Versatility of Terpyridine-Functionalised Aryl Tetrazoles: Photophysical Properties, Ratiometric Sensing of Zinc Cations and Sensitisation of Lanthanide Luminescence

Article abstract of DOI:10.1002/ejic.201700663

Four new tetrazole-containing species, in conjugation with terpyridine moieties through phenyl or pyridyl linkers, have been synthesised and characterised. In the series, the tetrazole functional groups are either in their acidic form or are alkylated at the N2 position with a methyl group. The photophysical properties of the species reveal moderate UV or efficient blue fluorescent emission, with photoluminescence quantum yields of around 30 % and 80 % for UV and blue emission, respectively. The spectral profiles can be reversibly modulated through protonation/deprotonation, with changes being consistent with an increase of the electron density on the tetrazole rings upon deprotonation or a decrease of the electron density on the terpyridines through protonation. The tetrazole-containing species were also investigated for fluorescence sensing of biologically and environmentally important metal ions, highlighting a ratiometric response to the presence of Zn²⁺. Furthermore, this ratiometric response could be well discriminated from that of interfering Cd²⁺ ions. Lastly, the species have been investigated as ligands for Eu³⁺ and Yb³⁺ cations, revealing efficient sensitisation, to give typical red and near-infrared emissions, respectively.

Full text of DOI:10.1002/ejic.201700663

A Journal of
Accepted Article
Title: Versatility of terpyridine functionalised aryl tetrazoles:
photophysical properties, ratiometric sensing of zinc cations and
sensitisation of lanthanide luminescence
Authors: Phillip Wright, Jacek Kolanowski, Filipek Wojciech, Evan
Moore, Stefano Stagni, Elizabeth New, and Massimiliano
Massi
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.201700663
Link to VoR: http://dx.doi.org/10.1002/ejic.201700663

