Efficient electrochemiluminescent cyclometalated iridium(III) complexes: Synthesis, photophysical and electrochemiluminescent properties

Article abstract of DOI:10.1016/j.jorganchem.2011.03.015

A series of new cyclometalated iridium(III) complexes for electrochemiluminescence (ECL) system were synthesized and fully characterized. Using tri-n-propylamine (TPA) as an oxidative-reductive co-reactant, their ECL properties were studied in acetonitrile (CH₃CN) and mixed CH ₃CN/H₂O (50:50, v/v) solutions, respectively. Meanwhile, the influencing factors of ECL efficiencies, including working electrode, pH, and surfactant were investigated. A remarkable ECL enhancement (up to about 13.5 times), in comparison with the commonly used Ru(bpy)₃²⁺ (2,2′-bipyridyl) ruthenium(II), is observed from Ir(FPP)₂(acac) (where FPP is 2-(4-fluorophenyl)-4-phenylpyridine, acac = acetylacetone) at Pt disk electrode. At the same time, an increase in ECL efficiency is also observed in surfactant media. This study provided a new method for further improving and tuning the ECL efficiency by designing new iridium complexes with the appropriate cyclometalated or ancillary ligands.

Full text of DOI:10.1016/j.jorganchem.2011.03.015

Journal of Organometallic Chemistry 696 (2011) 2445e2450
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Efficient electrochemiluminescent cyclometalated iridium(III) complexes:
Synthesis, photophysical and electrochemiluminescent properties
*
Chunxiang Li, Juan Lin, Xiaoyan Yang, Jun Wan
State Key Laboratory Base of Eco-chemical Engineering, College of Chemistry and Molecular Engineering, Qingdao University of Science and Technology, Qingdao 266042, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of new cyclometalated iridium(III) complexes for electrochemiluminescence (ECL) system
were synthesized and fully characterized. Using tri-n-propylamine (TPA) as an oxidativeereductive co-
reactant, their ECL properties were studied in acetonitrile (CH3CN) and mixed CH3CN/H2O (50:50, v/v)
solutions, respectively. Meanwhile, the influencing factors of ECL efficiencies, including working
electrode, pH, and surfactant were investigated. A remarkable ECL enhancement (up to about 13.5
Received 23 November 2010
Received in revised form
2 March 2011
Accepted 8 March 2011
2þ
times), in comparison with the commonly used Ru(bpy)3 (2,20-bipyridyl) ruthenium(II), is observed
Keywords:
from Ir(FPP)2(acac) (where FPP is 2-(4-fluorophenyl)-4-phenylpyridine, acac ¼ acetylacetone) at Pt
disk electrode. At the same time, an increase in ECL efficiency is also observed in surfactant media. This
study provided a new method for further improving and tuning the ECL efficiency by designing new
iridium complexes with the appropriate cyclometalated or ancillary ligands.
Ó 2011 Elsevier B.V. All rights reserved.
Cyclometalated Ir complex
Electrochemiluminescence(ECL)
Synthesis
1. Introduction
Fem ¼ 0.1, and shows intense ECL via the annihilation reaction
[17e19]. These properties are due to efficient intersystem crossing
Electrogenerated chemiluminescence (ECL) has long been of
interest because it provides an important and powerful tool for
various applications owing to its simplicity, low cost and high
sensitivity. Among the various luminescent materials investigated
for ECL study, an important branch is metal complexes, and most of
the ECL studies on metal complexes have been focused on Ru(II)
complexes due to their relatively high emission quantum yield and
between the singlet and triplet exited states of the iridium(III)
[20]. The general formula of neutral heteroleptic complexes is [Ir
(C^N)2(X^X)] (X ¼ O, N), where the symbols C^N and X^X repre-
sent the cyclometalated and ancillary ligands, respectively. Both
the luminescent efficiency and emission wavelength of these
species can usually be tuned by the introduction of various
cyclometalated and ancillary ligands which can control the rela-
tive positions of HOMO and LUMO levels (oxidation potential and
reduction potential) [21]. Some recent reports also demonstrate
that iridium complexes really have interesting ECL properties, and
the possible mechanism has been proposed [22,23]. All these
prompted us to design a series of novel cyclometalated and
ancillary ligands to find new ECL reagents and to improve the
sensitivity of ECL sensors by replacing conventional the Ru
2þ
long excited-state lifetimes [1e4]. Though Ru(bpy)3 (2,20-bipyr-
idyl) ruthenium(II) and its derivatives have been studied as the
important ECL luminophores for decades [1,5e7], much effort has
been directed to develop new ECL luminophores to improve the
sensitivity.
