Cationic, luminescent cyclometalated iridium(iii) complexes based on substituted 2-phenylthiazole ligands

Article abstract of DOI:10.1039/c4dt03054k

Ten cationic heteroleptic iridium(iii) complexes, [Ir(emptz)₂(N^N)](PF₆) were prepared from a cyclometalated iridium bridged-chloride dimer involving two ethyl-4-methylphenylthiazole-5-carboxylate (emptz) ligands. One X-ray crystallo

Full text of DOI:10.1039/c4dt03054k

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Cationic, luminescent cyclometalated iridium(III)
complexes based on substituted 2-phenylthiazole
ligands†
Cite this: DOI: 10.1039/c4dt03054k
Emily C. Stokes,a Emily E. Langdon-Jones,a Lara M. Groves,a James A. Platts,a
Peter N. Horton,b Ian A. Fallis,a Simon J. Colesb and Simon J. A. Pope*a
Ten cationic heteroleptic iridium(III) complexes, [Ir(emptz)2(N^N)](PF6) were prepared from a cyclometa-
lated iridium bridged-chloride dimer involving two ethyl-4-methylphenylthiazole-5-carboxylate (emptz)
ligands. One X-ray crystallographic study was undertaken where the ancillary N^N ligand was 4,7-diphenyl-
1,10-phenanthroline and revealed the anticipated structure, showing a distorted octahedral coordination
geometry at Ir(III). The complexes were visibly luminescent with modestly structured emission at
540–590 nm and lifetimes (60–340 ns) consistent with phosphorescence. TD-DFT calculations suggest
that strong MLCT character contributes to the visible absorption characteristics, whilst the moderately
structured emission profiles indicate a 3MLCT/3IL admixture of states to the phosphorescence.
Received 3rd October 2014,
Accepted 3rd December 2014
DOI: 10.1039/c4dt03054k
www.rsc.org/dalton
lengths of such complexes, especially towards white light emit-
ters, which are of great material value.8
Introduction
Cationic, cyclometalated luminescent Ir(III) (d6) complexes
The use of 2-phenylbenzothiazole type cyclometalating
offer great promise in the development of photoactive com- ligands has been well documented9 and has yielded a variety
ponents for a variety of applications.1 For example, their use in of important complexes for various applications. Despite yield-
light emitting electrochemical cells (LEECs) has been well ing complexes with attractive photophysical properties,
established.2 There are also interests in the use of such species simpler phenylthiazole ligands are less well known with
as photosensitisers for visible light driven photochemical Ir(III).10
transformations including photooxidation,3 and biological
We are particularly interested in the development of emis-
imaging via confocal fluorescence microscopy.4 Recent sive Ir(III) compounds with scope for further functionality,
advances in cationic Ir(III) complexes have also described having previously studied Ir(III) species with tunable emis-
piezochromic behaviour5 and potential application as respon- sion11 and water solubility12 achieved via peripheral groups on
sive materials for data recording.6 From a photophysical per- the cyclometalating ligands. This article describes the syn-
spective cyclometalated Ir(III) systems are very attractive due to thesis and characterisation of a range of luminescent Ir(III)
their predictable ease of synthesis and robust (photo)chemical complexes [Ir(C^N)2(N^N)](PF6) that incorporate a cyclometa-
nature. The scope for ligand variants is huge and a great deal lated 2-phenylthiazole ligand, that is substituted with both
of effort continues to be invested in understanding the nature ethyl ester and methyl groups, and incorporate a third ancil-
and interplay of excited states localised on the complex.7 This lary ligand based upon different diimine-type chelates
is particularly true when considering tuning emission wave- (Scheme 1).
aSchool of Chemistry, Main Building, Cardiff University, Cardiff CF10 3AT, UK.
Results and discussion
Synthesis and characterisation of the ligands and complexes
E-mail: popesj@cardiff.ac.uk; Fax: +44 (0)29-20874030; Tel: +44 (0)29-20879316
bUK National Crystallographic Service, Chemistry, Faculty of Natural and
Ethyl-4-methyl-phenylthiazole-5-carboxylate (emptzH) was syn-
thesised from the condensation of thiobenzamide and ethyl
4-chloroacetoacetate in ethanol. For the diimine ligands,
edppz13 and piphen14 were synthesised according to variations
on the literature methods. New ligand edmdppz was syn-
thesised in an analogous manner to edppz, but using
Environmental Sciences, University of Southampton, Highfield, Southampton, SO17
1BJ England, UK
†Electronic supplementary information (ESI) available: Data collection para-
meters for both crystallographic studies, pictorial representations of the calcu-
lated frontier orbitals for [Ir(emptz)2(phen)]+, examples of cyclic voltammograms
and experimental data for the ligands. CCDC 1025666. For ESI and crystallo-
graphic data in CIF or other electronic format see DOI: 10.1039/c4dt03054k
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t-butyl)-phenylpyridylimidazo[4,5-f][1,10]phenanthroline (bpiphen),
gave ten new monometallic cationic complexes of the general
form [Ir(emptz)2(N^N)](PF6). This range of diimine ligands
(Scheme 1) was selected to study the potential influence on the
electronic properties of the complexes as well as provide
opportunities for further chemistry. For example, piphen,
ppiphen and bpiphen all possess an additional pyridine
coordination site, which could be utilised for further reactivity
towards larger-form multi-metallic luminescent architectures.
All new complexes were characterised using a range of
spectroscopic techniques. The 1H NMR spectra of the com-
plexes show aromatic regions with overlapping resonances
associated with the cyclometalated emptz and diimine ligands.
In three examples, additional resonances were noted in the ali-
phatic region and attributed to transesterification with
2-methoxyethanol. Such an observation has been noted before12
and is attributed to the reaction conditions and solvent utilised
for the complexation: the 2-methoxyethyl groups of [Ir(emptz)2-
(edppz)](PF6), [Ir(emptz)2(piphen)](PF6) and [Ir(emptz)2-
(ppiphen)](PF6) appeared as broadened triplets around 4.5 and
3.7 ppm together with a singlet ca. 3.3 ppm.
Both low and high resolution mass spectra were obtained
for the complexes revealing the parent cations of [M − PF6]+,
with the appropriate isotopic distribution for each case. Solid-
state IR spectra were also obtained on all complexes highlight-
ing the ester functionality (ca. 1720 cm−1) and the hexafluoro-
phosphate counter anion (ca. 835 cm−1).
