Effects of fluorine substituent on properties of cyclometalated iridium(III) complexes with a 2,2′-bipyridine ancillary ligand

Article abstract of DOI:10.1016/j.tet.2019.130686

Cationic cyclometalated Ir(III) complexes (Ir1-Ir5) with fluorine-substituted 2-phenylpyridine (ppy) derivatives as C^N cyclometalating ligands and 2,2′-bipyridine (bpy) as the ancillary ligand, have been synthesized and fully characterized. The influences of the number and the position of fluorine atoms at the cyclometalating ligands on the photophysical, electrochemical and oxygen sensing properties of the Ir(III) complexes have been investigated systematically. The introduction of fluorine on the C^N cyclometalating ligands of the complexes results in blue-shifts of the maximum emission wavelengths, and increases in the photoluminescence quantum yields (Φ_PL), phosphorescence lifetimes and energy gaps, compared to the non-fluorinated [Ir(ppy)₂(bpy)]⁺PF₆^? (Ir0). Among them, 2-(2,4-difluorophenyl)pyridine-derived Ir4 shows the maximum blue-shift (514 nm vs. 575 nm for Ir0) and the highest Φ_PL (50.8% vs. 6.5% for Ir0). The complex Ir3 with 2-(4-fluorophenyl)-5-fluoropyridine as C^N ligand exhibits the highest oxygen sensitivity and excellent operational stability in 10 cycles within 4000 s.

Full text of DOI:10.1016/j.tet.2019.130686

Journal Pre-proof
Effects of fluorine substituent on properties of cyclometalated iridium(III) complexes
with a 2,2′-bipyridine ancillary ligand
Yan Chen, Chun Liu, Lei Wang
PII:
S0040-4020(19)31061-0
https://doi.org/10.1016/j.tet.2019.130686
TET 130686
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 25 July 2019
Revised Date: 6 October 2019
Accepted Date: 12 October 2019
Please cite this article as: Chen Y, Liu C, Wang L, Effects of fluorine substituent on properties of
cyclometalated iridium(III) complexes with a 2,2′-bipyridine ancillary ligand, Tetrahedron (2019), doi:
https://doi.org/10.1016/j.tet.2019.130686.
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Effects of fluorine substituent on properties of cyclometalated iridium(III) complexes with a
2,2’-bipyridine ancillary ligand
Yan Chen, Chun Liu,* Lei Wang
State Key Laboratory of Fine Chemicals, Dalian University of Technology, Ling gong Road 2,
Dalian 116024, China. E-mail: cliu@dlut.edu.cn
1

Abstract:
Cationic cyclometalated Ir(III) complexes (Ir1-Ir5) with fluorine-substituted
2-phenylpyridine (ppy) derivatives as C^N cyclometalating ligands and 2,2’-bipyridine (bpy) as
the ancillary ligand, have been synthesized and fully characterized. The influences of the number
and the position of fluorine atoms at the cyclometalating ligands on the photophysical,
electrochemical and oxygen sensing properties of the Ir(III) complexes have been investigated
systematically. The introduction of fluorine on the C^N cyclometalating ligands of the complexes
results in blue-shifts of the maximum emission wavelengths, and increases in the
photoluminescence quantum yields (
Φ
PL), phosphorescence lifetimes and energy gaps, compared
-
to the non-fluorinated
[Ir(ppy)2(bpy)]+PF6
(Ir0).
Among
them,
2-(2,4-difluorophenyl)pyridine-derived Ir4 shows the maximum blue-shift (514 nm vs. 575 nm for
Ir0) and the highest ΦPL (50.8% vs. 6.5% for Ir0). The complex Ir3 with
2-(4-fluorophenyl)-5-fluoropyridine as C^N ligand exhibits the highest oxygen sensitivity and
excellent operational stability in 10 cycles within 4000 s.
Keywords: Fluorine, Ir(III) complex, Photophysical property, Electrochemical property, Oxygen
sensitivity.
2

