Energy level tuning of blue emitting and electron transporting vinylene bis(vinyl quinolinyl)benzene derivatives: synthesis, characterisation, thin film characterisation and performance in OLEDs

Article abstract of DOI:10.1039/c5tc00932d

A number of thermally stable, conjugated, blue-emitting vinylene bis(vinyl quinolinyl)benzene derivatives were prepared and three of them were characterised by single crystal X-ray crystallography. They exhibit blue to bluish-green emission (fluorescence and electroluminescence) depending on the substituents. Their effectiveness as electron transporters in red and green organic light emitting diodes (OLEDs) has been explored. The phenyl and naphthyl substituted compounds were found to be superior to Alq₃ in OLEDs as electron transporters. The electron mobility of the parent molecule, phenyl, thienyl and naphthyl substituted compounds were determined to be 8.0 × 10^-7, 3.3 × 10^-6, 5.5 × 10^-6 and 8.0 × 10^-6 cm² V^-1 s^-1 respectively. Lifetime measurements were carried out for the red and green fluorescent devices and compared with Alq₃ as an electron transporter. Some vinylene bis(vinyl quinolinyl)benzene derivatives show significantly longer lifetimes than analogous devices made with Alq₃ as the electron transport layer. Purple to dark blue emitting devices were achieved from two of the derivatives.

Full text of DOI:10.1039/c5tc00932d

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Kathirgamanathan, S. Surendrakumar, S. Ravichandran, M. Kumaraverl, J. Antipan-Lara, S.
Ganeshamurugan, L. Bushby, J. Tidey and A. J. Blake, J. Mater. Chem. C, 2015, DOI:
10.1039/C5TC00932D.
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Journal of Materials Chemistry C
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DOI: 10.1039/C5TC00932D
Journal of Materials Chemistry C
RSCPublishing
ARTICLE
Energy level tuning of blue emitting and electron
transporting vinylene bis(vinyl quinolinyl) benzene
derivatives: synthesis, characterisation, thin film
characterisation and performance in OLEDs
Cite this: DOI: 10.1039/x0xx00000x
Received 00th January 2012,
Accepted 00th January 2012
Poopathy Kathirgamanathan *a, Sivagnanasundram Surendrakumara,
Seenivasagam Ravichandrana, Muttulingam Kumaraverla, Juan Antipan Laraa,
Subramaniam Ganeshamurugana, Lisa M. Bushbya, Jeremiah P. Tideyb and
Alexander J. Blake*b
DOI: 10.1039/x0xx00000x
www.rsc.org/
A number of thermally stable, conjugated, blue emitting vinylene bis(vinyl quinolinyl)benzene
derivatives were prepared and three of them were characterised by singly crystal Xꢀray
crystallography. They exhibit blue to blueish green emission (fluoresecence and
electroluminescence) depending on the substituents. Their effectiveness as electron
transporters in red and green organic light emitting diodes (OLEDs) has been explored. The
phenyl and naphthyl substituted compounds were found to be superior to Alq3 in OLEDs as
electron transporters. The electron mobility of the parent molecule, phenyl, thienyl and
naphthyl substituted compounds were determined to be 8 x 10ꢀ7, 3.3 x 10ꢀ6, 5.5 x 10ꢀ6 and 8 x
10ꢀ6
cm2 Vꢀ1 sꢀ1 respectively. Lifetime measurements were carried out for the red and green
fluorescent devices and compared with Alq3 as an electron transporter. Some vinylene
bis(vinyl quinolinyl) benzene derivatives show significantly longer lifetimes than analogous
devices made with Alq3 as the electron transport layer.
Purple to dark blue emitting devices were achieved from two of the derivatives.
are multilayer devices, typically composed of (i) a hole injector
[e.g. copper phthalocyanine (CuPc), 4,4’,4”ꢀtris[Nꢀ(2ꢀ
1. Introduction
naphthyl)ꢀNꢀphenylꢀamino)triphenylamine
(2ꢀTNATA),
Manipulating the electronic, optical and thermal properties of
tripyrazinocyclohexane(s)1ꢀ3], (ii) a hole transporter [e.g., N,N’ꢀ
bisꢀ(1ꢀnaphthalenyl)ꢀN,N’ꢀbisꢀphenyl(1,1’ꢀbiphenyl)ꢀ4,4’ꢀ
diamine, (αꢀNPB)], (iii) an emissive layer (host + dopant), (iv)
an electron transporter [e.g. tris(8ꢀhydroxyquinoline)aluminium
(Alq3)], (v) an electron injector (e.g., LiF, CsF, lithium
quinolates) and (vi) a cathode (e.g. Al)4ꢀ6 to provide charge
balance so that efficient devices can be produced. Hole
transporters and electron transporters can also be doped with an
acceptor or donor, respectively, to increase the conductivities of
the respective layers5ꢀ6, 12ꢀ29
organic semiconductors is a major area of research as they find
13ꢀ18
widespread applicability1ꢀ7,
.
Over the last five years
organic light emitting diodes (OLEDs) have evolved into a
mature technology and flexible OLEDs are also under
development1.
Displays based on organic light emitting diodes (OLEDs)
have become one of the significant flat panel display
technologies, as evidenced by the production of active matrix
OLEDs for mobile phones by Samsung SDI and the
introduction of 56” OLEDꢀTVs by Samsung and LG Displays
(Korea). However, high performance organic semiconductors
are still required to improve the performance of these devices.
It is well known that the HOMOꢀLUMO levels of the
organic semiconductors play a major role in the performance of
OLED devices and thus we wanted to probe the band gap
tuning with a system such as oligophenylvinylene which
permits a large range of synthetic variations. Furthermore, the
quinolinoyl moiety is both electron transporting and
fluorescent. This paper investigates both properties.
There is a continuing demand for reduction of the power
consumption and operating voltage of OLEDs and for a
lengthening of their lifetime. Charge transport (hole and
electron) materials, whether pure or doped, are an integral part
of any OLED. It has been reported that nearly 60% of the total
electrical power loss in OLEDs is due to the transport layers
(hole injecting layer, 5.1 %; hole transporting layer, 7.7 %; hole
blocking layer, 5.8 %; electron transporting layer, 35.9 % and
electron injecting layer, 5.7 %) for a phosphorescent green
device. The remainder is due to the emissive layer (39.8%)9
The lifetime is also critically dependent on the nature of the
.
Long operational lifetimes and high electroluminescent
efficiencies are very important to commercial success. OLEDs
This journal is © The Royal Society of Chemistry 2013
J. Name., 2013, 00, 1-3 | 1

Journal of Materials Chemistry C
Page 2 of 17
VJieowuArrtnicalelONnlainme e
ARTICLE
DOI: 10.1039/C5TC00932D
transporters employed. Improvements in efficiencies of up to Scheme 1. Synthesis of selected bis(vinyl quinolinyl) benzene
70% have been reported by Kathirgamanathan et al1 and Kido derivatives
et al8 when Alq3, is replaced by some novel electron
transporters in otherwise identical devices.
