Novel phosphorescent iridium(III) complexes containing 2-thienyl quinazoline ligands: Synthesis, photophysical properties and theoretical calculations

Article abstract of DOI:10.1039/c5ra17437f

The easy tailoring of organic ligands of iridium(iii) complexes provides a facile way to tune their opto-electronic properties for applications in high efficiency phosphorescent light emitting diodes. Herein, a series of yellow and red emitting phosphorescent iridium complexes based on 2-thienyl quinazoline derivatives are successfully synthesized and systematically characterized with various opto-electronic properties. The X-ray crystal structures demonstrate that the iridium centers in the complexes with bulky substituents on the 4-position of quinazolyl rings prefer to chelate with the N atoms in the 1-position of quinazolyl rings. Both experiment and theoretical studies indicate that the steric hindrance along with the electron-donating effect of substituents on the C^N ligands enhances the emission quantum yields, accompanied by significant emission shifts. Two yellow phosphorescent iridium complexes (Ir2 and Ir3) are successfully designed and exhibit moderate emission efficiencies, through the incorporation of bulky ligands with strong electron-donating abilities (piperidine for Ir2 and 2,6-dimethyl-phenoxy for Ir3, respectively). The synergistic effect of electron structure and hindrance of ligand is believed to be a promising strategy for tuning the opto-electronic properties of iridium complexes.

Full text of DOI:10.1039/c5ra17437f

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Novel phosphorescent iridium(III) complexes
containing 2-thienyl quinazoline ligands: synthesis,
Cite this: RSC Adv., 2015, 5, 97841
photophysical properties and theoretical
calculations†
Qunbo Mei,‡ Jiena Weng,‡ac Zhijie Xu,a Bihai Tong,b Qingfang Hua,a Yujie Shi,a
a
*
a
ac
*
Juan Song and Wei Huang
The easy tailoring of organic ligands of iridium(III) complexes provides a facile way to tune their opto-
electronic properties for applications in high efficiency phosphorescent light emitting diodes. Herein,
a series of yellow and red emitting phosphorescent iridium complexes based on 2-thienyl quinazoline
derivatives are successfully synthesized and systematically characterized with various opto-electronic
properties. The X-ray crystal structures demonstrate that the iridium centers in the complexes with bulky
substituents on the 4-position of quinazolyl rings prefer to chelate with the N atoms in the 1-position of
quinazolyl rings. Both experiment and theoretical studies indicate that the steric hindrance along with
the electron-donating effect of substituents on the C^N ligands enhances the emission quantum yields,
accompanied by significant emission shifts. Two yellow phosphorescent iridium complexes (Ir2 and Ir3)
are successfully designed and exhibit moderate emission efficiencies, through the incorporation of bulky
ligands with strong electron-donating abilities (piperidine for Ir2 and 2,6-dimethyl-phenoxy for Ir3,
respectively). The synergistic effect of electron structure and hindrance of ligand is believed to be
a promising strategy for tuning the opto-electronic properties of iridium complexes.
Received 28th August 2015
Accepted 4th November 2015
DOI: 10.1039/c5ra17437f
www.rsc.org/advances
have received a surge of interest in design of high performance
two-color (blue and yellow/orange) and white OLEDs (WOLEDs)
because of both in device efficiency and fabrication cost.2
Introduction
Phosphorescent iridium(III) cyclometalated complexes have
attracted great attention as emitting guest materials in organic
light-emitting diodes (OLEDs) owing to their advantageous
properties, such as high quantum efficiency, relatively short
lifetime and excellent color purity.1,2 Nowadays, full visible-
spectrum monochromatic phosphorescent OLEDs (PhOLEDs)
can be easily realized by using iridium complexes as emissive
phosphors. The external quantum efficiencies of the blue, green
and red PhOLEDs have achieved or even exceeded 20%.3
Recently, yellow/orange phosphorescent iridium complexes
Moreover, the yellow/orange phosphorescent iridium
complexes are benecial to improve the device efficiencies as
well as the color rendering index for four-color (blue, green,
yellow/orange and red) WOLEDs.4 However, it remains an
urgent demand to realize desired power efficiency (exceed 100
lm Wꢀ1) at high luminance in yellow/orange PhOLEDs, which
plays an important role in WOLEDs for practical lighting
applications.2 Herein, the development of appropriate materials
and elaborate device structures is still greatly demanded.
Experimental and theoretical studies reported to date have
established that the phosphorescence emission of iridium
complexes can be easily tailored with various electron donating
or withdrawing ligands.5,6 In particular, modication of cyclo-
metalating ligand (C^N ligand), for example, ppy (2-phenyl-
pridinato-C2, N), is able to tune the emission color over the
entire visible region.5 Since the p* orbital of the pyridyl ring of
the ppy ligand governs the lowest unoccupied molecular orbital
(LUMO) level of the ppy based iridium complexes,7 adding
electron-donating groups to the pyridyl rings is supposed to
raise the LUMO level, which results in enlarged band gap and
blue-shied emission. It is noted that one promising way to
increase the quantum efficiency of organic light emitting
aKey Laboratory for Organic Electronics and Information Displays, Institute of
Advanced Materials(IAM), Jiangsu National Synergetic Innovation Center for
Advanced Materials (SICAM), Nanjing University of Posts & Telecommunications, 9
Wenyuan Road, Nanjing 210023, China. E-mail: iamqbmei@njupt.edu.cn
bCollege of Metallurgy and Resources, Anhui University of Technology, Ma'anshan,
Anhui 243002, P. R. China
cKey Laboratory of Flexible Electronics (KLOFE), Institute of Advanced Materials(IAM),
Jiangsu National Synergetic Innovation Center for Advanced Materials (SICAM),
Nanjing Tech University, 30 South Puzhu Road, Nanjing 211816, China. E-mail:
iamwhuang@njupt.edu.cn
† Electronic supplementary information (ESI) available. CCDC 1402154–1402157.
