Novel aggregation-induced emission and thermally activated delayed fluorescence materials based on thianthrene-9,9′,10,10′-tetraoxide derivatives

Article abstract of DOI:10.1039/c6ra03281h

Two novel luminescent molecules based on thianthrene-9,9′,10,10′-tetraoxide derivatives, named tCzDSO2 and 3tCzDSO2, have been synthesized and characterized. The compound tCzDSO2 emits intense aggregation-induced emission (AIE) with a high photoluminescence quantum yields (Φ_F) of 0.92 at room temperature in the solid state. Simultaneously, by increasing the proportion of carbazole units, 3tCzDSO2 exhibits both AIE and thermally activated delayed fluorescence (TADF) in the solid state with Φ_F of 0.19 in air and 0.41 in N₂ atmosphere. The two compounds also display a bathochromic effect due to their intramolecular charge transfer (ICT) attribute. The time-dependent DFT predicted the singlet and triplet splitting (ΔE_ST) values of tCzDSO2 and 3tCzDSO2 to be 0.29 eV and 0.06 eV, respectively. The ΔE_ST of 3tCzDSO2 is small enough to allow efficient reverse intersystem crossing (RISC), leading to the TADF property at room temperature. As a result, the molecular design provides a simple and effective approach to integrate the features of AIE and TADF into one compound.

Full text of DOI:10.1039/c6ra03281h

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Novel aggregation-induced emission and thermally activated delayed
fluorescence materials based on thianthrene-9,9’,10,10’-tetraoxide
derivatives
Kaiyong Sun, Wei Jiang,* Xinxin Ban, Bin Huang, Zhaohang Zhang, Muyang Ye and Yueming Sun*
School of Chemistry and Chemical Engineering, Southeast University, Nanjing, 210096, Jiangsu, P. R. China
*eꢀmail: 101011462@seu.edu.cn (W. Jiang); eꢀmail: sun@seu.edu.cn (Y. Sun).
Abstract: Two novel luminescent molecules based on thianthreneꢀ9,9’,
10,10’ꢀtetraoxide derivatives, named tCzDSO2 and 3tCzDSO2, have been
synthesized and characterized. The compound tCzDSO2 emits intense
aggregationꢀinduced emission (AIE) with a high photoluminescence quantum yields
(ΦF) of 0.92 at room temperature in the solid state. Simultaneously, by increasing the
proportion of carbazole units, 3tCzDSO2 exhibits both AIE and thermally activated
delayed fluorescence (TADF) in the solid state with ΦF of 0.19 in air and 0.41 in N2
atmosphere. The two compounds also display a bathochromic effect due to their
intramolecular charge transfer (ICT) attribute. The timeꢀdependent DFT predicted the
singlet and triplet splitting (∆EST) values of tCzDSO2 and 3tCzDSO2 are 0.29 eV and
0.06 eV, respectively. The ∆EST of 3tCzDSO2 is small enough to allow efficient
reverse intersystem crossing (RISC), leading to the TADF property at room
temperature. As a result, the molecular design provides a simple and effective
approach to integrate the features of AIE and TADF into one compound.
Key words: Thianthreneꢀ9,9’,10,10’ꢀtetraoxide, Aggregationꢀinduced emission,
Thermally activated delayed fluorescence, Singletꢀtriplet splitting
Introduction
In the past decade, considerable efforts have been made toward the development of
organic luminescent materials for fabricating highꢀperformance organic lightꢀemitting