Scheme 1 Ligands used in this study.
2,9-dimethyl-1,10-phenanthroline-5,6-dione as the precursor.
New ligands ppiphen and bpiphen were both synthesised from
1,10-phenanthroline-5,6-dione using a one-pot method and
isolated in moderate yield.
X-ray crystallography studies
The monometallic mixed ligand iridium complexes were
synthesised utilising the well-established method15 of firstly
isolating the dichloro-bridged dimer species followed by sub-
sequent addition of the ancillary ligand. Thus, reaction of
dimeric 1 (Scheme 2), isolated from the reaction of IrCl3·xH2O
and emptzH, and different diimines (N^N), namely 2,2′-bipyri-
dine (bpy), 4,4′-dimethyl-2,2′-bipyridine (dmbpy), 1,10-phen-
throline (phen), 2,9-dimethyl-1,10-phenathroline (dmphen),
4,7-diphenyl-1,10-phenanthroline (dpphen), ethyl-dipyrido[3,2-
a:2′,3′-c]phenazine-11-carboxylate (edppz), ethyl-3,6-dimethyl-
Single crystals of [Ir(emptz)2(dpphen)](PF6) were isolated from
vapour diffusion of Et2O into a concentrated CHCl3 solution of
the complex over a period of 48 h at −20 °C, and found to be
suitable for X-ray diffraction studies. The bond lengths and
bond angles for [Ir(emptz)2(dpphen)](PF6) are reported in
Table 1, and the associated data collection parameters are
reported in Table S1, ESI.†
The structure (Fig. 1) confirmed the proposed formulation,
and showed that the Ir(III) ion in this complex adopts a dis-
torted octahedral coordination geometry. The bond lengths
are typical of this complex type.11 The trans angles at the metal
ion range from 168.0(3)° to 175.2(3)° for [Ir(emptz)2(dpphen)]+.
As expected the diimine ligand was coordinated trans to the
cyclometalated phenyl rings and the complex retains the cis-C,
C and trans-N,N chelating arrangement of the original chloro-
bridged dimer. The Ir–N bond lengths for the diimine ligand
are longer than the emptz ligands. The structure of
[Ir(emptz)2(dpphen)]+ also revealed that the phenyl substitu-
ents of the dpphen ligand were twisted out of planarity from
the phenanthroline unit by ca. 56°.
dipyrido[3,2-a:2′,3′-c]phenazine-11-carboxylate
(edmdppz),
pyridylimidazo[4,5-f][1,10]phenanthroline (piphen), 1-phenyl
pyridylimidazo[4,5-f][1,10]phenanthroline (ppiphen) and 1-(4-
Density functional theory (DFT) studies
DFT calculations (computed using the B3LYP hybrid func-
tional) were performed to investigate the electronic absorption
bands of [Ir(emptz)2(phen)]+ and the orbitals involved in
these. The crystal structure illustrated in Fig. 1 was truncated
by replacement of phen-based Ph groups with H, and the
Scheme 2 Synthesis of the complexes.
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Table 1 Selected bond lengths (Å) and angles (°) for [Ir(emptz)2(dpphen)](PF6)
Bond length (Å)/angle (°)
Ir(1)–N(1)
2.074(6)
2.064(6)
2.147(6)
2.145(6)
2.033(7)
2.031(8)
2.055(7)
2.087(6)
2.149(6)
2.146(6)
2.016(8)
2.025(7)
C(21)–Ir(1)–C(1)
C(21)–Ir(1)–N(21)
C(1)–Ir(1)–N(21)
C(21)–Ir(1)–N(1)
C(1)–Ir(1)–N(1)
N(21)–Ir(1)–N(1)
C(21)–Ir(1)–N(42)
C(1)–Ir(1)–N(42)
N(21)–Ir(1)–N(42)
N(1)–Ir(1)–N(42)
C(21)–Ir(1)–N(41)
C(1)–Ir(1)–N(41)
N(21)–Ir(1)–N(41)
N(1)–Ir(1)–N(41)
N(42)–Ir(1)–N(41)
C(21)–Ir(1)–C(1)
90.6(3)
79.8(3)
91.8(3)
92.7(3)
80.0(3)
168.9(2)
170.1(3)
99.3(3)
100.0(2)
88.7(2)
93.0(3)
175.2(3)
85.8(2)
102.9(2)
77.1(2)
90.6(3)
C(101)–Ir(2)–C(121)
C(101)–Ir(2)–N(101)
C(121)–Ir(2)–N(101)
C(101)–Ir(2)–N(121)
C(121)–Ir(2)–N(121)
N(101)–Ir(2)–N(121)
C(101)–Ir(2)–N(142)
C(121)–Ir(2)–N(142)
N(101)–Ir(2)–N(142)
N(121)–Ir(2)–N(142)
C(101)–Ir(2)–N(141)
C(121)–Ir(2)–N(141)
N(101)–Ir(2)–N(141)
N(121)–Ir(2)–N(141)
N(142)–Ir(2)–N(141)
C(101)–Ir(2)–C(121)
91.9(3)
80.6(3)
91.5(3)
91.0(3)
80.1(3)
168.0(3)
94.0(3)
173.1(3)
85.9(3)
103.3(2)
170.7(3)
97.3(3)
100.3(3)
89.4(2)
76.9(2)
91.9(3)
Ir(1)–N(21)
Ir(1)–N(41)
Ir(1)–N(42)
Ir(1)–C(1)
Ir(1)–C(21)
Ir(2)–N(101)
Ir(2)–N(121)
Ir(2)–N(141)
Ir(2)–N(142)
Ir(2)–C(101)
Ir(2)–C(121)
strong MLCT character, but in this case the ligand in question
is the phenylthiazole. The more typical excitation of a 5d elec-
tron into the π* MO on phen (which is the LUMO here) is poss-
ible, but is either weak (450 nm) or high energy (371 nm).
