Click-Derived Triazolylidenes as Chelating Ligands: Achievement of a Neutral and Luminescent Iridium(III)-Triazolide Complex

Article abstract of DOI:10.1021/acs.inorgchem.8b01806

Versatility in the synthesis of triazole derivatives was exploited to obtain convenient mesoionic carbenes working as chelating or cyclometalating ligands for the preparation of cationic or neutral iridium(III) complexes. We present the synthesis and characterization of three new cationic cyclometalating iridium(III) complexes (1-3-BF₄) and a neutral one (4), equipped with functionalized triazolylidene ligands. All the complexes are obtained in good yields, present irreversible or quasi-reversible oxidation and reduction processes, and display good photophysical stability. The complexes emit from ³MLCT or ³LC states, depending on the nature of the ancillary ligand. Compounds 1-3-BF₄ display very low photoluminescence quantum yields (PLQY ≈ 1% in acetonitrile solution). Density functional theory calculations show that the luminescence of these three complexes is quenched by the presence of low-lying ³MC states, leading to a reversible detachment of the neutral ancillary ligands from the metal coordination sphere. On the contrary, this nonradiative deactivation pathway is not present in the case of the neutral complex 4, which in fact shows PLQYs above 10% and is the best emitter of the series. Moreover, complex 4 represents the first reported example of a photochemically and thermally stable neutral triazolide iridium(III) complex.

Full text of DOI:10.1021/acs.inorgchem.8b01806

Article
pubs.acs.org/IC
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
Click-Derived Triazolylidenes as Chelating Ligands: Achievement of
a Neutral and Luminescent Iridium(III)−Triazolide Complex
Elia Matteucci,† Filippo Monti,‡ Rita Mazzoni,† Andrea Baschieri,*,†,⊥ Claudia Bizzarri,*,§
and Letizia Sambri*,†
†
̀
Dipartimento di Chimica Industriale “Toso Montanari”, Universita di Bologna, Viale Risorgimento 4, 40136 Bologna, Italy
‡
̀
Istituto per la Sintesi Organica e la Fotoreattivita, Consiglio Nazionale delle Ricerche, Via P. Gobetti 101, 40129 Bologna, Italy
§Institute of Organic Chemistry, Karlsruhe Institute of Technology (KIT), Fritz-Haber-Weg 6, 76131 Karlsruhe, Germany
S
* Supporting Information
ABSTRACT: Versatility in the synthesis of triazole derivatives was exploited
to obtain convenient mesoionic carbenes working as chelating or cyclo-
metalating ligands for the preparation of cationic or neutral iridium(III)
complexes. We present the synthesis and characterization of three new
cationic cyclometalating iridium(III) complexes (1−3-BF4) and a neutral one
(4), equipped with functionalized triazolylidene ligands. All the complexes are
obtained in good yields, present irreversible or quasi-reversible oxidation and
reduction processes, and display good photophysical stability. The complexes
3
3
emit from MLCT or LC states, depending on the nature of the ancillary
ligand. Compounds 1−3-BF4 display very low photoluminescence quantum
yields (PLQY ≈ 1% in acetonitrile solution). Density functional theory
calculations show that the luminescence of these three complexes is quenched
3
by the presence of low-lying MC states, leading to a reversible detachment of the neutral ancillary ligands from the metal
coordination sphere. On the contrary, this nonradiative deactivation pathway is not present in the case of the neutral complex 4,
which in fact shows PLQYs above 10% and is the best emitter of the series. Moreover, complex 4 represents the first reported
example of a photochemically and thermally stable neutral triazolide iridium(III) complex.
Chart 1. Examples of Bidentate Triazole and Triazolylidene
Ligands
INTRODUCTION
■
The outstanding success of the copper(I) catalyzed “click”
azide−alkyne cycloaddition reaction (CuAAC),1,2 which
regioselectively yields 1,4-disubstituted 1,2,3-triazoles, can be
ascribed, among others, to the possibility of synthesizing
libraries of ligands to be exploited for the creation of metal
complexes and related applications. Notably, by means of an
alkylation−deprotonation reaction sequence, the CuAAC
products can be easily converted in the corresponding
triazolylidenes, which belong to the class of mesoionic
carbenes (MIC),3,4 that are N-heterocyclic carbenes
(NHCs)5,6 which structure cannot be drawn without a charge
separation.
Triazolylidenes joined the parent triazoles to be used as
mono- or polydentate ligands in organometallic chemistry. In
fact, the synthetic strategy to form 1,2,3-triazole rings allows
the easy design of final derivatives by varying the wingtip
substituents. In particular, 4-phenyl- and 4-(pyrid-2′-yl)-1,2,3-
triazoles A (with X = C and N, respectively, Chart 1), have
been extensively exploited in the formation of metal complexes
acting as catalysts7,8 and luminescent materials.9−18 Besides
such derivatives, even the corresponding triazolylidenes can
offer large opportunities of application as bidentate cyclo-
metalating or donor ligands thanks to their strong electron-
donating character, which is generally higher than those of
their NHC analogues,19−22 concurrently to their relative
simple synthesis. As a consequence, their use as ligands for
the synthesis of metal complexes has recently received great
attention, and a wide range of applications have been reported,
especially in the area of homogeneous catalysis,23−27 with
many examples of ruthenium(II)-23 and iridium(III)-
based23−27 catalysts, as attested by various reviews that have
appeared in the literature.7,28−30
On the contrary, luminescent complexes containing
triazolylidene ligands were not extensively studied so far.
Only a few examples of ruthenium(II) and iron(II)31,32
derivatives have been reported in literature, together with the
Received: June 29, 2018
© XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.8b01806
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
only one report on an iridium(III) complex from our
laboratory.33
Chart 2. Iridium(III) Complexes Presented in This Study
Luminescent iridium-based complexes are one of the most
widely used classes of derivatives for solid-state emitting
devices such as organic light-emitting diodes (OLEDs)34−38
and light-emitting electrochemical cells (LECs),39,40 used for
displays and lighting. In fact, such emitters exhibit unique
photophysical properties (i.e., wide color tunability, high
photoluminescence quantum yields, excellent stability, and
good solubility), along with general easy synthesis and
possibility to modify their emission output simply by a precise
variation of the ligands.41 By virtue of this versatility, there is
still plenty of room for the design and development of new
library of ligands with electronic properties suitable for the fine
color tuning of luminescent complexes.
Pushing forward our investigations on nonconventional
ancillary ligands for luminescent iridium(III) complexes,42−44
we focused our attention on bidentate ligands containing a
1,2,3-triazolylidene functionalized with a heteroaryl in the 4-
position. In fact, we recently reported the first use of 1-benzyl-
3-methyl-4-(pyrid-2′-yl)-1H-1,2,3-triazolylidene B (R = Bz,
Chart 1) as neutral ligand to obtain phosphorescent cationic
cyclometalated iridium(III) complexes.33 In this context, we
now expanded the use of such derivatives by varying the
substituents on the triazolylidene ring and by employing them
as neutral ancillary or cyclometalating ligands to get new
luminescent cationic and neutral iridium(III) complexes. In
fact, taking into account the recent studies on the σ-donor and
π-acceptor properties of bidentate ligands,45 it seemed
interesting to substitute the pyridine with a 1,2,3-triazole to
evaluate the effects of a different heteroaryl on complex
behavior, envisioning that, besides the classical coordination as
N^C neutral ligand, such triazole−triazolylidene derivatives
can act also as C^C anionic ligand (C and D, Chart 1).
In detail, we present herein the synthesis and character-
ization of three new cationic iridium(III) complexes (1−3-
BF4) and a neutral one (4) carrying 2-phenylpyridine (Hppy)
as cyclometalating ligand and differently functionalized
triazolylidenes as ancillary ligands (Chart 2). For the sake of
completeness, the properties of the obtained complexes are
also compared with those of previously reported ones such as
the structural analogues 5,46,47 6,48 7,48 and 810 (see Chart 3).
Chart 3. Selected Iridium(III) Complexes as Analogues of
the Investigated Series
RESULTS AND DISCUSSION
■
Synthesis. The 4-(heteroaryl)-1,2,3-triazoles 9a and b49
and 9c10 were synthesized through a copper-mediated azide−
alkyne cycloaddition (CuAAC) by reaction of 2-ethynylpyr-
idine and 1,4-bis(trimethylsilyl)buta-1,3-diyne, respectively,
with the required organic azides, according to previously
reported procedures.
10b-I both only in 13% yield. For compound 11b-I, the
structure was also confirmed by X-ray analysis (see crystal data
in the Supporting Information). However, considering that the
consecutive reaction conditions required for the formation of
the carbene are counterion dependent, we decided to carry on
the synthesis of iridium(III) complexes with both triflates and
iodide precursors to evaluate potential differences.
Regarding bis-triazole 9c, the monomethylation was
performed only with MeI because previous experiments
carried out in our lab showed that the formation of the
corresponding carbene from the triflate triazolium salt
sluggishly occurred. Monomethylated triazolium 10c-I50 was
obtained in very good yields (81%) and proved to be suitable
for the rapid formation of the corresponding carbene employed
in the subsequent in situ complex formation, as discussed later
in the text.
To get the triazolium salts precursors of triazolylidenes,
MeOTf and MeI were tested as methylating agents for 2-
pyridine triazoles 9a and b (Scheme 1). Surprisingly, we always
obtained monomethylated products, with a regioselectivity
strictly connected to the nature of the methylating reagent, as
determined through one-dimensional (1D) and two-dimen-
sional (2D) NMR experiments. Indeed, with MeOTf the
methylation occurs only at N-3 of the triazole ring giving 10a-
OTf and 10b-OTf in 59 and 54% yield, respectively. On the
contrary, the undesired methylation of the pyridine nitrogen
preferentially occurred in the reaction with MeI. Pyridinium
salts 11a-I and 11b-I were obtained as major products in over
60% yields, together with the desired triazolium salts 10a-I and
B
DOI: 10.1021/acs.inorgchem.8b01806
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Scheme 1. Synthesis of the Methylated Triazolylidene Precursors
Scheme 2. Synthesis of Complexes
Once the triazolium salts were obtained, we progressed to
the corresponding iridium(III) complexes. In detail, pyridine
triazolium salts 10a-OTf and 10b-OTf reacted51 with Ag2O in
ACN in the presence of KCl to give the silver(I) triazolylidene
complexes 12a-OTf and 12b-OTf, which were isolated and
directly used in the next step without purification (Scheme 2).
The obtained carbenes were added to a solution of
[Ir(ppy)2(μ-Cl)]2 in DCM/EtOH = 3/1 to produce, by
means of a Ag−Ir transmetalation step, the corresponding
complexes 1-OTf and 2-OTf, which, when treated with
NH4BF4, were converted to the tetrafluoroborates salts 1-BF4
and 2-BF4 in 66 and 76% overall yields, respectively.
Concerning the iodide triazolium derivatives, a one-pot
procedure was set up by reacting 10a-I, 10b-I, and 10c-I with
[Ir(ppy)2(μ-Cl)]2 in DCM in the presence of Ag2O: the Ag-
triazolylidenes was formed in situ, and then a silver−iridium
transmetalation took place to get the iridium complexes 1-I, 2-
I, and 3-I that, when treated with NH4BF4, gave the
corresponding complexes 1-BF4, 2-BF4, and 3-BF4 by anion
exchange in 49, 84, and 54% total yields, respectively (Scheme
2).
a downshift of the signal corresponding to a benzylic-CH2,
suggesting that a cyclometalation occurred on the triazolyl
substituent of the triazolylidene.
Given the importance of neutral tris-cyclometalated iridium-
(III) complexes for applications distinct from charged ones, we
investigated the possibility to increase the yield of 4. In
addition, neutral complex 4 resulted a very interesting
derivative considering that stable triazolide metal complexes
are rather rare, being isolated only some copper-,52,53
palladium-,54 and platinum-55 triazolides and one example of
iridium(III) triazolide complex that anyway proved to
rearrange to the more stable triazole derivative upon heating
or light irradiation.48
Any attempt to increase the yield of 4 by changing the
reaction conditions from 10c-I failed, therefore we turned our
attention to the possibility to convert the cationic complex to
its neutral derivative. We succeeded in this synthesis by
treating complex 3-BF4 with K2CO3 in refluxing 2-
ethoxyethanol to give 4 in 68% yield (Scheme 3). The relative
high temperature and the presence of the base favored the
switching of the binding mode of the bis-chelating ligand from
The two synthetic strategies let to obtain identical
complexes 1-BF4 and 2-BF4 in comparable yields from
triazolium salts. However, considering the low selectivity in
obtaining iodide derivatives 10a-I and 10b-I, the route starting
from triflate salts 10a-OTf and 10b-OTf seemed preferable,
despite requiring a two-step reaction sequence and longer
reaction times.
