Copper(i) complexes with bipyridyl and phosphine ligands: A systematic study

Article abstract of DOI:10.1039/c2dt30698k

Phosphorescent copper(i) complexes carrying 2,2′-bipyridyl derivatives and phosphine ligands have been prepared and fully characterised. The role of the bipyridyl as well as the phosphine ligands in defining the optical, as well as the chemical properties of the complexes, are discussed. The light emission of these complexes is investigated as a function of the molecular geometry: rigid complexes with restricted freedom to rearrange in the excited state are found to show a quantum yield of phosphorescence one order of magnitude higher than those complexes with no steric constraint. The complexes have been extruded in a polymer matrix as a proof of principle of their processability.

Full text of DOI:10.1039/c2dt30698k

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PAPER
Copper(I) complexes with bipyridyl and phosphine ligands: a systematic
study
Inmaculada Andrés-Tomé,a John Fyson,a Fernando Baiao Dias,b Andy P. Monkman,b Giuliano Iacobellisc
and Paolo Coppo*a
Received 28th March 2012, Accepted 23rd May 2012
DOI: 10.1039/c2dt30698k
Phosphorescent copper(I) complexes carrying 2,2′-bipyridyl derivatives and phosphine ligands have been
prepared and fully characterised. The role of the bipyridyl as well as the phosphine ligands in defining the
optical, as well as the chemical properties of the complexes, are discussed. The light emission of these
complexes is investigated as a function of the molecular geometry: rigid complexes with restricted
freedom to rearrange in the excited state are found to show a quantum yield of phosphorescence one order
of magnitude higher than those complexes with no steric constraint. The complexes have been extruded in
a polymer matrix as a proof of principle of their processability.
degradation of the complexes even in the absence of oxygen.
Thermal characterisation further confirmed the poor stability of
Introduction
Copper(I) coordination complexes bearing arylphosphine ligands
are gathering tremendous interest as phosphorescent active
materials for organic light emitting devices (OLEDs),1,2 polymer
light emitting devices (PLEDs)3,4 and organic light emitting
electrochemical cells (OLECs).5,6
those complexes, probably due to a weak bond between the
alkynyl ligand and the trinuclear copper(I) cluster.
In this work, we present novel tetra-coordinated copper(I) com-
plexes based on phosphine ligands and 2,2′-bipyridyl derivatives.
While the first generation of Cu(I) light emitting devices did
not compare in performance with OLEDs manufactured with
Ir(III) cyclometalated coordination complexes, recent reports
suggest Cu(I) complexes provide an efficient alternative to the
expensive and rare iridium metal.7,8 Challenges still need to be
overcome for copper to enter the OLED market: in particular the
emission needs to cover the full RGB colour gamut and active
materials need to prove stable in operation. While the rules gov-
erning the emission in heavy metals such as iridium(III) and
platinum(II) are generally understood, literature reports on struc-
turally similar copper(I) compounds appear to show inconsistent
optical properties.9 From previous publications, it seems clear
that geometrical issues play a major role in determining the
optical properties of the complexes, over the electronic structure
of the ligand.10–13
Synthesis of the complexes
The synthetic protocol to prepare complexes 1–3(a–c) involves
room temperature reaction of (CH3CN)4CuBF4 with stoichio-
metric amounts of the bidentate phosphine ligands (bis(2-diphe-
nylphosphino)phenyl ether (1) or 9,9-dimethyl-4,5-bis-
(diphenylphosphino)xanthene (2), or a double molar amount of
triphenylphosphine (3), and 2,2′-bipyridyl. Purification of the
yellow, air stable Cu1+ complexes by precipitation in diethyl
ether–hexane mixtures affords the complexes in excellent yield
(see Fig. 1). In all cases, the complexes were obtained as BF4
salts, as shown in the 19F NMR, which show a strong signal at
ca. −150 ppm, consistent with the presence of a BF4− group.14
Phosphine ligands play a crucial role in securing the stability
of the complexes. Attempts to prepare analogous complexes car-
rying solely 2,2′-bipyridyl ligands failed, due to disproportiona-
tion of the Cu(I) ion to Cu(II) and metallic copper deposited at
the bottom of the vessel. Cu(I) complexes carrying solely phos-
phine ligands and showing poor emission were reported else-
where and were therefore not investigated in this work.15–17
The complexes discussed here showed excellent shelf life at
room temperature in air and no sign of degradation or oxidation
was detected upon several months of storage in the solid state,
by comparison of elemental analyses before and after storage.
