Noncrystalline blue-emitting 9,10-diphenylanthracene end-capped with triphenylamine-substituted fluorene

Article abstract of DOI:10.1016/j.jphotochem.2011.11.003

Two blue-emitting oligomers, namely FDPA1 and FDPA2 containing 9,10-diphenylanthracene core end-capped with triphenylamine-substituted fluorene has been synthesized and characterized. The spiro-configuration end-capping groups imparts two compounds with p

Full text of DOI:10.1016/j.jphotochem.2011.11.003

Journal of Photochemistry and Photobiology A: Chemistry 227 (2012) 59–64
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Journal of Photochemistry and Photobiology A:
Chemistry
journal homepage: www.elsevier.com/locate/jphotochem
Noncrystalline blue-emitting 9,10-diphenylanthracene end-capped with
triphenylamine-substituted fluorene
Yujian Zhanga, Yanxian Jinb, Ru Baic, Zhenwei Yua, Bin Hua, Mi Ouyanga,∗, Jingwei Suna, Chunhui Yua,
Junlei Liua, Cheng Zhanga,∗
a State Key Laboratory Breeding Base of Green Chemistry-Synthesis Technology, College of Chemical Engineering and Materials Science, Zhejiang University of Technology, Chaowang
Road 18#, Hangzhou, PR China
b School of Pharmaceutical and Chemical Engineering, Taizhou University, Linhai, PR China
c School of Electronic Information, Hangzhou Dianzi University, Hangzhou, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Two blue-emitting oligomers, namely FDPA1 and FDPA2 containing 9,10-diphenylanthracene core end-
capped with triphenylamine-substituted fluorene has been synthesized and characterized. The spiro-
configuration end-capping groups imparts two compounds with pronounced morphological stability
(Tg > 185 ◦C, Td > 420 ◦C) and excellent hole injection ability (EHOMO > −5.27 eV) with the advantageous
optical characteristics of corresponding core. Scanning electron microscope (SEM) and X-ray diffraction
(XRD) reveal that the two oligomers form excellent amorphous films and possess good morphological
stability after annealing.
Received 21 June 2011
Received in revised form
28 September 2011
Accepted 11 November 2011
Available online 20 November 2011
Keywords:
9,10-Diphenylanthracene
Hole-injection
© 2011 Elsevier B.V. All rights reserved.
Blue-emitting material
Thermal stability
1. Introduction
Excellent electrochemical stability and photoluminescence (PL)
make anthracene derivatives attract the intensive attention and
Organic light-emitting devices (OLEDs) based on small
molecules have attracted great attention in the past decades, due
to their potential applications in flat-panel displays and solid state
lighting resources [1–3]. Among the three primary-color emitters in
OLEDs, blue-light emitting materials are of particular importance,
which cannot only be used as a blue light source [4,5] but also as a
host materials to generate colors else by downhill energy transfer
to a suitable emissive dopant [6,7]. Unfortunately, the intrinsically
wide band-gap of blue materials makes it difficult to inject carriers
(holes or electrons) into emitters. As a result, the performance of
blue OLEDs remains relatively poor in comparison with that of red
and green OLEDs [8,9]. Additionally, the durability, which strongly
depends on the thermal and morphological stability of materials,
is another key factor for the device operation efficiency and life-
time [10]. Whereas, amorphous materials, thanks to their high glass
transition temperature (Tg), are receiving special attention due to
the effectively suppression of the crystallization for the film.
have been developed as an attractive building block and starting
material in OLEDs [11–15]. Among them, 9,10-diphenylanthracene
(DPA) is one of the most representative blue fluorescent mate-
rials for its excellently fluorescent properties both in solution
and in the solid state [16–18]. However, an obvious deficiency
of tendency to crystallize in thin film limit the further appli-
cation of the DPA in blue OLEDs due to its crystal formation
resulting in rough surface, grain boundaries or pin holes that
eventually lead to device failure [19–21]. To date, various strate-
gies have been developed to suppress the formation of crystal,
such as the introduction of sterically hindered t-butyl groups
[22,27], bulky substituents [21,24,25] and spiro-annulated struc-
tures [26]. Nevertheless, there are few reports on DPA derivatives
end-capped with nonplanar molecular structures, which directly
avoid their close packing and crystallization. Another intractable
issue is the high ionization potential of anthracene-based com-
pounds [23,27,28], which produces a relatively large hole-injection
barrier from indium tin oxide (ITO) (−4.8 eV). To overcome the
problem, hole-injection/transporting triarylamines were incorpo-
rated into the C2, C6 or C9, C10-positions of anthracene [28–32].
