Two-photon luminescence from polar bis-terpyridyl-stilbene derivatives of Ir(III) and Ru(II)

Article abstract of DOI:10.1039/c0dt00750a

Four structurally related iridium(iii) and ruthenium(ii) complexes bearing two polar terpyridyl-stilbene derived chromophores 4-(4-{2-[4-(methoxy)phenyl] ethenyl}phenyl)-2,2′-6′,2′′-terpyridine (ttpyeneanisole) and 4-(4-{2-[phenyl]ethenyl}phenyl)-2,2′-6′,

Full text of DOI:10.1039/c0dt00750a

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www.rsc.org/dalton | Dalton Transactions
Two-photon luminescence from polar bis-terpyridyl-stilbene derivatives of
Ir(III) and Ru(II)†
Louise S. Natrajan,*a Anita Toulmin,a Alex Chewa and Steven W. Magennis*a,b
Received 29th June 2010, Accepted 3rd September 2010
DOI: 10.1039/c0dt00750a
Four structurally related iridium(III) and ruthenium(II) complexes bearing two polar terpyridyl–stilbene
derived chromophores 4-(4-{2-[4-(methoxy)phenyl]ethenyl}phenyl)-2,2¢-6¢,2¢¢-terpyridine
(ttpyeneanisole) and 4-(4-{2-[phenyl]ethenyl}phenyl)-2,2¢-6¢,2¢¢-terpyridine (tpystilbene) have been
synthesised and characterised in the solid state and in solution. In the solid state, the dihedral angle
subtending the pyridyl and tolyl groups of 27.1◦ in the Ir(III) complex [Ir(ttpyeneanisole)2]·3PF6 is more
acute than in the Ru(II) derivative [Ru(tpystilbene)2]·2PF6 (35.5◦), indicating the presence of a greater
degree of p-delocalisation across the terpyridine unit in the former compound. Their luminescence
properties in fluid solution have been investigated following both resonant and non-resonant excitation.
We have shown that each of the complexes undergoes two-photon excitation when excited in the near
infrared (740 to 820 nm), with two-photon absorption cross sections in the range 11–67 ¥ 10-50 cm4 s
photon-1. The larger cross sections for the Ir(III) complexes reflect the differences observed in the solid
state. This work therefore demonstrates that such complexes are promising as luminescent markers for
3D imaging and illustrates that simple functionalisation of the chromophores and the choice of metal
can lead to marked enhancements in the two-photon cross sections (s2) compared to those of simpler
heteroleptic polypyridyl based derivatives.
In the case of two-photon excitation (TPE) with a single
monochromatic laser source, which accounts for the majority of
Introduction
Materials that undergo multiphoton excitation,1 the simultaneous
absorption of two or more photons, are finding increasing use
in many applications including up-converting lasing,2 3D data
storage,3 optical power limiting,4 microfabrication,5 3D fluores-
cence microscopy,6 photodynamic therapy7 and the targeted deliv-
ery of bioactive molecules.8 The multiphoton process is mediated
via intermediate ‘virtual’ excited states. The selection rules for one-
photon excitation (OPE) and multiphoton excitation may result
in different excited states being accessed or, as commonly occurs,
the multiphoton absorption of low-energy photons populates
the same excited states that are accessible through one-photon
absorption.1 Multiphoton excitation has several advantages over
conventional one photon excitation. For imaging applications,
the non-linear absorption of a focused laser beam enables 3D
control of the excitation process. Furthermore, molecules may
undergo multiphoton absorption in the near-infrared region,
where many materials (including biological tissue) have low one-
photon absorption coefficients, thereby allowing deeper light
penetration (typically, up to several hundred mm).9
studies,1–8 two photons of approximately half the energy of the
resonant excited state are absorbed. A quantitative measure for
the probability of two-photon absorption (TPA) for a compound
is the two-photon absorption cross-section (s2),10 which can
be viewed as the two photon equivalent of the one-photon
molar absorption coefficient e. There are a variety of synthetic
approaches to increase s2 and these tend to be based on increasing
the p network conjugation within the framework of a molecule,
or the generation of large changes in excited state polarisation
following photoexcitation.11 Large values of s2 can arise from
centrosymmetric charge transfer and substantial values can be
achieved in push–pull electron donor–acceptor (D–A) diads, in D–
p–A type assemblies, and variants thereof. These structural motifs
have been applied extensively to the construction of organic-
based chromophores yielding materials with remarkably high two-
photon absorption cross sections.1 By contrast, far fewer metal-
based chromophores have been investigated even though they
possess attractive chemical and photophysical properties.12–16
Second and third row transition metal oligopyridyl complexes
lend themselves particularly well to non-linear processes.17,18 For
instance, the rich photochemistry of the charge transfer excited
triplet states of Ir (and Ru) complexes with an N6 coordination
sphere gives rise to long phosphorescent lifetimes in aerated fluid
solution in the microsecond time domain.19 Compounds with long
radiative lifetimes offer improved temporal discrimination over
organic fluorophores and enable the application of time gating
techniques to eliminate short-lived background fluorescence and
scattered light.20 In addition, these complexes are almost optically
transparent at wavelengths above 750–800 nm and are kinetically
and photochemically robust. Interestingly, cyclometallated Ir(III)
aSchool of Chemistry, The University of Manchester, Oxford Road, Manch-
ester, UK, M13 9PL. E-mail: louise.natrajan@manchester.ac.uk; Fax: +44
(0)161 275 4616; Tel: +44 (0)161 275 1426
bPhoton Science Institute, The University of Manchester, Oxford Road,
Manchester, UK, M13 9PL. E-mail: steven.magennis@manchester.ac.uk;
Tel: +44 (0)161 275 1014
† Electronic supplementary information (ESI) available: Positive elec-
trospray mass spectra of the complexes including calculated isotope
patterns and emission and excitation spectra of the uncomplexed ligands
in DMSO. CCDC reference numbers 783187 and 783188. For ESI
and crystallographic data in CIF or other electronic format see DOI:
10.1039/c0dt00750a
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Scheme 1 Synthesis of ligands and complexes; R = H, OMe, M = Ir (x = 3), Ru (x = 2).
derivatives can exhibit more unusual non-linear optical properties
including both TPA and reversible saturated absorption (RSA)
and simultaneous one and two-photon phosphorescence.14
In this contribution, we report the synthesis, one-photon and
two-photon photophysical behaviour of several bis terpyridyl Ir3+
and Ru2+ complexes. The terpyridine ligands, 4-(4-{2-[4-(metho-
xy)phenyl]-ethenyl}phenyl)-2,2¢-6¢,2¢¢-terpyridine
(ttpyeneani-
sole) and 4-(4-{2-[phenyl]ethenyl}phenyl)-2,2¢-6¢,2¢¢-terpyridine
(tpystilbene), have been structurally elaborated by Wittig
condensation to afford, when complexed, polar D–p–A–p–
D
conjugated chromophores with appreciable two-photon
absorption cross sections.
