f) G. J. Ryan, S. Quinn, T.
Gunnlaugsson, Inorg. Chem. 2008, 47, 401-403.
[
25] a) D. Srikun, E.W. Miller, D.W. Domaille, C.J. Chang, J. Am. Chem. Soc.
2008, 130, 4596-4597; b) E.B. Veale, T. Gunnlaugsson, J. Org. Chem.
2008, 73, 8073-8076.; c) R. Shunmugam, G. N. Tew, Chem. Eur. J. 2008,
14, 5409-5412; d) L. Lin-Bo, J. Shun-Jun, L. Wei-Hong, Chin. J. Chem.,
2008, 26, 417-420; e) C. S. Bonnet, M. Devocelle, T. Gunnlaugsson, Org.
[44] a) X. Li, Z. Yang, Chem. Biol. Interact., 2015, 232, 77-84; b) J. R.
Lakowicz, Principles of Fluorescence Spectroscopy, Springer, New York,
3rd edn, 2006.
Biomol. Chem., 2012, 10, 126–133; f) J. Zhou, C. Fang, Y. Liu, Y. Zhao,
N. Zhang, X. Liu, F. Wang, D. Shangguan, Org. Biomol. Chem. 2015, 13,
[45] Y.-Q. Wang, H.-M. Zhang, G.-C. Zhang, W.-H. Tao, S.-H. Tang, J. Lumin.
2007, 126, 211–218.
3931–3935.
[
26] a) A. J. Amoroso, S. J. A. Pope, Chem. Soc. Rev. 2015, 44, 4723-4742;
b) S. J. Butler, L. Lamarque, R. Pal, D. Parker, Chem. Sci. 2014, 5, 1750-
[46] a) D. Hvasanov, A. F. Mason, D. C. Goldstein, M. Bhadbhade, P.
Thordarson, Org. Biomol. Chem. 2013, 11, 4602-4612; b) P. Laine, F.
Bedioui, P. Ochsenbein, V. Marvaud, M. Bonin, E. Amouyal J. Am. Chem.
Soc. 2002, 124, 1364–1377.
1756.
[
[
27] a) A. Thibon, V. C. Pierre, Anal. Bioanal. Chem. 2009, 394, 107-120; b)
M. Delbianco, V. Sadovnikova, E. Bourrier, G. Mathis, L. Lamarque, J.
M. Zwier, D. Parker, Angew. Chem. Int. Ed. 2014, 53, 10718-10722;
Angew. Chem. 2014, 126, 10894-10898.
[47] L. R. Melby, N. J. Rose, E. Abramson, J. C. Caris, J. Am. Chem.
Soc. 1964, 86, 5117–5125.
[48] M. E. Reichmann, S. A. Rice, C. A. Thomas, P. Doty, J. Am. Chem. Soc.
1954, 76, 3047–3053.
28] (a) F. J. Steemers, W. Verboom, D. N. Reinhoudt, E. B. VanderTol and
J. W. Verhoeven, J. Am. Chem. Soc., 1995, 117, 9408–9414; (b) H. Xu,
H. L. Wang, X. H. Zhu, K. Yin, G. Y. Zhong, X. Y. Hou, W. Huang, J.
Phys. Chem. B, 2006, 110, 3023–3029.
[
[
29] a) G. Bobba, Y. Bretonnière, J.-C. Frias, D. Parker, Org. Biomol. Chem.
2003, 1, 1870-1872; b) G. Bobba, R. S. Dickins, J. A. G. Williams, C. F.
G. C. Geraldes, et al., J. Chem. Soc. Perkin Trans., 2001, 2, 1729-1737.
30] a) V. Divya, M. L. P. Reddy, R. Pavithran, Dalton Trans. 2013, 42,
15249–15262; b) V. Divya, V. Sankar, K. G. Raghu, M. L. P. Reddy,
Dalton Trans. 2013, 42, 12317-12323; c) D. B. Ambili Raj, S. Biju, M. L.
P. Reddy, Inorg. Chem. 2008, 47, 8091−8100.
[
[
31] a) J. Yu, L. Zhou, H. Zhang, Y. Zheng, H. Li, R. Deng, Z. Peng, Z. Li,
Inorg. Chem. 2005, 44, 1611-1618; b) J. Li, H. Li, P. Yan, P. Chen, G.
Hou, G. Li, Inorg. Chem. 2012, 51, 5050−5057; c) J. Sun, B. Song, Z. Ye,
J. Yuan, Inorg. Chem. 2015, 54, 11660−11668; d) J. Shi, Y. Hou, W. Chu,
X. Shi, H. Gu, B. Wang, Z. Sun, Inorg. Chem. 2013, 52, 5013-5022.
32] a) M. J. Frisch, G. W. Trucks, H. B. Schlegel, et al., Gaussian 09,
Revision D.01, Gaussian, Inc., Wallingford, CT, 2009; b) L. Yang, X.
Wang, G. Zhang, X. Chen, G. Zhang, J. Jiang, Nanoscale, 2016, 8,
17422–17426.
[
[
33] B. Rajamouli, V. Sivakumar, New J. Chem. 2017, 41, 1017-1027.
34] a) W. D. Horrocks, Jr. D. R. Sudnick, J. Am. Chem. Soc. 1979, 101, 334-
340; b) A. Beeby, I. M. Clarkson, R. S. Dickins, S. Faulkner, D. Parker,
L. Royle, A. S. de Sousa, J. A. G. Williams, M. Woods, J. Chem. Soc.,
Perkin Trans. 2, 1999, 493-504.
[
35] G. R. Choppin, D. R. Peterman, Coord. Chem. Rev. 1998, 174, 283–299.
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201701495
FULL PAPER
Entry for the Table of Contents
FULL PAPER
pH-Responsive Luminescent
Europium(III) Probe: A luminescent
ternary pH-responsive probe,
Key Topic*
Kritika Gupta and Ashis K. Patra*
[
3
Eu(tta) (naptpy)] was designed
Page No. – Page No.
utilizing acid-sensitive -diketonate
for potential anion sensing via
A Luminescent pH-Responsive
3+
Ternary Eu Complex of β-diketonate
lanthanide based displacement assay.
and Terpyridine Derivative as
Sensitizing Antenae: Photophysical
Aspects, Anion Sensing and
Biological Interactions
This article is protected by copyright. All rights reserved.