Alternating aromatic and transannular chromophores with and without linker: Effect of transannular π-π interaction on the optical property of dithiaparacyclophane-based copolymers

Article abstract of DOI:10.1021/ma035902+

A series of bithiophene-cyclophane (PPP-type), acetylene-fluorene- acetylene-cyclophane (PPE-type), and ethylene-fluorene-ethylene-cyclophane (PPV-type) copolymers, namely, 4-6, was synthesized via a nickel-catalyzed reaction, a palladium-catalyzed Sonaga

Full text of DOI:10.1021/ma035902+

3546
Macromolecules 2004, 37, 3546-3553
Articles
Alternating Aromatic and Transannular Chromophores with and
without Linker: Effect of Transannular π-π Interaction on the Optical
Property of Dithiaparacyclophane-based Copolymers
Weilin g Wa n g,† J ia n w ei Xu ,†,‡ Yee-Hin g La i,*,† a n d F u k e Wa n g†,‡
Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543 and
Institute of Materials Research and Engineering, 3 Research Link, Singapore 117602
Received December 15, 2003; Revised Manuscript Received March 11, 2004
ABSTRACT: A series of bithiophene-cyclophane (PPP-type), acetylene-fluorene-acetylene-cyclophane
(PPE-type), and ethylene-fluorene-ethylene-cyclophane (PPV-type) copolymers, namely, 4-6, was
synthesized via a nickel-catalyzed reaction, a palladium-catalyzed Sonagashira reaction, and a Heck
coupling, respectively. Unlike in the fluorene-cyclophane copolymer 3, the transannular π-π interaction
of the cylophane unit in copolymer 4 resulted in a significant blue shift in its emission spectrum compared
to a reference polymer, giving it an essentially blue emitting light. By introducing an acetylene or ethylene
linker in going from 3 to 5 or 6, the effective conjugation in the polymer backbone due to higher rigidity
in coplanarity decreased the effect of the transannular π-π interaction. While the PPV-type copolymer
6 still exhibited an appreciable red shift in both absorption and emission with respect to a reference
polymer, negligible shifts were observed for copolymer 5.
In tr od u ction
[3.3]paracyclopane polymers 3a -c,13 showed that the
transannular effect in the [3.3]cyclophane unit is suf-
ficiently strong to allow tuning of the optical properties
of copolymers 3a -c. [2.2]Paracyclophane-based poly-
mers 1 are synthetically less accessible if functional-
ization on the cyclophane is desired. Dithia[3.3]para-
cyclophanes could, however, be readily prepared by
coupling reactions under high dilution conditions.14 We
report here a successful modulation in the optical prop-
erties of the bithiophene-dithia[3.3]paracyclophane
copolymer 4 by the transannular effect of the [3.3]cyclo-
phane unit. Additional effects derived from the intro-
duction of a conjugated linker such as those in copoly-
mers 5 and 6 were discussed in comparison to the
properties of the parent copolymers 3.13
The broad applicability of conjugated polymers in
light-emitting diodes,1 field-effect transistors,2 light-
emitting electrochemical cells,3 solar cells,4 and sensors5
has attracted continuing interest in the design and
synthesis of structurally diverse conjugated polymers
that exhibit the various desired properties. Among the
organic conjugated polymers, the properties of poly(p-
phenylenevinylenes) (PPVs) have been extensively stud-
ied and documented,1a,6 while poly(p-phenylenes) (PPPs)7
and poly(p-phenyleneethynylenes) (PPEs)8 have also
received considerable attention because of their favor-
able emission characteristics. Fluorene is one of the
most universally employed building blocks in construct-
ing conjugated copolymers that show blue-light-emitting
characteristics. A large number of fluorene-based co-
polymers derived from comonomers such as benzenoids,
thiophene, tertiary aromatic amine, benzothiadiazole,
and benzooxadiazole were prepared by various synthetic
coupling reactions.9 The PPV-type and PPE-type fluo-
rene-based copolymers have also been explored10 in
attempts to tune their spectral and electrical properties
by incorporating various conjugated units into the
polymer backbone.11 The unique transannular π-π
interaction in [2.2]paracyclophane was employed in
copolymers 1 that exhibited novel optical properties in
comparison to the corresponding linear conjugated
reference compounds.12 Our preliminary study of an
example of copolymers 2, namely, the fluorene-dithia-
* To whom correspondence should be addressed. Fax: 65-
67791691. E-mail: chmlaiyh@nus.edu.sg.
Exp er im en ta l Section
Gen er a l. All reactions were carried out under nitrogen.
Commercially available reagents and solvents were used
† National University of Singapore.
‡ Institute of Materials Research and Engineering.
10.1021/ma035902+ CCC: $27.50 © 2004 American Chemical Society
Published on Web 04/20/2004

Macromolecules, Vol. 37, No. 10, 2004
Alternating Aromatic and Transannular Chromophores 3547
without further purification. 1H and 13C NMR spectra were
recorded on a Bruker ACF300 spectrometer in CDCl3. EIMS
and FAB-MS spectra were recorded using a Micromass 7034E
mass spectrometer. Elemental analysis was conducted on a
Perkin-Elmer 240C elemental analyzer for C, H, and S
determination at the Chemical and Molecular Analysis Center,
Department of Chemistry, National University of Singapore.