Fig. 1 Thermal ellipsoid drawings of [Ir(ttpyeneanisole)2]3+ (top) and
[Ru(tpystilbene)2]2+ (bottom) at the 30% probability level. H atoms, PF6
counterions and lattice solvent molecules omitted for clarity.
Results and Discussion
Synthesis of ligands and complexes
Solid state structure of the complexes. Deep red blocks of
[Ir(ttpyeneanisole)2]·3PF6 were deposited by layering an acetoni-
trile solution of the complex with diethyl ether (3 : 1 v:v) whereas
red single crystals of [Ru(tpystilbene)2]·2PF6 were grown by slow
evaporation of a concentrated acetone solution of the complex;
selected interatomic distances and angles are given in Table 1.
In both structures (Fig. 1), the coordination geometries of the
metal cations are distorted from a perfect octahedron evidenced by
the terpyridine–metal bite angles and the angles between the two
ortho pyridine substituents on the central ring. Respectively, these
are measured at 159.04◦ and 103.4 for [Ru(tpystilbene)2]·2PF6
and 158.07◦ and 104.0◦ in [Ir(ttpyeneanisole)2]·3PF6. The metal–
The ligands ttpyeneanisole and tpystilbene and their corre-
sponding iridium and ruthenium complexes were prepared as
illustrated in Scheme 1. 4¢-(p-Tolyl)-2,2¢:6¢,2¢¢-terpyridine, (ttpy)
was prepared in good yield according to a published procedure
using the Kro¨hnke methodology.21 The tolyl group was then
brominated by a free radical reaction using N-bromosuccinimide
in CCl4 in the presence of a catalytic amount of benzoyl peroxide
initiator whilst irradiating with a UV lamp.22,17 4¢-(Phenyl-p-
bromomethyl)-2,-2¢:6¢,2¢¢-terpyridine was then near quantitatively
converted to the phosphonium bromide salt by heating with PPh3
in toluene.17 Finally, the Wittig reaction was employed to extend
the conjugation of the terpyridine units by reaction of anisaldehyde
or benzaldehyde with ttpy phosphonium bromide and KOtBu in
dry THF. After extensive trituration in methanol, the ligands were
isolated analytically pure as pale yellow solids in moderate yields
(39–49%).
˚
nitrogen bond distances in both complexes (range 2.066(3) A–
˚
1.94(2) A) are unremarkable and as with the bond angles (Table 1),
˚
Table 1 Selected interatomic distances (A) and angles (deg) for
[Ir(ttpyeneanisole)2]·3PF6 and [Ru(tpystilbene)2]·2PF6
The ruthenium adducts were prepared using standard
methodologies23 and the iridium complexes by modification of
the procedures described by Sauvage and Williams24,25 (Scheme 1)
by treatment of the corresponding metal chloride salt with one
or two equivalents of the ligands. The complexes were purified
by metathesis with NH4PF6 and repeated recrystallisation from
acetone–ether or acetonitrile–ether. In the case of the complex
[Ir(ttpyeneanisole)2]·3PF6, this resulted in the precipitation of
X-ray quality single crystals whose structure was elucidated by
diffraction analysis (Fig. 1).
[Ir(ttpyeneanisole)2]·3PF6 [Ru(tpystilbene)2]·2PF6
M(1)–N(1)
M(1)–N(2)
M(1)–N(3)
2.00(2)
2.045(19)
1.94(2)
2.066(3)
2.062(3)
1.976(4)
N(3)–M(1)–N(3)¢ 177.4(11)
178.98(17)
100.24(13
92.31(19)
79.03(12)
158.07(13)
92.11(19)
N(3)–M(1)–N(2)¢
N(2)–M(1)–N(2)¢
N(3)–M(1)–N(1)
N(2)–M(1)–N(1)
N(1)–M(1)–N(1)¢
99.8(8)
89.6(10)
80.7(8)
159.0(9)
87.9(12)
10838 | Dalton Trans., 2010, 39, 10837–10846
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Table 2 One- and two-photon properties of the ligands and complexes
b
Compound
l
abs /nm
lex/nmd
l
em/nm
t
MeCN/nsa
t
MeOH/nsa
UMeCN
s2/GMc
f
f
f
f
f
f
tpystilbenee
289, 336
287, 352
292, 377
323, 434
312, 496
310, 497
405
405
405
405
405
405
420
460
550
560
540
600
1
2
ttpyeneanisolee
[Ir(tpystilbene)2]·3PF6
[Ir(ttpyeneanisole)2]·3PF6
[Ru(tpystilbene)2]·2PF6
[Ru(ttpyeneanisole)2]·2PF6
1346
1536
2
1428
1512
2
0.0059
0.0026
0.0059
0.0029
67
58
12
11
3
3
a Lifetimes quoted at 405 nm excitation using a 550 –650 nm bandpass interference filter and are subject to 10% error. b Quantum yields determined
relative to quinine sulfate in 1M H2SO4 at 350 nm excitation, f = 0.58; estimated error 20%. c Two-photon cross section, s2, at 740 nm, GM = 10-50 cm4
s photon-1; estimated error 30%. d Identical results within error were determined at 375 nm excitation. e Measurements performed in DMSO. f Value
not measured.
are within the range of those previously reported for mono and
bis-terpyridyl Ir and Ru complexes.25,26 More pertinent to the
photophysical properties of the complexes, it is interesting to
note that the pyridyl and phenyl rings are not mutually co-
planar and are twisted considerably out of the plane of the
chelating terpyridine unit. This twist is more pronounced in the
[Ru(tpystilbene)2]2+ cation, where the dihedral angle between the
central pyridyl ring and the tolyl group is 35.5◦ and that between
the tolyl and phenyl substituent is 28.4◦. In the solid state structure
of [Ir(ttpyeneanisole)2]·3PF6 however, the pyridyl–tolyl dihedral
angle of 27.1◦ is considerably more acute possibly reflecting a
greater degree of p-delocalisation across the ttpy unit, whereas
the twist angle between the tolyl and the phenyl ring bearing the
methoxy substituent has opened up to 37.6◦.
