Synthesis and optical properties of starburst carbazoles based on 9-phenylcarbazole core

Article abstract of DOI:10.1055/s-2006-950266

New well-defined starburst carbazole derivatives, which contain N-phenylcarbazole as the central core joining 9-hexylcarbazole or 9-phenylcarbazole as arms, are presented. All these compounds were obtained via Suzuki cross-coupling in moderate yields. Their structures were confirmed by ¹H NMR, MALDI-TOF mass spectrometry and elementary analysis. Moreover, the fluorescence spectra showed that these compounds exhibited good blue fluorescence with the maximum wavelengths ranging from 410 nm to 430 nm. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2006-950266

LETTER
2841
Synthesis and Optical Properties of Starburst Carbazoles Based on
9-Phenylcarbazole Core
S
ynthesis andOpti
u
cal Propertie
o
s
of Starburs
-
t
C
arba
z
L
oles iang Feng,a Shun-Jun Ji,*a Wen-Yong Lai,b Wei Huang*b,c,d
a
Key Laboratory of Organic Synthesis of Jiangsu Province, College of Chemistry and Chemical Engineering,
Suzhou (Soochow) University, Hengyi Road, Suzhou Industrial Park, Suzhou 215123, P. R. of China
Fax +86(512)65880089; E-mail: shunjun@suda.edu.cn
b
c
Institute of Advanced Materials (IAM), Fudan University, 220 Handan Road, Shanghai 200433, P. R. of China
Institute of Advanced Materials (IAM), Nanjing University of Posts and Telecommunications, 66 XinMoFan Road,
Nanjing 210003, P. R. of China
d
Faculty of Engineering, National University of Singapore, 9 Engineering Drive 1, Singapore 117576, Republic of Singapore
Fax +86(25)83492349; E-mail: wei-huang@njupt.edu.cn
Received 25 May 2006
synthesis and optical properties of some novel starburst
carbazole derivatives, which contain three short carbazole
chains linked to a central rigid core. In these structures,
the central core and chains are all carbazole units. We sup-
Abstract: New well-defined starburst carbazole derivatives, which
contain N-phenylcarbazole as the central core joining 9-hexylcarba-
zole or 9-phenylcarbazole as arms, are presented. All these com-
pounds were obtained via Suzuki cross-coupling in moderate yields.
1
Their structures were confirmed by H NMR, MALDI–TOF mass posed that not only would they have highly efficient hole-
spectrometry and elementary analysis. Moreover, the fluorescence
transporting capability, but also high thermal and electro-
spectra showed that these compounds exhibited good blue fluores-
chemical stability.
cence with the maximum wavelengths ranging from 410 nm to 430
To synthesize the target starburst carbazole derivatives,
our design was to attach carbazole arms directly to the
central core via Suzuki cross-coupling. First, 9-(4-bro-
mophenyl)-3,6-dibromocarbazole (1)6 was synthesized as
the key intermediate for the whole procedure via a two-
step reaction as shown in Scheme 1. This compound (1)
served as the central core.
nm.
Key words: carbazole, starburst, boronic acids, Suzuki cross-cou-
pling, fluorescence
During the past several years, the synthesis and applica-
tion of carbazole derivatives have been of great interest
for the chemists and material scientists because these
compounds are quite interesting due to their intrinsic pho-
tophysical and redox properties. They exhibit relatively
intense luminescence and undergo reversible oxidation
processes which make them suitable as hole carriers.1
Moreover, carbazole can be easily functionalized at its
3-, 6-, or 9-position and the carbazole moiety is beneficial
for raising the glass transition temperature and thermal
stability.2 Carbazole derivatives are widely used as build-
ing blocks for potential organic semiconductors3 and or-
ganic light-emitting diodes.4 Despite the huge amount of
work already invested in these various applications, it is
clear that further progress in these fields requires an inten-
sification of the research effort focused on the design and
synthesis of new compounds with electrochemical, opti-
cal, and electronic properties specifically tailored for each
type of application.
H
N
i
Br
Br
+
48%
Br
Br
ii
N
N
83%
Br
Br
1
Scheme 1 Reagents and conditions: (i) CuSO4, K2CO3, 220 °C; (ii)
NBS, DMF, 0 °C.
Second, we synthesized bromo derivatives 2–77 to
achieve boronic acids 8–11 as the other key intermediates
to construct the starbursts. Compounds 2–5 were obtained
by the reaction of 9-hexylcarbazole or 9-phenylcarbazole
with N-bromosuccinimide in N,N-dimethylformamide.
