Synthesis, Characterization, and Photochromic Studies of Cyclometalated Iridium(III) Complexes Containing a Spironaphthoxazine Moiety

Article abstract of DOI:10.1021/acs.organomet.9b00359

A series of cyclometalated iridium(III) complexes has been designed and synthesized, and their photophysical, photochromic, and electrochemical properties have been studied. The X-ray crystal structure of complex 2 has been determined. The emission properties of the complexes have been shown to be readily perturbed through the modification of the electronic properties of the phenylpyridine ligand. With different substituents at the phenylpyridine ligand of iridium(III) complexes of 1 (-H), 2 (-OMe), 3 (-CHO), and 4 (-CF₃), they can display intense ³MLCT [dπ(Ir) → π*(diimine)] luminescence from 530 to 640 nm to span across the green to orange region. The spectral assignment is also in agreement with the electrochemical studies and DFT calculations. In addition, the photochromic behavior can be easily modulated by varying the substituents on the C^∧N ligand without the need for tedious modification of the spirooxazine framework. By analyzing the kinetic profiles of backward bleaching reactions, less electron-rich iridium(III) complexes can stabilize the merocyanine form with a higher activation barrier. The studies have provided not only fundamental understanding on structure-property relationships that govern the versatile luminescence behavior of these Ir(III) complexes but also the guiding principles in the molecular design for the future developments of visible light-driven photoswitches.

Full text of DOI:10.1021/acs.organomet.9b00359

Article
pubs.acs.org/Organometallics
Cite This: Organometallics XXXX, XXX, XXX−XXX
Synthesis, Characterization, and Photochromic Studies of
Cyclometalated Iridium(III) Complexes Containing a
Spironaphthoxazine Moiety
†
,‡
‡
‡
‡
‡
Jie Liu, Alan Kwun-Wa Chan, Maggie Ng, Eugene Yau-Hin Hong, Nathan Man-Wai Wu,
,
†
,†,‡
Lixin Wu,* and Vivian Wing-Wah Yam*
†State Key Laboratory of Supramolecular Structure and Materials and College of Chemistry, Jilin University, Changchun 130012, PR
China
‡
Institute of Molecular Functional Materials (Areas of Excellence Scheme, University Grants Committee (Hong Kong) and
Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong SAR, PR China
*
S Supporting Information
ABSTRACT: A series of cyclometalated iridium(III) com-
plexes has been designed and synthesized, and their
photophysical, photochromic, and electrochemical properties
have been studied. The X-ray crystal structure of complex 2
has been determined. The emission properties of the
complexes have been shown to be readily perturbed through
the modification of the electronic properties of the phenyl-
pyridine ligand. With different substituents at the phenyl-
pyridine ligand of iridium(III) complexes of 1 (−H), 2
(
−OMe), 3 (−CHO), and 4 (−CF ), they can display intense
3
3
MLCT [dπ(Ir) → π*(diimine)] luminescence from 530 to
6
40 nm to span across the green to orange region. The spectral assignment is also in agreement with the electrochemical studies
∧
and DFT calculations. In addition, the photochromic behavior can be easily modulated by varying the substituents on the C N
ligand without the need for tedious modification of the spirooxazine framework. By analyzing the kinetic profiles of backward
bleaching reactions, less electron-rich iridium(III) complexes can stabilize the merocyanine form with a higher activation
barrier. The studies have provided not only fundamental understanding on structure−property relationships that govern the
versatile luminescence behavior of these Ir(III) complexes but also the guiding principles in the molecular design for the future
developments of visible light-driven photoswitches.
INTRODUCTION
from the visible light-absorbing metal-to-ligand charge transfer
MLCT) excited state using a less destructive and less harmful
■
(
Due to the potential applications in the development of optical
data storage, molecular switching and various other applica-
tions, the exploration of photochromic materials has attracted
excitation source. For example, we have reported the
3
photosensitization of spirooxazine moiety by MLCT excited
13
1
−9
state of rhenium(I) tricarbonyl diimine complex system. The
strategy has also been adopted in other metal complex systems,
tremendous interests in many research areas. Photochromic
spirooxazines are one of the most popular families among
photochromic compounds due to their reversible chemical
transformations and clean interconversion between two
different molecular states simply triggered by light and
19
21
for instance, Zn and Pt, as an important approach to fine-
tune their photophysical and photochromic properties.
Cyclometalated iridium(III) complexes have been demon-
strated to display intense phosphorescence at room temper-
ature. They are widely explored in the field of organic light-
emitting diodes (OLEDs) and molecular sensors as lumino-
1
0,11
heat.
In general, spirooxazines undergo a photoinduced
ring-opening reaction to form a merocyanine (MC) structure
under UV light excitation, and most researches have focused
on the organic system. It was only until 1998 that there has
been a growing trend in the studies of integrating spirooxazine
moiety as ligand into different metal centers to give interesting
classes of metal complexes with novel and distinctive
22−29
phores,
while their utilizations in photochromic reaction
or sensitization are relatively less explored. Moreover, the
3
energy of the MLCT excited state of the Ir(III) complexes can
be easily modulated by introducing different substituent groups
∧
1
2−21
on the cyclometalating C N ligand to adjust the energy of the
properties.
In particular, one important strategy that has
highest occupied molecular orbital (HOMO) as well as the
been demonstrated in these spirooxazine metal complex
systems is the achievement of intramolecular photosensitiza-
1
3,17,20
tion.
One way to achieve photosensitization of the
Received: May 27, 2019
spirooxazine moiety is by intramolecular triplet energy transfer
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.9b00359
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Article
Scheme 1. Synthetic Routes to Spirooxazine-Containing Bipyridine Ligand and Cyclometalated Iridium(III) Complexes
Figure 1. Structure of complex 2 with atomic numbering. Hydrogen atoms have been omitted for clarity. Thermal ellipsoids are shown at the 30%
probability level.
overall optical bandgap. Therefore, it is envisaged that the
combination of the rich excited state properties of Ir(III)
complexes with the photochromic spirooxazine-containing
ligand may provide attractive features for the development of
multifunctional photoswitchable materials. Herein are de-
scribed the design and synthesis of a series of spirooxazine-
containing cyclometalated Ir(III) complexes. Complexes 1−4
with the photochromic spirooxazine-containing diimine ligand,
together with the phenylpyridine (ppy) ligands of different
electronic properties, 1 (−H), 2 (−OMe), 3 (−CHO), and 4
(−CF ) have been prepared to provide an in-depth
3
investigation into fine-tuning their optical features (Scheme
B
DOI: 10.1021/acs.organomet.9b00359
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Organometallics
). The crystal structure and photophysical, photochromic, and
electrochemical properties of these complexes have been
investigated in detail to rationalize the molecular design
strategy in coupling the tunable optical and excited state
properties of the iridium(III) complexes for their application as
photochromic materials.
Article
1
the iridium(III) atom, and the C−Ir−N and N−Ir−N bond
angles are between 174.3 and 174.7°, deviating from the ideal
180° due to the steric demand exerted by the bite angles of the
ppy-OMe and diimine ligands. The two ppy-OMe ligands are
coordinated to the iridium(III) center in a cis configuration.
The trans influence of the carbon donors renders slightly
longer Ir−N bond lengths for the diimine ligand (2.139 and
RESULTS AND DISCUSSION
Synthesis. The synthetic routes of spirooxazine-containing
2
.151 Å) than that in the ppy-OMe ligand (2.038 and 2.042
■
Å). The bite angles of C−Ir−N in the ppy-OMe ligand (80.4
and 80.5°) are slightly larger than the N−Ir−N angle of the
diimine ligand (76.3°). Similar observations have been
reported in the related cyclometalated iridium(III) polypyr-
bipyridine ligand (bpy-SO) and four iridium(III) complexes
∧
+
−
[
Ir(C N) (bpy-SO)] PF (complexes 1−4) are shown in
2
6
Scheme 1. The free ligand of bpy-SO was synthesized by
17
∧
∧
+
31−35
modification of a literature method. The cyclometalated
chloride-bridged Ir(III) dimers, [Ir(C N) (μ-Cl)] , were
idine systems, [Ir(C N)
2
(N N)] .
The bond length of
∧
the spiro C−O moiety in complex 2 is 1.461 Å, which is
2
2
3
0
obtained by the Nonoyama reaction. Substitution of
slightly longer than the common bond length of a C−O bond
36−39
∧
[
Ir(C N) (μ-Cl)] with the diimine ligands in anhydrous
(1.43 Å) in other oxazine systems.
This indicates that the
2
2
dichloromethane at 50 °C, followed by metathesis with KPF6,
afforded pure forms of complexes 1−4 after purification by
column chromatography on silica gel and subsequent
recrystallization from dichloromethane/hexane. The identities
spiro carbon−oxygen bond may be more readily cleaved when
compared to the ordinary C−O bond, a phenomenon that is
3
6−39
commonly found in the spirooxazine system.
In addition,
the interplanar angle between the indoline and naphthoxazine
planes of 2 is 87.98°, which suggests an essentially orthogonal
arrangement among these π-conjugated rings, possibly to
minimize the steric repulsion between the spirooxazine system
of neighboring molecules.
Photophysical Properties. The electronic absorption
spectra of the free ligand, bpy-SO, in CH Cl shows very
intense intraligand (IL) π−π* absorption bands of the
bipyridine and indoline moieties at about 280 and 300 nm,
as well as moderately intense IL π−π* absorption of the
naphthoxazine moiety observed at 318, 348, and 365 nm as
1
of iridium(III) complexes 1−4 have been confirmed by H
NMR spectroscopy, MALDI-TOF mass spectrometry, and
satisfactory elemental analyses. Complex 2 has also been
structurally characterized by X-ray crystallography.
1
9,37,38
X-ray Crystal Structure Determination. Single crystals
of complex 2 have been obtained by slow diffusion of hexane
into a concentrated dichloromethane solution of the complex.
