Syntheses of 1,1-Diethyl- or -Dihexyl-3,4-Diphenyl-2,5-Dibromo- or -Bis(Trimethylsilyl)Siloles and Electrochemical Properties for Lithium Ion Battery

Article abstract of DOI:10.1002/bkcs.11911

1,1-Diethyl- and 1,1-dihexyl-3,4-diphenyl-2,5-dibromosiloles (3a and 3b, respectively) as well as 1,1-diethyl- and 1,1-dihexyl-3,4-diphenyl-2,5-bis(trimethylsilyl)siloles (4a and 4b, respectively) were prepared by intramolecular reductive cyclization and

Full text of DOI:10.1002/bkcs.11911

Article
DOI: 10.1002/bkcs.11911
BULLETIN OF THE
J. Y. Park et al.
KOREAN CHEMICAL SOCIETY
Syntheses of 1,1-Diethyl- or -Dihexyl-3,4-Diphenyl-2,5-Dibromo- or -Bis
(Trimethylsilyl)Siloles and Electrochemical Properties for Lithium Ion
Battery
Ji Young Park,† Young Min Jung,‡ and Young Tae Park†,
*
†Department of Chemistry, Keimyung University, Daegu 42601, South Korea.
*E-mail: ytpark@kmu.ac.kr
‡Division of Green Energy Research, Daegu Gyeongbuk Institute of Science and Technology, Daegu
42988, South Korea
Received August 20, 2019, Accepted October 21, 2019
1,1-Diethyl- and 1,1-dihexyl-3,4-diphenyl-2,5-dibromosiloles (3a and 3b, respectively) as well as
1,1-diethyl- and 1,1-dihexyl-3,4-diphenyl-2,5-bis(trimethylsilyl)siloles (4a and 4b, respectively) were pre-
pared by intramolecular reductive cyclization and bromination or trimethylsilylation of diethyl- or
dihexyl-bis(phenylethynyl)silanes (2a and 2b), respectively. The IR stretching frequencies for all the syn-
thesized silole derivatives appeared within the range 1543–1566 cm−1. The UV–vis absorption data of the
siloles in THF include absorption peaks at 303–326 nm, with molar absorptivities ranging from
2.63 × 103 to 5.99 × 103 L/(cmÁmol). In the excitation spectra, maximum excitation bands were found at
355–371 nm, while maximum emission peaks in the fluorescence spectral data were observed at
419–443 nm. Cyclic voltammograms (CVs) of 3a and 3b revealed oxidation peaks at 0.16 and 0.58 V,
and reduction peaks at −0.25 and − 0.28 V, respectively. Meanwhile, CVs of 4a and 4b showed two oxi-
dation peaks between −0.46 and 0.14 V, and two reduction peaks between −1.32 and − 0.69 V, respec-
tively. Thermogravimetric ananysis (TGA) experimental data illustrated that all the synthesized siloles
were thermally stable at temperatures up to 150 ꢀC with only 0.3–3% loss of their original masses under
nitrogen. The long cycling performance of anodes 4a and 4b, at 1.0 A/g current density, exhibited initial
discharge/charge capacities of 1967/754 and 5559/1174 mAh/g with Coulombic efficiencies of 38.2 and
21.1% after 20 and 15 cycles, respectively.
