φ-Conjugated molecules based on truxene cores and pyrene substitution:Synthesis and properties

Article abstract of DOI:10.3184/174751913X13639408275103

Two starburst molecules based on pyrene with truxene cores, PYT and PYET, have been designed and synthesised by Pd(0)-catalysed Suzuki coupling and Sonogashira coupling reactions, respectively. Due to the different conjugation length, the solution absorption and emission spectra of PYET in dilute THF were redshifted compared with those of PYT. The solid absorption and emission spectra of PYET were also redshifted. Their thermal decomposition temperatures (T _d) were over 400 °C, and the glass transition temperatures (T_g) were 96 and 124 °C, respectively, which showed that both materials possess good thermal stability. Electrochemical analysis implied that the HOMOs of PYET and PYT were similar.

Full text of DOI:10.3184/174751913X13639408275103

242 RESEARCH PAPER
APRIL, 242–247
JOURNAL OF CHEMICAL RESEARCH 2013
π-Conjugated molecules based on truxene cores and pyrene substitution:
synthesis and properties
Chao Tanga*, Xu-Dong Liua, Feng Liua, Xu-liang Wanga, Hui Xua, Rui-Lan Liua,b, Zhou Ronga,b
and Wei Huanga*
aKey Laboratory for Organic Electronics and Information Displays (KLOEID), Singapore-Jiangsu Joint Research Centre for Organic/Bio
Electronics & Information Displays (COEID), Institute of Advanced Materials (IAM), Nanjing University of Posts andTelecommunications
(NUPT), Nanjing 210046, P. R. China
bCollege of Automation, Nanjing University of Posts andTelecommunications (NUPT), Nanjing 210046, P. R. China
Two starburst molecules based on pyrene with truxene cores, PYT and PYET, have been designed and synthesised
by Pd(0)-catalysed Suzuki coupling and Sonogashira coupling reactions, respectively. Due to the different conjuga-
tion length, the solution absorption and emission spectra of PYET in dilute THF were redshifted compared with those
of PYT. The solid absorption and emission spectra of PYET were also redshifted. Their thermal decomposition tem-
peratures (Td) were over 400 °C, and the glass transition temperatures (Tg) were 96 and 124 °C, respectively, which
showed that both materials possess good thermal stability. Electrochemical analysis implied that the HOMOs of
PYET and PYT were similar.
Keywords: truxene, pyrene, starburst, organic semiconductors
With the development of organic light-emitting diodes
(OLEDs), organic field-effect transistors (OFETs) and organic
photovoltaic cells (OPVs), organic electronic materials have
attracted great scientific and commercial attention. There are
two types of organic semiconductors (OSCs) divided by struc-
ture, small molecules and polymers. Small molecule OSCs
have the advantage of easy purification by general column
chromatography, whilst the polymer OSCs possess good rheo-
logical behaviour, which means a device can be fabricated by
cheap and easy techniques such as spin-coating, ink-jet and
screen printing.1 The recently keenly researched OSCs, rigid
π-conjugated star-shaped molecules, possess the characteris-
tics of both π-conjugated polymers and small molecules. They
have well-defined conjugation lengths and the structures are
characterised by uniformity, absence of chain defects and ease
of purification and characterisation, which is a benefit for
systematic investigation of the relationships between the
structures of the molecules and their properties2–4. At present,
developing new type of π-conjugated materials with novel
cores and arms is one of the interesting challenges for
materials chemists.
With a large conjugated aromatic ring, pyrene not only has
high photoluminescence efficiency and high carrier mobility,
but also is a common building block which can enhance the
hole-injection ability of the compounds. For example, our
group designed and synthesised a series of compounds based
on pyrene and fluorene5–9. Studies show that the hole-injection
properties of the materials had been obviously improved. The
HOMOs of the non-conjugated pyrene substituted fluorenes
are close to the common hole-injection materials such as
phthalocyanine copper (II) (CuPc) and poly(3,4-ethylene-
dioxythiopheyl): polystyrenesulfonate (PEDOT:PSS). Electro-
luminescence (EL) devices based on such compounds without
hole-injection layers showed maximum luminance close to 20,
000 cd m−2 and the maximum efficiency over 3.0 cd A−1.