GPC analyses were carried out using a Perkin-Elmer model
200 HPLC system calibrated using polystyrene as standard
and THF as eluent. FT-IR spectra were recorded on a Bio-
Red TFS 156 spectrometer. TGA was conducted on a DuPont
Thermal Analyst 2100 system with a TGA 2950 thermogravi-
metric analyzer in air or nitrogen. UV-vis and fluorescence
spectra were obtained using a Shimadzu UV 3101PC UV-
vis-NIR spectrophotometer and a Perkin-Elmer LS 50B
luminescence spectrometer with a xenon lamp as light source,
respectively.
removed, and the residue was chromatographed on silica gel
using hexane/CH2Cl2 (4:1) as eluant to afford 11 as a white
1
solid (30%), mp 105-106 °C. H NMR δ 7.39 (d, J ) 5.3 Hz,
2H), 7.24 (s, 2H), 7.19 (s, 4H), 7.01 (d, J ) 5.3 Hz, 2H), 3.79
(d, J ) 15.0 Hz, 2H), 3.78 (d, J ) 15.0 Hz, 2H), 3.68 (d, J )
15.0 Hz, 4H), 2.41-2.31 (m, 2H), 2.17-2.07 (m, 2H), 1.46-
1.11 (m, 24H), 0.82 (t, J ) 7.0 Hz, 6H). 13C NMR δ 140.36,
135.70, 135.60, 135.06, 133.58, 132.61, 129.47, 129.36, 128.31,
124.30, 38.20, 34.90, 31.77, 30.12, 29.19, 28.58, 22.64, 14.08.
Anal. Calcd for C40H52S4: C, 72.67; H, 7.93; S, 19.40. Found:
C, 72.79; H, 8.18; S, 19.69. MS (EI) m/z 660 (M+).
5,8-Bis[2-(5-br om o-3-n -octylth ien yl)]-2,11-d ith ia [3.3]-
paracyclophane (12). A solution of Br2 (0.4 g, 2.5 mmol) in
AcOH/CHCl3 was added dropwise to a solution of 11 (0.66 g,
1.0 mmol) in CHCl3 cooled in an ice-water bath. The mixture
was stirred for 24 h and extracted with CH2Cl2. The organic
layer was washed with aqueous Na2CO3 and dried over
Na2SO4. The crude product was chromatographed on a silica
gel column using hexane as eluent to afford 12 as a white solid
Syn th esis. 1,4-Bis(methoxymethyl)-2,5-bis[2-(3-n-octylthie-
nyl)]benzene (9a ). A solution of 7 (3.24 g, 10 mmol) and 8 (24.25
g, 50 mmol) in DMF (60 mL) was carefully degassed by three
freeze-thaw cycles, and the catalyst Pd(PPh3)4 (0.069 g, 0.06
mmol) was added. After the mixture was heated at 110 °C for
10 h, the solvent was removed under vacuum. The product
was dissolved in diethyl ether, and the resulting solution was
washed with aqueous 0.5 M KF, water, and brine and dried
over sodium sulfate. The solvent was removed, and the residue
was chromatographed on silica gel using hexane as eluent to
1
(72%), mp 131-133 °C. H NMR δ 7.16 (s, 2H), 7.12 (s, 4H),
6.94 (s, 2H), 3.76 (d, J ) 14.3 Hz, 2H), 3.75 (d, J ) 15.2 Hz,
2H), 3.67 (d, J ) 14.3 Hz, 2H), 3.63 (d, J ) 15.2 Hz, 2H), 2.30-
2.20 (m, 2H), 2.05-1.95 (m, 2H), 1.35-0.96 (m, 24H), 0.83 (t,
J ) 7.0 Hz, 6H). 13C NMR δ 141.12, 136.89, 135.77, 135.28,
133.57, 131.89, 131.02, 129.44, 129.24, 111.13, 38.16, 34.72,
31.69, 29.85, 29.07, 29.01, 28.50, 22.57, 14.00. Anal. Calcd for
C
40H50Br2S4: C, 58.67; H, 6.15; S, 15.66; Br, 19.51. Found: C,
1
58.72; H, 6.24; S, 15.78; Br, 19.34. MS (EI) m/z 816 (M+).
give 9a as colorless crystals (70%), mp 69-70 °C. H NMR δ
7.44 (s, 2H), 7.28 (d, J ) 5.1 Hz, 2H), 6.98 (d, J ) 5.1 Hz, 2H),
4.32 (s, 4H), 3.29 (s, 6H), 2.40 (t, J ) 7.7 Hz, 4H), 1.54-1.21
(m, 24H), 0.86 (t, J ) 6.8 Hz, 6H). 13C NMR δ 140.20, 136.84,
134.62, 133.03, 131.01, 128.16, 124.13, 71.68, 58.16, 31.80,
30.53, 29.34, 29.16, 28.54, 22.59, 14.01. Anal. Calcd for
1,4-Dimethyl-2,5-bis[2-(3-n-octylthienyl)]benzene (14). A so-
lution of 8 (24.25 g, 50 mmol) and 13 (2.64 g, 10 mmol) in DMF
(60 mL) was carefully degassed by three freeze-thaw cycles,
and Pd(PPh3)4 (0.069 g, 0.06 mmol) was added. After the
mixture was heated at 110 °C for 10 h, the solvent was
removed under vacuum. The product was dissolved in diethyl
ether, and the resulting solution was washed with aqueous
0.5 M KF, water, and brine and dried over sodium sulfate.
The solvent was removed, and the residue was chromato-
graphed on silica gel using hexane as eluent to give 14 as a
C
34H50S2O2: C, 73.59; H, 9.08; S, 11.56. Found: C, 73.42; H,
9.10; S, 11.28. MS (EI) m/z 554 (M+).
1,4-Bis(bromomethyl)-2,5-bis[2-(3-n-octylthienyl)]benzene (9b).
HBr gas was bubbled vigorously through a solution of 9a (5.54
g, 10 mmol) in CHCl3 (100 mL) for 1 h. The reaction mixture
was then stirred for another 10 h, neutralized with 2 M
NaHCO3, and extracted with ether. The organic extracts were
combined, washed with brine, and dried over magnesium
sulfate. The solvent was removed, and the residue was
chromatographed on silica gel using hexane as eluent to give
9b as a white solid (89%), mp 55-57 °C. 1H NMR δ 7.45 (s,
2H), 7.34 (d, J ) 4.9 Hz, 2H), 7.01 (d, J ) 4.9 Hz, 2H), 4.41 (s,
4H), 2.43 (t, J ) 7.8 Hz, 4H), 1.56-1.22 (m, 24H), 0.86 (t, J )
6.6 Hz, 6H). 13C NMR δ 141.19, 137.53, 134.38, 132.96, 128.47,
124.82, 31.82, 30.63, 30.42, 29.33, 29.16, 28.69, 22.61, 14.05.