2. Experimental
A good electron transporter (et) should have the following
characteristics10ꢀ13: (i) high electron affinity to match with the
Device fabrication
work function (W.F.) of the cathode, thus reducing the energy
barrier; (ii) high electron mobility (µe > 1 x 10ꢀ5 cm2 Vꢀ1 Sꢀ1) to
aid the transport of electrons into the emissive layer and
efficiently confine the excitons in this layer; (iii) a reversible
electrochemical reduction with a sufficiently high reduction
potential; (iv) a high ionisation potential (I.P.) to serve as a hole
blocker (I.P. > 6 e.V.); (v) a high glass transition temperature
and melting point; (vi) thermal stability up to at least 250°C
(high Tg/Tm/Td); (vii) stability under evaporation conditions for
a period of at least 144 hours if vacuum processing is
employed; (viii) good stability to moisture and oxygen; (ix)
capable of forming amorphous film so that crystallisation
induced degradation is avoided; (x) photostability; (xi) if
phosphorescent emitters are used, the triplet energy level of the
et should be higher than that of the phosphorescent emitters;
(xii) processability to produce uniform and pinholeꢀfree films
either by evaporation (small molecules) or by solution casting.
A variety of ets based on metal quinolinolate(s) (e.g. Alq3,
Inq3, Gaq3, Scq3, Mgq2), oxadiazole(s), imidazole(s), pyridine
Electronꢀonly devices were fabricated by evaporating E278ꢀST
and a selected number of its derivatives of layer thickness of 50
to 120 nm into a ITO/LiF/E278ꢀX/LiF/Al device structure.
Alq3 devices were also made for comparison. Holeꢀonly
devices were also fabricated as ITO/MoO3/E278ꢀX/MoO3/Al
using E278ꢀST, E278ꢀPhꢀST and αꢀNPB (for comparison).
Detailed electroluminescent characteristics were carried out
only on E278ꢀST, E278ꢀPhꢀST and E278ꢀThꢀST since we had
crystal structures for them only. The device structure was ITO
(anode)/E278ꢀX (50 nm)/LiF (1 nm)/Al (cathode).
Trilayer devices were also fabricated in order to establish
the electron transporting characteristics of Eꢀ278ꢀX the devices.
The device structure was ITO/ZnTpTP(HIL)/αꢀNPB (HTL)/Eꢀ
278ꢀX /LiF/Al.
Electroluminescent devices were fabricated by vacuum
thermal evaporation method using a multiꢀchamber OLED pilot
machine (Solciet OLED System, purchased from ULVAC,
Japan). The devices were fabricated on a patterned (pixelated
ITO substrate 40 ohms per square, surface resistance); Hitachi
High Tech., Japan), cleaned with water, acetone, isopropyl
alcohol and water (in that order), dried at 150 °C for 20
minutes and then subjected to ozone cleaning (UV irradiation,
185 nm) at 150 °C for 10 minutes. The substrate was then
plasmaꢀcleaned in the presence of oxygen for 25 seconds and
moved into the vacuum chamber from which the hole injector
[(5,10, 15, 20ꢀtetra(pꢀtolyl)ꢀ21H, 23Hꢀporphine)zinc(II)]
(ZnTpTP), 20 nm for red devices and 50 nm for green devices,
hole transporter [N,N’ꢀbisꢀ(1ꢀnaphthalenyl)ꢀN,N’ꢀbisꢀphenylꢀ
(1,1’ꢀbiphenyl)ꢀ4,4’ꢀdiamine, (αꢀNPB), 50 nm], host: dopant
[Alq3, (50 nm): (0.1 nm) dopant (N,N’ꢀdiphenylquinacridone
(DPQA), coꢀevaporation], electron transporter [either Alq3 or
Zrq4 (20 nm)] Eꢀ278ꢀX were sequentially deposited. The
evaporation rates of ZnTpTP, αꢀNPB, (Alq3, DPQA), E278ꢀX
and LiF (electron injector) were 1 Å/s, 1.6 Å/s, (1 Å/s, 0.1 Å/s),
1 Å/s and 0.05 Å/s respectively.
derivatives,
perfluorinated
oligophenylene(s),
silole(s),
phenanthroline(s), boron compounds and pyrimidone(s) have
been reported7, 8. However, despite its low electron mobility
and instability to holes, Alq3 has remained the material of
choice due to its low cost and acceptable OLED lifetimes. Alq3
has three major drawbacks: (i) it leaves behind a considerable
amount of residue during sublimation purification and OLED
production conditions: (ii) the operating voltage is still
relatively high and (iii) there is a perceived toxicity of
aluminium compounds.
We have been interested in charge transporting materials for
OLEDs over the last 20 years. Metal complexes leave behind
residues on evaporation under manufacturing conditions. Thus,
nonꢀmetalꢀbased electron transporters which could potentially
leave no residue under vacuum thermal evaporation conditions
are of immense value to OLED manufacturers. This paper
reports our successful attempt in synthesising organic electron
transporters.
Here we report the synthesis and application of bis(vinyl
quinolinyl) benzene derivatives as nonꢀmetal based alternative
electron transporters superior in performance to the
“workhorse” Alq3. We also report energy level tuning by
substituting the bis (vinyl quinolinyl) benzene (hereafter called
E278ꢀST) with phenyl (E278ꢀPhꢀST), thienyl (E278ꢀThꢀST),
naphthyl (E278ꢀNpꢀST) and pyrenyl (E278ꢀPyrꢀST). The
substituted quinolinyl derivatives were synthesised by Suzukiꢀ
Miyaura coupling as illustrated in Scheme 1.
Directly from the vacuum chamber, all the devices were
encapsulated using UV curable adhesive (Nagase) with glass
back plates in a glove box filled with dry nitrogen so that the
devices were not exposed to air. The electrical and optical
measurements were carried out by a computerꢀcontrolled
Keithley 2400 Source Meter and
a Minolta (CSꢀ1000)
spectrometer, respectively. HOMOꢀLUMO levels were
determined by cyclic voltammetry (by computerꢀcontrolled
potentiostat PAR 273 or CHI 600D) and from band gap
measurements by absorption spectroscopy of thin films
Br
Ar
O
O
H
H
produced by vacuum thermal evaporation.
Capacitance
[PPh3]4Pd
Ar
B
+
+
K2CO3
OMe
N
CH3
measurements were made on thin films as well as compacted
discs using an impedance analyser (Hewlett Packard, 4284A).
DC conductivity measurements of the materials were also
N
CH3
HO
reflux; 18h
Ar
Ar
Acetic anhydride
reflux, 6h
+
CH3
OHC
CHO
N
performed on compacted discs using a twoꢀprobe method24
N
N
.
Ar
S
3. Results and Discussion
Ar =
H
E-278-Th-ST
E-278-Np-ST
E-278-Ph-ST
3.1 Physical properties
E-278-PyR-ST
E-278-ST
The band gap of the E278ꢀST derivatives under investigation
was determined from the absorption edge of thin films
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 2012

Page 3 of 17
Journal Name
Journal of Materials Chemistry C
View Article Online
ARTICLE
DOI: 10.1039/C5TC00932D
The asymmetric unit of E278ꢀST comprises two halfꢀ
molecules disposed about crystallographic inversion centres.
The two molecules differ in their degree of planarity: one is
planar to within 0.031 Å, while the other is only planar to
within 0.197 Å and exhibits a marked sinusoidal shape. This is
also illustrated by the dihedral angles: while those between the
fused rings of the quinolinyl group [1.19(13), 1.16(13) °] are
produced by vacuum thermal evaporation (Fig. 1). It is
immediately apparent that phenyl and thienyl substituents lower
the band gap while napthyl and pyrenyl substituents increase
the band gap. Due to the increased conjugation, the band gap of
the fused ring system is expected to decrease, but contrary to
expectation, the band gap of the fused ring substitution
increases with increasing conjugation. We believe that this is
due to nonꢀplanarity of the molecules, E278ꢀNpꢀST and E278ꢀ
PyRꢀST which twists the quinolinyl moiety, thus increasing the
band gap.