For ESI and crystallographic data in CIF or other electronic format see DOI:
10.1039/c5ra17437f
‡ These authors contributed equally to this work.
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alkylation of piperidine or diphenylamine with 4-chloro-2-
(thiophen-2-yl)quinazoline in the presence of NaH in a polar
solvent according to the literature procedures.12 Meanwhile, the
ligand L3 is prepared with similar method by taking place of
NaH with nely ground potassium carbonate. Since the chlo-
rine atom on quinazolinyl ring can be functionalized easily,
these reactions are proceeded in mild conditions and give
satisfactory yields. And then, the iridium complexes are
synthesized according to the Nonoyama's method.13 The clas-
sical dimeric iridium(III) intermediate (C^N)2Ir(m-Cl)2Ir(C^N)2
are prepared by direct reaction of IrCl3$xH2O with Ln (n ¼ 1–4).
Subsequently, complexes Ir1–Ir4 are readily synthesized from
the dimers and 2-picolinic acid in DCM solution by a conven-
tional synthetic method, which are puried by column chro-
matography on aluminum oxide and isolated in good yield
(31.4–61.7%).
Scheme 1 Chemical structures of complexes Ir1–Ir4.
material is proposed as the steric hindrance approach, together
with highly stability of spectra in device performance.8
According to our previous work,9 the steric hindrance effect of
spirouorene can suppress the aggregation of conjugated
polymer chain leading to high efficiency and stable blue emis- X-ray crystal structures
sion. Recently, we further proposed a supramolecular steric
High-quality single crystals of complexes Ir1–Ir4 (ESI†) are ob-
hindrance approach with spirouorene based iridium complex
that exhibited impressive quantum yields and spectral
stability.10 Therefore, it is reasonable to utilize the synergistic
effect of electron structure and hindrance of ligand to design
high efficient yellow/orange iridium complexes by introducing
of appropriate electron-donating bulky substituent into the
quinazolinyl ring.11
tained by slow diffusion of their tetrahydrofuran solution into
isopropanol and characterized by X-ray crystallography (Fig. 1).
The corresponding crystallographic data are collected in ESI.†
All crystals exhibit distorted octahedral geometries around the
iridium center with two C^N ligands and one N^O ligand. The
two nitrogen atoms of C^N ligands exhibit cis-C, C and trans-N,
N chelate dispositions. Selected bond lengths and angles are
listed in Tables S2 and S3.† As shown in Fig. 1, while the iridium
In this work, four novel yellow/orange iridium complexes
Ir1–Ir4 are reported, which consist of 2-thienyl quinazoline
(TQZ) derivative as the C^N ligands and a picolinate (pic) as the
ancillary N^O ligand (Scheme 1). Diamine (piperidine (PD) and
diphenylamine (DPA)) and 2,6-dimethyl-phenoxy (DMP) are
introduced as electron-donating groups at the 4 position of the
quinazolinyl group to tuning the emission color. The incorpo-
ration of PD and DMP is aim to enhance appropriate electron-
donating effect without extending conjugation on the C^N
ligand p-system. The time-depended density functional theory
(TD-DFT) calculation based on the rst triplet excited state (T1)
optimized structures shows that both PD and DMP groups
affect the LUMO level than the highest occupied molecular
orbital (HOMO) level, resulting in a larger band gap and then
leading the emission of Ir2 and Ir3 blue-shied as compared to
Ir1. Conversely, the incorporation of DPA substituent is capable
to improve the electron-donating effect but increase the p-
conjugated system on the C^N ligand, which change the band
gap slightly. In addition, all these substituents can provide
steric hindrance around the metal to increase the photo-
luminescence quantum yields (PLQYs).
Results and discussion
Synthesis
The synthetic procedures of the cyclometalated ligands L1–L4
and the relevant complexes Ir1–Ir4 are depicted in Scheme 2.
Every step of the reactions sequence proceeded efficiently to
give good or moderate yield of the target products. The cyclo-
Scheme 2 Synthesis of the ligands L1–L4 and iridium(III) complexes
metalated ligand L2 and L4 are conveniently synthesized by N- Ir1–Ir4.
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data collected from these spectra are summarized in Table 1. As
most iridium complexes, the dominant absorption bands at
240–350 nm can be assigned to spin-allowed p–p* transitions
from the C^N ligands. The lower-energy absorption bands,
which extends up to 600 nm, can be attributed to a mixture of
ligand-to-ligand charge transfer (LLCT, p(C^N) / p*(C^N))
and metal-to-ligand charge transfer (MLCT, dp(Ir) / p*(C^N))
transitions. This is conrmed by theoretical calculations (Table
2 and Fig. 3). The absorption spectra of complexes Ir2–Ir4
incorporating the electron-donating diamine or phenolic group
are red-shied compared to Ir1. The presence of DPA moiety,
which possesses the best electron-donating capability among
the substituents incorporated in this work, makes the resulting
complex Ir4 strongest absorber in the visible range.
