Syntheses, crystal structure, photophysical property and theoretical study of a new series of iridium complexes with N-(diphenylphosphoryl)benzamide derivatives as the ancillary ligands

Article abstract of DOI:10.1016/j.jorganchem.2014.01.014

Seven iridium complexes with the general structure of (tfmppy) ₂Ir(L1-L7) (tfmppy = 4-trifluoromethylphenylpyridine) were synthesized, where ancillary ligands L1-L7 are fluorine- or trifluoromethyl- substituted (-F or -CF₃) N-(diphen

Full text of DOI:10.1016/j.jorganchem.2014.01.014

Journal of Organometallic Chemistry 755 (2014) 110e119
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Syntheses, crystal structure, photophysical property and theoretical
study of a new series of iridium complexes with N-
(diphenylphosphoryl)benzamide derivatives as the ancillary ligands
Tian-Yi Li a, Xiao Liang a, Chen Wu a, Li-Sha Xue a, Qiu-Lei Xu a, Song Zhang a, Xuan Liu a,
,
b,
**
You-Xuan Zheng a , Xiu-Qiang Wang
*
a State Key Laboratory of Coordination Chemistry, Nanjing National Laboratory of Microstructures, School of Chemistry and Chemical Engineering, Center
for Molecular Organic Chemistry, Nanjing University, Nanjing 210093, PR China
b School of Life Science, Nanjing University, Nanjing 210093, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Seven iridium complexes with the general structure of (tfmppy)2Ir(L1eL7) (tfmppy ¼ 4-trifluoromethyl
phenylpyridine) were synthesized, where ancillary ligands L1eL7 are fluorine- or trifluoromethyl-
substituted (eF or eCF3) N-(diphenylphosphoryl)benzamide derivatives. Single crystal X-ray diffraction
study was undertaken on all complexes, which showed that each adopted the distorted octahedral co-
ordination geometry with the conventional trans-N, cis-C arrangement in the coordination sphere.
Electrochemical study confirmed the electron-withdrawing eF and eCF3 substituents on the ancillary
ligands have effects on the IrIII/IV redox couples and HOMO/LUMO energy levels. Density functional
Received 29 October 2013
Received in revised form
3 January 2014
Accepted 14 January 2014
Keywords:
Iridium(III) complex
N-(Diphenylphosphoryl)benzamide
Ancillary ligand
Photoluminescence
Computational calculation
theory (DFT) calculation results showed that the HOMOs are composed of Ir 5d orbital (about 55%) and
p
orbitals of the phenyl rings (about 38%) in tfmppy ligands, whilst the LUMOs are mostly localized on both
the phenyl and pyridine rings of tfmppy (about 90%). All the complexes own the similar emission peaks
around 520 nm with short phosphorescent decay time about 2 ms at ambient temperature and relatively
high internal quantum efficiencies from 37.5 to 61.2%. This work showed that the iridium complexes with
N-(diphenylphosphoryl)benzamide derivatives as the ancillary ligands possess the potential as phos-
phorence dopants in the organic light-emitting diodes (OLEDs).
Ó 2014 Elsevier B.V. All rights reserved.
1. Introduction
these iridium complexes and triplet harvest can be expected, which
is advantageous to the emission from the triplet excited states, and
The iridium complexes with heterocyclic ligands have found a
wide range of applications in the context of photoactive molecular
materials. The strong spin-orbit coupling (SOC) introduced by the
central heavy atom can promote the triplet to singlet radiative
transition, so that such complexes may exhibit unusually high
phosphorescence quantum yields at ambient temperature, as well
as relatively short triplet lifetimes. In addition, inter-system
crossing (ISC) from the first singlet excited state (S1) to the triplet
state (typically T1) also can be accelerated. Since S1 is depopulated
to obtain a relatively high quantum yield (100% theoretically). On
the other hand, since the phosphorescence of iridium complexes
primarily originates from the triplet metal-to-ligand charge-
transfers (3MLCT) and the ligand-centered (3LC) transitions states
[2], the energy level of the excited state can be controlled by tuning
the energy levels of the ligands through substituent effects, which
leads to a wide flexible emission color range. Thus, such iridium
complexes have been widely studied for photocatalysts [3],
photochemical solar energy conversion [4], biological labels [5]
and, in particular, phosphorescent dopants in the organic light-
emitting diodes (OLEDs) [6e9].
at a rate (1012
s
ꢀ1) much faster than that of phosphorescent radi-
ꢀ1) [1], fluorescence is depressed in
ative emission rate (108e109
s
In pursuit of highly emissive iridium complexes, many hetero-
leptic complexes with the structure of Ir(C^N)2(LX) have been
developed, where C^N is a monoanionic cyclometallated ligand (e.g.,
phenylpyridine (ppy), 4-trifluoromethylphenylpyridine (tfmppy))
and LX stands for an ancillary ligand (e.g., acetylacetonate (acac),
picolinate (pic)). With the help of the density functional theory
* Corresponding author. Tel.: þ86 25 83596775; fax: þ86 25 83314502.
** Corresponding author.
E-mail addresses: yxzheng@nju.edu.cn (Y.-X. Zheng), xqwang@nju.edu.cn
(X.-Q. Wang).
0022-328X/$ e see front matter Ó 2014 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2014.01.014

T.-Y. Li et al. / Journal of Organometallic Chemistry 755 (2014) 110e119
111
(DFT) and the time-dependent DFT (TD-DFT) calculations, an
insight of the photophysical property in such complexes reveals
that the highest occupied molecular orbital (HOMO) is usually
dominated by the central iridium atom, whereas the lowest un-
occupied molecular orbital (LUMO) is primarily localized on the
cyclometallated ligands. As a result, heteroleptic complexes own
the similar phosphorescence profile as that of the previously pop-
ular fac-triscyclometallated (fac ¼ facial) iridium complexes [2,10].
Although ancillary ligand does not make contribution to the lowest
excited state directly, it indeed alters the energy levels of the
excited states by modifying the electron density at the metal center.
Thus, the photophysical property and carrier mobility of iridium
complexes can be tuned through functional substitutes on both
cyclometallated and ancillary ligands.
According to this guideline, our group have proved that the
heteroleptic complex (tfmppy)2Ir(tpip) (tpip ¼ tetraphenylimido
diphosphinate) possesses valuable properties for electrolumines-
cent devices, such as high quantum yield, short lifetime and high
electron transition mobility, due to the newly developed ancillary
ligand tpip with greater polar P]O moieties [11e13]. In this paper,
on the basis of tetraphenylimidodiphosphinate, we altered one of
the P]O moiety to C]O moiety and synthesized a new series of N-
(diphenylphosphoryl)benzamide derivatives, L1eL7, as the ancil-
lary ligands and their corresponding iridium complexes, Ir1eIr7,
with 4-trifluoromethylphenylpyridine as the cyclometallated li-
gands. This paper presents the syntheses, crystal structures and
spectroscopic property of these iridium complexes, together with
detailed theoretical study.
The luminescence quantum efficiencies were calculated by a
comparison of the emission intensities (integrated areas) of a
standard sample fac-Ir(ppy)3 and the unknown samples in dea-
erated acetonitrile solutions of 5 ꢁ 10ꢀ5 mol Lꢀ1 according to the
Eq. [14e16]
ꢀ
ꢁꢀ
ꢁꢀ
ꢁ
2
Iunk
Istd
Astd
Aunk
hunk
hstd
Funk
¼
Fstd
where Funk and Fstd are the luminescence quantum yield values of
the unknown samples and fac-Ir(ppy)3 solutions (Fstd ¼ 40% [16]),
respectively. Iunk and Istd are the integrated emission intensities of
the unknown samples and fac-Ir(ppy)3 solutions, respectively. Aunk
and Astd are the absorbance values of the unknown samples and
fac-Ir(ppy)3 solutions at their excitation wavelengths, respectively.
hunk and hstd terms represent the refractive indices of the corre-
sponding acetonitrile (1.345, pure solvent was assumed).