Photophysical properties
One-photon absorption and emission properties. The ground
state electronic absorption spectra of the complexes were recorded
in acetonitrile solutions; the principle absorption maxima are
listed in Table 2 and the spectra are shown in Fig. 2. The spectra
of all the complexes display several intense broad transitions in
the UV region (between 200 and 350 nm) which are assigned to
*
spin allowed ligand centred (LC) 1p–p transitions by comparison
with related aryl modified terpyridyl Ir3+ and Ru2+ complexes.25–27
In the Ru2+ complexes, these transitions are red shifted when
Fig. 2 UV–vis absorption spectra of a) [Ir(ttpyeneanisole)2]·3PF6 (black
trace) and [Ir(tpystilbene)2]·3PF6 (grey trace), b) [Ru(ttpyeneanisole)2]·
2PF6 (black trace) and [Ru(tpystilbene)2]·2PF6 (grey trace) in MeCN.
compared to the parent complexes [Ru(tpy)2]2+ and [Ru(ttpy)2]2+
and tail into the visible region owing to the increased conjugation
upon introduction of the pendent alkene and aromatic groups.
The 1MLCT absorption bands are observed at lower energy
(~ 497 nm) and are also located at longer wavelength than the bis
terpyridine and tolyl-terpyridine Ru(II) adducts (476 and 487 nm
respectively). In addition to the more localised ligand-centered
UV transitions, the Ir3+ complex [Ir(ttpyeneanisole)2]·3PF6 also
displays an intense broad absorption band at 434 nm. This visible
absorption is attributed to an intraligand charge transfer (ILCT)
the LC transitions which essentially remain the same as those
recorded in MeCN solution (324 nm). This shift to lower energy
in the more polar solvent is suggestive of a more polar excited
state and confirms the higher degree of charge separation in this
transition.
Unlike its cyclometallated counterpart (Ir(ppy)3) whose lumi-
nescence involves a substantial contribution from the 3MLCT
excited state, the photoluminescence from simple [Ir(tpy)2]3+
derivatives is longer lived and has been shown to originate from
*
transition, which is likely to be 1n-p in origin; the anisole group
acting as the electron donor and the coordinated terpyridine unit
as the electron acceptor. By contrast, this absorption feature in
the stilbene analogue [Ir(tpystilbene)2]·3PF6 is observed at much
higher energy (377 nm) and by the very nature of the ligand, must
3
*
ligand-based triplet transitions, primarily of p–p character.25
Earlier work has shown that the lifetime of this excited state
can be elongated by introduction of simple aryl substituents
at the 4¢ position of the central terpyridine ring. In aerated,
fluid MeCN solution at room temperature, the Ir3+ complexes
[Ir(ttpyeneanisole)2]·3PF6 and [Ir(tpystilbene)2]·3PF6 are both
strongly photoemissive when excited into the UV–vis absorption
1
*
be p–p in character. Although in these homoleptic complexes
there is no permanent dipole moment in the ground state, the
ILCT absorption band in [Ir(ttpyeneanisole)2]·3PF6 undergoes a
more pronounced solvatochromic shift in MeOH (445 nm) than
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bands (250–450 nm); they display broad featureless emission
bands centered at ca. 550 nm (Fig. 3). The absence of vibrationally
resolved features in these spectra observed in the unsubtituted
[Ir(tpy)2]3+ derivative24 and the fact the emission is red shifted by
ca. 100 nm with respect to the parent tpy compound reflects the
considerably higher degree of conjugation in the excited states
and possible co-involvement of close lying 3MLCT and lower
3
lying ILCT excited states. The fact that the emission bands are
somewhat broadened also suggests that a range of conformers
differing in dihedral angles between the terpyridyl and pendent
aryl groups exist in fluid solution at room temperature. Interest-
ingly, the excitation spectra (monitored at the emission maxima of
550 nm, Fig. 3) for both the Ir3+ compounds in question do not
correspond well to the absorption spectra, indicating that different
excited states result in the observed emission profile. The bands in
the excitation spectra are blue shifted with respect to those in the
absorption spectra, but follow the same general form giving further
weight to the argument that excited state mixing between the LC,
*
MLCT and p–p ILCT levels may be responsible for the emission.
However, whether the relative contribution of metal based orbitals
in this CT emission is significant remains unclear. For comparison,
in the complex [Ir(tpy-f-NMe2)2]3+, the lowest excited state has
*
been attributed to a 3n-p state and that in [Ir(tpy)(tpy-f-Ph)]3+ is
thought to be predominantely CT in origin.25
The emission is independent of excitation wavelength in
accordance with Kasha’s law and the radiative lifetimes in
air equilibrated MeCN follow monoexponential decay kinetics
and are 1.54 ms and 1.35 ms for [Ir(ttpyeneanisole)2]·3PF6 and
[Ir(tpystilbene)2]·3PF6 respectively. Similar values are recorded in
methanol solution. These lifetimes are significantly longer than in
[Ir(tpy)2]2+ itself (1.0 ms)25 but are shorter than that measured for
the tolyl-substituted derivative which has a radiative lifetime of 2.4
ms in MeCN. This significant decrease in lifetime may also imply
involvement of the 3MLCT level in the emissive state, since shorter
lifetimes are often observed in these systems in aerated media.25 In
addition, the potential for triplet metal-centered (3MC) states to
contribute to non radiative quenching of the emissive state cannot
be ruled out.
In contrast to Ir3+ terpyridine complexes, the Ru2+ counterparts
3
are, in general, only weakly emissive from their MLCT states
(tMLCT £ 1 ns) at room temperature; this is because the lower
lying 3MC states are thermally accessible from the 3MLCT excited
states which provides a rather efficient pathway for non-radiative
energy loss in fluid solution.28 However, the Ru2+ derivatives of
ttpyeneanisole and tpystilbene display no emission that is metal
based in character, but rather exhibit short lived (2–3 ns) visible
emission, which is a superposition of two features. This emission
is likely to be ligand based fluorescence and phosphorescence
which originates from the ligand excited states as inferred from
examination of the excitation spectra (Fig. 4) and excitation and
emission spectra of the uncomplexed ligands.†
The quantum yields of emission in aerated MeCN (Table 1) of
all the complexes are less than 1% but are of a similar magnitude
to compounds such as [Ir(tpy)(tpy-f-Ph)]3+, [Ir(tpy-f-Ph)2]3+ and
[Ir(tpy-mesityl)2]3+ whose quantum yields were determined in
degassed solutions where triplet oxygen annihilation is negligible.25
Fig. 3 Corrected steady state emission (black traces) and excitation spec-
tra (grey traces) of a) [Ir(ttpyeneanisole)2]·3PF6, b) [Ir(tpystilbene)2]·3PF6,
c) [Ru(ttpyeneanisole)2]·2PF6 (dark grey trace, excitation spectrum mon-
itored at 550 nm emission and light grey trace, excitation spectrum
monitored at 450 nm emission) and d) [Ru(tpystilbene)2]·2PF6 (dark grey
trace, excitation spectrum monitored at 550 nm emission and light grey
trace, excitation spectrum monitored at 450 nm emission) recorded at
350 nm excitation in MeCN.