Keywords: 1,1-Diethyl or 1,1-dihexyl-3,4-diphenyl-2,5-dibromosilole, 1,1-Diethyl or 1,1-dihexyl-
3,4-diphenyl-2,5-bis(trimethylsilyl)silole, Photoelectronic characterizations, Electrochemical properties
Introduction
synthetic methods.21–23 We previously published the syn-
theses of silole-bearing π-conjugated materials, such as
poly(3,4-diphenyl-1,1-disubstituted-2,5-silole)s, via Gri-
gnard metathesis polymerization of 2,5-dibromo-
3,4-diphenyl-1,1-disubstituted-siloles using the Grignard
reagent.24 In addition, we have studied the syntheses and
electrochemical characteristics (e.g., cyclic voltammogram
[CV]) of poly[(3,4-diphenyl-1,1-disubstituted-2,5-silolene)-
co-(disubstituted-silylene)]s bearing the 2,5-silolene and
silylene moieties using n-butyllithium.25
We have also been interested in the synthesis and proper-
ties of poly(carbosilagermane)s contained within chromo-
phores of 3,4-diphenyl-2,5-silolene and disubstituted-
germylene, for example, poly[(1,1-diethyl-3,4-diphenyl-
2,5-silolene)-co-(disubstitutedgermylene)]s.26
Silole has a skeleton of 1-silacyclopenta-2,4-diene,1 which
is a heterocyclic diene, and contains an unusual π-electronic
system resulting in a lowest unoccupied molecular orbital
energy level much lower than, for example, cyclopenta-2,-
4-diene by 1.289 eV.2 This is attributed to σ*–π* conjuga-
tion originating from an interaction between the silylene σ*
orbital and the butadiene π* orbital.3
Silole derivatives bearing such a π-conjugated structure
have been intensively studied for electronic device applica-
tions due to their unique electronic properties.4–7 From the
viewpoint of basic electrochemistry, siloles-containing
π-conjugated materials have also attracted significant atten-
tion for their application in electroluminescence,6,8–12
photoluminescence,13–18 and organic field-effect transis-
tors.19 Dendrimers end-capped with siloles exhibit blueish
green fluorescence emission, suggesting these materials
may be useful for electroluminescent devices.20
Energy storage systems, such as the lithium-ion battery,
have received considerable interest due to their wide use in
electronics and electric vehicles.27,28 Recently, organic
electrode materials have emerged as popular alternatives to
inorganic materials and carbon-involved composites, for
next generation lithium-ion batteries.29,30
Conjugated polymeric materials bearing silacyclopenta-
2,4-diene, i.e., silolene, are prepared by several different
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The synthesis, as well as photoelectronic and electro-
chemical properties, of carbosilanes containing siloles have
been studied in many ways thus far.31–33 To our knowl-
edge, there have not been any previous reports on the elec-
trochemical properties, such as long cycling performance of
anode materials, for silole derivatives like 4a and 4b, and
their application to the lithium ion battery.
Herein, we report the synthesis of 1,1-diethyl- and
1,1-dihexyl-3,4-diphenyl-2,5-dibromosiloles (3a and 3b,
respectively) as well as 1,1-diethyl and -dihexyl-3,-
4-diphenyl-2,5-bis(trimethylsilyl)siloles (4a and 4b, respec-
tively). In addition, photoelectronic characteristics
(excitation, absorption, and emission spectra in the solution
phase), thermal properties (utilizing thermogravimetric ana-
nysis [TGA] method), and their electrochemical properties
(CVs and long cycling performance of active anodes) are
reported for the first time.
10 ꢀC/min in a nitrogen atmosphere applied at a 20 mL/min
flushing rate. Cell properties obtained using charge/
discharge experiments performed using a WonATech
Multichannel Potentiostat/Galvanostat WMPG-1000 (Seoul,
Korea).
Diethylbis(phenylethynyl)silane (2a).
Diethylbis(phen-
ylethynyl)silane (2a) was prepared by treatment of
dichlorodiethylsilane (1a) with phenylacetylene using n-
butyllithium in accordance with a published method.24,35
A
yellowish viscous liquid 2a (26.0 g, 96.3%) was obtained
quantitatively. 1H NMR (500 MHz, CDCl3): δ 0.90–0.95 (q,
J = 7.8 Hz, 4H), 1.21–1.24 (t, J = 7.7 Hz, 6H), 7.32–7.38
(m, 6H), 7.55–7.57 (m, 4H). 13C NMR (125 MHz, CDCl3):
δ 6.507, 7.313, 88.749, 106.631, 122.642, 128.132, 128.747,
132.077. 29Si NMR (99 MHz, CDCl3): δ −30.712. IR (neat)
νmax: 3080, 3057, 3032, 2956, 2933, 2913, 2874, 2157
̃
(vC ≡ C), 1008, 965, 915, 831, 754, 723, 686 cm−1.
