Supramolecular template-directed synthesis of stable and high-efficiency photoluminescence 9,10-diphenylanthryl-bridged ladder polysiloxane

Article abstract of DOI:10.1002/pola.24021

A soluble well-defined 9,10-diphenylanthryl-bridged ladder polysiloxane (DPAnLP) was prepared via supramolecular assembly-directed condensation polymerization of silanols. The ladder superstructure (LS) was obtained via a synergistic interaction of H-bond

Full text of DOI:10.1002/pola.24021

Supramolecular Template-Directed Synthesis of Stable and
High-Efficiency Photoluminescence 9,10-Diphenylanthryl-Bridged
Ladder Polysiloxane
JINTAO ZHANG,1 ZHIZE CHEN,1 WENXIN FU,1 PING XIE,1 ZHIBO LI,1 SHOUKE YAN,2 RONGBEN ZHANG1
1State Key Laboratory of Polymer Physics and Chemistry, Beijing National Laboratory for Molecular Sciences,
Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
2State Key laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing 100029, China
Received 1 February 2010; accepted 9 March 2010
DOI: 10.1002/pola.24021
Published online in Wiley InterScience (www.interscience.wiley.com).
ABSTRACT: A soluble well-defined 9,10-diphenylanthryl-bridged
ladder polysiloxane (DPAnLP) was prepared via supramolecular
assembly-directed condensation polymerization of silanols.
The ladder superstructure (LS) was obtained via a synergistic
interaction of H-bonding and p–p stacking between polymeri-
zable precursor 2-tert-butyl-9,10-bis(methyldihydroxylsilyl)an-
thracene in organic solvent. The resultant LS was then used as
template to direct the condensation of silanol groups to obtain
DPAnLP with high regularity. It was found that DPAnLP can
emit blue light (430 nm) with great stability and high efficiency
in both solution and solid film, which indicated a well organiz-
ing of fluorophore within confined environment (ladder struc-
ture). TGA and DSC measurements showed that DPAnLP had
good thermal stability, and cyclic voltammetry detection gave
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a low-lying highest occupied molecular orbital level.
2010
Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48:
2491–2497, 2010
KEYWORDS: ladder polymer; luminescence; polysiloxanes; self-
assembly; supramolecular structures
INTRODUCTION Conjugated compounds have been attracting
considerable attention arising from their electrooptical prop-
erties and thereof multiple applications in display technique
and other fields.1,2Among them, anthracene and its deriva-
tives have been widely studied because of their interesting
photo- and electroluminescent properties as well as good
electrochemical properties.3–5 To improve their poor film-
forming and processing properties,6 polymeric materials con-
taining anthracene moieties were developed.7–12 However,
random chain aggregation of aromatic subunit easily under-
mines the stability of luminescent properties and thus dete-
riorates materials’ long-term stability and emission efficiency,
which is the biggest problem affecting the performance of
light-emitting diodes (LEDs).13–15 To solve this problem, sev-
eral methods, such as copolymerization or blending of conju-
gated polymers with other materials and grafting of large
sterically hindered groups or oligomer on polymer backbone,
have been developed to tune resultant polymer microstruc-
ture.16–18 Toward this goal, we adopt a different strategy to
incorporate light-emitting unit into polymer backbone while
forming well-defined ladder structure to afford good stability
and solubility in common solvents.
single-chained polysiloxane. In addition, they possess great
adhesion to various substrates and good solubility in com-
mon organic solvents, which can be readily used to prepare
thin film devices. Consequently, their unique structure
promises great opportunities of application in numerous
areas.19–22 In the early 1980s, our group proposed a novel
‘‘supramolecular architecture-directed stepwise coupling/
polymerization’’ (SCP) synthesis strategy, in which the supra-
molecular assemblies from reactive monomer precursors
gave well-defined ladder superstructure (LS) and were used
as templates to direct polymerization.23 Within the LS, the
double-stranded polymer backbones were bridged with
bulky flat molecules, which offer noncovalent interactions to
direct oriented self-assembly. Using this strategy, a series of
regular organo-bridged ladder polysiloxanes have been
successfully synthesized by using different supramolecular
interactions, such as H-bonding, p–p stacking, and donor–
acceptor effect.24–26 We thus consider using a light-emitting
unit as the bridge within ladder polysiloxane to optimize
their properties. Herein, we report the synthesis of blue
light photoluminescence (PL) 9,10-diphenylanthryl-bridged
ladder polysiloxane (DPAnLP) via SCP method (Scheme 1).
