Cyclometalated cinchophen ligands on iridium(iii): Towards water-soluble complexes with visible luminescence

Article abstract of DOI:10.1039/c3dt51098k

Eight cationic heteroleptic iridium(iii) complexes, [Ir(epqc) ₂(N^N)]⁺, were prepared in high yield from a cyclometalated iridium bridged-chloride dimer bearing two ethyl-2- phenylquinoline-4-carboxylate (epqc) ligands. Two X-ray cry

Full text of DOI:10.1039/c3dt51098k

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Cyclometalated cinchophen ligands on iridium(III):
towards water-soluble complexes with visible
Cite this: DOI: 10.1039/c3dt51098k
luminescence†
Rebecca A. Smith, Emily C. Stokes, Emily E. Langdon-Jones, James A. Platts,
Benson M. Kariuki, Andrew J. Hallett* and Simon J. A. Pope*
Eight cationic heteroleptic iridium(III) complexes, [Ir(epqc)2(N^N)]+, were prepared in high yield from a
cyclometalated iridium bridged-chloride dimer bearing two ethyl-2-phenylquinoline-4-carboxylate (epqc)
ligands. Two X-ray crystallographic studies were undertaken on selected complexes (where the ancillary
ligand N^N = 4,4’-dimethyl-2,2’-bipyridine and 4,7-diphenyl-1,10-phenanthroline) each confirming the
proposed formulations, showing an octahedral coordination at Ir(III). In general, the complexes are lumi-
nescent (620–630 nm) with moderately long lifetimes indicative of phosphorescence. Hydrolysis of the
ethyl ester moieties of the epqc ligands gave the analogous cinchophen-based complexes, which were
water-soluble and visibly luminescent (568–631 nm). The spectroscopic and redox characterisation of the
complexes was complemented by DFT and TD-DFT calculations, supporting the assignment of dominant
3MLCT to the emissive character.
Received 26th April 2013,
Accepted 29th May 2013
DOI: 10.1039/c3dt51098k
www.rsc.org/dalton
luminescence emission wavelengths through variation of
cyclometalating ligands and ancillary ligands (predominantly
Introduction
There has been considerable attention and effort disbursed for cationic complexes) renders such complexes very useful,
on iridium(III) complexes with cyclometalated ligands, due to particularly in electrochemiluminescence (ECL).6 For example,
their tuneable and generally efficient photoluminescence pro- increasing the π-conjugation of phenylpyridine by adding an
perties and subsequent performance in a variety of photo- aromatic ring (to give phenylquinoline) bathochromically
physical and electronic applications.1 Such complexes are shifts the 3π–π* and triplet metal-to-ligand charge transfer
capable of showing intense phosphorescence at room temp- (3MLCT) emission due to lower lying π* orbitals.7 Conse-
erature;2 the heavy atom iridium centre mediating strong quently, there have been several reports of phenylquinoline
spin–orbit coupling and intersystem crossing (ISC), mixing derivatives as cyclometalating ligands with various ancillary
the singlet and triplet excited states and generating high phos- ligands.8 However, many applications of Ir(III) complexes in
phorescent efficiencies. As a consequence, cyclometalated this context, including biologically-related uses, require water
iridium complexes have found many applications in a variety solubility. Surprisingly then, there have only been a handful
of opto-electronically related applications, such as electro- of reports of water-soluble iridium cyclometalated complexes,
chemical cells,3 photovoltaics,4 and luminescence imaging.5 most commonly where the ancillary diimine ligands are func-
Their ability to perform in such roles relies upon an under- tionalised with solubilising groups such as sugars,8j,l tria-
standing of their excited state properties, which can be modu- zoles,9 polyethyleneglycol (PEG),10 bioconjugates11 and
lated by altering the cyclometalating and/or ancillary ligand carboxylate groups,12 as well as the bis-cyclometalated bis-
associated with the iridium centre. The ability to tune aqua complexes;13 reports of water-solubilising fuctionalisa-
tion at the cyclometalating ligand are extremely rare.14 The
purpose of this paper is to present the synthesis and photo-
physical properties of a class of iridium complex that incor-
School of Chemistry, Main Building, Cardiff University, Cardiff CF10 3AT, UK.
E-mail: popesj@cardiff.ac.uk, hallettaj@cardiff.ac.uk; Fax: +44 (0) 29-20874030;
porate cyclometalated cinchophen-based ligands, providing a
convenient route towards water-soluble complexes with exploi-
table photophysical properties; the structural, spectroscopic,
electrochemical and photophysical studies are presented
together with supporting DFT and TD-DFT calculations on the
complexes.
Tel: +44 (0) 29-20879316
†Electronic supplementary information (ESI) available: Data collection para-
meters for the crystallographic studies, electrochemical data for 3a–h, pictorial
representations of the calculated frontier orbitals for 3a–h and 4a–h and Carte-
sian coordinates obtained from DFT calculations. CCDC 907280 and 907282.
For ESI and crystallographic data in CIF or other electronic format see DOI:
10.1039/c3dt51098k
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good yields (>75%). The resultant complexes 3a–h were soluble
in a range of common organic solvents.
Results and discussion
Synthesis and characterisation of the ligands and complexes
The conversion of complexes 3a–g to their corresponding
As an aside, it is noteworthy that many of the literature reports free acids was achieved by stirring the esterified complexes in
on functionalised phenylquinoline compounds describe bio- an equi-volume mixture of 1 M KOH and acetone under an
logical activities15 with applications as anti-malarial, anti- inert atmosphere. Subsequent neutralisation with 1 M HCl,
inflammatory and antibacterial agents;16 ester-functionalised removal of solvent and extraction with methanol (allowing
phenylquinoline compounds have shown promise as amyloid removal of KCl) led to the isolation of complexes 4a–g as their
fibril17 and reverse transcriptase18 inhibitors. Ethyl-2-phenyl- chloride salts, [Ir(pqca)2(N^N)]Cl. However, 1H NMR spec-
quinoline-4-carboxylate (epqcH) was prepared by simply dis- troscopy and mass spectrometry indicated that it was not possi-
solving and heating 2-phenylquinoline-4-carboxylic acid ble to isolate 4h by this method, the reasons for which are
(cinchophen) in ethanol with a few drops of conc. H2SO4. The currently unknown.
precursor iridium chloro-bridged dimer [(epqc)2Ir(µ-Cl)2Ir-
All new complexes were characterised using a range of spec-
(epqc)2] (2) was synthesised according to established literature troscopic techniques. Firstly, the 1H NMR spectra of complexes
conditions.19 Compound 2 readily reacted (Scheme 1) with a 3a–h are complicated in the aromatic region with overlapping
range of selected diimine-type ligands in 2-methoxyethanol; resonances associated with the cyclometalated and diimine
work-up and counter anion exchange yielded the crude mono- ligands; the retention of the ethyl ester functionality was
metallic complexes, [Ir(epqc)2(N^N)]PF6 {N^N = 2,2′-bipyridine observed in the aliphatic region. The 2-methoxyethyl groups of
(bpy) 3a; 4,4′-dimethyl-2,2′-bipyridine (dmbpy) 3b; 1,10-phe- 3c appeared as broadened triplets at 4.46 and 3.68 ppm
nanthroline (phen) 3d; 4,7-diphenyl-1,10-phenanthroline (dip) together with a singlet at 3.30 ppm. 31P–{1H} NMR spec-
−
3e; dipyrido[3,2-a:2′,3′-c]phenazine (dppz) 3f; benzo[i]dipyrido- troscopy confirmed the presence of the PF6 ion with a signa-
[3,2-a:2′,3′-c]phenazine (dppn) 3g; naphtha[2,3-a]dipyrido[3,2- ture septet (1JPF) at ca. −145 ppm in all cases. Low and high
h:2′,3′-f]phenazine-5,18-dione (qdppz) 3h}. For the reaction of resolution mass spectra were obtained for the complexes 3a–h
2 and diethyl-2,2′-bipyridine-4,4′-dicarboxylate (debpy), the and each confirmed the identity of the cationic, monomeric
ethyl ester groups of bpy were selectively converted to 2-meth- species of type [(epqc)2Ir(N^N)]+, revealing the parent cations
oxyethyl esters in situ, as informed by 1H NMR spectroscopy of [M − PF6]+ in each case, with the appropriate isotopic distri-
and mass spectrometry therefore giving [Ir(epqc)2(dmbpc)]PF6 bution. Complex purity was confirmed by elemental analysis.
