W(CO)6-Mediated desulfuroligomerization of bis-dithioacetals. New synthesis of substituted oligo(phenylene-vinylenes)

Article abstract of DOI:10.1016/S0022-328X(00)00839-1

Treatment of bisdithioacetals of 1,4-diaroylbenzenes (4) with W(CO)₆ in refluxing chlorobenzene afforded the corresponding substituted oligophenylenevinylenes (OPVs) (5). Average molecular weights determined by GPC indicate that OPVs 5 have 5-13 repetitive substituted phenylenevinylene units with narrow polydispersities. Emission in the blue-green to green region was observed for these OPVs depending on the nature of the substituent. The electron-donating alkoxy substituent shifted the emission to the longer wavelength whereas the electron-withdrawing trifluoromethyl group caused a blue shift in the fluorescence spectra.

Full text of DOI:10.1016/S0022-328X(00)00839-1

Journal of Organometallic Chemistry 624 (2001) 63–68
www.elsevier.nl/locate/jorganchem
W(CO)6-Mediated desulfuroligomerization of bis-dithioacetals.
New synthesis of substituted oligo(phenylene–vinylenes)
Chung-Wai Shiau, Clifton K.F. Shen, Wei Pan, Chi-Hong Kuo, Shen Chung Kao,
Tien-Yau Luh *
Department of Chemistry, National Taiwan Uni6ersity, Taipei, 106, Taiwan, ROC
Received 18 August 2000; accepted 17 October 2000
Dedicated to Professor J.-F. Normant on the occasion of his 65th birthday
Abstract
Treatment of bisdithioacetals of 1,4-diaroylbenzenes (4) with W(CO)6 in refluxing chlorobenzene afforded the corresponding
substituted oligophenylenevinylenes (OPVs) (5). Average molecular weights determined by GPC indicate that OPVs 5 have 5–13
repetitive substituted phenylenevinylene units with narrow polydispersities. Emission in the blue–green to green region was
observed for these OPVs depending on the nature of the substituent. The electron-donating alkoxy substituent shifted the emission
to the longer wavelength whereas the electron-withdrawing trifluoromethyl group caused a blue shift in the fluorescence spectra.
© 2001 Elsevier Science B.V. All rights reserved.
Keywords: Desulfuroligomerization; Bis-dithioacetals; Oligophenylenevinylenes (OPVs)
1. Introduction
Conjugated polymers have been demonstrated to ex-
hibit
diverse
electroactive
properties
[1].
Poly(phenylene–vinylene) (PPV) (1) is known for its
photoconductivity behavior and, more recently, electro-
luminescence phenomenon [2]. Modification of the
structure of PPV has paved the way to furnish desired
band gap in such a way that efficient multicolor display
applications in the LED device could be achieved. For
example, the alkoxy-substituted polymer 2 exhibits or-
ange light emission [3]. The HOMO–LUMO energy
gap can even be narrowed to the red light region by
incorporating a cyano substituent onto the olefinic moi-
ety (e.g. 3) [4]. Soluble analogs of PPV with aryl
substituents at the olefinic carbons have attracted much
attention [5–10]. The Wittig reaction, McMurry reac-
tion as well as dehydrochlorination and dehalogenation
reactions have been employed for the synthesis of aryl-
substituted PPVs.
Various models suggest that the photophysical prop-
erties of certain conjugated polymers can be represented
by those of a short fragment of the corresponding
chromophores [11]. In other words, selective synthesis
of certain conjugated oligomers having narrow polydis-
persity may furnish the desired band gap for efficient
multicolor display applications [12]. About a decade
ago, we disclosed a novel W(CO)6-mediated desulfur-
dimerization of dithioacetals leading to the correspond-
ing dimeric olefins (Eq. (1)) [13–15]. This reaction
provides a new entry for the dimerization of carbonyl
moiety under neutral conditions with tolerance to a
variety of functional groups. It is envisaged that this
reaction can be extended to the synthesis of substituted
oligophenylenevinylenes (OPVs) 5 from the correspond-
ing rigid bis-dithioacetals 4. Described herein is a full
* Corresponding author.
