A new class of organic semiconductors for solution processed OTFTs: Synthesis and characterization of pyrrolo-perylene derivatives with different end groups

Article abstract of DOI:10.1016/j.dyepig.2013.12.001

New pyrrolo-perylene derivatives, a new class of organic semiconductor, were designed for solution processed organic thin film transistors (OTFTs). Newly designed 2-(naphthalen-2-yl)thiophene end capped pyrrolo-perylene, 3,10-bis(5-(naphthalen-2-yl)thiophen-2-yl)-1-(2-octyldodecyl)-1H-phenanthro[1, 10,9,8-cdefg]carbazole (NTPP), and bithiophene end capped pyrrolo-perylene, 3,10-bis([2,2′-bithiophen]-5-yl)-1-(2-octyldodecyl)-1H-phenanthro[1,10,9, 8-cdefg]carbazole (BTPP), were synthesized by Suzuki coupling and Stille coupling reaction, respectively. NTPP and BTPP showed good solubility in common organic solvents and were characterized by various spectroscopy. Solution processed OTFTs using BTPP exhibited high field-effect mobilities up to 0.11 cm² V^-1 s^-1 with an on/off ratio of 1 × 10⁴ and a very small threshold voltage of 0 V, while OTFTs using NTPP exhibited far lower performances. The high mobility of BTPP is attributed to three dimensional multi-layered crystalline structure based on the results of the two dimensional grazing incidence X-ray diffraction pattern analysis and theoretical calculation using Gaussian, together with morphological study.

Full text of DOI:10.1016/j.dyepig.2013.12.001

Accepted Manuscript
A New Class of Organic Semiconductors for Solution Processed OTFTs: Synthesis
and Characterization of Pyrrolo-perylene Derivatives with Different End Groups
Kwang Hun Park, Hui-Jun Yun, Wanxiang Lu, Dae Sung Chung, Soon-Ki Kwon, Yun-
Hi Kim
PII:
S0143-7208(13)00472-5
10.1016/j.dyepig.2013.12.001
DYPI 4198
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 26 September 2013
Revised Date: 29 November 2013
Accepted Date: 4 December 2013
Please cite this article as: Park KH, Yun H-J, Lu W, Chung DS, Kwon S-K, Kim Y-H, A New Class
of Organic Semiconductors for Solution Processed OTFTs: Synthesis and Characterization of
Pyrrolo-perylene Derivatives with Different End Groups, Dyes and Pigments (2014), doi: 10.1016/
j.dyepig.2013.12.001.
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ACCEPTED MANUSCRIPT
A New Class of Organic Semiconductors for Solution Processed
OTFTs: Synthesis and Characterization of Pyrrolo-perylene
Derivatives with Different End Groups
Kwang Hun Park,a Hui-Jun Yun,a Wanxiang Lu,a Dae Sung Chung,b Soon-Ki Kwon,a
Yun-Hi Kim*c
aSchool of Materials Science and Engineering and (ERI), Gyeongsang National
University, Jinju, 660-701, Republic of Korea.
Fax: +82-55-753-6311 E-mail address: skwon@gnu.ac.kr
bDepartment of Chemical Engineering, Chung-Ang National University, Seoul
156–756, South Korea
cDepartment of Chemistry and Research Institute of Natural Science (RINS),
Gyeongsang National University, Jinju, 660-701, Republic of Korea.
Abstract
New pyrrolo-perylene derivatives, a new class of organic semiconductor, were
designed for solution processed organic thin film transistors (OTFTs). Newly
designed
2-(naphthalen-2-yl)thiophene
end
capped
pyrrolo-perylene,
3,10-bis(5-(naphthalen-2-yl)thiophen-2-yl)-1-(2-octyldodecyl)-1H-phenanthro[1,10,9,
8-cdefg]carbazole (NTPP), and bithiophene end capped pyrrolo-perylene,
3,10-bis([2,2'-bithiophen]-5-yl)-1-(2-octyldodecyl)-1H-phenanthro[1,10,9,8-cdefg]car
bazole (BTPP), were synthesized by Suzuki coupling and Stille coupling reaction,
respectively. NTPP and BTPP showed good solubility in common organic solvents
and were characterized by various spectroscopy. Solution processed OTFTs using
BTPP exhibited high field-effect mobilities up to 0.11 cm2V-1s-1 with an on/off ratio
of 1 × 104 and a very small threshold voltage of 0 V, while OTFTs using NTPP
exhibited far lower performances. The high mobility of BTPP is attributed to three
dimensional multi-layered crystalline structure based on the results of the two
dimensional grazing incidence X-ray diffraction pattern analysis and theoretical
calculation using Gaussian, together with morphological study.
Keyword: OTFT (organic thin film transistor); semiconductor; solution process;
pyrrolo-perylene; end-group effect
1