Recently, the luminescent materials used for OLED (organic
light emitting devices) such as Al(III) [8], Pt(II) [9], Os(II) [10], Eu
(II) [11], and cyclometalated Ir(III) [12e17] complexes have been
studied as new ECL reagents. Among the various transition metal
complexes, researchers pay much more attention to the cyclo-
metalated iridium (III) complexes, which are promising materials
for ECL studies for their remarkable photoluminescent properties.
For example, (pq)2Ir(acac) (pq ¼ 2-phenylquinoline, acac ¼ acety-
lacetonate), has an excellent luminescence property with
2þ
(bpy)3 complex.
In this work, several neutral tris-chelate iridium(III) complexes, Ir
(FPP)2(acac), Ir(FBPI)2(acac), Ir(FBPI)2(pic), Ir(FBPI)2(pmp), and Ir
(MDX)2(acac) (FPP ¼ 2-(4-fluorophenyl)-4-phenylpyridine, FBPI ¼ 1-
(4-fluorobenzyl)-2-(4-fluorophenyl)-1H-benzo[d] imidazole, MDX ¼
2,5-dip-tolyl-1,3,4-oxadiazole, pic ¼ picolinic acid, pmp ¼ 2-((phe-
nylimino) methyl) phenol) (Fig. 1) were prepared and their investi-
gations of the structure, optical, and electrochemical properties are
reported. The effects of various factors on the ECL behavior, such as
pH, working electrode, the concentration of electrolyte, and surfac-
tant were also examined.
* Corresponding author. Tel./fax: þ86 532 84022750.
E-mail address: moze0802@yahoo.com.cn (J. Wan).
0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.03.015

2446
C. Li et al. / Journal of Organometallic Chemistry 696 (2011) 2445e2450
CH3
O
O
N
N
O
N
N
O
O
O
N
N
N
Ir
O
O
N
O
N
N
N
Ir
2
Ir
Ir
O
Ir
F
F
2
F
2
2
2
F
F
F
F
CH3
Ir(FPP)2(acac)
Ir(FBPI)2(pmp)
Ir(FBPI) 2(pic)
Ir(MDX)2(acac)
Ir(FBPI)2(acac)
Fig. 1. Structures of iridium complexes used in ECL study.
F
F
Cl
Cl
N
N
N
N
Ir
Ir
O
N
N
Hacac,Na 2CO3
2-ethoxyethanol, H2O
120°C, 24h
IrCl3. 3H2O
+
Ir
2-ethoxyethanol
120°C, 12h
N
N
O
F
F
2
2
F
F
2
F
F
Ir(FBPI)2(acac)
Scheme 1. Synthesis of the Ir(FBPI)2(acac) complex.
2. Results and discussion
characterized by 1H NMR, elemental analysis, IR and mass spec-
troscopy. High-purity samples of complexes for electrochemical
and luminescence investigations were obtained by crystallization.
Single crystals of complexes Ir(FPP)2(acac) and Ir(MDX)2(acac) were
grown from CH2Cl2 solution and characterized by X-ray
crystallography.
The crystallographic data are shown in Table 1, and the selected
bond lengths and angles are given in Tables 2 and 3, respectively.
The crystal structures are shown in Fig. 2. The complex, Ir
(FPP)2(acac), crystallizes in the monoclinic unit cell with space
group C2/c, while complex Ir(MDX)2(acac) in triclinic with Pe1. In
the two structures, iridium (III) adopts a distorted octahedral
geometry, with the C and N atoms belonging to cyclometalated
ligands in cis and trans configurations, respectively. The Ir
(FPP)2(acac) molecule lies in a two-fold axis crystallographically,
which accounts for an equivalent pattern in the proton NMR peaks
of the two chelated ligands. The IreC bond lengths (1.954e2.013 Å)
are within the interval observed for the corresponding distance in
iridium C^N chelates with similar geometry and ligand environ-
ments [24].
2.1. Synthesis and characterization of iridium complexes
Theiridium complexes are prepared by a conventional two-step
sequence as shown in Scheme 1, taking Ir(FBPI)2(acac) for example.