Unfortunately, such direct substitution of electron-donor groups
decreases energy gap significantly due to extended conjuga-
tion lengths, which ultimately results in unwanted red-shift of
∗
Corresponding authors. Tel.: +86 571 88320027; fax: +86 571 88320027.
E-mail addresses: ouyang@zjut.edu.cn (M. Ouyang), czhang@zjut.edu.cn
(C. Zhang).
1010-6030/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jphotochem.2011.11.003

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Y. Zhang et al. / Journal of Photochemistry and Photobiology A: Chemistry 227 (2012) 59–64
emission peak. Thus, the development of new approaches that
can lead to stabilization of amorphous state and excellent hole-
injection/transportation ability is particularly critical for obtaining
highly efficient blue-emitting anthracene-based materials without
the decrease of optical performance.
142.7, 136.9, 134.8, 131.1, 131.0, 129.1, 129.0, 128.8, 128.7, 120.7,
35.6, 33.6, 22.6, 14.1. MS(EI): m/e 600.1(M+).
2.2.2. 4-(9-(4-Bromophenyl)-fluoren-9-yl)-N,N-di-p-tolylaniline
(4)
In this contribution, the synthesis and physical and chemical
properties of two thermally stable materials FDPA1and FDPA2
(Scheme 1), containing DPA as main core unit, are reported.
End-capping triphenylamine (TPA)-substituted fluorene (TPAF) is
incorporated into DPA unit to retain the large band gap of the orig-
inal DPA core. In addition, end-capping fluorene and TPA moieties
are connected through the sp3-hybridized carbon atom, which may
not only hinder close packing and crystallization but also result
in pronounced morphological stability of amorphous materials.
Meanwhile, the hole-injection/transportation ability of molecules
is efficiently improved.
A solution of CF3SO3H (1.84 mL, 20 mmol) in appropriate
1,4-dioxane (20 mL) was added drop wise to a mixture solu-
tion of 3 (3.4 g, 10 mL) [33] and N,N-Bis(4-methylphenyl)aniline
(2.7 g, 10 mmol) in 1,4-dioxane (80 mL). The reaction mixture
was stirred at 80 ◦C under nitrogen until starting material was
no longer detectable by TLC (8 h). The mixture was poured into
saturated NaHCO3 solution and extracted with CHCl3. After the
crude product was further purified by column chromatogra-
phy (EtOAc/hexane = 1/20) to give the desired product 4 (4.6 g,
77.8%).
1H NMR (500 MHz, CDCl3) ı 7.78 (d, J = 7.5 Hz, 2H), 7.42–7.33
(m, 6H), 7.32–7.26 (m, 2H), 7.11 (d, J = 8.5 Hz, 2H), 7.05 (d, J = 8.5 Hz,
4H), 6.99 (dd, J = 10.5 Hz, 6H), 6.87 (d, J = 8.5 Hz, 2H), 2.31 (s, 6H);
13C NMR (CDCl3 500 MHz) ı 151.0, 146.9, 145.4, 145.1, 140.0, 137.6,
132.5, 131.2, 129.9, 129.8, 128.6, 127.7, 127.6, 126.0, 124.7, 121.8,
120.6, 120.2, 64.5, 20.8; MS(EI): m/e 591.2(M+).
2. Experimental
2.1. Chemicals and instruments
9-(4-Bromophenyl)-fluoren-9-ol
[33]
and
2,6-
2.2.3.
dibromoanthracene-9,10-dione [28] were synthesized as reported
previously. All chemical reagents were used as received from
commercial sources without further purification. And the solvents
used in the reaction were purified following routine procedures.
1H and 13C NMR spectra were recorded on Bruker Avance III
500-MHz spectrometer using the chloroform-d as the solvent.
High-resolution mass spectrometric measurements were carried
out on a Brüker autoflex MALDI-TOF-MS spectrometer. Elemental
analyses were performed using the Thermo-Finnigan Flash EA-
1112 (CE, Italy) instrument. UV–vis spectra were measured using a
Shimadzu UV-1800 spectrophotometer. PL spectra were obtained
using a Perkin-Elmer LS-55 luminescence spectrophotometer.