10,15-Dihydro-5H-diindeno[1,2-a:1′,2′-c]-fluorene (truxene)
is a planar heptacyclic polyarene,10–12 which can be formally
regarded as a C3-symmetrically-fused fluorene trimer. Due to
its unique three-dimensional topology, the truxene moiety
is easily functionalised by diverse substituents at the C2, 3, 7,
8, 12 and 13 positions and at the C5, 10 and 15 positions13.
Truxene is an excellent choice to use as a core for the construc-
tion of star-shaped molecules giving its rigid structures, good
thermal and chemical stabilities and high quantum yields14. As
an attractive building block and starting material, the various
functional organic materials based on truxene can be applied
to many optoelectronic fields such as those involving liquid
crystals,15 OLEDs,16–18 fluorescence sensors,19 organic solar
cells,20–21 OFETs,22 lasers,23–24 light-harvesting systems25 and
two-photon absorption26.
In this paper, two truxene-centred materials with different
arms, PYT and PYET (Scheme 1) have been designed and syn-
thesised by Pd(0)-catalysed Suzuki cross-coupling reactions
and Sonogashira cross-coupling reactions, respectively. The
thermal, photophysical and electrochemical properties of these
compounds have been studied and their structure–property
relationships are discussed.
Experimental
All reactions were monitored by TLC using precoated glass sheets
purchased byYantai Huiyou Silica Gel Developing Co. Ltd. (0.20 mm
with fluorescent indicator UV254 and 365). Column chromatography
was carried out using flash silica gel from Qingdao Haiyang Chemical
1
Co. Ltd. (200–300 mesh). H NMR was recorded using a Bruker
spectrometer at 400 MHz. Molecular masses were determined by a
Shimadzu GCMS-QP2010 and Shimadzu matrix-assisted laser
desorption/ionisation time-of-flight mass spectrometer (MALDI-
TOF-MASS). Elemental analyses were performed on a Vario III ele-
mental analyser. Thermogravimetric analysis (TGA) and differential
scanning calorimetry (DSC) were performed using a purged nitrogen
atmosphere at a heating rate of 10 °C min−1. Absorption and photolu-
minescence (PL) emission spectra of the materials were measured
in THF using a SHIMADZU UV-3600 spectrophotometer and a
SHIMADZU RF-5301PC spectrophotometer, respectively. Cyclic
voltammetry (CV) was performed on an Eco Chemie’sAutolab instru-
ment. The HOMO, LUMO and the energy gap between them (∆E)
were measured by cyclic voltammetry (CV). The HOMO/LUMO
energy levels of the compounds are estimated based on the reference
energy level of ferrocene (4.8 eV below the vacuum): HOMO/LUMO=
–[Eonset + 4.8 eV] and Eonset is the onset potential of the oxidation or the
reduction.
Commercial grade reagents were used without further purification.
All the solvents for characterisation were used after redistillation.
The THF was refluxed with sodium filament in the presence of benzo-
phenone until a persistent blue colour appeared and then distilled.
Petroleum ether was used.
1-(4,4,5,5-Tetramethyl-1,3,2-di-oxaborolan-2-yl)pyrene (1): Com-
pounds 1 was synthesised according to procedures in the literature.7
Yellowish solid, 6.51 g, yield: 55.8%; m.p. 121 °C. 1H NMR
(400 MHz, CDCl3) δ (ppm): 9.08 (d, J = 9.2 Hz, 1H), 8.54 (d, J =
7.6 Hz, 1H), 8.0–8.24 (m, 7H), 1.50 (s, 12H). GC-MS (CH2Cl2): m/z:
328.
* Correspondent. Email: iamctang@njupt.edu.cn

JOURNAL OF CHEMICAL RESEARCH 2013 243
1-Ethynylpyrene (2): Compound 2 was synthesised according to
procedures in the literature.5 Brown solid, 3.85 g, yield: 86.1%; m.p.
