Synthesis and characterization of novel monodisperse starburst oligo(fluoreneethynylene) based on truxene moiety

Article abstract of DOI:10.1246/cl.2008.178

A series of novel monodisperse star-shaped oligo(fluoreneethynylene)s, which contain hexahexyltruxene as the central core linked with oligo(fluoreneethynylene) as the arms, are presented. Copyright

Full text of DOI:10.1246/cl.2008.178

1
78
Chemistry Letters Vol.37, No.2 (2008)
Synthesis and Characterization of Novel Monodisperse Starburst Oligo(fluoreneethynylene)
Based on Truxene Moiety
1
1
1
1
ꢀ1
ꢀ2
Qing-Quan Chen, Feng Liu, Zhun Ma, Bo Peng, Wei Wei, and Wei Huang
State Key Laboratory for Advanced Photonic Materials & Devices, Fudan University, Shanghai 200433, P. R. China
Institute of Advanced Materials (IAM), Nanjing University of Posts and Telecommunications, Nanjing 210003, P. R. China
1
2
(Received November 1, 2007; CL-071204; E-mail: iamww@fudan.edu.cn, wei-huang@njupt.edu.cn)
A series of novel monodisperse star-shaped oligo(fluorene-
R R
R
R
R R
i
ii
iv
R
TMS
R
ethynylene)s, which contain hexahexyltruxene as the central
core linked with oligo(fluoreneethynylene) as the arms, are pre-
sented.
I
I
I
iii
R
1
R
R
R
R
iv
TMS
R
v
Br
2
R
R
vi
vi
v
R = C6H13
Poly(aryleneethynylene)s (PAE) are important conjugated
1
1
1
2
3
TMS
R
R
R
R
3
4
materials, widely used in advanced biodetection schemes,
2
3
R
R
R
R
R
R
R R
light-emitting diodes, and transistor-type applications, by
virtues of their high fluorescence quantum yield and excellent
stability, and easily synthesized by either the Heck–Cassar–
TMS
v
R
R
R
R
5
6
4
Scheme 1. Reagents and conditions: (i) C6H13Br, triethylben-
zylammonium chloride, 50% aqueous NaOH, DMSO, rt, 6 h;
ii) I2, KIO3, AcOH, H2SO4, H2O, reflux, 8 h; (iii) NBS, CHCl3,
Sonogashira coupling or by alkyne metathesis. As a general
matter, the photophysical properties of PAEs are critically
dependent upon chain ordering, conformation and selection of
suitable aromatic building blocks.
Recently, charge-transporting dendrimers, as an important
(
5
rt, 6 h; (iv) PdCl2(PPh3)2, CuI, (CH3)3Si(CꢁCH), toluene/tri-
ꢂ
ethylamine, rt (or 70 C) 24 h; (v) KOH, THF/CH3OH, rt; (vi)
PdCl2(PPh3)2, CuI, toluene/triethylamine, 50 C, 10 h.
ꢂ
6
class of organic semiconducting material, have become increas-
ingly important as the active component for use in various
applications.7 The truxene moiety, by virtue of its unique
three-dimensional topology, is an attractive building motif for
use as potential dendrimer building block via readily available
functionalization at C-2, C-7, C-12-positions and C-5, C-10,
reactants and the reacting temperature to lower the reacting
activity of aryl iodide and terminal alkyne. Any of the higher-
generation oligo(fluoreneethynylene) were prepared by de-pro-
tection of the products coming from the Sonogashira reaction
of compound 1 and the lower-generation oligo(fluoreneethynyl-
ene). 2,7-Iodo-9,9-dihexylfluorene and 2-ethynyl-9,9-dihexyl-
8
C-15-positions respectively, widely investigated for extensive
use as a starting material for the construction of larger poly-
arenes and bowl-shaped fragment of the fullerenes, liquid crys-
tals, and C3 tripod materials in asymmetric catalysis and chiral
recognition.9
Up to the present, most of the studies on dendrimers contain-
ing acetylene units are that based on phenylacetylene. But there
have been few reports of their use in optoelectronic devices,
for the planarity of the phenylacetylene-containing dendrimers
allows the emissive chromophores to interact strongly in the
solid state.7
11
fluorene were prepared according to the literature. The Sono-
gashira reaction of compound 1 and 2-ethynyl-9,9-dihexylfluo-
rene (2) gave dimeric(fluoreneethynylene) having terminal
trimethylsilylethynyl groups in quantitative yield. After depro-
tection with KOH solution, the dimeric(fluoreneethynylene) 4
was gained. The process was repeated, i.e., the trimeric-
(fluoreneethynylene) 6 was gained too. The final step to
DAE1–DAE3 is outlined in Scheme 2. As shown in Scheme 2,
the truxene core was introduced by C–C bond connection at its
2
-position with terminal alkynes of oligo(fluoreneethynylene)
In this paper, we design and synthesize a series of novel
monodisperse star-burst oligo(fluoreneethynylene)s, based on
the truxene moiety as the core unit, and study their properties
preliminary.
arms catalyzed by Pd(PPh3)4/CuI through Sonogashira reaction.
As anticipated the products were all efficiently achieved with the
H
To synthesize the target star-burst oligo(fluoreneethynyl-
ene)s, our design was to attach oligo(fluoreneethynylene) arms
directly to the central core via Sonogashira reaction. Firstly,
R
R
Br
0
0
0
2,7,12-tribromo-5,5 ,10,10 ,15,15 -hexahexyltruxene (7) was
synthesized as the key intermediate for the whole procedure
R
R
n
R
R = C H
i
6
13
R
2 ( or 4, 6)
R
1
0
3
8 - 52%
R
according to the literature. The compound 7 served as the
central core.
R
R
Br
R
Br
R
7
R
R
Secondly, oligo(fluoreneethynylene) derivatives 2, 4, and 6
were prepared as the other key intermediates to construct the
star-bursts, as shown in Scheme 1. In this step, it is more impor-
tant to generate the moderate-yield intermediates to [2-(9,9-di-
hexyl-7-iodofluoren-2-yl)ethynyl]trimethylsilane (1). In order
to get compound 1, it is vital to control the proportion of the
R
R
n
H
DAE1 n = 1
DAE1 n = 2
DAE1 n = 3
R
R
n
H
Scheme 2. Reagents and conditions: (i) Pd(PPh ) , CuI, tol-
3
4
ꢂ
uene/diisopropylamine, 70 C, 48 h.
Copyright Ó 2008 The Chemical Society of Japan

