Phenanthrene derivatives combined charge transport properties and strong solid-state emission

Article abstract of DOI:10.1007/s11426-019-9451-x

As bifunctional materials, phenanthrene derivatives 2,7-diphenylphenanthrene and 2,7-di(styryl)phenanthrene (DPPa and DSPa) were designed and studied. Both materials show charge transport properties and strong solid-state emission. The hole mobility was m

Full text of DOI:10.1007/s11426-019-9451-x

SCIENCE CHINA
Chemistry
•
ARTICLES•
https://doi.org/10.1007/s11426-019-9451-x
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Phenanthrene derivatives combined charge transport properties
and strong solid-state emission
*
*
Jinfeng Li, Chenguang Li, Lingjie Sun, Xiaotao Zhang , Shanshan Cheng & Wenping Hu
Tianjin Key Laboratory of Molecular Optoelectronic Sciences, Department of Chemistry, School of Science, Tianjin University &
Collaborative Innovation Centre of Chemical Science and Engineering (Tianjin), Tianjin 300072, China
Received January 12, 2019; accepted February 28, 2019; published online April 11, 2019
As bifunctional materials, phenanthrene derivatives 2,7-diphenylphenanthrene and 2,7-di(styryl)phenanthrene (DPPa and
DSPa) were designed and studied. Both materials show charge transport properties and strong solid-state emission. The hole
2
−1 −1
mobility was measured to be 1.6 and 0.4 cm V
s for DPPa and DSPa, respectively. While the photoluminescence quantum
yield of DPPa and DSPa was as high as 37.13% and 62.36%, respectively.
phenanthrene derivatives, OFET, strong solid-state emission
Citation:
Li J, Li C, Sun L, Zhang X, Cheng S, Hu W. Phenanthrene derivatives combined charge transport properties and strong solid-state emission. Sci China
Chem, 2019, 62, https://doi.org/10.1007/s11426-019-9451-x
1
Introduction
a sufficiently high number of excited states to initiate lasing
[10–14].
Organic field-effect transistors (OFETs) have been ex-
tensively studied both experimentally and theoretically, as
they have potential for using in low-cost, large-area elec-
tronic applications such as smart cards, radio-frequency
identification tags (RFID), and flat panel displays [1–5].
However, with the development of science and technology,
single functional devices no longer meet the requirements.
One sample is organic light-emitting field-effect transistors
Although high carrier mobility and efficient solid-state
emission realized in a single device are so important, it still
remains challenging to design such bifunctional molecules. It
is because achieving high mobility in organic semi-
conductors (OSCs) generally requires compact packing with
strong and plentiful intermolecular interactions [15]. In
other words, larger intermolecular π-overlaps in combination
with larger transfer integrals and lower reorganization energy
result in better electronic property. However, such interac-
tions tend to quench the solid-state luminescence [16–18].
Anthracene is the smallest organic semiconductor, which
(OLETs), a novel class of organic multi-functional devices,
which integrate organic light emitting diodes (OLEDs) and
OFETs in a single device [6–8]. In active matrix electro-
luminescent displays, OLEDs require FETs to control their
luminance [9]. As for OLETs, optoelectronic characteristics
can be controlled by themselves. Good OLETs should
combine high carrier mobility with efficient solid-state
emission. Another sample is organic electrically pumped
lasers. To achieve better application, materials need to am-
plify their own emission and carry enough current to provide
2
−1 −1
shows low charge-carrier mobility of only 0.02 cm V
s
at 170–180 K [19]. However, its crystals possess blue
emission with a high absolute photoluminescence quantum
yield (PLQY) of 64% [20]. Derivatives of anthracene show
good performance, such as 2,6-diphenylanthracene (DPA)
2
−1 −1
with high mobility of 34 cm V
s
and PLQY of 41.2%
[15], 2,6-di(2-naphthyl)anthracene (dNaAnt) with mobility
2
−1 −1
s
as high as 12.3 cm V
and PLQY of 29.2% [7]. We
believe that phenanthrene should possess the similar per-
*Corresponding authors (email: zhangxt@tju.edu.cn; chengss@tju.edu.cn)
©
Science China Press and Springer-Verlag GmbH Germany, part of Springer Nature 2019
chem.scichina.com link.springer.com

