Bipolar fluorophores based on intramolecular charge-transfer moieties of sulfone for nondoped deep blue solution-processed organic light-emitting diodes

Article abstract of DOI:10.1016/j.dyepig.2020.108242

Dipolar emitters exhibited excellent performance in organic light-emitting diode (OLED). However, these molecules had intramolecular charge-transfer (ICT) properties, which posed challenge to obtain deep blue emission. In this study, three fluorophores were designed by introducing carbazole and diphenylamine as electron donors and sulfone as electron acceptor due to their mild charge-accepting properties and twisted angles. These materials appeared almost in vertical angles of the dihedral configuration, and exhibited high thermal and electrochemical stability, suitable for solution-processed OLED. The solution-processed non-doped devices based on these three emitters were realized, where two emissions within the standard deep blue emission range were achieved with the Commission International e de l'Eclairage (CIE) coordinates of (0.16, 0.12) and (0.16, 0.15).

Full text of DOI:10.1016/j.dyepig.2020.108242

Journal Pre-proof
Bipolar fluorophores based on intramolecular charge-transfer moieties of sulfone for
nondoped deep blue solution-processed organic light-emitting diodes
Liang Cao, Lei Zhang, Qiang Wei, Jiasen Zhang, Dongjun Chen, Sheng Wang, Su
Shi-jian, Tao Wang, Ziyi Ge
PII:
S0143-7208(19)32171-0
DOI:
https://doi.org/10.1016/j.dyepig.2020.108242
DYPI 108242
Reference:
To appear in: Dyes and Pigments
Received Date: 12 September 2019
Revised Date: 28 December 2019
Accepted Date: 21 January 2020
Please cite this article as: Cao L, Zhang L, Wei Q, Zhang J, Chen D, Wang S, Shi-jian S, Wang T,
Ge Z, Bipolar fluorophores based on intramolecular charge-transfer moieties of sulfone for nondoped
deep blue solution-processed organic light-emitting diodes, Dyes and Pigments (2020), doi: https://
doi.org/10.1016/j.dyepig.2020.108242.
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Author Statement
All person have made substantial contributions to the work reported in manuscript,
including Liang Cao, Lei Zhang, Jiasen Zhang, Dongjun Chen, performed data
acquirement, data analysis and wrote the manuscript; Sheng Wang helped perform the
analysis with constructive discussions; Qiang Wei revised the manuscript; Tao Wang,
Shi-jian Su and Ziyi Ge contributed to the conception of the study.

Bipolar Fluorophores Based on Intramolecular Charge-Transfer
Moieties of Sulfone for Nondoped Deep Blue Solution-Processed
Organic Light-Emitting Diodes
Liang Caoa,b,1, Lei Zhangb,c,1, Qiang Weib,c*, Jiasen Zhanga,b, Dongjun Chend, Sheng
Wanga, Shi-jian Sud,*, Tao Wanga* and Ziyi Geb,c*
a Key Laboratory of Advanced Textile Materials and Manufacturing Technology, Ministry of Education, Zhejiang
Sci-Tech University, Hangzhou 310018, P.R. China
b Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201, China
c Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences
d State Key Laboratory of Luminescent Materials and Devices, Institute of Polymer Optoelectronic Materials and
Devices, South China University of Technology, Guangzhou, 510640, P. R. China.
* E-mail: weiqiang@nimte.ac.cn, taotao571@hotmail.com, geziyi@nimte.ac.cn, mssjsu@scut.edu.cn
1: These two authors contributed equally to this work
ABSTRACT: Dipolar emitters exhibited excellent performance in organic light-emitting diode
(OLED). However, these molecules had intramolecular charge-transfer (ICT) properties, which
posed challenge to obtain deep blue emission. In this study, three fluorophores were designed by
introducing carbazole and diphenylamine as electron donors and sulfone as electron acceptor due
to their mild charge-accepting properties and twisted angles. These materials appeared almost in
vertical angles of the dihedral configuration, and exhibited high thermal and electrochemical
stability, suitable for solution-processed OLED. The solution-processed non-doped devices based
on these three emitters were realized, where two emissions within the standard deep blue emission
range were achieved with the Commission International e de l’Eclairage (CIE) coordinates of
(0.16, 0.12) and (0.16, 0.15).
Keywords: intramolecular charge-transfer; bipolar fluorophores; deep blue; single layer, organic
light-emitting diodes
1. Introduction
OLED have the advantages of self-luminance, low driving voltage, wide color gamut, wide
viewing angle, ultra-thin and many more, therefore they are considered as the next generation of
display technology [1-3]. For the fabrication of OLED, solution processing is preferred as it is
suitable for large-scale processing of flexible devices at low cost. To realize full-color display of
OLED, blue light-emitting materials are essential[4, 5]. However, these materials have deeper
frontier molecular orbital (FMO) as compared to red and green light-emitting materials, which
often resulted to poor performances. Dipolar materials with D-A structures have attracted
tremendous attentions [6-12], because it can increase both hole and electron mobility[13, 14] to
achieve 100% internal quantum efficiency with low efficiency roll-off[8, 15-17]. However, due to