All these complexes are photoluminescent in uid DCM
solutions at room temperature (Fig. 2). The complexes Ir1–Ir4
exhibit broad and structured-less emission originating from the
mixed transitions of 3MLCT, 3LLCT and 3ILCT (intraligand
charge transfer), which is demonstrated by the TD-DFT calcu-
lation shown below. The complex Ir1 shows an orange phos-
phorescent emission peak at 602 nm. Comparing with the
complex Ir1, the emission maxima of Ir4 red-shis about 17 nm,
which owing to an increase of the p-conjugated system. Both Ir2
and Ir3 are blue-shied with respect to Ir1 and exhibit intense
yellow emission maxima at 586 nm. The almost overlap between
the emission spectra of Ir2 and Ir3 indicates that both complexes
emit from the lowest energy excited state which is not located on
the substituted piperidyl or phenolic groups (see Theoretical
studies section). The emission spectra of the complexes Ir1, Ir2
Fig. 1 Single crystal structures of complexes Ir1–Ir4.
atom in the complex Ir1 chelates with N at the 3 position of the
quinazolyl ring, the introduction of substituent signicantly
enhances the steric hindrance of the C^N ligands, leading the
iridium atoms in the complexes Ir2–Ir4 chelate with N at the 1
position of the quinazolyl ring. Therefore, the Ir–N bonds
around the iridium center of Ir2–Ir4 are slightly longer than that
of Ir1, while the Ir–C bonds are slightly shorten. Additionally,
the C–Ir–C angles of Ir2–Ir4 are in the range of 92.6ꢁ ꢂ 95.3ꢁ,
which are obviously enlarged comparing to that of Ir1 (86.9ꢁ).
Photophysical properties
Effects of different electron-donating substituents on the pho-
tophysical and electrochemical properties have been investi-
gated. The UV-vis absorption and photoluminescent (PL)
spectra of Ir(III) complexes Ir1–Ir4 in dichloromethane (DCM) at
room temperature are shown in Fig. 2 and the spectroscopic
Table 2 Electrochemical characteristics of complexes Ir1–Ir4
b
Complex
Eoxa (V)
Ebandgap (nm)
HOMOc (eV)
LUMOd (eV)
Ir1
Ir2
Ir3
Ir4
0.71
0.46
0.67
0.54
2.27
2.38
2.31
2.25
ꢀ5.42
ꢀ5.17
ꢀ5.37
ꢀ5.25
ꢀ3.15
ꢀ2.79
ꢀ3.06
ꢀ3.00
a
Oxidation potentials recorded in deoxygenated DCM solutions with
0.1 M (nBu4NPF6) as supporting electrolyte, referenced to the Fc/Fc+
b
couple. Ebacndgap determined from the absorption edge of the iridium
complexes. HOMO levels calculated using the equation: HOMO ¼
ꢀ[Eox ꢀ E(Fc/Fc+) + 4.8]. LUMO levels calculated using the equation:
d
Fig. 2 UV-vis absorption (left) and photoluminescence (right) spectra
of complexes Ir1–Ir4 in DCM solutions at room temperature.
LUMO ¼ HOMO + Ebandgap
.
Table 1 Photophysical characteristics of complexes Ir1–Ir4
In DCM solutiona
In PMMA lmb
d (%)
s
d (ms)
lem (nm)
F (%)
s (ms)
kre (ꢃ105 sꢀ1
)
knre (ꢃ105 sꢀ1
)
c
Complex
labs (nm)
lem (nm)
F
Ir1
Ir2
Ir3
Ir4
302, 430
602
586
586
619
15 (12)
26 (19)
34 (20)
60 (40)
0.38 (0.17)
0.65 (0.21)
0.79 (0.36)
0.70 (0.39)
596
584
583
609
26
73
43
57
1.53
2.28
2.97
1.42
1.70
3.20
1.45
4.01
4.84
1.18
1.92
3.03
253, 313, 361
311, 380, 450, 560
266, 318, 391
a
Measured in DCM solutions (1 ꢃ 10ꢀ5 mol Lꢀ1) at room temperature. b Measured in thin lms doped in PMMA at 2% concentration. c Excitation
wavelength ¼ 400 nm. d The quantum yields (F) and li time (s) are recorded both in DCM solutions before (in bracket) and aer deoxygenation. e kr
and knr are calculated according to the equations: kr ¼ F/s and knr ¼ (1 ꢀ F)/s.
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ligands efficiently suppresses the aggregation of Ir4. The
excited-state lifetimes of all these complexes are on the
hundred-nanoseconds scale in DCM solutions and on the
microseconds scale in solid PMMA doping lms. It is well
known that long lifetime will give rise to the emission satura-
tion but usually causes the great triplet–triplet annihilation.
Therefore, the suitable lifetime of these iridium complexes will
be benecial to improve the efficiency of OLEDs.
Electrochemical properties
The CV experiments are carried out using ferrocenium (Fc+)/Fc
as the internal standard. All complexes exhibit reversible oxida-
tion process in degassed DCM and show oxidation peaks ranging
from 0.46 to 0.71 V (Fig. S2†). Based on the rst oxidation
potential and optical absorption edge of the UV-vis spectra,
HOMO, LUMO and the HOMO–LUMO energy gaps (Eg) of Ir1–Ir4
are estimated (Table 2).11,14 The introduction of PD and DMP
groups into the quinazolinyl ring results in larger increase of
LUMO levels than HOMO levels due to the reduction process
mainly involves the p* orbital of the quinazolinyl ring fragment
while the oxidation process mainly involves the p orbital of the
thienyl ring fragment. In the case of Ir4, the incorporation of
DPA groups signicantly extends the p-conjugated system of the
C^N ligand, and promotes the HOMO level more than the LUMO
level, leading to a slight decrease of Eg.
Theoretical studies
To gain deeper insight into the photophysical and electro-
chemical properties of complexes Ir1–Ir4, DFT and TD-DFT
calculations are carried out using the Gaussian 09 program
package.15 Both the ground state (S0) and T1 optimized struc-
tures of Ir1–Ir4 are investigated. The calculated transition
wavelength and main assignment are summarized in Table 3.