Aiming to improve materials stability, emission efficiency,
and solubility, we consider following aspects in polymer
design: (1) selecting the well-known luminophore 9,10-
Because of the unique double-stranded molecular structure,
ladder polysiloxanes are found to have much greater resist-
ance to irradiation, thermal and chemical degradation than a
Correspondence to: Z. Li (E-mail: zbli@iccas.ac.cn) or S. Yan (E-mail: skyan@mail.buct.edu.cn) or R. Zhang (E-mail: zhangrb@iccas.ac.cn)
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Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 48, 2491–2497 (2010) 2010 Wiley Periodicals, Inc.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
by rotary evaporation, and the product was dissolved in
ether (300 mL). The ether solution was washed using cold
DI water (800 mL), and the aqueous solution was further
washed twice with ether (50 mL). The combined organic
fractions were dried over magnesium sulfate, and the vola-
tiles were removed in vacuum to give a foamy residue. To
this residue were added potassium iodide (9.0 g, 54 mmol),
sodium hypophosphite monohydrate (9.0 g, 102 mmol), and
acetic acid (90 mL). Then, the mixture was refluxed for 2 h.
After cooling the solution to room temperature, a white pre-
cipitate was collected, washed with DI water, and dried. A
total of 7.88 g of pure product was obtained by recrystalliza-
tion from THF. Yield, 95%.
1H NMR (CDCl3, 400 MHz, d, ppm): 1.28 (s, 9H, ACH3),
7.33–7.37 (m, 6H, C6H4, H-6 and H-7 of anthracene), 7.47
(dd, 1H, J1 ¼ 9.0 Hz, J2 ¼ 2.0 Hz, H-3 of anthracene), 7.57 (d,
1H, J ¼ 1.4 Hz, H-1 of anthracene), 7.63 (m, 3H, H-4, H-5,
and H-8 of anthracene), 7.73–7.76 (m, 4H, C6H4); MALDI-TOF
MS (m/z) calcd. for C30H24Br2, 544.02; found, 544.1 [M þ
H]þ.
Synthesis of Methyldiethoxylsilyl Chloride
Methyltrichlorosilane (150 mL, 127 mmol) and alcohol (146
mL, 254 mmol) (molar ratio 1:2) were slowly mixed in pe-
troleum ether 30–60 (120 mL) at its boiling point. The mix-
ture was then distilled to give a colorless liquid product
ꢁ
(127–128 C) with 63% yield (135 g).
1H NMR (CDCl3, 400 MHz, d, ppm) 0.45 (s, 3H, SiACH3),
1.25 (t, 6H, J ¼ 7.3 Hz, ACH2CH3), 3.87 (q, 4H, J ¼ 7.2 Hz,
AOCH2CH3); 29Si NMR (59.6 MHz, d, ppm) ꢀ29.32.
SCHEME 1 Synthetic route for DPAnLP.
diphenylanthracene as ladder bridge to prevent undesired
aggregation, (2) incorporating a tert-butyl group to minimize
random aggregation of planar anthracene units and improve
the material solubility,27 and (3) expecting that the ladder
polysiloxane backbone will provide materials good thermal
stability and film-forming capability as well as adhesive abil-
ity to various substrates, which are advantageous for the fab-
rication of optoelectronic devices with high performance.