the intramolecular charge-transfer (ICT) properties in dipolar materials, most of the emitters are
designed with long wavelength, which pose a challenge to design deep-blue emitters.
In order to achieve deep blue emission, the D-A molecules need to have weak ICT effect and short
conjugation length[13, 14, 18-32]. Therefore, in this work, three deep blue emitting compounds
based on sulfone intramolecular charge-transfer type were designed and synthesized as shown in
Scheme 1, which possessed two sulfonyl groups as electron acceptors (A) and carbazoles or
triphenylamine as an electron donor (D). These D-π-A type molecules have ICT character with
large dihedral angles and significant energy gap between highest occupied molecular orbital
(HOMO) and lowest unoccupied molecular orbital (LUMO), which are both beneficial for
generating short-wavelength emissions[33]. In addition, these fluorophores exhibited good
photophysical, thermal, electrochemical and electroluminescence properties. Solution-processed
non-doped OLED were then fabricated, in which two of it exhibited deep blue emission with CIE
of (0.16, 0.15) and (0.16, 0.11).
2. Synthesis
2.1 Materials
(9-phenyl-9H-carbazol-3-yl)boronic
acid,
acid,
(4-(9H-carbazol-9-yl)phenyl)boronic
acid,
(4-(diphenylamino)phenyl)boronic
2,7-dibromo-9,9-dioctyl-9H-fluorene,
bis(pinacolato)diboron were purchased from TCI. Tetrakis(triphenylphosphine)palladium
(Pd(PPh3)4), bis(triphenylphosphine)palladium(II)dichloride(PdCl2(PPh3)2) and
1,1'-bis(diphenylphosphino)ferrocenedichloropalladium(II) (PdCl2(dppf)) were purchased from
Shanxi Kaida Chemical Engineering Co., Ltd. Other reagents and solvents were purchased from
Sinopharm Group Chemical Reagent Co., Ltd. The 1,4-dioxane was refluxed with sodium and
benzophenone under argon atmosphere, then distilled. The synthetic routes of 6a, 6b and 6c were
outlined in Scheme 1.
Scheme 1. The synthetic routes of 6a, 6b and 6c.
2.2 Synthesis
2.2.1 Synthesis of 2.2.1 3-(7-bromo-9,9-dioctyl-9H-fluoren-2-yl)-9-phenyl-9H-carbazole (1a),
9-(4-(7-bromo-9,9-dioctyl-9H-fluoren-2-yl)phenyl)-9H-carbazole (1b) and 4-(7-bromo-9,9-

dioctyl-9H-fluoren-2-yl)-N,N-diphenylaniline (1c)
(9-phenyl-9H-carbazol-3-yl)boronic acid (2.87g, 0.010 mol), 2,7-dibromo-9,9-dioctyl-9H-fluorene
(6.58 g, 0.012 mol), PdCl2(PPh3)2 (0.1 g), H2O (5 ml) and K2CO3 (6g, 0.043 mol) were added to a
o
250 ml flask with 40 ml THF. The mixture was heated at 78 C under argon atmosphere for 12h.
After cooling down, the resulting mixture was extracted with CH2Cl2, and the organic layer was
collected and dried with MgSO4. The solvent was removed and purified by silica gel
1
chromatography to obtain white solid, yield 95% (6.74 g). H NMR (400 MHz, Chloroform-d) δ
8.40 (d, J = 1.5 Hz, 1H), 8.23 (d, J = 7.7 Hz, 1H), 7.75 (d, J = 7.9 Hz, 1H), 7.70 (ddd, J = 7.6, 6.0,
1.7 Hz, 2H), 7.66 – 7.55 (m, 6H), 7.52 – 7.47 (m, 4H), 7.47 – 7.41 (m, 2H), 7.36 – 7.27 (m, 1H),
2.20 – 1.89 (m, 4H), 1.24 – 1.02 (m, 20H), 0.80 (t, J = 7.0 Hz, 6H), 0.70 (s, 4H). 13C NMR (101
MHz, Chloroform-d) δ 153.24, 141.43, 138.63, 137.70, 133.81, 129.95, 127.56, 127.09, 126.34,
126.18, 125.60, 123.97, 121.70, 120.98, 120.43, 120.10, 120.04, 118.79, 110.04, 109.96, 55.53,
40.33, 31.79, 29.98, 29.22, 29.19, 23.78, 22.60, 14.06. The synthesis procedures of 1b was similar
to 1a. It was obtained as a white powder in yield of 90 %. 1b: 1H NMR (400 MHz, Chloroform-d)
δ 8.17 (d, J = 7.8 Hz, 2H), 7.88 (d, J = 8.0 Hz, 2H), 7.77 (d, J = 7.9 Hz, 1H), 7.67 (d, J = 8.0 Hz,
3H), 7.63 (d, J = 1.6 Hz, 1H), 7.60 (d, J = 7.8 Hz, 1H), 7.49 (tdd, J = 5.2, 3.1, 1.4 Hz, 4H), 7.46 –
7.39 (m, 2H), 7.31 (t, J = 7.4 Hz, 2H), 2.09 – 1.92 (m, 4H), 1.24 – 1.03 (m, 20H), 0.81 (t, J = 7.0
Hz, 6H), 0.69 (h, J = 6.0, 5.5 Hz, 4H). 13C NMR (101 MHz, Chloroform-d) δ 153.27, 151.27,
140.89, 140.55, 139.54, 130.09, 128.54, 127.37, 126.25, 126.21, 125.99, 123.48, 121.43, 121.24,
121.19, 120.37, 120.25, 120.02, 109.84, 55.61, 40.34, 31.79, 29.96, 29.20, 23.77, 22.62, 14.08.
The synthesis procedures of 1c was similar to 1a. It was obtained as a yellow powder in yield of
87 %. 1c: 1H NMR (400 MHz, Chloroform-d) δ 7.69 (d, J = 7.9 Hz, 1H), 7.54 (dd, J = 7.8, 3.2 Hz,
4H), 7.51 (s, 1H), 7.45 (d, J = 7.4 Hz, 2H), 7.31 – 7.23 (m, 4H), 7.16 (t, J = 7.2 Hz, 6H), 7.04 (t, J
= 7.3 Hz, 2H), 1.95 (tt, J = 13.4, 6.7 Hz, 4H), 1.28 – 0.96 (m, 20H), 0.80 (t, J = 7.1 Hz, 6H), 0.70 –
0.58 (m, 4H). 13C NMR (101 MHz, Chloroform-d) δ 153.20, 151.03, 147.68, 147.21, 139.91,
138.90, 129.96, 129.30, 127.79, 126.15, 125.66, 124.42, 123.96, 122.98, 120.98, 120.91, 120.02,
55.48, 40.32, 31.77, 29.95, 29.20, 29.18, 23.72, 22.60, 14.06.
2.2.2 Synthesis of 3-(9,9-dioctyl-7-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9H-fluoren
-2-yl)-9-phenyl-9H-carbazole (2a), 9-(4-(9,9-dioctyl-7-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-
yl)-9H-fluoren-2-yl)phenyl)-9H-carbazole (2b), 4-(9,9-dioctyl-7-(4,4,5,5-tetramethyl-1,3,2-dioxa
borolan -2-yl)-9H-fluoren-2-yl)-N,N-diphenylaniline (2c)
1a (1.126g, 0.0016 mol), Bis(pinacolato)diboron (2g, 0.0078 mol), PdCl2(dppf) (0.05 g) and KoAc
(0.8g, 0.0081 mol) were dissolved in 1,4-dioxane. The reaction solution was stirred under 87oC for
4 h. After cooling down, the mixture was filtered through a short pad of silica with
dichloromethane (DCM). The solvent was removed under reduced pressure, and the residue was
further purified by silica gel chromatography to give a white solid (1.03 g), with yield of 85%. 1H
NMR (400 MHz, Chloroform-d) δ 8.41 (s, 1H), 8.23 (d, J = 7.7 Hz, 1H), 7.82 (dd, J = 9.9, 7.7 Hz,
2H), 7.78 (s, 1H), 7.76 – 7.67 (m, 3H), 7.67 – 7.56 (m, 5H), 7.49 (d, J = 8.6 Hz, 2H), 7.43 (d, J =
4.0 Hz, 2H), 7.35 – 7.28 (m, 1H), 2.10 – 2.00 (m, 4H), 1.40 (s, 12H), 1.22 – 0.99 (m, 20H), 0.79 (t,
J = 7.0 Hz, 6H), 0.70 (s, 4H). 13C NMR (101 MHz, Chloroform-d) δ 152.12, 150.17, 144.01,
141.42, 139.58, 137.73, 134.04, 133.83, 129.94, 128.89, 127.54, 127.09, 126.15, 125.67, 123.97,
123.54, 121.79, 120.45, 120.40, 120.09, 118.97, 118.83, 110.02, 109.95, 83.70, 55.26, 40.32,