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Introduction
Organic thin film transistors (OTFTs) have attracted a lot of interest because of
their potential as replacements for conventional silicon-based transistors in low-end
electronic applications, as well as the possible applicability as base elements for the
development of new opto-electronic products.[1–5]. OTFT active materials can be
divided into two classes according to their processing methods, i.e., solution
processing and vacuum deposition processing.[6–9] Solution processed organic
semiconductors have attracted considerable interest because of the low fabrication
costs; deposition of semiconductor layer by ink jet printing, spin-casting, and
dipping.[4,5] They also have higher compatibility with plastic substrates than silicon
based thin film transistor (TFT), and diverse potential applications, such as in driving
circuits of large-area flexible display panels, new generation smart cards, integrated
logic circuits, and sensors etc. [ 11– 13]
Consequently, the design and synthesis of new class of solution processable
π-conjugated organic semiconductors are attracting increasing attention.[14] Among
those materials, perylene has been widely used as a dye molecule [15-17], because of its
high fluorescence quantum yield and chemical stability. The intimate packing of
perylene molecules provides rich photophysical and photochemical properties that are
[20]
important for many technological applications.[18-19] N-Annulation of perylene
where nitrogen atoms are annulated at the bay position can be exploited for improved
solubility because additional flexible alkyl chains can be easily introduced by an
alkylation reaction. In addition, the electron-donating character of amines can increase
the electron density of the entire π-system and lead to new opto-electronic properties.
Recently, Ong et al. reported that the introduction of nitrogen atoms can significantly
increase the stability of materials.[21] Further, as an end-capping unit, the
incorporation of sulfur as a thiophene substructure would give rise to a variety of
intra- and intermolecular interactions, such as van der waals interactions, π-π stacking,
and sulfur-sulfur interactions, which are essential to achieve high charge mobility.
2

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In this work, we designed a new class of pyrrolo-perylene derivatives that offers
the advantages of both perylene and pyrrole as the main core. 2-(Naphthalen-2-yl)
thiophene and bithiophene are introduced for end-capping to increase intermolecular
interaction. The newly designed dragonfly shaped 2-(naphthalen-2-yl)thiophene end
capped pyrrolo-perylene (NTPP) and bithiophene end-capped pyrrolo-perylene,
(BTPP) are expected to have high hole mobility due to their rich electron density.
They are also anticipated to have high stability due to the N-annulated perylene and
good solubility as a result of introducing alkyl groups into the N-position of
pyrrolo-perylene.
2. Experiment
2.1. Measurements.
A Genesis II FT-IR spectrometer was used to record IR spectra. 1H-NMR spectra
were recorded with the use of an Avance 300 MHz NMR Bruker spectrometers, and
chemical shifts are reported in ppm units with tetramethylsilane as an internal
standard. A thermogravimetric analysis (TGA) was performed under nitrogen on a TA
instrument 2050 thermogravimetric analyzer. The sample was heated with a 10
o
o
oC/min heating rate from 50 C to 800 C. Differential scanning calorimeter (DSC)
was conducted under nitrogen on a TA instrument 2100 differential scanning
o
o
o
calorimeter. The sample was heated with the 10 C/min from 30 C to 300 C. Mass
spectrum was measured by Jeol JMS-700 mass spectrometer. UV-vis absorption
spectra and photoluminescence (PL) spectra were measured by Perkin Elmer
LAMBDA-900 UV/VIS/NIR spectrophotometer and LS-50B luminescence
spectrophotometer, respectively. Cyclic voltammograms of the oligomers were
recorded on a epsilon E3 at a room temperature in a 0.1 M solution of
tetrabutylammonium perchrolate (Bu4NClO4) in acetonitrile under nitrogen gas
protection at a scan rate of 50 mV/s. A Pt wire was used as the counter electrode and a
Ag/AgNO3 electrode as the reference electrode. Synchrotron X-ray diffraction
3