Scheme 3. Optimized Synthesis of the Neutral Complex 4
Remarkably, during the synthesis of 3-I, a small amount of a
luminescent byproduct, later identified as 4, was isolated. This
compound proved to be much less polar than 3-I, and a
1
comparison of their H NMR spectra (see Figures S18 and
S23) revealed the disappearance of the singlet at 9.68 ppm and
C
DOI: 10.1021/acs.inorgchem.8b01806
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
C∧N to C∧C, furnishing the tris-cyclometalated complex 4, as
an uncommon example of triazolide-containing complex.
Notably, conversely to the previously reported example of
iridium(III) complex 7 (see Chart 3) having a pyridine−
triazolide ancillary ligand,48 complex 4 proved to be more
stable than the starting cationic complex under heating,
probably due to the higher acidity of the triazole proton
produced by the electron withdrawing effect of triazolylidenes;
in other words, the overall electronic properties of the
triazolylidene−triazolide ligand allow the stabilization of the
neutral complex 4, as further demonstrated by electrochemical
studies and density functional theory (DFT) calculation, vide
infra.
The electrochemical cell was equipped with a Pt-disk as
working electrode, a Pt wire as auxiliary electrode, and an Ag
wire as quasi reference electrode. After each set of measure-
ments, ferrocene (Fc) was added to the solution to calibrate
the potential according to its value.56 The voltammograms
were also recorded at different scan rates (i.e., 50, 200, and 500
mV/s), and the results are reported in the Supporting
Information (Figures S25−S32 and Tables S1−S4). In Table
1, the first oxidation and the first reduction potentials are
reported versus the ferrocene/ferrocenium redox couple for all
the investigated complexes. These redox data were also used to
calculate the frontier molecular orbitals (HOMO and LUMO)
of the complexes based on the value of Fc/Fc+ with respect to
the zero vacuum level (i.e., −4.8 eV);57 these HOMO−LUMO
estimates are also compared to DFT data.
All compounds were fully characterized by NMR spectros-
1
copy (see Figures S1−S24) and mass spectrometry. The H
NMR spectra of both triazolium salts and cationic complexes
exhibit some differences depending on the counteranion;
therefore, we considered important to make explicit the nature
of the anion in the numbering of the salt structures. Notably,
the 1H NMR spectra of the final BF4 complexes obtained from
triflates and iodides are equivalent and display the pattern
typical of mer-like derivatives with the N atoms of the phenyl−
pyridine cyclometalating ligands in trans position.
Electrochemistry. We investigated the electrochemical
properties of iridium(III) complexes 1−3-BF4 and 4 by means
of cyclic voltammetry in acetonitrile solutions at a scan rate of
100 mV/s (Figure 1).
All of the complexes present irreversible or quasi-reversible
oxidation and reduction processes. The charged complexes
(i.e., 1−3-BF4) have very similar oxidation potentials. In
particular, the first oxidation occurs at +0.7 V, corresponding
to a value of the HOMO that is almost identical for all these
three complexes. On the contrary, the neutral complex 4 has
the first oxidation peak at lower potential (+ 0.44 V), which is
irreversible as in case of the charged complexes. This can be
rationalized with the fact that the ancillary ligand of complex 4
chelates the metal through an anionic triazolide, beside the
neutral mesoionic carbene unit; this results in a much stronger
σ-donation to the positively charged iridium ion, facilitating
the oxidation of the metal. The first reduction peaks of 1-BF4
and 2-BF4 are quasi-reversible and occur at −2.02 V; therefore,
the HOMO−LUMO gap of 1-BF4 and 2-BF4 is very similar, as
also proved by photophysical data (see below).
Interestingly, when the pyridine moiety of the ancillary
ligand is replaced by a triazole unit, the reduction potentials of
the corresponding complexes are lowered by approximately
300 and 600 mV for 3-BF4 and 4, respectively (Table 1).
Consequently, the neutral complex 4 displays a higher LUMO
compared to all the cationic counterparts, as expected on
purely electrostatic basis. Because the HOMO of complex 4 is
destabilized by approximately 300 mV with respect to the one
of 3-BF4, this results in an almost identical HOMO−LUMO
gap for both complexes. This finding is corroborated by
photophysical measurements (e.g., the emission energy of the
two complexes is very similar). Moreover, it should be
emphasized that the strong LUMO destabilization observed
for complexes 3-BF4 and 4 leads to an increased HOMO−
LUMO gap, compared to the 1-BF4 and 2-BF4 analogues. This
is further confirmed by theoretical calculations and by the blue-
shift of their emission maxima (see below).
Figure 1. Cyclic voltammograms of the iridium(III) complexes
investigated in this work. Scan rate: 100 mV/s; CH3CN solution with
0.1 M TBAPF6.
The electrochemically calculated HOMO−LUMO gaps
(ΔEHL) correlate very well with the ones estimated by DFT
Table 1. Electrochemical Data in Acetonitrile (0.1 M TBAPF6) and Frontier Orbital Energy Levels of Complexes
(Experimental and Calculated)
a
c
electrochemical data
DFT calculated energy
b
d
sample
Eox (V)
Ered (V)
EHOMO (eV)
ELUMO (eV)
ΔEHL (eV)
EHOMO (eV)
ELUMO (eV)
ΔEDFT (eV)
1-BF4
2-BF4
3-BF4
4
0.75
0.72
0.72
0.44
−2.02
−2.02
−2.34
−2.63
−5.55
−5.52
−5.52
−5.24
−2.78
−2.78
−2.46
−2.17
2.78
2.73
3.05
3.06
−5.77
−5.78
−5.77
−5.39
−2.10
−2.12
−1.71
−1.28
3.67
3.66
4.06
4.11
a
b
c
Scan rate 100 mV/s, potentials relative to ferrocene/ferrocenium couple. ΔEHL = ELUMO − EHOMO; DFT calculations were carried out at the
d
M06/6-31G(d,p) and cc-pVTZ-ECP60MDF(Ir) level of theory in acetonitrile using PCM. ΔEDFT = ELUMO − EHOMO
.
D
DOI: 10.1021/acs.inorgchem.8b01806
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Figure 2. Energy diagram showing the energy values of the frontier Kohn−Sham molecular orbitals of 1+−3+ and 4 in acetonitrile. For some
relevant orbitals, the corresponding isosurface is also displayed for the sake of clarity (isovalue = 0.04 e1/2 bohr−3/2).
methods (ΔEDFT), as reported in Figure S33. Because the
HOMO and LUMO values are indirectly related to the
oxidation and reduction potentials,57−59 electrochemical data
are used to estimate the effect exerted by the ancillary ligands
on the investigated complexes. This furnished a basis for a
better understanding of the electronic features of the reported
iridium(III) complexes.
Theoretical Calculation: Ground-State Properties.
The molecular geometries and the electronic properties of all
the synthesized complexes were investigated by means of DFT
calculations. The M06 hybrid meta exchange-correlation
functional60,61 was used in combination with the 6-31G(d,p)
basis set62 for all the nonmetal atoms. On the contrary, the
Stuttgart/Cologne relativistic pseudopotential and its related
correlation-consistent triple-ζ basis set were adopted for the
iridium center.63 The ground state geometries of all complexes
were fully optimized without symmetry constrains in
acetonitrile and dichloromethane using the polarizable
continuum model (PCM).64−66
Due to the lack of any available X-ray structure of 1−3-BF4
and 4, several guesses were made to localize the global
minimum on the ground-state potential energy surface of each
of the investigated compounds. For all the complexes, a
distorted octahedral coordination is assumed around the
iridium center, with the pyridyl moieties of the two ppy
ligands in trans to each other, as commonly observed in the
vast majority of cyclometalated iridium(III) complexes.35,39,40
Particular attention was paid to the identification of the most
stable conformer in the case of complexes 1-BF4, 3-BF4, and 4
due to the presence of one or two flexible benzyl substituents
on the triazolylidene ligand. In fact, if the phenyl substituent
(when close to the iridium center, as in 2-BF4) is known to
make a well-defined π−π interactions with the ppy ligands
generating the so-called “cage-effect”,39,67,68 the situation is
more complicated for the benzyl analogue, where several
conformations are experimentally observed.46,47,69
and the corresponding model compounds are named 1+, 2+,
and 3+, respectively. It is worth noting that, despite the
unsymmetrical nature of the triazolylidene-based ligand of 4,
this complex adopts a pseudo-C2 symmetry, indicating that the
positive charge on the triazolylidene ring is relatively well
delocalized over the entire ligand, as depicted in Figure S34.
In Figure 2 are reported the energy diagrams and the frontier
molecular orbitals of the investigated series (Chart 2). For all
the cationic complexes (i.e., 1+−3+), the HOMO is mainly
located on the iridium center and on both the cyclometalated
moieties of each ppy ligands.13,39 Moreover, also the HOMO
energy is virtually identical for all these complexes (i.e., ≈ −5.8
eV, Figure 2), indicating that the ancillary ligands do not
strongly affect the electrostatic field around the iridium ion, as
also corroborated by electrochemical data (Table 1).
A similar qualitative scenario is also observed for the
LUMO, which is always centered on the π* orbitals of the
ancillary ligand for all the cationic complexes under
investigation. Anyway, the LUMO energy is strongly affected
by the type of ancillary ligand and its related substituents. In
the case of complexes 1+ and 2+, having a differently
substituted pyridyl−triazolylidene ligand, the LUMO energy
is comparable (i.e., − 2.10 vs −2.12 eV, respectively),
indicating that the presence of a benzyl or phenyl substituent
does not strongly influence the electronic properties of the
related compounds.
Notably, the replacement of the pyridyl substituent with a
triazolyl one (on the triazolylidene-based ligand) is able to
strongly destabilize the corresponding π* orbitals and, thus,
the LUMO energy (compare 3+ and 1+, Figure 2); as a
consequence, complex 3+ displays a larger HOMO−LUMO
gap. It is also worth mentioning that the LUMO of 3+ becomes
very close in energy to the LUMO+1 (ΔE = 0.14 eV, Figure
2), opening a pathway to low-lying ligand-centered excited
states (see below).
On the other hand, the molecular-orbital energy diagram of
complex 4 strongly differs from all the previous ones because it
is shifted to more positive energies (Figure 2). This effect can
be easily justified considering the charge neutrality of 4.
Anyway, as for the cationic analogues, the HOMO of complex
The minimum-energy fully optimized geometries are
reported in Table S5−S8 for all the investigated complexes.
In the case of the ionic complexes 1-BF4, 2-BF4, and 3-BF4,
−
the BF4 counteranion was not included in the calculations,
E
DOI: 10.1021/acs.inorgchem.8b01806
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
4 is again located on the metal center and on both the
cyclometalated moieties of the ppy ligands. On the contrary, as
far as the LUMO is concerned, an orbital flipping is observed;
in fact, upon cyclometalation, the π* orbital of the triazolyl−
triazolylidene ligand of complex 4 becomes so high in energy
that turns out to be the LUMO+2, while the LUMO and
LUMO+1 are now centered on the π* orbitals of the two ppy
ligands (Figure 2). As a consequence, a predominantly LC
emission (centered on the ppy ligands) would be expected for
4 (see below).
Photophysical Properties. All the investigated complexes
1−3-BF4 and 4 are stable in acetonitrile and dichloromethane
solutions for months and do not show degradation under
standard laboratory conditions. The electronic absorption
spectra were recorded in acetonitrile at room temperature
(Figure 3).
The investigated complexes show poor to moderate
emission in oxygen-free acetonitrile solution (Table 2).
Complexes 1-BF4 and 2-BF4 display a broad and structureless
photoluminescence emission bands. This featureless emission
3
is assigned to a MLCT excited-state, as commonly observed
in cationic iridium(III) complexes such as [Ir(ppy)2(bpy)]+
(bpy = 2,2′-bipyridine).70 Complexes 1-BF4 and 2-BF4 present
emission features similar to the neutral iridium(III) pyridyl−
triazolide complexes studied by Swager and coworkers (i.e.,
complex 7 in Chart 3),48 such as the low quantum yield and
band shape. The photoluminescence was investigated also in
dichloromethane. The emission maxima have very small
dependence on solvent polarity. A possible explanation is
that the emissive state has a consistent contribution from 3LC,
but this is not confirmed by DFT calculations, so it is excluded.
A more plausible explanation is that the investigated complexes
possess an emitting state that is less polar than the ground state
(see below).
On the contrary, the photoluminescence spectra of
complexes 3-BF4 and 4 present a more structured emission,
both in acetonitrile and in dichloromethane.
