Thermally activated delayed fluorescence material with aggregation-induced emission properties for highly efficient organic light-emitting diodes

Article abstract of DOI:10.1039/c7tc04934j

Luminescent materials with aggregation-induced emission (AIE) properties exhibit high solid state emission, while thermally activated delayed fluorescence (TADF) materials can fully harvest singlet and triplet excitons to achieve efficient electroluminescence (EL). Herein, the amalgamation of AIE and TADF properties, termed aggregation-induced emission and thermally activated delayed fluorescence (AIE-TADF), is a promising strategy to design novel desirable luminescent materials. In this paper, a new tailor-made material, DCPDAPM, is obtained based on carbazole as the skeleton, 9,9-dimethyl-9,10-dihydroacridine as the donor group and benzophenone as the acceptor group. Its structure is fully characterized by elemental analysis, NMR spectroscopy and mass spectrometry. Furthermore, its thermal stability, photophysical properties, and electrochemical properties are investigated systematically. The results show that this AIE-TADF compound exhibits good thermal stability, electrochemical stability and AIE and TADF properties. Ultimately, using DCPDAPM and DCPDAPM doped into CBP as light-emitting layers, a non-doped OLED (device A) and doped OLEDs (device B, device C and device D) were fabricated and studied. Device A displays green light with a turn-on voltage of 3.2 V, a maximum brightness of 123:371 cd m^-2, a maximum current efficiency of 26.88 cd A^-1, a maximum power efficiency of 15.63 lm W^-1 and an external quantum efficiency of 8.15%. Among the doped OLEDs (device B, device C and device D), device D shows the best EL performance with a turn-on voltage of 3.6 V, a maximum brightness of 116:100 cd m^-2, a maximum current efficiency of 61.83 cd A^-1, a maximum power efficiency of 40.45 lm W^-1 and an external quantum efficiency of 19.67%. These results adequately demonstrate the practicability of combining AIE and TADF to explore new efficient emitters.

Full text of DOI:10.1039/c7tc04934j

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Fine-tuning of gold nanorod dimensions and plasmonic properties using
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Page 1 of 33
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DOI: 10.1039/C7TC04934J
Thermally activated delayed fluorescence material with aggregation-induced emission
properties for highly efficient organic light-emitting diodes
Yaodong Zhaoa#, Weigao Wangc#, Chen Guid, Li Fanga, Xinlei Zhanga, Shujuan Wanga, Shuming
Chenc*, Heping Shia,b*, Ben Zhong Tangb,d*
(a) School of Chemistry and Chemical Engineering, Shanxi University, Taiyuan 030006, PR China.
*Eꢀmail: hepingshi@sxu.edu.cn
(b) State Key Laboratory of Luminescent Materials and Devices, South China University of
Technology, Guangzhou, Guangdong, 510640, PR China. *Eꢀmail: tangbenz@ust.hk
(c) Department of Electrical and Electronic Engineering, South University of Science and
Technology of China, Shenzhen, Guangdong, 518055, P. R. China. *Email:
chen.sm@sustc.edu.cn
(d) Department of Chemistry, Institute for Advanced Study, Division of Biomedical Engineering,
Division of Life Science, State Key Laboratory of Molecular Neuroscience, Institute of
Molecular Functional Materials, The Hong Kong University of Science and Technology, Clear
Water Bay, Kowloon, Hong Kong, China. *Eꢀmail: tangbenz@ust.hk
Yaodong Zhao# and Weigao Wang# have equal contribution
Abstract
Luminescent materials with aggregationꢀinduced emission (AIE) property have high solid state
emission, while thermally activated delayed fluorescence (TADF) materials can fully harvest
singlet and triplet excitons to achieve efficient electroluminescence (EL). Herein, amalgamation of
1

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AIE and TADF property, termed as aggregationꢀinduced emission and thermally activated delayed
fluorescence (AIEꢀTADF), is a promising strategy to design novel admirable luminescent materials.
In this paper, a new tailorꢀmade material, DCPDAPM, is obtained based on carbazole as skeleton,
9,9ꢀdimethylꢀ9,10ꢀdihydroacridine as donor group and benzophenone as accept group. Its structure
is fully characterized by elemental analysis, NMR spectroscopy and mass spectrometry.
Furthermore, thermal stabilities, photophysical properties, and electrochemical properties are
investigated systematically. The results show that this AIEꢀTADF compound exhibits good thermal
stability, electrochemical stability and AIE as well as TADF properties. Ultimately, using
DCPDAPM and DCPDAPM doped in CBP as lightꢀemitting layer, the nonꢀdoped OLED (Device
A) and doped OLEDs (device B, device C and device D) were fabricated and studied. Device A
displays green light with a turnꢀon voltage of 3.2V, a maximum brightness of 123371 cd mꢀ2, a
maximum current efficiency of 26.88 cd Aꢀ1, a maximum power efficiency of 15.63 lm/w and a
external quantum efficiency of 8.15%. For doped OLEDs of device B, device C and device D,
Device D shows best EL performance with a turnꢀon voltage of 3.6V, a maximum brightness of
116100 cd mꢀ2, a maximum current efficiency of 61.83 cd Aꢀ1, a maximum power efficiency of
40.45 lm/w and a external quantum efficiency of 19.67%. These results adequately demonstrate the
practicability of combine AIE and TADF to explore new efficient emitters.
Keywords:
Carbazole;
9,9ꢀdimethylꢀ9,10ꢀdihydroacridine
;
benzophenone;
Aggregationꢀinduced emission; Thermally activated delayed fluorescence; Electroluminescence
2