31.82, 30.04, 29.25, 29.21, 24.98, 24.90, 23.79, 22.61, 14.08. The synthesis procedures of 2b was
1
similar to 2a. It was obtained as a white powder in yield of 91 %. 2b: H NMR (400 MHz,
Chloroform-d) δ 8.17 (d, J = 7.6 Hz, 2H), 7.90 (d, J = 7.4 Hz, 2H), 7.84 (d, J = 6.7 Hz, 2H), 7.81 –
7.73 (m, 2H), 7.68 (d, J = 7.9 Hz, 4H), 7.50 (d, J = 8.0 Hz, 2H), 7.44 (t, J = 7.5 Hz, 2H), 7.31 (t, J
= 7.2 Hz, 2H), 2.07 (s, 4H), 1.41 (s, 12H), 1.13 (d, J = 48.0 Hz, 20H), 0.86 – 0.75 (m, 6H), 0.68 (s,
4H). 13C NMR (101 MHz, Chloroform-d) δ 140.91, 140.67, 133.88, 128.91, 128.56, 127.33,
125.98, 123.46, 121.49, 120.57, 120.34, 119.98, 119.14, 109.86, 83.75, 55.33, 40.30, 31.80, 30.00,
29.21, 29.19, 24.97, 24.88, 23.75, 22.61, 14.07. The synthesis procedures of 2c was similar to 2a.
1
It was obtained as a yellow powder in yield of 89 %. 2c: H NMR (400 MHz, Chloroform-d) δ
7.81 (d, J = 7.6 Hz, 1H), 7.77 – 7.73 (m, 2H), 7.70 (d, J = 7.5 Hz, 1H), 7.58 – 7.51 (m, 4H), 7.31 –
7.23 (m, 4H), 7.16 (t, J = 7.0 Hz, 6H), 7.04 (t, J = 7.3 Hz, 2H), 2.07 – 1.92 (m, 4H), 1.39 (s, 12H),
1.21 – 0.98 (m, 20H), 0.79 (t, J = 7.1 Hz, 6H), 0.63 (s, 4H). 13C NMR (101 MHz, Chloroform-d) δ
152.03, 150.13, 147.72, 139.85, 135.64, 133.82, 129.29, 128.84, 127.83, 125.46, 124.39, 124.01,
122.93, 120.99, 120.36, 118.96, 83.70, 55.20, 40.29, 31.79, 30.00, 29.22, 29.19, 24.97, 23.73,
22.60, 14.07.
2.2.3 Synthesis of 4,4'-sulfonylbis(bromobenzene) (3)
Diphenylsulfane (4 g, 0.021 mol) and Br2 (9.95 g, 0.063 mol) were added into a flask to stir at
room temperature for 6h. After that, 300 mL mixed solution of H2O2:CH3COOH = 1:1 ( v : v ) was
added to react for 10 h, and was further purified by silica gel column chromatography to give
white solid， with yield of 73%. 1H NMR (400 MHz, Chloroform-d) δ 7.81 – 7.76 (m, 4H), 7.68 –
7.63 (m, 4H). 13C NMR (101 MHz, Chloroform-d) δ 141.63, 133.18, 129.28, 127.66.
2.2.4 Synthesis of 3-(7-(4-((4-bromophenyl)sulfonyl)phenyl)-9,9-dioctyl-9H-fluoren-2-yl)-
9-phenyl-9H-carbazole (4a), 9-(4-(7-(4-((4-bromophenyl)sulfonyl)phenyl)-9,9-dioctyl-9H-fluoren
-2-yl)phenyl)-9H- carbazole (4b), 4-(7-(4-((4-bromophenyl)sulfonyl)phenyl)-9,9-dioctyl-9H
-fluoren-2-yl)-N,N- diphenylaniline (4c)
Similar to the preparation of 1a, 2a (1.516g, 0.002 mol), 3 (1.13 g, 0.003 mol), PdCl2(PPh3)2 (100
mg) and K2CO3 (1g, 0.007 mol) were dissolved in 30 ml THF and H2O (5 ml). After that, white
solid (0.76 g) was obtained, with yield of 41%. 1H NMR (400 MHz, Chloroform-d) δ 8.41 (s, 1H),
8.24 (d, J = 7.7 Hz, 1H), 8.01 (d, J = 8.4 Hz, 2H), 7.85 (d, J = 8.6 Hz, 2H), 7.83 – 7.77 (m, 4H),
7.72 (d, J = 8.3 Hz, 2H), 7.69 – 7.63 (m, 4H), 7.63 – 7.53 (m, 5H), 7.50 (d, J = 8.5 Hz, 2H), 7.44
(d, J = 3.7 Hz, 2H), 7.32 (dt, J = 8.0, 4.2 Hz, 1H), 2.15 – 1.97 (m, 4H), 1.21 – 1.01 (m, 20H), 0.77
(t, J = 7.0 Hz, 10H). 13C NMR (101 MHz, Chloroform-d) δ 152.00, 151.86, 140.42, 138.80,
137.68, 137.46, 132.63, 129.95, 129.16, 128.21, 128.00, 127.57, 127.09, 126.38, 126.20, 125.61,
123.98, 123.48, 121.77, 121.63, 120.42, 120.33, 120.19, 120.11, 118.82, 110.05, 109.97, 55.41,
40.39, 31.77, 29.98, 29.19, 29.17, 23.85, 22.58, 14.03. The procedure for synthesizing 4b was
1
similar as above. It was obtained as a white powder in yield of 56 %. 4b: H NMR (400 MHz,
Chloroform-d) δ 8.17 (d, J = 7.7 Hz, 2H), 8.02 (d, J = 8.5 Hz, 2H), 7.90 (d, J = 8.4 Hz, 2H), 7.87 –
7.76 (m, 6H), 7.68 (q, J = 8.6, 8.1 Hz, 6H), 7.60 – 7.53 (m, 2H), 7.50 (d, J = 8.1 Hz, 2H), 7.44 (t, J
= 7.6 Hz, 2H), 7.31 (t, J = 7.0 Hz, 2H), 2.07 (dd, J = 11.6, 4.0 Hz, 4H), 1.21 – 1.02 (m, 20H), 0.82
– 0.65 (m, 10H). 13C NMR (101 MHz, Chloroform-d) δ 152.05, 151.99, 141.45, 140.88, 140.54,
139.65, 137.88, 132.64, 129.17, 128.55, 128.24, 128.05, 127.37, 126.48, 126.24, 125.99, 123.48,
121.69, 121.50, 120.52, 120.41, 120.38, 120.03, 109.83, 55.49, 40.39, 31.76, 29.96, 29.17, 23.84,
22.59, 14.04. The synthesis procedures of 4c was similar to 4a. It was obtained as a powder in
yield of 54 %. 4c: 1H NMR (400 MHz, Chloroform-d) δ 8.00 (d, J = 8.4 Hz, 2H), 7.85 (d, J = 8.6

