M. Cang et al.
Dyes and Pigments 195 (2021) 109672
other hand, its application as a donor or acceptor is basically uninter-
ested. In fact, there are few reports on blue fluorophores that simply use
AN as a donor or acceptor. Previous studies describe devices that either
exhibit excellent performance but deviation of the light wavelength
from the blue region or emission of blue light but poor performance. For
example, Wang et al. [30]. reported two kinds of new chromophores
containing one or two tetrahedral centers in 1- or 2-fold
fluorene-functionalized AN derivatives. The device exhibits blue emis-
sion with an EL wavelength peak at 440 nm and CIE coordinates of
(0.16,0.08), although showing a maximum current efficiency of only
1.4 cd Aꢀ 1 and a turn-on voltage of 4.3 V. Additionally, Prachumrak
et al. [31] used 9-(fluoren-2-yl)AN combined with thiophene and tri-
phenylamine to prepared a series of blue-light-emitting small molecules.
The device showed excellent performance with a high maximum lumi-
nance of 8459 cd mꢀ 2 at 8.8 V, a maximum current efficiency of 3.2 cd
Aꢀ 1, and a low turn-on voltage of 3.0 V; however, the EL peak wave-
length could not be controlled in the deep-blue-light-emitting region
[25]. These findings demonstrate the difficulty associated with fabri-
cating efficient AN-based organic deep-blue-light-emitting materials
[32–34]. Therefore, development of deep-blue AN-based fluorescent
materials that simultaneously achieve high color purity, high efficiency,
and low-efficiency roll-off EL remains a significant challenge.
respectively. Photoluminescence quantum yield was carried out with
FLS980 spectrometer. The lifetimes of nondoped films were measured
on an Edinburgh FLS-980 with an EPL-375 optical laser.
2.3. Electrochemical measurements
Cyclic voltammetry (CV) was performed with a BAS 100 W Bio-
analytical System, using a glass carbon disk (diameter = 3 mm) as the
working electrode, a platinum wire with a porous ceramic wick as the
auxiliary electrode, and Ag/Ag+ (Ag/AgNO3) as the reference electrode
standardized by the redox couple ferrocenium/ferrocene. All solutions
were purged with a nitrogen stream for 10 min before measurement. The
procedure was performed at room temperature, and a nitrogen atmo-
sphere was maintained over the solution during measurements.
2.3.1. Thermal stability measurements
Thermal gravimetric analysis was undertaken on a Perkin-Elmer
◦
◦
thermal analysis system from 30 C to 600 C at a heating rate of 10
K minꢀ 1 and a nitrogen flow rate of 80 mL minꢀ 1. Differential scanning
calorimetry (DSC) analysis was carried out using a NETZSCH (DSC-204)
instrument from 30 ◦C to 300 ◦C at a heating rate of 10 K minꢀ 1 while
flushing with nitrogen. All DFT calculations were carried out with the
Gaussian 09 B.01 Package at the level of M062X/6-31+G(d,p).
In this study, we designed and synthesized a novel deep-blue fluo-
rescent molecule [3-(4-(anthracen-9-yl)phenyl)-4,5-diphenyl-4H-1,2,4-
triazole; ANTZ] that utilizes AN as an electron-donor (D) combined with
a twisting-group triazole as an electron acceptor (A). The twisted mo-
lecular conformation is beneficial for inhibiting the fluorescence-
quenching process and stabilizing the high fluorescence quantum effi-
ciency from the emission center. Additionally, the simplified D-A
structure promotes the balance of carrier injection and transport, which
helps maintain the highly efficient light emission of the EL device. The
photoluminescence quantum efficiency (PLQY) of ANTZ is equal to 52%
(in 10ꢀ 5 M ether solution), and single crystal analysis revealed that the
twisted molecular structure increased the space between the molecules,
thereby ensuring fluorescence emission from the original single mole-
cule and precluding fluorescence quenching by aggregation. Use of
ANTZ as the light-emitting layer allowed fabrication of a nondoped
OLED Device I that exhibited ideal EL performance with an emission
peak of 429 nm and CIE coordinates of (0.17, 0.13) located in the deep-
blue region. The turn-on voltage (3.3 V) suggested balanced carrier-
injection/transport ability. And the efficiency roll-off is only 3.0%,
this value is significantly better than most molecules with AN as the
core. All the results prove the success of our design and the D-A structure
of ANTZ enabled use of AN as an emission center in the EL device.