Complex 3c could not be isolated in satisfactory purity. NMR
and mass analysis do show the presence of the complex, but
attempts to purify it resulted in significant amounts of free ligand
We recently reported on trinuclear copper complexes, whose
emission wavelengths extend across the range of the visible
spectrum and show efficient phosphorescence at room tempera-
ture in degassed solutions.14 Although the alkynyl trinuclear
copper(I) complexes show unique optical features, in our hands
they were unstable. In particular, the electrochemistry led to fast
aWolfson Centre for Materials Processing, Brunel University, Kingston
Lane, Uxbridge, UB8 3PH, UK. E-mail: paolo.coppo@brunel.ac.uk;
Fax: +44 (0)1895269737; Tel: +44 (0)1895266127
bDepartment of Physics, Durham University, South Road, Durham
DH1 3LE, UK
cDipartimento di Chimica, Universita’ degli Studi di Bari, 70126 Bari,
Italy
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Fig. 2 Extruded phosphorescent polypropylene doped with complex
2c (green) and 2a (orange).
halogenated solvents, as well as polar solvents such as aceto-
nitrile and dimethylformamide. Thin films for optical measure-
ments of absorption and emission spectra were prepared by spin
coating 2% w/v PMMA solutions in dichloromethane, contain-
ing 0.16% w/v of the desired complex as dopant.
The complexes can also be extruded as dopants in a polymer
matrix. PMMA doped with 1% w/w of the complexes was pro-
cessed in a Haake MiniLab co-rotating twin screws extruder at
200 °C and the extruded material was manually drawn into a
fibre of ca. 1 mm thickness. The resulting fibres showed bright
luminescence under UV excitation at 360 nm as proof of stability
at high temperature. PMMA fibres are transparent but very
brittle, therefore, using the same method, polypropylene was
extruded with complexes 1–3(a–c) and even in this case flexible
luminescent extruded polymer fibres were obtained (see Fig. 2).
Thermogravimetric analysis (TGA) of complexes 1–3(a–c)
showed the stability to be dependent upon the coordinating phos-
phine ligand (see Fig. 3). Triphenylphosphine coordinated com-
plexes 3a–b show far lower thermal stability than complexes
1–2(a–c). The increased rigidity of the ligand, combined with
the availability of the oxygen’s electron pairs in 1 and 2 type
structures, results in exceptional thermal stability. In the case
of triphenylphosphine bound complexes 3(a–b), the weight
loss occurring at temperatures in excess of 200 °C is not
accompanied by any endothermic signal detectable by scanning
differential calorimetry, suggesting the process is degradation
rather than evaporation of the complex (see Fig. 4).
Fig. 1 Chemical structure of complexes 1–3. a: R = R′ = H; b: R = H,
R′ = CH3; c: R = CH3, R′ = H. BF4¬ is the counter ion in all complexes.
and discolouration, as a sign of oxidation. It is likely that the
combined effect of steric hindrance of the bipyridyl ligand and
the weak Cu–P bond in the case of triphenylphosphine result in
an unstable complex.
This observation is further confirmed by the multi-step nature
of the TGA trace for complex 3a. Complexes 1a–c show melting
points in excess of 230 °C, characterised by large sharp
endothermic signals in the DSC traces. In the case of complex
1c the melting point is significantly lower, possibly induced by a
distorted geometry. No recrystallisation peak was detected in the
cooling step, as a sign of irreversible thermal behaviour.