Hz, 2H), 7.77 (dd, J = 11.8, 8.1 Hz, 4H), 7.66 (d, J = 8.6 Hz, 2H), 7.59 – 7.50 (m, 6H), 7.29 (d, J =
7.6 Hz, 4H), 7.15 (d, J = 6.5 Hz, 6H), 7.04 (s, 2H), 2.01 (dd, J = 10.3, 5.8 Hz, 4H), 1.21 – 0.93 (m,
20H), 0.77 (t, J = 7.0 Hz, 6H), 0.73 – 0.55 (m, 4H). 13C NMR (101 MHz, Chloroform-d) δ 151.76,
147.66, 137.53, 132.63, 129.30, 129.15, 128.20, 127.99, 127.79, 126.37, 125.68, 124.43, 123.94,
122.99, 121.59, 120.97, 120.29, 120.19, 55.35, 40.37, 31.74, 29.95, 29.16, 23.79, 22.56, 14.02.
2.2.5 Synthesis of 9-(heptadecan-9-yl)-2,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)
-9H-carbazole (5)
Similar to the procedure for synthesizing 2a, white solid of 5 (10.78 g, yield 82%) was obtained.
1H NMR (400 MHz, Chloroform-d) δ 8.12 (t, J = 8.9 Hz, 2H), 8.02 (s, 1H), 7.88 (s, 1H), 7.66 (d, J
= 7.5 Hz, 2H), 4.69 (tt, J = 10.2, 5.2 Hz, 1H), 2.33 (qt, J = 9.8, 4.7 Hz, 2H), 1.94 (ddt, J = 18.8,
10.3, 5.0 Hz, 2H), 1.39 (s, 24H), 1.29 – 1.04 (m, 24H), 0.82 (t, J = 7.0 Hz, 6H). 13C NMR (101
MHz, Chloroform-d) δ 126.05, 120.03, 119.72, 115.44, 83.70, 83.50, 56.37, 33.84, 33.70, 31.77,
31.74, 29.48, 29.37, 29.32, 29.28, 29.20, 29.14, 26.78, 26.70, 24.95, 22.59, 14.06.
2.2.6
3,3'-(((4,4'-(9-(heptadecan-9-yl)-9H-carbazole-2,7-diyl)bis(4,1-phenylenesulfonyl))bis(4,1-phenyl
ene))bis(9,9-dioctyl-9H-fluorene-7,2-diyl))bis(9-phenyl-9H-carbazole) (6a)
9,9'-((((4,4'-(9-(heptadecan-9-yl)-9H-carbazole-2,7-diyl)bis(4,1-phenylenesulfonyl))bis(4,1-pheny
lene))bis(9,9-dioctyl-9H-fluorene-7,2-diyl))bis(4,1-phenylene))bis(9H-carbazole) (6b) and
Synthesis
of
，
4,4'-(((4,4'-(9-(heptadecan-9-yl)-9H-carbazole-2,7-diyl)bis(4,1-phenylenesulfonyl))bis(4,1-phenyl
ene))bis(9,9-dioctyl-9H-fluorene-7,2-diyl))bis(N,N-diphenylaniline) (6c)
Similar with the synthesis of 1a, Pd(PPh3)4 (0.05 g) and additional ethanol were used (5 ml) under
o
85 C for 24 h. After cooling down, the mixture was extracted with CH2Cl2, organic layer was
dried by MgSO4. The solvent was removed and subjected to silica gel column chromatography to
give a white solid, with yield of 69%. Then product was recrystallized from ethanol and
1
dichloromethane. ( 6a): H NMR (400 MHz, CDCl3) δ [ppm] 8.43 (s, 2H), 8.25 (d, J=7.76 Hz,
2H), 8.20 (dd, J=8.24, 12.32 Hz, 2H), 8.11 (d, J=8.20 Hz, 7H), 8.03 (q, J=8.40 Hz, 1H), 7.81-7.85
(m, 12H), 7.74 (d, J=8.24 Hz, 5H), 7.69 (s, 2H), 7.61-7.68(m, 9H), 7.58 (d, J=7.12 Hz, 4H),
7.50-7.53 (m, 4H), 7.46 (d, J=3.84 Hz, 6H), 7.32-7.36 (m, 2H), 4.65-4.68 (m, 1H), 2.31-2.35 (m,
2H), 1.95-2.15 (m, 10H), 1.09-1.18 (m, 64H), 0.76-0.81 (m, 26H). 13C NMR (400 MHz, CDCl3) δ
[ppm] 151.9, 151.8, 147.2, 146.7, 141.7, 141.5, 141.4, 140.4, 140.2, 139.9, 138.8, 137.6, 133.7,
129.9, 128.3, 128.2, 127.9, 127.5, 127.0, 126.3, 126.1, 125.5, 123.9, 123.4, 121.7, 121.6, 120.4,
120.3, 120.1, 120.0, 118.7, 110.0, 109.9, 55.4, 40.3, 33.7, 31.7, 31.6, 29.9, 29.3, 29.2, 29.1, 29.0,
26.7, 23.8, 22.5, 14.0. TOF-MS (m/z): Calcd: 2097.2; Found: 2097.4 (M++1). Anal. Calcd (%) for
C147H161N3O4S2: C 84.16, H 7.73, N 2.00, O 3.05, S 3.06; Found: C, 84.14; H, 7.75; N, 2.02; O,
3.06; S, 3.08.
The synthesis procedures of 6b was similar to 6a. It was obtained as a white powder in yield of
1
74 %. 6b: H NMR (400 MHz, CDCl3) δ [ppm] 8.23(s, 1H), 8.20 (d, J=7.76 Hz, 5H), 8.13 (d,
J=8.2 Hz, 8H), 7.92 (d, J=8.44 Hz, 4H), 7.86 (t, J=7.64 Hz, 12H), 7.76 (s, 1H), 7.71 (t, J=7.84 Hz,
8H), 7.62 (d, J=7.96 Hz, 2H), 7.59 (s, 3H), 7.52 (d, J=8.16 Hz, 4H), 7.46 (t, J=7.16 Hz, 6H), 7.33
(t, J=6.96 Hz, 4H), 4.66-4.68 (m, 1H), 2.33-2.36 (m, 2H), 2.10 (d, J=6.16 Hz, 7H), 1.96-2.04 (m,
3H), 1.10-1.20 (m, 64H), 0.74-0.82 (m, 26H). 13C NMR (400 MHz, CDCl3) δ [ppm] 152.0, 151.9,
147.2, 146.6, 141.3, 140.8, 140.5, 140.1, 139.9, 139.6, 138.0, 136.8, 128.5, 128.4, 128.2, 128.1,
127.9, 127.3, 126.4, 126.2, 125.9, 123.4, 121.6, 121.4, 120.5, 120.3, 120.0, 109.8, 55.4, 40.4, 33.7,