0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(00)00839-1

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C.-W. Shiau et al. / Journal of Organometallic Chemistry 624 (2001) 63–68
5a–c are stable up to 300–350°C. A typical TGA curve
is shown in Fig. 1. OPV 5d having an electron-with-
drawing CF3 group was unstable above 200°C.
As can be seen in Table 1, only low molecular weight
species 5e (corresponding to three repeating
thienylenevinylene units) was obtained. A TGA study
showed that 5e started to decompose at 100°C. The
presence of the thiophene unit in the backbone appar-
ently affects the stability. It is noteworthy that the
OPVs 5 were synthesized under refluxing chlorobenzene
conditions and it is therefore not surprising to find that
the Mn for 5e was lower than those for other OPVs.
It is interesting to note that no Tg was observed for
5c. As described earlier [15], the methoxy-substituted
analog exhibited much lower Tg (92°C) than those of
other related OPVs. The long chain aliphatic alkoxy
substituent may account for the discrepancy.
1
The H-NMR spectra of 5 showed high field signals
(ca l 3.8–4.0), which may be attributed to the residual
dithiolane moiety at the terminal units of the OPVs.
However, the relative intensity of these peaks with
respect to those in the aromatic region varies with the
substrates in comparison with the average molecular
weights of these OPVs. In order to solve this dis-
crepancy, we have examined the spectroscopic proper-
ties of 5 in detail.
The infrared spectrum of 5a showed a weak absorp-
tion at 1659 cm−1 which is characteristic for a diaryl
ketone functionality. With the exception of 5c, all other
oligomers 5b, 5d, and 5e behaved similarly, an absorp-
tion at 1650 cm−1 being observed. The mechanism of
the Group 6 metal carbonyl-promoted desulfurdimer-
ization of dithiolanes has been investigated [13b,d]. A
thioketone intermediate has been isolated and a radical
fragmentation has been suggested leading to a thioke-
tone intermediate which may further react under the
reaction conditions to afford the dimeric olefin (Scheme
2) [13b,d]. It is noteworthy that thioketals 4 can also
serve as promoters for the Mo(CO)6-catalyzed ring
opening metathesis polymerization of norbornene
derivatives [17]. It is also known that a thioketone
moiety is susceptible to hydrolysis upon exposure to air
or moisture. This may account for the carbonyl absorp-
tion in the infrared region. These observations indicate
that the terminal dithiolane group may be transformed
Scheme 1.
account of the new synthesis and properties of
aryl-substituted OPVs [16].
(1)
2. Results and discussion
The monomeric starting materials 4 were conve-
niently synthesized according to the sequence outlined
in Scheme 1. The details are described in Section 3.
Treatment of 4 with W(CO)6 in refluxing chlorobenzene
for 48–60 h afforded the corresponding substituted
OPVs 5. The results are summarized in Table 1.
Average molecular weights determined by gel perme-
ation indicate that OPVs 5a–d have 5–13 repeating
substituted phenylenevinylene units with quite narrow
polydispersities. TGA investigations showed that OPVs
Table 1
Synthesis and physical properties of oligomers 5
5
% Yield
Mn
PDI
Tg
uem (nm)
bf
|×1015
(V−1 cm−1
)
a
b
c
d
e
80
82
62
81
67
3380
4330
2740
3010
990
1.4
1.2
1.8
1.5
1.2
175
188
530
530
543
500
0.01
0.02
0.03
0.02
5
1000
2000
2
134
1

C.-W. Shiau et al. / Journal of Organometallic Chemistry 624 (2001) 63–68
65
Fig. 1. TG curve of 5c. TGA was performed under nitrogen flow at a heating rate of 10°C min−1
.
into the corresponding thioketone moiety which was
then hydrolyzed during the work-up to generate the
carbonyl functionality. Accordingly, the terminal
groups of 5 may contain either dithiolane moiety or the
carbonyl group. As shown in Section 3, the microanaly-
sis data also showed that the carbon content is slightly
less than the theoretical prediction1.
contains ca 16 units and are consistent with the GPC
results (ca. 13 units).