A perspective drawing of complex 2 is depicted in Figure 1,
and the selected bond lengths and angles are summarized in
Table 1. Complex 2 adopts a distorted octahedral geometry at
2
2
1
7,40
reported in the literature.
Complexes 1−4 in dichloro-
methane exhibit very intense absorptions at 280−360 nm and
moderately intense bands at about 380−500 nm in their
electronic absorption spectra (Figure S1). With reference to
previous studies on iridium(III) bipyridine complexes and
related spironaphthoxazine-containing transition metal com-
plexes, the intense absorption bands at 280−360 nm are
assigned to the IL π−π* transitions of spirooxazine-containing
Table 1. Selected Bond Lengths [Å] and Bond Angles [deg]
with Estimated Standard Deviations (esds) in Parentheses
for Complex 2
C(11)−Ir(1)
C(12)−Ir(1)
Ir(1)−N(1)
C(45)−O(7)
C(11)−Ir(1)−N(1)
C(12)−Ir(1)−N(2)
N(3)−Ir(1)−N(4)
2.023(6)
2.009(6)
2.038(5)
1.461(10)
80.5(2)
Ir(1)−N(2)
Ir(1)−N(3)
Ir(1)−N(4)
2.042(5)
2.151(5)
2.139(5)
∧
bipyridine ligand and C N ligands, whereas the relatively low-
C(11)−Ir(1)−N(3)
C(12)−Ir(1)−N(4)
N(1)−Ir(1)−N(2)
174.4(2)
174.3(2)
174.72(19)
energy bands are assigned as a mixture of spin-allowed and
80.4(2)
76.25(19)
spin-forbidden metal-to-ligand and ligand-to-ligand charge
13,17,21,41−46
transfer (MLCT/LLCT) transitions.
The photo-
Table 2. Photophysical Data for the Complexes
emission
medium
(T [K])
λem [nm]
0
absorption λmax [nm] (εmax [dm mol cm−1])
3
−1
a
(τ [ns])
b
φem
kr [s−1]e
compound
2
2
2
9.59 × 105
1
294 (45000), 368 (14120), 404 sh (9230), 494 (1600)
CH Cl (298)
625 (44.8)
540
677
640 (38.8)
550
679
4.3 × 10−
2
2
c
glass (77)
glass (77)
d
c
1
2
(PMC)
(PMC)
278 (51550), 294 sh (43740), 347 (29560), 390 sh (11370), 512 (1230)
CH Cl (298)
3.5 × 10−
9.02 × 105
5.54 × 106
2
2
c
glass (77)
glass (77)
c
2
3
273 (67000), 292 (61850), 363 (20150), 384 sh (13020), 423 (6810),
CH Cl (298)
600 (4.4)
2.43 × 10−
2
2
4
78 (2880)
c
c
glass (77)
glass (77)
521, 563, 608
685
530 (18.4)
489, 526, 560
675
3
4
(PMC)
(PMC)
2
3.36 × 106
322 (22930), 348 (16390), 420 sh (4650), 478 sh (1640)
CH Cl (298)
6.19 × 10−
2
2
c
glass (77)
glass (77)
c
4
a
b
c
d
e
In dichloromethane at 298 K. Excitation wavelength at ca. 420 nm. EtOH−MeOH (4:1, v/v). PMC: photomerocyanine form. Radiative rate
constant is calculated by k = Φ/τ, where Φ is the luminescence quantum yield and τ is the luminescence lifetime.
r
C
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Article
physical data for the ligand and the complexes are summarized
in Table 2.
tionary state (PSS). However, the open form is thermally
unstable and quickly undergoes bleaching reaction back to the
closed form. The kinetics for the bleaching reactions of the
merocyanine open forms of complexes 1−4, after excitation at
365 nm, have been investigated in tetrahydrofuran solution by
UV−vis absorption spectroscopy at various temperatures. By
monitoring the absorbance at 600 nm for complexes 1−4, the
kinetic properties for the thermal backward bleaching reactions
are measured and the activation parameters are determined
using the Eying and Arrhenius equations. The UV−vis spectral
changes of the open forms of complexes 1−4 with time, along
with the decay traces for the absorbance at 600 nm are shown
in Figures S5−S12, and Figure S13 shows the difference in
UV−vis spectra between the close form and open form in the
Supporting Information. The Eyring and Arrhenius plots have
also been constructed accordingly to obtain the thermody-
namic activation parameters (Table 3). The positive values for
Upon excitation at λ = 366 nm, the free bpy-SO ligand
exhibits two emission bands at 440 and 530 nm in CH Cl at
2
2
room temperature (Figure S2), attributed to the ligand-
1
2,13,17
centered π−π* excited state.
Excitation of complexes 1−
4
in dichloromethane at λ > 400 nm at room temperature
shows tunable luminescence properties (Figure 2). Intense
Table 3. Activation Parameters for the Bleaching Reaction
of the Complexes in Tetrahydrofuran Solution
⧧
⧧
⧧
ΔH
kJ mol−1)
ΔS
ΔG
298K
−1
(kJ mol−1)
Ea (kJ mol−1)
(
(J mol K−1
)
Figure 2. Normalized emission spectra of complexes 1−4 in degassed
1
2
3
4
79.1 ± 1.59
75.86 ± 1.09
84.21 ± 1.32
85.07 ± 1.73
19.86 ± 5.3
73.18 ± 3.17
72.47 ± 2.17
73.66 ± 2.63
73.80 ± 3.45
81.59 ± 1.58
78.35 ± 1.08
86.71 ± 1.31
87.56 ± 1.72
dichloromethane at room temperature.
11.36 ± 3.64
35.39 ± 4.39
37.81 ± 5.77
structureless emission has been observed, and the emission
energy maxima are between 530 and 640 nm, which are
∧
dependent on the electronic properties of the C N ligands.
These structureless emission bands are assigned to be
the activation enthalpies indicate that the bleaching reaction is
17,19
3
originated from the MLCT [dπ(Ir) → π*(diimine)] excited
a thermally activated process.
The activation entropy of
3
state, probably mixed with some LC character for complexes
the complexes are determined to be in the range from +11.36
−
1 −1
1
−4. The increasing electron-deficiency of the aryl moiety on
to +37.81 J mol K , which follow the same trend as their
∧
⧧
the C N ligands from 2 (−OMe) to 1 (−H), to 3 (−CHO),
corresponding ΔH values. With the increase in electron
∧
and to 4 (−CF ) would give a lower-lying dπ(Ir)/π(Ar)
deficiency of the C N ligands (−OMe < −H < −CHO <
3
HOMO energy, leading to a gradual hypsochromic shift of the
emission band, with emission energy in the order of 2 (640
nm) < 1 (625 nm) < 3 (600 nm) < 4 (530 nm), which is
−CF ), the rates of the bleaching reaction decrease (2 > 1 > 3
3
> 4) at the same temperature with the ascending value of their
⧧
⧧
ΔH and the free energy of activation ΔG
as well as the
2
98K
3
3
consistent with the MLCT/ LLCT(Ar → py) origin. This has
also been supported by the TD-DFT calculations.
activation energy E . This may be due to the electron-deficient
nature of the C N ligands, which can stabilize the merocyanine
a
∧
Complexes 1−4 also exhibit luminescence in EtOH−MeOH
form. Similar findings have also been reported on the
stabilization of 6-nitro-merocyanine (6-nitro-BIPS) against
thermal backward reaction to the spirooxazine form compared
(
4:1 v/v) glass from 489 to 608 nm at 77 K (Figure S3). The
3
emissions are also tentatively assigned as MLCT phosphor-
3
48,49
escence, probably mixed with some LC character for 1−4.
to the unsubstituted and more π-conjugated analogue,
Upon excitation at 365 nm, the free ligand and complexes 1−4
in dry-ice−acetone baths at 195 K can also be transformed
from the closed forms to the corresponding open forms with
reduced thermal bleaching reaction rates. The open forms of
complexes 1−4 and the free ligand show emission bands at
given the electron-deficient nature of the nitro-substituent
which can inductively stabilize the dipolar resonance forms of
merocyanine to increase the activation barrier for the thermal
4
8,49
backward reaction.
A careful investigation of the variation
⧧
⧧
between ΔH and ΔS in complexes 1−4 has been performed
and an isokinetic relationship has been observed (Figure 3).
This shows a common bleaching reaction mechanism for the
complexes. From the slope of the plot, an isokinetic
temperature of 344 K for the bleaching reaction is obtained.
Besides, it is interesting to note that with the attachment of
−CF substituents to aryl ring of the C N ligand, the MLCT
excited energy of the current spirooxazine-containing cyclo-
metalated iridium(III) system can be shifted to a higher energy
6
75−685 nm in EtOH−MeOH (4:1 v/v) glass at 77 K (Figure
S4). The emission profiles and energies of the open
merocyanine forms of the complexes and the free ligand are
∧
similar and insensitive to the change in the C N ligands.
3
Therefore, the emissions are assigned as LC phosphorescence
∧
3
of the merocyanine form of the spironaphthoxazine moi-
3
1
7,19,47
ety.
Bleaching Reaction Kinetics. Complexes 1−4 have been
found to display a drastic color change in degassed
tetrahydrofuran solution upon excitation at 365 nm, attributed
to the photochromic reaction. The mechanism of photo-
chromic reaction of the spirooxazine is suggested to go through
the photocleavage of the relatively weak spiro carbon−oxygen
bond, resulting in the formation of the photomerocyanine form
with an increased extent of π-conjugation at the photosta-
−
1
of about 225 kJ mol (530 nm), which is higher or
comparable to the triplet excited state energies of spirooxazines
−
1
17
(210−225 kJ mol ). Moderately intense MLCT absorption
in the range of 400−500 nm in the visible region have also
been observed in the current iridium(III) system. As a result,
by further modifying their structure and electronic properties,
it is possible to employ less destructive visible light to sensitize
D
DOI: 10.1021/acs.organomet.9b00359
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Article
∧
associated with the reduction of the C N ligands, as they are
57−63
commonly observed in related system.