1
3c (dmbpc = di-2-methoxyethyl-2,2′-bipyridine-4,4′-dicarboxy-
Upon hydrolysis of the ester groups, the H NMR spectra of
late). It should be noted that the ethyl ester functionality of the isolated analogues 4a–g all confirmed the absence of the
the cyclometalated cinchophen ligand was retained in all ethyl, or 2-methoxyethyl groups in the case of 4c, yielding 2,2′-
cases. Further purification for each complex was achieved bipyridyl-4,4′-dicarboxylic acid (bpdc), as well as improved
using column chromatography (silica; MeOH–CH2Cl2, 1 : 9) resolution of the aromatic resonances. The absence of a reso-
with elution of the first red band and subsequent removal of nance in the 31P–{1H} NMR spectra indicated the exchange of
−
solvent giving the complexes as pure red-coloured powders in PF6 with Cl− counter ions in the deprotected species. The
Scheme 1 Synthetic route to complexes [Ir(epqc)2(N^N)]PF6 3a–h and [Ir(pqca)2(N^N)]Cl 4a–g.
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corresponding mass spectra were easily obtained: complexes
4a–g confirmed the identity of the cationic, monomeric
species of type [Ir(pqca)2(N^N)]+ showing the characteristic
cluster of peaks associated with the [M − Cl]+ parent ion.
Solid-state IR spectra were also obtained on all complexes
highlighting the conversion from ester (ca. 1720 cm−1) to car-
boxylate (ca. 1580 cm−1) via significant low energy shifts in
−
ν(CvO), and the absence of the PF6 counter ion stretch (ca.
835 cm−1) confirming exchange with chloride.
Fig. 1 (a) Ortep representation of [Ir(epqc)2(dmbpy)]+ 3b (50% probability
X-ray crystallography studies
−
ellipsoids, solvent molecules, PF6 anion and hydrogen atoms have been
Single crystals of 3b and 3e suitable for X-ray diffraction
studies were isolated following vapour diffusion of Et2O into
concentrated CHCl3 or MeCN solutions of the complexes, over
a period of 48 h at −20 °C. The bond lengths and bond angles
are reported in Table 1, and the associated data collection
parameters are reported in Table S1, ESI.†
omitted for clarity) and (b) showing non-bonding contact interactions between
chelating ligands.
The structures obtained for the three complexes (Fig. 1a
and 2a) confirmed the proposed formulations, and show that
the iridium(III) center in these [Ir(epqc)2(N^N)]+ complexes
adopts a distorted octahedral coordination geometry. trans
Angles at the metal centers ranged from 168.0(3)° to 172.4(3)°
for 3b and 168.0(3)° to 174.9(3)° for 3e. The diimine ligand is
always coordinated trans to the cyclometalated phenyl rings;
the complexes retain the cis-C,C and trans-N,N chelating dis-
position of the original chloro-bridged dimer as reported in
related examples.7c,20 The trans-influence of the carbon
donors rendered slightly longer Ir–N bond lengths for the
diimine ligands {2.182(8) and 2.158(7) Å for 3b} than the epqc
ligands {2.094(8) and 2.112(8) Å for 3b}. The bite angles of the
epqc ligands (80.0(4)° and 80.3(4)° for 3b) were slightly larger
than that of N^N ligands {75.1(3) for 3b}. Similar observations
have been reported in related cyclometalated iridium(III) poly-
pyridine systems [Ir(pq)2(N^N)]+.1e,7c,d,20 For 3e the structure
showed that the phenyl substituents of the 4,7-diphenyl-1,10-
phenanthroline ligand are twisted out of planarity from the
phenanthroline unit by 55.1° and 50.2° respectively. In
addition, as with related phenylquinoxaline complexes,7d,21
there is a distortion within the quinoline moiety caused by the
Fig. 2 (a) Ortep representation of [Ir(epqc)2(dip)]+ 3e (50% probability ellip-
soids, solvent molecules, PF6− anion and hydrogen atoms have been omitted for
clarity) and (b) showing non-bonding contact interactions between chelating
ligands.
steric interactions between the chelating ligands (Fig. 1b and
2b). Some of the inter-ligand C⋯C and C⋯N non-bonding
contact distances (Table 1) are shorter than 3.4 Å (i.e. the sum
of the van der Waals radii of the atoms). This results in the
phenyl groups of the epqc ligand showing deformation angles
of 14.1° and 19.1° for 3b and 17.5° and 28.6° for 3e with
respect to the quinoline fragment of the ligand.
The bond lengths and angles of 3b and 3e were compared
with the optimised values calculated from density functional
theory (DFT) studies (also see DFT section and Table 1). In
general, a reasonable agreement was obtained between the
theoretical and experimentally observed bond lengths,
although some small differences were found. The calculated
Ir–Nbipyridine bond lengths, Ir–N(3) and Ir–N(4), are 0.038 and
0.062 Å longer than the experimental values for 3b. In the case
of the cyclometalated Ir–C bonds, calculated values are very
similar to the experimentally obtained data for Ir–C(1) in 3b
and 3e; similarly the Ir–Nquinoline bonds, where the calculated
and experimental values are comparable. Again, the calculated
structures reveal C⋯C and C⋯N interactions between the
ligands. The calculated deformation angles of the quinoline
fragment are much lower for 3b and 3e.
Table 1 Selected bond lengths (Å) and angles (°) for complexes 3b and 3e
Bond length (Å)/
angle (°)
Calculated
value
Calculated
value
3b
3e
Ir(1)–N(1)
Ir(1)–N(2)
Ir(1)–N(3)
Ir(1)–N(4)
Ir(1)–C(1)
Ir(1)–C(19)
C(14)⋯N(3)
C(32)⋯N(4)
N(1)–Ir(1)–N(2)
N(1)–Ir(1)–C(1)
N(2)–Ir(1)–C(19)
C(1)–Ir(1)–C(19)
2.094(8)
2.112(8)
2.182(8)
2.158(7)
1.998(9)
2.001(9)
3.140a
2.107
2.107
2.220
2.220
1.997
1.997
3.127
3.128
172.1
80.0
2.078(6)
2.107(7)
2.190(6)
2.153(7)
1.989(8)
2.005(8)
3.009a
2.107
2.107
2.218
2.218
1.997
1.997
3.128
3.128
172.8
79.9
3.173a
3.232a
170.7(3)
80.0(4)
80.3(3)
89.2(4)
173.3(3)
79.4(5)
79.9(3)
88.6(3)
Density functional theory (DFT) studies
80.0
90.1
79.9
90.5
DFT calculations (computed using the B3PW91 hybrid func-
tional) were performed to investigate the frontier orbitals and
provide qualitative descriptions of the highest occupied
a Non-bonded metrics and those involving planes/centroids were not
included in the refinement, and thus do not have an e.s.d.
