Synthesis of novel π-conjugated polymers having [2.2]paracyclophane skeleton in the main chain. Extension of π-conjugated length via the through-space

Article abstract of DOI:10.1021/ma011170e

Novel π-conjugated polymers having [2.2]paracyclophane in the main chain were synthesized. The extension of π-conjugation via the through-space was observed according to the UV-vis absorption spectral data in comparison with those of the model compounds.

Full text of DOI:10.1021/ma011170e

Macromolecules 2002, 35, 587-589
587
Communications to the Editor
Sch em e 1
Syn th esis of Novel π-Con ju ga ted P olym er s
Ha vin g [2.2]P a r a cyclop h a n e Sk eleton in th e
Ma in Ch a in . Exten sion of π-Con ju ga ted
Len gth via th e Th r ou gh -Sp a ce
Ya su h ir o Mor isa k i a n d Yosh ik i Ch u jo*
Department of Polymer Chemistry, Graduate School of
Engineering, Kyoto University, Yoshida, Sakyo-ku,
Kyoto 606-8501, J apan
Received J uly 6, 2001
Revised Manuscript Received November 8, 2001
In tr od u ction . [2.2]Paracyclophane, in which two
benzene rings are close to each other and facing, is
attracted to the structure, reactivity, and physical
properties.1 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
π-electron systems, have been investigated.2 In addition,
several polymers having paracyclophane in the main
chain (in the course of developing new processes for
cross-linking resins)3 or in the side chain4 and oligo-
thiophene-substituted polymers with a [2.2]paracyclo-
phane core5 have been studied so far. In 1986, Mizogami
and Yoshimura reported that the first synthesis of
polymetacyclophane by polycondensation reaction of an
oxidative dimer of 8,16-dihydroxy[2.2]metacyclophane,
which exhibited a conductivity of 0.25 S cm-1 by doping
with H2SO4 vapor.6 However, no π-conjugated polymers
using the longitudinal π-π interaction of paracyclo-
phane as a repeating unit have yet been reported. On
the other hand, the synthesis of novel π-conjugated
polymers has received extensive attention due to their
unique optical, electrochemical, and nonlinear optical
properties.7 [2.2]Paracyclophane seems to be a promis-
ing candidate for the aryl unit of π-conjugated polymers,
e.g., poly(phenylene-ethynylene) and poly(phenylene-
vinylene). Here, we report on the first preparation and
physical properties of novel π-conjugated polymers
based on poly(p-phenylene-ethynylene) derivatives8 via
the through-space having a [2.2]paracyclophane skel-
eton in the main chain.
The procedure for the synthesis of the [2.2]para-
cyclophane-containing polymer (3) was as follows
(Scheme 1).11,12 Treatment of 1 with 2 in the presence
of a catalytic amount of PdCl2(PPh3)2 (5 mol % to an
acetylene unit), PPh3, and CuI in 1:1 THF:HNPri at
2
refluxed temperature for 48 h under a nitrogen atmo-
sphere gave the dark-orange fluorescent solution. After
filtration of the precipitated ammonium salt, the dark-
orange filtrate was concentrated and poured into a large
amount of MeOH to obtain the corresponding polymers
(3a -c) in 70-98% yields as an orange powder. The
polymers obtained were soluble in common solvents
such as THF, CH2Cl2, CHCl3, and toluene and only
partly soluble in DMF and acetone. These polymers
were characterized by 1H and 13C NMR spectra. The
molecular weight measurements were performed by gel
permeation chromatography (GPC) in THF eluent using
a calibration curve of polystyrene standards (Table 1).
For example, the polymer 3b (R ) n-dodecyl) had a
number-average molecular weight (Mn) of 8000, which
corresponds to a degree of polymerization of 11.5, with
Mw/Mn of 1.8. On the other hand, the reaction of 1 with
diethynylbenzene (R ) H) and dimethoxydiethynylben-
Resu lts a n d Discu ssion . We initially examined
palladium-catalyzed polymerization of pseudo-p-dibromo-
[2.2]paracyclophane (1) with dialkoxy-substituted di-
ethynylbenzenes (2a -c). 1 was prepared by iron-
catalyzed dibromination of [2.2]paracyclophane and
recrystallization.9 Compounds 2a -c were synthesized
by treating the corresponding 2,5-diiodo-1,4-bis(alkoxy)-
benzenes10a with trimethysilylacetylene in the presence
of a catalytic amount of palladium complex and follow-
ing desilylation.10b
* Corresponding author. E-mail:
kyoto-u.ac.jp.
chujo@chujo.synchem.
10.1021/ma011170e CCC: $22.00 © 2002 American Chemical Society
Published on Web 12/21/2001