3.0
Band Gap from Absorption Edge
Band Gap from PL
equiv
alent
in the
two
2.8
molec
ules,
2.6
2.4
2.2
the
angles
betwe
en the
quinol
inyl
group
s and
the
x=
ST
Ph-ST
Th-ST Np-ST Pyr-ST
centra
l
E278-x
pheny
l rings
[1.95(
13),
Figure 1 Comparison of band gaps from absorption edge of
photoluminescence
3.2 Crystal structure analysis
12.80(
13) °]
differ
marke
dly.
Crystals of E278ꢀST, E278ꢀPhꢀST and E278ꢀThꢀST suitable for
singleꢀcrystal Xꢀray crystallographic studies were grown by
slow vacuum sublimation at a temperature of 300 °C and a
pressure of 5 x 10ꢀ6 Torr. The tube furnace where the
compounds were sublimed crystallised had a gradient of three Molecules of E278ꢀST pack in a herringbone arrangement
different temperature zones. The temperature of the material (Figure 2) as the result of CH…π, π…π and CH…N
containing bulb of the tube was gradually increased and kept at interactions.
300 °C. The crystals were obtained at the temperature zone of
250 °C.
Diffraction data were collected at 120(2) K on Agilent
Figure 2 Upper, view of a single molecule of E278ꢀST; lower,
Technologies SuperNova diffractometers equipped with
packing of molecules of E278ꢀST. N atoms are shaded blue, C
black and H light grey
microfocus copper Xꢀray sources, mirror optics and Atlas or
Eos CCD detectors. Data collection and processing utilised
CrysAlisPRO34 The structures were solved by direct methods35
and refined using fullꢀmatrix least squares36, 37. Rotation
In E278ꢀPhꢀST, the asymmetric unit comprises a halfꢀ
molecule, the other half of which is generated by the operation
of an inversion centre. The dihedral angle between the fused
rings of the quinolinyl group [1.91(7) °] is somewhat greater
than in E278ꢀST; that between the quinolinyl group and the
central phenyl ring [12.19(7) °] is similar to the value in one of
the molecules of E278ꢀST. However, a significant deviation
from planarity arises from the twist of the terminal phenyl ring
relative to the quinolinyl group, where the mean torsion angle is
24.30(7) °. Packing in E278ꢀPhꢀST (Figure 3) also involves a
herringbone motif but this comprises C−H…π interactions
disorder in the thiophene rings was modelled with the use of
similarity and planarity restraints to the relevant geometric
parameters; restraints were also applied to the displacement
parameters of the thiophene ring; the occupancy of the major
component refined to 0.8426(9). Crystal structure diagrams
were produced using MERCURY38 and other material was
produced for publication
using OLEX237.
CCDC
1044135−1044137 contain the supplementary crystallographic
data for this paper in CIF format. These data can be obtained
free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif
.
This journal is © The Royal Society of Chemistry 2012
J. Name., 2012, 00, 1-3 | 3

Journal of Materials Chemistry C
Page 4 of 17
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ARTICLE
Journal Name
DOI: 10.1039/C5TC00932D
only: the twisting of the terminal phenyl ring allows it to form
one of the most favourable of these interactions.
shaded yellow, N blue, C black and H light grey. Only the
major component is shown for each disordered thiophene ring
3.3 Thermal characterisation
Differential Scanning Calorimetry (DSC). DSC was carried out
on E278ꢀST, E278ꢀPhꢀST, E278ꢀThꢀST, E278ꢀNpꢀST and
E278ꢀPyRꢀST. DSC of the E278ꢀST derivatives (Fig. 5, also
see Table 1) show higher melting points than that of the parent
compound (E278ꢀST, 246 °C). The melting point follows the
order E278ꢀST < E278ꢀPyrꢀST < E278ꢀNpꢀST < E278ꢀPhꢀST <
E278ꢀThꢀST. The increase in the melting point is expected as
aromatic side groups and fused ring systems enhance the
rigidity of a molecule and thus increases the energy required to
melt a material. Further, the higher melting point of E278ꢀThꢀ
ST (330 °C) compared to E278ꢀPhꢀST (312 °C) could be
explained on the basis that the former is a planar molecule and
the latter is not (the phenyl substituent is out of plane) as
reducing the efficiency of the packing of the crystal structure
(refer to Figure 3).
Only E278ꢀNpꢀST and E278ꢀPyrꢀST showed glass
transition temperatures (of 94 °C and 88 °C, respectively) and
we indeed found them to sublime to produce amorphous
Figure 3 Upper, view of a single molecule of E278ꢀPhꢀST;
lower, packing of molecules of E278ꢀPhꢀST. N atoms are
shaded blue, C black and H light grey
100
50
Molecules of E278ꢀThꢀST have no crystallographically
imposed symmetry and are planar to within 0.168 Å. The
thiophene rings are both disordered by a rotation of ca. 180 °
about the bonds to their respective quinolinyl groups: the
major/minor occupancies are 0.8426(9)/0.1574(9) and
0.8491(9)/0.1509(9). The dihedral angles of 7.57(8) ° and
8.01(8) ° between the major thiophene components and the
linked quinolinyl groups may partly reflect the limitations of
the disorder modelling. The dihedral angles between the central
phenyl rings and its two flanking quinolinyl groups are 8.01(8)
and 11.25(7) °, producing the net effect of a molecule that is
more planar than E278ꢀPhꢀST. Packing in E278ꢀThꢀST (Figure
4) takes the form of another herringbone motif involving
C−H…π interactions.
0
30
20
-50
E278 ST
E278 Ph-ST
E278 Th-ST
E278 Np-ST
E278 PyR-ST
10
Np-ST-SS
PyR-ST(SS)
0
100
200
300
400
-100
100
200
Temperature/ (oC)
300
400
powders whereas E278ꢀST, E278ꢀPhꢀST and E278ꢀThꢀST all
formed crystals on slow sublimation.
Figure 5 Differential scanning calorimetry of E278ꢀST, E278ꢀ
PhꢀST, E278ꢀThꢀST, E278ꢀNpꢀST and E278ꢀPyRꢀST; inset
shows the Tg of E278ꢀNpꢀST and E278ꢀPyRꢀST
Thermogravimetric analysis (TGA). TGA (Fig. 6) under
nitrogen shows that all the compounds are stable in air in
excess of 300 °C. E278ꢀPhꢀST, E278ꢀNpꢀST, E278ꢀPyrꢀST
and E278ꢀThꢀST are stable up to 400 °C and E278ꢀThꢀST is
remarkably stable up to 499 °C (weight loss of only 2.5 %). It
is important that E278ꢀST and E278ꢀPhꢀST do not leave behind
any residues. The compounds are also stable under multiple
100
80
60
Figure 4 Upper, view of a single molecule of E278ꢀThꢀST;
lower, packing of molecules of E278ꢀThꢀST. S atoms are
E278-ST
E278 Ph-ST
E278 PyR-ST
40
E278 NP-ST
E278 Th-ST
20
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 2012
0
200
400
600
800
Temperature/ (oC)

Page 5 of 17
Journal Name
Journal of Materials Chemistry C
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ARTICLE
DOI: 10.1039/C5TC00932D
sublimation purification.
