Photophysical and electrochemical properties of phenanthroline-based bis-cyclometallated iridium complexes in aqueous and organic media

Article abstract of DOI:10.1002/ejic.201100639

The electrochemical and photophysical properties of biscyclometallated iridium(III) complexes containing phenanthroline-based ligands have been investigated and compared in organic and aqueous media. Complexes having general formula [Ir(ppy)₂(N

Full text of DOI:10.1002/ejic.201100639

FULL PAPER
DOI: 10.1002/ejic.201100639
Photophysical and Electrochemical Properties of Phenanthroline-Based Bis-
cyclometallated Iridium Complexes in Aqueous and Organic Media
[a]
[a]
[a][‡]
and David J. D. Wilson[a]
Reshmi V. Kiran, Conor F. Hogan,* Bruce D. James,
Keywords: Iridium / Electrochemistry / Luminescence / Density functional calculations
The electrochemical and photophysical properties of bis-
cyclometallated iridium(III) complexes containing phen-
anthroline-based ligands have been investigated and com-
spectroelectrochemical experiments indicate that electrolysis
produces significant changes to the UV region of the spec-
trum associated with the ppy moieties. Significantly, this
pared in organic and aqueous media. Complexes having ge- demonstrates that the highest occupied molecular orbital
+
/–
neral formula [Ir(ppy)
2
( N_ N)] were synthesized, where ppy
(HOMO) is not entirely metal based but is also associated
with the cyclometallating ligand. The variation in emission
maxima between the iridium complexes was small in organic
and aqueous media, but the colour of the emission depends
on solvent polarity and strongly on temperature. Most signifi-
cantly, the quantum yields for these species are also strongly
influenced by the solvent: high quantum yields, ranging from
is the cyclometallating ligand, 2-phenylpyridine, and N_ N
represents one of the following phenanthroline based li-
gands: 1,10-phenanthroline (phen), 4,7-diphenyl-1,10-phen-
anthroline (dpp) and 4,7-diphenyl-1,10-phenanthrolinedisulf-
onate (BPS). In the case of [Ir(ppy)
located on the phenyl ring of BPS dramatically increases the
–
–
2 3
(BPS)] , the SO group
aqueous solubility of the complex compared to the dpp com- 14.0 to 28.6%, are observed in CH
2
Cl
2
. However, in aqueous
–
plex, which is only soluble in organic media. The chloride
salt of the underivatized phen complex, though not as soluble
media the water-soluble complexes, [Ir(ppy)
[Ir(ppy)
2
BPS] and
2
phen] , exhibited significantly diminished quantum
+
as the BPS chelated complex, is sufficiently soluble (Ͼ 1 m
M
)
yields of 2.5 and 2.6%, respectively. Theoretical calculations
confirm the spectroscopic assignments and that the HOMO is
significantly delocalized over the metal and cyclometallating
ligands. The relationship between the electrochemical, spec-
troscopic and theoretical results is discussed.
for sensing and other applications in aqueous media. The
electrochemical response depends markedly on the medium;
all the complexes showed reversible behaviour in organic
2
media, whereas the oxidative electrochemistry of [Ir(ppy) -
BPS]– and [Ir(ppy)
phen] was irreversible. Results from
+
2
Introduction
(bpy), 1,10Ј-phenanthroline (phen) or structurally similar li-
+
gands. For example, [Ir(ppy) phen] has been reported to
2
Luminescent cyclometallated iridium complexes have
captured the interest of many scientists, principally as trip-
let emitters in organic light emitting diode devices,
increasingly for potential applications in biological and
chemical sensing and bioimaging.
Due to strong spin–orbit coupling promoted by the
heavy metal centre,[10] charged heteroleptic and neutral
homoleptic iridium complexes often exhibit high quantum
yields and long excited state lifetimes in organic media. Bis-
produce coreactant electrochemiluminescent (ECL) emis-
2+
sion four times more intense than [Ru(bpy) ] in acetoni-
3
[
1–7]
and
[11]
trile.
Photoluminescent quantum yields of up to 0.43
have been reported for a range of such complexes contain-
[
8]
[9]
[12]
ing phen ligands suitably derivatized for bioconjugation.
+
[
Ir(ppy) dpp] , where dpp is 4,7-diphenyl-1,10-phen-
2
anthroline, has been shown to be highly emissive and to
[13]
have promising electroluminescent properties.
Although the photochemical properties of iridium com-
plexes have been the subject of intensive investigation in
recent years, their behaviour in aqueous media remains
largely unexplored. This is an undesirable situation because
many of the proposed applications for these materials are
based in aqueous media. A series of water-soluble irid-
ium(III) bis-terpyridine complexes has been recently syn-
thesized by Williams et al., some of which display high in-
cyclometallated complexes of the general formula [Ir( C_ N) -
2
+
(
N_ N)] , where C_ N is a cyclometallating ligand and N_ N is
a chelating diimine ligand, have received considerable inter-
est. The C_ N ligand is commonly a 2-phenylpyridine (ppy)
derivative, whereas N_ N is typically based on 2,2Ј-bipyridine
[
a] Department of Chemistry, La Trobe Institute for Molecular
Science, La Trobe University,
Victoria 3086, Australia
tensity and extremely long-lived emission in aqueous solu-
E-mail: c.hogan@latrobe.edu.au
[8d,14]
tion.
Konishi et al. have described the synthesis and
[
‡] Deceased on July 8, 2009; this paper is dedicated to his memory.
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201100639.
photophysical properties of a tris-cyclometallated irid-
ium(III) complex bearing the bulky ligand 3Ј,5Ј-bis(4-
4816
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2011, 4816–4825

Properties of Phenanthroline Based Bis-cyclometallated Iridium Complexes
carboxylphenyl)-3-(2-pyridyl)biphenyl-4-yl, which has the groups each retain a sodium cation. In solution, the com-
–
potential for sensing heavy metals such as lead, cadmium plex exists as [Ir(ppy) BPS] (see Supporting Information,
2
[
15]
and mercury. Lo et al. have described the properties of a Figures S1–S10 for its characterization).
series of bis-cyclometallated iridium complexes containing
biotin-derivatized bipyridine ligands. Some photophysical
properties in mixed aqueous/organic media have been re-
ported, and the application of the complexes in live cell
imaging has been demonstrated.[ The most substantial
study to date on the luminescent properties of cyclometall-
ated iridium complexes in aqueous media is that of Jiang et
al.[ In a study focused on cell imaging applications, the
16]
17]
authors have reported a series of bis-cyclometallated com- Scheme 1. Synthesis of [Ir(ppy)
BPS]–.
2
plexes with an ancillary ligand of the zwitterionic diimine
4-carboxy-2,2Ј-bipyridine-4Ј-carboxylate, with variation of
the cyclometallating ligands.
