Synthesis of novel alternating π-conjugated copolymers having [2.2]paracyclophane and fluorene units in the main chain leading to the blue light-emitting materials

Article abstract of DOI:10.1246/cl.2002.194

Novel through-space π-conjugated polymers having [2.2]paracyclophane and fluorene units were synthesized by Heck-Sonogashira coupling reaction. The polymers exhibited strong blue fluorescence in solution and in the solid state.

Full text of DOI:10.1246/cl.2002.194

1
94
Chemistry Letters 2002
Synthesis of Novel Alternating ꢀ-Conjugated Copolymers Having [2.2]Paracyclophane and
Fluorene Units in the Main Chain Leading to the Blue Light-Emitting Materials
ꢀ
Yasuhiro Morisaki and Yoshiki Chujo
Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University, Yoshida, Sakyo-ku, Kyoto 606-8501
(Received November 9, 2001; CL-011129)
Novelthrough-space ꢀ-conjugated polymers having [2.2]para-
cyclophane and fluorene units were synthesized by Heck-Sonoga-
shira coupling reaction. The polymers exhibited strong blue
fluorescence in solution and in the solid state.
[
2.2]Paracyclophane, in which two benzene rings are close to
each other and facing, attracts attention to the structure, reactivity,
1
and physicalproperties. A number of paracyclophane derivatives
have been prepared, and their physical properties, especially optical
and electronic properties due to the characteristic interactions
between the two co-facial ꢀ-electron systems, have been
Scheme 1.
R
R
PdCl (PPh ) / PPh / CuI
2
2
3 2
3
investigated. In addition, severalnon-conjugated po ly mers having
a [2.2]paracyclophane skeleton in the main chain (in the course of
+
I
I
4
THF, NEt , 50
for 48 h
3
3
developing new processes for crosslinking resins) or in the side
4
5a-c
R = a Hexyl; b Dodecyl; c 2-Ethylhexyl
chain have been prepared so far. In 1986, Mizogami and a co-
worker reported the first synthesis of polymetacyclophane, which
R
R
ꢁ1
exhibited a conductivity of 0.25 S cm by doping with a H2SO4
5
vapor. However, no ꢀ-conjugated polymers using the longitudinal
ꢀ
reported, except in our recent study, in which we found that the
-ꢀ interaction of paracyclophane as a repeating unit have yet been
n
6a-c
polymer 1 showed the extension of ꢀ-delocalization via the
6
Scheme 2.
through-space with ꢀ-ꢀ stacking of [2.2]paracyclophane.
C12H25
O
mers 6a-c in good isolated yields (Table 1). The structure of the
1
13
13
polymer was confirmed by H and CNMR spectra. All polymers
were soluble in common solvents such as THF, CHCl3, CH2Cl2, and
toluene.
OC12H25
n
The molecular weight measurements were performed by gel
permeation chromatography (GPC) in eluent CHCl3 using the
calibration curve of polystyrene standards, as summarized in
Table 1. For example, the polymer 6b (R ¼ n-dodecyl) had the
number average molecular weight (Mn) of 26400, which corre-
sponds to a degree of polymerization of 35, with Mw/Mn of 2.6. The
molecular weight of the polymer was highly dependent on the
choice of the kind of each monomer. Namely, the treatment of
pseudo-p-dibromo[2.2]paracyclophane with 2,7-diethynyl-9,9-di-
dodecylfluorene by the same catalyst system described above under
1
The synthesis of novel ꢀ-conjugated polymers has received
extensive attention due to their unique optical, electrochemical, and
7
non-linear optical properties. Recent research activity in particular
has focused significant interest on the photoluminescence (PL) and
electroluminescence (EL) from the first demonstration of the
8
polymer-based light–emitting diode (LED) in 1990. Polyfluorenes
have become more important in recent years due to their efficient
9
;10
blue PL and EL properties. In the present study, we prepared the
novel ꢀ-conjugated polymers based on poly(p-phenylene-ethyny-
lene) derivatives having [2.2]paracyclophane and fluorene units in
the main chain, and found that the polymers showed strong blue
fluorescence in solution and in the solid state.
ꢂ
the severer reaction condition, at 85 C for 72 h, gave 6b in 60%
yield with a degree of polymerization of only 7 (Mn ¼ 5400).
The opticalproperties of the po ly mers 6a-c were examined, and
the results are summarized in Table 2. The maxima of the
Monomer 4 was synthesized according to the reaction sequence
outlined in Scheme 1, and 2,7-diiodofluorenes 5a-c were synthe-
sized by diiodination of fluorene and phase transfer alkylation in
good yields.11 The polymers 6a-c were synthesized by Heck-
Table 1. Results of the synthesis of copolymers 6a-c having [2.2]para-
cyclophane and fluorene units
Polymer
Yield/%a
Mwb
Mnb
Mw/Mnb
6
a
76
76
85
48000
66800
31000
18500
26400
9800
2.6
2.5
3.2
1
2
Sonogashira reaction, as shown in Scheme 2. The polymerization
of 4 with 5a-c in the presence of a catalytic amount of PdCl2(PPh3)2/
6
b
6
c
ꢂ
PPh3/CuI in THF-NEt3 at 50 C for 48 h under a nitrogen
atmosphere proceeded smoothly to give the corresponding poly-
aIsolated yields after reprecipitation into MeOH. bGPC (CHCl3),
polystyrene standards.
Copyright Ó 2002 The ChemicalSociety of Japan