It is known that the benzylic carbonꢀsulfur bond can
be reduced upon treatment with Group 6 metal car-
bonyl in ethereal solvent. The a-hydrogen of such ethe-
real solvent may be responsible for this reduction and is
presumably abstracted by a radical intermediate. The
alkoxy substituent in 4c contains such active hydrogen.
During the course of the desulfurization process, it
seems likely that the reduction of the carbonꢀsulfur
bond may occur such that the yield of the correspond-
ing thioketones may be affected. In other words, the
relative quantity for the formation of the corresponding
thioketones from 4c might be less than those of related
reactions. It is therefore not surprising to see that no
residual ketone was detected in the reaction of 4c under
similar conditions.
Oligomers 5a–d exhibit continuous absorptions in
the UV and visible regions up to 450 nm. The red
thiophene analog 5e becomes transparent beyond 600
nm. The fluorescence spectra of 5a–d and their quan-
tum yields (bf) were also measured (Table 1). Emission
in the blue–green to green region was observed depend-
ing on the nature of the substituent. The electron-do-
nating alkoxy substituent shifted the emission to the
longer wavelength (543 nm) whereas the electron-with-
drawing trifluoromethyl group caused a blue shift (500
1
The use of the H-NMR provides an important tool
in the elucidation of the structures of the polymers. As
described in detail in Section 3, the relative chemical
shifts for ortho protons in the starting dithioacetals and
diketones are very characteristic and therefore can be
employed as a reference for the end group of the
polymers. Oligomer 5a was chosen as an example to
elucidate this point. The 1H-NMR of 5a exhibited
residual absorptions at low field (at l 7.75, br d J=6.0
Hz) attributed to the aromatic ortho protons of the
diaryl ketone moiety. The absorptions at l 7.31–7.58
were assigned to the aromatic ortho protons of the
dithiolane of the diaryl ketone functionality. The ratio
of the intensities of the absorption at l 7.75, the
residual peaks of the dithiolane moiety (l 3.70–3.90)
and that of the absorptions for the other aromatic
protons (l 6.39–7.31) of 5a was ca 1:1.3:59. There are
four ortho protons for each aryl ketone moiety as well
as for its corresponding dithiolane group. In addition,
each of the internal diphenylvinylene-phenylene units
contains 14 protons. These results indicate that OPV 5a
1 As pointed by one reviewer, formation of a small amount of
cyclic oligomers may account for the shortage of dithioacetal groups
in the final material. Although we can not completely rule out this
possibility, it seem less likely because oligomers 5 have relatively low
molecular weights and their structures are quite rigid.
Scheme 2.

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C.-W. Shiau et al. / Journal of Organometallic Chemistry 624 (2001) 63–68
nm) in the fluorescence spectra. It is noteworthy that
OPVs having a substituted aryl group will enhance the
fluorescence quantum yields. Conductivity measure-
ments for 5 doped with iodine indicate that these OPVs
are poor conductors (Table 1). Presumably, the aryl-
substituents may reduce the extension of conjugation
because of the steric reason. In other words, the conju-
gated moieties become less planar than their unsubsti-
tuted PPV counterparts. Electron-donating sub-
stituents, however, slightly enhanced the conductivity.
In summary, we have demonstrated a new route for
the synthesis of aryl-substituted oligo(phenylene–
vinylenes) under neutral conditions in good yield. A
variety of functional groups can survive under these
conditions. Relatively narrow polydispersity was ob-
served in most of these OPVs. The photophysical prop-
erties of these OPVs can be tuned by introducing
substituents at the olefinic carbons.