Dihexylbis(phenylethynyl)silane (2b). Dihexylbis(phen-
ylethynyl)silane (2b) was prepared by the treatment of
dichlorodihexylsilane (1b) with phenylacetylene using n-
Experimental Section
General. All chemicals used for the experiments were pur-
chased from Sigma-Aldrich Company Sigma-Aldrich Korea
Corporation (Seoul, Korea). All the glassware used was set
up, then flame-dried utilizing a burner under a stream of
argon prior to experiments. All solvents were distilled
before use according to methods reported in the literature.34
For example, tetrahydrofuran was distilled from fine
chopped sodium metal along with benzophenone ketyl prior
to use.34 1H and 13C nuclear magnetic resonance (NMR)
spectral data were collected using a JEOL 500 MHz FT-
NMR spectrometers (Tokyo, Japan) using CDCl3 as the
solvent. Chemical shifts in all the NMR spectra were mea-
sured utilizing the residual proton peak of CDCl3 and tetra-
methylsilane (TMS) as an internal standard. Infra-red
spectroscopy was performed using a Thermo Scientific FT-
IR iD50 spectrophotometer (Milwaukee, WI, USA) fourier
transform - infrared spectroscopy (FT-IR) iD50 spectropho-
tometer. Ultraviolet-visible (UV–vis) absorption experi-
ments were carried out using a Hewlett Packard 8453
spectrophotometer (USA). We recorded the excitation and
fluorescence emission spectra using a fluorescence spectro-
photometer from Horiba Fluorolog-3-11 fluorescence
spectrophotometer (Edison, NJ, USA). We conducted
cyclic voltammetry using a Bio-Logic Science Instrument,
model VSP, Potentiostat (Claix, France) with a three-
electrode cell system comprised of a platinum wire counter
electrode, Ag/AgCl reference electrode, and copper work-
ing electrode with a potential window from +2 to −2 V.
We prepared the working electrode by dipping the copper
electrode in a hexane solution containing each synthesized
silole derivative, followed by removal of the solvent via
evaporation using a dry oven. We examined thermal prop-
erties of the obtained silole materials utilizing a thermal
analysis instrument from Shimadzu TGA-50 (Kyoto, Japan).
For these studies, we incrementally increased the tempera-
ture of the TGA from 25 to 900 ꢀC with a heating rate of
butyllithium in accordance with a published method.24,35
A
yellowish viscous liquid 2b (35.0 g, 94.0%) was obtained
quantitatively. 1H NMR (500 MHz, CDCl3): δ 0.8–1.66 (m,
26H), 7.27–7.42 (m, 6H), 7.42–7.60 (m, 4H). 13C NMR
(125 MHz, CDCl3): δ 14.148, 14.810, 22.604, 23.670,
31.521, 32.731, 89.469, 106.535, 122.843, 128.171,
128.737, 132.145. 29Si NMR (99 MHz, CDCl3):
δ
−34.697. IR (neat) νmax: 3079, 3057, 3032, 2955, 2921,
̃
2854, 2158 (vC ≡ C), 1099, 1068, 1026, 995, 958, 913, 832,
753, 687 cm−1
.
2,5-Dibromo-1,1-diethyl-3,4-diphenyl-silole (3a).
2,5-
Dibromo-1,1-diethyl-3,4-diphenyl-silole (3a) was synthesized
via intramolecular reductive cyclization of the compound 2a,
followed by bromination according to the literature.24,35
A
1
pale brownish powder 3a (3,40 g, 32.5%) was obtained. H
NMR (500 MHz, CDCl3): δ 1.04–1.09 (q, J = 7.8 Hz, 4H),
1.18–1.21 (t, J = 7 Hz, 6H), 7.00–7.02 (m, 4H), 7.17–7.22
(m, 6H). 13C NMR (125 MHz, CDCl3): δ 1.477, 6.536,
120.770, 127.355, 127.499, 128.948, 137.040, 157.216. 29Si
NMR (99 MHz, CDCl3): δ 8.521. IR (neat) νmax: 3026, 3055,
2962, 2930, 2908, 2877, 1566 (νC=C), 1076, 1064, 1022,
953, 933, 912, 764, 729, 693, 637 cm−1.
