Fine-tuning of photophysical and electronic properties of materials for photonic devices through remote functionalization

Article abstract of DOI:10.1002/ejic.201200394

We report four new iridium(III) complexes of the type [Ir(ppy) ₂(N^N)][PF₆] in which N^N is a 4,6-diphenyl-2,2'- bipyridine and the 4-phenyl ring is substituted at either the para or meta positions [4-Me, N^N = 1; 4-Br, N^N = 2; 3,5-Br₂, N^N = 3; 3,5-(C₆H₄-4-NPh₂)₂, N^N = 4]. The complexes have been fully characterized, and single-crystal diffraction analyses of [Ir(ppy)₂(N^N)][PF₆] (N^N = 1-3) confirmed that each [Ir(ppy)₂(N^N)]⁺ cation exhibits face-to-face π-stacking between the pendant phenyl substituent of the N^N ligand and the cyclometallated phenyl ring of an adjacent [ppy]^- ligand. In solution, the complexes are short-lived emitters; the emission maxima for [Ir(ppy)₂(1)][PF₆], [Ir(ppy)₂(2)][PF ₆], and [Ir(ppy)₂(4)][PF₆] are similar (λ_em = 600-608 nm), but the presence of the two bromo substituents in [Ir(ppy)₂(3)][PF₆] produces a redshift of ca. 30 nm. The solid-state photoluminescent emission spectra of thin films of the complexes are similar to those in solution. The performances of the complexes as electroluminescent components in light-emitting electrochemical cells (LECs) have been evaluated. The electroluminescence spectra show slight blueshifts with repect to the photoluminscence bands. LEC turn-on times vary from instantaneous for N^N = 2 to 2 h for N^N = 1. The device data suggest that the incorporation of Br substituents into the N^N co-ligand may not be beneficial. Four [Ir(ppy)₂(N^N)][PF₆] (N^N = 4,6-diphenyl-2,2'-bipyridine derivative) complexes have been synthesized and characterized. In solution, the complexes are short-lived emitters with emission maxima between 600 and 635 nm; the solid-state emission spectra are similar. The performances of the complexes as electroluminescent components in LECs have been evaluated. Copyright

Full text of DOI:10.1002/ejic.201200394

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Date: 02-07-12 16:04:05
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FULL PAPER
DOI: 10.1002/ejic.201200394
Fine-Tuning of Photophysical and Electronic Properties of Materials for
Photonic Devices Through Remote Functionalization
Andreas M. Bünzli,[a] Henk J. Bolink,[b,c] Edwin C. Constable,*[a]
Catherine E. Housecroft,*[a] Markus Neuburger,[a] Enrique Ortí,[b] Antonio Pertegás,[b] and
Jennifer A. Zampese[a]
Keywords: Iridium / Ligand design / Photophysical properties / Electroluminescence / X-ray diffraction
We report four new iridium(III) complexes of the type [Ir(ppy)2-
[Ir(ppy)2(4)][PF6] are similar (λem = 600–608 nm), but the pres-
ence of the two bromo substituents in [Ir(ppy)2(3)][PF6] pro-
duces a redshift of ca. 30 nm. The solid-state photolumines-
cent emission spectra of thin films of the complexes are sim-
ilar to those in solution. The performances of the complexes
as electroluminescent components in light-emitting electro-
chemical cells (LECs) have been evaluated. The electrolumi-
nescence spectra show slight blueshifts with repect to the
photoluminscence bands. LEC turn-on times vary from in-
∧
∧
(N N)][PF6] in which N N is a 4,6-diphenyl-2,2Ј-bipyridine
and the 4-phenyl ring is substituted at either the para or meta
∧
∧
∧
positions [4-Me, N N = 1; 4-Br, N N = 2; 3,5-Br2, N N = 3;
∧
3,5-(C6H4-4-NPh2)2, N N = 4]. The complexes have been
fully characterized, and single-crystal diffraction analyses of
∧
∧
[Ir(ppy)2(N N)][PF6] (N N
= 1–3) confirmed that each
∧
[Ir(ppy)2(N N)]+ cation exhibits face-to-face π-stacking be-
∧
tween the pendant phenyl substituent of the N N ligand and
∧
∧
the cyclometallated phenyl ring of an adjacent [ppy]– ligand.
In solution, the complexes are short-lived emitters; the emis-
sion maxima for [Ir(ppy)2(1)][PF6], [Ir(ppy)2(2)][PF6], and
stantaneous for N N = 2 to 2 h for N N = 1. The device data
∧
suggest that the incorporation of Br substituents into the N N
co-ligand may not be beneficial.
ligand,[10,11] and a combinatorial approach has been used
for rapid screening of potential emitters.[12] An inherent
problem of the iridium(III) emitters is their limited stability
in LEC devices.[13,14] To overcome this we are currently fo-
cusing on a strategy to exploit intracation face-to-face π-
Introduction
Octahedral iridium(III) complexes of the type [Ir(ppy)2-
L]+, in which [ppy]– is the cyclometallated 2-phenylpyr-
idinato ligand and L is a neutral, bidentate ligand, are cur-
rently being developed for application in light-emitting elec-
trochemical cells (LECs).[1] These devices incorporate ionic,
heavy d-block metal complexes in the light-emitting layer.
Efficient electroluminescence can be achieved by using salts
∧
stacking between [ppy]– and N N chelating ligands to in-
crease device lifetimes,[15–20] a strategy previously shown to
have profound effects on the photophysical properties of
this class of compounds.[21] The success of this approach
∧
of [Ir(ppy)2L]+ in which L is an N N chelating ligand. The
∧
has led us to screen many [Ir(ppy)2(N N)]+ complexes to
first breakthrough came with the efficient performance of
[Ir(ppy)2(dtbbpy)][PF6] (dtbbpy = 4,4Ј-di-tert-butyl-2,2Ј-bi-
pyridine).[2] Since this report, much progress has been made
through combined experimental and theoretical studies to
effectively tune the electroluminescent behaviour of this
family of emitters[3–5] and by combining orange and blue
emitters to produce white light-emitting LECs.[6–9] Tuning
the emission wavelength is achieved by functionalizing the
gain a better appreciation of the structural and electronic
properties of the ligand that result in improved perform-
ances in LECs. Our approach has been to explore the struc-
tures in the complexes to independently optimize the cyclo-
metallation and N,NЈ-donor ligands in conjunction with
computational studies to ensure the desired colour is
achieved.
In this paper we describe four complexes of the type
∧
[ppy]– ligands and/or varying and functionalizing the N N
∧
∧
[Ir(ppy)2(N N)][PF6]. The ligand N N is based on 4,6-di-
phenyl-2,2Ј-bipyridine in which the 4-phenyl ring is substi-
tuted at either the para or meta positions (Scheme 1). The
6-phenyl substituent is included in the ligand design to facil-
itate the intracation π-stacking. The para-substituted li-
gands 1 and 2 contain electron-releasing and -withdrawing
substituents, respectively, and on going from 2 to 3, the elec-
tron-withdrawing effects are enhanced. The bromo deriva-
tives 2 and 3 are useful building blocks for further function-
alization, and this is exemplified by the conversion of 3 into
[a] Department of Chemistry, University of Basel,
Spitalstrasse 51, 4056 Basel, Switzerland
Fax: +41-61-267-1008
E-mail: edwin.constable@unibas.ch
catherine.housecroft@unibas.ch
[b] Instituto de Ciencia Molecular, Universidad de Valencia,
Catedrático José Beltrán 2, 46980 Paterna, Spain
[c] Fundació General de la Universidad de Valencia (FGUV),
P. O. Box 22085, 46010 Valencia, Spain
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201200394.
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E. C. Constable, C. E. Housecroft et al.