111 °C. 1H NMR (400 MHz, CDCl3) δ (ppm): 8.59 (d, 1H), 8.04–8.22
(m, 8H), 3.63 (s, 1H). GC-MS (CH2Cl2): m/z: 226.
for 12 h. The reaction mixture was quenched with saturated ammo-
nium chloride and extracted twice with petroleum ether. The com-
bined organic extracts were dried with anhydrous MgSO4. After the
solvent was removed, the residue was purified by column chromato-
graphy using petroleum ether as eluent to provide the yellow solid
(6.8 g, yield: 80.3%); m.p. 70 °C.1H NMR (400 MHz, CDCl3) δ (ppm):
8.38 (d, J = 7.6 Hz, 3H), 7.46–7.49 (m, 3H), 7.35–7.42 (m, 6H), 2.94–
3.01 (m, 6H), 2.05–2.13 (m, 6H), 0.84–0.95 (m, 36H), 0.59–0.62 (m,
18H), 0.49–0.53 (m, 12H). 13C NMR (100 MHz, CDCl3) δ (ppm):
153.7, 144.8, 140.4, 138.4, 126.3, 125.9, 124.7, 122.2, 55.6, 36.9,
31.5, 29.5, 23.9, 22.3, 13.9. MALDI-TOF-MS (m/z): calcd. for C63H90
846.7, found 847.6.
The melting points of 1 and 2 are not given in the literature.5,7
5,5,10,10,15,15-Hexahexyl-10,15-dihydro-5H-diindeno[1,2-
a:1′,2′-c]fluorine (TrH):27,28 n-Butyllithium (1.6 M solution in hex-
anes) (50 mL, 0.08 mol) was added dropwise to a solution of truxene
(3.42 g, 0.01 mol) in dry THF (60 mL), over 30 min by syringe at
room temperature and the mixture stirred for another 1 h. Then,
n-hexylbromide (14 mL) was added slowly and the mixture stirred
Scheme 1 Synthesis of PYT and PYET.

244 JOURNAL OF CHEMICAL RESEARCH 2013
2,7,12-Tribromo-5,5,10,10,15,15-hexahexyl-10,15-dihydro-5H-
diindeno[1,2-a:1′,2′-c]fluorine(TrHBr):27,28 Dichloromethane,bromine
(0.6 mL) was added dropwise to a solution of TrH (2.1 g, 2.48 mmol)
in 45 mL over about 15 min. The tail gas was treated with sodium
hydroxide solution .The reaction was stirred overnight and kept in a
dark place. Then, the mixture was poured into saturated sodium thio-
sulfate solution and stirred for 0.5 h to remove the excess of bromine.
The organic phase was collected and dried with anhydrous MgSO4.
After the solvent was removed, the residue was purified by column
chromatography using petroleum ether as eluent to give the white
solid (2.2 g, yield: 81.8%); m.p. 217 °C.1H NMR (400 MHz, CDCl3)
δ (ppm): 8.17 (d, J = 8.0 Hz, 3H), 7.56 (d, J = 4.0 Hz, 3H), 7.52 (d,
J = 8.0 Hz, 3H), 2.81–2.88 (m, 6H), 1.98–2.05 (m, 6H), 0.83–0.95 (m,
36H), 0.60–0.64 (m, 18H), 0.43–0.50 (m, 12H). 13C NMR (100 MHz,
CDCl3) δ (ppm): 155.9, 144.9, 138.9, 137.6, 129.4, 125.9, 125.5,
121.1, 56.0, 36.8, 31.5, 29.4, 23.9, 22.3, 13.9. MALDI-TOF-MS
(m/z): calcd for C63H87Br3 1080.4, found 1084.8.
Results and discussion
Since unsubstituted truxene is sparingly soluble in common
organic solvents, six hexyl substituents were introduced at the
C5, 10, 15 positions of the truxene core, which cannot only
efficiently enhance the solubility of the target compounds and
alleviate intermolecular interactions in the solid state, but also
might increase the yield and facilitate the purification of the
desired products. The detailed synthesis of the two starbursts,
PYT and PYET, is outlined in Scheme 1. 1-Bromopyrene was
subjected to halogen-lithium exchange with n-BuLi at –78 °C
in THF. The resulting mixture was subsequently reacted with
the isopropoxyboronic acid pinacol ester to achieve the
desired boronic ester 1 (55.8% yield). Compound 2 was syn-
thesised by Sonogashira reaction (86.1% yield) from 1-bromo-
pyrene and trimethylsilylacetylene, followed by elimination of
the protecting group, TMS, by using KOH in THF/CH3OH
solution. A Suzuki coupling reaction was employed between
the tribromide TrHBr and pyrene boronic ester 1 to obtain the
target compounds PYT (>60% yield). Sonogashira coupling
reaction was employed between the pyrene ethyne 2 and tri-
bromide TrHBr to achieve the target compound PYET (>60%
yields). Both the pyrene-functionalised truxenes in this report
were purified by flash column chromatography. They were
characterised by 1H NMR, 13C NMR and matrix-assisted
laser desorption/ionisation time-of-flight mass spectrometry
and elemental analysis. The results were consistent with the
proposed structures.
