Synthesis of π-conjugated two generation dendrimer composed of p-phenylenevinylene dendron and triphenylamine surface group

Article abstract of DOI:10.1246/cl.2012.516

π-Conjugated two generation dendrimer composed of p-phenylenevinylene dendron and triphenylamine surface group was synthesized via a convergent route. The dendrimer shows high solubility in organic solvents and fluorescence emission resulting from the p-phenylenevinylene site.

Full text of DOI:10.1246/cl.2012.516

doi:10.1246/cl.2012.516
516
Published on the web April 28, 2012
Synthesis of ³-Conjugated Two Generation Dendrimer Composed
of p-Phenylenevinylene Dendron and Triphenylamine Surface Group
Masanobu Mizusaki,*1 Yuichiro Yamada,1 Satoru Obara,2 and Kentaro Tada2
1Corporate Research and Development Group, Sharp Corp., 2613-1 Ichinomoto-cho, Tenri, Nara 632-8567
2Photosensitive Materials Research Center, Toyo Gosei Co. Ltd., 4-2-1 Wakahagi, Inzai, Chiba 270-1609
(Received March 5, 2012; CL-120189; E-mail: mizusaki.masanobu@sharp.co.jp)
³-Conjugated two generation dendrimer composed of p-
precipitate and evaporating the filtrate under reduced pressure.
The purification which was performed by column chromatog-
raphy on silica gel (eluent: CH2Cl2/n-hexane) gave a yellow
solid of 2 in 92% yield. The compound 2 was confirmed by
1H NMR analysis.5 Aldehyde compound of first generation
dendron 3 (Scheme 1) was prepared by the following. A N,N-
dimethylacetamide solution containing compound 2, 3,5-di-
bromobenzaldehyde, palladium acetate, triphenylphosphine, and
sodium carbonate was stirred for 24 h under N2 atmosphere at
110 °C. After cooling to rt, CH2Cl2 and water were added to the
reaction mixture, and the organic layer was extracted. The
organic layer was washed with water, and dried with MgSO4.
Evaporation of the solvent yielded an oily crude product. The
crude product was purified by column chromatography on silica
gel (eluent: CH2Cl2/n-hexane) to give a yellow solid of 3 in
63% yield. The compound 3 was confirmed by 1H NMR
analysis.5 Vinyl compound of first generation dendron 4
(Scheme 1) was then synthesized. A dry THF solution contain-
ing methyltriphenylphosphonium bromide and potassium tert-
butoxide was stirred for 2 h under N2 atmosphere at rt. Then, a
dry THF solution containing compound 3 was added dropwise,
and stirred for an additional 2 h at rt. After quenching the
reaction by adding acetone, the reaction mixture was filtered.
The filtrate was evaporated under reduced pressure to give crude
phenylenevinylene dendron and triphenylamine surface group
was synthesized via a convergent route. The dendrimer shows
high solubility in organic solvents and fluorescence emission
resulting from the p-phenylenevinylene site.
³-Conjugated dendrimer is a strong candidate for organic
semiconductor materials because of its high solubility in organic
solvents and charge-carrier transport and emission properities.1-3
Most of the ³-conjugated dendrimers reported previously have
introduced aliphatic moieties such as a dibutylamino group,
which do not show the ³-conjugation, as a surface group. Hence
the charge-carrier transportation would be restricted by the
surface group even though the solubility is high. On the
contrary, we have focused on the ³-conjugated dendrimer
composed of p-phenylenevinylene dendron and triphenylamine
surface group G2D3-PV(TPA) dendrimer 1 shown in Figure 1,
which both the dendron and surface group show hole-carrier
transport.4 In this article, we will report a synthesis of the
dendrimer 1. The dendrimer 1 was prepared via a convergent
route described below.
4-(Diphenylamino)styrene (2) was synthesized as follows.
A dry THF solution containing methyltriphenylphosphonium
bromide and potassium tert-butoxide was stirred for 2 h under
N2 atmosphere at rt. Then, a dry THF solution containing
4-(diphenylamino)benzaldehyde was added dropwise, and stir-
red for an additional 2 h at rt. After quenching of the reaction by
adding acetone, a crude product was obtained by removing the
Br2C6H3CHO
Pd(OAc)2
(C6H5)3P
N
N
N
Na2CO3
CHO
2
3
N
N
N
N
CH3P(C6H5)3Br
(CH3)3COK
N
N
N
N
4
N
N
N
N
Br2C6H3CHO
Pd(OAc)2
(C6H5)3P
N
Na2CO3
N
N
N
N
CHO
N
5
Figure 1. Chemical structure of the dendrimer 1 (G2D3-PV(TPA)).
Scheme 1. Synthesis of the two generation dendron 5.
Chem. Lett. 2012, 41, 516-517
© 2012 The Chemical Society of Japan www.csj.jp/journals/chem-lett/