Even though the
changes are small, the reduction potential can still be
∧
correlated to the electron-deficient nature of the C N ligands,
with 4 being most electron-deficient and having the least
negative reduction potential (−1.40 V). the others follow the
order 3 (−1.46 V) > 1 (−1.47 V) > 2 (−1.49 V), arising from
∧
the larger stabilization of the π*(C N) orbital with the most
∧
electron-deficient C N ligands. It is also noted that the trend
of the HOMO−LUMO energies determined from the
electrochemical studies is in accordance with their lumines-
cence energies, suggesting the rational design strategy in fine-
tuning the spectroscopic properties of the iridium(III)
complexes by variation of their electronic features. This may
provide the opportunity in coupling the spectroscopic
properties to their functional applications.
Figure 3. Plot of activation enthalpy against activation entropy for the
bleaching reactions of the open forms of complexes 1−4.
the photochromic ring-opening reaction via the MLCT excited
state. This further indicates the vital role in the structure−
property correlation of the cyclometalated iridium(III)
complexes and how this provides the tunability and functions
as a unique class of photochromic materials. Therefore, with
the appropriate molecular design strategy, it is possible to build
versatile molecular materials with switchable and desirable
functions.
Computational Study. To investigate the electronic
structures and the nature of the absorption and emission
origins of these iridium(III) complexes, density functional
theory (DFT) and time-dependent DFT (TDDFT) calcu-
lations have been performed on complexes 1−4. Given in
Figure S26 are the ground-state geometries of 1−4 optimized
in dichloromethane with the hybrid B3LYP functional using
Electrochemical Studies. The electrochemical properties
of the cyclometalated iridium(III) diimine complexes are
studied by cyclic voltammetry in acetonitrile (0.1 mol
64
the Coulomb-attenuating method (CAM-B3LYP), which
combines the hybrid qualities of B3LYP and the long-range
correction. In 1−4, the Ir−C bonds are ca. 2.0 Å while the Ir−
N bonds are ca. 2.1 Å, and the angles of the trans ligands at the
metal center are ca. 173°, indicating that complexes 1−4 have
similar structures. Moreover, the optimized structure of 2 is
consistent with the experimental X-ray crystal structure shown
in Figure 1, as their bond lengths and bond angles are close to
each other. The simulated absorption spectra of 1−4 are
shown in Figures S27−S30. The first 15 singlet−singlet
transitions of 1−4 computed by the TDDFT/CPCM
(CH Cl ) method are summarized in Table S2, and selected
−
3 n
dm Bu NPF ). The electrochemical data are summarized
4
6
in Table 4. Generally, complexes 1−4 show an irreversible
Table 4. Electrochemical Data for the Complexes in
a
Acetonitrile Solution
oxidation E [V] vs SCE
reduction E1/2 [V] vs SCE
pa
b
c
compound
(ΔE [mV])
(ΔE [mV])
p
p
1
2
3
4
[+1.11], +1.40 (80)
[+1.11], +1.31 (81)
[+1.11], +1.60 (70)
[+1.12], +1.87 (84)
−0.91 (89), −1.47 (69)
−0.92 (95), −1.49 (76)
−0.88 (87), −1.46 (65)
−0.88 (86), −1.40 (76)
2
2
a
Using 0.1 mol dm−3 nBu NPF at 298 K. Working electrode, glassy
carbon; scan rate, 100 mV s . ΔE = (E − E ). E = (Epa
E )/2; E and E are peak anodic and peak cathodic potentials,
molecular orbitals involved in the transitions are shown in
Figures S31−S34. It should be noted that the singlet−triplet
transitions have zero oscillator strengths as spin−orbit
coupling is neglected in the TDDFT calculations. For the
sake of the comparison of the low-energy singlet−triplet
transitions in the experimental and simulated absorption
spectra, the regions from 300 to 600 nm showing the
singlet−triplet transitions with arbitrary oscillator strengths
are included in the insets in Figures S27−S30. From Table S2
and Figures S31−S34, the S → S transitions of 1−4 have
4
6
−1
b
c
+
p
pa
pc
1/2
pc
pa
pc
respectively.
oxidation wave at ca. +1.11 V and a quasi-reversible oxidation
couple at potentials between ca. +1.31 and +1.87 V versus SCE
(
Figures S14−S17). The first irreversible oxidative wave is
assigned to the oxidation of the spirooxazine moiety, which is
0
1
analogous to that observed for the related [Re(CO) (bpy-
3
1
7
21
negligibly small oscillator strengths (0.001), so the S → S
0 2
SO)Cl] and platinum(II) bipyridine complexes. With
reference to the electrochemical studies on related classes of
transition is considered. For 1, 3, and 4, the S → S transitions
0
2
5
0−56
are attributed to the excitations from the dπ orbital of the
cyclometalated iridium(III) diimine complexes,
the
∧
metal center with mixing of the π orbital on the C N ligands to
second quasi-reversible oxidation couples are assigned to
∧
the π* orbital on the C N ligands. Therefore, their low-energy
metal-centered Ir(IV/III) oxidation process with significant
1
∧
absorption bands can be assigned as MLCT [dπ(Ir) →
contribution from the C N ligands. The potential for the
∧
π*(C N)] transition. For 2, the S → S transition is attributed
oxidation is found to be in the order 4 (+1.87 V) > 3 (+1.60
0
2
to the excitation from the dπ orbital of the metal center with
some mixing of the π orbital on the C N ligands to the π*
orbital on the two pyridine moieties of the diimine ligand. As a
V) > 1 (+1.40 V) > 2 (+1.31 V), in line with the electron-
∧
∧
deficient nature of the C N ligands: −CF > −CHO > −H >
3
∧
−
OMe. The electron-deficient C N ligand can stabilize the
dπ(Ir) orbital, rendering more positive potential required for
the oxidation process.
result, the low-energy absorption band of 2 can be assigned as
1
1
predominantly MLCT [dπ(Ir) → π*(diimine)]/ LLCT
∧
In contrast, complexes 1−4 exhibit the first quasi-reversible
reduction couples at ca. −0.88 to −0.92 V versus SCE, which is
tentatively assigned to reduction of the diimine ligands
[π(C N) → π*(diimine)] transition. Due to the large spin−
orbit coupling associated with the heavy Ir atom, it is possible
for the spin-forbidden singlet-to-triplet MLCT transition
computed at 430−480 nm to also have some contribution to
the low-energy absorption band.
(
Figures S14−S17). The second quasi-reversible reduction
couples at ca. −1.40 to −1.49 V versus SCE are tentatively
E
DOI: 10.1021/acs.organomet.9b00359
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Given in Figure 4a is the orbital energy level diagram, which
shows the energies of the frontier molecular orbitals of 1−4.
To further investigate the nature of the emissive states,
geometry optimizations on the lowest-lying triplet excited state
(
T ) of 1−4 have been performed with the unrestricted
1
formalism, namely, UCAM-B3LYP/CPCM (CH Cl ). Shown
2
2
in Figure 4b are the plots of spin density of the T states of 1−
1
4
. The spin density is mainly localized on the metal center and
∧
the C N ligands in all complexes and on the two pyridine
moieties of the diimine ligand in 1, 2, and 4, supporting the
3
∧
MLCT [dπ(Ir) → π*(C N or diimine)] character of the T
1
3
∧
states of 1−4, with some mixing of LLCT [π(C N) →
π*(diimine)] character in 1, 2, and 4. The emission
wavelengths of 1−4, which are approximated by the energy
difference between the S and T states at their corresponding
0
1
optimized geometries, are summarized in Table S3. The
emission wavelength shows a red shift in energy upon going
from 4 (472 nm) to 2 (479 nm), to 3 (484 nm), and to 1 (552
nm). In general, this trend is in fair agreement with that
observed in the experiment, except that the emission energy of
2
is overestimated, as observed in other theoretical studies in
which the CAM-B3LYP functional usually overestimates
transition energies.
65−67
CONCLUSION
■
A new class of spironaphthoxazine-containing cyclometalated
Ir(III) complexes has been designed, synthesized, and
characterized. Their photophysical, photochromic, and electro-
chemical properties have been studied. Readily tunable
luminescence colors and excited state properties can be
achieved by rational ligand design with respect to their
chemical intuition. It is interesting to note that the excited
energy state can be gradually tuned across the visible spectrum
3
with respect to the MLCT [dπ(Ir) → π*(diimine)] excited
∧
Figure 4. (a) Orbital energy level diagram of the frontier molecular
orbitals (H = HOMO and L = LUMO) and (b) plots of spin density
state by a simple modification of the substituent at the C N
ligand. The electrochemical data are also found to be in
accordance with their luminescence bandgap energies. The
nature of the absorption and emission origins of these
iridium(III) complexes have also been confirmed by DFT
and TDDFT calculations. More importantly, the photo-
chromic behavior can be easily and complementarily
(
isovalue = 0.002) of the T states of 1−4 optimized at the CAM-
1
B3LYP level.
Consistent with the results of the electrochemical studies, the
HOMOs of 1−4 are of similar energies, which range from
−
7.08 to −7.05 eV. For all complexes except 2, the HOMOs
∧
modulated by changing the substituents on the C N ligand
are the π orbitals localized on the indoline moiety of the
diimine ligand and, therefore, are less affected by the
without the need for tedious modification of the spirooxazine
framework. By analyzing the kinetic profiles of backward
bleaching reactions, more electron-deficient iridium(III)
complexes can stabilize the merocyanine open form with a
higher activation barrier. Additionally, by further optimizing
the molecular design, it is possible to employ less destructive
visible light to drive the photochromic ring-opening reaction
via the MLCT sensitization. This work may provide important
value and guiding principle, especially in the structure−
property correlation for the future developments of visible
light-driven photoswitches, which is less destructive for
potential applications of photoresponsive materials.