FULL PAPER
4, which contains electron-donating triphenylamino substit- 139.6 to 123.7 ppm, respectively). The electrospray mass
uents. Although the complex [Ir(ppy)2(1)][PF6] has been spectrum of 2 exhibits peaks at m/z = 387.7, 409.1 and
previously reported,[19] it has not, to the best of our knowl- 797.1 assigned to [M + H]+, [M + Na]+ and [2 M + Na]+,
edge, been tested in LEC devices. The aim of this study was respectively, with isotope patterns that match those simu-
to compare the solution and solid-state properties of lated. Ligand 3 was characterized by 1H and 13C NMR
∧
∧
[Ir(ppy)2(N N)][PF6] with N N = 1–4, including their per- spectroscopy (assigned by using COSY, HMQC, HMBC
formances in LEC devices.
and NOESY techniques); the spectra are consistent with
the substitution pattern shown in Scheme 1. Signals arising
from the 6-phenyl-2,2Ј-bipyridine domain are little altered
in relation to those observed for 1 and 2. The base peak in
the ESI mass spectrum was observed at m/z = 467.0, consis-
tent with [M + H]+. Similarly, for 4, the dominant peak in
the ESI mass spectrum (m/z = 795.7) arises from the [M +
1
H]+ ion. The H and 13C NMR spectra for a CDCl3 solu-
tion of 4 were fully assigned by using 2D methods and are
consistent with the presence of two diphenylamino substitu-
ents (Scheme 1). The electronic absorption spectra of chlo-
roform solutions of 1–4 exhibit intense, high-energy bands
arising from π*ǟπ transitions. The increased values of εmax
on going from 1–3 to 4 are consistent with the introduction
of additional aromatic substituents. All four compounds are
emissive (λem = 348–365 nm for 1–3 and 451 nm for 4) when
irradiated in the UV region corresponding to their most
intense absorptions.
Complex Synthesis and Solution Characterization
∧
∧
Scheme 1. Structures of ligands 1–4 and atom labelling for NMR
spectroscopic assignments.
The complexes [Ir(ppy)2(N N)][PF6] with N N = 1–4
were synthesized by the reaction of the dimer [Ir(ppy)2(μ-
[25,26]
Cl)]2
with one of the ligands 1–4 followed by anion
exchange by addition of ammonium hexafluoridophosphate
(Scheme 2). The electrospray mass spectrum of each iso-
lated complex exhibits a peak envelope corresponding to
the [M – PF6]+ ion with an isotope pattern consistent with
that simulated.
Results and Discussion
Ligand Synthesis and Characterization
Compound 1 has previously been reported,[19,22] but we
chose to prepare the ligand by using the solventless, grind-
ing method of Cave and Raston.[23] Compounds 1, 2 and 3
were prepared by sequential aldol condensation of aceto-
phenone and 4-methylbenzaldehyde, 4-bromobenzaldehyde
or 3,5-dibromobenzaldehyde, respectively, in the presence of
base, followed by Michael addition of 2-acetylpyridine, and
finally addition of ammonium acetate. After column
chromatography, 1–3 were isolated in yields of 19–26%.
Compound 4 was prepared by palladium-catalysed Suzuki
coupling of 3 with 4-(diphenylamino)phenylboronic acid
and was isolated in 82% yield. For 1, the 1H NMR spectro-
scopic data are consistent with those previously pub-
lished,[19,20] and for the sake of completeness we provide the
∧
Scheme 2. Syntheses of [Ir(ppy)2(N N)][PF6] (L = 1–4). Reagents:
∧
(i) N N, MeOH/CH2Cl2 (see Exp. Sect.), (ii) NH4PF6. Atom label-
ling of the [ppy]– ligands for NMR spectroscopic assignments.
full assignment, achieved through 2D techniques, of the 13
C
NMR spectrum in the Exp. Sect. Compared with those of
The complexes were characterized in solution (CD2Cl2)
1
1
1, the H and 13C NMR spectroscopic signatures of 2[24] by H and 13C NMR spectroscopy, the spectra being as-
show changes consistent with the change of an Me to a Br signed by using COSY, DEPT, HMQC, HMBC and
∧
substituent (Scheme 1), that is, the loss of the signals at δ = NOESY techniques. In each [Ir(ppy)2(N N)]+ cation, the
2.44 ppm (1H) and δ = 21.4 ppm (13C) arising from the Me two [ppy]– ligands are non-equivalent because of the lack
∧
group, and shifts of the signals for HH3 (δ = 7.34 to of a C2 axis passing through the N N chelate. Well-resolved
1
7.65 ppm) and CH3 and CH4 (δ = 129.9 to 132.4, and 139.4/ 500 MHz H NMR spectra were obtained, as exemplified
2
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Fine-Tuning of Properties of Materials for Photonic Devices
in Figure 1 for [Ir(ppy)2(3)][PF6]. The proton signals arising 298 K that it is difficult to differentiate between pairs of
from the cyclometallated ring C are distinguished from proton signals from pyridine rings B and D (Figure 1).
those of ring A by a NOESY cross-peak between HG3 and However, on cooling from 298 to 243 K one of the pair of
HC4. As confirmed in the crystallographic study described signals for HB6 and HD6 shifts significantly to lower fre-
below, the pendant phenyl ring (ring G, Scheme 1) lies quency (δ = 6.63 to 6.47 ppm) and, because of its proximity
above one of the cyclometallated rings (defined as ring C), to the pendant phenyl ring, we assign this signal to HD6
leading to close through-space separation of the protons of (Figure 2). All the signals for the protons in the pyridine
1
these rings. In the room-temperature H NMR spectrum it ring E of coordinated ligand 3 broaden on cooling, but the
is less easy to unambiguously differentiate between pairs of reason for this is not clear.
signals for pyridine rings B and D (Scheme 2). Protons HF3
The electronic absorption spectra of CD2Cl2 solutions of
∧
∧
and HF5 are distinguished by the observation of a cross- [Ir(ppy)2(N N)][PF6] with N N = 1–4 are shown in Fig-
peak between the signals for HF5 and HG2. No HE3–HF3 ure 3. All the complexes exhibit intense bands in the UV
cross-peak could be observed because of the near overlap region attributed to ligand-based π*ǟπ transitions. The
of these resonances in the 1D spectrum. The broadening of similarity of the spectra for [Ir(ppy)2(1)][PF6], [Ir(ppy)2-
the signal for HG2 (Figure 1) is indicative of the slow rota- (2)][PF6] and [Ir(ppy)2(3)][PF6] was expected, because the
tion of the phenyl ring G on the NMR timescale. On cool- complexes differ only in the peripheral non-aromatic sub-
ing a CD2Cl2 solution of [Ir(ppy)2(3)][PF6], the signals aris-
ing from HG2 [δ = 6.6 (br.) ppm at 298 K) and HG3 (δ =
6.78 ppm at 298 K) collapse, and at 243 K four broad reso-
nances are observed (δ = 5.97 and ca. 7.1 ppm assigned to
HG2/G6 and δ = 6.61 and 6.89 ppm assigned to HG3/G5, Fig-
ure 2). The large difference in the chemical shifts of the HG2
and HG6 proton signals is consistent with these protons fac-
ing into and away from the ring current of arene ring C.
Earlier, we noted in the 1H NMR spectrum recorded at
Figure 3. Electronic absorption spectra of CH2Cl2 solutions of
∧
∧
[Ir(ppy)2(N N)][PF6]: N N = 1 (·· – ··), 2 (······), 3 (––) and 4 (- - -).
Figure 1. 500 MHz 1H NMR spectrum of a CD2Cl2 solution of
[Ir(ppy)2(3)][PF6] (298 K). Atom labelling as in Schemes 1 and 2.
∧
Figure 4. Emission spectra of [Ir(ppy)2(N N)][PF6] (in CH2Cl2):
∧
N N = 1 (·· – ··, λex = 279 nm), 2 (······, λex = 229 nm), 3 (––, λex
= 232 nm) and 4 (- - -, λex = 229 nm).