2
Li et al. Sci China Chem
formance as an isomer of anthracene.
In this article, we report two phenanthrene derivatives 2,7-
diphenylphenanthrene and 2,7-di(styryl)phenanthrene
DPPa and DSPa in Scheme 1). The molecular design is
(
based on the following considerations: (1) phenanthrene, as
isomeride of anthracene, should have semiconducting and
emission porperties; (2) prolonging conjugation length to
increase intermolecular π-overlaps can improve mobility.
The results show that DPPa and DSPa are good bifunctional
materials. Both materials exhibit high emission and semi-
conducting properties. For DPPa, mobility is measured to be
Scheme 1 Synthetic route of DPPa and DSPa.
were added and then heated to 90 °C and stirred for 24 h. The
system was then filtered, washed successively with di-
chloromethane, water, ethanol and purified by sublimation
2
−1 −1
[21]. DPPa was obtained as a white solid, with a yield of
1
.6 cm V s with PLQYof 37.13%. As to DSPa, PLQY is
1
2
−1 −1
72.6%. HNMR (600 MHz, CDCl ): δ (ppm) 8.77 (d, 2H),
3
as high as 62.36%, with mobility of 0.4 cm V s .
8
(
.12 (d, 2H), 7.94 (dd, 2H), 7.84 (s, 2H), 7.79 (dd, 4H), 7.52
t, 4H), 7.41 (m, 2H). MALDI-TOF: 329.6. Anal. calculated
for C H (%): C 94.51%, H 5.49%. Experimental: C
2
4
16
2
Experimental
9
4.31%, H 5.70%.
2
.1 General method
2
.2.2 Synthesis of compound DSPa
All reagents and chemicals were obtained from commercial
sources and used without further purification. H NMR
1
Styrylboronic acid (0.33 g, 2.2 mmol, 2.2 eq.), 2,7-di-
bromophenanthrene (0.34 g, 1 mmol, 1 eq.), Na CO (2.0 M)
and Pd(PPh ) (0.058 g, 0.05 mmol, 5% eq.) were added to a
2
3
spectra were taken in CDCl with tetramethylsilane (TMS, δ
3
3
4
0
.00 ppm) as internal standard at room temperature and were
two-neck bottle under N . Toluene (8 mL) and H O (4 mL)
2
2
recorded on Bruker 600 NMR spectrometer (Germany). UV-
Vis spectra were obtained on SHIMADZU UV-3600 UV-
Vis-NIR spectrophotometer (Japan). Photoluminescence
were added and then heated to 90 °C and stirred for 24 h. The
system was then filtered, washed successively with di-
chloromethane, water, and ethanol and purified by sub-
limation [21]. DSPa was obtained as a white solid, with a
yield of 78.69%. HNMR (600 MHz, CDCl ): δ (ppm) 8.64
(PL) spectra were recorded on a HITACHI F-7000 spectro-
fluorometer (Japan). Thermal gravimetric analysis (TGA)
was carried out on a METTLER TOLEDO TGA2 apparatus
1
3
−
1
(d, 2H), 7.94 (d, 2H), 7.88 (dd, 2H), 7.75 (s, 2H), 7.60 (m,
(
Switzerland) with a scanning rate of 10 °C min . Absolute
4
H), 7.40 (t, 4H), 7.31 (m, 6H). MALDI-TOF: 381.7; Anal.
quantum yield measurement (LabSphereR, FluoroMax-4,
HORIBA JobinYvon, PLQY software package) was used for
powder sample. In this experimental setup, it is possible to
measure the PLQY no need of this word at this point using
the integrating sphere in combination with a commercial
fluorimeter. Emission spectra including the scattering region
of excitation light were recorded for both blank and test
samples, and these spectra were corrected with instrumental
factors to calculate the quantum yield. Cyclic voltammetirc
calculated for C H (%): C 94.20%, H 5.80%. Experi-
mental: C 94.33%, H 5.57%.
3
0
22
2
.3 Substrate treatment
Substrate was treated with the following steps: (1) SiO /Si
wafers containing 300 nm-thick SiO layers were succes-
sively cleaned with deionized water, isopropanol, deionized
water, piranha solution (70:30, v/v, H SO /H O ), deionized
water, isopropanol, and oxygen plasma (10 min, 80 W). (2)
Surface modification of the Si/SiO wafers by octadecyltri-
chlorosilane (OTS) was then carried out by a vapor deposi-
tion method in a vacuum chamber (0.1 Pa). The Si/SiO2
wafer was first dried at 90 °C (for 1.5 h) to remove moisture,
and then maintained at 120 °C (for 2 h) to allow for de-
position of OTS. After being cooled to room temperature, the
substrate was washed successively with n-hexane, tri-
chloromethane, and isopropanol.
2
2
2
4
2
2
(CV) measurements were conducted using a CHI660C
electrochemistry station with tetrabutlyammonium hexa-
fluorophosphate (Bu NPF ) as electrolyte (0.001 M in dry
2
4
6
CH Cl ). The working, counter and reference electrodes
2
2
were Glassy carbon, Pt wire and Ag/AgCl, respectively.
OFET characteristics were recorded by a Keithley 4200 SCS
and Micromanipulator 6150 probe station (USA).
2
.2 Materials and synthesis
2
.2.1 Synthesis of compound DPPa
2
.4 Preparation of organic single microcrystal
Phenylboronic acid (0.27 g, 2.2 mmol, 2.2 eq.), 2,7-di-
bromophenanthrene (0.34 g, 1 mmol, 1 eq.), Na CO (2.0 M)
To get small single crystal for fabricating devices, vacuum
sublimation is not suitable for these two materials. Because
the crystals obtained by this method are much thicker, which
2
3
and Pd(PPh ) (0.058 g, 0.05 mmol, 5% eq.) were added to a
3
4
two-neck bottle under N . Toluene (8 mL) and H O (4 mL)
2
2