Two-photon absorption and emission properties. To investigate
whether these complexes could be excited by a multiphoton
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67 GM for [Ir(ttpyeneanisole)2]·3PF6 and [Ir(tpystilbene)2]·3PF6,
respectively) are similar to each other but approximately six times
larger than for the Ru(II) analogues. In comparison, the one-
photon extinction coefficients at 370 nm for all four complexes
are very similar.
To investigate the origin of the two-photon transition, the cross-
section was measured as a function of excitation wavelength from
740–820 nm (Fig. 5). The low resolution of these spectra preclude
a detailed analysis, but they suggest that there are a number
of distinct spectral transitions that can occur via a two-photon
process, analogous to the structured one-photon excitation spectra
(Fig. 3).
Fig. 4 Dependence of luminescence intensity on excitation power fol-
lowing non-resonant excitation at 740 nm a) [Ir(ttpyeneanisole)2]·3PF6
(ꢀ) and [Ir(tpystilbene)2]·3PF6 (᭹) b) [Ru(ttpyeneanisole)2]·2PF6 (᭹)
[Ru(tpystilbene)2]·2PF6 (ꢀ) in MeCN. The solid line shows the best straight
line fit to the data (R = 99.9%).
process, solutions were irradiated with an ultrafast titanium
sapphire laser. The complexes had negligible one-photon
absorption at the near infrared excitation wavelengths.
Luminescence, with the same broad spectrum that was observed
upon resonant excitation, was detected from MeCN solutions of
the complexes. Operating the laser in continuous wave mode, but
with the same average power, resulted in no detected luminescence.
The luminescence intensity was studied as a function of excitation
Fig. 5 Two-photon excitation spectra of a) [Ir(ttpyeneanisole)2]·3PF6
and [Ir(tpystilbene)2]·3PF6, and b) [Ru(ttpyeneanisole)2]·2PF6 and
[Ru(tpystilbene)2]·2PF6 in MeCN. Estimated uncertainties are 30%.
power, which demonstrated that
a two-photon excitation
mechanism is operating for all four complexes. Fig. 4 shows
the results of the power dependence measurements with an
excitation wavelength of 740 nm; the slope of the logarithmic
plots is 2 within experimental error, which is strong evidence that
a two-photon process is occurring. Similar results were obtained
for excitation at 800 nm.
To assess the efficiency of the two-photon process, the two-
photon cross-section (s2), the luminescence intensity of each
complex was compared to that of a reference compound, rho-
damine B in methanol, for which the two-photon cross section
is known.10 The results for excitation at 740 nm are shown in
Table 1. The Ru(II) complexes have similar cross sections, 11 and 12
GM for [Ru(ttpyeneanisole)2]·2PF6 and [Ru(tpystilbene)2]·2PF6,
respectively. The cross sections of the Ir(III) complexes (58 and
The measured two-photon cross sections are considerably larger
than many other heteroleptic transition metal polypyridyl and
acetylide complexes12–14 demonstrating that these structures are
a good starting point to develop multiphoton-active materials.
Of course, for use in 3D luminescence imaging, the emission
process must also be efficient. The measured one-photon quantum
yields for these complexes are in general, quite low (0.3–0.6%), so
developments to optimise this aspect should proceed in parallel
with attempts to improve the cross sections; it is however worth
noting that a cross section of 0.1 GM has been suggested to be
sufficient for biological applications in live specimen samples.29
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Table 3 Data
[Ir(ttpyeneanisole)2]·3PF6 and [Ru(tpystilbene)2]·2PF6
collection
and
structural
refinement
for
Conclusions
We have prepared a series of photoluminescent Ir(III) and
Ru(II) complexes bearing two polar terpyridine ligands. These
chromophores have been structurally elaborated from simpler
terpyridine derivatives to incorporate a stilbene and ene-anisole
moiety by Wittig condensation affording donor–p–acceptor–p–
donor assemblies. The solid state structures of representative com-
pounds [Ir(ttpyeneanisole)2]·3PF6 and [Ru(tpystilbene)2]·2PF6
have been determined; the dihedral angle between the pyridyl
and tolyl groups is rather more acute in the Ir(III) complex
[Ir(ttpyeneanisole)2]·3PF6 and indicates the presence of a greater
degree of p-delocalisation across the ttpy unit in this compound
than in the Ru(II) derivative. All four complexes exhibit green
one-photon photoluminescence when excited in the UV–vis,
with relatively large quantum yields in air-equilibrated solutions
compared to structurally similar compounds. In both families
of complexes, the emission is principally ligand based in origin,
and in the case of the Ir(III) complexes [Ir(ttpyeneanisole)2]·3PF6
and [Ir(tpystilbene)2]·3PF6, the one-photon emission lifetimes are
in the microsecond range. All complexes undergo efficient two-
photon absorption when excited with a femtosecond titanium
sapphire laser in the near infrared, giving rise to luminescence
profiles that are analogous to the one-photon emission. The two-
photon cross-sections (s2), measured as a function of excitation
wavelength, correspond well to the one-photon excitation spectra,
indicating the emission originates from the same excited states.
The Ir(III) complexes in particular show substantial values of s2
which suggests that the excited state conformations of the aromatic
rings possess a higher degree of co-planarity relative to those in the
Ru(II) analogues, thereby affording a higher degree of excited state
p-delocalisation. The comparatively high values of s2 (evaluated
against previously reported metal polypyridyl and acetylide-type
compounds) further demonstrates that simple functionalisation
of platinum group metal-containing chromophores markedly
increases the probability of two-photon absorption, which renders
these compounds, or derivatives thereof, suitable candidate dyes
for two-photon applications in aerated media. Work towards
elucidating the exact nature of the excited states involved in the
two-photon processes in tandem with improving the two-photon
cross sections and quantum yields of luminescence is currently in
progress.