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analyses of semiconductor films were performed at the 10C1 beam line (wavelength
=1.096Å ) and at the 3C beam line of the Pohang Accelerator Laboratory (PAL). An
atomic force microscope (AFM; Digital Instrument Multimode SPM) operated in
tapping-mode was used to image the surface morphology of the semiconductor films.
Electrical characteristics of the TFTs were measured under ambient conditions using
Keithley 2400 and 236 source/measure units. For all measurements, the channel
length (L) was 100 mm and the channel width (W) was 1000 mm. Field-effect
mobilities were extracted in the saturation regime from the slope of the source–drain
current.
2.2. Device fabrication
OTFTs were fabricated using solution processing. Top-contact OTFTs were
fabricated on the common gate of a highly n-doped silicon wafer with a 300 nm thick
thermally grown SiO2 dielectric layer. The surface of the substrate was modified with
Octyltrichlorosilane (OTS). Organic semiconducting layer was spin-coated onto the
substrate at 2000 rpm from a 0.7 wt% chloroform solution to a thickness of 60 nm.
Gold source and drain electrodes (thickness 50 nm) were deposited on top of the thin
film surface through a shadow mask. The channel length L was 150 ꢀm and the
channel width W was 1000 ꢀm. The OTFT characteristics were determined under
ambient conditions without taking precautionary measures to protect the TFT devices
from exposure to oxygen and moisture. The OTFTs were found to exhibit typical
p-channel TFT characteristics. The TFT mobilities were calculated in the saturation
regime by using the following equation: ID = (W/2L)ꢀCi(VG - VTH)2, where ID is the
drain source current in the saturated region, W and L are the channel width and length,
respectively, ꢀ is the field-effect mobility, Ci is the capacitance per unit area of the
insulation layer, and VG and VTH are the gate and threshold voltages, respectively.
The FETs characteristics were measured with a KEITHLEY 4200 semiconductor
characterization system at an air atmosphere.
4

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2.3. Materials.
Perylene, N-bromosuccinimide (NBS), and 1,4-dioxane were purchased from
Aldrich. Tetrakis(triphenylphosphine)palladium was purchased from Umicore. All
reagents purchased commercially were used without further purification.
Tetrahydrofuran (THF) was dried over sodium / benzophenone.
2.4. Synthesis of BTPP and NTPP.
2.4.1. 1-Nitroperylene (1)
Compound 1 was synthesized according to the literature. [22] 1H-NMR (DMSO):
8.57-8.53 (dd, 2H), 8.04-7.95 (m, 4H), 7.84-7.68 (m, 4H), 7.60-7.58(t, 1H).
2.4.2. 1H-phenanthro[1,10,9,8-cdefg]carbazole (2)
Compound 2 was also synthesized according to the literature. [23] 1H-NMR
(DMSO): 12.19 (s, 1H), 8.77-8.74 (d, 2H), 8.19-8.17 (d, 2H), 7.99-7.92 (dd, 4H),
7.85-7.79 (t, 2H).
2.4.3. 2-Octyldodecyl 4-methylbenzenesulfonate (3)
A solution of 2-octyldodecan-1-ol (5 g, 16.7 mmol) of pyridine (4 g, 50.5 mmol)
o
was cooled to below 20 C and 4-methylbenzene-1-sulfonyl chloride (3.5 g, 18.4
mmol) was added under stirring. The reaction mixture was stirred for 3 h after the
addition was completed. The temperature of the reaction mixture was held below 20
oC. The reaction mixture was treated with a large excess of cold dilute hydrochloric
acid. The ester was extracted by ethyl acetate and the organic phase was separated and
dried over magnesium sulfate. The product was obtained by a flash column
1
chromatography using hexane as an eluent. Yield: 6.37 g (83%). H-NMR (CDCl3):
7.81-7.78 (d, 2H), 7.36-7.33 (d, 2H), 3.93-3.91 (d, 2H), 2.45 (s, 3H), 1.61-1.55 (m,
1H), 1.26-1.23 (m, 32H). 0.91-0.87 (t, 6H).
5