Apart from the aforementioned work, there has been lit-
tle detailed study into the photophysical properties and vir-
Electrochemistry
The electrochemical properties of the bis-cyclometallated
tually no investigation of the electrochemical properties of iridium(III) complexes were investigated in both organic
bis-cyclometallated heteroleptic iridium(III) complexes in and aqueous media using cyclic voltammetry. The results
pure aqueous media. Our group has recently reported the for the complexes in CH Cl and aqueous solution are sum-
2
2
analytically useful chemiluminescence of the new batho- marized in Table 1. Due to the limited cathodic potential
phenanthroline sulfonate (BPS) complex, [Ir(ppy) BPS]Cl, window of CH Cl , in some cases redox potential data in
2
2
2
as well as the related [Ir(ppy) phen]Cl and [Ir(ppy) bpy]Cl CH CN are also presented.
2
2
3
8a]
(
bpy = bipyridine) in aqueous solution.[ In this contri-
2 2
Table 1. Formal potentials (E°) in aqueous and CH Cl media, and
excited state redox potentials (E*) for the complexes studied. Val-
bution we present the first full electrochemical and photo-
physical characterization of phen-based bis-cyclometallated
iridium(III) complexes in both organic and aqueous media.
The water-soluble complexes [Ir(ppy) BPS] and [Ir(ppy) -
phen] are compared with [Ir(ppy) dpp] ,which is only sol-
ues in parenthesis represent quasi- or irreversible peaks. Data for
2+
[
Ru(bpy)
3
]
are included for comparison.
–
2
2
Aqueous
Organic[c]
+
+
2
E° [V]
E° [V]
uble in organic media. Our interest in these materials is
driven by potential sensing applications related to their che-
miluminescent, electrochemiluminescent and photolumines-
cent properties. Our results provide insights into the nature
of the charge transfer (CT) leading to the excited state in
this class of complex.
(
vs. Ag/AgCl) (vs. ferrocene)
Complex
Ir(ppy)
BPS]–
Ir(ppy)
Ir(ppy)
[Ir(ppy) Cl]
Ir3+/4+
(1.10)[a]
(1.08)
–
–
Ir3+/4+
N_ N
ppy
–
E*ox[f] E*red[f]
[
[
[
2
0.89
0.90
0.86
0.53,
–1.81
(–1.83) (–2.52)
–1.84
–
–1.41 0.50
–1.61 0.58
–1.49 0.51
+
[b]
[d]
2
phen]
+
[d]
2
dpp]
(–2.42)
–
2
2
–
–
[e]
0.80
[
Ru(bpy)
3
]2+
1.08
0.98
–1.72,
–
–1.15 0.41
–
1.97
Results and Discussion
[
4
a] 0.1 m LiClO , 5 mm complex. [b] Phosphate buffer (0.2 m), 1 mm
complex. [c] In CH Cl /0.2 m TBAPF , 1 mm complex. [d] In
CN/0.2 m TBAPF , 1 mm complex. [e] A single redox couple
6
is observed at 0.6 V vs. Fc in acetonitrile (see Supporting Infor-
Synthesis
2
2
6
CH
3
The synthesis of the iridium complexes was carried out
in two steps. The dichloro-bridged dimer was synthesized mation). [f] Excited state redox potentials estimated using E*
=
ox
using a modification of a procedure by Sprouse.[18] The irid-
ium complexes were obtained by cleaving the chloride
bonds of the dimer with the corresponding diimine ligands
+
0–0
–
0–0
+
E°(A /A) – E and E*red = E°(A/A ) + E , where E°(A /A) and
–
0–0
E°(A/A ) are the ground state redox potentials and the E energy
is estimated from the low-temperature emission data in Table 3.
(
phen, dpp or BPS) as shown in Scheme 1 for the BPS com-
–
plex. These reactions require mild conditions, and products
were obtained in high yields. One or both of column purifi- [Ir(ppy) phen] and [Ir(ppy) dpp] dissolved in CH Cl are
The cyclic voltammetric responses for [Ir(ppy) BPS] ,
2
+
+
2
2
2
2
cation and recrystallization was required to obtain pure presented in Figure 1. In organic media the electrochemical
1
products. All complexes were characterized using 1D ( H, responses of the three complexes are characterized by a sin-
1
3
C) and 2D NMR (COSY, DEPT, heteronuclear single gle reversible oxidative wave between 0.86 and 0.90 V vs.
quantum coherence). ESI mass spectrometry and elemental ferrocene. This may be formally attributed to the oxidation
analysis were also carried out. The positions of the sulfo- of the iridium metal centre [Ir3
+/4+
] although, as will be dis-
nate groups are not specified for commercially available cussed later, the molecular orbital associated with this pro-
BPS; NMR spectroscopy revealed that the sulfonate groups cess is significantly distributed over other parts of the com-
are located in the meta positions on the phenyl rings rather plex. The phen complex also shows an irreversible wave due
than the para, which is often assumed. [Ir(ppy) BPS]Cl ex- to the oxidation of its chloride counterion. In the range of
2
ists as a chloride salt in the solid state because the sulfonate –1.81 to –1.84 V vs. ferrocene, a single wave is observed for
Eur. J. Inorg. Chem. 2011, 4816–4825
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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R. V. Kiran, C. F. Hogan, B. D. James, D. J. D. Wilson
FULL PAPER
each complex, which is attributed to the one-electron re-
For comparison, the electrochemistry of the dimeric
[8b,12,19]
duction of the N_ N ligand.
In CH CN, [Ir(ppy) - starting material was investigated under the same condi-
3
2
+
+
[23]
dpp] and [Ir(ppy) phen] exhibit similar patterns to those tions. As previously noted,
the dimer remains intact in
2
observed in CH Cl . The larger potential window available weakly coordinating CH Cl where two redox waves were
2
2
2
2
in CH CN allowed the observation of a further quasi-re- observed at 0.53 and 0.80 V vs. ferrocene corresponding to
3
versible redox couple at more negative potentials of –2.42 the oxidation of the two iridium centres. No other waves
+
+
and –2.52 V for [Ir(ppy) dpp] and [Ir(ppy) phen] , respec- were observed for the dimer within the potential window of
2
2
tively (Figures S11 and S12, Supporting Information). this solvent, however several irreversible processes corre-
These are attributed to the reduction of the cyclometallat- sponding to the reduction of the ppy ligands were noted in
ing ppy ligands, which is known to occur at a more negative CH CN solvent at more negative potentials. Moreover, in
3
potential than diimine ligands.[
12,19c,20]
We were unable to CH CN one reversible Ir
3+/4+
voltammetric wave was ob-
3
–
make a similar observation for [Ir(ppy) BPS] due to its lim- served at the positive end of the voltammogram rather than
2
ited solubility in CH CN.
two. This is a result of cleavage of the dimer to form a
solvent-coordinated mononuclear complex [Ir(ppy) (CH -
CN)Cl] (Figure S14, Supporting Information).