Heating the cyclometalated ligand with IrCl3$3H2O in solution
(ethoxyethanol: H2O ¼ 3:1 (V)) gives a dichloro-bridged ortho-
metalated dimers. Then, treatment of the dimers with an appro-
priate ancillary ligands and Na2CO3 in acetyl acetone solution gives
the corresponding cyclometalated iridium complexes with the
overall yield of about 28e38%. The obtained complexes were
Table 1
Crystal data and structure refinement for Ir(FPP)2(acac) and Ir(MDX)2(acac).
Complex
Ir(FPP)2(acac)
39H29N2O2F2Ir
787.84
monoclinic
C2/c
Ir(MDX)2(acac)
Empirical formula
Formula weight
Crystal system
Space group
Unit cell dimensions
a (Å)
C
C37H33N4O4Ir$CH2Cl2
874.82
triclinic
Pe1
20.445(7)
10.359(4)
15.171(5)
90
93.626(4)
90
3207(2)
4
1.632
10.299(3)
13.330(4)
14.184(4)
92.487(4)
108.287(3)
98.325(4)
1821.2(9)
2
1.595
868
3.857
0.22 ꢁ 0.24 ꢁ 0.28
2.1e26.0
7036 [R (int) ¼ 0.032]
7036/0/448
1.008
b (Å)
c (Å)
Table 2
Selected bond distance (Å) and angle (ꢂ) for Ir(FPP)2(acac).
a
b
g
(deg)
(deg)
(deg)
Bond distance (Å)
Ir(1)eC(1)
Ir(1)eN(1)
Ir(1)eO(1)
1.954(7)
2.062(4)
2.110(5)
N(1)eC(7)
N(1)eC(11)
1.330(8)
1.360(8)
Volume, Å3
Z
D
calc, g/cm3
Bond angle (ꢂ)
F(000)
1552
4.213
Abs coeff, mmꢀ1
Crystal Size, mm
O(1)eIr(1)eC(1)
O(1)eIr(1)eN(1A)
N(1)eIr(1)eC(1)
N(1)eIr(1)eN(1A)
O(1A)eIr(1)eC(1)
N(1A)eIr(1)eC(1)
O(1A)eIr(1)eN(1A)
N(1A)eIr(1)eC(1A)
91.4(2)
94.59(18)
80.0(2)
171.7(2)
174.5(2)
94.1(2)
O(1)eIr(1)eO(1A)
O(1)eIr(1)eC(1A)
O(1A)eIr(1)eN(1)
N(1)eIr(1)eC(1A)
N(1A)eIr(1)eC(1)
C(1)eIr(1)eC(1A)
O(1A)eIr(1)eC(1A)
Ir(1)eO(1)eC(19)
88.13(18)
174.5(2)
94.59(18)
94.1(2)
94.1(2)
89.6(3)
0.24 ꢁ 0.26 ꢁ 0.32
2.0e26.0
3131[R (int) ¼ 0.031]
3131/0/198
1.062
q
range
Independent reflections
Data/restraint/parameters
Goodness-of-fit on F2
91.39(18)
80.0(2)
91.4(2)
125.5(5)
R
0.0439
0.0580
0.1234
wR
0.0903

C. Li et al. / Journal of Organometallic Chemistry 696 (2011) 2445e2450
2447
Table 3
process are collected in Table 4. In the region of positive potential, all
of the complexes exhibit a single one-electron-transfer reversible
process. As an example, the CV curve of positive potential for Ir
(MDX)2(acac) is shown in Fig. 4, the observed oxidative wave
(E1/2 ¼ 0.71 V vs Fc/Fcþ) is assigned to Ir(MDX)2(acac)0/þ1. The redox
chemistry shows that the peak current ratio (ia/ic) and peak sepa-
Selected bond distance (Å) and angle (ꢂ) for Ir(MDX)2(acac).
Bond distance (Å)
Ir(1)eO(3)
Ir(1)eO(4)
Ir(1)eN(1)
Ir(1)eN(3)
2.127(5)
2.126(5)
2.029(7)
2.030(7)
Ir(1)eC(1)
Ir(1)eC(17)
N(1)eN(2)
N(3)eN(4)
2.013(7)
2.008(8)
1.392(10)
1.393(10)
ration (DEpp) is 0.90 and 0.08 V, respectively, indicating a reversible
Bond angle (ꢂ)
one-electron-transfer system. As previously reported [27e29], the
oxidation of this species can be mainly attributed to the metal center,
with a substantial contribution from the ligands, however, the
reduction process are mainly localized on the ligands, with only
a partial contribution from the metal center.