2.2. Crystallography
Diffraction data for Ir1, Ir2, Ir3, Ir4, Ir5, Ir6 and Ir7 were
collected on a Siemens (Bruker) SMART CCD diffractometer using
ꢀ
monochromated Mo-K
a
radiation (
l
¼ 0.71073 A) at room tem-
perature. Cell parameters were retrieved using SMART software,
and SAINT [17] program was used to reduce the highly redundant
data sets. Lorentz and polarization effects were corrected. Ab-
sorption corrections were performed with SADABS [18] supplied by
Bruker. Data were collected using a narrow-frame method with
scan widths of 0.30 in
u .
and an exposure time of 4 s frameꢀ1
ꢂ
The molecular structures were solved by direct methods and
refined by full-matrix least squares on F2 using the program
SHELXL-97 [19]. The positions of the metal atoms and their conjoint
coordination atoms were located by the Patterson method directly
on E-maps; other non-H atoms were found in alternating difference
Fourier syntheses and least-squares refinement cycles. All non-H
atoms were treated anisotropically. H atoms were fixed in calcu-
lated positions and they were allowed to ride on their parent C
atoms and refined with a uniform value of Uiso. Where the struc-
tures are disordered, various geometrical (SADI) and displacement
(SIMU) restrictive parameters were employed to obtain more
reasonable structures.
2. Experimental section
2.1. General information
All reactions were performed under nitrogen atmosphere. Re-
actants were used without further purification as commercial
grade. Organic solvents for synthetic reactions were carefully dried
and distilled prior to use. 1H NMR (DMSO-d6) and 13C NMR (CDCl3)
spectra were run on a Bruker AM 500 and a Bruker AM 300 spec-
trometer, respectively. The chemical shifts (d) were given in ppm
based on internal TMS. The mass spectrometry (MS) spectra were
obtained on an electrospray ionization (ESI) mass spectrometer
(LCQ fleet, Thermo Fisher Scientific) for ligands. The high resolution
mass spectra measurements (HR EI-MS) were recorded on an
Agilent 6540 UHD Accurate-Mass Q-TOF LC/MS for all materials.
Melting points (M.p.) were determined on a Focus X-4 micro
melting point apparatus. Elemental analyses for C, H, and N were
performed on an Elementar Vario MICRO analyzer. Cyclic voltam-
mogram (CV) curves were recorded at room temperature under
2.3. Computational details
Full geometry optimizations of the complexes in the singlet
ground-state were carried out using density functional theory
(DFT) method [20]. The Beche’s LYP (B3LYP) [21e23] exchange-
correlation functional was employed, which had been proven to
be efficient for the geometry optimization of complexes with heavy
metals [24,25]. No symmetry constraint was applied during the
geometry optimizations. On the basis of the optimized molecular
structures, the absorption properties in CH2Cl2 were studied by
time-dependent DFT (TD-DFT) [26,27] method using both B3LYP
and M06-2x [28] exchange-correlation functional, and the solvent
effect of CH2Cl2 was taken into consideration with the appliance of
the conductor-like polarizable continuum model (C-PCM) [29]. To
cover the experimental range, the first 60 vertical excitations were
taken into consideration and only the spin-allowed singletesinglet
nitrogen protection in deaerated acetonitrile, using
a three-
electrode cell equipped with a Pt disk working electrode, a Pt
wire counter electrode, and a Agþ/Ag reference electrode on a
computer-controlled IM6ex electrochemical and chemilumines-
cent system (Zahner) using tetra-n-butylammomiumperchlorate
(0.1 M) as the supporting electrolyte with a potential scan rate of
50 mV sꢀ1 during the measurements. All potentials are calibrated
with Fcþ/Fc in acetonitrile as a reference. UVevis absorption
spectra were measured on a Shimadzu UV-3100 spectrophotom-
eter as CH2Cl2 solutions (5.0 ꢁ 10ꢀ6 M). Photoluminescence (PL)
spectra were obtained on a Hitachi F-4600 PL spectrometer as
deaerated CH2Cl2 solutions (5.0 ꢁ 10ꢀ5 M) at room temperature and
77 K, as well as for the neat solid powders. Neither emission nor
excitation spectra were corrected. Luminescence lifetime curves
were measured on an Edinburgh Instruments FLS920P fluorescence
spectrometer and the data were treated as one-order exponential
fitting using OriginPro 8 software.
transitions were calculated. Concerning the basis sets, a “double-x”
quality basis set LANL2DZ [30] was used for iridium atom and the 6-
31G(d,p) [31] basis set was employed for other non-metal atoms
through the process of all the calculations.
All the calculations were carried out with Gaussian 09 software
package [32]. GaussSum 2.2 program [33] was used for the stimu-
lations (simulated with Gaussian distribution with a Full Width at

112
T.-Y. Li et al. / Journal of Organometallic Chemistry 755 (2014) 110e119
Half-Maximum set FWHM ¼ 5000 cmꢀ1) and analyses of electronic
absorption spectra. QMForge program was used to give accurate
percentage data of frontier molecular orbitals.
J ¼ 7.6 Hz, 2H), 7.38 (t, J ¼ 8.0 Hz, 4H). MS (ESI) Calcd for [M ꢀ H]ꢀ:
m/z 356.3, found: m/z 356.2. HR EI-MS Calcd for [M þ Na]þ: m/z
380.0622, found: m/z 380.0622.
L3. 0.60 g Benzamide and 1.78 g chlorobis(4-(trifluoromethyl)
phenyl)phosphine gave 0.76 g L3 (1.66 mmol, 33.1%). M.p.: 159e
2.4. Syntheses
161 ꢂC. 1H NMR (500 MHz, DMSO-d6)
d
10.61 (d, J ¼ 9.4 Hz, 1H), 8.14
The syntheses routes of the tfmppy main ligand [11], seven
ancillary ligands of N-(diphenylphosphoryl)benzamide derivatives
L1eL7 [34], and the corresponding iridium complexes Ir1eIr7 are
shown in Scheme 1.
(dd, J ¼ 11.8, 8.3 Hz, 4H), 8.00 (d, J ¼ 7.7 Hz, 2H), 7.93 (d, J ¼ 7.1 Hz,
4H), 7.66 (t, J ¼ 7.3 Hz, 1H), 7.54 (t, J ¼ 7.6 Hz, 2H). MS (ESI) Calcd for
[M ꢀ H]ꢀ: m/z 456.3, found: m/z 456.3. HR EI-MS Calcd for
[M þ Na]þ: m/z 480.0559, found: m/z 480.0559.
L4. 0.88
g 3,4,5-Trifluorobenzamide and 1.10 g chlor-
2.4.1. General syntheses of L1eL7 ligands
odiphenylphosphine gave 0.89 g L4 (2.36 mmol, 47.3%) as white
Benzamide derivatives (5.00 mmol), DMAP (N,N-dimethylpyr-
idin-4-amine, 8.00 mmol) and chlorodiphenylphosphine de-
rivatives (5.00 mmol) were dissolved in anhydrous THF (20 mL) and
refluxed for 10 h. The mixtures were filtered to remove the white
byproducts and the rapid column chromatography (silica, petro-
leum ether:EtOAc ¼ 3:1) of the solutions gave the white interme-
diate products. Then, 0.5 mL 30% H2O2 was added into the
intermediate products THF solutions to give the target products as
white powders after stirring for 2 h at room temperature.