5,5,10,10,15,15-Hexahexyl-2,7,12-tri(pyren-1-yl)-10,15-dihydro-
5H-diindeno[1,2-a:1′,2′-c]fluorene (PYT): To a 100 mL flask, com-
pound TrHBr (1.00 g, 0.92 mmol), compound 1 (1.21 g, 3.69 mmol)
and tetrakis(triphenylphosphine) palladium (0.22 g, 0.19 mmol) were
added. The flask was degassed and a N2 atmosphere introduced. Then
degassed toluene (45 mL) and aqueous 2.0 M K2CO3 (10 mL) were
injected. The reaction mixture was stirred at 90 °C for 48 h. After it
was cooled to room temperature, the reaction mixture was quenched
with saturated sodium bicarbonate solution and extracted twice with
dichloromethane (200 mL). The combined organic extracts were dried
with anhydrous MgSO4. The solvent was removed under reduced
pressure. The residue was purified by column chromatography using
petroleum ether/dichloromethane (20:1) as eluent to provide the white
1
solid (0.84 g, yield: 63.2%). H NMR(400 MHz, CDCl3) δ (ppm):
The UV–Vis absorption and photoluminescence spectra of
the two materials were measured both in dilute THF solutions
and in film fabricated by spin-coating (the procedure was as
follows: the THF solution of the materials is dropped onto a
quartz substrate; then, under vacuum the substrate is rotated
for 20 s at the rate of 1000 rpm.), the corresponding data are
summarised in Table 1. In solution absorption spectra, the
onset absorption edge showed a red shift about 22 nm from
PYT to PYET (Fig. 1). This was due to the increase of conju-
gation length, resulting from a more conjugated pyrenyl-ethy-
nyl group at the C2, 7 and 12 position of the truxene moiety in
PYET. Both absorption spectra showed characteristic peaks
of the truxene group (peaks at around 316 nm, which are due
to a truxene-centred π–π* transition).29 The λmax of PYT was
358 nm, which was redshifted in comparison with truxene
because of the increased conjugation length. For PYET,
the new absorption band at 328 nm can be attributed to the
ethynyl-substituted truxene unit.10 The two peaks in the long
wavelength region at 387 nm and 411 nm could be ascribed to
the ethynyl modified conjugated derivative of truxene.2 Both
absorption spectra in film states exhibited redshifts which
implied the existence of intermolecular π–π aggregation in the
solid state.
8.61 (d, J = 8.4 Hz, 3H), 8.38 (d, J = 9.2 Hz, 3H), 8.33 (d, J = 8.0 Hz,
3H), 8.18–8.25 (m, 9H), 8.15 (d, J = 4.8 Hz, 6H), 8.03–8.12 (m, 6H),
7.81 (s, 3H), 7.73 (d, J = 8.0 Hz, 3H), 3.14–3.21 (m, 6H), 2.23–2.30
(m, 6H), 1.26 (s, 9H), 1.06–1.11 (m, 39H), 0.72–0.75 (m, 18H). 13C
NMR(100 MHz, CDCl3) δ (ppm): 153.9, 145.5, 139.6, 139.2, 138.4,
138.2, 131.6, 131.1, 130.6, 128.7, 128.6, 127.8, 127.5, 127.5, 127.5,
126.1, 125.5, 125.2, 125.2, 125.1, 124.8, 124.8, 124.7, 124.7, 56.0,
37.1, 31.6, 29.7, 22.4, 14.1. MALDI-TOF-MS (m/z): calcd for C111H114
1446. 9, found 1446.5. Anal. Calcd: C, 92.07; H, 7.93. Found: C,
92.03; H, 7.79%.