O(3)eIr(1)eO(4)
O(3)eIr(1)eN(1)
O(3)eIr(1)eN(3)
O(3)eIr(1)eC(17)
O(4)eIr(1)eN(3)
O(4)eIr(1)eC(1)
O(4)eIr(1)eC(17)
89.1(2)
98.8(2)
89.6(3)
87.0(3)
98.5(2)
92.1(3)
175.7(3)
N(1)eIr(1)eC(1)
N(1)eIr(1)eC(17)
N(3)eIr(1)eC(1)
N(3)eIr(1)eC(17)
C(1)eIr(1)eC(17)
N(1)eIr(1)eN(3)
Ir(1)eN(1)eN(2)
79.6(3)
93.8(3)
91.9(3)
79.8(3)
91.8(3)
169.2(3)
137.9(5)
2.4. Electrochemiluminescence
The ECL performances for the synthesized complexes were
studied with TPA as an “oxidativeereductive” co-reactant in
CH3CN. The ECL spectra of these complexes are obtained in CH3CN
and show some differences compared to the luminescence, being
slightly broader in shape (Figs. 3 and 5), with lmax approximately
shifted 10 nm, respectively, indicating that the ECL emission is due
to the MLCT transitions [13,17]. This difference is probably due to
the concentration variation and the lower resolution of the ECL
instrument. To learn more about the new ECL, various factors
influencing ECL such as the concentration of co-reactant and sup-
porting electrolyte, and working electrode were studied in CH3CN.
The results show that the optimum conditions for the system are:
working electrode is Pt disk electrode; the concentrations of TPA
and Bu4NPF6 are 0.025 and 0.05 M, respectively. Extremely high ECL
efficiencies are obtained with the iridium complexes as emitter
except Ir(FBPI)2(pmp). Under the same concentration of emitter, Ir
(FPP)2(acac) and Ir(MDX)2(acac) show 13.5 and 11.5 times, respec-
tively, compared to Ru(bpy)32þ/TPA system. According to the
references [17,22], it is believed that the complexes have suitable
oxidation potential. On one hand, it should be positive enough for
an efficient generation of TPAꢃþ (potential of TPA/TPAꢃ is 0.80 V vs
Ag/AgCl) [30]. On the other hand, they have relatively low oxidation
potential to be easily oxidized to Ir complex positive ions. And the
relative stability of metal complexes during the ECL measurements
can generate these high ECL efficiencies. The FECL of Ir(MDX)2(acac)
is more 40 times higher than that of Ir(ppy)3 (ppy ¼ 2-phenyl-
pyridine) reported by Richter [13]. Lee reported that (pq)2Ir(acac)
and (pq)2Ir(tmd) (pq ¼ 2-phenylquinoline anion, tmd ¼ 2,20,6,60-
tetramethylhepta-3,5-dione anion) gave very high ECL compared to
Ir(MDX)2(acac) (6 and 4 times for (pq)2Ir(acac) and (pq)2Ir(tmd),
respectively) [17]. Though synthesized Ir complexes in this paper
can not give the highest efficiency, the results can provide extensive
2.2. Absorption and fluorescent emission
The absorption spectra and phosphorescence emission spectra of
all complexes were recorded at room temperature in CH3CN solu-
tion and are reported in Fig. 3. The results are gathered in Table 4.
The UV region displays the ligand-centered (LC)
p / p
* transitions
as the most intense absorption bands, for each species. The shoul-
ders appearing in the range of 330e453 nm are likely due to charge-
transfer (CT) transitions, with their nature being both spin-allowed
1MLCT and spin-forbidden 3MLCT according to the previous reports
and the calculations of Hay [25]. On irradiation with appropriate
wavelengths, all of the iridium complexes show strong photo-
luminescence in CH3CN, while falling in green to red region. It is
attributed to the presence of an excited-state resulting from the
mixing of comparable percentages of 3LC and 3MLCT states, which is
in agreement with Bandini’s work concerning analogous iridium
complexes [26]. Strong spin-orbit coupling of central metal atoms
facilitates the spin-forbidden 3MLCT transitions of the metal
complexes. The photoluminescence efficiencies (Fem) for these
2þ
iridium complexes are substantially greater than Ru(bpy)3
(Fem w 0.042), ranging from 0.125, as in the case of Ir(MDX)2(acac),
to 0.268 for Ir(FBPI)2(pmp). This intense phosphorescence of
complexes is readily visible in the daylight using UV light.