Synthesis of 2-tert-Butyl-9,10-
bis(methyldiethoxylsilyl)anthracene (M1)
Compound 1 (2.72 g, 5 mmol) was dissolved in THF (150
mL) followed by dropwise addition of n-butyllithium (6.9
ꢁ
mL, 1.6 M in hexane) at ꢀ78 C. The reaction was stirred for
about 8 h before methyldiethoxylsilyl chloride (3 mL, 12
mmol) was added. The mixture was then slowly warmed up
to room temperature. After about 5 h, THF and unreacted
methyldiethoxylsilyl chloride were removed by vacuum dis-
tillation. The obtained solid was treated with dichlorome-
thane (300 mL)/water (50 mL) system, and the organic
phase was dried over sodium sulfate. The concentrated solu-
tion (5 mL) was isolated by chromatography on silica gel
columns (CH2Cl2/petroleum ether ¼ 1/1 and ethyl acetate/
petroleum ether ¼ 1/40). After removing eluents, 1.46 g of
light yellow powder was obtained. Yield, 45%; Rf ¼ 0.5
(ethyl acetate/petroleum ether ¼ 1/9).
EXPERIMENTAL
Materials
Dibromobenzene, 2-tert-butylanthraquinone, potassium iodide,
sodium hypophosphite monohydrate, methyltrichlorosilane,
and n-butyllithium (1.6 M in hexane) were purchased from
Alfa Aesar and used as received. Tetrahydrofuran (THF) and
dioxane were distilled over sodium benzophenone complex.
Synthesis of 2-tert-Butyl-9,10-bis(4-
bromophenyl)anthracene (1)
1H NMR (CDCl3, 400 MHz, d, ppm): 0.51 (s, 6H, SiACH3),
1.25 (s, 9H, A(CH3)3), 1.30–1.36 (t, 12H, J ¼ 7.3 Hz,
AOCH2CH3), 3.95 (q, 8H, J ¼ 7.2 Hz, AOCH2 CH3), 7.29–7.31
(m, 2H, H-6 and H-7 of anthracene), 7.42 (dd, 1H, J1 ¼ 8.2
Hz, J2 ¼ 1.8 Hz, H-3 of anthracene), 7.49–7.52 (m, 4H, C6H4),
7.54 (d, 1H, J ¼ 1.2 Hz, H-1 of anthracene), 7.62 (m, 3H, H-4,
H-5, and H-8 of anthracene), 7.85–7.89 (m, 4H, C6H4); 29Si
NMR (59.6 MHz, d, ppm) ꢀ17.40; MALDI-TOF MS (m/z)
calcd. for C40H50O4Si2, 650.32; found, 650.2 Mþ.
1,4-Dibromobenzene (7.08 g, 30 mmol) was dissolved in an-
hydrous THF (300 mL) followed by slow addition of n-butyl-
lithium (18.75 mL, 1.6 M in hexane) under stirring at
ꢀ78 ꢁC. To the suspension, 2-tert-butylanthraquinone (3.84
g, 15 mmol) dissolved in THF (60 mL) was added dropwise
at ꢀ78 ꢁC. The mixture was then stirred for 3 h and then
slowly warmed up to room temperature. THF was removed
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Synthesis of 2-tert-Butyl-9,10-
bis(methyldihydroxylsilyl)anthracene (M2)
Star-822 differential scanning calorimeter at a scanning rate
of 610 ꢁC/min under nitrogen atmosphere. Thermogravi-
metric analyses (TGA) was performed using a 7 Series ther-
mal analysis system (Perkin-Elmer). The sample was heated
from 40 to 600 ꢁC at a rate of 10 ꢁC/min under nitrogen
purge (70 mL/min). Cyclic voltammetry was recorded on
CHI660B voltammetric analyzer (CH Instruments) with a
standard three-electrode electrochemical cell in a 0.1 M tet-
rabutylammonium tetrafluoroborate solution in CH2Cl2 at
room temperature under nitrogen with a scanning rate of
0.1 V/s. A glassy carbon working electrode, a Pt wire coun-
ter electrode, and an Ag/AgCl reference electrode were used.