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1. Introduction
In the past decades, significant efforts have been made toward the optimization of solidꢀstate
organic fluorescence materials for fabricating high efficiency OLEDs [1ꢀ4]. However, the maximal
internal quantum efficiency (IQE) of classical OLED is limited to be 25%, because emissive singlet
excitons constitute 25% and nonꢀemissive triplet excitons constitute 75% of the generated excited
states according to the spin quantum statistic rule [5ꢀ7]. Such small IQE strongly restricts the
development of OLED. In 2012, Adachi and coꢀworkers [8] made an important breakthrough of
enabling pure organic materials to efficiently utilize excitons in OLEDs via thermally activated
delayed fluorescence (TADF). In contrast to traditional organic emitters that can only use singlet
excitons for light emission, TADF emitters could harvest both triplet excitons and singlet states to
afford light luminescence via reverse intersystem crossing (RISC) from triplet excitons to singlet
states [9ꢀ13]. With low nonꢀradiative rates and efficient singlet emission, in principle the TADF
approach can result in devices with near 100% IQE. Herein, a sufficiently small energy gap (ꢁEST)
between the singlet (S1) and triplet (T1) states is desired for efficient TADF molecules. According to
the molecular design principle, we can achieve a small ꢁEST by minimizing the overlap between the
highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO).
Based on this principle, numerous TADF materials have been designed with different kernels, such
as triazines [14, 15], thioxanthone [16], oxadiazoles [17], phenyl vinyl carbazole [18], and sulfones,
[19, 20]. Nevertheless, most TADF molecules have some challenges which have seriously impeded
their development and practical applications. Just like most TADF molecules, luminescence
weakened obviously in the solid state due to the πꢀπ stacking and the formation of excimers and
exciplexes, which is termed as aggregationꢀcaused quenching (ACQ) effect [21ꢀ23].
In 2001, Tang's group observed an intriguing phenomenon called aggregationꢀinduced emission
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(AIE) which can effectively overcome the drawbacks of ACQ: a new luminogen has faint emission
in its dilute solution but becomes highly emissive in the aggregated form [24]. Most typical AIE
compounds are due to a substantial inhibition of the twisting of the individual groups around the
single bond in the solid or aggregate state. At the same time, the helical molecular configuration of
these compounds can effectively inhibit the close πꢀπ stacking between molecules. To date, many
AIE materials have been widely researched and employed for construction of stable, efficient
nonꢀdoped OLEDs [25ꢀ31].
Based on the researches above, the TADF process with high exciton utility rate is capable of
harvesting both S1 and T1 excitons for light emission. Therefore, merging TADF emitters with AIE
characteristics could be an advisable strategy to develop excellent aggregationꢀinduced emission
and thermally activated delayed fluorescence (AIEꢀTADF) materials for efficient, stable, and
lowꢀcost nonꢀdoped OLEDs. In the design concept, various types of TADF materials with
aggregationꢀinduced emission properties have been reported in recent years. Chi et al designed and
synthesized a series novel AIEꢀDF compound with phenothiazine moieties and/or asymmetric
structures. Their study first reveals it is feasible to obtain highly efficient fluorescent materials by
combining AIE and TADF [32]. Zhang et al synthesized a symmetrical TADF molecules with 9,
9ꢀdimethylꢀ9, 10ꢀdihydroacridine (DMAC) as donors and benzophenone (BP) as acceptor. The
nonꢀdoped device based on it achieved a maximum EQE of 18.9%, a power efficiency of 59 lm W
−1 [33]. Yasuda et al designed and investigated luminescent organic–inorganic conjugated systems
based on oꢀcarboranes directly bonded to electron donating and electronꢀaccepting pꢀconjugated
units with excellent properties of AIE and TADF [34]. Li et al designed and investigated a series of
triphenylamineꢀtriphenylethylene compounds with excellent properties of AIE and TADF. The
device exhibited a maximum current efficiency of 12.8 cd Aꢀ1 [35]. Sun et al synthesized two new 9,
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9’, 10, 10’ꢀtetraoxidethianthrene derivatives, tCzDSO2 and 3tCzDSO2, which displayed admirable
performance of AIE and TADF [36]. Huang et al developed an AIEꢀTADF material with carbazol
and anthraquinone groups. The nonꢀdoped device based on it showed efficient electroluminescence
properties with maximum current efficiency of 10.6 cd A–1 [37]. Tang and coꢀworkers synthesized a
new tailorꢀmade luminogen DBTꢀBZꢀDMAC with an unsymmetrical structure. DBTꢀBZꢀDMAC
possesses obvious AIE and TADF properties. Nonꢀdoped OLED based on DBTꢀBZꢀDMAC neat
film achieved excellent EL efficiencies [38].
Inspired by the design principle of AIEꢀTADF molecules, we synthesized a novel AIEꢀTADF
compound of 3,5ꢀbisꢀcarbazolꢀ9ꢀylꢀphenyl)ꢀ[4ꢀ(9,9ꢀdimethylꢀ9Hꢀacridinꢀ10ꢀyl)ꢀphenyl]ꢀmethanone
(DCPDAPM) in good yields. Details of the synthetic routes, procedures and characterization data
are given in the Scheme 1 and Experimental section. As shown, DCPDAPM is developed by fusing
carbazole as skeleton, 9,9ꢀdimethylꢀ9,10ꢀdihydroacridine as donor group and benzophenone as
accept group. Such structure character makes DCPDAPM possess a twisted conformation to realize
admirable AIE and TADF properties, and these properties have been studied in the discussion. In
addition, good EL efficiencies are also achieved in nonꢀdoped and doped OLED based on
DCPDAPM.
2. Experimental
Unless otherwise stated, all relevant chemicals and common organic solvents were obtained from
commercial suppliers and were used without further purification. Tetrahydrofuran（THF）was
refluxed with sodium and benzophenone mixture under dry nitrogen instantly prior to use.
Furthermore, all the reactions were carried out under a nitrogen atmosphere.
2.1. Synthesis
2.2.1 Synthesis of 9,9′ꢀ(5ꢀBromoꢀ1,3ꢀphenylene)bis(9Hꢀcarbazole)(1)
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In a 250 mL round bottom flask , carbazole (8.35 g, 50 mmol), 1,3,5ꢀtribromobenzene (7.85 g, 25
mmol), CuI (0.48 g, 2.5 mmol), 18ꢀcrownꢀ6 (1.0 g, 3.8 mmol), potassium carbonate (18.3 g, 75
mmol), and oꢀdichlorobenzene (100 mL) was added and stirred at 180 °C for 24 h under nitrogen.
After reaction, the mixture was cooled to room temperature, and quenched with water and extracted
with chloroform. The combined organic layer was washed with distilled water three times and dried
over anhydrous magnesium sulfate. Then the solvent was evaporated in vacuum. The crude product