Chemistry Letters 2002
195
Table 2. Opticalproperties of the po ly mers 6a-c and 1
Absorbance/nma Emission/nma,b
ing [2.2]paracyclophane and fluorene units in the main chain. The
photoluminescence spectra of the polymers showed a strong blue
light emission in solution and in the solid state, compared with the
fluorene-containing polymers reported so far. An appropriate
transannular ꢀ-ꢀ overlap of [2.2]paracyclophane in the polymer
backbone is important for efficient transfer of the electronic charge
or energy. The polymers obtained are promising candidates for
blue light-emitting materials with extreme photoluminescence and
electroluminescence.
Polymer
CHCl3
Film
CHCl3 (ÈF)
Film
6
6
6
1c
a
b
c
372
370
371
319, 384
370
368
371
312, 383
393, 412 (0.59)
393, 415 (0.58)
393, 415 (0.65)
411, 483 (0.30)
397, 424
397, 418
398, 428
523
2
a
Absorption and emission spectra were recorded in dilute CHCl3
solutions at room temperature. Excited at 370 nm (1:0 ꢃ 10ꢁ5 M).
b
c
Ref. 6.
References and Notes
absorption spectra of 6a-c in the CHCl3 solution at room
temperature were around 370 nm (Table 2). The absorption and
emission spectra of the polymer 6b, as a typicalrepresentative
example, are shown in Figure 1. The polymer 6b showed the
absorption peak at 370 nm (" ¼ 39200) and an onset at 418 nm,
which indicates the energy band gap as 2.98 eV. The peak of the
absorption spectra of the polymer films was almost the same as in
the solution. As shown in Figure 1, the polymer 6b exhibited strong
blue fluorescence with the peak maximum at 415 nm, (a shoulder
peak at 425 nm and a weak peak at 393 nm), which was blue-shifted
by 68 nm compared to those of the polymer 1 (Table 2). The
emission peak maximum was independent on the concentration of
the polymer solution, and in the film state the peak maximum at
1
2
For recent reviews, see: a) F. V o¨ gtle, in ‘‘Cyclophane Chemistry,’’
Wiley & Sons, New York (1993). b) J. Shultz and F. V o¨ gtle, Top. Curr.
Chem., 172, 42 (1994).
Bazan, Mukamel, and co-workers recently reported the unique
photophysicalproperties of a series of sti bl enoids having a [2.2]para-
cyclophane core: a) G. C. Bazan, W. J. Oldham, Jr., R. J. Lachicotte, S.
Tretiak, V. Chernyak, and S. Mukamel, J. Am. Chem. Soc., 120, 9188
(1998). b) S. Wang, G. C. Bazan, S. Tretiak, and S. Mukamel, J. Am.
Chem. Soc., 122, 1289 (2000). c) J. Zyss, I. Ledoux, S. Volkov, V.
Chernyak, S. Mukamel, G. P. Bartholomew, and G. C. Bazan, J. Am.
Chem. Soc., 122, 11956 (2000).
3
a) R. A. Meyers, J. W. Hamersma, and H. E. Green, J. Polym. Sci.,
Polym. Lett. Ed., 10, 685 (1972). b) K. P. Sivaramakrishnan, C. Samyn,
I. J. Westerman, D. T. Wong, and C. S. Marvel, J. Polym. Sci., Polym.
Chem. Ed., 13, 1083 (1975). c) D. M. Chang and C. S. Marvel, J. Polym.
Sci., Polym. Chem. Ed., 13, 2507 (1975). d) S. Lin and C. S. Marvel, J.
Polym. Sci., Polym. Chem. Ed., 21, 1151 (1983).
4
18 nm was observed in a visible blue region. In contrast, in the case
of the polyfluorenes, variation of the emission color (peak maxima
at around 430 nm) is possible via the substitution pattern at 9-
position of the fluorene unit and/or via the change of a co-
monomer.9 In addition, Bunz and co-workers recently reported
the synthesis of poly(fluorenylene-ethynylen) by alkyne metathesis
and poly(9,9-didodecylfluorenylene-ethynylene) showed emission
4
5
