Positively charged iridium(lll) triazole derivatives as blue emitters for light-emitting electrochemical cells

Article abstract of DOI:10.1002/adfm.201000223

Cationic blue-emitting complexes with (2,4-difluoro)phenylpyridine and different 1,2,3-triazole ligands are synthesized with different counterions. The influence of the substituents on the triazole ligand is investigated as well as the influence of the co

Full text of DOI:10.1002/adfm.201000223

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Positively Charged Iridium(III) Triazole Derivatives as
Blue Emitters for Light-Emitting Electrochemical Cells
By Mathias Mydlak, Claudia Bizzarri, David Hartmann, Wiebke Sarfert,
¨
Gunter Schmid, and Luisa De Cola*
double layers. As a result, fabrication of
thick luminescent devices without affecting
their efficiencies is possible, as well as the
preparation of large surface LEECs.
Cationic blue-emitting complexes with (2,4-difluoro)phenylpyridine and
different 1,2,3-triazole ligands are synthesized with different counterions. The
influence of the substituents on the triazole ligand is investigated as well as
the influence of the counterions. The substituents do not change the emission
energy but, in some cases, slightly modify the excited-state lifetimes and the
emission quantum yields. The excited-state lifetimes, in apolar solvents,
are slightly dependent on the nature of the counterion. A crystal structure of
one of the compounds confirms the geometry and symmetry postulated on
the basis of the other spectroscopic data. Light-emitting electrochemical cell
devices are prepared and the recorded emission is the bluest with the fastest
response time ever reported for iridium complexes.
The first OLEECwas reported byPei et al.
and consists of a polymer where a salt was
added to have mobile ions.[3] Instead of
using additional salts in the emissive layer,
the emitters can be salts themselves. The
first LEEC based on a cationic transition
metal complex was reported in 1996 by
Rubner et al.[1] In 2004, we reported a LEEC
based on a dinuclear ruthenium complex as
dopant of a polymer, exhibiting a two-color
behavior.[7] At the moment, the most
common materials are cationic metal
complexes based on iridium,[8–21] ruthenium,[6,15,22–26]
osmium,[27] platinum,[28,29] and even copper.[30,31] Even positively
charged polymers made from zinc-terpyridine complexes have
been prepared showing electroluminescence.[32] The most
common counterion is hexafluorophosphate because complexes
can be easily precipitated and purified with this anion. Other
studied counterions include chloride, perchlorate, and
tetrafluoroborate.[31]
A drawback of LEECs is that usually the turn-on time, the time
needed to see the emission after the application of the voltage, is
very long (minutes or hours) due to the slow diffusion of charges
that results in the formation of the double-layers. This prevents
their use in display applications but LEECs are still very appealing
for lighting devices where large-area emission and cheap and easy
processing are required. In order to decrease the turn-on time of
LEECdevicesionicliquidshavebeenemployedtoreplacethemore
common polymeric matrices used to process the emissive
layer.[21,25,33] In fact, ionic liquids allow good film formation,
sincemostofthechargedspeciesaresolubleinthesesolutionsand
they increase the amount of mobile ions inside the layer, especially
since the cations of the ionic liquids show a higher mobility than
the relatively bulky monocationic complexes. On the other hand,
the use of bulky charged complexes avoids concentration
quenching inside the device by increasing the distance between
the emissive complexes.[9,34]
1. Introduction
Light-emitting electrochemical cells (LEECs) represent an inter-
esting possible alternative to the more-investigated organic light-
emitting diodes (OLEDs). The difference between OLEDs and
LEECs resides on the use of charged complexes that provide the
ionic transport in the device. In other words, the mobile ions in the
layer move towards the electrodes upon application of a voltage,
and this migration causes a drop of potential at the electrodes and,
as a result, charge injection becomes easier and will take place
when the applied voltage exceeds the potential corresponding to
the bandgap of the electroluminescent material.[1–6] Therefore, no
additional layers are needed in the device and the emissive layer
can be solution processed, which makes industrial manufacturing
easier. The LEEC devices also have other advantages such as that
the electrodes of LEECs can be made of cheaper and less reactive
materials than in OLEDs, since the work functions have no
influenceonthechargeinjection. Furthermore,theappliedvoltage
does not drop over the bulk film but only within the thin ionic
[*] Prof. L. De Cola, M. Mydlak, C. Bizzarri
¨
¨
¨
Westfalische Wilhelms-Universitat Munster
Physikalisches Institut and Center for Nanotechnology (CeNTech)
Mendelstrasse 9, 48149 Mu¨nster (Germany)
E-mail: decola@uni-muenster.de
In this paper, we report the synthesis, characterization, and
photophysical and electrochemical properties of a series of
monocationic iridium complexes bearing two difluorophenylpyr-
idine (dfppy) ligands and a pyridine-N-substituted-1,2,3-triazole.
Oneofthecomplexeshasalsobeencrystallizedtoshowthegeneral
structureandgeometryofthecomplexesandtheX-raydataarealso
Dr. D. Hartmann, Dr. W. Sarfert, Dr. G. Schmid
Siemens AG, Corporate Technology, CTMM1
¨
Gunther-Scharowsky Strasse 1, 91058 Erlangen (Germany)
DOI: 10.1002/adfm.201000223
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discussed. The use of triazole ligands already explored by our
group for OLED technology has the advantage of an easy
transformation of neutral complexes into charged ones by
substitution on the N3-atom of the triazole moiety.[35]
Furthermore, the LUMO of this ligand is higher in energy than
the LUMO of the more widely used bipyridine andphenanthroline
ligands, maintaining the high-energy emission of the triazole
complexes, which falls into the blue region of the visible
spectrum.[9,11,36–44] We demonstrate that these charged complexes
are blue emitters, also in electroluminescent devices, and can be
used as an electroluminescent layer in combination with ionic
liquids in LEEC devices. We also compare the influence of the
substituent andthecounterionsonthephotophysicalpropertiesas
well as on device characteristics. To the best of our knowledge, the
complexesreported inthis paperarethe bluestelectroluminescent
compounds, with the fastest turn on time ever reported. A similar
emission energy was observed for a different class of iridium
complexes.[10]
was the only one that had to be carried out under anhydrous
conditions, following a new synthetic route.[47,48] After the
reaction, aqueous ammonia solution (32%) was added to
the reaction mixture and stirred for 1 h in order to remove the
catalyst forming the characteristic blue water-soluble
tetraamminediaquacopper(II) complex, [Cu(NH3)4(H2O)2]2þ
.