31.7, 29.9, 29.3, 29.2, 29.1, 26.8, 23.8, 22.5, 14.0; TOF-MS (m/z): Calcd: 2097.2; Found: 2097.4
(M++1). Anal. Calcd (%): C147H161N4O4S2: C, 84.16; H, 7.73; N, 2.00; O, 3.05; S, 3.06; Found: C,
84.12; H, 7.71; N, 1.98; O, 3.01; S, 3.04.
The synthesis procedures of 6c was similar to 6a. It was obtained as a faint yellow powder in yield
of 70 %. 6c: 1H NMR (400 MHz, CDCl3) δ [ppm] 8.20 (dd, J=8.28, 12.20 Hz, 2H), 8.10-8.12 (m,
8H), 7.84 (t, J=8.44 Hz, 8H), 7.78 (t, J=7.68 Hz, 4H), 7.75 (s, 1H), 7.55-7.60 (m, 13H), 7.47 (s,
2H), 7.29 (t, J=8.16 Hz, 8H), 7.18 (t, J=8.16 Hz, 12H), 7.06 (t, J=7.32 Hz, 4H), 4.63-4.67 (m, 1H),
2.31-2.35 (m, 2H), 1.95-2.05 (m, 10H), 1.06-1.18 (m, 64H), 0.79 (t, J=6.84 Hz, 18H), 0.70 (d,
J=6.24 Hz, 8H). 13C NMR (400 MHz, CDCl3) δ [ppm] 151.9, 151.7, 147.6, 147.2, 146.6, 141.5,
140.1, 140.0, 139.9, 139.0, 137.6, 135.3, 129.2, 128.3, 128.1, 127.9, 127.7, 126.3, 125.6, 124.4,
123.9, 122.9, 121.5, 120.9, 120.2, 120.1, 55.3, 40.3, 33.7, 31.7, 31.6, 29.9, 29.3, 29.2, 29.1, 26.7,
23.7, 22.5, 14.0; TOF-MS (m/z): Calcd: 2101.2; Found: 2101.4 (M++1). Anal. Calcd (%):
C147H165N3O4S2: C, 83.99; H, 7.91; N, 2.00; O, 3.04; S, 3.05; Found: C, 84.01; H, 7.92; N, 1.98; O,
3.07; S, 3.07.
3. Results and discussion
3.1 Synthesis
1a, 1b and 1c were prepared from Suzuki Coupling, and then subjected to Miyaura boration to
obtain the precursor of 4. Diphenylsulfane was brominated and oxidized to give 4,4'-sulfonylbis
(bromobenzene), which was then reacted quantitatively with intermediate 2 to produce 3. Finally,
2 equivalents of 4 and 1 equivalents of 5 were coupled to yield the target product 6 via Suzuki.
After recrystallization for several times, these fluorescence materials were utilized as emitters
without sublimation. Thanks to their large alkyl chains, these emitters exhibited good solubility
and film-forming ability in conventional organic solvents like chloroform, THF and so on, which
were suitable for fabrication through spin-coating.
3.2 Photophysical properties
The UV-vis absorption and photoluminescence (PL) spectra of 6a, 6b and 6c in solution and film
are shown in Fig. 1. The maximum UV absorption of these materials in the film state were peaked
at 359 nm, 355 nm, 374 nm, respectively, which could be attributed to ICT transition and the result
of π-π* transitions. Compared with absorption in solution, the UV absorption spectra in film state
showed a slight bathochromic-shift, similar to previously reported literatures[34]. By the on-tail of
the absorption curves, band gaps (Eg) of these compounds were calculated to be 3.01, 3.08 and
2.94 eV as shown in Table 1. The fluorescence emission peaks in film state were found at 447nm,
428nm and 468nm, respectively. From the fluorescence spectra, 6a and 6b showed deep blue
emissions as shown in Fig. 1. It should be noted that these materials showed hypsochromic shift
by 24 nm, 9 nm and 62 nm from DCM solution to thin film state. The hypsochromic shift could be
attributed to the highly twisted configurations between the donor and acceptor in solution state and
strong intermolecular π-π stacking in film state.