The lowest energy absorption of Ir1 is mainly characterized by
HOMO / LUMO transition. As shown in Fig. 3 and Table S4,†
Fig. 3 Molecular orbital diagrams and energies for Ir1–Ir4 at their
lowest singlet state (S0) (top) and first excited triplet state (T1) (bottom) in the case of Ir1, the electron distribution of the HOMO is
geometries.
mainly located on both the whole C^N ligand (63.5%) and Ir(dp)
(33.0%), whereas that of LUMO primarily resides on one of the
C^N ligands (91.7%). The lowest energy absorptions of Ir2–Ir4
and Ir4 in PMMA doping lms are similar to those in uid DCM
solutions, while Ir3 doping PMMA lm exhibits structured
emission spectrum at room temperature (Fig. S1†).
are characterized by HOMO / LUMO and HOMO / LUMO+1
transitions. Their electron distributions of the HOMO are
similar to each other, which are composed of the p orbital of the
2-thienyl quinazoline moiety of both the C^N ligand (62.2%,
62.8% and 64.2% for Ir2–Ir4, respectively) and Ir(dp) (34.7%,
34.3% and 34.5% for Ir2–Ir4, respectively). All the substituents
incorporated in the 2-thienyl quinazoline moiety have no elec-
tron distribution to the HOMO. It is observed that the LUMOs of
Ir2–Ir4 are also predominately located on one of the C^N
ligands (95.7%, 90.9% and 94.5% for Ir2–Ir4, respectively),
which are similar to that of Ir1. The LUMOꢀ1 of Ir3 and Ir4 is
primarily contributed by the other C^N ligand (89.6% and
94.5% for Ir3 and Ir4, respectively), while that of Ir2 is
composed of both the other C^N ligand and N^O ligand
(97.1%). These results suggest that the lowest energy absorp-
tions of Ir1–Ir4 can be ascribed to the mixture of p–p* and
MLCT transition. The simulated absorption spectra (Fig. S3†) in
The phosphorescent lifetime and emission quantum yield of
these complexes are investigated in both DCM solution and the
thin lm state (2 wt% in PMMA). The complex Ir1 exhibit a low
quantum yield of 15% and 26% in deoxygenated DCM solutions
and PMMA lm, respectively. The incorporation of the diamine
and phenolic substituents on the 2-thienyl quinazoline ligands
provides steric hindrance and signicantly increases the emis-
sion quantum yield of the complexes Ir2–Ir4 (Table 1). While the
complexes Ir2 and Ir3 exhibit signicant higher emission effi-
ciency in PMMA doping lm (F ¼ 73% and 43%, respectively)
than in deoxygenated solutions (F ¼ 26% and 34%, respec-
tively), the complex Ir4 shows similar emission quantum yield
in both environments (F ¼ 60% and 57%, respectively), indi-
cating that the incorporation of DPA substituents in C^N
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Table 3 Lowest singlet and triplet excited states for complexes Ir1–Ir4 from TD-DFT calculations
Complex
State
lmax,cal (nm)
f
Main assignments
Character
Ir1
S1
T1
476.20
713.63
0.0294
0.0000
H / L (0.69520)
MLCT/LLCT
H / L (0.59802); Hꢀ1 / L (0.25900); H
3MLCT/3LLCT/3ILCT
/ L+4 (ꢀ0.16374)
Ir2
S1
T1
444.47
689.60
0.0819
0.0000
H / L (0.67989); H / L+1 (ꢀ0.15104)
H / L (0.61778); Hꢀ1 / L (0.25596); H
/ L+4 (0.10814)
MLCT/LLCT
3MLCT/3LLCT/3ILCT
Ir3
Ir4
S1
T1
S1
T1
453.06
679.64
475.87
715.71
0.1029
0.0000
0.0757
0.0000
H / L (0.66627); H / L+1 (ꢀ0.20197)
H / L (0.61449); Hꢀ1 / L (0.27359)
H / L (0.68069); H / L+1 (0.16802)
H / L (ꢀ0.59565); Hꢀ1 / L (ꢀ0.27210);
Hꢀ3 / L (ꢀ0.17371)
MLCT/LLCT
3MLCT/3LLCT/3ILCT
MLCT/LLCT
3MLCT/3LLCT/3ILCT
DCM are almost consistent with the result of the experimental donating substituent (such as PD and DMP) to the 4 position
data. of the quinazolinyl ring of TQZ ligand results in a different
The TD-DFT calculations at the T1 optimized geometry show chelate manner, leading to signicantly blue-shis of phos-
that the lowest energy triplet state of Ir1–Ir4 is mainly composed phorescence band. Noted that the incorporation of bulky
of three transition congurations (two transition congurations electron-donating substituents not only appropriately enhances
for Ir3). The detailed information is listed in Table 3. As shown the electron-donating effect without extending the conjugation
in Fig. 3 and Table S5,† the HOMO of Ir1–Ir4 is primarily located of C^N ligands, but also provides steric hindrance around the
at the 2-thienyl quinazoline moieties of the both C^N ligands iridium center to increase the PLQYs. Both of the electro-
and iridium atom, which is similar to that in the ground state. chemical and theoretical studies suggest that a PD or DMP
As compared to the HOMO, the HOMOꢀ1 of Ir1–Ir3 has more substituent on the quinazolinyl ring exhibits higher impact on
contribution from the both C^N ligands. However, the incor- the LUMO level than the HOMO level, resulting in a larger
poration of DPA substituent on C^N ligand signicantly affect triplet excited state energy. All these results indicate that the 2-
the HOMOꢀ1 of Ir4, which is mainly delocalized over one of the thienyl quinazoline based iridium complexes are potential high
C^N ligand with the contribution form the DPA moiety (44.3%) efficiency yellow/orange PhOLEDs materials. The strategy based
and 2-thienyl quinazoline moiety (23.1%). The LUMOs of Ir1– on the synergistic effect of electron structure and hindrance
Ir4 are predominately resides on one of C^N ligands (96.8%, offers an effective tool to adjust the opto-electronics properties
91.6%, 88.8% and 93.9%, respectively). The LUMO+4 of Ir1 and in material design towards
Ir2 exhibit similar electron distributions, primarily located on electronics.