∧
substituents on the two C N ligands. For 2, the HOMO is
the dπ orbital on the metal center mixed with the π orbital on
∧
the C N ligands, which is degenerate with the HOMO−1,
where the π orbital is localized on the indoline moiety of the
diimine ligand. The LUMO of 2 (−1.74 eV) is less negative
than that of 1 (−1.78 eV), whereas those of 3 (−1.84 eV) and
4
(−1.91 eV) are more negative than that of 1. Since the
LUMOs of 1−4 are predominantly localized on the two
pyridine moieties of the diimine ligand, the LUMO would be
destabilized upon the introduction of the electron-donating
∧
−
OMe group to the C N ligands in 2 and stabilized upon the
introduction of the electron-deficient −CHO and −CF
3
∧
EXPERIMENTAL SECTION
groups to the C N ligands in 3 and 4. The above trends are
consistent with the results in the electrochemical studies, in
which the potentials of the irreversible oxidation wave of the
four complexes are more or less the same. In comparison to 1,
complexes 3 and 4 have less negative reduction potentials, and
■
Materials and Reagents. 4′-Methyl-2,2′-bipyridine-4-carboxylic
5
7
acid,
1,3,3-trimethyl-9′-hydroxy-spiroindolinenaphthoxazine
5
8
59
(
SO), 2-(2,4-bis-trifluoromethyl-phenyl)-pyridine, and 2-(2,4-
60
dimethoxy-phenyl)-pyridine were synthesized as described pre-
viously. 1,3,3-Trimethyls-piroindolinenaphth-oxazine-9′-yl4′-methyl-
2
has more negative reduction potential. As a result, 3 (5.23
2
,2′-bipyridyl-4-carboxylate (bpy-SO) was synthesized by modifica-
17
eV) and 4 (5.17 eV) have a narrower HOMO−LUMO energy
gap, while the energy gap of 2 (5.31 eV) is larger with respect
to 1 (5.29 eV).
tion of a reported procedure. Dichloromethane was distilled over
calcium hydride before use for synthesis. All other reagents were
analytical-grade and were used as received.
F
DOI: 10.1021/acs.organomet.9b00359
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Syntheses. [(ppy) Ir(μ-Cl)] (Di-μ-chlorotetrakis[2-(2-pyridinyl-
1H), 8.59 (d, J = 8.5 Hz, 2H), 8.40 (d, J = 19.2 Hz, 2H), 8.21 (d, J =
5.7 Hz, 1H), 8.12 (d, J = 5.4 Hz, 1H), 7.85 (d, J = 5.6 Hz, 1H), 7.81
(d, J = 8.8 Hz, 1H), 7.68 (dd, J = 18.3, 9.1 Hz, 4H), 7.54 (t, J = 5.1
Hz, 2H), 7.38 (d, J = 8.5 Hz, 1H), 7.30 (d, J = 5.6 Hz, 1H), 7.21 (d, J
= 7.5 Hz, 1H), 7.09 (d, J = 7.3 Hz, 1H), 7.02 (d, J = 8.8 Hz, 1H), 6.91
(dd, J = 14.2, 6.7 Hz, 3H), 6.58 (d, J = 7.7 Hz, 1H), 6.19 (s, 2H), 5.43
(dd, J = 16.5, 1.9 Hz, 2H), 3.96 (s, 6H), 3.53 (t, J = 14.2 Hz, 6H),
2
2
κN)phenyl-κC]di-iridium). IrCl ·xH O (263 mg, 0.88 mmol) and 2-
3
2
phenylpyridine (300 mg, 1.94 mmol) were dissolved in ethoxyethanol
15 mL) and water (5 mL). The mixture was refluxed under N for 24
(
2
h. After cooling down to room temperature, the system was filtered
and washed by ethanol. The product was isolated as a yellow solid.
1
Yield: 262 mg, 56%. H NMR (500 MHz, CDCl , 298 K, relative to
3
1
3
Me Si): δ = 9.27 (d, J = 6.5 Hz, 4H), 7.89 (d, J = 7.8 Hz, 4H), 7.76 (t,
2.76 (s, 3H), 2.64 (s, 3H), 1.35 (d, J = 2.7 Hz, 6H). C NMR (125
4
J = 7.2 Hz, 4H), 7.51 (d, J = 7.8 Hz, 4H), 6.82−6.74 (m, 8H), 6.58 (t,
MHz, CDCl , 298 K): δ = 166.72, 166.57, 162.26, 162.00, 161.89,
3
J = 7.2 Hz, 4H), 5.95 (d, J = 6.5 Hz, 4H).
160.20, 160.14, 157.15, 155.01, 154.90, 154.26, 152.24, 151.34,
150.94, 149.85, 149.46, 148.38, 148.32, 147.53, 144.85, 139.38,
137.85, 137.80, 135.81, 131.62, 130.11, 129.83, 129.58, 128.04,
127.71, 127.60, 126.10, 124.63, 124.52, 124.13, 123.43, 123.38,
122.97, 121.50, 121.39, 121.33, 119.92, 119.06, 116.95, 112.82,
108.36, 108.25, 107.16, 98.82, 93.18, 93.11, 55.12, 54.77, 51.88, 29.64,
25.43, 21.55, 20.77. MALDI-TOF MS: m/z = 1160.5867. Elemental
analyses calcd (%) for C H F IrN O P: C 55.17, H 4.01, N 6.43.
[
(dOMeppy) Ir(μ-Cl)] (Di-μ-chlorotetrakis[2-(2-pyridinyl-κN)-3,5-
2 2
bis(methoxyl)phenyl-κC]di-iridium). The procedure was similar to
that described for the synthesis of [(ppy) Ir(μ-Cl)] except 2-(2,4-
2
2
dimethoxy-phenyl)-pyridine (417 mg, 1.94 mmol) was used in place
1
of 2-phenylpyridine. Yield: 317 mg, 55%. H NMR (500 MHz,
CDCl , 298 K, relative to Me Si): δ = 9.22 (d, J = 5.2 Hz, 4H), 8.58
3
4
(
4
3
d, J = 9.8 Hz, 4H), 7.64 (dd, J = 9.8, 5.2 Hz, 4H), 6.63 (t, J = 5.2 Hz,
H), 5.94 (d, J = 2.2 Hz, 4H), 5.10 (d, J = 2.2 Hz, 4H), 3.86 (s, 12H),
.35 (s, 12H).
6
0
52
6
6
7
Found: C 55.58, H 4.27, N 6.09.
Complex 3. The procedure was similar to that described for the
synthesis of complex 1 except [(pba) Ir(μ-Cl)] (272 mg, 0.23 mmol)
[
(pba) Ir(μ-Cl)] (Di-μ-chlorotetrakis[5-formyl-2-(2-pyridinyl-κN)-
2 2
2
2
phenyl-κC]di-iridium). The procedure was similar to that described
for the synthesis of [(ppy) Ir(μ-Cl)] except 4-(2-pyridinyl)-
was used in place of [(ppy) Ir(μ-Cl)] and dichloromethane/ethyl
2 2
2
2
acetate (10:1 v/v) was used as eluent in the column chromatography.
1
benzaldehyde (355 mg, 1.94 mmol) was used in place of 2-
Yield: 262 mg, 46%. H NMR (500 MHz, CDCl , 298 K, relative to
3
1
phenylpyridine. Yield: 281 mg, 54%. H NMR (500 MHz, CDCl ,
Me Si): δ = 9.75 (d, J = 4.8 Hz, 2H), 9.18 (s, 1H), 8.48 (s, 1H), 8.37
3
4
2
8
4
98 K, relative to Me Si): δ = 9.52 (s, 4H), 9.27 (d, J = 5.8 Hz, 4H),
.05 (d, J = 8.1 Hz, 4H), 7.93 (t, J = 7.8 Hz, 4H), 7.67 (d, J = 8.1 Hz,
H), 7.30 (dd, J = 7.8, 1.4 Hz, 4H), 6.98 (t, J = 5.8 Hz, 4H), 6.36 (d, J
(s, 1H), 8.16−8.11 (m, 2H), 8.10−8.05 (m, 2H), 7.89 (ddd, J = 11.0,
10.0, 5.0 Hz, 4H), 7.78 (dd, J = 9.6, 4.6 Hz, 3H), 7.74 (d, J = 5.6 Hz,
1H), 7.71−7.65 (m, 2H), 7.58 (t, J = 7.3 Hz, 2H), 7.38−7.27 (m,
4H), 7.22 (t, J = 7.4 Hz, 1H), 7.09 (d, J = 7.1 Hz, 1H), 7.02 (d, J = 8.8
Hz, 1H), 6.90 (t, J = 7.5 Hz, 1H), 6.74 (d, J = 17.0 Hz, 2H), 6.58 (d, J
= 7.7 Hz, 1H), 2.75 (s, 3H), 2.64 (s, 3H), 1.35 (d, J = 2.9 Hz, 6H).
4
=
1.4 Hz, 4H).
[
(dCF ppy) Ir(μ-Cl)] (Di-μ-chlorotetrakis[2-(2-pyridinyl-κN)-3,5-
3 2 2
bis(trifluoromethyl)-phenyl-κC]di-iridium). The procedure was sim-
ilar to that described for the synthesis of [(ppy) Ir(μ-Cl)] except 2-
1
3
2
2
C NMR (125 MHz, CDCl , 298 K): δ = 192.60, 165.74, 165.51,
3
(
2,4-bis-trifluoromethyl-phenyl)-pyridine (566 mg, 1.94 mmol) was
1
1
61.99, 157.23, 154.38, 152.99, 151.29, 151.06, 149.74, 149.62,
49.56, 149.41, 149.23, 147.48, 144.91, 140.03, 139.14, 139.08,
1
used in place of 2-phenylpyridine. Yield: 400 mg, 56%. H NMR (500
MHz, CDCl , 298 K, relative to Me Si): δ = 9.24 (d, J = 5.2 Hz, 4H),
3
4
137.00, 136.92, 135.74, 132.85, 132.55, 131.61, 130.07, 129.80,
8
.47 (d, J = 8.2 Hz, 4H), 8.00 (t, J = 8.2 Hz, 4H), 7.49 (s, 4H), 7.04
1
1
1
29.73, 128.07, 127.99, 127.54, 126.62, 125.72, 125.61, 125.11,
25.02, 124.81, 124.71, 122.96, 121.50, 121.29, 121.21, 119.97,
18.97, 117.05, 112.85, 107.19, 98.83, 51.88, 31.60, 29.62, 25.41,
(
t, J = 6.5 Hz, 4H), 6.02 (s, 4H)
Complex 1. The complex was prepared by a modification of
III
61,62
literature method used for the related Ir diimine complexes.
