Synthesis, photophysical and electrochemical properties of aza-boron-diquinomethene complexes

Article abstract of DOI:10.1016/j.dyepig.2013.05.009

A series of aza-boron-diquinomethene (aza-BODIQU) complexes with different aryl-substituents (B1-B6) were synthesized and characterized. Their photophysical properties were investigated systematically via spectroscopic and theoretical methods. All complexes exhibit strong ¹π-π* absorption bands and intense fluorescent emission bands in the visible spectral region at room temperature. The fluorescence spectra in solution show the mirror image features of the S₀→S₁ absorption bands, which can be assigned to the ¹π-π*/¹ICT (intramolecular charge transfer) emitting states. Except for B6, all complexes exhibit high photoluminescence quantum yields (Φ_PL = 0.47-0.93). The spectroscopic studies and theoretical calculations indicate that the photophysical properties of these aza-BODIQUs can be tuned by the appended aryl-substituents, which would be useful for rational design of boron-fluorine complexes with high emission quantum yield for organic light-emitting applications.

Full text of DOI:10.1016/j.dyepig.2013.05.009

Accepted Manuscript
Synthesis, photophysical and electrochemical properties of aza-boron-
diquinomethene complexes
Danfeng Wang, Rui Liu, Chen Chen, Shifan Wang, Jin Chang, Chunhui Wu, Hongjun
Zhu, Eric R. Waclawik
PII:
S0143-7208(13)00174-5
10.1016/j.dyepig.2013.05.009
DYPI 3946
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 26 March 2013
Revised Date: 3 May 2013
Accepted Date: 11 May 2013
Please cite this article as: Wang D, Liu R, Chen C, Wang S, Chang J, Wu C, Zhu H, Waclawik ER,
Synthesis, photophysical and electrochemical properties of aza-boron-diquinomethene complexes, Dyes
and Pigments (2013), doi: 10.1016/j.dyepig.2013.05.009.
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1.2
1.0
0.8
0.6
0.4
0.2
0.0
N
B
B1
B2
B3
B4
B5
N
F
N
F
R
B6
B1-B6
R
B1, R= H, B2, R= t-Bu, B3, R= CF3, B4, R= NO2
B5, R=
N
B6, R=
N
400
450
500
550
600
650
Wavelength (nm)
Abstract: A series of aza-boron-diquinomethene complexes B1-B6 exhibit sharp absorption and
emission bands with high photoluminescence quantum yields (ΦPL = 0.47 - 0.93).

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Highlights
Our work succeeds in synthesizing a series of aza-boron-diquinomethene complexes.
These complexes show high fluorescence quantum yields and thermal stability.
Optical, electrochemical properties and DFT calculations were investigated.
These complexes are expected to be promising light-emitting materials in OLEDs.

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Synthesis, photophysical and electrochemical properties of
aza-boron-diquinomethene complexes
Danfeng Wanga, Rui Liua, Chen Chena, Shifan Wanga, Jin Changb, Chunhui Wua,
Hongjun Zhua*, Eric R. Waclawikb
a
Department of Applied Chemistry, College of Science, Nanjing University of
Technology, Nanjing 210009, P. R. China
b
Discipline of Chemistry, Queensland University of Technology, 2 George St.,
Brisbane 4000, Australia
*Corresponding author. Phone: +86-25-83172358. Fax: +86-25-83587428. E-mail:
zhuhj@njut.edu.cn
1

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ABSTRACT
A series of aza-boron-diquinomethene (aza-BODIQU) complexes with different
aryl-substituents (B1-B6) were synthesized and characterized. Their photophysical
properties were investigated systematically via spectroscopic and theoretical methods.
1
All complexes exhibit strong π-π* absorption bands and intense fluorescent emission
bands in the visible spectral region at room temperature. The fluorescence spectra in
solution show the mirror image features of the S0→S1 absorption bands, which can be
1
assigned to the π-π*/1ICT (intramolecular charge transfer) emitting states. Except for
B6, all complexes exhibit high photoluminescence quantum yields (ΦPL = 0.47-0.93).
The spectroscopic studies and theoretical calculations indicate that the photophysical
properties of these aza-BODIQUs can be tuned by the appended aryl-substituents,
which would be useful for rational design of boron-fluorine complexes with high
emission quantum yield for organic light-emitting applications.
Keywords:
Fluorescence; Synthesis; Optical properties; Electrochemical properties; Boron-fluorine
complexes; DFT calculations.
2

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1. Introduction
Boron dipyrromethene (BODIPY) complexes have attracted great interest in the past
two decades due to their potential applications in molecular probes, photodynamic
therapy, laser dyes, nonlinear optical materials and solar cells [1]. These various
applications are intrinsically based on their rich photophysical properties, such as
strong ground-state absorption, intense fluorescent emission, high photoluminescence
quantum yield and high chemical stability. In addition, their photophysical properties
can be readily tuned by structural modifications, which provide additional opportunities
to meet the different requirements for diverse applications.
In the past decade, the core structure of BODIPY has been modified and developed
into its aza-derivatives, such as aza-boron-dipyrromethene, aza-boron-diindolmethene,
aza-boron-dipyridomethene, aza-boron-diquinomethene, ect., as shown in Scheme 1 [2].
These complexes exhibit high photoluminescence quantum yields, good
electron-transporting property and excellent thermal stability, which could be utilized in
organic light emitting devices (OLEDs) [3,4]. Compared to the traditional BODIPYs,
the pyridoamine-based BODIPY were first synthesized by Boyer and co-workers in
1993 [5], and then photophysically investigated by Jorge Bañuelos and co-workers in
2011 [6]. In many cases, the quinoline-based compounds show better electron mobility
than pyrrole and pyridine derivatives [7], suggesting that quinoline structure is also a
good candidate in the construction of boron-fluorine complexes. Recently, Kondakova
and co-workers reported an aza-boron-diquinomethene complex, which was utilized as
a deep blue fluorescent emitting material in the fabrication of white OLEDs (ηp,1000
=
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30 lm W-1) [8]. Although the results are intriguing, the investigation on the
aza-boron-diquinomethene is still limited. In order to improve the optical properties by
structural modification, understanding the structure-property correlation becomes
critical. Taking all these factors into consideration, the development of new BF2
complexes, the investigation of their photophysical properties and structure-property
relationships are still feasible, challengeable and potentially valuable.