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2.4.4. 1-(2-Octyldodecyl)-1H-phenanthro[1,10,9,8-cdefg]carbazole (4)
A mixture of 1H-phenanthro[1,10,9,8-cdefg]carbazole (1 g, 3.8 mmol), NaH (135
mg, 5.63 mmol), and 2-octyldodecyl 4-methylbenzenesulfonate (2.6 g, 5.74 mmol) in
dry 100 mL tetrahydrofuran (THF) was stirred at 66 0C for 12 h under nitrogen. After
0
cooling to room temperature, the mixture was stirred for 30 min at 0 C before 2 mL
of water was added dropwise. The reaction mixture was then poured into water and
the product was extracted by diethyl ether. The solvent was evaporated under reduced
pressure, and the crude product was purified by column chromatography on a silica
gel using hexane as an eluent to yield a yellow oil product. Yield: 1.3 g (64 %).
1H-NMR (CDCl3): 8.67-8.65 (d, 2H), 8.15-8.12 (d, 2H), 7.91-7.88 (d, 2H), 7.85-7.80
(t, 2H), 7.74-7.71 (d, 2H), 4.46-4.44 (d, 2H), 2.25-2.19 (m, 1H), 1.48-1.21 (m, 32H).
0.94-0.87 (m, 6H).
2.4.5. 3,10-Dibromo-1-(2-octyldodecyl)-1H-phenanthro[1,10,9,8-cdefg]carbazole
(5)
In the absence of light, NBS (0.94g, 5.28mmol) was added to a solution of
1-(2-octyldodecyl)-1H-phenanthro[1,10,9,8-cdefg]carbazole (1.3 g, 2.4 mmol) in
dichloromethane (100 mL) and the reaction solution was stirred for 2 h. The mixture
was washed with a saturated aqueous solution of NH4Cl, dried over MgSO4 and
concentrated to dryness. The residue was purified by column chromatography using
1
hexane as an eluent. Yield: 0.9 g (54 %). H-NMR (CDCl3): 8.26-8.25 (d, 2H),
8.10-8.07 (d, 2H), 7.70-7.65 (t, 2H), 7.55 (s, 2H), 3.86-3.84 (d, 2H), 1.88 (m, 1H),
1.28-1.17 (m, 32H), 0.87 (m, 6H). 13C-NMR (CDCl3):132.008, 130.05, 128.09,
125.77,125.38, 124.22, 122.07, 118.40, 117.28, 116.4, 50.5, 40.0, 32.3, 32.08, 31.28,
30.02, 29.58, 29.89, 29.67, 26.79, 23.03, 14.87
2.4.6. 2-(Naphthalen-2-yl)thiophene (6)
Magnesium (1.94 g, 79.8 mmol) was added to
a
3-neck flask.
2-Bromonaphthalene (16.51 g, 79.8 mmol) and THF (400 mL) were added dropwise
6

ACCEPTED MANUSCRIPT
o
to the flask. The reactant mixture was refluxed for 2 h at about 100 C. The resulting
solution of Grignard reagent was then added dropwise to a solution of
2-bromothiophene (10 g, 61 mmol) and Ni(dppp)Cl2 (where dppp is
diphenylphosphinopropane) (0.99 g, 3 mol%) in an ice-bath. The mixture was then
stirred overnight at room temperature and quenched with 1N-HCl. The organic layer
was separated and extracted successively with ether. The combined ether solution was
washed with H2O and dried over anhydrous MgSO4. After removal of the solvent, the
resulting product was subjected to purification by flash chromatography using a silica
1
gel with hexane as an eluent. Yield: 9.4 g (73%). H-NMR (CDCl3): 8.08 (s, 1H),
7.89-7.83 (t, 3H), 7.80-7.79 (d, 1H), 7.50-7.46 (m, 2H), 7.34 (d, 2H), 7.15-7.14 (t,
1H).
2.4.7. 4,4,5,5-Tetramethyl-2-(5-(naphthalen-2-yl)thiophen-2-yl)-1,3,2-dioxaborol
-ane (7)
A hexane solution of n-butyl lithium (2.5 M, 34.2 mL) was added to a THF
o
solution (250 mL) of 2-(naphthalen-2-yl)thiophene (15.0 g, 71.3 mmol) at -78 C.
After the mixture was stirred for
1
h
at room temperature,
2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (19.9g, 103.9mmol) was added
at -40oC. After stirring for 10 h at room temperature, the reaction mixture was poured
into water. The organic layer was separated and dried over MgSO4 and concentrated
under reduced pressure. The crude product was purified by means of column
chromatography using hexane and ethyl acetate as eluent. Yield: 7.19g (29.9%).
1H-NMR (CDCl3): 8.13 (s, 1H), 7.88-7.80 (m, 4H), 7.67-7.66 (d, 1H), 7.54-7.48 (m,
3H), 1.39 (s, 12H).
2.4.8.
3,10-Bis(5-(naphthalen-2-yl)thiophen-2-yl)-1-(2-octyldodecyl)-1H-
phenanthro[1,10,9,8-cdefg]carbazole (NTPP)
A potassium carbonate (2M, 20 mL) was added to a solution of
3,10-dibromo-1-(2-octyldodecyl)-1H-phenanthro [1,10,9,8-cdefg] carbazole (3 g,
4.26 mmol) and 4,4,5,5-tetramethyl-2-(5-(naphthalen-2-yl)thiophen-2-yl)-1,3,2-
7