[Ir(ttpyeneanisole)2]·
3PF6
[Ru(tpystilbene)2]·2PF6
Diffractometer type
Formula
Bruker APEXII CCD Bruker APEXII CCD
C60 H50.67 F18 Ir N6 O4.33 C58 H44 F12 N6 O P2 Ru
P3.33
Mr
1600.50
1232.00
¯
Cell setting, space group Trigonal, R3c
Orthorhombic, Pbam
15.5722(5), 19.0829(6),
20.3472(7)
˚
a, b, c/A
25.3220(18),
25.3220(18),
51.3290(18)
90.00, 90.00, 120.00
28503(3)
18
1.687
Mo-Ka
1.84–23.58
2.304
a, b, g (◦)
90.00, 90.00, 90.00
6046.4(3)
4
3
˚
V/A
Z
Dx/Mg m-3
Radiation type
q range (◦)
m/mm-1
1.353
Synchrotron
1.96–26.38
0.392
150(2)
0.058
Block, red
0.05, 0.04, 0.02
w with narrow frames
0.9807
0.9922
50953, 6353, 4854
T/K
R(int)
Crystal form, colour
Crystal size/mm
150(2)
0.132
Block, dark red
0.10, 0.06, 0.04
Data collection method f and w
Tmin
Tmax
0.8023
0.9135
9064, 4732, 1914
No. of measured,
independent and
observed reflections
R[F2 > 2s(F2)], wR(F2), 0.1076, 0.2614, 1.018 0.0652, 0.1987, 1.126
S
No. of reflections
No. of parameters
(D/s)max
4732
423
0.002
1.388, -0.723
6353
384
0.000
0.807, -0.905
-3
˚
Drmax, Drmin/e A
Elemental analyses were performed by the microanalytical
services at the University of Manchester using a Carlo ERBA
Instruments CHNS–O EA1108 elemental analyzer (C, H, N and
S analysis) and a Fisons Horizon Elemental Analysis ICP-OED
spectrometer for metals and halogens.
All NMR spectra were recorded on a Bruker Avance 400
spectrometer, operating frequency 400 MHz (1H), 100 MHz (13C),
variable temperature unit set at 300 K, unless otherwise stated.
Chemical shifts are reported in parts per million relative to TMS
and referenced to the residual proton resonances in d6-DMSO, d3-
acetonitrile, or d6-acetone. Absorption spectra were recorded in
H2O on a T60U spectrometer (PG Instruments Ltd.) using fused
quartz cells with a path length of 1 cm.
X-ray diffraction data for [Ru(tpystilbene)2]·2PF6 were collected
at 150 K using a Bruker APEX II CCD diffractometer on station
9.8 of the Synchrotron Radiation Source at CCLRC Daresbury
Laboratory, at 0.69040 A◦, from a silicon 111 monochromator
using w scans. Crystal data, data collection and structural refine-
ment parameters are given in Table 3. The structure was solved by
direct methods using the program SHELXS-97.21. The refinement
and all further calculations were performed using SHELXL-97.30
Data were corrected for Lorenz and polarisation factors and
an absorption correction applied using Bruker SADABS. The
structure was completed by iterative cycles of DF-syntheses and
a full matrix least square refinement and all non-H atoms were
refined anisotropically. Difference Fourier syntheses were em-
ployed in positioning idealised hydrogen atoms and were allowed
to ride on their parent C or N-atoms. The structure contained
Experimental
General details
All chemical reagents and metal salts were obtained from
the Aldrich Chemical Company and were used as supplied.
The compounds 4¢-(p-tolyl)-2,2¢:6¢,2¢¢-terpyridine,21 4¢-(phenyl-
p-bromomethyl)-2,-2¢:6¢,2¢¢-terpyridine22
and
4-(2,2¢:6¢,2¢¢-
terpyridyl-4¢)-benzyl triphenylphosphonium bromide17 were
prepared according to literature procedures. Reagent grade THF
was dried over potassium/benzophenone and distilled prior to
use.
Mass spectra were obtained using positive electrospray in
acetonitrile or methanol solutions on a Micromass Platform II
spectrometer, or by MALDI using methanol solutions with an
ALPHA maxtrix on a Micromass TOF Spec 2E spectrometer.
10842 | Dalton Trans., 2010, 39, 10837–10846
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s2SfS hRnSCRFS PR
=
a large number of disordered solvent molecules which could not
be modelled and the application of SQUEEZE31 was required.
Data for [Ir(ttpyeneanisole)2]·3PF6 were collected on a Nonius
k-CCD four circle diffractometer using graphite-monochromated
Mo-Ka radiation at 150 K. Data were corrected for Lorenz and
polarisation factors and absorption corrections were applied by
the multi-scan method using the SORTAV program.32
(1)
s2RfR hSnRCS FRPS
where f is the quantum yield of fluorescence, h is a term that
accounts for the wavelength-dependent collection efficiency of the
fluorescence (due to the reflectance/transmission of the various
optical components and the sensitivity of the detector), n is
the refractive index of the solvent, C is the concentration, F is
the integrated fluorescence signal from the recorded spectrum,
P is the excitation power, and S and R refer to sample and
reference, respectively. The sample and reference were always
recorded under identical conditions on the same day, so the P
terms cancel. We have also omitted the h terms due to the similarity
in spectra for sample and reference, which should not introduce
CCDC reference numbers: 783187 for [Ru(tpystilbene)2]·2PF6
and 783188 for [Ir(ttpyeneanisole)2]·3PF6.
Photophysical characterisation
The quantum yields of luminescence of the complexes were
determined relative to quinine sulfate in 0.1 M H2SO4, which has
a known quantum yield of 58% at 350 nm excitation at 295 K. The
details of this approach have been described in detail elsewhere.33
Steady state luminescence properties of the ligands and com-
plexes were determined using a PerkinElmer LS50B or LS55
fluorimeter operating in fluorescence mode. Time resolved lu-
minescence measurements of the ligands were recorded using
a modified Edinburgh instruments mini-Tau system by time
correlated single photon counting using an EPL 405 picosecond
diode laser as the excitation source. Lifetimes were obtained by tail
fit on the data obtained, and quality of fit judged by minimization
of reduced chi-squared and residuals squared. In this modified set-
up samples were excited by a pulsed diode laser emitting at 405 nm
with a pulse duration of 90 ps. The repetition rate of the laser was
set to 2 microseconds to ensure the sample had fully decayed
between excitation events. Two 2¢ lenses were used to collect the
emission and match the f-number of a monochromator (Acton
research, SpectraPro 500i). A Hamamatsu H7422 PMT was
attached to the output slit of the monochromator which gave an
instrument response function with FWHM of ~400 picoseconds.
The monochromator was set to 420 or 460 nm corresponding to
the emission maxima of the ligands. Time resolved luminescence
measurements of the complexes were recorded using an Edinburgh
instruments mini-Tau system by time correlated single photon
counting using an EPL 375 or EPL 405 picosecond diode laser
as the excitation source. Lifetimes were obtained by tail fit on
the data obtained, and quality of fit judged by minimization of
reduced chi-squared and residuals squared.