Anal. Calcd for C32H44S2Br2: C, 58.89; H, 6.79; S, 9.83; Br,
24.49. Found: C, 58.97; H, 6.88; S, 9.79; Br, 24.28. MS (EI)
m/z 650 (M+).
1,4-Bis(mercaptomethyl)-2,5-[2-(3-n-octylthienyl)]benzene (9c).
A solution of 9b (6.52 g, 10 mmol) and thiourea (1.67 g, 22
mmol) in ethanol (100 mL) was slowly brought to reflux and
heated for 6 h. The solvent was removed under reduced
pressure. The dithiouronium salt was then refluxed in 4%
aqueous NaHCO3 for 3 h. The mixture was neutralized and
extracted with ether and washed sequentially with water and
brine. The combined organic extracts were dried over anhy-
drous sodium sulfate. The mixture was chromatographed on
silica gel using hexane/CH2Cl2 (4:1) as eluent to yield 9c as a
yellow liquid (50%), mp 49-52 °C. 1H NMR δ 7.35 (s, 2H), 7.31
(d, J ) 5.2 Hz, 2H), 7.01 (d, J ) 5.2 Hz, 2H), 3.63 (d, J ) 8.0
Hz, 4H), 2.43 (t, J ) 7.7 Hz, 4H), 1.70 (t, J ) 8.0 Hz, 2H),
1.55-1.23 (m, 24H), 0.87 (t, J ) 6.8 Hz, 6H). 13C NMR δ
140.57, 139.66, 134.19, 133.44, 132.78, 128.43, 124.45, 31.83,
30.64, 29.35, 29.19, 28.70, 26.14, 22.62, 14.06. Anal. Calcd for
1
white solid (65%). H NMR δ 7.24 (s, 2H), 7.12 (d, J ) 5.4 Hz,
2H), 6.72 (d, J ) 5.4 Hz, 2H), 2.57 (t, J ) 7.8 Hz, 4H), 2.37 (s,
6H), 1.65-1.24 (m, 24H), 0.90 (t, J ) 6.6 Hz, 6H). 13C NMR δ
138.83, 137.31, 133.72, 130.60, 130.29, 128.17, 125.82, 33.40,
30.95, 29.44, 29.34, 29.19, 28.69, 22.61, 14.67, 14.02. Anal.
Calcd for C32H46S2: C, 77.67; H, 9.37; S, 12.96. Found: C,
77.31; H, 9.25; S, 12.74. MS (EI) m/z 504 (M+).
1,4-Bis[2-(5-bromo-3-n-octylthienyl)]-2,5-dimethylbenzene (15).
This was prepared by a similar procedure as described for 12.
1H NMR δ 7.22 (s, 2H), 6.77 (s, 2H), 2.56 (t, J ) 7.8 Hz, 4H),
2.36 (s, 6H), 1.62-1.28 (m, 24H), 0.91 (t, J ) 6.6 Hz, 6H). 13C
NMR δ 140.01, 137.11, 135.14, 133.96, 132.68, 129.68, 111.04,
32.87, 30.84, 29.93, 29.36, 29.23, 28.66, 22.69, 14.69, 14.13.
Anal. Calcd for C32H44S2Br2: C, 58.89; H, 6.79; S, 9.83, Br,
24.48. Found: C, 59.04; H, 7.04; S, 9.97, Br, 24.67. MS (EI)
m/z 650 (M+).
Gen er a l P r oced u r e for th e P r ep a r a tion of P olym er s
4 a n d 16. 12 or 15 (10 mmol), anhydrous NiCl2 (0.75 mmol),
PPh3 (10 mmol), 2,2′-bipyridine (0.75 mmol), and zinc powder
(31 mmol) were mixed, degassed thoroughly, and maintained
under argon. DMF (15 mL) was added, and the reaction
mixture was stirred at 85 °C for 20 h. The mixture was cooled
to room temperature and extracted with CHCl3. The organic
layer was poured into cold methanol. The yellow solid precipi-
tated was collected by filtration. The solid was washed for 24
h in a Soxhlet apparatus using acetone. The soluble polymer
was extracted with chloroform from the residue in the Soxhlet
apparatus.
Polymer 4. Yield: 66%. 1H NMR δ 7.35-7.25 (br, m), 3.88-
3.74 (br, m) 2.40-2.03 (br, m), 1.67-1.18 (br, m), 0.86-0.84
(br, m). Anal. Calcd for (C40H50S4)n: C, 72.89; H, 7.65; S, 19.46.
Found: C, 71.46; H, 7.90; S, 18.59.
Polymer 16. Yield: 75%. 1H NMR δ 7.36-6.98 (br, m), 2.73-
2.64 (br, m), 2.24 (br, s), 1.68-1.27 (br, m), 0.88-0.86 (br, m);
Anal. Calcd for (C32H44S2)n: C, 95.10; H, 10.97; S, 15.87.
Found: C, 94.57; H, 10.47; S, 15.48.
C
32H46S4: C, 68.76; H, 8.29; S, 22.95. Found: C, 68.99; H, 8.38;
S, 23.10. MS (EI) m/z 558 (M+).