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dioxaborolane (3.3 g, 9.81 mmol) in toluene (100 mL). The mixture was bubbled with
nitrogen for 30 min. Tetrakis(triphenylphosphine)palladium(0) (0.25 g, 5 % mol) was
then added and the mixture was heated to 90 oC for 24 h under a nitrogen atmosphere.
The reaction mixture was cooled to room temperature. Water was subsequently added
and the mixture was extracted with dichloromethane (200 mL). The combined organic
fractions were dried over MgSO4 and concentrated under reduced pressure. The crude
product was purified by column chromatography using hexane: dichloromethane (1:1)
as an eluent. Yield: 2.64 g (64.5 %), mp: 189 oC 1H-NMR (CDCl3): 8.80-8.77 (d, 2H),
8.6 (d, 2H), 8.2 (s, 2H), 8.02(s, 2H), 7.94-7.87 (m, 10H), 7.6 (d, 2H), 7.56-7.48 (m,
13
6H), 4.6 (d, 2H), 2.3 (s, 1H), 1.44 -1.16 (m, 32H), 0.82 (m, 6H). C-NMR (CDCl3):
144..5, 143.8, 134.1, 133.2, 132.8, 132.3, 131.0, 129.9, 129.0, 128.5, 128.4, 128.2,
128.1, 126.9, 126.3, 125.4, 125.2, 124.7, 124.6, 124.3, 121.7, 117.7, 115.3, 50.5, 40.2,
32.2, 32.1, 31.2, 30.3, 30.0, 29.9, 29.6, 26.8, 23.0, 14.45. FT-IR (KBr) (cm-1) 3059
(aromatic C-H), 2931, 2833 (aliphatic C-H), 1671-1512 (aromatic C=C). MS(EI) m/z
961 (M+).
2.4.9. 3,10-Bis([2,2'-bithiophen]-5-yl)-1-(2-octyldodecyl)-1H-phenanthro[1,10,9,8-
cdefg]carbazole (BTPP)
Under an atmosphere of nitrogen, 3,10-dibromo-1-(2-octyldodecyl)-1H-phenanthro
[1,10,9,8-cdefg]carbazole
(11.24
(16.0
g,
g,
15.97
35.14
mmol),
mmol) and
2,2'-bithiophen-5-yltributylstannane
tetrakis(triphenylphosphine)palladium(0) (0.5 g, 0.43 mmol) were dissolved in
toluene (100 mL). After the reaction mixture was stirred at 90 oC for 24 h, water (500
mL) was added and the mixture was extracted with dichloromethane. The combined
organic fractions were dried over MgSO4 and concentrated under reduced pressure.
The crude product was purified by column chromatography using hexane:
o
1
dichloromethane (1:10) as an eluent. Yield: 6.7 g (48 %), mp: 120 C. H-NMR
(CDCl3): 8.77-8.74 (d, 2H), 8.56-8.53 (d, 2H), 7.95 (s, 2H), 7.91-7.86 (t, 2H),
7.40-7.35 (m, 4H), 7.31-7.29 (m, 4H), 7.11-7.08 (m, 2H), 4.61-4.59 (d, 2H), 2.3 (m,
1H), 1.42-1.12 (m, 32H), 0.85-0.81 (m, 6H). 13C-NMR (CDCl3): 142.69, 138.7, 137.5,
8

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137.1, 132.3, 132.05, 129.2, 127.89, 127.69, 127.65, 125.06, 124.32, 124.2, 123.6,
115.1, 114.9, 45.14, 43.15, 31.9, 31.7, 29.95, 29.63, 29.60, 29.33, 29.30, 26.42, 22.68,
14.12. FT-IR (KBr) (cm-1) 3053 (aromatic C-H), 2929, 2839 (aliphatic C-H), 1519
(aromatic C=C). MS(EI) m/z 873 (M+).
9