588 Communications to the Editor
Macromolecules, Vol. 35, No. 3, 2002
Ta ble 1. Syn th eses a n d Op tica l P r op er ties of P olym er s 3a -ca
c
c
c
polymer
R
yieldb (%)
Mw
Mn
Mw/Mn
UV λmaxd (nm)
ꢀd
PL λmaxd,e (nm)
3a
3b
3c
n-C8H17 (2a )
n-C12H25 (2b)
n-C16H33 (2c)
73
98
70
5300
14000
8600
3100
8000
5900
1.7
1.8
1.5
370
384
380
5500
11500
10900
501
517
505
a
A mixture of 1 (0.30 mmol), 2 (0.30 mmol), PdCl2(PPh3)2 (0.030 mmol), PPh3 (0.060 mol), CuI (0.040 mmol), THF (2.0 mL), and
HNPri (2.0 mL) in a 50 mL Pyrex flask was refluxed for 48 h under nitrogen atmosphere. Isolated yields after reprecipitation into
b
2
MeOH. c GPC (THF), polystyrene standards. Absorption and emission spectra were recorded in dilute CHCl3 solutions at room
d
temperature. e Excited at 380 nm (2.0 × 10-4 M).
and 47 nm relative to 4b having a paracyclophane core
(λmax ) 337 nm). This result indicates the extension of
π-delocalization length via the through-space based on
two facing benzene rings of [2.2]paracyclophane. The
absorption spectrum of the polymer 3b film was slightly
red-shifted against the solution with λmax values of about
390 nm. In the fluorescence emission spectrum of the
solution of 3a -c in chloroform (2.0 × 10-4 M) at room
temperature on excitation at 380 nm, the emission
peaks of 3a -c were observed near 510 nm in a visible
green region. In the case of polymer 3b, the dependence
on concentration was also measured (Figure 1B). The
spectra of highly diluted solution (5.0 × 10-7 M)
displayed an emission peak at 460 and 412 nm and a
shoulder at 510 nm. This shoulder became an intense
peak and was red-shifted about 7 nm, as the concentra-
tion was increased from 5.0 × 10-7 to 2.0 × 10-4 M.
These findings suggested that the emission peak at 517
nm in concentrated solution would be the result of
intermolecular excimer formation.14 In addition, 3b
showed a quantum yield of 0.30 in CHCl3 solution by
using 9-anthracenecarboxylic acid in CH2Cl2 as a stan-
dard (Φ ) 0.442).15 In the measurement of fluorescence
quantum yields, the absorbance of each sample was
below 0.05 at the excitation wavelength (380 nm). On
the other hand, the formation of excimer in the solid
film resulted in a decrease in luminescence yield, and
the weak emission λmax of 3b was observed at 523 nm.
In conclusion, we have synthesized novel π-conjugated
polymers having [2.2]paracyclophane in the main chain.
The extension of π-conjugation via the through-space
was observed according to the UV-vis absorption
spectral data in comparison with those of the model
compounds. Further studies on the electronic and
thermal properties of 3 and on the synthesis of novel
π-conjugated polymers via the through-space using π-π
interaction are now underway.
Refer en ces a n d Notes
(1) For recent reviews, see: (a) Vo¨gtle, F. In Cyclophane
Chemistry; Wiley & Sons: New York, 1993. (b) Shultz, J .;
Vo¨gtle, F. Top. Curr. Chem. 1994, 172, 42.
(2) Bazan, Mukamel, and co-workers recently reported the
F igu r e 1. (A) Absorption spectra of polymer 3b and model
compounds 4a and 4b in CHCl3. (B) Dependence on concentra-
tion of fluorescence spectra of polymer 3b in CHCl3 solution
(excitation wavelength at 380 nm).
unique photophysical properties of a series of stilbenoid
dimers having a [2.2]paracyclophane core: (a) Bazan, G. C.;
Oldham, W. J ., J r.; Lachicotte, R. J .; Tretiak, S.; Chernyak,
V.; Mukamel, S. J . Am. Chem. Soc. 1998, 120, 9188. (b)
Wang, S.; Bazan, G. C.; Tretiak, S.; Mukamel, S. J . Am.
zene (R ) Me) gave a low molecular weight oligomer
due to their poor solubility.
Chem. Soc. 2000, 122, 1289. (c) Zyss, J .; Ledoux, I.; Volkov,
S. Chernyak, V.; Mukamel, S.; Bartholomew, G. P.; Bazan,
G. C. J . Am. Chem. Soc. 2000, 122, 11956.
The optical properties of polymers 3a -c obtained
above were examined, and the results are summarized
in Table 1. The UV-vis spectra of 3a -c in a dilute