(ppy) Ir(μ-Cl)] (246 mg, 0.23 mmol) and bpy-SO (270 mg, 0.5
22.67, 21.55, 20.76, 14.14. MALDI-TOF MS: m/z = 1096.6238.
[
Elemental analyses calcd (%) for C H F IrN O P: C 56.08, H 3.57,
2
2
58 44
6
6
5
mmol) were refluxed in degassed dichloromethane under nitrogen for
N 6.77. Found: C 56.36, H 3.68, N 6.53.
3
days. After cooling down to room temperature, KPF (418 mg, 2.3
Complex 4. The procedure was similar to that described for the
synthesis of complex 1 except [(dCF ppy) Ir(μ-Cl)] (371 mg, 0.23
6
mmol) was added, and the mixture was stirred for 2 h. After removal
of the solvent under reduced pressure, the residue was purified by
column chromatography with dichloromethane-ethyl acetate (60:1 v/
v) as eluent. Subsequent recrystallization of the product from
3
2
2
mmol) was used in place of [(ppy) Ir(μ-Cl)] . Yield: 268 mg, 40%.
2
2
1
H NMR (500 MHz, CDCl , 298 K, relative to Me Si): δ = 9.24 (s,
3
4
1
H), 8.54 (s, 1H), 8.49−8.44 (m, 2H), 8.37 (d, J = 2.2 Hz, 1H), 8.19
dichloromethane/hexane afforded the pure product. Yield: 354 mg,
(dd, J = 5.6, 1.4 Hz, 1H), 7.97 (dd, J = 10.0, 4.4 Hz, 3H), 7.91 (d, J =
1
6
5%. H NMR (500 MHz, CDCl , 298 K, relative to Me Si): δ = 9.13
5.8 Hz, 1H), 7.86 (d, J = 5.6 Hz, 1H), 7.75−7.68 (m, 4H), 7.65 (d, J
= 8.9 Hz, 1H), 7.59 (d, J = 4.6 Hz, 1H), 7.42 (t, J = 6.3 Hz, 1H),
7.38−7.35 (m, 1H), 7.34−7.28 (m, 2H), 7.22 (t, J = 7.6 Hz, 1H),
7.09 (d, J = 7.1 Hz, 1H), 7.02 (d, J = 8.9 Hz, 1H), 6.90 (t, J = 7.4 Hz,
1H), 6.58 (d, J = 7.7 Hz, 1H), 6.47 (d, J = 17.1 Hz, 2H), 2.76 (d, J =
3
4
(
=
s, 1H), 8.39 (d, J = 9.4 Hz, 2H), 8.18 (d, J = 5.6 Hz, 1H), 8.07 (dd, J
5.6, 1.2 Hz, 1H), 7.90 (d, J = 8.1 Hz, 2H), 7.80 (d, J = 5.6 Hz, 1H),
7.75 (dd, J = 15.0, 7.5 Hz, 2H), 7.69 (d, J = 8.9 Hz, 3H), 7.65 (d, J =
5.7 Hz, 1H), 7.57 (dd, J = 9.3, 5.2 Hz, 3H), 7.29 (dt, J = 8.8, 2.4 Hz,
1H), 7.22 (t, J = 7.7 Hz, 1H), 7.18 (s, 1H), 7.15 (t, J = 6.6 Hz, 1H),
7.10 (dd, J = 12.9, 6.8 Hz, 2H), 7.03 (td, J = 7.5, 2.4 Hz, 2H), 6.99 (d,
1
3
4.0 Hz, 3H), 2.64 (d, J = 1.6 Hz, 3H), 1.35 (d, J = 3.7 Hz, 6H).
C
NMR (125 MHz, CDCl , 298 K): δ = 163.06, 162.77, 161.80, 157.06,
3
J = 8.9 Hz, 1H), 6.91 (dt, J = 14.4, 7.1 Hz, 3H), 6.57 (d, J = 7.8 Hz,
H), 6.32 (dd, J = 22.6, 7.4 Hz, 2H), 2.73 (d, J = 3.9 Hz, 3H), 2.52
154.23, 153.68, 153.29, 153.09, 151.11, 151.01, 150.57, 150.50,
150.18, 149.36, 148.88, 147.50, 144.91, 144.45, 140.71, 139.39,
135.74, 131.59, 131.21, 130.97, 130.79, 129.97, 129.85, 129.57,
128.34, 128.20, 128.07, 127.96, 127.83, 127.52, 126.75, 126.46,
125.59, 124.50, 123.83, 122.95, 122.34, 121.65, 121.50, 119.97,
118.95, 117.09, 112.83, 107.18, 98.89, 98.82, 53.80, 51.92, 51.88,
29.71, 29.62, 29.28, 25.43, 25.39, 21.61, 20.75. MALDI-TOF MS: m/
z = 1312.3337. Elemental analyses calcd (%) for C H F IrN O P:
1
1
3
(
d, J = 1.6 Hz, 3H), 1.38−1.29 (m, 6H). C NMR (125 MHz,
CDCl , 298 K): δ = 167.54, 167.33, 162.20, 157.25, 154.42, 152.33,
3
1
1
1
1
1
1
2
51.35, 151.02, 150.99, 149.92, 149.79, 149.46, 149.08, 148.89,
47.50, 144.86, 143.61, 143.48, 139.48, 138.37, 138.32, 135.76,
31.86, 131.66, 131.61, 130.88, 130.76, 130.06, 129.68, 129.56,
28.06, 127.75, 127.52, 126.19, 124.79, 124.69, 124.29, 123.91,
23.78, 122.95, 122.82, 122.75, 121.49, 119.94, 119.64, 119.54,
19.07, 116.96, 112.84, 107.17, 98.84, 98.82, 51.89, 51.88, 29.62,
5.43, 21.50, 20.77. MALDI-TOF MS: m/z = 1040.9835. Elemental
6
0
40 18
6
3
C 49.42, H 2.76, N 5.76. Found: C 49.57, H 3.06, N 5.51.
1
Physical Measurements and Instrumentation. H NMR and
C{1H} NMR spectra were obtained on a Bruker DRX 500 (500
1
3
analyses calcd (%) for C H F IrN O P: C 56.70, H 3.74, N 7.09.
Found: C 56.93, H 3.89, N 6.91.
Complex 2. The procedure was similar to that described for the
MHz) spectrometer at 298 K with chemical shifts reported relative to
5
6
44
6
6
3
tetramethylsilane (Me Si). All MALDI-TOF mass spectra were
4
recorded on a Autoflex speed TOF/TOF mass spectra. Elemental
analysis was carried out on a Vario micro cube analyzer from
Elementar. The single-crystal structure was obtained on a R-AXIS
RAPID X-ray single crystal diffractometer.
synthesis of complex 1 except [(dOMeppy) Ir(μ-Cl)] (301 mg, 0.23
2
2
mmol) was used in place of [(ppy) Ir(μ-Cl)] . Yield: 324 mg, 54%.
2
2
1
H NMR (500 MHz, CDCl , 298 K, relative to Me Si): δ = 9.12 (s,
3
4
G
DOI: 10.1021/acs.organomet.9b00359
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
UV−vis absorption spectra were recorded using a Varian Cary 50
UV−vis spectrophotometer. Steady-state excitation and emission
spectra at room temperature and at 77 K were obtained on an
Edinburgh Instruments FS5 spectrofluorometer. Measurements of the
glass state in ethano/methanol (4:1 v/v) at 77 K were similarly
conducted with liquid nitrogen filled in the optical Dewar flask. All of
the solutions for the photophysical studies were degassed on a high-
vacuum line in a two-compartment cell consisting of a 10 mL Pyrex
bulb and a 1 cm path length quartz cuvette that was sealed from the
atmosphere by a Bibby Rotaflo HP6 Teflon stopper. The solutions
were rigorously degassed with at least four successive freeze−pump−
thaw cycles. Luminescence quantum yields were measured by the
optical dilute method and a degassed solution of [Ru(bpy) ]Cl in
dichloromethane by density functional theory (DFT) with the hybrid
B3LYP functional using the Coulomb-attenuating method (CAM-
6
4
B3LYP), in conjunction with the conductor-like polarizable
6
9,70
continuum model (CPCM).
To compute the singlet−singlet
71−73
transitions of the four complexes, TDDFT
calculations have
been performed on the optimized S geometries at the same level of
0
theory. To gain more insight into the emissive states, the geometries
of the lowest-lying triplet excited states (T ) were optimized with the
1
unrestricted formalism, namely, UCAM-B3LYP/CPCM (CH Cl ).
2
2
Vibrational frequencies of all the stationary points have been
computed to verify that each was a minimum (NIMAG = 0) on
the potential energy surface. The Cartesian coordinates of the
optimized S and T geometries of 1−4 are given in the Supporting
3
2
0
1
acetonitrile (φ = 0.062, excitation wavelength at 436 nm) was used as
the reference. Emission lifetime of solution samples were measured on
Edinburgh Instrument FLS 920 spectrometer. The excitation source is
Edinburgh Instrument picosecond-pulsed diode laser (Model EPL-
Information. For all calculations, the LanL2DZ basis set with effective
7
4−76
core potential (ECP)
was applied to describe Ir with f-type
77
polarization functions (ζ = 0.938), whereas the 6-31G(d,p) basis
78−80
set
was utilized to describe all other atoms. All the DFT and
4
05) with 405 nm output. The emission decay signals were captured
TDDFT calculations were performed with a pruned (99,590) grid for
numerical integration.
by a Hamamatsu R928 PMT which was connected to a board (Becker
and Hickel SPC-130) and analyzed using the exponential fit (tail-fit
data analysis) with the model I(t) = I exp(−t/τ), where I(t) and I
0
0
ASSOCIATED CONTENT
Supporting Information
■
stand for the luminescence intensities at times t and 0.