Table 1. Solution photoluminescence spectroscopic data for the
∧
∧
hexafluoridophosphate salts of [Ir(ppy)2(N N)]+ with N N =
1–4.[a]
[nm] τ[b] [ns]
φPL [%]
max
Complex cation
λex [nm] λem
[Ir(ppy)2(1)]+
[Ir(ppy)2(2)]+
[Ir(ppy)2(3)]+
[Ir(ppy)2(4)]+
279
229
232
229
600
56.8
57.8
59.0
26.1
19.9
14.0
11.0
5.2
608
635
604
Figure 2. Variable-temperature 500 MHz 1H NMR spectra of a
CD2Cl2 solution of [Ir(ppy)2(3)][PF6].
[a] Lifetime and quantum yields were measured in CH2Cl2 at room
temperature. [b] For lifetime measurements, λex = 300 nm.
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Table 2. Cyclic voltammetric data with respect to Fc/Fc+.[a]
Complex
Eox [V]
Ered [V]
[Ir(ppy)2(1)][PF6]
[Ir(ppy)2(2)][PF6]
[Ir(ppy)2(3)][PF6]
[Ir(ppy)2(4)][PF6]
+0.88ir, +1.17/+1.10qr
+0.92ir, +1.20/+1.14qr
+0.91ir, +1.19/+1.13qr
+0.92/+0.83, +1.18/+1.12qr
–1.75/–1.68, –2.34ir, –2.57ir
–1.67/–1.60, –2.14ir, –2.29/–2.23qr, –2.57ir
–1.64/–1.57, –2.06ir, –2.22ir, –2.31/–2.27qr, –2.57ir
–1.46/–1.40, –2.03ir, –2.28/–2.20qr
[a] Determined in MeCN solutions with [tBu4N][PF6] as supporting electrolyte and a scan rate of 0.1 Vs–1 (ir = irreversible; qr =
quasireversible).
∧
stituents. The enhanced absorption properties of [Ir(ppy)2- 171.1(3)° for N N = 1, 2 and 3, respectively]. As antici-
(4)][PF6] are consistent with the introduction of six ad- pated, the pendant phenyl substituent in each cation is
ditional arene rings (Scheme 1). The absorption bands tail twisted out of the plane of the bpy domain to which it is
into the visible region, giving rise to the observed orange attached to permit face-to-face π-stacking with the cyclo-
colour of the complexes. All four complexes are emissive metallated phenyl ring of an adjacent [ppy]– ligand (Fig-
when excited in the UV region (see caption to Figure 4). ure 8). The angles between the least-squares planes of the
The emission maxima for [Ir(ppy)2(1)][PF6], [Ir(ppy)2- bpy unit and the 6-substituted phenyl ring are 69.8(3),
(2)][PF6] and [Ir(ppy)2(4)][PF6] are similar, whereas the 73.4(3) and 63.4(5)° in [Ir(ppy)2(1)]+, [Ir(ppy)2(2)]+ and
presence of the two bromo substituents in [Ir(ppy)2(3)][PF6] [Ir(ppy)2(3)]+, respectively. The efficiency of each interac-
results in a redshift of ca. 30 nm (Figure 4). Table 1 summa- tion can be assessed by looking at the angles between the
rizes the emission data and reveal that the emissions are least-squares planes of the two phenyl rings and the separa-
short-lived with low photoluminescent quantum yields.
tion of their centroids. These parameters are 14.9° and
All four complexes are electrochemically active, and cy- 3.6 Å in [Ir(ppy)2(1)]+, 13.9° and 3.5 Å in [Ir(ppy)2-
clic voltammetric data are presented in Table 2; unless (2)]+, and 15.3° and 3.6 Å in [Ir(ppy)2(3)]+. Although the
stated otherwise, processes are reversible. Each of the intercentroid distances are consistent with π-stacking,[29]
∧
∧
[Ir(ppy)2(N N)][PF6] complexes with N N = 1–3 exhibits the angles between the planes of the rings are not optimal,
an irreversible oxidation at ca. +0.9 V, whereas this oxi- but are, nonetheless, consistent with those observed in re-
dation is reversible for [Ir(ppy)2(4)][PF6]. A second oxi- lated structures.[30] The arene ring of each of the tolyl, 4-
dation process, which is quasi-reversible, is observed for bromophenyl and 3,5-dibromophenyl substituents is twisted
each complex at a more positive potential. A series of li- out of the plane of the bpy unit by 36.9° in [Ir(ppy)2(1)]+,
gand-based reductions is exhibited by each complex. The 26.0° in [Ir(ppy)2(2)]+ and 38.0° in [Ir(ppy)2(3)]+. This twist-
electrochemical behaviour is consistent with that of related ing is assumed to be the consequence of packing forces, and
complexes.[27]
it will also minimize repulsive interactions between ortho-
hydrogen atoms of adjacent rings. Packing interactions in
[Ir(ppy)2(1)][PF6] are dominated by edge-to-face CH···π
and CH···F contacts, and there is no intercation face-to-
Solid-State Structures of the Complexes
∧
The solid-state structures of [Ir(ppy)2(N N)][PF6] for
∧
N N = 1–3 were determined by single-crystal X-ray diffrac-
tion, suitable crystals being grown from a CH2Cl2 solution
of the complex overlaid with Et2O or by slow evaporation
of solvent of a CH2Cl2 solution of the complex. The
∧
[Ir(ppy)2(N N)]+ cations are chiral. Although [Ir(ppy)2-
(2)][PF6]·2CH2Cl2 crystallizes in the centrosymmetric space
group P21/c with both enantiomers in the unit cell, it is
interesting to note that [Ir(ppy)2(1)][PF6] and [Ir(ppy)2-
(3)][PF6] crystallize in the chiral space group P212121.
Figures 5–7 present the structures of the [Ir(ppy)2(1)]+,
[Ir(ppy)2(2)]+ and [Ir(ppy)2(3)]+ cations, and selected bond
lengths and angles are listed in the captions. Each iridi-
um(III) coordination sphere is octahedral with the two cy-
clometallated [ppy]– ligands bound so that their N donor
atoms are in a trans arrangement, consistent with related
Figure 5. ORTEP representation of the structure of the [Ir(ppy)2-
(1)]+ cation in [Ir(ppy)2(1)][PF6] (ellipsoids plotted at the 30%
probability level and H atoms omitted). Selected bond parameters:
Ir1–N1 2.136(4), Ir1–N2 2.213(4), Ir1–C30 2.011(4), Ir1–C41
2.021(4), Ir1–N4 2.043(4), Ir1–N3 2.045(4) Å; N1–Ir1–N2
76.16(15), C41–Ir1–N4 80.1(2), C30–Ir1–N3 80.8(2), C41–Ir1–N1
∧
structures (49 entries with {Ir(ppy)2(N N)} coordination
spheres in the CSD, Conquest version 5.33 with Feb 2012
updates[28]). The corresponding N–Ir–N bond angle is in-
variant among the complexes [171.40(18), 171.14(18) and 174.96(19), C30–Ir1–N2 167.51(17), N4–Ir1–N3 171.40(18)°.