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molecular orbital (HOMO) and lowest unoccupied molecular
orbital (LUMO) energy levels.
For the [Ir(epqc)2(N^N)]+ complexes, the energy levels of the
HOMO are sufficiently different (ΔE > 0.2 eV) from the other
MOs to be considered independent. In each case the HOMO
was located on the metal 5d(Ir) centre and cyclometalated
phenyl rings (Fig. S1, ESI†), with little or no coverage of the
ancillary diimine ligands. However, varying the diimine
ligands does impart a subtle perturbation of the HOMO
energy (EHOMO = −7.66 to −7.84 eV). The LUMO for the com-
plexes is, in many cases, close enough in energy to be con-
sidered isoenergetic with other close-lying MOs (e.g. LUMO +
1, LUMO + 2). For the complexes where this is not the case (3c,
3f, 3g and 3h), the LUMOs are predominantly delocalised over
the diimine ligands as with previous studies of related com-
pounds.7d For 3a, 3b, 3d and 3e the orbitals show a mixture of
diimine and phenylquinoline localisation. The diimine
imparts a larger degree of variation in the energy levels of the
LUMO energy (ELUMO = −4.71 to −5.47 eV), with 3h showing
the lowest LUMO energy level (ELUMO = −5.47 eV) and, there-
fore, smallest bandgap (Ebandgap = 2.29 eV). These results
suggest that the lowest energy absorption is predicted to com-
prise of significant MLCT character and that variation of the
diimine ligand could lead to a small degree of tuneable optical
properties within this series of complexes. The corresponding
cinchophen complexes (4a–h) showed the same general locali-
sation of the frontier orbitals, but revealed a drop in both the
HOMO and LUMO energies by an average of 0.12 eV and
0.13 eV, respectively (Fig. S2, ESI†).
Fig. 3 UV-vis spectra of selected [Ir(epqc)2(N^N)]PF6 complexes in MeCN
solutions (5 × 10−5 M).
Table 3). Strong absorption bands between 250 and 380 nm
1
were assigned to spin allowed π–π* ligand-centered (LC) tran-
sitions arising from both the cyclometalated and diimine
ligands within each complex. Weaker bands at 380–480 nm in
the visible region were assigned to spin-allowed metal-to-
ligand charge transfer bands (1MLCT) with the possibility of
spin-forbidden 3MLCT transitions contributing to the weaker
low-energy shoulder. For 3h it is also likely that ligand-centred
transitions associated with the anthraquinone moiety also con-
tribute in this wavelength region; previous studies have shown
that such species can possess intra-ligand CT (formally n–π*)
character, which is likely to contribute to the lower energy
parts of the spectral profile. The variation in coordinated
diimine ligand imparts only a very minor variation in the wave-
length positioning of the visible absorption bands. As expected
the absorption spectra of the corresponding carboxylic acid
derivatives 4a–g (5 × 10−5 M MeOH) share many of the same
common features. The principal observation from these
spectra is that the visible MLCT-based bands appear as a
defined transition ca. 430–455 nm.
Electrochemical studies
The electrochemical characteristics of the [Ir(epqc)2(N^N)]PF6
(3a–h) complexes were studied in de-oxygenated CH2Cl2. The
HOMO energy levels (EHOMO) were determined from the ioni-
sation potential of the first oxidation (Ir3+/4+) by direct corre-
0/1+
lation with the redox couple of FeCp2
. The cyclic
TD-DFT calculations (Table 2) in simulated MeCN suggest
the assignment of the lowest lying absorption bands as having
substantial MLCT character. For 3a the lowest energy absorp-
tion involves excitation from HOMO (Ir-5d + phenyl-π) to
LUMO + 1 (quinoline-π*), predicted to lie at 528 nm (oscillator
strength = 0.04 au), and so coincides reasonably closely with
the lowest energy shoulder feature seen in Fig. 4. A set of stron-
ger bands centred around 370 nm (387 nm, 0.15 au; 375 nm,
0.17 au; 359 nm, 0.10 au) is also predicted, again in good
agreement with Fig. 4. These bands consist of varying combi-
nations of Ir-5d and epqc-π orbitals excited into epqc-π* orbi-
tals, but have no contribution from the ancillary bpy-π*
orbitals. In comparison, TD-DFT simulation of 3c in MeCN
results in broadly the same pattern of predicted bands at
520 nm (0.04 au), 406 nm (0.06 au), 389 nm (0.07 au) and
384 nm (0.09 au), although the higher energy bands are
reduced in intensity relative to the low energy MLCT band. In
this complex, two low energy bands involving excitation from
HOMO (Ir 5d + phenyl-π) to LUMO and LUMO + 1 (bipy-π* and
quinoline-π*, respectively) are predicted at 564 and 522 nm,
voltammograms, measured at a platinum disc electrode (scan
rate υ = 200 mV s−1, 1 × 10−3 M solutions, 0.1 M [NBu4][PF6] as
a supporting electrolyte), each showed one non-fully reversible
oxidation (Table S2, ESI†), over the range +1.38 to +1.45 V. The
extent of the irreversibility can be ascribed to the contribution
of the cyclometalating ligands to the electron density of the
HOMO,22 which in this case is calculated to be ca. 45% from
DFT studies. The EHOMO values were determined using the
relevant equations23 and the resultant values fall in the narrow
range −5.72 to −5.83 eV (Table S3, ESI†). Each complex also
showed one or two partially reversible or irreversible reduction
waves, assigned to ligand-centred processes involving both the
diimine and phenylquinoline ligands, with complex 3h
showing at least four reduction processes, some of which must
be associated with the highly reducible anthraquinone
fragment.
Electronic properties of the complexes
The UV-vis absorption spectra of complexes 3a–h were
obtained as aerated MeCN solutions (5 × 10−5 M) (Fig. 3,
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Table 2 Calculated excitation wavelengths for 3a and 4a from TD-DFT studies showing the dominant transitions
3a (ester)
λa (nm)
4a (acid)
λ (nm)
4a (carboxylate)
f b
Character
f
Character
λ (nm)
f
Character
528
411
387
385
375
359
0.0422
0.0538
0.1495
0.0469
0.1743
0.1040
HOMO → LUMO + 1
HOMO − 1 → LUMO
HOMO − 2 → LUMO + 1
HOMO − 2 → LUMO
HOMO − 3 → LUMO
HOMO − 4 → LUMO
HOMO − 4 → LUMO + 1
HOMO − 4 → LUMO
HOMO − 4 → LUMO + 1
543
420
394
392
383
366
0.0348
0.0509
0.1245
0.0421
0.1547
0.1732
HOMO → LUMO + 1
HOMO − 1 → LUMO
HOMO − 2 → LUMO + 1
HOMO − 2 → LUMO
HOMO − 3 → LUMO
HOMO − 4 → LUMO + 1
456
406
381
366
363
356
0.056
0.021
0.056
0.115
0.060
0.045
HOMO → LUMO
HOMO − 3 → LUMO
HOMO − 3 → LUMO + 1
HOMO − 6 → LUMO + 2
HOMO − 3 → LUMO + 3
HOMO − 7 → LUMO + 1
359
0.0815
364
0.0478
HOMO − 4 → LUMO
HOMO − 1 → LUMO + 2
355
0.037
HOMO − 7 → LUMO + 2
a Excitation wavelength. b Oscillator strength.