In this work, we designed and synthesized a series of new BF2 complexes with
different aryl-substituents on the core structure. The synthetic routes and the structures
of the target complexes are displayed in Scheme 2. The t-Bu, -NPh2 and carbazolyl
groups were chosen as the electron-donating substituent and the NO2 and CF3 groups
were chosen as electron-withdrawing substituents. The photophysical and
electrochemical properties of these complexes were systematically investigated with the
aim of understanding the structure-property correlations and developing novel blue
light-emitting materials. Furthermore, a novel and versatile synthesis procedure for
symmetrical N-arylation of heteroarylamines with high efficiency and selectivity was
also developed.
2. Experimental section
2.1. Materials
All solvents and reagents for synthesis were purchased from Aldrich, TCI and
Sinopharm Chemical Regent Co. Ltd. and used as is unless otherwise stated.
Tetrahydrofuran (THF), toluene and N,N-diisopropylethylamine (DIEA) were distilled
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under N2 over sodium benzophenone ketyl. Tetra-n-butylammonium perchlorate
(TBAP) and ferrocene were purified by recrystallization twice from ethanol. The
related boronic acids were synthesized according to the literature procedures [9]. Silica
gel (200-300 mesh) used for chromatography was purchased from Sinopharm Chemical
Reagent Co. Ltd.
2.2. Measurements
1H NMR and 13C NMR spectra were recorded on a Bruker 300 MHz or 400 MHz
spectrometer using DMSO-d6 or CDCl3 as the solvent. Chemical shifts were referred to
the internal standard tetramethylsilane (TMS). 19F NMR spectra were recorded at room
temperature with CFCl3 as internal standard at 376 MHz. Melting points (m.p.) were
taken on an X-4 microscope electrothermal apparatus (Taike China). The elemental
analyses were performed with a Vario El III elemental analyzer. Mass spectra were
obtained on a VG12-250 mass spectrometer and an Agilent 1100 mass spectrometer.
UV-Vis spectra were recorded using an HP-8453 UV/Vis/near-IR spectrophotometer
(Agilent) with a 1 cm quartz cell. Photoluminescence spectra were carried out on a
LS-55 spectrofluorometer (Perkin-Elmer). Photoluminescence quantum yields were
carried out on a LFS920 spectrofluorometer (Edinburgh). Electrochemical experiments
were carried out using a CHI 660C electrochemistry workstation (CHI-USA). A
standard one-compartment three-electrode cell was used with a Pt electrode as the
working electrode, a Pt wire as the counter electrode and an Ag/AgNO3 electrode (Ag
in 0.1 M AgNO3 solution) as the reference electrode. TBAP (0.1 M) was used as the
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supporting electrolyte. The scan rate was 100 mV S-1. Differential scanning calorimetry
(DSC) was conducted on a DSC instruments (NETZSCH DSC 204).
2.3. DFT calculations
Quantum chemical calculations were performed for complexes B1-B6, in order to
understand the nature of the ground state and the low-lying excited states. All
calculations were conducted at the DFT level of theory, in conjunction with the B3LYP
functional [10] and the 6-31G* basis set [11], as implemented in the Gaussian 09
program package [12]. In this work, geometry optimization and the frontier molecular
orbitals were simulated for each of the compound.
2.4. Synthesis
2.4.1. Synthesis of 6-bromoquinoline (1)
Glycerol (60.0 mL, 0.82 mol), FeSO4·7H2O (7.00 g, 0.025 mol), p-bromoaniline
(34.40 g, 0.20 mol), and nitrobenzene (12.5 mL, 0.13 mol) were added to a
three-necked round bottom flask with mechanical stirring. H2SO4 (35.0 mL, 0.64 mol)
was added to the system slowly while kept the temperature blow 100 °C. The mixture
was then heated to reflux for 20 h. After cooling to r.t., adjusted pH to 7 with 50%
NaOH aq. solution and extracted with diethyl ether. The extraction was dried over
MgSO4 and concentrated in vacuo. The product was isolated by reduced pressure
distillation. Fraction was collected at 138-140 °C, 16 torr (lit. [13] 161-162 °C, 22 Torr).
1
Light yellow liquid was afforded (11.90 g, 28.6% yield). H NMR (300 MHz,
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DMSO-d6) δ (ppm): 9.00 (d, J = 4.1 Hz, 1H), 8.37 (d, J = 8.3 Hz, 1H), 8.28 (d, J = 1.7
Hz, 1H), 8.02 (d, J = 9.2 Hz, 1H), 7.89 (dd, J1 = 9.0 Hz, J2 = 2.1 Hz, 1H), 7.62 (q, J =
8.3 Hz, 1H)
2.4.2. Synthesis of 6-bromoquinoline N-oxide (2)
M-chloroperoxybenzoic acid (m-CPBA) (5.07 g, 29.4 mmol) was added slowly to a
CH2Cl2 solution of 1 (6.00 g, 26.7 mmol) at r.t., then stirred overnight. The reaction
was filtered and the filtrate was treated with saturated NaHCO3 solution until no CO2
gas yield. Then, adjusted pH = 10 with 3 N NaOH aq. solution and extracted with
CH2Cl2 50 mL three times. The solvent was removed under reduced pressure. The
crude product was then purified by silica gel column chromatography (2%
methanol/CH2Cl2). Pale yellow solid was afforded (4.00 g, 66.9% yield), m.p. 137-139
1
°C (lit. [14] 140-142 °C). H NMR (400 MHz, CDCl3) δ (ppm): 8.63 (d, J = 9.3 Hz,
1H), 8.55 (d, J = 6.0 Hz, 1H), 8.05 (d, J = 1.9 Hz, 1H), 7.83 (dd, J1 = 9.3 Hz, J2 = 2.0
Hz, 1H), 7.67 (d, J = 8.5 Hz, 1H), 7.34 (dd, J1 = 8.5 Hz, J2 = 6.0 Hz, 1H).
2.4.3. Synthesis of 2,6-dibromoquinoline (3)
To a round bottom flask was charged 6-bromoquinoline N-oxide (2) (1.27 g, 5.7
mmol) and sodium hydroxide (0.44 g, 11.0 mmol) in water (12.0 mL) and CH2Cl2 (6.0
mL), benzoyl chloride (8.5 mmol, 1.0 mL) was added slowly to the vigorously stirred
mixture [15]. A reflux was observed when the addition was nearly completed. Then the
flask was then cooled to 5 °C with ice-bath, and addition was resumed. After 1 h
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stirring, the precipitate was filtered off, rinsed well with water (50 mL) and CH2Cl2 (50
mL) respectively, then dried in the air, white product was obtained.