4
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Fine-Tuning of Properties of Materials for Photonic Devices
face π-stacking. In [Ir(ppy)2(2)][PF6], pairs of cations asso- N3i 3.54 Å with closest contacts of Br1···C25i 3.40(1) and
ciate through short Br···Br contacts [Br1···Br1i 3.4617(8) Å; Br1···C26i 3.54(1) Å; symmetry code: i = x, 1 + y, z]. In-
symmetry code: i = –x, 1 – y, –1 – z].[31,32] The [ppy]– pyr- tercation face-to-face π-stacking does not play an impor-
idine ring containing atom N2 engages in a poorly efficient tant role in crystal packing, except for a poorly efficient
π-stack with the [ppy]– phenyl ring containing C22i (sym- interaction between pairs of [ppy]– ligands containing
metry code: i = x, 3/2 – y, –1/2 + z; angle between the least- atoms C33 and N4ii (symmetry code: ii = 2 – x, –1/2 + y,
squares planes of the rings 7.4°, centroid···centroid separa- 3/2 – z; angle between least-squares planes of rings 17.6°,
tion 4.2 Å). Packing forces are dominated by CH···F and centroid···centroid separation 3.9 Å). Edge-to-face CH···π
CH···Cl interactions offset by repulsive short H···H con- and CH···F contacts are the dominant packing interactions.
tacts, particularly those between centrosymmetric pairs of
cations (H31···H41ii 2.35 Å; symmetry code: ii = 1 – x, 1 –
y, 1 – z). In [Ir(ppy)2(3)][PF6], the two bromo substituents
are involved in short Br···F and Br···π interactions
[Br2···F10 3.034(9) Å and Br1···centroid of ring containing
Figure 8. Intracation face-to-face π-stacking in (a) [Ir(ppy)2(1)]+,
(b) [Ir(ppy)2(2)]+ and (c) [Ir(ppy)2(3)]+.
Solid-State Photophysical Properties and
Electroluminescent Devices
The solid-state photoluminescence emission spectra of
∧
∧
thin films containing [Ir(ppy)2(N N)][PF6] (N N = 1–4)
and the ionic liquid 1-butyl-3-methylimidazolium hexafluo-
∧
ridophosphate (IL) in an [Ir(ppy)2(N N)]+/IL molar ratio
Figure 6. ORTEP representation of the structure of the [Ir(ppy)2-
(2)]+ cation in [Ir(ppy)2(2)][PF6]·2CH2Cl2 (ellipsoids plotted at the
30% probability level and H atoms omitted). Selected bond param-
eters: Ir1–N1 2.039(5), Ir1–N2 2.047(5), Ir1–N3 2.138(5), Ir1–N4
2.223(5), Ir1–C11 1.996(5), Ir1–C22 2.035(6), C42–Br1 1.894(6) Å;
N3–Ir1–N4 75.99(18), N1–Ir1–C11 80.7(2), N2–Ir1–C22 79.9(2),
N1–Ir1–N2 171.14(18), N4–Ir1–C11 168.27(19), N3–Ir1–C22
174.8(2)°.
of 4:1 are displayed in Figure 9a. The photoluminescence
spectra are similar to those obtained for the complexes in
CD2Cl2 solution (Figure 4). The emission peak from
[Ir(ppy)2(3)][PF6] at 629 nm is the most redshifted; emission
maxima were observed for [Ir(ppy)2(2)][PF6], [Ir(ppy)2-
(4)][PF6] and [Ir(ppy)2(1)][PF6] at 608, 604 and 601 nm,
respectively. The similarity of the solid- and solution-based
data demonstrates that the excited state is not severely affec-
ted by the environment as has been observed in other sys-
tems.[33] The photoluminescent quantum yields (PLQY) of
the complexes in the configuration described above are
0.15, 0.11, 0.13 and 0.08 for [Ir(ppy)2(1)][PF6], [Ir(ppy)2-
(2)][PF6], [Ir(ppy)2(3)][PF6] and [Ir(ppy)2(4)][PF6], respec-
tively.
The electroluminescence of LECs prepared from the four
complexes in the layer composition as described above is
shown in Figure 9b. The emission band maxima are found
at 588, 597 and 595 nm for the complexes [Ir(ppy)2(1)][PF6],
[Ir(ppy)2(2)][PF6] and [Ir(ppy)2(4)][PF6], respectively,
whereas for [Ir(ppy)2(3)][PF6], the emission is at 620 nm.
The slightly blueshifted emissions with respect to the photo-
luminescence spectra may be due to optical effects caused
by the presence of the metal top electrode and specific re-
gions in the film where the electrons and holes recombine
and the light originates. This leads to a different optical
path for the generated photons, which may explain the
slight difference between PL and EL emission. The LECs
were driven by using a recently reported method of a pulsed
Figure 7. ORTEP representation of the structure of the [Ir(ppy)2-
(3)]+ cation in [Ir(ppy)2(3)][PF6] (ellipsoids plotted at the 30%
probability level and H atoms omitted). Selected bond parameters:
Ir1–C44 2.014(10), Ir1–C33 2.029(10), Ir1–N4 2.032(8), Ir1–N3
2.045(8), Ir1–N1 2.146(7), Ir1–N 2.253(6), C19–Br1 1.908(9), C21–
Br2 1.891(9) Å; N1–Ir1–N2 75.3(3), C33–Ir1–N3 80.5(5), C44–Ir1–
N4 81.1(4), N4–Ir1–N3 171.1(3), C33–Ir1–N2 167.2(4), C44–Ir1–
N1 177.2(4)°.
Eur. J. Inorg. Chem. 0000, 0–0
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E. C. Constable, C. E. Housecroft et al.
FULL PAPER
implies it is easier to maintain the pre-set average current
density due to the reduced injection barrier. An important
parameter of LECs is the turn-on time (ton), in this work
defined as the time to reach 75 cdm–2. All devices turn on
within 2 h of operation, which is primarily due to the se-
lected mode of operation for the LECs. Interestingly, the
lowest ton is reached for the LEC using [Ir(ppy)2(2)][PF6],
which shows 85 cdm–2 instantly upon operation. The LECs
using [Ir(ppy)2(3)][PF6] and [Ir(ppy)2(4)][PF6] have ton val-
ues of 0.9 and 0.4 h, respectively, whereas the LEC using
[Ir(ppy)2(1)][PF6] needs 2 h to reach 75 cdm–2. The lumi-
nance continues to increase for the LECs, and – as the cur-
rent density is constant – the device efficacy is easily de-
duced by dividing the luminance by the constant current
density (100 Am–2).
∧
Figure 9. (a) Photoluminescence spectra for [Ir(ppy)2(N N)][PF6]/
IL (4:1) in the solid state and (b) electroluminescence spectra for
∧
ITO/PEDOT:PSS/[Ir(ppy)2(N N)][PF6]/IL (4:1)/Al LECs under a
∧
bias of 4 V [N N = 1 (·· – ··), 2 (······), 3 (––) and 4 (- - -)].
Figure 10. Luminance and average voltage (inset) versus time for
∧
ITO/PEDOT:PSS/[Ir(ppy)2(N N)][PF6]/IL(4:1)/Al LEC devices
under an average pulsed current of 100 Am–2 (1000 Hz and 50%
duty cycle). N N = 1 (·· – ··), 2 (······), 3 (––) and 4 (- - -).
∧
current with an average current density of 100 Am–2 using
a block wave at a frequency of 1000 Hz and a duty cycle
of 50%.[34] These driving conditions were selected, because
The initial driving voltages applied are an indication of
current driving leads to fast turn-on times, and pulsed driv- the ionic conductivity of the film as the displacement of
ing stabilizes the doped regions leading to increased life- ions is required to reduce the injection barrier for electrons
times. More importantly, the lifetimes observed with this and holes. The voltage applied increases going from the
driving method are linked to the intrinsic stability of the LEC using [Ir(ppy)2(1)][PF6], [Ir(ppy)2(3)][PF6], [Ir(ppy)2-
device and complex used.
(4)][PF6] and finally [Ir(ppy)2(2)][PF6]. In particular, the
Typical performances obtained with the LECs prepared large difference in driving voltage for LECs using [Ir(ppy)2-
from [Ir(ppy)2(1)][PF6], [Ir(ppy)2(2)][PF6], [Ir(ppy)2(3)][PF6] (1)][PF6] and [Ir(ppy)2(2)][PF6] is peculiar as there is only a
or [Ir(ppy)2(4)][PF6] are presented in Figure 10 and are small difference in the chemical structure of the bpy-based
summarized in Table 3. As LECs are dynamic systems, the ligand (Scheme 1).
field-induced ionic movement reduces the injection barrier
The stabilities of the different devices cannot easily be
for holes and electrons and, as a consequence, luminance compared as the luminance levels are quite different. How-
increases as the voltage decreases. The decrease in voltage ever, one observes that the devices using the complexes with
∧
Table 3. Performance for ITO/PEDOT:PSS/[Ir(ppy)2bpy][PF6]/IL(4:1)/Al LEC devices [N N = 1 (·· – ··), 2 (······), 3 (––) and 4 (- - -)]
driven at a pulsed current with an average current density of 100 Am–2 by using a block wave at a frequency of 1000 Hz and a duty cycle
of 50%.
