Carbazolyl-substituted quinazolinones as high-triplet-energy materials for phosphorescent organic light emitting diodes

Article abstract of DOI:10.1016/j.dyepig.2017.03.066

A series of carbazolyl-substituted quinazolinones were designed and synthesized by the Pd-catalyzed Buchwald-Hartwig, Suzuki and Heck cross-coupling reactions. Their optical, photophysical, thermal, electrochemical, and electroluminescent properties were

Full text of DOI:10.1016/j.dyepig.2017.03.066

Accepted Manuscript
Carbazolyl-substituted quinazolinones as high-triplet-energy materials for
phosphorescent organic light emitting diodes
Dalius Gudeika, Dmytro Volyniuk, Viktorija Mimaite, Roman Lytvyn, Rita Butkute,
Oleksandr Bezvikonnyi, Gintaras Buika, Juozas V. Grazulevicius
PII:
S0143-7208(17)30200-0
10.1016/j.dyepig.2017.03.066
DYPI 5893
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 1 February 2017
Revised Date: 28 March 2017
Accepted Date: 29 March 2017
Please cite this article as: Gudeika D, Volyniuk D, Mimaite V, Lytvyn R, Butkute R, Bezvikonnyi O,
Buika G, Grazulevicius JV, Carbazolyl-substituted quinazolinones as high-triplet-energy materials
for phosphorescent organic light emitting diodes, Dyes and Pigments (2017), doi: 10.1016/
j.dyepig.2017.03.066.
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ACCEPTED MANUSCRIPT
Carbazolyl-substituted quinazolinones as high-triplet-energy materials for
phosphorescent organic light emitting diodes
Dalius Gudeika, Dmytro Volyniuk, Viktorija Mimaite, Roman Lytvyn, Rita Butkute,
Oleksandr Bezvikonnyi, Gintaras Buika, Juozas V. Grazulevicius
Graphical abstract
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Current density, mA/cm

ACCEPTED MANUSCRIPT
Carbazolyl-substituted quinazolinones as high-triplet-energy materials for
phosphorescent organic light emitting diodes
1
1
1
2
1
Dalius Gudeika , Dmytro Volyniuk , Viktorija Mimaite , Roman Lytvyn , Rita Butkute , Oleksandr
1
1
1*
Bezvikonnyi , Gintaras Buika , Juozas V. Grazulevicius
1
Department of Polymer Chemistry and Technology, Kaunas University of Technology, Radvilenu pl.
9, LT- 50254, Kaunas, Lithuania;
1
2
Ivan Franko National University of Lviv, Department of Organic Chemistry, 6 Kyryla & Mefodiya St,
UA-79005 Lviv, Ukraine
*
Corresponding author. E-mail address: juogra@ktu.lt (Juozas Vidas Grazulevicius)
Abstract
A series of carbazolyl-substituted quinazolinones were designed and synthesized by the Pd-catalyzed
Buchwald-Hartwig, Suzuki and Heck cross-coupling reactions. Their optical, photophysical, thermal,
electrochemical, and electroluminescent properties were investigated. The characterization of the
synthesized compounds was carried out using experimental and theoretical methods. The determined
geometries of the compounds lead to the HOMO distribution on the quinazolinone moiety and the
different donor substituents. The synthesized compounds form glasses with the glass transition
o
temperatures ranging from 97 to 159 C. Their solutions in tetrahydrofuran absorb electromagnetic
radiation in the range of 210-420 nm and emit in the range of 350-600 nm. The Stokes shifts recorded
for the dilute solutions of compounds ranged from 48 to 134 nm, while those observed for the solid
films were similarly in the range of 46-113 nm. The highest fluorescence quantum yield of 44.3% was
recorded for the solution of 3-(9-ethyl-9H-carbazol-3-yl)-5-((E)-2-(9-ethyl-9H-carbazol-3-yl)ethenyl)-
2
-methylquinazolin-4(3H)-one. The triplet energy levels established for the dilute solutions of the
1

ACCEPTED MANUSCRIPT
compounds from their phosphorescence spectra at 77 K were found to be in the range of 2.55-2.99 eV.
The ionization potentials of the synthesized compounds established by photoelectron emission
technique in air ranged from 5.35 to 5.66 eV. The electrochemical properties of the derivatives were
studied by cyclic voltammetry. All the studied compounds showed irreversible oxidation and no
reduction waves. Their repeated cyclic voltammetry scans displayed increasing changes in the cyclic
voltammetry traces, proving that a series of electro-polymerization reactions of the radical cations
occurred. Time-of-flight hole drift mobility of the solid layer of 5-(bis(4-tert-butyldiphenyl)amino)-3-
-
3
2
(
9-ethyl-9H-carbazol-3-yl)-2-methylquinazolin-4(3H)-one reached 1.1×10 cm /Vs at an electric field
5
of 8.1×10 V/cm. This compound was tested as a host in the green and blue phosphorescent organic
light emitting diodes achieving maximum external quantum efficiencies of ca. 7.1 and 6.9%,
respectively.
Keywords: quinazolinone, Buchwald-Hartwig, Suzuki, Heck reactions, organic light emitting diode,
electro-polymerization reaction.
1
. INTRODUCTION
Organic materials possessing extended π-conjugation received great attention in recent years
owing to their useful photophysical and charge transport properties, which make them potential
materials for the application in electronic and optoelectronic devices [1,2].
Much effort was devoted to establish structure-property relationships in order to develop new
materials with desired properties. Due to the electron-donating capabilities associated with the
nitrogen atom in the carbazole ring, derivatives of carbazole represent a very popular family of
functional organic compounds because of their interesting optical properties, low redox potentials,
high chemical and thermal stability, good charge-transporting properties [3,4]. Nitrogen atom of
2

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carbazole moiety can be functionalized by alkylation or arylation reactions to enhance the solubility
and to improve other properties of the resulting derivatives [5]. Many carbazole-containing molecules
are known to exhibit relatively intense luminescence and high glass transition temperatures [6,7]. For
these reasons they have been extensively investigated for the applications in optoelectronic devices
such as organic light-emitting diodes (OLEDs) and dye-sensitized solar cells. [8,9]. Carbazole can
also be easily functionalized by electrophilic aromatic substitution at its C-3, and C-6 positions with
high electron density, and hence a large number of 3,6-functionalized carbazole derivatives were
reported [10,11].
Quinazolinone derivatives were actively studied as they represent an important class of
compounds due to their wide range of intrinsic biological activities [12]. Use of quinazolinone
derivatives as semiconductors may potentially furnish capability of organic optoelectronic devices. To
our knowledge, no systematic study on structurally well-defined carbazole-quinazolinone systems
focusing on the effect of the connectivity between the carbazole and quinazolinone moieties on their
electronic, optical, photoelectrical, electrochemical, and electroluminescent properties was reported so
far. In this context, we became interested in 9-ethylcarbazolyl-substituted quinazolinone derivatives,
in which the number of different electron-donating groups (3,6-di-tert-butylcarbazole, 4,4’-
dimethoxydiphenylamine, 4,4’-di-tert-butyl-diphenylamine, 9-ethyl-3-vinyl-9H-carbazole, 2-(N-
methylcarbazol-3-yl)-4,4,5,5-tetramethyl-[1,3,2]-dioxaborolane) are linked at C-5 position of
quinazolinone moiety.
Here, we report on the synthesis of differently-substituted quinazolinones and on their thermal,
photophysical, photoelectrical, redox properties, and demonstrate the applicability of these materials
as hosts for phosphorescence organic light emitting diodes. Joint experimental and theoretical
aproaches are employed in order to characterize the synthesized derivatives, and to better understand
the structure-property relationships.
3