Then we utilized a repetitive procedure for the conversion
of bromo derivatives 2 and 4 into the corresponding bo-
ronic acids 8 and 107 via lithiation with n-butyllithium,
followed by quenching with triisopropyl borate and hy-
drolysis under acidic conditions. When boronic acids 8
and 10 were coupled by Suzuki methodology with 3 or 5,
the next generation of bromo derivatives 6 and 7 were ob-
tained (a three-fold excess of 3 or 5 over boronic acids 8
and 10 was used to diminish biscoupling at both sides of
Starburst oligomers with a central core have been proven
to be very useful in field-effect transistors, light-emitting
diodes and photovoltaic cells5 because starburst mole-
cules consisting of linear molecule arms with a central
core would bring new electrical, optical and morphologi-
cal properties. Starburst conjugated architectures have at-
tracted increasing attention as possible alternatives to
linear conjugated oligomers. In this paper, we describe the
SYNLETT 2006, No. 17, pp 2841–2845
Advanced online publication: 09.10.2006
DOI: 10.1055/s-2006-950266; Art ID: W10606ST
© Georg Thieme Verlag Stuttgart · New York
1
7
.1
0
.2
0
0
6

2842
G.-L. Feng et al.
LETTER
C6H13
N
iii
C6H13
N
2
3
96%
i
Br
C6H13
N
94%
iii
89%
H
N
Br
Br
N
N
iii
4
5
94%
ii
N
Br
Br
87%
iii
84%
Br
C6H13
N
C6H13
N
HO
C6H13
Br
B
OH
N
v
iv
iv
2
71%
79%
85%
OH
B
N
N
HO
C6H13
C6H13
8
6
9
HO
N
B
OH
N
Br
iv
iv
vi
N
4
83%
75%
76%
N
N
OH
B
HO
11
7
10
Scheme 2 Reagents and conditions: (i) 1-bromohexane, KOH, TBAB, DMSO, 100 °C; (ii) 1-iodobenzene, K2CO3, CuI, 1,10-phenanthroline
(0.1 equiv), p-xylene, 180 °C; (iii) NBS, DMF, darkness, 0 °C; (iv) n-BuLi (1.2 equiv), THF, –78 °C, (i-PrO)3B (1.5 equiv), H2O–HCl; (v)
compound 3, Pd(PPh3)4, K2CO3 (2 M), toluene, 80 °C; (vi) compound 5, Pd(PPh3)4, K2CO3 (2 M), toluene, 80 °C.
3 or 5). The syntheses of compounds 9 and 118 were al- The UV–Vis spectra of 12–15 are shown in Figure 1. As
most the same as that of compounds 8 and 10 (Scheme 2). shown in Figure 1, the absorption spectra of the molecules
12–15 exhibited a peak at about 305 nm due to the same
The final step to 12–159 is outlined in Scheme 3. As
N-phenylcarbazole core. Another absorption peak was ob-
served for 12, 13, 14 and 15 at 245, 250, 250 and 254 nm,
respectively. We observed that the effective conjugation
length increased with increasing molecular size.
shown in Scheme 3, the carbazole moiety was introduced
by C–C bond connection at its 3-position through a Suzu-
ki cross-coupling of 1 with various arylboronic acids cat-
alyzed by Pd(PPh3)4.
The emission spectra of 12–15 in dichloromethane so-
As anticipated the products bearing 9-hexylcarbazole or
9-phenylcarbazole arms were all efficiently achieved with
the moderate yields. Moreover, the solubility of 12 and 14
was observed to be better than that of 13 and 15.
lution (1 × 10–5 M) and the solid state are presented in
Figure 2. Their excitation wavelengths were all fixed at
305 nm. It was found that their maximum wavelengths of
fluorescence differed from each other. From the fluores-
cence of 12 and 14, the red-shift phenomenon of 14 com-
pared with 12 in dichloromethane solution or in the solid
state was due to the extended conjugated system of side
arms in 14. The same phenomenon was also observed for
15 with respect to 13. At the same time, the red-shift phe-
The photophysical properties of compounds 12–15 were
first examined in a diluted dichloromethane solution (ca.
10–5 M). Then, thin films used for fluorescence measure-
ments were obtained by spin-coating dichloromethane so-
lution (ca. 10 mg/mL) onto quartz plates at 1000 rpm. All
compounds exhibited excellent film-forming properties.