2,5-Dibromo-1,1-dihexyl-3,4-diphenyl-silole (3b). 2,5-
Dibromo-1,1-dihexyl-3,4-diphenyl-silole (3b) was synthe-
sized via intramolecular reductive cyclization of the com-
pound 2b, and bromination according to the literature.24,35
A pale brownish powder 3b (3.00 g, 31.9%) was obtained.
1H NMR (500 MHz, CDCl3): δ 0.91–1.01 (m, 10H),
1.23–1.58 (m, 16H), 6.95–6.97 (m, 4H), 7.15–7.19 (m,
6H). 13C NMR (125 MHz, CDCl3): δ 9.684, 14.148,
22.575, 22.854, 31.416, 32.683, 121.826, 127.345,
127.518, 128.948, 137.155, 156.775. 29Si NMR (99 MHz,
CDCl3): δ 6.176. IR (neat) νmax: 3024, 3057, 2953, 2922,
̃
2853, 1557 (νC=C), 1075, 1060, 1025, 952, 766, 697 cm−1
.
2,5-Bis(trimethylsilyl)-1,1-diethyl-3,4-diphenyl-silole
(4a). 2,5-Bis(trimethylsilyl)-1,1-diethyl-3,4-diphenyl-silole
16
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Synthesis of 1,1-Diethyl- or -Dihexyl-3,4-Diphenyl-2,5-Dibromo- or -Bis
(Trimethylsilyl)Siloles and Electrochemical Properties
BULLETIN OF THE
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KOREAN CHEMICAL SOCIETY
(4a) was synthesized via intramolecular reductive cycliza-
tion of the compound 3a, and trimethylsilation according to
the literature.8,24,35 A pale brownish powder product 4a
(5.00 g, 49.5%) was obtained. 1H NMR (500 MHz,
CDCl3): δ −0.16 (s, 18H), 0.92–0.96 (m, 4H), 0.98–1.01
(m, 6H), 6.82–6.84 (m, 4H), 6.99–7.03 (m, 6H). 13C NMR
(125 MHz, CDCl3): δ 0.470, 5.211, 7.285, 125.934,
126.865, 128.833, 141.628, 143.087, 171.077. 29Si NMR
(99 MHz, CDCl3): δ −10.04, 29.90. IR (neat) νmax: 3022,
̃
3057, 2951, 2895, 2873, 1543 (νC=C), 1071, 1034, 1006,
952, 914, 831, 776, 753, 695, 684 cm−1
.
2,5-Bis(trimethylsilyl)-1,1-dihexyl-3,4-diphenyl-silole (4b).
2,5-Bis(trimethylsilyl)-1,1-dihexyl-3,4-diphenyl-silole (4b)
was synthesized via intramolecular reductive cyclization of
the compound 2b, and trimethylsilation according to the lit-
erature.8,24,35 A pale brownish powder product 4b (5.00 g,
54.4%) was obtained. 1H NMR (500 MHz, CDCl3): δ
−0.15 (s, 18H), 0.88–1.02 (m, 10H), 1.27–1.44 (m, 16H),
6.79–6.90 (m, 4H), 6.96–7.11 (m, 6H). 13C NMR
(125 MHz, CDCl3): δ 0.642, 13.620, 14.196, 22.710,
23.890, 31.675, 33.172, 125.915, 126.846, 128.766,
142.732, 143.058, 170.520. 29Si NMR (99 MHz, CDCl3): δ
Scheme 1. Synthesis of siloles 3a, 3b, 4a, and 4b.
−10.20, 26.56. IR (neat) νmax: 3057, 3021, 2953, 2916,
̃
2850, 1545 (νC=C), 1467, 1242, 1043, 1003, 954, 913,
831, 779, 756, 698 (vSi─C) cm−1
.