was purified by column chromatography on silica gel using (petroleum ether/dichloromethane=6:1
v/v) as the eluent to obtain the product as a white solid (6.0 g, 50%).1H NMR (600 MHz, CDCl3 ): δ
8.14 (d, J = 7.7 Hz, 4H), 7.86 (d, J = 1.7 Hz, 2H), 7.79 (s, 1H), 7.54 (d, J = 8.2 Hz, 4H), 7.46 (t, J =
7.6 Hz, 4H), 7.33 (t, J = 7.4 Hz, 4H).
2.1.2 Synthesis of (3,5ꢀbisꢀcarbazolꢀ9ꢀylꢀphenyl)ꢀ(4ꢀbromoꢀphenyl)ꢀmethanone (2)
In a 250 mL round bottom flask with 70 mL dried THF, 5.0 g (10.3 mmol) of compound 1 was
o
added under nitrogen. The mixture was cooled to ꢀ78 C, and 17.4 mL of tꢀBuLi was added drop
o
wise using a syringe. The mixture was stirred for 1 h at ꢀ78 C and then stirred for 9 h at the room
temperature. Then the mixture solution was cooled to ꢀ78 oC again and 5.7g（30.9 mmol） of
4ꢀBromobenzaldehyde was slowly added into the reaction solution. The mixture was stirred for 1 h
at ꢀ78 oC and then stirred overnight at the room temperature. Subsequently, the mixture was stirred
for 10 minutes under iceꢀwater. Then，50 mL ice water was added to quench the reaction and made
the hydrolysis reaction. The resulting mixture was extracted with dichloromethane for three times.
The combined organic layers were dried over anhydrous magnesium sulfate. After filtration and
solvent evaporation, the crude product was purified by silicaꢀgel column chromatography
(dichloromethane/petroleum ether mole radio was 1:3, v/v). The pure product obtained was
dissolved in 40 mL dichloromethane in 250 mL round bottom flask, then 6.7 g Pyridinium
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Chlorochromate was added. The mixture was stirred for 12 h. The precipitate was filtrated and the
filtrate was evaporated under the reduced pressure. After solvent evaporation, the crude product was
purified by column chromatography over silica gel with dichloromethane/petroleum ether (1:1, v/v)
mixture as eluent, providing the product as a yellow solid in 45% yield.
1H NMR (600 MHz, CDCl3), δ（ppm）: δ8.19 (dd, J = 7.9, 5.1 Hz, 3H), 7.99 ꢀ 7.87 (m, 4H), 7.69 (d,
J = 8.2 Hz, 2H), 7.51 (t, J = 7.7 Hz, 2H), 7.46 – 7.35 (m, 6H), 7.25 (t, J = 7.4 Hz, 2H), 6.87 (dd, J =
47.8, 8.4 Hz, 4H). 13C NMR (151 MHz, CDCl3), δ（ppm）:δ 194.96 140.04 , 135.01 , 133.13 ,
130.09 , 128.91 , 126.44 , 126.38 , 126.13 , 124.08 , 123.46 , 121.02 , 120.65 , 120.60 , 120.26 ,
109.73 , 109.68 . m/z: [M + H]+ calcd for C37H23BrN2O [M+1]+: 590.1032, found 590.1049. Anal.
Calcd for C37H23BrN2O: C 75.13%, H 3.92% and N 4.74%. Found: C 75.11%, H 3.94 % and N
4.73%.
2.1.3Synthesis of
(3,5ꢀbisꢀcarbazolꢀ9ꢀylꢀphenyl)ꢀ[4ꢀ(9,9ꢀdimethylꢀ9Hꢀacridinꢀ10ꢀyl)ꢀphenyl]ꢀmethanone
(DCPDAPM)
Under a nitrogen atmosphere, 0.67 g (1.86 mmol) of 9,10ꢀDihydroꢀ9,9ꢀdimethylacridine was added
quickly into a solution of compound 2 (1.0 g, 1.6 mmol), P(tꢀBu)3 (0.16 mL, 0.16 mmol) and
K2CO3 (0.88 g, 6.4 mmol) in 50 mL dry methylbenzene at the room temperature. The mixture was
stirred under nitrogen for 1 h. Then, Pd(OAc)2 (0.08 mmol, 0.018 g) was added. The mixture was
o
stirred for 30 minutes at the room temperature. Then the mixture was heated at 120 C and refluxed
for 12 h. After being cooled to room temperature, the resulting mixture was poured into water and
extracted with dichloromethane for three times. The organic phase was collected and washed with
water and dried with anhydrous Mg2SO4. The solvent was removed under vacuum and then the
residue was purified by column chromatography with petroleum ether/CH2Cl2 (2:1) as an eluent to
give compound DCPDAPM in 51% yield. 1H NMR (600 MHz, CDCl3)，δ（ppm）: δ 8.31 (d, J =8.2
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Hz, 1H), 8.20 (d, J =7.5 Hz, 3H), 8.06ꢀ7.87 (m, 5H), 7.75ꢀ7.67 (m, 3H), 7.55ꢀ7.33 (m, 15H), 7.06 ꢀ
6.94 (m, 3H), 6.73 (d, J =8.3 Hz, 1H), 1.62 (s, 6H). 13C NMR (151 MHz, CDCl3), δ（ppm）: δ
198.08, 143.73, 143.11, 136.21, 132.99, 132.72, 132.28, 131.08, 130.36, 129.91, 129.28, 129.16,
127.98,126.95, 126.40, 126.23, 123.79, 123.57, 123.47, 123.10, 122.94, 116.94, 112.73, 112.63,
38.78, 33.96. m/z: [M + H]+ calcd for C52H37N3O [M+1]+: 720.2937, found 720.2941. Anal. Calcd
for C52H37N3O: C 86.76%, H 5.18% and N 5.84%. Found: C 86.78%, H 5.16% and N 5.83%.
2.2. Measurements and characterization
1H NMR and 13C NMR were measured on a Bruker 600 MHz spectrometer using deuterated
chloroform as solvent, respectively. Highꢀresolution mass spectra (HRMS) were recorded on an
Autoflex III (MALDIꢀTOFꢀMS). Elemental analysis was performed on an Element Analysis System.
UV spectra was obtained on a Shimadzu UVꢀ2450 absorption spectrophotometer. Fluorescence
measurements were conducted on a Shimadzu RFꢀ5301PC fluorescence spectrometer.
Thermogravimetric analysis (TGA) was carried out on a TA Instruments TGA 2050
o
thermogravimetric analyzer under nitrogen at a heating rate of 10 C minꢀ1 from room temperature
to 500 oC. Differential scanning calorimetry (DSC) was performed using a Q2000 DSC differential
scanning calorimeter under a N2 atmosphere. The cyclic voltammetry (CV) was measured using
glassy carbon electrode as the working electrode, an Ag/Ag+ (0.01 M AgNO3) as the reference
electrode and Pt wire as the counter electrode, respectively. The decomposition temperature was
performed by thermogravimetric analysis (TGA) under nitrogen atmosphere using TGA 2050
thermogravimetric instrument with a heating rate of 10 °C/min from room temperature to 800 °C.
Time resolved PL spectra and transient PL decay were measured with Edinburgh Instruments
FLS920. The samples were loaded in a cryostat and temperature was cooled down 77 K.
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2.3. Device fabrication and measurement
First, to investigate the ability of DCPDAPM as a green emitter, a multilayer nonꢀdoped OLED
with a configuration of ITO/HATCN (20 nm)/TAPC (30nm)/DCPDAPM (25 nm)/Tmpypb (40
nm)/LiF
(1
nm)/Al
(150
nm)
were
fabricated,
where
dipyrazino[2,3ꢀf:2',3'ꢀh]quinoxalineꢀ2,3,6,7,10,11ꢀhexacarbonitrile (HATCN) serves as a hole
injection layer, TAPC and TmPyPb serve as holeꢀ and electronꢀtransporting layers, respectively .
Second, three doped OLEDs comprising CPB as the host material and DCPDAPM as the dopant
were fabricated. The structures of the doped OLEDs are: ITO/HATCN 20nm/TAPC 30nm/
DCPDAPM（x wt%）:CBP 25nm /Tmpypb 40nm/LiF 1nm/Al 150nm. The specific constructions of
the devices are shown as following. Glass substrates preꢀcoated with a 95ꢀnmꢀthin layer of indium
tin oxide (ITO) with a sheet resistance of 20 ꢂ per square were thoroughly cleaned for 10 minutes
in ultrasonic bath of acetone, isopropyl alcohol, detergent, deionized water, and isopropyl alcohol
and then treated with O2 plasma for 20 min in sequence. Organic layers were deposited onto the