Then diethyl ether was added, and the aqueous layer was
separated. The organic layer was washed with water until the
washings reached pH 7.
Toformthefinalcomplex,thetriazolesandthedichloro-bridged
iridium complex were stirred together in a dichloromethane/
ethanol mixture (3:1) overnight.[46,49] The complexes were purified
by repeated recrystallization. They have been characterized using
1H NMR and 19F NMR spectroscopy, high-resolution mass
spectrometry, and elemental analysis. Additionally, a crystal
structure of complex 8a was obtained in order to illucidate the
structure. Synthetic details and the full characterization can be
found later.
2.1.1. Crystal Structure of Complex 8a
The crystal structure depicted in the Supporting Information, S1
shows that the nitrogen atoms of the two dfppy ligands are trans to
2. Results and Discussion
˚
each other with Ir–N bond lengths of 2.056 and 2.048 A,
respectively. The Ir–C bond lengths of the cyclometalating carbon
2.1. Synthesis and Characterization
˚
atoms on these ligands are 2.017 and 2.011 A, respectively.
The longest bond lengths to Ir are from the nitrogen atoms on the
triazole ligand from the pyridine moiety with a distance of 2.179
˚
and 2.128 A from the triazole moiety. The torsion angle between
the triazole and the first phenyl ring is 27.748 and the torsion angle
between the phenyl rings of the biphenyl part is ꢀ15.018.
Scheme 1 represents a general synthetic route to prepare
the ligands that will be then used for complexation as shown
in Scheme 2. The 1,2,3-triazoles were prepared by click
chemistry,[45,46] that is, copper-catalyzed Huisgen cycloadditions.
2-Ethynylpyridine was reacted with a substituted azide under
the conditions given in Scheme 2 to give the desired product in
one step. The synthesis of the previously reported triazole 1
2.2. Photophysical Characterization
2.2.1. Absorption and Emission Spectroscopy
The absorption spectra of the complexes 5–8
were recorded in dichloromethane solutions at
room temperature (Fig. 1 for 5a–8a, Supporting
Information, S2 for 5b–8b and 4). The absorp-
tion bands at high energy (240–320 nm) can be
assigned to p!pꢁ transitions involving the
coordinated ligands. In particular, the main
peakat ꢂ250 nm aretransitions localized onthe
dfppy ligands and on the triazole moiety, while
at lower energy (300–320 nm) the pyridine
moieties of the ligands are the major players.
The weaker absorption bands (320–450 nm) are
assigned to spin-allowed singlet-to-singlet
metal-to-ligand charge-transfer (1MLCT) and
at lower energies to spin-forbidden singlet-to-
triplet metal-to-ligand charge-transfer (3MLCT)
transitions. These last bands are quite intense
despite the forbidden character. This is due to
the heavy metal atom effect, which causes a
strong spin-orbit coupling.[50]
It is interesting to notice that the absorption
spectra of the biphenyl derivative compounds
Scheme 1. 1,2,3-triazole ligands and appropriate click conditions for the different ligands.
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Scheme 2. General route for the preparation of the iridium complexes presented in this paper including the studied counterions and the abbreviations
used.
8a and 8b show another band with high intensity at 290 nm (see
Supporting Information, S2). This bandisdueto p!pꢁ transitions
on the biphenyl substituent on the triazole ligand, which can be
confirmed by the absorption spectrum of the free ligand, which
shows a similar band at 294 nm.
All the investigated complexes show bright blue emission at
room temperature in solution. They are almost identical despite
the different substitution on the triazole ligand. The photolumi-
nescence (PL) spectra for complexes 5a and 7a, 6a and 8a, and 5–8b
in degassed dichloromethane solution arefound in Figure2 and in
the Supporting Information, S3a and S3b. They have similar
structured features with an intense band at 452 nm, a second less
intense vibronic progression at 483 nm and a shoulder around
505 nm. The structured emission spectrum is due to a large
amount of ligand-centered (3LC) character of the excited state,
which is indeed a mixture between 3MLCTand 3LC states. [17,51–53]
To the best of our knowledge these complexes are amongst the
bluest charged iridium complexes ever reported.[8,10,54] Their
emission quantum yields are remarkably high for charged
complexes in solution and for all the complexes, yields are around
25%, except for complex 8, in degassed solution. The emission
quantum yields dramatically decrease in aerated solution due to
Figure 1. Absorption spectra of complexes 5a (ꢀ), 6a (ꢃꢃꢃ), 7a (- - -), and 8a
(ꢀ ꢃ ꢀ) in CH2Cl2 solutions at room temperature.
Figure 2. Normalized RT emission spectra of the complexes 5a (ꢀ) and 7a
(- - -) in deaerated solutions in dichloromethane excited at 352 nm.
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the quenching by oxygen, confirming the triplet character of the
emission. Complexes 8a and 8b show emission quantum yields
around 10%.
solutions. The compounds show oxidations in the range of
þ1.19 to þ1.27 V. Compounds 6a and 6b only show semi-
reversible oxidations. Compared to neutral Ir complexes with
two dfppy ligands and a pyridine-1,2,4-triazole ligand with
oxidations at around þ0.96 V the oxidations occur at higher
potential due to the absence of the negative charge on the nitrogen
of the triazole ligand, resulting in a much weaker sigma-donation,
which makes the iridium ion more positive than in neutral
complexes.[35] This causes a more difficult oxidation of the
metal, which is less electron rich, and an increase in the
oxidation potential is observed. The first reductions of the
complexes are not fully reversible and can be assigned to a
reduction of the pyridine rings on the ancillary ligands. Values in
the same range have been reported for complexes containing
phenylpyridines and pyridine-pyrazoles or bipyridines as ancillary
ligands.[10,37,40,41,44] The second reductions, which are around
ꢀ2.5 V, are assigned to the fluorinated phenylpyridines.