(2b). Subsequently, reductive intramolecular cyclization of
2a and 2b using Li+Naphth−, anhyd. ZnCl2, and NBS
afforded 3a and 3b, respectively. The identity of 3a and 3b
were confirmed using several spectroscopic methods, includ-
ing NMR and IR studies. Some spectroscopic properties of
Fabrication of Anode for Lithium Ion Batteries. Upon
mixing the active material (4a or 4b) with conductor
super P, and binder polyvinylidenefluoride at an appropriate
ratio, the mixture was stirred using a zirconia ball-milling
in N-methylpyrrolidone for 24 h. The resulting well-mixed
solution of electrode material was coated onto the current
collector Cu foil using a doctor blade, and vacuum-dried
under increasing temperature conditions from 50 to 110 ꢀC
over a 12-h period. The cell assembly of a 2032 type coin
cell for the measurement of electrochemical properties, was
performed inside a glove box under Argon atmosphere.
Batteries were fabricated as half cells and the prepared
active materials were employed as the working electrode.
Lithium (Li) metal was used as the counter electrode, and
polypropylene (PP) was used as the separator. The electro-
lyte solution contained 1.0 M LiPF6 in ethylene carbonate
and dimethyl carbonate at a 3:7 (vol.%) ratio.
1
compounds 3a, 3b, 4a, and 4b are listed in Table 1. The H
NMR spectra of 3a and 3b illustrate multiplet peaks at
1.04–1.21 and 0.91–1.58 ppm, due to the presence of C2H5
and C6H13 groups, respectively.35–37 The 13C NMR spectra
of 3a and 3b, reveal two carbon peaks at 1.48 and 6.54 ppm
due to the C2H5 group directly bound to the silole Si atom,
and six carbon peaks between 9.68 and 32.68 ppm due to
the C6H13 group directly bound to the silole Si atom.35–37 In
the 29Si NMR spectra of 3a and 3b, the silicon peaks were
found at 8.52 and 6.18 ppm, respectively.38
Scheme 1 also illustrates the synthesis of 2,5-bis(trimethyl-
silyl)-1,1-diethyl- (4a) and -dihexyl-3,4-diphenyl-1-silole
(4b) as previously reported using 2a and 2b as starting mate-
rials, respectively.3,24 Briefly, intramolecular reductive cycli-
zation, followed by in situ trimethylsilylation of 2a and 2b
using lithium naphthalenide and trimethylchlorosilane
afforded compounds 4a and 4b, respectively. The identity of
4a and 4b were confirmed using several spectroscopic
methods. The 1H NMR spectra of 4a and 4b exhibit multiplet
peaks at 0.92–1.01 and 0.88–1.44 ppm, originated from the
C2H5 and C6H13 groups, respectively.35–37 The 13C NMR
spectra of 4a and 4b reveal two peaks at 5.21 and 7.29 ppm
due to the C2H5 group directly bound to the silole Si atom,
and six carbon peaks between 13.62 and 33.17 ppm due to
the C6H13 group directly bound to the silole Si atom.35–37 In
the 29Si NMR spectra of 4a and 4b, the silicon peak attached
The absorption, excitation, fluorescence emission data,
TGA thermogram traces and CVs for 3a, 3b, 4a, and 4b
along with the long cycling performance data for 4a and 4b
are described below.
Results and Discussion
Synthesis.
Scheme 1 illustrates the preparation of
1,1-diethyl- (3a) and 1,1-dihexyl-2,5-dibromo-3,4-diphenyl-
1-silole (3b) using the two-step reaction protocol reported
previously.3,24 Dichlorodiethyl- (1a) or dihexylsilane (1b)
were treated with lithium phenylacetylide, prepared in situ in
THF via the reaction of ethynylbenzene with n-butyllithium,
to obtain diethyl- (2a) or dihexylbis(phenylethynyl)silane
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Synthesis of 1,1-Diethyl- or -Dihexyl-3,4-Diphenyl-2,5-Dibromo- or -Bis
(Trimethylsilyl)Siloles and Electrochemical Properties
BULLETIN OF THE
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Synthesis of 1,1-Diethyl- or -Dihexyl-3,4-Diphenyl-2,5-Dibromo- or -Bis
(Trimethylsilyl)Siloles and Electrochemical Properties
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to the silole ring appeared at 29.90 and 26.56 ppm,
respectively.38
The maximum fluorescence band, λem,max, observed at
443 nm in the fluorescence spectrum of 3a, was obtained
using an excitation wavelength, λex, of 371 nm in THF, is
depicted in Figure 1 (_.._) and listed in Table 1. The maxi-
mum fluorescence values, λem,max, for 3b, 4a, and 4b mea-
sured using excitation wavelengths, λex, of 372, 356, and
355 nm were 438, 424, and 419 nm, respectively, as sum-
marized in Table 1. The strong emission peaks in the fluo-
rescence emission spectra of the prepared siloles are
attributed to the chromophores of phenyl and diene groups
in the 3,4-diphenyl-silole ring.40 Furthermore, the full wid-
ths at half maximum (FWHM) in the fluorescence spectra
of 3a, 3b, 4a, and 4b were measured to be 67, 117, 93, and
97 nm, respectively, as listed in Table 1.