To a re-sealable Schlenk tube was charged the white product, POBr3 (2.20 g, 7.7
mmol, 1.5-2 equiv.) and dry toluene (5.0 mL) as the solvent under N2, heated to reflux
overnight. After cooling to r.t., the mixture was poured on ice, washed with saturated
NaHCO3 and extracted with CH2Cl2 several times. Remove the solvent under reduced
1
pressure. Off-white solid was afforded (1.16 g, 70.5% yield), m.p. 160-163 °C. H
NMR (400 MHz, CDCl3) δ (ppm): 7.99 (d, J = 2.1 Hz, 1H), 7.94 (t, J = 8.6 Hz, 2H),
7.82 (dd, J1 = 9.0 Hz, J2 = 2.1 Hz, 1H), 7.56 (d, J = 8.6 Hz, 1H).
2.4.4. Synthesis of 6-bromoquinolin-2-amine (4)
To a round bottom flask was charged 2 (2.24 g, 10.0 mmol, 1.0 equiv), 40 mL
trifluorotoluene and 20 mL chloroform under N2. After compound 2 was dissolved, the
mixture was cooled to 0-10 °C with an ice-bath. T-butylamine (5.3 mL, 50.0 mmol, 5.0
equiv) was added followed by Ts2O (6.50 g, 20.0 mmol, 2.0 equiv) while the
temperature was kept at 5-12 °C. If the reaction was not completed within 30 min,
portions of t-butylamine (0.6 equiv. to 4.0 equiv.) and Ts2O (0.3 equiv. to 2.3 equiv.)
would be charged until the reaction completed. The reaction was then treated with TFA
25 mL at 70 °C for 10 h. Most of the solvents could be removed under vacuum. The oil
residue was diluted with CH2Cl2 and quenched with 50% aq solution NaOH to pH 9-10.
The aqueous layer was extracted with CH2Cl2 (50 mL) three times. The combined
organic layers were dried with MgSO4. The solvent was removed by reduced pressure
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and the crude product was then purified by silica gel column chromatography (2%
MeOH/CH2Cl2) to give the desired 4 as a gray solid (1.75 g, 78.3% yield), m.p.
1
139-145 °C (lit. [16] 141-146 °C). H NMR (400 MHz, CDCl3) δ (ppm): 7.79 (d, J =
8.8 Hz, 1H), 7.76 (d, J = 2.2 Hz, 1H), 7.61 (dd, J1 = 8.9 Hz, J2 = 2.2 Hz, 1H), 7.52 (d, J
= 8.9 Hz, 1H), 6.73 (d, J = 8.8 Hz, 1H), 4.83 (s, 2H).
2.4.5. Synthesis of bis(6-bromoquinolin-2-yl)amine (5)
To a re-sealable Schlenk tube was charged with bis(2-diphenylphosphinophenyl)
ether (0.3016 g, 0.560 mmol, 4% mmol), 4 (3.28 g, 14.7 mmol), 2,6-diboromoquinoline
3 (4.00 g, 14.0 mmol), t-BuONa (1.88 g, 19.6 mmol), and degassed dry toluene (120
mL). The Schlenk tube was capped and carefully subjected to three cycles of
evacuation-backfilling with N2. Finally, Pd(OAc)2 (0.1258 g, 0.560 mmol, 4% mmol)
was added. It was then sealed and immersed into a 110 °C oil bath. After 5 h reflux, the
mixture was cooled to r.t., diluted with THF and ethyl ether, filtered, concentrated, and
purified by silica gel column chromatography (2% MeOH/CH2Cl2) to afford the
product. White solid (5.30 g, 88.2% yield), m.p. 237-238 °C. 1H NMR (400 MHz,
DMSO-d6) δ (ppm): 10.63 (s, 1H), 8.26 (s, 4H), 8.13 (d, J = 2.0 Hz, 2H), 7.81 – 7.72
(m, 4H). 13C NMR (101 MHz, CDCl3) δ (ppm): 152.63, 145.85, 137.08, 133.19, 129.56,
128.81, 126.08, 117.55, 114.84. TOF-MS (ES+) calcd. for C18H11Br2N3 [M + 1]+: 427.9,
found 428.1. Elemental analysis calcd. (%) for C18H11Br2N3: C, 50.38; H, 2.58; N, 9.79,
found C, 50.08; H, 2.53; N, 10.15.
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2.4.6. Synthesis of bis(6-phenylquinolin-2-yl)amine (8a)
To a round bottom flask was charged 5 (1.00 g, 2.3 mmol), K2CO3 (0.63 g, 4.6 mmol),
Pd(dppf)2Cl2 (0.0673 g, 0.0920 mmol, 0.4% mol), benzeneboronic acid 6a (0.85 g, 7.0
mmol) [17]. The flask was capped and carefully subjected to three cycles of
evacuation-backfilling with N2. A degassed solution of dioxane/H2O (3:1 v/v) 10 mL
was then injected to the system and heated to reflux with oil bath for 12 h. After cooling
to r.t., it was diluted with CH2Cl2 (100 mL) and filtered. The filtration was then dried
with Na2SO4 and the solvent was removed under reduced pressure. The crude product
was purified by silica gel column chromatography (2% MeOH/CH2Cl2). White solid
was afforded (0.91 g, 93.2% yield), m.p. 249-255 °C. 1H NMR (400 MHz, DMSO-d6) δ
(ppm): 10.58 (s, 1H), 8.33 (dd, J1 = 22.7 Hz, J2 = 9.0 Hz, 4H), 8.18 (d, J = 2.1 Hz, 2H),
8.02 (dd, J1 = 8.7 Hz, J2 = 2.1 Hz, 2H), 7.89 (d, J = 8.7 Hz, 2H), 7.82 (d, J = 7.2 Hz,
4H), 7.53 (t, J = 7.7 Hz, 4H), 7.40 (t, J = 7.4 Hz, 2H). 13C NMR (101 MHz, DMSO-d6)
δ (ppm): 153.32, 146.12, 137.92, 135.19, 129.02, 128.64, 127.35, 127.04, 126.71,
125.12, 124.71, 114.82. TOF-MS (ES+) calcd. for C30H21N3 [M + 1]+: 424.2, found
424.2. Elemental analysis calcd. (%) for C30H21N3: C, 85.08; H, 5.00; N, 9.92, found C,
85.34; H, 4.79; N, 9.87.
