Synthesis and properties of new fluorene-containing copolymer via the catalytic dehydrocoupling reaction of 9,9-dipropargyl fluorene and 4,4′-diphenyl-2,6-dibromo-dithieno-[3,2-b:2′,3′-d]silole

Article abstract of DOI:10.1080/15421406.2016.1200925

New fluorene-containing copolymer was prepared via the catalytic dehydrocoupling reaction of 9,9-dipropargylfluorene and 4,4′-diphenyl-2,6-dibromo-dithieno-[3,2-b:2′,3′-d]silole in 44% yield. The resulting polymer was completely soluble in common organic

Full text of DOI:10.1080/15421406.2016.1200925

Molecular Crystals and Liquid Crystals
ISSN: 1542-1406 (Print) 1563-5287 (Online) Journal homepage: http://www.tandfonline.com/loi/gmcl20
Synthesis and properties of new fluorene-
containing copolymer via the catalytic
dehydrocoupling reaction of 9,9-dipropargyl
fluorene and 4,4′-diphenyl-2,6-dibromo-dithieno-
[3,2-b:2′,3′-d]silole
Gab Yong Lee, Yeong-Soon Gal & Sang-Gu Lee
To cite this article: Gab Yong Lee, Yeong-Soon Gal & Sang-Gu Lee (2016) Synthesis and
properties of new fluorene-containing copolymer via the catalytic dehydrocoupling reaction of 9,9-
dipropargyl fluorene and 4,4′-diphenyl-2,6-dibromo-dithieno-[3,2-b:2′,3′-d]silole, Molecular Crystals
and Liquid Crystals, 635:1, 167-171, DOI: 10.1080/15421406.2016.1200925
To link to this article: http://dx.doi.org/10.1080/15421406.2016.1200925
Published online: 01 Nov 2016.
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Date: 10 February 2017, At: 05:55

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
, VOL. , –
http://dx.doi.org/./..
Synthesis and properties of new fluorene-containing copolymer
via the catalytic dehydrocoupling reaction of ,-dipropargyl
fluorene and ,ꢀ-diphenyl-,-dibromo-dithieno-[,-b:ꢀ,
ꢀ-d]silole
Gab Yong Leea, Yeong-Soon Galb, and Sang-Gu Leea
aDepartment of Life Chemistry and Research Facilities Center, Catholic University of Daegu, Gyeongsan,
Gyeongsangbuk-do, Korea; bDepartment of Fire Safety, Kyungil University, Gyeongsan, Gyeongsangbuk-do,
Korea
ABSTRACT
KEYWORDS
dehydrocoupling; silole;
photoluminescence;
quantum yield; fluorene
derivative; cross-linking;
diacetylenic
New fluorene-containing copolymer was prepared via the catalytic
dehydrocouplingreactionof9,9-dipropargylfluoreneand4,4ꢀ-diphenyl-
2,6-dibromo-dithieno-[3,2-b:2ꢀ,3ꢀ-d]silole in 44% yield. The resulting
polymer was completely soluble in common organic solvents. The ther-
malbehaviorsandopticalproperties oftheresultingpolymerweremea-
sured and discussed. The chemical structure of polymer was character-
ized by NMR, IR, and UV-visible spectroscopies. The polymer showed
characteristic wide UV-visible absorption band and blue PL maximum
value at 440 nm, which is corresponding photon energy of 2.82 eV. The
quantum yield (6.44%) of poly(DPF-DTS) was found to be 5 times higher
than that of poly(DPF-bithiophene)).
Introduction
Polyacetylene is the most fundamental π-conjugated polymer, and this material has been
the subject of extensive research since a doped polyacetylene film was found to be highly
electrically conductive [1–3]. The conjugated oligomers and polymers are commonly used
in electronic devices because of electrical properties and their potential utility in pho-
tonic and electronics application [4–5]. The electronics and photonics technologies have
opened their materials base to organics, in particular π-conjugated oligomers and polymers
[6–7]. Fluorene containing poly(phenylenevinylene) derivatives were good candidates as
blue light-emitting organic materials for light-emitting devices and other purposes [8–10].
The oxidative-coupling of fluorene compound was used for the synthesis of diacetylene
polymer [11] and the poly(fluorenyleneethylene)s were prepared by alkyne metathesis of
(9,9-dialkyl)fluoren-2,7-yleneethylenes [12]. In 9,9ꢀ-spirofluorene of the polymer chains, the
fluorene moieties are orthogonally arranged and connected via a commonly tetracoordinated
carbon [13].
Dipropargyl monomers offer a variety of synthetic pathways to different polymer structures
[4, 14–15]. New crosslinkable acetylenic polymers were prepared by the palladium-catalyzed
carbon-carbon coupling reactions between the diiodobenzene and diethyldipropargyl
CONTACT Sang-GuLee
leesg@cu.ac.kr
of Daegu, Gyeongsan -, Gyeongsangbuk-do, Korea.
DepartmentofLifeChemistryandResearchFacilitiesCenter, CatholicUniversity
©  Taylor & Francis Group, LLC