Processing of the complexes and thermal analysis
Complexes 1–3(a–c) were obtained as amorphous powders by
precipitation. The solubility of these complexes is excellent in
8670 | Dalton Trans., 2012, 41, 8669–8674
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Fig. 5 Absorption spectra of complexes 1–3(a–c).
Fig. 3 TGA traces of complexes 1–3(a–c).
on the aromatic ligands (see Fig. 5). The absorption maxima are
consistent across the structures, suggesting that the geometrical
and electronic structure of these complexes in the ground state is
very similar. The absorption spectra recorded in PMMA thin
films show analogous maxima, although in this case the molar
extinction coefficients could not be reproducibly measured. The
absorption spectra were found to be in agreement with those
published by Rader et al. for similar compounds.18
Complexes 1–3(a–b) do not show phosphorescence at room
temperature in organic solvents, either in the presence of oxygen
or in degassed solutions. However, they do emit at 77 K in a
glass, indicating that the flexibility of the system and possible
solvent quenching are the cause of the lack of emission observed
in solution. Conversely, complexes 1–2c are phosphorescent in
solution in the absence of oxygen, thus confirming a rigid struc-
ture is necessary for a radiative path to compete with non radia-
tive relaxation. The solution quantum yields of 1–2c are 5.2%
and 1.6%, respectively.
When complexes 1–3(a–c) are processed as 5% w/w dopants
in a polymethylmethacrylate (PMMA) film, emission is observed
at room temperature, even in the presence of air (see Fig. 6).
This result reflects the previous observations in tetra-coordinated
Cu(I) complexes, where the rigidity of the complex is key to
efficient phosphorescence.10
Tetra coordinated Cu(I) complexes with phosphine and pyri-
dine type ligands are reported to have a moderate distortion from
the ideal tetrahedral geometry.19–21 During this work, we were
unable to isolate single crystals of the size required for X-ray dif-
fraction based structure refinement and we therefore assume the
structures of complexes 1–3(a–c) to be similarly distorted from
an ideal tetrahedral geometry.
Fig. 4 DSC trace of complex 1a.
Complexes with triphenylphosphine and 9,9-dimethyl-4,5-bis-
(diphenylphosphino)xanthene as ligands do not show any sig-
nificant thermal process up to 300 °C. In summary, the thermal
analysis suggests all complexes are stable within a sensible range
and suitable for applications such as OLEDs and OLECs.
However, complexes containing triphenylphosphine as the
ligand can only be processed from solution as they show thermal
decomposition above 200 °C, rather than a clean evaporation
(Fig. 3).
When the excited state is not locked in a rigid configuration,
alternatives to a radiative decay path can be found, involving
geometrical rearrangement. Extensive structural rearrangements
occurring in the excited state are confirmed by the relatively
large Stokes shifts observed in copper(I) complexes, often
exceeding a 150 nm gap between the emission and absorption
maxima.
Optical spectroscopy
UV-vis absorption spectroscopy of complexes 1–3(a–c) in
dichloromethane solutions reveals two sets of features. Broad
absorption features centred around 370 nm with a molar extinc-
tion coefficient ε in the region of 1–5000, characteristic of
metal-to-ligand-charge-transitions (MLCT) are observed.
second set of features of higher intensity (ε = 10 000–50 000)
centred around 280 nm are assigned to π–π* transitions centred
A
The quantum yield of photoluminescence was measured in
5% doped PMMA films spin coated from a dichloromethane
solution, using an integrating sphere, following the method
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Fig. 7 Cyclic voltammetry of complex 1b in degassed, anhydrous
acetonitrile.
Fig. 6 Emission spectra of complexes 1–3(a–c) in PMMA films.
Table 1 Optical UV-vis absorption maxima at room temperature in
dichloromethane
in all cases in PMMA films as a sign of single, rather than mul-
tiple emissions at room temperature.