5,8-Bis[2-(3-n -octylth ien yl)]-2,11-d ith ia [3.3]pa r a cyclo-
phane (11). A solution of 9c (1.67 g, 3.0 mmol) and 10 (0.79,
3.0 mmol) in degassed toluene was added dropwise with
stirring to a solution of KOH (0.56 g, 10 mmol) and in ethanol
(1 L). After the addition was completed, the reaction mixture
was stirred for 20 h at room temperature. The solvent was

3548 Wang et al.
Macromolecules, Vol. 37, No. 10, 2004
Syn th esis. 9,9-Di-n-hexyl-2,7-bis[(trimethylsilyl)ethylnyl]-
fluorene (18). A solution of trimethylsilyl acetylene (1.08 g, 11
mmol) in triethylamine (20 mL) was slowly added to a solution
of 17 (2.46 g, 5.0 mmol), (Ph3P)2PdCl2 (0.175 g, 0.25 mmol),
and CuI (0.047 g, 0.25 mmol) in triethylamine (50 mL) under
nitrogen at room temperature. The reaction mixture was then
stirred at 70 °C for 8 h. The solvent was then removed under
reduced pressure, and the residue was chromatographed on
silica gel using hexane as eluent to give 18 as a yellow solid
(62%), mp 121-123 °C. 1H NMR δ 7.58 (d, J ) 7.3 Hz, 2H),
7.45 (dd, J ) 8.0 Hz, 1.0 Hz, 2H), 7.41 (s, 2H), 1.95-1.90 (m,
4H), 1.13-1.01 (m, 12H), 0.76 (t, J ) 7.0 Hz, 6H), 0.53-0.51
(m, 4H), 0.28 (s, 18H). 13C NMR δ 150.91, 140.81, 131.18,
126.18, 121.73, 119.76, 106.06, 94.21, 55.19, 40.31, 31.49,
29.64, 23.58, 22.56, 13.92. Anal. Calcd for C35H50Si2: C, 79.78;
H, 9.56. Found: C, 80.07; H, 9.59. MS (EI) m/z 526 (M+).
2,7-Diethynyl-9,9-di-n-hexylfluorene (19). An aqueous KOH
solution (6 mL, 20%) was diluted with methanol (25 mL) and
added to a stirred solution of 18 (2.63 g, 5 mmol) in THF (50
mL). The mixture was stirred at room temperature for 6 h and
extracted with hexane. The organic fraction was washed with
water and dried over sodium sulfate. The crude product was
chromatographed on silica gel using hexane as eluent. Recrys-
tallization of the product from methanol gave 19 as yellow
temperature for 18 h. The solvent was removed in vacuo, and
the residue was extracted with ether. The organic layer was
washed with water and dried over Na2SO4. The crude product
was chromatographed on silica gel using hexane/ethyl acetate
(20:1) as eluent to give 22 as a light yellow solid (51%), mp
1
52-54 °C. H NMR δ 10.08 (s, 2H), 7.93-7.87 (m, 6H), 2.08-
2.03 (m, 4H), 1.07-0.98 (m, 12H), 0.69 (t, J ) 6.8 Hz, 6H),
0.54-0.48 (m, 4H). 13C NMR δ 192.06, 152.83, 145.58, 136.43,
130.21, 123.38, 121.29, 55.53, 39.97, 31.35, 29.43, 23.72, 22.41,
13.86. Anal. Calcd for C27H34O2: C, 83.03; H, 8.77. Found: C,
82.74; H, 8.51; MS (EI) m/z 390 (M+).
9,9-Di-n-hexyl-2,7-bis(hydroxymethyl)fluorene (23a ). To a
solution of 22 (3.90 g, 10 mmol) in ethanol (50 mL) was added
NaBH4 (0.38 g, 10 mmol). The mixture was stirred at room
temperature for 6 h, and the solvent was removed to yield an
oily residue. The crude product was chromatographed on silica
gel using CH2Cl2 as eluent to give 23a as a light yellow oil
(93%). 1H NMR δ 7.66 (dd, J ) 7.32 Hz, J ) 1.05 Hz, 2H),
7.33 (s, 2H), 7.32 (d, J ) 7.29 Hz, 2H), 4.77 (s, 4H), 1.98-1.92
(m, 4H), 1.14-1.02 (m, 12H), 0.75 (t, J ) 7.0 Hz, 6H), 0.62-
0.60 (m, 4H). 13C NMR δ 151.34, 140.38, 139.79, 125.73, 121.51,
119.63, 65.72, 55.01, 40.30, 31.45, 29.66, 23.73, 22.54, 13.93.
Anal. Calcd for C27H36O2: C, 82.61; H, 9.24. Found: C, 82.51;
H, 9.60; MS (EI) m/z 392 (M+).
1
crystals (80%), mp 35.0-35.4 °C. H NMR δ 7.63 (d, J ) 7.7
2,7-Bis(chloromethyl)-9,9-di-n-hexylfluorene (23b). To a solu-
tion of 23a (3.92 g, 10 mmol) in benzene (30 mL) was added a
solution of SOCl2 (3.57 g, 30 mmol) in benzene (10 mL). The
mixture was heated at 50 °C for 4 h. The reaction mixture
was cooled to room temperature, consecutively washed with
saturated aqueous NaHCO3 an H2O, and dried over Na2SO4.
The solvent was removed, and the crude product was chro-
matographed on silica gel using hexane as eluent to give 23b
Hz, 2H), 7.47 (dd, J ) 7.7 Hz, 1.4 Hz, 2H), 7.45 (s, 2H), 3.15
(s, 2H), 1.96-1.90 (m, 4H), 1.14-1.01 (m, 12H), 0.76 (t, J )
7.0 Hz, 6H), 0.58-0.53 (m, 4H). 13C NMR δ 151.02, 140.95,
131.21, 126.51, 120.81, 119.92, 84.49, 55.17, 40.19, 31.44,
29.58, 23.62, 22.52, 13.91. Anal. Calcd for C29H34: C, 91.04;
H, 8.96. Found: C, 91.58; H, 8.89. MS (EI) m/z 382 (M+).
Gen er a l P r oced u r e for th e P r ep a r a tion of P olym er s
5a -c a n d 21. 2,7-Diethynyl-9,9-dihexylfluorene 19 (191 mg,
0.5 mmol), monomer 20a -c13 or 2,5-dibromo-p-xylene 13 (0.5
mmol), (Ph3P)2PdCl2 (35 mg, 0.03 mmol), and CuI (28 mg, 0.15
mmol) were added to a mixture of degassed toluene (14 mL)
and diisopropylamine (6 mL). The mixture was vigorously
stirred at 70 °C for 24 h under nitrogen. After the mixture
was cooled to room temperature, it was extracted with
chloroform. The combined organic extracts were poured slowly
into cold methanol. The precipitated solid was washed with
methanol, water, and methanol successively. The product was
further washed with acetone in a Soxhlet apparatus for 24 h
to remove oligomers and catalyst residues. The polymer was
then dried under vacuum at room temperature.