Fig. 1. a).The normalized UV-Vis absorption spectra in DCM of 6a, 6b and 6c; b). The normalized UV-visible
absorption spectrum in film states; c). The PL spectrum in DCM; d). The PL spectrum in film states.
Photoluminescence quantum yields (PLQYs) for 6a, 6b, 6c were listed in Table 1. Among the
three, 6b showed the highest PLQYs with 50.4% at film state. However, when compared to
solution state, all the PLQYs of 6a 6b and 6c in film state were lower, which could be attributed to
the concentration quenching of common fluorescence materials. The fluorescence spectra of three
emitters (Fig. 2) were slightly bathochromically-shifted with the increase of solvent polarity (from
non-polar solvent such as toluene to polar solvents such as THF and DCM), indicating the weak
ICT characteristics for the excited states of the three emitters. Compared to 6a and 6c, 6b showed
better stability in deep blue emission with different polar solvents. This was mostly attributed to
the tail end of molecule structure that had smaller dipole moment than the others. The
time-resolved photoluminescence (TRPL) spectra of the three emitters were measured and
different decay life of three emitters were clearly observed in Fig. S32. It was found that 6b had a
fairly longer life (τ6b: 15.2 ns) than 6c (τ6c: 7.7 ns) and 6a (τ6a: 4.7 ns).

Fig. 2. Normalized PL spectra measured in toluene (TOL), chlorobenzene (CB), tetrahydrofuran (THF),
trichloromethane (CHF), dichloromethane (DCM) of a) 6a, b) 6b and c) 6c.
Table 1. The thermal, photophysical and electrochemical properties of the 6a, 6b and 6c emitters
e,f
Compounds
Tg/Td
(oC)
λmaxAbsa,b
λmaxPLa,b
PLQYa,b
HOMO/LUMOc
HOMO/LUMOd
Eg
(nm)
(nm)
(%)
(eV)
(eV)
(eV)
6a
6b
6c
103.68/416.7
106.79/417.8
92.52/426.9
353/359
347/355
363/374
471/447
437/428
530/468
74.8/45.9
79.2/50.4
69.3/39.4
-4.95/-1.94
-5.24/-2.16
-4.94/-2.00
-5.21/-1.80
-5.34/-1.88
-4.94/-1.81
3.01/3.41
3.08/3.46
2.94/3.13
a. The maximum UV-vis absorption peaks and PL spectra in DCM.
b. The maximum UV-vis absorption peaks and PL spectra in thin film.
c. Calculated from the formula HOMO = - (4.40 + Eox) (eV), LUMO = HOMO + Eg (eV).
d. Calculated by Gaussian 03 software at the B3LYP/6-31G (d, p) level.
e. Eg = 1240/λ ( λ is the wavelength of the on-set of the UV-vis absorption spectrum)
f. Eg calculated by Gaussian 03 software at the B3LYP/6-31G (d, p) level).
3.2 Thermal properties
The thermal properties of 6a, 6b and 6c were analyzed by thermogravimetric analysis (TGA) and
differential scanning calorimetry (DSC) under nitrogen atmosphere at 10 K.min-1 as shown in Fig.
3. The thermal decomposition temperature (Td) at 5% weight loss of the three materials 6a, 6b and
6c were higher than 400 oC. The three materials also had high glass transition temperatures (Tg) of
o
o
o
103.68 C, 106.79 C and 92.52 C respectively. The high thermal stability can usually be
attributed to the high contains of polar groups of sulfone, and rigid aromatic rings and aromatic
systems [38, 39]. The higher Td and Tg of the materials enabled better stability during OLED’s
working time.