Conversely, the effect of the phosphine ligand in tuning the
emission properties is negligible.
Abs. λmax/nm
1a 385; 287
2a 382; 281
3a 357; 270
1b 377; 284
2b 375; 280
3b 354; 264
1c 372; 286
2c 375; 282
Em λmax/nm Φ/% τ/μs E1/2 ox/V E1/2 red/V
559
560
550
544
558
537
528
530
3.3
9.0 0.72
−1.73
−1.54
−1.93
−1.66
−1.71
−1.64
−1.58
−1.56
0.1 11.5 0.67
0.4 10.0 0.83
0.3 11.2 0.66
1.1 10.7 0.74
0.2 10.7 0.81
14.5 15.7 0.82
33.3 15.1 0.81
Electrochemistry
Cyclic voltammetry was performed on complexes 1–3(a–c) in
CH3CN, using the redox couple Cp2Fe/Cp2Fe+ as the internal
reference. All complexes show a first oxidation wave at
0.6–0.8 V vs. Cp2Fe/Cp2Fe+, which, by comparison to similar
complexes, can be assigned to metal centred oxidation to Cu(II).1,3
Oxidation on the metal is likely to result in significant geometri-
cal rearrangement, as divalent copper ions prefer a flatter geo-
metry. In solution, the complexes are likely to be unstable upon
oxidation, as indicated by an irreversible wave. Further oxi-
dations are detected at higher voltages (see Fig. 6), which are
likely to be localised on the phosphine ligands, by comparison
with the cyclic voltammetry signals of the corresponding free
ligands in solution. These signals are also irreversible. All com-
plexes show a reduction wave centred at −(1.7–1.9 V) vs.
Cp2Fe/Cp2Fe+. In phosphorescent metal complexes, this signal
is typically assigned to a reduction centred on the bipyridyl
ligand. The reduction wave is only partially reversible, in solu-
tion, as is often the case in transition metal complexes (Fig. 7).28
Emission maxima in 5% PMMA films. Quantum yields and lifetimes of
photoluminescence in 5% PMMA films. Redox potentials in anhydrous,
degassed acetonitrile vs. Cp2Fe/Cp2Fe+ used as internal reference.
published by Porres et al.22 Whilst complexes of the a and b
series show low to very low quantum yields, complexes of the c
series are surprisingly efficient (see Table 1). In this work the
effect of substituents of the bipyridyl ligand is striking clear: the
steric hindrance of methyl groups on position 6 and 6′ results in
better shielding of the copper core of the complexes and in
enhanced emission. In the same complexes, the optical band gap
is significantly narrower than in complexes without methyl
groups on the bipyridyl ligand or where the methyl groups sit
outside the core of the complex. Complexes 1–2c show blue
shifted emission and narrower band shape as a result of a lesser
degree of distortion in the excited state, although no appreciable
shift is observed in the absorption spectrum. This is a clear sign
that the restrictive geometrical effect of the methyl groups, rather
than the electronic effect, is responsible for the difference in
optical behaviour among these complexes. The metal-to-ligand
charge transfer nature of the excited state results in a partially
oxidised copper ion, which prefers a flattened geometry.23–27
The presence of the methyl groups prevents the rearrangement to
a certain degree, resulting in blue shifted and enhanced emission.
The lifetime of the emitting species is in the region of 10 μs,
consistent with the assignment as a MLCT excited state. The fea-
tureless emission spectra are in contrast with those observed by
Rader et al.18 at 77 K and single exponential decay was observed
Conclusions
This systematic study of bipyridyl Cu(I) complexes with diphos-
phine ligands shows that the structure of the ligand is important
in defining the optical as well as chemical and physical proper-
ties of mono valent copper complexes. Efficient radiative decay
from the triplet excited state is detected only when a bipyridyl
ligand is carrying bulky methyl groups facing the copper
nucleus. The methyl groups act as a shield towards external
quenching, as well as preventing extensive geometrical
rearrangement in the excited state. The effect is enhanced, as
well as blue shifted emission, by virtue of a more rigid configur-
ation. Complexes where the methyl groups are facing the outer
8672 | Dalton Trans., 2012, 41, 8669–8674
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side of the complex, as well as complexes without methyl
groups, show a mainly non radiative decay path, both in solution
and in the solid state.