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diodes (OLEDs).1ꢀ6 However, most conventional luminophores built with
πꢀconjugated planar chromophores suffer from the notorious aggregationꢀcaused
quenching (ACQ).7,8 The conventional luminescent materials exhibit strong
luminescence in solution but weakened emission in their aggregated states, which
depresses the device performances, hindering the evolution of OLEDs. Even though
the doping method may alleviate the ACQ effect, but it requires hardꢀtoꢀcontrol
techniques and may suffer from other adverse problems, such as phase separation and
unstable emission colors at high voltages. In 2001, Tang et al discovered a novel
phenomenon of AIE that prevents the ACQ effect efficiently.9 The combination of
AIEꢀactive units and conventional ACQ building blocks has generated various
luminogens with excellent solidꢀstate emission, which function outstandingly as
lightꢀemitting layers for undoped OLEDs.10ꢀ14 However, common AIE luminescent
materials can only harvest singlet excitons to realize a theoretical internal quantum
efficiency of 25% due to spinꢀforbidden interactions, limiting the efficiency of
OLEDs.
Thermally activated delayed fluorescence (TADF) materials have attracted much
attention in recent years because both singlet and triplet excitons can be harvested to
achieve high efficiency. For a TADF molecule, a small ∆EST is required to promote
the upꢀconversion of triplet excited state to singlet excited state. Recently, a series of
Eꢀtype TADF emitters with small ∆EST were developed by Adachi et al.15ꢀ20 as an
alternative to achieving external quantum efficiencies (EQEs) higher than
conventional fluorescent emitters. To achieve high efficiency, the most commonly
method was via bipolar compounds based on intramolecular charge transfer (ICT)
within systems containing donor and acceptor moieties. In an ICT based compound,
the highest occupied molecule orbital (HOMO) and lowest unoccupied molecule
orbital (LUMO) would be localized at the donor and acceptor moieties, respectively.
Thus, a small overlap between HOMO and LUMO leads to a small ∆EST. However, a
common problem for TADF OLEDs is exciton concentration quenching caused by
singletꢀtriplet and tripletꢀtriplet annihilation, restricting the application of undoped
OLEDs. To overcome this problem, a special compound with the features of TADF

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and AIE is required to ensure efficient triplet harvesting, and more importantly, to
overcome the ACQ effect. Whereas, to the best of our knowledge, there has been few
studies about AIEꢀactive TADF compounds. Xu et al. have successfully synthesized
an AIEꢀactive TADF compound with a high photoluminescence quantum yield of
93.3%, which is the highest quantum yield for longꢀlifetime emitters.21 Then, they
also synthesized a single whiteꢀlightꢀemitting organic molecule with the features of
AIE and TADF.22 Wang et al. have successfully developed the TADF device with
maximum EQE value of 21.5% by using AIEꢀactive TADF compound as an emitter.23
In this work, we designed and synthesized two compounds, tCzDSO2 and
3tCzDSO2, which with the features of AIE and AIEꢀactive TADF, respectively. Both
of them have a typical DꢀA structure with thianthrene 9,9’,10,10’ꢀtetraoxide (DSO2)
as an electron accepter and 3,6ꢀDiꢀtertꢀbutylꢀ9Hꢀcarbazole (tCz)/ carbazole dendrons
(3tCz) as an electron donor unit. The tCzDSO2 emits intense AIE with a high ΦF of
0.92 due to the efficient elimination of ACQ effect. Meanwhile, compound 3tCzDSO2
exhibits not only AIE, but also TADF in the solid state, which can prevent the ACQ
effect and utilize the triplet excitons efficiently. The TGA and DSC demonstrated that
both of them have excellent thermal properties with high morphological stability. The
higher decomposition temperature (Td) and glassꢀtransition temperature (Tg) of
3tCzDSO2 due to the higher molecular weight are favorable to improve the
filmꢀforming performance during device operation. In addition, the 3tCzDSO2 shows
greater separation of the HOMO and LUMO orbitals in the DFT calculations. The
∆EST of tCzDSO2 and 3tCzDSO2 were calculated to be 0.29 eV and 0.06 eV,
respectively. The transient photoluminescence (PL) decay showed compound
3tCzDSO2 have a long lifetime, indicating the triplet excited state can upꢀconvert to
singlet excited state by RISC. This change in ∆EST can be explained well in the
modification of molecular structures. This work provides a simple and effective
approach to obtain AIEꢀactive TADF compound by reducing the ∆EST in the
modification of molecular structures.