517
1
0.8
0.6
0.4
0.2
0
P(O)(OEt)2
P(O)(OEt)2
NaH
+
5
1
(EtO)2(O)P
6
300
350
400
450
500
Scheme 2. Synthesis of dendrimer 1.
Wavelength/nm
product. The crude product was purified by column chromatog-
raphy on silica gel (eluent: CH2Cl2/n-hexane) to give a yellow
solid of 4 in 99% yield. The compound 4 was confirmed by
1H NMR analysis.5 Aldehyde compound of second generation
dendron 5 (Scheme 1) was prepared. A N,N-dimethylacetamide
solution containing compound 4, 3,5-dibromobenzaldehyde,
palladium acetate, triphenylphosphine, and sodium carbonate
was stirred for 24 h under N2 atmosphere at 110 °C. After
cooling to rt, CH2Cl2 and water were added, and the organic
layer extracted. The organic layer was washed with water, and
dried with MgSO4. Evaporation of the solvent yielded an oily
crude product. The crude product was recrystallized from
CH2Cl2/n-hexane to give a yellow solid of 5 in 60% yield.
Figure 2. UV-vis absorption spectrum for a thin film of the
dendrimer 1.
Ex. 401 nm
Ex. 305 nm
450
500
550
600
Wavelength/nm
Figure 3. Fluorescence spectra for the thin film of the dendrimer
with excitation at 305 and 401 nm.
1
The compound 5 was confirmed by H NMR analysis.5 G2D3-
PV(TPA) dendrimer 1 (Scheme 2) was synthesized as follows.
Benzotriphosphonate 6 was prepared following a method
reported by Deb et al.6 A dry THF solution containing 6, 5,
and sodium hydride was stirred for 3 h under N2 atmosphere at
rt. During the reaction, sodium hydride was added a few times.
After the reaction, a small amount of water was added and the
solvent evaporated. The residue was dissolved in CH2Cl2, and
dried with MgSO4. Evaporation of the solvent yielded a crude
product. The crude product was purified by column chromatog-
raphy on silica gel (eluent: CH2Cl2/n-hexane) to give a yellow
solid of the G2D3-PV(TPA) dendrimer 1 in 72% yield. The
dendrimer 1 was confirmed by 1H NMR, 13C NMR, and IR
analyses.7
The weight-average molecular weight and number-average
molecular weight estimated by gel permeation chromatography
(GPC) were 4500 and 4300, respectively, and the molecular
weight distribution was 1.05. The standard polymer and eluent
for GPC were polystyrene and THF, respectively. Since the
calculated molecular weight is 4229, the obtained molecular
weights by GPC correspond with the calculated value. The
dendrimer 1 dissolves in CHCl3, CH2Cl2, toluene, N-methyl-
In conclusion, the ³-conjugated dendrimer 1 was synthe-
sized via a convergent route. The dendrimer shows narrow
molecular weight distribution, and the molecular weights by
GPC correspond with the calculated value. It shows high
solubility and emission. Further study related to device perform-
ance such as organic light-emitting diodes is now being
attempted.
References and Notes
1
2
3
4
5
J. M. Lupton, I. D. W. Samuel, R. Beavington, P. L. Burn, H. Bässler,
Adv. Mater. 2001, 13, 258.
T. D. Anthopoulos, J. P. J. Markham, E. B. Namdas, J. R. Lawrence,