Representative waves of the measurements can be seen in the
Supporting Information, S4.
The excited-state lifetimes are somewhat dependent on the
counterion present in the complex. We believe that in dichlor-
omethane, where the ions are very close to each other, the different
counterions could be responsible for a slightly different packing
between the cationic and the anionic part. To confirm this
hypothesis the lifetimes of the complexes 6a and 6b were
investigated also in a polar solvent (acetonitrile), where the ions
should be solvated and separated. The data show almost identical
lifetimes of 1.69 and 1.65 ms, respectively, for the two different
counterions. We also compared the absorption and emission
spectra of 6b in the two solvents (see Supporting Information, S8),
but no appreciable changes were detected. The excited-state
lifetimesofthecomplexesarerathershort,below1 ms,(seeTable1)
for iridium complexes and are very similar for all the complexes
with the exception of the complexes bearing the biphenyl
substituent on the triazole.
Forthese, thelifetimes are almost fourtimes higher, which isan
apparent contradiction for these complexes. When the biphenyl is
present on the triazole the lowest excited state should be lower in
energy than the ligand with saturated group as substituent.
Furthermore, the higher conjugation, triazole and two phenyls,
lower the triplet excited state of the ligand, allowing a stronger
mixing between the with the 3MLCT states. Therefore we believe
that in the case of the complexes 8a and 8b the lowest excited state
2.4. Device Properties
2.4.1. Fabrication of LEEC Devices
All LEEC devices incorporating the triazole-based complex
materials were fabricated by spin-coating on indium tin oxide
(ITO)-coveredglasssubstrates.Thetypicallayerstructuresketched
in the schematic view of Figure 3 consists of 100 nm poly(3,4-
3
involves the substituted triazole ligand and has a stronger LC
character than for the other complexes, due to a larger mixing
(closer energy) of the ligand-centered states with the 3MLCTstates.
This different, more ligand-centered character would explain the
longer excited-state lifetimes on one hand, and the lower quantum
yields ontheother hand (Table1). Furthermore, the free rotationof
the phenyl rings in the excited state would influence the non-
radiative decay rates, therefore reducing the emission quantum
yields. These non-radiative contributions can be calculated
through the radiative and non-radiative rate constants (see
Supporting Information, S6), which indeed show lower radiative
rate constants for complexes 8a and 8b.[53]
ethylenedioxythiophene):poly(styrenesulfonate)
(PEDOT:PSS)
and 70 nm of emitting layer composed of the chosen iridium
complex blended with an ionic liquid tetrabutylammonium
trifluoromethanesulfonate (TBAOTf), which accelerates the
charge injection into the emitting layer and hence reduces the
turn-on time of the device. The reduction of turn-on times in
LEECs using ionic liquids like 1-butyl-3-methylimidazolium
hexafluorophosphate (BMIMþPF6 ) was already shown by
–
Malliaras et al.[55] After depositing the PEDOT:PSS layer, the
emitting layer was prepared: 10 mg transition metal complex
materialtogetherwithionicliquidweredilutedin1 mLacetonitrile
in a mole ratio 1:1. The solution was filtered using a 0.1 mm PTFE-
filter, spin-coatedontop ofthePEDOT:PSSlayer, andtheresulting
film was baked for 2 h at 80 8C under vacuum. Finally, a 150–
200 nm thick aluminum layer was evaporated on top used as a
2.3. Electrochemical Characterization
Inordertoinvestigatethefrontierorbitalsofthecompounds,cyclic
voltammetry (CV) was performed in freshly distilled acetonitrile
Table 1. Absorption and emission spectra, quantum yield, lifetime and redox potentials of complexes 5a–8b [a].
ꢀ1
lmax,abs [b][nm] (e ꢄ104
M
cmꢀ1
)
lmax,em [c][nm]
t [ms] deaer.
Fem deaer.[d]
1
1
Red
Complex
E = 1/2Ox [V]
E =
[V]
2
2
5a
5b
6a
6b
7a
7b
8a
8b
248(5.13), 302(2.14,sh), 362(5.50)
248(5.24), 303(2.03,sh), 363 (5.89)
247(4.99), 302(1.90,sh), 363(5.49)
453(1), 483 (0.87)
453(1), 483 (0.87)
452(1), 483 (0.87)
452 (1), 483 (0.87)
453(1), 483(0.93)
453(1), 483(0.94)
452 (1), 482 (0.88)
452 (1), 482 (0.87)
0.68
0.58
0.73
0.63
0.87
0.72
2.24
2.05
0.21
0.21
0.15
0.22
0.24
0.17
0.11
0.09
1.22[f]
1.24[f]
1.27[e]
1.25[e]
1.19[e]
1.22[e]
1.26[e]
1.25[e]
ꢀ2.18[f], ꢀ2.59[f]
ꢀ2.16[f], ꢀ2.59[f]
ꢀ2.17[f], ꢀ2.51 [f]
ꢀ2.14[f], ꢀ2.57 [f]
ꢀ2.02[f], ꢀ2.44[e]
ꢀ2.01[f], ꢀ2.42[e]
ꢀ2.08[f], ꢀ2.52[f]
ꢀ2.07[f], ꢀ2.52[f]
247(5.27), 303(1.97,sh), 363(5.63)
259(7.73), 304(3.29,sh), 362(8.73)
259(8.34), 314(3.44,sh), 362(7.97)
261(3.89), 291(3.85), 314(2.71,sh), 358(6.13)
262(4.76), 290(4.73), 314(3.32,sh), 360(7.48)
[a] All data for complexes in dichloromethane. [b] ‘‘sh’’ denotes a shoulder. [c] lexc ¼ 350 nm. [d] Quantum yields were measured in an integrating sphere
system. [e] Irreversible. [f] Not fully reversible.