a) J. Furukawa and J. Nishimura, J. Polym. Sci., Polym. Lett. Ed., 14, 85
(1976). b) D. T. Longone and D. T. Glatzhofer, J. Polym. Sci., Polym.
Chem. Ed., 24, 1725 (1986). c) D. T. Longone and J. H. Glans, J. Polym.
Sci., Polym. Chem. Ed., 26, 405 (1988). d) S. Iwatsuki, T. Itoh, M. Kubo,
and H. Okuno, Polym. Bull., 32, 27 (1994).
S. Mizogami and S. Yoshimura, J. Chem. Soc., Chem. Commun., 1985,
1736.
Y. Morisaki and Y. Chujo, Macromolecules, in press.
R. D. McCullough, P. C. Ewbank, in ‘‘Handbook of Conducting
Polymers,’’ 2nd ed., ed. by T. A. Skotheim, R. L. Elsenbaumer, and
J. R. Reynolds, Marcel Dekker, New York (1997).
J. H. Burrousghes, D. D. C. Bradey, A. R. Brown, R. N. Marks, K.
Mackay, R. H. Friend, P. L. Burns, and A. Holmes, Nature, 347, 539
;10
1
4
6
7
peaks at 426 and 447 nm in CHCl3 solution. In comparison with
these reported fluorene–containing polymers, the titled compounds
6
a-c are one of the polymers, which show an emission peak at the
lowest wavelength. Furthermore, the fluorescence quantum yields
ÈF) of the polymers 6a-c were determined for highly diluted
CHCl3 solutions. 6a-c showed a quantum yield of around 0.60 using
8
9
1
(
(
1990).
First application of polyfluorene to EL diodes was reported in 1991: Y.
Ohmori, M. Uchida, K. Muro, and K. Yoshino, Jpn. J. Appl. Phys., 30
L1941 (1991).
Foe example, see: a) A. Charas, J. Morgado, J. M. G. Martinho, L.
Alc a´ cer, and F. Cacialli, Chem. Commun., 2001, 1216. b) D. Marsitzky,
R. Vestberg, P. Blainey, B. T. Tang, C. J. Hawker, and K. R. Carter, J.
Am. Chem. Soc., 123, 6965 (2001) and references therein.
S. H. Lee, T. Nakamura, and T. Tsutsui, Org. Lett., 3, 2005 (2001).
a) H. A. Dieck and R. F. Heck, J. Organomet. Chem., 93, 259 (1975). b)
K. Sonogashira, Y. Tohda, and N. Hagihara, Tetrahedron Lett., 16, 4467
9
-anthracenecarboxylic acid in CH2Cl2 as a standard (ÈF ¼ 0:442).
In conclusion, we synthesized alternating copolymers combin-
0
(1)
(3)
1
1
1
2
(1975).
A typical procedureis as follows. A mixture of 4 (77 mg, 0.30 mmol), 5b
1
3
(
226 mg, 0.30 mmol), PdCl2(PPh3)2 (210 mg, 0.030 mmol), PPh3
157 mg, 0.060 mmol), CuI (76 mg, 0.040 mol), NEt3 (2.0 mL), and
(2)
(4)
(
THF (4.0 mL) was placed in a 50-mL Pyrex flask under nitrogen
atmosphere. The reaction was carried out at 50 C for 48 h with stirring.
ꢂ
After the reaction mixture was cooled, ammonium salt was filtered off
and washed with THF. The filtrate was concentrated and dried in vacuo.
The residue was dissolved in CHCl3 and poured into MeOH (50 mL)
twice to precipitate the polymer. The resulting polymer (6b) was
filtered, washed with MeOH, and dried in vacuo to give 169 mg
1
(
(
0.022 mmol, 76%). H NMR (270 MHz, CDCl3); ꢁ 0.69 (br, 4H), 0.85
br, 6H), 1.20 (m, 36H), 2.02 (br, 4H), 3.00 (m, 4H), 3.32 (br, 2H), 3.77
br, 2H), 6.58 (m, 2H), 6.69 (m, 2H), 7.09 (m, 2H), 7.38–7.77 (m, 6H);
250 300
400
500
600
700
(
Wavelength / nm
1
3
C NMR (67.5 MHz, CDCl3); ꢁ 14.1, 22.7, 23.8, 29.3, 29.6
Figure 1. UV-visible spectra of 6b (1) in CHCl3 solution and (2) in
the film state, and fluorescence emission spectra of 6b (3) in CHCl3
(overlapping signals), 30.1, 31.9, 34.2, 40.3, 55.3, 90.1, 93.7, 120.0,
122.4, 124.8, 130.0, 133.1, 134.5, 137.2, 139.6, 140.6, 142.1, 151.2.
14 N. G. Pschirer and U. H. F. Bunz, Macromolecules, 33, 3961 (2000).
ꢁ5
solution (1:0 ꢃ 10 M) and (4) in the film state, on the excitation at
70 nm.
3