Emission quantum yields were measured relative to known
standards.71 Although the photoluminescence quantum yields
are not very high (Table 2), they are comparable with those
reported for other iridium(III) mesoionic carbene com-
plexes.33 For the cationic complexes 1−3-BF4, PLQYs are
higher in dichloromethane than in acetonitrile solutions,
suggesting that in a more polar and coordinative solvent the
nonradiative deactivation pathways play a more predominant
role in quenching the emission. On the contrary, the neutral
complex 4 does not show any remarkable difference in its
PLQYs between the two solvents (i.e., about 12% for both
dichloromethane and acetonitrile solutions). These exper-
imental findings suggest that metal-centered (3MC) states
could play an important role in quenching the luminescence of
complexes 1−3-BF4 and that such states may involve ligand
decoordination, possibly assisted by the solvent (see below).
The experimental photoluminescent properties of the
investigated complexes are compared with selected analogues
already reported in literature, to find a relationship between
their structure and their photophysical behavior. Complex 5 is
the compound that has the major similarity with 1-BF4, but the
ancillary ligand coordinates via a N^N chelating mode (cf.
Chart 3 and 2). Notably, by going from this N^N mode to the
N^C one of the triazolylidene in 1-BF4, there is a remarkable
red-shift in the emission maximum (i.e., 478 vs 557 nm in
acetonitrile at 298 K, respectively) and a lowering of the
Figure 3. UV−vis absorption spectra in CH3CN solution at 293 K.
The main absorption bands at high energy (λ ≤ 340 nm)
can be assigned to π−π* transitions, involving the ppy and the
mesoionic carbene ligand.33,39,40 The weaker absorption bands
(350−450 nm) are assigned to spin-allowed transitions to a
singlet metal-to-ligand charge-transfer state (1MLCT) and to
3
spin-forbidden population of the triplet excited state MLCT,
although a contribution from ligand centered (LC) cannot be
excluded at this stage. Interestingly, the absorption profiles of
1-BF4 and 2-BF4 are extremely similar, indicating that the
different substitution in the triazole ring do not involve any
substantial change in the electronic transitions of these two
complexes.
Table 2. Photophysical Properties of the Complexes at 293 K
a
c
d
e
f
sample
absorption max. (ε) [nm (103 M−1 cm−1)]
emission max. (nm)
PLQY (%)
τ
(ns)
kr (104 s−1
)
knr (105 s−1
)
a
a
a
a
a
1-BF4
260(42.1); 309(13.4); 344(9.3);
383(4.7); 415 (3.0)
260(43.9); 309(14.8); 344(9.8);
383(4.8); 415 (3.2)
255(43.8); 300(17.2); 343(6.5);
383(4.3); 415(2.6)
253(42.6); 265(44.6); 300(23.4);
320(19.1); 370(7.52); 402(4.1); 450(1.2)
557
560
574
573
1.1
49
207
59
212
a
22.5
202
b
b
b
a
b
b
b
4.7
22.8
46.0
a
a
a
a
2-BF4
3-BF4
4
0.5
8.5
169
b
b
b
b
7.1
33.5
43.9
a
a
a
a
b
490(1) , 505 (0.99)
488(0.83) , 511(1)
498(1) , 525 (0.80)
493(1) , 522 (0.77)
0.2
28 (52%) , 2.1 (48%)
b
b
b
b
0.6
67 (66%) , 2.6 (34%)
a
a
b
a
a
a
a
12.5
11.1
473
453
26.4
18.5
b
b
b
b
b
24.6
19.6
a
b
c
In acetonitrile. In dichloromethane. Quantum yields were measured in oxygen-free solutions (i.e., argon-saturated), using [Ru(bpy)3]Cl2 in air-
equilibrated water solution (PLQY: 0.028) as reference for complexes 1-BF4 and 2-BF4 and norharmane in air-equilibrated 0.05 M H2SO4(aq.)
d
e
f
(PLQY: 0.58) for complexes 3-BF4 and 4.71 Excited-state lifetime measured in oxygen-free solutions. kr = PLQY/τ. knr = 1/τ − kr
F
DOI: 10.1021/acs.inorgchem.8b01806
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
photoluminescence quantum yields (i.e., 30% vs 1% in
acetonitrile at 298 K).70 Comparable effects are already
observed for a similar couple of iridium(III) complexes (i.e.,
7 and 6 in Chart 3), where the benzylic group of the triazole-
based ligand was replaced by a long aliphatic chain.48 In fact,
also in that case, the complex having the pyridyl-triazole in the
C^N cyclometalating mode (7) presents an emission at lower
energy with a smaller quantum yield.48
contrary, the main difference between the two complexes
resides in their emission quantum yield, which is around four
times lower in the case of 8 (i.e., 2.8 vs 12.5% for 8 and 4,
respectively−data in acetonitrile at 298 K, see Chart 3 and
Table 2). As for 3-BF4, this phenomenon can be tentatively
attributed to the higher lability of the Ir−N (triazole) bond in
the triplet excited states, leading to easily accessible non-
3
emissive MC states (see below).
As demonstrated by the comparison between 5 and 6 (Chart
3), the substituent in 1-position of the 1,2,3-triazole ring does
not strongly affect the photophysical properties of the related
complexes.48,70 Accordingly, complex 2-BF4, which differs
from 1-BF4 only because of a phenyl substituent on the 1,2,3-
triazolylidene ring instead of a benzyl one, has very similar
absorption and emission properties (Chart 2, Figure 3 and 4).
Theoretical Calculation: Excited-State Properties. To
rationalize the absorption and emission properties of all the
investigated samples, a combined DFT and time-dependent
DFT (TD-DFT) approach was adopted, and the excited-state
properties of the complexes were investigated both in
acetonitrile and dichloromethane, to allow a direct comparison
with experimental data.
To model the experimental absorption spectra in Figure 3,
the lowest 100 vertical excitations were calculated at the
optimized geometry of the ground state (S0) in acetonitrile,
using the linear response formalism; the calculated spectra are
reported in Figure S35−S38. In the case of complexes 1+ and
2+, the first spin-allowed vertical excitation (i.e., S0 → S1) is a
1MLCT transition calculated at 445 nm and it is associated
with a pure HOMO → LUMO excitation with almost zero
oscillator strength (i.e., f < 0.001). In fact, for these two
complexes, the lowest transition which is mainly responsible
for the absorption band, experimentally observed around 400
nm, is the S0 → S2 excitation (f ≈ 0.05), namely a mixed
MCLT/LC transition involving both the iridium ion and the
ppy ligands (Figures S35 and S36). On the contrary, for both
3+ and 4, this latter transition corresponds to the S0 → S1
excitation and it is calculated to occur at approximately 405 nm
with an oscillator strength around 0.03. This is the reason why
all the investigated complexes appear to display a similar
experimental absorption profile at longer wavelengths (Figure
3).
In Tables S9−S12 are listed the lowest-energy triplet
excitations for all the complexes within the series, reported
in terms of natural transition orbital (NTO) couples.72
Surprisingly, for complexes 1+ and 2+, the lowest-lying triplet
transition (i.e., S0 → T1, estimated at approximately 2.68 eV) is
not associated with a HOMO → LUMO excitation, and it
corresponds to an LC transition involving the neutral pyridyl−
triazolylidene ligand, with some MLCT contribution from the
iridium dπ orbitals (Table S9 and S10). The next two triplet
excited states (i.e., T2 and T3) lie at 2.73 and 2.77 eV above S0
and are associated with transitions mainly involving the two
ppy cyclometalating ligands. Finally, only at approximately 2.79
eV above the ground state, it can be found T4, which is the
triplet state formally populated by the HOMO → LUMO
excitation.
Figure 4. Emission spectra in CH3CN (solid line) and in CH2Cl2
(dashed-dotted line) of Ir(III)complexes studied in this work.
On the contrary, the replacement of the pyridine moiety in 4-
position of the 1,2,3-triazolylidene ring with a triazole
substituent has dramatic effects on the photophysical proper-
ties of the related iridium(III) complexes (e.g., compare 1-BF4
and 3-BF4). In fact, the emission of complex 3-BF4 becomes
more structured and shifts to higher energy with respect to 1-
BF4, with a remarkable decrease in the emission quantum yield
(Chart 2 and Table 2). Such experimental findings can be
justified considering a change in the nature of the emitting
states, as better explained in the theoretical section (see
below).
The triazole moiety of the mesoionic triazolylidene ligand of
the cationic complex 3-BF4 can be exploited for chelating the
iridium center also in a C^C coordination mode, formally
leading to the neutral complex 4. Surprisingly, such a
substantial change does not strongly perturb the energy and
the emission profile of complex 4, compared to 3-BF4, but it is
able to drastically increase its emission quantum yield of more
than 20 times (Table 2). This is due to the lack of low-lying
3MC states that, on the contrary, are able to quench the
luminescence of complex 3-BF4 (see theoretical section).
Complex 4 can be compared to its analogue charged
complex 8, having a bis-triazole ligand in N^N coordination
mode (Chart 3).10 Both complexes have the same emission
profile, although 8 displays a slight hypsochromic shift
compared to 4. This is in agreement with the fact that the
anionic C^C ligand of 4 displays a higher field strength,
compared to the neutral N^N counterpart of 8. On the
A similar excited-state scenario is also observed for 3+, but
the order of these triplet states is different (cf. Table S9−S11).
In fact, while the energy of the two triplets centered on the ppy
cyclometalating ligands remains virtually the same also for
complex 3+, the replacement of the pyridyl moiety with the
triazolyl one (on the triazolylidene ligand) lifts the energy of
the corresponding triplet state to 2.99 eV above S0. As a
consequence, what was T1 in complexes 1+ and 2+ turns out to
be T3 in 3+.
In the case of the neutral complex 4, as for the cationic
analogue 3+, the lowest triplet state at the Franck−Condon
region is centered on the ppy cyclometalating ligands, with
some MLCT contribution (cf. Tables S11 and S12). On the
G
DOI: 10.1021/acs.inorgchem.8b01806
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
3
contrary, in complex 4, the LC transition mainly localized on
the triazolylidene ligand is now lowered in energy and becomes
T2 (i.e., 2.74 eV above S0 vs 2.99 in the case of 3+).
triazolylidene ligand (where the LUMO is located) is able to
counterbalance the ground-state dipole moment, leading to an
almost apolar 3MLCT excited state (i.e., the dipole moment of
1+ in T4 is reduced to 2.7 0.1 D, see Figure S39). That is the
reason why negligible solvatochromic effects are observed in
the emission spectra of both 1-BF4 and 2-BF4, despite the
To assess the nature of the emitting states, spin-unrestricted
DFT calculations were carried out to optimize the lowest
triplet state of all the investigated complexes and the
corresponding geometries are reported in Tables S13−S16.
In the case of both 1+ and 2+, after full geometry relaxation, the
lowest triplet turns out to be the forth triplet state at the
Franck−Condon region (i.e., T4), as reported in Figure 5. As
3
strongly predominant MLCT nature of their emitting states.
A totally different scenario is observed for complexes 3+ and
4, where the fully relaxed lowest triplet state is found to be
centered on the ppy cyclometalating ligands (Figure 5),
indicating an emission with a strong 3LC character. This is the
reason why it is experimentally found that both complexes
display a very similar phosphorescence spectrum with a
vibronically structured profile that is virtually unaffected by
the polarity of the solvent (Figure 4). In the case of complex
3+, the emitting state is straightaway T1, because no root-
flipping phenomena are observed for such a state upon
relaxation (cf. Table S11 and Figure 5). On the other hand, for
complex 4, the scenario is more complicated due to the pseudo
C2-symmetry of the molecule, leading to the presence of two
nearly degenerate triplet states (i.e., ΔESCF ≈ 0.002 eV), each
of them centered on one of the two ppy ligands. These two
minima can convert into one another through an intermediate
located 0.12 eV above them (Figure S40). Therefore, these two
minima can be considered in fast equilibration and equally
populated at room temperature. Due to their virtually identical
energy and nature, from now onward, they will be treated as a
unique emitting state (i.e., T1).
Figure 5. Spin-density distribution for the lowest-energy emitting
triplet states of complexes 1+−3+ and 4 in their fully relaxed
geometries, computed in acetonitrile (isovalues: 0.002 e bohr−3).