Two-photon excitation was performed with a 82 MHz pulsed
titanium sapphire laser (Tsunami, Spectra Physics). A portion
of the excitation beam was split and detected with a laser
spectrum analyser, and the spectrum was monitored continuously
to ensure pulse stability (ca. 10 nm FWHM). Neutral density
filters attenuated the beam, which passed through a dichroic mirror
(650DCSPXR, Chroma) and was focused with a 40¥ objective (PF,
NA = 0.60, Nikon) onto the sample, which was in a 1 cm pathlength
cuvette. The incident power was monitored throughout (Uno
meter and PH100-Si head, Gentech). The sample fluorescence
was collected by the same objective and reflected from the dichroic
mirror, passed through a shortpass filter (HQ 575/150, Chroma)
to remove residual excitation light and detected by a fibre-coupled
spectrometer (Ocean Optics QE65000).
S
a significant error. For f , we use the quantum yields measured
for the complexes under one-photon conditions (Table 1). For
rhodamine B in methanol, we have used the wavelength-dependent
values of s2 reported recently34 and a value of f = 0.7.35 We
estimate an experimental precision of 30%. The experimental
setup was verified by observing the expected quadratic dependence
of fluorescence of rhodamine B in methanol on excitation intensity.
R
Synthesis of ligands and complexes
Preparation of 4-(4-{2-[4-(methoxy)phenyl]ethenyl}phenyl)-2,2¢-
6¢,2¢¢-terpyridine (ttpyeneanisole). Under N2, a flamed out
Schlenk flask was loaded with 4-(2,2¢:6¢,2¢¢-terpyridyl-4¢)-benzyl
triphenylphosphonium bromide (1.2 g, 1.81 mmol) and potassium
tert-butoxide (1.46 g, 7.24 mmol). The flask was immersed in an
ice bath and 40 mL dry THF added by cannula; the solution
was stirred at 0 ◦C for 30 min during which time the solution
turned bright orange. 0.246 g (1.81 mmol) p-anisaldehyde was
then added dropwise over 20 min and the solution slowly warmed
to room temperature and stirred for a further 72 h. After this time,
the reaction was quenched by the addition of ice water, and all
solvents removed under reduced pressure. Methanol was added
to the residue (60 mL) and the solution stirred overnight at room
temperature. The precipitated yellow solid was isolated by vacuum
filtration, washed with water (3 ¥ 10 mL), methanol (5 ¥ 10 mL)
and diethylether (3 ¥ 10 mL) to afford a pale yellow solid that
exhibits limited solubility in CHCl3 and DMSO, 0.39 g, 49%.
+
MALDI MS (alpha): m/z 452 {M + H} (100%). NMR/CDCl3
dH: 8.68 (s, H3¢, H5¢), 8.67 (dd, 3JHH 4.0 Hz, 4JHH 1.6 Hz, H6, H6¢¢)
(overlapping signals, 4H), 8.61 (d, 2H, 3JHH 8.0 Hz, H3, H3¢¢), 7.85
(d, 3JHH 8.4 Hz, H7, H7¢), 7.82 (td, 3JHH 8.4 Hz, JHH 1.6 Hz, H4,
4
H4¢¢) (overlapping signals, 4H), 7.56 (d, 2H, 3JHH 8.4 Hz, H8, H8¢¢),
7.43 (d, 2H, 3JHH 8.8 Hz, H14, H14¢), 7.23 (m, 2H, H5, H5¢¢), 7.10 (d,
1H, 2JHH 16.4 Hz, H10/H11), 6.97 (d, 1H, 2JHH 16.4 Hz, H10/H11),
3
6.85 (d, 2H, JHH 8.4 Hz, H13, H13¢), 3.78 (s, 3H, OMe). UV–vis
(DMSO) lmax (e/mol-1dm3cm) = 287 (30400), 352 (42500). Anal.
Calcd. For C30H23N3O: C 81.61, H 5.25, N 9.52. Found: C 81.32,
H 5.31, N 9.41.
Preparation
of
4-(4-{2-[phenyl]ethenyl}phenyl)-2,2¢-6¢,2¢¢-
terpyridine (tpystilbene). Under N2, a flamed out Schlenk
flask was loaded with 4-(2,2¢:6¢,2¢¢-terpyridyl-4¢)-benzyl
triphenylphosphonium bromide (0.8 g, 1.21 mmol) and
potassium tert-butoxide (0.97 g, 4.83 mmol). The flask was
immersed in an ice bath and 40 mL dry THF added by cannula;
the solution was stirred at 0 ◦C for 30 min during which time the
The two-photon cross sections, s2, were measured by recording
spectra of the complexes in MeCN (ca. 10-4 M) and comparing
them to that of a standard, rhodamine B in methanol, as described
previously using eqn (1).10
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3
solution turned bright orange. 0.128 g (1.21 mmol) benzaldehyde
was then added dropwise over 20 min and the solution slowly
warmed to room temperature and stirred for a further 24 h.
After this time, the reaction was quenched by the addition of
ice water, and all solvents removed under reduced pressure. The
product was extracted into CH2Cl2, and washed with H2O and
brine. The organic layer was dried over MgSO4 and all volatiles
were removed under reduced pressure. Methanol was added to
the solid (40 mL) and the solution stirred overnight hours at
room temperature. The precipitated solid was isolated by vacuum
filtration, washed with methanol (5 ¥ 10 mL) and diethylether
(3 ¥ 10 mL) to afford a white powder, 0.19 g, 39%.
2H, JHH 8.4 Hz, H13, H13¢), 3.74 (s, 6H, OMe). UV–vis (MeCN)
lmax (e/mol-1dm3cm) = 233 (sh), (37600), 287 (sh), (45000), 310
(61200), 328 (sh), (52300), 357 (42500), 497 (35600). Accurate
Mass ES+ MS (MeCN): composition C60H46N6O2Ru1, theoretical
492.1357, measured 492.1355, error 0.5 ppm.