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2. Experimental section
General information
All solvents and materials were used as received from commercial sources without
1
further purification. H NMR and 13C HMR spectra were recorded on a BRUKER
AMX 300 MHz and 75 MHz instrument relative to Si(CH3)4 as internal standard.
Molecular masses were determined by matrixꢀassisted laser desorptionꢀionization
timeꢀofꢀflight mass spectrometry (MALDIꢀTOFꢀMS) using a BRUKER DALTONICS
instrument, with aꢀcyanoꢀhydroxycinnamic acid as a matrix. Absorption and
photoluminescence emission spectra of the target compound were measured using a
SHIMADZU UVꢀ2450 spectrophotometer and a HORIBA FLUOROMAXꢀ4
spectrophotometer, respectively. The solid PL quantum efficiency was measured with
an integrating sphere under an excitation wavelength of 380 nm. Cyclic voltammetry
were performed on a CHI750C voltammetric analyzer in CH2Cl2 solutions (10ꢀ3 M)
(oxidation process) at a scan rate of 100 mV s−1 with a platinum plate as the working
electrode, a silver wire as the pseudoꢀreference electrode, and a platinum wire as the
counter electrode. The supporting electrolyte was tetrabutylammonium
hexafluorophosphate (0.1 M) and ferrocene was selected as the internal standard.
Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC)
curves were recorded with a Netzsch simultaneous thermal analyzer (STA) system
(STA 409PC) and DSC 2910 modulated calorimeter under a dry nitrogen gas flow at a
heating rate of 10 °C min−1. The films preparation as follows: In a general procedure,
the quartz plate substrates were precleaned carefully and treated by UV ozone for 4
min. The solutions with the concentration of 10 mg mL−1 were spin coated onto the
quartz plate substrate and dried in vacuum.
Quantum chemical calculations
The geometrical and electronic properties of tCzDSO2 and 3tCzDSO2 were
performed with the Gaussian 09 program package. The calculation was optimized at
the B3LYP/6ꢀ31G (d) level of theory. The molecular orbitals were visualized using

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Gaussview 5.0.
Materials
The 3,6ꢀDiꢀtertꢀbutylꢀ9Hꢀcarbazole 1 and carbazole dendrons 2 were synthesized
according to the literature methods.24,25
Preparation of 2-bromo-thianthrene
To a stirred solution of thianthrene (3 g, 13.85 mmol) in THF (100 mL) at room
temperature under N2 was added Br2 (4.64 g, 29 mmol). After the addition was
completed the mixture was heated at 80°C for 5 h. Then, the reaction mixture was
extracted with dichloromethane and washed with water. The organic layer was dried
by anhydrous Na2SO4 and filtered. The product was isolated by silica gel column
chromatography using hexane as eluent to afford a white solid (2.15 g, 50%).1H NMR
(300 MHz, CDCl3, δ ) : 7.23ꢀ7.26 (m, 2H), 7.30ꢀ7.36 (m, 2H), 7.45ꢀ7.48 (m, 2H),
7.61 (d, J = 2.0 Hz, 1H); 13C NMR (75 MHz, CDCl3, δ ) : 121.4, 127.7, 127.9, 128.8,
128.8, 129.6, 130.5, 131.2, 134.7, 134.8, 135.2, 137.7; MS (MALDIꢀTOF) [m/z]:
calcd for C12H7BrS2: 293.92, found: 293.80. Anal. Calcd (%) for C12H7BrS2: C, 48.82;
H, 2.39. found: C, 48.82; H, 2.38.
Preparation of 2-Bromo-thianthrene 9,9’,10,10’-tetraoxide
To a stirred solution of 2ꢀbromoꢀthianthrene (2 g, 6.80 mmol) in AcOH (50 mL) at
room temperature was added 30% H2O2 (7.8 g, 68 mmol). Then, the mixture was
heated at 110 °C for 2h. After this mixture cooled to room temperature, the reaction
mixture was extracted with dichloromethane and washed with water. The organic
layer was dried by anhydrous Na2SO4 and filtered. The product was reꢀcrystallized
from ethyl acetate to give a colorless solid (2.38 g, 97%).1H NMR (300 MHz, CDCl3,
δ ) : 7.83ꢀ7.86 (m, 2H), 7.94 (d, J= 5.1 Hz, 1H), 8.09 (d, J= 8.1 Hz, 1H), 8.24ꢀ8.27 (m,
13
2H), 8.37 (s, 1H); C NMR (75 MHz, DMSO, δ ) : 125.8, 125.8, 126, 128.3, 128.4,
128.5, 134.8, 135, 137.7, 137.9, 139.6; MS (MALDIꢀTOF) [m/z]: calcd for
C12H7BrO4S2: 359.22, found: 359.80. Anal. Calcd (%) for C12H7BrO4S2: C, 40.12; H,
1.96. found: C, 40.12; H, 1.97.
Preparation
of
3,6-Di-tert-butyl-9-(9,9’,10,10’-tetraoxo-5,10-dihydro-5,10-
thianthren-2-yl)-9H-carbazole (tCzDSO2)