The TD-DFT calculated emission energies are computed to
be 2.26 eV (549 nm) and 2.32 eV (534 nm) for 3+ and 4,
respectively. These values are in good agreement with the
mean-photon energy of the emission spectra recorded in room-
temperature acetonitrile solution and reported in Figure S41
(i.e., 2.46 eV for 3-BF4 and 2.41 eV for 4). Despite the
emission energy and the nature of the emitting state of 3-BF4 is
virtually identical to that of complex 4, a remarkable difference
in their photoluminescence quantum yields is observed, with
the emission of complex 3-BF4 being almost 50 times
quenched if compared to that of 4 (e.g., PLQY = 0.2 vs
12.5% for 3-BF4 and 4, respectively, see data in Table 2 in
room-temperature acetonitrile solutions). Such a dramatic
difference can be attributed to an important nonradiative
deactivation pathway that is able to effectively kill the
luminescence of complex 3+, but that is not present in 4.
already mentioned above, such a state is highly MLCT in
nature, resulting from a HOMO → LUMO excitation in which
one electron is promoted from the iridium d orbitals to the π*
on the triazolylidene ligand (cf. Figure 5 and Tables S9 and
S10). This theoretical finding can justify the unstructured
emission profiles experimentally observed for 1-BF4 and 2-BF4
(Figure 4), which is typical of MLCT transitions. The emission
from that state is estimated to occur at 600 nm for both 1+ and
2+, in good agreement with the experimental data; in fact, the
mean-photon energy of the emission spectra recorded in room-
temperature acetonitrile solution for 1-BF4 and 2-BF4 is 2.15
and 2.19 eV, respectively (to be compared with the theoretical
value of 2.07 eV for both 1+ and 2+).
It is also worth mentioning that, despite the emission of
these complexes arises from 3MLCT states, the energy
associated with such radiative transitions is not strongly
affected by the polarity of the solvent, as experimentally
observed in Figure 4. For instance, in the case of complex 1+,
the estimated emission in dichloromethane is calculated to
occur at 609 nm, only 0.03 eV lower in energy with respect to
the one computed in acetonitrile (i.e., 600 nm, see above).
This absence of marked solvatochromism in the emission
spectra is rather uncommon for MLCT emitting state, but it
can be easily rationalized considering the dipole moments of
the ground state (S0) and of the emitting triplet (T4).73 The
mesoionic nature of the pyridyl−triazolylidene ligand, having a
formally positively charged nitrogen atom on the 5-membered
ring, induces a very large dipole moment on S0 (e.g., 12.7 0.3
D for 1+, both in acetonitrile and dichloromethane solution),
with the positive charge of the dipole pointing in the direction
of such ligand (Figure S39). On the contrary, the lowest triplet
excited state, due to its charge-transfer nature, is much less
polar than the ground state; in fact, the promotion of one
electron from the HOMO to the π* orbitals of the pyridyl−
As already pointed out in literature,39 nonemissive MC
3
levels are well-known to offer effective radiationless pathways
to the emitting state in cyclometalated iridium(III) complexes.
3
The population of such MC states formally results from the
excitation of an electron from the occupied pseudo-t2g (dπ)
orbitals of the iridium center (where the HOMO is generally
located) to the unoccupied pseudo-eg (dσ*) orbitals of the
metal itself, which are usually found at high energy and, as a
consequence, not easily populated.39 Anyway, it has been
3
proved that, more often than expected, MC states play an
efficient role in quenching the phosphorescence of cyclo-
metalated iridium(III) complexes,67,74−76 also in combination
with carbene-based ligands.77,78 Generally, the optimized
3
geometry of a MC state in a cyclometalated iridium(III)
complex involves the elongation and breaking of an Ir−N
bond, resulting in the decoordination of the corresponding
ancillary or cyclometalated ligand from the metal coordination
sphere. As a result, five- or four-coordinated structures can be
H
DOI: 10.1021/acs.inorgchem.8b01806
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
3MC minimum-energy geometry can be reached by the
decoordination of the pyridyl moiety of the triazolylidene
ligand, in such a way that the pyridyl nitrogen atom points
outside the iridium coordination sphere (Figure 6, bottom);
therefore, the partially uncoordinated ligand is no more planar
and an inter-ring dihedral angle of 55° and 64° is formed for 1+
formed, with the iridium center in a trigonal-bipyramidal or
square-planar geometry, respectively.77
Considering the possible elongation and/or breaking of the
Ir−N bond involving the triazolylidene-based ligand, we were
able to localize a low-lying 3MC state for complex 3+. In Figure
6 (top) is reported the fully relaxed minimum-energy geometry
3
and 2+, respectively. In the case of 1+, the MC state is found
to be only 0.01 eV above the emitting triplet (Figure 6,
bottom); while, for 2+, the nonemissive state becomes even a
little bit more stable than the emitting state by 0.09 eV.
Despite the roughness of the adopted theoretical model
(lacking the evaluation of activation energy barriers and
dynamic effects), all these computational findings correlate
well to the experimental trend in the emission quantum yields
of 1-BF4 and 2-BF4. In fact, as reported in Table 2, the PLQY
of complex 1-BF4 (having the 3MC state at little higher energy
than the emitting one) is twice as much as the one of 2-BF4 (in
3
which the MC level becomes slightly lower).
The minimum-energy geometries of the 3MC states
calculated for complexes 1+−3+ and discussed in the present
section are reported in Tables S17−S19, for the sake of
completeness.
CONCLUSIONS
■
We have reported a series of cationic iridium(III) complexes
1−3-BF4 and a neutral one 4 equipped with triazolylidenes as
ancillary ligands. A simple procedure for the synthesis of the
1,2,3-triazolylidene rings with a pyridine or a triazole moiety in
4-position was efficiently set up and the corresponding
iridium(III) complexes were obtained through a silver−iridium
transmetalation. The complexes were synthesized in good
yields and fully characterized. In particular, the switching of the
binding mode of the bis-chelating ligand 10c-I from C^N to
C^C furnishes the neutral tris-cyclometalated complex 4 as an
uncommon example of a stable triazolide-containing complex.
By comparison with the previously reported example of neutral
iridium(III) complex having a pyridine−triazolide ancillary
ligand (7, Chart 3), complex 4 was found to be more stable
than the starting cationic complex 3-BF4, probably due to the
higher acidity of the triazole proton produced by the electron
withdrawing effect of triazolylidenes. In other words, the
overall electronic properties of the triazolylidene−triazolide
ligand allow the stabilization of the neutral complex 4. These
properties are reflected on its photoluminescence quantum
yield that is around four times higher than the quantum yield
of its analogue charged complex 8, having a bis-triazole ligand
in N^N coordination mode, 60 times higher than the quantum
yield of the starting cationic complex 3-BF4 and 60 times
higher than the quantum yield of the neutral complex 7 having
a pyridyl-triazole ligand in the C^N cyclometalating mode
(Chart 2 and Chart 3). This work gives entry to a new class of
charged and neutral phosphorescent iridium(III) complexes,
which can be now expanded by rational design of the
mesoionic carbene and/or the ancillary ligands to enhance
the luminescent properties and potential applications thereof.
Figure 6. Schematic energy diagram showing the adiabatic energy
differences between the ground (S0), the emitting (Tem), and the
metal-centered (3MC) states and the emission energy (Eem
)
calculated for complex 3+ (top) and complex 1+ (bottom). The
fully relaxed minimum-energy geometry of the 3MC state is also
reported, together with the associated spin-density distribution
(isovalues: 0.002 e bohr−3). All data are computed in acetonitrile
using PCM.
associated with such 3MC state, in which the triazole moiety of
the triazolylidene ligand undergoes a full 180°-rotation around
the inter-ring dihedral angle of the ligand, causing a complete
decoordination from the iridium center. These excited-state
distortions lead to a trigonal-bipyramidal complex that was
found to be 0.42 eV more stable than the minimum-energy
geometry of the emitting triplet (i.e., T1). A very effective
population (if not predominant) of this 3MC state is therefore
expected to occur upon excitation of complex 3+, and this state
would definitely play a role in the radiationless deactivation of
3+ since the 3MC minimum is only 0.12 eV above S0 (Figure 6,
top). This scenario can easily justify the extremely low PLQY
experimentally observed for complex 3-BF4 (Table 2).
3
Obviously, such a type of MC state cannot be present in
complex 4 because the corresponding triazolylidene-based
ligand chelates the metal center only through much more
stable Ir−C bonds (i.e., a purely cyclometalating one and a
carbene-type analogue).78 The lack of such low-lying MC
3
states explains the larger PLQY values reported for complex 4
(Table 2).
Following this approach, we also investigated the presence of
3
similar MC states for complexes 1+ and 2+. In fact, both
EXPERIMENTAL SECTION
■
complexes display PLQYs around or below 1% in room-
temperature acetonitrile solution, due to the presence of
remarkably fast nonradiative processes (compare kr and knr in
General Information. Analytical grade solvents and commercially
available reagents were used as received unless otherwise stated.
Chromatographic purifications were performed using 70−230 mesh
silica. 1H, 19F, and 13C NMR spectra were recorded on a Varian Inova
300 MHz, on a Mercury 400 MHz or on an Inova 600 MHz
spectrometer. Chemical shifts (δ) are reported in ppm relative to
3
Table 2) that can be ascribed to the presence of MC states.
Indeed, DFT calculations were able to locate such states very
close in energy to the emitting ones. For both complexes, the
I
DOI: 10.1021/acs.inorgchem.8b01806
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
residual solvent signals for 1H and 13C NMR (1H NMR: 7.26 ppm for
CDCl3, 3.34 ppm for CD3OD, 1.94 ppm for CD3CN, 2.50 ppm for
DMSO; 13C NMR: 77.0 ppm for CDCl3, 48.9 ppm for CD3OD, 1.32
ppm for CD3CN, 39.5 ppm for DMSO). 19F NMR spectra were
recorded at 376.25 MHz or at 564.3 MHz using trichlorofluor-
ometane as external standard. 13C NMR spectra were acquired with
1H broad band decoupled mode. Coupling constants are given in
Hertz. The high-resolution mass spectra (HRMS) were obtained with
a Waters Q-TOF-MS instrument using electrospray ionization (ESI).
General Procedures. 2-(1-Benzyl-1H-1,2,3-triazol-4-yl) pyridine
9a,49 2-(1-phenyl-1H-1,2,3-triazol-4-yl) pyridine 9b,49 1,1′-dibenzyl-
1H,1′H-4,4′-bi(1,2,3-triazole) 9c,10 1-benzyl-3-methyl-4-(pyridin-2-
yl)-1H-1,2,3-triazol-3-ium trifluoromethanesulfonate 10a-OTf,33
1,1′-dibenzyl-3-methyl-4,4′-bis(1H-1,2,3-triazol)-3-ium iodide 10c-
I50 were prepared according to reported methods.
MHz) δ: 151.3 (CH), 144.0 (C), 142.7 (C), 139.3 (CH), 136.0 (C),
133.1 (CH), 131.6 (CH), 128.4 (CH), 127.1 (CH), 125.8 (CH),
122.6 (CH), 42.1 (CH3). HRMS (ESI-QTOF) ([M]+): m/z calcd for
[C14H13N4]+ 237,1135; found: 237.1138 and 11b-I (444 mg, 1.22
1
mmol, 61% yields) H NMR (600 MHz, CD3CN) δ: 4.56 (s, 3H),
7.60−7.65 (m, 1H), 7.65−7.70 (m, 2H), 8.00−8.05 (m, 3H), 8.55−
8.60 (m, 2H), 8.85 (d, 1H, JHH = 6.3 Hz), 9.27 (s, 1H). 13C NMR
(100 MHz, D6-DMSO) δ: 147.4 (CH), 145.3 (CH), 145.2 (C),
139.1 (C), 135.9 (C), 130.1 (CH), 129.8 (CH), 128.1 (CH), 127.0
(CH), 126.6 (CH), 120.8 (CH), 48.6 (CH3). HRMS (ESI-QTOF)
([M]+): m/z calcd for [C14H13N4]+ 237,1135; found: 237.1139.
General Procedure for the Synthesis of Complexes 1-BF4
and 2-BF4 from 1H-1,2,3-Triazol-3-ium Triflates. The desired
1H-1,2,3-triazol-3-ium triflate (0.08 mmol) was dissolved in ACN (6
mL), and then KCl (0.80 mmol, 10 equiv) and Ag2O (0.28 mmol, 3.5
equiv) were added. The resulting mixture was stirred under N2 at
room temperature in the absence of light. After 24 h, the formed solid
was filtered off and washed with ACN (10 mL). The resulting
solution was then concentrated under reduced pressure to give a
white solid that was dissolved in DCM/EtOH = 3/1 (8 mL), and
[Ir(ppy)2Cl]2 (0.04 mmol, 0.5 equiv) was added. After the solution
was stirred for 24 h at room temperature, the solvent was evaporated,
and the crude reaction mixture was purified by column chromatog-
raphy to give the expected Ir-complex as triflate salt that was dissolved
in DCM/EtOH = 5/1 (12 mL). Then, NH4BF4 (40 equiv) was
added. The resulting mixture was stirred at rt for 2 h; water (10 mL)
was added, and the product was extracted with DCM (2 × 10 mL).
The organic layer was dried over Na2SO4 and the solvent evaporated.