The experiments were calibrated with the internal standard
ferrocene/ferrocenium (Fc) redox system assuming that the
energy level of Fc is 4.8 eV under vacuum.
To a solution of M1 (2.6 g, 4 mmol) in THF (300 mL), water
(4 mL) and two drops of 0.5 M HCl were added with stirring
at 0 ꢁC. After 12 h, ether (80 mL) and water (80 mL) were
added. The ether layer was separated and washed with
water (25 mL) three times. The solution was then dried over
sodium sulfate and filtered. The filtrate was condensed to
ꢂ20 mL and precipitated using hexane (50 mL) followed by
filtration to give a cake-like product. The product was dried
under vacuum at room temperature, and 1.92 g of white
powder was obtained. Yield, 89.2%.
1H NMR (acetone-d6, 400 MHz, d, ppm) 0.41 (s, 6H, SiACH3),
1.26 (s, 9H, A(CH3)3), 5.64 (s, 4H, AOH), 7.09 (dd, 1H, J1
8.8 Hz, J2 ¼ 2.0 Hz, H-3 of anthracene), 7.25–7.50 (m, 5H,
C6H4, H-1 of anthracene), 7.60–7.66 (m, 5H, H-4, H-5, H-6, H-
7, and H-8 of anthracene), 7.95–7.98 (m, 4H, C6H4); 29Si
NMR (59.6 MHz, d, ppm) ꢀ19.55; MALDI-TOF MS (m/z)
calcd. for C32H34O4Si2, 538.2; found, 538.3 [M þ H]þ.
¼
RESULTS AND DISCUSSION
Synthesis and Characterization of Monomers and
DPAnLP
Compound 1 was synthesized referring to literature proce-
dure.27 M1 was prepared through lithium-halogen exchange
followed by treatment with methyldiethoxylsilyl chloride
from 1. To minimize possible side reactions, we used anhy-
drous THF and kept reaction temperature at ꢀ78 ꢁC. The
reaction was monitored using thin layer chromatography.
Purified target product was obtained after column chroma-
tography with yield of 45%. M2 was synthesized through
hydrolysis of M1. In this reaction, dilute M1 solution
(ꢂ0.013 M in THF), diluted acid (0.5 M HCl) as catalyst, and
Preparation of DPAnLP
M2 (1.08 g, 2 mmol) was dissolved in THF/dioxane (50 mL,
v/v ¼ 1:1). Then, two drops of concentrated H2SO4 were
added to the mixture to catalyze the condensation reaction.
The reaction medium was stirred at 40 ꢁC for 96 h. To end
cap the terminal silanol group of the polymer, pyridine (0.64
g, 8 mmol) and trimethylchlorosilane (0.88 g, 8 mmol) dis-
solved in THF/dioxane (10 mL, v/v ¼ 1/1) were added
dropwise into the flask under stirring. The mixture was
stirred at room temperature for another 24 h. Filtration was
applied to remove the small amount of gel generated during
the condensation process. Adding water (10 mL) to the fil-
trate caused instantaneous precipitation of a white solid,
which was dried in a vacuum oven at 40 ꢁC for 24 h to
obtain the desired polymer (DPAnLP) with 86% yield
(0.87 g).
ꢁ
low temperature (0 C) were used to suppress the undesired
condensation between the formed silanols. HCl was removed
via water wash from ether solution, and white product was
precipitated from hexane. Note that M2 needed to be stored
in an environment free of base or acid for following use
because of highly reactive silanols (Scheme 1).