1. Introduction
Fluorine is a special element with the strongest electronegativity and the atomic radius with
the size near to the hydrogen atom.[1] Its unique electronic structure allows fluorine atoms to
structurally modify the molecules by simply replacing the hydrogen atom, thereby effectively
adjusting the properties of compounds. Compared with pure organic compounds,[2-4]
phosphorescent heavy-metal complexes based on metal-to-ligand charge-transfer transition
(3MLCT) exhibit superior photophysical properties.[5-7] Among them, cyclometalated iridium(III)
complexes, due to relatively long lifetimes, high luminescent quantum yields, flexible tuning of
photophysical and electrochemical properties by ligands,[8, 9] have been often used as highly
efficient emitters in organic light-emitting diodes (OLEDs),[10-18] light-emitting electrochemical
23]
cells (LECs),[19-21] cell imaging,[22,
systems.[28-30]
water redox[24-27] and phosphorescent chemosensing
In 2008, He et al. synthesized an Ir(III) complex [Ir(dfppy)2(pzpy)]+PF6 (dfppy =
2-(2,4-difluorophenyl)pyridine, pzpy = 2-(1H-pyrazol-1-yl)pyridine), which demonstrated the
-
bluest light emission (460 nm) in the LEC at that time.[19] In the same year, [Ir(dfppy)2(bpy)]+PF6
-
was prepared by Yu et al. and used as a phosphorescent dye for staining the cytoplasm of living
cells.[22] In 2011, Wang et al. reported that introduction of fluorine substituent at the 6-position of
the benzothiazolyl moiety of the 2-phenylbenzothiazole ligand, the corresponding complex
(F-bt)2Ir(acac) exhibited excellent performances of OLEDs.[31] Very recently, Wang et al.
-
synthesized an Ir(III) complex [Ir(F2bpy)2(ppba)]+PF6 (ppba = 4-(6-(1H-pyrazol-1-yl)pyridin-3-yl)
3

benzaldehyde) by introducing fluorine atoms into the 2 and 6 positions of the bpy. This complex
was used as a photosensitizer for photocatalytic water-reduction, providing the hydrogen
generation yield up to 312 µmol in 5 h.[27] We have a long-standing interest in investigating the
structure-property relationship of cyclometalated complexes.[32-37] In 2015, we found that
introduction of fluorine into the cyclometalating ligands strongly improved the photostability of
the corresponding cyclometalated Pt(II) complexes.[38] Recently, we synthesized a fluorinated
Ir(III) complex Ir(DPAFppy)2(acac), which showed an obviously prolonged phosphorescent
lifetime and enhanced oxygen sensitivity than that of the non-fluorinated complex
Ir(DPAppy)2(acac).[36] Thus, the literature reports disclose that fluorine is an interesting and
unique substituent for the modification of functional molecules. Therefore, systematical
investigation on the effects of the position and the number of the fluorine atoms at the target
molecules is of great importance for the design of novel phosphorescent systems with high
performances.
In this work, five fluorinated cationic cyclometalated Ir(III) complexes (Ir1-Ir5) with
2,2’-bipyridine (bpy) as N^N ancillary ligand were synthesized (Scheme 1), which were used to
explore the effects of the position and the number of fluorine atoms on the photophysical and
electrochemical properties of the corresponding Ir(III) complexes, compared with a
non-fluorinated complex Ir0. In addition, the oxygen sensitivity and operational stability of the
Ir(III) complexes were studied.
2. Results and discussion
4

2.1 Synthesis and characterization of complexes
Chemical structures of the Ir(III) complexes are shown in Scheme 1 (the detailed synthetic
protocols are shown in Scheme S1, see Supporting Information). The cyclometalating ligands
L0-L5 were prepared via a palladium-catalyzed ligand-free and aerobic Suzuki-Miyaura reaction in
aqueous ethanol developed by our group,[39] chemical structures of L0-L5 are shown in Scheme S2.
Cyclometalated Ir(III) complexes were synthesized in three-steps from the IrCl3·3H2O with the
corresponding ligands to form the chloride-bridged dimers initially, followed by treatment with the
2,2’-bipyridine (bpy), and then an anion exchange reaction to obtain the target Ir(III) complexes.[34,
40]
Scheme 1 Chemical structures of the Ir(III) complexes for this study.
2.2 UV−Visible Absorption Spectra and Emission Spectra
UV-vis absorption spectra of L0-L5 and Ir0-Ir5 in CH2Cl2 at room temperature are presented
in Fig. 1 and the corresponding photophysical data are given in Table 1. All complexes exhibit
intense absorption with high molar extinction coefficients (ε = 2.92-6.23 × 104 M-1 cm-1). The
5