The obtained solid was dissolved in a minimum amount of DCM,
precipitated by Et2O addition, and filtered to give Ir-complex as
tetrafluoroborate salt.
Caution: Although we experienced no difficulties in handling these
nitrogen-rich compounds, small scale and best safety practices are
strongly encouraged.
Synthesis of 1-Benzyl-3-methyl-4-(pyridin-2-yl)-1H-1,2,3-triazol-
3-ium Iodide 10a-I and 2-(1-Benzyl-1H-1,2,3-triazol-4-yl)-1-meth-
ylpyridin-1-ium Iodide 11a-I. 2-(1-Benzyl-1H-1,2,3-triazol-4-yl)
pyridine 9a (472 mg, 2.00 mmol) was dissolved in anhydrous ACN
(12 mL), and MeI (0.624 mL, 10.0 mmol, 5 equiv) was added. The
solution was refluxed for 24 h under N2. Then, the solvent was
removed and the crude was purified by column cromatography on
silica gel with DCM/MeOH as eluent, from 95/5 to 7/3 ratio, to give
10a-I (98 mg, 0.26 mmol, 13% yields). 1H NMR (300 MHz,
CD3OD) δ: 4.64 (s, 3H), 5.91 (s, 2H), 7.45−7.50 (m, 3H), 7.55−
7.65 (m, 3H), 7.95−8.10 (m, 2H), 8.81 (bd, 1H, JHH = 5.0 Hz), 9.32
(s, 1H). 13C NMR, (CD3OD, 100 MHz) δ: 151.1 (CH), 144.3 (C),
142.4 (C), 139.1 (CH), 133.2 (C), 130.7 (CH), 130.3 (CH), 130.3
(CH), 129.9 (CH), 126.8 (CH), 125.6 (CH), 58.4 (CH2), 41.6
(CH3). HRMS (ESI-QTOF) ([M]+): m/z calcd for [C15H15N4]+
251.1291; found 251.1295 and 11a-I (537 mg, 1.42 mmol, 71%
General Procedure for the Synthesis of the Complexes
from 1H-1,2,3-Triazol-3-ium Iodides. The desired 1H-1,2,3-
triazol-3-ium iodide (0.06 mmol) was dissolved in DCM (15 mL),
and Ag2O (0.15 mmol, 2.6 equiv) was added. The resulting mixture
was stirred under N2 at room temperature in the absence of light.
After 2 h, [Ir(ppy)2Cl]2 (0.03 mmol, 0.5 equiv) was added, and the
mixture was stirred for additional 24 h at room temperature under N2
in the absence of light. Then, the solid was filtered off, washed with
DCM (25 mL), and the combined solutions were concentrated under
reduced pressure. The crude product was purified by column
chromatography to give the expected Ir-complex as iodide salt that
was dissolved in DCM/EtOH = 5/1 (20 mL), and NH4BF4 (40
equiv) was added. The resulting mixture was stirred at rt for 48 h;
water (15 mL) was added, and the product was extracted with DCM
(2 × 20 mL). The organic layer was dried over Na2SO4 and the
solvent evaporated. The obtained solid was dissolved in a minimum
amount of DCM, precipitated by Et2O addition and filtered to give Ir-
complex as tetrafluoroborate salt.
1
yields) H NMR (600 MHz, CD3CN) δ: 4.45 (s, 3H), 5.76 (s, 2H),
7.35−7.50 (m, 5H), 7.94 (bt, 1H, JHH = 7.0), 8.43 (dd, 1H, JHH = 8.3
Hz, JHH = 1.1 Hz), 8.51 (bt, 1H, JHH = 7.9 Hz), 8.79 (d, 1H, JHH = 6.3
Hz), 8.87 (s, 1H). 13C NMR (125 MHz, CD3CN) δ: 49.4 (CH3),
55.0 (CH2), 127.4 (CH), 129.4 (CH), 129.5 (CH), 129.6 (CH),
129.7 (CH), 130.0 (CH), 135.9 (C), 139.5 (C), 146.3 (CH), 147.3
(C), 147.8 (CH). HRMS (ESI-QTOF) ([M]+): m/z calcd for
[C15H15N4]+ 251.1291; found 251.1294.
Synthesis of 1-Phenyl-3-methyl-4-(pyridin-2-yl)-1H-1,2,3-triazol-
3-ium Trifluoromethanesulfonate 10b-OTf. 2-(1-Phenyl-1H-1,2,3-
triazol-4-yl) pyridine 9b (460 mg, 2.07 mmol) was dissolved in
anhydrous DCM (10 mL), and MeOTf (0.28 mL, 2.48 mmol, 1.2
equiv) was added dropwise. The solution was refluxed for 24 under
N2; the solvent was removed, and and the crude was purified by
column chromatography on silica gel (DCM/MeOH = 95/5) to give
10b-OTf (432 mg, 1.1 mmol, 54% yields. 1H NMR (400 MHz,
CDCl3) δ 10.07 (s, 1H), 8.74 (dq, JHH = 0.8, JHH = 4.8, 1H), 8.40 (dt,
−
[Ir(ppy)2(ptb)]+BF4 (1-BF4). From triazolium triflate 10a-OTf 44
mg, 0.053 mmol yields = 66%. From triazolium iodide 10a-I 25 mg,
1
0.029 mmol yields = 49%. H NMR (600 MHz, CDCl3) δ: 4.67 (s,
J
HH = 0.8, JHH = 8.0, 1H), 8.11−8.07 (m, 2H), 7.92 (dt, JHH = 2.0, JHH
3H), 4.90−4.97 (AB system, 2H), 6.25 (d, 1H, JHH = 7.4 Hz), 6.33
(d, 1H, JHH = 7.7 Hz), 6.55 (d, 2H, JHH = 7.6 Hz), 6.82 (bd, 1H, JHH
= 7.5 Hz), 6.85−7.00 (m, 4H), 7.01 (bt, 1H, JHH = 7.5 Hz), 7.05−
7.15 (m, 3H), 7.18 (bt, 1H, JHH = 7.5 Hz), 7.44 (d, 1H, JHH = 7.7
Hz), 7.49 (d, 1H, JHH = 5.7 Hz), 7.60−7.70 (m, 4H), 7.82 (d, 2H, JHH
= 7.0 Hz), 7.95 (d, 1H, JHH = 5.7 Hz), 8.04 (dt, 1H, JHH = 7.9 Hz, JHH
= 1.4 Hz), 8.32 (d, 1H, JHH = 8.2 Hz). 13C NMR (150 MHz, CDCl3)
δ: 39.4 (CH3), 56.1 (CH2), 118.9 (CH), 119.3 (CH), 121.0 (CH),
122.3 (CH), 122.6 (CH), 122.7 (CH), 123.6 (CH), 124.5 (CH),
124.5 (CH), 125.7 (CH), 126.8 (CH), 128.0 (CH), 128.4 (CH),
130.1 (CH), 130.6 (CH), 131.1 (CH), 131.3 (CH), 134.3 (C), 136.3
(CH), 137.4 (CH), 139.8 (CH), 142.6 (C), 144.4 (C), 148.0 (CH),
148.8 (C), 149.7 (C), 150.3 (C), 152.1 (CH), 153.9 (CH), 164.9
(C), 167.2 (C), 168.7 (C), 171.4 (C). 19F NMR (564.3 MHz,
CDCl3) δ: −153.22 (s). HRMS (ESI-QTOF) ([M]+): m/z calcd for
C37H30IrN6: 749,2132; found: 749,2115.
= 8.0, 1H), 7.66−7.60 (m, 3H), 7.47 (ddd, JHH = 0.8, JHH = 4.8, JHH
=
8.0, 1H), 4.79 (s, 3H). 13C NMR (100 MHz, CDCl3) δ 149.6 (CH),
142.6 (C), 141.9 (C), 138.5 (CH), 134.6 (C), 132.1 (CH), 130.5
(CH), 127.6 (CH), 126.0 (CH), 125.9 (CH), 121.3 (CH), 41.8
(CH3). 19F NMR (376.25 MHz, CDCl3) δ −78.4 (s). HRMS (ESI-
QTOF) ([M]+): m/z calcd for [C14H13N4]+ 237,1135; found:
237.1139
Synthesis of 1-Phenyl-3-methyl-4-(pyridin-2-yl)-1H-1,2,3-triazol-
3-ium Iodide 10b-I and 2-(1-Phenyl-1H-1,2,3-triazol-4-yl)-1-meth-
ylpyridin-1-ium Iodide 11b-I. 2-(1-Phenyl-1H-1,2,3-triazol-4-yl)
pyridine 9b (444 mg, 2.00 mmol) was dissolved in anhydrous ACN
(12 mL), and MeI (0.624 mL, 10.00 mmol, 5 equiv) was added. The
solution was refluxed for 24 h under N2; the solvent was removed, and
the crude was purified by column chromatography on silica gel with
DCM/MeOH = 9/1 as eluent to give 10b-I (95 mg, 0.26 mmol, 13%
yields). 1H NMR (600 MHz, CD3CN) δ: 4.67 (s, 3H), 7.60−7.65 (m,
1H), 7.75−7.80 (m, 3H), 8.00−8.05 (m, 2H), 8.10−8.15 (m, 2H),
8.86 (bt, 1H, JHH = 4.9 Hz), 9.47 (s, 1H). 13C NMR, (CD3CN, 100
−
[Ir(ppy)2(ptp)]+BF4 (2-BF4). From triazolium triflate 10b-OTf 50
mg, 0.06 mmol, yields = 76%. From triazolium iodide 10b-I 42 mg,
J
DOI: 10.1021/acs.inorgchem.8b01806
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
1
0.05 mmol, yields = 84%. H NMR (600 MHz, CDCl3) δ: 4.75 (s,
3H), 5.93 (d, 1H, JHH = 7.6 Hz), 6.20 (d, 1H, JHH = 7.4 Hz), 6.47 (bt,
1H, JHH = 7.2 Hz), 6.70 (bt, 1H, JHH = 7.6 Hz), 6.90−7.05 (m, 7H),
(TBAPF6). The concentration of the samples was in the millimolar
range (3 mM for complexes 1-BF4, 2-BF4, and 3-BF4, and 1.5 mM for
complex 4). TBAPF6 (electrochemical grade, 99%, Fluka) was used as
the supporting electrolyte, subject to recrystallization from an ethanol
solution and dried at 60 °C under vacuum.
7.07 (bt, 1H, JHH = 6.5 Hz), 7.15−7.20 (m, 2H), 7.37 (d, 1H, JHH
=
7.8 Hz), 7.56 (d, 1H, JHH = 5.8 Hz), 7.60−7.70 (m, 3H), 7.75−7.85
(m, 2H), 7.85 (bt, 1H, JHH = 5.6 Hz), 8.06 (bt, 1H, JHH = 7.9 Hz),
8.19 (bt, 1H, JHH = 5.9 Hz), 8.36 (d, 1H, JHH = 8.1 Hz). 13C NMR
(150 MHz, CDCl3) δ: 39.6 (CH3), 118.8 (CH), 119.3 (CH), 120.7
(CH), 122.3 (CH), 122.5 (CH), 122.6 (CH), 123.9 (CH), 123.9
(CH), 124.2 (CH), 124.5 (CH), 125.7 (CH), 128.5 (CH), 129.2
(CH), 129.7 (CH), 130.6 (CH), 130.9 (CH), 131.2 (CH), 136.5
(CH), 137.2 (C), 137.4 (CH), 139.6 (CH), 142.1 (C), 144.3 (C),
149.0 (CH), 149.6 (C), 149.7 (C), 150.4 (C), 152.0 (CH), 15308
(CH), 164.0 (C), 167.5 (C), 168.6 (C), 171.1 (C). 19F NMR (564.3
MHz, CDCl3) δ: −153.11 (s). HRMS (ESI-QTOF) ([M]+): m/z
calcd for C36H28IrN6: 735,1976; found: 735,1965.
Photophysics. UV−vis absorption spectra were recorded with a
PerkinElmer Lambda 750 double-beam UV/vis-NIR spectrometer
equipped with a 6 × 6 cell changer unit at 20 °C. Luminescence at
room temperature was measured using a Jobin−Yvon Fluoromax 4
fluorimeter with a step width of 1 nm and an integration time of 0.8 s.
All measurements were performed in pressure resistant quartz
cuvettes with septum from Hellma. CH2Cl2 solvent for spectroscopic
measurements was supplied by Merck (Uvasol). Photoluminescence
quantum yields were determined utilizing as reference Ru(bpy)3Cl2 (6
H2O) in water or normharmane in 0.1 N aqueous solution of H2SO4.
Lifetime measurements were performed by time-correlated single-
photon counting method (TCSPC) with a DeltaTime kit for
DeltaDiode source on FluoroMax systems, including DeltaHub and
DeltaDiode controller. The light-source was a NanoLED 366 nm.