Table 3 Photophysical properties of [Ir(epqc)2(N^N)]PF6 (3a–h) complexesa
Complex λabsa (nm)
λema (nm)
627
τ
a,b (ns)
Φa
3a
3b
3c
3d
3e
3f
470 (4500), 350 (22 000),
219
211
189
178
181
210
173
0.022
0.020
0.020
0.029
0.019
0.019
0.018
292 (39 500), 268 (45 650)
467 (4200), 350 (23 500),
290 (46 500), 265 (55 300)
464 (2850), 352 (18 150),
291 (39 500), 267 (47 850)
460 (4500), 356 (25 750),
288 (52 750), 269 (65 350)
465 (3550), 344 (23 300),
290 (55 950), 269 (59 000)
463 (3650), 364 (29 700),
272 (82 550)
630
620
630
628
628
3g
461 (5450), 416 (12 100),
398 (13 550), 327 (58 600),
292 (51 900), 266 (68 200)
460 (4550), 367 (29 500),
278 (83 750)
628
Fig. 4 Normalised luminescence emission spectra of selected [Ir(epqc)2(N^N)]-
PF6 complexes in MeCN solutions (5 × 10−5 M).
c
3h
426
2.1 (57%),
<1 (43%)
—
but with very low intensity (<0.001 au), suggesting the possi-
bility of MLCT/LLCT character.
a MeCN solution. b λex = 459 nm. c Not measured.
Deprotection of the ester to yield complex 4a was modelled
using both the neutral acid and deprotonated carboxylate form. be excited up to a wavelength of ca. 520 nm. Time-resolved
In the neutral complex, calculations predict a red-shift of the emission lifetime measurements revealed that the decays were
absorption bands discussed above by ca. 15 nm, and alteration single-exponential, in each case ca. 200 ns, typical of 3MLCT
of the relative intensities of the absorptions, with predicted character. The complexes each exhibited modest quantum
bands lying at 544 nm (oscillator strength of 0.04 au), 394 nm yields (Φ) in aerated MeCN, in line with related species. For
(0.12 au), 383 nm (0.15 au) and 365 nm (0.18 au). In contrast, 3h, the emission profile was very different, with a higher
simulation of the deprotonated carboxylate form of 4a indicates energy peak at 422 nm (τ < 5 ns), which was assigned to a
a substantial blue-shift of the absorption bands, with the lowest ligand-centred transition arising from the anthraquinone
energy absorption with significant oscillator strength coming at chromophore, with no evidence of a comparable MLCT tran-
456 nm (0.6 au), and a more intense band at 365 nm (0.12 au). sition. The absence of 3MLCT emission is attributed to the
The latter approach is in much better agreement with the quenching of that state by the anthraquinone-based ancillary
experimental data, such that modelling 4a as the bis-carboxylate ligand.
form seems to be more appropriate.
For ease of comparison the corresponding emission and
Steady state luminescence measurements were conducted excitation of the deprotected complexes 4a–g were obtained in
1
on aerated MeCN solutions, irradiating the MLCT wavelength MeCN, MeOH and water. With the exception of 4f these
(λex = 450 nm) absorption (Table 3, Fig. 4). The emission species all showed a hypsochromic shift of ca. 50 nm in the
maxima for complexes 3a–g show very little variation 3MLCT emission maxima (Table 4). Similar measurements in
(627–630 nm), are broad and featureless, and typically character- water resulted in an emission peak at ca. 595 nm, revealing the
istic of MLCT-based transitions.24 This variation is less than solvent-sensitivity and dipolar nature of the excited state.
that predicted by TD-DFT (see ESI†), possibly suggesting a Emission wavelengths in methanol were typically intermediate
diminished diimine contribution to the excited state. Corres- between those for water and acetonitrile (for example, Fig. 5).
ponding excitation spectra showed that the complexes could Relative to the esterified analogues (3a–g), the measured
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Table 4 Photophysical properties of [Ir(pqca)2(N^N)]Cl (4a–g) complexesa
Experimental section
CH3CN
H2O
CH3OH
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-
Complex
λem/nm
τ/ns
λem/nm
τ/ns
λem/nm
τ/ns
4a
4b
4c
4d
4e
4f
569
572
574
574
577
631
568
211
320
258
439
322
174
113
592
594
589
590
608
630
598
261
223
190
201
619
58
583
586
582
584
585
630
584
414
383
385
446
370
82
1
meter and recorded in CDCl3 or MeOD solutions. H and 13C–
{1H} NMR chemical shifts (δ) were determined relative to
internal tetramethylsilane, Si(CH3)4 and are given in ppm.
Low-resolution mass spectra were obtained by the staff at
Cardiff University. High-resolution mass spectra were carried
out at the EPSRC National Mass Spectrometry Service at
Swansea University, UK. UV-Vis studies were performed on a
Jasco V-650 spectrophotometer fitted with a Jasco temperature
control unit in MeCN or MeOH solutions (5 × 10−5 M) at 20 °C.
Photophysical data were obtained on a JobinYvon–Horiba
Fluorolog spectrometer fitted with a JY TBX picoseconds
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 con-
figured for 372 or 459 nm output operating at 500 kHz. Lumi-
nescence 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)
4g
199
297
a λex = 459 nm.
Fig. 5 Normalised luminescence emission spectra of 4g in various solvents
(5 × 10−5 M).
lifetimes were generally extended for complexes 4a–g reflecting disc. The reference was a silver wire separated from the test
the increased energy gap. However, in water the lifetime values solution by a fine porosity frit and an agar bridge saturated
also varied greatly as a function of the type of diimine ligand, with KCl. Solutions (10 ml CH2Cl2) were 1.0 × 10−3 mol dm−3
with 4e (likely to be the most hydrophobic of the diimines in in the test compound and 0.1 mol dm−3 in [NBun4][PF6] as the
this study) displaying the longest lifetime (τ = 619 ns), supporting electrolyte. Under these conditions, E0, for the one-
suggesting greater shielding of the excited state from the sur- electron oxidation of [Fe(η-C5H5)2] added to the test solutions
rounding solvent.
as an internal calibrant, is +0.46 V in CH2Cl2.27 Unless speci-
The longer emission wavelength of 4f in all solvents fied, all electrochemical values are at υ = 200 mV s−1. Micro-
appears somewhat anomolous and could be due to a number analyses were performed by London Metropolitan University,
of factors. With reference to the TD-DFT calculations, the pro- UK.
tonation state of the cinchophen ligands influences the emis-
sion wavelength. Repeating the measurement in 0.1 M NaOH
Data collection and processing
blue-shifted the emission peak to ca. 590 nm, in accordance Diffraction data for 3b and 3e were collected on a Nonius Kappa-
with the other complexes in the cinchophen-based series. CCD using graphite-monochromated Mo-Kα radiation (λ =
However, it is difficult to rationalise why only 4f (versus 4g, for 0.71073 Å) at 150 K. Software package Apex 2 (v2.1) was used for
example) would retain a protonated carboxylic acid form. An the data integration, scaling and absorption correction.
alternative explanation considers the role of protonation at the
dppz ligand. The closely related species [Ir(ppy)2(dppz)]+ 25
Structure analysis and refinement
reveals λem = 630 nm in MeCN and is thus very comparable to The structure was solved by direct methods using SHELXS-97
4f. However, H-bonding interactions with the phenazine nitro- and was completed by iterative cycles of ΔF-syntheses and full-
gens can dramatically influence the emission properties; in matrix least squares refinement. All non-H atoms were refined
fact, [Ir(ppy)2(dppz)]+ is non-emissive in water, unlike 4f. The anisotropically and difference Fourier syntheses were
reported photophysics of [Ir(ppy)2(dppn)]+ 25 also compare very employed in positioning idealised hydrogen atoms and were
well (λem = 583 nm in MeOH) to 4g, and thus the differences in allowed to ride on their parent C-atoms. All refinements were
emission wavelength for 4f could be due to protonation inter- against F2 and used SHELX-97.28 CCDC reference numbers
actions at dppz26 (of course, these would also be sensitive to 907280 and 907282 contain the supplementary crystallo-
the addition of 0.1 M NaOH).
graphic data for this paper.