Thermal analysis was performed on a Diamond TG/DTA 6300
(PerkinElmer, USA) in the temperature range of 100–800 ◦C. The
differential scanning calorimetry (DSC) analysis was performed on
a TA Instruments DSC2920. A CHI 660C electrochemical analyzer
was applied to conduct the electrochemical measurements. X-ray
diffraction (XRD) measurements of thin films were performed on
X’Pert Pro diffractometer.
4-Methyl-N-(4-(9-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-
yl)phenyl)-fluoren-9-yl)phenyl)-N-(p-tolyl)aniline
(5)
4
(3 g, 5 mmol), 4,4,4ꢀ,4ꢀ,5,5,5ꢀ,5ꢀ-octamethyl-2,2ꢀ-bis(1,3,2-
dioxaborolane) (1.3 g, 5.2 mmol), KOAc (1.4 g, 14.2 mmol), and
Pd(dppf)Cl2 (30 mg) were mixed in anhydrous DMSO (25 mL). Then,
the mixture was degased by purging with N2. The solution was
heated at 80 ◦C for 24 h under N2. After the reaction mixture cooled,
the solvent was evaporated and the product was extracted with
chloroform. The organic extracts were washed with brine, and then
dried over MgSO4. After, the solvent was evaporated. Finally, the
crude product was purified through columnchromatography (hex-
ane/EtOAc, 12:1) to give 5 (1.4 g, 45%).
1H NMR (500 MHz, CDCl3) ı 7.77 (d, J = 7.5 Hz, 2H), 7.69 (d,
J = 8.0 Hz, 2H), 7.41 (d, J = 7.5 Hz, 2H), 7.39–7.23 (m, 6H), 7.04
(d, J = 8.5 Hz, 4H), 6.99 (dd, J = 15 Hz, 6H), 6.85 (d, J = 8.5 Hz, 2H),
2.30 (s, 6H), 1.32 (s, 12H); 13C NMR (CDCl3 500 MHz) ı 151.2,
149.5, 146.7, 145.2, 140.1, 138.3, 134.7, 132.4, 129.8, 128.7, 127.5,
127.4, 126.2, 124.6, 121.9,120.1, 83.7, 65.2, 24.8, 20.8; MS(EI): m/e
639.2(M+).
2.2. Synthesis
2.2.4. General procedure for the synthesis of compounds FDPA1,
2.2.1. 2,6-Dibromo-9,10-bis(4-butylphenyl)anthracene (BrDPA)
[31]
FDPA2
A
mixture of anthracene-based core (1 mmol), 5 (1.4 g,
The 1-bromo-4-butylbenzene (2.12 g, 10 mmol) dissolved in
diethyl ether (100 mL) was mixed with 6.25 mL of n-butyllithium
(1.6 M in hexane) in diethyl ether (100 mL) at −78 ◦C. To the suspen-
sion, 2,6-dibromoanthraquinone (1.8 g, 5.0 mmol) in diethyl ether
(20 mL) was added dropwise at −78 ◦C. After stirring for 1 h at the
room temperature, the mixture was poured into an aqueous HCl
solution (2 M) and the organic phase separated. The water phase
was extracted with ether (3 × 50 mL). The combined organic frac-
tions were dried over magnesium sulfate and the diethyl ether
was removed to get residue. And then, to this residue were added
potassium iodide (3.0 g, 18 mmol), Na2H2PO2 (3.0 g, 34 mmol), and
acetic acid (30 mL), and the mixture was heated under reflux for 3 h.
The precipitated product in the reaction vessel was filtered with a
glass filter and washed with water to give compound BrDPA (0.92 g,
30.7%).
2.2 mmol), Pd(PPh3)4 (0.3 g, 0.27 mmol), Na2CO3 (2.0 M, 3.0 mL),
and toluene (50 mL)/THF (30 mL) was stirred at 90 ◦C for 48 h under
the atmosphere of nitrogen. After the mixture cooled, 200 mL of
CHCl3 was added to the reaction mixture. The organic portion was
separated and washed with brine before dried over anhydrous
MgSO4. The solvent was evaporated off, and the solid residues
were purified by column chromatography to afford the desired
product.
FDPA1 (0.73, 60.8%); 1H NMR (500 MHz, CDCl3) ı 7.84 (d,
J = 7.5 Hz, 4H), 7.66 (dd, J = 6.5 Hz, 4H), 7.61 (d, J = 7.5 Hz, 4H), 7.44
(m, 8H), 7.38 (t, J = 7.5 Hz, 4H), 7.30 (dd, J = 14.5 Hz, 8H), 7.14 (d,
J = 8.5 Hz, 4H), 7.05 (d, J = 8.5 Hz, 8H), 7.00 (d, J = 8.5 Hz, 8H), 6.93
(d, J = 8.5 Hz, 4H), 2.30 (s, 12H); MALDI-TOF-MS (m/z) 1200.5(M+);
Anal. Calcd for C92H68N2: C, 91.96; H, 5.70; N, 2.33 Found: C, 91.89;
H, 5.88; N, 2.23.