Computational Details. DFT calculations were carried out using
the D.01 revision of the Gaussian 09 program package80 in
combination with the M06 global-hybrid meta-GGA exchange-
correlation functional.60,61 The fully relativistic Stuttgart/Cologne
energy-consistent pseudopotential with multielectron fit was used to
replace the first 60 inner-core electrons of the iridium metal center
(i.e., ECP60MDF)63 and was combined with the associated triple-ζ
basis set (i.e., cc-pVTZ-PP basis);63 for all other atoms, the Pople 6-
31G(d,p) basis set was adopted.62
−
[Ir(ppy)2(btb)]+BF4 (3-BF4). 29.7 mg, 0.032 mmol Yields= 54%
from triazolium iodide 10c-I. 1H NMR (600 MHz, CDCl3) δ: 4.42 (s,
3H), 4.80 (d, 1H, JHH = 14.5 Hz), 4.86 (d, 1H, JHH = 14.5 Hz), 5.50
(d, 1H, JHH = 14.4 Hz), 5.54 (d, 1H, JHH = 14.4 Hz), 6.29 (dd, 1H,
JHH = 7.5 Hz, JHH = 0.7 Hz), 6.38 (dd, 1H, JHH = 7.7 Hz, JHH = 0.7
Hz), 6.57 (d, 2H, JHH = 7.7 Hz), 6.75−6.80 (m, 1H), 6.82 (dt, 1H,
J
HH = 7.5 Hz, JHH = 1.2 Hz), 6.85−6.95 (m, 3H), 6.98 (bt, 1H, JHH
7.8 Hz), 7.11 (bt, 2H, JHH = 7.7 Hz), 7.20 (bt, 1H, JHH = 7.4 Hz),
7.25−7.35 (m, 5H), 7.45 (d, 1H, JHH = 7.8 Hz), 7.55 (d, 1H, JHH
=
=
5.7 Hz), 7.60−7.70 (m, 4H), 7.80−7.85 (m, 2H), 8.85 (s, 1H). 13C
NMR (150 MHz, CDCl3) δ: 38.3 (CH3), 55.5 (CH2), 56.1 (CH2),
118.8 (CH), 119.2 (CH), 121.0 (CH), 122.2 (CH), 122.6 (CH),
122.7 (CH), 122.8 (CH), 124.0 (CH), 124.4 (CH), 126.9 (CH),
128.2 (CH), 128.4 (CH), 128.8 (CH), 128.9 (CH), 129.0 (CH),
129.9 (CH), 130.0 (CH), 131.1 (CH), 131.6 (CH), 133.6 (C), 134.3
(C), 136.3 (CH), 137.1 (CH), 139.9 (C), 142.8 (C), 143.4 (C),
144.5 (C), 147.7 (C), 149.2 (CH), 153.0 (CH), 160.7 (C), 167.0
(C), 168.9 (C), 169.6 (C). 19F NMR (564.3 MHz, CDCl3) δ:
−156.87 (s). HRMS (ESI-QTOF) ([M]+): m/z calcd for C41H34IrN8:
829,2507; found: 829,2512.
All the reported complexes were fully optimized without symmetry
constraints, using a time-independent DFT approach, in their ground
state (S0), triplet emitting state and metal-center one (3MC); all the
optimization procedures were performed using the PCM to simulate
acetonitrile or dichloromethane solvation effects.64−66 Frequency
calculations were always used to confirm that every stationary point
found by geometry optimizations was actually a minimum on their
corresponding potential-energy surfaces (no imaginary frequencies).
For all the complexes, the S0 minimum-energy geometry was
optimized starting from several possible conformers, suggested by
both chemical intuition or available X-ray structures for analogue
structures. To investigate the nature of the emitting state, geometry
optimizations and frequency calculations were performed at the spin-
unrestricted UM06 level of theory (imposing a spin multiplicity of 3),
using the S0 minimum-energy geometry as starting point. The
emission energy from the lowest triplet excited state was estimated by
subtracting the SCF energy of the emitting state (Tn) in its minimum
conformation from that of the singlet ground state having the same
geometry of Tn. The 3MC states were optimized using the same spin-
unrestricted DFT approach, but several educated guesses were used as
starting geometries.
Synthesis of Complex [Ir(ppy)2(btb)] 4. Complex 3-BF4 (25 mg,
0.027 mmol, 1 equiv) was dissolved in 2-ethoxyethanol (5.0 mL), and
K2CO3 (37 mg, 0.27 mmol, 10.0 equiv) was added. The resulting
mixture was refluxed under N2 for 24 h. After cooling, the reaction
was quenched with water (15 mL), and the product was extracted
with DCM (2 × 10 mL). The combined organic layers were dried
over Na2SO4, filtered, and the solvent evaporated under vacuum. The
crude was purified by flash chromatography on silica gel (petroleum
ether/EtOAc= 1/1) to give complex 4 (15 mg, 0.018 mmol) in 67
1
yields %. H NMR (600 MHz, CDCl3) δ: 4.45 (s, 3H), 4.67 (d, 1H,
HH = 14.5 Hz), 4.75 (d, 1H, JHH = 14.5 Hz), 4.81 (d, 1H, JHH = 15.2
J
Hz), 4.86 (d, 1H, JHH = 15.2 Hz), 6.30 (dd, 1H, JHH = 7.1 Hz, JHH
1.3 Hz), 6.40−6.45 (m, 3H), 6.55−6.65 (m, 2H), 6.65 (d, 2H, JHH
7.6 Hz), 6.75−6.80 (m, 4H), 6.90−6.95 (m, 2H), 7.01 (bt, 1H, JHH
=
=
=
TD-DFT calculations,81−83 carried out at the same level of theory
used for geometry optimizations, were used to simulate the electronic
absorption spectra of the investigated molecules in their optimized S0
geometry, by computing the lowest-energy 100 vertical excitations of
singlet spin multiplicity. Using the same approach, also the first 25
triplet excitations were calculated and their nature was assessed by the
help of NTO analysis.72
7.3 Hz), 7.05−7.10 (m, 2H), 7.16 (bt, 1H, JHH = 7.4 Hz), 7.30−7.35
(m, 1H), 7.40−7.45 (m, 2H), 7.45−7.50 (m, 2H), 7.60 (d, 1H, JHH
=
8.2 Hz), 7.89 (bt, 2H, JHH = 6.1 Hz). 13C NMR (150 MHz, CDCl3)
δ: 37.0 (CH3), 53.0 (CH2), 55.1 (CH2), 118.3 (CH), 118.4 (CH),
120.0 (CH), 120.2 (CH), 121.4 (CH), 121.7 (CH), 124.1 (CH),
124.2 (CH), 126.2 (CH), 126.4 (CH), 127.2 (CH), 127.4 (CH),
127.6 (CH), 128.1 (CH), 129.3 (CH), 129.4 (CH), 131.3 (CH),
132.0 (CH), 134.5 (CH), 134.8 (CH), 135.8 (C), 138.7 (C), 143.8
(C), 144.2 (C), 149.1 (C), 150.5 (C), 152.7 (CH), 153.3 (CH),
160.0 (C), 163.1 (C), 164.4 (C), 165.3 (C), 168.9 (C), 169.1 (C).
HRMS (ESI-QTOF): m/z calcd for C41H33IrN8: 829,2507; found:
829,2500 [M + H]+.
All the pictures showing molecular geometries, orbitals, and spin-
density surfaces were created using GaussView 5.84
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.8b01806.
Electrochemical Characterization. Cyclic voltammetry experi-
ments were performed with a Metrohm Autolab PGSTAT101 at
room temperature inside a glovebox. The electrochemical cell was
equipped with a Pt-disc as working electrode, an Ag-wire quasi-
reference electrode, and a Pt wire as counter electrode. Ferrocene was
used as internal standard (0.38 V vs SCE).79 The electrochemical
characterization, cyclic voltammetry (CV), was performed in dry
acetonitrile/0.1 M tetrabutylammonium hexafluorophosphate
Crystal structures and crystallographic data of com-
pound 11b-I; NMR spectra of the ligands and of
complexes 1−3-BF4 and 4; electrochemical data of
complexes 1−3-BF4 and 4 in acetonitrile solutions at
K
DOI: 10.1021/acs.inorgchem.8b01806
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
different scan rates; DFT and TD-DFT data with the
Article
Electron Transfer, Photochemistry, Magnetic Bistability, and
Catalysis. Z. Anorg. Allg. Chem. 2017, 643 (9), 554−584.
(8) Valencia, M.; Pereira, A.; Muller-Bunz, H.; Belderrain, T. R.;
Perez, P. J.; Albrecht, M. Triazolylidene-Iridium Complexes with a
Pendant Pyridyl Group for Cooperative Metal-Ligand Induced
Catalytic Dehydrogenation of Amines. Chem. - Eur. J. 2017, 23
(37), 8901−8911.
(9) Beyer, B.; Ulbricht, C.; Escudero, D.; Friebe, C.; Winter, A.;
Gonzalez, L.; Schubert, U. S. Phenyl-1h-[1,2,3]Triazoles as New
Cyclometallating Ligands for Iridium(III) Complexes. Organometallics
2009, 28 (18), 5478−5488.
(10) Donato, L.; Abel, P.; Zysman-Colman, E. Cationic Iridium(III)
Complexes Bearing a Bis(Triazole) Ancillary Ligand. Dalton Trans
2013, 42 (23), 8402−8412.
(11) Fernandez-Hernandez, J. M.; Beltran, J. I.; Lemaur, V.; Galvez-
Lopez, M. D.; Chien, C. H.; Polo, F.; Orselli, E.; Frohlich, R.; Cornil,
J.; De Cola, L. Iridium(III) Emitters Based on 1,4-Disubstituted-1h-
1,2,3-Triazoles as Cyclometalating Ligand: Synthesis, Character-
ization, and Electroluminescent Devices. Inorg. Chem. 2013, 52 (4),
1812−1824.
(12) Fernandez-Hernandez, J. M.; Yang, C. H.; Beltran, J. I.;
Lemaur, V.; Polo, F.; Frohlich, R.; Cornil, J.; De Cola, L. Control of
the Mutual Arrangement of Cyclometalated Ligands in Cationic
Iridium(III) Complexes. Synthesis, Spectroscopy, and Electro-
luminescence of the Different Isomers. J. Am. Chem. Soc. 2011, 133
(27), 10543−10558.
(13) Ladouceur, S.; Fortin, D.; Zysman-Colman, E. Enhanced
Luminescent Iridium(III) Complexes Bearing Aryltriazole Cyclo-
metallated Ligands. Inorg. Chem. 2011, 50 (22), 11514−11526.
(14) Baschieri, A.; Muzzioli, S.; Fiorini, V.; Matteucci, E.; Massi, M.;
Sambri, L.; Stagni, S. Introducing a New Family of Biotinylated
Ir(III)-Pyridyltriazole Lumophores: Synthesis, Photophysics, and
Preliminary Study of Avidin-Binding Properties. Organometallics
2014, 33 (21), 6154−6164.
optimized geometries of the ground state, of the lowest
triplet state, and of the metal-centered state of
complexes 1+−3+ and 4 calculated in acetonitrile;
emission and excitation spectra of all the complexes in
room-temperature acetonitrile solution (PDF)
Accession Codes
CCDC 1844614 contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge
via www.ccdc.cam.ac.uk/data_request/cif, by emailing data_
request@ccdc.cam.ac.uk, or by contacting The Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge
CB2 1EZ, UK; fax: +44 1223 336033.
AUTHOR INFORMATION
Corresponding Authors
*(L.S.) E-mail: letizia.sambri@unibo.it.
*(C.B.) E-mail: claudia.bizzarri@kit.edu.
*(A.B.) E-mail: andrea.baschieri2@unibo.it.
■
ORCID
Filippo Monti: 0000-0002-9806-1957
Rita Mazzoni: 0000-0002-8926-9203
Andrea Baschieri: 0000-0002-2108-8190
Letizia Sambri: 0000-0003-1823-9872
Present Address
⊥A.B.: Dipartimento di Chimica “Giacomo Ciamician”,
̀
Universita di Bologna, Via San Giacomo 11, 40126 Bologna,
Italy.
Notes
(15) Felici, M.; Contreras-Carballada, P.; Vida, Y.; Smits, J. M. M.;
Nolte, R. J. M.; De Cola, L.; Williams, R. M.; Feiters, M. C. Ir-III and
Ru-II Complexes Containing Triazole-Pyridine Ligands: Lumines-
cence Enhancement Upon Substitution with Beta-Cyclodextrin.
Chem. - Eur. J. 2009, 15 (47), 13124−13134.