Fig. 3. TGA a) and DSC b) curves of 6a, 6b and 6c;
3.3 Theoretical calculations and electrochemical properties
To further explore the molecules’ geometry and electronic density distributions, Gaussian 03
program at the B3LYP/6-31G (d, p) level was applied to calculate electronic structure and the
FMO. The characteristic results were listed in Table 1. The HOMO of these molecules was mainly
located on the fluorene, triphenylamine or carbazole units, while the LUMO was almost
distributed on the sulfone and carbazole moieties. Note that the separation of HOMO and LUMO
distribution would reduce the communication of electron donor and acceptor, beneficial to form
blue emitting.
6a HOMO (564) -5.215eV
6b HOMO (564) -5.342 eV
6c HOMO (566）-4.946 eV
6a LUMO (565) -1.803 eV
6b LUMO (565) -1.885 eV
6c LUMO (567) -1.809 eV

Fig. 4. HOMO and LUMO energy levels of 6a, 6b and 6c calculated from Gaussian 03
Meanwhile, the geometrical configuration of the three molecules (6a, 6b and 6c) were compared,
as shown in Fig. 5. 6a and 6b had larger twist angle for the alkyl chain and sulfone moieties twist
angles approached 90o, favorable for reducing the overlapping of FMO and increasing the
molecule’s solubility. In addition to the sulfone moiety, there was almost 90o dihedral angle
between the triphenylamine terminal group and the molecular body of 6c, which could inhibit the
molecular aggregation in the solid state and also reduce the red-shifting effect owing to ICT.
6a
6b
6c
Fig. 5. Molecular geometry modeling of 6a, 6b and 6c.
To study the practical electrochemical behavior of 6a, 6b and 6c, cyclic voltammetry (CV) curves
were shown in Fig. 6. Based on the initial oxidation sites Eox (0.55eV, 0.84eV and 0.54eV), the
HOMO energy levels were estimated to be -4.95 eV, -5.24 eV and -4.94 eV via the empirical
equation HOMO = (Eox + 4.40) eV. Meanwhile, the LUMOs were estimated from HOMO and Eg,
which were calculated to be -2.34 eV, -2.56 eV and -2.40 eV. The DFT results showed the HOMO

energy levels at -5.21eV, -5.34eV, -4.49-eV , due to the same molecule core, the similar LUMO
energy levels of 6a, 6b and 6c be found at -1.80 eV, -1.88 eV, -1.81 eV respectively, Compared
with DFT results, experimental measurement values showed smaller energy gap. This different
most probably attributed to the fact that DFT calculation was conducted on single molecules,
while the experiments were conducted on the emitters in solution. In spite of the differences in
DFT and experiment results, both of them showed the same consequence that 6a, 6b had deeper
HOMO energy levels and 6c had smallest Eg in these emitters. Compareing the energy gap of 6a
and 6b, 6b with larger energy gap almost attributed to the different bond positions of
9-phenyl-9H-carbazole. The triphenylamine made 6c to show shallower HOMO and narrower
energy gap which promoted fluorescence wavelength red shift to 530 nm. In other words, the
deeper HOMO and larger energy gap are significant for the design of deep blue fluorescence
emitter.
Fig. 6. Cyclicvoltammetry characteristics of 6a, 6b and 6c
3.4 Electroluminescent (EL) properties
The electroluminescence performance of these materials was evaluated by fabricating OLED
through spin coating method. The device structure was ITO / PEDOT: PSS (30nm) / emissive
layer (EML) (50nm) / 2,4,6-tris(biphenyl-3-yl)-1,3,5-triazine (T2T) (50nm) / LiF (1nm) / Al
(100nm). Among them, ITO and Al served as anode and cathode, PEDOT: PSS as hole injection
and transport layer, and the synthesized blue-emitting materials as EML layer. Meanwhile, T2T
was selected as electron transport and hole blocking layer and LiF as the electron injection layer.
The energy levels of each layer are shown in Fig. 7 a). The non-doped devices based on these
three emitters showed standard blue emission peaks at 454 nm, 444 nm and 474 nm with the CIE
of (0.16, 0.12), (0.16, 0.15) and (0.16, 0.27), respectively. In addition, those devices showed quite
stable electroluminescence at different luminance from 0.1 to 100 cd.m-2.
The charge mobility as a key parameter that can evaluate the performance of devices. Here, the
space charge limited current (SCLC) method was employed to calculate the charge mobility of the
single carrier devices. Herein, two types of single carrier devices configuration were fabricated,
ITO / PEDOT: PSS (30nm) / EML(50nm) / LiF (1nm) / Al (100nm) as hole-only devices (H-type)