1
as a colorless oil (85%). H NMR δ 7.66 (d, J ) 7.3 Hz, 2H),
7.35 (d, J ) 7.3 Hz, 2H), 7.34 (s, 2H), 4.68 (s, 4H), 1.97-1.92
(m, 4H), 1.14-1.04 (m, 12H), 0.76 (t, J ) 6.8 Hz, 6H), 0.62-
0.60 (m, 4H). 13C NMR δ 151.61, 140.78, 136.60, 127.56, 123.22,
120.01, 55.18, 46.86, 40.15, 31.40, 29.59, 23.69, 22.53, 14.00.
Anal. Calcd for
C27H34Cl2: C, 75.51; H, 7.98; Cl, 16.51.
Found: C, 75.27; H, 7.95; Cl, 16.30. MS (EI) m/z 428 (M+).
9,9-Di-n-hexyl-2,7-bis(triphenylphosphoniomethyl)fluorene
dichloride (23c). A mixture of 23b (4.29 g, 10 mmol) and Ph3P
(5.77 g, 22 mmol) in DMF (35 mL) was stirred at 100 °C for 5
h. The reaction mixture was cooled to room temperature and
poured into dry diethyl ether (400 mL). The precipitate was
collected by filtration and recrystallized from ethanol to afford
1
1
Polymer 5a . Yield: 75%; a fibrous yellow solid. H NMR δ
23c as a white solid (90%), mp 333-338 °C. H NMR δ 7.70-
7.56 (br, s), 7.17 (br, s), 4.48 (br, d), 4.17 (br, d), 3.88 (br, s),
7.60 (m, 30H), 7.37 (d, J ) 7.7 Hz, 2H), 7.02 (d, J ) 7.7 Hz,
2H), 6.94 (s, 2H), 5.48 (d, J ) 14.3 Hz, 4H), 1.78-1.47 (m,
4H), 1.11-0.75 (m, 18 H), 0.22-0.20 (m, 4H). 13C NMR δ
151.28, 140.46, 134.88, 134.43, 134.29, 130.84, 130.18, 130.01,
126.42, 126.30, 125.29, 120.36, 118.61, 117.47, 58.41, 54.90,
39.97, 31.73, 31.60, 30.98, 29.64, 23.86, 22.69, 18.37, 14.05.
Anal. Calcd for C63H64Cl2P2: C, 79.33; H, 6.72. Found: C,
79.04; H, 6.64. MS (FAB): 952 (M+).
3.69 (br, d), 2.03 (br, s), 1.26-0.79 (br, m). FT-IR (KBr) 3053,
2926, 2852, 1602, 1462, 1419, 1373, 1257, 1101, 889, 743 cm-1
.
Anal. Calcd for (C43H46S2)n: C, 82.38; H, 7.39. Found: C, 81.03;
H, 7.24.
1
Polymer 5b. Yield: 68%; a fibrous yellow solid. H NMR δ
7.80-7.60 (br, m), 7.48-7.45 (br, m), 7.35-7.16 (br, m), 6.95-
6.50 (br, m), 4.31-3.19 (br, m), 3.90 (br, s), 2.04-1.97 (br, m),
1.25-0.71 (br, m). FT-IR (KBr) 3059, 2957, 2926, 2851, 1607,
1462, 1395, 1207, 1043, 870, 654 cm-1. Anal. Calcd for
(C45H50S2O2)n: C, 78.67; H, 7.34. Found: C, 78.04; H, 7.12.
Polymer 5c. Yield: 62%; a fibrous green solid. 1H NMR δ
7.68-7.53 (br, m), 3.87 (br, s), 1.99 (br, s), 1.59-1.09 (br, m),
0.78 (br, s). FT-IR (KBr) 3057, 2926, 2853, 2205, 1604, 1462,
1377, 1261, 1095, 1024, 896, 817, 692, 520 cm-1. Anal. Calcd
for (C45H44S2N2)n: C, 79.84; H, 6.55; N, 4.14. Found: C, 78.32;
H, 6.70; N, 4.05.
2,7-Diethenyl-9,9-di-n-hexylfluorene (23d ). An aqueous solu-
tion of NaOH (2.5 g/15 mL water) was added to a mixture of
23c (6.91 g, 10 mmol) and aqueous formaldehyde (37%, 30 mL)
in water (15 mL). The resulting solution was stirred at room
temperature for 18 h, and the mixture was extracted with
ether. The organic layer was separated, washed with water
and brine, and then dried over anhydrous sodium sulfate. The
crude product was chromatographed on silica gel using hexane
1
as eluent to give 23d as a colorless oil (86%). H NMR δ 7.71
Polymer 21. Yield: 75%; a fibrous green solid. 1H NMR δ
7.68 (br, s), 7.52-7.50 (br, m), 7.43-7.40(br, m), 2.54-2.36 (br,
m), 1.99 (br, s), 1.07-0.64 (br, m). FT-IR (KBr) 3059, 3030,
2926, 2827, 1600, 1491, 1462, 1377, 1260, 1095, 1019, 887, 820,
721, 528 cm-1. Anal. Calcd for (C35H40)n: C, 91.25; H, 8.75.
Found: C, 90.01; H, 8.87.