Preparation of ruthenium bis{4-(4-{2-[phenyl]ethenyl}-phenyl)-
2,2¢-6¢,2¢¢-terpyridine}·2PF6
([Ru(tpystilbene)2]·2PF6). Under
N2, an ethanolic solution of RuCl3·xH2O (0.064 g, 10 mL) and
tpystilbene (0.070 g, 0.171 mmol) was heated to reflux temperature
for 15 h. After this time, the precipitated solid was isolated by
filtration, washed with H2O (2 ¥ 5 mL), EtOH (5 ¥ 5 mL) and
CH2Cl2 (2 ¥ 5 mL) then dried to yield 0.11 g of Ru(tpystilbene)·Cl3
as an insoluble red–brown powder (87% based on tpystilbene). In
the dark and under N2, 0.073 g AgOTf (0.283 mmol) was then
added to a slurry of Ru(tpystilbene)·Cl3 (0.050 g, 0.081 mmol) in
12 mL EtOH–acetone (1 : 4 v:v). The solution was then heated at
reflux temperature for 24 h. The red solution was subsequently
filtered through a pad of celite, and all volatiles removed under
reduced pressure. The residue was dissolved in 10 mL EtOH and
0.033 g tpystilbene (0.081 mmol) added as a solid. The resultant
slurry was heated to reflux temperature for 3 days (or until all the
terpyridine ligand had been consumed), then all volatiles were
removed by rotary evaporation. 15 mL methanol was added to
the red solid, the solution filtered through a pad of celite and
a saturated aqueous solution of NH4PF6 added to precipitate
the product as the PF6 salt. The precipitated solid was isolated
by filtration and recrystallised three times from MeCN–Et2O to
afford 0.046 g of Ru(tpystilbene)2·3PF6 as a red powder in 51%
yield. Single crystals were grown from slow evaporation of a
concentrated acetone solution at room temperature.
+
MALDI MS (alpha): m/z 411 {M + H} (100%). NMR/CDCl3
dH: 8.77 (s, H3¢, H5¢), 8.75 (d, 3JHH 4.0 Hz, H6, H6¢¢) (overlapping
3
3
signals, 4H), 8.68 (d, 2H, JHH 8.0 Hz, H3, H3¢¢), 7.93 (d, JHH
3
4
8.4 Hz, H7, H7¢), 7.90 (td, JHH 8.0 Hz, JHH 1.6 Hz, H4, H4¢¢)
(overlapping signals, 4H), 7.66 (d, 2H, 3JHH 8.0 Hz, H8, H8¢¢), 7.56
3
(d, 2H, JHH 7.2 Hz, H14, H14¢), 7.36 (m, 4H, H5, H5¢¢, H10, H11),
7.30 (t, 1H, 3JHH 7.2 Hz, H15), 7.20 (d, 2H, 3JHH 5.6 Hz, H13, H13¢).
dC: 156.29, 155.98, 149.70, 138.15, 137.43, 137.18 (quarternary C2,
C2¢¢, C2¢, C6¢, C6, C9, C12), 149.16 (C3¢, C5¢), 136.90 (C6, C6¢¢), 129.55
(C14, C14¢), 128.00, 128.75, 127.85, 123.86 (C5, C5¢¢ C10, C11, C15),
127.62 (C7, C7¢), 127.05 (C8, C8¢), 126.65 (C13, C13¢), 121.40 (C3,
C3¢¢), 118.55 (C6, C6¢¢). UV–vis (DMSO) lmax (e/mol-1dm3cm) =
289 (27700), 336 (46200). Anal. Calcd. For C29H21N3: C 84.64, H
5.14, N 10.21. Found: C 84.50, H 4.81, N 10.15.
Preparation of ruthenium bis{4-(4-{2-[4-(methoxy)phenyl]-
ethenyl}-phenyl)-2,2¢-6¢,2¢¢-terpyridine}·2PF6
([Ru(ttpyeneani-
sole)2]·2PF6). Under N2, an ethanolic solution of RuCl3·xH2O
(0.071 g, 15 mL) and ttpyeneanisole (0.10 g, 0.226 mmol) was
heated to reflux temperature for 15 h. After this time, the
precipitated solid was isolated by filtration, washed with H2O
(2 ¥ 5 mL), EtOH (5 ¥ 5 mL) and CH2Cl2 (2 ¥ 5 mL) then
dried to yield 0.124 g of Ru(ttpyeneanisole)·Cl3 as an insoluble
red–brown powder (85% based on ttpyeneanisole). In the dark
and under N2, 0.078 g AgOTf (0.303 mmol) was then added to a
slurry of Ru(ttpyeneanisole)·Cl3 (0.050 g, 0.087 mmol) in 15 mL
EtOH–acetone (1 : 4 v:v). The solution was then heated at reflux
temperature for 24 h. The red solution was subsequently filtered
through a pad of celite, and all volatiles removed under reduced
pressure. The residue was dissolved in 12 mL EtOH and 0.038
g (0.087 mmol) ttpyeneanisole added as a solid. The resultant
slurry was heated to reflux temperature for 3 days (or until all the
terpyridine ligand had been consumed), then all volatiles were
removed by rotary evaporation. 15 mL methanol was added to
the red solid, the solution filtered through a pad of celite and
a saturated aqueous solution of NH4PF6 added to precipitate
the product as the PF6 salt. The precipitated solid was isolated
by filtration and recrystallised three times from MeCN–Et2O to
afford 0.052 g of [Ru(tpystilbene)2]·3PF6 as a red powder in 47%
yield.
ES+ MS (MeCN) m/z 1069 {M - PF6} (4%), 462 {M - 2 ¥
+
PF6}2+ (100%). NMR/d6-acetone dH: 9.38 (s, 4H, H3¢, H5¢), 8.98 (d,
4H, 3JHH 8.0 Hz, H6, H6¢¢), 8.29 (d, 4H, 3JHH 8.4 Hz, H7, H7¢¢), 7.99
(td, 4H, 3JHH 8.0 Hz, 4JHH 1.2 Hz H4, H4¢), 7.88 (d, 4H, 3JHH 8.4 Hz,
3
3
H8, H8¢¢), 7.73 (d, 2H, JHH 5.2 Hz, H3, H3¢¢), 7.58 (d, 4H, JHH
7.2 Hz, H14, H14¢), 7.40 (d, 2H, 2JHH 16.4 Hz, H10/H11), 7.30 (m, 8H,
H10/H11, H5, H5¢¢), 7.24 (m, 6H, H13, H13¢, H15). UV–vis (MeCN)
lmax (e/mol-1dm3cm) = 223 (sh), (31600), 274 (sh), (24300), 287
(sh) (30900), 312 (47600), 335 (47600), 353 (48000), 496 (28400).
Accurate Mass ES+ MS (MeCN): composition C58H42N6Ru1,
theoretical 461.6201, measured 461.6196, error 1.0 ppm.