European Journal of Inorganic Chemistry
10.1002/ejic.201700663
Versatility of terpyridine functionalised aryl tetrazoles: photophysical properties, ratiometric sensing
of zinc cations and sensitisation of lanthanide luminescence
a
b
b
c
d,
Phillip J. Wright, Jacek L. Kolanowski, Wojciech Filipek, Evan G. Moore, Stefano Stagni *, Elizabeth J.
b,
a,
New, * Massimiliano Massi *
a
Curtin Institute of Functional Materials and Interfaces - Department of Chemistry, Curtin University,
WA 6102, Australia.
b
School of Chemistry, The University of Sydney, NSW 2006, Australia.
c
School of Chemistry and Molecular Biosciences, University of Queensland, QLD 4072, Australia.
d
Department of Industrial Chemistry “Toso Montanari” - University of Bologna, Bologna 40136, Italy.
Abstract
Four new tetrazole-containing species in conjugation with terpyridine moieties via a phenyl or pyridyl
linker have been synthesised and characterised. In the series, the tetrazole funcational groups are either
in their acidic form or alkylated at the N2 position with a methyl group. The photophysical properties of
the species revealed moderate UV or efficient blue fluorescent emission, with photoluminescence
quantum yields around 30% and 80% for UV and blue emission, respectively. The spectral profiles could
be reversibly modulated via protonation/deprotonation, with changes consistent with an increase in the
electron density on the tetrazole ring upon deprotonation or lowering of the electron density on the
terpyridine via protonation. The tetrazole-containing species were also investigated for the fluorescent
1
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201700663
sensing of biologically and environmentally important metal ions, highlighting a ratiometric response to
2
+
the presence of Zn . Furthermore, this ratiometric response could be well discriminated from that of
2
+
3+
3+
interfering Cd ions. Lastly, the species have been investigated as ligands for Eu and Yb cations,
revealing efficient sensitisation to give typical red and near infrared emission, respectively.
Introduction
As a functional group, tetrazoles have found widespread use in the design of molecular species for
[
1]
[2]
diverse applications, including medicinal chemistry, coordination polymers, crystal growth
[
3]
[4-6]
inhibition and luminescent materials.
Tetrazoles are five-membered aromatic heterocycles
possessing four adjacent N atoms. In terms of acidity, tetrazoles have pK
a
values similar to carboxylic
acids, so negatively charged tetrazolates are easily accessible via deprotonation reactions.[7,8] For this
[
9]
reason, tetrazoles are considered to be more metabolically stable bioisosteres of carboxylic acids. The
2
presence of four sp -hybridised lone pairs on the nitrogen atoms allows the construction of complex
[
2]
molecular architectures via bridging multiple metal ions, and many of these examples have been
reported for species containing both transition metals and lanthanide elements.[10-15]
In the area of luminescent metal complexes, tetrazoles have proven to very versatile ligands, both from
the point of view of coordination modes and modulation of photophysical properties. We have been
interested in this area for some time, highlighting the construction of multinuclear luminescent
assemblies with metallic cations such as Re(I),[16] Ir(III), Ru(II), Cu(I)[17] and Pt(II).[18] Furthermore, we
have shown how coordinated tetrazoles can undergo facile reaction with electrophilic reagents, thus
modulating the photophysical properties of the complex.[19] These complexes have proven to be useful
[5]
[12]
2
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201700663
in applications such as organic light emitting devices[20] and molecular probes for live cell imaging.[21] In
these studies, the luminescent properties mainly originate from the final metal complex rather than the
tetrazole-containing ligands.
Figure 1. Terpyridine functionalised tetrazole species investigated in this work.
In trying to expand the scope of tetrazole-containing species for luminescent applications, we have
decided to investigate molecular architectures composed of a tetrazole functional group conjugated to a
terpyridine moiety via either a phenyl or pyridyl linker. The rationale for the design of this series (Figure
1
) was to access ligands with intrinsic photophysical properties that could be modulated via reversible
interaction with electrophiles and Lewis acids, as well as complexation with transition and lanthanide
metal cations. In the newly synthesised compounds, the tetrazole functional groups are either in their
acid form or alkylated with a methyl substituent at the N2 position. This work reports the synthetic
protocols for the construction of the terpyrdine-functionalised tetrazoles shown in Figure 1, along with
the investigation of their intrinsic photophysical properties and their sensitivity to
3
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201700663
protonation/deprotonation reactions. Furthermore, the versatility of these species for luminescent
2
+
applications are highlighted in the ratiometric sensing of Zn cations, with discrimination of interference
2
+
from Cd cations, as well as sensitisation of visible red emission and near-infrared emission via
3
+
3+
complexation with Eu and Yb , respectively.
Results and Discussion
Synthesis and spectroscopic characterisation
Following a published procedure,[22] the precursor NCPhTpy was prepared by reaction of 4-
cyanobenzaldehyde and pyridine-2-carboxyaldehyde in ethanol and in the presence of potassium
hydroxide and aqueous ammonia. The targeted species HTzPhTpy was then prepared via 1,3-dipolar
cycloaddition between sodium azide and NCPhTpy in toluene (Figure 2), following slight modifications of
a reported procedure.[23]
Figure 2. Synthesis of the ligand HTzPhTpy. Reagents and conditions: i) KOH, NH
Et NHCl, NaN , toluene, 18 h, reflux.
4
OH, EtOH, 18 h, rt; ii)
3
3
4
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201700663
1
13
HTzPhTpy was characterised by IR, H-NMR and C-NMR spectroscopy. The IR spectrum displays a band
−1
at 1603 cm , corresponding to the CN stretch of the tetrazole moiety, and the spectrum was absent of a