3
2
3
[
23]
In aqueous media the electrochemical behaviour of the
–
two water-soluble iridium complexes, [Ir(ppy) BPS] and
2
+
[
Ir(ppy) phen] , is substantially different from that ob-
2
served in the organic solvents (Figure 2). As in the organic
solvents, a voltammetric signal is observed above 1.0 V vs.
+
Ag/AgCl in each case, {1.08 and 1.10 V for [Ir(ppy) phen]
2
–
and [Ir(ppy) BPS] , respectively}. However, unlike those in
2
organic solution, in aqueous media the waves are irrevers-
ible or quasi-irreversible in nature. The ligand reductions
are not observed in water as only the positive region of the
potential scale is accessible. It is interesting to note that the
reversibility of the oxidative wave due to [Ir(ppy) -
2
–
BPS] increases with increasing scan rate. The plot on the
right in Figure 2 illustrates the response for the BPS com-
plex in aqueous solution at 0.05 and at 1 V/s. At the faster
scan rate the return peak for the rereduction of the complex
is more prominent. No such scan rate dependence was ob-
+
served for [Ir(ppy) phen] up to 50 V/s. Although the prox-
2
imity of the redox waves to the solvent limit precluded sen-
sible kinetic analysis by modelling or other means, it is clear
that the process responsible for the observed chemical irre-
versibility in these systems is more rapid in [Ir(ppy) -
2
+
–
phen] . In [Ir(ppy) BPS] , the process is sufficiently slow to
2
+
be manifested on the cyclic voltammetric timescale.
2 2
Figure 1. Cyclic voltammetry of (a) [Ir(ppy) dpp] , (b) [Ir(ppy) -
–
+
2 2 2 6
BPS] and (c) [Ir(ppy) phen] in CH Cl containing 0.2 m TBAPF .
The concentration was 1 mm in each case, a 3 mm diameter glassy
carbon (GC) electrode was used in (a) and (c) and a 2 mm diameter
platinum electrode was used in (b). The main scan in each case was
–1
run at 0.2 Vs , (b) shows an additional scan (dashed line) run at
–
1
1
.0 Vs .
–
The response for [Ir(ppy) BPS] at the faster scan rate of
2
–
1
1
.0 Vs in the positive region of the voltammogram is also
shown in Figure 1. The narrowing of the return wave and
the fact that it becomes more prominent with increasing
scan rate (Figure S13, Supporting Information) is consis-
tent with the complex being weakly adsorbed in the neutral
[
21]
(
oxidized) state. Repeated cycling (Ͼ 10 cycles) results in
some build up of material on the electrode, which eventually
blocks the surface and results in diminished current. De-
spite this, the redox potentials obtained from the initial
scans should approximate the pure solution phase values at
slow scan rates well.[
Figure 2. Aqueous cyclic voltammetry of the water-soluble iridium
2
complexes using a 3 mm diameter GC electrode. 1 mm [Ir(ppy) -
phen]+ at 0.2 Vs in 0.2 m phosphate buffer (left) and 5 mm
–1
22]
–
–1
[Ir(ppy)
2
BPS] in 0.1 m LiClO
4
at 0.05 and 1.0 Vs (right).
4818
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© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2011, 4816–4825

Properties of Phenanthroline Based Bis-cyclometallated Iridium Complexes
Absorption Spectroscopy
The UV/Vis absorption spectra of [Ir(ppy) phen] and
ionic) ligand is expected to be higher than that of an isoelec-
tronic but neutral polypyridine ligand. In particular, on the
+
2
+
[19a,24]
basis of data for similar complexes,
the bands peaking
–
[
Ir(ppy) BPS] in H O and that of [Ir(ppy) dpp] in CH Cl
2 2 2 2 2
at wavelengths less than 270 nm are assigned to ppy-centred
transitions, whereas absorption in the 270–300 nm range is
attributed to the diimine ligand. A well-defined peak is seen
at approximately 285 nm for the two diphenylphen com-
plexes, which is absent for the unsubstituted phen complex.
Therefore, this is assigned to a π–π* transition centred on
are illustrated in Figure 3 (see Figure S15 in Supporting In-
formation for raw spectra). The electronic absorption spec-
troscopic data in both solvents (where solubility allows) are
summarized in Table 2. Solvent polarity (CH Cl vs. H O)
2
2
2
does not influence the positions of the absorption bands.
For cyclometallated iridium(III) diimine systems, intense
absorption bands below 320 nm are assigned to spin al-
lowed π–π* ligand-centred (LC) transitions that occur in
the cyclometallated ppy and the N_ N phen-based ligands.
the phenyl rings of the diimine ligands. In accordance with
[3,19c,20a,25]
the literature,
the less intense absorption bands
observed at lower energy (320–440 nm) are attributed to a
spin allowed CT transition where CT occurs from the
HOMO to a phen-ligand based π* orbital. The correct as-
signment of these bands as metal-to-ligand MLCT
[
[
dπ(Ir)Ǟπ*(phen)] or ligand-to-ligand LLCT bands
[
17,19a]
π(ppy)Ǟπ*(phen)]
depends on the nature of the
HOMO and the extent to which it is delocalized over the
metal and the ppy ligand. The very weak absorption bands
above 440 nm are the result of spin forbidden CT transi-
tions, which are more pronounced in iridium complexes
compared to analogous ruthenium complexes due to heavy
metal induced spin–orbit coupling.
Spectroelectrochemistry
The changes observed in the absorption spectra of
+
[
Ir(ppy) phen] in CH Cl over a period of ca. 10 min as
2
2
2
the solution is oxidized using a Pt gauze working electrode
biased at 1.25 V vs. Ag/AgCl are depicted in Figure 4. Only
Figure 3. Absorbance spectra of 10 μm [Ir(ppy)
and [Ir(ppy) O and [Ir(ppy)
BPS]– (middle) in H
line) in CH Cl
2
phen]+ (bottom)
+
2
2
2
dpp] (top solid
2
2
(spectra offset for clarity). The upper dashed curve
shows an expanded view of the visible region of the [Ir(ppy)
2
-
phen]+ spectrum.
Table 2. Absorbance data for the iridium complexes in CH
O at 298 K.