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3. Results and Discussion
New semiconductors, NTPP and BTPP were synthesized according to the
procedure shown in Scheme 1. They were easily synthesized through manifold
chemical reactions such as nitration reaction, tosylation reaction, bromination, and
Suzuki and Stille coupling reactions. The obtained NTPP and BTPP were
1
characterized by H-NMR, IR and mass spectra and the results were consistent with
the predicted chemical structures. Both NTPP and BTPP are very soluble in
chloroform and other halogenated solvents at room temperature. They are also soluble
in other nonpolar solvents such as toluene while they show slightly lower solubility in
ethyl acetate and ethyl ether. The solution processed OTFT can be easily made by the
good solubility of NTPP and BTPP.
The thermal properties of the synthesized NTPP and BTPP were evaluated by
means of a thermogravimetric analysis (TGA) and differential scanning calorimetry
(DSC) in a nitrogen atmosphere. TGA revealed that the obtained NTPP and BTPP
o
present high thermal stability. The 5% weight loss was observed at 477 C for NTPP
o
and 458 C for BTPP. In the heating and cooling traces, a single endothermic and
exothermic transition, respectively, was observed at a temperature of 188 oC and 167
oC for NTPP, and 119 oC and 91 oC for BTPP, respectively (Fig. 1).
The UV-vis spectra in a dilute chlorobenzene showed absorption at 350, 410, and
472 nm for NTPP and 350, 410, and 471 nm for BTPP, respectively. NTPP and BTPP
showed similar absorption characteristic although the end group is different. The
spectral absorptions of the thin films of both NTPP and BTPP were red shifted and
broadened, with an absorption maximum at 493 nm for NTPP and at 480 nm for
BTPP. This result may have originated from aggregation or excimer formation due to
π→π* stacking, or from the intermolecular interaction caused by the planar structure
of pyrrolo-perylene derivatives (Fig. 2).
Cyclic voltammetry measurements of the thin films were carried out in a 0.1M
solution of tetrabutylammonium perchlorate (BuNClO4) in acetonitrile, under
nitrogen gas protection, at a scan rate of 50 mV/s. From electrochemical data and
10

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optical band gap, the HOMO and LUMO energy levels for NTPP were determined to
be - 5.16 eV and - 3.04 eV, respectively. In the same way, the HOMO and LUMO
levels for BTPP were determined to be - 5.18 eV and - 2.96 eV, respectively. The
determined HOMO levels of NTPP and BTPP match well with the work function of
gold metal.（-5.1 eV）Furthermore, they are lower than those of most regioregular
polythiophenes (-4.9 – -5.0 eV), thus indicating higher oxidative stability than
polythiophenes (Table 1).
The crystallinity of the thin film was investigated via a X-ray diffraction (XRD)
analysis. Fig. 3 (a) shows out of plane XRD spectra of the NTPP and BTPP film
processed by spin-coating from a 0.5 wt% chloroform solution. The surface of the
substrate was pretreated with octachlorotrisilane (OTS) in order to reduce the surface
energy between the film and the SiO2 interface, as well as to compensate any defects
on the surface of SiO2 layer. As shown in Fig. 3, BTPP shows clear Bragg diffraction
peaks while no Bragg diffraction peaks are observed in the film of NTPP. This
indicates that NTPP has amorphous nature as a result of its inability to undergo
appropriate molecular crystalline organization in the thin film. The results may be
explained by the critical role of end groups in the molecular self assembly of
pyrrolo-pyrene derivatives. The thin film XRD pattern of BTPP displayed a primary
diffraction peak at 2Ө = 2.5° (d-spacing 25.1 Å) with the second-order diffraction at
2Ө = 5.0° (d-spacing 12.5 Å). When we consider the length of the molecular long axis
via a molecular simulation using density function theory (DFT) B3LYP/6-31G*
methods in the Gaussian 03 program, the thin film XRD pattern of BTPP indicates
that the orientation of BTPP lattice is vertically oriented on the substrate and grew
along the out-of-plane direction. In other words, BTPP preferentially adopted an
“edge-on” orientation relative to the substrate (Fig. 4). This vertical orientation on the
substrate with the π-π stacking direction (parallel to the substrate) is known to be
favorable for in-plane charge transport.[21] As shown in Fig. 3 (b), the crystalline
structure of the BTPP films were further studied by means of two dimensional grazing
incidence X-ray diffraction. (2D GIXD). The Bragg diffraction patterns along qz
(out-of-plane) reveal a series of (00l) diffraction peaks consistent with our previous
11