M2 was found to be able to spontaneously assemble into LS
via presumably synergistic interactions of silanols’ square-
planar H-bonding28 and 9,10-diphenylanthryl bridges’ p–p
stacking (Scheme 1). The noncovalent LS was then used to
direct condensation polymerization of reactive silanol groups
to form target DPAnLP. As the weak noncovalent interactions
are extremely susceptible to external conditions, for example,
temperature, the electrodonating ability of medium, and the
polarity of medium, extreme precautions were taken to avoid
breaking LS during the polymerization and thus ensure the
formation of high-ordered DPAnLP instead of branched or
crosslinking products. After trying several selective solvent
systems and reaction conditions, we found that the polymer-
ization performed in THF/dioxane (v/v ¼ 1/1) mixture
FTIR (KBr, thin film, cmꢀ1): 1600 (phenyl), 1259 (SiACH3),
1010–1100 (SiAOASi). 1H NMR (CDCl3, 400 MHz, d, ppm):
0.85–0.96 (br s, 3H, SiACH3), 1.27 (br s, 9H, A(CH3)3), 6.47–
6.58, 7.06–7.10, and 7.28–7.91 (br m, 15H, phenyl-H); 29Si
NMR (59.6 MHz, d, ppm): ꢀ22.31.
Characterization
Gel permeation chromatography (GPC) was performed on a
Waters 150-C GPC equippꢁed with Ultrastyragel columns
(HT2, HT3, and HT4) at 35 C. THF was used as eluent, and
polystyrene standards were used as calibrations. The FTIR
measurement was performed with a Perkin-Elmer80 spec-
trometer, and the samples were prepared using solvent cast-
ing on KBr flake. UV–vis spectra were obtained on a Shi-
madzu UV–vis spectrometer model UV-1601PC. Fluorescence
spectra were recorded on a Hitachi F-4500. NMR spectra
were obtained on a Bruker Avance DPS-400 (400 MHz) spec-
trometer. MALDI-TOF mass spectrometric measurements
were performed on a Bruker Biflex MALDI-TOF mass spec-
trometer. X-ray diffraction (XRD) analysis was recorded on a
Rigaku D/MAX 2400 diffractometer. Differential scanning cal-
orimetry (DSC) was measured by using a Mettler Toledo
ꢁ
below 50 C gave the best results. We supposed that the rea-
sons were possibly due to the characteristics of THF/dioxane
mixture, which has low polarity and low electrodonating
ability. In particular, Williams used to point out that the
acidic environment is favorable to the formation of H-bond-
ing between the silanols.29 In addition, acidic catalyst usually
has stronger condensing ability than basic ones for silanols
with electrodonating groups.29 Therefore, concentrated
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
FIGURE 2 1H NMR spectra of M1, M2, and DPAnLP.
FIGURE 1 FTIR spectra of M1, M2, and DPAnLP.
group change during the process of hydrolysis and
condensation.
sulfuric acid was chosen as the condensation catalyst. Com-
pletion of polymerization was determined by FTIR. To stabi-
lize DPAnLP, Me3SiCl was used to end cap SiAOH end
groups at the end of polymerization. The separated yield
was about 86%. Solubility test found that DPAnLP was read-
ily soluble in CH2Cl2, THF, acetone, and so forth. The weight-
average molecular weight (Mw) of DPAnLP was determined
to be 57.9 kDa with PDI ¼ 1.46 by GPC in THF with polysty-
rene as standards.
Confirmation of the Ladder Structure of LS and DPAnLP
As the LS is not only the precursor but also the template of
polymerization to form ladder polymers in SCP strategy, for-
mation of defect-free and stable LS would be a key point of
preparing ladder polymers with high regularity. Freeze-dry-
ing was used to prepare solid samples provided that fast
cool could presumably maintain the nanostructure of LS.