Syn th esis. 2,7-Diformyl-9,9-di-n-hexylfluorene (22). A solu-
tion of n-BuLi (1.60 M, 20.5 mmol) was added dropwise under
nitrogen to a cooled (-78 °C) solution of 17 (4.92 g, 10 mmol)
in dry THF (70 mL). The resulting mixture was stirred at -78
°C for 1 h, and a mixture of dry DMF (2.5 mL) and dry THF
(20 mL) was added. The reaction mixture was stirred at room
(d, J ) 8.0 Hz, 2H), 7.49 (d, J ) 8.0 Hz, 2H), 7.48 (s, 2H), 6.90
(dd, J ) 17.4 Hz, 10.8 Hz, 2H), 5.89 (d, J ) 17.4 Hz, 2H), 5.34
(d, J ) 10.8 Hz, 2H), 2.13-2.08 (m, 4H), 1.23-1.17 (m, 12H),
0.87 (t, J ) 6.8 Hz, 6H), 0.80-0.77 (m, 4H). 13C NMR δ 151.43,
140.85, 137.51, 136.65, 125.35, 120.58, 119.77, 112.96, 54.99,
40.55, 31.70, 31.55, 29.80, 23.80, 22.75, 22.66, 14.17, 14.03.
Anal. Calcd for C29H38: C, 90.09; H, 9.91. Found: C, 89.93; H,
9.98. MS (EI) m/z 386 (M+).
Gen er a l P r oced u r e for th e P r ep a r a tion of P olym er s
6 a n d 24. A mixture of 20a (1.0 mmol) or 13, 23d (0.386 g,
1.0 mmol), Pd(OAc)2 (0.009 g, 0.04 mmol), tri-o-tolylphosphine
(0.061 g, 0.2 mmol), and tributylamine (0.5 mL) in DMF (10

Macromolecules, Vol. 37, No. 10, 2004
Alternating Aromatic and Transannular Chromophores 3549
mL) was heated at reflux under nitrogen for 2 days. The
mixture was poured into cold methanol (200 mL), and the
precipitate was collected by filtration. The product was redis-
solved in a minimum volume of THF and reprecipitated by
adding the THF solution dropwise into cold methanol. The
resulting solid was washed with methanol and acetone and
then extracted by chloroform in a Soxhlet extractor. The
desired polymer was isolated after removal of chloroform under
reduced pressure. The polymer was then dried under vacuum.
Polymer 6. Yield: 30%; a yellow-green solid. 1H NMR δ 7.75
(br, 2H), 7.61 (br, 2H), 7.54 (br, 2H), 7.51 (br, 2H), 7.47-7.42
(br, 2H), 7.18-7.00(br, 6H), 2.04-0.76 (br, 26H). FT-IR (KBr)
3085, 3006, 2926, 2857, 1678, 1604, 1464, 1356, 1259, 1097,
1043, 896, 869 cm-1. Anal. Calcd for (C45H50S2)n: C, 82.57; H,
7.65. Found: C, 82.01; H, 7.21.
Sch em e 1. Syn th esis of P olym er s 4 a n d 16a
Polymer 24. Yield: 63%; a yellow-green solid. 1H NMR δ
7.70 (br, 2H), 7.57 (br, 2H), 7.51 (br, 2H), 7.47 (br, 2H), 7.42-
7.37 (br, 2H), 7.19-7.13 (br, 2H), 2.58 (br, 6H), 2.04-0.76 (br,
26H). FT-IR (KBr) 3015, 2924, 2852, 1676, 1598, 1491, 1460,
1375, 1255, 1028, 956, 881, 808, 746 cm-1. Anal. Calcd for
(C37H44)n: C, 90.93; H, 9.07. Found: C, 90.09; H, 8.59.
a
Reagents and conditions: (i) Pd(PPh3)4/DMF, 110 °C; (ii)
HBr/CHCl3, room temperature; (iii) NH2C(S)NH2/ethanol/
NaHCO3, reflux; (iv) KOH/Cs2CO3/ethanol/toluene, high dilu-
tion conditions; (v) Br2/CHCl3/AcOH, room temperature; (vi)
anhydrous NiCl2/PPh3/2,2′-bipyridine/Zn powder/DMF, 85 °C.
Sch em e 2. Syn th esis of P olym er s 5 a n d 21a
Resu lts a n d Discu ssion
Syn th esis of Mon om er s a n d P olym er s. The gen-
eral synthetic route to polymer 4 and its reference
polymer 16 is outlined in Scheme 1. The palladium-
catalyzed coupling reaction between 7 and 2-tri-n-
butylstannyl-3-n-octylthiophene 8 afforded compound
9a . Treatment of 9a with HBr in chloroform gave the
desired dibromide 9b, which reacted with thiourea
followed by base hydrolysis to afford the dithiol 9c. The
coupling reaction between 9c and 1,4-bis(bromomethyl)-
benzene 10 under high dilution conditions afforded the
desired dithia[3.3]paracyclophane 11. Bromination of 11
with bromine in CHCl3/AcOH (1:1) afforded the dibromo
monomer 12. Similarly, the palladium-catalyzed cou-
pling reaction between 8 and 13 gave compound 14,
which upon bromination led to the dibromo monomer
15. Polymerization of 12 or 15 was achieved according
to the literature method.15 The polymers 4 and 16 were
obtained in yields of 66% and 75%, respectively.
a
Reagents and conditions: (i) (PPh3)2PdCl2/CuI/(CH3)3SiCt
CH/(Et)3N, 70 °C; (ii) CH3OH/THF/KOH, room temperature;
(iii) Pd(PPh3)4/CuI/diisopropylamine/toluene, 70 °C.