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Table 2. Summary of the device characteristics.
Complex
tmax[a] [s]
Lmax[b] [cd mꢀ2
]
lmax,EL[c] [nm]
Lifetime [d] [min]
5a
5b
6a
6b
7a
8b
390
240
860
120
180
310
14.5
19.4
44.9
31.4
42.7
32.1
460, 488
460, 488
460, 488
456, 488
460, 488
456, 488
38.0
10.5
24.5
3.4
10.0
28.6
Figure 3. Schematic view of the device structure.
[a] Time required to reach the maximum luminance. [b] Maximum lumi-
nance value for a constant bias voltage 5.0 V applied to the device.
[c] Wavelength peak measured in electroluminescence at 5.5 V. [d] Time
to reach the half of the maximum luminance under a constant bias voltage
5.0 V.
cathode,andthedevicewasencapsulatedbyaglasscappinglayerto
protect the organic layers against penetrating oxygen and water.
The active lighting area was 4 mm2.
2.4.2. Electroluminescent Properties of LEECs
In Figure 5 the electroluminescent spectra for the complexes 5a
and5bmeasuredatafixedvoltage(5.5 V)areshown.Ascanbeseen
the devices exhibited blue electroluminescence with a first
emission maximum at a wavelength of 456–460 nm and a second
maximum at 488 nm. This characteristic double peak emission
was also observed for the complexes 6–8 having a first peak at 456–
460 nm and a second peakat 488 nm. Hence, as observed in case of
the PL spectra in degassed dichloromethane solution, all LEEC
devices show almost identical emission maxima independent of
the counterions (Fig. 5). We have also compared the electro-
luminescent spectra with the solid-state spectra of the complexes
recorded both in ionic liquid and in a poly(methyl methacrylate)
(PMMA) matrix. The results (Supporting Information, S7a and b)
demonstrate that the matrix has a negligible influence on the
emission properties. In the electroluminescence spectra the two
spectral peaks are slightly shifted towards higher wavelength
values compared to the PL data from 452 to 456–460 nm and from
482 to 488 nm. Such wavelength shifting phenomena for blue-
emitting iridium LEECs have also been reported in recent
papers.[41] Ithastobeconsideredthatthespectralshiftisverysmall
for a device using ionic liquids. For recently reported good blue
LEEC devices the use of ionic liquids made the EL spectrum shift
66 nm to the red.[10]
As an example in Figure 4 the corresponding results for the time-
dependent luminance (L) and current (C) of the triazol-based
iridium complexes 5a and 5b are presented. The L(t) and C(t)
characteristics are based on averaged data of up to 6 single devices
for each complex. For a description of the light measurements
please refer to the experimental part. For the shown complex, the
maximum luminance exhibits a comparable magnitude for both
types of counterions with 19.4 cd mꢀ2 for the devices with PF6
counterions (5b) and 14.5 cd mꢀ2 for the devices with BF4
counterions (5a). However, the lifetime (time to reach the half of
the maximum luminance) is higher for the latter one (38.0 min for
5a and 10.5 min for 5b). Averaged data for tmax (time required to
reach the maximum luminance), Lmax (maximum luminance),
and lifetime for complexes 5a, 5b, 6a, 6b, 7a, and 8b are depicted in
Table 2. For the investigated set of complexes, tmax ranges between
120 (6b) and 860 s (6a), Lmax between 14.5 (5a) and 44.9 cd mꢀ2 (6a)
and the lifetime between 3.4 (6a) and 38 min (5a). The short time
scale for tmax in the range of seconds is facilitated by the TBAOTf
ionic-liquid blend. The observed differences in the device
performance of the complexes, further device optimizations with
regard to brightness, and lifetime, as well as the role of the
counterions, are currently still under investigation and out of the
scope of this work.
Figure 4. LEEC device L and C measured at fixed voltage (5.0 V) as a
function of time for the complexes 5a (ꢀ) and 5b (ꢃꢃꢃ).
Figure 5. Electroluminescent spectra and pictures of LEEC devices biased
at 5.5 V based on complexes 5a (ꢀ) and 5b (ꢃꢃꢃ).
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through the device and through the photodiodes were measured by current
meters from National Instruments (NI9219). The maximal allowed current
through the devices was limited to 40 mA (current compliance). Using a
spectral camera (PR650) the photodiodes were calibrated and the
electroluminescent spectra of the different LEEC devices were detected
in the visible range between 380 and 780 nm.
3. Conclusions
We have reported a series of phosphorescent cationic iridium(III)
complexes based on N-substituted pyridine-1,2,3-triazoles. The
complexes were synthesized in reasonable yields and fully
characterized. They show blue PL and electroluminescence. The
turn-on times of the devices are in the range of seconds and show
only small spectral shifts despite the use of ionic liquids. To our
knowledge these are the bluest LEEC devices reported showing
such fast device-response times.
X-ray Crystallography: Data sets were collected with
a Nonius
KappaCCD diffractometer equipped with a rotating anode generator.
Programs used were as follows: data collection COLLECT [58], data
reduction Denzo-SMN [59], absorption correction SORTAV [60,61] and
Denzo [62], structure solution SHELXS-97 [63], structure refinement
SHELXL-97 [64], and graphics SCHAKAL [65].
Synthesis and Characterization: All reagents were analytical grade and
used as received. Solvents were purified according to the standard
procedures [66]. All reactions were performed under inert atmosphere
(Schlenk-line techniques), except where noted. Column chromatography
(CC) was performed with silica gel 60 (particle size 63–200 mm, 230–
400 mesh, Merck) using common flash procedures [67]. NMR spectra were
recorded on an ARX 300 or an AMX 400 from Bruker Analytische
Messtechnik (Karlsruhe, Germany). The 1H NMR chemical shifts (d) of
the signals are given in ppm and referenced to residual protons in the
deuterated solvents: chloroform-d1 (7.26 ppm), dimethyl sulfoxide-d6
(2.50 ppm), or acetone-d6 (2.09 ppm). The 19F NMR chemical shifts are
referenced to CFCl3 (0.00 ppm) as an internal standard. The signal
splittings are abbreviated as follows: s, singlet; d, doublet; t, triplet; q,
quartet; m, multiplet. All coupling constants (J) are given in Hertz (Hz).