treated with 4-octyloxyphenyllithium [prepared from
tert-BuLi (2.2 M, 10 ml, 22 mmol) and 4-octyloxybro-
mobenzene (5.7 g, 20.0 mmol)] in THF (20 ml) at
−78°C for 3 h. The diol thus obtained was oxidized
with MnO2 (1.90 g, 21.0 mmol) to yield 7c (4.3 g, 88%):
m.p. 77–78°C (EtOAc–hexane); IR (KBr) w 1639 (s),
1603 cm−1 1H-NMR (CDCl3, 300 MHz) l 0.87 (t,
;
J=6.7 Hz, 6 H), 1.27–1.50 (broad, 20 H), 1.80 (quint,
J=6.5 Hz, 4 H), 4.02 (t, J=6.5 Hz, 4 H), 6.94 (d,
J=8.5 Hz, 4 H), 7.80 (s, 4 H), 7.82 (d, J=8.5 Hz, 4 H);
13C-NMR (CDCl3, 50 MHz) l 14.1, 22.6, 26.0, 29.1,
29.2, 29.3, 31.8, 68.3, 114.2, 129.3, 129.4, 132.6, 141.1,
163.2, 194.9; HRMS Calc. for C36H46O4: 542.3396.
Found: 542.3384; Anal. Calc.: C, 79.65; H, 8.55. Found:
C, 79.24; H, 8.35%.
3.4. 1,4-Bis-(4-trifluoromethylbenzoyl)benzene (7d)
In a manner similar to that described in the general
procedure, the reaction of 6a (0.48 g, 3.5 mmol) with
4-trifluoromethylphenylmagnesium bromide (1 M, 7.1
ml, 7.1 mmol) followed by oxidation with MnO2 (0.65
g, 7.20 mmol) to afford 7d (1.20 g, 81%): m.p. 209–
3. Experimental
3.1. General procedure for the preparation of 7
210°C (EtOAc–hexane); IR (KBr) w 1650 (s) cm−1
;
A mixture of 6 (one equivalent) and Grignard reagent
or organolithium reagent (2.2 equivalents) in THF was
stirred at room temperature (r.t.) for 12 h and quenched
with NH4Cl. The organic layer was separated and the
aqueous layer was extracted twice with ether. The com-
bined organic layers were washed with brine and dried
(MgSO4). The solvent was removed in vacuo to give a
residue that was dissolved in CH2Cl2. MnO2 was then
added and the mixture was stirred at r.t. for 12 h. After
filtration through silica gel, the solvent was removed in
vacuo and the residue was recrystallized to give 7.
1H-NMR (CDCl3, 300 MHz) l 7.77 (d, J=7.9 Hz, 4
H), 7.92 (d, J=7.9 Hz, 8 H); 13C-NMR (CDCl3, 100
MHz) l 123.5 (q, J=1083 Hz), 125.6 (q, J=15.2 Hz),
130.0, 130.2, 134.3 (q, J=130.8 Hz), 139.8, 140.2,
194.76; MS (FAB) m/z (rel. intensity) 523 (M++1, 33),
307 (100), 289 (49), 273 (9); HRMS Calc. for
C22H12O2F6: 422.0741. Found: 422.0753; Anal. Calc.: C,
62.57; H, 2.86. Found: C, 62.33; H, 2.89%.
3.5. 2,5-Bisbenzoylthiophene (7e)
In a manner similar to that described in the general
procedure, the reaction of 6e (1.45 g, 10 mmol) with
PhMgBr (1 M, 20.0 ml in ether, 20.0 mmol) was
followed by oxidation with MnO2 (1.9 g, 20 mmol) to
give 7e (2.11 g, 72%): m.p. 108–109°C (EtOAc–hex-
3.2. 1,4-Bis-(4-tert-butylbenzoyl)benzene (7b)
In a manner similar to that described in the general
procedure, 6a (2.01 g, 15.0 mmol) in THF (50 ml) was
allowed to react with 4-tert-butyl-phenylmagnesium
bromide (32 ml, 1 M in ether, 32 mmol) to give the
corresponding diol which was then treated with MnO2
(3.10 g, 35 mmol) followed by usual work-up to give 7b
(4.41, 74%): m.p. 160–162°C (EtOAc–hexane); IR
ane); IR (KBr) w 1632 (s), 1596 cm−1 1H-NMR
;
(CDCl3, 200 MHz) l 7.45–7.62 (m, 6 H), 7.64 (s, 2 H),
7.87 (dt, J=6.83, 1.56 Hz, 4 H); 13C (CDCl3, 50 MHz)
l 128.5, 129.2, 132.9, 133.7, 137.1, 148.4, 188.0; HRMS
Calc. for C18H12O2S: 292.0558. Found: 292.0564; Anal.