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2ꢀBromoꢀthianthrene 5,5,10,10ꢀtetraoxide (1 g, 2.8 mmol), 3,6ꢀDiꢀtertꢀbutylꢀ9Hꢀ
carbazole (0.93 g, 3.4 mmol), K2CO3 (0.48 g, 3.4 mmol), copper(I) iodide (0.006 g,
0.3 mmol), and 1,10ꢀphenanthroline (0.006 g, 0.3 mmol) were added to 20 mL of
dried DMF. The mixture was heated at 160 °C for 12 h under nitrogen atmosphere.
After this mixture cooled to room temperature, the reaction mixture was extracted
with dichloromethane and washed with water. The organic layer was dried by
anhydrous Na2SO4 and filtered. The product was isolated by silica gel column
chromatography using petroleum ether/ethyl acetate (3:1) as eluent to afford a bright
1
green solid (1.08 g, 70%). H NMR (300 MHz, DMSO, δ ) :1.42 (s, 18H), 7.52 (t, J=
13
8.4 Hz, 4H), 8.08 (t, J= 4.5 Hz, 2H), 8.29ꢀ8.44 (m, 6H), 8.53 (d, J= 8.4 Hz, 1H); C
NMR(75 MHz, DMSO, δ ) :31.7, 34.6, 109.1, 117, 122, 123.9, 124.2, 125.9, 126,
128.5, 130.9, 134.9, 135, 137.4, 138.2, 138.4, 140.2, 142.7, 144.2; MS (MALDIꢀTOF)
[m/z]: calcd for C32H31NO4S2: 557.72, found: 557.23. Anal. Calcd (%) for
C32H31NO4S2: C, 68.91; H, 5.60; N, 2.51. found: C, 68.89; H, 5.59; N, 2.50.
Preparation of 3,6-bis(3,6-di-tert-butyl-9H-carbazole-9yl)-(9,9’,10,10’-tetraoxo-5,
10-dihydro-5,10-thianthren-2-yl)-9H-carbazole (3tCzDSO2)
The synthetic method of 3tCzDSO2 was according to that of tCzDSO2 with a yield
1
of 41.7%. H NMR (300 MHz, DMSO, δ ) :1.42 (s, 36H), 7.33 (d, J= 8.7 Hz, 4H),
7.48 (d, J= 6.9 Hz), 7.73 (d, J= 10.5 Hz, 2H), 7.88 (d, J= 8.7 Hz, 2H), 8.09ꢀ8.14 (m,
2H), 8.30 (s, 4H), 8.41ꢀ8.44 (m, 2H), 8.53 (d, J= 8.1 Hz, 1H), 8.66 (d, J= 8.1 Hz, 1H),
13
8.73 (s, 3H); C NMR (75 MHz, DMSO, δ ) : 31.8, 34.4, 109.0, 110.8, 111.3, 114.5,
115.6, 116.6, 119.9, 122.6, 123.6, 124.6, 126.0, 126.1, 131.2, 132.4, 138.1, 138.8,
139.3, 141.9, 142.2; MS (MALDIꢀTOF) [m/z]: calcd for C64H61N3O4S2: 1000.32,
found: 999.65. Anal. Calcd (%) for C64H61N3O4S2: C, 76.84; H, 6.15; N, 4.20. found:
C, 76.81; H, 6.14; N, 4.18.
Results and discussion
Synthesis and characterization
The synthesis routes and chemical structures of tCzDSO2 and 3tCzDSO2 are shown