L1 [34]. 0.60 g Benzamide and 1.10 g chlorodiphenylphosphine
gave 0.75 g L1 (2.34 mmol, 46.8%). M.p.: 167e169 ꢂC. 1H NMR
powder. M.p.: 182e184 ꢂC. 1H NMR (500 MHz, DMSO-d6)
d
10.45 (s,
1H), 8.03e7.93 (m, 2H), 7.89 (dd, J ¼ 12.4, 7.6 Hz, 4H), 7.60 (t,
J ¼ 7.0 Hz, 2H), 7.58e7.50 (m, 4H). MS (ESI) Calcd for [M ꢀ H]ꢀ: m/z
374.3, found: m/z 374.2. HR EI-MS Calcd for [M þ Na]þ: m/z
398.0528, found: m/z 398.0528.
L5. 0.70
odiphenylphosphine gave 0.63 g L5 (1.85 mmol, 37.0%). M.p.: 189e
191 ꢂC. 1H NMR (500 MHz, DMSO-d6)
10.34 (s, 1H), 8.06 (s, 2H),
g
4-Fluorobenzamide and 1.10
g
chlor-
d
7.87 (s, 4H), 7.58 (d, J ¼ 4.7 Hz, 2H), 7.53 (s, 4H), 7.35 (s, 2H). MS (ESI)
Calcd for [M ꢀ H]ꢀ: m/z 338.3, found: m/z 338.2. HR EI-MS Calcd for
[M þ H]þ: m/z 340.0897, found: m/z 340.0898.
(500 MHz, DMSO-d6)
d
10.30 (d, J ¼ 8.9 Hz, 1H), 7.98 (d, J ¼ 7.7 Hz,
L6. 0.88 g 3,4,5-Trifluorobenzamide and 1.28 g chlorobis(4-
fluorophenyl)phosphine gave 0.44 g L6 (1.08 mmol, 21.5%). M.p.:
2H), 7.86 (dd, J ¼ 12.4, 7.8 Hz, 4H), 7.63 (d, J ¼ 7.5 Hz, 1H), 7.58 (d,
J ¼ 7.2 Hz, 2H), 7.54 (d, J ¼ 3.0 Hz, 2H), 7.53e7.50 (m, 4H). MS (ESI)
Calcd for [M ꢀ H]ꢀ: m/z 320.3, found: m/z 320.2. HR EI-MS Calcd for
[M þ H]þ: m/z 322.0991, found: m/z 322.0994.
176e179 ꢂC. 1H NMR (500 MHz, DMSO-d6)
d 10.49 (s,1H), 8.02e7.96
(m, 4H), 7.94 (s, 2H), 7.39 (t, J ¼ 8.1 Hz, 4H). MS (ESI) Calcd for
[M ꢀ H]ꢀ: m/z 410.3, found: m/z 410.2. HR EI-MS Calcd for
[M þ Na]þ: m/z 434.0340, found: m/z 434.0340.
L2. 0.60 g Benzamide and 1.28 g chlorobis(4-fluorophenyl)
phosphine gave 0.77 g L2 (2.17 mmol, 43.3%). M.p.: 182e184 ꢂC. 1H
L7. 0.70
g 4-Fluorobenzamide and 1.28 g chlorobis(4-
NMR (500 MHz, DMSO-d6)
J ¼ 7.7 Hz, 2H), 7.96e7.87 (m, 4H), 7.63 (t, J ¼ 7.3 Hz, 1H), 7.51 (t,
d
10.33 (d, J ¼ 8.9 Hz, 1H), 7.97 (d,
fluorophenyl)phosphine gave 0.36 g L7 (0.971 mmol, 19.4%). M.p.:
112e115 ꢂC. 1H NMR (500 MHz, DMSO-d6)
d
10.36 (d, J ¼ 8.7 Hz,1H),
Scheme 1. Synthetic routes of the ligands and complexes.

T.-Y. Li et al. / Journal of Organometallic Chemistry 755 (2014) 110e119
113
8.06 (dd, J ¼ 8.4, 5.6 Hz, 2H), 7.94 (dt, J ¼ 13.7, 7.2 Hz, 4H), 7.41 (d,
(tfmppy)2Ir(L4) (Ir4). 0.40 g [(tfmppy)2Ir(
m
-Cl)]2 and 0.24 g L4
J ¼ 12.5 Hz, 2H), 7.39e7.34 (m, 4H). MS (ESI) Calcd for [M ꢀ H]ꢀ: m/z
374.3, found: m/z 374.2. HR EI-MS Calcd for [M þ Na]þ: m/z
398.0528, found: m/z 398.0528.
gave 0.17 g Ir4 (0.17 mmol, 42.9%). 1H NMR (500 MHz, CDCl3)
d 9.19
(d, J ¼ 5.6 Hz, 1H), 8.28 (d, J ¼ 5.6 Hz, 1H), 7.92 (d, J ¼ 8.1 Hz, 1H),
7.90e7.83 (m, 3H), 7.79 (t, J ¼ 7.8 Hz, 1H), 7.70 (d, J ¼ 8.1 Hz, 1H),
7.66 (d, J ¼ 8.1 Hz,1H), 7.64e7.53 (m, 3H), 7.50e7.35 (m, 5H), 7.30 (d,
J ¼ 10.3 Hz, 2H), 7.22e7.16 (m, 1H), 7.15 (d, J ¼ 5.4 Hz, 1H), 7.13e7.10
(m, 2H), 6.60 (t, J ¼ 6.6 Hz, 1H), 6.50 (s, 1H), 6.26 (s, 1H). 13C NMR
2.4.2. General syntheses of iridium complexes Ir1eIr7
IrCl3$3H2O (1.76 g, 5.0 mmol) and tfmppy (2.45 g, 11.0 mmol) in
6.0 mL 2-ethoxyethanol and 3.0 mL distilled water were heated at
120 ꢂC for 12 h. After the solution was cooled, the addition of 30 mL
water gave a bright yellow precipitate which was filtered and
(75 MHz, CDCl3)
d 206.90, 174.53, 166.77, 149.72, 149.31, 145.33,
143.80, 137.48, 137.05, 131.04, 130.92, 130.85, 130.76, 130.64, 129.16,
128.36, 128.19, 128.11, 127.95, 127.64, 123.34, 123.24, 122.74, 122.32,
119.03, 118.68, 118.11. HR EI-MS Calcd for [M þ H]þ: m/z 1012.1321,
found: m/z 1012.1323. Anal. calcd for C43H26O2N3PF9Ir: C 51.09, N
4.16, H 2.59. Found: C 51.30, N 3.89, H 2.31.
washed with distilled water and ethanol, yielding 3.09
[(tfmppy)2Ir( -Cl)]2 (2.30 mmol, 92.0%). The -chloro-bridged
dimer complex was used for the subsequent reaction without
characterization and further purification. [(tfmppy)2Ir( -Cl)]2
(0.40 g, 0.30 mmol) and L1eL7 (0.65 mmol) in mL 2-
g
m
m
m
(tfmppy)2Ir(L5) (Ir5). 0.40 g [(tfmppy)2Ir(
m
-Cl)]2 and 0.22 g L5
5
gave 0.14 g Ir5 (0.15 mmol, 74.5%). 1H NMR (500 MHz, CDCl3)
d
9.23
ethoxyethanol were heated at 120 ꢂC. Potassium tert-butoxide
(0.07 g, 0.65 mmol) in 5.0 mL MeOH was injected into the mixtures
dropwise. After 12 h, the precipitates were filtered, washed with
ethanol and gave the products as bright yellow powders. The pure
complexes were obtained from recrystallization by using solvent
diffusion of MeOH into CH2Cl2 solutions.