5,5,10,10,15,15-Hexahexyl-2,7,12-tris(pyren-1-ylethynyl)-10,15-
dihydro-5H-diind-eno[1,2-a:1′,2′-c]fluorene (PYET): Compound
TrHBr (1.00 g, 0.92 mmol), compound 2 (0.84 g, 3.69 mmol), tetrak
is(triphenylphosphine) palladium (0.22 g, 0.19 mmol) and cuprous
iodide (35.0 mg) were added to a 150 mL flask. The flask was degassed
and a N2 atmosphere introduced. Then degassed toluene (45 mL) and
diisopropylamine (45 mL) were injected. The reaction mixture was
stirred at 70 °C for 48 h. After it was cooled to room temperature, the
reaction mixture was quenched with saturated sodium bicarbonate
solution and extracted twice with dichloromethane (200 mL). The
combined organic extracts were dried with anhydrous MgSO4.
The solvent was removed under reduced pressure. The residue was
purified by column chromatography using petroleum ether/dichloro-
methane(15:1) as eluent to provide the yellow-green solid (0.91 g,
1
yield: 65.1%). H NMR(400 MHz, CDCl3) δ (ppm): 8.81 (d, J =
9.2 Hz, 3H), 8.46 (d, J = 8.0 Hz, 3H), 8.42 (d, J = 8.8 Hz, 3H), 8.32–
8.19 (m, 9H), 8.15–8.05 (m, 6H), 7.83–7.81 (m, J = 6.4 Hz, 6H), 7.62
(s, 3H), 7.57 (d, J = 8.4 Hz, 3H), 3.08–3.16 (m, 6H), 2.13–2.21 (m,
6H), 1.24 (s, 9H), 1.04–1.10 (m, 39H), 0.66–0.70 (m, 18H). 13C NMR
(100 MHz, CDCl3) δ (ppm): 153.9, 146.1, 140.5, 138.2, 132.0, 131.4,
131.3, 131.2, 130.2, 129.7, 128.4, 128.2, 127.3, 126.3, 125.7, 125.7,
125.7, 124.7, 124.7, 124.6, 124.5, 121.4, 118.1, 96.1, 89.2, 56.0, 53.5,
37.1, 31.6, 29.6, 24.1, 22.4, 14.0. MALDI-TOF-MS (m/z): calcd.
for C117H114 1518.9, found 1519.60. Anal. Calcd: C, 92.44; H, 7.56.
Found: C, 92.28; H, 7.64%.
For the solution emission spectra in dilute THF solutions,
PYT and PYET behaved differently. PYT had a maximum
emission at 410 nm, while PYET displayed a well-structured
emission band with two characteristic peaks at 421 nm and
441 nm. The difference between them could be ascribed to the
acetylenic bond, which might lead to new energy levels. In the
solid state emission, both the materials are red-shifted about
50 nm and the emission bands are broad and structureless,
Table 1 Photophysical properties of PYT and PYET
Molecules
λabs,max/nm
Solution
λem,max/nm
Solution
∆E/eV (abs. edge/nm)
HOMO/eV
LUMO/eVa
film
film
PYT
PYET
356
411
358
417
410
421,441
462
494
2.93
2.88
–5.74
–5.75
–2.81
–2.87
a LUMO = HOMO–∆E (solution state band gap)

JOURNAL OF CHEMICAL RESEARCH 2013 245
Fig. 2 The oxidation CV curves of PYT (a) and PYET (b).
Fig. 1 Absorption (a) and photoluminescence (b) spectra of
PYET and PYT in solution and film.
properties of the two starburst materials were determined by
DSC in a nitrogen atmosphere at a heating rate of 10 °C min−1,
the glass transition temperature (Tg) of PYT is 124 °C, while
that of PYET is 96 °C (Fig. 3). Although the molecular weight
increased from 1446 (PYT) to 1518 (PYET), three bridge acet-
ylene bonds at the C2, C7 and C12 of the truxene moiety in
PYET result in a lower glass transition temperature (Tg) than
that of PYT. The reason might be that the effect of molecular
weight increasing is insignificant, but the alkynyl group with
two single bonds endows PYET with a more varied configura-
tion, which might be related to steric hindrance. That is, the
steric hindrance between the pyrene groups and the truxene
core in PYET is much smaller than that in PYT. The glass
transition in small molecules is different to that in polymers.