Figure 6 Thermogravimetric analysis of E278ꢀST, E278ꢀPhꢀ
ST, E278ꢀPyRꢀST, E278ꢀNpꢀST and E278ꢀThꢀST
Table 1 Physical properties of E278ꢀST and its derivatives
Compound
STRUCTURE
M.
O
P
.
(DSC) Tg /oC
TGA / % wt Band gap
NSET /OC
loss
/eV
N
E278ꢀST
246
312
ꢀ
ꢀ
400 (0%)
2.70
N
N
E278ꢀPhꢀST
E278ꢀThꢀST
400 (0%)
2.58
2.59
N
N
S
330
ꢀ
499 (2.5%)
S
N
N
E278ꢀNpꢀST
276
94
400 (0.5%)
2.79
N
N
E278ꢀPyRꢀST
266
88
400 (3%)
2.88
N
3.4. Optical measurements
Absorption and fluorescence spectroscopy in solution. The
derivatives of E278ꢀST, namely E278ꢀPhꢀST, E278ꢀThꢀST,
E278ꢀNpꢀST and E278ꢀPyrꢀST, were all found to be fluorescent
both in solution and as thin films produced by vacuum thermal
evaporation (VTE).
Fig. 7 shows the photoluminescent
characteristics of the bis(vinyl quinolinyl) benzene derivatives
under exposure to UV light. Absorption and fluorescence
spectroscopy were carried out in chloroform (Fig. 8).
This journal is © The Royal Society of Chemistry 2012
J. Name., 2012, 00, 1-3 | 5

E278 ST
Journal of Materials Chemistry C
Page 6 of 17
E278 Ph-ST
1.0
1.0
E278 Pyr-ST
E278 Np-ST
E278 Th-ST
E278-ST
ARTICLE
VJieowuArrtnicalelONnlainme e
DOI: 10.1039/C5TC00932D
0.8
0.6
0.4
0.2
0.8
0.6
0.4
0.2
0.0
E278 Ph-ST
E278 Pyr-ST
E278 Np-ST
E278 Th-ST
respectively. We attribute these differences in the PL peak
positions as arising primarily from the substituents effects as
the peak position of the of the thin films were largely invariant
of the thickness of the film.
Table 2 E278 series: absorption and fluorescence
Comp
ound
Absorption
Fluorescence
peak λmax
nm in CHCl3
solution
Absorption
peak λmax /
nm thin film
Fluorescence
peak λmax /
nm thin film
peak λmax
nm in
/
/
0.0
CHCl3
250
300
350
400
450
λ/nm
500
550
600
650
solution
(extinction
coefficient)
379
Figure 7 Emission of E278ꢀST and its derivatives in CHCl3
under normal lighting conditions (top) and upon exposure to
UV radiation (bottom)
E278ꢀ
ST
439
429
302, 418(sh)
372, 442(sh)
378
455, 485(sh)
511, 541(sh)
511, 555(sh)
521
(4.90 x 104)
E278ꢀ
PhꢀST
393
(1.00 x104)
Figure 8 Absorption and emission spectra of E278ꢀST (parent)
and its derivatives in chloroform
E278ꢀ
ThꢀST
403
(3.90 x 103)
437, 460(sh)
430
Thin film absorption and fluorescence. UVꢀVis absorption
and fluorescence spectroscopy was carried out on thin films
(thickness approximately 100 nm) produced by vacuum thermal
evaporation (Fig. 9). All the materials were sublimed without
decomposition and with no loss of vacuum during evaporation.
The results are summarised in Table 2.
E278ꢀ
NpꢀST
388
(4.00 x 104)
364
E278ꢀ
PyRꢀ
ST
364
(6.98 x 104)
438
363
466(sh), 494
E278 ST
E278 Ph-ST
E278 PyR-ST
E278 Np-ST
E278 Th-ST
E278 ST
E278 Ph-ST
E278-Pyr-ST
E278-Np-ST
E278 Th-ST
0.8
1.0
0.8
0.6
0.4
0.2
0.0
1.0
Alq3
1.0
E278- ST
E278 Ph-ST
E278 Th-ST
E278 Np-ST
E278 Pyr-ST
0.8
0.6
0.4
0.2
0.0
0.6
0.4
0.2
0.0
200
300
400
500
600
λ/nm
100
150
200
250
300
350
Temperature/oC
Figure 9 Absorption and emission spectra of the thin film of
E278ꢀST (parent) and its derivatives
Figure 10 Evaporation rate of E278ꢀST, E278ꢀPhꢀST, E278ꢀ
ThꢀST, E278ꢀNpꢀST and E278ꢀPyRꢀST compared to the
evaporation rate of Alq3
The evaporation rate vs temperature plots are shown in Fig. 10.
The E278ꢀPyrꢀST has the lowest evaporation temperature
required to obtain similar evaporation rate to Alq3 while all the
E278ꢀST derivatives require higher temperature than Alq3.
This can be possibly attributed to the large size of the
pyrenyl group and the consequent diminished intermolecular
interaction.
The photoluminescence (PL) of the thin films (Fig. 9)
(where the molecules are constrained) are all red shifted (to
longer wavelengths) as expected compared to the PL of the
solutions where the molecules are free to move. The red shift
(λfilm – λsolution) for E278ꢀST, E278ꢀPhꢀST, E278ꢀNpꢀST, E278ꢀ
PyRꢀST and E278ꢀThꢀST are 16, 105, 91, 56 and 63 nm
3.5. Electrochemical properties
Cyclic voltammetry was performed in dichloromethane
containing the analyte E278ꢀST (0.01 mM), E278ꢀPhꢀST (0.5
mM), E278ꢀThꢀST (0.1 mM) or E278ꢀNpꢀST (0.1 mM) except
for E278ꢀPhꢀST whose CV was also carried out in acetonitrile
because of its poor solubility in dichloromethane (Fig. 12).
E278ꢀPyrꢀST was so insoluble in most organic solvents suitable
for electrochemistry, that its CV could not be performed.
6 | J. Name., 2012, 00, 1-3
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Journal Name
Journal of Materials Chemistry C
View Article Online
ARTICLE
DOI: 10.1039/C5TC00932D
where NHE = Normal Hydrogen Electrode.
The E1/2 values employed here were determined from the
derivative of the cyclic voltammograms. From the absorption
band edge of the evaporated thin films, the band gaps of the
compounds were deduced and then the LUMO levels were
calculated.
The HOMOꢀLUMO levels of the E278ꢀST, PhꢀST, ThꢀST,
NpꢀST and PyRꢀST are shown in Fig. 13 where they are
compared with the HOMOꢀLUMO of the hole transporter,
NPB and the electron transporter, Alq3.
αꢀ
x,y:0.309,0.467
x,y:0.258,0.519
x,y:0.393,0.528
E278-ST
E278-Ph-ST
E278-Th-ST
Figure 11 Single layer electroluminescent devices of E278ꢀST,
E278ꢀPhꢀST, E278ꢀThꢀST (top), CIE x,y colour coordinates
and the photoluminescence of thin films under 365 nm
irradiation (bottom)
Figure 13 HOMOꢀLUMO energy levels of E278 series
3.6. Electrical characterisation
Background
E278 ST/CH Cl
2
2
Electron-only single layer devices. The electronꢀonly devices
(Set A) were fabricated where the anode and the cathode were
LiF/Al. Thus, Glass/ITO/LiF /E278ꢀX/LiF/Al where X = ST,
PhꢀST, ThꢀST. Control devices were also made with Alq3 (Fig.