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in Scheme 1. 2-bromoꢀthianthrene was prepared through bromination reaction. Then,
2-bromoꢀthianthrene was oxidized to 2ꢀBromoꢀthianthrene 9,9’,10,10’ꢀtetraoxide. The
compounds tCzDSO2 and 3tCzDSO2 were synthesized by the classic Ullmann
reaction. Finally, the products were purified by column chromatography to give the
1
pure products. H and 13C NMR spectroscopy, mass spectrometry, and elemental
analysis were used to characterize the molecular structures.
Scheme 1 Synthetic routes and chemical structures of tCzDSO2 and 3tCzDSO2.
Thermal Properties
The thermal properties of tCzDSO2 and 3tCzDSO2 were investigated by using
thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC)
under a nitrogen atmosphere. According to Fig. 1, tCzDSO2 exhibited excellent
thermal stability with a 5% weightꢀloss Td as high as 371 °C, while Td of 3tCzDSO2 is
reached at a temperature of 432 °C. This value is about 61°C above tCzDSO2, which
is attributed to the high molecular weight of 3tCzDSO2. In addition, the DSC curves
record wellꢀdefined Tg of 110 °C (tCzDSO2) and 141 °C (3tCzDSO2).
Simultaneously, no noticeable signals related to the crystallization or melting is
observed in the DSC curves. Such excellent thermal properties with high
morphological stability are favorable to improve the OLEDs performance during

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device operation.
100
80
60
40
20
0
tCzDSO2
3tCzDSO2
50
100
150
Temperature (oC)
0
100
200
300
400
500
600
Temperature (oC)
Fig. 1 TGA curves of tCzDSO2 and 3tCzDSO2. Inset: Corresponding DSC traces.
Photophysical Properties
The photophysical properties of two compounds were measured by UVꢀvis absorption
and photoluminescence (PL) spectra as shown in Fig. 2 and Table 1. As depicted in
Fig. 2a, both compounds exhibit three major absorption bands locate at the 285 nm ꢀ
295 nm, 324 nm ꢀ 347 nm and 388 nm ꢀ 410 nm in the UVꢀvis absorption. The
absorption spectra of tCzDSO2 and 3tCzDSO2 exhibits two strong absorption peaks
at 285ꢀ295 nm can be attributed to the nꢀπ* transitions of in
3,6ꢀDiꢀtertꢀbutylꢀ9Hꢀcarbazole and carbazole dendrons. Meanwhile, the peak at 324
nm ꢀ 347 nm in two compounds are correspond to carbazoleꢀ and thianthrene
9,9’,10,10’ꢀtetraoxideꢀcentered nꢀπ* transitions. The strong peak at 388 nm and the
weak peak at 410 nm for tCzDSO2 and 3tCzDSO2 can be assigned to the ICT
transitions. The optical bandgap (Eg) can be estimated from the edge of the UVꢀvis
absorption, giving the values of 2.82 eV and 2.58 eV for tCzDSO2 and 3tCzDSO2,
respectively. Upon UV excitation, the PL spectra of tCzDSO2 and 3tCzDSO2 exhibit
the peaks at 522 nm/554 nm and 544 nm/595 nm in the film/solution, respectively. Fig.
2b and Fig. 2c showed the ICT characteristics of the two compounds via their
gradually redꢀshifted and broadened fluorescent emissions upon increasing the