6.94–7.10 ppm (m, 12H, arom.). 13C NMR in CDCl3: 151.90;
149.23; 139.47; 133.05; 132.02; 130.37; 129.01; 126.18;
123.55 ppm. ESI-MS: 481.0 N^NCuPPh3 ; 219.0 N^NCu+.
+
The phosphine ligands play a crucial role in stabilising the
complexes, as shown in thermal analysis. Triphenylphosphine is
the weakest among the ligands involved in this study and com-
plexes 3a–b are less stable as a consequence.
The combined effects of a sterically hindered bipyridyl ligand
and a rigid, strong coordinating diphosphine ligand results in
complexes with exceptional stability and a good quantum yield
of photoluminescence in the solid state. Such complexes are
particularly interesting for OLED and OLEC applications.
Elem. anal. %: C: 66.33 (calc. 66.48) H: 4.20 (calc. 4.61).
Complex 1b: H NMR in CDCl3: 8.26 (d, 2H, J = 7.9 Hz,
1
pyr.); 8.15 (d, 2H, J = 8.0 Hz, pyr.); 7.20–7.30 (m, 8H, arom.);
7.16 (t, 8H, J = 7.3 Hz, arom.); 7.00 (d, 2H, J = 7.7 Hz, pyr.);
6.90–6.99 (m, 10H, arom.); 6.69–6.75 ppm (m, 2H, arom.).
13C NMR in CDCl3: 158.32; 151.75; 150.85; 148.71; 134.39;
133.17; 133.05; 130.14; 128.86; 123.54; 21.44 ppm. ESI-MS:
784.9 M+; 600.9 Cu(P^P)+. Elem. anal. %: C: 65.61 (calc.
66.03); H: 4.11 (calc. 4.62); N: 3.21 (calc. 3.21).
1
Complex 2b: H NMR in CDCl3: 8.42 (d, 2H, J = 7.9 Hz,
pyr.); 7.79 (d, 2H, J = 7.8 Hz, pyr.); 7.62 (d, 2H, J = 7.9 Hz,
pyr.); 7.26 (t, 6H, J = 7.7 Hz, arom.); 7.12 (t, 10H, arom.);
6.82–6.94 (m, 8H, arom.); 6.45 (m, 2H, arom.); 2.55 (s, 6H,
CH3); 1.79 ppm (s, 6H, CH3). 13C NMR in CDCl3: 155.04;
151.79; 151.32; 148.08; 132.90; 129.99; 128.86; 126.98;
124.90; 124.12; 120.04; 36.25; 28.06; 21.44 ppm. ESI-MS:
824.9 M+; 640.9 Cu(P^P)+. Elem. anal. %: C: 67.68 (calc.
67.08); H: 4.40 (calc. 4.86); N 2.65 (calc. 3.07).
Experimental
Absorption spectra were recorded with a Perkin Elmer Lambda
650S UV-vis spectrophotometer. Emission spectra and lifetimes
were recorded with a Horiba Jobin Ivon Fluorolog 4 fluorimeter.
NMR spectra were recorded with a JEOL 400 MHz spectrometer
using the resonance peak of the solvent as an internal reference.