2 2
Cl and
H
2
4
–1
–1
Complex
Solvent
λ
abs [nm] (εϫ10 [m cm ])
2
3
2
3
2
3
2
3
2
53(4.6), 264(4.7), 333(1.0),
81(0.8), 411(0.4), 450(0.1), 461(0.1)
52(4.5), 264(4.7), 333(1.0),
67(0.7), 411(0.4), 450(0.1), 453(0.1)
56(3.4), 270(3.9), 286(3.5),
34(1.3), 387(0.8), 450(0.1), 466(0.1)
56(6.0), 270(6.4), 285(6.1),
[
Ir(ppy)
2
phen]+
CH
2
Cl
2
2
H O
[Ir(ppy)
2
2
dpp]+
BPS]–
CH
2
2
Cl
Cl
2
2
[Ir(ppy)
CH
33(2.4), 386(1.4), 450(0.2), 466(0.2)
52(5.6), 265(5.8), 279(5.6),
H
2
O
329(1.9), 373(1.1), 412(0.3),
50(0.2), 455(0.1)
4
–
4
Figure 4. UV/Vis spectroelectrochemical response for 1ϫ10
[
m
Although the two types of ligand on these complexes are
structurally similar, they are electronically diverse, and it is
well established that the energy of the lowest unoccupied
+
2 2 2 6
Ir(ppy) phen] in CH Cl containing 0.1 m TBAPF , with the oxi-
dation potential held constant at 1.25 V using a Pt gauze electrode
in a thin layer cell. The arrows indicate the direction of change in
molecular orbital (LUMO) for the cyclometallated (an- peak magnitudes over the course of the experiment (≈ 10 min).
Eur. J. Inorg. Chem. 2011, 4816–4825
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R. V. Kiran, C. F. Hogan, B. D. James, D. J. D. Wilson
FULL PAPER
relatively minor changes are evident in the visible region of Table 3. Photophysical properties of iridium complexes in various
media.
the spectrum on electrolysis of the solution. This is in con-
2+
trast to the situation with complexes such as [Ru(bpy) ]
[c]
[c]
3
Complex
Ir(ppy)
Solvent
λmax [nm]
Φ
p
Φ
p
2
+
or [Ru(phen)3] where a MLCT band at 460 nm is lost
completely on oxidation of the metal centre from the 2+ to
(aerated) (degassed)
phen]Cl[e] CH
[a]
[a]
[a]
[a]
[
2
2 2
Cl
584
605
0.045
0.019
0.140
0.026
[
26]
the 3+ state. The most significant change to the spectrum
of the iridium complex on oxidation is the loss of the band
at 253 nm, which is assigned to a πǞπ* ppy (LC) transi-
tion. This change is observed in both dichloromethane and
water (Figure S16, Supporting Information). Although the
peak substantially returns on stepping the potential to a
more reducing value (0.5 V) in CH Cl , in aqueous solution
H
2
O
EtOH/MeOH
EtOH/MeOH
594
515, 534
(
77 K)
dpp]Cl[d] CH
0.078[b]
0.344[b]
[
Ir(ppy)
2
2
Cl
2
587
602
528, 555
EtOH/MeOH
EtOH/MeOH
(77 K)
2
2
[Ir(ppy)
2
BPS]Cl
CH Cl
2
2
583
616
0.113
0.023
0.286
0.025
the loss is irreversible.
2
H O
Clearly, oxidation of the complex results in changes to a
MO closely associated with ppy. These observations
strongly suggest that the HOMO in these complexes is ap-
preciably associated with a cyclometallated ligand and not
simply the metal centre. Moreover, reversible electrochemis-
try observed in organic media should not be taken as evi-
dence of a purely metal-based redox orbital. These observa-
tions have implications for the assignment of the CT transi-
tions leading to the excited state in these complexes.
EtOH/MeOH
EtOH/MeOH
605
537, 564
(77 K)
[
Ru(bpy)
3
]2+
CH Cl
2
2
606
623
616
581, 626,
694
0.028
[b]
0.042
[b]
[a]
[a]
2
H O
0.028
0.042
EtOH/MeOH
EtOH/MeOH
(77 K)
[
a] Chloride salt. [b] PF
6
salt. [c] Quantum yields measured using
as the reference and 450 nm as the excitation wave-
length. [d] Various quantum yields have previously been reported
2
+
Ru(bpy)
3
+
for [Ir(ppy)
the standard;
2
dpp] {Φ in CH
2
Cl
CN = 18.2%, using [Ir(ppy)
as the standard;[ Φ in CH
CN = 53%, using [Ru(4,7-diphenyl-
,10-phen) ]Cl as the standard}.
have previously been reported for [Ir(ppy)
2
= 20%, using coumarin 540 as
[
27]
Φ in CH
3
2
(bpy)]PF
6
2a]
Photoluminescence
3
[13]
1
3
2
[e] Various quantum yields
phen][PF ] {Φ in
All three complexes exhibit intense photoluminescence
under the conditions used in this study. Specifically, in
dichloromethane, water and alcohol (1:4 EtOH/MeOH) at
ambient temperatures and in alcohol glass at 77 K. Photo-
luminescence data are summarized in Table 3, which in-
2
6
[
27]
CH
CH
in CH
2
Cl
CN = 11.9%, using [Ir(ppy)
Cl = 14%, using Rhodamine 6G as the standard}.
2
= 7%, using coumarin 540 as the standard;
Φ in
[
2a]
3
2
(bpy)]PF as the standard;
6
Φ
[11]
2
2
2
+
cludes the corresponding data for [Ru(bpy)3] (a pure
MLCT emitter) obtained under the same conditions for
comparative purposes. In organic media, the values of the solvatochromic redshift with increased solvent polarity, and
photoluminescent quantum yields (Φ ) decrease in the or- the distinct broadening of the spectrum in water apparent
p
–
+
+
der [Ir(ppy) BPS] Ͼ [Ir(ppy) dpp] Ͼ [Ir(ppy) phen]
Ru(bpy) ] . The high intensity of the luminescence in substantial charge separation exists. As illustrated in Fig-
Ͼ
in Figure 5 (a) are indicative of a CT excited state where
2
+
2
2
2
[
3
dichloromethane is evidenced by large values of Φ , which ure 5 (b), each of the iridium complexes displays a batho-
p
range from 14.0–28.6%, compared to 4.2% for [Ru- chromic shift when excited in more polar solvents such as
2
+
(
bpy)3] in the same medium. However, in aqueous media EtOH/MeOH and H O compared with dichloromethane.