Photophysical data from both the solutions and the solid
nomenon of 12–15 was found in the solid state in compar-
ison with those in dichloromethane solution, which
indicated that interaction between molecules existed in
state are summarized in Table 1.
the solid state.
Synlett 2006, No. 17, 2841–2845 © Thieme Stuttgart · New York

LETTER
Synthesis and Optical Properties of Starburst Carbazoles
2843
H13C6
N
N
10, i
8, i
N
N
72%
76%
Br
C6H13
N
13
N
12
N
N
C6H13
N
C6H13
Br
Br
H13C6
N
N
N
N
9, i
11, i
N
N
63%
61%
N
H13C6
N
C6H13
N
N
N
N
15
14
C6H13
N
N
C6H13
Scheme 3 Reagents and conditions: (i) Pd(PPh3)4, K2CO3 (2 M), toluene, 80 °C, 48 h.
Table 1 Absorption and Fluorescence Spectra of 12–15 in Dichlo-
To summarize, we have synthesized four novel starburst
molecules with a central carbazole core via Suzuki cross-
coupling. By using N-alkyl- and N-phenylcarbazole units
as side chains, all the products were obtained with better
solubility properties in common organic solvents. More-
over, their absorption and fluorescence in dichlo-
romethane solution were studied. They have different
emitting fluorescence wavelengths ranging from 410 nm
to 430 nm, which makes them good blue-light-emitting
materials. The application of novel starburst molecules
with a central core is underway in our laboratory.
romethane Solution and the Solid State
Compound labs
lem
lem
max
max
max
(nm)
(nm, solution)
(nm, solid)
12
13
14
15
245, 305
250, 305
250, 305
254, 305
418
415
421
418
424
418
427
420
Acknowledgment
This work was partially supported by the National Natural Science
Foundation of China (Grants 60 325412, 90406021, and 50428303),
the Shanghai Commission of Science and Technology (Grants
03DZ11016 and 04XD14002), and the Shanghai Commission of
Education under Grant 03SG03. The work was also supported by a
research grant from the Innovation Project for Graduate student of
Jiangsu Province, the Key Laboratory of Organic Synthesis of Ji-
angsu Province (No. JSK008), the National Science Foundation of
Jiangsu Province (No. BK2004038 and BK2006048) and the Natio-
nal Natural Science Foundation of China (No. 20172039 and
20472062).
Figure 1 The normalized UV–Vis absorption spectra of carbazole
derivatives 12–15 in dichloromethane solution with the concentration
of 1 × 10–5 M.
Synlett 2006, No. 17, 2841–2845 © Thieme Stuttgart · New York

2844
G.-L. Feng et al.
LETTER
(5) (a) Grafe, A.; Janietz, D.; Frese, T.; Wendorff, J. H. Chem.
Mater. 2005, 17, 4979. (b) Wu, L. Y.; Lin, J. T.; Tao, Y. T.;
Balasubramaniam, E.; Su, Y. Z.; Ko, C. W. Chem. Mater.
2001, 13, 2626. (c) Li, J. Y.; Ma, C. W.; Tang, J. X.; Lee, C.
S.; Lee, S. T. Chem. Mater. 2005, 17, 615. (d) Li, J. Y.; Liu,
D.; Li, Y. Q.; Lee, C. S.; Kwong, H. L.; Lee, S. T. Chem.
Mater. 2005, 17, 1208. (e) Feng, G. L.; Lai, W. Y.; Ji, S. J.;
Huang, W. Tetrahedron Lett. 2006, 47, 7089. (f) Lai, W.
Y.; Zhu, R.; Fan, Q. L.; Hou, L. T.; Cao, Y.; Huang, W.
Macromolecules 2006, 39, 3707.
(6) (a) Zhang, Q.; Chen, J. S.; Cheng, Y. X.; Wang, L. X.; Ma,
D. G.; Jing, X. B.; Wang, F. S. J. Mater. Chem. 2004, 14,
895. (b) Justin Thomas, K. R.; Lin, J. T.; Tao, Y. T.; Ko, C.
W. J. Am. Chem. Soc. 2001, 123, 9404.
(7) (a) Tavasli, M.; Bettington, S.; Bryce, M. R.; Batsanov, A.
S.; Monkman, A. P. Synthesis 2005, 1619.
(b) Kanibolotsky, A. L.; Berridge, R.; Skabara, P. J.;
Perepichka, I. F.; Bradley, D. D. C.; Koeberg, M. J. Am.
Chem. Soc. 2004, 126, 13695.