Luminescent quantum yields were measured in a 4 inch
Labsphere integrating sphere used in a Horiba Jobin Ivon Fluoro-
max 2 spectrophotometer, using the procedure described.22
Chemicals were purchased from Aldrich, with the highest
purity commercially available and used without further purifi-
cation. The complexes were prepared following the method pub-
lished by Min et al.1 A dichloromethane solution (10 mL) of the
bipyridyl ligand, (1 mmol) and the diphosphine ligand (1 mmol;
triphenylphosphine 2 mmol), was added drop-wise to a dichloro-
methane solution (10 mL) of tetrakis (acetonitrile) copper(I)
tetrafluoroborate (0.314 g; 1 mmol). The reaction was stirred for
one hour in air at room temperature. The reaction mixture was
filtered, concentrated to 5 mL and precipitated in diethyl ether–
hexanes mixtures. The process was repeated twice. The products
were filtered and allowed to dry in air. Yields: 1a = 95%, 1b =
84.5%, 1c = 74.0%, 2a = 66.3%, 2b = 88.3%, 2c = 53.0%, 3a =
33.6%, 3b = 61.2%.
1
Complex 3b. H NMR in CDCl3: 8.37 (d, 2H, J = 8.0 Hz,
pyr.); 8.09 (d, 2H, J = 7.9 Hz, pyr.); 7.34 (t, 6H, J = 7.7 Hz,
arom.); 7.18 (t, 12H, J = 7.5 Hz, arom.); 7.11 (m, 2H, pyr.); 7.03
(m, 12H, arom.); 2.54 ppm (s, 6H, CH3). 13C NMR in CDCl3:
151.97; 151.47; 148.68; 133.15; 132.33; 130.24; 128.94;
+
126.84; 124.21; 21.45 ppm. ESI-MS: 509.12 N^NCuPPh3 .
Elem. anal. %: C 66.96 (calc. 67.10); H: 4.46 (calc. 4.93);
N: 3.33 (calc. 3.26).
1
Complex 1c. H NMR in CDCl3: 8.06 (d, 2H J = 8.0 Hz,
Pyr.); 7.90 (d, 2H, J = 7.9 Hz, pyr.); 7.20–7.30 (m, 8H, arom.);
7.16 (t, 8H, J = 7.3 Hz, arom.); 6.92 (d, 2H, J = 7.7 Hz, pyr.);
6.90–6.99 (m, 10H, arom.); 6.85–6.91 (m, 2H, arom.). 2.18 ppm
(s, 6H, CH3). 13C NMR in CDCl3: 158.13; 152.42; 132.98;
132.91; 130.07; 128.8; 126.09; 120.46; 26.54 ppm. ESI-MS:
784.9 M+; 600.9 Cu(P^P)+. Elem. anal. %: C: 65.26
(calc. 66.03); H: 4.12 (calc. 4.62); N: 2.93 (calc. 3.21).
1
Complex 2c. H NMR in CDCl3: 8.02 (d, 2H, J = 7.9 Hz,
1
Complex 1a: H NMR in CDCl3: 8.42 (d, 2H, J = 3.9 Hz,
pyr.); 7.87 (d, 2H, J = 7.8 Hz, pyr.); 7.61 (d, 2H, J = 7.9 Hz,
pyr.); 7.30 (t, 6H, J = 7.7 Hz, arom.); 7.16 (t, 10H, arom.);
7.00–7.09 (m, 8H, arom.); 6.82 (m, 2H, arom.); 1.98 (s, 6H,
CH3); 1.66 ppm (s, 6H, CH3). 13C NMR in CDCl3: 157.73;
155.11; 152.11; 139.11; 133.17; 130.18; 128.88; 125.72;
120.05; 36.17; 28.39; 26.66 ppm. ESI-MS: 824.9 M+; 640.9
Cu(P^P)+. Elem. anal. %: C: 66.42 (calc. 67.08); H: 4.41
(calc. 4.86); N: 3.00 (calc. 3.07).
pyr.); 8.33 (d, 2H, J = 8.0 Hz, pyr.); 8.00 (t, 2H, J = 7.8 Hz,
pyr.); 7.20–7.31 (m, 8H, arom.); 7.16 (t, 8H, J = 7.3 Hz, arom.);
7.02 (d, 2H, J = 7.7 Hz, pyr.); 6.90–6.99 (m, 10H, arom.);
6.69–6.75 ppm (m, 2H, arom.). 13C NMR in CDCl3: 158.30;
151.71; 149.22; 138.97; 134.39; 133.06; 132.08; 130.08;
130.22; 128.89; 125.98; 125.23; 122.94; 120.51 ppm. ESI-MS:
757.1 M+. 601.0 Cu(P^P)+. Elem. anal. %: C: 65.56 (calc.
65.38) H: 3.92 (calc. 4.29).