Chemistry Letters Vol.37, No.2 (2008)
179
Table 1. Physical properties of DAE1–DAE3
Tg=Td
ꢀ
abs,max/nm
ꢀemi,max/nm (ꢀex/nm)
Compound
ꢂ
(
C)
Solution
Solid Film
Solution
Solid Film
DAE1
DAE2
DAE3
187.9/369
161.5/378
151.6/388
354, 375
378, 396
387, 404
351,377
380,399
385,406
384, 401/(375)
407, 429/(375)
416, 439/(385)
447,472/(375)
440,466/(380)
444,471/(385)
moderate yields. Moreover, all the products show excellent sol-
ubility. Noticeably, in this step, it is very sensitive to trifle oxy-
gen, which promotes the coupling of oligo(fluoreneethynylene)
to form fluoreneethynylene dimer. The photophysical properties
of compounds DAE1–DAE3 were first examined in a diluted
chloroform solution (ca. 10 M). Then, thin films used for
fluorescence measurements were obtained by spin-coating
chloroform solution (ca. 10 mg/mL) onto quartz plates at
inclined to be fainted. The shapes of the absorption peaks
are the same for the chloroform solutions and films. From
Figure 1b, the fluorescence emission spectra for DAE1–DAE3
ꢃ5
in chloroform solution (1 ꢄ 10 M) show two absorption bands,
which progressively red-shift and increase with chain length
extended. In comparison with those in solution, the emission
peaks of DAE1–DAE3 in the solid state red-shift markedly
(shown in Figure 1d). Such red shifts could be attributed either
to the difference in energy-transfer processes between film and
solution due to the presence of rotational conformation in the
solution reducing the conjugation of the chromophore, or to
ꢃ5
1000 rpm. All compounds exhibited excellent film-forming
properties. Photophysical data from both the solution and the
solid films are summarized in Table 1.
13
The thermal stabilities of DAEs were determined by ther-
malgravimetric analysis (TGA) and differential scanning calo-
rimetry (DSC) under nitrogen, as shown in Table 1 (or Figure
the effect of packing and local geometry of the DAEs, which
1
4
is quite common in PAEs materials.
1
4
This work was financially supported by the NSFC under
Grants 60578039, 90406021, and 50428303.
S1 in Supporting Information). It can be observed that the
5% weight-loss temperatures (Td), with the oligo(fluorene-
ꢂ
ethynylene) arms extended, increased from 369 to 388 C. No-
ticeably, the Td of DAE3 with three repeated fluoreneethynylene
units have already higher than the linear poly(fluoreneethynyl-
References and Notes
1
I. B. Kim, J. N. Wilson, U. H. F. Bunz, Chem. Commun. 2005, 1273;
M. D. Disney, J. Zheng, T. M. Swager, P. H. Seeberger, J. Am. Chem.
Soc. 2004, 126, 13343; N. Dicesare, M. R. Pinto, K. S. Schanze, J. R.
Lakowicz, Langmuir 2002, 18, 7785.
1
2
ꢂ
ene) (PFE). In the DSC trace of heating (10 C/min) up to
ꢂ
250 C, there are no obvious glass-transition temperature (Tg)
observed for the three star-burst compounds. Noticeably, when
2
N. G. Pschirer, T. Miteva, U. Evans, R. S. Roberts, A. R. Marshall,
D. Neher, M. L. Myrick, U. H. F. Bunz, Chem. Mater. 2001, 13, 2691;
C. Schmitz, P. Posch, M. Thelakkat, H. W. Schmidt, A. Montali, K.
Feldman, P. Smith, C. Weder, Adv. Funct. Mater. 2001, 11, 41; C. A.