The latter is the beginning motion of chain segment but in
small organic molecules, there is no corresponding chain
segment. Then the glass transition always means the beginning
of the rotation motion of some part of the molecule. As to PYT
and PYET, the beginning of rotation motion might be taking
place at the bonds between truxene and pyrene groups. Because
the steric hindrance in PYET is much smaller than that in PYT,
the energy needed for the activation of molecule rotation
motion of the former is also much smaller than the latter. This
might be the reason that the glass transition temperature of
PYET is much lower than that of PYT. When both materials
were heated again after annealing, no glass transition tempera-
ture was observed [Fig. 3 (c) and (d)]. No melting temperature
(Tm) was found for the two materials upon heating to 200 °C,
revealing that PYT and PYET were amorphous materials.
The DSC examination confirmed that PYT and PYET are
stable amorphous materials. No crystallisation procedure was
observed during the DSC trace. These results demonstrate that
PYT and PYET have good thermal stability even though they
are low molecular weight organic compounds.
which is typical of excimer emission owing to the pyrene and
truxene chromophores.5
The electrochemical behaviour of PYT and PYET was
investigated by cyclic voltammetry (CV) with a standard three
electrode electrochemical cell in 0.1 M tetrabutylammonium
tetrafluoroborate (Bu4NBF4) in dichloromethane at room
temperature under nitrogen with a scanning rate of 200 mV s−1.
A platinum working electrode, a platinum counter electrode
and an Ag/AgNO3 (0.1 M) reference electrode were used. The
oxidation onset potentials were measured to be 0.94 and
0.95V, respectively (Fig. 2). The corresponding HOMO energy
levels were thus estimated to be -5.74 and -5.75 eV,30 indicat-
ing that the HOMOs of the truxene derivatives were not
improved as were expectated. Compared with our previous
work,7 we believe that only the non-conjugated pyrene unit can
obviously improve the hole-injection of these materials.
From the UV–Vis absorption spectra, the onset absorption
of PYT and PYET were measured to be 423 nm and 430 nm,
and the band gaps (∆E) were thus calculated to be 2.93 and
2.88 eV for PYT and PYET, respectively. Then the LUMO
can be estimated to be –2.81 and –2.87 eV, respectively. The
corresponding data are also summarised in Table 1.
Thermal properties
The thermal stability of the two materials in nitrogen was
evaluated by thermogravimetric analysis (TGA). Thermal
decomposition temperatures (5% weight loss temperature, Td)
for PYT and PYET were both over 400 °C. The TGA results
indicate that the materials are thermally stable enough to be
used as organic electronic materials. The phase-transition

246 JOURNAL OF CHEMICAL RESEARCH 2013
Fig. 3 The DSC traces of PYT (a) and PYET (b); the traces of PYT (c) and PYET (d) after annealing.
Conclusion
(211134) and Innovation Project of SCI&Tech for College
Graduates of Jiangsu Province(CXLX11-0420). Chao Tang
and Xu-Dong Liu contributed equally to this work.
In conclusion, we have designed and synthesised two new con-
jugated starburst molecules bearing pyrene moieties as arms
and truxene as a core (PYET and PYT) by Pd(0)-catalysed
cross-coupling reactions. The conjugated star-shaped materi-
als possess good solubility in common organic solvents
and exhibit different absorption and emission behaviour in
solutions and in thin films, which is attributed to the different
conjugated length. The smooth thin film for absorption and PL
spectra could be achieved by an easy spin-coating technique.
The two materials also have good thermal stability. The Td
each of them was over 400 °C, and the Tg of PYET and PYT
were 96 and 124 °C, respectively. The Tg of PYET is lower
than that of PYT. The reasons might be as follows: (1) the
effect of increased molecular weight (from 1446(PYT)
to 1518(PYET)) to Tg could be negligible; (2) compared to
polymers, the glass transition temperature of the small organic
molecules originated from the rotation motion of some part of
the molecule. So the PYET with smaller steric hindrance needs
lower energy to activate the rotation between truxene and
pyrene units. Each of the compounds had analogous HOMOs,
which were not improved by the introduced pyrene units.
These results indicate that the two compounds are candidates
for application in organic electronics.
Received 8 October 2012; accepted 14 February 2013
Paper 1201560 doi: 10.3184/174751913X13639408275103
Published online: 19 April 2013
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This work was financially supported by National Basic
ResearchProgramofChina(973Programno. 2009CB930601),
National Natural Science Foundation of China under Grants
20904023 and 61203213, the Priority Academic Program
Development of Jiangsu Higher Education Institutions, the
Innovation Group of Ministry of Education of China(IRT1148),
Natural Science Foundation for Colleges and Universities in
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