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polarity of solvent, indicating the typical photoinduced ICT process and the effective
electronic communication between the donor and acceptor units. The solid ΦF of
tCzDSO2 and 3tCzDSO2 are 0.92 and 0.19/0.41, respectively. Such high ΦF can
attribute to the suitable DꢀA molecular structures.
(a)
1.0
0.8
0.6
0.4
0.2
0.0
tCzDSO2
Abs Solution
PL Solution
PL Film
3tCzDSO2
Abs Solution
PL Solution
PL Film
300
400
500
600
700
Wavelength (nm)
(b)
1.0
0.8
0.6
0.4
0.2
0.0
tCzDSO2
Hexane
Toluene
Dichloromethane
Trichloromethane
Tetrahydrofuran
300
400
500
600
700
800
Wavelength (nm)

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(c)
1.0
0.8
0.6
0.4
0.2
0.0
3tCzDSO2
Hexane
Toluene
Trichloromethane
Dichloromethane
300
400
500
600
700
800
900
Wavelength (nm)
Fig. 2 (a) The absorption and emission spectra of tCzDSO2 and 3tCzDSO2 in flim and CH2Cl2. (b)
PL spectra of tCzDSO2 in different solvents. (c) PL spectra of 3tCzDSO2 in different solvents.
Table 1 Physical properties of the compounds
a
b
b
c
c
d
e
e
Tg/ Td
λabs
λem
λem
ΦF
Eg
Eg
HOMO/LUMO e
[eV]
HOMO/LUMO f
[eV]
∆EST
[eV]
[°C]
[nm] (log ε)
[nm]
553
[nm]
520
[%]
[eV]
3.39
[eV]
2.82
284(6.5),292
(6.49),325(6.
3),337(6.34),
388(6.34)
tCzDSO2
371/110
92
ꢀ5.64/ꢀ2.25
ꢀ5.18/ꢀ2.46
ꢀ5.60/ꢀ2.78
0.29
285(5.77),29
5(5.78),334(
5.3),346(5.3)
,397(4.69)
3tCzDSO2 432/141
595
547
19/41
2.72
2.58
ꢀ5.32/ꢀ2.74
0.06
a
b
Measured by DSC/TGA at a heating rate of 10 °C mimꢀ1. Measured in CH2Cl2 (10ꢀ5 M). ε
c
d
denotes the molar extinction coefficient. Measured in thin film on quartz substrate. Estimated
e
from the optical absorption edge, Eg =1240/λonset. Obtained from quantum calculations by using
f
B3LYP/6ꢀ31G(d). Calculated by HOMO = ꢀ(4.8+ꢀꢁꢆꢂꢇꢃꢄꢅ) eV, and LUMO = HOMO + Eg,
ꢆꢇ
where ꢀ
is the onset potential of the oxidation.
ꢁꢂꢃꢄꢅ

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AIE Properties
The photoluminescence spectra of tCzDSO2 and 3tCzDSO2 in aqueous THF with
different THF/water ratios were shown in Fig. 3. Water was used as a nonsolvent for
the compounds. The reason was that the compounds must aggregate in the aqueous
mixtures with high water fractions (fw). As shown in Fig. 3, emission of tCzDSO2 in
the pure THF was very weak that only weak signal was recorded with maxima at 533
nm. Simultaneously, emission of 3tCzDSO2 in the pure THF was almost no PL signal
was recorded. With increasing fw, the PL intensities initially decrease due to the
increased solvent polarity. Then, the PL intensities start to increase at the fw of 60%
and 70% for tCzDSO2 and 3tCzDSO2, respectively. At a high fw of 90%,
luminescence was significantly enhanced for tCzDSO2 and 3tCzDSO2. The PL
intensities enhancement was induced by aggregation of molecules, thus testifying to
their AIE active. Notably, in comparison with the commonly reported AIE moieties,
such as tetraphenyl ethylene (TPE), silole and 9,10ꢀdistyrylanthracene, the two
compounds belong to a new class of AIE compounds due to their novel structures.
(a)
tCzDSO2
f
(vol%)
w
0
10
20
30
40
50
60
70
80
90
90
0
400
450
500
550
600
650
Wavelength (nm)