I. D. W. Samuel, S.-C. Lo, P. L. Burn, Org. Electron. 2003, 4, 71.
J. L. Segura, R. Gómez, N. Martín, D. M. Guldi, Org. Lett. 2001, 3,
2645.
M. Mizusaki, M. Yamahara, Y. Yamada, S. Obara, K. Tada, Polym. J.
2009, 41, 508.
Spectral data for 2; 1H NMR (400 MHz, CDCl3): ¤ 7.29-7.22
(m, 6H), 7.08 (d, J = 8.4 Hz, 4H), 7.03-6.98 (m, 4H), 6.65 (dd,
J = 18 Hz, 11 Hz, 1H), 5.63 (d, J = 18 Hz, 1H), 5.14 (d, J = 11 Hz,
1H). Spectral data for 3; 1H NMR (400 MHz, CDCl3): ¤ 10.01 (s,
1H), 7.85 (d, J = 1.6 Hz, 2H), 7.79 (t, J = 1.6 Hz, 1H), 7.41 (d,
J = 8.4 Hz, 4H), 7.27 (t, J = 7.8 Hz, 8H), 7.18 (d, J = 16 Hz, 2H),
7.12 (d, J = 8.4 Hz, 8H), 7.07-7.02 (m, 8H and 2H). Spectral data for
4; 1H NMR (400 MHz, CDCl3): ¤ 7.48 (s, 1H), 7.48 (t, J = 7.2 Hz,
8H), 7.39-7.37 (m, 6H), 7.11-6.96 (m, 20H), 6.73 (dd, J = 18 Hz,
11 Hz, 1H), 5.81 (d, J = 18 Hz, 1H), 5.28 (d, J = 11 Hz, 1H). Spectral
data for 5; 1H NMR (400 MHz, CDCl3): ¤ 10.08 (s, 1H), 7.94 (d,
J = 1.6 Hz, 2H), 7.91 (t, J = 1.6 Hz, 1H), 7.54 (s, 6H), 7.42 (d,
J = 8.8 Hz, 8H), 7.31-7.17 (m, 4H and 16H), 7.14-7.11 (m, 4H and
16H), 7.08-7.01 (m, 16H and 4H). Spectral data for 1; mp: 201-
222 °C. TLC: Rf = 0.395 (One spot was observed with developing
solvent of toluene/n-hexane). 1H NMR (400 MHz, CDCl3): ¤ 7.55 (s,
3H), 7.52 (s, 6H), 7.43 (s, 3H), 7.35 (s, 12H), 7.26 (s, 6H), 7.23 (d,
J = 8.4 Hz, 24H), 7.16-7.12 (m, 12H and 48H), 7.05-6.89 (m, 18H
and 96H), 6.80 (d, J = 16 Hz, 12H). 13C NMR (CDCl3): ¤ 147.4,
147.1, 138.0, 137.7, 137.3, 131.2, 129.2, 128.3, 127.4, 126.6, 124.4,
123.4, 122.9.
pyrrolidone, £-butyrolactone, and THF up to a concentration of
¹1
10 mg mL
.
Figure 2 represents a UV-visible absorption spectrum. A
50 nm thick dendrimer 1 film prepared by spin-coating from a
CHCl3 solution on a quartz substrate was used. Two typical
absorption peaks centered at 300 and 400 nm are observed,
the former due to the triphenylamine and the latter to the p-
phenylenevinylene.4 Steady-state fluorescence spectra were
measured with the same sample used for the measurement of
absorption spectrum. Figure 3 indicates fluorescence spectra
with excitation at 305 and 401 nm. Fluorescence emission with
excitation at 401 nm is clearly observed, indicating that the p-
phenylenevinylene site shows emission. On the contrary, the
fluorescence intensity with excitation at 305 nm is comparably
weak. There is a possibility that energy transfer occurs from the
excited state of the triphenylamine group to the p-phenyl-
enevinylene moiety.
6
7
S. K. Deb, T. M. Maddux, L. Yu, J. Am. Chem. Soc. 1997, 119, 9079.
The 1H NMR and IR spectra, and GPC data of dendrimer 1 are in
Supporting Information. Supporting Information is available elec-
tronically on the CSJ-Journal Web site, http://www.csj.jp/journals/
chem-lett/index.html.
Chem. Lett. 2012, 41, 516-517
© 2012 The Chemical Society of Japan
www.csj.jp/journals/chem-lett/