2.4.7. Synthesis of bis(6-(4-(tert-butyl)phenyl)quinolin-2-yl)amine (8b)
Compound 8b was synthesized according to the method described for compound 8a.
1
Yellow solid was afforded, the yield was 90.5%, m.p. > 300 °C. H NMR (400 MHz,
CDCl3) δ (ppm): 8.16 (d, J = 8.9 Hz, 1H), 8.05 (d, J = 8.9 Hz, 1H), 7.93 (s, 3H), 7.67 (d,
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J = 8.3 Hz, 2H), 7.52 (d, J = 8.4 Hz, 2H), 1.39 (s, 9H). TOF-MS (ES+) calcd. for
C38H37N3 [M - t-BuPh + 1]+: 404.2, found 404.2. Elemental analysis calcd. (%) for
C38H37N3: C, 85.19; H, 6.96; N, 7.84, found C, 85.23; H, 7.00; N, 7.77.
2.4.8. Synthesis of bis(6-(4-(diphenylamino)phenyl)quinolin-2-yl)amine (8c)
Compound 8c was synthesized according to the method described for compound 8a.
1
Red solid was afforded, the yield was 88.7%, m.p. 278-279 °C. H NMR (400 MHz,
DMSO-d6) δ (ppm): 10.52 (s, 1H), 8.35 – 8.21 (m, 4H), 8.10 (d, J = 1.9 Hz, 2H), 7.96
(dd, J1 = 8.8 Hz, J2 = 2.0 Hz, 2H), 7.83 (d, J = 8.8 Hz, 2H), 7.73 (d, J = 8.7 Hz, 4H),
7.38 – 7.27 (m, 8H), 7.05-7.09 (m, 16H). 13C NMR (101 MHz, CDCl3) δ (ppm): 152.56,
147.66, 147.29, 146.23, 138.18, 136.28, 134.42, 129.33, 129.12, 127.84, 127.29,
125.23, 124.61, 124.48, 123.99, 123.02, 114.46. TOF-MS (ES+) calcd for C54H39N5 [M
- C27H19N2 + 1]+: 387.2, found 387.1. Elemental analysis calcd. (%) for C54H39N5: C,
85.57; H, 5.19; N, 9.24, found C, 85.32; H, 5.14; N, 9.39.
2.4.9. Synthesis of difluoro-boron complex of bis(6-bromoquinolin-2-yl)amine (7)
To a three-necked round bottom flask was charged 5 (1.40 g, 3.3 mmol) and dry
toluene under N2. DIEA (1.6 mL, 9.9 mmol) was slowly injected to the toluene solution.
After 10 minutes’ stirring, BF3·Et2O (3.5 mL, 13.2 mmol) was injected dropwise to the
solution. The reaction was then refluxed overnight. After cooling to room temperature,
the precipitate was filtered off and dried in air for 2 h. The precipitate was added into
100 mL water and stirred for 30 min, adjusted pH to 7 with saturated NaHCO3. Filtrated
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and dried in the air for 2 h, washed with diethyl ether and isopropyl ether respectively
to give the crude product. It was then purified by silica column chromatography
1
(CH2Cl2) to afford 7 as a yellow solid (1.27 g, 80.6% yield), m.p. > 300 °C. H NMR
(400 MHz, DMSO-d6) δ (ppm): 8.40 – 8.31 (m, 2H), 8.29 (d, J = 2.3 Hz, 1H), 8.00 (dd,
J1 = 9.3 Hz, J2 = 2.4 Hz, 1H), 7.35 (d, J = 9.1 Hz, 1H). 19F NMR (376 MHz, DMSO-d6)
δ (ppm): -125.14 (q, JB,F = 75.2 Hz). TOF-MS (ES+) calcd for C18H10BBr2F2N3 [M - Br2
+ 1]+: 318.09, found 318.3. Elemental analysis calcd. (%) for C18H10BBr2F2N3: C,
45.33; H, 2.11; N, 8.81, found C, 45.36; H, 2.35; N, 8.50.
2.4.10. Synthesis of difluoro-boron complex of bis(6-phenylquinolin-2-yl)amine (B1)
Complex B1 can be synthesized from both of the two synthetic routes, one described
for 8a via a boron complexation with complex 7 and the other described for 7 via a
Suzuki coupling with 8a, as shown in Scheme 2. In comparison, route 2 shows a higher
overall yield (80.1%) with more synthetic steps, while route 1 exhibits a more
straightforward way to obtain the target products. B1 was obtained as bright yellow
1
solid, the yield was 75.6% (route 1) and 80.1% (route 2), m.p. 269-270 °C. H NMR
(400 MHz, CDCl3) δ (ppm): 8.72 (d, J = 9.1 Hz, 1H), 8.08 (d, J = 9.1 Hz, 1H), 7.99 (dd,
J1 = 9.1 Hz, J2 =2.1 Hz, 1H), 7.89 (d, J = 2.0 Hz, 1H), 7.70 (d, J = 7.3 Hz, 2H), 7.51 (t,
J = 7.6 Hz, 2H), 7.41 (t, J = 7.3 Hz, 1H), 7.24 (d, J = 9.1 Hz, 1H). 13C NMR (101 MHz,
CDCl3) δ (ppm): 154.09, 140.73, 139.54, 137.94, 137.70, 130.37, 129.04, 127.83,
127.17, 126.04, 125.07, 123.11, 122.26. 19F NMR (376 MHz, CDCl3) δ (ppm): -126.54
(q, JB,F = 75.2 Hz). TOF-MS (ES+) calcd. for C30H20BF2N3 [M + 1]+: 472.2, found
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472.1. Elemental analysis calcd. (%) for C30H20BF2N3: C, 76.45; H, 4.28; N, 8.92,
found C, 76.37; H, 4.42; N, 8.90.
2.4.11. Synthesis of difluoro-boron complex of bis(6-(4-(tert-butyl)phenyl)quinolin-
2-yl)amine (B2)
Complex B2 was synthesized according to the method described for complex B1.