2
the quantum yields for the iridium complexes are signifi- Because the polarities of the complexes at ground and ex-
cantly reduced and the order is reversed with both [Ir(ppy) - cited state are substantially different; a change in the sol-
2
+
–
phen] (2.6%) and [Ir(ppy) BPS] (2.5%) being outper- vent polarity leads to greater stabilization. This results in a
2
formed by the ruthenium standard (4.2%).
change in energy gap between these electronic states, which
Little variation was observed in the wavelength of the results in a shift of the energies of the emission maxima.
maximum emission between the three phen-based iridium
The photoluminescent spectra of all three iridium com-
plexes are illustrated in Figure 5 (c), both in fluid alcoholic
complexes in the same media. For example, in CH Cl , λ
2
2
max
ranged between 583 and 587 nm, the results in alcohol and medium at 298 K and in a 77 K alcohol glass. There is a
water being similarly invariant (see Table 3). These observa- significant blueshift apparent for the complexes at low tem-
tions parallel the electrochemical data presented earlier, perature compared to the ambient temperature spectra.
where the oxidation and first reduction formal potentials Moreover, whereas the room temperature spectra are broad
0
(
E ) were similar for each complex.
and featureless, the spectra in 77 K alcohol glass display
A noteworthy observation is the solvatochromism dis- structure. A blueshift at low temperature is typical of CT
played by these complexes at ambient temperatures, where states and its magnitude is related to the degree of charge
the emission maxima are found to be dependant on the po- separation between the ground and excited states. [Ru-
2
+
larity of the solvent.
(bpy) ] , which is regarded as a typical MLCT emitter, dis-
3
–
–1
The emission spectra of [Ir(ppy) BPS] in dichlorometh- plays a shift of 948 cm under the conditions used here,
2
ane and water are plotted in Figure 5 (a). The significant and analogous ruthenium and osmium complexes are
4820
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© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2011, 4816–4825

Properties of Phenanthroline Based Bis-cyclometallated Iridium Complexes
2 2 2
Figure 5. Effect of medium on photoluminescence of iridium complexes. (A) Emission spectra of [Ir(ppy) Cl
BPS]– at 298 K in CH
(
blue) and H
2
O (red). (B): Effect of medium on photoluminescent emission energy of the three iridium complexes compared with
in H O, CH Cl , 1:4 EtOH/MeOH solution at 298 K and 1:4 EtOH/MeOH glass at 77 K. (C): Emission spectra of [Ir(ppy)
phen] (green), [Ir(ppy) dpp] (blue) and [Ir(ppy)
EtOH/MeOH solution at 298 K (dashed lines).
2+
[Ru(bpy)
3
]
2
2
2
2
-
+
+
–
2
2
BPS] (red) in 4:1 EtOH/MeOH glass at 77 K (spectra on the left) and in fluid 4:1
known to display shifts of typically no more than ficantly larger than that expected for a MLCT state. These
–
1
2
000 cm . The magnitude of the blueshifts observed for the observations are consistent with an excited state with sub-
–
1
iridium complexes studied here (2093–2582 cm ) are signi- stantial LLCT character.
–
Figure 6. Electron-density maps of frontier MOs in [Ir(ppy)
complex (bottom).
2
(BPS)] (top). MO contributions to HOMO and LUMO for each iridium
Eur. J. Inorg. Chem. 2011, 4816–4825
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
4821

R. V. Kiran, C. F. Hogan, B. D. James, D. J. D. Wilson
FULL PAPER
Theoretical Calculations
as estimated from ground state potentials and low tempera-
ture emission data, point to a significant level of photo-
chemical activity for these species compared with [Ru-
As expected from the electrochemical and spectroscopic
data, the nature of the phen-type ligand has only a small
effect on the nature of the frontier MOs of the complex.
Very similar properties and topologies are found for the
HOMO and LUMO of each iridium complex as illustrated
in Figure 6. In each case the HOMO comprises contri-
butions from both the iridium atom (30–40%) and the
phenyl (π) ring of the ppy ligands (50–60%). The delocal-
ization of the HOMO of these complexes is consistent with
the experimental evidence from spectroelectrochemistry and
photoluminescence. In each case the LUMO (and
LUMO+1) is almost exclusively composed of the phen
core. The next highest energy MOs (LUMO+2, LUMO+3)
are associated with delocalized π* orbitals on the ppy li-
gand. Plots of MO topologies for all complexes, as well as
contributions to each MO for frontier MOs, are included in
the Supporting Information (Figure S17). The calculated
energies of the HOMO, LUMO and HOMO–LUMO gap
also exhibit little variability (Table S1, Supporting Infor-
mation).
The time dependent (TD)-DFT results generally support
the assignment of absorption bands from the experimental
data. The assignment of transitions as being either pure
MLCT or LLCT would not be justified due to the delocal-
ization of the MOs, in particular the HOMO, of these com-
plexes. Moreover, the presence of spin–orbit coupling in
heavy metal complexes such as these further obfuscates the
separation between singlet and triplet states, as well as CT
states.
2+
(
bpy) ] .
3
Spectroelectrochemical experiments show that the most
significant change to the absorption spectrum of [Ir(ppy) -
2
+
phen] on electrochemical oxidation is the loss of a band at
253 nm assigned to a ppy-based π–π* transition. Mirroring
the voltammetric data, the loss of the band, which is
irreversible in aqueous media, is recovered in organic sol-
vent on re-reduction. These observations suggest that for
such iridium complexes the electron abstracted on oxidation
is not from the dπ orbital, but from an orbital that is largely
ligand based.
In the localized MO approximation, oxidation and re-
duction processes are viewed as metal or ligand centred.
For example, in the case of the ruthenium complexes, the
metallic nature of the HOMO is clear cut. Such arbitrary
classification of electronic transitions and electronically ex-
cited states loses its meaning when the states involved can-
[
29]
not be described by localized MO configurations.
From
an electrochemical standpoint, the implication is that the
assignment of the first oxidative couple in these complexes
3+
4+
as simply Ir /Ir is not strictly correct. Similarly, the na-
ture of the CT transition leading to the excited state cannot
be defined as MLCT or LLCT from a photochemical per-
spective and certainly such an assignment should not be
made on the basis of the reversibility of the oxidative redox
couple in organic solvent.
The dependence of the emission wavelength on solvent
polarity and the large blueshifts observed on going from
fluid media to low temperature glass support the assign-
ment of the excited state as being significantly LLCT in
nature. LLCT states are expected to be more distorted than
MLCT states with respect to the ground state. Therefore,
relatively higher stabilization occurs in polar solvents and a
more significant redshift in emission is observed.
The absorption bands at lower energy (above 400 nm)
are generally associated with a greater degree of MLCT,
although inclusion of spin–orbit coupling would be re-
quired to accurately model this region of the spectrum. The
highest energy bands reported in Table S2 (Supporting In-
formation) correspond to ppy-centred transitions, whereas
bands corresponding to transitions to the diimine ligand
are slightly lower in energy. This is in agreement with the
assignment from the experimental spectra outlined above.