Complex cation
ton [h]
Lmax [cdm–2]
t1/2 [h]
Efficacy [cdA–1]
PLQY [%]
Power efficiency [lmW–1]
EQE [%]
[Ir(ppy)2(1)]+
[Ir(ppy)2(2)]+
[Ir(ppy)2(3)]+
[Ir(ppy)2(4)]+
2.0
instant
0.9
455
115
101
83
530
8.3
2.9
250
4.4
1.1
1.4
0.8
14.7
11.4
12.9
7.76
2.72
0.33
0.25
0.25
2.12
0.60
0.95
0.43
0.4
6
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Fine-Tuning of Properties of Materials for Photonic Devices
the bromine substituents have a significantly lower stability
than the LECs using complexes containing ligand N N =
1 and 4. This would suggest that the presence of Br substit-
ylpyridine (1.964 g, 16.2 mmol) was then added. The mixture was
ground to a paste and then a solid. After drying in a desiccator,
the solid was milled to give a beige powder. This was dissolved in
a solution of NH4OAc (12.5 g, 162 mmol) in PEG-300 (200 mL)
and the mixture heated at reflux for 18 h. Water (100 mL) was
added to the cooled mixture and the sticky product was separated,
washed with water (50ϫ 2 mL) and dissolved in Et2O. Removal of
the solvent gave a brown solid, which was dissolved in CH2Cl2 and
washed with aqueous NaHCO3 and water. The organic layer was
dried with MgSO4, filtered, and the solvents were evaporated to
dryness to give a brown solid, which was purified by column
chromatography (silica, CH2Cl2 changing to CH2Cl2/MeOH,
100:1; then alumina, changing to CH2Cl2/MeOH, 100:1). Com-
pound 2 was isolated as a pale-yellow solid (1.24 g, 3.20 mmol,
∧
uents is not beneficial for the operation of LECs.
Conclusions
As a part of our systematic investigation of iridium com-
plexes for incorporation into LECs, we have prepared and
characterized four iridium(III) complexes [Ir(ppy)2-
∧
∧
(N N)][PF6] in which N N is a 4,6-diphenyl-2,2Ј-bipyr-
idine and the 4-phenyl ring is substituted at either the para
or meta positions with electron-releasing or -withdrawing
1
19.7%). M.p. 147 °C. H NMR (500 MHz, CDCl3): δ = 8.76 (d, J
= 4.5 Hz, 1 H, HE6), 8.73 (d, J = 8.0 Hz, 1 H, HE3), 8.70 (s, 1 H,
HF3), 8.19 (d, J = 7.2 Hz, 2 H, HG2), 7.95 (m, 2 H, HF5+E4), 7.73
(d, J = 8.5 Hz, 2 H, HH2), 7.65 (d, J = 8.5 Hz, 2 H, HH3), 7.54 (t,
J = 7.4 Hz, 2 H, HG3), 7.47 (t, J = 7.3 Hz, 1 H, HG4), 7.42 (m, 1
H, HE5) ppm. 13C NMR (126 MHz, CDCl3): δ = 157.7 (CF6), 155.5
(CE2/F2), 155.2 (CE2/F2), 149.3 (CF4), 148.2 (CE6), 139.2 (CG1), 138.3
(CE4), 137.5 (CH1), 132.4 (CH3), 129.5 (CG4), 129.0 (CH2/G3), 128.9
(CH2/G3), 127.2 (CG2), 124.4 (CE5), 123.7 (CH4), 122.3 (CE3), 118.6
(CF5), 117.7 (CF3) ppm. UV/Vis (CHCl3, 5.68ϫ10–6 moldm–3):
λmax (ε) = 265 (43000), 312 nm (8000 dm3 mol–1 cm–1); emission
(CHCl3, 4.75ϫ10–5 moldm–3, λex = 312 nm): λem = 354, 363 nm.
MS (ESI): m/z = 387.7 [M + H]+ (calcd. 387.1), 409.1 [M + Na]+
(calcd. 409.0), 797.1 [2 M + Na]+ (calcd. 797.1). C22H15BrN2
(387.28): calcd. C 68.23, H 3.90, N 7.23; found C 68.08, H 4.18, N
6.90.
∧
substituents (Scheme 1). The N N ligands were designed
to permit intracation face-to-face π-stacking between the
cyclometallated phenyl ring of one [ppy]– ligand and the
pendant 6-phenyl substituent of the co-ligand. X-ray dif-
fraction data for three of the complexes confirmed this so-
lid-state feature. In solution, the complexes are short-lived
∧
emitters (λem = 600–608 nm for N N = 1, 2 and 4, and
∧
635 nm for N N = 3), and the solid-state photolumines-
cence emission spectra of thin films of the complexes are
little different from those in CH2Cl2 solution. Evaluation
of the performances of the iridium(III) complexes in LECs
revealed that the electroluminescence spectra are slightly
blueshifted with respect to the photoluminescence spectra,
and the LEC turn-on times range from instantaneous for
∧
∧
Compound 3: Ligand 3 was prepared in a manner similar to that
for 2 (see the Supporting Information) and was isolated as a white
N N = 2 to 2 h for N N = 1. The device data suggest that
∧
the incorporation of Br substituents into the N N co-li-
1
solid (26%). M.p. 187 °C. H NMR (500 MHz, CDCl3): δ = 8.74
gand are not beneficial and confirm our general belief that
halogens should be avoided as substituents in ligands de-
signed for use in LECs.
(d, J = 4.8 Hz, 1 H, HE6), 8.69 (d, J = 8.0 Hz, 1 H, HE3), 8.58 (s,
1 H, HF3), 8.19 (d, J = 7.1 Hz, 2 H, HG2), 7.89 (m, 4 H, HH2+E4+F5),
7.75 (t, J = 1.6 Hz, 1 H, HH4), 7.54 (t, J = 7.4 Hz, 2 H, HG3), 7.48
(t, J = 7.3 Hz, 1 H, HG4), 7.39 (m, 1 H, HE5) ppm. 13C NMR
(126 MHz, CDCl3): δ = 157.7 (CF6), 156.3 (CF2), 155.7 (CE2), 148.9
(CE6), 147.6 (CF4), 142.4 (CH1), 139.0 (CG1), 137.5 (CE4), 134.5
(CH4), 129.6 (CG4), 129.2 (CH2), 129.0 (CG3), 127.2 (CG2), 124.3
(CE5), 123.8 (CH3), 121.9 (CE3), 118.4 (CF5), 117.5 (CF3) ppm. UV/
Vis (CHCl3, 5.15ϫ10–6 moldm–3): λmax (ε) = 240 (47000), 254
(45000), 316 nm (9000 dm3 mol–1 cm–1); emission (CHCl3,
5.15ϫ10–5 moldm–3, λex = 255 nm): λem = 365 nm. MS (ESI): m/z
= 467.0 [M + H]+ (calcd. 467.0). C22H14Br2N2 (466.17): calcd. C
56.68, H 3.03, N 6.01; found C 56.59, H 3.04, N 6.02.
Experimental Section
General: See the Supporting Information.
Compound 1: The ligand was prepared in a manner similar to a
literature method[20] but by adapting it to employ the solventless
protocol of Cave and Raston[23] (see the Supporting Information).
The CDCl3 solution 1H NMR spectroscopic data are in agreement
with those reported in the literature.[19,20] The following characteri-
zation data have not previously been reported for 1. M.p. 125 °C.