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2
. EXPERIMENTAL
2
.1. Materials and instrumentation
2
-Acetamido-5-bromobenzoic
acid,
4,4’-dimethoxydiphenylamine,
4,4’-di-tert-butyl-
tri-tert-
diphenylamine,
3-amino-9H-ethyl-carbazole,
9-ethyl-9H-carbazole-3-carbaldehyde,
butylphosphine solution (1.0 M in toluene), tri(o-tolyl)phosphine (P(o-tolyl) ), palladium(II) acetate
3
(Pd(OAc) ), bis(triphenylphosphine)palladium(II) (Pd(PPh ) Cl ), triethylamine, phosphoryl chloride
2 3 2 2
(
POCl ), potassium tert-butoxide, methyltriphenylphosphonium bromide (CH PPh ) were purchased
3
3
3
from Aldrich, TCI Europe, Acros and used without further purification. Solvents were dried and
purified by distillation.
o
o
3
,6-Di-tert-butyl-9H-carbazole (3a) [13] (m.p. 221-222 C, lit. [14] m.p. 228 C), 2-(N-
o
methylcarbazol-3-yl)-4,4,5,5-tetramethyl-[1,3,2]-dioxaborolane (3b) [15] (m.p. 143-144 C, lit. [15]
o
o
m.p. 150.6-151.8 °C), 9-ethyl-3-vinyl-9H-carbazole (3c) [16] (m.p. 62-63 C, lit. [17] m.p. 66-67 C)
were prepared according to the published procedures.
1
13
1
H and C NMR spectra were recordered using Varrian Unity Inova (300 MHz ( H), 75.4 MHz
1
3
(
C)) spectrometer at room temperature. Infrared (IR) spectra were recorded using Perkin Elmer
Spectrum GX spectrometer. Mass (MS) spectra were obtained on a Waters ZQ 2000 (Milford, USA).
Elemental analysis was performed with an Exeter Analytical CE-440 Elemental Analyser. Differential
scanning calorimetry (DSC) measurements were carried out using a Q100 TA DSC series thermal
o
analyzer at a heating rate of 10 C/min under nitrogen flow. Thermogravimetric analysis (TGA) was
e
performed on a Mettler Toledo TGA/SDTA 851 under nitrogen. Melting points were recorded on
Electrothermal MEL-TEMP melting point apparatus. UV absorption spectra were recorded on Perkin
Elmer Lambda 35 spectrometer. Fluorescence spectra were recorded with a Perkin Elmer LS 55 and
Edinburgh Instruments FLS980 spectrometers. Phosphorescence spectra were recorded on Edinburgh
Instruments FLS980 spectrometer at the temperature of liquid nitrogen (nominally 77 K).
4

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Fluorescence quantum yields (Φ ) of the solutions and solid films were carried out by absolute
F
method with FLS980 fluorescence spectrometer and using integrating sphere of 120 mm inside
diametre of the spherical cavity. All the measurements were carried out at the room temperature.
Solid-state ionization potentials (IP ) were established by electron photoemission in air method as
PE
reported earlier [18,19]. For the measurements the layers on ITO glass were prepared by drop casting
from the solutions of the compounds in tetrahydrofuran (THF). The samples were illuminated with the
monochromatic light obtained using the deep UV deuterium light source ASBN-D130-CM and
CM110 1/8 m monochromator. The negative voltage of 500 V was supplied to the sample substrate.
The counter-electrode was placed at the distance of 3 mm from the sample surface. The counter-
electrode was connected to the input of the 6517B Keithley electrometer for the photocurrent
measurement. An energy scan of the incident photons was performed while increasing the photon
energy hv. In this scan direction, no electrons were emitted until hv exceeded the ionization potential
of the layer. The cyclic voltammetry (CV) measurements were carried out by a three-electrode
assembly cell from Bio-Logic SAS and a micro-AUTOLAB Type III potentiostat-galvanostat. The
+
working electrode was a glassy carbon, the reference electrode and the counter electrode were Ag/Ag
0
.01 M and Pt wire, respectively. Argon-purged dichloromethane (DCM) with tetrabutylammonium
hexafluorophosphate (Bu NBF ) 0.1 M was used as electrolyte. The experiments were calibrated with
4
6
+
+
the standard ferrocene/ferrocenium (Fc /Fc) redox system [20]. Half-wave redox potential for Fc/Fc
was established to be 0.285 V vs. Ag. The charge mobilities of the studied materials were estimated
by the time-of-flight (TOF) technique [21]. The layers for the TOF measurements were prepared by a
vacuum vapor deposition onto precleaned glass substrates with indium-tin oxide (ITO) electrodes at
−
6
vacuum below 3·10 mBar. The layer of aluminum with the thickness of a 60 nm was deposited on
the organic film as the upper electrode. The thickness of the organic layers was between 1.3 and 5 ꢀm.
The measurements were carried out at room temperature. For generation of charge carriers a Nd:YAG
laser (EKSPLA NL300) with the wavelength of 355 nm and 3-6 ns pulse width was used as a light
source. Electric fields were applied by a 6517B Keithley electrometer. The photocurrent was
5

ACCEPTED MANUSCRIPT
measured with a digital stragescope Tektronix TDS 3032C through a resistance. The transit times t
tr
2
were used to calculate the charge carrier mobility ꢀ by the equation ꢀ = d /Vt , where d is the
tr
thickness of the studied films and V is the applied voltage to the electrodes of the TOF structures.
Phosphorescent OLEDs (PhOLEDs) were fabricated by thermal vacuum deposition under the vacuum
-6
higher than 3×10 mBar. The host:guest emission layers from two different sources were deposited by
co-deposition of host (m/m 90%) with deposition rate of ca. 1 Å/s and dopant (m/m 10%) with
deposition rate of ca. 0.1 Å/s. A Keithley source meter 2400-C, a 6517B Keithley electrometer, a
calibrated silicon photodiode plased in front of the PhOLEDs, and an Avantes AvaSpec-2048XL
spectrometer were utilized for recording of the current density-voltage and current density-luminance
characteristics and electroluminescence (EL) spectra of the devices. The current, power and external
quantum efficiencies were estimated utilizing the current density, luminance, and EL spectra as
reported earlier [22]. Density function theory (DFT) and time dependent density function theory
(TDDFT) were performed using Gaussian 09 software employing B3LYP functional and 6-31G(d,p)
basis set [23]. Up to 40 excited states were calculated and theoretical absorption spectra were obtained
by considering a band half-width at half-maximum of 0.3 eV.
2
.2. Synthesis
5
-Bromo-3-(9-ethyl-9H-carbazol-3-yl)-2-methylquinazolin-4(3H)-one (2a). N-Acetyl-5-bromo
anthranilic acid (1a) (5 g, 19.38 mmol) was added to a solution of 3-amino-9-ethyl-carbazole (1b)
4.05 g, 19.31 mmol) in dry toluene (60 ml). POCl (12 ml) was added dropwise during 40 min with
(
3
stirring, and then the reaction mixture was refluxed for 8 hrs. After cooling to the room temperature,
the reaction mixture was diluted with ice-water, treated with 15% K CO solution and extracted with
2
3
chloroform. The organic phase was dried over Na SO , concentrated and the crude product was
2
4
purified by column chromatography using hexane/toluene (1:3) as eluent followed by recrystallization
o
1
from the solvent mixture of eluent to obtain 2a (yield: 5.69 g, 68%), m.p. 270-272 C. H NMR
6