Fig. S1 (ESI†) shows the diagrammatical representation of the
calculated HOMO−1, HOMO and LUMO. The calculated
HOMO–LUMO energy gap of 3.43 eV compared closely to that
reported (3.32 eV) for [Ir(ppy)2(bpy)]+ (where ppy = 2-phenyl-
pyridine).1a
Electrochemical studies
The electrochemical characteristics of the [Ir(emptz)2(N^N)]-
(PF6) complexes were studied in de-oxygenated CH2Cl2. The
cyclic voltammograms, measured at a platinum disc electrode
(scan rate ν = 200 mV s−1, 1 × 10−3 M solutions, 0.1 M [NBu4]-
[PF6] as a supporting electrolyte), each (for example, Fig. S2
and S3 in the ESI†) generally showed one non-fully reversible
oxidation around +1.55 V, which was assigned to the Ir3+/4+
couple. The comparative potential for [Ir(ppy)3] is +1.0
V/NHE.16 Related cationic complexes, recorded under identical
conditions, that incorporate cyclometalated cinchophen-type
ligands12 for example [Ir(epqc)2(bpy)](PF6) (where epqc = ethyl-
2-phenylquinoline-4-carboxylate), possess an Ir3+/4+ couple around
+1.40 V. Therefore these results clearly suggest that the Ir(III)
ion is relatively stabilised in the emptz variants versus epqc.
The complexes also showed fully reversible (for the bpy, phen,
dpphen, ppiphen, edmdppz) or quasi-reversible (dmbpy,
dmphen, piphen, edppz, bpiphen) reduction waves. The
Fig. 1 Structural representation of [Ir(emptz)2(dpphen)]+. Just one of
the crystallographically different moieties is shown with the solvent
molecules, PF6− anion and hydrogen atoms omitted for clarity.
resulting cation’s structure optimized. Absorption bands at
this optimal geometry were then calculated using scalar relati-
vistic TD-DFT in a simulated acetonitrile environment and are
reported in Table 2. These data predict the lowest energy band
at 450 nm to be very weak, but that a stronger band exists at
444 nm. This band is dominated by excitation of an electron
from the HOMO to LUMO+1: analysis of MO coefficients indi-
cates that the HOMO has significant 5d character (23.5%),
while LUMO+1 is almost exclusively located on the thiazole
rings (1.7% 5d character). Thus, we assign this band as having
Table 2 Calculated absorption wavelengths for [Ir(emptz)2(phen)]+ from TD-DFT studies
λa (nm)
fb
Character
λ (nm)
f
Character
450
444
435
405
371
367
0.0002
0.159
0.0001
0.0469
0.0584
0.0116
HOMO → LUMO
365
355
348
345
344
339
0.1135
0.0003
0.0541
0.0367
0.0385
0.0151
HOMO−1 → LUMO+2
HOMO−2 → LUMO+1
HOMO−2 → LUMO+2
HOMO−2 → LUMO+3
HOMO−1 → LUMO+3
HOMO−4 → LUMO
HOMO → LUMO+1
HOMO → LUMO+2
HOMO → LUMO+3
HOMO−1 → LUMO
HOMO−1 → LUMO+1
a Absorption wavelength. b Oscillator strength.
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former were assigned to ligand-centred processes involving the conjugation of the fused chromophore. Slightly weaker bands
diimine whilst the latter may include contributions from the (ε ∼ 7000 M−1 cm−1) at 400–475 nm were assigned to spin-
phenylthiazole ligands. The cyclic voltammetry of [Ir- allowed metal-to-ligand charge transfer bands (1MLCT). These
(ppy)2(bpy)]+ has been reported to show quasi-reversible waves correlate remarkably well with the absorption band at 444 nm
(in acetonitrile versus SCE) at +1.32 and −1.40 V,17 the former calculated using TD-DFT, and thus lend support to the theore-
attributed to the Ir3+/4+ couple.18
tical methodology used. For complexes of the dppz derivatives
and arylimidazo[4,5-f][1,10]phenanthroline-type ligands, n–π*
transitions should also be present, albeit at lower molar
absorption coefficients that may preclude their observation.
The coordinated N^N ligand imparts little influence on the
energy of the 1MLCT transition, an observation that may be
explained by the TD-DFT prediction that the absorption
ca. 445 nm predominantly involves the phenylthiazole, rather
than the N^N ligand.
Electronic properties: UV-vis and luminescence data
The UV-vis absorption spectra of the complexes were recorded
as aerated MeCN solutions (10−5 M) (Fig. 2, Table 3). Strong
absorption bands between 200 and 400 nm were assigned to
the various spin allowed 1π–π* ligand-centred transitions
arising from both the cyclometalated and diimine ligands of
the complexes. Both dppz-derived species show additional
bands at 370 and 390 nm, which are attributed to the extended
For [Ir(emptz)(phen)](PF6), the collected absorption and
electrochemical data for this complex were utilised to deter-
mine EHOMO = −5.87 eV, ELUMO = −3.31 eV (where −EHOMO
=
Eox − EFc/Fc+ + 4.8) and Ebandgap = 2.56 eV. The DFT calculated
values for EHOMO and ELUMO were −6.06 eV and −2.63 eV
respectively, with a resultant calculated Ebandgap of 3.43 eV,
suggesting that DFT overestimates the level of the LUMO; a
similar observation has been noted previously for
[Ir(ppy)2(bpy)]+.1a
The room temperature solution state emission spectra
(Table 3) for all of the complexes showed visible luminescence
around 550 nm with a low energy shoulder at ca. 586 nm (for
comparison [Ir(ppy)bpy)]+ emits at 602 nm in MeCN from a
3
mixed LLCT/3MLCT excited state).1a These results are also in
line with [Ir(C^N)2(bpy)](PF6) (where C^N = 4-methyl-2-phe-
nylthiazole) which has a reported emission at 584 nm and has
been successfully utilised as a photosensitiser for hydrogen
generation from water.10b Importantly, the emission character-
istics are retained across the entire range of different functio-
Fig. 2 UV-vis spectra for [Ir(emptz)2(N^N)]PF6 complexes in MeCN
solutions (10−5 M).