From the viewpoint of the excitation and fluorescence
data we can speculate that the silole derivatives 3a, 3b, 4a,
and 4b are comprised of chromophores contained within
the silolene derivative, i.e., 3,4-diphenyl-1-silacylopent-
2,4-dienylene, phenyl and diene groups.40 Furthermore,
siloles with electron-releasing substituents, such as the Br
atoms in 3a and 3b, show moderate bathochromic shifts (i.
e., 19–23 nm) of their absorption and fluorescence emission
maxima in comparison to the trimethylsilyl substituted
siloles, 4a and 4b.41
Cyclic Voltammetry Properties. We examined the cyclic
voltammetric properties of compounds 3a, 3b, 4a, and 4b
by coating the synthesized compounds onto copper elec-
trodes. The working electrode copper film was fabricated
by immersing a copper electrode into a hexane solution
containing each of the synthesized compounds.
A representative CV of silole 3a on a copper electrode
immersed in an electrolyte bath of aqueous sulfuric acid
solution (H2SO4, 1.0 M) is shown as trace (a) in Figure 2.
The CV data for 3a and 3b, listed in Table 1, show an oxi-
dation peak at 0.58 and 0.16 V vs. the Ag/Ag+ reference
electrode, respectively. Reduction peaks for 3a and 3b were
observed at −0.25 and − 0.28 V vs. the Ag/Ag+ reference
electrode, respectively. On the basis of these results, the
reduction may illustrate the transformation of 3a and 3b
into their equivalent anions, for example [3a]− and [3b]−,
respectively. A similar phenomenon may occur for the
reverse process of oxidation, involving the transformation
of [3a]− and [3b]− anions back to 3a and 3b,
respectively.42,43
The synthesized compounds were also characterized by
FT-IR spectroscopy with the results summarized in
Table 1. The FT-IR spectroscopic results of 3a, 3b, 4a, and
4b illustrated typical stretching frequencies of dienes within
a silole ring between 1543 and 1566 cm−1, illustrating that
the conjugated dienes inside the silole ring remained intact
throughout the trimethylsilylation reaction conditions.39
Photoelectronic Properties. We examined the photoelec-
tronic properties of 3a, 3b, 4a, and 4b using absorption,
excitation, and fluorescence measurements in tetrahydrofu-
ran. Typical selected properties of siloles 3a, 3b, 4a, and
4b are listed in Table 1.
A representative absorption spectral trace of 3a in tetra-
hydrofuran is shown in Figure 1 (—). The maximum
absorption, λabs,max
,
of 3a is found at 326 nm
(ε = 3.50 × 103/(cm.M)), with the trace reaching 396 nm.
Similarly, the absorption spectra of materials 3b, 4a, and
4b illustrate strong absorbance maxima (λabs,max) at
325, 303 and 304 nm, respectively, as shown in the
Table 1. The strong absorption maxima in the UV–vis spec-
tral traces of materials 3a, 3b, 4a, and 4b are due to the
presence of chromophores, mainly the phenyl, as well as
the diene functional groups within the 3,4-diphenyl-silole
ring.40
The spectrophotometric excitation trace of 3a showed a
strong maximum, λex,max, at 371 nm, using a 443 nm detec-
tion wavelength, λdet, as depicted in Figure 1 (− −) and
listed in Table 1. The excitation traces of 3b, 4a, and 4b at
the detection wavelengths 438, 424, and 419 nm, revealed
strong excitation maxima at 372, 356, and 355 nm, respec-
tively, as summarized in Table 1. The excitation bands in
the spectral data of 3a, 3b, 4a, and 4b are ascribed to the
chromophores of phenyl and diene groups in the
3,4-diphenyl-silole ring.40
326
371
443
Absorption
Excitation
Emission
The CV data for silole 4a on a copper working electrode
in an electrolyte bath of aqueous potassium hydroxide solu-
tion (KOH, 1.0 M) is illustrated as trace (b) in Figure 2.
