Facile synthesis of novel nonplanar arylamine-centered oligofluorenes based on complicated 9,9-diarylfluorene building blocks by friedel-crafts reaction

Article abstract of DOI:10.1246/cl.2008.622

The syntheses of two well-defined organic nanomaterials. TDFF-TPA and TDFF-FBCz. with highly nonplanar structures, based on complicated 9,9-diarylfluorenes (DAF) by BF₃·OEt₂-mediated Friedel-Crafts reactions are presented. Copyright

Full text of DOI:10.1246/cl.2008.622

622
Chemistry Letters Vol.37, No.6 (2008)
Facile Synthesis of Novel Nonplanar Arylamine-centered Oligofluorenes
Based on Complicated 9,9-Diarylfluorene Building Blocks by Friedel–Crafts Reaction
Bao-Min Zhao,1 Ni-Na Fu,2 Ling-Hai Xie,2 Lian-Hui Wang,ꢀ1 and Wei Huangꢀ2
1Laboratory of Advanced Materials, Fudan University, 220 Handan Road, Shanghai 200433, P. R. China
2Institute of Advanced Materials, Nanjing University of Posts and Telecommunication,
66 XinMoFan Road, Nanjing 210003, P. R. China
(Received February 27, 2008; CL-080219; E-mail: wlhui@fudan.edu.cn, wei-huang@njupt.edu.cn)
The syntheses of two well-defined organic nanomaterials,
TDFF-TPA and TDFF-FBCz, with highly nonplanar structures,
.
based on complicated 9,9-diarylfluorenes (DAF) by BF3 OEt2-
mediated Friedel–Crafts reactions are presented.
R
R
C6H13 C6H
13OH
OH
N
R
B
HO
TPA
HO
2
N
Br
Br
R
R
R
Pd(Ph3P)4,
BF3·Et2O
CH2Cl2
3
1
K2CO3 / toluene,
R
80 °C
C6H13
C6H13
R =
TDFF-TPA
R
Fluorene-based oligomers with a well-defined structure
have attracted considerable attention because they may function
as model compounds for poly[2,7-(9,9-dialkyl)fluorenes] (PFs),
which are thought to be promising candidates for blue light
emitting diodes (LEDs),1,2 and potential active materials for
applications in liquid crystals,3,4 LEDs,5,6 field-effect transis-
tors,7 and amplified spontaneous emitters.8,9 Among the deriva-
tives of fluorene, starburst and dendritic molecules have shown
particularly impressive performance. However, most of them
were synthesized via iterative reactions involving tedious purifi-
cation steps and low yieldings,10 which impaires the materials’
scale-up and commercial applications.
Scheme 1.
R
C6H13
R
C6H13
R
R
H
N
N
Br
3
C6H13
C6H13
C6H13
C6H13
N
N
BF3·Et2O
CH2Cl2
L-Proline
CuI, DMSO
K2CO3
R
R
Br
N
R
R
TDFF-FBCz
C6H13
C6H13
FBCz
R =
Scheme 2.
Previous investigations have demonstrated that the injection
of electrons dominates in fluorene-based polymers and oligo-
mers.11 To increase the efficiency of the devices, the hole injec-
tion needs to be significantly boosted. The introduction of hole-
transporting chromophores such as carbazole and triphenyl-
amine (TPA) groups12–14 into the fluorene-based derivatives
may promote the injection and transport of holes. On the other
hand, the film quality and the morphology of the surface also
need to be optimized.15 The deposition of high-quality films
by solution-based spin-coating is most desirable for device
fabrication.1
To increase hole injection and improve the quality of
the films while still retaining the excellent optical and thermal
properties of oligo-fluorenes, we have successfully synthesized
novel fluorene-based compounds, TDFF-TPA and TDFF-FBCz,
with TPA and/or carbazole derivative as core and peripheral
to synthesize TDFF-TPA and TDFF-FBCz, as shown in
Schemes 1 and 2. Initially, we tried the divergent route to synthe-
size the target compound TDFF-TPA, as shown in Scheme 1.