(d, J ¼ 5.5 Hz, 1H), 8.34 (d, J ¼ 5.5 Hz, 1H), 7.99 (dd, J ¼ 8.0, 6.1 Hz,
2H), 7.91 (t, J ¼ 6.2 Hz, 2H), 7.89 (s, 1H), 7.85 (d, J ¼ 8.1 Hz, 1H), 7.76
(t, J ¼ 7.7 Hz, 1H), 7.69 (d, J ¼ 8.1 Hz, 1H), 7.65 (d, J ¼ 8.1 Hz, 1H), 7.55
(t, J ¼ 7.7 Hz, 1H), 7.45 (s, 1H), 7.42 (dd, J ¼ 10.9, 7.2 Hz, 4H), 7.27 (d,
J ¼ 7.4 Hz, 1H), 7.16 (t, J ¼ 8.3 Hz, 2H), 7.14e7.09 (m, 2H), 7.08 (d,
J ¼ 5.0 Hz, 1H), 6.96 (t, J ¼ 8.6 Hz, 2H), 6.58 (t, J ¼ 6.5 Hz, 1H), 6.51 (s,
(tfmppy)2Ir(L1) (Ir1). 0.40 g [(tfmppy)2Ir(
(0.65 mmol) gave 0.37 g Ir1 (0.38 mmol, 63.8%). 1H NMR
(500 MHz, CDCl3)
m
-Cl)]2 and 0.21 g L1
1H), 6.29 (s, 1H). 13C NMR (75 MHz, CDCl3)
d 206.90, 174.53, 166.77,
149.72, 149.31, 145.33, 143.80, 137.48, 137.05, 131.04, 130.92, 130.85,
130.76, 130.64, 129.16, 128.36, 128.19, 128.11, 127.95, 127.64, 123.34,
123.24, 122.74, 122.32, 119.03, 118.68, 118.11. HR EI-MS Calcd for
[M þ H]þ: m/z 976.1509, found: m/z 976.1509. Anal. calcd for
d
8.37 (d, J ¼ 5.6 Hz, 1H), 8.00 (d, J ¼ 7.5 Hz, 2H),
7.93 (d, J ¼ 7.7 Hz, 1H), 7.90 (d, J ¼ 8.1 Hz, 2H), 7.85 (d, J ¼ 8.1 Hz,
1H), 7.75 (t, J ¼ 7.4 Hz, 1H), 7.69 (d, J ¼ 8.1 Hz, 1H), 7.65 (d,
J ¼ 8.1 Hz, 1H), 7.54 (t, J ¼ 7.4 Hz, 1H), 7.42 (dt, J ¼ 13.1, 7.5 Hz, 6H),
7.31 (d, J ¼ 7.6 Hz, 2H), 7.28e7.23 (m, 2H), 7.16 (t, J ¼ 6.7 Hz, 2H),
7.12 (d, J ¼ 8.1 Hz, 1H), 7.08 (td, J ¼ 7.6, 3.0 Hz, 2H), 6.57 (t,
J ¼ 6.5 Hz, 1H), 6.52 (s, 1H), 6.29 (s, 1H). 13C NMR (75 MHz, CDCl3)
C43H28O2N3PF11Ir: C 52.98, N 4.31, H 2.89. Found: C 53.01, N 4.39, H
2.63.
(tfmppy)2Ir(L6) (Ir6). 0.40 g [(tfmppy)2Ir(
gave 0.14 g Ir6 (0.13 mmol, 65.3%). 1H NMR (500 MHz, CDCl3)
m
-Cl)]2 and 0.26 g L6
d
9.13
d
206.90, 174.53, 166.77, 149.72, 149.31, 145.33, 143.80, 137.48,
(d, J ¼ 5.5 Hz, 1H), 8.28 (d, J ¼ 5.5 Hz, 1H), 7.94 (d, J ¼ 8.1 Hz, 1H),
7.89 (d, J ¼ 8.3 Hz, 2H), 7.85 (d, J ¼ 8.5 Hz,1H), 7.81 (t, J ¼ 7.8 Hz,1H),
7.70 (d, J ¼ 8.1 Hz, 1H), 7.65 (dd, J ¼ 15.9, 7.8 Hz, 2H), 7.61e7.54 (m,
2H), 7.42e7.33 (m, 2H), 7.21 (t, J ¼ 6.6 Hz,1H), 7.17 (d, J ¼ 8.2 Hz,1H),
7.15 (s, 1H), 7.12 (d, J ¼ 8.9 Hz, 2H), 6.80 (t, J ¼ 7.7 Hz, 2H), 6.69 (t,
J ¼ 6.5 Hz, 1H), 6.49 (s, 1H), 6.23 (s, 1H). 13C NMR (75 MHz, CDCl3)
137.05, 131.04, 130.92, 130.85, 130.76, 130.64, 129.16, 128.36, 128.11,
127.95, 127.64, 123.34, 123.24, 122.74, 122.32, 119.03, 118.68, 118.11.
HR EI-MS Calcd for [M þ H]þ: m/z 958.1604, found: m/z 958.1604.
Anal. calcd for C43H29O2N3PF6Ir: C 53.97, N 4.39, H 3.05. Found: C
53.68, N 4.24, H 3.35.
(tfmppy)2Ir(L2) (Ir2). 0.40 g[(tfmppy)2Ir(
m
-Cl)]2 and 0.23 g L2
d 206.90, 174.53, 166.77, 149.72, 149.31, 145.33, 143.80, 137.48,
gave 0.48 g Ir2 (0.48 mmol, 80.3%). 1H NMR (500 MHz, CDCl3)
d
9.17
137.05, 131.04, 130.92, 130.85, 130.76, 130.64, 129.16, 128.36, 128.19,
128.11, 127.95, 127.64, 123.34, 123.24, 122.74, 122.32, 119.03, 118.68,
118.11. HR EI-MS Calcd for [M þ H]þ: m/z 1048.1132, found: m/z
1048.1132. Anal. calcd for C43H24O2N3PF11Ir: C 49.33, N 4.01, H 2.31.
Found: C 49.32, N 4.08, H 2.52.