Table 3 Photophysical and redox properties of the [Ir(emptz)2(N^N)]PF6 complexes
Complex
Ea/V
λabs b/nm
λem b,c/nm
λem c/nm (77 K)
τ
b,d/ns
ϕb
[Ir(emptz)2(bpy)]PF6
+1.56, −1.33
+1.51, −1.43
+1.53, −1.35
+1.59, −1.46
+1.53, −1.30
+1.54, −1.29
+1.67, −0.81
+1.57, −1.16
+1.53, −1.30
+1.58, −1.30
269 (26 000), 305 (35 200),
370 (7000), 442 (6700)
267 (26 200), 305 (34 400),
369 (8000), 446 (7000)
272 (47 700), 297 (35 100),
317 (29 200), 368 (9400), 439 (7400)
283 (35 100), 369 (9400), 435 (5700)
549, 586 sh
549, 588 sh
549, 586 sh
554, 593 sh
549, 587 sh
550, 594 sh
557, 595 sh
549, 586 sh
550, 587 sh
548, 586 sh
538, 558, 582, 604 sh,
634, 656 sh
540, 559, 583, 606 sh,
635, 659 sh
541, 559, 586, 608 sh,
633 sh, 658 sh
545, 564, 590, 614 sh,
642 sh
538, 558, 582, 601, 631,
658 sh
539, 556, 582, 604 sh,
632, 659 sh
282
260
270
308
269
60
0.014
0.012
0.012
0.011
0.015
0.0003
0.002
0.012
0.015
0.012
[Ir(emptz)2(dmbpy)]PF6
[Ir(emptz)2(phen)]PF6
[Ir(emptz)2(dmphen)]PF6
[Ir(emptz)2(dpphen)]PF6
[Ir(emptz)2(edppz)]PF6
[Ir(emptz)2(edmdppz)]PF6
[Ir(emptz)2(piphen)]PF6
[Ir(emptz)2(ppiphen)]PF6
[Ir(emptz)2(bpiphen)]PF6
289 (53 800), 368 (13 500), 435 (8100)
282 (10 100), 367 (21 800),
389 (17 800), 437 (8800)
283 (93 900), 369 (21 600),
388 (18 200), 436 (7600)
280 (67 000), 318 (47 300),
367 (14 500), 435 (9300)
282 (66 700), 371 (11 900),
397 (9000), 439 (8600)
559, 601, 659
184
257
340
286
542, 558, 584, 606 sh,
632 sh, 658 sh
538, 558, 582, 603,
631, 659 sh
537, 558, 581, 604 sh,
632, 657 sh
282 (71 200), 371 (12 100),
398 (9200), 440 (8600)
a Potentials measured in CH2Cl2 solutions at 200 mV s−1 with 0.1 M [NBu4][PF6] as supporting electrolyte calibrated with Fc/Fc+. b MeCN, room
temperature solution. c λex = 380 nm. d λex = 372 nm.
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nalised diimine ligands, with minor variations in λem observed measurements (Fig. 4) showed that the triplet states of the free
according to ligand type. The emission lifetimes were obtained dppz ligands must lie in close proximity to the emitting state
in aerated solvent and were typically in the range 180–340 ns, of the complexes, which has been noted in studies using Re(I)
which is consistent with an emitting state of triplet character. complexes.20 Barton has previously reported the related
The quantum yields were obtained using aerated MeCN solu- complex [Ir(ppy)2(edppz)]Cl to be non-emissive in MeCN,
tions and were typically between 1–2%. This is comparable to although [Ir(ppy)2(dppz)]Cl emits at 634 nm, which is clearly a
the cationic cinchophen Ir(III) complexes described in related lower energy than the emptz species described here.13 There-
studies.12 The quantum yield for [Ir(ppy)2(bpy)](PF6) is higher fore it is likely that in MeCN at room temperature quenching
at ca. 9% but was obtained using degassed MeCN.19
pathways via dppz-localised excited states are operable in these
Low temperature emission spectra of each complex were two complexes.
also obtained on MeOH–EtOH (1 : 1) glasses and revealed a
highly structured emission profile. When compared to the
room temperature measurements (Fig. 3) it is clear that the
Experimental section
spectra share key features. The vibronically structured spectra
suggest a significant ligand-centred triplet component (attrib-
uted to the phenylthiazole ligand) to the emitting state at 77 K,
which also contributes at room temperature.
The comparative room temperature data for the dppz-type
complexes [Ir(emptz)2(edppz)]PF6 and [Ir(emptz)2(edmdppz)]-
PF6 revealed shorter lifetimes (60 and 184 ns) and lower
quantum yields (<0.002%) which were indicative of quenching
processes. Further investigation using low temperature
All reactions were performed with the use of vacuum line and
Schlenk techniques. Reagents were commercial grade and
used without further purification. 1H and 13C-{1H} NMR
spectra were recorded on an NMR-FT Bruker 400 or 250 MHz
and 31P-{1H} NMR spectra on a Joel Eclipse 300 MHz spectro-
meter and recorded in CDCl3 or MeOD solutions. H and 13C-
1
{1H} NMR chemical shifts (δ) were determined relative to
internal tetramethylsilane, Si(CH3)4 and are given in ppm.
Low-resolution mass spectra (LRMS) were obtained by the staff
at Cardiff University. High-resolution mass spectra (HRMS)
were carried out at the EPSRC National Mass Spectrometry
Service at Swansea University, UK. UV-Vis studies were per-
formed on a Jasco V-650 spectrophotometer fitted with a Jasco
temperature control unit in MeCN or MeOH solutions (10−5
M) at 20 °C. Photophysical data were obtained on a Jobin-
Yvon–Horiba Fluorolog spectrometer fitted with a JY TBX pico-
seconds photodetection module in MeCN, MeOH or H2O
solutions. Emission spectra were uncorrected and excitation
spectra were instrument corrected. The pulsed source was a
Nano-LED configured for 372 or 459 nm output operating at
500 kHz. Luminescence lifetime profiles were obtained using
the JobinYvon–Horiba FluoroHub single photon counting
module and the data fits yielded the lifetime values using the
provided DAS6 deconvolution software. Electrochemical
studies were carried out using a Parstat 2273 potentiostat in
conjunction with a three-electrode cell. The auxiliary electrode
was a platinum wire and the working electrode a platinum
(1.0 mm diameter) disc. The reference was a silver wire separ-
ated from the test solution by a fine porosity frit and an agar
bridge saturated with KCl. Solutions (10 ml CH2Cl2) were 1.0 ×
10−3 mol dm−3 in the test compound and 0.1 mol dm−3 in
[NBu4][PF6] as the supporting electrolyte. Under these con-
ditions, E0, for the one-electron oxidation of [Fe(η-C5H5)2]
added to the test solutions as an internal calibrant, is +0.46 V
in CH2Cl2.21 Unless specified, all electrochemical values are at
Fig. 3 Normalised emission spectra of [Ir(emptz)2(dpphen)]PF6
obtained at 293 K (MeCN) and 77 K (EtOH–MeOH glass).