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spectrum (300 MHz, DMSO, δ, ppm): 8.25 (d, 1H, J = 2.0 Hz, Ar), 8.22 (d, 1H, J = 2.4 Hz, Ar), 8.16
(d, 1H, J = 7.8 Hz, Ar), 8.03 (dd, 2H, J = 7.8 Hz, J = 2.4 Hz, Ar), 7.80 (d, 1H, J = 8.7 Hz, Ar), 7.68
1 2
(
d, 1H, J = 8.7 Hz, Ar), 7.57-7.48 (m, 2H, Ar), 7.26 (t, 1H, J = 7.5 Hz, Ar), 4.54 (q, 2H, J = 7.2 Hz,
1
13
J = 7.2 Hz, -CH ), 2.20 (s, 3H, -CH ), 1.39 (t, 3H, J = 7.2 Hz, -CH ). C NMR spectrum (75.4 MHz,
2
2
3
3
CDCl , δ, ppm): 162.21, 148.06, 145.35, 135.63, 132.98, 132.15, 131.72, 128.66, 125.27, 123.83,
3
1
22.58, 120.25, 118.92, 117.11, 114.25, 112.08, 111.53, 108.26, 102.36, 100.73, 48.22, 22.82, 15.02.
-1
IR (KBr), υ, cm : 3438 (C-H ), 2962, 2931 (C-Haliph), 1682 (C=Oquinazolinone), 1607, 1519, 1484
ar
+
+
(
C=C ), 1271, 1188 (C-N), 1011, 989 (CH ). MS (APCI , 20 V), m/z: 433 ([M+H] ).
ar ar
5
-(3,6-Di-tert-butyl-9H-carbazol-9-yl)-3-(9-ethyl-9H-carbazol-3-yl)-2-methylquinazolin-
4
(3H)-one (1). The mixture of 2a (0.5 g, 1.16 mmol), 3,6-di-tert-butyl-9H-carbazole (3a) (0.39 g,
1
.39 mmol), Pd(OAc) (0.012 g, 0.058 mmol), tri-tert-butylphosphine solution (1.0 M in toluene)
2
(0.008 g, 0.038 mmol), potassium tert-butoxide (0.32 g, 2.89 mmol) and 25 ml of dry toluene was
o
heated at 120 C for 24 h under nitrogen. After cooling, the reaction mixture was diluted with ethyl
acetate and the organic phase was washed with water and brine. After being dried over MgSO and
4
filtered, the solvent was removed and the residue was purified by column chromatography using
1
hexane/toluene (1:3) as eluent to obtain amorphous compound 1 (yield: 0.46 g, 64 %). H NMR (300
MHz, CDCl , δ, ppm): 8.54 (d, 1H, J = 2.3 Hz, Ar), 8.17 (d, 2H, J = 1.4 Hz, Ar), 8.10 (d, 1H, J = 7.7
3
Hz, Ar), 8.03 (dd, 2H, J = 7.7 Hz, J = 2.4 Hz, Ar), 7.99 (d, 1H, J = 2.4 Hz, Ar), 7.94 (d, 1H, J = 8.6
1
2
Hz, Ar), 7.61 (d, 1H, J = 8.6 Hz, Ar), 7.56 (dd, 1H, J = 8.2 Hz, J = 1.1 Hz, Ar), 7.49 (dd, 2H, J =
1
2
1
7
2
3
1
1
3
.7 Hz, J = 1.4 Hz, Ar), 7.45 (dd, 2H, J = 7.7 Hz, J = 1.4 Hz, Ar), 7.39 (dd, 1H, J = 8.6 Hz, J =
2 1 2 1 2
.1 Hz, Ar), 7.32-7.29 (m, 1H, Ar), 4.52-4.41 (m, 2H, -CH ), 2.39 (s, 3H, -CH ), 1.52 (t, J = 7.2 Hz,
2
3
1
3
H, -CH ), 1.45 (s, 18H, 2×C(CH ) ). C NMR spectrum (75.4 MHz, CDCl , δ, ppm): 162.6, 155.7,
3
3 3
3
46.1, 143.3, 140.7, 139.8, 139.0, 136.6, 132.9, 128.6, 126.5, 124.9, 124.3, 124.2, 123.9, 123.8, 122.3,
-1
22.2, 120.8, 119.9, 119.4, 116.3, 109.7, 109.1, 108.6, 34.7, 32.0, 26.9, 24.7, 13.9. IR (KBr), υ, cm :
031 (C-H ), 2925, 2832 (C-Haliph), 1670 (C=Oquinazolinone), 1603, 1502, 1478 (C=C ), 1249, 1188 (C-
ar
ar
7