Mass spectrometry was performed in the Department of Chemistry,
University of Mu¨nster. Electrospray ionization (ESI) mass spectra were
recorded on a Bruker Daltonics (Bremen, Germany) MicroTof with loop
injection. Elemental analysis was recorded at the University of Milan, Italy.
2-(2,4-difluorophenyl)pyridine and (F2ppy)2Ir(m-Cl)2Ir(F2ppy)2 were
prepared as previously reported [49]. The 1,2,3-triazole based ligands
were prepared by copper(I)-catalyzed click chemistry. Ligands 1 and 2
(Scheme 1) have been reported before with different synthetic routes
[47,68–71]. For ligand 1 we report a new procedure, and the route used
for ligand 2 was taken from a similar compound with a phenyl ring instead
of the pyridine [72]. The triazole 2 could be easily synthesized in a
dichloromethane/ethanol mixture (4:1) in the presence of [Cu(MeCN)4]PF6
and precipitated from the reaction mixture. Washing with dichloro-
methane/ethanol and filtration through silica gave a pure product. Ligand 3
was synthesized by a one-pot reaction starting from aniline. The azide
necessary for the reaction was generated in situ with tert-butylnitrite and
azidotrimethylsilane, followed by a classical click reaction [73]. Triazole 4
was obtained using the classical click chemistry conditions, with copper(II)-
sulfate and sodium ascorbate to generate the catalytic Cu(I) in situ. The
work-up was similar to the one of 1. It turned out to be very helpful to stir
the reaction mixtures with 32% ammonia solution for 30 min before
starting the work-up. Since the pyridine-triazoles are capable of binding to
copper the reaction yield was lowered strongly because of the formation of
copper complexes with the product. The presence of copper can be
monitored easily by the color of the ammonia solution because it turns blue
due to the formation of a copper(II) tetrammonium complex. After washing
with ammonia the solution needs to be washed with water until pH 7 is
reached.
4. Experimental
Photophysics: Absorption spectra were measured on a Varian Cary 5000
double-beam UV-Vis-NIR spectrometer and baseline corrected. Steady-
state emission spectra were recorded on a HORIBA Jobin-Yvon IBH FL-322
Fluorolog 3 spectrometer equipped with a 450 W xenon-arc lamp, double-
grating excitation and emission monochromators (2.1 nm mmꢀ1 disper-
sion; 1200 grooves mmꢀ1), and a Hamamatsu R928 photomultiplier tube
or a TBX-4-X single-photon-counting detector. Emission and excitation
spectra were corrected for source intensity (lamp and grating) by standard
correction curves. Time-resolved measurements were performed using
the time-correlated single-photon-counting (TCSPC) option on the
Fluorolog 3. NanoLED (402 nm; FHWM < 750 ps) with repetition rates
between 10 kHz and 1 MHz used to excite the sample. The excitation
sources were mounted directly on the sample chamber at 908 to a double-
grating emission monochromator (2.1 nm mmꢀ1 dispersion; 1200 grooves
mmꢀ1) and collected by a TBX-4-X single-photon-counting detector. The
photons collected at the detector are correlated by a time-to-amplitude
converter (TAC) to the excitation pulse. Signals were collected using an IBH
Data Station Hub photon counting module and data analysis was
performed using the commercially available DAS6 software (HORIBA Jobin
Yvon IBH). The quality of the fit was assessed by minimizing the reduced
chi squared function (x2) and visual inspection of the weighted residuals.
Luminescence quantum yields were measured with a Hamamatsu
Photonics absolute PL quantum yield measurement system (C9920-02)
equipped with a L9799-01 CW Xenon light source (150 W), monochro-
mator, C7473 photonic multi-channel analyzer, integrating sphere, and
employing U6039-05 PLQY measurement software (Hamamatsu
Photonics, Ltd., Shizuoka, Japan).
All solvents were spectrometric grade. Deaerated samples were
prepared by the freeze-pump-thaw technique.
Cyclic Voltammetry: CV was performed in a gas-tight single-compart-
ment three-electrode cell using a Voltalab 40 system from Radiometer
Analytical that consists of a PGZ301 potentiostat and Voltamaster 4
software. The working electrode is a Pt disc, the counter electrode a Pt
wire, and an Ag wire was used as a pseudoreference electrode. CVs were
elucidated and compared using IGOR. All glassware was dried prior to
use. The compounds (electrolyte, analyte, and reference) were placed in a
Schlenk flask that was then evacuated and heated with a heat gun to
eliminate any moisture and oxygen that had entered during addition [56].
The flask was then evacuated and filled three times with dry N2. The solvent
was added via syringe directly to the sealed Schlenk flask, the solution
sonicated if necessary and then degassed for 10 min with a gentle stream of
dry N2 [57]. After degassing, the solution was added, via syringe, to the
electrochemical cell under a positive N2 pressure. The solution was kept
under a positive N2 pressure during the measurements (see Supporting
Information, S3).
Device Preparation: PEDOT:PSS (Clevios AI4083) was supplied by H. C.