Preparation of iridium bis{4-(4-{2-[4-(methoxy)phenyl]-
ethenyl}-phenyl)-2,2¢-6¢,2¢¢-terpyridine}·3PF6
([Ir(ttpyeneani-
sole)2]·3PF6). According to a modification of a literature
procedure,24,25 under N2, a mixture of IrCl3·xH2O (0.050 g,
0.167 mmol) and ttpyeneanisole (0.148 g, 0.335 mmol) in ethylene
glycol (12 mL) was heated at 100 ◦C for 2.5 h. After this time,
the temperature was raised to 195 ◦C and the reaction mixture
maintained at this temperature for a further 1.5 h. The dark
red solution was cooled and added to a saturated solution of
NH4PF6 to precipitate the complex as the PF6 salt. The dark red
precipitate was isolated by vacuum filtration and washed with
H2O (3 ¥ 5 mL), MeOH (3 ¥ 5 mL) and Et2O (3 ¥ 5 mL). Repeated
recrystallisation (3–5 times) from MeCN–Et2O afforded dark red
crystals of [Ir(ttpyeneanisole)2]·3PF6 in 53% yield (0.121 g).
+
ES+ MS (MeCN) m/z 1130 {M - PF6} (6%), 492 {M - 2 ¥
2+
PF6} (100%). NMR/d6-acetone dH: 9.36 (s, 4H, H3¢, H5¢), 8.96
(d, 4H, 8.0 Hz, H6, H6¢¢), 8.25 (d, 4H, 3JHH 8.4 Hz, H7, H7¢¢), 7.99
(td, 4H, 3JHH 8.0 Hz, 4JHH 1.6 Hz H4, H4¢), 7.84 (d, 4H, 3JHH 8.4 Hz,
H8, H8¢¢), 7.73 (dd, 2H, 3JHH 5.6 Hz, 4JHH 0.8 Hz, H3, H3¢¢), 7.52 (d,
4H, 3JHH 8.8 Hz, H14, H14¢), 7.35 (d, 2H, 2JHH 16.4 Hz, H10/H11),
7.24 (m, 4H, H5, H5¢¢), 6.97 (d, 2H, 2JHH 16.4 Hz, H10/H11), 6.89 (d,
ES+ MS (MeCN) m/z 1366 {M - PF6} (8%), 610 {M - 2 ¥
+
PF6}2+ (34%), 358 {M - 3 ¥ PF6}3+ (100%). NMR/d6-acetone dH:
9.57 (s, 4H, H3¢, H5¢), 9.17 (d, 4H, 8.0 Hz, H6, H6¢¢), 8.37 (td,
10844 | Dalton Trans., 2010, 39, 10837–10846
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3JHH 8.0 Hz, 4JHH 1.2 Hz H4, H4¢), 8.34 (d, 3JHH 8.0 Hz, H7, H7¢¢)
(overlapping signals, 8H), 8.24 (dd, 3JHH 6.0 Hz, 4JHH 0.8 Hz, H3,
H3¢¢), 7.94 (d, 4H, 3JHH 8.4 Hz, H8, H8¢¢), 7.62 (m, 8H, H5, H5¢¢, H14,
H14¢¢), 7.47 (d, 2H, 2JHH 16.4 Hz, H10/H11), 7.27 (d, 4H, H10/H11),
4 C. Giradot, B. Cao, J.-C. Mulatier, P. L. Baldeck, J. Chauvin, D. Riehl,
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6.97 (d, 4H, JHH 8.8 Hz, H13, H13¢), 3.81 (s, 6H, OMe). UV–vis
(MeCN) lmax (e/mol-1dm3cm) = 222 (sh), (55640), 250 (48830), 323
(77100), 434 (40180). Anal. Calcd. For C60H46N6O2P3F18Ir·2H2O:
C 46.61, H 3.26, N 5.44. Found: C 46.81, H 3.25, N 5.24.
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Preparation of iridium bis{4-(4-{2-[phenyl]ethenyl}-phenyl)-2,2¢-
6¢,2¢¢-terpyridine}·3PF6 ([Ir(tpystilbene)2]·3PF6). Under N2, a
mixture of IrCl3·xH2O (0.022 g, 0.075 mmol) and tpystilbene
(0.050 g, 0.147 mmol) in ethylene glycol (7 mL) was heated at
100 ◦C for 2.5 h. After this time, the temperature was raised to 195
◦C and the reaction mixture maintained at this temperature for a
further 1.5 h. The dark orange solution was cooled and added to
a saturated solution of NH4PF6 to precipitate the complex as the
PF6 salt. The orange precipitate was isolated by vacuum filtration
and washed with H2O (3 ¥ 5 mL), MeOH (3 ¥ 5 mL) and Et2O (3 ¥
5 mL). Repeated recrystallisation (4–5 times) from acetone–Et2O
afforded an orange powder of [Ir(tpystilbene)2]·3PF6 in 34% yield
(0.036 g).
+
ES+ MS (MeCN) m/z 1305 {M - PF6} (9%), 1159 {M - 2 ¥
+
+
3+
PF6 + H} (6%), 508 {M - 2 ¥ PF6} (54%), 339 {M - 3 ¥ PF6}
(100%). NMR/d6-acetone dH: 9.45 (s, 4H, H3¢, H5¢), 9.06 (d, 4H,
3JHH 7.2 Hz, H6, H6¢¢), 8.26 (d, 4H, JHH 8.0 Hz, H7, H7¢¢), 8.14
3
(m, 4H, H4, H4¢), 7.91 (d, 4H, 3JHH 8.0 Hz, H8, H8¢¢), 7.58 (d, 4H,
H14, H14¢), 7.48 (m, 8H, H3, H3¢¢, H5, H5¢¢), 7.34 (m, 6H, H10, H11,
3
H15), 6.74 (d, 4H, JHH 7.6 Hz, H13, H13¢). UV–vis (MeCN) lmax
(e/mol-1dm3cm) = 252, (56580), 292 (63360), 320 (sh) (56030), 377
(29240). Anal. Calcd. For C58H42N6P3F18Ir·2H2O: C 46.87, H 3.12,
N 5.65. Found: C 46.44, H 2.78, N 5.58.
Acknowledgements
We thank the EPSRC for funding a Career Acceleration Fellow-
ship (LSN) and an Advanced Research Fellowship (SWM) and
The Leverhulme Trust for a postdoctoral fellowship (LSN). We
also thank Dr Alisdair Macpherson for his assistance with the
titanium sapphire laser, Dr David Binks and Dr Stuart Stubbs for
help with the lifetime measurements of the uncomplexed ligands
and Dr Robin Pritchard and Dr Rachel Shaw for the X-ray
crystallographic data collection of [Ir(ttpyeneanisole)2]·3PF6 and
[Ru(tpystilbene)2]·2PF6 respectively.
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