ITOꢀcoated substrates by highꢀvacuum (< 5 × 10−4 Pa) thermal evaporation. Deposition rates were
controlled by independent quartz crystal oscillators, which are 1~2 Å s−1 for organic materials, 0.1
Å s−1 for LiF, and 6 Å s−1 for Al, respectively. The emission area of the devices is 3 × 3 mm−2 as
shaped by the overlapping area of the anode and cathode. The electroluminescent (EL) spectra
were measured on a Hitachi MPFꢀ4 fluorescence spectrometer. The current densityꢀvoltage
characteristics of the OLED were recorded on a Keithley 2400 Source Meter. The current
densityꢀvoltageꢀluminance curves were carried out with a 3645 DC power supply combined with a
1980A spot photometer and was recorded simultaneously. All measurements were operated at room
temperature under ambient conditions.
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3. Results and discussion
3.1 Synthesis and thermal property
Scheme 1 displays the synthetic route to DCPDAPM. The starting material 1 was synthesized by a
modified Ullmann condensation of carbazole with 1,3,5ꢀtribromobenzene. Then, compound 2 was
was prepared by compound 1 and 4ꢀmethylbenzaldehyde according to the nucleophilic addition
reaction. The final product DCPDAPM was obtained with a high yield by the modified Ullman
coupling reaction between compound 2 and 9,10ꢀDihydroꢀ9,9ꢀdimethylacridine. All of the
intermediates and DCPDAPM were separated by using column chromatography. The compound 1
1
and 2 were confirmed by 1H NMR, whereas DCPDAPM was fully characterized by H NMR, 13C
NMR, MS and elemental analysis. DCPDAPM is soluble in many common organic solvents such as
dichloromethane, tetrahydrofuran and toluene, while it is not soluble in water and methyl alcohol.
The thermal properties of DCPDAPM were characterized using thermogravimetric analysis (TGA)
and differential scanning calorimetry (DSC) under a nitrogen atmosphere (Fig. S1). The results
reveal that the decomposition temperature (Td) corresponding to a 5.0% weight loss of its original
weight is 309 and the glass transition temperature (Tg) is 72 . The Td and Tg of DCPDAPM is
attributed to its higher molecular weight and larger conjugated system. The Td and Tg indicate that
DCPDAPM has good thermal and morphological stability, which is suitable for the lightꢀemitting
device applications. The corresponding data are summarized in Table 1.
3.2 Theoretical calculations
The advisable design tactics for TADF molecules is to minimize the electron cloud overlap between
their HOMO and LUMO by distributing these orbital on different moieties, resulting in a small S1–
T1 energy splitting (ꢁEST) and efficient upꢀconversion from the T1 to the S1 state through reverse
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intersystem crossing (RISC) [34]. The structures of the ground state, singlet state and triplet state
were optimized using Gaussian 09 software base on density function theory (DFT) at the B3LYP/6–
31 G (d, p) level. The optimized structure and calculated electronic configuration of the HOMOs
and LUMOs of the ground state are shown in Fig. 1. As shown, HOMO of DCPDAPM is mainly
located on 9,9ꢀdimethylꢀ9,10ꢀdihydroacridine fragment, while its LUMO is mainly located on the
benzophenone fragment. Accordingly, the HOMO and LUMO of DCPDAPM supply obvious
spatial separation, leading to a small calculated ꢁEST value of 0.08eV and the notable
intramolecular charge transfer (ICT) effect. Such small ꢁEST ensures that RISC process could be
implemented from singlet to triplet state, demonstrating the potential of TADF property. In addition,
the optimized twisted conformation of DCPDAPM could reduce the πꢀπ interactions and the
ACQ effect, demonstrating potential of AIE. The calculated HOMOꢀLUMO gap for DCPDAPM is
2.82eV.
3.3 Optical Properties
The UVꢀvis absorption spectra of DCPDAPM (1×10ꢀ5M) in various solvents are shown in Fig. S2.
The high energy absorption band at 280ꢀ320 nm is attributed to the πꢀπ* electronic transitions of the
skeleton of DCPDAPM and the low energy absorption band at 320ꢀ360 nm is assigned to an
intramolecular charge transfer (ICT) band from the acridine moiety to the benzophenone moiety of
DCPDAPM. Evidently, the absorption spectra of DCPDAPM exhibited the similar maximum
absorption peak in different solvents. It is assurming that their structures and electronic
characteristics of the ground state are independent of the solvent polarity. On the contrary,
fluorescence spectra (Fig. S3) showed strong dependence on solvent polarities. For example, the
maximum of the DCPDAPM emission shifts from 473 nm in nꢀhexane to 510 nm in DMSO,
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indicating a large increase in polarity in the excited state. The relevant data are placed in Table 1.
The photoluminescence behavior of DCPDAPM in aqueous THF with different THF/water ratios
were studied, in which THF acts as the solvent and water acts as the nonꢀsolvent. Fig.2 displays the
PL spectra of DCPDAPM in THFꢀwater solvent mixtures with different water fractions (fw) at an
excitation wavelength of 380 nm. In dilute THF solution (10−5 M), DCPDAPM gives weak PL at
558 nm with a low photoluminescence (PL) quantum yield (ΦPL) of 6.2%, measured by a calibrated
integrating sphere. When more water is added (fw＞80%), a green emission peak at 535 nm rapidly
increase, along with the emission band centered at 558 nm gradually decrease. As the water fraction
is increased from 80 to 90 vol%, the AIEꢀTADF emission center to shift to the shorter wavelength.
This is due to the twisted molecular configuration of DCPDAPM can effectively inhibit the close
πꢀπ stacking between molecules. And the rigidification of molecular structure in the aggregated
state also gives rise to lowered reorganization energy, which lead to the blue shifted emission
relative to that in THF solution. When fw=95%, the fluorescence intensity increased to maximum at
535 nm with a ΦPL of 76.1%. These results show that DCPDAPM has the prominent AIE
characteristics.
△
For a small EST is conducive to the occurrence of TADF, the experimental ΔEST of DCPDAPM
in solid state is estimated from the fluorescence spectra at room temperature and the
phosphorescence spectra at 77 K. As Fig. S4 shown, DCPDAPM exhibited strong solid state
emission, peaking at 518 nm and 492 nm in fluorescence spectra and the phosphorescence spectra,
respectively. Singlet energy of DCPDAPM is calculated to be 2.82 eV, from fluorescence spectra
and triplet energy of DCPDAPM is 2.72 eV, from phosphorescence spectra. Finally, it exhibited a
remarkable small ꢁEST value of 0.10 eV. For the experimental △EST is far less than standard △
EST value (0.24eV) of TADF[39], the result demonstrates the triplet excited state can upꢀconvert to
12