both the C^N ligands with more contributions from the qui-
a bright future of organic
nazolinyl groups than thienyl groups. And the HOMOꢀ3 of Ir4
Experiment section
is mainly contributed by both the C^N ligands with 42.3%
contributions from the DPA moieties. These features indicate
that the nature of T1 state of Ir1–Ir4 mainly consists of a mixture
of 3MLCT, 3LLCT and 3ILCT (intraligand charge transfer). In
addition, the vertical energy difference between T1 and S0 is
computed by performing a single-point calculation of S0 at the
optimized minimum-energy geometry of T1 to estimate the
phosphorescence emission energy.16 The calculation results
show that the vertical emission energies of these complexes are
1.84 eV (671.8 nm, Ir1), 1.89 eV (653.9 nm, Ir2), 1.90 eV (649.4
nm, Ir3) and 1.80 eV (687.3 nm, Ir4). Although these energies
are underestimated compared to the experimental values,
reasonable correlations can be found between the theoretical
and experimental values for the maximum emission (Fig. S4†).
Materials and methods
All commercial reagents were used without further purication,
unless otherwise noted. N,N-dimethylacetamide (DMAc), and
N,N-dimethylformamide (DMF) were dried by standard proce-
dures before use. Dichloromethane (DCM) suitable for electro-
chemical and photospectral experiments was obtained by
distillation over calcium hydride, silica gel (200–300 mesh,
Qingdao Haiyang) was used for column chromatography.
1
The H and 13C NMR (d in ppm) spectra were recorded on
a Bruker Ultra Shield Plus 400 MHz spectrometer with TMS as
the internal standard and CDCl3 and DMSO-d6 as solvent. Mass
spectra were acquired by a Bruker Daltonics matrix-assisted
laser desorption/ionization time-of-ight mass spectrometer
(MALDI-TOF-MASS). UV-vis absorption spectra were recorded
on a Shimadzu UV-3600 UV-vis-NIR Spectrophotometer. Steady
state uorescence spectra were obtained with a Shimadzu RF-
Conclusions
In summary, a strategy of electron structure and steric 5301PC Fluorescence Spectrophotometer. Photoluminescence
hindrance effect are incorporated to design and synthesise four quantum yields were determined by using an integrating
new yellow to red phosphorescent iridium complexes contain- sphere. Lifetime studies were performed with Edinburgh FL920
ing TQZ derivatives. The introduction of appropriate electron- photocounting system with a semiconductor laser as the
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excitation source. For the thin lm quantum yields and lifetime 162.25, 149.11, 148.28, 137.84, 135.15, 132.63, 129.86, 128.97,
data measurements, materials (1 mg) were rst dissolved in 1 127.41, 126.79, 126.45, 121.34.
mL of DCM containing PMMA (20 mgꢀ1), and spin-coated at
2-(Thiophen-2-yl)quinazoline (L1). Lithium aluminium
a speed of 1500 rpm for 30 s onto the quartz slides. Cyclic vol- hydride (LiAlH4) (0.76 g, 20 mmol) and 7 mL dry THF were
tammetric (CV) measurements were carried out with a CHI660C placed in a three-necked round-bottomed ask equipped with
electrochemical workstation (Shanghai Chenhua, China) a magnetic stir bar and a 100 mL dropping funnel with pressure
utilizing the three electrode conguration consisting of a glassy equalization arm. A solution of ThQO (1.14 g, 5 mmol) in 20 mL
carbon (working electrode), platinum wire (auxiliary electrode) anhydrous THF was added to the dropping funnel and added
and Ag/AgNO3 (reference electrode) electrodes. The experiments dropwise to the solution of LiAlH4 (0.76 g, 20 mmol) in 7 mL dry
were done in dry DCM using 0.1 M tetrabutyl ammonium hex- THF at room temperature with stirring under N2 atmosphere.
auorophosphate as supporting electrolyte at a scanning rate of The mixture was heated at 70 ꢁC for 12 h. Aer cooled, the
0.1 V sꢀ1 at room temperature. Ferrocene was selected as the mixture was poured into ice-water. The aluminium hydroxide
standard. The crystallographic data for Ir1–Ir4 were collected on precipitate was ltered off and the ltrate was extracted for
a EnrafNoius & EnrafNoius (CAD4/PC) at 296 K with graphite- several times with ethyl acetate, dried over anhydrous MgSO4,
˚
monochromated Mo Ka radiation (l ¼ 0.71073 A). The cell then puried by chromatography on silica gel with a mixture of
parameters were retrieved using Bruker SMART soware and petroleum and ether–ethyl acetate as the eluent to give 2-
rened using Bruker SAINT on all observed reections. All the (thiophen-2-yl)-3,4-dihydroquinazoline as a light yellow solid.