Bright yellow solid, the yield was 72.3% (route 1) and 83.1% (route 2) respectively,
m.p. > 300 °C. 1H NMR (400 MHz, CDCl3) δ (ppm): 8.70 (d, J = 9.0 Hz, 1H), 8.05 (d,
J = 9.1 Hz, 1H), 7.99 (dd, J1 = 9.1 Hz, J2 =2.1 Hz, 1H), 7.87 (d, J = 2.0 Hz, 1H), 7.64
(d, J = 8.3 Hz, 2H), 7.53 (d, J = 8.4 Hz, 2H), 7.21 (d, J = 9.0 Hz, 1H), 1.39 (s, 9H). 19F
NMR (376 MHz, CDCl3) δ (ppm): -126.59 (q, JB,F = 71.4 Hz). HR-MS-ESI+ calcd. for
C38H36BF2N3 [M + 1]+: 584.2970, found 584.3054. Elemental analysis calcd. (%) for
C38H36BF2N3: C, 78.22; H, 6.22; N, 7.20, found C, 78.13; H, 6.31; N, 7.15.
2.4.12 Synthesis of difluoro-boron complex of bis(6-(4-(trifluoromethyl)phenyl)
quinolin-2-yl)amine (B3)
Complex B3 was synthesized according to the method described for compound 8a
using 7 and 6c as reactants. Bright yellow solid, the yield was 85.6%, m.p. > 300 °C. 1H
NMR (400 MHz, CDCl3) δ (ppm): 8.75 (d, J = 9.2 Hz, 1H), 8.11 (d, J = 9.0 Hz, 1H),
7.99 (dd, J1 = 9.0 Hz, J2 =2.1 Hz, 1H), 7.93 (d, J = 1.9 Hz, 1H), 7.79 (dd, J1 = 18.5 Hz,
J2 = 8.3 Hz, 4H), 7.29 (s, 1H). 19F NMR (376 MHz, CDCl3) δ (ppm): -126.35 (q, JB,F
=
71.4 Hz). HR-MS-ESI+ calcd. for C32H18BF8N3 [M + 1]+: 608.1466, found 608.1546.
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Elemental analysis calcd. (%) for C32H18BF8N3: C, 63.29; H, 2.99; N, 6.92, found C,
63.38; H, 3.21; N, 6.64.
2.4.13 Synthesis of difluoro-boron complex of bis(6-(4-nitro)phenyl)quinolin-2-yl)
amine (B4)
Complex B4 was synthesized according to the method described for compound 8a
using 7 and 6d as reactants. Bright yellow solid, the yield was 67.6%, m.p. > 300 °C.
1
This complex exhibits poor solubility in many solvents, which makes it hard to get H
NMR. Elemental analysis calcd. (%) for C30H18BF2N5O4: C, 64.19; H, 3.23; N, 12.48,
found C, 64.78; H, 3.07; N, 12.66.
2.4.14 Synthesis of difluoro-boron complex of bis(6-(4-(9H-carbazol-9-yl)phenyl)
quinolin-2-yl)amine (B5)
Complex B5 was synthesized according to the method described for compound 8a
using 7 and 6e as reactants. Bright yellow solid, the yield was 78.1%, m.p. > 300 °C. 1H
NMR (400 MHz, DMSO-d6) δ (ppm): 8.63 (d, J = 9.2 Hz, 1H), 8.52 (d, J = 9.1 Hz, 1H),
8.49 (d, J = 2.1 Hz, 1H), 8.36 (dd, J1 = 9.2 Hz, J2 = 2.2 Hz, 1H), 8.30 (d, J = 7.8 Hz,
2H), 8.18 (d, J = 8.5 Hz, 2H), 7.84 (d, J = 8.5 Hz, 2H), 7.56 – 7.45 (m, 4H), 7.40 (d, J =
9.1 Hz, 1H), 7.36 – 7.29 (m, 2H). 19F NMR (376 MHz, DMSO-d6) δ (ppm): -125.04 (q,
JB,F = 75.2 Hz). Elemental analysis calcd. (%) for C54H34BF2N5: C, 80.90; H, 4.27; N,
8.74, found C, 80.79; H, 4.35; N, 8.77.
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2.4.15 Synthesis of difluoro-boron complex of bis(6-(4-(diphenylamino)phenyl)
quinolin-2-yl)amine (B6)
Complex B6 was synthesized according to the method described for complex B1.
1
Orange solid, the yield was 73.8% (route 1), 78.0% (route 2), m.p. 264-267 °C. H
NMR (400 MHz, DMSO-d6) δ (ppm): 8.64 (d, J = 9.1 Hz, 1H), 8.56 (d, J = 8.8 Hz, 1H),
8.39 (d, J = 1.9 Hz, 1H), 8.28 (dd, J1 = 9.3 Hz, J2 = 1.9 Hz, 1H), 7.80 (d, J = 8.7 Hz,
2H), 7.48 (d, J = 9.1 Hz, 1H), 7.36 (t, J = 7.9 Hz 4H), 7.09 – 7.13 (m, 8H). 19F NMR
(376 MHz, DMSO-d6) δ (ppm): -125.12 (q, JB,F = 82.7 Hz). Elemental analysis calcd.
(%) for C54H38BF2N5: C, 80.50; H, 4.75; N, 8.69, found C, 80.60; H, 4.35; N, 8.86.
3. Results and discussion
3.1. Synthesis and characterization
Scheme 2 outlines the synthetic route for complexes B1-B6. The boronic acids
(6a–6f) were synthesized according to the literature procedures [9]. Both intermediates
3 and 4 were prepared from compound 2 respectively, in which compound 4 was
obtained via a two-step-synthesis involving a procedure of t-butyl protection and
deprotection. In addition, when the mixture of trifluorotoluene/CHCl3 (2:1 v/v) was
used as solvent instead of trifluorotoluene in the synthetic procedure of 4, the yield
increased from 47.3% to 73.5%. The intermediate bis(6-bromoquinolin-2-yl)amine (5)
was tried to synthesized by using quinoline N-oxide as starting material, then tosylation
by 4-toluene sulfonyl chloride (TsCl) and aimination by ammonia gas to afford the
desired product. This is supposed to be the simplest method to obtain diquinolinamine
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derivatives, which was reported by Couturier and co-workers [18] in 2006 (Scheme S1).
However, no target product but 2-hydroxyquinoline was afforded in 73.6% yield in this
work. Although other quinoline N-oxides derivatives were attempted as starting
materials, 2-hydroxyquinoline derivatives were obtained. Finally, as shown in Scheme
2, compound 5 was synthesized by 3 and 4 in the presence of Pd-catalyst and t-BuONa
in 88.2% yield.