Tris[4-(2,7-dibromo-9-phenyl-9H-fluoren-9-yl)phenyl]amine
(Br6F-TPA) was synthesized with 87% yield through the
.
BF3 OEt2-mediated Friedel–Crafts reaction of TPA with tertiary
alcohol 1.16 However, Br6F-TPA is difficult to be dissolved in
general solvents due to its rigid aromatic rings without any flex-
ible alkyl chains. Therefore, it is difficult to carry out the Suzuki
reaction so as to have all bromo groups substituted by 2-(9,9-di-
hexyl)fluorene, even if much excess of boric acid 2 was added
and the reaction was kept for quite a long time. The final product
TDFF-TPA is difficult to be separated from various by-products.
The convergent route are preferred considering three impor-
tant factors, such as the separation of by-procucts, the Friedel–
Crafts reactivity in the dehydration cross-coupling reaction,
and the convenience of scale-up. As shown in Scheme 1,
TDFF-TPA with high yield (>90%) was synthesized by the
reaction between TPA (1 equiv) and the intermediate 3 (3.3
equiv), which was obtained based on 1 and 2 by the Suzuki con-
densation reaction with the yield of 89%. In this process, the
trace by-products were easily removed with silica gel column.
To tune the distance between the terfluorene dendrons,
TDFF-FBCz was also designed. The carbazole is an important
optoelectrical building block for organic semiconductors
due to its remarkable hole-transporting ability, thermal stability,
great solubility, and extended glassy state. As shown in
Scheme 2, FBCz was synthesized as a core via the Ullmann re-
action, catalyzed with CuI and K2CO3 in DMSO.24 Compared to
the diphenylamino analogue, the rigid structure of the carbazoyl
.
dendrons of 9,9-diarylfluorene (DAF) through the BF3 OEt2-
mediated Friedel–Crafts reaction.16 Because the triphenylamine
or carbazole core connected to the sp3-hybridized carbon atom at
the C-9 position of the fluorene moiety, which serves as a spacer
to block extended ꢀ-conjugation,17 the conjugation length and
triplet energy of each individual building block in the resulting
composite should remain essentially unperturbed. In addition,
the 3D cardo structure of substituted fluorene derivative should
improve the system’s rigidity and hinder any unwanted aromatic
ꢀ-stacking interactions, resulting in an amorphous material
possessing enhanced morphological stability.18 Such unique
nonplanar conformation of these two compounds results in their
amorphous state in nature and makes it difficult to pack them
into detrimental aggregation in the film state.19
Both divergent and convergent routes were considered
Copyright Ó 2008 The Chemical Society of Japan

Chemistry Letters Vol.37, No.6 (2008)
Table 1. Physical properties of TDFF-TPA and TDFF-FBCz
623
a
a
UV ꢁmax
/nm
PL ꢁmax
/nm
Oxidationd
Eox/V
Reductiond
Ered/V
Compounds
ꢂf/%b
Tg/ꢂC
Td/ꢂCc
TDFF-TPA
TDFF-FBCz
349
349
399/420
400/425
65
79
120
143
422
428
0.742
0.785
ꢃ2:26
ꢃ2:23
aMeasured in THF solvent (10ꢃ6 M). 9,10-Diphenylanthracene in the cyclohexane solvent as standard. The temperature was recorded
corresponding to a 5% weight loss in air. Onset oxidation and reduction potentials versus an Ag/Agþ reference.
b
c
d
properties of TDFF-TPA and TDFF-FBCz, as shown in Table 1.