1H NMR (500 MHz, CDCl3) ı 7.86 (d, J = 2.0 Hz, 2H), 7.58 (d,
J = 9.5 Hz, 2H), 7.43 (d, J = 8.0 Hz, 4H), 7.38 (dd, J = 10.5 Hz, 2H), 7.33
(d, J = 8.0 Hz, 4H), 2.85–2.78 (m, 4H), 1.80 (dt, J = 15.5, 4H), 1.52 (dd,
J = 14.5 Hz, 4H), 1.05 (t, J = 7.5 Hz, 6H); 13C NMR (500 MHz, CDCl3) ı
FDPA2 (0.46, 31.7%); 1H NMR (500 MHz, CDCl3) ı 7.88 (s, 2H),
7.76 (t, J = 8.5 Hz, 6H), 7.57 (dd, J = 9.0, 2H), 7.43 (t, J = 7.5 Hz, 8H),
7.41–7.34 (m, 12H), 7.29 (d, J = 7.5 Hz, 2H), 7.23–7.8 (m, 6H), 7.04
(d, J = 8.0 Hz, 12H), 6.97 (d, J = 7.5 Hz, 8H), 6.86 (d, J = 8.0 Hz, 4H),

Y. Zhang et al. / Journal of Photochemistry and Photobiology A: Chemistry 227 (2012) 59–64
61
Scheme 1. Syntheses of compounds FDPA1 and FTPA2.
2.80 (t, J = 7.5 Hz, 4H), 2.30 (s, 12H), 1.75–1.79 (m, 4H), 1.45–1.51
3.2. Photophysical properties
(m, 4H), 1.02 (t, J = 7.5 Hz, 6H); MALDI-TOF-MS (m/z) 1465.7 (M+);
Anal. Calcd for C111H92N2: C, 91.76; H, 6.33; N, 1.91 Found: C, 91.89;
H, 6.14; N, 1.97.
Fig. 1 presented the UV–vis absorption and PL spectra of FDPA1
and FDPA2 recorded both in chloroform solution and the film
state. The absorption bands ranging from 288 to 350 nm could be
attributed to the n–␲* transition of the peripheral end-capping
groups [34]. Additionally, their characteristic vibronic bands in the
region from 350 to 450 nm were assigned to the ␲–␲* transitions
of the anthracene core [23]. Herein, it was noteworthy that the
␲–␲* absorption transitions were slightly red-shifted by 2 nm for
FDPA1 and 1 nm for FDPA2 compared to that of DPA [35] as well
as Ph-DPAN [28], respectively. Interestingly, in comparison with
Ph-DPAN, the emission peaks at 446.6 nm for FDPA2 showed an
evident blue-shift due to the weak intermolecular interactions.
The results clearly confirmed that the introduction of end-capping
groups did not lead to the expansion of conjugation remarkably. In
contrast, the PL emission wavelength of two oligomers presented
slight red-shift from solution to solid film. Besides, the full widths at
half maximum (FWHM) were 56.6 and 55.8 nm for FDPA1, 58.9 and
69.4 nm for FDPA2 in solution and in the film respectively. The sim-
ilarity in the FWHM and the small difference between the emission
peak of sample in the solution and solid state implied that the bulky
end-capping TPAF groups effectively enhanced steric hindrance,
which significantly hindered the chose packing and molecular
interactions resulting in fluorescence quenching. Moreover, the
peripheral end-capping groups with a negligible conjugation with
3. Results and discussion
3.1. Synthesis and characterization
Scheme 1 illustrates the synthetic route for the preparation of
DPA derivative consisting of a DPA core and two TPA-substituted
fluorene peripheries. The Grignard reaction of fluorenone with
(p-bromophenyl)-magnesium bromide gave the corresponding
tertiary alcohol 3. Acid-promoted Friedel–Crafts type substitu-
tion of N,N-Bis(4-methylphenyl)aniline with 3 afforded bromide
4 in high yield. Subsequently, the compound 4 underwent cross-
coupling reaction with the pinacol ester of diboron to give the key
intermediate arylboronic ester. Ultimately, the Pd-catalyzed Suzuki
coupling reaction was employed between arylboronic ester and
9,10-dibromo-anthracene or dibromide BrTPA to afford the corre-
sponding compounds FDPA1 or FDPA2 with 60.8% and 31.7% yield,
respectively. Elemental analysis, 1H NMR and MALDI-TOF-MS were
utilized to confirm the structure. Unfortunately, the target com-
pounds did not show excellent solubility, thus, no 12C NMR spectra
were available in common organic solvent.