As shown in Scheme 2, two different synthetic routes (route 1 and route 2) could be
utilized to prepare the target complexes (B1-B6), depending on the designed
substituents on the aza-BODIQU moiety and the reaction sequence of Suzuki coupling
and boron complexation. In comparison, route 2 exhibits a higher overall yield for B1,
B2 and B6 than route 1. However, in terms of versatile synthesis of the target
complexes, route 1 takes less intermediates, which is approved a better synthetic route
for all complxes. In addition, the final complexation step was achieved via modified
procedure reported by Bañuelos and co-workers [6]. The crude product was purified by
washing with water, diethyl ether and isopropyl ether, respectively. All complexes
(B1–B6) are air-stable and soluble in CH2Cl2, CHCl3, acetone, tetrahydrofuran, DMF
1
and dimethyl sulfoxide. H NMR, 19F NMR and elemental analyses confirmed the
proposed structures for all complexes except B4, due to its poor solubility. 13C NMR
data was not obtained due to the poor solubility of this sample, although different
solvents were attempted.
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3.2. Thermal properties
The thermal properties of aza-boron-diquinomethene B1-B6 were investigated by
differential scanning calorimetry (DSC) analyses, shown in Table 1. Complexes B1-B6
are thermally stable and lack any detectable phase transitions from 50 °C to 230 °C (Fig.
S7). Compared with other complexes in this series, the Tg and Tm of B2 and B4 were
not observed in the scan scale from 50 °C to 400 °C, which indicating their robust
thermal stability at this temperature range. Furthermore, complex B2 exhibits
interesting exothermic peak which may result from the crystallizing progress while
others exhibit endothermic peaks. All these complexes exhibit good thermal stability
with high glass transition temperatures (> 187 °C) and melt transitions temperatures (>
257 °C), which is required for the thermal stability of the OLED devices.
3.3. Electronic absorption
The UV-Vis absorption of B1-B6 obeys Lambert-Beer’s law in the concentration
range studied (2×10-5 - 2×10-7 mol L-1) in CH2Cl2, suggesting that no dimerization or
oligomerization occurs within this concentration range in CH2Cl2. The UV-Vis
absorption and emission spectra of B1-B6 in CH2Cl2 and in the solid state are shown in
Fig. 1 and Fig. 2, respectively. The photophysical parameters are summarized in Table
2. As shown in Fig. 1 and Table 2, complexes B1-B5 show sharp and strong absorption
(ε = 5.6 × 104 to 8.2 × 104 L mol-1 cm-1) in the range of 401 nm to 457 nm in CH2Cl2
solution, while complex B6 shows a relatively broad band (ε = 2.5 × 104 L mol-1 cm-1)
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1
at 471 nm. The absorption bands of B1-B5 can be assigned to the π-π* transition
localized on the conjugated aromatic rings, considering their intense and structured
absorption bands and minor solvatochromic effect (Fig. S2). The bathochromically shift
1
in complex B6 could be attributed to a π-π* mixed intramolecular charge transfer
(1ICT) transition, which is originated from the appended strong electron-donating NPh2
substituents to the central aza-BODIQU component. Compared to the ground-state
absorption of difluoro-boron-triaza-anthracene (BTAA) [6] (i.e. the parent complex),
complexes B1-B6 with different substituents exhibit a significant increase of the
1
absorption coefficients and the π-π* transition bands bathochromically shift. The
1
minor solvent effect (in Supporting information, Fig. S2) also supports the π-π*
assignment for their absorption bands. In addition, compared with the absorption
spectra in solution, broader absorption bands with significant bathochromic shifts are
observed in the solid state (Fig. 2 and Table 2). This could be attributed to the
molecular stacking in the solid state, which suggests an increased conjugation length in
their solid state due to the π-stacking of the planar conformations of
aza-boron-diquinomethene. The assignment of the absorption band is also supported by
the density functional theory (DFT) and time-dependent density function theory
(TDDFT) calculations, which will be discussed in the following section.
3.4. Theoretical calculations
The ground-state electron density distribution of the HOMO (highest occupied
molecular orbital) and LUMO (lowest unoccupied molecular orbital) are illustrated in
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Fig. 3. The HOMO-LUMO energy differences (energy band gaps, calculated Egcal) are
presented in Table 3. Due to the nearly coplanar geometry, the π-electrons in the
HOMO of B1-B6 are delocalized over the entire molecule backbone, offering effective
orbital interactions among the stacked π-systems, while their LUMOs are mainly
localized on the aza-BODIQU moieties. Therefore, the HOMOꢀLUMO transition that
is the dominant contributing configuration to the S1 state in B1-B6 should be ascribed
1
to a mixture of π-π* and ICT characters, which is consistent with their UV-Vis
absorption assignments. The results clearly demonstrate that strong electron-donating
substituent, such as NPh2 in B6, increases the energy level of HOMO more than that of
1
LUMO, thus the HOMO-LUMO gap decreases, causing a red-shift of the π-π*/ICT
band. This trend follows that observed from the UV-Vis absorption measurement.
Compared to B1, when electron-withdrawing substituents such as CF3 and NO2 groups
are introduced on the phenyl ring in B3 and B4, their HOMOs and LUMOs are almost
delocalized on the whole molecule. Meanwhile, when the t-Bu, carbazolyl and NPh2 are
chosen as electron-donating substituents in B2, B5 and B6, their LUMOs are mainly
delocalized on the aza-BODIQU components. However, in the case of B5 and B6,
calculations indicate that ICT transition occurred from the carbazolyl and NPh2 groups
to their aza-BODIQU moieties. This could also explain the bathochromic shifts
observed in the absorption of B5 and B6 compared with other complexes, especially for
B6 bearing strong electron-donating substituents like NPh2 [19]. As is evident from
cal
Table 3, the trend of the predicted Eg values (3.17-3.70 eV) is in consistent with the
opt
estimated Eg
(energy band gaps, calculated from the ground-state absorption,
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2.45-2.70 eV) in Table 2.