ACCEPTED MANUSCRIPT
N), 1022, 819, 738 (CH ). Anal. Calc. for C H N O: C, 81.87; H, 6.71; N, 8.88; O, 2.54%. Found:
ar
43 42
4
+
+
C, 81.90; H 6.65; N, 8.93%. MS (APCI , 20 V), m/z: 631 ([M+H] ).
-(Bis(4-tert-butyldiphenyl)amino)-3-(9-ethyl-9H-carbazol-3-yl)-2-methylquinazolin-4(3H)-
5
one (2) was synthesized by the similar procedure as compound 1. The mixture of 2a (0.5 g, 1.16
mmol), 4,4‘-di-tert-butyl-diphenylamine (0.39 g, 1.39 mmol), Pd(OAc) (0.012 g, 0.058 mmol), tri-
2
tert-butylphosphine solution (1.0 M in toluene) (0.008 g, 0.038 mmol), potassium tert-butoxide (0.32
g, 2.89 mmol) and 25 ml of dry toluene was used for the synthesis. The product was purified by
column chromatography using hexane/toluene (1/2) as eluent followed by recrystallization from the
o
1
eluent mixture of solvents to obtain white crystals of 2 (yield: 0.49 g, 67%), m.p. 292-293 C. H
NMR (300 MHz, CDCl , δ, ppm): 8.06 (d, 1H, J = 7.8 Hz, Ar), 7.97 (d, 1H, J = 1.7 Hz, Ar), 7.89 (d,
3
1
H, J = 2.4 Hz, Ar), 7.57-7.46 (m, 7H, Ar), 7.28-7.31 (m, 4H, Ar), 7.08 (d, 4H, J = 8.5 Hz, Ar), 4.52-
1
3
4
.37 (m, 2H, -CH ), 2.28 (s, 3H, -CH ), 1.50 (d, 3H, J = 7.2 Hz, -CH ), 1.32 (s, 18H, -CH ). C NMR
2
3
3
3
spectrum (75.4 MHz, CDCl , δ, ppm): 163.3, 152.9, 146.9, 146.39 (s), 144.5, 142.3, 140.5, 139.6,
3
1
29.6, 129.1, 127.5, 126.3, 124.9, 124.3, 123.7, 122.4, 121.7, 120.7, 119.9, 119.3, 117.8, 109.4, 108.8,
-1
5
3.4, 37.8, 34.3, 31.4, 24.4, 13.9. IR (KBr), υ, cm : 2996 (C-H ), 2916, 2816 (C-Haliph), 1665
ar
(
C=Oquinazolinone), 1589, 1489, 1476 (C=C ), 1242, 1192 (C-N), 1018, 813, 731 (CH ). Anal. Calc. for
ar ar
+
C H N O: C, 81.61; H, 7.01; N, 8.85; O, 2.53%. Found: C, 81.28; H 7.33; N, 8.87%. MS (APCI , 20
43
44
4
+
V), m/z: 634 ([M+H] ).
-(Bis(4-methoxyphenyl)amino)-3-(9-ethyl-9H-carbazol-3-yl)-2-methylquinazolin-4(3H)-one
3) was synthesized by the similar procedure as compound 1. The mixture of 2a (0.5 g, 1.16 mmol),
,4‘-dimethoxydiphenylamine (0.32 g, 1.39 mmol), Pd(OAc) (0.012 g, 0.058 mmol), tri-tert-
5
(
4
2
butylphosphine solution (1.0 M in toluene) (0.008 g, 0.038 mmol), potassium tert-butoxide (0.32 g,
.89 mmol) in 25 ml of dry toluene was used for the synthesis. The product was purified by column
chromatography using hexane/toluene (1/2) as eluent followed by recrystallization from the mixture of
2
o
1
solvents of the eluent to obtain white crystals of 3 (yield: 0.41 g, 61%), m.p. 238-239 C. H NMR
(
300 MHz, CDCl , δ, ppm): 8.06 (d, 1H, J = 7.8 Hz, Ar), 7.96 (d, 1H, J = 1.8 Hz, Ar), 7.74 (d, 1H, J =
3
8

ACCEPTED MANUSCRIPT
2
.7 Hz, Ar), 7.53-7.49 (m, 3H, Ar), 7.48 (d, 1H, J = 8.1 Hz, Ar), 7.42 (dd, 1H, J = 8.9 Hz, J = 2.7
1 2
Hz, Ar), 7.11-7.07 (m, 5H, Ar), 6.86-7.79 (m, 5H, Ar), 4.51-4.37 (m, 2H, -CH ), 3.81 (s, 6H, -OCH ),
2
3
1
3
2
1
1
3
.27 (s, 3H, -CH ), 1.51 (t, 3H, J = 7.2 Hz, -CH ). C NMR spectrum (75.4 MHz, CDCl , δ, ppm):
3 3 3
63.3, 156.2, 152.8, 147.6, 141.6, 140.3, 139.7, 129.4, 129.3, 127.9, 127.6, 126.7, 126.4, 125.2, 123.9,
-1
22.6, 121.8, 120.7, 119.9, 119.5, 115.5, 114.9, 109.4, 108.9, 68.0, 55.5, 25.6, 13.9. IR (KBr), υ, cm :
085 (C-H ), 2931, 2833 (C-Haliph), 1676 (C=Oquinazolinone), 1602, 1506, 1483 (C=C ), 1241, 1197 (C-
ar
ar
N), 1032, 828, 747 (CH ). Anal. Calc. for C H N O : C, 76.53; H, 5.55; N, 9.65; O, 8.27%. Found:
ar
37 32
4
3
+
+
C, 76.48; H 5.53; N, 9.71%. MS (APCI , 20 V), m/z: 581 ([M+H] ).
-(9-Ethyl-9H-carbazol-3-yl)-5-((E)-2-(9-ethyl-9H-carbazol-3-yl)ethenyl)-2-
methylquinazolin-4(3H)-one (4). The reaction mixture consisting of 2a (0.5 g, 1.16 mmol), 9-ethyl-
3
3
0
-vinyl-9H-carbazole (3c) (0.31 g, 1.39 mmol), Pd(OAc) (0.017 g, 0.077 mmol), P(o-tolyl) (0.018 g,
2 3
.057 mmol), DMF (10 mL), and triethylamine (3 mL) was placed into the flask which was
o
preliminarily degassed and purged with nitrogen. The mixture was heated at 90 C for 24 h under N .
2
Then, it was filtered, and the filtrate was poured into distilled water and extracted with
dichloromethane. The organic layer was dried with anhydrous magnesium sulfate and concentrated by
vacuum evaporation. The crude product was purified by column chromatography using
hexane/toluene (1/1) as eluent followed by recrystallization from the eluent mixture of solvents to
o
1
obtain white crystals of 4 (yield: 0.31 g, 47%), m.p. 267-268 C. H NMR (300 MHz, CDCl , δ, ppm):
3
8
3
7
.43 (d, 1H, J = 2.0 Hz, Ar), 8.30 (d, 1H, J = 1.4 Hz, Ar), 8.17 (d, 1H, J = 7.7 Hz, Ar), 8.12-8.02 (m,
H, Ar), 7.74 (dd, 2H, J = 8.5 Hz, J = 2.4 Hz, Ar), 7.63-7.58 (m, 1H, Ar), 7.57-7.53 (m, 2H, Ar),
1
2
.52-7.47 (m, 3H, Ar), 7.47-7.42 (m, 3H, Ar), 7.37 (dd, 1H, J = 8.6 Hz, J = 2.1 Hz, Ar), 7.31-7.25
1
2
1
3
(
m, 1H, Ar), 4.50-4.37 (m, 4H, -CH ), 2.34 (s, 3H, -CH ), 1.55 (s, 3H, -CH ), 1.42 (s, 3H, -CH ). C
2 3 3 3
NMR spectrum (75.4 MHz, CDCl , δ, ppm): 163.6, 154.8, 147.0, 140.5, 140.5, 139.9, 137.1, 131.9,
3
1
1
30.9, 128.9, 128.1, 127.1, 126.5, 126.5, 125.9, 124.9, 124.8, 122.9, 120.8, 120.5, 119.9, 119.4, 119.0,
-1
09.6, 108.8, 37.7, 24.7, 13.9. IR (KBr), υ, cm : 3012 (C-H ), 2922, 2815 (C-Haliph), 1667
ar
(
C=Oquinazolinone), 1603, 1511, 1481 (C=C ), 1243, 1172 (C-N), 955 (trans, -CH=CH), 818, 736 (CH ).
a
r
a
r
9