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(b)
3tCzDSO2
f
(vol%)
w
0
10
20
30
40
50
60
70
80
90
0
90
400
450
500
550
600
650
700
Wavelength (nm)
Fig. 3 Photoluminescence (PL) spectra of tCzDSO2 (a) and 3tCzDSO2 (b) in THF/water mixtures
with different amounts of water (fw). c = 10 ꢁM.
Electrochemical properties
The electrochemical properties of tCzDSO2 and 3tCzDSO2 were characterized by the
electrochemical
cyclic
voltammetry
(CV)
using
tetrabutylammonium
hexafluorophosphate (TBAPF6) as the supporting electrolyte and ferrocene as the
internal standard. As shown in Fig. 4, during the anodic scan in dichloromethane,
tCzDSO2 and 3tCzDSO2 exhibited reversible oxidation behavior, which can be
attributed to the oxidation of electronꢀdonating 3,6ꢀdiꢀtertꢀbutylcarbazole moiety and
the introduction of two tertꢀbutyl groups at the 3,6 positions of outlayer carbazole
units, respectively. No reduction waves were detected. On the basis of the onset
potentials for oxidation, the HOMO energy levels tCzDSO2 and 3tCzDSO2 were
estimated to be ꢀ5.60 eV and ꢀ5.32 eV, respectively. The reason is that the HOMO of
tCzDSO2 is mainly concentrated in the tCz and DSO2 units, while the HOMO of
3tCzDSO2 is distributed over the whole 3tCz moiety. Thus, the calculated HOMO
value of 3tCzDSO2 is 0.28 eV higher than that of tCzDSO2, which better matches the
work function of anode for the injection of holes. The results are further confirmed by
DFT calculations. The LUMO energy levels tCzDSO2 and 3tCzDSO2 were estimated
from the HOMO energy level and Eg were ꢀ2.78 eV and ꢀ2.74 eV.

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tCzDSO2
3tCzDSO2
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
Potential (V vs Fc/Fc+)
Fig. 4 Oxidation part of the CV curves of tCzDSO2 and 3tCzDSO2 in dichloromethane.
Delayed fluorescence
The transient photoluminescence (PL) decay characteristics of two compounds in
solid film were depicted in Fig. 5 and data was listed in Table S1. As shown in Fig. 5a
and Table S1, tCzDSO2 only have a fast decay with a lifetime of 16 ns, which can be
assigned to fluorescence. However, as depicted in Fig. 5b, 3tCzDSO2 have
twoꢀcomponent decays, that is, a fast decay with a lifetime of 29 ns and a slow decay
with a lifetime of 1.6 ꢁs can be attributed to fluorescence and delayed fluorescence
decay, respectively. Thus, the triplet excited state can upꢀconvert to the singlet excited
state by RISC. The results indicated that 3tCzDSO2 shows better solidꢀstate triplet
harvesting, which is favorable to improve the efficiency of OLEDs. The delayed
component of 3tCzDSO2 showed remarkable temperature dependence when the
temperature increased from 150 K to 300 K (see Fig. S1a), consistent with other
TADF materials. Meanwhile, the delayed fluorescence emission for 3tCzDSO2
decreases with decreasing temperature (see Fig. S1b), confirming the thermally
assisted mechanism. These results proved the presence of thermal activation energy
for the delayed fluorescence.15 In addition, the ΦF of 3tCzDSO2 increased from 0.19
in air to 0.41 in N2 atmosphere, also indicating the existence of delayed fluorescence.