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the singlet excited state easily by RISC, revealing the high potential of DCPDAPM as TADF
emitters. The relevant data are listed in Table 2.
In normal conditions, the upꢀconversion of triplet excitons that are necessary to produce delayed
fluorescence can be characterized by transient PL decay curves and further confirmed by
oxygenꢀsensitive behavior with PL spectra. According to the literature method [40, 41], the delayed
fluorescence of DCPDAPM was measured in THF solution. As shown in Fig.S5, an increasing
singleꢀexponential lifetime of delayed fluorescence ranging from 4.3 ns to 8.2 ns for DCPDAPM at
300K was observed after oxygen degassing by nitrogen. This observation indicated that a typical
oxygenꢀsensitive behavior in THF solution was characterized, and the corresponding PL spectra are
shown in the insets. Then, the transient photoluminescence decay characteristics of DCPDAPM in
thin films were investigated and depicted. As shown in Fig. 3, the fluorescence decay is sensitive to
temperature. As the temperature increases from 100 to 300 K, the longꢀlived component becomes
apparently higher because the high temperature can promote TADF process. At ambient
temperature (300 K) the neat film has a prompt fluorescence decay time (τprompt) of 34.2 ns and a
delayed fluorescence decay time (τTADF) of 8.1 ꢃs.
These results with prompt and delayed emissive components are consistent with TADF behavior
[13]. Considering the research results above, DCPDAPM possesses small energy gap (ꢁEST) and
outstanding delayed fluorescence lifetime, making them excellent TADF materials.
3.4 Electrochemical properties
The electrochemical properties of DCPDAPM were investigated by cyclic voltammetry (CV) in an
acetonitrile solution (1×10ꢀ3 M) with 0.1 M tetrabutylammonium perchlorate as the supporting
electrolyte under N2 atmosphere. The CV curve of DCPDAPM was shown in Fig. S6. DCPDAPM
13