Calc.: C, 73.95; H, 4.14. Found: C, 73.97; H, 4.30%.
1
(KBr) w 1645 (s), 1604 cm−1; H-NMR (CDCl3, 200
MHz) l 1.35 (s, 18 H), 7.50 (d, J=8.4 Hz, 4 H), 7.77
(d, J=8.4 Hz, 4 H), 7.85 (s, 4 H); 13C-NMR (CDCl3,
50 MHz) l 31.1, 35.2, 125.4, 129.6, 130.2, 134.2, 140.8,
156.8, 195.8; HRMS Calc. for C28H30O2: 398.2245.
Found: 398.2255. Anal. Calc.: C, 84.38; H, 7.59. Found:
C, 83.18; H, 7.52%.
3.6. General procedure for the preparation of
bisdithioacetal 4
A CHCl3 solution of 7 (one equivalent) and 1,2-
ethanedithiol (three equivalents) in the presence of a
catalytic amount of BF3·Et2O was refluxed for 10 h. The
mixture was poured into 10% NaOH and the layers
were separated. The organic layer was washed with
water and dried (MgSO4). The solvent was removed in
3.3. 1,4-Bis-(4-octyloxybenzoyl)benzene (7c)
In a manner similar to that described in the general
procedure, 6a (1.34 g, 10.0 mmol) in THF (50 ml) was

C.-W. Shiau et al. / Journal of Organometallic Chemistry 624 (2001) 63–68
67
vacuo and the residue was recrystallized from hexane–
ethyl acetate to give 4.
chlorobenzene was refluxed for 48–60 h. After cooling
to room temperature, the black mixture was filtered
and the residue was washed with ethyl acetate. The
filtrate was evaporated in vacuo. The residue was evac-
uated at r.t. under vacuum to remove the excess
W(CO)6 and then taken up in chloroform. Methanol
was added to precipitate 5 which was filtered and
evacuated under vacuum.
3.6.1. Bisdithioacetal 4a
91%: m.p. 213–214°C (CHCl3–hexane); 1H-NMR
(CDCl3, 200 MHz) 3.38 (s, 8 H), 7.10–7.30 (m, 6 H),
7.47 (s, 4 H), 7.59 (d, J=6.0 Hz, 4 H); 13C (50 MHz,
CDCl3) l 40.1, 76.5, 127.2, 127.8, 127.9, 128.0, 143.2,
143.4, 144.4. Anal. Calc. for C24H22S4: C, 65.71, H,
5.05. Found: C, 65.84, H, 4.94%.
3.8. OPV 5a
In a manner similar to that described in the general
procedure, a mixture of 4a (1.13 g, 2.58 mmol) and
W(CO)6 (3.6 g, 10.2 mmol) in chlorobenzene (20 ml)
was refluxed for 48 h followed by usual work-up to
afford 5a (0.51 g, 78%): H-NMR (CDCl3, 200 MHz):
l (ratio) 3.70–3.95 (1), 6.50–7.90 (46). Mn=3380
3.6.2. Bisdithioacetal 4b
68%: m.p. 270–272°C (CHCl3–hexane); 1H-NMR
(CDCl3, 300 MHz) l 1.27 (s, 18 H), 3.37 (s, 8 H), 7.26
(d, J=8.6 Hz, 4 H), 7.48 (s, 4 H), 7.49 (d, J=8.6 Hz,
4 H); 13C (50 MHz, CDCl3) l 31.3, 34.4, 40.1, 76.4,
124.9, 127.81, 127.87, 141.2, 143.5, 150.1; HRMS Calc.
for C32H38S4 550.1856. Found: 550.1842. Anal. Calc.:
C, 69.77; H, 6.95. Found: C, 69.86; H, 6.90%.