Dalton Trans.
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Paper
DFT studies
CDCl3) δC = 169.6, 166.4, 156.9, 148.7, 147.4, 145.0, 140.2,
138.3, 131.6, 130.4, 130.1, 129.1, 128.1, 127.8, 126.9, 125.5,
125.1, 124.1, 123.5, 120.6, 116.6, 62.2, 14.4 ppm. UV-vis
(MeCN): λmax (ε/dm3 mol−1 cm−1) 470 (4500), 350 (22 000), 292
(39 500), 268 (45 650) nm. Elemental analysis: Calcd (%) for
C46H36N4O4IrPF6: C, 52.82, H, 3.47, N, 5.36; Found: C, 52.90,
H, 3.48, N, 5.36. ES MS found m/z 901.3, calculated m/z 901.0
for [M − PF6]+. HR MS found m/z 901.2370, calculated m/z
901.2363 for [C46H36N4O4191Ir]+. IR (solid): ν 1722 (CO), 837
DFT geometry optimisation and orbital calculations were per-
formed on the Gaussian 03 program.29 Geometry optimis-
ations were carried out without constraints using the B3PW91
functional. The LANL2DZ30 basis set was used for the Ir
centers, and was invoked with pseudo-potentials for the core
electrons, a 6-31G(d,p)31 basis set for all coordinating atoms
with a 6-31G32 basis set for all remaining atoms. All optimis-
ations were followed by frequency calculations to ascertain the
nature of the stationary point (minimum or saddle point).
TD-DFT studies were performed in Gaussian0933 using the
same functional, but with 6-31G(d) on all non-metal atoms,
and also included a simulated MeCN or H2O environment
using the polarised continuum model (PCM) approach.34 For
prediction of absorption spectra, the geometry used to calcu-
late orbital and other properties was used without modifi-
cation. For prediction of emission, however, the triplet state
was allowed to relax to its optimal geometry using unrestricted
B3PW91 in the gas phase, prior to solvated TD-DFT.
(PF6−) cm−1
[Ir(epqc)2(dmbpy)]PF6 3b. Prepared similarly from
.
2
(0.069 g, 0.037 mmol) and 4-4′-dimethyl-2,2′-bipyridine
(dmbpy) (0.0136 g, 0.074 mmol). Yield = 0.058 g, 85%. 1H
3
NMR (250 MHz, CDCl3) δH = 8.51 (2H, s), 8.47 (2H, d, JHH
=
3
7.9 Hz), 8.01–7.81 (4H, m), 7.72 (2H, d, JHH = 7.9 Hz),
7.52–7.31 (4H, m), 7.2–7.0 (4H, m), 6.95 (2H, app. t, JHH = 8.5
Hz). 6.83 (2H, app. t, JHH = 7.3 Hz), 6.50 (2H, d, JHH = 7.3
Hz), 4.62 (4H, q, 3JHH = 7.1 Hz), 2.47 (6H, s), 1.56 (6H, t, 3JHH
3
3
3
=
7.2 Hz) ppm. 13C–{1H} NMR (75 MHz, CDCl3) δC = 169.7, 165.2,
155.2, 152.7, 148.9, 146.6, 145.1, 138.7, 134.8, 131.5, 129.8,
129.5, 128.8, 127.6, 127.2, 126.4, 125.3, 123.3, 122.4, 120.2,
118.6, 65.9, 21.3, 15.4 ppm. UV-vis (MeCN): λmax (ε/dm3 mol−1
Synthesis
The ligands ethyl 2-phenylquinoline-4-carboxylate (epqcH) 1,35 cm−1) 467 (4200), 350 (23 500), 290 (46 500), 265 (55 300) nm.
dipyrido[3,2-a:2′,3′-c]phenazine (dppz),36 benzo[i]dipyrido[3,2- Elemental analysis: Calcd (%) for C48H40N4O4IrPF6: C, 53.68,
a:2′,3′-c]phenazine (dppn)37 and naphtha[2,3-a]dipyrido[3,2- H, 3.75, N, 5.22; Found: C, 53.86, H, 3.79, N, 5.26. ES MS
h:2′,3′-f]phenazine-5,18-dione (qdppz)38 were prepared accord- found m/z 929.3, calculated m/z 929.3 for [M − PF6]+. HR MS
ing to reported procedures.
found m/z 927.2650, calculated m/z 927.2650 for
[Ir(epqc)2(µ-Cl)2Ir(epqc)2] 2 was prepared by variation of the [C48H40N4O4191Ir]+. IR (solid): ν 1720 (CO), 829 (PF6−) cm−1
.
standard literature procedures for other bridged-chloride
[Ir(epqc)2(dmbpc)]PF6 3c. Prepared similarly from
2
dimers.19 Thus, IrCl3·3H2O (0.266 g, 0.75 mmol) and epqcH (0.069 g, 0.049 mmol) and diethyl-2,2′-bipyridine-4,4′-dicarboxy-
(0.520 g, 2.02 mmol) in 2-methoxyethanol–water (3 : 1, 8 ml) late (0.028 g, 0.098 mmol). Yield = 0.072 g, 74%. 1H NMR
3
were heated at reflux for 48 h. Water (25 ml) was added to give (250 MHz, CDCl3) δH = 8.67 (2H, d, JHH = 7.5 Hz), 8.58 (2H, d,
a dark purple precipitate, which was filtered and dried in 3JHH = 7.6 Hz), 8.43–8.34 (2H, m), 8.16–8.05 (4H, m), 7.55 (2H,
3
3
vacuo. The product was used in subsequent reaction without d, JHH = 7.5 Hz), 7.45 (2H, app. t, JHH = 8.7 Hz), 7.35–7.19
further purification.24
(4H, m), 7.08 (2H, app. t, JHH = 8.7 Hz), 6.88 (2H, app. t, JHH
3
3
3
3
[Ir(epqc)2(bpy)]PF6 3a. [(epqc)2Ir(μ-Cl)2Ir(epqc)2] 2 (0.061 g, = 7.6 Hz), 6.51 (2H, d, JHH = 7.6 Hz), 4.52 (4H, q, JHH = 7.2
0.04 mmol) and 2,2′-bipyridine (0.013 g, 0.08 mmol) in Hz), 4.46 (4H, br t), 3.68 (4H, br t), 3.30 (6H, s), 1.48 (6H, t,
2-methoxyethanol (5 ml) were heated at 120 °C for 16 h. The 3JHH = 7.2 Hz) ppm. 13C–{1H} NMR (75 MHz, CDCl3) δC
=
solvent was then removed in vacuo and the crude product dis- 169.6, 166.4, 162.9, 156.7, 150.1, 148.4, 147.1, 144.9, 140.7,
solved in MeCN (4 ml). KPF6 (1.05 g, 5.705 mmol) in water 139.0, 134.8, 131.6, 130.0, 129.0, 127.7, 127.1, 124.9, 124.0,
(2 ml) was added and the solution stirred for 10 min. Water 123.2, 120.5, 118.8, 116.6, 70.3, 65.6, 62.9, 61.9, 15.2 ppm. UV-
(20 ml) was added and the product extracted with CH2Cl2 (2 × vis (MeCN): λmax (ε/dm3 mol−1 cm−1) 464 (2900), 352 (18 200),
20 ml). The combined organic phases were washed with water 291 (39 500), 267 (47 900) nm. Elemental analysis: Calcd (%)
(30 ml) and brine (30 ml) before being dried over MgSO4. The for C54H48N4O10IrPF6: C, 51.88, H, 3.87, N, 4.48; Found: C,
solution was filtered and the solvent removed in vacuo. The 51.74, H, 3.84, N, 4.46. ES MS found m/z 1105.3, calculated m/z
crude product was then purified by column chromatography 1105.2 for [M − PF6]+. HR MS found m/z 1105.2977, calculated
(silica, CH2Cl2). After elution of unreacted organics with m/z 1103.2977 for [C54H48N4O10191Ir]+. IR (solid): ν 1724 (CO),
CH2Cl2 the product was eluted as the first red fraction with 835 (PF6−) cm−1
CH2Cl2–MeOH (9 : 1). The product was concentrated in volume [Ir(epqc)2(phen)]PF6 3d. Prepared similarly from 2 (0.064 g,
.