The complexes are highly emissive in organic media but
significantly less so in water. For example the photolumi-
–
nescent quantum yield (Φ ) for [Ir(ppy) BPS] plunges from
p
2
2
8.6 to 2.5% on going from CH Cl to H O. The strong
2 2 2
solvent dependence of Φ is in contrast with pure MLCT
p
Conclusions
emitters such as [Ru(bpy)3]2 and is clearly related to the
+
The synthesis and characterization of the luminescent, nature of the excited state. This significant effect is likely
water-soluble, bis-cyclometallated iridium(III) complex related to the distorted nature of the excited state, due to its
[
Ir(ppy) BPS]Cl has been described. The electrochemical LLCT character, which being more photochemically active,
2
and photophysical properties of this complex and [Ir(ppy)2- could lead to nonemissive deactivation interactions with
phen]Cl have been investigated in both water and organic polar solvents. This instability is mirrored in the difference
media and compared with the properties of [Ir(ppy)2- in electrochemical reversibility between organic and aque-
dpp][PF ] in an organic medium.
ous media when the electron is removed from the HOMO
6
Reversible electrochemical waves are observed for the electrolytically rather than by optical excitation. Based on
oxidation of these complexes at positive potentials in or- our observations of other complexes (for example com-
ganic solvents; however, the same redox couples are plexes containing a bipyridine based auxiliary ligand), it
irreversible in aqueous media. This is in contrast with com- would appear that the sensitivity of the quantum yields and
2
+
2+
plexes such as [Ru(bpy)3] or [Ru(phen) ] , for which re- the electrochemical characteristics is quite general for bis-
3
versible electrochemistry is observed in both organic and cyclometallated iridium complexes of this type.
[
28]
aqueous media.
It is also noteworthy that the excited
DFT calculations showed that the LUMO in each of the
state redox potentials for the iridium complexes (Table 1), complexes is dominated by the diimine ligand, whereas the
4822
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© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2011, 4816–4825

Properties of Phenanthroline Based Bis-cyclometallated Iridium Complexes
HOMO contains significant contributions from both the (3 m KCl) reference electrode was used. In organic solvents, a Ag
wire pseudo reference was used, in which case peaks were refer-
metal and the ppy ligands. The metal contributions to the
enced to the formal potential of ferrocene (0.31 V vs. SCE) mea-
HOMOs are relatively low (≈ 30%) compared to Ir(ppy)3
sured in situ.[ Nonaqueous reference electrodes were prepared
30]
(≈ 50%). This strongly supports the picture painted by the
using the same solvent as in the test solution with the same concen-
tration of electrolyte (0.1 m or 0.2 m TBAPF ). Spectroelectrochem-
electrochemical, spectroscopic and spectroelectrochemical
data, that the nature of the transition leading to the excited
state in these materials is not adequately described as
MLCT as it is, to a significant extent, an intraligand transi-
tion.
6
ical measurements were made using a 1 mm path length cuvette as
the electrochemical cell using a 0.5ϫ0.7 mm platinum gauze as
working electrode, platinum counter and Ag wire (quasi-reference
electrode) or Ag/AgCl (reference). Solutions were degassed with
The dependence of the luminescent intensity on solvent nitrogen (99.99% Linde) for a minimum of 5 min prior to com-
polarity has obvious implications for the application of bis- mencing an experiment. All electrochemical measurements were
carried out at 23Ϯ5 °C.
cyclometallated iridium complexes in sensing, which is al-
most exclusively carried out in aqueous environments. Al-
Photochemistry: UV/Vis spectra were recorded using a Varian Cary
though such applications are frequently alluded to for this UV/Vis spectrometer. Emission spectra were recorded using a Var-
class of iridium complex in the literature, the vast majority ian Cary Eclipse fluorescence spectrophotometer. Correction fac-
tors from 320–850 nm were determined using a calibrated lamp
of investigations focus exclusively on their properties in or-
(
Optronic Labs Spectral Irradiance standard OL245M) combined
ganic media. Apart from the luminescence, the irreversible
nature of the electrochemistry in aqueous solution has par-
ticular ramifications for the application of these materials
in ECL-based sensing. Nonetheless, we will show in a sub-
sequent publication that their ECL sensing properties rival
those of the dominant ruthenium complexes under some
circumstances.
with a constant current power supply (Optronic Labs OL65A).
Room temperature measurements were made using 1 cm quartz
cells with screw top lids and septa, whereas, for low temperature
(
77 K) measurements, a 1 cm diameter glass tube cooled with liquid
nitrogen was used. The excitation and emission slits were set at
nm band pass for all experiments. In determining the emission
5
maxima (λmax) or the area under the emission spectrum, the origi-
nal spectrum was first corrected for variation in photomultiplier
tube (PMT) responsivity with wavelength using the predetermined
instrumental correction factors. Quantum yields were determined
using the following equation:
Experimental Section
Chemicals: Tris(2,2Ј-bipyridyl)ruthenium(II) dichloride hexahy-
drate, [Ru(bpy)
chloride hydrate (IrCl
99.9%), bathophenanthrolinedisulfonic disodium (99.9%), 4,7-di-
phenyl-1,10-phenanthroline (99.9%), 1,10-phenanthroline (99%),
lithium perchlorate (LiClO , Ͼ 99%), sodium chloride (NaCl,
9.5%), dichloromethane (CH Cl , 99.9%), acetonitrile (CH CN,
9.9%) and ethoxyethanol (99%) from Aldrich were employed
3
]Cl
2
·6H
2
O (Ͼ 99%), iridium trichloride hydro-
x x x
Φ = Φref (Grad )
/Gradref)(η2 /η2ref
3
·xH
2
O·xHCl, Ͼ 99.9%), 2-phenylpyridine
where Φref is the quantum yield of the reference complex,
(
]2+, whose photoluminescence quantum yield is known
Ru(bpy)
to be 0.042 in H Grad is the gradient of the
[
3
[31]
[11]
2
O
and CH
2
Cl
2
,
4
absorbance vs. integrated emission intensity graph, using at least
five different concentrations with absorbance below 0.1 and achiev-
9
9
2
2
3
2
ing R close to 1, x denotes sample and ref is the reference and η
without further purification, whereas ethanol and methanol were
distilled. Potassium Phosphate Dibasic (K HPO , Ͼ 98%) was ob-
tained from May & Baker and Potassium Phosphate Monobasic
KH PO , Ͼ 99%) was purchased from Ajax Chemicals. [Ru(bpy) ]-
PF was obtained by converting the Cl salt to PF by metathasis.
is the refractive index of the solvent used. Quantum yield determi-
nations were conducted at room temperature (21Ϯ3 °C). Solutions
were thoroughly degassed with nitrogen in septum-sealed quartz
cells prior to measurements.