XRD was then applied to characterize ordering of LS.21 As
shown in Figure 4, the XRD profile of freeze-dried LS sample
from THF/dioxane solution (v/v ¼ 1/1, 10 mg/mL) shows
two characteristic peaks with 2h around 7.68ꢁ (1.15 nm)
and 11.50ꢁ (0.77 nm) corresponding to ladder width and
ladder thickness, respectively. Moreover, 29Si NMR spectrum
of LS in Figure 3 shows a distinct resonance (d ¼ ꢀ19.55
The progress of hydrolysis and condensation process could
1
be well monitored by FTIR, H NMR, and 29Si NMR. For FTIR
spectra (Fig. 1), the peak around 1600 cmꢀ1 is attributed to
phenyl group, whereas the peaks around 2960 and 1260
cmꢀ1 are ascribed to SiACH3 group. Moreover, M1 shows
strong peaks at 1165, 1078, and 1022 cmꢀ1, which is attrib-
uted to asymmetric SiAOAC stretch for the ethoxy group,
and symmetric SiAOAC stretch falls at 796 cmꢀ1. For M2,
these peaks from ethoxy group disappear, and characteristic
peaks of hydroxyl group emerge, indicating the complete hy-
drolysis of M1. The large absorption band at 3293 cmꢀ1 cor-
responds to hydrogen-bonded silanols, and the peak around
853 cmꢀ1 is originated from the SiAO stretching vibration of
SiAOHs group. For the FTIR spectrum of DPAnLP, the char-
acterizing absorptions of SiAOH group disappear, and two
strong peaks in the region of 1000–1100 cmꢀ1 show up,
which corresponds to asymmetric SiAOASi stretching vibra-
tion. For 1H NMR characterization (Fig. 2), when M1 is
hydrolyzed to M2, resonances of hydrogens in SiAOCH2CH3
[d 3.95 (m, 8H) and 1.30–1.36 (t, 12H) ppm] disappear, and
protons of SiAOH [d 5.64 (s, 4H) ppm] show up. Completion
of polymerization is confirmed from the disappearance of
SiAOH protons, suggesting formation of DPAnLP. Also, chem-
ical shift variation in 29Si NMR spectra among M1 (d ¼
ꢀ17.40 ppm), M2 (d ¼ ꢀ19.55 ppm), and DPAnLP (d ¼
ꢀ22.31 ppm) shown in Figure 3 also supports the functional
FIGURE 3 29Si NMR spectra of M1, M2 (in the form of ladder
superstructure), and DPAnLP.
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ARTICLE
and molecular weight. As a result, the ladder width of LS
may vary slightly depending on sample’s histories. Such
effects were observed before.30 Here, a less electron-donat-
ing solvent and freeze-drying method were combined to pre-
pare XRD samples, which might lead to relative smaller lad-
der width of LS compared with corresponding DPAnLP.
However, the exact mechanism was not clear given available
data. As for ladder thickness, molecular simulation image of
DPAnLP gives about 0.75 nm of an alternating structure,
which is supposed to result from the steric repulsion
between t-butyl groups. In addition, the diffusing peak in the
region of 2h ꢃ 20ꢁ–25ꢁ (d ꢃ 0.44–0.35 nm) is assigned to
the p–p interaction distance between adjacent 9,10-dipheny-
lanthryl. The intensity of this peak is increased for DPAnLP
when compared with LS, which may be ascribed to the
stronger p–p interactions within covalent-linked DPAnLP
than those within supramolecular LS. Similarly, the XRD
result, as well as the signal peak at d ¼ ꢀ22.31 ppm with D
< 1 ppm, fully verifies the high regular ladder structure of
DPAnLP. Apparently, the regular ladder structure maintained
after silanol condensation. We suppose that the DPAnLP
would have much better stability compared to its LS precur-
sor as the double covalent linkage between 9,10-diphenyl-
anthryl will increase its stability and intramolecular
ordering.