intense short wavelength absorption bands in the range of 200-325 nm are primarily due to the
spin-allowed intra-ligand (1π-π*) transitions. The weak absorption with lower extinction
coefficients absorption bands in the range of 350-450 nm can be assigned to mixing among
metal-to-ligand and ligand-to-ligand charge transfer (MLCT/LLCT) together with ligand-centered
(3π-π*) transitions.[41-42]
Fig. 1 UV-Vis absorption spectra of C^N cyclometalating ligands L0-L5 (a) and Ir(III)
complexes Ir0-Ir5 (b) (10-5 mol/L in CH2Cl2) at room temperature.
Fig. 2 Emission spectra of Ir0-Ir5 (10-5 mol/L in CH2Cl2) at room temperature.
6

The normalized emission spectra of Ir0-Ir5 in CH2Cl2 are shown in Fig. 2. These
fluorine-substituted cyclometalated Ir(III) complexes exhibit intense emission bands at 514-575
nm, and the photoluminescence quantum yields were 6.5%, 12.5%, 11.2%, 28.6%, 50.8%, 37.9%,
respectively. The results indicate that the introduction of fluorine atoms on the cyclometalating
ligands increases the
ΦPL of these complexes compared with Ir0. When only one fluorine atom is
introduced into the 4-position of the phenyl moiety (Ir1, ΦPL = 12.5%) or the 5-position of the
pyridyl ring (Ir2, ΦPL = 11.2%), the increase in ΦPL is nearly the same, while the ΦPL of the
complexes increases markedly with the increase of the number of fluorine atoms. Especially, the
2-(2,4-difluorophenyl)pyridine derived Ir4 (ΦPL = 50.8%) achieves the highest
ΦPL. The
introduction of fluorine atoms on the cyclometalating ligands also results in blue-shifts of the
ꢂꢃꢄ
maximum emission wavelengths ꢀ
of Ir(III) complexes. Moreover, the position of the
ꢁꢂ
fluorine atoms at the cyclometalating ligands affects the properties of the complexes to different
ꢂꢃꢄ
extents. For example, Ir1 with a fluorine atom at the 4-position of the phenyl ring (ꢀ
= 542
ꢁꢂ
ꢂꢃꢄ
nm) exhibits a larger blue-shift than that of Ir2 with 5-fluorinated pyridyl ring (ꢀ
= 567 nm).
ꢁꢂ
The normalized emission spectra of ethylcellulose (EC) films doped with Ir0-Ir5 (0.5 wt%) were
also measured (see Fig. S1). As shown in Table 1, the emission maxima of Ir0-Ir5 in EC films are
ranging from 485 to 525 nm. Compared with the emission spectra in solution, the emission spectra
in EC films of the complexes exhibit a blue-shift due to the rigidochromic effect.[43]
7

Table 1 Photophysical data of Ir0-Ir5.
λabsa (nm)
λemb (nm)
In CH2Cl2
τd (µs) krc (105 s-1) knrc (105 s-1)
Complex
c
Фsolution
256(4.58) 268(4.54)
575(CH2Cl2)
525(EC film)
Ir0
0.065
0.58
1.14
1.13
1.10
16.1
7.67
382(0.72
)
253(6.13) 268(6.23) 542(CH2Cl2)
Ir1
Ir2
0.125
0.112
369(1.01)
502(EC film)
567(CH2Cl2)
493(EC film)
515(EC film)
260(4.16) 270(4.25)
0.69
1.62
12.9
312(1.93)
534(CH2Cl2)
476(EC film)
503(EC film)
268(4.70) 308(2.23)
Ir3
Ir4
Ir5
0.286
0.508
0.379
1.23
1.29
1.01
2.32
3.94
3.75
5.81
3.81
6.15
370(0.59)
514(CH2Cl2)
462(EC film)
485(EC film)
250(4.52) 262(4.36)
301(2.47) 362(0.73)
524(CH2Cl2)
471(EC film)
497(EC film)
238(2.65) 262(2.92)
298(1.89) 363(0.41)
a Measured in CH2Cl2 at a concentration of 10-5 M and extinction coefficients (104 M-1cm-1) are shown in
parentheses, the absorption maxima are the values in bold style.
b The emission maxima are the values in bold style (λexc = 400 nm).
c The quantum yields (Фsolution) in deoxygenated CH2Cl2 were measured with [Ir(ppy)2(acac)] (ФPL = 0.34) as a
standard, radiative and nonradiative decay rates of kr and knr were calculated from kr = ФPL × τ-1, knr = τ-1 - kr.
d Excitation wavelength: 405 nm; monitor wavelength: the maximum emission wavelength of the corresponding
complex in CH2Cl2.
Fluorine substituent has a significant influence on phosphorescence lifetimes (Table 1). The
lifetimes (τ) of Ir(III) complexes in CH2Cl2 were measured to be 0.58-1.29 µs at room temperature
8