(d, J ¼ 5.6 Hz, 1H), 8.36 (d, J ¼ 5.5 Hz, 1H), 7.98 (d, J ¼ 7.6 Hz, 2H),
7.95e7.89 (m, 3H), 7.87 (d, J ¼ 8.2 Hz, 1H), 7.77 (t, J ¼ 7.8 Hz, 1H),
7.70 (d, J ¼ 8.1 Hz, 1H), 7.66 (d, J ¼ 8.1 Hz, 1H), 7.62 (t, J ¼ 7.8 Hz, 1H),
7.46e7.38 (m, 3H), 7.31 (t, J ¼ 7.7 Hz, 2H), 7.17 (dd, J ¼ 12.0, 7.0 Hz,
2H), 7.14e7.05 (m, 3H), 6.77 (dd, J ¼ 8.6, 6.7 Hz, 2H), 6.66 (t,
J ¼ 6.5 Hz, 1H), 6.50 (s, 1H), 6.27 (s, 1H). 13C NMR (75 MHz, CDCl3)
(tfmppy)2Ir(L7) (Ir7). 0.40 g [(tfmppy)2Ir(
m
-Cl)]2 and 0.24 g L7
gave 0.09 g Ir7 (0.09 mmol, 43.1%). 1H NMR (500 MHz, CDCl3)
d
9.16
d
206.90, 174.53, 166.77, 149.72, 149.31, 145.33, 143.80, 137.48,
(d, J ¼ 5.6 Hz, 1H), 8.34 (d, J ¼ 5.6 Hz, 1H), 8.01e7.94 (m, 2H), 7.91 (d,
J ¼ 8.0 Hz, 2H), 7.88 (d, J ¼ 7.5 Hz, 2H), 7.78 (t, J ¼ 7.8 Hz, 1H), 7.70 (d,
J ¼ 8.1 Hz, 1H), 7.64 (dd, J ¼ 18.1, 8.1 Hz, 2H), 7.44e7.35 (m, 2H), 7.19
(d, J ¼ 7.0 Hz, 1H), 7.16 (d, J ¼ 8.6 Hz, 1H), 7.13 (s, 1H), 7.12e7.06 (m,
2H), 6.96 (t, J ¼ 8.6 Hz, 2H), 6.78 (t, J ¼ 7.9 Hz, 2H), 6.67 (t, J ¼ 6.5 Hz,
137.05, 131.04, 130.92, 130.85, 130.76, 130.64, 129.16, 128.36, 128.19,
128.11, 127.95, 127.64, 123.34, 123.24, 122.74, 122.32, 119.03, 118.68,
118.11. HR EI-MS Calcd for [M þ H]þ: m/z 994.1415, found: m/z
994.1415. Anal. calcd for C43H27O2N3PF8Ir: C 52.02, N 4.23, H 2.74.
Found: C 51.42, N 4.87, H 2.92.
1H), 6.50 (s, 1H), 6.26 (s, 1H). 13C NMR (75 MHz, CDCl3)
d 206.90,
(tfmppy)2Ir(L3) (Ir3). 0.40 g [(tfmppy)2Ir(
m
-Cl)]2 and 0.29 g L3
174.53, 166.77, 149.72, 149.31, 145.33, 143.80, 137.48, 137.05, 131.04,
130.92, 130.85, 130.76, 130.64, 129.16, 128.36, 128.19, 128.11, 127.95,
127.64, 123.34, 123.24, 122.74, 122.32, 119.03, 118.68, 118.11. HR EI-
MS Calcd for [M þ H]þ: m/z 1012.1321, found: m/z 1012.1321.
Anal. calcd for C43H26O2N3PF9Ir: C 51.09, N 4.16, H 2.59. Found: C
50.89, N 4.22, H 2.73.
gave 0.31 g Ir3 (0.28 mmol, 46.7%). 1H NMR (500 MHz, CDCl3)
d
9.17 (d, J ¼ 5.6 Hz, 1H), 8.31 (d, J ¼ 5.6 Hz, 1H), 8.10 (dd, J ¼ 11.6,
8.2 Hz, 2H), 8.02 (d, J ¼ 7.3 Hz, 2H), 7.93 (d, J ¼ 8.1 Hz, 1H), 7.86 (d,
J ¼ 8.1 Hz, 1H), 7.79 (t, J ¼ 7.8 Hz, 1H), 7.74e7.64 (m, 4H), 7.59 (dd,
J ¼ 10.8, 8.4 Hz, 2H), 7.54 (t, J ¼ 7.8 Hz, 1H), 7.45 (t, J ¼ 7.4 Hz, 1H),
7.34 (t, J ¼ 7.7 Hz, 4H), 7.20 (dd, J ¼ 14.1, 7.1 Hz, 2H), 7.14 (d,
J ¼ 8.0 Hz, 1H), 6.55 (t, J ¼ 6.6 Hz, 1H), 6.52 (s, 1H), 6.25 (s, 1H). 13
C
3. Results and discussion
NMR (75 MHz, CDCl3)
d 206.90, 174.53, 166.77, 149.72, 149.31,
145.33, 143.80, 137.48, 137.05, 131.04, 130.92, 130.85, 130.76,
130.64, 129.16, 128.36, 128.19, 128.11, 127.95, 127.64, 123.34,
123.24, 122.74, 122.32, 119.03, 118.68, 118.11. HR EI-MS Calcd for
[M þ H]þ: m/z 1094.1351, found: m/z 1094.1351. Anal. calcd for
3.1. Syntheses and X-ray crystallography
Although the synthesis of L1 has been reported [34], triethyl-
amine, which is hard to dehydration, was required as a base in the
reaction. Here we demonstrate that the 4-dimethylaminopyridine
(DMAP) could also make the reaction efficient. The electron-
C
45H27O2N3PF12Ir: C 49.45, N 3.84, H 2.49. Found: C 49.48, N 3.79,
H 2.58.

114
T.-Y. Li et al. / Journal of Organometallic Chemistry 755 (2014) 110e119
Fig. 1. Molecular structures of Ir1eIr7 with thermal ellipsoids shown at 50% probability level. The hydrogen atoms are omitted for clarity.
withdrawing fluorine and trifluoromethyl substituents were
introduced in either or both benzamides and chlor-
odiphenylphosphines moieties, hoping to alter the energy levels of
frontier molecular orbitals in the complexes and change the pho-
tophysical properties consequently.
The single crystals of Ir1, Ir2, Ir3, Ir4, Ir5, Ir6 and Ir7 were ob-
tained by using solvent diffusion of MeOH into CH2Cl2 solutions of
the complexes at room temperature. The Oak Ridge thermal ellip-
soidal plot (ORTEP) diagrams of the complexes are shown in Fig. 1.
The parameters of the refined single crystals are selected in Table 1.
Important bond lengths and angles revealing the coordination
sphere are listed in Table S1 as Supporting information.
The single crystal structure diagrams in Fig. 1 reveal that each
complex possesses the pseudo-octahedral coordination geometry,
which is typical for heteroleptic iridium complexes. The relative
coordination geometry of the cyclometallated phenylpyridine li-
gands is retained from that of the precursors with cis-C,C and trans-
N,N coordination and the chelated N-(diphenylphosphoryl)benza-
mide derivatives bond through oxygen donor atoms. From a steric
perspective it is noted that one of the phenyl moieties attached to
phosphorus atom is bent into a parallel position with the pyridine
moiety in phenylpyridine ligand in an effort to minimize the in-
teractions caused by sterically crowded diphenylphosphoryl moi-
ety. As
a result of this packing effect, the hexatomic-ring
coordination structure of ancillary ligand and iridium center is
disturbed. The phosphorus atom is obviously drawn along with the
packing phenyl moiety, as well as the conjoint nitrogen and oxygen
atoms.
Among all the coordination bonds, the IreO bonds are the
ꢀ
longest (2.151e2.246 A). It is not surprising to find that the IreC
ꢀ
bonds (1.965e2.025 A) are shorter than IreN bonds (2.028e
ꢀ
2.049 A) in each complex, suggesting the stronger coordination
effect of IreC bonds than IreN bonds. Consequently, the N(1)eIre
N(2) bond angles are twisted slightly, ranging from 174.18ꢂ to
Table 1
Parameters associated with the single crystal diffraction data collection for Ir1, Ir2, Ir3, Ir4, Ir5, Ir6 and Ir7.