2
4
(
[
2
4
3
6
]
2
6
Computational Methods: DFT calculations were carried out within
Unless otherwise stated, all solutions were freshly prepared with
deionized water (Milli Q, Millipore).
the Gaussian 09 suite of programs.[ Ground state geometries
32]
[
33]
were optimized in the absence of solvent with B3LYP
and
General Characterization: NMR spectra were obtained with a
Bruker Avance 300 MHz spectrometer operating at 27 °C. Mea-
surements were carried out in deuterated methanol, deuterated
chloroform or deuterium oxide. MS was performed by ionizing the
samples in 50:50 water/methanol mixture by ESI with a Finnigan
LTQ FT hybrid mass spectrometer (Bremen, Germany) with linear
ion trap and Fourier transform ion cyclotron resonance. Elemental
Analyses (C, N, H, S, Cl) were obtained by the Campbell Microan-
alytical Laboratory, University of Otago, New Zealand.
[34]
mPW1PW91 functionals in conjunction with the 6-31+G(d) ba-
sis set for nonmetal atoms and the LANL2DZ basis set and core
[35]
[36]
potential for iridium.
Only mPW1PW91 results are presented
as it has been shown previously that this functional yields reliable
[37]
results. Symmetry of the optimized ground state structures is C
{
2
+
+
–
2 1 2 2
[Ir(ppy) phen] } and C {[Ir(ppy) dpp] , [Ir(ppy) BPS] }. Final
single-point energy calculations were carried out at the LANL2DZ/
6
-31+G(d) optimized geometries using the SDD basis and core po-
[36a,38]
[39]
tential (MWB)
for Ir and the TZVP basis set for all other
atoms. The polarizable continuum model[ selfconsistent reaction
field was used to model solvent effects at the gas-phase optimized
geometries with solvents as dichloromethane and water. HOMO
40]
Electrochemistry: Cyclic voltammetry was carried out using a PC-
controlled CH660 potentiostat with picoamp booster & faraday
cage (CH instruments) or a μ-Autolab Type II (Eco Chemie, Ne-
therlands) electrochemical workstation. A conventional three-elec-
and LUMO energies were calculated using DFT MOs, as well as
2
[41]
trode cell was used, with platinum 1 cm gauze as the counter elec-
with TD-DFT
using the SDD/TZVP basis sets, which may be
trode. The working electrodes used were disks of different materials
expected to yield accurate and reliable LUMO energies. Excitation
energies to singlet and triplet excited states were investigated with
TD-DFT, with 40 states calculated. SCF convergence criteria of
(Pt and GC) and different dimensions (3 mm diameter GC and
2
mm diameter Pt) shrouded in Teflon. They were cleaned by pol-
–
8
ishing with 0.3 μm alumina on a felt pad and sonicating in acetone
followed by MQ water for 5 min. For aqueous systems, an Ag/AgCl
10 a.u. was employed throughout. Molecular orbital analysis was
carried out with the AOMix program.[
42]
Eur. J. Inorg. Chem. 2011, 4816–4825
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
4823

R. V. Kiran, C. F. Hogan, B. D. James, D. J. D. Wilson
FULL PAPER
Synthesis: The syntheses of [Ir(ppy)
1
2
Cl]
2
, [Ir(ppy)
2
phen]Cl and
of orange pure product. H NMR (300 MHz, CD
2
Cl
2
): δ = 6.48
[
Ir(ppy)
2
dpp][PF
6
] were carried out using modifications of pre-
(d, J = 7.5 Hz, 2 H), 6.97 (t, J = 6.6 Hz, 2 H), 7.04 (t, J = 7.5 Hz,
2 H), 7.16 (t, J = 7.5 Hz, 2 H), 7.51 (d, J = 6.0 Hz, 2 H), 7.65 (m,
viously published methods.
1
2
0 H), 7.75 (d, J = 5.4 Hz, 2 H), 7.82 (m, 4 H), 8.01 (d, J = 8.0 Hz,
[
Ir(ppy) Cl] : The dimer was synthesized by modifying the pro-
2
2
1
3
H), 8.19 (s, 2 H), 8.40 (d, J = 5.4 Hz, 2 H) ppm. C NMR
Cl ): δ = 119.74, 122.67, 123.11, 124.80, 126.20,
[18]
cedure reported by Sprouse, which involved reacting iridium tri-
chloride with 2-phenylpyridine and purifying using flash
(
300 MHz, CD
2
2
1
1
26.72, 129.05, 129.43, 129.54, 129.77, 130.59, 131.65, 135.24,
38.08, 143.75, 147.30, 148.56, 149.72, 150.55, 150.96, 167.73 ppm.
chromatography (silica/dichloromethane) producing an 85% yield.
1
2 2
H NMR (300 MHz, CD Cl ): δ = 5.89 (d, J = 6.9 Hz, 4 H), 6.62
t, J = 7.6 Hz, 4 H), 6.80 (t, J = 6.4 Hz, 4 H), 6.83 (t, J = 6.4 Hz,
C
46
H
32
F
6
4 2
IrN P·2H O (978.0 + 36.0): calcd. C 54.43, H 3.58, N
(
4
5.52; found C 54.36, H 3.48, N 5.69. ESI-MS: m/z = 833.2 [M –
H), 7.57 (d, J = 7.7 Hz, 4 H), 7.80 (t, J = 6.5 Hz, 4 H), 7.94 (d,
+
6
PF ] .
13
J = 7.9 Hz, 4 H), 9.23 (d, J = 5.8 Hz, 4 H) ppm. C NMR
300 MHz, CDCl ): δ = 118.70, 122.50, 123.60, 129.01, 130.30,
36.60, 144.02, 144.80, 151.50, 168.01 ppm. Ir
1072.11): calcd. C 49.29, H 3.01, N 5.23; found C 49.04, H 3.23,
N 5.05.
(
1
(
3
Supporting Information (see footnote on the first page of this arti-
cle): Further details of the structural characterisation, electrochem-
ical properties, spectroscopic properties and results from theoretical
calculations.