ACCEPTED MANUSCRIPT
Anal. Calc. for C H N O: C, 81.79; H, 5.63; N, 9.78; O, 2.79%. Found: C, 81.71; H 5.62; N, 9.82%.
3
9
32
4
+
+
MS (APCI , 20 V), m/z: 573 ([M+H] ).
-(9-Ethyl-9H-carbazol-3-yl)-2-methyl-5-(9-methyl-9H-carbazol-3-yl)quinazolin-4(3H)-one
5). The mixture of 2a (0.5 g, 1.16 mmol), 2-(N-methylcarbazol-3-yl)-4,4,5,5-tetramethyl-[1,3,2]-
dioxaborolane (3b) (0.4 g, 1.37 mmol), Pd(PPh ) Cl (0.03 g, 0.046 mmol), and Na CO (1,6 g, 11.57
3
(
3
2
2
2
3
mmol) in 20 mL of THF/water (19/1 v/v) was degassed with nitrogen for 3-5 min. Then the reaction
mixture was stirred at reflux under nitrogen for 24 h. After recooling, water (50 ml) was added and the
mixture was extracted with CH Cl (3×50 ml). The combined organic phase was washed with water
2
2
(
50 ml) and brine solution (50 ml), dried over anhydrous Na SO , filtered and the solvent was
2 4
removed to dryness. Purification by column chromatography over silica gel eluting with the mixture
of chloroform and hexane (3:1) followed by recrystallization from the mixture of solvents of the
o
1
eluent enabled to obtain white crystals of 5 (0.32 g, 51%). M.p. 257-258 C; H NMR (300 MHz,
CDCl , δ, ppm): 8.64 (s, 1H, Ar), 8.47 (s, 1H, Ar), 8.35-8.30 (m, 2H, Ar), 8.18 (d, 1H, J = 7.8 Hz,
3
Ar), 7.91 (d, 1H, J = 8.6 Hz, Ar), 7.82 (dd, 2H, J = 8.6 Hz, J =3.8 Hz, Ar), 7.72-7.68 (m, 2H, Ar),
1
2
7
.63 (d, 1H, J = 8.6 Hz, Ar), 7.52-7.47 (m, 3H, Ar), 7.25-7.18 (m, 3H, Ar), 4.59-4.48 (m, 2H, -CH2),
1
3
3
.93 (s, 3H, -NCH ), 2.24 (s, 3H, -CH ), 1.40 (t, 3H, J = 7.1 Hz, -CH ). C NMR spectrum (75.4
3
3
3
MHz, CDCl , δ, ppm): 158.2, 148.6, 146.8, 144.5, 135.8, 135.3, 133.6, 133.3, 131.6, 131.2, 131.1,
3
1
1
2
30.7, 126.4, 124.8, 123.6, 123.2, 122.1, 121.7, 121.2, 121.0, 120.6, 119.7, 119.5, 118.8, 114.4, 113.6,
-1
12.3, 111.4, 111.1, 110.9, 108.4, 107.6, 49.3, 43.6, 22.1, 14.3. IR (KBr), υ, cm : 3035 (C-H ), 2929,
ar
834 (C-Haliph), 1672 (C=Oquinazolinone), 1605, 1509, 1481 (C=C ), 1253, 1182 (C-N), 1025, 821, 742
ar
(
CH ). Anal. Calc. for C H N O: C, 81.18; H, 5.30; N, 10.52; O, 3.00%. Found: C, 81.14; H 5.32;
ar 36 28 4
+
+
N, 10.57%. MS (APCI , 20 V), m/z: 533 ([M+H] ).
3
. RESULTS AND DISCUSSION
1
0

ACCEPTED MANUSCRIPT
3
.1. Synthesis and characterization
Scheme 1 shows synthetic routes to carbazolyl-substituted quinazalinones having different donor
substituents at C-5 position of quinazolinone moiety. Commercially available 2-acetamido-5-
bromobenzoic acid (1a) was condensed with 3-amino-9-ethyl-carbazole (1b) in refluxing
POCl /toluene to obtain bromo quinazolinone 2a. Compounds 1, 2 and 3 were synthesized by one-
3
step method i.e. by the Pd-catalyzed Buchwald-Hartwig cross-coupling reaction [24] between 5-
bromo-3-(9-ethyl-9H-carbazol-3-yl)-2-methylquinazolin-4(3H)-one (2a) and 3,6-di-tert-butyl-9H-
carbazole (3a), 4,4’-di-tert-butyl-diphenylamine or 4,4’-dimethoxydiphenylamine. Compound 4 was
synthesized by Heck reaction of 2a with 9-ethyl-3-vinyl-9H-carbazole (3c) in the presence of
palladium(II) acetate and tri-o-tolylphosphine. Compound 5 was obtained via Suzuki cross-coupling
reaction of 2a with 2-(N-methylcarbazol-3-yl)-4,4,5,5-tetramethyl-[1,3,2]-dioxaborolane (3b). The
synthesized compounds were purified by column chromatography and recrystallization. The yields
1
13
ranged from 42 to 64%. The chemical structures were confirmed by IR-, H NMR, C NMR and
mass spectrometries as well as by elemental analysis. The obtained compounds exhibited good
solubility in common organic solvents such as dichloromethane, chloroform, chlorobenzene, toluene.
1
1

ACCEPTED MANUSCRIPT
N
N
N
N
N
O
N
N
N
N
O
O
O
N
N
1
6 %
N
4
2
2 %
3
1 %
4
5
H
O
N
H
N
H
N
3a
O
O
tBuCl, AlCl
,
3
DCM, R.T., 24 h
Pd(OAc)
t-BuOK, Tol, 90 C, 24 h
2
, P(o-tolyl)3,
H
o
N
Cz
N
N
2 3
Pd(OAc) , P(o-tolyl) ,
N
O
DMF, TEA,
o
9
0
C, 24 h
O
N
N
N
N
NH
POCl /Toluene
3
Br
+
4
64 %
O
OH
Reflux
N
Br
N
H
2
N
2a
O
1a
1b
3c
O
B
THF, PdCl
CO , H
C, 24h
2
(PPh
O,
3
)
2
,
Methyltriphenylphosphonium
bromide, t-BuOK
O
THF, R.T., 12 h
K
2
3
2
N
o
80
3
b
N
N
O
N
CHO
CzCHO
N
N
5
54 %
Scheme 1. Synthetic routes to 1-5.
3
.2. Geometries and molecular orbitals
Carbazolyl-substituted quinazolinones 1-5 were studied using quantum chemical calculations. The
optimized geometries and frontier orbitals of the isolated molecules are presented in Fig 1. In these
compounds carbazole attached at N atom of quinazolinone form torsion angle of 87-93° with central
fragment. In the case of molecules 1, 4 and 5, the size of torsion angles between the planes of the
second carbazole and quinazolinone moieties are different. Carbazole with central fragment show
torsion angles of 53° and 37° in 1 and 5, respectively, while compound 4 having ethenyl-containing
linkage demonstrate flat configuration. The torsion angles between phenyl rings and quinazolinone
moiety in the structures of 2 and 3 are in the range of 40-48°. The determined geometries of 1-5 lead
to the HOMO distribution on the quinazolinone moiety and the different donor substituents. The
1
2