TDFF-TPA
TDFF-FBCz
TDFF-TPA
TDFF-FBCz
TDFF-TPA
TDFF-FBCz
TDFF-TPA
TDFF-FBCz
Their decomposition temperatures (Td) are up to 420 ꢂC
corresponding to a 5% weight loss in air with no weight loss
at lower temperature. Thus, both TDFF-TPA and TDFF-FBCz
show satisfying thermostabilities, which is the typical property
of oligofluorenes or polyfluorenes with the 9 position of fluorene
moiety substituted by aryl functional groups.19 The glass-transi-
tion temperatures (Tg) of TDFF-FBCz is higher than that of
TDFF-TPA. In addition, both the cathode and anode scans of
TDFF-TPA and TDFF-FBCz are reversible according to the
electrochemical investigation,24 which indicate their stabilities
towards the redox process and potential application for LEDs.18
1.0
0.8
0.6
0.4
0.2
0.0
400
Wavelength(nm)
450
500
550
600
300
350
400
450
Figure 1. Absorption and fluorescence spectra of TDFF-TPA
and TDFF-FBCz in THF solution (hole) and solid state (solid).
moiety is more liable to afford a glassy state.20 In addition, under
the same Ullmann reaction conditions, 9H-carbazole seemed to
react more efficiently with 2,7-dibromo-9,9-dihexylfluorene
than diphenylamine.21,22 TDFF-FBCz was successfully synthe-
sized with 83% yield using the same convergent procedure
as TDFF-TPA. According to their GPC profiles, both of their
polydistribution index were lower than 1.02. This one-step
Friedel–Crafts type reaction is not only simple but, because
of the use of inexpensive reactants at room temperature and
using this synthetic strategy, TDFF-TPA and TDFF-FBCz can
be produced readily on a 5 g scale.
The optical properties of TDFF-TPA and TDFF-FBCz were
investigated by UV–vis absorption and photoluminescence (PL)
spectroscopies in the THF solution as well as in the spin-casted
film (shown in Figure 1). TDFF-TPA and TDFF-FBCz showed
the nearly identical absorption profiles in THF and solid film
(left of Figure 1), which suggests that the absorption band in
the range of 300–400 nm is contributable to the dendrons of
terfluorene units in TDFF-TPA and TDFF-FBCz.23 And, there
is slightly red-shifted for their absorption peaks in solid state.
As shown in Figure 1 (right), TDFF-FBCz shows the typical
emission of terfluorene, which is somewhat different from that of
TDFF-TPA. Considering their difference in structure, the spatial
distance of the dendrons in TDFF-FBCz is larger than that in
TDFF-TPA, so the interaction of dendrons in TDFF-FBCz is
not as significant as that in TDFF-TPA. In addition, the PL spec-
tra of TDFF-FBCz have small fwhm value (ꢁ43 nm) compared
to TDFF-TPA. The PL emission wavelength of TDFF-TPA and
TDFF-FBCz in THF and solid film does not change significantly,
which suggests that the unique conformation of TDFF-TPA and
TDFF-FBCz significantly reduces aggregation in solid state as
well as in solution. Furthermore, analysis of TDFF-TPA and
TDFF-FBCz by PL quantum efficiencies reveals that both of
them are highly fluorescent materials with very efficient blue
emission in solution (the quantum yielding data are summarized
in Table 1) (see Supporting Information),24 which might be
attributed to their unique 3D structure.
This work was financially supported by the NSFC under
Grants nos. 60235412, 90406021, 60537030, and 30425020.
References and Notes
1
Y. Geng, A. Trajkovska, S. W. Culligan, J. J. Ou, H. M. P. Chen, D. Katsis,
S. H. Chen, J. Am. Chem. Soc. 2003, 125, 14032.
2
3
G. Klaerner, R. D. Miller, Macromolecules 1998, 31, 2007.
Y. Geng, S. W. Culligan, A. Trajkovska, J. U. Wallace, S. H. Chen, Chem.
Mater. 2003, 15, 542.
4
5
6
Y. Geng, A. Trajkovska, D. Katsis, J. J. Ou, S. W. Culligan, S. H. Chen,
J. Am. Chem. Soc. 2002, 124, 8337.
S. W. Culligan, Y. Geng, S. H. Chen, K. Klubek, K. M. Vaeth, C. W. Tang,
Adv. Mater. 2003, 15, 1176.