9,9-di-n-hexylfluorene 19 was prepared from a palla-
dium(II)-catalyzed Sonagashira cross-coupling reaction
between 2,7-dibromo-9,9-dihexylfluorene 17 and trim-
ethylsilyl acetylene followed by subsequent removal of
the trimethylsilyl protecting group upon base treat-
ment.16 The dithiaparacyclophanes 20a -c were pre-
pared by coupling the corresponding pair of dithiol and
dibromide under high dilution conditions.13 The pal-
The synthetic route to the monomers and the corre-
sponding copolymers 5a -c and 6 is shown in Schemes
2 and 3, respectively. The key monomer 2,7-diethynyl-

3550 Wang et al.
Sch em e 3. Syn th esis of P olym er s 6 a n d 24a
Macromolecules, Vol. 37, No. 10, 2004
a
Reagents and conditions: (i) DMF/n-BuLi/THF; (ii) NaBH4/
F igu r e 1. 1H NMR spectra of (a) 4 and (b) 5a in CDCl3
(asterisk (*) indicates residual water and CHCl3).
ethanol, room temperature; (iii) SOCl2/benzene, 50 °C; (iv)
PPh3/DMF, 100 °C; (v) 37% formaldehyde/NaOH, room
temperature; (vi) tri-o-tolylphosphine/Pd(OAc)2/DMF/Bu3N,
160 °C.
ladium-catalyzed cross-coupling condensation reac-
tions17 leading to the PPE-type copolymers 5a -c and
21 proceeded well between 20a -c or 13 and 19. The
copolymers 5a -c were isolated in good yields of 62-
75%. Polymers 5a and 5b were isolated as yellow solids,
while 5c and 21 were green solids.
The bis(organolithium) compound prepared from di-
bromo 17 and n-BuLi reacted readily with DMF to
afford the dialdehyde 22. Reduction of 22 with NaBH4
followed by treatment with SOCl2 gave the dichloro
compound 23b, which formed the bis(phosphonium) salt
23c with triphenylphosphine. A Wittig reaction between
23c and formaldehyde gave the divinyl monomer 23d .
The PPV-type copolymers 6 and 24 were prepared from
Heck reactions18 between 23d and 20a or 13, respec-
tively.19 Our attempts to modify the experimental
parameters led to reasonable yields (30% and 63%,
respectively) for the desired polymers 6 and 24 when
reactions were carried out in DMF at reflux for 48 h.
Due to the high reaction temperature employed, tri-n-
butylamine with a higher boiling point was used to
replace the more commonly used tri-n-ethylamine to
prevent loss of the base during the reaction.
F igu r e 2. Powder X-ray diffraction pattern of copolymers
5a -c.
Ta ble 1. Molecu la r Weigh ts, P r od u ct Yield s, a n d Th er m a l
An a lysis Da ta of P olym er s 4-6, 16, 21, a n d 24
polymer
Mn
Mw
Mw/Mn
yield (%)
Td (°C)
4
16
5a
5b
5c
21
6
4 100
31 400
56 700
48 500
43 300
44 800
3 300
7 000
38 100
88 600
77 200
76 400
82 800
5 900
1.70
1.21
1.56
1.59
1.76
1.84
1.78
1.91
66
75
75
68
62
75
30
63
322
409
330
288
256
382
300
400
The structures of all polymers prepared in our work
1
were characterized by H NMR spectroscopic and ele-
ment analyses. Figure 1 illustrates two representative
1
1H NMR spectra of polymers 4 and 5a . In the H NMR
spectrum of 5a , for example, the signals appearing in
the range of δ 7.64-7.50 correspond to those in fluorene
while those at δ 7.22-7.15 are assigned to those in the
paracyclophane. The multiplets at δ 3.69-4.48 are
characteristic of benzylic protons of dithiacyclophanes,
indicating that the paracyclophane units remain intact
during the polymerization. Figure 2 shows the wide-
angle X-ray diffraction patterns of copolymers 5a -c.
Unlike the linear PPEs20 which are semicrystalline and
exhibit a lamellar structure, the polymers 5a -c display
predominantly an amorphous phase. The introduction
of the paracyclophane units in these polymers may be
responsible for the relatively less-ordered packing of
polymer chains.
24
3 600
6 900
summarized in Table 1. Thermal stability of the poly-
mers was investigated by thermogravimetric analysis
(TGA). The PPE-type copolymers 5a -c showed inferior
thermal stability to the reference polymer 21 possibly
due to desulfurization of the dithiaparacyclophane
moiety. A decrease in decomposition temperature (Td)
going from 16 to 4 and 24 to 6 was also observed
possibly due to a similar reason. The glass phase
transition of all the dithiaparacyclophane-based copoly-
mers was not noticeable by differential scanning calo-
rimetry. The molecular weight of polymers 5a -c with
a polydiversity in the range of 1.56-1.76 was about
43 000 and higher. Those of 4 and 6 were, however, very
much lower at 3300-4100. This could be a result of the
more efficient Songashira reaction compared to the Heck
and nickel(0)-catalyzed coupling reactions.
All polymers prepared in our work were readily
soluble in common organic solvents such as THF,
chloroform, toluene, and xylenes. The molecular weights
of the polymers determined by gel permeation chroma-
tography (GPC) against the polystyrene standards are

Macromolecules, Vol. 37, No. 10, 2004
Alternating Aromatic and Transannular Chromophores 3551
Ta ble 2. Op tica l Da ta a n d F lu or escen ce Qu a n tu m Yield
of P olym er s 3-6, 16, 21, 24, a n d 25
λ
max(THF)a (nm)
λ
max(film)a (nm)
b
polymer
abs
em
abs
em
φF
3a
25
4
16
5a
5b
5c
21
6
361
411 (428)
376
441
367
417 (440)
385
454
0.75
0.50
0.17
0.15
0.22
0.16
0.15
0.24
0.21
330
374
344
333
374
350
469
480
378 (408) 471 (427, 448) 386 (410) 484 (515)
384 (411) 471 (426, 500) 388 (424) 492 (518)
385 (408) 471 (429, 503) 390 (416) 479
379 (402) 468 (423, 443) 384
400
478 (523)
476 (444,
461 (445)
403
504, 535)
464 (495)
24
390
450 (483)
395
0.49
a
Data in parentheses are wavelengths of shoulders and sub-
b
peaks. The φF of the polymer in a THF solution was measured
by using quinine sulfate (ca. 1 × 10-5 M solution in 0.1 M H2SO4,
assuming φF of 0.55) as a standard.
F igu r e 4. UV-vis absorption and fluorescence spectra of (a)
5a and 21 and (b) 6 and 24 measured from solutions (ca. 1 ×
10-5 M) in THF at room temperature.