ACCEPTED MANUSCRIPT
electron density of LUMO in 2, 3 and 5 is predominantly localized on the ethyl-carbazole unit, while
in 1 electron cloud is shifted to the quinazolinone moiety. Only compound 4 has the similar LUMO
distribution as that of HOMO i.e. the LUMO is localized on the quinazolinone moiety extending on
the conjugated double bond linkage and ethyl-carbazole.
<
Insert Figure 1>
3
.3. Thermal properties
The thermal stabilities of the compounds were estimated by TGA under a nitrogen atmosphere.
The 5% weight loss temperatures (Tdec-5%) of 1-5 are summarized in Table 1. TGA curves are shown
in the Supporting Information (Fig. S1, SI).
<
Insert Table 1>
o
Tdec-5% of the compounds were found to be rather high and ranged from 418 to 437 C. 4,4’-Di-
tert-butyl-diphenylamino- and 4,4’-di-methoxydiphenylamino-substituted compounds 2 and 3
exhibited higher thermal stability than 3,6-di-tert-butylcarbazolyl-substituted quinazolinone 1.
Compound 4 having 9-ethyl-3-vinylcarbazyl substituent showed the lowest 5% weight loss
temperature.
Quinazolinones 1-5 were isolated after the synthesis as the crystalline substances. However, they
could be transformed into molecular glasses by cooling their melts as it was confirmed by DSC. DSC
thermograms of compound 2 are shown in Fig. 2.
<
Insert Figure 2>
1
3

ACCEPTED MANUSCRIPT
When the sample of 2 was heated during DSC experiment the endothermal melting signal was
o
observed at 297 C. The cooling scan did not show any signal of crystallization. The following heating
o
scan revealed only the glass transition at 154 C. The similar behavior in DSC experiments was
observed for compounds 1, 3-5. In the first heating scans compounds 1, 3-5 showed endothermic
o
melting signals at 224, 242, 269 and 260 C, respectively. In the repeated heating scans these
o
compounds showed only glass transitions at 132, 146, 157 and 159 C, respectively. High T values of
g
compounds 1-5 allow to predict high morphological stability of their molecular glasses. T of
g
compounds 4 and 5 having 9-ethyl-3-ethenylcarbazolyl and N-methylcarbazolyl substituents,
o
respectively, was found to be higher by 25 and 27 C than that of compound 1 with 3,6-di-tert-
butylcarbazolyl donor substituent. Apparently tert-butyl groups present in compound 1 ensure
plasticizing effect of its glass. T of compound 2 containing tert-butyl groups at the 4,4’-positions of
g
o
the diphenylamino moiety was found to be higher by 8 C than that of compound 3 with methoxy
groups at the 4,4’-positions of the diphenylamino moiety. This observation can apparently be
explained by the higher molar mass of compound 2, which results in the stronger intermolecular
interaction in the glassy state.
3
.4. Optical and photophysical properties
UV absorption and fluorescence (FL) spectra of dilute THF solutions of 1-5 are shown in Fig. 3.
The wavelengths of low-energy absorption and emission maxima of the solutions and the solid films,
Stokes shifts are summarized in Table 2. The TDDFT calculations in gas phase were performed to
identify low-energy transitions in the absorption spectra of compounds 1-5 (Table S1).
<
Insert Table 2>
<
Insert Figure 3>
1
4

ACCEPTED MANUSCRIPT
The profiles of absorption spectra of compounds 1-5 were found to be similar. The theoretical
absorption spectra (Fig. S2) indicate that low energy excitations (S →S , S →S ) of 1, 2, 3 and 5 have
0
1
0
2
charge transfer (CT) character. These excitations are mainly contributed by the transitions
HOMO→LUMO, LUMO+1, LUMO+2. In the case of compound 4, S →S corresponds to the
0
1
transition in the same 9-ethyl-3-ethenylcarbazolyl and quinazolinone moieties. This transition
characterizes the lowest energy absorption band of 4 which is red-shifted in respect to those of
compounds 1-3 and 5 (Fig. 3a). The results obtained show that compound 4 has more extended
conjugated π-electron system due to the presence of ethenyl-linkage.
a
edge
λ
opt
From the spectroscopic absorption edge (
, nm), the optical band gap ( Eg ) values were
opt
Eg
a
edge
estimated according to the formula
=1240/
λ
[25], and were found to range in the order: 1 > 5 >
2
> 3 > 4 (Table 4). FL spectra of the dilute solutions of 1-5 are characterized the single peaks with
the intensity maxima in the range of 403-483 nm. Fig. 3c displays fluorescence decay curves of the
dilute THF solutions of the studied compounds recorded at the fluorescence band maxima. The
fluorescence transients of the dilute THF solutions of the compounds can be well described by the
single exponential functions with the lifetimes (τ) ranging from 0.91 to 6.47 ns (Table 3). Both
bathochromic shift of FL spectrum and longer lifetime observed for compound 3 can be explained by
more twisted molecular structure in the excited state, compared with those observed for the other
compounds. The shortest τ (0.91 ns) obtained for compound 4 that was characterized by higher
fluorescence quantum yield (Φ ) (Table 2) can apparently be explained by enhanced π-electron
F
delocalization due to more planar molecular structure of 4 (dihedral angle between the quinazolinone
o
and 9-ethyl-3-vinylcarbazolyl moieties of 1 , Fig. 1).
<
Insert Figure 4>
1
5

ACCEPTED MANUSCRIPT
Fig. 4 shows the normalized absorption and emission spectra of the solid films of compounds 1-5.
The absorption spectra are slightly red-shifted as compared with the corresponding spectra of the
dilute solutions. This observation can be explained by the intermolecular interaction, which takes
place in the films [26]. The emission maxima of the solid samples of 1-5 were found to be in the range
from 411 to 485 nm with the excitation wavelength of 350 nm.
<
Insert Table 3>
The FL spectrum of the solid layer of 1 was very similar to these recorded for dilute THF solution
of 1; while the FL spectra of the solid layers of 4-5 were found to be slightly red-shifted compared to
FL spectra of the solutions of the compounds apparently due to intermolecular interactions (Fig. 3b
and 4b). FL spectra of the solid samples of most of the compounds, except that of compound 5 were
similar to those of dilute solutions, which implied the low probability of the formation of excited
dimers of compounds in the solid state. Fl spectrum of the solid film of compound 5 had a shoulder at
ca. 490 nm (Fig. 4b) which can be assigned to the formation partially overlapped excimers.
PL decay transients for the solid layers of compounds 1-5 were also recorded (Fig. S3). Double-
2
exponential fits were used for the statistical representation of the decay curves (χ values were not
higher than 1.3). The lifetimes with the different fractional intensities are summarized in Table 3. The
lifetimes of the first (fast) time decay components were found to be lower than those recorded for
dilute THF solutions of 1-5 (Table 3). The different values of dielectric constant of both the media and
the intermolecular interactions in the solid state could be the reasons of this observation. The longer-
lived decay components observed for compounds 1-5 can probably be associated with the formation
of the intermolecular excimers in the layers. This assumption is supported by the observation that the
solid-state PL spectra of compounds 1-5 are broader than those of THF solutions. The solid-state PL
spectrum of 5 even contains shoulder (Fig. 4b) [27]. In addition, the slow decay components could be
1
6