and ITO / EML(50nm) / (T2T) (50nm) / LiF (1nm) / Al (100nm) as electron-only devices (E-type),
the current density dependence of voltage (J1/2-V) curves is presented in Fig. S33. The hole
mobility (μh) and electron mobility (μe) of the three emitters are calculated by fitting the
Mott-Gurney square law.
9
8
ꢊꢋ
ꢌꢍ
ꢀꢁꢂꢃꢂ
ꢄ
ꢅꢆꢅꢇꢈꢉ
where ꢅꢆ (8.855 × 10−12 F/m) is the permittivity of free space, ꢅꢇ is the relative dielectric constant
of the three materials (typically ≈ 3), L is the thickness of film. V is the applied voltage and J is
current density across device. The µh of 6a, 6b and 6c were calculated to be 1.28×10-4 cm2 V-1 s-1,
1.51×10-4 cm2 V-1 s-1 and 1.17×10-4 cm2 V-1 s-1, while µe of 6a, 6b and 6c were calculated to be
1.05×10-5 cm2 V-1 s-1, 9.77×10-5 cm2 V-1 s-1 and 7.2×10-5 cm2 V-1 s-1. Obviously, devices based on
the three emitters have showed high µh than µe, mostly attributed to delocalized π electron density
of donor and acceptor.
Fig. 7. a) Diagram of the non-doped blue light-emitting device and electroluminescence (EL) spectra of 6a (b), 6b
(c) and 6c (d) devices at different current density.
Compared with PL spectra in film states, a bathochromic-shift of more than 10 nm was observed
in the EL spectra. And this redshift could be explained by the increased thickness through spin
coating process[35, 36]. The current density-voltage-luminance (J-V-L) curves are plotted in Fig.
8 a). The turn-on voltages of the devices based on 6a, 6b and 6c devices were 6.2, 7.3, 6.1 V,
indicating that the most facile charge injection took place in 6b based devices mostly due to the
planar configuration of 6b emitters. Meanwhile, the device brightness was increased by increasing
the voltage with the maximum brightness of 2354.1 cd/cm2, 1226.2 cd/cm2 and 2457.2 cd/cm2. as
shown in Fig. 8. a) and Table 2. The external quantum efficiency (EQE) of 6a, 6b and 6c were
0.71%, 0.42% and 0.65%, which also showed that there was no obvious efficiency roll-off by
increasing current density. However, the OLED did not show high efficiency, which might be
attributed to the effects of aggregation-caused quenching[37]. Another possible reason was that
these emitters could not take advantage of the triplet excitons like what other materials did such as
TADF and TTA materials [38-40].

Fig. 8 a) Normalized EL Spectra; b). Current density-voltage-luminance (J-V-L) curves; c). Current efficiency (CE)
curves; d). EQE characteristics of OLED based on the three non-doped emitters.
Table. 2. The EL parameters of devices of 6a (A), 6b (B) and 6c (C)
At 100 cd/m2
At 1000 cd/m2
a
Von
CEmax
(cd/A)
PEmax
EQEmax
(%)
CIEb
(x,y)
λmaxEL
V
CE
PE
EQE
(%)
V
CE
PE
EQE
(%)
Devices
(V)
(lm/W)
(nm)
(V)
(cd/A)
(lm/W)
(V)
(cd/A)
(lm/W)
A
B
C
6.2
7.3
6.1
2.67
1.01
3.36
1.19
0.61
1.36
0.71
0.42
0.65
0.16,0.15
0.16,0.12
0.16,0.27
454
448
489
9.0
10.9
8.8
2.67
0.79
3.36
0.93
0.23
1.20
0.71
0.26
0.65
12.2
15.4
11.6
1.85
0.55
2.68
0.47
0.11
0.73
0.50
0.18
0.52
a) Recorded at the luminance of 1 cd/m2;
b) Recorded at the current of 10 mA/m2
4. Conclusions
Three bipolar fluorophores based on the electron acceptor of sulfone moieties with intramolecular
charge transfer properties were designed and synthesized. The three materials had a highly
distorted spatial geometry and separation of the electron density distribution. The dihedral angle
was close to 90o in the molecular configuration containing sulfone moieties, especially in 6c
containing triphenylamine end group. These fluorophores exhibited deep-blue photoluminescence,
good thermal stability and reversible electrochemical behaviors, and therefore were applied into
OLED with deep-blue electroluminescence. Solution-processed non-doped OLED were
subsequently fabricated, two of which exhibited deep blue emission with CIE of (0.16, 0.15) and
(0.16, 0.11). Those devices showed stable deep-blue emission and marginal roll-off, highlighting
the potential of our newly synthesized deep blue emitters.
Acknowledgments
This work is financially supported by the National Key R&D Program of China

(2016YFB0401000,2017YFE0106000), National Natural Science Foundation of China (21805296,
21876158, 51773212, 21574144 and 21674123), Zhejiang Provincial Natural Science Foundation
of China (LR16b040002), Natural Science Foundation of Ningbo City (2018A610134), Ningbo
Municipal Science and Technology Innovative Research Team (2015B11002 and 2016b10005),
CAS Key Project of Frontier Science Research (QYZDB-SSW-SYS030), CAS Key Project of
International Cooperation (174433KYSB20160065) and Zhejiang Provincial Natural Science
Foundation of China (Grant No.LY20B040002).
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Highlights
▲
Two deep-blue electroluminescence were designed and synthesized which with the CIEx,y of
(0.16, 0.12) and (0.16, 0.15)
▲ These materials appeared almost vertical angles of the dihedral configuration.
▲ These materials exhibited high thermal and electrochemical stability.
▲The OLED devices of this article were fabricated through solution-process with nondoped

Dear Editor,
We solemnly declare there are no conflicts of interest to all authors
Best regards.
Sincerely yours,
Prof. Ziyi Ge
Ningbo Institute of Materials Technology and Engineering,
Chinese Academy of Sciences,
Tel: +86-0574-86690273
E-mail: geziyi@nimte.ac.cn