F igu r e 3. UV-vis absorption and fluorescence spectra of 4
and 16 measured from solutions (ca. 1 × 10-5 M) in THF at
room temperature.
believed to play a role in altering their spectral shifts.
Such a steric effect could be easily relieved in 16 by a
slight twist of the benzene ring, while in polymer 4, with
the bulkier dithiaparacyclophane, relief of the steric
strain is expected to be more difficult. This will result
in varied degrees of coplanarity of the thiophene and
benzene rings in the polymer backbones of 4 and 16.
A comparison (Table 2) of the UV-vis absorption and
photoluminescence (PL) spectra of polymers 5a and 21
and 6 and 24 in THF (ca. 1 × 10-5 M) is illustrated in
Figure 4. Introduction of an acetylene linker and going
from 21 to 5a does not result in any appreciable shift
in either the absorption or emission λmax of 5a (Figure
4a), both emitting blue-green light. In addition, in
contrast to the reported alkoxy-substituted PPE 26,21
which exhibited an absorption red shift by as much as
40 nm going from solution to thin film, there was only
a relatively small red shift observed for 5a (Table 2).
Changing the linker to an ethylene unit and going from
the PPV-type copolymer 24 to the cyclophane-based
polymer 6 displayed appreciable red shifts (ca. 10 nm,
Figure 4b) in both emission and electronic spectra. The
emission spectral profile of 6, however, differs signifi-
cantly from 24 in that the former shows a more intense
shoulder at about 449 nm while 24 has a weaker but
more apparent shoulder close to 480 nm. The copolymer
6 like 5a exhibits only a small absorption shift (Table
2) going from solution to solid film.
Op tica l P r op er ties. The spectroscopic properties of
the polymers prepared in this work were determined
both in solution (THF) and as a thin film. Their optical
properties are summarized in Table 2. Transparent and
uniform films of the polymers were prepared on quartz
by spin-casting their solutions in chloroform at room
temperature. In our earlier report,13 a significant red
shift was observed going from the reference polymer 25
to the cyclophane-based polymer 3a (Table 2) resulting
from the transannular π-π interaction in the cyclo-
phane unit. Changing the aromatic chromophore from
fluorene in 3a to bithiophene in 4, however, led to a very
different observation (Table 2; Figure 3). In comparison
to the reference polymer 16, the cyclophane-based
polymer 4 exhibited a significant absorption red shift
by 30 nm but its emission λmax was unexpectedly blue-
shifted by 28 nm. In fact, such a considerable blue shift
in emission light was consistent going from solution to
thin film. These changes particularly in the emission
spectra of 4 indicate a reverse effect by the transannular
π-π interaction of the cyclophane unit on optical
property of the polymer backbone going from 3a to 4
compared to their respective reference polymers. The
above observation suggests that while the transannular
effect consistently leads to a significant shift in the
emission λmax, it also serves as a novel tuning parameter
for the color of the emission light in copolymer 2 with
different aromatic chromophores. Apart from the effect
of transannular π-π interaction, steric interaction
resulted from the octyl groups in 4 and 16 is also

3552 Wang et al.
Macromolecules, Vol. 37, No. 10, 2004
Con clu sion
In summary, a series of dithia[3.3]paracyclophane-
based PPP-, PPE-, and PPV-type copolymers 3-6,
respectively, were prepared in this work. The transan-
nular π-π interaction in the cyclophane unit in the
PPP-type 3a -c and 4 induces significant shifts in their
absorption and emission spectra compared to those of
reference polymers. Both copolymers 3a and 4 emit blue
light, but their emission shifts in opposite direction
compared to their respective reference polymers, indi-
cating that the transannular effect could be employed
as a tuning parameter in this series of copolymers with
different aromatic chromophores linked to the cyclo-
phane. Introduction of a linker between the cyclophane
and the aromatic chromophore will apparently improve
the rigidity in coplanarity in the polymer backbone and
enhance its conjugation effect. This decreases the impact
of the transannular π-π effect in copolymer 6 and
makes it ineffective in copolymers 5, which exhibit
optical properties derived essentially from only its
polymer backbone similar to their reference polymer 21.
F igu r e 5. Fluorescence spectra of polymers 5a -c measured
from solutions (ca. 1 × 10-5 M) in THF at room temperature.
The effect of transannular π-π interaction on the
optical properties of the copolymers 3a and 4-6 is
evidently dependent on the presence or absence and the
nature of the “linker” between the cyclophane and the
aromatic chromophore. In the absence of a linker, the
through-space π-π interaction of the two parallel-
stacked benzene rings of the dithiaparacyclophane in
the PPP-type copolymers 3a and 4 results effectively
in significant absorption and emission shifts. The PPV-
type copolymer 6 shows relatively smaller shifts com-
pared to those in 3a and 4, and in contrast, the PPE-
type copolymer 5a (as well as 5b and 5c; refer to later
discussion) exhibits negligible shifts relative to the
reference polymer 21. An apparent correlation is that
between the transannular effect and the effective con-
jugation in these copolymers. The polyaryl nature in the
polymer backbone of 3a and 4 will provide, due to steric
reasons, higher backbone flexibility to coplanarity of the
polymer chain. The backbone conjugation may thus be
more sensitive to changes in electronic effect induced
by the transannular π-π interaction. On the contrary,
the linear acetylene linker in 5 introduces higher
backbone rigidity to coplanarity, thus maximizing the
conjugation effect in the polymer backbone but mini-
mizing the impact of the transannular π-π interaction,
resulting in very similar absorption and emission spec-
tra of 5a and 21. Earlier reports22 indicate that an
ethylene linker allows better electron delocalization
than an acetylene unit in some polymers. The ethylene
linker, however, also allows more conformational flex-
ibility to the polymer backbone, thus moderating the
transannular effect to an intermediate impact.
Ack n ow led gm en t. Financial support for the work
was provided by the National University of Singapore
(NUS). We thank the staff of the Chemical and Molec-
ular Analysis Centre, Department of Chemistry, NUS,
for their technical assistance.
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