*
S
The thermal bleaching reaction of spirooxazines is known to follow
first-order kinetics at various temperatures. The kinetics for the
bleaching reaction were determined by measurement of the UV−vis
spectral changes at various temperatures by use of a Varian Cary 50
UV−vis spectrophotometer, with temperature controlled by a Lauda
RM6 compact low-temperature thermostat. The first-order rate
constants were obtained by taking the negative value of the slope of
a linear least-squares fit of ln[(A − A )/(A − A )] against time
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.9b00359.
UV−vis absorption spectra of complexes 1−4 in
dichloromethane at room temperature; normalized
emission spectra of close form and open form complexes
∞
0
∞
1
−4 in EtOH/MeOH (4:1 v/v) at 77 K; data of
according to eq 1:
bleaching reaction kinetics; NMR spectra of the
ln[(A − A )/(A − A )] = −kt
(1)
∞
0
∞
iridium(III) complexes; ground-state geometries of 1−
4
optimized in dichloromethane; simulated absorption
where A, A , and A∞ are the absorbances at the absorption wavelength
0
maximum of the photomerocyanine at times t, 0, and infinity,
respectively, and k is the rate constant of the reaction. The kinetics
parameters were obtained by a linear least-squares fitting of ln (k/T)
aginst 1/T according to the linear expression of the Eying equation
spectra of 1−4 with first 15 singlet−singlet transitions
computed by the TDDFT/CPCM (CH Cl ) method;
2
2
selected molecular orbitals involved in the transitions; a
text file of all computed molecule (PDF)
Cartesian coordinates in a format for convenient
visualization (XYZ)
(
eq 2), ln k against 1/T according to the Arrhenius equation (eq 3),
⧧
and the change in Gibbs free energy of activation (ΔG ) at 298 K
were determined according to eq 4:
⧧
−1
≠
Accession Codes
ln(k/T) = −(ΔH /R)(1/T) + ln(k h ) + (ΔS /R)
(2)
(3)
(4)
B
CCDC 1909997 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, or by emailing
data_request@ccdc.cam.ac.uk, or by contacting The Cam-
bridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
ln(k) = −E /RT + ln A
a
⧧
⧧
⧧
ΔG = ΔH − TΔS
⧧
⧧
where ΔH and ΔS are the changes in activation enthalpy and
entropy, respectively, T is the temperature, and k , R, h, and A are
B
Boltzmann’s constant, the universal gas constant and the Planck
constant, and the frequency factor, respectively.
AUTHOR INFORMATION
Corresponding Authors
E-mail: wwyam@hku.hk (V.W.-W.Y.).
*E-mail: wulx@jlu.edu.cn (L.W.).
■
Cyclic voltammetric measurements were performed by using a CH
Instruments, Inc. model CHI 660C electrochemical analyzer.
Electrochemical measurements were performed in acetonitrile
*
n
solution with 0.1 M Bu NPF as supporting electrolyte at room
4
6
temperature. The reference electrode was an Ag/AgNO (0.1 mol
ORCID
3
−
3
dm in acetonitrile) electrode, and the working electrode was a glassy
carbon electrode (CH Instruments, Inc.) with a platinum wire as the
counter electrode. The working electrode surface was first polished
with a 1 μm alumina slurry. It was then rinsed with ultrapure
deionized water and sonicated in a beaker containing ultrapure water
for 5 min. The polishing and sonication steps were repeated twice,
and the working electrode was finally rinsed under a stream of
ultrapure deionized water. The ferrocenium-ferrocene couple
Lixin Wu: 0000-0002-4735-8558
Vivian Wing-Wah Yam: 0000-0001-8349-4429
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
V.W.-W.Y. acknowledges support from The University of
Hong Kong under the URC Strategically Oriented Research
Theme (SORT) on Functional Materials for Molecular
Electronics and Jilin University. This work has been supported
by the State Key Laboratory of Supramolecular Structure and
Materials of Jilin University and the University Grants
/0
63
(
FeCp2+ ) was used as the internal reference. All solutions for
electrochemical studies were deaerated with prepurified argon gas
before measurement.
Computational Methodology. All calculations in this study
68
were performed with the Gaussian 09 program suite. The ground-
state (S ) geometries of complexes 1−4 were fully optimized in
0
H
DOI: 10.1021/acs.organomet.9b00359
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Committee Areas of Excellence Scheme (AoE/P-03/08) and a
General Research Fund (GRF) grant from the Research Grants
Council of Hong Kong Special Adminstrative Region, P.R.
China (HKU 17334216). The computations were performed
using research computing facilities offered by Information
Technology Services, The University of Hong Kong.
(19) Bao, Z.; Ng, K. Y.; Yam, V. W. W.; Ko, C. C.; Zhu, N.; Wu, L.
Syntheses, Characterization, and Photochromic Studies of Spiroox-
azine-Containing 2,2′-Bipyridine Ligands and Their Zinc(II) Thiolate
Complexes. Inorg. Chem. 2008, 47, 8912−8920.
(20) Ko, C. C.; Wing-Wah Yam, V. Transition Metal Complexes
with Photochromic Ligands Photosensitizationand Photoswitch-
able Properties. J. Mater. Chem. 2010, 20, 2063−2070.
(21) Li, Y.; Tam, A. Y. Y.; Wong, K. M. C.; Li, W.; Wu, L.; Yam, V.
REFERENCES
W. W. Synthesis, Characterization, and the Photochromic, Lumines-
cence, Metallogelation and Liquid-Crystalline Properties of Multi-
functional Platinum(II) Bipyridine Complexes. Chem. - Eur. J. 2011,
■
(
1) Berkovic, G.; Krongauz, V.; Weiss, V. Spiropyrans and
Spirooxazines for Memories and Switches. Chem. Rev. 2000, 100,
1
(
7, 8048−8059.
1
741−1753.
2) Kawata, S.; Kawata, Y. Three-Dimensional Optical Data Storage
Using Photochromic Materials. Chem. Rev. 2000, 100, 1777−1788.
3) Tian, H.; Yang, S. Recent Progresses on Diarylethene Based
Photochromic Switches. Chem. Soc. Rev. 2004, 33, 85−97.
4) Raymo, F. M.; Tomasulo, M. Electron and Energy Transfer
Modulation with Photochromic Switches. Chem. Soc. Rev. 2005, 34,
27−336.
5) Tian, H.; Wang, S. Photochromic Bisthienylethene as Multi-
Function Switches. Chem. Commun. 2007, 8, 781−792.
6) Jukes, R. T. F.; Bozic, B.; Belser, P.; De Cola, L.; Hartl, F.
22) Liu, Y.; Sun, X.; Wang, Y.; Wu, Z. Quantum Chemical
(
Characterization and Design of Homoleptic Ir(III) Complexes
Employing Triphenylamine-Featured Thiazole-Based Ligand for
Efficient Phosphors in OLEDs. Synth. Met. 2014, 198, 67−75.
(
(23) Liao, J.; Chi, Y.; Sie, Z. T.; Ku, C. H.; Chang, C. H.; Fox, M. A.;
(
Low, P. J.; Tseng, M. R.; Lee, G. H. Ir(III)-Based Phosphors with
Bipyrazolate Ancillaries; Rational Design, Photophysics, and Applica-
tions in Organic Light-Emitting Diodes. Inorg. Chem. 2015, 54,
10811−10821.
(24) Yang, X.; Feng, Z.; Zhao, J.; Dang, J.; Liu, B.; Zhang, K.; Zhou,
G. Pyrimidine-Based Mononuclear and Dinuclear Iridium(III)
Complexes for High Performance Organic Light-Emitting Diodes.
ACS Appl. Mater. Interfaces 2016, 8, 33874−33887.
(25) Chen, Z.; Wang, L.; Su, S.; Zheng, X.; Zhu, N.; Ho, C. L.;
Chen, S.; Wong, W. Y. Cyclometalated Iridium(III) Carbene
Phosphors for Highly Efficient Blue Organic Light-Emitting Diodes.
ACS Appl. Mater. Interfaces 2017, 9, 40497−40502.
3
(
(
Photophysical and Redox Properties of Dinuclear Ru and Os
Polypyridyl Complexes with Incorporated Photostable Spiropyran
Bridge. Inorg. Chem. 2009, 48, 1711−1721.
(
7) Poon, C. T.; Lam, W. H.; Wong, H. L.; Yam, V. W. W. A
Versatile Photochromic Dithienylethene-Containing A-Diketonate
Ligand: Near-Infrared Photochromic Behavior and Photoswitchable
Luminescence Properties upon Incorporation of a Boron(III) Center.
J. Am. Chem. Soc. 2010, 132, 13992−13993.
(26) Kumar, S.; Surati, K. R.; Lawrence, R.; Vamja, A. C.; Yakunin,
S.; Kovalenko, M. V.; Santos, E. J. G.; Shih, C. J. Design and Synthesis
of Heteroleptic Iridium(III) Phosphors for Efficient Organic Light-
Emitting Devices. Inorg. Chem. 2017, 56, 15304−15313.
(
8) Yoon, J.; de Silva, A. P. Sterically Hindered Diaryl Benzobis-
thiadiazole)s as Effective Photochromic Switches. Angew. Chem., Int.
Ed. 2015, 54, 9754−9756.