M. Sudhakar, P. I. Djurovich, T. E. Hogen-Esch, M. E. Thompson, J. Am.
Chem. Soc. 2003, 125, 7796.
T. P. I. Saragi, T. F. Lieker, J. Salbeck, Adv. Funct. Mater. 2006, 16, 966.
7
8
9
J. Salbeck, M. Schorner, T. Fuhrmann, Thin Solid Films 2002, 417, 20.
¨
¨
N. Johansson, J. Salbeck, J. Bauer, F. Weissortel, P. Broms, A. Andersson,
¨
W. R. Salaneck, Adv. Mater. 1998, 10, 1136.
10 W.-Y. Lai, Q.-Q. Chen, Q.-Y. He, Q.-L. Fan, W. Huang, Chem. Commun.
2006, 1959.
11 S.-C. Chang, G. He, F.-C. Chen, T.-F. Guo, Y. Yang, Appl. Phys. Lett. 2001,
79, 2088.
12 C. Xia, R. C. Advincula, Macromolecules 2001, 34, 5854.
13 B. Liu, W.-L. Yu, Y.-H. Lai, W. Huang, Chem. Mater. 2001, 13, 1984.
14 J. Li, D. Liu, Y. Li, C.-S. Lee, H.-L. Kwong, S. Lee, Chem. Mater. 2005,
17, 1208.
15 W.-J. Shen, R. Dodda, C.-C. Wu, F.-I. Wu, T.-H. Liu, H.-H. Chen, C. H. Chen,
C.-F. Shu, Chem. Mater. 2004, 16, 930.
16 L.-H. Xie, X.-Y. Hou, Y.-R. Hua, C. Tang, F. Liu, Q.-L. Fan, W. Huang, Org.
Lett. 2006, 8, 3701.
17 C.-L. Chiang, C.-F. Shu, Chem. Mater. 2002, 14, 682.
18 a) P.-I. Shih, C.-H. Chien, F.-I. Wu, C.-F. Shu, Adv. Funct. Mater. 2007, 17,
3514. b) Q. Kong, D. Zhu, Y. Quan, Q. Chen, J. Ding, J. Lu, Y. Tao, Chem.
Mater. 2007, 19, 3309.
19 a) X.-M. Liu, J. Xu, X. Lu, C. He, Org. Lett. 2005, 7, 2829. b) W. J. Oldham,
R. J. Lachicotte, G. C. Bazan, J. Am. Chem. Soc. 1998, 120, 2987.
20 H. Inomata, K. Goushi, T. Masuko, T. Konno, T. Imai, H. Sasabe, J. J. Brown,
C. Adachi, Chem. Mater. 2004, 16, 1285.
21 a) Z. H. Li, M. S. Wong, Y. Tao, J. Lu, Chem.—Eur. J. 2005, 11, 3285.
b) J. Huang, C. Li, Y.-J. Xia, X.-H. Zhu, J. Peng, Y. Cao, J. Org. Chem.
2007, 72, 8580.
22 a) J. Teetsov, M. A. Fox, J. Mater. Chem. 1999, 9, 2117. b) X. Gong, P. K. Iyer,
D. Moses, G. C. Bazan, A. J. Heeger, S. S. Xiao, Adv. Funct. Mater. 2003,
13, 325.
23 J. Salbeck, N. Yu, J. Bauer, F. Weissortel, H. Bestgen, Synth. Met. 1997,
91, 209.
24 General experimental procedures and characterization data for all products: 3,
Br6F-TPA, FBCz, TDFF-TPA, and TDFF-FBCz. Supporting Information is
also available electronically on the CSJ-Journal Web site, http://www.csj.jp/
journals/chem-lett/index.html.
Thermogravimetric analysis (TGA) and differential scan-
ning calorimetry (DSC) are carried out to investigate the thermal
Published on the web (Advance View) May 3, 2008; doi:10.1246/cl.2008.622