(8) Synthesis of Compounds 9 and 11; Typical Procedure
To a solution of the corresponding 3-bromocarbazole
derivatives 6 or 7 (10 mmol) in anhyd THF (50 mL) was
slowly added n-BuLi (2.5 M in hexane, 4.8 mL, 12.0 mmol)
at –78 °C. At this temperature, the reaction mixture was
stirred for 1 h before adding triisopropyl borate (3.5 mL,
15.0 mmol). The mixture was allowed to warm to r.t. for
15 h. It was quenched with HCl (2.0 M, 40 mL) and poured
into a large amount of water. After extraction with Et2O (3 ×
20 mL), the organic portions were washed with brine before
drying over anhyd MgSO4 and the solvent was evaporated to
afford the crude carbazoleboronic acids. The crude product
was purified by column chromatography on a silica gel
column, eluting with PE and EtOAc (2:1) to afford
carbazoleboronic acids, which were then dried in vacuo at
35 °C.
Figure 2 The fluorescence emission spectra of 12–15 in dichloro-
methane solution (1 × 10–5 M) and the solid state.
Compound 9: 1H NMR (400 MHz, CDCl3): d = 8.54 (s, 1
H), 8.34–8.38 (m, 2 H), 8.12 (d, J = 8.0 Hz, 1 H), 7.78–7.82
(m, 3 H), 7.60 (s, 1 H), 7.25–7.48 (m, 6 H), 4.34–4.39 (m, 4
H), 1.90–1.98 (m, 4 H), 1.20–1.46 (m, 12 H), 0.88–0.90 (m,
6 H).
References and Notes
(1) (a) Baba, A.; Onishi, K.; Knoll, W.; Advincula, R. C. J.
Phys. Chem. B 2004, 108, 18949. (b) Kundu, P.; Justin
Thomas, K. R.; Lin, J. T.; Tao, Y. T.; Chien, C. H. Adv.
Funct. Mater. 2003, 13, 445.
(2) (a) Kuwabara, Y.; Ogawa, H.; Inada, H.; Noma, N.; Shirota,
Y. Adv. Mater. (Weinheim, Ger.) 1994, 6, 677. (b) Koene,
B. E.; Loy, D. E.; Thompson, M. E. Chem. Mater. 1998, 10,
2235. (c) Brien, D. F.; Burrows, P. E.; Forrest, S. R.; Koene,
B. E.; Loy, D. E.; Thompson, M. E. Adv. Mater. (Weinheim,
Ger.) 1998, 10, 1108.
(3) (a) Wakim, S.; Bouchard, J.; Simard, M.; Drolet, N.; Tao,
Y.; Leclerc, M. Chem. Mater. 2004, 16, 4386. (b) Wakim,
S.; Bouchard, J.; Blouin, N.; Michaud, A.; Leclerc, M. Org.
Lett. 2004, 6, 3413. (c) Sonntag, M.; Kreger, K.; Hanft, D.;
Strohriegl, P.; Setayesh, S.; Leeuw, D. D. Chem. Mater.
2005, 17, 3031. (d) Drolet, N.; Morin, J. F.; Leclerc, N.;
Wakim, S.; Tao, Y.; Leclerc, M. Adv. Funct. Mater. 2005,
15, 1671. (e) Morin, J. F.; Leclerc, M.; Ades, D.; Siove, A.
Macromol. Rapid Commun. 2005, 26, 761.
(4) (a) Van D, A.; Bastiaansen, J. J. A. M.; Kiggen, N. M. M.;
Langeveld, B. M. W.; Rothe, C.; Monkman, A.; Bach, I.;
Stossel, P.; Brunner, K. J. Am. Chem. Soc. 2004, 126, 7718.
(b) Morin, J. F.; Drolet, N.; Tao, Y.; Leclerc, M. Chem.
Mater. 2004, 16, 4619. (c) Justin Thomas, K. R.; Velusamy,
M.; Lin, J. T.; Tao, Y. T.; Chien, C. H. Adv. Funct. Mater.
2004, 14, 387. (d) Brunner, K.; Dijken, A. V.; Borner, H.;
Bastiaansen, J. J. A. M.; Kiggen, N. M. M.; Langeveld, B.
M. W. J. Am. Chem. Soc. 2004, 126, 6035.
Compound 11: 1H NMR (400 MHz, CDCl3): d = 8.60 (s, 1
H), 8.36–8.40 (m, 2 H), 8.07–8.14 (m, 2 H), 7.80–7.86 (m, 2
H), 7.58–7.70 (m, 4 H), 7.28–7.50 (m, 12 H).