−1
nitrile peak at 2225 cm , indicating absence of starting material.
Due to the low solubility of this compound in common deuterated solvents and the presence of multiple
1
overlapping peaks, the H-NMR spectrum of HTzPhTpy was difficult to interpret (Figure S1). The
spectrum in deuterated DMSO shows broad signals between 8.80-8.95 ppm, 8.20-8.35 ppm, and 7.67-
7
.76 ppm, with integration ratio of 6:6:2, matching the proposed structure. Excess triethylamine was
therefore added to the deuterated DMSO solution to promote the formation of the more soluble
1
triethylammonium tetrazolate salt [HNEt
3
][TzPhTpy]. The resulting H-NMR spectrum (Figure S1)
becomes more defined, showing as expected seven peaks appearing in the aromatic region between
1
3
9
.00 and 7.00 ppm, belonging to the phenyl and pyridine rings. The C-NMR spectrum for this
compound exhibits thirteen signals corresponding to those expected for the product. In particular, the
formation of the tetrazole ring is supported by the presence of a peak at 160.3 ppm.[24,25]
Figure 3. Synthesis of the ligand HTzPyTpy. Reagents and conditions: i) CuCN, DMF, 4 h, 120 C; ii)
Et
3
NHCl, NaN
3
, toluene, 18 h, reflux; iii) KOH, NH OH, EtOH, 18 h, rt.
4
5
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201700663
An alternative sequence was followed for the preparation of HTzPyTpy (Figure 3). Firstly, 2-
cyanopyridine-5-carboxyalhedyde, NCPyCHO, was prepared by reaction of 2-bromopyridine-5-
carboxyalhedyde with copper(I) cyanide in DMF, according to a previously published procedure.[26]
A
1
,3-dipolar cycloaddition reaction was then performed on NCPyCHO for the formation of the tetrazole
ring in HTzPyCHO.[23] The species HTzPyCHO was analysed by IR, H-NMR, and C-NMR spectroscopy.
1
13
−1
The IR spectrum for this compound has key signals at 1704 cm , corresponding to the aldehyde
−1
carbonyl group, and 1605 cm for the tetrazole CN stretch.
1
The H-NMR spectrum matches the desired product, showing a singlet at 10.20 ppm corresponding to
the H atom of the CHO substituent, along with one singlet and two doublets belonging to the three H
1
3
atoms of the pyridine ring. The C-NMR spectrum displays seven signals consistent with the proposed
structure, with noteworthy resonances at 191.8 ppm, corresponding to the aldehyde C atom, and 154.6
ppm, corresponding to the tetrazolic C atom.[24,25]
The terpyridine moiety was formed by reaction of HTzPyCHO with pyridine-2-carboxyaldehyde in
ethanol and in the presence of potassium hydroxide and aqueous ammonia.[22] The product was
−1
characterised by IR spectroscopy and showed a signal at 1597 cm , corresponding to the tetrazole CN
1
stretch. The product was also characterised by H-NMR spectroscopy after the addition of excess
triethylamine (Figure S2) to display better resolved peaks, as in the previous case of HTzPhTpy.
Alkylation of the tetrazole ring in HTzPhTpy was first attempted by reaction with trifluoroacetic acid and
sulfuric acid in tert-butanol. This procedure was chosen since its regioselectivity for the N2 position of
the tetrazole ring was previously demonstrated.[27,28] However, this reaction failed to yield the target
alkylated species. Therefore, HTzPhTpy was treated with methyl iodide and potassium carbonate in
acetonitrile at reflux. These conditions allowed the isolation of a mixture of methylated regioisomers at
6
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201700663
the N1 and N2 position of the tetrazole ring, with an approximate ratio of 4:6, respectively, evidenced by
NMR analysis. The two regioisomers could be easily separated via column chromatography. The identity
of MeTzPhTpy was confirmed by the appearance of a singlet corresponding to three H atoms at 4.42
1
ppm in the H-NMR spectrum, belonging to the methyl substituent (Figure S3). Furthermore, the
1
3
resonance at 165.0 ppm belonging to the tetrazolic C atom in the C-NMR spectrum confirmed the
methylation at the N2 atom of the tetrazole ring.[24,25]
To install a consistent alkylating functional group bound to the tetrazole ring, the same methylation
protocol was applied to HTzPyTpy. The analysis at the end of the reaction by NMR revealed the
expected mixture of regioisomers in a 6:4 ratio for the N1 and N2 methylated products, respectively.
Unfortunately, these could not be separated by column chromatography. A new synthetic strategy was
therefore adopted for the preparation of MeTzPyTpy (Figure 4). Firstly, the previously prepared 2-(1H-
tetrazol-5-yl)pyridine-5-carboxyaldehyde, HTzPyCHO, was methylated by reaction with methyl iodide
and potassium carbonate. The methylation yielded a 4:6 mixture of N1 and N2 alkylated regioisomers,
which could be easily purified by column chromatography. Then, the isolated MeTzPyCHO was reacted
with pyridine-2-carboxyaldehyde, potassium hydroxide, and aqueous ammonium hydroxide to yield the
targeted terpyridine functionalised species MeTzPyTpy.[22] The presence of a singlet at 4.49 ppm for the
1
methyl substituent in the H-NMR spectrum confirmed the identity of the target compound (Figure S4),
whereas the N2 isomer was determined by the resonance of the tetrazolic C atom at 164.8 ppm in the
13C-NMR spectrum.[24,25]
7
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201700663
Figure 4. Synthetic procedure for the preparation of MeTzPyTpy. Reagents and conditions: i) CH
CO , CH CN, 12 h, reflux; ii) KOH, NH OH, EtOH, 18 h, rt.
3
I,
K
2
3
3
4
Photophysical properties
A summary of the photophysical properties of HTzPhTpy, HTzPyTpy, MeTzPhTpy, and MeTzPyTpy
recorded in acetonitrile is reported in Table 1. The absorption profiles of the four species (Figure 5)
highlight the presence of intense and structured bands in the region between 200 and 350 nm. These
bands are mainly ascribed to spin-allowed -* transitions with possible admixtures of n-* transitions
in the lower energy region of the broad bands. The lowest energy shoulders appear red-shifted for
HTzPhTpy and HTzPyTpy when compared to the two methylated species MeTzPhTpy and MeTzPyTpy.
8
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201700663
-
5
Table 1. Photophysical properties from acetonitrile solutions (ca 10 M).
Compound
Absorption
Emission (298 K)
4

