D. Yang et al.
Organic Electronics 95 (2021) 106187
Herein, we report two TADF emitters, 9-(4-(dimesitylboryl)phenyl)-
J = 14.9 Hz, 1H), 7.52 (d, J = 7.9 Hz, 1H), 7.44–7.37 (m, 5H), 7.33 (d, J
= 7.5 Hz, 2H), 6.84 (d, J = 7.2 Hz, 2H), 6.75 (t, J = 14.7 Hz, 2H), 6.68
′
9
9
H-3,9 -bicarbazole (CCDMB) and 10-(9-(4-(dimesitylboryl)phenyl)-
1
3
H-carbazol-3-yl)-10H-phenoxazine (PCDMB), where a triarylborane
(d, J = 14.7 Hz, 2H), 6.08 (d, J = 7.6 Hz, 2H), 5.63 (s, 2H) C NMR
moiety was used as an electron acceptor, 3-substituted carbazole as a
first electron donor in common and carbazole and phenoxazine moieties
as second electron donors, respectively (Fig. 1). The double donor sys-
tem was introduced not only to increase the electron donating ability of
two emitters which would induce efficient intramolecular charge
transfer (ICT) for radiative decay [17–20] but also to reduce overlap
between the HOMO and LUMO by the distortion of two consecutive
3
(75.47 MHz, CDCl ): δ 141.2, 140.2, 140.1, 136.8, 133.5, 129.0, 127.7,
126.6, 126.5, 125.0, 123.6, 123.2, 122.6, 121.2, 120.7, 119.8, 113.5,
111.2, 109.3, 46.9, 31.6, 24.1, 22.7.
′
2.1.4. Synthesis of 9H-3,9 -bicarbazole (4)
′
To a solution of 9-benzyl-9H-3,9 -bicarbazole (2, 1.74 g, 4.12 mmol)
in 80 ml of DMSO was added potassium tert-butoxide (t-BuOK, 4.62 g,
dihedral angles (
α
1
and
α
2
, Fig. 1). Our study was focused on in-
41.2 mmol) in 20 ml of tetrahydrofuran (THF) at once and subjected to
terrelations of D-A twist angles, electron-donating ability of D, and
OLED device efficiency. CCDMB-based OLED devices showed deep blue
CIE coordinates of (0.16, 0.12) but a maximum EQE of 5.5%. On the
other hand, PCDMB-based devices exhibited a maximum EQE of 22.3%
with green emission (CIE coordinates of (0.21, 0.45)).
oxygen (O
100 ml of water and stirred for 6 h. The crude mixture was filtered,
extracted with DCM (50 ml × 3), dried over anhydrous Na SO , and
concentrated in vacuo. The desired product 4 was obtained as a white
2
) bubbling for 3 h. The resulting mixture was treated with
2
4
1
solid (1.26 g, 3.79 mmol, 92% yield). H NMR (300 MHz, CDCl
s, 1H), 8.25 (d, J = 1.5 Hz, 1H), 8.22 (d, J = 7.7 Hz, 2H), 8.09 (d, J =
7.8 Hz, 1H), 7.67 (d, J = 8.5 Hz, 1H), 7.59 (dd, J = 1.8, 8.5 Hz, 1H), 7.53
d, J = 6.4 Hz, 2H), 7.48–7.39 (m, 4H), 7.34 (d, J = 1.7 Hz, 1H), 7.32 (d,
3
): δ 8.29
(
2
. Experimental section
(
1
3
2
2
.1. Preparation
J = 11.2 Hz, 2H); C NMR (75.47 MHz, CDCl
29.4, 126.6, 126.0, 125.5, 124.4, 123.1, 123.0, 120.6, 120.4. 120.0,
119.7. 119.6. 111.7, 111.0, 110.0.