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Y. Zhang et al. / Journal of Photochemistry and Photobiology A: Chemistry 227 (2012) 59–64
Fig. 1. The absorption and PL spectra of the target compounds in solution and in film.
the DPA core effectively retained the large band gap of the original
DPA. The fluorescence quantum yields (˚F) of FDPA1 and FDPA2
were measured as 0.67 and 0.62, respectively, in dilute chloroform
solutions using DPA (˚F = 0.9, in cyclohexane) as a standard. The
optical energy band-gaps FDPA1 and FDPA2 were 2.98 and 2.78 eV,
respectively.
of the emissive materials. Under successive multiple potential
scans (10 scans), the CV curves remained less change, demon-
strated the excellent electrochemical stability of the as-prepared
materials. In short, the incorporation of TPA-based end-caps effec-
tively improved the hole transport/injection ability of DPA without
obvious altering energy gap of the corresponding core, DPA and
Ph-DPAN.
3.3. Electrochemical properties
3.4. Theoretical estimation of molecular orbitals
As shown in Fig. 2, cyclic voltammetry (CV) was performed to
examine the electrochemical properties of the obtained oligomers.
The anode scans demonstrated similar values of onset oxidation
potential (EOX) for both DPA-based oligomer (0.90 V for FDPA1
and 0.89 V for FDPA2). To assess the charge injecting proper-
ties, the estimated HOMO energy levers were −5.28 eV for FDPA1
and −5.27 eV for FDPA2, respectively (HOMO = −(EOX + 4.38 eV)).
The LUMO energy levers of FDPA1 and FDPA2 were −2.30 and
−2.49 eV, respectively, calculated from HOMO energy level and
energy gap (Eg) determined from the threshold of the optical
absorption. The results demonstrated that the high HOMO energy
level of FDPA1-2 greatly reduced the energy barrier for hole-
injection from the ITO anode (WITO = −4.8 eV) to and the emissive
chromophore. Additionally, the conjugation length and structure
of the core had little influence on the ability of hole-injection
of materials. Fig. 2 also showed the reversible p-doping pro-
cesses of compounds, indicating the high stability for hole-injection
The optimized geometries and spatial distributions of FDPA1
and FDPA2 were calculated by means of density functional the-
ory (DFT) at the level of B3LYP/6-31G(d). The bulky phenyl and
triarylamines group at the 9-position of fluorene were signif-
icantly twisted toward the fluorene backbone, resulting in a
noncoplanar structure, as shown in Fig. 3. This three-dimensionally
non-coplanar conformation hindered intermolecular interactions
effectually and thus, suppressed molecular crystallize and improve
morphological stability of thin film. Moreover, the fluorene and
phenyl moieties were connected through the sp3-hybridized car-
bon atom at the 9-position of fluorene, which effectively blocked
the conjugation between them. These theoretical results were con-
sistent with the above experimental results. The HOMO orbitals
were predominantly concentrated on the triphenylamino group.
For compound FDPA1, the LUMO orbitals were mainly located on
the DPA core. However, for oligomer FDPA2, the electron density
distributions of the LUMO were partially spread to phenyl moieties
at the 3- and 6-positions of the anthracene. The above-mentioned
results strongly explained the phenomena that the HOMO level of
FDPA1 was higher than that of FDPA2. Consequently, the molec-
ular orbital analysis clearly proved our molecular design strategy
was effective.
20
Eox=0.89 V
16
12
FDPA1
FDPA2
8
4
0
Eox=0.90 V
-4
-8
-12
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
Potential (V vs Ag/AgCl)
Fig. 2. Cyclic voltammograms of compounds FDPA1 and FDPA2 (10 scans) in CH2Cl2
with 0.10 M of TBAP as a supporting electrolyte, scan rate 50 mV s−1
Fig. 3. Pictorial representations of Frontier molecular orbitals calculated at B3LYP/6-
31G for compounds FDPA1 and FDPA2.
.