ν = 200 mV s−1
.
Crystallography
Suitable crystals were selected and measured following a stan-
dard method22 on a Rigaku AFC12 goniometer equipped with
an enhanced sensitivity (HG) Saturn724+detector mounted at
the window of a FR-E+SuperBright molybdenum rotating
Fig. 4 Normalised 77 K emission spectra of [Ir(emptz)2(edppz)]PF6 and
[Ir(emptz)2(edmdppz)]PF6 and corresponding free ligands.
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anode generator with VHF Varimax optics (70 µm focus) at (ca. 3 mL), precipitated by the slow addition of Et2O and dried
1
100 K. Cell determination, data collection, reduction, cell in vacuo. Yield: 0.145 g, 64%. H NMR (400 MHz, CDCl3): δH
=
refinement and absorption correction were carried out using 9.33 (2H, d, 3JHH = 8.2 Hz), 8.85 (2H, app. dt, JHH = 7.9, 1.4 Hz),
CrystalClear-SM Expert 3.1b27.23 Structures were solved using 8.56 (2H, app. dd, JHH = 1.0, 5.6 Hz), 8.38 (2H, dd, JHH = 0.9,
SUPERFLIP24 and refined using SHELXL-2013.25
7.7 Hz), 8.18–8.14 (2H, m), 7.76 (2H, app. dt, JHH = 0.9, 17.4
For ([Ir(emptz)2(dpphen)](PF6) there is a molecule of ether Hz), 7.66 (2H, app. dt, JHH = 7.6, 1.3 Hz), 7.10 (2H, d, 3JHH = 7.5
3
disordered over the inversion centre, along with a disordered Hz), 4.98 (4H, q, JHH = 7.1 Hz, OCH2CH3), 2.49 (6H, s, CCH3),
3
ethoxy group. As such, various geometrical and displacement 2.00 (6H, t, JHH = 7.1 Hz, OCH2CH3) ppm. UV-Vis (CH3CN):
restraints and constraints were employed.
λmax/nm (ε/M−1 cm−1) = 442 (6700), 370 (7000), 305 (35 200),
CCDC reference number 1025666 [Ir(emptz)2(dpphen)]PF6, 269 (26 000). LRMS (ES+) found m/z 841.00; calculated 841.01
contains the supplementary crystallographic data for this for [M − PF6]+. HRMS (ES+) found m/z 841.1478; calculated
paper.
841.1487 for [C36H32N4O4S2Ir]+. IR (solid): ν 1719 (CvO), 1256,
1244 (C–O), 835 (PF6−) cm−1
.
DFT studies
[Ir(emptz)2(dmbpy)]PF6
DFT geometry optimisation and orbital calculations were per-
formed on the Gaussian09 program.26 Geometry optimisations As for [Ir(emptz)2(bpy)]PF6, but using 1 (0.080 g, 0.06 mmol)
were carried out without constraints using the B3LYP func- and 4,4′-dimethyl-2,2′-bipyridine (0.026 g, 0.14 mmol). The
tional. The Stuttgart-Dresden27 basis set and effective core crude product was purified by column chromatography (silica,
potential was used for Ir centre, along with 6-31G(d)28 basis set CH2Cl2). After elution of unreacted organics with CH2Cl2 the
for all remaining atoms. TD-DFT studies were performed in product was eluted as the only orange fraction with CH2Cl2–
1
Gaussian0929 using the same functional, but with 6-31+G(d,p) MeOH (9 : 1). Yield: 0.039 g, 35%. H NMR (400 MHz, CDCl3):
3
on all non-metal atoms, and also included a simulated MeCN δH = 8.55 (2H, s), 7.64 (2H, app. d, JHH = 7.2 Hz), 7.59 (2H, d,
3
environment using the polarised continuum model (PCM) 3JHH = 5.6 Hz), 7.12 (2H, d, JHH = 5.4 Hz), 7.04–7.00 (2H, m),
approach.30
6.93–6.89 (2H, m), 6.36 (2H, d, 3JHH = 7.6 Hz), 4.26 (4H, q, 3JHH
= 7.1 Hz, OCH2CH3), 2.57 (6H, s, CH3), 1.79 (6H, s, CH3), 1.28
Synthesis
3
(6H, t, JHH = 7.1 Hz, OCH2CH3) ppm. UV-Vis (CH3CN): λmax
/
Ethyl-4-methyl-2-phenylthiazole-5-carboxylate
(emptzH),31 nm (ε/M−1 cm−1) = 446 (7000), 369 (8000), 305 (34 400), 267
1,10-phenanthroline-5,6-dione,32
2,9-dimethyl-1,10-phen- (26 200). LRMS (ES+) found m/z 869.24; calculated 869.08 for
anthroline-5,6-dione,33 ethyl-3,4-diaminobenzoate,34 ethyl- [M − PF6]+. HRMS (ES+) found m/z 869.1795; calculated
dipyrido[3,2-a:2′,3′-c]phenazine-11-carboxylate (edppz),35 pyri- 869.1801 for [C38H36N4O4S2Ir]+. IR (solid): ν 1716 (CvO), 1253,
dylimidazo[4,5-f][1,10]phenanthroline (piphen),14 were syn- 1242 (C–O), 824 (PF6−) cm−1
.
thesised according to the literature methods or subtle
variations thereupon.
[Ir(emptz)2(phen)]PF6
[Ir(emptz)2(µ-Cl)2Ir(emptz)2] 1 was prepared via a variation As for [Ir(emptz)2(bpy)]PF6, but using 1 (0.049 g, 0.03 mmol)
of the standard literature procedures for chloro-bridged and 1,10-phenanthroline (0.014 g, 0.08 mmol). The crude
dimers: IrCl3·xH2O (0.214 g, 0.15 mmol) was dissolved in product was purified by column chromatography (silica,
2-methoxyethanol (6 mL) and water (2 mL), emptzH (0.353 g, CH2Cl2). After elution of unreacted organics with CH2Cl2 the
1.43 mmol) was added and the solution stirred at 120 °C for product was eluted as the only orange fraction with CH2Cl2–
1
48 h. Water (approx. 20 mL) was added to give a bright orange MeOH (9 : 1). Yield: 0.035 g, 51%. H NMR (400 MHz, CDCl3):
precipitate. The product was used in subsequent reactions δH = 8.68 (2H, app. dd, JHH = 8.3, 1.3 Hz), 8.18 (2H, s), 8.15
without further purification. Yield: 0.481 g, 94%.