chloroform solution at room temperature exhibited
absorption maxima near 310 and 380 nm. The UV-vis
spectrum of 3b was compared with those of two model
compounds (4a and 4b),13 as shown in Figure 1A. The
spectra showed a red shift of 15 nm for the absorption
of 3b (λmax ) 384 nm) relative to 4a (λmax ) 369 nm)
(3) (a) Meyers, R. A.; Hamersma, J . W.; Green, H. E. J . Polym.
Sci., Polym. Lett. Ed. 1972, 10, 685. (b) Sivaramakrishnan,
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Macromolecules, Vol. 35, No. 3, 2002
Communications to the Editor 589
D. T.; Glans, J . H. J . Polym. Sci., Polym. Chem. Ed. 1988,
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to the typical Heck-Sonogashira reaction condition.11 4a :
A pale yellow solid: Rf ) 0.33 (SiO2, eluent, hexane/CH2-
Cl2 ) 4/1). 1H NMR (270 MHz, CDCl3): δ 0.88 (t, J ) 7.6
Hz, 6H), 1.25-1.36 (m, 32H), 1.51 (m, 4H), 1.84 (m, J ) 6.4
Hz, 4H), 2.31 (s, 3H), 2.51 (s, 3H), 4.02 (t, J ) 6.4 Hz, 4H),
7.00 (s, 2H), 7.04 (d, J ) 8.0 Hz, 2H), 7.22 (d, J ) 8.0 Hz,
2H), 7.33 (s, 2H). 13C NMR (67.5 MHz, CDCl3): δ 14.1, 20.2,
20.7, 22.7, 26.1, 29.3, 29.5, 29.6 (overlapping signals), 31.9,
69.5, 89.6, 94.1, 114.0, 116.5, 129.1, 129.3, 132.3, 134.9,
137.2, 153.5. Anal. Calcd for C50H70O2: C, 85.41; H, 10.04.
Found: C, 85.32; H, 10.15. 4b: A white solid: Rf ) 0.37
(SiO2, eluent, hexane/CHCl3 ) 3/1). 1H NMR (270 MHz,
CDCl3): δ 0.87 (t, J ) 6.7 Hz, 6H), 0.88 (t, J ) 6.7 Hz, 6H),
1.25-1.46 (m, 72 H), 1.78 (m, J ) 7.1 Hz, 4H), 1.90 (m, J )
6.7 Hz, 4H), 2.88 (m, 2H), 3.00 (m, 2H), 3.31 (m, 2H), 3.77
(m, 2H), 3.94 (t, J ) 6.7 Hz, 4H), 4.05 (t, J ) 6.7 Hz, 4H),
6.49 (d, J ) 7.8 Hz, 2H), 6.58 (s, 2H), 6.85 (m, 4H), 7.08 (m,
4H). 13C NMR (67.5 MHz, CDCl3): δ 14.1, 22.7, 26.1, 26.2,
29.3, 29.4, 29.5, 29.6, 29.7 (overlapping signals), 31.2, 33.8,
34.1, 68.8, 69.4, 89.4, 93.6, 113.2, 113.9, 116.0, 118.7, 125.1,
130.4, 133.1, 137.2, 139.5, 142.1, 152.7, 154.1. Anal. Calcd
for C80H120O4: C, 83.86; H, 10.56. Found: C, 83.64; H, 10.80.
(14) For review on excimer formation and luminescence in
conjugated polymers, see: Conwell, E. Trends Polym. Sci.
1997, 5, 218. See also: (a) Reference 10a. (b) Cornil, J .; dos
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(6) Mizogami, S.; Yoshimura, S. J . Chem. Soc., Chem. Commun.
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(12) A typical procedure is as follows. A mixture of 1 (110 mg,
0.30 mmol), 2b (148 mg, 0.30 mmol), PdCl2(PPh3)2 (210 mg,
0.030 mmol), PPh3 (157 mg, 0.060 mmol), CuI (76 mg, 0.040
mol), HNPri (2.0 mL), and THF (2.0 mL) was placed in a
2
50 mL Pyrex flask equipped with a magnetic stirring bar
and a reflux condenser under nitrogen atmosphere. The
reaction was carried out under reflux (bath temperature 85
°C) for 48 h with stirring. After the reaction mixture was
cooled, ammonium salt was filtered off and washed with
THF. The filtrate was concentrated and poured into MeOH
(50 mL) to precipitate the polymer. The resulting polymer
(3b) was filtered, washed with MeOH, and dried in vacuo
(15) The quantum yield (Φunk) of unknown sample was calculated
by the following equation: Φunk ) Φstd[AstdFunk/AunkFstd]-
[nD,unk/nD,std]2 where Astd and Aunk are the absorbance of the
standard and unknown sample, respectively, Fstd and Funk
are the corresponding relative integrated fluorescence in-
tensities, and nD is the refractive index [CH2Cl2 (nD ) 1.424)
and CHCl3 (nD ) 1.446) were used].
1
to give 208 mg (0.030 mmol, 98%) as an orange powder. H
NMR (270 MHz, CDCl3): δ 0.89 (br, 6H), 1.25-1.59 (br,
36H), 1.96 (br, 4H), 2.94-3.05 (m, 4H), 3.36 (m, 2H), 3.82
(m, 2H), 4.14 (br, 4H), 6.43-6.55 (m, 4H), 7.06-7.16 (m,
4H). 13C NMR (67.5 MHz, CDCl3): δ 14.1, 22.7, 26.3, 29.7
(overlapping signals), 31.9, 34.1, 34.2, 69.6, 89.6, 95.2, 114.0,
116.3, 125.0, 130.3, 133.3, 137.2, 139.6, 142.2, 153.6.
(13) The model compounds 4a and 4b were prepared according
MA011170E