Li et al. Sci China Chem
3
are not good for device performance [22–26]. So, we need to
sublimate materials with tube furnace at atmospheric pres-
sure (Figure 1(a)) [27]. For DPPa, T1 and T2 was set to 245
and 150 °C respectively, keeping 5 h. As to DSPa, T1 and T2
was set to 290 and 180 °C respectively, keeping 5 h. High-
purity argon was used as the carrier gas (100 sccm). Crystals
grown on Si/SiO substrates are shown in Figure 1(b–g).
2
With this method, we can get large and thin single crystals.
Moreover, many large crystals are erected on the substrate,
so we can transfer them to OTS modified Si/SiO substrates
2
for fabricating devices.
2
.5 Device fabrication and characterization
First, the crystals were transferred onto the OTS modified
substrate. Then, “gold-layer sticking” technique was used to
fabricate bottom-gate top-contact transistors (Figure 1(a))
[
28]. The field-effect transistor characteristics were mea-
Figure 1 (a) Thin single crystal preparation method; (b–d) DPPa single
crystal for bright field, dark field and fluorescence images; (e–g) DSPa
single crystal for bright field, dark field and fluorescence images (color
online).
sured at room temperature in air on a Keithley 4200 SCS and
Micromanipulator M150 probe station, and the mobility was
extracted from the saturation region by use of the following
equation: I =(W/2L)C μ(V −V ) (where I is the drain
current, L and W are the channel length and width, C is the
2
DS
i
G
T
DS
i
insulator capacitance per unit area, μ is the field-effect mo-
bility, V is gate voltage, V is the extrapolated threshold
G
T
voltage) [29].
3
Results and discussion
3
.1 Thermal, optical and electrochemical properties
Thermal stability of DPPa and DSPa were measured by
thermogravimetric analysis (TGA) (Figure S1, Supporting
Information online). Both materials show good stability with
sublimation temperature of 323 and 365 °C (T , corre-
d
Figure 2 (a) Absorption and photoluminescence spectra of DPPa in so-
lution and solid state; (b) photoluminescence spectra of DSPa in solution
and solid state; (c, d) CV curves of DPPa and DSPa (color online).
sponding to a 5% weight loss) for DPPa and DSPa, re-
spectively. Absorption spectra of DPPa and DSPa in
solution have a vibronically structured band (Figure 2(a, b)).
The absorption peak of DPPa in dichloromethane solution
appears at λ=316 and 295 nm, corresponding to 0-0 and 0-1
vibronic peak, respectively. For DSPa, absorption spectrum
in solution shows the peak at λ=374 and 357 nm, corre-
sponding to 0-0 and 0-1 vibronic peak, respectively. The
corresponding peaks of the absorption spectra for DPPa and
DSPa in solids are λ=376, 357 nm and λ=402, 381 nm, re-
spectively. Compared with absorption spectra in solution of
two materials, the absorption spectra of solid demonstrate an
obvious bathochromic shift, indicating strong intermolecular
interactions in the solid state. The 0-0 peak of DPPa (Figure
−
1
shift of 1422 and 2097 cm for solution and solid respec-
tively. Two materials show bright blue emission, as displayed
in Figure S2. The solid-state photoluminescence quantum
yield of DPPa and DSPa was measured to be 37.13% and
62.36%, respectively. The fluorescence lifetime was 44.67
and 4.78 ns for DPPa and DSPa respectively (Figure S3).
The absorption and emission spectra exhibit distinct vibronic
sidebands for both materials. The 0-0 peaks for DPPa and
DSPa are much stronger than the corresponding 0-1 transi-
tions in solid states indicating the formation of J-aggregates
[30]. The optical gap determined from the onset peak of
absorption spectrum in solution was 3.63 and 3.16 eV for
DPPa and DSPa respectively. The highest occupied mole-
cular orbital level (HOMO) for DPPa and DSPa was mea-
2
(a)) appears at 376 and 403 nm for solution and solid re-
−
1
spectively. Stokes shift of solid is 1782 cm which is smaller
−
1
than that of solution (5050 cm ). For DSPa (Figure 2(b)),
the 0-0 peak appears at 395 and 439 nm, generating a Stokes