(10 )

[nm]

[ns]

-
1
-1
[
nm] ([M cm ])
HTzPhTpy
295 (2.06)
426
400
356
362
2.62
3.36
2.84
2.76
0.77
2
2
53 (1.15)
31 (1.51)
HTzPyTpy
295 (3.32)
0.85
0.32
0.28
2
2
53 (2.31)
30 (2.16)
MeTzPhTpy
MeTzPyTpy
283 (3.93)
2
2
55 (2.51)
32 (1.66)
282 (2.76)
2
53 (2.44)
Figure 5. Absorption (left) and emission (right) profiles for the synthesised species from acetonitrile
-5
solutions (ca 10 M). The emission spectra were recorded upon excitation at 290 nm.
The emission profiles, shown in Figure 5, display broad bands in the late UV region with similar maxima
at 356 and 362 nm for the methylated species MeTzPhTpy and MeTzPyTpy, respectively. On the other
hand, HTzPhTpy and HTzPyTpy display red-shifted profiles in the blue region, peaking at 426 and 400
nm, respectively. This red-shifted emission might be explained by the more electron-rich nature of the
unmethylated tetrazole rings, which could also exist in solution as a zwitterionic form displaying donor-
9
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201700663
acceptor behaviour between the anionic tetrazolate ring and cationic protonated form of the terpyridine
moiety. This conclusion is also corroborated by the slight blue-shift of HTzPyTpy with respect to
HTzPhTpy, as the presence of the pyridine linker for the former causes a reduction of the electron
density of the tetrazole ring via charge delocalisation. HTzPhTpy and HTzPyTpy display strong emission
intensity with quantum yield () values measured at 0.77 and 0.85, respectively. The quantum yield
reduces to moderate upon methylation, with values at 0.32 for MeTzPhTpy and 0.28 for MeTzPyTpy. In
all cases, the excited state lifetime decay () is very short, of the order of few nanoseconds, which is
consistent with spin-allowed fluorescent emission.
Photophysical changes upon addition of acids and bases
The relative energy of the excited states for the synthesised species can be readily influenced by acid-
base equilibria occurring on the tetrazole and terpyridine substituents. To investigate the effect of these
equilibria on the luminescent properties, we measured the changes in the absorption and emission
spectra upon sequential addition of camphorsulfonic acid in acetonitrile solutions. The methylated
species MeTzPhTpy and MeTzPyTpy were firstly investigated, as this system is absent from the added
protonation equilibrium occurring on the tetrazole substituent.
The sequences of absorption and emission plots for acetonitrile solutions of MeTzPhTpy and MeTzPyTpy
are shown in Figure 6, where each sequential spectrum represents an addition of 0.33 equivalents of
acid. The trend in the absorption plots is analogous and highlights the progressive appearance of a red-
shifted band peaking around 330 nm, and the presence of two isosbestic points in each spectrum. The
corresponding emission profiles also show an analogous trend, where the UV emission band
1
0
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201700663
progressively disappears with the concomitant appearance of a broader red-shifted band of aqua-
coloured emission for MeTzPhTpy and blue emission for MeTzPyTpy. This trend is rationalised by
protonation occurring at the terpyridine substituent causing a stabilisation of the * orbitals. The
effective result is a reduction of the HOMO-LUMO gap. The blue shifted emission for the protonation of
MeTzPyTpy, with respect to MeTzPhTpy, is rationalised by the fact that the protonation can also occur
at the 2-pyridyltetrazole position, hence stabilising the  orbitals to a greater extent with consequent
widening of the HOMO-LUMO gap.
Figure 6. Changes in the absorption and emission spectral profiles for acetonitrile solutions of
MeTzPhTpy (top) and MeTzPyTpy (bottom) upon addition of camphorsulfonic acid. Each sequential line
represents an addition of 0.33 equivalents of acid. The starting profile is represented by the black line
and the final profile is represented by the light brown line. The emission spectra are recorded upon
excitation at 290 nm.
1
1
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201700663
Under similar conditions, the changes in the absorption and emission profiles for HTzPhTpy and
HTzPyTpy were monitored (Figure S5). In this case, the initial spectra were recorded from a solution
containing each species and one equivalent of tetrabutylammonium hydroxide to completely
deprotonate the tetrazole ring. The profiles highlight changes upon addition of acids, but the resulting
spectra resemble a more complex superimposition of bands. The superimposition could originate from
protonation occurring on the terpyridine moiety and equilibrating with acid-base equilibria occurring on
the tetrazole ring for HTzPhTpy, and on the 2-pyridyltetraole site for HTzPyTpy. Unlike the methylated
derivatives, a clear trend could not be easily established, although significant variations of the
absorption and emission spectra are clearly highlighted.
2
+
2+
Ratiometric fluorescence sensing of Zn and discrimination from Cd interference
The pH-induced fluorescence changes of the synthesised tetrazole species and the presence of well-
established terpyridine metal-binding motifs prompted us to assess the use of these species for the
fluorescent sensing of metal ions. For this investigation, the emission properties were measured in
buffered aqueous medium using an excitation wavelength of 290 nm (Figure 7). Similar to the ligands in
acetonitrile, the fluorescence spectra in buffered aqueous media highlight broad bands between 350
and 500 nm. The trends in emission maxima are analogous to the previously performed measurements,
with a more blue-shifted emission originating from the methylated MeTzPhTpy with respect to
HTzPhTpy and HTzPyTpy. The emission profile of MeTzPyTpy appears more complex, with the presence
of multiple maxima. However, it should be noted that MeTzPyTpy exhibits reduced solubility in aqueous
1
2
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201700663
solvent compared to the other three species; hence the spectral profile was measured from non ideal
conditions (non transparent solution).
Figure 7. Normalised emission spectra of the aqueous solutions (10 µM in 20 mM HEPES buffer, pH 7.4),
recorded with excitation at 290 nm.
The screen of fluorescence responses of the ligands to a wide range of biologically-relevant metal ions
revealed that most first row transition metal ions cause quenching of fluorescence (Figure 8). On the
other hand, spectroscopically silent alkali and alkali earth cations produce little change in the fluorescent
2
+
emission of the ligands. In contrast, a unique response of each ligand to Zn was observed. A Job’s plot
2
+
analysis of the emission intensity at 380 nm against the molar fraction of Zn cations revealed a 2:1
ligand-to-metal binding stoichiometry in the case of MeTzPyTpy (Figure S6). This result suggests that the
main mode of interaction is through coordination at the terpyridine site. A study of the other ligands
was attempted through Job’s plots, but the responses were less straightforward to interpret. Zn2+
induced a change in the spectral profile of HTzPhTpy, with the fluorescence maximum shifting from 410
to 480 nm (Figure 8a). By monitoring the ratio of intensity for the emission at 480 nm and 410 nm, it is
1
3
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201700663
2
+
2+
possible to distinguish Zn from all other investigated metal ions. Similarly, the addition of Zn to
HTzPyTpy induced a fluorescence increase, as well as the appearance of shoulders at 360 and 480 nm
2
+
(
Figure 8b), which can be used to identify the presence of Zn over other metal ions. For MeTzPhTpy,
2
+
addition of Zn caused a marked ratiometric change, with a new emission maximum at 500 nm (Figure
2
+
8
c). The integrated emission intensity at this new peak increases uniquely for Zn . The general
appearance of red shifted peaks is analogous to the results obtained via protonation of the species, and
2
+
could be ascribed to the coordination of Zn to the terpyridine moiety, therefore lowering the energy of
2
+
delocalised * orbitals. Finally, Zn alone was found to induce increased emission of the 380 nm peak of
MeTzPyTpy (Figure 8d).
1
4
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201700663
Figure 8. Fluorescent response (excitation at 290 nm) of the solutions (10 µM in 20 mM HEPES buffer,
pH 7.4) of (a) HTzPhTpy, (b) HTzPyTpy, (c) MeTzPhTpy (red), (d) MeTzPyTpy to biologically relevant
metal ions (10 eq): ligands alone (black, solid line), Zn(II) (black, dashed line), Li(I) (dark green, solid),
Na(I) (dark green, dashed), K(I) (dark green, dotted), Mg(II) (light green, solid), Ca(II) (light green,
dashed), Cr(III) (light green, dotted), Mn(II) (blue, solid), Fe(II) (blue, dashed), Co(II) (blue, dotted), Ni(II)
(red, solid), Cu(II) (red, dashed), Cu(I) (red, dotted). Fluorescent spectra (left) and selected parameters
(right) - specific for each different ligand - allowing for the distinction of Zn(II) from other metals: (a)
fluorescence emission ratio at 480 nm / 410 nm, (b) fluorescence intensity at 360 nm, (c) integrated
emission intensity from 500 nm to 550 nm (d) integrated emission intensity from 340 nm to 500 nm.
2
+
These results demonstrate the potential of these ligands to act as selective sensors of Zn , whether
alone or incorporated into more elaborate molecular systems. Furthermore, all ligands exhibit a
1
5
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201700663
2
+
ratiometric response to Zn , which is a particularly valuable mode of fluorescence sensing as emission
ratios are independent of fluorophore concentration and other background parameters.[29] Zinc is an
essential metal ion biology, performing a plethora of roles including structure stabilisation, Lewis acid
catalysis ,[30] and putative roles in signalling.[31] As a result, there is great interest in detecting this metal
2
+
[32,33]
ion in cellular studies, and to this end a number of Zn -selective sensors have been reported,
the
majority of which are based on ligands bearing pyridyl coordinating motifs, consistent with the findings
presented in this work.
2
+
2+
A longstanding challenge in the fluorescent sensing of Zn is the potential interference from Cd , which
can induce similar fluorescence changes due to its similar chemical nature.[34] While basal cellular Cd2+
2
+
2+
levels are not expected to be sufficiently high to interfere with Zn sensing in biological studies, Cd is
2
+
itself a highly toxic metal, and the measurement of cellular Cd levels in systems potentially subjected
2
+
[35]
to Cd exposure is therefore important. Furthermore, since cadmium is widely-used in industry, its
unambiguous detection in environmental samples (which are likely to contain considerable background
2
+
2+
2+
Zn ) is also essential. We therefore compared the responses of the ligands to Cd and Zn (Figure 9).
2
+
When we monitored the response to Cd according to the same parameters reported above, we found
2
+
2+
similar fluorescence changes to those observed for Zn (Figure S7). However, Cd induced unique
spectral changes for HTzPhTpy, HTzPyTpy and MeTzPhTpy (Figure 9a-c). In contrast MeTzPyTpy showed
2
+
2+
the same spectral form in the presence of both Zn and Cd (Figure 9d). For the former set of ligands,
we have therefore been able to identify parameters that enable the unambiguous discrimination of Zn2+
2
+
from Cd . This unique feature of these ligands may enable the development of fluorescent assays for
2
+
2+
distinguishing Cd from Zn in complex mixtures, whether industrial, environmental or biological
samples.
1
6
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201700663
Figure 9. Fluorescent response (excitation at 290 nm) of the solutions (10 µM in 20 mM HEPES buffer,
pH 7.4) of (a) HTzPhTpy, (b) HTzPyTpy, (c) MeTzPhTpy (red), (d) MeTzPyTpy to 10 eqivalents of Zn(II)
and Cd(II). (10 eq) and cadmium. Fluorescent spectra (left panels) of the ligand alone (solid lines) and in
the presence of Zn(II) (dashed lines) and Cd(II) (dotted lines). Bar graphs (right panels) represent the
selected parameters, which enable the distinction of Zn(II) and Cd(II) from other biologically relevant
metals (black bars) and from each other (grey bars, except d), which does not enable the distinction), in
particular: a) ratio of fluorescence intensity at 480/410 nm (black) and 480/44 nm (grey) b) normalised
intensity of fluorescence at 360 nm (black) and normalised intergrated intensity at 460-560 nm (grey) c)
normalised intergrated intensity of fluorescence at em 500-550 nm (black) and the ratio of intensities at