13C NMR (126 MHz, CDCl3): δ = 157.4 (CF6), 156.0 (CE2+F2),
150.4 (CF4), 148.4 (CE6), 139.6 (CG1/H4), 139.4 (CG1/H4), 138.0
(CE4), 135.7 (CH1), 129.9 (CH3) 129.3 (CG4), 128.9 (CG3), 127.3
(CG2/H2), 127.2 (CG2/H2), 124.1 (CE5), 122.1 (CE3), 118.7 (CF5),
Compound 4: Compound
3
(795 mg, 1.71 mmol), 4-(di-
phenylamino)phenylboronic acid (1.06 g, 3.67 mmol) and Na2CO3
(730 mg, 6.9 mmol) were dissolved in toluene (200 mL) and water
(50 mL). The reaction mixture was degasssed with N2 for 30 min,
and then [Pd(PPh3)4] (197 mg, 0.17 mmol) was added. The mixture
was heated at reflux in the dark for 5 d. After cooling, the two
phases were separated, and the organic layer was washed with H2O
(2ϫ 50 mL), dried with MgSO4 and filtered. Removal of the sol-
vent gave a yellow oil, which was purified by column chromatog-
raphy (silica, toluene/ethyl acetate, 20:1; then alumina, toluene/cy-
clohexane, 1:1). Ligand 4 was isolated as a white powder (1.09 g,
117.7
(CF3),
21.4
(CH3)
ppm.
UV/Vis
(CHCl3,
6.82ϫ10–6 moldm–3): λmax (ε)
=
264 (46000), 315 nm
(10000 dm3 mol–1 cm–1); emission (CHCl3, 6.82ϫ10–6 moldm–3,
λex = 264 nm): λmax = 348, 359 nm. MS (ESI): m/z = 323.2 [M +
H]+ (calcd. 323.2), 345.1 [M + Na]+ (calcd. 345.1), 667.2 [2 M +
Na]+ (calcd. 667.3).
1
Compound 2: KOH (1.09 g, 19.5 mmol) was dissolved in MeOH
(50 mL) and H2O (10 mL) whilst stirring in an ice bath, and aceto-
phenone (1.948 g, 16.2 mmol) and 4-bromobenzaldehyde (3.00 g,
16.2 mmol) were added slowly. After stirring for 1 h, a white pre-
cipitate formed. The crude product was transferred to a mortar
and combined with solid NaOH (650 mg, 16.2 mmol), and 2-acet-
1.40 mmol, 81.9%). M.p. 255 °C. H NMR (500 MHz, CDCl3): δ
= 8.80 (s, 1 H, HF3), 8.74 (overlapping d, 2 H, HE3+E6), 8.25 (d, J
= 7.2 Hz, 2 H, HG2), 8.10 (s, 1 H, HF5), 7.95 (s, 2 H, HH2), 7.91 (t,
J = 7.9 Hz, 1 H, HE4), 7.86 (s, 1 H, HH4), 7.63 (d, J = 8.6 Hz, 4
H, HI2), 7.56 (t, J = 7.5 Hz, 2 H, HG3), 7.48 (t, J = 7.3 Hz, 1 H,
HG4), 7.39 (m, 1 H, HE5), 7.30 (t, J = 7.9 Hz, 8 H, HJ3), 7.20
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E. C. Constable, C. E. Housecroft et al.
FULL PAPER
(overlapping d, 12 H, HI3+J2), 7.07 (t, J = 7.3 Hz, 4 H, HJ4) ppm.
7.5 Hz, 2 H, HG3), 6.61 (t, J = 7.5 Hz, overlapping br. signal, 3 H,
HA4+G2), 6.40 (t, J = 7.4 Hz, 1 H, HA5), 5.97 (d, J = 7.6 Hz, 1 H,
13C NMR (126 MHz, CDCl3): δ = 157.4 (CF6), 156.2 (CE2+F2),
150.6 (CF4), 148.8 (CE6), 147.7 (CI4+J1), 142.3 (CH3), 139.9 (CH1), HC6), 5.59 (d, J = 7.6 Hz, 1 H, HA6) ppm. 13C NMR (126 MHz,
139.5 (CG1), 137.5 (CE4), 134.8 (CI1), 129.5 (CJ3), 129.3 (CG4), 128.9
CD2Cl2): δ = 169.4 (CB2), 167.7 (CD2), 166.6 (CF6), 158.0 (CE2/F2),
(CG3), 128.2 (CI2), 127.3 (CG2), 126.0 (CH4), 124.6 (CJ2), 124.4 157.3 (CE2/F2), 151.5 (CF4/A1), 150.9 (CE6), 150.5 (CF4/A1), 149.5
(CH2), 124.1 (CE5), 124.0 (CI3), 123.2 (CJ4), 121.9 (CE3), 118.9
(CB6/D6), 149.4 (CB6/D6), 147.4 (CC1), 143.5 (CA2/C2), 143.2 (CA2/C2),
139.9 (CE4), 138.7 (CG1), 138.6 (CB4/D4), 138.2 (CB4/D4), 134.6
(CF5), 118.0 (CF3) ppm. UV/Vis (CHCl3, 4.91ϫ10–5 moldm–3):
λmax (ε) = 247 (76000), 312 nm (60000 dm3 mol–1 cm–1); emission (CH1), 133.4 (CH2/H3), 132.0 (CA6), 131.3 (CC5), 130.8 (CC6), 130.2
(CHCl3, 4.91ϫ10–5 moldm–3, λex = 320 nm): λem = 451 nm. MS
(ESI): m/z = 795.7 [M + H]+ (calcd. 795.3). C58H42N4 (795.00): 125.9 (CE3), 125.1 (CA3/C3), 125.0 (CA3/C3), 124.0 (CD5), 123.3
calcd. C 87.63, H 5.32, N 7.05; found C 87.35, H 5.58, N 7.01.
(CC4), 122.9 (CB5), 121.4 (CA4+F3), 120.4 (CB3+D3) ppm; CH4 signal
(CA5), 129.6 (CG4+H2/H3), 128.4 (CG3+E5), 127.9 (CG2), 127.5 (CF5),
not observed. IR (solid): ν = 3051 (w), 1684 (w), 1653 (w), 1607
˜
[Ir(ppy)2(1)][PF6]: yellow suspension of [Ir2(ppy)4(μ-Cl)2]
A
(s), 1583 (m), 1558 (w), 1541 (w), 1522 (w), 1506 (w), 1477 (s), 1439
(w), 1423 (m), 1383 (w), 1315 (w), 1269 (w), 1227 (w), 1163 (m),
1074 (m), 1063 (m), 1030 (m), 1007 (m), 878 (w), 835 (s), 785 (m),
750 (s), 719 (m), 690 (m), 669 (w), 651 (w), 631 (w) cm–1. UV/Vis
(55.4 mg, 0.052 mmol) and 1 (33.2 mg, 0.103 mmol) in MeOH was
placed in a vial in a microwave reactor at 120 °C for 2 h. The
orange solution was cooled to room temperature, and an excess of
NH4PF6 was added. The mixture was stirred for 30 min and was
then concentrated to dryness. Purification by column chromatog-
raphy (alumina, CH2Cl2 changing to CH2Cl2/MeOH, 100:1; then
silica, CH2Cl2 changing to CH2Cl2/MeOH, 100:1) yielded [Ir(ppy)2-
(CH2Cl2, 9.97ϫ10–6 moldm–3): λmax (ε)
= 229 (47000), 271
(66000), 297 nm (sh, 56000 dm3 mol–1 cm–1); emission (CH2Cl2,
9.97ϫ10–6 moldm–3, λex = 229 nm): λem = 608, 637 (sh) nm. MS
(ESI): m/z
=
887.5 [M
–
PF6]+ (calcd. 887.2).