Breen, J. R. Tischler, V. Bulovic, T. M. Swager, Adv. Mater. 2005, 17,
1981.
ꢂ
ꢂ
cooling (ꢃ10 C/min) from 250 C down to room temperature,
their glass-transition temperatures (Tg) were observed to be
ꢂ
187.9, 161.5, and 151.6 C for DAE1, DAE2, and DAE3,
respectively, which greatly higher than the linear PFE.
1
2
3
4
Y. Xu, P. R. Berger, J. N. Wilson, U. H. F. Bunz, Appl. Phys. Lett. 2004,
85, 4219.
U. H. F. Bunz, Adv. Polym. Sci. 2005, 177, 1; X. Zhao, M. R. Pinto, L. M.
Hardison, J. Mwaura, J. Muller, H. Jiang, D. Witker, V. D. Kleiman, J. R.
Reynolds, K. S. Schanze, Macromolecules 2006, 39, 6355.
The UV–vis absorption and fluorescence emission spectra of
DAE1–DAE3 are shown in Figure 1. The absorption spectra for
compounds DAE1–DAE3 both in solution and in the solid state
show two absorption bands, which progressively red-shift with
chain length extended. In solution, the short-wavelength peak
ranges from 354 to 374 nm; the long-wavelength peak ranges
from 375 to 388 nm. With the oligo(fluoreneethynylene) arms
extended, the intensity of the short-wavelength peak was
strengthened and the interval of two absorption bands was
5
U. H. F. Bunz, J. M. Imhof, R. K. Bly, C. G. Bangcuyo, L. Rozanski,
D. A. VandenBout, Macromolecules 2005, 38, 5892; T. Miteva, L.
Palmer, L. Kloppenburg, D. Neher, U. H. F. Bunz, Macromolecule
2000, 33, 652; C. E. Halkyard, M. E. Rampey, L. Kloppenburg, S. L.
Studer-Martinez, U. H. F. Bunz, Macromolecule 1998, 31, 8655; J.
Kim, T. M. Swager, Nature (London) 2001, 411, 1030.
Y. Shirota, J. Mater. Chem. 2005, 15, 75.
6
7
8
S. Lo, P. L. Burn, Chem. Rev. 2007, 107, 1097.
DAE1
DAE2
DAE3
A
B
DAE1
DAE2
DAE3
V. N. Bliznyuk, S. A. Carter, J. C. Scott, G. Kl a¨ rner, R. D. Miller, D. C.
Miller, Macromolecules 1999, 32, 361.
M. M. Boorum, Y. V. Vasil’ev, T. Drewello, L. T. Scott, Science 2001,
solution state
solution state
9
294, 828; A. Sygula, P. W. Rabideau, J. Am. Chem. Soc. 2000, 122,
6323; T. S. Perora, J. K. Vij, Adv. Mater. 1995, 7, 919; X.-Y. Cao,
W.-B. Zhang, J.-L. Wang, X.-H. Zhou, H. Lu, J. Pei, J. Am. Chem.
Soc. 2003, 125, 12430; J. Pei, J.-L. Wang, X.-Y. Cao, X.-H. Zhou,
W.-B. Zhang, J. Am. Chem. Soc. 2003, 125, 9944.
DAE1
DAE2
DAE3
DAE1
DAE2
DAE3
C
D
10 A. L. Kanibolotsky, R. Berridge, P. J. Skabara, I. F. Perepichka, D. D. C.
Bradle, M. Koeberg, J. Am. Chem. Soc. 2004, 126, 13695.
solid film
solid film
1
1
1
2
S. H. Lee, T. Nakamura, T. Tsutsui, Org. Lett. 2001, 3, 2005.
X. Zhan, Y. Liu, G. Yu, X. Wu, D. Zhu, R. Sun, D. Wang, A. J. Epstein,
J. Mater. Chem. 2001, 11, 1606.
13
Y. Kim, S. Kwom, D. Yoo, M. F. Rubner, M. S. Wrighton, Chem. Mater.
1997, 9, 2699.
250
300
350
400
450 400
450
500
550
600
650
Wavelength /nm
14 Supporting Information is available electronically on the CSJ-
Journal Web site, http://www.csj.jp/journals/chem-lett/.: General experi-
mental procedures, 1H and C spectra for compounds 1, 2, 4, 6, and
DAE1–DAE3, and characterization data for all products.
13
Figure 1. The absorption and fluorescence spectra of DAE1–
ꢃ5
DAE3 in chloroform solution (1 ꢄ 10 M) and the solid film.
Published on the web (Advance View) January 19, 2008; doi:10.1246/cl.2008.178