Ir1
Ir2
Ir3
Ir4
Ir5
Ir6
Ir7
Formula
C43H29F6IrN3O2P
956.88
Monoclinic
P21/n
13.3295(4)
19.9555(6)
14.2885(4)
90
97.1550(10)
90
C43H27F8IrN3O2P
992.85
Monoclinic
P21/n
13.3226(10)
19.7284(15)
14.5722(11)
90
96.3670(10)
90
C45H27F12IrN3O2P
1092.87
Monoclinic
P21/c
14.4337(8)
23.7048(13)
13.7494(7)
90
111.913(2)
90
C43H26F9IrN3O2P
1010.84
Triclinic
C43H28F7IrN3O2P
974.85
Monoclinic
P21/n
13.364(11)
20.114(17)
14.351(12)
90
96.892(12)
90
C43H24F11IrN3O2P
1046.84
Monoclinic
P21/n
10.1550(7)
15.8578(11)
24.4654(17)
90
96.5590(10)
90
C43H26F9IrN3O2P
1010.86
Monoclinic
P21/n
13.1209(11)
19.4821(16)
14.4441(12)
90
95.8500(10)
90
Formula weight
Crystal system
Space group
ꢁ
Pı
ꢀ
a [A]
11.956(3)
12.148(4)
15.466(5)
96.493(4)
102.451(4)
115.984(3)
1915.8(10)
2
ꢀ
b [A]
ꢀ
c [A]
a
b
g
[ꢂ]
[ꢂ]
[ꢂ]
3
ꢀ
V/[A ]
3771.10(19)
4
3806.4(5)
4
4364.4(4)
4
3830(6)
4
3914.0(5)
4
3673.0(5)
4
Z
F(000)
1880
1944
2136
988
1912
2040
1976
Reflns collected
25,495
34,050
34,728
15,374
19,713
32,962
32,626
Unique(Rint
R1, wR2 [I > 2
)
8653(0.0208)
0.0276, 0.0688
0.0351, 0.0724
1.033
8725(0.0491)
0.0331, 0.0876
0.0420, 0.0976
1.068
8546(0.0118)
0.0595, 0.1469
0.0633, 0.1477
1.039
7427(0.0203)
0.0594, 0.1463
0.0620, 0.1473
1.010
6562(0.0414)
0.0478, 0.1115
0.0548, 0.1125
1.033
8539(0.0922)
0.0409, 0.0971
0.0627, 0.1082
1.016
8394(0.0449)
0.0287, 0.0716
0.0388, 0.0768
1.075
s(I)]
R1, wR2 [all data]
GOF [F2]
CCDC number
930983
930984
930985
930986
930987
930988
930989
P
P
P
P
R1
¼
kFoj ꢀ jFck/ jFoj, wR2 ¼ [ [w(F2o ꢀ F2c)2]/ w(Fo2)2]1/2
.

T.-Y. Li et al. / Journal of Organometallic Chemistry 755 (2014) 110e119
115
175.70ꢂ. Concerning the bond angles between the two phenyl
Table 2
Electrochemical data of the complexes Ir1eIr7.
moieties and phosphorus atom, since one of the phenyl rings is
almost fixed in the parallel position with the pyridine ring, the
other automatically adjust a most favorable structure which forms a
flare angle around 109ꢂ.
Complex
Eox/Va
Ered/Va
EHOMO/eVb
Ebandgap/eVc
ELUMO/eVd
Ir1
Ir2
Ir3
Ir4
Ir5
Ir6
Ir7
þ0.997
þ1.014
þ1.053
þ1.031
þ1.004
þ1.049
þ1.022
þ0.931
þ0.947
þ0.979
þ0.959
þ0.941
þ0.986
þ0.959
ꢀ5.53
ꢀ5.54
ꢀ5.58
ꢀ5.56
ꢀ5.53
ꢀ5.57
ꢀ5.55
2.47
2.51
2.53
2.61
2.57
2.58
2.56
ꢀ3.06
ꢀ3.03
ꢀ3.05
ꢀ2.95
ꢀ2.96
ꢀ2.99
ꢀ2.99
3.2. Electrochemistry
The electrochemical behaviors of these iridium complexes were
investigated by cyclic voltammetry in deaerated acetonitrile in or-
der to determine the HOMO/LUMO energy levels (EHOMO/ELUMO).
The ionization potential for the first oxidation (IrIII/IV) can be used to
establish EHOMO by assuming that the absolute level of the Fc0/I
redox couple is 4.8 eV below the vacuum level, and further LUMO
energy levels can be calculated from the HOMOs and energy
bandgaps obtained from the lowest-energy absorption edges of the
UVevis spectra. The cyclic voltammograms of the complexes Ir1e
Ir7 (5 ꢁ 10ꢀ4 M) solutions show distinct reversible redox peaks and
the oxidation peaks are in the region of 1.00e1.05 V (Fig. 2). These
positive oxidation potentials are attributed to the center IrIII/IV ox-
idations, in accordance with the reported cyclometallated IrIII
systems.
Although the differences among oxidation potentials are not
obvious, the electron-withdrawing eCF3 and eF substituents on
the ancillary ligands led to certain anodic shift of the oxidation
potential. This is demonstrated by the oxidation potential se-
quences of Ir3 (1.053 V) > Ir2 (1.014 V) > Ir1 (0.997 V), and Ir6
(1.049 V) > Ir4 (1.031 V) > Ir7 (1.022 V) > Ir5 (1.004 V) > Ir1
(0.997 V). Meanwhile, from the sequences of the oxidation peaks, it
can be concluded that the amount of the substituents in the
ancillary ligands have predominant influences and the electron-
withdrawing unit of eCF3 has a little effect than that of F. Conse-
quently, the HOMO resultant values (Table 2), using the reported
equations [24,35], range from ꢀ5.53 to ꢀ5.58 eV for complexes
Ir1eIr7. The introduction of the electron-withdrawing moieties of
eCF3 and F can decrease the HOMO energy levels. Specifically, for
the complex Ir3 with eCF3 substituents, the HOMO values
are ꢀ5.58 eV and for complexes Ir6, Ir4, Ir7, Ir2 and Ir5 with F
atoms, the HOMO data are ꢀ5.57, ꢀ5.56, ꢀ5.55, ꢀ5.54
and ꢀ5.53 eV, respectively.
Oxidation potentials measured as MeCN solutions at 50 mV sꢀ1 with 0.10 M n-
a
Bu4NClO4 as supporting electrolyte calibrated with ferrocene.
b
The HOMO energy levels were calculated using the equation
e HOMO
(eV) ¼ Eox ꢀ EFc/Fcþ þ 4.8.
c
Ebandgap energies were determined from the absorption edge of the iridium
complexes.
d
The LUMO energy levels were calculated using the equation LUMO
(eV) ¼ HOMO þ Ebandgap
.
the B3LYP hybrid functional) were undertaken. The resultant
assessment of the frontier orbitals provides a qualitative insight
into the HOMO and LUMO energy levels. Contour plots of the
frontier molecular orbitals (FMOs) are shown in Fig. 3, while the
energies and descriptions of them, in terms of % composition of
ligand and metal orbitals, are collected in Table 3. The detailed
information for other frontier molecular orbitals of all the com-
plexes is given in Table S2 as Supporting information.