(2H, app. dd, JHH = 5.1, 1.3 Hz), 7.83 (2H, app. dd, JHH = 8.2,
5.1 Hz), 7.71 (2H, app. dd, JHH = 7.7, 0.9 Hz), 7.12–7.07 (2H,
[Ir(emptz)2(bpy)]PF6
3
m), 7.00–6.96 (2H, m), 6.48 (2H, d, JHH = 7.5 Hz), 4.19 (4H, q,
3
1
(0.165 g, 0.11 mmol) and 2,2′-bipyridine (0.046 g, 3JHH = 7.1 Hz, OCH2CH3), 1.48 (6H, s, CH3), 1.14 (6H, t, JHH
=
0.29 mmol) in 2-methoxyethanol (5 mL) were heated at 120 °C 7.0 Hz, OCH2CH3) ppm. UV-Vis (CH3CN): λmax/nm (ε/M−1
for 16 h. The solvent was then removed in vacuo and the crude cm−1) = 439 (7400), 368 (9400), 317 (29 200), 297 (35 100), 272
product dissolved in MeCN (4 mL). KPF6 (1 g, 5.43 mmol) in (47 700), 229 (52 400). LRMS (ES+) found m/z 865.15; calculated
water (2 mL) was added and the solution stirred for approx. 865.05 for [M − PF6]+. HRMS (ES+) found m/z 865.1482; calcu-
10 min. Water (approx. 20 mL) was added and the product lated 865.1488 for [C38H32N4O4S2Ir]+. IR (solid): ν 1719 (CvO),
extracted with CH2Cl2 (2 × 20 mL). The combined organic 1256, 1244 (C–O) 833 (PF6−) cm−1
.
phases were washed with water and dried over MgSO4. The
solution was filtered and the solvent removed in vacuo. The
[Ir(emptz)2(dmphen)]PF6
crude product was then purified by column chromatography As for [Ir(emptz)2(bpy)]PF6, but using 1 (0.080 g, 0.06 mmol)
(silica, CH2Cl2). After elution of unreacted organics with and 2,9-dimethyl-1,10-phenanthroline (0.036 g, 0.17 mmol).
CH2Cl2 the product was eluted as the only orange fraction with The crude product was purified by column chromatography
CH2Cl2–MeOH (9 : 1). The product was concentrated in volume (silica, CH2Cl2). After elution of unreacted organics with
Dalton Trans.
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1
CH2Cl2 the product was eluted as the only orange fraction with 30%. H NMR (400 MHz, CDCl3): δH = 9.78 (2H, dd, JHH = 8.3,
1
CH2Cl2–MeOH (9 : 1). Yield: 0.053 g, 46%. H NMR (400 MHz, 6.5 Hz), 9.06 (1H, s), 8.51 (1H, dd, JHH = 9.0, 1.8 Hz), 8.41 (1H,
3
3
CDCl3): δH = 8.49 (2H, d, JHH = 8.3 Hz), 8.01 (2H, s), 7.58 (2H, d, JHH = 9.0 Hz), 7.86 (2H, dd, JHH = 8.4, 3.8 Hz), 7.56 (2H, d,
d, JHH = 8.9 Hz), 7.54 (2H, d, JHH = 6.9 Hz), 6.39 (2H, app. t, 3JHH = 7.7 Hz), 6.97–6.93 (2H, m), 6.84–6.81 (2H, m), 6.21 (2H,
3
3
3JHH = 7.2 Hz), 6.80 (2H, app. dt, JHH = 7.5, 1.1 Hz), 6.18 (2H, d, d, JHH = 7.8 Hz), 4.47 (2H, q, JHH = 7.1 Hz, OCH2CH3), 4.19
3
3
3JHH = 7.7 Hz), 4.23 (4H, q, 3JHH = 7.1 Hz, OCH2CH3), 2.08 (6H, (4H, q, 3JHH = 7.1 Hz, OCH2CH3), 2.14 (6H, s, CH3), 1.72 (6H, s,
s, CH3), 1.50 (6H, s, CH3), 1.14 (6H, t, 3JHH = 7.0 Hz, OCH2CH3) CH3), 1.45 (3H, t, JHH = 7.1 Hz, OCH2CH3), 1.20 (3H, t, JHH
=
3
3
ppm. UV-Vis (CH3CN): λmax/nm (ε/M−1 cm−1) = 435 (5700), 369 7.9 Hz, OCH2CH3) ppm. UV-Vis (CH3CN): λmax/nm (ε/M−1
(9400), 283 (35 100), 228 (53 800). LRMS (ES+) found m/z cm−1) = 436 (7600), 388 (18 200), 369 (21 600), 283 (93 900).
893.22; calculated 893.10 for [M − PF6]+. HRMS (ES+) found m/ LRMS (ES+) found m/z 1067.23; calculated 1067.26 for [M −
z 893.1797; calculated 893.1801 for [C40H36N4O4S2Ir]+. IR PF6]+. HRMS (ES+) found m/z 1067.2215; calculated 1067.2231
(solid): ν 1717 (CvO), 1093 (C–O), 837 (PF6−) cm−1
.
for [C49H42N6S2O6Ir]+. IR (solid): ν 1713 (CvO), 1257, 1244
(C–O), 829 (PF6−) cm−1
.