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(a)
tCzDSO2
103
102
101
100
0.05
0.10
0.15
0.20
Time (µs)
(b)
3tCzDSO2
103
102
101
100
0
1
2
3
4
5
6
Time (µs)
Fig. 5 Transient PL decay profiles of tCzDSO2 (a) and 3tCzDSO2 (b) in solid films.
DFT calculations
The threeꢀdimensional geometries and the frontier molecular orbital energy levels of
tCzDSO2 and 3tCzDSO2 were calculated using density functional theory (DFT). The
results were depicted in Table 1, and the HOMOs and LUMOs of two compounds
were in shown in Fig.6. The geometries of two compounds in Fig.6 show that the
thianthrene 9,9’,10,10’ꢀtetraoxide and carbazole are significantly twisted, resulting in
a nonꢀplanar structure in each molecule. The HOMOs of the tCzDSO2 and 3tCzDSO2

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are evenly delocalized over the outer 3,6ꢀDiꢀtertꢀbutylꢀ9Hꢀcarbazole and carbazole
dendrons, respectively. The LUMOs are evenly delocalized over the thianthrene
9,9’,10,10’ꢀtetraoxide. However, in comparison with tCzDSO2, the 3tCzDSO2 shows
greater separation of the HOMO and LUMO orbitals. To predict the energy difference
(∆EST) between the lowest S1 and the lowest T1 levels, Time dependent density
functional theory (TDꢀDFT) calculations were performed, based on the ground state
geometries when optimized by the DFT (B3LYP/6ꢀ31G(d)). The ∆EST values of
tCzDSO2 and 3tCzDSO2 were 0.29 eV and 0.06 eV, respectively, confirming the
smaller overlap between the HOMO and LUMO of 3tCzDSO2. The smaller ∆EST
values of 3tCzDSO2 indicated a potentially high RISC, thus causing the TADF
phenomenon.
Fig. 6 Optimized geometries and calculated HOMO and LUMO density maps for tCzDSO2 and
3tCzDSO2 by DFT calculations in Gaussian 09 at the B3LYP/6ꢀ31G (d) level.
Conclusion
In summary, two novel compounds, namely tCzDSO2 and 3tCzDSO2, composed of
electronꢀdonating 3,6ꢀDiꢀtertꢀbutylꢀ9Hꢀcarbazole (tCz)/carbazole dendrons (3tCz) and
electronꢀaccepting thianthrene 9,9’,10,10’ꢀtetraoxide, have been designed and
synthesized. The compound tCzDSO2 exhibits intense AIE with a high ΦF of 0.92 in

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the solid state. Simultaneously, the compound 3tCzDSO2 exhibits AIEꢀactive TADF,
which provide the ΦF of 0.19 and 0.41 in air and N2 atmosphere, respectively. The
∆EST of tCzDSO2 and 3tCzDSO2 are 0.29 eV and 0.06 eV, respectively. The DFT
calculations demonstrate that the ∆EST of 3tCzDSO2 was minimized by the increased
proportion of carbazole units, which can induce the separating of the HOMO and
LUMO. This report provides a simple and effective approach to obtain AIEꢀactive
TADF compound, and is significant for the potential application in nondoped OLED.
Meanwhile, further studies about devices preparation are currently in progress in our
laboratory.
Acknowledgments
We are grateful for the grants from the National Natural Science Foundation of China
(51103023 and 21173042), National Basic Research Program China (2013CB932902),
Jiangsu Higher Education Institutions of China (NO. 14KJB150003) and Jiangsu
Planned Projects for Postdoctoral Research Funds (No. 1501011A). We are also
thankful for the support of the Scientific Research Foundation of Graduate School of
Southeast University.
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By introducing more proportion of carbazole, the newly designed molecule
3tCzDSO2 integrates the features of AIE and TADF with extremely small ∆EST.