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observation. Furthermore, we can observe multiple spots along the qz at a given qxy.
This suggests that the BTPP thin film has three dimensional molecular packing
structure, which can lead to high charge carrier mobility.
The thin film morphology of NTPP and BTPP was also studied by means of atomic
force microscopy (AFM) as shown in Fig. 5. It is clearly shown that BTPP has large
crystalline domains, while NTPP has featureless amorphous morphology. Collectively,
the structural and morphological studies indicate that BTPP adopt three dimensional
multi-layered crystalline structure, while NTPP does not have any long range ordered
crystalline structure.
OTFTs were fabricated by using thin films of BTPP and NTPP as the active layer,
and its electrical properties were characterized. The mobility (ꢀFET) and threshold
voltage (VTH) of the OTFTs were obtained from eq. (1), for the saturation regimes.
IDsat=(W/2L)ꢀFETCi(VG-VTH)2,
(1)
Where L is the channel length, W the channel width, and Ci the capacitance per unit
area of the gate dielectric layer (Ci=10 nF/cm2 for 300-nm-thick SiO2 ) The NTPP
and BTPP thin-film transistors were found to exhibit typical p-channel FET
characteristics. Table 2 summarizes the field effect mobilities as well as the on/off
current ratios and the threshold voltages obtained with BTPP film and NTPP film as
active semiconducting layers obtained by a solution process at different annealing
temperatures and using different solvents. As shown in Table 2, the best mobility of
devices was obtained by spin-coating chloroform solutions of BTPP and NTPP on an
OTS treated substrate. From the Table 2, the best mobility, on/off ratio, and VTH were
0.0024 cm2/Vs, 2.89 x 105, -8.55V for NTPP and 0.11cm2/Vs, 1 x 104, 0V for BTPP.
The representative transfer and output characteristics of BTPP based OFETs are
shown in Fig. 6. The mobility of BTPP with bithiophene end group is 2 orders higher
than that of NTPP with naphthyl thiophene end group. It may be resulted that BTPP
has three dimensional multi-layered crystalline structure, while NTPP does not have
any long range ordered crystalline structure as shown in the XRD and AFM results.
From the results, it is suggested that the end groups have the critical role in
molecular self-assembly of pyrrolo-pyrene derivatives for OTFT.
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4. Conclusion
new
A
family
of
pyrro-pyrene
derivatives
containing
2-(naphthalen-2-yl)thiophene (NTPP) and 2,2'-bithiophene (BTPP) were synthesized
by Suzuki and Stille coupling. NTPP and BTPP are suitable for solution processes,
implying that both materials have good solubility in halogenated solvents and
nonpolar solvents. The critical role of end groups in the molecular self assembly of
pyrrolo-pyrene derivatives was verified by characterization of out-of-plane XRD and
AFM images of NTPP and BTPP. From the out-of–plane XRD pattern and DFT
calculation using Gaussian, it was suggested that BTPP has high crystallinity with an
“edge-on” orientation relative to the substrate. A TFT incorporating BTPP with
bithiophene end groups exhibited excellent field effect mobility of 0.11 cm2V-1s-1 , an
on/off ratio of 1 x 104 and a threshold voltage of 0 V, which resulted from three
dimensional multi-layered crystalline structure.
Acknowledgments
This work was supported by Nano-Material Technology Development Program
through the NRF funded by Ministry of Education (2012049647) and by the Basic
Science Research Program through the National Research Foundation of Korea (NRF),
and by ministry of Education, Science and Technology (Grant number: 2012047047)
and New and Renewable Energy Technology Development Program of KETEP by
the Ministry of Knowledge Economy (20113020010070)
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Table 1. Optical, electrochemical, and thermal properties of NTPP and BTPP
Solution
Film
UV [nm]
Bandgap
[eV][a]
2.12
HOMO
[eV][b]
- 5.16
LUMO
[eV][c]
- 3.04
- 2.96
Td
[oC][d]
477
Tc1
[oC][e]
188
Tc2
[oC][f]
167
Tc3
[oC][g]
189
UV [nm]
PL [nm]
560
PL [nm]
604
NTPP
BTPP
472
471
493
480
550
571
2.22
- 5.18
458
119
91
120
[a] Calculated from the absorption edge wavelength. [b] Estimated from the onset oxidation potentials.
[c] Calculated from (HOMO level – Bandgap). [d] Decomposition temperature at a 5% weight loss. [e]
Transition temperature of the first heating process from DSC at a rate of 10 oC min-1. [f] Transition
temperature of first cooling process from DSC at a rate of 5 oC min-1. [g] Transition temperature of the
second heating process from the DSC at a rate of 10 oC min-1.
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Table 2. Characteristics of field-effect transistor based on NTPP and BTPP
Ts
Mobility
VTh
SS
Solvent
Xylene
Surface
OTS
Ion/Ioff
(oC)
( V )
V/dec
䟉cm2/(Vs))
NTPP
BTPP
0.0024
0.013
0.008
2.89E+05
1.00E+04
1.00E+04
-8.55
-10
-4.1
3.0
3.3
60
Bare
100
-10
CHCl3
60
100
60
0.11
0.02
0.07
0.02
1.00E+04
1.00E+04
1.00E+04
1.00E+04
0
1.4
2.5
1.5
2.6
OTS
-4
-2
-4
Ph-Cl
HMDS
100
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Figure Captions
Scheme 1. Synthetic schemes of NTPP and BTPP
Fig. 1. TGA and DSC curve of (a) NTPP and (b) BTPP
Fig. 2. UV-Vis. Absorption and PL spectra of (a) NTPP and (b) BTPP
Fig. 3. (a) Out-of-plane X-ray diffraction patterns of NTPP and BTPP (b) 2D-GIXD
patterns of BTPP
Fig. 4. DFT calculation using Gaussian for (a) BTPP and (b) NTPP and (c) suggested
molecular orientation of BTPP
Fig. 5. Height-mode AFM images of (a) BTPP film and (b) NTPP film. The vertical
scales of (a) and (b) represent 120 and 15 nm, respectively
Fig. 6. (a) Transfer and (b) Output characteristics of BTPP based OFET
20