1
(1)][PF6] as an orange solid (75 mg, 0.077 mmol, 75%). H NMR
C44H31BrF6IrN4P·0.6CH2Cl2 (1083.79): calcd. C 49.43, H 2.99, N
(500 MHz, CD2Cl2): δ = 8.70 (d, J = 1.5 Hz, 1 H, HF3), 8.65 (d, J
= 8.2 Hz, 1 H, HE3), 8.14 (td, J = 8.1, 1.0 Hz, 1 H, HE4), 7.90 (d,
J = 4.9 Hz, 1 H, HE6), 7.85 (overlapping m, 3 H, HB3+B4+D3), 7.81
(d, J = 8.3 Hz, 2 H, HH2), 7.76 (t, J = 8.2 Hz, 1 H, HD4), 7.71 (d,
J = 5.7 Hz, 1 H, HB6), 7.68 (d, J = 1.6 Hz, 1 H, HF5), 7.61 (d, J =
5.4 Hz, 1 H, HD6), 7.54 (d, J = 7.6 Hz, 1 H, HC3), 7.42 (d, J =
8.4 Hz, 2 H, HH3), 7.39 (d, J = 6.4 Hz, 1 H, HE5), 7.25 (d, J =
7.6 Hz, 1 H, HA3), 7.08 (m, 1 H, HD5), 7.04 (m, 1 H, HB5), 6.96
(overlapping m, 2 H, HC4+G4), 6.83 (t, J = 7.4 Hz, 1 H, HC5), 6.76
(t, J = 7.5 Hz, 2 H, HG3), 6.61 (t, J = 7.5 Hz, 1 H, HA4), 6.6 (br.,
HG2), 6.40 (t, J = 7.4 Hz, 1 H, HA5), 5.98 (d, J = 7.7 Hz, 1 H,
HC6), 5.60 (d, J = 7.6 Hz, 1 H, HA6), 2.45 (s, 3 H, Me) ppm. 13C
NMR (126 MHz, CD2Cl2): δ = 169.4 (CB2), 167.8 (CD2), 166.4
(CF6), 157.7 (CE2/F2), 157.5 (CE2/F2), 151.6 (CA1), 150.9 (CE6), 149.5
(CB6/D6), 149.3 (CB6/D6), 147.5 (CC1), 143.5 (CC2), 143.3 (CA2),
142.5 (CH4), 139.8 (CE4), 138.7 (CB4/D4), 138.5 (CB4/D4), 138.4
(CG1), 132.6 (CH1), 131.9 (CA6), 131.3 (CC5), 130.9 (CH3), 130.8
(CC6), 130.1 (CA5), 129.5 (CG4), 128.4 (CG3), 128.3 (CE5), 127.9
(CG2), 127.8 (CH2), 127.3 (CF5), 125.6 (CE3), 125.1 (CA3/C3), 125.0
(CA3/C3), 123.9 (CD5), 123.3 (CC4), 122.9 (CB5), 121.3 (CA4), 120.9
5.17; found C 49.42, H 2.95, N 5.28.
1
[Ir(ppy)2(3)][PF6]: H NMR (500 MHz, CD2Cl2): δ = 8.65 (d, J =
8.2 Hz, 1 H, HE3), 8.63 (d, J = 1.6 Hz, 1 H, HF3), 8.16 (t, J =
7.9 Hz, 1 H, HE4), 7.96 (d, J = 1.5 Hz, 2 H, HH2), 7.90 (d, J =
5.3 Hz, 1 H, HE6), 7.89 (t, J = 1.5 Hz, 1 H, HH4), 7.85 (overlapping
m, 3 H, HB3+D3+B4/D4), 7.77 (t, J = 7.8 Hz, 1 H, HB4/D4), 7.68 (d,
J = 5.8 Hz, 1 H, HB6/D6), 7.63 (d, J = 5.7 Hz, 1 H, HB6/D6), 7.60
(d, J = 1.6 Hz, 1 H, HF5), 7.55 (d, J = 7.8 Hz, 1 H, HC3), 7.42 (m,
1 H, HE5), 7.25 (d, J = 7.8 Hz, 1 H, HA3), 7.10 (t, J = 6.6 Hz, 1 H,
HB5/D5), 7.05 (m, 1 H, HB5/D5), 6.97 (overlapping t, 2 H, HC4+G4),
6.83 (t, J = 7.5 Hz, 1 H, HC5), 6.78 (t, J = 7.6 Hz, 2 H, HG3), 6.62
(t overlapping br. signal, 3 H, HA4+G2), 6.40 (t, J = 7.4 Hz, 1 H,
HA5), 5.96 (d, J = 7.6 Hz, 1 H, HC6), 5.59 (d, J = 7.6 Hz, 1 H,
HA6) ppm. 13C NMR (126 MHz, CD2Cl2): δ = 169.3 (CB2), 167.7
(CD2), 166.8 (CF6), 158.0 (CE2/F2), 156.8 (CE2/F2), 151.1 (CE6), 150.8
(CA1), 149.3 (CB6/D6), 149.2 (CB6/D6), 148.7 (CF4), 147.1 (CC1),
143.5 (CH1), 143.3 (CA2+C2), 139.7 (CE4), 139.4 (CG1), 138.6
(CB4/D4), 138.5 (CB4/D4), 136.5 (CH4), 131.9 (CA6), 131.3 (CC5),
130.6 (CC6), 130.2 (CA5), 129.7 (CH2), 129.65 (CG4), 128.4 (CE5),
128.3 (CG3), 127.9 (br., CG2), 127.7 (CF5), 125.7 (CE3), 125.0 (CA3),
124.9 (CC3), 124.6 (CH3), 123.9 (CB5/D5), 123.3 (CC4), 122.9
(CB5/D5), 121.3 (CA4/F3), 121.2 (CA4/F3), 120.3 (CB3+D3) ppm. IR
(CF3), 120.4 (CB3/D3), 120.3 (CB3/D3), 21.7 (CMe) ppm. IR (solid): ν
˜
= 3042 (w), 1684 (w), 1653 (m), 1607 (m), 1578 (w), 1558 (m), 1541
(w), 1506 (w), 1477 (s), 1420 (w), 1315 (w), 1267 (w), 1227 (w),
1165 (w), 1063 (w), 1028 (w), 883 (w), 835 (s), 815 (s), 791 (m), 756
(s), 731 (s), 698 (m), 631 (w) cm–1. UV/Vis (CH2Cl2,
1.00ϫ10–5 moldm–3): λmax (ε) = 228 (43000), 272 (64000), 308 nm
(solid): ν = 3041 (w), 1653 (w), 1607 (m), 1582 (w), 1537 (w), 1477
˜
(m), 1442 (w), 1423 (w), 1385 (w), 1356 (w), 1301 (w), 1269 (w),
1225 (w), 1165 (w), 1063 (w), 1030 (w), 878 (w), 831 (s), 785 (m),
754 (w), 727 (m), 702 (m), 694 (w), 651 (w) cm–1. UV/Vis (CHCl3,
5.04ϫ10–6 moldm–3): λmax (ε) = 230 (49000), 270 (70000), 395 nm
(sh, 6000 dm3 mol–1 cm–1); emission (CHCl3, 5.15ϫ10–5 moldm–3,
λex = 232 nm): λem = 635 nm. MS (ESI): m/z = 967.30 [M – PF6]+
(calcd. 967.04). C44H30Br2F6IrN4P (1111.72): calcd. C 47.54, H
2.72, N 5.04; found C 47.55, H 2.90, N 5.13.
(sh,
56000 dm3 mol–1 cm–1);
emission
(CH2Cl2,
1.00ϫ10–5 moldm–3, λex = 279 nm): λem = 600 nm. MS (ESI): m/z
= 823.3 [M – PF6]+ (calcd. 823.2). C45H34F6IrN4P·0.5CH2Cl2
(1010.43): calcd. C 54.08, H 3.49, N 5.54; found C 54.00, H 3.53,
N 5.66.
[Ir(ppy)2(2)][PF6], [Ir(ppy)2(3)][PF6], and [Ir(ppy)2(4)][PF6]: For the
preparations, see the Supporting Information.