Optical Properties of DPAnLP
Because of good solubility in organic solvents, DPAnLP can
be easily fabricated to films by casting, spin-coating, and dip-
ping techniques. Based on this, the UV–vis absorption and PL
properties of DPAnLP were investigated both in THF solu-
tion and thin film (Fig. 5). Transparent and uniform polymer
films were prepared on quartz by spin-casting from THF so-
lution at room temperature. The kmax values are in the range
of 260–460 nm. Absorption band between 350 and 400 nm
with characteristic vibronic pattern can be attributed to the
p!p* transition of anthracene.31 DPAnLP exhibits an emis-
sion band around 430 nm with kex ¼ 374 nm. Note that
there is only less than 2 nm red shift for UV–vis and PL
spectra when the sample was varied from solution to film,
suggesting no aggregation of chromophore during film prep-
aration. We suppose that the negligible variation of spectra
between solution and film was due to confinement of 9,10-
diphenylanthryl moieties within individual double-stranded
ladder structure. Postsolution processing did not induce sub-
stantial change of local rearrangement of 9,10-diphenyl-
anthryl units, which as return offered good film-forming
property. The fluorescence quantum efficient yield (UF) of
DPAnLP in THF is found to be 0.89 using 9,10-diphenylan-
thracene as a reference standard (cyclohexane solution, UF ¼
0.9).32 This value is notably higher than the reported values
for some anthracene-containing compounds, such as 0.47
of 2-tert-butyl-9,10-bis[4-(iminostilbenyl)phenyl]anthracene27
and 0.44 of 9-phenyl-10-(4-triphenylamine)anthracene.33 As
expected, DPAnLP has good emission stability at high temper-
ature because intramolecular aggregation of chromophores is
effectively prevented by the rigid ladder structure, and inter-
molecular aggregation of chromophores is disfavored by the
FIGURE 4 (a) XRD profiles of LS (namely the assembly of M2)
and DPAnLP; (b) molecular-simulated DPAnLP with five repeat
units (by Materials Studio).
ppm) with a half-height width (D) of less than 1 ppm, indi-
cating that all Si-atoms in LS are in the almost identical
chemical environment. It is known that the narrower the res-
onance peak of the silicon atoms, the higher the regularity.23
These results support our assumption that LS primarily con-
sists of regular ladder structure, instead of randomly inter-
laced or branched structures.
The ladder structure of DPAnLP was also verified from XRD
characterization. The XRD profile of DPAnLP film (ca. 15
lm) on glass slide cast from its THF solution (10 mg/mL)
shows two peaks at 2y around 6.06ꢁ (1.46 nm) and 11.70ꢁ
(0.76 nm), respectively, (Fig. 4). According to previous
report,16 the former represents the intramolecular chain-to-
chain distance (i.e., the width of the ladder) of the polymer,
and the latter is the thickness of the macromolecular chain.
This result is consistent with the predicted values (1.48 and
0.75 nm) on the basis of molecular simulation calculation
(by Materials Studio). Note that the ladder width of DPAnLP
(1.46 nm) is larger than that of LS (1.15 nm). It is known
that LS is noncovalent supramolecular aggregates, and its
dimension is subject to variation of numerous environmental
factors, for example, solvents, sample preparation procedure,
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FIGURE 6 The cyclic voltammograms of DPAnLP at a scan rate
of 0.1 V/s.
fore, compared to 5.70 eV of 9-phenyl-10-(4-triphenylami-
ne)anthracene,33 the lower IP value, namely the lower HOMO
level, means higher hole-injection ability.
Thermal Property of DPAnLP
We also investigated thermal stabilities of DPAnLP using
TGA and DSC (Fig. 7). DPAnLP begins to decompose at
318.6 ꢁC and losses about 50% of its weight at 407.4 ꢁC.
DSC measurement shows only a glass transition temperature
FIGURE 5 (a) Absorption and photoluminescence emission
spectra of DPAnLP in THF solution and thin film; (b) emission
intensity of the spin-coated DPAnLP film before and after
annealing at 200 ꢁC for 2 h (kex ¼ 374 nm).
repulsion of bulky tert-butyl groups. PL spectra ꢁof DPAnLP
show little variation after heating the film at 200 C in air for
2 h (Fig. 5). This result demonstrates that DPAnLP is free of
low energy defects (e.g., caused by crystallization) and has
great thermal and color stability.
Electrochemistry of DPAnLP
Electrochemical behaviors of DPAnLP were investigated
using cyclic voltammetry (Fig. 6). Onset of oxidation wave
determined with ferrocene as internal reference is 0.85 V.