em 525/440 nm (grey) d) normalised intergrated intensity at em 340 - 500 nm (black) and the ratio of
intensities at em 340–400 nm / 500–550 nm (grey). Horizontal dashed lines on the bar graphs represent
the threshold value in the case of fluorescence ratios, which enable the distinction of Zn(II) from Cd(II)
from other metal ions.
1
7
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201700663
3
+
3+
Sensitisation of Eu and Yb luminescence
The capacity of the synthesised species to sensitise lanthanide luminescence was then explored. As a
3
first step, the relative energy of the triplet -* excited states of the ligands was estimated by adding
3
+
[36]
excess Gd in acetonitrile solution. [Gd(NO
3
)
3
n
(DMSO) ] was chosen due to its higher solubility in
organic solvents.[37] Figure 10 shows all four absorption profiles after the addition of Gd , highlighting
the appearance of red-shifted bands around 340 nm, which are ascribed to the complexation of the
3+
[
4]
terpyridine moiety. The emission profiles of these solutions were measured after freezing to 77 K, to
3
enhance the phosphorescent decay from the -* excited states. All the complexes exhibit intense
structured bands between 400 and 700 nm, with some residual peaks at wavelengths shorted than 400
1
nm attributed to residual fluorescent decay from -* excited states (Figure 10). From each of the
phosphorescent emission bands, the energies of the 0-0 transitions could be estimated, and the
corresponding values are reported in Table 2. From these values, it can be seen that four species could
3
+
3+
be potential sensitisers for the visible red emission of Eu and the NIR emission of Yb . For the latter,
while the difference in energy between the -* and the Yb3+ 2F5/2 accepting state is above 10,000 cm-1,
3
2
+
a sensitisation mechanism involving a ligand-to-metal charge transfer state with formation of Yb could
facilitate energy transfer.[38-40]
1
8
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201700663
3
+
Figure 10. Left: absorption profiles of the synthesised species in the presence of excess Gd ions from
-
5
acetonitrile solutions. Right: Emission profiles ~10 M acetonitrile solutions of the synthesised species in
3
+
the presence of excess Gd cations at 77 K, with excitation wavelength set at 310 nm.
3
Table 2. Estimated energies for the triplet state -* 0-0 transition for the synthesised species in the
3
+
3
3+ 5
3+ 7
presence of excess Gd , and energy difference between the -* and the Eu
D
0
or Yb
F5/2 excited
states.
3
3
5
3
7
Compound
E
0-0 ( -*)
[
E ( -* - D
0
)
E ( -* - F5/2
)
-
1
-1
-1
cm ]
[cm ]
[cm ]
HTzPhTpy
HTzPyTpy
MeTzPhTpy
MeTzPyTpy
21,052
22,222
21,052
22,000
3,552
4,722
3,552
4,722
10,652
11,822
10,652
11,822
3
+
3+
Table 3. Summary of the photophysical data for the sensitisation of Eu and Yb luminescence from
-
5
diluted (ca 10 M) acetonitrile solutions.
Emission (298 K)