2.3. Electrochemistry
The electrochemical properties of these complexes were
employed in CH3CN solution by cyclic voltammetry at room
temperature, in which the ieV response can provide information on
the kinetics of the electron-transfer reaction and thermodynamics of
the electrodeeelectrolyte interface. The potentials of oxidation
Fig. 2. ORTEP diagram of Ir(FPP)2(acac) and Ir(MDX)2(acac).

2448
C. Li et al. / Journal of Organometallic Chemistry 696 (2011) 2445e2450
12000
1.2
1.0
0.8
0.6
0.4
0.2
0.0
Ir(FPP) (acac)
2
Ir(FBPI)2(pic)
Ir(FPP)2(acac)
Ir(MDX)2(acac)
Ir(FBPI)2(pmp)
Ir(FBPI)2(acac)
B
Ir(FBPI) (acac)
A
2
10000
8000
6000
4000
2000
0
Ir(FBPI) (pic)
2
Ir(FBPI) (pmp)
2
Ir(MDX) (acac)
2
450 500 550 600 650 700
Wavelength (nm)
250 300 350 400 450 500
Wavelength (nm)
Fig. 3. Absorption and Photoluminescence spectra of 10 M Iridium complexes in CH3CN solution at 25 ꢂC; Excitation wavelengths are as followed: Ir(FPP)2(acac): 340 nm; Ir
(FBPI)2(acac): 320 nm; Ir(FBPI)2(pic): 325 nm; Ir(MDX)2(acac): 310 nm; Ir(FBPI)2(pmp): 330 nm.
information for future ECL studies. The low Efficiency of Ir
(FBPI)2(pmp), Ir(FBPI)2(pic) and Ir(FBPI)2(acac) is mainly contrib-
uted to the poor solubility.
3. Conclusions
A series of new air-stable cyclometalated iridium(III) complexes
were prepared and fully characterized by studying their crystallo-
graphic, luminescence, and electrochemical properties. The ECL
behavior of the synthesized Ir(III) complexes and specific influences
of ECL efficiency have been investigated. Extremely efficient ECLs,
some of which even approached 13.5ꢁ higher than that of Ru
(bpy)32þ, have been observed with TPA as a co-reactant at
reasonable voltage and pH levels. Additionally, ECL efficiency is
increased in the presence of surfactant. The synthesized Ir(III)
chelates emit over a range of wavelengths, from blue to green,
which allow designing efficient multicolor ECL systems to achieve
the analysis of multiple analytes in the same solution. The fact that
the electrochemical and ECL behavior of Ir(III) complexes are very
To use these types of compounds in immunoassays and DNA
analysis, the ECL performances in mixed CH3CN/H2O (50:50, v/v)
and aqueous (0.1 M KH2PO4) solutions were also studied, respec-
tively. Appreciable decrease of the ECL intensity in mixed solution
for these complexes can be observed (summarized in Table 4),
which may be due to the poor solubility and unstability of
complexes in presence of H2O, especially for Ir(FBPI)2(pic) and Ir
(FBPI)2(pmp). The surfactant Triton X-100 (poly-(ethylene glycol)
tert-octylphenyl ether) was adopted for Ir(FPP)2(acac) and Ir
(MDX)2(acac) system in order to regulate solubility of complexes
and improve ECL efficiency in mixed solution. Fig. 6 illustrates the
relationship between surfactant concentration and ECL intensity
for Ir(FPP)2(acac) and Ir(MDX)2(acac). The ECL intensity is increased
significantly in presence of surfactant, especially for Ir(MDX)2
(acac), which is reached up to approximately 8 times stronger than
that of no surfactant addition. It is believed that adsorption of
Triton X-100 renders the electrode more hydrophobic, facilitating
TPA and luminophore oxidation and leading to higher ECL inten-
sities, according to Richter’s point [14]. This provides a promising
method to obtain high efficiency in mixed solution.
2þ
similar to those of Ru(bpy)3 indicates that our highly efficient Ir
(III) complexes can be used in many interesting applications by
replacing conventional the Ru(bpy)32þ complex. It is expected that
the sensitivity of ECL sensors can be increased more than 10 times.
Further study about the application of the Ir (III) complexes in ECL
sensors is in progress.