9) Nakashima, T.; Tsuchie, K.; Kanazawa, R.; Li, R.; Iijima, S.;
(
(
(27) Su, N.; Shen, C.; Zheng, Y. Efficient Electroluminescence of
Galangau, O.; Nakagawa, H.; Mutoh, K.; Kobayashi, Y.; Abe, J.;
Kawai, T. Self-Contained Photoacid Generator Triggered by Photo-
cyclization of Triangle Terarylene Backbone. J. Am. Chem. Soc. 2015,
Sky-Blue Iridium(III) Complexes for Organic Light-Emitting Diodes.
Dyes Pigm. 2018, 159, 100−106.
(28) Xia, J.; Liang, X.; Yan, Z.; Wu, Z.; Zhao, Y.; Zheng, Y.; Zhang,
1
37, 7023−7026.
10) Chu, N. Y. C. Photochromism of spiroindolinonaphthoxazine.
I. Photophysical Properties. Can. J. Chem. 1983, 61, 300−305.
11) Baillet, G.; Giusti, G.; Guglielmetti, R. Comparative Photo-
degradation Study between Spiro[indolineoxazine] and Spiro-
indolinepyran] Derivatives in Solution. J. Photochem. Photobiol., A
993, 70, 157−161.
12) Khairutdinov, R. F.; Giertz, K.; Hurst, J. K.; Voloshina, E. N.;
W. Iridium(III) Phosphors with Bis(Diphenylphorothioyl)-Amide
Ligand for Efficient Green and Sky-Blue OLEDs with EQE of Nearly
(
2
8%. J. Mater. Chem. C 2018, 6, 9010−9016.
29) Jang, J. H.; Park, H. J.; Park, J. Y.; Kim, H. U.; Hwang, D. H.
Orange Phosphorescent Ir(III) Complexes Consisting of Substituted
-Phenylbenzothiazole for Solution-Processed Organic Light-Emitting
Diodes. Org. Electron. 2018, 60, 31−37.
30) Nonoyama, M. Benzo[h]quinolin-10-yl-N Iridium(III) Com-
plexes. Bull. Chem. Soc. Jpn. 1974, 47, 767−768.
31) Lo, K. K. W.; Chung, C. K.; Lee, T. K. M.; Lui, L. H.; Tsang, K.
(
(
[
1
(
2
(
Voloshin, N. A.; Minkin, V. I. Photochromism of Spirooxazines in
Homogeneous Solution and Phospholipid Liposomes. J. Am. Chem.
Soc. 1998, 120, 12707−12713.
(
H. K.; Zhu, N. New Luminescent Cyclometalated Iridium(III)
Diimine Complexes as Biological Labeling Reagents. Inorg. Chem.
(
13) Yam, V. W. W.; Ko, C. C.; Wu, L.; Wong, K. M. C.; Cheung, K.
K. Syntheses, Crystal Structure, and Photochromic Properties of
Rhenium(I) Complexes Containing the Spironaphthoxazine Moiety.
Organometallics 2000, 19, 1820−1822.
2
(
003, 42, 6886−6897.
32) Lo, K. K. W.; Chung, C. K.; Zhu, N. Synthesis, Photophysical
and Electrochemical Properties, and Biological Labeling Studies of
Cyclometalated Iridium(III) Bis(pyridylbenzaldehyde) Complexes:
Novel Luminescent Cross-Linkers for Biomolecules. Chem. - Eur. J.
(
14) Bahr, J. L.; Kodis, G.; de la Garza, L.; Lin, S.; Moore, A. L.;
Moore, T. A.; Gust, D. Photoswitched Singlet Energy Transfer in a
Porphyrin-Spiropyran Dyad. J. Am. Chem. Soc. 2001, 123, 7124−7133.
2
(
003, 9, 475−483.
(
15) Querol, M.; Bozic, B.; Salluce, N.; Belser, P. Synthesis, Metal
33) Neve, F.; La Deda, M.; Crispini, A.; Bellusci, A.; Puntoriero, F.;
Complex Formation, And Switching Properties of Spiropyrans Linked
Campagna, S. Cationic Cyclometalated Iridium Luminophores:
Photophysical, Redox, and Structural Characterization. Organo-
metallics 2004, 23, 5856−5863.
to Chelating Sites. Polyhedron 2003, 22, 655−664.
(
16) Kopelman, R. A.; Snyder, S. M.; Frank, N. L. Tunable
Photochromism of Spirooxazines via Metal Coordination. J. Am.
(34) Smith, R. A.; Stokes, E. C.; Langdon-Jones, E. E.; Platts, J. A.;
Chem. Soc. 2003, 125, 13684−13685.
Kariuki, B. M.; Hallett, A. J.; Pope, S. J. A. Cyclometalated
Cinchophen Ligands on Iridium(III): Towards Water-Soluble
Complexes with Visible Luminescence. Dalton Trans 2013, 42,
10347−10357.
(35) Frey, J.; Curchod, B. F. E.; Scopelliti, R.; Tavernelli, I.;
Rothlisberger, U.; Nazeeruddin, M. K.; Baranoff, E. Structure−
Property Relationships Based on Hammett Constants in Cyclo-
metalated Iridium(III) Complexes: Their Application to the Design of
(
17) Ko, C. C.; Wu, L.; Wong, K. M. C.; Zhu, N.; Yam, V. W. W.
Synthesis, Characterization and Photochromic Studies of Spiroox-
azine Containing 2,2’-Bipyridine Ligands and Their Rhenium(I)
Tricarbonyl Complexes. Chem. - Eur. J. 2004, 10, 766−776.
(
18) Jukes, R. T. F.; Bozic, B.; Hartl, F.; Belser, P.; De Cola, L.
Synthesis, Photophysical, Photochemical, and Redox Properties of
Nitrospiropyrans Substituted with Ru or Os Tris(bipyridine)
Complexes. Inorg. Chem. 2006, 45, 8326−8341.
I
DOI: 10.1021/acs.organomet.9b00359
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
a Fluorine-Free Firpic-Like Emitter. Dalton Trans 2014, 43, 5667−
physical and Electrochemical Properties of Cyclometallated Iridium-
(III) Complexes with Phenylated Bipyridine Ligands. Eur. J. Inorg.
Chem. 2005, 2005, 110−117.
(53) Hanss, D.; Freys, J. C.; Bernardinelli, G.; Wenger, O. S.
Cyclometalated Iridium(III) Complexes as Photosensitizers for Long-
Range Electron Transfer: Occurrence of a Coulomb Barrier. Eur. J.
Inorg. Chem. 2009, 2009, 4850−4859.
(54) Chirdon, D. N.; McCusker, C. E.; Castellano, F. N.; Bernhard,
S. Tracking of Tuning Effects in Bis-Cyclometalated Iridium
Complexes: A Combined Time Resolved Infrared Spectroscopy,
Electrochemical, and Computational Study. Inorg. Chem. 2013, 52,
8795−8804.
(55) Lee, J.; Park, H.; Park, K. M.; Kim, J.; Lee, J. Y.; Kang, Y. Deep-
Blue Phosphorescent Iridium(III) Dyes Based on Fluorine function-
alized Bis(2,30-Bipyridyl) Ligand for Efficient Organic Light-Emitting
Diodes. Dyes Pigm. 2015, 123, 235−241.
(56) Pritchard, V. E.; Rota Martir, D.; Zysman-Colman, E.; Hardie,
M. J. Multimetallic and Mixed Environment Iridium(III) Complexes:
A Modular Approach to Luminescence Tuning Using a Host
Platform. Chem. - Eur. J. 2017, 23, 8839−8849.
(57) Ryan, D. M.; Coggins, M. K.; Concepcion, J. J.; Ashford, D. L.;
Fang, Z.; Alibabaei, L.; Ma, D.; Meyer, T. J.; Waters, M. L. Synthesis
and Electrocatalytic Water Oxidation by Electrode-Bound Helical
Peptide Chromophore-Catalyst Assemblies. Inorg. Chem. 2014, 53,
8120−8128.
(58) Kim, M. R.; Cheong, I. W. Stimuli-Triggered Formation of
Polymersomes from W/O/W Multiple Double Emulsion Droplets
Containing Poly(styrene)-block-poly (N-isopro-pylacrylamide-co-spi-
ronaphthoxazine methacryloyl). Langmuir 2016, 32, 9223−9228.
(59) Xu, Q. L.; Wang, C. C.; Li, T. Y.; Teng, M. Y.; Zhang, S.; Jing,
Y. M.; Yang, X.; Li, W. N.; Lin, C.; Zheng, Y. X.; Zuo, J. L.; You, X. Z.
Syntheses, Photoluminescence, and Electroluminescence of a Series of
Iridium Complexes with Trifluoromethyl-Substituted2-Phenylpyri-
dine as the Main Ligands and Tetraphenylimidodiphosphinate as
the Ancillary Ligand. Inorg. Chem. 2013, 52, 4916−4925.
(60) Astles, P. C.; Brealey, C.; Brown, T. J.; Facchini, V.;
Handscombe, C.; Harris, N. V.; McCarthy, C.; McLay, I. M.;
Porter, B.; Roach, A. G.; Sargent, C.; Smith, C.; Walsh, R. J. A.
Selective Endothelin A Receptor Antagonists. 3. Discovery and
Structure-Activity Relationships of a Series of 4-Phenoxybutanoic
Acid Derivatives. J. Med. Chem. 1998, 41, 2732−2744.
(61) Lu, F.; Nabeshima, T. A Highly Selective And Sensitive Turn-
On Chemodosimeter for Hypochlorous Acid Based on An Iridium-
(III) Complex and Its Application to Bioimaging. Dalton Trans 2014,
43, 9529−9536.
(62) Paul, A.; Das, N.; Halpin, Y.; Vos, J. G.; Pryce, M. T. Carboxy
Derivatised Ir(III) Complexes: Synthesis, Electrochemistry, Photo-
physical Properties snd Photocatalytic Hydrogen Generation. Dalton
Trans 2015, 44, 10423−10430.
(63) Connelly, N. G.; Geiger, W. E. Chemical Redox Agents for
Organometallic Chemistry. Chem. Rev. 1996, 96, 877−910.