1
Complex 2a: H NMR in CDCl3: 8.54 (d, 2H, J = 8.0 Hz,
pyr.); 8.09 (d, 2H, J = 7.8, pyr.); 8.02 (d, 2H, J = 7.8 Hz, pyr.);
7.62 (t, 2H, J = 7.5 Hz, arom.); 7.26 (t, 6H, J = 7.7 Hz, arom.);
7.12 (t, 10H, arom.); 6.79–6.95 (m, 8H, arom.); 6.50 (d, 2H,
J = 7.9 Hz, pyr.); 1.76 ppm (s, 6H, CH3). 13C NMR in CDCl3:
154.91; 151.74; 148.65; 139.60; 133.80; 132.78; 131.20;
130.08; 128.93; 127.18; 123.53; 119.90; 36.26; 28.12 ppm.
ESI-MS: 796.9 M+. 641.0 Cu(P^P)+. Elem. anal. %: C: 66.79
(calc. 66.49; H: 4.47 (calc. 4.55); N: 3.13 (calc. 3.16).
Acknowledgements
Dr P. Meadows and Dr H. Sasakawa at JEOL UK are
gratefully acknowledged for their help in NMR spectroscopy.
The National Mass Spectrometry Service at Swansea
University is acknowledged for the ESI analyses on the
complexes. P. C. wishes to acknowledge RCUK for a Research
Fellowship. I. A. T. wishes to acknowledge Brunel University
for a generous scholarship.
1
Complex 3a: H NMR in CDCl3: 8.50 (d, 2H, J = 3.9 Hz,
pyr.); 8.28 (d, 2H, J = 8.0 Hz, pyr.); 8.08 (t, 2H, J = 7.8 Hz,
pyr.); 7.34 (t, 6H, J = 7.7 Hz, arom.); 7.18 (t, 12H, arom);
This journal is © The Royal Society of Chemistry 2012
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14 I. Andres-Tomé, C. J. Winscom and P. Coppo, Eur. J. Inorg. Chem.,
2010, 3567.
Notes and references
15 R. Venkateswaran, M. S. Balakrishna, S. M. Mobin and H. M. Tuononen,
Inorg. Chem., 2007, 46, 6535.
1 J. Min, Q. Zhang, W. Sun, Y. Cheng and L. Wang, Dalton Trans., 2011,
40, 686.
16 G. Accorsi, N. Armaroli, B. Delavaux-Nicot, A. Kaeser, M. Holler,
J.-F. Nieregarten and A. Degli Esposti, THEOCHEM, 2010, 962, 7.
17 R. Hou, T.-H. Huang, X.-J. Wang, X.-F. Jiang, Q.-L. Ni, L.-C. Gui,
Y.-J. Fan and Y.-L. Tan, Dalton Trans., 2011, 40, 7551.
18 R. A. Rader, D. R. McMillin, M. T. Buckner, T. G. Matthews,
D. J. Casadonte, R. K. Lengel, S. B. Whittaker, L. M. Darmon and
F. E. Lytle, J. Am. Chem. Soc., 1981, 103, 5906.
2 Q. Zhang, J. Ding, Y. Cheng, L. Wang, Z. Xie, X. Jing and F. Wang, Adv.
Funct. Mater., 2007, 17, 2983.