[nm]
618a

[s]


r

i

Ln3
+
[s]
2,802
2,749
2,747
2,806
1,200b
Compound
HTzPhTpy
HTzPyTpy
MeTzPhTpy
MeTzPyTpy
HTzPhTpy
HTzPyTpy
3+
3+
3+
3+
Eu
Eu
Eu
Eu
Yb
Yb
Yb
Yb
1,225
1,194
1,087
1,263
10.07
10.62
9.64
0.239
0.208
0.249
0.214
-
-
-
-
0.437
0.434
0.396
0.450
0.008
0.009
0.008
0.007
0.545
0.478
0.630
0.476
-
-
-
-
5
a
618
618a
618a
980
980
980
980
3+
3+
3+
3+
b
1,200
MeTzPhTpy
MeTzPyTpy
1,200b
1,200b
8.48
a
 7F
transition is reported; b
Only the more intense maximum belonging to the hypersensitive D
0
2
literature value.
1
9
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201700663
The addition of [Eu(NO
3
)
3
n
(DMSO) ] to acetonitrile solutions of the four species showed the typical red
emission upon excitation at 310 nm. The four emission spectra are virtually superimposable,
3
+
[41]
demonstrating that the Eu complexes in solution are very similar (Figure 11). The profiles are
composed of the typical line-like peaks corresponding to the 5D  7F
(J = 0-4) transitions. No residual
0
J
fluorescent or phosphorescent emission from the ligand was observed in the spectra. The 5D
 7F
is
0
0
-1
visible and has a calculated full width at half maximum below 60 cm , again supporting the fact that the
emissive species have a unique and similar coordination environment.[41] The quantum yield values are
r
in the 0.20-0.25 range. From the spectral profiles, the radiative decay ( ) values, reported in Table 3, can
be calculated by means of the equation
-
1
3
( ) = AMD,0n (Itot/IMD)
r
-1
where AMD,0 is a constant of value 14.65 s , n is the refractive index of the solvent, and Itot/IMD is the ratio
of the integrated intensity of the whole spectrum (Itot) versus the integrated intensity of the magnetic
dipole transition 5D
as the ratio of / , and the sensitisation efficiency () as the ratio of /
indicate that all the four species are good sensitisers of Eu luminescence, with efficiencies ranging from
 7F
0
1
r
(IMD). From the values of  , the intrinsic quantum yield (
i
) can be calculated
r
i
. The data, reported in Table 3,
3
+
3
+
0
.48 to 0.63. These data are consistent with previously reported luminescence properties of Eu centres
bound to terpyridine-type ligands. [11,42]
2
0
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201700663
-
5
Figure 11. Emission profiles from diluted (ca 10 M) acetonitrile solutions of the synthesised species in
3
+
3+
the presence of excess Eu (left) or Yb (right), with excitation wavelength set at 310 nm.
The addition of [Yb(NO
quenching of the ligand-centred emission with concomitant sensitisation of the Yb luminescence
Figure 11). A broad band in the NIR region with characteristic peak at 980 nm is evident in each case,
3
)
3
n
(DMSO) ] to acetonitrile solutions of the four species also caused the
3
+
(
which is ascribed to the radiative decay occurring from the 2F5/2  2F7/2 transition. The excited state
lifetime decay is similar in all cases and ranges between 8.48 and 10.62 s, which are typical values for
3
+
3+
Yb NIR emission. From these values, and assuming a radiative decay for Yb at 1,200 s, the intrinsic
quantum yields of these complexes can be estimated to be just below 0.01. These values are typical for
3
+
[42]
Yb complexes sensitised by terpyridine ligands.
Conclusions
In this work, four new tetrazole-containing species were synthesised, characterised, and investigated in
relations to their photophysical properties. The species are composed of protonated or methylated
2
1
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201700663
tetrazole moieties conjugated to terpyridine functional groups, and spaced by either a phenyl or pyrdyl
ring. The compounds are emissive in the UV-blue region of the spectrum and exhibit high (77-85%) to
moderate quantum yields (28-32%) for the pronated and methylated species, respectively. Significant
variations in the emission profiles of the methylated species could be detected upon addition of acids
and bases, consistent with protonation of the terpyridine functional group causing a lowering of the
HOMO-LUMO gap. The remaining protonated tetrazole species also showed variations, albeit with more
complicated trends due to the added protonation site on the tetrazolate ring. The species were studied
as sensors for important biological and environmental metal cations, highlighting a selective and
2
+
ratiometric response to Zn compared to other transition, alkali and alkali earth cations. Furthermore,
2
+
2+
the response of the species to the detection of Zn could be well discriminated from Cd cations. Lastly,
the synthesised species were investigated as sensitisers for lanthanide luminescence, highlighting
3
+
3+
efficient sensitisation for red emitting Eu and near infrared emitting Yb cations. This work has
highlighted terpyrdine-functionalised tetrazole species as very versatile molecules with useful
luminescent properties and potential application in fields such as sensing and optical materials.
Experimental Section
General considerations
All reagents and solvents were purchased from Sigma Aldrich and used as received without further
(DMSO)
] (Ln = Gd , Eu , Yb ) , NCPhTpy,[22] and NCPyCHO[26] precursors
3
+
3+
3+
3+ [37]
purification. The [Ln(NO
)
3 3
n
were prepared according to previously published procedures Nuclear magnetic resonance spectra,
2
2
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201700663
consisting of 1H and 13C, were recorded using a Bruker Avance 400 spectrometer (400.1 MHz for 1H,
1
13
1
00 MHz for 13C) at 300 K. H and C chemical shifts were referenced to residual solvent signals.
Infrared spectra were recorded in the solid state, using an attenuated total reflectance Perkin-Elmer
−1
Spectrum 100 FT-IR, equipped with a diamond stage. Compounds were scanned from 4000 to 650 cm .
The intensities of the IR bands are reported as strong (s), medium (m), or weak (w). Melting points were
determined Using a BI Barnstead Electrothermal 9100 apparatus. Elemental analyses were obtained at
the Central Science Laboratory, University of Tasmania, using a Thermo Finnigan EA 1112 Series Flash.
Photophysical measurements
Absorption spectra were recorded at room temperature using a Perkin Elmer Lambda 35 UV/Vis
spectrometer. Uncorrected steady state emission and excitation spectra were recorded from air-
equilibrated solutions on an Edinburgh FLSP980 spectrometer equipped with a 450 W Xenon arc lamp,
double excitation and double emission monochromators and a Peltier cooled Hamamatsu R928P
photomultiplier tube (185-850 nm) as well as a Hamamatsu R5509-42 photomultiplier for detection of
NIR radiation (spectra range 800-1400 nm). Emission and excitation spectra were corrected for source
intensity (lamp and grating) and emission spectral response (detector and grating) by a calibration curve
supplied with the instrument. According to the approach described by Demas and Crosby,[43]
luminescence quantum yields were measured in optically dilute solutions (O.D. < 0.1 at excitation
wavelength) obtained from absorption spectra on a wavelength scale [nm] and compared to the
reference emitter by the following equation:
2
3
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201700663
2
é
ùé
úê
ûë
ùé ùé
ù
ú
Ar
(
(
lr
)
)
Ir
(
(
lr
)
)
nx Dx
F = F ê
ú
x
r
ê
2
úê
Ax
lx
Ix
lx
ën ûë D û
r
r
ë
û
where A is the absorbance at the excitation wavelength , I is the intensity of the excitation light at the
excitation wavelength , n is the refractive index of the solvent, D is the integrated intensity of the
luminescence and  is the quantum yield. The subscripts r and x refer to the reference and the sample,
respectively. The quantum yield determinations were performed at identical excitation wavelength for
the sample and the reference, therefore cancelling the I
species were measured against an air-equilibrated aqueous solution of quinine sulfate in 0.1 M H
used as reference (
= 0.546).[44] Emission lifetimes (τ) were determined with the time-correlated single
photon counting (TCSPC) technique with the same Edinburgh FLSP920 spectrometer using pulsed
picosecond LEDs (EPLED 295 or EPLED 360, FHWM < 800 ps) as the excitation source, with repetition
rates between 10 kHz and 1 MHz, and the above-mentioned R928P PMT as detector. On the other hand,
r
(
r
x
)/I (
x
) term in the equation. The synthesised
2
SO
4
r
3
+
emission lifetimes of Ln cations were determined with a microsecond flash-lamp as the excitation
2
source. The goodness of fit was assessed by minimising the reduced  function and by visual inspection
of the weighted residuals. The solvents used for the preparation of the solutions for photophysical
investigations was of spectrometric grade. The prepared solution was filtered through a 0.2 mm syringe
filter before measurement. Experimental uncertainties are estimated to be ±8% for lifetime
determinations, ±20 % for quantum yields, ±2 nm and ±5 nm for absorption and emission peaks.
2
4
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201700663
Synthetic details
Synthesis of HTzPhTpy. To toluene (50 mL) in an ice bath, triethylamine (0.8 mL, 5.8 mmol) and HCl (0.70
mL, 5.8 mmol) were combined and stirred until fuming subsided. NCPhTpy (1.93 g, 5.8 mmol) and NaN
0.4 g, 5.8 mmol) were added and the mixture was stirred at reflux overnight. The solvent was
evaporated under reduced pressure and the solid recrystallised from water (50 mL) and then washed
3
(
−1
with (3×20mL) DCM. Yield: 0.750 g (35 %). M.p. 280 ◦C dec. IR /cm : 3046 m, 2444 m, 1683 w, 1605 w,
1
1
593 s, 1581 s, 1542 s, 1470 m, 1393 s, 1295 w, 1113 w, 1076 w, 1008 s, 890 w, 842 w, 793 s. H-NMR
(
DMSO-d ) δ/ppm: 8.78-8.75 (4H, m), 8.66 (2H, d, J = 8.1 Hz), 8.26 (2H, d, J = 8.8 Hz), 8.02 (2H, app t, J =
6
13
8
1
.6 Hz), 7.97 (2H, d, J = 8.4Hz), 7.54-7.49 (2H, m). C-NMR (DMSO-d
49.4, 149.2, 137.4, 135.8, 133.6, 127.0, 126.7, 124.5, 120.9, 117.6.ꢀAnal. Calcd (%) for
O): C 69.35, H 4.02, N 25.73. Found: C 69.54, H 3.85, N 25.60.
6
) δ/ppm: 160.3 (N C), 155.7, 155.0,
4
HTzPhTpy·0.2(H
2
Synthesis of HTzPyCHO. To toluene (40 mL) in an ice bath, triethylamine (0.52 mL, 3.7 mmol) and HCl
0.41 mL, 3.7 mmol) were combined and stirred until fuming subsided. 2-cyanopyridine-5-
carboxyalhedyde (0.5 g, 3.7 mmol) and NaN (0.24 g, 3.7 mmol) were added and the mixture was stirred
(
3
at reflux overnight. The mixture was extracted with water (30 mL) and the aqueous phase was acidified
and the formed precipitate was filtered. The remaining aqueous solution was extracted with ethyl
acetate (3x15 mL). The organic phase was collected and dried over magnesium sulfate and the solvent
was removed under reduced pressure giving an off-white solid. Yield: 0.32 g (40 %). M.p. 220 ◦C dec. IR
−1