calculations for the structure determination were carried out Next, 2-(thiophen-2-yl)-3,4-dihydroquinazoline (0.88 g, 4.11
using the SHELXTL-97 crystallographic soware package (Shel- mmol) and manganese dioxide (MnO2) (0.72 g, 8.22 mmol) in
drick, 1997) with a full-matrix least-squares technique based on dry CHCl3 (20 mL) was stirred at 60 ꢁC for 2 h in air. Aer
F2.17 Hydrogen atoms were placed theoretically and rode on cooled, the mixture was ltered and the ltrate was extracted for
their parent atoms in the nal renement. Crystal data and several times with CHCl3 and dried over anhydrous MgSO4.
processing parameters are summarized in Table S1, ESI.†
Then, the crude product was puried by chromatography on
silica gel with a mixture of petroleum and ether–ethyl acetate as
the eluent to give L1 as a light yellow solid. Yield: 80.5%. m.p.:
130–132 C. H NMR (400 MHz, DMSO) d (ppm): 9.57 (s, 1H),
8.15–8.02 (m, 2H), 8.01–7.89 (m, 2H), 7.78 (dd, J ¼ 5.0, 1.2 Hz,
1H), 7.66 (m, 1H), 7.23 (m, 1H). 13C NMR (100 MHz, DMSO)
d (ppm): 161.84, 135.49, 131.45, 129.72, 129.11, 128.45, 127.85,
127.80, 123.55.
Computational details
1
ꢁ
The singlet ground-state (S0) geometries of Ir1–Ir4 were fully
optimized by the Becke's three-parameter exchange functional
and Lee–Yang–Parr correlation functional (B3LYP) method18
based on the experimental single crystal structural parameters.
And the geometries of the lowest-lying triplet excited (T1) states
were optimized by the unrestricted Becke's three-parameter
hybrid exchange functional along with Lee–Yang–Parr correla-
tion functional (UB3LYP) method.19 The electronic transition
energies including electron correlation effects were computed
by the time dependent density functional theory (TD-DFT)
method using the B3LYP or UB3LYP functional.20 The
LANL2DZ basis set was used for the iridium centers.21 For other
atoms, 6–31g(d) basis sets were employed.22 TD-DFT approach
was applied to predict their absorption and emission properties
in DCM using the polarizable continuum model (PCM)
approach.23
4-Chloro-2-(thiophen-2-yl)quinazoline (CThQ). ThQO (3.42
g, 15 mmol) was added to 20 mL CHCl3, then 10 mL phosphorus
oxychloride was added and the mixture was reuxed for 12 h
under N2 atmosphere. Aer cooled, the mixture was poured into
ice-water and rendered to alkaline by dilute ammonia. The
resulting precipitate was ltered off and puried by chroma-
tography on silica gel with a mixture of petroleum and ethyl
acetate as the eluent to give CThQ as a light yellow solid. Yield:
1
ꢁ
83.5%. m.p.: 120–122 C. H NMR (400 MHz, DMSO) d (ppm):
8.24 (dd, J ¼ 3.8, 1.0 Hz, 1H), 8.10 (dd, J ¼ 7.9, 1.4 Hz, 1H), 7.86
(dd, J ¼ 5.0, 1.0 Hz, 1H), 7.82–7.72 (m, 1H), 7.65 (d, J ¼ 7.7 Hz,
1H), 7.52–7.41 (m, 1H), 7.22 (m, 1H). 13C NMR (100 MHz,
DMSO) d (ppm): 162.21, 148.49, 137.26, 135.19, 132.92, 130.32,
128.99, 126.93, 126.87, 126.47, 121.22.
Synthesis
2-(Thiophen-2-yl)quinazolin-4(3H)-one (ThQO). A mixture of
4-(Piperidin-1-yl)-2-(thiophen-2-yl)quinazoline (L2). A 65%
2-thiophene carboxaldehyde (3.41 g, 30 mmol), anthranilamide suspension of sodium hydride (0.74 g, 10 mmol) in paraffin oil
(4.08 g, 30 mmol) and NaHSO3 (6.24 g, 60 mmol) in DMAc (30 was added slowly to a solution of piperidine (0.25 mL, 2.5
mL) was stirred at 150 ꢁC for 8 h under N2 atmosphere. Then the mmol) in anhydrous DMF (25 mL). Aer stirred for 1 h at room
reaction mixture was cooled to room temperature and poured temperature under N2 atmosphere, a solution of CThQ (0.50 g, 2
into 500 mL water with stirring. The precipitate was collected by mmol) in anhydrous DMF (10 mL) was added dropwise under
ltration, washed with water and puried by chromatography N2 atmosphere while stirring and the mixture was stirred at
on silica gel with CH2Cl2 as the eluent to give 2-(thiophen-2-yl) room temperature for 24 h. Aer reaction, the resulting mixture
quinazolin-4(3H)-one as a white crystal. Yield: 93.0%. m.p.: 268– was poured into water and extracted with ethyl acetate. The
1
270 ꢁC. H NMR (400 MHz, DMSO) d (ppm): 12.64 (s, 1H), 8.22 organic phase was combined, washed with brine, dried over
(dd, J ¼ 3.8, 1.1 Hz, 1H), 8.11 (dd, J ¼ 7.9, 1.2 Hz, 1H), 7.86 (dd, J anhydrous magnesium sulfate and ltered. The solvent was
¼ 5.0, 1.1 Hz, 1H), 7.82–7.75 (m, 1H), 7.68–7.57 (m, 1H), 7.51– completely removed and the residue was puried by column
7.41 (m, 1H), 7.22 (m, 1H). 13C NMR (100 MHz, DMSO) d (ppm): chromatography over silica gel to give L2 as a light yellow
97846 | RSC Adv., 2015, 5, 97841–97848
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crystal. Yield: 50.1%. m.p.: 101–103 ꢁC. 1H NMR (400 MHz, aluminum oxide. It was further puried by reprecipitation from
DMSO) d (ppm): 7.96–7.86 (m, 2H), 7.75 (d, J ¼ 4.2 Hz, 2H), 7.68 ethanol to give corresponding iridium complexes Ir1–Ir4.