Ionization potential (IP) is thus estimated to be 5.65 eV
according to the Halmiton Equation: IP (eV) ¼ Eooxnset þ 4.8.34
In addition, band gap (Egap) estimated from UV absorption
spectra is about 2.92 eV, and then electron affinity (EA) is
calculated to be 2.73 eV according to EA ¼ IP ꢀ Egap. It is
known that the oxidation process and IP value are closely
correlated with the removal of electrons (hole-injection)
from the highest occupied molecular orbital (HOMO). There-
FIGURE 7 (a) TGA curve and (b) DSC trace of DPAnLP.
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ARTICLE
(Tg) around 152.0 ꢁC, however, without any melting peaks.
The Tg is surprisingly higher than those of anthracene-con-
taining small molecules, for example, 104 C of 9-phenyl-10-
11 Wild, A.; Egbe, A. M. D.; Birckner, E.; Cimrova´, V.; Baumann,
R.; Grummt, U.; Schubert, S. U. J Polym Sci Part A: Polym
Chem 2009, 47, 2243–2261.
ꢁ
(4-triphenylamine)-anthracene.33 We suppose the increase of
Tg was due to the introduction of regular ladder polysiloxane
chain. For DPAnLP, its high Tg is probably an underlying rea-
son for its great thermal and color stability, which opens a
promising synthetic strategy in polymer chemistry to make
stable and efficient luminescence polymer materials.
12 Mo, Y.; Deng, X.; Jiang, X.; Cui, Q. J Polym Sci Part A:
Polym Chem 2009, 47, 3286–3295.
13 Burn, P. L.; Lo, S. C. I.; Samuel, D. W. Adv Mater 2007, 19,
1675–1688.
14 Wu, W. C.; Yeh, H. C.; Chan, L. H.; Chen, C. T. Adv Mater
2002, 14, 1072–1075.
15 Amrutha, S. R.; Jayakannan, M. Macromolecules 2007, 40,
CONCLUSIONS
2380–2391.
In summary, a blue light PL DPAnLP was synthesized using
the SCP method. Its high regularity was well characterized
using XRD and 29Si NMR. Compared with common anthra-
cene-containing compounds, the ladder structure and the
tert-butyl group effectively prevent the undesired aggrega-
tion of chromophores and offer a higher UF of 0.89. The
unique ladder polysiloxane structure offers DPAnLP better
film-forming ability, thermal stability, and emission stability.
Electrochemistry measurement shows a low-lying HOMO
level. Moreover, our versatile synthetic strategy offers an op-
portunity to prepare various PL polymeric materials and
may lead to preparation of electroluminescence polymeric
materials after slight modification.
16 Qiu, S.; Lu, P.; Liu, X.; Shen, F. Z.; Liu, L. L.; Ma, Y. G.;
Shen, J. C. Macromolecules 2003, 36, 9823–9829.
17 Mikroyannidis, J. A.; Fenenko, L.; Yahiro, M.; Adachi, C.
J Polym Sci Part A: Polym Chem 2007, 45, 4661–4670.
18 Zhu, B.; Han, Y.; Sun, M. H.; Bo, Z. S. Macromolecules 2007,
40, 4494–4500.
19 Gu, H. W.; Xie, P. D.; Shen, Y.; Fu, P. F.; Zhang, J. M.; Shen,
Z. R.; Tang, Y. X.; Cui, L. B.; Kong, X.; Wei, F.; Wu, Q.; Bai, F.
L.; Zhang, R. B. Adv Mater 2003, 15, 1355–1358.
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Zhang, R. B.; Fu, P. F. J Mater Chem 2002, 12, 2325–2330.
21 Brown, J. F.; Vogt, L. H.; Katchman, A.; Eustance, J. W.;
Financial support was received from the Outstanding Youth
Fund (No. 20425414) and the NSFC (Nos. 50073028,
29974036, 20174047, 50521302) as well as MOST under grant
No. 2007CB935902 and 2007CB935904.
Kiser, K. M.; Krantz, K. W.
6194–6195.
J Am Chem Soc 1960, 82,
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