C
44
H32Cl
2
2 4
N
[
Ir(ppy)
shown in Scheme 1. [Ir(ppy)
phenanthrolinedisulfonic disodium (99.9%, Aldrich) (171 mg,
.29 mmol) were heated to reflux in 90:10 ethanol/water (150 mL)
2
BPS]Cl: [Ir(ppy)
2
BPS]Cl was synthesized using the route
2
Cl] (154 mg, 0.14 mmol) and batho-
2
Acknowledgments
0
under nitrogen for 6 h. The mixture, which had changed colour
from yellow to luminescent orange, was rotary evaporated to give
crude orange crystals. The crude product was purified using a Se-
phadex LH-20 column (length 10 cm, diameter 2 cm) with a 20:80
mixture of methanol/ethanol. The purified solution was rotary
evaporated and the solid recovered. The complex was dried over-
night to obtain 84% yield of a bright orange powder, which was
characterized using NMR, MS, IR and microanalysis. The complex
contains chloride counterions in the solid state because the sulfo-
nate groups retain their sodium counterions. Nonetheless, the com-
We would like to acknowledge helpful discussions on this work
with Dr. John Christie, La Trobe University. We acknowledge the
Australian research council (ARC) for a discovery project (grant
number DP1094179). The authors acknowledge support from the
National Computational Infrastructure National Facility (NCI-
NF), Victorian Partnership for Advanced Computing (VPAC), Vic-
torian Life Science Computing Initiative (VLSCI) and the high-
performance computing facility of La Trobe University.
[
1] W.-Y. Lai, J. W. Levell, A. C. Jackson, S.-C. Lo, P. V. Bern-
plex carries a net negative charge when dissolved in aqueous or
hardt, I. D. W. Samuel, P. L. Burn, Macromolecules 2010, 43,
1
organic solution. H NMR (300 MHz, CD
3
OD): δ = 6.36 (d, J =
6986–6994.
7
7
2
.5 Hz, 2 H), 6.86 (t, J = 7.4 Hz, 2 H), 6.96 (t, J = 7.5 Hz, 4 H),
.59 (d, J = 6.1 Hz, 2 H, 6-H), 7.62 (s, 2 H), 7.66 (d, J = 4.34 Hz,
H), 7.73 (d, J = 5.2 Hz, 2 H8) 7.81 (m, 4 H), 8.02 (m, 4 H), 8.09
[
2] a) J. I. Goldsmith, W. R. Hudson, M. S. Lowery, T. H. An-
derson, S. Bernhard, J. Am. Chem. Soc. 2005, 127, 7502–7510;
b) M. Kirch, J. M. Lehn, J. P. Sauvage, Helv. Chim. Acta 1979,
62, 1345–1384.
(d, J = 8.1 Hz, 2 H, 4-H), 8.09 (s, 2 H), 8.34 (d, J = 5.2 Hz, 2 H,
5
1
1
1
-H) ppm. 13C NMR (300 MHz, CD
OD): δ = 119.31, 121.97, [3] K. K. W. Lo, D. C. M. Ng, C. K. Chung, Organometallics 2001,
3
20, 4999–5001.
22.83, 124.32, 125.67, 126.59, 128.53, 129.02, 129.77, 130.91,
31.22, 135.42, 137.94, 143.74, 145.71, 146.97, 148.52, 149.70,
50.16, 167.44, ppm. C46H38ClIrN Na O S ·2H O (1080.6 + 36.0):
4 2 6 2 2
[
4] a) A. P. de Silva, H. Q. N. Gunaratne, T. Gunnlaugsson,
A. J. M. Huxley, C. P. McCoy, J. T. Rademacher, T. E. Rice,
Chem. Rev. 1997, 97, 1515–1566; b) J. N. Demas, B. A. De-
Graff, Coord. Chem. Rev. 2001, 211, 317–351; c) W. S. Tang,
X. X. Lu, K. M. C. Wong, V. W. W. Yam, J. Mater. Chem.
calcd. C 47.01, H 3.46, Cl 3.04, N 4.82, S 5.55; found C 47.50, H
+
3
.46, Cl 3.09, N 4.82, S 5.55. ESI-MS: m/z = 1037.09 [M – Cl] .
–1
IR: ν˜ 3431 (OH, br.) cm .
Ir(ppy) phen]Cl: [Ir(ppy) phen]Cl was synthesized by using the
procedure described by King (similar to Scheme 1).
reacting [Ir(ppy) Cl] with 1,10-phenanthroline in CH
ing the product using an ethanolic sephadex LH-20 column, recrys-
tallizing from CH Cl and toluene to yield 80% of orange pure
product. H NMR (300 MHz, CDCl ): δ = 6.41 (d, J = 7.5 Hz, 2
H), 6.93 (t, J = 6.6 Hz, 2 H), 6.99 (t, J = 7.5 Hz, 2 H), 7.10 (t, J =
.5 Hz, 2 H), 7.33 (d, J = 6.6 Hz, 2 H), 7.76 (m, 4 H), 7.94 (m, 4
H), 8.26 (d, J = 5.0 Hz, 2 H), 8.44 (s, 2 H), 8.97 (d, J = 8.2 Hz, 2
2005, 15, 2714–2720; d) Z. H. Lin, Y. G. Zhao, C. Y. Duan,
B. G. Zhang, Z. P. Bai, Dalton Trans. 2006, 3678–3684; e) R. P.
Brinas, T. Troxler, R. M. Hochstrasser, S. A. Vinogradov, J.
Am. Chem. Soc. 2005, 127, 11851–11862.
[
2
2
[23]
It involved
Cl , purify-
2
2
2
2
[
5] a) S. Zanarini, E. Rampazzo, S. Bonacchi, R. Juris, M. Mar-
caccio, M. Montalti, F. Paolucci, L. Prodi, J. Am. Chem. Soc.
2
2
2
009, 131, 14208–14209; b) J. L. Delaney, C. F. Hogan, J. Tian,
1
3
W. Shen, Anal. Chem. 2011, 83, 1300–1306.
[6] G. J. Barbante, C. F. Hogan, D. J. D. Wilson, N. A. Lewcenko,
F. M. Pfeffer, N. W. Barnett, P. S. Francis, Analyst 2011, 136,
7
1329–1338.
H) ppm. 13C NMR (300 MHz, CDCl
): δ = 119.46, 122.63, 123.08,
24.64, 126.56, 128.89, 130.67, 131.53, 131.66, 137.95, 139.29,
43.39, 146.40, 148.25, 149.32, 150.45, 167.69 ppm.
24ClIrN ·2.5H O (716.3 + 45.0): calcd. C 53.64, H 3.84, Cl
.65, N 7.36; found C 53.49, H 3.77, Cl 4.05, N 7.08. ESI-MS: m/z
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34
H
4
2
4
=
+
681.1 [M – Cl] .
Ir(ppy) dpp][PF ]: [Ir(ppy)
modified procedure from Bolink (Scheme 1). It involved reacting
Ir(ppy) Cl] with 4,7-diphenyl-1,10-phenanthroline in CH Cl be-
fore precipitating the product as a PF salt, which was purified
further using an ethanolic Sephadex LH-20 column, yielding 80%
[
2
6
2 6
dpp][PF ] was synthesized using a
[13]
2895.
[
2
2
2
2
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4824
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Received: June 23, 2011
Published Online: September 22, 2011
Eur. J. Inorg. Chem. 2011, 4816–4825
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
4825