The CV data for 4a and 4b, listed in Table 1, reveals two
oxidation peaks for each compound at −0.45, −0.04, and
− 0.46, 0.14 V vs. the Ag/Ag+ reference electrode, respec-
tively. The two reduction peaks for each of 4a and 4b were
observed at −0.74, −1.12, and − 0.69, −1.32 V, vs. the
Ag/Ag+ reference electrode, respectively. On the basis of
these results, the reduction may illustrate the transforma-
tions of 4a and 4b into their equivalent anions, for exam-
300
350
400
450
Wavelength (nm)
500
550
600
Figure 1. Absorbance, excitation, and fluorescence emission
spectrophotometric traces of compound 3a in THF.
ple, [4a]−, [4a]−2
,
and [4b]−, [4b]−2
,
respectively.
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Synthesis of 1,1-Diethyl- or -Dihexyl-3,4-Diphenyl-2,5-Dibromo- or -Bis
(Trimethylsilyl)Siloles and Electrochemical Properties
BULLETIN OF THE
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0.014
(a)
0.012
0.010
0.008
0.006
0.004
0.002
0.000
-0.002
-0.004
-0.8
-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8
1.0
Potential (V vs. Ag/AgCl)
(b) 6e-5
4e-5
Figure 3. Thermogravimetric (TGA) traces of 3a, 3b, 4a, and 4b
under nitrogen.
2e-5
attributed to the thermal decomposition of functional
groups on the silole ring, for example, the phenyl, bromine,
ethyl, and hexyl functionalities.37 Between temperatures of
600 and 900 ꢀC an additional 0.3–4% of their initial masses
were lost.
The siloles 4a and 4b were very thermally stable up to
150 ꢀC with only a 0.3–0.7% decrease in their original
masses under nitrogen being observed. These siloles were
found to suffer rapid losses in their mass when heated
above 150 ꢀC, with 88 to 99% of their initial mass lost
between 150 and 400 ꢀC. The loss of mass of the siloles is
attributed to thermal decomposition of functional groups on
the silole ring, e.g., the phenyl, trimethylsilyl, ethyl, and
hexyl functionalities.37 Between temperatures of 600 and
900 ꢀC an additional 0.1–9% of their initial masses
were lost.
In summary, each of the siloles 3a, 3b, 4a, and 4b were
thermally stable under nitrogen up to 150 ꢀC with less than
0.3–3% losses of the initial mass observed, and 72–96% of
their initial mass remaining at 200 ꢀC under N2 atmosphere.
These results are illustrated in Figure 3 and summarized in
Table 1.
Long Cycling Performance Property. We examined the
long cycling performance properties of the anode silole
materials 4a and 4b at 1 A/g current density, as guided by
their CV data in Figure 4.
0
-2e-5
-4e-5
-6e-5
-8e-5
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
Potential (V vs. Ag/AgCl)
Figure 2. CV traces of (a) 3a in an aqueous 1.0 M H2SO4 solu-
tion and (b) 4a in an aqueous 1.0 M KOH solution.
Similarly, the reverse process of oxidation may involve the
transformation of [4a]−, [4a]−2, and [4b]−, [4b]−2 anions
back to 4a and 4b, respectively.42,43 Furthermore, siloles
with electron-releasing substituents, such as the Br atoms in
3a and 3b, show low-lying first oxidation potential levels,
(i.e., Epa) in comparison with the trimethylsilyl substituted
siloles 4a and 4b, respectively.22
The photoelectronic and cyclic voltammetric properties
of 3a, 3b, 4a, and 4b illustrate the potential utility of the
prepared silole derivative materials, specifically 1,1-diethyl
or dihexyl-3,4-diphenyl-1-silacyclopenta-2,4-diene, in elec-
trochemical device applications.