Y. Zhang et al. / Journal of Photochemistry and Photobiology A: Chemistry 227 (2012) 59–64
63
Fig. 4. TGA and DSC thermogram of the oligomers under a nitrogen atmosphere
Fig. 6. X-ray diffraction patterns of the samples: (a) FDPA1 film and (b) after heating
to 100 ◦C for 10 h; (c) FDPA2 film and (d) after heating to 100 ◦C for 10 h; (e) film for
DPA.
with heating rate of 10 ◦C min−1
.
3.5. Thermal properties
To further confirm the rationality of our molecular design
strategy, the thin films were prepared on the surface of ITO via
spin-coating. The morphological stability of FDPA1 and FDPA2 was
systematically investigated by scanning electron microscope (SEM)
and X-ray diffraction (XRD). The surface morphologies in Fig. 5a
and b clearly revealed that the films exhibited fairly smooth and
uniform surface. In contrast, DPA film in Fig. 5c displayed a rough
surface dotted with lots of crystal block. These images provided
the intuitive evidence that the presence of the peripheral end-
capping groups effectively reduced the tendency to crystallization.
Expectably, the XRD results were in agreement with the proposals
above. As shown in Fig. 6e, the XRD curve of the DPA film exhibited
sharp and intense reflections, indicating excellent crystallinity of
the film. However, a weak, broad, and diffused peak was observed
in the thin film of FDPA1 and FDPA2 (Fig. 6a and c), presented the
degradation crystallinity of the film or might be even amorphous.
More importantly, there was negligible morphological change on
The thermal properties of the nonplanar oligomers were inves-
tigated by thermogravimetric analysis (TGA) and differential
scanning calorimetry (DSC), as shown in Fig. 4. Two oligomers,
FDPA1 and FDPA2 possessed thermal decomposition temperature
(Td: 5% weight loss) as high as 422.6 and 449.8 ◦C respectively,
which were higher than that of the corresponding core, DPA and
Ph-DPAN [28,35]. With the second heating scan, the glass transi-
tion at 186.8 ◦C for FDPA1 and 202.5 ◦C for FDPA2, was observed
evidently. These observations indicated that the enhanced thermal
stability of amorphous films was attributed to the existence of the
rigid fluorene end-caps, which effectually suppressed the tendency
to crystallization and increased the Tg of compounds. In general, the
higher for Tg and Td of light-emitting materials, the film morpho-
logical properties are the more stable during the operation of the
device.
Fig. 5. SEM images of FDPA1, FDPA2 and DPA films; top, before heated (a–c); down, after heated at 100 ◦C (d–f) for 10 h under air atmosphere. Inset in (f) is the magnified
SEM images.

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Y. Zhang et al. / Journal of Photochemistry and Photobiology A: Chemistry 227 (2012) 59–64
the FDPA1 and FDPA2 film after annealed at 100 ◦C for 10 h under
air atmosphere as shown in Fig. 5d and e, respectively. The XRD
pattern of the heated sample was nearly the same as that of the
original sample except for the slight changes in diffraction peaks
intensity (Fig. 6b and d). As a comparison, DPA film suffered obvi-
ous crystallizing after the same thermal treating, and large-scale
quadrate particles with edge length ranging from 0.5 to 1.2 ␮m
were observed in Fig. 5f. The above results further indicated the
thermal stability of oligomers FDPA1 and FDPA2 was better than
that of corresponding core. The presence of the end-capping TPAF
group hindered close packing and crystallization may be the reason
for the increase of film morphological stability.
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4. Conclusions
In conclusion, two novel non-coplanar oligomers containing
DPA unit as the core and two TPAF units as the peripheries
were facilely prepared by Suzuki coupling and Friedel–Crafts reac-
tion. Amorphous and spiro-configuration molecular gives excellent
performances, such as good thermal, morphological stabilities,
excellent fluorescence quantum yield and wide energy gap, to the
two blue-emitting oligomers. Additionally, the presence of TPA
improved the hole-injection and -transporting ability of the result-
ing materials. Therefore, it is reasonably inferred that a novel class
of blue-emitting materials with excellent thermal and electro-
chemical stability, high fluorescence quantum yield as well as high
HOMO energy levels is expected to be achieved via this end-capping
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Acknowledgements
The authors gratefully thank the support of National Basic
Research Program of China (2010CB635108, 2011CBA00700), Nat-
ural Science Foundation of Zhejiang Province, China (Y4090260),
Major Science and Technology, Special and Priority Themes of Zhe-
jiang Province, China (2009C14004).
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