[Ir(emptz)2(dpphen)]PF6
[Ir(emptz)2(piphen)]PF6
As for [Ir(emptz)2(bpy)]PF6, but using 1 (0.080 g, 0.06 mmol)
and 4,7-diphenyl-1,10-phenanthroline (0.041 g, 0.12 mmol) As for [Ir(emptz)2(bpy)]PF6, but using 1 (0.051 g, 0.04 mmol)
The crude product was purified by column chromatography and piphen (0.026 g, 0.09 mmol). The crude product was puri-
(silica, CH2Cl2). After elution of unreacted organics with fied by column chromatography (silica, CH2Cl2). After elution
CH2Cl2 the product was eluted as the only orange fraction with of unreacted organics with CH2Cl2 the product was eluted as
1
CH2Cl2–MeOH (9 : 1). Yield: 0.084 g, 65%. H NMR (400 MHz, the first yellow fraction with CH2Cl2–MeOH (99 : 1). Yield:
3
CDCl3): δH = 8.22 (2H, d, JHH = 5.3 Hz), 8.12 (2H, s), 7.75–7.71 0.034 g, 41%. 1H NMR (400 MHz, CDCl3): δH = 9.14 (2H, app. t,
(4H, m), 7.55–7.50 (10H, m), 7.12–7.08 (2H, m), 7.02–6.98 (2H, 3JHH = 7.9 Hz), 8.90–8.74 (2H, br. s), 8.26–8.22 (4H, m),
3
3
3
m), 6.51 (2H, d, JHH = 7.6 Hz), 4.22 (4H, q, JHH = 7.1 Hz, 8.03–8.00 (1H, m), 7.96–7.92 (1H, m), 7.72 (2H, d, JHH = 7.5
3
3
3
OCH2CH3), 1.66 (6H, s, CH3), 1.25 (6H, t, JHH = 7.1 Hz, Hz,), 7.10 (2H, app. t, JHH = 7.4 Hz), 7.00 (2H, app. t, JHH
=
OCH2CH3) ppm. UV-Vis (CH3CN): λmax/nm (ε/M−1 cm−1) = 435 7.5 Hz), 6.47 (2H, t, JHH = 6.9 Hz), 4.17 (4H, q, JHH = 7.1 Hz,
(8100), 368 (13 500), 289 (53 800). LRMS (ES+) found m/z OCH2CH2OCH3), 3.53–3.49 (4H, m, OCH2CH2OCH3), 3.32 (6H,
1017.30; calculated 1017.25 for [M − PF6]+. HRMS (ES+) found s, OCH3), 1.51 (6H, s, CH3) ppm. LRMS (ES+) found m/z
m/z 1017.2111; calculated 1017.2115 for [C50H40N4O4S2Ir]+. IR 1043.20; calculated 1042.21 for [M − PF6−]. HRMS (ES+) found
3
3
(solid): ν 1707 (CvO), 1258, 1246 (C–O), 835 (PF6−) cm−1
.
m/z 1043.1833; calculated 1043.2105 for [C46H40N7O6S2Ir]+. IR
(solid): ν 1716 (CvO), 1256, 1230 (C–O), 837 (PF6−) cm−1
.
[Ir(emptz)2(edppz)]PF6
[Ir(emptz)2(ppiphen)]PF6
As for [Ir(emptz)2(bpy)]PF6, but using 1 (0.052 g, 0.04 mmol)
and edppz (0.029 g, 0.08 mmol). The crude product was puri- As for [Ir(emptz)2(bpy)]PF6, but using 1 (0.060 g, 0.04 mmol)
fied by column chromatography (silica, CH2Cl2). After elution and ppiphen (0.029 g, 0.08 mmol). The crude product was pur-
of unreacted organics with CH2Cl2 the product was eluted as ified by column chromatography (silica, CH2Cl2). After elution
the third orange fraction with CH2Cl2–MeOH (99 : 1). Yield: of unreacted organics with CH2Cl2 the product was eluted as
1
0.018 g, 20%. H NMR (250 MHz, CDCl3): δH = 9.84–9.80 (2H, the third orange fraction with CH2Cl2–MeOH (9 : 1). Yield:
3
1
m), 9.07 (1H, app. d, JHH = 1.2 Hz), 8.51–8.50 (1H, m), 8.45 0.021 g, 20%. H NMR (400 MHz, CDCl3): δH = 9.29–9.28 (1H,
3
3
(1H, d, JHH = 9.0 Hz), 8.28 (2H, d, JHH = 5.1 Hz), 8.05–8.00 m), 8.54 (2H, app. dd, JHH = 4.6, 1.6 Hz), 7.71 (2H, dd, JHH
=
3
(2H, m), 7.75–7.72 (2H, m), 7.14–7.00 (4H, m), 6.49 (2H, d, 7.6, 2.0 Hz), 7.68 (1H, d, JHH = 1.1 Hz), 7.65–7.63 (9H, m),
3JHH = 7.6 Hz), 4.45 (2H, q, 3JHH = 7.1 Hz, OCH2CH3), 4.27–4.24 7.44–7.43 (2H, m), 7.08 (2H, d, JHH = 7.7 Hz), 6.98–6.97 (2H,
3
3
(4H, m, OCH2CH2OCH3), 3.54–3.50 (4H, m, OCH2CH2OCH3), d, JHH = 7.5 Hz), 6.49–6.41 (2H, m), 4.27–4.26 (4H, m, OCH2-
3.24 (6H, s, OCH3), 1.64 (6H, s, CH3) 1.44 (3H, t, JHH = 7.1 Hz, CH2OCH3), 3.55–3.53 (4H, m, OCH2CH2OCH3), 3.27 (6H, s,
3
OCH2CH3) ppm. UV-Vis (CH3CN): λmax/nm (ε/M−1 cm−1) = 437 OCH3), 1.53 (6H, s, CH3) ppm. UV/Vis (CH3CN): λmax/nm
(8800), 389 (17 800), 367 (21 800), 282 (10 100). LRMS (ES+) (ε/M−1 cm−1) = 439 (8600), 397 (9000), 371 (11 900), 282
found m/z 1099.24; calculated 1099.26 for [M − PF6]+. HRMS (66 700). LRMS (ES+) found m/z 1118.25; calculated 1118.31 for
(ES+) found m/z 1099.2115; calculated 1099.2129 for [M − PF6−]. HRMS (ES+) found m/z 1118.2328; calculated
[C49H42N6O8S2Ir]+. IR (solid): ν 1707 (CvO), 1244 (C–O), 833 1118.2341 for [C52H43N7O6S2Ir]+. IR (solid): ν 1716 (CvO),
(PF6−) cm−1
.
1257, 1242 (C–O), 833 (PF6−) cm−1
.