3
): δ 142.0, 140.2, 138.6,
1
.1.1. Synthesis of 9-benzyl-3-iodo-9H-carbazole (1)
To a stirred solution of 3-iodocarbazole (4.19 g, 14.31 mmol) and
tetrabutylammonium iodide (0.53 g, 1.43 mmol) dissolved in 90 ml of
dimethyl sulfoxide (DMSO) was added 6 ml of 50% aqueous potassium
hydroxide (KOH) solution. To the resulting mixture was injected drop-
wise benzyl bromide (7.34 g, 42.93 mmol) in 30 ml of DMSO. The
resulting mixture was stirred for 2 h, poured into 300 ml of water and
extracted with 100 ml of dichloromethane (DCM), dried over anhydrous
2.1.5. Synthesis of 10-(9H-carbazol-3-yl)-10H-phenoxazine (5)
To a stirred solution of compound 3 (2.80 g, 6.39 mmol) dissolved in
160 ml of DMSO was added t-BuOK (7.17 g, 63.90 mmol) in 40 ml of
THF and subjected to oxygen bubbling for 3 h. The resulting mixture was
filtered, extracted with DCM (50 ml × 3), dried over anhydrous Na
2 4
SO ,
and concentrated in vacuo to afford compound 5 (2.20 g, 6.31 mmol,
1
sodium sulfate (Na
2
4
SO ) and concentrated under reduced pressure. The
3
92% yield) as a yellowish white powder. H NMR (300 MHz, CDCl ): δ
resulting precipitate was recrystallized from 200 ml of methyl alcohol to
8.25 (s, 1H), 8.07 (d, J = 8.0 Hz, 2H), 7.67 (d, J = 8.4 Hz, 1H), 7.51 (d, J
furnish 9-benzyl-3-iodo-9H-carbazole (5.21 g, 95% yield) as a white
= 5.9 Hz, 2H), 7.38 (dd, J = 8.4, 1.5 Hz, 1H), 6.73 (d, J = 7.1 Hz, 2H),
1
13
solid. H NMR (300 MHz, chloroform-d (CDCl
3
)): δ 8.45 (s, 1H), 8.10 (d,
6.65–6.62 (m, 3H), 6.58–6.55 (m, 3H); C NMR (75.47 MHz, CDCl ): δ
3
J = 7.8 Hz, 1H), 7.70 (d, J = 7.8 Hz, 1H), 7.48 (d, J = 7.5 Hz, 1H), 7.40
140.0, 138.9, 131.2, 130.2, 127.1, 126.6, 125.4, 123.4, 123.3, 123.0,
120.6, 120.4, 120.0, 115.4, 113.5, 113.0, 111.0, 110.5.
(
t, J = 8.0 Hz, 2H), 7.35–7.27 (m, 3H), 7.18 (d, J = 8.6 Hz, 1H), 7.14 (d,
1
3
J = 7.4 Hz, 2H), 5.51 (s, 2H); C NMR (75.47 MHz, CDCl
3
): δ 140.7,
39.8, 136.7, 134.1, 129.3, 128.9, 127.7, 126.6, 126.4, 125.6, 121.8,
20.6, 119.8, 111.1, 109.1, 81.9, 46.6.
′
1
1
2.1.6. Synthesis of 9-(4-bromophenyl)-9H-3,9 -bicarbazole (6)
A mixture of 4 (1.26 g, 3.79 mmol), 1-bromo-4-iodobenzene (1.29 g,
4
4 2 3
.55 mmol), CuSO (0.47 g, 1.90 mmol) and K CO (2.1 g, 15.2 mmol) in
′
2
.1.2. Synthesis of 9-benzyl-9H-3,9 -bicarbazole (2)
10 ml of o-DCB was refluxed for 12 h. The reaction mixture was cooled
down to RT and extracted with DCM (50 ml × 3), dried over anhydrous
A mixture of 9-benzyl-3-iodo-9H-carbazole (1, 2.02 g, 6.89 mmol),
carbazole (1.73 g, 10.34 mmol), copper sulfate (CuSO
4
, 0.87 g, 3.45
2 4
Na SO , and concentrated under reduced pressure. The crude product
mmol) and potassium carbonate (K
2
CO
3
, 3.81 g, 27.6 mmol) dissolved
was purified by silica gel column chromatography (SiO2, Hex:DCM =
◦
1
in 15 ml of o-dichlorobenzene (o-DCB) was refluxed at 180 C for 12 h.