Starck and TBAOTf from Sigma Aldrich. In order to investigate the
electroluminescent properties of the LEEC devices the luminance was
detected as a function of time at an applied bias voltage of 5 V (constant
voltage mode). All electro-optical measurements were powered by using a
power source meter E3646A from Agilent Technologies. The resulting light
output was detected by calibrated photo diodes. The induced currents
Py-1,2,3-triazole-adamantyl (1). A solution of 2-ethynylpyridine (196 mL,
1.94 mmol) and 1-azidoadamantane (344 mg, 1.94 mmol) in distilled dry
tetrahydrofuran (THF) was purged with nitrogen. CuBr (55.6 mg,
0.38 mmol) and PMDTA (N,N,N0,N0,N-pentamethyl diethylenetriamine)
(81 mL, 0.38 mmol) in distilled dry THF were added and the solution was
stirred at room temperature (RT) for 48 h. Ammonia solution (32%) was
added and the solution was stirred for 1 h. Then the solution was extracted
between water and diethyl ether. The combined organic phases were
washed with brine, dried over MgSO4 and filtered through silica. The
1
solvent was removed to yield an off-white solid (506 mg, 93%). H NMR
(300 MHz, CDCl3, d): 8.49 (ddd, J ¼ 4.9, 1.7, 0.9, 1H), 8.16 (s, 1H), 8.12 (dt,
J ¼ 8.0, 1.0, 1H), 7.69 (td, J ¼ 7.8, 1.8, 1H), 7.20–7.06 (m, 1H), 2.21 (s,
10H), 1.70 (d, J ¼ 12.7, 7H). MS (ESI þ , MeOH): m/z 281.1752
([M þ H]þ), 303.1579 ([M þ Na]þ).
Adv. Funct. Mater. 2010, 20, 1812–1820
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Py-1,2,3-triazole-benzyl (2). To a solution of 2-ethynylpyridine (1.18 mL,
11.68 mmol) and benzyl azide (1.55 g, 11.64 mmol) in 100 mL MeCN an
aqueous solution of CuSO4 (517 mg, 2.07 mmol) and sodium ascorbate
(2.77 g, 13.98 mmol) was added. The last two reagents were dissolved in a
minimum volume of water. A bright orange solid formed and the mixture
heated up. After addition of 15 mL of MeCN the solid dissolved over 5 h and
was left to stir at RT overnight. All solvents were removed under reduced
pressure, the orange solid was suspended in ethyl acetate and sonicated.
The suspension was filtered and the solvent was removed under reduced
pressure to yield an off-white solid. (1.51 g, 54%). 1H NMR (300 MHz,
acetone, d): 8.55 (ddd, J ¼ 4.8, 1.7, 0.9, 1H), 8.43 (s, 1H), 8.10 (dt, J ¼ 7.9,
1.0, 1H), 7.85 (td, J ¼ 7.7, 1.8, 1H), 7.48–7.32 (m, 5H), 7.28 (ddd, J ¼ 7.5,
4.8, 1.2, 1H), 2.81 (s, 2H).
Py-1,2,3-triazole-phenyl (3). Aniline (1.02 g, 11.0 mmol) was dissolved in
30 mL of dried and freshly distilled MeCN in a 100 mL round-bottomed
flask under N2 flow and cooled to 0 8C in an ice bath. Tert-butyronitrite
(1.74 g, 17 mmol) was added, followed by TMSN3 (1.31 g, 11.0 mmol). The
resulting solution was stirred at RT until thin-layer chromatography (TLC)
measurements showed no presence of aniline anymore. 2-Ethynylpyridine
(1.13 g, 11.0 mmol) was dissolved in the same round-bottomed flask for a
one-pot reaction. CuSO4ꢃH2O (206 mg, 0.8 mmol) and sodium ascorbate
(660 mg, 3.3 mmol) were added to the solution and the resulting mixture
was stirred at RT overnight. The solvent was evaporated under reduced
pressure and the product was diluted with dichloromethane, to be
extracted three times with 35% ammonia solution. The organic phases
were dried over MgSO4, the solvent was evaporated under reduced
pressure and the product purified by chromatography on silica gel and
dichloromethane/methanol (99:1) as eluent to achieve 7 (1.20 g, 49%). 1H
NMR (300 MHz, CDCl3, d): 8.69 (s, 1H), 8.60 (dq, J ¼ 6, 1H), 8.29 (dt, J ¼ 9,
1H), 7.82 (m, 3H), 7.56–7.32 (m, 5H). MS (ESI þ , MeOH, m/z): calcd.
222.25; found 223.09 [MþH]þ, 245.08 [M þ Na]þ.
to remove the excess of the sodium or ammonium salts, respectively. After
drying, the compounds were recrystallized from ethanol four times and
dried under vacuum afterwards.
(F2ppy)2 Ir Py-1,2,3-triaz-adamantyl BF4 (5a). 1H NMR (300 MHz,
CD2Cl2, d): 9.46 (s, 1H), 8.70 (d, J ¼ 8.2, 1H), 8.31 (d, J ¼ 8.5, 2H), 8.09
(d, J ¼ 6.3, 1H), 7.91–7.76 (m, 4H), 7.52 (dd, J ¼ 17.1, 6.2, 2H), 7.33
(d, J ¼ 6.2, 1H), 7.13–6.96 (m, 2H), 6.57 (d, J ¼ 18.0, 1H), 5.75 (t, J ¼ 9.9,
2H), 2.23 (s, 2H), 2.21 (s, 7H), 1.76 (s, 7H). 19F NMR (282 MHz, CD2Cl2,
d): ꢀ106.71 (d, J ¼ 10.9, 1H), ꢀ107.93 (d, J ¼ 10.4, 1H), ꢀ109.10
(d, J ¼ 10.9, 1H), ꢀ110.20 (d, J ¼ 10.4, 1H), ꢀ151.60–152.10 (m, 2H).
HRMS: [M]þ calcd. 809.1624, found 809.1587. Anal. calcd. for
C39H32BF8IrN6: C 49.85; H 3.43; N 8.94; found: C 49.82, H 3.47, N 8.84.