14). We also fabricated electronꢀonly devices (Set B),
Glass/ITO/Mg, Ag/E278ꢀX/Mg, Ag/Al where X = ST, PhꢀST
and NpꢀST (Fig. 15). We fitted the current density (Jd) vs. Field
(E) to diode, Fowler Nordheim and space charge limited current
(SCLC) models11ꢀ12 and found that the data fitted well to the
SCLC model, but not to others. The conductivity (DC and AC)
and the permittivity of the materials were measured on
compacted discs (two probe method) 24. The conductivity of the
complexes was so low (< 1 x 10ꢀ8 S cmꢀ1) that four probe
measurements could not be carried out 19ꢀ23. The data are
summarised in Table 3.
E278-Ph-ST/CH Cl
2
2
E278 Ph-ST/CH CN
3
E278 Th-ST/CH Cl
2
2
E278-Np-ST/CH Cl
2
2
0.5
0.0
0.0
0.4
0.8
1.2
1.6
Voltage (V vs. Ag/AgCl)
Figure 12 Cyclic voltammetry of E278ꢀST, E278ꢀPhꢀST,
E278ꢀThꢀST and E278ꢀNpꢀST in dichloromethane and also
E278ꢀPhꢀST in acetonitrile
Table 3 DC and AC conductivity (100 kHz) and relative
permittivity (compacted discs)
Compound
DC
AC conductivity
(σ) S cmꢀ1 at
100 kHz
Relative
permittivity at
100 kHz (εr = ε/ε0
conductivity
(σ) S cmꢀ1
The supporting electrolyte was tetrabutylammonium
hexafluorophosphate (0.2 M) in all case. The working, auxiliary
and reference electrodes were Pt (foil), Pt (wire) and Ag/AgCl
respectively. The CVs were performed in both the oxidation (0
to 1.8 V) and reduction (0 to ꢀ2 V) regions. The CVs were
found to be irreversible in both anodic and cathodic scans
except for E278ꢀNpꢀST which gave quasiꢀreversible peaks in
the anodic scans (Figure 12). Since the cathodic cycles were
found to be irreproducible except for E278ꢀST, we decided to
use the anodic scans for the determination of the HOMO levels.
The HOMO levels were determined from the equation in
reference26.
Alq3
5 x 10ꢀ13
5 x 10ꢀ13
1 x 10ꢀ13
5 x 10ꢀ10
5 x 10ꢀ10
2 x 10ꢀ10
3.06 ± 0.10
3.1 ± 0.10
3.2 ± 0.10
E278ꢀST
E278ꢀPhꢀST
E278ꢀThꢀST
E278ꢀNpꢀST
1 x 10ꢀ12
9 x 10ꢀ12
5 x 10ꢀ10
6 x 10ꢀ9
3.3 ± 0.10
3.0 ± 0.10
HOMO or LUMO = ꢀ ((E1/2 vs. NHE) + 4.40) eV
This journal is © The Royal Society of Chemistry 2012
J. Name., 2012, 00, 1-3 | 7

Journal of Materials Chemistry C
Page 8 of 17
VJieowuArrtnicalelONnlainme e
ARTICLE
DOI: 10.1039/C5TC00932D
The devices of ITO/Mg/Ag/E278ꢀX/Mg/Ag/Al (Set B,
Figure 15), where X = ST, PhꢀST and NpꢀST) show current
injection in the following order: E278ꢀNpꢀST > E278ꢀST >
E278ꢀPhꢀST at all field strength tested. We observed that
ITO/LiF/E278ꢀNpꢀST/LiF /Al devices were unstable and
irreproducible while E278ꢀThꢀST was not stable with Mg/Ag
contact. It should be noted that the reason for the reduction in
the magnitude of the current for a given field compared to the
ITO/LiF/E278ꢀX/LiF/Al devices is due to the fact that the work
function of Mg/Ag (3.7 eV) is higher than that of LiF/Al (3.4
eV).
1200
300
250
200
1000
150
100
50
800
0
0.0 0.2 0.4 0.6 0.8 1.0
600
400
200
It can be deduced that the electron injection characteristics
should follow the order E278ꢀNpꢀST > E278ꢀST > E278ꢀPhꢀST
> E278ꢀThꢀST > Alq3 at least at medium and high fields
employed in OLED devices.
E278-ST(120nm)
E278-Ph-ST (100nm)
Alq
(55nm)
3
E278 Th-ST(65nm)
Thin film conductivity was determined from the Ohmic
0
0
region (Jd
charge region (Jd
∝
V) and the mobility was calculated from the space
1
2
3
4
V2) using the equation1, 32
-1
∝
E / MVcm
Figure 14 Electronꢀonly devices, current density (mA cmꢀ2) vs
field (MV cmꢀ1); Device structure: ITO/LiF (0.5 nm)/E278ꢀ
X/LiF (0.5 nm)/Al (75 nm)
JSCLC = (9/8) ε ꢁ V2/d3
where JSCLC = current density in the SCLC region, ε =
permittivity, ꢁ = mobility, V = voltage and d = thickness. The
data obtained from the holeꢀonly and electronꢀonly devices are
summarised in Table 4.
In the case of Alq3 based devices, a negative differential
resistance (NDR) was observed. This behaviour has been
observed by ourselves in a large number of devices whether
Table 4 Thin film conductivity, electron and hole mobility of
Alq3, E278ꢀST, E278ꢀPh_ST, E278ꢀThꢀST and E278ꢀNpꢀST
they were single or multilayer as has been observed by others39
.
The reason for this behaviour could be attributed to a number
of factors such as (i). The reduction of Alq3 at the cathode39c
(ii). Tunnelling effects 39e, (iii). adventitious doping of Alq3 with
nitrogen during encapsulation in a nitrogen filled glove box,
Thin film
conductivity
(S cmꢀ1)
Thin film
conductivity
(S cmꢀ1)
from holeꢀ
only devices
Electron
mobility
Hole
mobility
(µh/cm2 Vꢀ1
sꢀ1) from
holeꢀonly
devices
(µe/cm2 Vꢀ1
sꢀ1) from
from
generating hopping sites (guest hopping sites, GHS)39d-e
.