3 O. Moudam, A. Kaeser, B. Delavaux-Nicot, C. Duhayon, M. Holler,
G. Accorsi, N. Armaroli, I. Seguy, J. Navarro, P. Destruel and
J.-F. Nierengarten, Chem. Commun., 2007, 3077.
4 Q. Zhang, Q. Zhou, Y. Cheng, L. Wang, D. Ma, X. Jing and F. Wang,
Adv. Mater., 2004, 16, 432.
19 M. Navarro, O. A. Corona, T. Gonzalez and M. V. Capparelli, Acta
Crystallogr., Sect. E: Struct. Rep. Online, 2008, 64, m533.
20 L. M. Engelhardt, C. Pattawatchai, A. H. White and P. C. Healy, J. Chem.
Soc., Dalton Trans., 1985, 125.
21 T. Yu, Z. Wang, Y. Zhao, X. Wen, H. Zhang and D. Fan, Inorg. Chim.
Acta, 2012, 383, 78.
5 Q. Zhang, Q. Zhou, Y. Cheng, L. Wang, D. Ma, X. Jing and F. Wang,
Adv. Funct. Mater., 2006, 16, 1203.
6 N. Armaroli, G. Accorsi, M. Holler, O. Moudam, J.-F. Nierengarten,
Z. Zhou, R. T. Wegh and R. Welter, Adv. Mater., 2006, 18, 1313.
7 M. Hashimoto, S. Igawa, M. Yashima, I. Kawata, M. Hoshino and
M. Osawa, J. Am. Chem. Soc., 2011, 133, 10348.
22 L. Porres, A. Holland, L. O. Palsson, A. P. Monkman, C. Kemp and
A. Beeby, J. Fluoresc., 2006, 16, 267.
23 M. Z. Zgierski, J. Chem. Phys., 2003, 118, 4045.
24 Z. A. Siddique, Y. Yamamoto, T. Ohno and K. Nozaki, Inorg. Chem.,
2003, 42, 6366.
25 L. X. Chen, G. B. Shaw, I. Novozhilova, T. Liu, G. Jennings,
K. Attenkofer, G. J. Meyer and P. Coppens, J. Am. Chem. Soc., 2003,
125, 7022.
26 A. Robertazzi, A. Magistrato, P. De Hoog, P. Carloni and J. Reedijk,
Inorg. Chem., 2007, 46, 5873.
8 J. C. Deaton, S. C. Switalski, D. Y. Kondanov, R. H. Young,
T. D. Pawlik, D. J. Giesen, S. B. Harkins, A. J. M. Miller,
S. F. Mickenberg and J. C. Peters, J. Am. Chem. Soc., 2010, 132, 9499.
9 A. Barbieri, G. Accorsi and N. Armaroli, Chem. Commun., 2008, 2185.
10 G. Accorsi, N. Armaroli, C. Duhayon, A. Saquet, B. Delavaux-Nicot,
R. Welter, O. Moudam, M. Holler and J.-F. Nierengarten, Eur. J. Inorg.
Chem., 2010, 164.
11 M. Ruthkosky, C. A. Kelly, F. N. Castellano and G. J. Meyer, Coord.
Chem. Rev., 1998, 171, 309.
12 L. Yang, J.-K. Feng, A.-M. Ren, M. Zhang, Y.-G. Ma and X.-D. Liu,
Eur. J. Inorg. Chem., 2005, 1867.
27 T. Gunaratne, M. A. J. Rodgers, D. Felder, J. F. Nierengarten, G. Accorsi
and N. Armaroli, Chem. Commun., 2003, 3010.
28 P. Coppo, E. A. Plummer and L. De Cola, Chem. Commun., 2004,
1774.
13 R. D. Costa, D. Tordera, E. Ortí, H. J. Bolink, J. Schönle, S. Graber,
C. E. Housecroft, E. C. Constable and J. A. Zampese, J. Mater. Chem.,
2011, 21, 16108.
8674 | Dalton Trans., 2012, 41, 8669–8674
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