(dd, J ¼ 5.0, 1.2 Hz, 1H), 7.45 (m, 1H), 7.17 (dd, J ¼ 5.0, 3.7 Hz,
Ir1. 61.7% yield; red solid. 1H NMR (400 MHz, DMSO)
1H), 3.74 (d, J ¼ 5.0 Hz, 4H), 1.71 (s, 6H). 13C NMR (100 MHz, d (ppm): 9.49 (s, 1H), 8.72 (s, 1H), 8.21 (d, J ¼ 8.0 Hz, 1H), 8.15–
CDCl3) d (ppm): 164.84, 156.41, 152.71, 145.09, 132.32, 128.93, 8.04 (m, 2H), 8.02–7.85 (m, 5H), 7.77–7.64 (m, 3H), 7.67–7.50
128.46, 128.23, 127.97, 125.19, 124.33, 115.42, 50.95, 26.00, (m, 3H), 6.45 (d, J ¼ 4.8 Hz, 1H), 6.20 (d, J ¼ 4.8 Hz, 1H). 13C
24.89.
NMR (100 MHz, CDCl3) d (ppm): 173.03, 167.99, 167.19, 159.68,
4-(2,6-Dimethylphenoxy)-2-(thiophen-2-yl)quinazoline (L3). 158.77, 150.77, 150.58, 149.09, 148.26, 138.42, 136.35, 136.30,
A mixture of CThQ (0.50 g, 2 mmol), 2,6-dimethylphenol (0.29 g, 134.38, 132.82, 131.83, 131.11, 131.09, 128.68, 128.58, 128.11,
2.4 mmol) and K2CO3 (0.55 g, 4 mmol) in anhydrous DMF was 127.60, 127.38, 127.33, 126.74, 126.35, 120.98, 120.96. MS:
stirred at 120 ꢁC for 4 h under N2 atmosphere. Aer reaction, the (MALDI-TOF) m/z: 738.9 [M + 2H]+.
resulting mixture was poured into water, the precipitate was
Ir2. 55.8% yield; red solid. 1H NMR (400 MHz, DMSO)
ltered and the residue was puried by column chromatog- d (ppm): 8.26 (d, J ¼ 8.0 Hz, 1H), 7.94 (m, 2H), 7.80 (dd, J ¼ 12.1,
raphy over silica gel to give L3 as a light yellow crystal. Yield: 8.7 Hz, 3H), 7.71 (m, 1H), 7.53 (dd, J ¼ 11.5, 4.2 Hz, 1H), 7.47 (s,
1
ꢁ
86.1%. m.p.: 149–151 C. H NMR (400 MHz, CDCl3) d (ppm): 1H), 7.36 (t, J ¼ 7.2 Hz, 1H), 7.27 (s, 2H), 7.14 (t, J ¼ 7.3 Hz, 1H),
8.39 (d, J ¼ 7.7 Hz, 1H), 8.00 (d, J ¼ 8.5 Hz, 1H), 7.88 (m, 1H), 6.75 (d, J ¼ 8.3 Hz, 1H), 6.23 (s, 1H), 5.90 (s, 1H), 4.04–3.75 (m,
7.71 (d, J ¼ 3.7 Hz, 1H), 7.59 (s, 1H), 7.39 (dd, J ¼ 5.0, 1.1 Hz, 8H), 1.96–1.56 (m, 12H). 13C NMR (100 MHz, CDCl3) d (ppm):
1H), 7.17 (s, 3H), 7.03 (dd, J ¼ 4.9, 3.8 Hz, 1H), 2.17 (s, 6H). 13
C
172.76, 169.84, 169.34, 164.54, 164.37, 153.07, 152.28, 151.82,
NMR (100 MHz, CDCl3) d (ppm): 165.48, 157.03, 152.55, 149.91, 150.91, 147.56, 139.09, 137.17, 136.67, 134.14, 134.10, 132.75,
143.71, 134.09, 130.75, 129.84, 129.42, 128.51, 127.99, 127.79, 132.24, 130.79, 129.62, 127.69, 127.21, 126.03, 125.45, 124.95,
126.54, 125.67, 123.64, 114.52, 16.60.
123.62, 122.55, 122.42, 113.28, 112.86, 50.79, 50.61, 31.58,
N,N-Diphenyl-2-(thiophen-2-yl)quinazolin-4-amine (L4).
A
26.19, 26.15, 24.79, 24.71, 22.65, 14.12. MS: (MALDI-TOF) m/z:
65% suspension of sodium hydride (0.74 g, 10 mmol) in 905.5 [M + 2H]+.