/cm : 2592 m br., 1705 s, 1605 s, 1575 m, 1370 m, 1263 m, 1205 w, 1178 w, 1116 w, 1039 w, 1016 w,
1
8
45 w.ꢀ H-NMR (DMSO-d
6
) δ/ppm: 10.20 (1H, s, CHO), 9.27 (1H, s), 8.50 (1H, d, J = 6.4 Hz), 8.42 (1H, d, J
2
5
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201700663
=
8.2 Hz). A peak at 1.90 indicated the presence of acetic acid, probably resulting from the extraction of
1
3
the acidic aqueous solution with ethyl acetate. C-NMR (DMSO-d
51.7, 147.6, 138.3, 132.3, 123.0. Anal. Calcd (%) for HTzPyCHO·0.1(CH
Found: C 47.49, H 2.76, N 38.76.
6
) δ/ppm: 191.8 (CHO), 154.6 (N
4
C),
1
3
COOH): C 47.74, H 3.00, N 38.66.
Synthesis of HTzPyTpy. 2-acetylpyridine (0.37 mL, 3.32 mmol) was added to a solution of HTzPyCHO (0.2
g, 1.1 mmol) in EtOH (20 mL). KOH pellets (0.2 g, 3.3 mmol) and NH OH (28.0-30.0% NH aqueous
4
3
solution, 0.5 mL, 3.3 mmol) were then added to the solution, which was then stirred overnight at room
temperature. The mixture was filtered and the solid left to dry under vacuum for 5 minutes. The solid
was then dissolved in minimal water. The water was acidified to yield an off-white solid, which was
−1
filtered and dried in air. Yield: 0.13 g (40 %). M.p. 282 ◦C dec. IR /cm : 3370 m, 2701 m, 1618 w, 1597
1
s, 1563 w, 1530 s, 1497 w, 1435 w, 1338 w, 1300 w, 1278 w, 1239 w, 1172 w, 1007 w, 993 w, 791 w. H-
NMR (DMSO-d
.24 (1H, d, J = 8.4 Hz), 8.05 (2H, app t, J = 7.8 Hz), 7.57-7.53 (2H, m). C-NMR (DMSO-d
C), 156.0, 155.0, 151.8, 149.5, 147.6, 146.9, 137.8, 135.3, 131.6, 124.8, 121.9, 121.2, 118.0.ꢀThis
compound was found to be very hygroscopic and reproducible elemental analysis could not be obtained.
6
) δ/ppm: 9.18 (1H, s), 8.79-8.78 (4H, m), 8.68 (2H, d, J = 8.2 Hz), 8.39 (1H, d, J = 8.2 Hz),
1
3
8
6
) δ/ppm: 161.1
(N
4
Synthesis of MeTzPhTpy. HTzPhTpy (0.25 g, 0.66 mmol) was combined with K
2
CO in acetonitrile (15 mL)
3
and stirred for 1 minute. CH I (44 μL, 0.66 mmol) was added and the mixture was stirred at reflux
3
overnight. The mixture was filtered and the solvent removed under reduced pressure. The leftover solid
was loaded onto Brockmann II basic alumina and eluted with DCM. The first fraction was recovered and
the target compound was obtained as a white solid after removal of the solvent. Yield: 0.075 g (30 %).
2
6
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201700663
−1
M.p. 227 ◦C dec. IR /cm : 3062 w, 1601 w, 1582 w, 1565 m, 1543 m, 1479 m, 1465 m, 1423 m, 1388
1
w, 1263 w, 1139 w, 918 w, 845.ꢀ H-NMR (CDCl
3
) δ/ppm: 8.79 (2H, s), 8.74 (2H, d J = 8.1 Hz), 8.68 (2H, d,
J = 8.1 Hz), 8.28 (2H, d, J = 8.4 Hz), 8.04 (2H, d, J = 8.4 Hz), 7.92-7.87 (2H, m, J = 2.4 Hz), 7.39-7.35 (2H,
13
m), 5.29 (3H, s). C-NMR (CDCl
3
) δ/ppm: 165.0 (N
28.0, 127.5, 124.1, 121.6, 119.0, 39.7 (CH ). Anal. Calcd (%) for MeTzPhTpy·0.2(CH
.29, N 24.01. Found: C 68.27, H 3.98, N 24.14.
4
C) 156.2, 156.1, 149.5, 149.2, 140.4, 137.1, 128.0,
1
4
3
2
Cl ): C 68.23, H
2
Synthesis of MeTzPybCHO. HTzPyCHO (0.45 g, 2.5 mmol) was combined with K
2
CO in acetonitrile (25
3
mL) and stirred for 1 minute. CH I (0.20 mL, 3 mmol) was added and the mixture was stirred at reflux
3
overnight. The mixture was filtered and the solvent removed under reduced pressure. The solid was
loaded onto silica and eluted with a mixture of 1:1 of hexane and ethyl acetate. The first fraction was
recovered and the target compound was obtained as a white solid after removal of the solvent. Yield:
−1
0
.157 g (33 %). M.p. 178-179 ◦C. IR /cm : 2865, 1692 s, 1677 s, 1592 s, 1525 w, 1443 w, 1391 m, 1206
1
m, 1051 m, 840 m. H-NMR (CDCl
3
) δ/ppm: 10.18 (1H, s, CHO), 9.20 (1H, s, H6), 8.41 (1H, d, J = 6.4 Hz,
1
3
H3), 8.33 (1H, d, J = 6.4 Hz, H4), 4.48 (3H, s, CH
3
). C-NMR (CDCl
). Anal. Calcd (%) for MeTzPyCHO·0.1(CH
0.90, H 3.89, N 35.91. Found: C 51.27, H 3.96, N 35.65.
3
) δ/ppm: 190.1 (CHO), 164.2 (N
4
C),
1
5
52.5, 151.2, 137.3, 131.9, 122.7, 40.0 (CH
3
3
CO CH CH
2
2
3
): C
Synthesis of MeTzPyTpy. 2-Acetylpyridine (0.2 mL, 1.6 mmol) was added to a solution of MeTzPyCHO
0.15 g, 0.8 mmol) in EtOH (10 mL). KOH pellets (0.1 g, 1.8 mmol) and NH OH(aq) (28.0-30.0% NH
(
4
3
aqueous solution,0.24 mL, 2.2 mmol) were then added to the solution which was stirred overnight at
room temperature. The mixture was filtered and the solid washed with EtOH (4 mL) and dried in air.
2
7
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201700663
−1
Yield: 0.1 g (31 %). M.p. 273 ◦C dec IR /cm : 3054 w, 1603 m, 1585 s, 1566 s, 1467 s, 1440 w, 1404 s,
1
1
120 w, 1041 w, 1015 w, 836 m. H-NMR (CDCl
3