3.5. Photoluminescence
The photoluminescence of complexes B1-B6 in different solvents were investigated
at room temperature. Their normalized emission spectra in CH2Cl2 at a concentration of
1 × 10-7 mol/L are illustrated in Fig. 1. The emission band maxima and quantum yields
are listed in Table 2. Excitations of these compounds at their respective absorption band
maximum at room temperature results in structured blue to green luminescence, as
shown in Fig. 1. The Stokes shifts of these compounds are quite small and the emission
lifetimes are in the nanosecond regime (Table 2). Taking these features into account,
1
we can assign the observed emission to the π-π* state. Furthermore, tailed spectra are
observed in the region of 500-550 nm. This indicates that their emission colors contain
more blue but less greenish component, which is desirable for the blue or blue-green
light emitting materials. It is noted that the emission of B6 is quite different from that
of other complexes, due to the ICT process [20] caused by the NPh2 substituent with
strong electron-donating ability. The significant bathochromic shift of B6 in both
absorption and emission spectra are observed, owning to the intra-molecular electron
push-pull effect.
The photoluminescence quantum yields (ΦPL) of the B1-B6 were measured in
CH2Cl2 solution, using compound 9,10-diphenylanthracene as standard (ΦPL = 0.97 in
cyclohexane solution) at r.t. [21]. All the complexes exhibit relatively high ΦPL in the
range of 0.47-0.93, except for complex B6 (ΦPL = 0.01). Their ΦPL in CH2Cl2 solution
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follow the trend of B1 > B2 > B5> B3 > B4 > B6, in which complex B1 exhibits the
highest photoluminescence quantum yield (ΦPL = 0.93). When the core structure was
substituted with either electron-withdrawing or electron-donating groups, the ΦPL of the
complexes decreased. Additionally, the complexes with electron-withdrawing
substituents exhibit ralative lower photoluminescence quantum yields compared to
those with electron-donating substituents. The emission quenching of B6 is induced by
the ICT process, due to the strong electron-donating effect of NPh2 substituent [20].
Solvent dependence study was performed in solvents with various polarities, such as
hexane, toluene, CH2Cl2, THF, acetonitrile and methanol (Fig. S2-3). The minor
solvatochromic effect and structured emission bands observed for B1-B5 indicate the
1π-π* dominated features of their emitting states. However, the emission bands of
complex B6 bathochromically shift to longer wavelengths in more polar solvents (i.e.,
CH2Cl2 and THF) compared to those in solvents with lower polarity (i.e., hexane and
toluene), as exemplified in Fig. 4. The drastic positive solvatochromic effect observed
in B6 but not in the other complexes should be attributed to the electron-donating
groups (NPh2), which enhances electron transfer from the symmetrical peripheral
chromophores to the aza-BODIQU motif. This feature is commonly seen from
compounds with charge transfer character, and also supported by the DFT calculation
results.
3.6. Electrochemical Properties.
The electrochemical properties of complex B1-B6 were determined by cyclic
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voltammetry (CV) in a mixed solvent of CH3CN/CH2Cl2 (7:3 v/v) at a scan rate of 100
mV s-1 using tetra-n-butylammonium perchlorate as supporting electrolyte. Potentials
were standarlized with ferrocene-ferrocenium (Fc/Fc+) couple as internal reference vs
Ag/AgNO3. The cyclic voltammograms of B1-B6 are illustrated in Fig. 5, and their
electrochemical properties are summarized in Table 4. As shown in Fig. 5, cyclic
voltammograms of B1-B6 all exhibit oxidation waves (0.58-1.07 V). However, the
electroreduction processes are observed only in B1, B3, B4, while reduction process do
not exist in electron-withdrawning substituted complexes (B2, B5, B6), it is thought
that the electronic factors on the aza-BODIQU moiety may be the main possible reason
for the less sensitivity of the reduction potentials [22]. Corresponding energy levels of
the HOMOs for B1-B6 are calculated from the onset of the oxidation peaks. Cyclic
voltammogram of B1 shows three electro-oxidation processes (0.70-1.63 V). Among
them, only B6 shows one reversible cathodic wave with a monoelectronic exchange,
which can be attributed to the oxidation of NPh2 substituents of aza-BODIQU to its
radical cation (B6/B6+•) [23]. As presented in Table 3, the calculated HOMO levels are
ranging from -5.28 ~ -5.61 eV and the LUMO energy levels were estimated in the
range of -2.63 ~ -2.95 eV, which are close to the LUMO level of AlQ3 (a widely used
electron transporting chelate and a green emitter, LUMO = 2.8 eV) [24]. These results
suggest that these complexes are potential electron-transporting (n-type) materials for
OLEDs.
4. Conclusions
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In summary, we present the synthesis of aza-boron-diquinomethene complexes
(B1-B6) and the symmetrical synthesis for aza-diquinomethene and its derivatives with
high efficiency and selectivity. Electron-donor and electron-acceptor were introduced
to the system and their thermal stabilities, photophysical properties, electrochemical
behaviors and theoretical calculations were investigated systematically. These materials
showed robust thermal stability with high glass transition temperatures (> 187 °C) and
melt transitions temperatures (> 257 °C). Absorption and emission spectra were
1
recorded in both CH2Cl2 solution and solid states. All complexes exhibit strong π-π*
absorption in the visible spectral region, while strong electron-donating substituent
NPh2 causes a red-shift of the 1ICT/1π-π* band. The assignment of the absorption bands
is supported by DFT calculations. All complexes exhibit intense blue to green
1π-π*/1ICT emission with relative high photoluminescence quantum yields (0.47-0.93),
except for B6 (ΦPL = 0.01). Their photoluminescence quantum yields follow the trend
of B1 > B2 > B5> B3 > B4 > B6. Moreover, these complexes show the low-lying
LUMO energy levels (-2.63 ~ -2.92eV), which is desirable for electron transfer. The
robust thermal stability, intense blue emission and relatively high photoluminescence
quantum yields suggest that these complexes could be promising candidates as organic
light-emitting materials.
Acknowledgment.
We greatly acknowledge the financial support in part by Postgraduate Innovation
Fund of Jiangsu Province (2011, CXZZ11_0366) and Innovation program of Shanghai
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institute of technical physics of the Chinese academy of sciences (2013, Q-DX-36,
Q-DX-37).
Supporting information
Synthetic route of diquinolinamines. Emission spectra of B1-B6 in the solid state and in
CH2Cl2 solution. Normalized absorption and emission spectra of B1-B6 in different
solvents. Absorption and emission spectra of B1-B6 in CH2Cl2 of different
concentrations. DSC thermograms of B1-B6. Detailed DFT and TDDFT calculation
results for B1-B6.