(9) Synthesis of Starburst Compounds 12–15; General
Procedure
To a degassed (N2) solution of 9-(4-bromophenyl)-3,6-
dibromocarbazole (1; 1.0 g, 2.1 mmol) and Pd(PPh3)4
catalyst (0.5 g, 0.44 mmol, 7 mol% per C–Br bond) in
toluene (30 mL), a solution of carbazoleboronic acid (9.45
mmol) in toluene (20 mL) and a 2 M aq K2CO3 solution (13
mL) were added via syringe. The reaction mixture was
stirred at 80 °C for 48 h. After cooling, the product was
extracted with CH2Cl2, washed with water and dried over
MgSO4. The solvent was evaporated to afford the crude
mixture. After column chromatography on silica gel, eluting
with PE and CH2Cl2 (5:1), pure compounds 12–15 were
obtained. All the compounds were fully characterized. The
analytical and spectral data for these compounds follow:
Compound 12: 1H NMR (400 MHz, CDCl3): d = 8.58 (s, 2
H), 8.46 (d, J = 7.6 Hz, 3 H), 8.21 (d, J = 7.6 Hz, 3 H), 8.01
(d, J = 7.4 Hz, 2 H), 7.78–7.88 (m, 6 H), 7.65 (d, J = 7.4 Hz,
2 H), 7.43–7.56 (m, 7 H), 7.25–7.30 (m, 6 H), 4.32–4.39 (m,
6 H), 1.89–1.92 (m, 6 H), 1.28–1.37 (m, 18 H), 0.87–0.91
(m, 9 H). Anal. Calcd for C72H70N4: C, 87.23; H, 7.12; N,
5.65. Found: C, 87.30; H, 7.27; N, 5.60. MS (MALDI–
TOF): m/z [M+] calcd for C72H70N4: 991; found: 991.
Compound 13: 1H NMR (400 MHz, CDCl3): d = 8.60 (s, 2
Synlett 2006, No. 17, 2841–2845 © Thieme Stuttgart · New York

LETTER
Synthesis and Optical Properties of Starburst Carbazoles
2845
H), 8.52 (d, J = 7.6 Hz, 3 H), 8.26 (d, J = 7.6 Hz, 3 H), 8.02
0.84–0.92 (m, 18 H). Anal. Calcd for C126H127N7: C, 87.00;
H, 7.36; N, 5.64. Found: C, 87.15; H, 7.13; N, 5.80. MS
(MALDI–TOF): m/z [M+] calcd for C126H127N7: 1739;
found: 1739.
(d, J = 7.4 Hz, 2 H), 7.76–7.86 (m, 6 H), 7.63–7.68 (m, 12
H), 7.44–7.57 (m, 12 H), 7.25–7.36 (m, 6 H). Anal. Calcd for
C72H46N4: C, 89.41; H, 4.79; N, 5.79. Found: C, 89.23; H,
4.82; N, 5.43. MS (MALDI–TOF): m/z [M+] calcd for
C72H46N4: 967; found: 967.
Compound 15: 1H NMR (400 MHz, CDCl3): d = 8.64 (s, 2
H), 8.58–8.62 (m, 6 H), 8.50 (s, 3 H), 8.22–8.23 (m, 3 H),
8.05 (d, J = 7.4 Hz, 2 H), 7.78–7.88 (m, 12 H), 7.39–7.67 (m,
42 H), 7.24–7.26 (m, 9 H). Anal. Calcd for C126H79N7: C,
89.49; H, 4.71; N, 5.80. Found: C, 89.32; H, 4.49; N, 5.94.
MS (MALDI–TOF): m/z [M+] calcd for C126H79N7: 1691;
found: 1691.
Compound 14: 1H NMR (400 MHz, CDCl3): d = 8.63 (s, 2
H), 8.54–8.57 (m, 6 H), 8.45 (s, 3 H), 8.17–8.20 (m, 3 H),
8.04 (d, J = 7.4 Hz, 2 H), 7.79–7.90 (m, 10 H), 7.67 (d, J =
7.4 Hz, 2 H), 7.25–7.49 (m, 15 H), 7.20–7.23 (m, 6 H), 4.3–
4.4 (m, 12 H), 1.82–1.97 (m, 12 H), 1.25–1.56 (m, 36 H),
Synlett 2006, No. 17, 2841–2845 © Thieme Stuttgart · New York