(to ca. 3 ml) and precipitated by the slow addition of Et2O 0.041 mmol) and 1,10-phenanthroline monohydrate (0.015 g,
1
(5 ml) and dried in vacuo. Yield = 0.055 g, 76%. 1H NMR 0.082 mmol). Yield = 0.060 g, 82%. H NMR (250 MHz, CDCl3)
(250 MHz, CDCl3) δH = 8.51 (2H, s), 8.42 (2H, d, 3JHH = 5.8 Hz), δH = 8.66 (2H, d, 3JHH = 7.6 Hz), 8.52–8.36 (4H, m), 8.23 (2H, d,
3
3
8.23 (2H, d, JHH = 7.5 Hz), 8.05–7.8 (6H, m), 7.70–7.35 (6H, 3JHH = 7.6 Hz), 8.16 (2H, d, JHH = 7.5 Hz), 7.92–7.77 (4H, m),
m), 7.21 (2H, app. t, 3JHH = 7.6 Hz), 7.02 (2H, app. t, JHH = 7.5 7.70–7.51 (4H, m), 7.33 (2H, d, JHH = 8.2 Hz), 6.90 (2H, app. t,
3
3
Hz), 6.86 (2H, app. t, JHH = 7.6 Hz), 6.53 (2H, d, JHH = 7.6 3JHH = 7.6 Hz), 6.80 (2H, app. t, JHH = 7.6 Hz), 6.63 (2H, d,
3
3
3
Hz), 4.50 (4H, m), 1.52 (6H, m) ppm. 13C–{1H} NMR (75 MHz, 3JHH = 7.5 Hz), 4.58 (4H, q, JHH = 7.3 Hz), 1.53 (6H, t, JHH
=
3
3
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7.3 Hz) ppm. 13C–{1H} NMR (75 MHz, CDCl3) δC = 169.6, 164.9, 7.1 Hz), 1.48 (6H, t, 3JHH = 7.1 Hz) ppm. 13C–{1H} NMR (75 MHz,
156.9, 149.6, 148.9, 147.9, 144.6, 138.6, 136.9, 135.0, 130.7, CDCl3) δC = 170.2, 165.0, 150.5, 149.8, 148.7, 148.5, 145.2,
130.0, 129.7, 128.8, 127.7, 127.4, 126.6, 125.2, 124.3, 123.5, 138.9, 138.4, 136.5, 136.0, 135.2, 133.7, 131.8, 131.3, 130.0,
120.3, 118.6, 62.0, 14.1 ppm. UV-vis (MeCN): λmax (ε/dm3 mol−1 129.0, 128.8, 128.2, 128.1, 127.6, 127.1, 126.7, 125.3, 124.7,
cm−1) 460 (4500), 356 (25 800), 288 (52 800), 269 (65 400) nm. 124.0, 119.6, 63.0, 14.4 ppm. UV-vis (MeCN): λmax (ε/dm3 mol−1
Elemental analysis: Calcd (%) for C48H36N4O4IrPF6: C, 53.88, cm−1) 461 (5400), 416 (12 100), 398 (13 500), 327 (58 600), 292
H, 3.39, N, 5.24; Found: C, 53.75, H, 3.51, N, 5.28. ES MS (51 900), 266 (68 200) nm. Elemental analysis: Calcd (%) for
found m/z 925.2, calculated m/z 925.2 for [M − PF6]+. HR MS C58H40N6O4IrPF6: C, 57.00, H, 3.30, N, 6.88; Found: C, 57.01,
found m/z 923.2345, calculated m/z 923.2337 for H, 3.34, N, 6.76. ES MS found m/z 1077.2, calculated m/z
[C48H36N4O4191Ir]+. IR (solid): ν 1722 (CO), 833 (PF6−) cm−1
.
1077.3 for [M − PF6]+. HR MS found m/z 1075.2715, calculated
[Ir(epqc)2(dip)]PF6 3e. Prepared similarly from 2 (0.060 g, m/z 1075.2711 for [C58H40N6O4191Ir]+. IR (solid): ν 1719 (CO),
0.037 mmol) and 4,7-diphenyl-1,10-phenanthroline (0.025 g, 828 (PF6−) cm−1
.
1
0.074 mmol). Yield = 0.060 g, 78%. H NMR (250 MHz, CDCl3)
[Ir(epqc)2(qdppz)]PF6 3h. Prepared similarly from
2
δH = 8.61 (2H, s), 8.51 (2H, d, 3JHH = 5.6 Hz), 8.48 (2H, d, 3JHH
=
(0.068 g, 0.044 mmol) and qdppz (0.037 g, 0.090 mmol). Yield
3
1
8.2 Hz), 8.16 (4H, d, JHH = 7.5 Hz), 7.81 (2H, s), 7.78 (2H, d, = 0.094 g, 83%. H NMR (250 MHz, CDCl3) δH = 9.38 (2H, d,
3JHH = 5.6 Hz), 7.51–7.34 (10H, m), 7.38–7.28 (4H, m), 6.9–6.75 3JHH = 5.1 Hz), 8.64 (2H, s), 8.61 (2H, d, JHH = 5.0 Hz), 8.34
3
(4H, m), 6.61 (2H, d, 3JHH = 7.5 Hz), 4.60 (4H, q, 3JHH = 7.1 Hz), (2H, dd, JHH = 8.6 and 4.1 Hz), 8.13 (2H, app. t, JHH = 6.90
3
3
3
3
1.55 (6H, t, JHH = 7.1 Hz) ppm. 13C–{1H} NMR (75 MHz, Hz), 8.07–7.92 (3H, m), 7.70 (2H, app. t, JHH = 8.9 Hz), 7.56
3
3
CDCl3) δC = 170.0, 165.2, 156.7, 151.3, 148.6, 147.2, 145.3, (1H, d, JHH = 7.1 Hz), 7.44 (1H, app. t, JHH = 7.1 Hz), 7.38
138.8, 135.2, 131.6, 130.9, 130.1, 129.9, 129.3, 128.7, 128.2, (2H, app. t, 3JHH = 7.9 Hz), 7.28 (1H, app. t, 3JHH = 7.4 Hz), 7.19
3
127.9, 126.9, 126.7, 126.0, 125.6, 124.8, 124.4, 123.8, 120.5, (2H, app. t, JHH = 7.6 Hz), 7.15–7.02 (2H, m), 6.94 (2H, app. t,
119.1, 63.0, 14.4 ppm. UV-vis (MeCN): λmax (ε/dm3 mol−1 cm−1
)
3JHH = 7.5 Hz), 6.86 (2H, app. t, 3JHH = 7.3 Hz), 6.62 (2H, app. t,
465 (3600), 344 (23 300), 290 (55 900), 269 (59 000) nm. 3JHH = 5.74 Hz), 4.50 (4H, q, JHH = 7.2 Hz), 1.42 (6H, t, JHH
=
3
3
Elemental analysis: Calcd (%) for C60H44N4O4IrPF6: C, 58.96, 7.2 Hz) ppm. 13C–{1H} NMR (75 MHz, CDCl3) δC = 166.4, 156.7,
H, 3.63, N, 4.58; Found: C, 58.90, H, 3.57, N, 4.54. ES MS 148.9, 138.5, 136.5, 130.2, 130.0, 129.0, 127.9, 127.6, 125.5,
found m/z 1077.3, calculated m/z 1077.2 for [M − PF6]+. HR MS 124.1, 120.4, 120.3, 116.5, 62.1, 14.4 ppm. UV-vis (MeCN): λmax
found m/z 1075.2947, calculated m/z 1075.2963 for (ε/dm3 mol−1 cm−1) 460 (4550), 367 (29 500), 278 (83 750),
[C60H44N4O4191Ir]+. IR (solid): ν 1721 (CO), 835 (PF6−) cm−1
.