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shows a reversible oxidation process. The HOMO energy level can be calculated with the empirical
equation HOMO = －(Eox+ 4.40) eV [42], where Eox is the onset oxidation potential. The Eox
observed from CV curve is 0.97 eV and the HOMO energy level of DCPDAPM is cailulated to be
－5.37 eV. Moreover, the energy band gap (Eg) was estimated to be 2.76 eV by the absorption
edges of the UVꢀvis spectra. The LUMO energy level of DCPDAPM is－2.61 eV, which is
calculated from the HOMO energy level and Eg (ELUMO= EHOMO+Eg). The results are summarized in
Table 1. Furthermore, The CV curves remain unchanged under multiple successive potential scans,
indicating the excellent redox stability of DCPDAPM.
3.5 Electroluminescent properties
To demonstrate the benefits of the AIEꢀTADF emitters for optoelectronic applications, OLEDs
using DCPDAPM either as the nonꢀdoped emitting layer or as the emitting dopant in a host are
fabricated. The nonꢀdoped OLED (Device A) is fabricated with a configuration of ITO/HATCN (20
nm)/TAPC (30nm)/DCPDAPM (25 nm)/Tmpypb (40 nm)/LiF (1 nm)/Al (150 nm); The doped
devices BꢀD have configurations of ITO/HATCN (20nm)/TAPC (30nm)/ DCPDAPM (x wt %):CBP
(25nm)/Tmpypb
(40nm)/LiF
(1nm)/Al
(150nm).
In
these
devices,
dipyrazino[2,3ꢀf:2',3'ꢀh]quinoxalineꢀ2,3,6,7,10,11ꢀhexacarbonitrile (HATCN) serves as a hole
injection layer, TAPC and TmPyPb serve as holeꢀ and electronꢀtransporting layers, DCPDAPM and
different concentrations (x wt %) of DCPDAPM in CPB are adopted as the emitting layers. Since
CBP has a high triplet energy of 2.6 eV, it is selected as a host to efficiently forbid backward energy
transfer from the guest to the host materials and to confine the triplet excitons within the guest
materials. Moreover, the concentrations of DCPDAPM in CBP are further varied (6, 10 and 20 wt%)
to investigate the concentration effect on the OLED performances. The energy level diagrams of
14