electronꢀ
only devices
electronꢀ
only devices
2
E278-ST(88nm)
E278 Ph-ST (45nm)
E278-Np-ST(26nm)
Alq3
7.5 x 10ꢀ10
5.0 x 10ꢀ9
4.8 x 10ꢀ11
1.6 x ꢀ10
4.4 x 10ꢀ7
8 x 10ꢀ7
1.1 x 10ꢀ8
3 x 10ꢀ8
1
E278ꢀ
ST
0
E278ꢀ
PhꢀST
4.0 x 10ꢀ8
1.0 x 10ꢀ7
7.5 x 10ꢀ7
3.2 x 10ꢀ11
3.3 x 10ꢀ6
5.5 x 10ꢀ6
8 x 10ꢀ6
1.7 x 10ꢀ9
(a)
-1
-2
-3
-4
E278ꢀ
ThꢀST
(a)
(a)
E278ꢀ
NpꢀST
(a)
-4
-3
-2
-1
0
1
2
-1
Log (E/MVcm
)
Figure 15 Electronꢀonly devices, current density (mA cmꢀ2) vs
field (MV cmꢀ1); Device structure: Glass/ITO/Mg, Ag/E278ꢀ
X/Mg, Ag/Al
(a) not measured due to device instability
Hole-only devices. Holeꢀonly devices (ITO/MoO3 (10
nm)/E278ꢀX (100 nm)/MoO3 (10 nm)/Al (100 nm) were
fabricated only for E278ꢀST and E278ꢀPhꢀST (Fig. 16) as the
other materials were not stable during measurements. A control
device was also made with αꢀNPB, a wellꢀknown hole
transporter. We obtained a hole mobility of 1 x 10ꢀ5 cm2 Vꢀ1 sꢀ1
for αꢀNPB consistent with published data. Table 5 summarises
the electron and hole mobilities of E278ꢀST, E278ꢀPhꢀST,
The current density vs. field (Figure 14) for the electron
only (Set A) devices, ITO/LiF/E278ꢀST/LiF/Al show that the
electron injection characteristics of E278ꢀThꢀST was found to
be best (E278ꢀThꢀST > E278ꢀPhꢀST > E278ꢀST >>> Alq3) at
low field, but worst at high field (E278ꢀST > E278ꢀPhꢀST >
E278ꢀThꢀST >>> Alq3) but it is still better than Alq3. However,
the differences are small among the E278 derivatives, but they
were all significantly higher than Alq3.
8 | J. Name., 2012, 00, 1-3
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DOI: 10.1039/C5TC00932D
E278ꢀThꢀST
and
E278ꢀNpꢀST. 6) of the films would affect the device performance as well as
the optical properties19, 33
2500
50
.
a-NPB
E278-ST
E278 Ph-ST
40
Table 6 Degree of Anisotropy
30
2000
20
10
σelectron (thin film σhole (thin
only) only)
film
0
0.0
1500
0.5
1.0
1.5
2.0
/
σdisc
/
σdisc
Compound
Alq3
1000
1.5 x 103
1.0 x 106
4.0 x 105
1.0 x 105
8.33 x 104
9.6 x 101
500
E278ꢀST
3,2 x 102
E278ꢀPhꢀST
E278ꢀThꢀST
3.2 x 102
0
0.0
0.5
1.0
E / MVcm-1
1.5
2.0
Not available
Not available
Figure 16 Holeꢀonly devices, current density (mA cmꢀ2) vs E278ꢀNpꢀST
field (MVcmꢀ1); Device structure: Glass/ITO/MoO3/E278ꢀ
X/MoO3/Al
The hole injection was highest for αꢀNPB at all the 3.7. Light emitting devices
field tested. At low field (E < 1.6 MV cmꢀ1), the hole injection
current follow the order: αꢀNPB > E278ꢀST > E278ꢀPhꢀST and
at high field (E > 1.7 MVcmꢀ1), the order was αꢀNPB > E278ꢀ
PhꢀST > E278ꢀST.
Single layer light emitting devices. Single layer devices
(ITO/E278ꢀX/LiF/Al) were fabricated to determine the
transport properties of the E278ꢀST, E278ꢀPhꢀST and E278ꢀThꢀ
ST. The current injection (Fig. 17) seems to follow the order
E278ꢀST > E278ꢀThꢀST > E278ꢀPhꢀST although the electron
mobilities show E278ꢀThꢀST > E278ꢀPhꢀST > E278ꢀST, but the
differences in mobilities are quite small. We attribute the
current injection behaviour in the single layer light emitting
devices is entirely
Table 5 Comparison of electron and hole mobilities of Alq3,
E278ꢀST, E278ꢀPh_ST, E278ꢀThꢀST and E278ꢀNpꢀST
governed by the barrier height on the cathode side12 which is 0
eV, 0.06 eV and 0.58 eV for E278ꢀST, E278ꢀThꢀSt and E278ꢀ
PhꢀST respectively.
Electron mobility
(µe/cm2 Vꢀ1 sꢀ1)
from electronꢀonly
devices
Hole mobility
(µh/cm2 Vꢀ1 sꢀ1)
from holeꢀonly
devices
µe/µh
1800
4
1600
Alq3
4.4 x 10ꢀ7
8 x 10ꢀ7
1.1 x 10ꢀ8
3 x 10ꢀ8
40.0
26.7
1941
3
2
1
1400
0
-1
E278ꢀST
-2
1200
-3
-6
-5
-4
-3
-2
-1
0
1
E278 ST(100)
E278 Ph-ST(100)
E278 Th-ST(70)
Alq3
E278ꢀPhꢀST
3.3 x 10ꢀ6
1.7 x 10ꢀ9
1000
800
600
400
200
0
1.0
0.8
0.6
0.4
0.2
0.0
E278ꢀThꢀST
E278ꢀNpꢀST
5.5 x 10ꢀ6
8 x 10ꢀ6
a
a
NA
NA
0.0
0.2
0.4
0.6
0.8
1.0
(a) not measured due to device instability
0
2
4
6
8
-1
It is worth noting that the substitution of the phenyl
group and the consequent twisting of the molecule makes the
E278ꢀPhꢀST more electronꢀtransporting and less holeꢀ
transporting than the parent E278ꢀST (Table 5). The thin film
conductivity measured both under electron only condition and
hole only conduction are significantly higher than the
corresponding disc conduction (Table 6). This is not surprising
as the molecules orient themselves in films as opposed to discs
under isotropic compaction. The anisotropic behaviour (Table
E / MVcm
Figure 17 Single layer EL devices (ITO/E278ꢀX/LiF/Al;
where X= ST, PhꢀST and ThꢀST)
The devices were of poor efficiency and the maximum
luminance achieved was 21 cd mꢀ2. This is attributed to the
poor hole injection into E278ꢀX as no hole injector or
transporter was used. However, it is worth noting that the E278ꢀ
X/LiF/Al interface is more effective than Alq3/LiF/Al in terms
current injection. Further, the free Li formed at the LiF/Al
interface has no detrimental effect on the E278ꢀX systems2b.
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J. Name., 2012, 00, 1-3 | 9

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ARTICLE
Journal Name
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Electroluminescent characteristics of ITO/E278-X/LiF/Al.
The electroluminescent characteristics of the single layer
devices
Turn on voltage
(Vt/V) (a)
Current efficiency
/cdAꢀ1 (b)
Power efficiency /lm
Colour coordinates
CIE (x, y)
Cathode side
barrier /eV
Anode side barrier
/eV
Wꢀ1 (b)
2 x 10ꢀ2
1.6 x 10ꢀ2
2 x 10ꢀ3
E278ꢀST
0.00
0.58
0.06
1.3
3.0 ± 0.2
6.0 ± 0.2
3.5 ± 0.2
1 x 10ꢀ1
3.6 x 10ꢀ2
2.7 x 10ꢀ3
(0.309, 0.467)
(0.258, 0.519)
(0.393, 0.528)
E278ꢀPhꢀST
E278ꢀThꢀST
0.62
1.14
E278 ST/ Thin-film PL
E278 Ph-ST/ Thin-film PL
E278 Th-ST/Thinfilm PL
ITO/E278-ST(100)/LiF/Al, (0.309,0.467)
ITO/E278 Ph-ST(100)/LiF90.5)/Al(0.258,0.519)
ITO/E278 Th-ST(70)/LiF(0.5)/Al, (0.393,0.528)
Table 7 Electroluminescent performances of the single layer
devices for E278ꢀST, E278ꢀPhꢀST and E278ꢀThꢀST (a) at 1
cdmꢀ2; (b) at 10 cdmꢀ2
1.0
0.8
0.6
0.4
0.2
0.0
are summarised in Table 7. The performance of the single layer
electroluminescent devices was poor owing to the lack of hole
injection and consequent charge injection imbalance.