From the point of view of the electronic structure, all the com-
plex models display the typical features of complexes containing
iridium atom in a pseudo-octahedral coordination sphere. In detail,
the three highest occupied orbitals (HOMO, HOMO ꢀ 1 and
HOMO ꢀ 2) are mainly localized on the iridium atom while the
lowest unoccupied molecular orbitals are mainly localized on the
p
orbitals of phenylpyridine ligands. Population analyses (Table 3)
reveal that the distributions of the FMOs for all the complexes have
similar electron distributions on HOMOs and LUMOs. Specifically,
HOMOs consists of the d orbital (54.2e54.5%) of iridium atom and
orbitals (37.8e38.5%) of tfmppy, indicating substantial mixing of
the
p
p
orbitals of the ligands with the metal. HOMO ꢀ 1 and
HOMO ꢀ 2 are near-degenerate (energy difference is in the range of
0.02e0.03 eV), and share the similar contributions from mostly
iridium d orbital (>60%) together with
p orbitals of both ligands.
The LUMO and LUMO þ 1 are both predominantly located on the
p
3.3. Density function theory (DFT) study
orbitals (92.4e94.1%) of tfmppy. The almost degenerated couple of
LUMO and LUMO þ 1 are favorable for the stabilization of excited
electrons, which makes the complexes have better capability in
holding the excited electrons, and benefits electron transportation
In an effort to elucidate the nature of the electronic transitions
within this series of complexes, DFT calculations (computed using
process [36]. It is worthy to mention that most
p orbital contri-
butions from tfmppy on HOMOs are localized on the phenyl and the
contribution from the pyridine rings is negligible. But for LUMOs,
phenyl and pyridine rings share almost the equal contributions.
This provides a possible molecular design strategy for such iridium
complexes with phenylpyridine ligands that electron-donating and
electron-withdrawing substitutes can be attached to the phenyl
rings to alter HOMO energy levels, and LUMO energy levels can be
altered efficiently when attached the substitutes to the pyridine
rings. Meanwhile, according to previous reports, the quantum ef-
ficiency values of the phosphorescence emission of the iridium
complexes could be kept on a quite high level, since the LUMOs are
dominantly contributed by main ligands [37,38], and the following
experimental data prove this presumption.
Since the ancillary ligands have little contributions on HOMOs
(7.0e7.7%) and LUMOs (2.1e3.6%), it is not surprising that with the
change of the ancillary ligands, the energy levels of both HOMOs
and LUMOs do not have significant differences. As a result, the
HOMOeLUMO energy gaps are similar, and this can explain that the
Fig. 2. Cyclic voltammograms of the complexes Ir1eIr7.

116
T.-Y. Li et al. / Journal of Organometallic Chemistry 755 (2014) 110e119
Fig. 3. Contour plots of HOMOs (bottom) and LUMOs (top) of Ir1eIr7 with theoretical (black) and experimental (red, determined by cyclic voltammetry) energy levels. (For
interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
emission peaks of the complexes are all around 520 nm. However,
with the same tfmppy main ligand, the subtle variations on
the energy levels of FMOs can be ascribed to the electron-
withdrawing eF or eCF3 substitutes attached to the ancillary li-
gands. Definitely, due to the relativistic effects, absolute energy
levels cannot be reliably calculated for complexes of heavy
metal ions, but relative energy levels can still be informative. For
example, Ir3 with a eCF3 substitutes on ancillary ligand has the
lowest HOMO and LUMO energy levels (ꢀ5.58 and ꢀ3.05 eV,
respectively). For Ir5, Ir4, Ir7 and Ir6, with the increase of fluorine
atom number on ancillary ligands, the HOMO levels decrease
consequently (ꢀ5.44 > ꢀ5.47 z ꢀ5.46 > ꢀ5.49 eV) and this
sequence coincides with the experimental data (ꢀ5.53 > ꢀ5.56 z
ꢀ5.55 > ꢀ5.57 eV).
3.4. Photophysical property
The UVevis absorption spectra of the complexes were measured
in aerated CH2Cl2 solutions (Fig. 4(a), Table 4). The intense bands,
which observed in the ultraviolet part of the spectra, between 220
and 280 nm (ε > 104 Mꢀ1 cmꢀ1), can be assigned safely to the spin-
allowed 1
pep
* transition of the ligand-centered (1LC) states. In the
range of lower energy (300 <
l
< 525 nm), the absorption spectra
show subtle variations and can be assigned to singlet and triplet
MLCT transitions and ligand-to-ligand charge transfers [40e43],
suggesting that the electronic structures of the frontier orbitals are
almost the same in all the complexes, which has been proved by
earlier DFT studies.
Time-dependent DFT (TD-DFT) calculations in simulated CH2Cl2
on all the complexes well support the assignment of these bands. It
is noteworthy that compared with B3LYP functional, M06-2x
functional reproduces the absorption spectra profiles that match
the experimental data better, especially in the high-energy
range. The absorption energies with large oscillator strength,
their dominant configurations and transition nature are listed in
Table S3 and the simulated spectra are depicted in Fig. S1. To
facilitate the comparison, a broadening of the transition with
FWHM ¼ 5000 cmꢀ1 is applied to all calculated spectra. Taking Ir1
as example to discuss in detail (Fig. 4(b)), generally, a reasonable
agreement is obtained between the theoretical and experimental
spectra. The lowest-energy absorption with significant intensity
consists of excitation from the HOMO that localized on 5d orbital of
When compared the theoretical calculated energy levels with
the experimental data, HOMO energy levels are in good agreement
with the experimental ones and the difference is around 0.1 eV.
However, for LUMO energy levels, the calculated results are about
1.2 eV lower than experimental values. These differences simply
reflect the ignorance of relaxation effects, which may lower the
LUMO energies in great deal, during the theoretical calculation [39],
because the calculated values are approximations to vertical
oxidation/reduction potentials.
Table 3
Percentage distributions of HOMO and LUMO in the complexes Ir1eIr7.
Complex
Orbital
Energy/eV
Ebandgap/eV
Composition %
iridium (54.5%) and
nated by * orbitals of tfmppy (94.1%). This transition is predicted
to lie at 339 nm (oscillator strength ¼ 0.13 a.u.) which is in good
agreement with the energy gap ( EHOMOeLUMO), and possesses the
p orbital of tfmppy (37.8%) into LUMO domi-
Ir
L
tfmppy
p
Ir1
Ir2
Ir3
Ir4
Ir5
Ir6
Ir7
HOMO
LUMO
HOMO
LUMO
HOMO
LUMO
HOMO
LUMO
HOMO
LUMO
HOMO
LUMO
HOMO
LUMO
ꢀ5.43
ꢀ1.80
ꢀ5.45
ꢀ1.82
ꢀ5.48
ꢀ1.84
ꢀ5.47
ꢀ1.83
ꢀ5.44
ꢀ1.81
ꢀ5.49
ꢀ1.84
ꢀ5.46
ꢀ1.82
3.63
3.63
3.64
3.64
3.63
3.65
3.64
54.5
3.9
54.2
3.9
54.4
3.9
54.4
3.9
54.4
3.9
54.5
3.9
54.4
3.9
7.7
2.1
7.5
2.2
7.2
3.6
7.3
2.3
7.6
2.1
7.0
2.2
7.5
2.1
37.8
94.1
38.3
94.0
38.1
92.4
38.3
93.8
37.9
94.1
38.5
93.9
38.2
94.0
D
nature of MLCT. Since only singletesinglet transitions are taken into
consideration during the calculations, and there is no absorption
band in the range from 400 to 500 nm in the simulated spectrum.