After cooling down to room temperature (RT), the reaction mixture was
extracted with DCM (100 ml × 3). The combined organic layer was dried
3:1) to afford 6 (1.20 g, 2.47 mmol, 65% yield). H NMR (300 MHz,
CDCl
3
): δ 8.33 (s, 1H), 8.25 (d, J = 7.7 Hz, 2H), 8.16 (d, J = 7.7 Hz, 1H),
7.84 (d, J = 8.5 Hz, 2H), 7.60–7.56 (m, 4H), 7.52 (d, J = 10.1 Hz, 2H),
1
3
over anhydrous Na
2
SO
4
and concentrated under reduced pressure. Pu-
7.46–7.42 (m, 4H), 7.39–7.32 (m, 3H); C NMR (75.47 MHz, CDCl ): δ
3
rification by silica gel column chromatography (SiO
2
, n-hexane (Hex):
141.9, 141.4, 139.8, 136.5, 133.4, 133.2, 130.2, 128.8, 126.9, 125.9,
125.7, 124.6, 123.2, 123.1, 121.4, 120.7, 120.4, 119.7, 119.6, 110.7,
110.0, 109.8.
′
DCM = 3:1) gave 9-benzyl-9H-3,9 -bicarbazole (1.74 g, 4.12 mmol, 60%
1
yield). H NMR (300 MHz, CDCl
3
): δ 8.32 (s, 1H), 8.25 (d, J = 7.7 Hz,
2
H), 8.16 (d, J = 7.7 Hz, 1H), 7.59 (t, J = 8.5 Hz, 2H), 7.55 (t, J = 12.4
Hz, 2H), 7.48–7.41 (m, 4H), 7.38–7.33 (m, 6H), 7.30 (d, J = 3.0 Hz, 1H),
2.1.7. Synthesis of 10-(9-(4-bromophenyl)-9H-carbazol-3-yl)-10H-
phenoxazine (7)
1
3
7
1
1
1
.28 (d, J = 2.0 Hz, 1H), 5.64 (s, 2H)); C NMR (75.47 MHz, CDCl
3
): δ
42.1, 141.5, 139.9, 137.0, 129.4, 129.0, 127.8, 126.8, 126.6, 126.0,
25.6, 124.1, 123.3, 122.8, 120.8, 120.5, 119.9, 119.8, 119.7, 110.1,
09.5, 46.9.
A mixture of 5 (2.20 g, 6.31 mmol), 1-bromo-4-iodobenzene (2.14 g,
4 2 3
7.57 mmol), CuSO (0.80 g, 3.20 mmol) and K CO (3.48 g, 25.2 mmol)
dissolved in 20 ml of o-DCB was refluxed for 12 h. The reaction mixture
was cooled down to RT and extracted into DCM (50 ml × 3). The
2
.1.3. Synthesis of 10-(9-benzyl-9H-carbazol-3-yl)-10H-phenoxazine (3)
2 4
combined organic layer was dried over anhydrous Na SO and
A mixture of 9-benzyl-3-iodo-9H-carbazole (1, 4.00 g, 10.42 mmol),
concentrated under reduced pressure to afford 7 (2.16 g, 4.29 mmol,
phenoxazine (2.86 g, 15.63 mmol), CuSO
CO
4
(1.30 g, 5.22 mmol), and
68% yield) after purification by silica gel column chromatography (SiO2,
◦
1
K
2
3
(4.32 g, 31.26 mmol) in 35 ml of o-DCB was refluxed at 180 C for
Hex:DCM = 3:1). H NMR (300 MHz, CDCl
3
): δ 8.16 (d, J = 10.0 Hz,
1
2 h. The reaction mixture was cooled down to RT, extracted with DCM
SO . Purification by silica gel column
, Hex:DCM = 3:1) afforded the desired product 3
2H), 7.84 (d, J = 8.4 Hz, 2H), 7.63 (d, J = 8.6 Hz, 1H), 7.57 (d, J = 8.4
Hz, 2H), 7.52–7.45 (m, 2H), 7.71–7.35 (m, 2H), 6.78 (d, J = 7.1 Hz, 2H),
(
100 ml × 3), and dried over Na
2
4
1
3
chromatography (SiO
2
6.69–6.64 (m, 2H), 6.62 (t, J = 7.1 Hz, 2H), 6.04 (d, J = 7.4 Hz, 2H);
C
1
as a greenish white solid (2.80 g, 6.39 mmol, 61% yield). H NMR (300
MHz, CDCl
): δ 8.19 (d, J = 8.3 Hz, 2H), 7.65 (d, J = 8.5 Hz, 1H), 7.60 (t,
NMR (75.47 MHz, CDCl
3
): δ 144.0, 141.2, 140.0, 136.5, 135.2, 133.4,
131.3, 128.8, 128.4, 126.9, 125.6, 123.3, 123.0, 122.9, 121.5, 121.2,
3
2