Electroluminescence requires the injection of both holes and
electrons and this is determined by the barrier heights of the
anodic and cathodic sides. It should be mentioned that E278ꢀST
and E278ꢀThꢀST are planar molecules while E278ꢀPhꢀST is not
(as shown by the crystal structure, see Fig. 3). The turnꢀon
voltage follows the barrier presented to the device on both
anode and the cathode side.
400
450
500
550
600
650
λ/nm
Figure 19 Comparison of the electroluminescent (EL) and
photoluminescent (PL) spectra of the single layer devices of
E278ꢀST, E278ꢀPhꢀST and E278ꢀNpꢀST; Device Structure:
ITO/E278ꢀX (100 nm)/LiF/Al
Figure 20 Energy diagram of triꢀlayer device, ITO/ZnTpTP (10
nm)/αꢀNPB (50 nm)/E278ꢀX (50 nm)/LiF (0.5 nm)/Al
Figure 18 Energy level diagram of single layer device
(ITO/E278ꢀX/LiF/Al)
E278-X as an electron transporter in tri-layer
electroluminescent devices.
The EL spectra of E278ꢀPhꢀST and E278ꢀThꢀST were
almost identical to their respective PL spectra indicating that
the same excited state is involved whereas the EL spectrum of
E278ꢀST is substantially redꢀshifted compared to its PL and
featureless. We have established that there is no decomposition
on evaporation of E278ꢀST by taking samples from the
evaporated thin films and carrying out elemental analysis and
crystal structure where we obtained identical chemical
composition. Thus, we conclude that the red shift is due to the
effect of orientation of the molecule on the ITO and hence the
excited state is different of the E278ꢀX derivatives (Fig 19).
The difference in the orientation33 could result from the
evaporation rates employed in the device manufacture (1 Å sꢀ1)
as opposed to the thin film for PL produced in excess of 50 Å sꢀ
In order to increase the hole injection, we fabricated triꢀlayer
devices composed of a hole injecting layer and a hole
transporting layer. The hole injector ZnTpTP and the hole
transporter αꢀNPB were employed to enhance the hole injection
into the emissive layer; ITO/ZnTpTP (10 nm)/αꢀNPB (50
nm)/E278ꢀX (50 nm)/LiF (0.5 nm)/Al where the E278ꢀST,
E278ꢀPhꢀST and E278ꢀThꢀST act as both emissive and electron
transporting layer. The hole injector ZnTpTP was used to
enhance the hole injection and to planarize the ITO surface. αꢀ
NPB acts as the hole transporter. Their performances are
summarised in Table 8.
1
.
10 | J. Name., 2012, 00, 1-3
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DOI: 10.1039/C5TC00932D
Turn on voltage
(Vt)/V (a)
Current efficiency
Power efficiency
1931ꢀColour
coordinates CIE (x, y)
Barrier height with
αꢀNPB /eV
Cathode side barrier
height /eV
/cdAꢀ1 (b)
2.5 x 10ꢀ1
6.0 x 10ꢀ1
3.5 x 10ꢀ1
/lm Wꢀ1 (b)
1.0 x 10ꢀ1
2.7 x 10ꢀ1
1.2 x 10ꢀ1
E278ꢀST
0.80
0.12
0.64
0.00
0.58
0.06
4.5 ± 0.1
3.7 ± 0.1
5.2 ± 0.1
(0.351, 0.505)
(0.370, 0.546)
(0.362, 0.517)
E278ꢀPhꢀST
E278ꢀThꢀST
Table 8 Electroluminescent performances of the three layer Device structure: ITO/ZnTpTP (10 nm)/αꢀNPB (50 nm)/E278ꢀ
devices of ITO/ZnTpTP (10 nm)/αꢀNPB (50 nm)/E278ꢀX (50 X (50 nm)/LiF (0.5 nm)/Al
nm)/LiF (0.5 nm)/Al; where E278ꢀX = E278ꢀST, E278ꢀPhꢀST
and E278ꢀThꢀST
As in the case of single layer devices (namely, ITO/E278ꢀ
X/LiF/Al), the EL spectra of E278ꢀST is significantly different
from its thin film PL indicating that different excited states are
involved in the PL and EL. However, as in the case of single
layer devices, the EL and PL of the E278ꢀPhꢀST and E278ꢀThꢀ
ST are virtually identical indicating that the same excited states
are involved (Fig 21).
1000
100
10
100
80
60
40
20
0
E278 ST,(0.351,0.505)
E278 Ph-ST, (0.370,0.546)
E278 Th-ST, (0.362,0.517)
As expected14ꢀ15, the introduction of the hole transport layer
improves the current efficiency of E278ꢀST, E278ꢀPhꢀST,
E278ꢀThꢀST by 2.5, 17 and 130 fold.
E278 ST, (0.351, 0.505)
E278 Th-ST, (0.362,0.517)
E278 Ph-ST, (0.370,0.546)
E278 ST/TF/FL
E278 Th-ST/TF/FL
E278 Ph-ST/TF/FL
1
0
2
4
6
8
10
12
Voltage / V
1.0
0.8
0.6
0.4
0.2
Figure 22 Luminance and current density (J) vs voltage plots
of the devices: ITO/ZnTpTP (10 nm)/αꢀNPB (50 nm)/E278ꢀX
(50 nm)/LiF (0.5 nm)/Al
The current density vs voltage plot (Figure 22) shows that the
current injection is highest for E278ꢀPhꢀST and then E278ꢀST
and E278ꢀThꢀST in that order (i.e. E278ꢀPhꢀST > E278ꢀST >
E278ꢀThꢀST). The maximum luminance levels achieved for the
tri layer devices are around 400 cdmꢀ2 as a result of increased
hole injection compared to the single layer devices for which
the maximum luminance achieved was only 20 cd mꢀ2.