(16) Mydlak, M.; Bizzarri, C.; Hartmann, D.; Sarfert, W.; Schmid,
G.; De Cola, L. Positively Charged Iridium(III) Triazole Derivatives
as Blue Emitters for Light-Emitting Electrochemical Cells. Adv. Funct.
Mater. 2010, 20 (11), 1812−1820.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
C.B. acknowledges DFG-funded Collaborative Research
Centre (SFB) TRR 88/3MET “Cooperative Effects in
Homo- and Heterometallic Complexes”. C.B. thanks Prof. F.
Breher (KIT) and Prof. H.-A. Wagenknecht (KIT) for giving
access to electrochemical and photochemical equipment,
respectively.
(17) Naddaka, M.; Locatelli, E.; Colecchia, D.; Sambri, L.; Monaco,
I.; Baschieri, A.; Sasdelli, F.; Chiariello, M.; Matteucci, E.; Zani, P.;
Franchini, M. C. Hybrid Cholesterol-Based Nanocarriers Containing
Phosphorescent Ir Complexes: In Vitro Imaging on Glioblastoma Cell
Line. RSC Adv. 2015, 5 (2), 1091−1096.
REFERENCES
■
(1) Rostovtsev, V. V.; Green, L. G.; Fokin, V. V.; Sharpless, K. B. A
Stepwise Huisgen Cycloaddition Process: Copper(I)-Catalyzed
Regioselective ″Ligation″ of Azides and Terminal Alkynes. Angew.
Chem., Int. Ed. 2002, 41 (14), 2596−2599.
̈
(18) Orselli, E.; Albuquerque, R. Q.; Fransen, P. M.; Frohlich, R.;
Janssen, H. M.; De Cola, L. 1,2,3-Triazolyl-Pyridine Derivatives as
Chelating Ligands for Blue Iridium(III) Complexes. Photophysics and
Electroluminescent Devices. J. Mater. Chem. 2008, 18 (38), 4579.
(19) Chianese, A. R.; Kovacevic, A.; Zeglis, B. M.; Faller, J. W.;
Crabtree, R. H. Abnormal C5-Bound N-Heterocyclic Carbenes:
Extremely Strong Electron Donor Ligands and Their Iridium(I) and
Iridium(III) Complexes. Organometallics 2004, 23 (10), 2461−2468.
(20) Kelly, R. A.; Clavier, H.; Giudice, S.; Scott, N. M.; Stevens, E.
D.; Bordner, J.; Samardjiev, I.; Hoff, C. D.; Cavallo, L.; Nolan, S. P.
Determination of N-Heterocyclic Carbene (NHC) Steric and
Electronic Parameters Using the [(NHC)Ir(CO)(2)Cl] System.
Organometallics 2008, 27 (2), 202−210.
(2) Tornoe, C. W.; Christensen, C.; Meldal, M. Peptidotriazoles on
Solid Phase: [1,2,3]-Triazoles by Regiospecific Copper(I)-Catalyzed
1,3-Dipolar Cycloadditions of Terminal Alkynes to Azides. J. Org.
Chem. 2002, 67 (9), 3057−3064.
(3) Crabtree, R. H. Abnormal, Mesoionic and Remote N-
Heterocyclic Carbene Complexes. Coord. Chem. Rev. 2013, 257 (3−
4), 755−766.
(4) Donnelly, K. F.; Petronilho, A.; Albrecht, M. Application of
1,2,3-Triazolylidenes as Versatile Nhc-Type Ligands: Synthesis,
Properties, and Application in Catalysis and Beyond. Chem. Commun.
2013, 49 (12), 1145−1159.
(5) Hopkinson, M. N.; Richter, C.; Schedler, M.; Glorius, F. An
Overview of N-Heterocyclic Carbenes. Nature 2014, 510 (7506),
485−496.
(21) Poulain, A.; Canseco-Gonzalez, D.; Hynes-Roche, R.; Muller-
Bunz, H.; Schuster, O.; Stoeckli-Evans, H.; Neels, A.; Albrecht, M.
Synthesis and Tunability of Abnormal 1,2,3-Triazolylidene Palladium
and Rhodium Complexes. Organometallics 2011, 30 (5), 1021−1029.
(22) Yuan, D.; Huynh, H. V. 1,2,3-Triazolin-5-Ylidenes: Synthesis of
Hetero-Bis(Carbene) Pd(II) Complexes, Determination of Donor
Strengths, and Catalysis. Organometallics 2012, 31 (1), 405−412.
(6) N-Heterocyclic Carbenes: Effective Tools for Organometallic
Synthesis; Nolan, S. P., Eds.; Wiley-VCH, 2014, pp 1−22.
(7) Schweinfurth, D.; Hettmanczyk, L.; Suntrup, L.; Sarkar, B. Metal
Complexes of Click-Derived Triazoles and Mesoionic Carbenes:
L
DOI: 10.1021/acs.inorgchem.8b01806
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
(23) Bolje, A.; Hohloch, S.; van der Meer, M.; Kosmrlj, J.; Sarkar, B.
Ru-II, Os-II, and Ir-III Complexes with Chelating Pyridyl-Mesoionic
Carbene Ligands: Structural Characterization and Applications in
Transfer Hydrogenation Catalysis. Chem. - Eur. J. 2015, 21 (18),
6756−6764.
(24) Lalrempuia, R.; McDaniel, N. D.; Muller-Bunz, H.; Bernhard,
S.; Albrecht, M. Water Oxidation Catalyzed by Strong Carbene-Type
Donor-Ligand Complexes of Iridium. Angew. Chem., Int. Ed. 2010, 49
(50), 9765−9768.
(25) Maity, R.; Hohloch, S.; Su, C. Y.; van der Meer, M.; Sarkar, B.
Cyclometalated Mono- and Dinuclear Ir-III Complexes with ″Click″-
Derived Triazoles and Mesoionic Carbenes. Chem. - Eur. J. 2014, 20
(32), 9952−9961.
(26) Mendoza-Espinosa, D.; Gonzalez-Olvera, R.; Negron-Siva, G.
E.; Angeles-Beltran, D.; Suarez-Castillo, O. R.; Alvarez-Hernandez, A.;
Santillan, R. Phenoxy-Linked Mesoionic Triazol-5-Ylidenes as Plat-
forms for Multinuclear Transition Metal Complexes. Organometallics
2015, 34 (18), 4529−4542.
(27) Petronilho, A.; Llobet, A.; Albrecht, M. Ligand Exchange and
Redox Processes in Iridium Triazolylidene Complexes Relevant to
Catalytic Water Oxidation. Inorg. Chem. 2014, 53 (24), 12896−
12901.
(28) Aizpurua, J. M.; Fratila, R. M.; Monasterio, Z.; Perez-Esnaola,
N.; Andreieff, E.; Irastorza, A.; Sagartzazu-Aizpurua, M. Triazolium
Cations: From the ″Click″ Pool to Multipurpose Applications. New J.
Chem. 2014, 38 (2), 474−480.
(29) Crowley, J. D.; Lee, A. L.; Kilpin, K. J. 1,3,4-Trisubstituted-
1,2,3-Triazol-5-Ylidene ’Click’ Carbene Ligands: Synthesis, Catalysis
and Self-Assembly. Aust. J. Chem. 2011, 64 (8), 1118−1132.
(30) Scattergood, P. A.; Elliott, P. I. P. An Unexpected Journey from
Highly Tunable Phosphorescence to Novel Photochemistry of 1,2,3-
Triazole-Based Complexes. Dalton Trans 2017, 46 (47), 16343−
16356.
(31) Chabera, P.; Liu, Y. Z.; Prakash, O.; Thyrhaug, E.; El Nahhas,
A.; Honarfar, A.; Essen, S.; Fredin, L. A.; Harlang, T. C. B.; Kjaer, K.
S.; Handrup, K.; Ericson, F.; Tatsuno, H.; Morgan, K.; Schnadt, J.;
Haggstrom, L.; Ericsson, T.; Sobkowiak, A.; Lidin, S.; Huang, P.;
Styring, S.; Uhlig, J.; Bendix, J.; Lomoth, R.; Sundstrom, V.; Persson,
P.; Warnmark, K. A Low-Spin Fe(III) Complex with 100-Ps Ligand-
to-Metal Charge Transfer Photoluminescence. Nature 2017, 543
(7647), 695−699.
(32) Liu, Y. Z.; Kjaer, K. S.; Fredin, L. A.; Chabera, P.; Harlang, T.;
Canton, S. E.; Lidin, S.; Zhang, J. X.; Lomoth, R.; Bergquist, K. E.;
Persson, P.; Warnmark, K.; Sundstrom, V. A Heteroleptic Ferrous
Complex with Mesoionic Bis(1,2,3-Triazol-5-Ylidene) Ligands:
Taming the MLCT Excited State of Iron(II). Chem. - Eur. J. 2015,
21 (9), 3628−3639.
(33) Baschieri, A.; Monti, F.; Matteucci, E.; Mazzanti, A.; Barbieri,
A.; Armaroli, N.; Sambri, L. A Mesoionic Carbene as Neutral Ligand
for Phosphorescent Cationic Ir(III) Complexes. Inorg. Chem. 2016,
55 (16), 7912−7919.
(34) Evans, R. C.; Douglas, P.; Winscom, C. J. Coordination
Complexes Exhibiting Room-Temperature Phosphorescence: Evalua-
tion of Their Suitability as Triplet Emitters in Organic Light Emitting
Diodes. Coord. Chem. Rev. 2006, 250 (15−16), 2093−2126.
(35) Flamigni, L.; Barbieri, A.; Sabatini, C.; Ventura, B.; Barigelletti,
F. Photochemistry and Photophysics of Coordination Compounds:
Iridium. Photochemistry and Photophysics of Coordination Compounds II
2007, 281, 143−203.
(36) Liu, B. A.; Dang, F. F.; Feng, Z.; Tian, Z. Z.; Zhao, J.; Wu, Y.;
Yang, X. L.; Zhou, G. J.; Wu, Z. X.; Wong, W. Y. Novel Iridium(III)
Complexes Bearing Dimesitylboron Groups with Nearly 100%
Phosphorescent Quantum Yields for Highly Efficient Organic Light-
Emitting Diodes. J. Mater. Chem. C 2017, 5 (31), 7871−7883.
(37) Xu, X. B.; Guo, H. R.; Zhao, J.; Liu, B. A.; Yang, X. L.; Zhou, G.
J.; Wu, Z. X. Asymmetric Tris-Heteroleptic Iridium(III) Complexes
Containing a 9-Phenyl-9-Phosphafluorene Oxide Moiety with
Enhanced Charge Carrier Injection/Transporting Properties for
Highly Efficient Solution-Processed Organic Light-Emitting Diodes.
Chem. Mater. 2016, 28 (23), 8556−8569.
(38) Yang, X.; Guo, H.; Liu, B.; Zhao, J.; Zhou, G.; Wu, Z.; Wong,
W. Y. Diarylboron-Based Asymmetric Red-Emitting Ir(III) Complex
for Solution-Processed Phosphorescent Organic Light-Emitting Diode
with External Quantum Efficiency above 28%. Adv. Sci. (Weinh) 2018,
5 (5), 1701067.
(39) Costa, R. D.; Orti, E.; Bolink, H. J.; Monti, F.; Accorsi, G.;
Armaroli, N. Luminescent Ionic Transition-Metal Complexes for
Light-Emitting Electrochemical Cells. Angew. Chem., Int. Ed. 2012, 51
(33), 8178−8211.
(40) Hu, T.; He, L.; Duan, L.; Qiu, Y. Solid-State Light-Emitting
Electrochemical Cells Based on Ionic Iridium(III) Complexes. J.
Mater. Chem. 2012, 22 (10), 4206−4215.
(41) Zeng, Q. Y.; Li, F. S.; Guo, T. L.; Shan, G. G.; Su, Z. M. Large
Size Color-Tunable Electroluminescence from Cationic Iridium
Complexes-Based Light-Emitting Electrochemical Cells. Sci. Rep.
2016, 6, 1.
(42) Matteucci, E.; Baschieri, A.; Mazzanti, A.; Sambri, L.; Avila, J.;
Pertegas, A.; Bolink, H. J.; Monti, F.; Leoni, E.; Armaroli, N. Anionic
Cyclometalated Iridium(III) Complexes with a Bis-Tetrazolate
Ancillary Ligand for Light-Emitting Electrochemical Cells. Inorg.
Chem. 2017, 56 (17), 10584−10595.
(43) Monti, F.; Baschieri, A.; Matteucci, E.; Mazzanti, A.; Sambri, L.;
Barbieri, A.; Armaroli, N. A Chelating Diisocyanide Ligand for
Cyclometalated Ir(III) Complexes with Strong and Tunable
Luminescence. Faraday Discuss. 2015, 185, 233−48.