(the phosphorescence decay traces of Ir0-Ir5 illustrated in Fig. S3). The lifetimes increase in the
following order: Ir0 < Ir2 < Ir5 < Ir1 < Ir3 < Ir4. The results show that the substitution of
fluorine at the 4-position of the phenyl (Ir1, τ = 1.14 µs) prolongs the phosphorescence lifetime
obviously (Ir0, τ = 0.58 µs). Introducing a fluorine at the 5-position of the pyridyl or the
2-position of the phenyl of the cyclometalating ligands results in nearly the same phosphorescence
lifetimes for Ir3 (1.23 µs) and Ir4 (1.29 µs). The 2-(3,4,5-trifluorophenyl)pyridine-derived Ir5
also exhibits a prolonged lifetime (1.01 µs) compared to Ir0. However, introducing a fluorine
atom into the 5-position of pyridyl moiety of the C^N ligand gives only a little increased lifetime
for Ir2 (0.69 µs). The radiative decay rate (kr) and the nonradiative decay rate (knr) of the
complexes in CH2Cl2 were calculated (Table 1). Ir4 shows the longest lifetime (1.29 µs) and a
relatively higher radiative decay rate than other complexes, which is attributed to the
2-(2,4-difluorophenyl)pyridine ligand. These results are useful information for designing novel
Ir(III) complexes with a long lifetime.
2.3 Electrochemical properties
The electrochemical behaviors of these Ir(III) complexes were investigated in CH2Cl2, the
cyclic voltamograms of these Ir(III) complexes are provided in Fig. S4 and the corresponding data
are collected in Table 2. The onset oxidation potentials of Ir0-Ir5 are at 1.27 V, 1.54 V, 1.34 V,
1.68 V, 1.62 V and 1.79 V, respectively. It is found that the introduction of fluorine atoms into the
complexes can increase the onset oxidation potentials. Meanwhile, the onset oxidation potentials
of the complexes increase with the number of fluorine atoms. The position of the fluorine atoms at
9

the cyclometalating ligands affects the oxidation potentials of the corresponding complexes. It is
clear that Ir1 with a fluorine at the 4-position of the phenyl ring (1.54 V) exhibits a positive
potential than that of Ir2 with a fluorine at the 5-position of the pyridyl ring (1.34 V), indicating
the relative difficulty of oxidation.[44, 45] The HOMO-LUMO energy gaps are in the order of 2.74
eV (Ir4) > 2.70 eV (Ir5) > 2.68 eV (Ir3) > 2.56 eV (Ir1) > 2.47 eV (Ir2) > 2.45 eV (Ir0), which is
consistent with the results of emission spectra illustrated in Fig. 2. Specifically, Ir4 shows the
highest energy gaps, which is attributed to the addition of fluorine atoms at 2 and 4 positions of
the phenyl ring of the cyclometalating ligand.
Table 2 Electrochemical data of Ir0-Ir5.
a (V)
1.27
ꢅ
ꢌꢊꢍ
a (V)
EHOMOb (eV)
ELUMOc (eV)
Egd (eV)
ꢆꢈꢉꢊꢋ
ꢆꢈꢉꢊꢋ
Complex
ꢅ
ꢆꢇ
-1.18
-5.67
-5.94
-5.74
-3.23
-3.38
-3.28
2.45
2.56
2.47
Ir0
Ir1
Ir2
1.54
1.34
-1.02
-1.12
1.68
1.62
1.79
-1.00
-1.12
-0.92
-6.08
-6.02
-6.19
-3.40
-3.28
-3.48
2.68
2.74
2.70
Ir3
Ir4
Ir5
a 0.1 M [Bu4N]PF6 in CH2Cl2, scan rate 100 mV s−1, measured using a saturated calomel electrode (SCE) as the
standard.
b EHOMO (eV) = -e(4.4 + ꢅꢆꢆꢇꢈꢉꢊꢋ).
c ELUMO (eV) = -e(4.4 + ꢅꢌꢆꢊꢈꢍꢉꢊꢋ).
d
Eg = ELUMO - EHOMO. HOMO and LUMO denote the highest-occupied molecular orbital and the
lowest-unoccupied molecular orbital, respectively.
2.4 Oxygen sensitivity properties
10