212 (85 650) nm. Elemental analysis: Calcd (%) for
[Ir(epqc)2(dppz)]PF6 3f. Prepared similarly from 2 (0.072 g, C62H40N6O6IrPF6: C, 57.19, H, 3.10, N, 6.45; Found: C, 57.12,
0.046 mmol) and dppz (0.028 g, 0.099 mmol). Yield = 0.081 g, H, 3.18, N, 6.40. ES MS found m/z 1157.3, calculated m/z
3
75%. 1H NMR (250 MHz, CDCl3) δH = 9.46 (1H, d, JHH
=
1157.2 for [M − PF6]+. HR MS found m/z 1155.2587, calculated
8.0 Hz), 9.39 (1H, d, 3JHH = 8.1 Hz), 9.14 (1H, br s), 8.62–8.55 (2H, m/z 1155.2610 for [C62H40N6O6191Ir]+. IR (solid): ν 1722 (CO),
m), 8.46 (1H, d, 3JHH = 4.8 Hz), 8.30 (1H, app. t, 3JHH = 4.1 Hz), 1610 (CO), 832 (PF6−) cm−1
.
3
8.20–7.90 (4H, m), 7.85 (2H, app. t, JHH = 6.7 Hz), 7.80–7.75
[Ir(pqca)2(bpy)]Cl 4a. Complex 3a (0.036 g, 0.020 mmol) was
(2H, m), 7.71–7.61 (2H, m), 7.49–7.42 (2H, m), 7.30–7.23 (4H, dissolved in acetone (5 ml) and KOH (1 M soln, 5 ml) added.
3
m), 7.16–7.06 (2H, m), 6.80 (2H, app. t, JHH = 7.7 Hz), 6.56 The mixture was stirred at room temp. for 14 h. The solvent
3
3
(1H, d, JHH = 7.6 Hz), 4.46 (4H, q, JHH = 7.1 Hz), 1.55 (6H, t, was removed in vacuo and water (20 ml) added, followed by
3JHH = 7.1 Hz) ppm. 13C–{1H} NMR (75 MHz, CDCl3) δC
neutralisation with HCl (1 M soln). Water was removed in
=
169.7, 164.8, 156.3, 152.1, 149.6, 148.7, 148.3, 145.2, 142.8, vacuo and product was dissolved in MeOH (10 ml). The solu-
138.9, 138.6, 136.0, 135.1, 132.4, 131.5, 130.4, 129.5, 128.6, tion was filtered to remove salts and the solvent removed in
1
127.9, 127.3, 126.8, 124.5, 123.8, 118.9, 62.9, 14.2 ppm. UV-vis vacuo. Yield = 0.022 g, 65%. H NMR (400 MHz, MeOD) δH
=
(MeCN): λmax (ε/dm3 mol−1 cm−1) 463 (3600), 364 (29 700), 8.37 (2H, s), 8.20–8.15 (4H, m), 8.12 (2H, d, 3JHH = 7.7 Hz), 8.06
272 (82 600) nm. Elemental analysis: Calcd (%) for (2H, d, JHH = 7.7 Hz), 7.89 (2H, app. t, JHH = 8.0 Hz), 7.44
3
3
3
3
C54H38N6O4IrPF6: C, 55.34, H, 3.27, N, 7.17; Found: C, 55.42, (2H, app. t, JHH = 7.3 Hz), 7.30 (2H, d, JHH = 7.6 Hz), 7.23
H, 3.33, N, 7.08. ES MS found m/z 1027.3, calculated m/z (2H, app. t, 3JHH = 7.5 Hz), 7.03 (2H, app. t, 3JHH = 7.7 Hz), 6.87
1027.3 for [M − PF6]+. HR MS found m/z 1025.2561, calculated (2H, app. t, 3JHH = 7.7 Hz), 6.69 (2H, app. t, 3JHH = 7.4 Hz), 6.53
m/z 1025.2555 for [C54H38N6O4191Ir]+. IR (solid): ν 1724 (CO), (2H, d, JHH = 7.7 Hz) ppm. UV-vis (MeOH): λmax (ε/dm3 mol−1
3
830 (PF6−) cm−1
.
cm−1) 453, (1200), 333 (11 200), 285 (12 350) nm. ES MS found
[Ir(epqc)2(dppn)]PF6 3g. Prepared similarly from 2 (0.064 g, m/z 845.1, calculated m/z 844.9 for [M − Cl]+. HR MS found
0.041 mmol) and dppn (0.028 g, 0.084 mmol). Yield = 0.078 g, m/z 843.1710, calculated m/z 843.1711 for [C42H28N4O4191Ir]+.
1
3
78%. H NMR (250 MHz, CDCl3) δH = 9.43 (1H, d, JHH = 8.2 IR (solid): ν 1578 (CO) cm−1
.
3
Hz), 8.92 (1H, br s), 8.76 (1H, s), 8.66 (2H, app. t, JHH = 4.8
[Ir(pqca)2(dmbpy)]Cl 4b. Prepared similarly from 3b
Hz), 8.55 (1H, d, JHH = 4.8 Hz), 8.48–8.41 (2H, m), 8.38–8.31 (0.050 g, 0.088 mmol). Yield = 0.041 g, 80%. 1H NMR
3
(2H, m), 8.22 (1H, d, JHH = 6.7 Hz), 8.14–8.06 (2H, m), (250 MHz, MeOD) δH = 8.67 (2H, s), 8.70 (2H, d, 3JHH = 5.8 Hz),
3
3
3
8.03–7.94 (2H, m), 7.55–7.16 (7H, m), 7.10–6.95 (3H, m), 8.46 (2H, d, JHH = 8.2 Hz), 8.29 (2H, d, JHH = 8.2 Hz), 8.19
3
3
3
6.92–6.80 (3H, m), 6.71–6.54 (2H, m), 4.50 (4H, q, JHH
=
(2H, d, JHH = 7.6 Hz), 7.98 (2H, s), 7.95 (2H, app. t, JHH =
Dalton Trans.
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3
3
6.2 Hz), 7.73 (2H, app. t, JHH = 7.0 Hz), 7.44 (2H, d, JHH = 8.4 8.13–8.05 (3H, m), 7.98 (2H, app t), 7.87 (2H, br d), 7.75 (1H,
Hz), 7.27 (2H, app. t, 3JHH = 7.6 Hz), 6.82 (2H, app. t, 3JHH = 7.1 app. t), 7.59 (1H, app. t), 7.50–7.40 (3H, m), 7.21–7.12 (2H, m),
3
3
Hz), 6.67 (2H, d, JHH = 7.6 Hz), 2.57 (6H, s) ppm. 13C–{1H} 6.88–6.80 (2H, m), 6.61 (2H, d, JHH = 7.6 Hz) ppm. UV-vis
NMR (75 MHz, MeOD) δC = 171.1, 155.5, 1519, 151.2, 147.9, (MeOH): λmax (ε/dm3 mol−1 cm−1) 435 (1800), 335 (9000), 289
147.0, 146.2, 134.4, 130.2, 129.6, 129.3, 128.6, 127.6, 127.4, (18 400), 265 (23 400) nm. HR MS found m/z 969.1914, calcu-
126.9, 126.2, 125.0, 124.5, 124.3, 122.6, 114.3, 19.8 ppm. UV-vis lated m/z 969.1929 for [C50H30N6O4191Ir]+. IR (solid): ν 1575
(MeOH): λmax (ε/dm3 mol−1 cm−1) 450 (1600), 341 (6000), 286 (CO) cm−1
.