) δ/ppm: 9.26 (1H, s), 8.79 (2H, s), 8.74 (2H, d, J = 4.4
1
3
Hz), 8.68 (2H, d, J = 8.2 Hz), 8.41-8.34 (2H, m), 7.92-7.88 (2H, m), 7.40-7.37 (2H, m), 4.49 (3H, s). C-NMR
CDCl ) δ/ppm: 164.8 (N C) 156.5, 155.9, 149.3, 149.0, 147.1, 146.7, 137.2, 136.0, 135.6, 124.3, 122.5,
21.6, 119.0, 39.9 (CH ). Anal. Calcd (%) for MeTzPyTpy·(CH Cl ): C 63.76, H 3.99, N 26.63. Found: C
3.15, H 3.47, N 26.59.
(
3
4
1
6
3
2
2
Fluorescence sensing of metal ions
The fluorescent properties of the ligands and their response to metal ions were performed for 10 M
solutions of the ligands in HEPES buffer (20 mM, pH 7.4) containing 1% DMSO (HTzPhTpy, HTzPyTpy and
MeTzPhTpy) or 5% DMSO and 0.5% of acetic acid (MeTzPyTpy). To enable high throughput screening of
the fluorescent response, the emission spectra for all the ligands alone and in the presence of the metal
ions (10 eq) were collected on the PerkinElmer Enspire Plate Reader at the same settings (exc = 290 nm,
emission from 310 nm to 560 nm with 1 nm step size and 100 flashes per each sample).
Acknowledgments
The work was supported by the Australian Research Council (FT130100033 to MM, DP150100649 to
EJN). PJW wishes to thank Curtin University for the Australian Postgraduate Award. EJN thanks the
Westpac Bicentennial Foundation for a Research Fellowship.
2
8
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201700663
References
[
[
[
[
1]
2]
3]
4]
R. Herr, Bioorg. Med. Chem. 2002, 10, 3379–3393.
G. Aromí, L. Barrios, O. Roubeau, P. Gamez, Coord. Chem. Rev. 2010.
C. J. McMulkin, M. Massi, F. Jones, CrystEngComm 2015, 17, 2675–2681.
E. Andreiadis, R. Demadrille, D. Imbert, J. Pécaut, M. Mazzanti, Chem. Eur. J. 2009, 15,
9
458–9476.
[
[
5]
6]
S. Stagni, S. Colella, A. Palazzi, G. Valenti, S. Zacchini, F. Paolucci, M. Marcaccio, R. Q.
Albuquerque, L. De Cola, Inorg. Chem. 2008, 47, 10509–10521.
C. A. Strassert, C.-H. Chien, M. D. Galvez Lopez, D. Kourkoulos, D. Hertel, K. Meerholz,
L. De Cola, Angew. Chem. Int. Ed. 2010, 50, 946–950.
[
[
7]
8]
G. Koldobskii, V. Ostrovskii, Chemistry of Heterocyclic Compounds 1988, 24, 469–480.
G. Koldobskii, V. Ostrovskii, B. Gidaspov, Chemistry of Heterocyclic Compounds 1980,
1
6, 665–674.
[
[
9]
10]
T. Pinter, S. Jana, R. J. M. Courtemanche, F. Hof, J. Org. Chem. 2011, 76, 3733–3741.
D. D'alessio, A. N. Sobolev, B. W. Skelton, R. O. Fuller, R. C. Woodward, N. A.
Lengkeek, B. H. Fraser, M. Massi, M. I. Ogden, J. Am. Chem. Soc. 2014, 136, 15122–
1
5125.
[
[
[
[
[
[
11]
12]
13]
14]
15]
16]
M. Giraud, E. S. Andreiadis, A. S. Fisyuk, R. Demadrille, J. Pécaut, D. Imbert, M.
Mazzanti, Inorg. Chem. 2008, 47, 3952–3954.
S. Stagni, A. Palazzi, S. Zacchini, B. Ballarin, C. Bruno, M. Marcaccio, F. Paolucci, M.
Monari, M. Carani, A. J. Bard, Inorg. Chem. 2006, 45, 695–709.
D. D'alessio, S. Muzzioli, B. W. Skelton, S. Stagni, M. Massi, M. I. Ogden, Dalton Trans.
2
012, 41, 4736–4739.
P. J. Wright, S. Muzzioli, B. W. Skelton, P. Raiteri, J. Lee, G. Koutsantonis, D. S.
Silvester, S. Stagni, M. Massi, Dalton Trans. 2013, 42, 8188–8191.
P. J. Wright, S. Muzzioli, M. V. Werrett, P. Raiteri, B. W. Skelton, D. S. Silvester, S.
Stagni, M. Massi, Organometallics 2012, 31, 7566–7578.
M. V. Werrett, D. Chartrand, J. D. Gale, G. S. Hanan, J. G. MacLellan, M. Massi, S.
Muzzioli, P. Raiteri, B. W. Skelton, M. Silberstein, et al., Inorg. Chem. 2011, 50, 1229–
1
241.
[
[
[
[
[
17]
18]
19]
20]
21]
C. Femoni, S. Muzzioli, A. Palazzi, S. Stagni, S. Zacchini, F. Monti, G. Accorsi, M.
Bolognesi, N. Armaroli, M. Massi, et al., Dalton Trans. 2013, 42, 997–1010.
K. D. M. MaGee, P. J. Wright, S. Muzzioli, C. M. Siedlovskas, P. Raiteri, M. V. Baker, D.
H. Brown, S. Stagni, M. Massi, Dalton Trans. 2013, 42, 4233–4236.
M. V. Werrett, S. Muzzioli, P. J. Wright, A. Palazzi, P. Raiteri, S. Zacchini, M. Massi, S.
Stagni, Inorg. Chem. 2014, 53, 229–243.
M. V. Werrett, G. S. Huff, S. Muzzioli, V. Fiorini, S. Zacchini, B. W. Skelton, A. Maggiore,
J. M. Malicka, M. Cocchi, K. C. Gordon, et al., Dalton Trans. 2015, 44, 8379–8393.
C. A. Bader, T. Shandala, E. A. Carter, A. Ivask, T. Guinan, S. M. Hickey, M. V. Werrett,
P. J. Wright, P. V. Simpson, S. Stagni, et al., PLoS ONE 2016, 11, e0161557.
J. Wang, G. S. Hanan, Synlett 2005, 2005, 1251–1254.
[
[
[
[
22]
23]
24]
25]
K. Koguro, T. Oga, S. Mitsui, R. Orita, Synthesis 1998, 910–914.
R. Butler, V. Garvin, J. Chem. Soc., Perkin Trans. 1 1981, 390–393.
R. Butler, V. Garvin, H. Lumbroso, C. Liégeois, J. Chem. Soc., Perkin Trans. 2 1984,
7
21–725.
2
9
This article is protected by copyright. All rights reserved.