The oxygen sensors using ethylcellulose (EC) as an efficient matrix have been reported.[46]
Herein the oxygen sensitivity of the Ir(III) complexes was also studied in EC films. The
relationship between emission intensity and the concentration of oxygen is reflected by a two-site
model to fit the curved Stern-Volmer plots (SVPs) in the heterogeneous oxygen sensing films,
which can be described as follows (Eq 1).[32, 34-36, 38, 47]
ꢎ
ꢐ
ꢑ
ꢑ
ꢚ
ꢒ
=
=
+
Eq 1
ꢎ
ꢏ
ꢐ
ꢏ
ꢓꢔꢕ
∙ꢘ
ꢙ
ꢓꢔꢕ
∙ꢘ
ꢖꢗꢚ ꢙ
ꢚ
ꢖꢗꢒ
ꢚ
In the equation, I0 and τ0 are the unquenched luminescent intensity and lifetime in an inert
atmosphere. I and τ are the corresponding quantities in the presence of oxygen. f1 and f2 are the
fractions of the total emission for each component (f1 + f2 = 1). KSV1 and KSV2 are the Stern-Volmer
constants for the two components. ꢛꢜ is the partial pressure of oxygen. The weighted quenching
ꢚ
ꢠꢘꢘ
ꢠꢘꢘ
constant
ꢝ
(
ꢝ
= ꢡ ∙ ꢝꢞꢟꢓ + ꢡ ∙ ꢝꢞꢟꢢ) is the guide of the sensitivity of an oxygen sensor, and
ꢓ ꢢ
ꢞꢟ
ꢞꢟ
ꢠꢘꢘ
a higher value of
ꢝ
indicates that the sensor is more sensitive to oxygen.
ꢞꢟ
The dynamic responses of oxygen sensing films were tested against small steps of O2 partial
pressure variation (Fig. 3 and Fig. S5). The Stern-Volmer plots for oxygen sensing films of these
Ir(III) complexes immobilized in EC are shown in Fig. 4. The fitting results of the O2 sensing data
of these Ir(III) complexes are summarized in Table S1.
11

Fig. 3 Variation of the emission intensity of Ir3 incorporated into EC with the oxygen concentration.
Fig. 4 Stern-Volmer plots of Ir0-Ir5 oxygen sensing films.
The I0/I100 ratio (I0 and I100 represent the detected phosphorescent intensities from a film
exposed to 100% N2 and 100% O2, respectively) can be used to evaluate the oxygen sensitivity. As
the results shown in Table S1, the I0/I100 values of the Ir(III) complexes immobilized in EC films
ꢠꢘꢘ
are 2.34 (Ir0), 2.56 (Ir1), 3.00 (Ir2), 3.26 (Ir3), 2.64 (Ir4) and 2.84 (Ir5), respectively. The
ꢝ
ꢞꢟ
12

values of these Ir(III) complexes immobilized in EC films are 0.00269 (Ir0), 0.00359 (Ir1),
0.00444 (Ir2), 0.00542 (Ir3), 0.00412 (Ir4), 0.00430 (Ir5) Torr-1. The Ir3 immobilized EC film
ꢠꢘꢘ
exhibits the highest sensitivity to O2 at a
ꢝ
value of 0.00542 Torr-1. These results indicate that
ꢞꢟ
introducing fluorine atoms into the Ir(III) complexes can improve oxygen sensitivity compared to
the non-fluorinated Ir0.
2.5 Operational stability and photostability of oxygen sensing films
Reversibility and stability are important factors to influence the overall performance of a
sensor. Therefore, the operational stability tests of oxygen sensing films were conducted. It is clear
that the emission intensity responses of Ir3 are fully reversible when the atmosphere varies
periodically between 100% N2 and 100% O2 in 4000 s (Fig. 5). The complete reversibility of the
luminescence emission of the oxygen-sensitive films allows stable and continuous monitoring the
concentration of oxygen. Additionally, fast response time (6.3 s for switching from N2 to O2) and
recovery time (8.2 s for switching from O2 to N2) were obtained. Thus, the oxygen sensing films
of these cationic Ir(III) complexes exhibit complete reversibility with short response times (see
Fig. S6).
13