Thermal Properties. We examined the thermal stability
of the siloles 3a, 3b, 4a, and 4b using a thermogravimetric
analysis (TGA) systemꢀ whereby the temperature was
increased at a rate of 10 C/min under a constant stream of
nitrogen. The results are illustrated in Figure 3 and the data
summarized in Table 1. The siloles 3a and 3b were found
to be thermally stable up to 150 ꢀC with less than a 2–3%
decrease in their original masses under nitrogen. These
siloles were found to suffer rapid losses in their mass when
heated above 150 ꢀC, with 85–95% of their initial mass lost
between 150 and 300 ꢀC. The loss of mass of the siloles is
For the anode silole material 4a, the first discharge/
charge capacity was found to be 1967/754 mAh/g with
38.2% Coulomb efficiency at 20 cycles followed by a
908 mAh/g charge capacity with 46.1% Coulomb effi-
ciency achieved after 105 cycles. Subsequently, the charge
capacity of the anode material 4a slowly decreased to
517 mAh/g with 26.2% Coulomb efficiency after
1000 cycles.
For the anode material 4b, the initial discharge/charge
capacity was found to be 5559/1174 mAh/g with a lower
Coulomb efficiency of 21.1% at 15 cycles followed by a
Bull. Korean Chem. Soc. 2020, Vol. 41, 15–22
© 2019 Korean Chemical Society, Seoul & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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20

Synthesis of 1,1-Diethyl- or -Dihexyl-3,4-Diphenyl-2,5-Dibromo- or -Bis
(Trimethylsilyl)Siloles and Electrochemical Properties
BULLETIN OF THE
Article
KOREAN CHEMICAL SOCIETY
the silole derivatives are composed of the expected chromo-
phores, for example, phenyl and 1,4-diene of 3,4-diphenyl-
1-silacyclopenta-2,4-dienylene, within the silole skeleton.
CVs of 3a and 3b revealed oxidation peaks at 0.58 and
0.16 V, and reduction peaks at −0.25 and −0.28 V, respec-
tively. CVs of 4a and 4b revealed two oxidation peaks
ranging from −0.46 to 0.14 V, as well as two reduction
peaks ranging from −1.32 to −0.69 V. TGA revealed that
all siloles were thermally stable up to 150 ꢀC suffering only
a 0.3 to 3% loss of their original masses under nitrogen.
Finally, the long cycling performance of anodes 4a and 4b
exhibited initial discharge/charge capacities, at a 1 A/g cur-
rent density, of 1967/754 with 38.2% Coulomb efficiency
at 20 cycles, and 5559/1174 mAh/g Coulomb efficiency of
21.1% at 15 cycles, respectively. The photoelectronic and
electrochemical characteristics of 4a and 4b confirms their
utility for applications in novel electronic materials.
Et_TMS
(a)
2000
1800
1600
1400
1200
1000
800
600
400
0
200
400
600
800
1000
Cycle (n)
Hex_TMS
(b)
Acknowledgment. This research was supported by the
National Research Foundation of Korea (NRF) funded by
the Ministry of Education of the Republic of Korea (NRF-
2017R1D1A3B03028014).
7000
6000
5000
4000
3000
2000
1000
Supporting Information. All spectroscopic data including
NMR, IR, and UV–vis, along with TGA traces for the com-
pounds 2a, 2b, 3a, 3b, 4a, and 4b are available in the
online version of this article.
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Bull. Korean Chem. Soc. 2020, Vol. 41, 15–22
© 2019 Korean Chemical Society, Seoul & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.bkcs.wiley-vch.de
21

Synthesis of 1,1-Diethyl- or -Dihexyl-3,4-Diphenyl-2,5-Dibromo- or -Bis
(Trimethylsilyl)Siloles and Electrochemical Properties
BULLETIN OF THE
Article
KOREAN CHEMICAL SOCIETY
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www.bkcs.wiley-vch.de
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