168
G. Y. LEE ET AL.
malonate in quantitative yield [16]. The thermal curing behaviors of the resulting materials
are related to the polymer structures [17–18]. In our previous works, we reported the studies
on the synthesis and electro-optical properties of 9,9-dipropargylfluorene having reactive
acetylenic functionalities [19–22]. Silole derivatives having low-lying LUMO levels have been
reported to be useful as electron-transporting materials in EL devices [23].
Herein, we report the synthesis of new silole-containing polymers via the catalytic dehy-
drocoupling reaction of 9,9-dipropargylfluorene and 4,4ꢀ-diphenyl-2,6-dibromo-dithieno-
[3,2-b:2ꢀ,3ꢀ-d]silole as well as the thermal behaviors and optical properties of the resulting
polymer.
Experimental
Fluorene (Aldrich Chemicals., 98%) was used without further purification. Propargyl bro-
mide (Aldrich Chemicals, 80 wt % solution in toluene) was dried with CaH2 and distilled
under reduced pressure. 9,9-Dipropargylfluorene was prepared by the reaction of fluorene
and propargyl bromide with the catalyst of NaOH/PhCH2N+Et3Cl− as described in the pre-
vious paper [24].
The palladium catalyzed heck coupling reaction of 9,9-dipropargylfluorene and
4,4ꢀ-diphenyl-2,6-dibromo-dithieno-[3,2-b:2ꢀ,3ꢀ-d]silole was used for the synthesis of
fluorene-containing copolymer with acetylene moieties in the main chain as follows. 9,9-
Dipropargylfluorene (0.46 g.1.9 mmol) and the corresponding 4,4ꢀ-diphenyl-2,6-dibromo-
dithieno-[3,2-b:2ꢀ,3ꢀ-d]silole (0.84 g, 1.95 mmol), PdCl2(PPh3)2/CuI (0.005 g), and piperidine
(12 mL) were introduced in the reaction flask. The reaction was performed at 80°C for 6 hrs
under nitrogen atmosphere. The reaction mixture was poured into 200 mL MeOH with
stirring. The precipitated polymer was filtered, and washed with methanol, and then dried in
vacuum to give a yellowish powder (polymer yield: 44%).
FT-IR spectra were obtained with a Mattson Instrument Genesis II spectrometer using a
KBr pellet. NMR spectra were recorded on a Varian Gemini 200 MHz FT-NMR spectrom-
eter in CDCl3. The molecular weights of the polymers were determined by a gel perme-
ation chromatographer (Shimadzu LC10A) equipped with μ-Styragel columns using THF
as an eluent. TGA and DSC thermograms were taken on a Shimadzu DTG60 and DSC60
under nitrogen atmosphere at a scan rate of 10°C/min. The UV spectra were measured by
a Thermo Aquamate UV-VIS Spectrometer. Shimadzu Spectrofluorophotometer RF-5301PC
(Xen150W Xenon Lamp) was used for photo- and electroluminescence spectra.
Results and discussion
The palladium-catalyzed dehydrocoupling polymerization reaction of terminal diacetylenic
compound and dibromoaromatic compound was used for the synthesis of fluorene-
containing polymer with acetylene moieties in the main chain (Scheme 1).
The dehydrocoupling reaction of 9,9-dipropargylfluorene was performed at 80°C in the
presence of PdCl2(PPh3)2/CuI under nitrogen atmosphere. This reaction proceeded homo-
geneously to give a moderate yield of polymer (44%). The resulting poly(DPF-DTS) was
completely soluble in common organic solvents such as chloroform, chlorobenzene, toluene,
and xylene. The weight-average molecular weight (Mw) and the polydispersity(Mw/Mn) of
the present poly(DPF-DTS) were 1,810 and 1.28, respectively. This value is relatively low
compared to those of the similar homologues obtained by using more simple dihaloaro-
matic compounds such as 1,4-diiodobenzene and 9,10-diiodoanthracene [21, 22]. It may be