4
Li et al. Sci China Chem
sured from cyclic voltammetry (CV) to be −5.51 and
5.47 eV, respectively (Figure 2(c, d)). With optical gap,
lowest unoccupied molecular orbital level (LUMO) for
DPPa and DSPa was calculated to be −1.88 and −2.31 eV,
respectively. The data are summarized in Table 1.
molecule length is 17.742 Å with angle of 30.22°. As to
DSPa, molecule shows length of 22.177 Å with angle of
16.27° (Figure S5). Two molecules show typical herringbone
geometry packing (Figure 3(b, e)), which is similar to the
packing of pentacene molecules in crystals [31]. Single
crystals of two materials belong to pbca space group. Crystal
parameters of DPPa is a=7.3915(4) Å, b=7.0002(4) Å, and
c=33.307(2) Å. For DSPa, a=7.63406(15) Å, b=
6.85129(15) Å, and c=39.1171(8) Å (for .cif files of the
crystals see Supporting Information online). The DPPa
molecule is at a distance of 4.989–7.000 Å from the sur-
rounding molecules (Figure 3(c)). DSPa shows a distance of
4.870–6.851 Å from the surrounding molecules (Figure 3
(f)). Exciton tends to transport between two adjacent mole-
cules that are close in distance, so charge transport of both
molecules is along b-axis.
−
3
.2 Crystal analysis
Single crystals of DPPa and DSPa were grown by sub-
limation with a tube furnace. The X-ray diffraction (XRD)
patterns of two materials (Figure S4) show strong and sharp
diffraction peaks, indicating that the crystals are of high
quality. From the out-of-plane XRD pattern, we can imagine
that the lattices of two kinds of molecules are erected on the
substrate but have a certain angle. We can also get this in-
formation from the crystal structure (Figure 3(a, d)). If the
underlying molecules are perpendicular to the substrate, then
the lattice presents a certain angle to the substrate. For DPPa,
3
.3 Electrical measurement
Table 1 Photoelectric properties of the two materials
Device images are shown in Figure 4(a, b), where the
channel width to length ratio is 5:4 and 1:1 for DPPa and
DSPa, respectively. Two materials both exhibit p-type tran-
sistor behavior. Representative output and transfer char-
acteristics of the devices based on an individual DPPa and
DSPa single-crystal are shown in Figure 4(c–f). According
to the transfer characteristics (Figure 4(c, e)), the mobility μ,
HOMO
eV)
LUMO
(eV)
Materials
Eg (eV) PLQY (%) τ (ns)
(
DPPa
DSPa
−5.51
−5.47
−1.88
−2.31
3.63
3.16
37.13
62.36
44.67
4.78
threshold voltage V , and on/off ratio of the devices were
T
2
−1 −1
calculated out. DPPa was calculated to be 1.6 cm V s ,
8
−
16 V and 4.01×10 , respectively; while DSPa was calcu-
Figure 4 (a, b) Images of DPPa and DSPa transistors based on in-
dividual single-crystal; (c, d) typical transfer and output characteristics of
DPPa transistors based on individual single-crystal; (e, f) typical transfer
and output characteristics of DSPa transistors based on individual single-
crystal (color online).
Figure 3 (a, b) DPPa packing mode along a-axis and b-axis; (c) dis-
tances of DPPa from the surrounding molecules; (d, e) DSPa packing
mode along a-axis and b-axis; (f) distances of DSPa from the surrounding
molecules (color online).

Li et al. Sci China Chem
5
2
−1 −1
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5
6
7
8
9
4
Conclusions
In conclusion, two phenanthrene derivatives were designed
and synthesized. Both of them combined charge transport
properties and strong solid-state emission. For mobility
performance, DPPa and DSPa were measured to be 1.6 and
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Acknowledgements This work was supported by the National Key R&D
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