(44) Baschieri, A.; Muzzioli, S.; Matteucci, E.; Stagni, S.; Massi, M.;
Sambri, L. New Heterometallic Ir(III)2-Eu(III) Complexes: White
Light Emission from a Single Molecule. Dalton Trans 2015, 44 (1),
37−40.
(45) Suntrup, L.; Klenk, S.; Klein, J.; Sobottka, S.; Sarkar, B. Gauging
Donor/Acceptor Properties and Redox Stability of Chelating Click-
Derived Triazoles and Triazolylidenes: A Case Study with Rhenium-
(I) Complexes. Inorg. Chem. 2017, 56 (10), 5771−5783.
(46) Barbante, G. J.; Doeven, E. H.; Kerr, E.; Connell, T. U.;
Donnelly, P. S.; White, J. M.; Lopes, T.; Laird, S.; Wilson, D. J. D.;
Barnard, P. J.; Hogan, C. F.; Francis, P. S. Understanding
Electrogenerated Chemiluminescence Efficiency in Blue-Shifted
Iridium(III)-Complexes: An Experimental and Theoretical Study.
Chem. - Eur. J. 2014, 20 (12), 3322−3332.
(47) Connell, T. U.; White, J. M.; Smith, T. A.; Donnelly, P. S.
Luminescent Iridium(III) Cyclometalated Complexes with 1,2,3-
Triazole ″Click″ Ligands. Inorg. Chem. 2016, 55 (6), 2776−2790.
(48) Liu, S.; Muller, P.; Takase, M. K.; Swager, T. M. ″Click″
Synthesis of Heteroleptic Tris-Cyclometalated Iridium(III) Com-
plexes: Cu(I) Triazolide Intermediates as Transmetalating Reagents.
Inorg. Chem. 2011, 50 (16), 7598−7609.
(49) Crowley, J. D.; Bandeen, P. H.; Hanton, L. R. A One Pot Multi-
Component CuAAC ″Click″ Approach to Bidentate and Tridentate
Pyridyl-1,2,3-Triazole Ligands: Synthesis, X-Ray Structures and
Copper(II) and Silver(I) Complexes. Polyhedron 2010, 29 (1), 70−
83.
(50) Aizpurua, J. M.; Sagartzazu-Aizpurua, M.; Azcune, I.; Miranda,
J. I.; Monasterio, Z.; Garcia-Lecina, E.; Fratila, R. M. ’Click’ Synthesis
of Nonsymmetrical 4,4 ’-Bis(1,2,3-Triazolium) Salts. Synthesis 2011,
2737−2742.
(51) Keske, E. C.; Zenkina, O. V.; Wang, R. Y.; Crudden, C. M.
Synthesis and Structure of Silver and Rhodium 1,2,3-Triazol-5-
Ylidene Mesoionic Carbene Complexes. Organometallics 2012, 31 (1),
456−461.
(52) Nolte, C.; Mayer, P.; Straub, B. F. Isolation of a Copper(I)
Triazolide: A″Click″ Intermediate″. Angew. Chem., Int. Ed. 2007, 46
(12), 2101−2103.
(53) Winn, J.; Pinczewska, A.; Goldup, S. M. Synthesis of a Rotaxane
Cu-I Triazolide under Aqueous Conditions. J. Am. Chem. Soc. 2013,
135 (36), 13318−13321.
(54) Schuster, E. M.; Botoshansky, M.; Gandelman, M. Pincer Click
Ligands. Angew. Chem., Int. Ed. 2008, 47 (24), 4555−4558.
M
DOI: 10.1021/acs.inorgchem.8b01806
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
(55) Schuster, E. M.; Botoshansky, M.; Gandelman, M. Versatile,
Selective, and Switchable Coordination Modes of Pincer Click
Ligands. Organometallics 2009, 28 (24), 7001−7005.
(75) Sajoto, T.; Djurovich, P. I.; Tamayo, A. B.; Oxgaard, J.;
Goddard, W. A., 3rd; Thompson, M. E. Temperature Dependence of
Blue Phosphorescent Cyclometalated Ir(III) Complexes. J. Am. Chem.
Soc. 2009, 131 (28), 9813−22.
(76) Monti, F.; Baschieri, A.; Gualandi, I.; Serrano-Perez, J. J.;
Junquera-Hernandez, J. M.; Tonelli, D.; Mazzanti, A.; Muzzioli, S.;
Stagni, S.; Roldan-Carmona, C.; Pertegas, A.; Bolink, H. J.; Orti, E.;
Sambri, L.; Armaroli, N. Iridium(III) Complexes with Phenyl-
Tetrazoles as Cyclometalating Ligands. Inorg. Chem. 2014, 53 (14),
7709−7721.
(77) Kessler, F.; Costa, R. D.; Di Censo, D.; Scopelliti, R.; Orti, E.;
Bolink, H. J.; Meier, S.; Sarfert, W.; Gratzel, M.; Nazeeruddin, M. K.;
Baranoff, E. Near-Uv to Red-Emitting Charged Bis-Cyclometallated
Iridium(III) Complexes for Light-Emitting Electrochemical Cells.
Dalton Trans 2012, 41 (1), 180−91.
(78) Monti, F.; Kessler, F.; Delgado, M.; Frey, J.; Bazzanini, F.;
Accorsi, G.; Armaroli, N.; Bolink, H. J.; Orti, E.; Scopelliti, R.;
Nazeeruddin, M. K.; Baranoff, E. Charged Bis-Cyclometalated
Iridium(III) Complexes with Carbene-Based Ancillary Ligands.
Inorg. Chem. 2013, 52 (18), 10292−305.
(56) Gritzner, G.; Kuta, J. Recommendations on Reporting
Electrode Potentials in Nonaqueous Solvents (Recommendations
1983). Pure Appl. Chem. 1984, 56 (4), 461−466.
(57) Thelakkat, M.; Schmidt, H.-W. Synthesis and Properties of
Novel Derivatives of 1,3,5-Tris(Diarylamino)Benzenes for Electro-
luminescent Devices. Adv. Mater. 1998, 10 (3), 219−223.
(58) Miller, L. L.; Nordblom, G. D.; Mayeda, E. A. Simple,
Comprehensive Correlation of Organic Oxidation and Ionization
Potentials. J. Org. Chem. 1972, 37 (6), 916−918.
(59) Bredas, J. L.; Silbey, R.; Boudreaux, D. S.; Chance, R. R. Chain-
Length Dependence of Electronic and Electrochemical Properties of
Conjugated Systems: Polyacetylene, Polyphenylene, Polythiophene,
and Polypyrrole. J. Am. Chem. Soc. 1983, 105 (22), 6555−6559.
(60) Zhao, Y.; Truhlar, D. G. The M06 Suite of Density Functionals
for Main Group Thermochemistry, Thermochemical Kinetics,
Noncovalent Interactions, Excited States, and Transition Elements:
Two New Functionals and Systematic Testing of Four M06-Class
Functionals and 12 Other Functionals. Theor. Chem. Acc. 2008, 120
(1−3), 215−241.
(61) Zhao, Y.; Truhlar, D. G. Density Functionals with Broad
Applicability in Chemistry. Acc. Chem. Res. 2008, 41 (2), 157−167.
(62) Francl, M. M.; Pietro, W. J.; Hehre, W. J.; Binkley, J. S.;
Gordon, M. S.; Defrees, D. J.; Pople, J. A. Self-Consistent Molecular-
Orbital Methods 0.23. A Polarization-Type Basis Set for 2nd-Row
Elements. J. Chem. Phys. 1982, 77 (7), 3654−3665.
(63) Figgen, D.; Peterson, K. A.; Dolg, M.; Stoll, H. Energy-
Consistent Pseudopotentials and Correlation Consistent Basis Sets for
the 5d Elements Hf-Pt. J. Chem. Phys. 2009, 130 (16), 164108.
(64) Tomasi, J.; Persico, M. Molecular-Interactions in Solution - an
Overview of Methods Based on Continuous Distributions of the
Solvent. Chem. Rev. 1994, 94 (7), 2027−2094.
(65) Tomasi, J.; Mennucci, B.; Cammi, R. Quantum Mechanical
Continuum Solvation Models. Chem. Rev. 2005, 105 (8), 2999−3093.
(66) Cramer, C. J.; Truhlar, D. G. Continuum Solvation Models. In
(79) Pavlishchuk, V. V.; Addison, A. W. Conversion Constants for
Redox Potentials Measured Versus Different Reference Electrodes in
Acetonitrile Solutions at 25°C. Inorg. Chim. Acta 2000, 298 (1), 97−
102.
(80) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci,
B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H.
P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.;
Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.;
Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.;
Montgomery, Jr., J. A.; Peralta, J. E.; Ogliaro, F.; Bearpark, M.;
Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Keith, T.;
Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J.
C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam, J. M.;
Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo,
J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi,
R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.;
Zakrzewski, V. G.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.;
Dapprich, S.; Daniels, A. D.; Farkas, O.; Foresman, J. B.; Ortiz, J. V.;
Cioslowski, J.; Fox, D. J. Gaussian 09, Revision D.01; Gaussian, Inc.:
Wallingford, CT, 2013.
(81) Stratmann, R. E.; Scuseria, G. E.; Frisch, M. J. An Efficient
Implementation of Time-Dependent Density-Functional Theory for
the Calculation of Excitation Energies of Large Molecules. J. Chem.
Phys. 1998, 109 (19), 8218−8224.
(82) Casida, M. E.; Jamorski, C.; Casida, K. C.; Salahub, D. R.
Molecular Excitation Energies to High-Lying Bound States from
Time-Dependent Density-Functional Response Theory: Character-
ization and Correction of the Time-Dependent Local Density
Approximation Ionization Threshold. J. Chem. Phys. 1998, 108
(11), 4439−4449.
́
Solvent Effects and Chemical Reactivity; Tapia, O., Bertran, J., Eds.;
Springer: Netherlands, 2002; Vol. 17, pp 1−80.
(67) Costa, R. D.; Monti, F.; Accorsi, G.; Barbieri, A.; Bolink, H. J.;
Orti, E.; Armaroli, N. Photophysical Properties of Charged Cyclo-
metalated Ir(III) Complexes: A Joint Theoretical and Experimental
Study. Inorg. Chem. 2011, 50 (15), 7229−38.
(68) He, L.; Duan, L.; Qiao, J.; Zhang, D.; Wang, L.; Qiu, Y.
Enhanced Stability of Blue-Green Light-Emitting Electrochemical
Cells Based on a Cationic Iridium Complex with 2-(1-Phenyl-1h-
Pyrazol-3-Yl)Pyridine as the Ancillary Ligand. Chem. Commun.
(Cambridge, U. K.) 2011, 47 (22), 6467−9.
(69) Osiak, J. G.; Setzer, T.; Jones, P. G.; Lennartz, C.; Dreuw, A.;
Kowalsky, W.; Johannes, H. H. Twist It! The Acid-Dependent
Isomerization of Homoleptic Carbenic Iridium(III) Complexes.
Chem. Commun. 2017, 53 (23), 3295−3298.
(83) Bauernschmitt, R.; Ahlrichs, R. Treatment of Electronic
Excitations within the Adiabatic Approximation of Time Dependent
Density Functional Theory. Chem. Phys. Lett. 1996, 256 (4−5), 454−
464.
(84) Dennington, R.; Keith, T.; Millam, J. Gaussview, Version 5,
Semichem Inc.: Shawnee Mission, KS, 2009.
(70) Ladouceur, S.; Zysman-Colman, E. A Comprehensive Survey of
Cationic Iridium(III) Complexes Bearing Nontraditional Ligand
Chelation Motifs. Eur. J. Inorg. Chem. 2013, 17, 2985−3007.
(71) Brouwer, A. M. Standards for Photoluminescence Quantum
Yield Measurements in Solution (Iupac Technical Report). Pure Appl.
Chem. 2011, 83 (12), 2213−2228.
(72) Martin, R. L. Natural Transition Orbitals. J. Chem. Phys. 2003,
118 (11), 4775−4777.
(73) Kaim, W.; Kohlmann, S.; Ernst, S.; Olbrich-Deussner, B.;
Bessenbacher, C.; Schulz, A. What Determines the Solvatochromism
of Metal-to-Ligand Charge Transfer Transitions? A Demonstration
Involving 17 Tungsten Carbonyl Complexes. J. Organomet. Chem.
1987, 321 (2), 215−226.
(74) Treboux, G.; Mizukami, J.; Yabe, M.; Nakamura, S. Blue
Phosphorescent Iridium(III) Complex. A Reaction Path on the
Triplet Potential Energy Surface. Chem. Lett. 2007, 36 (11), 1344−
1345.
N
DOI: 10.1021/acs.inorgchem.8b01806
Inorg. Chem. XXXX, XXX, XXX−XXX