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DCPDAPM based multilayer OLEDs are shown in Fig. 4. The EL spectrum of nonꢀdoped device A
using DCPDAPM as emitting layer, displays a maximum emission peak locating at 521 nm with
ΦPL of 38.2%, showing that DCPDAPM emits green light with Commission International de
L'Eclairage (CIE) coordinate of (0.28, 0.59). The EL spectrum and CIE coordinate are shown in Fig.
5. Compared with the emission peaks of the films and the nanoparticles in 95 % aqueous mixture,
their electroluminescence spectrums are slightly blue shifted demonstrating that the EL emissions
originate from the amorphous emitting layer. In addition, device A exhibits excellent
electroluminescence properties with a turn on voltage of 3.2V, a maximum luminance of 123371 cd
mꢀ2, a maximum current efficiency of 26.88cd Aꢀ1, a maximum power efficiency of 15.63 lm/w and
a external quantum efficiency of 8.15%. When, at 1000 cd m−2, the device A shows the the ηC, ηP
and ηext are moderately decreased to 21.41 cd A−1, 15.28 lm W−1 and 6.488%, respectively, and the
corresponding current efficiency rollꢀoff is 20.4%. Current density–voltage–luminance curve is
depicted in Fig. 6; the current efficiency–current density curve is described in Fig. 7. The relevant
data are listed in Table 3. The low turnꢀon voltage and excellent bright luminance of Device A are
caused by the high charge injection rate and the efficient balanced chargeꢀtransport properties.
Hence, DCPDAPM is excellent of AIEꢀTADF materials for nonꢀdoped OLEDs.
The doped OLEDs of DCPDAPM in CBP host are turned on at low voltages of 3.6 V, and radiate
stable green EL emissions with the peaks at about 522 nm. These EL spectra and CIE coordinates
are also shown in Fig. 5. Through varying doping concentration, all of doped OLEDs show
excellent EL performance. The device B constructed with 6% DCPDAPM doped in CBP as an
emitting layer presents a maximum luminance of 67875 cd m−2, a maximum current efficiency of
40.68 cd A−1, a maximum power efficiency of 25.55 lm/w and a external quantum efficiency of
13.31%. When, at 1000 cd m−2, the OLED with 6 wt% DCPDAPM in CBP shows the the ηC, ηP
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and ηext are moderately decreased to 39.03 cd A−1, 21.89 lm W−1 and 12.77%, respectively, and the
corresponding current efficiency rollꢀoff is as small as 4%. The device C with 10% DCPDAPM
gives even better EL performance with a maximum luminance of 89010 cd m−2, a maximum current
efficiency of 50.14 cd A−1, a maximum power efficiency of 31.49 lm/w and a external quantum
efficiency of 16.18%. The OLED with 20 wt% DCPDAPM in CBP (device D) shows the best
maximum luminance, maximum current efficiency, maximum power efficiency and external
quantum efficiency of 116100 cd m−2, 61.83 cd A−1, 40.45 lm/w and 19.67%. Then the doped
OLED with 10 wt% DCPDAPM in CBP gives the ηC, ηP, and ηext are 48.49 cd A−1, 28.19 lm
W−1, and 15.65% at 1000 cd m−2 and the OLED with 20 wt% DCPDAPM in CBP shows the the ηC,
ηP and ηext are 61.45 cd A−1, 38.59 lm W−1 and 19.55%, respectively. The corresponding current
efficiency rollꢀoff of are 3.2% and 0.6% respectively. The efficiency rollꢀoff is apparently mitigated.
It can be concluded that the turnꢀon voltages are lowered; luminance is advanced as the increase of
luminogen contents in emitting layers. Compared with nonꢀdoped OLED, high maxima values of
doped OLEDs are slightly higher than the peak values of nonꢀdoped OLED, which may due to the
minor tripletꢀtriplet and/or singletꢀtriplet annihilations in condensed neat film. And electrons may
possibly be transmitted the emission layer to reach the hole injection layer, resulting in the low
efficiency at low dopant concentration. Compared with nonꢀdoped, the doped films also show
strong PL. For instance, the ΦPL of the doped film of DCPDAPM (20 wt%):CBP is 86.3%. Current
density–voltage–luminance curves are also depicted in Fig. 6, the current efficiency–current density
curves are also described in Fig. 7. These results are also listed Table 3.
These results reveal that DCPDAPM is favored to keep high EL efficiencies at high luminance by
further increasing the concentrations in CPB. It should be pointed out that the EL performances
were carried out in a nonꢀoptimized test device under ordinary laboratory conditions. The device
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performances may be further improved by optimizing the process conditions.
4. Conclusion
In summary, a new tailorꢀmade material (DCPDAPM) with an unsymmetrical DꢀAꢀD′ structure is
successfully synthesized. The structure was fully characterized systematically. Its properties are
investigated by experimental and theoretical methods. The results show that DCPDAPM is typical
AIEꢀTADF molecules with intriguing AIE and TADF properties, which can be reflected in their
high solid state fluorescence efficiency and small ꢁEST. The experimental ꢁEST value of
DCPDAPM is 0.10 eV. Furthermore, the nonꢀdoped OLED (Device A) and doped OLEDs (Device
B, Device C and Device D) were fabricated with DCPDAPM and DCPDAPM in CBP host as
lightꢀemitting layer, respectively. Among these OLEDs, the nonꢀdoped OLED (device A) provides
excellent peak EL efficiencies of 123371 cd m−2, 26.88 cd A−1, 15.63 lm/w, and 8.15%; while the
doped OLED (device D) with 20 wt% DCPDAPM in CBP shows the best maximum luminance,
maximum current efficiency, maximum power efficiency and external quantum efficiency of
116100 cd m−2, 61.83 cd A−1, 40.45 lm/w and 19.67%. This report provides an important guidance
to develop robust AIEꢀTADF materials with high solidꢀstate PL efficiencies and improve
electroluminescent efficiency of OLEDs.
Acknowledgments
This work was supported by Natural Science Foundation of Shanxi Province (No. 201601D011027);
Shanxi Scholarship Council of China (2016ꢀ014); International Science and Technology
Cooperation Foundation of Shanxi Province (No. 201703D421035); Open Fund of the State Key
Laboratory of Luminescent Materials and Devices, South China University of Technology (No.
2016ꢀskllmdꢀ09); Fund of State Key Laboratory of Elementoꢀorganic Chemistry, Nan kai
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University (No. 201615); National Natural Science Foundation of China (No. 61775090, 61405089);
The Guangdong Natural Science Foundation for Distinguished Young Scholars (No.
2016A030306017),The National Key R&D program of China (No. 2016YFB0401702) and The
Shenzhen Peacock Plan (No.KGTD2015071710313656). The authors express their sincere thanks
to the Advanced Computing Facilities of the Supercomputing Centre of Computer Network
Information Centre of Chinese Academy of Sciences for all the theoretical calculations.
Appendix A. Electronic Supplementary Information
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Table 1. Physical Properties of DCPDAPM
HOMO/LUMOf
(eV)
Eg
HOMO/LUMOh
d
e
g
a
b
c
Tg
Td
λabs
λem
λem
i
Eg (eV)
compound
(nm)
(nm) (nm)
(
°C
72
)
(
°C
)
(eV)
(eV)
DCPDAPM 288, 336 535 518
309
ꢀ5.37/ꢀ2.61
2.76
ꢀ5.03/ꢀ2.21
2.82
a Measured in THF.
b Measured in THF ：H2O (1:95).
c Measured in film.
d Obtained from DSC.
e Obtained from TGA
f Obtained from CV in CH3CN/nꢀBu4NClO4 and estimated from HOMO= ꢀ(Eox + 4.40); LUMO = HOMO + Eg.
g Calculated from the absorption edge, Eg= 1240/λonset
.
h Obtained from DFT calculations.
i Obtained from DFT calculations, Eg=LUMOꢀHOMO.