[Ir(emptz)2(edmdppz)]PF6
[Ir(emptz)2(bpiphen)]PF6
As for [Ir(emptz)2(bpy)]PF6, but using 1 (0.051 g, 0.035 mmol) As for [Ir(emptz)2(bpy)]PF6, but using 1 (0.055 g, 0.04 mmol)
and edmdppz (0.031 g, 0.081 mmol). The crude product was and bpiphen (0.032 g, 0.07 mmol). The crude product was pur-
purified by column chromatography (silica, CH2Cl2). After ified by column chromatography (silica, CH2Cl2). After elution
elution of unreacted organics with CH2Cl2 the product was of unreacted organics with CH2Cl2 the product was eluted as
eluted as the first yellow fraction with CH2Cl2. Yield: 0.026 g, the second orange fraction with CH2Cl2–MeOH (9 : 1). Yield:
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0.016 g, 17%. H NMR (400 MHz, CDCl3): δH = 9.26 (1H, dd,
JHH = 8.2, 1.5 Hz), 8.53–8.52 (2H, m), 8.16 (1H, dd, JHH = 5.3,
1.5 Hz) 8.08 (1H, dd, JHH = 5.1, 1.3 Hz), 7.83 (1H, dd, JHH = 8.2,
5.3 Hz), 7.74–7.65 (5H, m), 7.56 (1H, dd, JHH = 8.6, 5.1 Hz),
7.49–7.45 (2H, m), 7.41 (2H, dd, JHH = 4.7, 1.8 Hz), 7.10–7.05
(2H, m), 6.99–6.94 (2H, m), 6.46 (2H, dd, JHH = 17.8, 7.3 Hz),
T. Rees, C. Roldan-Carmona, L. Gil-Escrig, H. Bolink,
E. Baranoff and E. Zysman-Colman, J. Mater. Chem. C,
2014, 2, 5793; (c) J. M. Fernandez-Hernandez,
S. Ladouceur, Y. Shen, A. Iordache, X. Wang, L. Donato,
S. Gallagher-Duval, M. de Anda Villa, J. D. Slinker, L. De
Cola and E. Zysman-Colman, J. Mater. Chem. C, 2013, 1,
7440.
3
4.18 (4H, q, JHH = 3.6 Hz, OCH2CH3), 1.52 (6H, s, CH3), 1.37
(9H, s, CH3), 1.26–1.19 (6H, m, OCH2CH3) ppm. UV/Vis
(CH3CN): λmax/nm (ε/M−1 cm−1) = 440 (8600), 398 (9200), 371
(12 100), 282 (71 200). LRMS (ES+) found m/z 1114.41; calcu-
3 (a) J. I. Goldsmith, W. R. Hudson, M. S. Lowry,
T. H. Anderson and S. Bernhard, J. Am. Chem. Soc., 2005,
127, 7502; (b) S. Takizawa, R. Aboshi and S. Murata, Photo-
chem. Photobiol. Sci., 2011, 10, 895; (c) Y.-J. Yuan,
J.-Y. Zhang, Z.-T. Yu, J.-Y. Feng, W.-J. Luo, J.-H. Ye and
Z.-G. Zou, Inorg. Chem., 2012, 51, 4123; (d) A. J. Hallett,
N. White, W. Wu, X. Cui, P. N. Horton, S. J. Coles, J. Zhao
and S. J. A. Pope, Chem. Commun., 2012, 48, 10838;
(e) J. Sun, F. Zhong, X. Yi and J. Zhao, Inorg. Chem., 2013,
52, 6299.
4 For example: (a) W. H.-T. Law, L. C.-C. Lee, M.-W. Louie,
H.-W. Liu, T. W.-H. Ang and K. K.-W. Lo, Inorg. Chem.,
2013, 52, 13029; (b) B. Wang, Y. Liang, H. Dong, T. Tan,
B. Zhan, J. Cheng, K. K. W. Lo, Y. W. Lam and S. H. Cheng,
ChemBioChem, 2012, 13, 2729; (c) S. P.-Y. Li, T. S.-M. Tang,
K. S.-M. Yiu and K. K. W. Lo, Chem. – Eur. J., 2012, 18,
13342.
lated 1114.37 for [M
−
PF6−]. HRMS (ES+) found m/z
1114.2743; calculated 1114.2745 for [C54H47N7S2O4Ir]+. IR
(solid): ν 1716 (CvO), 1244, 1233 (C–O), 837 (PF6−) cm−1
.
Conclusions
This paper describes the synthesis, structural and spectro-
scopic properties of a range of cationic Ir(III) complexes that
incorporate cyclometalated substituted 2-phenylthiazole
ligands. The complexes are phosphorescent with an emitting
3
3
state that appears to have some mixed MLCT and IL charac-
ter. The precise nature of the ancillary N^N ligand influences
the observed lifetimes: the introduction of dppz-type ligands
partially quenches the emitting state, probably via low-lying
ligand-centred states localised on the dppz moiety.
5 G.-G. Shan, H.-B. Li, H.-T. Cao, D.-X. Zhu, P. Li, Z.-M. Su
and Y. Liao, Chem. Commun., 2012, 48, 2000.
Further work is possible with these complexes. We have pre-
viously shown that the introduction of ester groups onto the
cyclometalated ligand is a viable route to water-soluble phos-
phorescent species;12 such an approach will be investigated in
the future with these complexes. The piphen, ppiphen and
bpiphen derivatives also offer an additional pyridine coordi-
nation site, which will be investigated in the context of mixed
metal assemblies. It is also noteworthy that previous reports
have also shown that dppz complexes of Ir(III) can be used to
investigate redox reactions of DNA.36
6 H. Sun, S. Liu, W. Lin, K. Y. Zhang, W. Lv, X. Huang,
F. Huo, H. Yang, G. Jenkins, Q. Zhao and W. Huang, Nat.
Commun., 2014, 5, 3601.
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1028.
9 For example: (a) R. Gao, D. G. Ho, B. Hernandez, M. Selke,
D. Murphy, P. I. Djurovich and M. E. Thompson, J. Am.
Chem. Soc., 2002, 124, 14828; (b) R. Wang, D. Liu, H. Ren,
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16, 111.
Acknowledgements
We thank Cardiff University for financial support and the staff
of the EPSRC Mass Spectrometry National Service (University
of Swansea) for providing MS data. We also thank the EPSRC
for the use of the National Crystallographic Service at the Uni-
versity of Southampton.
Notes and references
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