Fig. 5 Reversibility and response time of Ir3 (0.5 wt%) immobilized in EC when cycling from 100% N2 to
100% O2 atmosphere.
3. Conclusions
In summary, six cationic cyclometalated Ir(III) complexes (Ir0-Ir5) were synthesized and
their photophysical, electrochemical and oxygen sensing properties were studied in detail. The
results indicate that the number and the position of the fluorine atoms at the cyclometalating
ligands significantly affect the properties of the Ir(III) complexes. The introduction of fluorine on
the cyclometalating ligands of the Ir(III) complexes makes the maximum emission wavelengths
blue-shifts and results in prolonged phosphorescence lifetimes and increases in photoluminescence
quantum yields and energy gaps as well. The 2-(2,4-difluorophenyl)pyridine derived Ir4 achieves
the maximum blue-shift (514 nm vs. 575 nm for Ir0) and the highest photoluminescence quantum
yield (50.8%). Furthermore, the fluorinated Ir(III) complexes immobilized ethylcellulose films
demonstrate excellent operational stability in oxygen sensing.
14

4. Experimental
4.1 Materials and instruments
All starting materials were commercially available and used without further purification. The
13
solvents were treated as required prior to use. 1H NMR and C NMR spectra were recorded on a
400 MHz Vaian DLG400 or a 500 MHz Bruker AVANCE Ⅲ. Mass spectra were recorded with a
MALDI micro MX spectrometer and a LTQ Orbitrap XL spectrometer. UV/Vis absorption spectra
were recorded on an HP8453 UV/Vis spectrophotometer. Emission spectra were recorded with a
HITACHI F-7000 fluorescence spectrophotometer. Photoluminescence quantum yields were
measured relative to [Ir(ppy)2(acac)] (ФP = 0.34 in CH2Cl2, under degassed conditions).
Phosphorescence lifetimes were measured on an Edinburgh FLS920 Spectrometer. Cyclic
voltammograms of the Ir(III) complexes were recorded on an electrochemical workstation
(BAS100B/W, USA) at room temperature in a 0.1 M [Bu4N]PF6 solution under argon conditions.
The phosphorescent intensity responses of sensing films of the Ir(III) complexes were recorded with
a F-7000 spectrofluorimeter.
4.2 Synthesis of cyclometalated Ir(III) complexes
Synthetic procedure of ligands L0-L5
A mixture of 2-bromopyridine derivatives (1 mmol), 1.5 equiv. of arylboronic acid, 2 equiv. of
K2CO3, Pd(OAc)2 (1.5 mol%), ethanol/water (3:1 v/v) was stirred at 80 °C in air for the indicated
time. The reaction mixture was added to brine (20 mL) and extracted with dichloromethane. The
solvent was concentrated under vacuum, and the product was isolated by column chromatography.
Synthetic procedure of Ir(III) complexes Ir0-Ir5
15