The ECL emission is also pH dependent in 50:50 (v/v) CH3CN/
H2O solutions, and maximum intensities observed were pH w8 for
Ir(MDX)2(acac) and pH w9 (The pH of buffer solutions was adjusted
by 0.1 M KH2PO4, 0.1 M K2HPO4 and 6 M NaOH) for Ir(FPP)2(acac),
4. Experimental sections
4.1. Apparatus
2þ
respectively (Fig. 7). Similar trends are observed for Ru(bpy)3
1H NMR spectra were measured on Bruker ARX-300 (300 MHz)
spectrometer, using TMS as internal standard. Mass spectra (MS)
were measured on a VG-ZAB-HS spectrometer with electron
impact ionization. Elemental analysis was performed on a Per-
kineElmer 240C elemental analyzer. The UVeVis spectra were
recorded on VARIAN Cary 5000 spectrometer. Phosphorescence
spectra were recorded by PerkineElmer LS 50B luminescence
using TPA as a co-reactant. This is important for potential applica-
tions since the pH of environmental and biological systems is w7.4
and would require less sample preparation prior to analysis. It also
improves that both ruthenium- and iridium-based complexes can
be presented in the same sample solution for multi-analyst ECL
determination.
Table 4
Optical and electrochemical properties of iridium complexes.
45
30
15
0
Complex
PL
lmax/nm Fem E1/2 (ox) (V)b lmax/nmb Rel FECL
Electrochemistry (V vs Fc/Fcþ)
a
c
CH3CN CH3CN/H2O
(50:50)
Ir(FPP)2(acac) 535
0.23 0.35
545
500
490
510
520
13.5
2.5
2
0.05
11.5
1.51
Ir(FBPI)2(acac) 497, 529 0.15 0.28
Ir(FBPI)2(pic) 486, 514 0.16 0.46
Ir(FBPI)2(pmp) 470, 524 0.27 0.45
0.107
0.088
0.081
6.53
-15
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Potential (V) vs Fc/Fc+
Ir(MDX)2(acac) 518
0.13 0.67
a
2þ
Values obtained in thoroughly degassed CH3CN solution using Ru(bpy)3
(
Fem ¼ 0.042) as a standard.
Fig. 4. Cyclic voltammogram (record at Pt electrode with scan rate Vp ¼ 100 mV sꢀ1) of
0.1 mM Ir(MDX)2(acac) in CH3CN solutions containing 0.1 M Bu4NPF6 as supporting
electrolyte. Potential scale according to the internal Fc/Fcþ reference redox system.
b
Values obtained in CH3CN.
Relative ECL efficiency with respect to Ru(bpy)3
c
2þ
(
FECL ¼ 1).

C. Li et al. / Journal of Organometallic Chemistry 696 (2011) 2445e2450
2449
Ir(FPP) (acac)
2
14000
12000
10000
8000
6000
4000
2000
0
1800
1600
1400
1200
200
150
100
50
Ir(MDX) (acac)
2
a
b
0
1000
400 450 500 550 600
Wavelength(nm)
800
600
6
7
8
pH
9
10
c
d
e
Fig. 7. ECL intensity vs pH for 10 mM Ir(FPP)2(acac) and Ir(MDX)2(acac) (CH3CN/H2O
(50:50, v/v). Each point is the average of three scans.
400 450 500 550 600 650 700 750
Wavelength (nm)
Fig. 5. ECL spectra of iridium complexes of 10
supporting electrolyte, TPA as oxidativeereductive co-reactant.
m
M in CH3CN solution: Bu4NPF6 as
0.24 mmol) and Na2CO3 (86 mg, 0.8 mmol) were dissolved in
2-ethoxyethanol (8 mL) and the mixture was then stirred under N2 at
100 ꢂC for 16 h. After cooling to room temperature, the precipitate
was filtered and washed with water, ethanol and acetone. The crude
product was flash chromatographed on silica gel using CH2Cl2 as
eluent to afford the desired Ir(III) complex.
spectrophotometer. Cyclic Voltammetry (CV) and ECL measure-
ments were carried out by ECL analysis system for multi-detector
and Electrochemical Analyzer (Xi’anruimai Analytical Instruments
Co., Ltd.) at room temperature.
Ir(FPP)2(acac), Yield: 32%. 1H NMR (CDCl3, 300 MHz)
d: 8.50 (d,
J ¼ 6.0 Hz, 2H), 8.00 (s, 2H), 7.80 (d, J ¼ 6.9 Hz, 4H), 7.52e7.68 (m,
8H), 7.39 (d, J ¼ 6.0 Hz, 2H), 6.58 (t, J ¼ 8.8 Hz, 2H), 6.02 (d, J ¼ 9.8 Hz,
2H), 5.29 (s, 1H), 1.86 (s, 6H). MS-ESI m/z: 787.8 (Mþ). Elem anal.