ACCEPTED MANUSCRIPT
explained by the excitation migration towards the non-radiative decay sites and/or by the crystalline
aggregate formation in the neat films [28].
The Stokes shifts recorded for the dilute THF solutions of compounds 1-5 ranged from 48 to 134
nm, while those observed for the solid films were similarly in the range of 46-113 nm. The highest
Stokes shift of the dilute solution of 3 can apparently be explained by the most considerable difference
of the conformations of the ground and excited states. The small Stokes shifts observed both for the
dilute solution and for the solid sample of 4 provides the information on the small changes in
geometry after excitation.
Compounds 1-3 and 5 due to their non-planar structure, apparently, exhibited photoinduced
charge transfer (CT) character in excited state. Therefore, the dilute THF solutions and solid films of
these compounds suffered from CT caused fluorescence quenching [29]. The solutions of compounds
1
-3 and 5, showed rather low values of Φ ranging from 5.8 to 12.2% (Table 2). Even lower Φ
F F
ranging from 0.4 to 1.7% were recorded for the condensed state due to aggregation induced
quenching. Compound 4 having rigid structure demonstrated relatively high fluorescence quantum
yield (44.3%) in dilute solution. However, the π–π stacking interactions of planar molecules of 4 in
the solid state induced non-radiative energy transfer, resulting in self-quenching of fluorescence [30].
Φ of the solid sample of 4 was found to be 1.1%.
F
The rigid structure of compound 4 brought about relatively high fluorescence quantum yield (ΦF)
of 44.3% for the dilute solution of the compound.
The photoluminescence (PL) and phosphorescence (Ph) spectra of the dilute solutions of the
studied compounds in THF recorded at liquid nitrogen temperature (77 K) are presented in Fig. 5. The
substitution mode was found to have influence on the phosphorescence spectra and triplet-energy
levels (E ) of compounds 1-5. Intense triplet emission was observed at low temperatures for
T
compounds 1-3 and 5 with 4,4’-di-tert-butyl-diphenyl, 3,6-di-tert-butylcarbazolyl and N-
methylcarbazolyl substituents, respectively (Fig. 5). However, the intensity of phosphorescence
emission for compound 4 was very low displaying extremely low quantum yield of phosphorescence
1
7

ACCEPTED MANUSCRIPT
of the compound. For this reason it was impossible to record phosphorescence spectrum of the
solution of 4 at the used gate (> 50 ms). The singlet- and triplet-energy levels (E and E ) were
S1
T1
determined from the onsets of the fluorescence and phosphorescence spectra, respectively (Table 4,
Fig. 5).
<
Insert Figure 5>
<
Insert Table 4>
3
.5. Electrochemical and electron photoemission properties
In order to investigate the electrochemical properties of the molecules (1-5), CV measurements
o
were performed at 25 C for DCM solutions. The CV profiles of compound 4 are shown in Fig. 6 as
an example. The electrochemical potentials and energy levels are summarized in Table 5.
<
Insert Figure 6>
<
Insert Table 5>
As shown in Fig. 6a, compound 4 exhibited two quasi-reversible oxidation processes. No
reduction waves were detected. The first oxidation peak corresponds to the removal of electrons from
the carbazolyl group, resulting in radical cations. Compound 4 is very sensitive towards
electrochemical oxidation due to the electron-rich and highly activated 3,3’-positions of two carbazole
moieties. Their repeated CV scans display an increasing change in the CV traces, proving that a series
of electro-polymerization reactions [31] of the radical cation species take place on the glassy carbon
electrode surface in the potential range 0-1.4 V. The similar quasi-reversible oxidation processes,
1
8

ACCEPTED MANUSCRIPT
electrochemical polymerization and the film formation on the electrode surface were observed for the
CVs profiles of 2-5 (Fig. S4). It is worth of noting that the first oxidation peaks of 2, 3 and 4 occured
at a lower potentials than that of 1, 5 (Table 5). This observation is in agreement with the UV
spectrometry data. The low-energy absorption bands of 2, 3 and 4 appeared at lower energies than
those of 1 and 5.
DPV spectra (Fig. 6b) of compounds 1-5 show absolute peaks of oxidation processes. The first
oxidation potential peaks of carbazolyl-substituted quinazolinones 1 (1.02 V), 4 (0.69 V) and 5 (0.76
V) are at a higher potentials than those of 4,4’-di-tert-butyl-diphenylamino- or 4,4’-di-
methoxyphenylamino-substituted quinazolinones 2 (0.64 V) and 3 (0.53 V).
Although other approaches were used to calculate the solid state ionization potential (IP ) based
CV
on electrochemical data [32], the conversion reported by the Forrest group [33] has a better correlation
between electrochemical data and ionization potential and afforded a better fit between optical
bandgap. According to the method reported by Forrest et al [33], IPCV value is calculated using the
ox
onset
E
equation IPCV = |-(1.4×1e×
vs Fc/V) − 4.6| eV. The electron affinity (EA ) was obtained from
CV
opt
Eg
the equation: EACV = −(|IP |−
). The values of EACV were found to range from -2.24 to -1.68 eV.
to 5.43 eV for
CV
The values of IPCV are given in Table 5. They ranged from 5.03 eV for
3
1.
Ionization potentials (IP ) of the solid layers of compounds 1-5 were estimated by photoelectron
PE
emission spectroscopy. Photoelectron emission spectra are shown in Fig. 7.
<
Insert Figure 7>
The intersection points of the linear parts of the photoelectron spectra drawn with the abscissa
axis gave the ionization potential values. IPEP values of derivatives 1-5 ranged from 5.35 to 5.66 eV
(Table 5). While the IPEP values are slightly larger than the corresponding ones obtained by CV
1
9

ACCEPTED MANUSCRIPT
(
IP ), both methods indicate the same tendencies. Carbazolyl-substituted quinazolinones 1, 4 and 5
CV
exhibited a little higher ionization potentials than diphenylamino-substituted compounds 2 and 3.
3
.6. Charge-transporting properties and performance in phosphorescent OLED
Time of flight measurements were used for the estimation of charge-transporting properties of
compounds 1-5. Fig. 8a displays the electric field dependencies of hole mobilities for the layers of
-4
-3
2
these compounds. The hole mobility values of 1-5 were in the range between 10 and 10 cm /V·s at
high electric fields. The best charge transport properties were observed for the layer of compound 2. It
-3
2
5
showed hole drift mobility of 1.1×10 cm /Vs at an electric field of 8.1×10 V/cm. The hole
mobilities for all the studied compounds were strongly dependent upon electric field. The
photocurrent profiles of hole carrier transport for 2 showed a low-dispersive behavior with a plateau
and subsequent drop (Fig. 8b). A dispersive behavior was found for the photocurrent profiles of hole
transport for 1, 3-5. These results indicate that hole transport is limited by bulk trapping for 1, 3-5,
whereas the hole transport is less influenced by this effect for 2.
<
Insert Figure 8>
Compound 2, which showed relatively high triplet level and hole transport with the low-
dispersity, was tested as a host in green (device A) and blue (device B) phosphorescent OLEDs.
Simple OLED structures were chosen utilizing 4,4’,4’’-tris[phenyl(m-tolyl)amino]triphenylamine (m-
MTDATA) and 4,7-diphenyl-1,10-phenanthroline (Bphen) for the hole- and electron-injecting layers,
respectively (Fig. S5). Tris[2-phenylpyridinato-C2,N]iridium(III) (Ir(ppy) ) and bis[2-(4,6-
3
difluorophenyl) pyridinato-C2,N](picolinato)iridium(III) (FIrpic) were exploited as green and blue
dopants in the fabricated phosphorescent OLEDs, respectively (Fig. S5).
2
0