Thus, the weak absorption in this range in the experimental spec-
trum can be assigned to spin-forbidden triplet metal-to-ligand
charge-transfer (3MLCT) transitions and 3p
ligands (d
e
p* transitions of the
pep*). A set of stronger transitions centered at around
260 nm (251 nm, 0.15 a.u.; 264 nm, 0.27 a.u.; 266 nm, 0.10 a.u.) are
also predicted, in good agreement with experimental shoulder
peaks. These bands consist of varying combinations of iridium

T.-Y. Li et al. / Journal of Organometallic Chemistry 755 (2014) 110e119
117
77 K (Fig. 5(a), Table 4). Emission spectra at room temperature
(Fig. 4(a), left) show the broad and structured emission maxima at
about 520 nm together with a shoulder peak at 560 nm. The
emission peaks are very close to that of the Ir(tfmppy)2(acac)
(522 nm) [11], indicating that this new series of ancillary ligands do
not affect the electronic structures of the frontier orbitals that
engaged in the emission process significantly and the change of the
ancillary ligand leads to a really subtle shift in the emission color. It
is quite prominent to identify a vibrational sideband pattern for
each complex in the room temperature emission spectrum, sug-
gesting that the emissive state has emission characteristic of
phosphorescence from a mixed-ligand-cantered-MLCT (LC-MLCT)
triplet state [44e46]. There is no evidence of any significant
emission around absorption bands at higher energies, which in-
dicates efficient inter-system crossing (ISC) from the high-energy
electronic excited states to the emitting states in these com-
plexes. Concerning the photoluminescent efficiency, complexes Ir2
and Ir7 have relatively higher quantum yields of 61.2% and 58.2%
than the Ir1 (57.2%), which has no eF and eCF3 substituents in the
ancillary ligand. However, Ir3, Ir4, Ir5 and Ir6 own relatively lower
quantum yields of 46.8%, 37.5% 47.8% and 47.4%, respectively, but
still comparable to the efficiency of fac-Ir(ppy)3 standard reference.
The sequence is well agreed with the emission intensities listed in
Fig. 4(a). This proves that the non-radiative energy decay paths of
most complexes are well depressed.
Emission spectra at 77 K (Fig. 5(a)) are divided into two main
emission peaks which locate in the range from 513 to 516 nm and
from 544 to 555 nm, respectively. This again demonstrates that the
mixed 3MLCT and 3LC character of the emissive states of the com-
plexes. As shown in Fig. 5(a) and Table 4, the phosphorescence
spectra of the IrIII complexes suffer the rigidochromic effect on
going from fluid to glassy solvent: the phosphorescence bands shift
to blue on going from RT to 77 K. The rigidochromic effect on some
kinds of transition metal complexes has been previously reported
[47,48]. This behavior usually indicates that the luminescent
excited state is coupled with nuclear rearrangements which are
affected by the state of the solvent. Because of the low viscosity of
the medium at RT, solvent molecules in the vicinity of the excited-
state molecule readily undergo reorientation by the dipoleedipole
interaction within the lifetime of the excited state, resulting in the
formation of the fully relaxed excited state. Thus, the emission at
room temperature occurs from the fully relaxed excited state. On
the other hand, the excited state at 77 K emits before the solvent
relaxation occurs, resulting in the rigidochromic effects on the
emission spectra. For solid state emissions at room temperature
(Fig. 5(b)), all the complexes exhibit emission peaks in the range
from 544 to 553 nm, which are substantially red-shifted from their
Fig. 4. (a) Absorption/emission spectra of Ir1eIr7 in aerated/deaerated CH2Cl2 solu-
tions. (5.0 ꢁ 10ꢀ6 M for absorption spectra and 5.0 ꢁ 10ꢀ5 M for emission spectra); (b)
Experimental spectrum (black) and theoretically simulated absorption spectrum (red)
of Ir1 in CH2Cl2. (For interpretation of the references to color in this figure legend, the
reader is referred to the web version of this article.)
d orbitals, tfmppy and part of L1
orbitals, suggesting contributions of MLCT and LLCT. The largest
intensity bands include excitations from iridium d orbitals and
orbitals of both tfmppy and L1 into * orbitals of tfmppy and L1,
indicating ILCT and LLCT mixed with part of MLCT character.
p orbitals excited into tfmppy p*
p
p
Photoluminescence measurements were conducted in dea-
erated CH2Cl2 solutions at room temperature (Fig. 4(a), Table 4) and
Table 4
Absorption and emission data of the complexes Ir1eIr7.
Complex
Absorptiona
Emission
lmax/nm (ε/103 Mꢀ1 cmꢀ1
)
Solution
Solid
lRemT /nmb
s
/m
sb
Fem/%c
l7em7K/nmd
lem/nm
s/ms
Ir1
Ir2
Ir3
Ir4
Ir5
Ir6
Ir7
230 (64.2), 260 (54.8)sh, 337 (8.0), 404 (4.2), 442 (3.2)
229 (59.0), 260 (52.7)sh, 336 (7.5), 404 (4.0), 445 (3.0)
232 (64.4), 259 (57.4)sh, 336 (8.0), 404 (4.0), 440 (3.0)
228 (51.4), 259 (44.4), 337 (6.4), 403 (2.8), 442 (1.9)
225 (59.2), 258 (41.2), 295 (18.6)sh, 332 (6.7), 403 (3.3), 440 (2.2)
227 (54.2), 257 (40.0), 294 (18.4)sh, 337 (6.4), 401 (3.1), 437 (2.2)
226 (62.4), 264 (71.8), 334 (7.0)W, 402 (3.5), 440 (2.3)
521
520
518
518
519
517
520
2.0
2.0
1.9
2.1
2.3
2.1
2.0
57.2
61.2
46.8
37.5
47.8
47.4
58.2
514, 552
513, 545
515, 552
514, 553
516, 554
515, 552
516, 555
553
548
550
548
549
544
549
2.0
2.4
2.3
2.3
2.6
2.7
2.1
a
Values were obtained from CH2Cl2 solutions (5 ꢁ 10ꢀ6 mol Lꢀ1) at room temperature, sh is marked as shoulder peak.
b
c
Data were collected from deaerated CH2Cl2 solutions (5 ꢁ 10ꢀ4 mol Lꢀ1) at room temperature.
Quantum efficiencies were calculated using fac-Ir(ppy)3
(
Fref ¼ 40%) in acetonitrile as reference.
d
Data were collected from deaerated CH2Cl2 solutions (5 ꢁ 10ꢀ4 mol Lꢀ1) at 77 K.

118
T.-Y. Li et al. / Journal of Organometallic Chemistry 755 (2014) 110e119
The electrochemical investigation and DFT calculation suggested
that the eF and eCF3 substituents on the ancillary ligands led to the
anodic shift of the oxidation potential and decrease the HOMO
energy levels. All the complexes own the similar emission peaks
around 520 nm with various intensities and quantum efficiencies
from 37.5 to 61.2% which suggesting the potential as phosphoresce
dopants in the OLEDs. A wide range of substituents, electron-
donating or -withdrawing units, can be attached to this kind of li-
gands in this way to obtain some promising complexes with
attractive emissive properties.
Acknowledgments
This work was supported by the Major State Basic Research
Development Program (2013CB922101, 2011CB808704) and the
National Natural Science Foundation of China (21371093).
Appendix A. Supplementary material
CCDC 930983, 930984, 930985, 930986, 930987 and 930988
contain the supplementary crystallographic 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.
Appendix B. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.jorganchem.2014.01.014.
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