Calcd. for C39H29F2N2O2Ir: C, 59.45; H, 3.71; N, 3.56. Found: C, 59.12;
H, 3.83; N, 3.42. IR (KBr, cmꢀ1): 3443 (m), 2360 (m), 1614 (m), 1579
(s), 1533 (m), 1409 (s), 1185 (m), 868 (w), 762 (m), 669 (w).
4.2. Materials and reagents
The cyclometalated ligands 2-(4-fluorophenyl)-4-phenylpyridine
(FPP), 1-(4-fluorobenzyl)-2-(4-fluorophenyl)-1H-benzo[d]imidazole
(FBPI) and 2,5-dip-tolyl-1, 3,4-oxadiazole (MDX) were made accord-
ing to the literature procedure [28,29]. IrCl3$3H2O Ru(bpy)3Cl2$6H2O
(98%), Tetra-n-butylammonium hexafluorophosphate (Bu4NPF6), tri-
n-propylamine (TPA) and Triton X-100 were purchased from Aldrich
and used without further purification. Potassium phosphate buffer
solutions were prepared with deionized water. Buffer Solutions
containing TPA were prepared similarly except that it was necessary
to stir vigorously to completely dissolve the amine. Other chemicals
and solvents were all of reagent grade for synthesis and used as
received.
Ir(FBPI)2(acac), Yield: 28%. 1H NMR (CDCl3, 300 MHz)
d: 7.72 (d,
J ¼ 7.6 Hz, 2H), 7.29e7.38 (m, 6H), 7.15 (s, 2H), 7.01e7.06 (m, 8H),
6.34e6.37 (m, 2H), 6.05(d, J ¼ 9.0 Hz, 2H), 5.68e5.86 (m, 4H), 5.31
(s, 1H), 1.85 (s, 6H). MS-ESI m/z: 929.7 (Mþ). Elem anal. Calcd. for
C45H33N4O2F4Ir: C, 58.12; H, 3.58; N, 6.02. Found: C, 58.15; H, 3.65;
N, 6.13. IR (KBr, cmꢀ1): 3440 (w), 3055 (w), 1585 (s), 1512 (s), 1498
(m), 1417(m), 1308 (m), 1257 (s), 1232 (s), 1068 (m), 847 (w), 820
(w), 757(m).
Ir(FBPI)2(pic), Yield: 38%. 1H NMR (CDCl3, 300 MHz)
d: 8.15 (d,
J ¼ 7.6 Hz, 2H), 7.73e7.87 (m, 6H), 7.26e7.33 (m, 2H), 7.12e7.20 (m,
8H), 6.72e6.75 (m, 2H), 6.14e6.16 (m, 4H), 5.50e5.75 (m, 4H). MS-
ESI m/z: 938.9 (Mþ). Elem anal. Calcd. for C46H30N4F4O2Ir: C, 58.84;
H, 3.22; N, 5.97. Found: C, 58.75; H, 3.15, N, 6.03. IR (KBr, cmꢀ1): 3448
(w), 3065 (w), 1659 (s), 1637 (m), 1599 (s), 1562 (m), 1510 (s), 1461
(m),1432 (m),1351 (m),1332 (m),1279 (m),1254 (m),1233 (m),1192
(m), 1164 (m), 1100 (w), 816 (m), 758 (m), 746 (m), 693 (w).
4.3. Synthesis of iridium(III) complexes
Iridium(III) complexes Ir(FPP)2(acac), Ir(FBPI)2(acac), Ir(FBPI)2
(pic), Ir(FBPI)2(pmp) and Ir(MDX)2(acac) were synthesized according
tothe literature procedure [31]. The mixture ofcyclometalated ligand
(FPP or FBPI, 2.2 mmol), IrCl3$3H2O (0.34 g, 1 mmol) in a mixed
solvent of 2-ethoxyethanol (10 mL) and water (3 mL) was stirred
under N2 at 120 ꢂC for 24 h. Cooled to room temperature, the
precipitate was collected by filtration and washed with water,
ethanol and acetone successively, and then dried in vacuum to give
a cyclometallated Ir(III)-chloro-bridged dimer. The dimer (0.12 g,
0.08 mmol), the desired ancillary ligand (acetylacetone, pmp or pic,
Ir(FBPI)2(pmp), Yield: 35%. 1H NMR (CDCl3, 300 MHz)
d: 8.07 (d,
J ¼ 7.9 Hz, 1H), 7.86 (d, J ¼ 7.6 Hz, 1H), 7.41e7.44 (m, 2H), 7.32e7.36
(m, 4H), 7.21e7.23 (m, 2H), 7.14e7.16 (m, 3H), 7.02e7.07(m, 7H),
6.87e6.89 (m, 3H), 6.23e6.38 (m, 5H), 6.00e6.07 (m, 2H), 5.99 (s,
2H), 5.53e5.64 (m, 4H). MS-ESI m/z: 1027.0 (Mþ). Elem anal. Calcd.