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References:
[1] (a) Loudet A, Burgess K. BODIPY dyes and their derivatives: syntheses and
spectroscopic properties. Chem Rev 2007;107:4891-932; (b) Boens N, Leen V, Dehaen
W. Fluorescent indicators based on BODIPY. Chem Soc Rev 2012;41:1130-72; (c)
Kamkaew A, Lim SH, Lee HB, Kiew LV, Chung LY, Burgess K. BODIPY dyes in
photodynamic therapy. Chem Soc Rev 2013;42:77-88; (d) Zhang ZY, Xu B, Su JH,
Shen LP, Xie YS, Tian H. Color-tunable solid-state emission of 2,2’-biindenyl-based
fluorophores. Angew Chem Int Ed 2011;50:11654-7. (e) Zhou Y, Xiao Y, Chi SM, Qian
XH. Isomeric boron-fluorine complexes with donor-acceptor architecture: strong
solid/liquid fluorescence and large stokes shift. Org Lett 2008;10:633-6; (f) Ulrich G,
Ziessel R, Harriman A. The chemistry of fluorescent BODIPY dyes: versatility
unsurpassed. Angew Chem Int Ed 2008;47:1184-201; (g) Ziessel R, Ulrich G, Harriman
A. The chemistry of BODIPY: a new El Dorado for fluorescence tools. New J Chem
2007;31:496-501; (h) Zhou Y, Xiao Y, Li D, Fu MY, Qian XH. Novel fluorescent
fluorine-boron complexes: synthesis, crystal structure, photoluminescence, and
electrochemistry properties. J Org Chem 2008;73:1571-4.
[2] (a) Poirel A, Nicola AD, Ziessel R. Oligothienyl-BODIPYs: red and near-infrared
emitters. Org Lett 2012;14:5696-9; (b) Gao L, Deligonul N, Gray TG. Gold(I)
complexes of brominated azadipyrromethene ligands. Inorg Chem 2012;51:7682-8; (c)
Kubota Y, Tsuzuki T, Funabiki K, Ebihara M, Matsui M. Synthesis and fluorescence
properties of a pyridomethene-BF2 complex. Org Lett 2010;12:4010-3; (d) Li HJ, Fu
WF, Li L, Gan X, Mu WH, Chen WQ, et al. Intense one- and two-photon excited
25

ACCEPTED MANUSCRIPT
fluorescent bis(BF2) core complex containing a 1,8-naphthyridine derivative. Org Lett
2010;12:2924-7; (e) Murtagh J, Frimannsson DO, O’Shea DF. Azide conjugatable and
pH responsive near-infrared fluorescent imaging probes. Org Lett 2009;11:5386-9; (f)
Adarsh N, Avirah RR, Ramaiah D. Tuning photosensitized singlet oxygen generation
efficiency of novel aza-BODIPY dyes. Org Lett 2010;12:5720-3; (g) Chibani S,
Guennic BL, Charaf-Eddin B, Maury O, Andraud C, Jacquemin D. On the computation
of adiabatic energies in aza-boron-dipyrromethene dyes. J Chem Theory Comput
2012;8:3303-13.
[3] (a) Sasabe H, Kido J. Multifunctional materials in high-performance OLEDs:
challenges for solid-state lighting. Chem Mater 2011;23:621-30; (b) Hayashi Y, Obata
N, Tamaru M, Yamaguchi S, Matsuo Y, Saeki A, et al. Facile synthesis of
biphenyl-fused BODIPY and its property. Org Lett 2012;14:866-9; (c) Li Y, Dolphin D,
Patrick BO. Synthesis of a BF2 complex of indol-2-yl-isoindol-1-ylidene-amine: a fully
conjugated azadipyrromethene. Tetrahedron Lett 2010;51:811-4; (d) Forgie JC, Skabara
PJ, Stibor I, Vilela F, Vobecka Z. New redox stable low band gap conjugated polymer
based on an EDOT-BODIPY-EDOT repeat unit. Chem Mater 2009;21:1784-6; (e) Hepp
A, Uirich G, Schmechel R, von Seggern H, Ziessel R. Highly efficient energy transfer
to a novel organic dye in OLED devices. Synth Met 2004;146:11-15.
[4] (a) Wen SW, Lee MT, Chen CH. Recent development of blue fluorescent OLED
materials and devices. J Disp Technol 2005;1:90-9; (b) Huang JH, Su JH, Tian H. The
development of anthracene derivatives for organic light-emitting diodes. J Mater Chem
2012;22:10977-89; (c) Yeh SJ, Wu MF, Chen CT, Song YH, Chi Y, Ho MH et al. New
26

ACCEPTED MANUSCRIPT
dopant and host materials for blue-light-emitting phosphorescent organic
electroluminescent devices. Adv Mater 2005;17:285-9.
[5] Sathyamoorthi G, Soong ML, Ross TW, Boyer JH. Fluorescent tricyclic
β-azavinamidine-BF2 complexes. Heteroat Chem 1993;4:603-8.
[6] Bañuelos J, Arbeloa FL, Martinez V, Liras M, Costela A, Moreno IG, et al.
Difluoro-boron-triaza-anthracene: a laser dye in the blue region. Theoretical simulation
of alternative difluoro-boron-diaza-aromatic systems. Phys Chem Chem Phys
2011;13:3437-45.
[7] (a) Ahmed E, Earmme T, Jenekhe SA. New solution-processable electron transport
materials for highly efficient blue phosphorescent OLEDs. Adv Funct Mater
2011;21:3889-99; (b) Tonzola CJ, Kulkarni AP, Gifford AP, Kaminsky W, Jenekhe SA.
Blue-light-emitting oligoquinolines: synthesis, properties, and high-efficiency
blue-light-emitting diodes. Adv Funct Mater 2007;17:863-74; (c) Tonzola CJ, Alam
MM, Bean BA, Jenekhe SA. New soluble n-type conjugated polymers for use as
electron transport materials in light-emitting diodes. Macromolecules 2004;37:3554-63;
(d) Tonzola CJ, Alam MM, Bean BA, Jenekhe SA. A new synthetic route to soluble
polyquinolines with tunable photophysical, redox, and electroluminescent properties.
Macromolecules 2005;38:9539-47.
[8] Kondakova ME, Deaton JC, Pawlik TD, Giesen DJ, Kondakov DY, Young RH, et al.
Highly efficient fluorescent-phosphorescent triplet-harvesting hybrid organic
light-emitting diodes. J Appl Phys 2010;107:014515-014515-13.
[9] (a) Wang KY, Chen C, Liu JF, Wang Q, Chang J, Zhu HJ, et al. Novel
27