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O
O S
O
C10H21
C8H17
Pyridine
O
S
O
C10H21
C8H17
CH3
+
OH
Cl
CH3
3
O
nꢁBuLi, C9H19BO3
THF
THF
Mg
S
S
S
Br
Br
B
O
+
7
6
NO2
6 wt% HNO3
C10H21
C8H17
NaH
N
NH +
3
CHCl3
TBAB
THF
1
4
2
C8H17
C10H21
O
S
B
O
N
S
S
Toluene
Br
Br
(NTPP)
NBS
MC
C10H21
C8H17
N
C8H17
C10H21
S
N
Sn(Bu)3
S
S
5
S
S
S
THF
(BTPP)
Scheme 1. Synthetic schemes of NTPP and BTPP
21

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NTPP
FirstHeating
Cooling
SecondHeating
100
90
80
70
60
50
40
NTPP
100
150
200
0
Temperature(C)
0
100
200
300
400
500
600
700
800
900
Temperature(0C)
BTPP
FirstHeating
Cooling
SecondHeating
100
BTPP
90
80
70
60
50
40
50
100
150
200
250
300
Temperature(oC)
0
100
200
300
400
500
600
700
800
900
Temperature(oC)
Figure 1. TGA and DSC curve of NTPP and BTPP
22

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UV(Solution)
NTPP
UV(Film)
PL(Solution)
PL(Film)
1.0
0.8
0.6
0.4
0.2
0.0
300
400
500
600
700
800
Wavelength(nm)
UV(Solution)
UV(Film)
PL(Solution)
PL(Film)
BTPP
1.0
0.8
0.6
0.4
0.2
0.0
300
350
400
450
500
550
600
650
700
750
800
Wavelength (nm)
Figure 2. UV-Vis. Absorption and PL spectra of NTPP and BTPP
23

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Figure 3. (a) Out-of-plane X-ray diffraction patterns of NTPP and BTPP (b)
2D-GIXD patterns of BTPP
24

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Figure 4. DFT calculation using Gaussian for BTPP and NTPP and suggested
molecular orientation of BTPP
25

ACCEPTED MANUSCRIPT
(a)
(b)
2μm
2μm
Figure 5. Height-mode AFM images of (a) BTPP film and (b) NTPP film. The
vertical scales of (a) and (b) represent 120 and 15 nm, respectively.
26

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Figure 6. (a) Transfer and (b) Output characteristics of BTPP based OFET
27

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Research highlight
►Pyrrolo-perylene-based organic semiconductors ►Naphtylthiophene end-capped pyrrolo-
perylene (NTPP) ► Bithiophene end-capped pyrrolo-perylene (BTPP) ►Three dimensional
multi-layered crystalline structure of BTPP ► High mobility of 0.11 cm2V-1s-1 with a very
small threshold voltage of 0 V