ACCEPTED MANUSCRIPT
Electroluminescence (EL) spectra of the devices A and B are shown in Fig. 9a. EL spectra of the
device A recorded at the different applied voltages are characterized by green emission with the
intensity maximum at ca. 516 nm, confirming the radiative recombination of excitons on Ir(ppy)3
[
34]. The green device A demonstrated the relatively low value of the turn-on voltage of ca. 3.0 V as
well as the relatively high values of maximum power and external quantum (EQE) efficiencies of ca.
3.2 lm/W and 7.1%, respectively (Fig. 9c,d). Blue emission with the intensity maxima at ca. 478 nm
2
of the device B at the different applied voltages was observed. The EL spectra of device B were much
broader compared to the FIrpic emission showing that the radiative recombination of excitons
occurred on both FIrpic and host 2 [35]. It is understandable since HOMO of FIrpic is much lower
compared to HOMO of host 2 providing the energy barer for holes (Fig. 9b). Therefore, the radiative
recombination on host 2 was also possible affecting not only EL spectra but also output characteristics
of device B (Fig. 9c,d). In addition, low performance of device B can be explained by the usage of
hole- and electron-transporting layers with low triplet energy levels of 2.67 eV for m-MTDATA and
2
.5 eV for Bphen as compared to 2.7 eV for FIrpic resulting in inefficient triplet exciton harvesting by
the blue phosphorescent emitter. Therefore, the structure of device B was modified by adding the
layer of 4,4′-cyclohexylidenebis[N,N-bis(4-methylphenyl)benzenamine] (TAPC) with triplet energy
of 2.87 eV as the hole-transporting and exciton-blocking layer and the layer of diphenyl-4-
triphenylsilylphenyl-phosphineoxide (TSPO1) with triplet energy of 3.36 eV as hole-blocking,
electron-transporting and exciton-blocking layer. 2,2’,2’’-(1,3,5-Benzinetriyl)-tris(1-phenyl-1-H-
benzimidazole) (TPBi) was employed for the preparation of electron-transporting (ET) layer (Fig. S5).
Practically, new device C was fabricated with the following structure ITO/m-MTDATA(30
nm)/TAPC(8 nm)/2:FIrpic(30 nm)/TSPO1(8 nm)/TPBi(30)/Ca:Al. The energy energy diagram of
device C is present in Fig. 9b. The characteristics of device C were better than those of device B (Fig.
9
c,d) but “white” EL of device C was far from blue emission of FIrpic (Fig. 9a). The high-energy
band of EL spectrum of device C was sufficiently similar to that of device B and it can be explained
by the same reasons. Low-energy band with the maximum at 588 nm can be attributed to electroplex
2
1

ACCEPTED MANUSCRIPT
of TAPC as this band is not observed neither in PL spectra of pure materials used in the device or in
the spectra of their solid-state mixtures. Thus, compound 2 is not exciplex-forming material as, for
example, 3-(2,7-dicyanocarbazol-9-yl)-9-ethylcarbazole [36]. The similar band was previously
observed in EL spectra of TAPC-based OLEDs [37]. In device D, TAPC was replaced by the layer of
compound 2. EL spectrum of devcice D practically originates from FIrpic emitter. This device
exhibits higher performance than devices B and C (Fig. 9). The blue device D is characterized by the
turn-on voltage of ca. 5.1 V, maximum power efficiency of ca. 11 lm/W and external quantum
efficiency (EQE) of ca. 6.9% (Fig. 9c,d). The characteristics of the fabricated and characterized
OLEDs show that quinazolinone-based compound 2 with relatively high triplet level and hole-
transporting property can be used for the fabrication electroluminescent devices. The similar
behaviours were observed for the quinazolinone-based compounds 1, 3-5 which were studied in the
structures of devices C and B replacing compound 2 in the light-emitting layer. The data of
electroluminescence study of compounds 1, 3-5 are presented in the SI (Fig. S6).
<
Insert Figure 9>
4
. CONCLUSIONS
Five quinazolinones with the different substitution pattern were synthesized and their thermal,
optical, photophysical, electrochemical, photoelectrical, and electroluminescent properties were
investigated. All the synthesized compounds formed glasses with the glass transition temperatures
o
ranging from 97 to 159 C. The 5% weight loss temperatures of the compounds were found to be
o
rather high and ranged from 397 to 451 C. The theoretical absorption spectra indicate that low energy
excitations (S →S , S →S ) of the synthesized compounds have charge transfer character. Only 3-(9-
0
1
0
2
ethyl-9H-carbazol-3-yl)-5-((E)-2-(9-ethyl-9H-carbazol-3-yl)ethenyl)-2-methylquinazolin-4(3H)-one
has the similar LUMO distribution as that of HOMO i.e. the LUMO is localized on the quinazolinone
2
2

ACCEPTED MANUSCRIPT
moiety extending on the conjugated double bond linkage and ethyl-carbazole. Fluorescence quantum
yields of dilute THF solutions of the synthesized materials ranged from 7.8 to 44.3%. The highest
value of triplet-energy of 2.99 eV was found for 5-(3,6-di-tert-butyl-9H-carbazol-9-yl)-3-(9-ethyl-9H-
carbazol-3-yl)-2-methylquinazolin-4(3H)-one. Dilute THF solutions of the compounds exhibited a
single exponential fluorescence decays with lifetimes ranging from 0.91 to 6.47 ns. The ionization
potentials of the films of the quinazolinone-based derivatives measured by the photoelectron emission
spectrometry ranged from 5.35 to 5.66 eV. The ionization potential values estimated by cyclic
voltammetry ranged from 5.03 to 5.43 eV and electron affinity values ranged from -2.24 to -1.68 eV.
All the synthesized compounds were found to be capable of transporting holes. The layers of most of
the compounds showed dispersive hole transport while that of 5-(bis(4-tert-butyldiphenyl)amino)-3-
(9-ethyl-9H-carbazol-3-yl)-2-methylquinazolin-4(3H)-one was characterized by low-dispersity hole
-3
2
transport. Time-of-flight hole mobilities in the layer of this material reached 1.1×10 cm /Vs at an
5
electric field of 8.1×10 V/cm at the room temperature. Utilizing this compound as the host, green and
blue phosphorescent organic light emitting diodes with turn-on voltage of ca. 3.0 and 5.1 V,
maximum power and external quantum efficiencies of ca. 23.2 and 11 lm/W and 7.1 and 6.9%,
respectively were fabricated.
Acknowledgments
This work was supported by the project of the Research Council of Lithuania“ (TAP LU-2-
2
016). D. Gudeika thanks Lithuanian Academy of Sciences for the support.
Appendix A. Supplementary data
Supplementary data related to this article can be found at http:// dx.doi.org.
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