(64) Yanai, T.; Tew, D. P.; Handy, N. C. A New Hybrid Exchange-
Correlation Functional Using the Coulomb-Attenuating Method
(CAM-B3LYP). Chem. Phys. Lett. 2004, 393, 51−57.
(65) Jacquemin, D.; Perpete, E. A.; Scalmani, G.; Frisch, M. J.;
Kobayashi, R.; Adamo, C. Assessment of the Efficiency of Long-Range
Corrected Functionals for Some Properties of Large Compounds. J.
Chem. Phys. 2007, 126, 144105.
(66) Nayyar, I. H.; Masunov, A. E.; Tretiak, S. Comparison of TD-
DFT Methods for the Calculation of Two-Photon Absorption Spectra
of Oligophenylvinylenes. J. Phys. Chem. C 2013, 117, 18170−18189.
(67) Caricato, M. Towards the Accurate Simulation of UV/Vis
Spectra in Solution: Combining the EOM-CCSD Method with
Polarizable Solvation Models within State-Specific and Linear-
Response Formalisms. Photochemistry 2014, 42, 197−214.
(68) 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.;
5
679.
(
36) Boeyens, J. C. A. The Conformation of Six-Membered Rings. J.
Cryst. Mol. Struct. 1978, 8, 317−320.
37) Millini, R.; Del Piero, G.; Allegrini, P.; Crisci, L.; Malatesta, V.
Structure of Photochromic Spiroxazines. I. 1,3,3-Trimethylspiro-
indoline-2,3′-[3H]-naphtho[2,1-b][1,4]oxazine]. Acta Crystallogr.,
Sect. C: Cryst. Struct. Commun. 1991, 47, 2567−2569.
38) Crano, J.; Knowles, D.; Kwiatkowski, P.; Flood, T.; Ross, R.;
(
[
(
Chiang, L.; Lasch, J.; Chadha, R.; Siuzdak, C. Structure of Three
Novel Photochromic Compounds; X-Ray Crystallographic and
Theoretical Studies. Acta Crystallogr., Sect. B: Struct. Sci. 1994, 50,
7
(
72−779.
39) Chamontin, K.; Lokshin, V.; Guglielmetti, R.; Samat, A.; Pepe,
G. 4-Methylspiro [4-azahomoadamantane-5, 3′-[3′H]naphth[2, 1-
b][1, 4]oxazine], a New Photochromic Spirooxazine. Acta Crystallogr.,
Sect. C: Cryst. Struct. Commun. 1998, 54, 670−672.
(
40) Favaro, G.; Masetti, F.; Mazzucato, U.; Ottavi, G.; Allegrini, P.;
Malatesta, V. Photochromism, Thermochromism and Solvatochrom-
ism of Some Spiro[Indolinoxazine]-Photomerocyanine Systems:
Effects of Structure and Solvent. J. Chem. Soc., Faraday Trans. 1994,
9
(
0, 333−338.
41) Ma, Y.; Liu, S.; Yang, H.; Wu, Y.; Yang, C.; Liu, X.; Zhao, Q.;
Wu, H.; Liang, J.; Li, F.; Huang, W. Water-Soluble Phosphorescent
Iridium(III) Complexes As Multicolor Probes for Imaging of
Homocysteine and Cysteine in Living Cells. J. Mater. Chem. 2011,
2
(
1, 18974−18982.
42) Woo, H.; Cho, S.; Han, Y.; Chae, W. S.; Ahn, D. R.; You, Y.;
Nam, W. Synthetic Control Over Photoinduced Electron Transfer in
Phosphorescence Zinc Sensors. J. Am. Chem. Soc. 2013, 135, 4771−
4
(
787.
43) Ru, J.; Guan, L.; Tang, X.; Dou, W.; Yao, X.; Chen, W.; Liu, Y.;
Zhang, G.; Liu, W.; Meng, Y.; Wang, C. Turn-on Phosphorescent
2
+
Chemodosimeter for Hg Based on a Cyclometalated Ir(III)
Complex and Its Application in Time-Resolved Luminescence Assays
and Live Cell Imaging. Inorg. Chem. 2014, 53, 11498−11506.
(
44) Skorka, Ł.; Filapek, M.; Zur, L.; Małecki, J. G.; Pisarski, W.;
Olejnik, M.; Danikiewicz, W.; Krompiec, S. Highly Phosphorescent
Cyclometalated Iridium(III) Complexes for Optoelectronic Applica-
tions: Fine Tuning of the Emission Wavelength through Ancillary
Ligands. J. Phys. Chem. C 2016, 120, 7284−7294.
(
45) Cho, W.; Sarada, G.; Maheshwaran, A.; Gal, Y.-S.; Nam, Y.;
Yong Lee, J.; Jin, S.-H. Solution-Processable Highly Efficient Deep-
Red and Orange Organic Light-Emitting Diodes Based on Multi-
Functional Ir(III) Complexes. J. Mater. Chem. C 2017, 5, 10029−
1
(
0038.
46) Liu, J.; Yuan, P. S.; Liang, A. H.; Ma, D. G. Synthesis of a Novel
Iridium Complex and Its Exhaustive Investigations of Photophysics,
Electrochemistry, Luminescent Mechanism and Electroluminescent
Performances. J. Lumin. 2018, 203, 83−89.
(
47) Hobley, J.; Wilkinson, F. Photochromism of Naphthoxazine-
Spiro-Indolinesby Direct Excitation and Following Sensitisation by
Triplet-Energy Donor. J. Chem. Soc., Faraday Trans. 1996, 92, 1323−
1
(
330.
48) Tian, Z.; Stairs, R. A.; Wyer, M.; Mosey, N.; Dust, J. M.; Kraft,
T. M.; Buncel, E. Spirooxazine to Merooxazine Interconversion in the
Presence and Absence of Zinc: Approach to a Bistable Photochemical
Switch. J. Phys. Chem. A 2010, 114, 11900−11909.
(
49) Stafforst, T.; Hilvert, D. Kinetic Characterization of Spiropyrans
in Aqueous Media. Chem. Commun. 2009, 287−288.
(
50) Lo, K. K. W.; Ng, D. C. M.; Chung, C. K. First Examples of
Luminescent CyclometalatedIridium(III) Complexes as Labeling
Reagents for Biological Substrates. Organometallics 2001, 20, 4999−
5
(
001.
51) Lo, K. K. W.; Chan, J. S. W.; Lui, L. H.; Chung, C. K. Novel
Luminescent Cyclometalated Iridium(III) Diimine Complexes That
Contain a Biotin Moiety. Organometallics 2004, 23, 3108−3116.
(
52) Lepeltier, M.; Kwok-Ming Lee, T.; Kam-Wing Lo, K.; Toupet,
L.; Le Bozec, H.; Guerchais, V. Synthesis, Structure, and Photo-
J
DOI: 10.1021/acs.organomet.9b00359
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.;
Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.;
Montgomery, J. A., Jr.; Peralta, J. E.; Ogliaro, F.; Bearpark, M.;
Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.; 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, 2009.
(
69) Barone, V.; Cossi, M. Quantum Calculation of Molecular
Energies and Energy Gradients in Solution by a Conductor Solvent
Model. J. Phys. Chem. A 1998, 102, 1995−2001.
(
70) Cossi, M.; Rega, N.; Scalmani, G.; Barone, V. Energies,
Structures, and Electronic Properties of Molecules in Solution with
the C-PCM Solvation Model. J. Comput. Chem. 2003, 24, 669−681.
(
71) 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, 8218−8224.
(
72) Bauernschmitt, R.; Ahlrichs, R. Treatment of Electronic
Excitations within the Adiabatic Approximation of Time Dependent
Density Functional Theory. Chem. Phys. Lett. 1996, 256, 454−464.
(
73) Casida, M. E.; Jamorski, C.; Casida, K. C.; Salahub, D. R.
Molecular Excitation Energies to High-Lying Bound States from
Timedependent Density-Functional Response Theory: Character-
ization and Correction of the Time-Dependent Local Density
Approximation Ionization Threshold. J. Chem. Phys. 1998, 108,
4
(
439−4449.
74) Hay, P. J.; Wadt, W. R. Ab Initio Effective Core Potentials for
Molecular Calculations. Potentials for K to Au Including the
Outermost Core Orbitals. J. Chem. Phys. 1985, 82, 270−283.
(
75) Wadt, W. R.; Hay, P. J. Ab Initio Effective Core Potentials for
Molecular Calculations. Potentials for Main Group Elements Na to Bi.
J. Chem. Phys. 1985, 82, 284−298.
(
76) Hay, P. J.; Wadt, W. R. Ab Initio Effective Core Potentials for
Molecular Calculations. Potentials for K to Au Including the
Outermost Core Orbitals. J. Chem. Phys. 1985, 82, 299−310.
(
77) Ehlers, A. W.; Bohme, M.; Dapprich, S.; Gobbi, A.; Hollwarth,
̈ ̈
A.; Jonas, V.; Kohler, K. F.; Stegmann, R.; Veldkamp, A.; Frenking, G.
̈
A Set of f-Polarization Functions for Psedo-Potential Basis Sets of the
Transition Metals Sc−Cu, Y−Ag and La−Au. Chem. Phys. Lett. 1993,
2
(
08, 111−114.
78) Hehre, W. J.; Ditchfield, R.; Pople, J. A. Self-Consistent
Molecular Orbital Methods. XII. Further Extensions of Gaussian-
Type Basis Sets for Sse in Molecular Orbital Studies of Organic
Molecules. J. Chem. Phys. 1972, 56, 2257−2261.
(
79) Hariharan, P. C.; Pople, J. A. The Influence of Polarization
Functions on Molecular Orbital Hydrogenation Energies. Theor.
Chim. Acta. 1973, 28, 213−222.
(
80) 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. XXIII. A Polarization-Type Basis Set for Second-
Row Elements. J. Chem. Phys. 1982, 77, 3654−3665.
K
DOI: 10.1021/acs.organomet.9b00359
Organometallics XXXX, XXX, XXX−XXX