(F2ppy)2 Ir Py-1,2,3-triaz-adamantyl PF6 (5b). 1H NMR (300 MHz,
CD2Cl2, d): 8.78 (s, 1H), 8.31 (d, J ¼ 7.9, 3H), 8.08 (td, J ¼ 7.8, 1.6, 1H),
7.84 (dt, J ¼ 7.6, 5.6, 3H), 7.52 (ddd, J ¼ 17.1, 5.8, 0.8, 2H), 7.36 (ddd,
J ¼ 7.6, 5.5, 1.3, 1H), 7.06 (dddd, J ¼ 18.1, 7.3, 5.9, 1.4, 2H), 6.57 (dddd,
J ¼ 18.0, 12.5, 9.2, 2.3, 2H), 5.74 (ddd, J ¼ 10.6, 8.6, 2.4, 2H), 2.25 (s, 3H),
2.20 (d, J ¼ 2.7, 6H), 1.85–1.71 (m, 7H). 19F NMR (282 MHz, CD2Cl2, d):
ꢀ71.32 (s, 3H), ꢀ73.83 (s, 3H), ꢀ106.64 (dt, J ¼ 10.8, 9.0, 1H), ꢀ107.76–
107.96 (m, 1H), ꢀ108.94–109.14 (m, 1H), ꢀ110.15 (dd, J ¼ 17.9, 7.5, 1H).
Mass L1-53-01 MS (ESI þ , MeOH, m/z): [M]þ 853.2224. Anal. calcd. for
C
39H32F10IrN6P: C 46.94, H 3.23, N 8.42; found: C 46.26, H 3.27, N 8.01.
(F2ppy)2 Ir Py-1,2,3-triaz-benzyl BF4 (6a). 1H NMR (300 MHz, CD2Cl2,
d): 9.04 (s, 1H), 8.38–8.25 (m, 3H), 8.06 (tt, J ¼ 7.9, 3.8, 1H), 7.90–7.76 (m,
3H), 7.68–7.59 (m, 1H), 7.51–7.43 (m, 1H), 7.42–7.29 (m, 6H), 7.04
(dddd, J ¼ 17.0, 7.3, 5.9, 1.4, 2H), 6.58 (dddd, J ¼ 14.8, 12.5, 9.2, 2.4, 2H),
5.77 (ddd, J ¼ 14.6, 8.5, 2.3, 2H), 5.70–5.55 (m, 2H), 1.64 (s, 2H). 19F NMR
(282 MHz, CD2Cl2, d): ꢀ106.65 (dt, J ¼ 10.8, 9.0, 1H), ꢀ107.48 (dt,
J ¼ 10.4, 9.0, 1H), ꢀ108.90–109.14 (m, 1H), ꢀ109.71–109.94 (m, 1H),
ꢀ151.35–151.49 (m, 3H). MS (ESI þ , MeOH, m/z): [M]þ 809.1587.
HRMS [M]þ calcd. 809.1624; found: 809.1587. Anal. calcd for
C36H24BF8IrN6: C 48.28, H 2.70, N 9.38; found: C 47.90, H 2.74, N 9.31.
(F2ppy)2 Ir Py-1,2,3-triaz-benzyl PF6 (6b). 1H NMR (300 MHz, CD2Cl2,
d): 8.63 (s, 1H), 8.31 (d, J ¼ 7.0, 2H), 8.14 (d, J ¼ 7.5, 1H), 8.05 (td, J ¼ 7.8,
1.6, 1H), 7.84 (t, J ¼ 6.8, 3H), 7.63 (d, J ¼ 5.0, 1H), 7.46 (d, J ¼ 5.0, 1H),
7.43–7.28 (m, 6H), 7.13–6.97 (m, 2H), 6.67–6.51 (m, 2H), 5.81–5.71 (m,
2H), 5.61 (s, 2H), 1.19 (t, J ¼ 7.0, 2H). 19F NMR (282 MHz, CD2Cl2, d):
ꢀ71.39 (s, 3H), ꢀ73.90 (s, 3H), ꢀ106.59 (dt, J ¼ 10.9, 9.0, 1H), ꢀ107.28–
107.47 (m, 1H), ꢀ108.95 (t, J ¼ 11.7, 1H), ꢀ109.77 (t, J ¼ 11.5, 1H). MS
(ESI þ , MeOH, m/z): [M]þ 809.1612. HRMS [M]þ calcd. 809.1624; found:
809.1642. Anal. calcd. for C36H24F10IrN6P: C 45.33, H 2.54, N 8.81; found:
C 45.29, H 2.51, N 8.71.
(F2ppy)2 Ir Py-1,2,3-triaz-phenyl BF4 (7a). 1H NMR (300 MHz, CDCl3, d):
9.77 (s, 1H), 8.75 (d, J ¼ 9, 1H), 8.25 (d, J ¼ 9, 2H), 8.07 (td, J ¼ 9, 3, 1H),
7.84–7.66 (m, 6H), 7.47 (m, 4H), 7.30 (t, J ¼ 6; 1H), 7.08–6.98 (m, 2H),
6.56–6.43 (m, 2H), 5.65 (td, J ¼ 9, 1.5, 2H). MS (ESI þ , MeOH, m/z): [M]þ
calcd. 795.95; found: 795.15. Anal. calcd for C35H22F8IrN6B: C 47.68, H
2.52, N 9.53; found: C 45.85, H 2.59, N 8.94.
(F2ppy)2 Ir Py-1,2,3-triaz-phenyl PF6 (7b). 1H NMR (300 MHz, CDCl3, d):
9.77 (s, 1H), 8.75 (d, J ¼ 9, 1H), 8.25 (d, J ¼ 9, 2H), 8.07 (td, J ¼9, 3, 1H),
7.84–7.66 (m, 6H), 7.47 (m, 4H), 7.30 (t, J ¼ 6; 1H), 7.08–6.98 (m, 2H),
6.56–6.43 (m, 2H), 5.65 (td, J ¼ 9, 1.5, 2H). MS (ESIþ, MeOH, m/z): [M]þ
calcd. 795.95; found: 795.15. Anal. calcd. for C35H22F10IrN6P: C 44.73, H
2.36, N 8.94; found: C 40.26, H 2.57, N 8.27.