1
(PDI=1.4).
3.9. OPV 5b
In a manner similar to that described in the general
procedure, a mixture of 4b (0.91 g, 1.65 mmol) and
W(CO)6 (2.3 g, 6.6 mmol) in chlorobenzene (20 ml) was
refluxed for 48 h followed by usual work-up to afford
5b (0.25 g, 82%): 1H-NMR (CDCl3, 300 MHz): l
(ratio) 1.18–1.42 (132), 3.85–3.92 (1), 6.7–7.08 (80); IR
(KBr) w 3083, 3054, 3030, 2965, 2907, 2870, 1908, 1664,
1606, 1511, 1474, 1464, 1406, 1396, 1364, 1270, 1202,
1109, 1020, 834, 798, 697, 565 cm−1. Mn=6167
(PDI=1.07); Anal. Calc. for (C28H30)n: C, 91.80; H,
8.30. Found: C, 89.49; H, 8.42%; quantum yield=
2.1%.
3.6.3. Bisdithioacetal 4c
91%: m.p. 162–164°C (CHCl3–hexane); 1H-NMR
(CDCl3, 300 MHz) l 0.86 (t, J=6.9 Hz, 6 H), 1.25–
1.50 (m, 20 H), 1.73 (quint, J=6.4 Hz, 4 H), 3.36 (s, 8
H), 3.90 (t, J=6.4 Hz, 4 H), 6.76 (d, J=8.7 Hz, 4 H),
7.47 (d, J=8.7 Hz, 8 H); 13C-NMR (CDCl3, 75 MHz)
l 14.0, 22.6, 26.0, 29.2, 29.3, 31.7, 40.0, 67.9, 76.3,
113.6, 127.7, 129.4, 135.9, 143.5, 158.2; HRMS Calc.
for C40H54O2S4: 694.3006. Found: 694.3002; Anal.
Calc.: C, 69.12; H, 7.83. Found: C, 68.88; H, 7.80%.
3.6.4. Bisdithioacetal 4d
90%: m.p. 156–157°C (CHCl3–hexane); 1H-NMR
(CDCl3, 300 MHz) l 3.30–3.50 (m, 8 H), 7.43 (s, 4 H),
7.52 (d, J=8.4 Hz, 4 H), 7.73 (d, J=8.4 Hz, 4 H); 13C
(CDCl3, 100 MHz), 40.5, 75.8, 124.0 (q, J=1083.2 Hz),
124.96 (q, J=15.2 Hz), 127.9, 128.6, 129.4 (q, J=130.4
Hz), 142.9, 148.7; HRMS Calc. for C26H20F6S4:
574.0352. Found: 574.0371; Anal. Calc.: C, 54.34; H,
3.51. Found: C, 54.42; H, 3.61%.
3.10. OPV 5c
In a manner similar to that described in the general
procedure, a mixture of 4c (0.66 g, 1.0 mmol) and
W(CO)6 (1.4 g, 4.0 mmol) in chlorobenzene (15 ml) was
1
converted to 5c (0.41 g, 62%). H-NMR (CDCl3, 200
MHz): l (ratio) 0.85 (3), 1.25–1.50 (12), 1.6–1.7 (2),
3.6–4.0 (7), 6.58– 6.90 (2); IR (KBr) w 2930, 2859,
1608, 1512, 1471, 1392, 1288, 1246, 1176, 1112, 1032,
831, 752, 724, 618, 523 cm−1; Anal. Calc. for
(C22H20O2)n: C, 84.7; H, 9.08. Found: C, 74.30; H,
8.65%. Mn=5848; PDI=1.02; quantum yield=3.2%.