The IrCl3·3H2O (0.2 mmol) was reacted with 2.5 equiv. of cyclometalating ligand in a mixture
of 2-ethoxyethanol and water (9 mL/3 mL) at 120 °C under nitrogen for 24 h. Upon cooling to room
temperature, the suspension was concentrated under vacuum. The solid was completely dried to
give the crude cyclometalated Ir(III) chloride-bridged dimer. Without further purification, the
dimeric Ir(III) complex reacted subsequently with 3 equiv. of the 2,2’-bipyridine in 2-ethoxyethanol
at 120 °C under nitrogen for 24 h. After cooling to room temperature, a 10-fold excess of KPF6 was
added. The reaction mixture was added to water (15 mL) and extracted with dichloromethane. The
crude product was purified by column chromatography.
Ir2: an orange solid, yield 85%; 1H NMR (400 MHz, DMSO-d6) δ 8.87 (d, J = 8.1 Hz, 2H),
8.36 (dd, J = 9.2, 5.5 Hz, 2H), 8.27 (dd, J = 11.2, 4.6 Hz, 2H), 8.01 (td, J = 9.2, 2.6 Hz, 2H), 7.90
(d, J = 7.6 Hz, 2H), 7.83 (d, J = 4.7 Hz, 2H), 7.75 - 7.63 (m, 2H), 7.59 (t, J = 2.6 Hz, 2H), 7.04 (t,
J = 7.5 Hz, 2H), 6.93 (t, J = 7.4 Hz, 2H), 6.23 (d, J = 7.5 Hz, 2H). 13C NMR (101 MHz, DMSO-d6)
δ 164.17, 158.96, 156.47, 155.62, 149.90, 149.17, 142.83, 139.79, 137.40, 131.09, 128.68, 126.90,
125.26, 122.52, 121.32. HRMS (MALDI-TOF, m/z): calcd for C32H22N4F2Ir [M - PF6]+ 693.1442,
found 693.1425; calcd for C22H12F4N2Ir [M - PF6 - bpy]+ 537.0749, found 537.0938.
1
Ir3: a yellow solid, yield 68%; H NMR (500 MHz, DMSO-d6) δ 8.88 (d, J = 8.2 Hz, 2H),
8.37 (dd, J = 9.2, 5.4 Hz, 2H), 8.30 (t, J = 7.9 Hz, 2H), 8.04 (td, J = 8.7, 4.2 Hz, 4H), 7.86 (d, J =
5.3 Hz, 2H), 7.75 - 7.64 (m, 2H), 7.57 (t, J = 2.5 Hz, 2H), 6.91 (td, J = 8.9, 2.5 Hz, 2H), 5.85 (dd,
J = 9.3, 2.5 Hz, 2H). 13C NMR (126 MHz, DMSO-d6) δ 163.81, 162.89, 162.87, 161.81, 158.56,
156.56, 155.48, 152.14, 152.10, 150.14, 139.97, 139.41, 137.50, 137.25, 128.80, 127.63, 127.55,
16

127.27, 127.12, 125.29, 121.47, 121.42, 117.08, 116.94, 109.84, 109.65. HRMS (LTQ, m/z): calcd
for C32H20F4N4Ir [M - PF6]+ 729.1253, found 729.1235.
1
Ir5: a yellow solid, yield 80%; H NMR (500 MHz, DMSO-d6) δ 8.91 (d, J = 8.2 Hz, 2H),
8.40 - 8.26 (m, 4H), 8.16 (dd, J = 10.8, 6.4 Hz, 2H), 8.05 (d, J = 5.2 Hz, 2H), 7.96 (dd, J = 11.4,
4.3 Hz, 2H), 7.76 - 7.64 (m, 2H), 7.56 (d, J = 5.7 Hz, 2H), 7.13 (t, J = 6.7 Hz, 2H). 13C NMR (126
MHz, DMSO-d6) δ 165.25, 156.31, 155.26, 154.42, 150.42, 149.62, 148.39, 148.30, 146.48,
146.40, 140.94, 140.52, 140.28, 139.19, 138.53, 138.41, 138.25, 129.36, 125.40, 125.15, 124.20,
120.78, 110.31, 110.17. HRMS (LTQ, m/z): calcd for C32H18F6N4Ir [M - PF6]+ 765.1065, found
765.1046.
Acknowledgements
The authors thank the financial support from the National Natural Science Foundation
of China (21978042, 21421005, U1603103), and Talent Fund of Shandong Collaborative
Innovation Center of Eco-Chemical Engineering (XTCXYX02).
17

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Highlights
1) The position and number of fluorine atoms affect properties of cationic Ir(III)
complexes.
2) Fluorinated cationic Ir(III) complexes show increased photoluminescence quantum
yields.
3) Fluorinated cationic Ir(III) complexes demonstrate excellent oxygen sensing
stability.

Dear Editor,
There is no conflict of interest to declare for the manuscript “Effects of fluorine
substituent on properties of cyclometalated iridium(III) complexes with a
2,2’-bipyridine ancillary ligand”.
Sincerely,
Chun Liu