4-Azido-biphenyl. 4-Bromo-biphenyl (1.4 g, 6.01 mmol) and sodium
azide (773 mg, 11.9 mmol) in 100 mL ethanol/water 3:1 were degassed by
bubbling of nitrogen for 5 min. Copper(I) iodide (228 mg, 1.2 mmol),
sodium ascorbate (59 mg, 0.3 mmol), and N,N’-dimethyl ethylenediamine
(0.2 mL, 1.9 mmol) were added and nitrogen was bubbled for another
3 min. The reaction mixture was refluxed for 6 h and the reaction was
monitored via TLC. After the reaction was finished a white precipitate was
filtered off, washed with water and dried under vacuum. (920 mg, 78%). 1H
NMR (300 MHz, CDCl3, d): 2.37 (dd, J ¼ 10.6, 4.1, 4H), 2.23 (t, J ¼ 7.4, 2H),
2.13 (t, J ¼ 7.3, 1H), 1.89 (d, J ¼ 8.6, 2H).
Py-1,2,3-triazole-biphenyl (4). 4-Azido-biphenyl (720 mg, 3.4 mmol), 2-
ethynylpyridine (380 mg, 3.7 mmol), and tetrakis(acetonitrile)copper(I)
hexafluorophosphate (273 mg, 0.7 mmol) in dichloromethane/methanol
4:1 were stirred at RT for 14 h. The product started precipitating after 1.5 h,
was filtered off, washed with water, and dried under vacuum to yield a light-
yellow solid (500 mg, 50%). 1H NMR (300 MHz, CDCl3, d): 8.49 (ddd,
J ¼ 4.9, 1.7, 0.9, 1H), 8.16 (s, 1H), 8.12 (dt, J ¼ 8.0, 1.0, 1H), 7.69 (td,
J ¼ 7.8, 1.8, 1H), 7.20–7.06 (m, 1H), 2.21 (s, 10H), 1.70 (d, J ¼ 12.7, 7H).
General Procedure for the Preparation of Iridium(III) Complexes with
Chloride Counterions: The dimer (F2ppy)2Ir(m-Cl)2Ir(F2ppy)2 and the
according 1,2,3-triazole were stirred in dichloromethane/ethanol 5:1
overnight. The starting materials were solubilized within 45 min. The
solvents were removed under reduced pressure. The resulting yellow solids
were dissolved in acetonitrile and filtered through celite. The solvent was
removed under reduced pressure and the solid was recrystallized from
ethanol three times and dried under vacuum.
General Procedure for Ion Exchange on the Iridium(III) Complexes: The
chloride counterion was exchanged to the desired tetrafluoroborate a or
hexafluorophosphate b by stirring the compound in a dichloromethane/
methanol mixture (10:1) with sodium tetrafluorborate or ammonium
hexafluorophosphate, respectively. The according complex with chloride
counterion was dissolved in an excess of dichloromethane. Another
solution of 15 equivalents of either ammonium hexafluorophosphate or
sodium tetrafluoroborate in methanol was added and the resulting turbid
mixture was stirred for 18 h at RT. After the removal of the solvents the
crude reaction mixture was suspended in water and sonicated for 5 min.
The precipitate was filtered off and washed with water excessively in order
(F2ppy)2 Ir Py-1,2,3-triaz-biphenyl BF4 (8a). 1H NMR (300 MHz, CD2Cl2,
d): 9.65 (s, 1H), 8.67 (d, J ¼ 7.8, 1H), 8.34 (d, J ¼ 9.2, 2H), 8.15 (t, J ¼ 7.9,
1H), 7.97 (d, J ¼ 8.8, 2H), 7.92–7.77 (m, 6H), 7.64 (d, J ¼ 6.9, 2H), 7.55
(d, J ¼ 5.0, 1H), 7.44 (dt, J ¼ 22.2, 7.0, 4H), 7.15–7.02 (m, 2H), 6.62 (ddd,
J ¼ 24.5, 12.1, 6.9, 2H), 5.84–5.74 (m, 2H), 5.33 (s, 3H). 19F NMR
(282 MHz, CD2Cl2, d): ꢀ106.34–106.74 (m, 1H), ꢀ107.37–107.71 (m, 1H),
ꢀ108.96 (t, J ¼ 11.7, 1H), ꢀ109.84 (t, J ¼ 11.5, 1H), ꢀ151.10 (dd, J ¼ 2.3,
1.1, 4H). MS (ESI þ , MeOH, m/z): [M]þ 871.1777. HRMS calcd. [M]þ
871.1781; found 871.1777. Crystals were grown from CH2Cl2. Anal. calcd.
for C41H26BF8IrN6 þ CH2Cl2: C 48.38, H 2.71, N 8.06; found: C 48.25, H
2.78, N 7.95.
(F2ppy)2 Ir Py-1,2,3-triaz-biphenyl PF6 (8b). 1H NMR (300 MHz, CD2Cl2,
d): 9.28 (s, 1H), 8.45 (d, J ¼ 7.9, 1H), 8.33 (dd, J ¼ 8.4, 1.0, 2H), 8.13 (td,
J ¼ 7.8, 1.6, 1H), 7.97–7.72 (m, 8H), 7.67–7.59 (m, 2H), 7.55 (dd, J ¼ 5.9,
Adv. Funct. Mater. 2010, 20, 1812–1820
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0.9, 1H), 7.51–7.33 (m, 4H), 7.09 (dddd, J ¼ 15.9, 7.4, 5.9, 1.3, 2H), 6.69–
6.49 (m, 2H), 5.83–5.74 (m, 2H), 5.32–5.29 (m, 1H). 19F NMR (282 MHz,
CD2Cl2, d): ꢀ71.04 (s, 3H), ꢀ73.56 (s, 3H), ꢀ106.48 (dt, J ¼ 10.8, 8.9, 1H),
ꢀ107.38–107.59 (m, 1H), ꢀ108.81–109.02 (m, 1H), ꢀ109.71–109.91 (m,
1H). MS (ESI þ , MeOH, m/z): [M]þ 871.1757. Anal. calcd. for
C41H26F10IrN6P þ CH2Cl2: 45.83, H 2.56, N 7.63; found: C 46.30, H
2.86, N 7.68.
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