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
169
Scheme . Synthesis of poly(DPF-DTS).
caused by the bulkiness and relative low reactivity of 4,4ꢀ-diphenyl-2,6-dibromo-dithieno-
[3,2-b:2ꢀ,3ꢀ-d]silole. The good solubility of polymer was judged to be originated by 9,9-
dipropargylfluorene moieties in main chain and/or the relatively low molecular weight.
The polymer structure was characterized by such spectroscopic methods as NMR, IR, and
UV-visible spectroscopies. Figure 1 shows the FT-IR spectra of DPF and poly(DPF-DTS).
The IR spectrum of DPF shows strong absorption at 3289 cm−1 due to the acetylenic ࣕC-H
stretching absorption. The IR spectrum of poly(DPF-DTS) did not show any absorption at
3289 cm−1, which is due to the complete reaction of terminal acetylenic functional groups.
The internal acetylenic -CࣕC- stretching vibration band of poly(DPF-DTS) was weakly
observed at 2212 cm−1. In the 1H-NMR spectrum of poly(DPF-DTS), the methylene proton
Figure . FT-IR spectra of DPF and poly(DPF-DTS) in KBr pellets.

170
G. Y. LEE ET AL.
Figure . The UV-visible absorption and photoluminescence (PL) spectra of poly(DPF-DTS).
peaks of propargyl group (CH2-CࣕC-DTS) at 3.11 ppm and that of propargyl group (-CH2-
CࣕC-CࣕCH2-) of poly(DPF) at 2.96 ppm were appeared. The broad aromatic fluorene and
silole proton peaks of poly(DPF-DTS) were appeared at 6.87–7.82 ppm.
The thermal behavior of poly(DPF-DTS) was examined by differencial scanning calorime-
ter and thermogravimeter. From the DSC curve of poly(DPF-DTS), it was found that a broad
exothermic peak was observed around 197°C (started at 157°C) in the first heating, whereas
there was no exothermic peak in the second heating. The broad exothermic peak is proba-
bly due to the thermal crosslinking of the internal acetylenic groups in the main chain of the
polymer. The thermal stability of poly(DPF-DTS) was also examined. It showed first rapid
weight loss in the range of 252–310°C and second rapid weight loss was observed in the range
of 502–600°C. The char yield for poly(DPF-DTS) after heating up to 600°C was 37%.
Figure 2 shows the UV-visible and photoluminescence (PL) spectra of poly(DPF-DTS)
measured from the solution (8.0×10−2 g/L) in chloroform at room temperature. The PL λmax
of poly(DPF-DTS) was observed in the range of 432–464 nm, which was similarly shifted in
comparison with that of poly(DPF-bithiophene), a similar homologue with bithiophene moi-
eties instead of DTS moieties. The solution of poly(DPF-DTS) emitted strong fluorescence at
the excitation wavelength of 350 nm. The emission spectrum of poly(DPF-DTS) shows emis-
sion maximum at 440 nm, which is corresponding photon energy of 2.82 eV. The PL quantum
yield of poly(DPF-DTS) in chloroform (1×10−5 M) was measured by comparing to quinine
sulfate (1×10−5 M) in 0.1 M H2SO4 as standard. The quantum yield (6.44%) of poly(DPF-
DTS) is the 5 times higher than that of a similar homologue, poly(DPF-bithiophene), which
may be explained by the contribution of DTS group in polymer main chain.
Conclusions
A new fluorene-containing copolymer with acetylene moieties in the main chain was pre-
pared via the palladium-catalyzed dehydrocoupling reaction of 9,9-dipropargylfluorene and
4,4ꢀ-diphenyl-2,6-dibromo-dithieno-[3,2-b:2ꢀ,3ꢀ-d]silole. The resulting polymer was com-
pletely soluble in common organic solvents such as chloroform, chlorobenzene, toluene, and
xylene. The polymer structure was characterized by such spectroscopic methods as NMR,
IR, and UV-visible spectroscopies. Poly(DPF-DTS) was found to start the thermal crosslink-
ing of the internal ethynyl moieties at the polymer main chain around 197°C. The quantum

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
171
yield of poly(DPF-DTS) is the 5 times higher than that of a similar homologue, poly(DPF-
bithiophene), which is probably due to the contribution of silole moiety in the polymer main
chain.
Acknowledgment
This work was supported by the research grants from the Catholic University of Daegu.
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