(16 800), 267 (18 600) nm. ES MS found m/z 873.2, calculated
[Ir(pqca)2(dppn)]Cl 4g. Prepared similarly from 3g (0.048 g,
1
m/z 873.0 for [M − Cl]+. HR MS found m/z 871.2018, calculated 0.039 mmol). Yield 0.029 g, 71%. H NMR (400 MHz, MeOD)
m/z 871.2024 for [C44H32N4O4191Ir]+. IR (solid): ν 1578 (CO) cm−1
.
δH = 9.49 (2H, d, JHH = 7.6 Hz), 8.80 (2H, s), 8.61 (2H, dd, JHH
3
[Ir(pqca)2(bpdc)]Cl 4c. Prepared similarly from 3c (0.055 g, = 5.3 and 1.4 Hz), 8.34–8.28 (4H, m), 8.20–7.85 (4H, overlap-
3
0.053 mmol). Yield = 0.044 g, 91%. 1H NMR (250 MHz, MeOD) ping m), 7.51–7.38 (5H, m), 7.33 (2H, d, JHH = 7.6 Hz),
3
3
δH = 8.68 (2H, br s), 8.38 (2H, s), 8.27 (2H, d, JHH = 5.7 Hz), 7.18–7.05 (3H, m), 6.81–6.70 (4H, m), 6.60 (2H, d, JHH = 7.7
8.19 (2H, app. t, 3JHH = 9.1 Hz), 7.92 (2H, s), 7.90 (2H, d, 3JHH
=
Hz) ppm. UV-vis (MeOH): λmax (ε/dm3 mol−1 cm−1) 429 (2600),
3
5.7 Hz), 7.43–7.31 (4H, m), 7.17 (2H, app. t, JHH = 7.7 Hz), 330 (17 700), 287 (24 200), 263 (33 800) nm. HR MS found m/z
6.98 (2H, app. t, 3JHH = 7.9 Hz), 6.80 (2H, app. t, 3JHH = 7.1 Hz), 1019.2089, calculated m/z 1019.2085 for [C54H32N6O4191Ir]+. IR
6.53 (2H, d, JHH = 7.2 Hz) ppm. 13C–{1H} NMR (75 MHz, (solid): ν 1578 (CO) cm−1
.
3
MeOD) δC = 172.2, 170.4, 160.4, 157.8, 151.0, 150.7, 148.1,
147.2, 146.3, 139.3, 135.4, 134.7, 130.3, 129.9, 129.6, 128.8,
128.6, 127.5, 127.0, 126.7, 126.3, 125.5, 124.4, 122.8, 116.5,
Conclusions
114.5 ppm. UV-vis (MeOH): λmax (ε/dm3 mol−1 cm−1) 449
(1300), 338 (5000), 287 (15 700), 262 (20 400) nm. ES MS found Water-soluble, luminescent iridium(III) complexes can be con-
m/z 933.1, calculated m/z 932.9 for [M − Cl]+. HR MS found veniently synthesised through the use of cinchophen-based
m/z 931.1507, calculated m/z 931.1508 for [C44H28N4O8191Ir]+. ligands. The Ir(III) coordination chemistry of ethyl-2-phenylqui-
IR (solid): ν 1578 (CO) cm−1
.
noline-4-carboxylate can be achieved using traditional
[Ir(pqca)2(phen)]Cl 4d. Prepared similarly from 3d (0.040 g, methods and the resultant cyclometalated complexes are toler-
0.043 mmol). Yield = 0.026 g, 70%. 1H NMR (400 MHz, MeOD) ant to the subsequent deprotection strategy. The new com-
3
δH = 8.81 (2H, s), 8.62 (2H, d, JHH = 5.8 Hz), 8.46 (2H, app. t, plexes of the form [Ir(pqca)2(N^N)]+ are luminescent via an
3
3
3JHH = 8.2 Hz), 8.29 (2H, d, JHH = 8.2 Hz), 8.19 (2H, d, JHH
=
excited state that is best described as possessing substantial
7.6 Hz), 7.98 (2H, s), 7.95 (2H, app. t, JHH = 6.2 Hz), 7.73 (2H, 3MLCT character; the CT nature was reflected in the solvent-
app. t, JHH = 7.0 Hz), 7.44 (2H, d, JHH = 8.4 Hz), 7.27 (2H, sensitive properties of the complexes. TD-DFT calculations also
app. t, 3JHH = 7.6 Hz), 6.91 (2H, app. t, 3JHH = 7.4 Hz), 6.82 (2H, revealed that careful modelling of the protonated form of the
3
3
3
3
3
app. t, JHH = 7.1 Hz), 6.67 (2H, d, JHH = 7.6 Hz) ppm. UV-vis carboxylic acid/carboxylate is necessary to allow a more precise
(MeOH): λmax (ε/dm3 mol−1 cm−1) 445 (2600), 339 (11 000), 266 approximation of the electronic characteristics of the complexes.
(37 400) nm. ES MS found m/z 869.1, calculated m/z 868.9 for
[M − Cl]+. HR MS found m/z 867.1704, calculated m/z 867.1711
for [C44H28N4O4191Ir]+. IR (solid): ν 1597 (CO) cm−1
.
Acknowledgements
[Ir(pqca)2(dip)]Cl 4e. Prepared similarly from 3e (0.030 g,
0.024 mmol). Yield 0.018 g, 76%. H NMR (400 MHz, MeOD) We thank Cardiff University and EPSRC for financial support,
δH = 8.84 (2H, s), 8.69 (2H, d, 3JHH = 7.6 Hz), 8.53 (2H, d, 3JHH
and the EPSRC National Mass Spectrometry Service Centre at
1
=
3
3
7.8 Hz), 8.31 (2H, d, JHH = 7.6 Hz), 7.93 (4H, app. t, JHH = 7.2 Swansea University.
3
Hz), 7.59–7.49 (12H, m), 7.35 (2H, app. t, JHH = 6.2 Hz), 7.28
(2H, app. t, 3JHH = 6.8 Hz), 6.98–6.88 (4H, m), 6.71 (2H, d, 3JHH
= 7.8 Hz) ppm. 13C–{1H} NMR (75 MHz, MeOD) δC = 172.2,
Notes and references
170.1, 151.0, 150.9, 150.7, 148.1, 147.2, 146.3, 135.4, 134.7,
130.3, 130.0, 129.7, 129.6, 128.8, 128.6, 128.5, 127.5, 127.4,
127.0, 126.7, 126.3, 125.5, 124.4, 122.8, 116.5, 114.5 ppm. UV-
vis (MeOH): λmax (ε/dm3 mol−1 cm−1) 448 (1700), 402 (1400),
336 (7900), 288 (22 400), 266 (22 600) nm. ES MS found m/z
1021.2, calculated m/z 1021.1 for [M − Cl]+. HR MS found m/z
1019.2333, calculated m/z 1019.2337 for [C56H36N4O4191Ir]+.
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