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Table 2 Energies of singlet and triplet states and fluorescence lifetimes of
DCPDAPM
i
j
l
S1 (eV)
T1 (eV)
ꢀESTk (eV)
τp (ns)
τdm (ꢁs)
compound
2.82
2.72
0.10
34.2
8.1
DCPDAPM
i Measured in solid at room temperature
j Measured in solid at 77 k.
k Calculated from the onset of peak fluorescence spectra and the phosphorescence spectra
l Prompt lifetime of DCPDAPM in solid at 300K
m Delay lifetime of DCPDAPM in solid at 300K

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Table 3 Electroluminescence properties (maximum values) of Device A, B, C and D
a
b
c
d
Von
Lmax
ηC,max
ηp,max
λEL f(nm)
CIE(x, y)
e
Device
ηext
(V) (cd mꢀ2) (cd Aꢀ1)
(lmWꢀ1)
A
B
C
D
3.2 123371
26.88
40.68
50.14
61.83
15.63
25.55
31.49
40.45
8.15
13.31
16.18
19.67
522
522
522
522
(0.28,0.59)
(0.24,0.55)
(0.24,0.56)
(0.26,0.56)
3.6
3.6
67875
89010
3.6 116100
（
continue） Electroluminescence properties (values at 1000 cd mꢀ2) of Device A, B, C and D
d
Vona (V)
ηC,max c (cd Aꢀ1)
ηp,max
e
Device
ηext
RO[%]
(lmWꢀ1)
A
B
C
D
4.4
5.6
5.4
5.0
21.41
39.03
48.49
61.45
15.28
21.89
28.19
38.59
6.488
12.77
15.65
19.55
20.4
4
3.2
0.6
a Turn on voltage at a brightness of 1 cd mꢀ2.
b Maximum luminance.
c Maximum current efficiency.
d Maximum power efficiency
e External quantum efficiency
f Electroluminescence peak.
RO current efficiency rollꢀoff from maximum value to that at 1000 cd m−2;

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Scheme 1 Synthetic route of DCPDAPM

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HOMO
LUMO
Fig. 1 HOMO and LUMO diagrams of DCPDAPM

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6000
5000
4000
3000
2000
1000
0
fw(vol %)
0
80
90
95
450
500
550
600
650
700
Wavelength/nm
Fig. 2. Fluorescence spectra and photographs of DCPDAPM in THF/water mixtures
with different water fraction. (excited at 360 nm).

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A
(A) Transient decay spectra of DCPDAPM at 300K.
B
(B)Temperature-dependent transient decay spectra
Fig. 3 Transient decay spectra of DCPDAPM in solid films

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Fig. 4 Energy level diagrams of DCPDAPM based multilayer OLEDs.