3.6.5. Bisdithioacetal 4e
80%: m.p. 137–138°C (CHCl3–hexane); 1H-NMR
(CDCl3, 200 MHz) l 3.37–3.57 (m, 8 H), 6.60 (s, 2 H),
7.22–7.33 (m, 6 H), 7.68 (d, J=6.2 Hz, 4 H); 13C-
NMR (CDCl3, 100 MHz) l 40.5, 72.7, 127.0, 127.5,
127.8, 127.9, 143.2, 151.5; HRMS Calc. for C22H20S5:
444.0168. Found: 444.0166; Anal. Calc.: C, 59.42; H,
4.13. Found: C, 59.07; H, 4.57%.
3.11. OPV 5d
In a manner similar to that described in the general
procedure, a mixture of 4d (0.42 g, 0.7 mmol) and
W(CO)6 (1.0 g, 2.9 mmol) in chlorobenzene (15 ml) was
1
transformed into 5d (0.32 g, 81%): H-NMR (CDCl3,
3.7. General procedure for desulfuroligomerization of 4
200 MHz): l (ratio) 3.80–3.90 (1), 6.72–7.94 (62), 7.75
(d, J=8.0 Hz, 3.4), 7.90–7.94 (4.7); IR (KBr) w 3034,
3052, 2931, 2859, 2020, 1981, 1924, 1729, 1670, 1618,
1510, 1467, 1412, 1327, 1266, 1168, 1127, 1114, 1068,
Under N2 atmosphere, a mixture of 4 (one equiva-
lent) and excess W(CO)6 (four equivalents) in

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C.-W. Shiau et al. / Journal of Organometallic Chemistry 624 (2001) 63–68
1019, 979, 958, 931, 861, 843, 805, 764, 701, 640, 630,
601, 506 cm−1; Anal. Calc. for (C22H12F6)n: C, 67.70;
H, 3.10. Found: C, 66.57; H, 4.02%. Mn=6205;
PDI=1.06. quantum yield=1.8%.
Acknowledgements
Support from the National Science Council and the
Ministry of Education of the Republic of China is
gratefully acknowledged.
3.12. Oligomer 5e
References
In a manner similar to that described in the general
procedure, a mixture of 4e (0.31 g, 0.7 mmol) and
W(CO)6 (1.0 g, 2.9 mmol) in chlorobenzene (15 ml) was
transformed into 5e (0.2 g, 67%): 1H-NMR (CDCl3,
200 MHz): l (ratio) 3.86–4.04 (1), 6.54–7.59 (22); IR
(KBr) w 3060, 3028, 2956, 2924, 2855, 1651, 1633, 1601,
1493, 1444, 1245, 1159, 1106, 1073, 1028, 916, 761, 734,
698, 570 cm−1. Mn=990 (PDI=1.2); Anal. Calc. for
(C18H12S)n: C, 83.04; H, 4.65. Found: C, 80.46; H,
5.55%.
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3.13. Fluorescence measurements
An Aminco-Bowman Series 2 luminescence spec-
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cence quantum yields of 5 were measured by the
optically dense measurement method at 22°C using the
same spectrometer. A solution of quinine sulfate
(Aldrich, USA) in 1.0 (N) H2SO4 (B10−5 M conc.)
was used as a standard (ƒf=0.52) for all quantum yield
measurement experiments. A solution of OPV 5 in
spectroscopic grade CHCl3 (10−5 M conc.) was used
for the measurement. Excitation wavelengths of all the
OPVs and of the standard were determined by a Shi-
madzu UV–vis spectrophotometer (1601PC) with an
absorbance value ranging between 0.1 and 0.2. Experi-
ments were conducted under identical conditions of
emission bandpass and the wavenumber integrated
value of the emission spectrum was calculated.
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3.14. DC electrical conducti6ity measurement
The oligomer was coated as a film on glass and the
d.c. electrical resistance was measured by a voltage
measurement unit (Keithley Model 236). The thickness
of the film was measured by surface profile measure-
ment (DEKTAK 3030ST). The conductivity was ob-
tained by the equation, |=length/(resistance×area) in
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units of V−1 cm−1
.
.