paraffin oil was added slowly to a solution of diphenylamine
Ir3. 31.4% yield; red solid. 1H NMR (400 MHz, DMSO)
(0.43 g, 2.5 mmol) in anhydrous DMF (15 mL). Aer stirred for 1 d (ppm): 8.35 (m, 3H), 7.98 (dd, J ¼ 7.6, 1.5 Hz, 1H), 7.86–7.75
h at room temperature under N2 atmosphere, a solution of (m, 3H), 7.75–7.67 (m, 1H), 7.63–7.48 (m, 3H), 7.41–7.29 (m,
CThQ (0.50 g, 2 mmol) in anhydrous DMF (10 mL) was added 2H), 7.29–7.17 (m, 6H), 6.71 (d, J ¼ 8.8 Hz, 1H), 6.47 (d, J ¼ 4.8
dropwise under N2 atmosphere while stirring and the mixture Hz, 1H), 6.14 (d, J ¼ 4.7 Hz, 1H), 2.11 (d, J ¼ 60.0 Hz, 12H). 13
C
was stirred at room temperature for 24 h. Aer reaction, the NMR (100 MHz, CDCl3) d (ppm): 172.53, 171.91, 170.96, 166.65,
resulting mixture was poured into water and extracted with 153.08, 153.07, 152.95, 152.53, 152.10, 149.62, 149.60, 147.10,
ethyl acetate. The organic phase was combined, washed with 139.33, 137.95, 136.82, 136.29, 134.46, 133.73, 133.25, 132.59,
brine, dried over anhydrous magnesium sulfate and ltered. 132.33, 127.93, 127.63, 126.03, 126.01, 125.88, 125.07, 124.89,
The solvent was completely removed and the residue was 124.44, 123.98, 121.80, 113.02, 112.34, 16.77. MS: (MALDI-TOF)
puried by column chromatography over silica gel to give L4 as m/z: 979.8 [M + 2H]+.
1
ꢁ
a light yellow crystal. Yield: 58.6%. m.p.: 182–183 C. H NMR
Ir4. 59.7% yield, red solid. 1H NMR (400 MHz, DMSO)
(400 MHz, DMSO) d (ppm): 7.82 (d, J ¼ 8.3 Hz, 1H), 7.71 (t, J ¼ d (ppm): 8.33 (d, J ¼ 8.6 Hz, 1H), 8.01 (m, 1H), 7.88 (d, J ¼ 4.8 Hz,
7.6 Hz, 1H), 7.64 (d, J ¼ 5.0 Hz, 1H), 7.57–7.50 (m, 1H), 7.40 (t, J 1H), 7.83 (dd, J ¼ 4.5, 4.0 Hz, 1H), 7.79–7.66 (m, 1H), 7.53–7.38
¼ 7.7 Hz, 4H), 7.31–7.14 (m, 8H), 7.11–7.05 (m, 1H). 13C NMR (m, 10H), 7.36–7.14 (m, 15H), 7.12–6.92 (m, 3H), 6.76–6.67 (m,
(100 MHz, CDCl3) d (ppm): 163.01, 156.95, 153.43, 146.99, 1H), 6.40 (d, J ¼ 4.8 Hz, 1H), 6.07 (d, J ¼ 4.7 Hz, 1H). 13C NMR
144.28, 132.63, 129.41, 129.35, 128.82, 128.66, 127.96, 126.51, (100 MHz, CDCl3) d (ppm): 172.68, 172.67, 170.73, 170.02,
126.21, 125.47, 124.94, 116.58.
163.44, 163.37, 153.13, 152.42, 151.32, 147.56, 146.40, 146.38,
General procedure for the preparation of iridium complexes 139.35, 137.55, 136.78, 134.58, 133.87, 132.64, 132.54, 131.95,
Ir1–Ir4. Ln (n ¼ 1–4, 0.84 mmol, 3 equiv.) and hydrated iridiu- 130.90, 129.48, 129.45, 127.01, 126.68, 126.16, 126.10, 114.53,
m(III) chloride (0.10 g, 0.28 mmol, 1 equiv.) were added in 113.97. MS: (MALDI-TOF) m/z: 1073.9 [M + 2H]+.
a mixture of 2-ethoxyethanol (9 mL) and distilled water (3 mL).
The mixture was stirred at 100 ꢁC for 24 h under nitrogen. Aer
cooled to room temperature, the precipitate was collected by
Acknowledgements
ltration and washed with water and ethanol. Subsequently, the The authors acknowledge nancial support from the National
cyclometalated Ir(III) m-chloride bridged dimer was dried under Basic Research Program of China (973 Program, 2012CB933301,
vacuum to afford a red solid. Cyclometalated Ir(III) m-chloride 2012CB723402), the Ministry of Education of China(IRT1148),
bridged dimer (0.025 mmol, 1 equiv.), 2-picolinic acid (0.25 the National Natural Science Foundation of China (BZ2010043,
mmol, 10 equiv.), K2CO3 (0.25 mmol, 10 equiv.) and DCM (25 21572001, 20974046, 20774043, 51173081, 50428303,
mL) were mixed in a round-bottom ask then stirred at room 61136003), the Priority Academic Program Development of
temperature for 8 h. Aer reaction, the mixture solution was Jiangsu Higher Education Institutions (PAPD, YX03001),
washed with deionized water and then extracted with DCM. The Synergetic Innovation Center for Organic Electronics and
organic extracts were collected and dried over Na2SO4. The Information Displays, Natural Science Foundation of Jiangsu
crude product was puried by column chromatography over Province, China (BM2012010), the Specialized Research Fund
This journal is © The Royal Society of Chemistry 2015
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for the Doctoral Program of Higher Education (SRFDP) 11 Q. Mei, L. Wang, Y. Guo, J. Weng, F. Yan, B. Tian and
(20113223110005), Jiangsu Planned Projects for Postdoctoral B. Tong, J. Mater. Chem., 2012, 22, 6878.
Research Funds(1402010B) and the Research Fund for Nanjing 12 Y. Fang, S. J. Hu, Y. Z. Meng, J. B. Peng and B. Wang, Inorg.
University of Posts and Telecommunications (NY213177).
Chim. Acta, 2009, 362, 4985; J. S. Parka, M. K. Songa, Y. S. Gal,
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13 J. S. Parka, M. K. Songa, Y. S. Gal, J. W. Lee and S. H. Jin,
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97848 | RSC Adv., 2015, 5, 97841–97848
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