2.3.2. Device fabrication and characterization
ITO-coated glass with a sheet resistance of 15–20 Ω cmꢀ 2 was used as
the substrate. Before device fabrication, the ITO glass substrates were
cleaned with isopropyl alcohol and deionized water, dried in an oven at
120 ◦C. After oxygen plasma cleaning for 4 min and finally transferred to
a vacuum deposition system with a base pressure greater than 5 × 10ꢀ 6
mbar for organic and metal deposition. The current–voltage–luminance
characteristics were measured by using a Keithley source measurement
unit (Keithley 2400 and Keithley 2000) with a calibrated silicon
photodiode. The EL spectra were measured by a Spectrascan PR705
spectrophotometer. EQEs were calculated from the luminance, current
density, and EL spectrum according to previous work [35].
3. Result and discussion
3.1. Synthesis and characterization
ANTZ synthesis is shown in Scheme 1. First, N′-benzoyl-4-bromo-
benzohydrazide (1) was synthesized by reaction of benzohydrazide and
4-bromobenzoyl chloride, followed by 3-(4-bromophenyl)-4,5-
diphenyl-4H-1,2,4-triazole (M1) synthesis and transfer from (1). ANTZ
was then synthesized by a classical Suzuki-coupling reaction between
anthracen-9-ylboronic acid and M1. The detailed synthesis steps are
shown blow, the nuclear magnetic resonance spectroscopy of the
product, and mass spectrometry and element analyses are described in
Supporting Information (Figs. S1 and S2).
2. Experimental section
2.1. Materials
All raw materials were commercially purchased from Aldrich
Chemical Co. or Energy Chemical Co., China. All solvents were distilled
over metallic sodium over calcium hydride. The other organic reagents
were all commercially available analytical-grade products and used as
received without further purification.
Synthesis of 3-(4-bromophenyl)-4,5-diphenyl-1,2,4-triazole (M1):
4-Bromo-benzoic chloride (3.63 g, 16.5 mmol) in dichloromethane
(25 mL) was added dropwise into a solution of benzohydrazide (2.25 g,
16.5 mmol) and triethylamine (3 mL) in dichloromethane (25 mL). The
resulting mixture was stirred for 4 h at room temperature and then
washed with water. The organic phase separated was evaporated to
remove the solvent, and then dried under reduced pressure (N′-benzoyl-
4-bromobenzohydrazide, 4.8 g, yield 91%). Aniline (5.59 g, 60.0 mmol)
and odichlorobenzene (60 mL) were charged into a 500 mL two necked
round-bottomed flask equipped with a reflux condenser. PCl3 (2.06 g,
15.0 mmol) was then slowly dropwised to the flask through a syringe
under a nitrogen atmosphere. Subsequently, N′-benzoyl-4-bromo-
benzohydrazide (3.19 g, 10.0 mmol) dissolved in o-dichlorobenzene (60
mL) was added to the mixture by dropping funnel, The resulting mixture
was stirred under N2 at 150 ◦C for 12 h and then cooled to room tem-
perature. Diethyl ether (200 mL) was poured into mixture to form a
2.2. Measurements
2.2.1. General measurements
1H and 13C NMR spectra were recorded on a Bruker AC500 spec-
trometer at 500 and 125 MHz, respectively, when the compounds were
dissolved in deuterated chloroform (CDCl3) with tetramethylsilane
(TMS) as the internal standard. The chemical shift for each signal was
reported in ppm units. The MALDI-TOF-MS mass spectra were measured
using an AXIMA-CFRTM plus instrument. UV–vis absorption and fluo-
rescence spectra of solution and films were measured by the Hitachi U-
4100 spectrophotometer and Hitachi F-4600 spectrophotometer,
2