for C53H36N5F4OIr: C, 61.98; H, 3.53; N, 6.82. Found: C, 62.03; H,
3.55; N, 6.73. IR (KBr, cmꢀ1): 3447 (m), 2924 (w), 2344 (w), 16079
(s), 1561 (m), 1510 (m), 1463 (m), 1433 (m), 1354 (w), 1279 (w), 1254
(w), 1230 (w), 1190 (m), 1168 (w), 1125 (w), 825 (w), 697 (w).
6000
Ir(MDX)2(acac), Yield: 32%. 1H NMR (CDCl3, 300 MHz)
d: 8.15 (d,
Ir(MDX) (acac)
2
Ir(FPP) (acac)
2
J ¼ 8.2 Hz, 4H), 7.51 (d, J ¼ 7.6 Hz, 2H), 7.41 (d, J ¼ 8.2 Hz, 4H), 6.75 (d,
J ¼ 7.6 Hz, 2H), 6.54(s, 2H), 5.30(s,1H), 2.49 (s, 6H), 2.18 (s, 6H),1.92 (s,
6H). MS-ESI m/z: 789.8 (Mþ). Elem anal. Calcd for C37H33N4O4Ir: C,
56.25; H, 4.21; N, 7.09. Found: C, 56.13; H, 4.13; N, 7.18. IR (KBr, cmꢀ1):
3445 (m), 2918 (w), 1584 (s), 1514 (s), 1498 (m), 1449 (m), 1403 (m),
1256 (m), 1149 (w), 1040 (w), 985 (w), 821 (w), 749 (w), 722 (w).
4500
3000
1500
0
0.0 0.3 0.6 0.9 1.2
4.4. X-ray crystallography
Triton X-100 (mM)
Suitable crystals of Ir(FPP)2(acac) and Ir(MDX)2(acac) were
obtained by slow evaporation of isobutanol into an CH2Cl2 solution
Fig. 6. ECL intensity vs concentration of surfactant for 10
(MDX)2(acac) (CH3CN/H2O (50:50, v/v). Each point is the average of three scans.
mM Ir(FPP)2(acac) and Ir

2450
C. Li et al. / Journal of Organometallic Chemistry 696 (2011) 2445e2450
of iridium complexes at room temperature. Diffraction data for
compound Ir(FPP)2(acac) and Ir(MDX)2(acac) were collected at
T ¼ 298(2) K. The data set was collected on a Bruker SMART APEX
CCD diffractometer with graphite monochromated Mo Ka radia-
Acknowledgment
This work was financially supported by the Natural Science
Foundation of China (No. 21075073 and No. 20971076).
tion (
l
¼ 0.710 73 Å). The cell parameters for the iridium
complexes were obtained from a least-squares refinement of the
spots (from 60 collected frames) using the SMART program [32].
All of the calculations for the structure determination were carried
out using the SHELXTL package (version 5.1) [33]. Initial atomic
positions were located by Patterson methods using XS, and the
structure of Ir(FPP)2(acac) was refined by least-squares methods
using SHELXTL package (version 5.1) with 3131 independent
Appendix A. Supplementary data
CCDC 791530 and 791531 contain the supplementary crystal-
lographic data for this paper. These data can be obtained free of
charge from the Cambridge Crystallographic Data Centre via www.
ccdc.cam.ac.uk/data_request/cif.
reflections within the range of
q
¼ 2.0e26.0ꢂ. The data for Ir
References
(MDX)2(acac) were
q
¼ 2.1e26.0ꢂ. Absorption corrections were
applied by using SADABS [34]. Calculated hydrogen positions were
input and refined in a riding manner along with the attached
carbons.
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ECL efficiencies (Fecl) were obtained by the literature methods
2þ
[12,36], using Ru(bpy)3
(
Fecl ¼ 1) as the standard. Reported
values are the average of at least three scans with a relative stan-
dard deviation of ꢄ5% for CH3CN and CH3CN/H2O (50:50 v/v).