1
[Ir(ppy)2(4)][PF6]: H NMR (500 MHz, CD2Cl2): δ = 8.77 (d, J =
1.5 Hz, 1 H, HF3), 8.64 (d, J = 8.2 Hz, 1 H, HE3), 8.15 (m, 1 H,
1
[Ir(ppy)2(2)][PF6]: H NMR (500 MHz, CD2Cl2): δ = 8.71 (d, J = HE4), 7.97 (overlapping m, 3 H, HH2+B4/D4), 7.92 (d, J = 5.2 Hz, 1
1.6 Hz, 1 H, HF3), 8.69 (d, J = 8.2 Hz, 1 H, HE3), 8.15 (t, J =
H, HE6), 7.86 (overlapping m, 3 H, HB3+D3+H4), 7.80 (d, J = 1.5 Hz,
7.9 Hz, 1 H, HE4), 7.89 (d, J = 5.4 Hz, 1 H, HE6), 7.85 (m, 3 H, 1 H, HF5), 7.77 (t, J = 8.4 Hz, 1 H, HB4/D4), 7.73 (d, J = 5.8 Hz, 1
HB3+D3+B4), 7.80 (dAB, J = 8.6 Hz, 1 H, HH2/H3), 7.76 (overlapping
H, HB6/D6), 7.65 (overlapping m, 5 H, HB6/D6+I2), 7.56 (d, J =
t, J = 7.9 Hz, 1 H, HD4), 7.73 (dAB, J = 8.6 Hz, 1 H, HH2/H3), 7.70 7.7 Hz, 1 H, HC3), 7.41 (m, 1 H, HE5), 7.30 (m, 9 H, HJ3+A3), 7.17
(d, J = 5.8 Hz, 1 H, HB6), 7.64 (overlapping d, 2 H, HF5+D6), 7.54 (d, J = 8.5 Hz, 4 H, HI3), 7.14 (d, J = 7.9 Hz, 8 H, HJ2), 7.11 (d,
(d, J = 7.8 Hz, 1 H, HC3), 7.39 (m, 1 H, HE5), 7.25 (d, J = 7.8 Hz,
J = 7.3 Hz, 1 H, HB5/D5), 7.07 (overlapping m, 5 H, HB5/D5+J4),
6.98 (overlapping t, 2 H, HC4+G4), 6.84 (t, J = 7.5 Hz, 1 H, HC5),
1 H, HA3), 7.09 (m, 1 H, HD5), 7.04 (m, 1 H, HB5), 6.96 (overlap-
ping m, 2 H, HC4+G4), 6.82 (t, J = 7.5 Hz, 1 H, HC5), 6.77 (t, J = 6.78 (t, J = 7.5 Hz, 2 H, HG3), 6.62 (t overlapping broad signal, J
8
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Fine-Tuning of Properties of Materials for Photonic Devices
= 7.5 Hz, 3 H, HA4+G2), 6.41 (m, 1 H, HA5), 5.99 (d, J = 7.6 Hz, 1
H, HC6), 5.62 (d, J = 7.6 Hz, 1 H, HA6) ppm. 13C NMR (126 MHz,
CD2Cl2): δ = 169.4 (CB2), 167.7 (CD2), 166.6 (CF6), 157.8 (CE2/F2),
157.3 (CE2/F2), 151.8 (CF4), 151.4 (CA1), 150.9 (CE6), 149.5 (CB6/
D6), 149.3 (CB6/D6), 148.6 (CI4), 148.0 (CJ1), 147.4 (CC1), 143.5 (CA2/
C2/H3), 143.35 (CA2/C2/H3), 143.3 (CA2/C2/H3), 139.8 (CE4), 138.7
(CB4/D4/G1), 138.6 (CB4/D4/G1), 138.3 (CB4/D4/G1), 136.9 (CH1), 134.1
(CI1), 132.0 (CA6), 131.3 (CC6), 130.8 (CC5), 130.1 (CA5), 129.9
(CJ3), 129.6 (CG4), 128.5 (CI2), 128.45 (CH4), 128.4 (CE5), 128.0
(CG2/G3/F5), 127.95 (CG2/G3/F5), 127.9 (CG2/G3/F5), 125.6 (CE3), 125.2
(CJ2+A4), 125.0 (CC3), 124.5 (CH2), 124.0 (CI3), 123.9 (CB5/D5), 123.8
(CJ4), 123.3 (CC4), 122.9 (CB5/D5), 121.6 (CA4/F3), 121.3 (CA4/F3),
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120.45 (CB3/D3), 120.4 (CB3/D3) ppm. IR (solid): ν = 3032 (w), 1684
˜
(w), 1652 (m), 1582 (s), 1555 (m), 1541 (m), 1506 (m), 1477 (m),
1429 (w), 1418 (w), 1387 (w), 1315 (w), 1269 (m), 1225 (w), 1163
(w), 1063 (w), 1030 (w), 876 (w), 833 (s), 785 (w), 752 (m), 727 (m),
692 (s), 669 (w), 660 (w), 648 (w) cm–1. UV/Vis (CHCl3,
5.00ϫ10–6 moldm–3): λmax (ε) = 229 (93000), 256 (92000), 272
(91000), 296 (96000), 342 nm (84000 dm3 mol–1 cm–1); emission
(CHCl3, 5.15ϫ10–6 moldm–3, λex = 229 nm): λem = 604 nm. MS
(ESI): m/z
=
1295.2 [M
–
PF6]+ (calcd. 1295.4).
C80H58F6IrN6P·0.2CH2Cl2 (1457.52): calcd. C 66.09, H 4.04, N
5.77; found C 65.95, H 4.05, N 5.94.
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CCDC-869670 {for [Ir(ppy)2(1)][PF6]}, -869671 {for [Ir(ppy)2(2)]-
[PF6]} and -869672 {for [Ir(ppy)2(3)][PF6]} contain the supplemen-
tary crystallographic data for this paper. These data can be ob-
tained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
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Supporting Information (see footnote on the first page of this arti-
cle): Additional experimental details and crystallographic data.
Acknowledgments
We acknowledge the financial support of the European Union
(CELLO, STRP 248043), the Spanish Ministry of Economy and
Competitivity (MINECOM) (MAT2011-24594, CTQ2009-8970),
and Consolider-Ingenio on Molecular Nanoscience (CSD2007-
00010), and the Generalitat Valenciana (Prometeo/2012/053), the
Swiss National Science Foundation, the Swiss National Center of
Competence in Research “Nanoscale Science”, the European Re-
search Council (Advanced Grant 267816 LiLo) and the University
of Basel. A. P. acknowledges the support of an FPI grant from
MINECOM. PD Dr. Daniel Häussinger is thanked for assistance
with the low-temperature NMR spectroscopic studies.
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Received: April 19, 2012
Published Online: ᭿
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© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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9

Job/Unit: I20394
/KAP1
Date: 02-07-12 16:04:05
Pages: 10
E. C. Constable, C. E. Housecroft et al.
FULL PAPER
LECs: Fine-Tuning Emissions
∧
∧
Four [Ir(ppy)2(N N)][PF6] (N N = 4,6-di-
phenyl-2,2Ј-bipyridine derivative) com-
plexes have been synthesized and charac-
terized. In solution, the complexes are
short-lived emitters with emission maxima
between 600 and 635 nm; the solid-state
emission spectra are similar. The perform-
ances of the complexes as electrolumin-
escent components in LECs have been
evaluated.
A. M. Bünzli, H. J. Bolink,
E. C. Constable,* C. E. Housecroft,*
M. Neuburger, E. Ortí, A. Pertegás,
J. A. Zampese ................................. 1–10
Fine-Tuning of Photophysical and Elec-
tronic Properties of Materials for Photonic
Devices Through Remote Functionali-
zation
Keywords: Iridium / Ligand design / Photo-
physical properties / Electroluminescence /
X-ray diffraction
10
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