0.0
400 450 500 550 600 650
λ/nm
Figure 21 Comparison of the electroluminescent (EL) and
photoluminescent (PL) spectra of the three layer devices;
This journal is © The Royal Society of Chemistry 2012
J. Name., 2012, 00, 1-3 | 11

Journal of Materials Chemistry C
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ARTICLE
Journal Name
DOI: 10.1039/C5TC00932D
TI Rubrene
E278 ST, (0.351, 0.505)
E278 Ph-ST, (0.370,0.546)
E278 Th-ST, (0362,0.517)
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
0.7
0.6
Figure 24 Energy level diagram for device structure:
ITO/ZnTpTP (20 nm)/ ꢀNPB (60 nm)/Alq3: Rub: DCJTI
(30:30:0.7 nm)/ETL (30 nm)/LiF (0.5 nm)/Al
0.5
0.4
0.3
0.2
0.1
0.0
α
Figure 25 Current density (linear and log) and luminance vs
voltage plots for the red device ITO/ZnTpTP (20 nm)/αꢀNPB
(60 nm)/Alq3: Rub: DCJTI (30:30:0.7 nm)/ETL (30 nm)/LiF
(0.5 nm)/Al
0
100 200 300 400 500
Alq3, (0.652, 0.347)
-2
Luminance / cdm
E278-ST, (0.647, 0.353)
E278-PhST, (0.651, 0.349)
E278-PyPh, (0.659, 0.341)
E278-Np-ST, (0.650, 0.350)
Figure 23 Current efficiency vs luminance and power
efficiency vs luminance plot of the devices: ITO/ZnTpTP (10
nm)/αꢀNPB (50 nm)/E278ꢀX (50 nm)/LiF (0.5 nm)/Al
Electron transporting characteristics of E278-X in red devices
7
6
4.5
4.0
Alq3 (0.652, 0.347)
E278-ST (0.647, 0.353)
E278-Ph-ST (0.651, 0.349)
E278-Np-ST (0.650, 0.350)
Red devices were fabricated using Alq3 and rubrene as coꢀhost
and
4ꢀ(dicyanomethylene)ꢀ2ꢀiꢀpropylꢀ6ꢀ(1,
1,
7,
7ꢀ
3.5
400
3.0
tetramethyljulolidylꢀ9ꢀenyl)ꢀ4Hꢀpyran (DCJTI) as the red
fluorescent emitter. The device performance of the red devices
(ITO/ZnTpTP (20 nm)/αꢀNPB (60 nm)/Alq3: Rub: DCJTI
(30:30:0.7 nm)/ETL (30 nm)/LiF (0.5 nm)/Al) are shown in
Fig. (25ꢀ28) and summarised in Table 9.
The efficiency improvement by both E278-Ph-ST and E278-
Naph-ST over Alq3 as etl is attributed mainly to their higher
electron mobility than Alq3. E278-Naph-ST has slightly deeper
HOMO level than the host Alq3, but the current efficiency
between the E278-Ph-ST and that of E278-Naph-ST is not
significant, but E278-Naph-ST gives higher power efficiency.
We believe that the main mechanism is enhanced electron
injection rather than any hole blocking property of E278-Naph-
ST.
5
105
4
4
10
300
2.5
103
3
2.0
200
102
2
1.5
100
101
1
1.0
100
0
0
0.5
0
4
8
12
16
100 101 102 103 104
Voltage / V
-2
Luminance / cdm
Figure 26 Current efficiency and power efficiency vs
luminance plots for the red device ITO/ZnTpTP (20 nm)/
αꢀ
NPB (60 nm)/Alq3: Rub: DCJTI (30:30:0.7 nm)/ETL (30
nm)/LiF (0.5 nm)/Al
Table 9 Performance data for the red devices. Device structure:
ITO/ZnTpTP (20 nm)/
αꢀNPB (60 nm)/Alq3: Rub: DCJTI
(30:30:0.7 nm)/ETL (30 nm)/LiF (0.5 nm)/Al
DCJ
Current density vs voltage plots (Fig. 25) show that E278ꢀ
Current efficiency
η /cd Aꢀ1 (b)
4.0 ± 0.1
Power efficiency
η /lm Wꢀ1 (b)
1.5 ± 0.1
CIE (x, y) (b)
Vt on /V (a)
Vop /V (b)
Alq3
3.0 ± 0.1
2.2 ± 0.1
2.0 ± 0.1
2.1 ± 0.1
2.1 ± 0.1
8.2 ± 0.1
7.5 ± 0.1
6.2 ± 0.1
8.0 ± 0.1
7.2 ± 0.1
(0.652, 0.347)
(0.647, 0.353)
(0.651, 0.349)
(0.650, 0.350)
(0.659, 0.341)
E278ꢀST
3.2 ± 0.1
1.2 ± 0.1
E278ꢀPhꢀST
E278ꢀNpꢀST
4.5 ± 0.1
2.2 ± 0.1
4.6 ± 0.1
1.8 ± 0.1
E278ꢀPyRꢀST
3.5 ± 0.1
1.5 ± 0.1
N
O
12 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 2012
NC
CN

Page 13 of 17
Journal Name
Journal of Materials Chemistry C
View Article Online
ARTICLE
DOI: 10.1039/C5TC00932D
PhꢀST seems to have the most efficient current injection,
followed by E278ꢀPyrꢀST, then E278ꢀST. E278ꢀNpꢀST is
surprisingly less effective in terms of current injection and only
as good as Alq3. Luminance vs voltage (Fig. 25) follows the
same trend. However, current efficiency of the devices at 1000
cdmꢀ2 shows that the efficiency of the devices with E278ꢀPhꢀST
(4.5 ± 0.1 cd Aꢀ1) is comparable to that with E278ꢀNpꢀST (4.6 ±
0.1 cd Aꢀ1) despite their differences in the HOMOꢀLUMO
levels (Fig. 26).
The current efficiency follows the order E278ꢀNpꢀST
=E278ꢀPhꢀST > Alq3 >E278ꢀPyrꢀST > E278ꢀST. Power
efficiency follows the order E278ꢀPhꢀST > E278ꢀNpꢀST >
E278ꢀPyrꢀST > Alq3 > E278ꢀST (Fig. 26).
Turnꢀon voltage (Vt) for all the E278ꢀX (X= E278ꢀST,
E278ꢀPhꢀST, E278ꢀNpꢀST, E278ꢀPyrꢀST) derivatives are all
comparable (2.1 ± 0.2 V, slightly higher than the band gap of
DCJTi, 2.06 eV) and much lower than the turnꢀon voltage when
Alq3 (3 V) was used as electron transport layer. The operating
voltage to achieve 1000 cd mꢀ2 follows the following order:
E278ꢀPhꢀST (6.2 ± 0.1 V) < E278ꢀPyrꢀST (7.2 ± 0.1 V) <
E278ꢀST (7.5 ± 0.1 V) < E278ꢀNpꢀST (8.0 ± 0.1 V) = Alq3
(8.2 ± 0.1 V).
1.0
0.8
0.6
0.4
0.2
0.0
)
(
Alq3 (0.652, 0.347)
E278-ST (0.647, 0.353)
E278-Ph-ST (0.651, 0.349)
E278-Np-ST (0.650, 0.350)
0
1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 11000
t/h
Figure 28 Voltage drift plots of the red devices ITO/ZnTpTP
(20 nm)/ ꢀNPB (60 nm)/Alq3: Rub: DCJTI (30:30:0.7
nm)/ETL (30 nm)/LiF (0.5 nm)/Al
α
The lifetime of only E278ꢀST, E278ꢀPhꢀST and Alq3 were
measured. Devices with E278ꢀNpꢀST were not stable at 500 cd
mꢀ2. The halfꢀlife of the devices with Alq3, E278ꢀST and E278ꢀ
PhꢀST as etl were found to be 2000 hours, 10000 hours and
6500 hours. The lifetime of the devices with E278ꢀST and
E278ꢀPhꢀST is five times and nearly three times the lifetime of
Alq3, respectively.
Normalised voltage drift after 6500 hours of operation was
found to be 0.93, 0.58, 0.40 for Alq3, E278ꢀST and E278ꢀPhꢀST
as etl indicating that the E278ꢀST and E278ꢀPhꢀST based
devices are more stable than Alq3.
Alq
(0.652, 0.347)
3
1.0
0.8
0.6
0.4
0.2
E278-ST (0.647, 0.353)
E278-Ph-ST (0.651,0.349)
E278-Np-ST (0.650,0.350)
0
4000
8000
12000
t/h
Electron transporting characteristics of E278-X in green devices
Figure 27 Lifetime plots for the red device ITO/ZnTpTP (20
nm)/αꢀNPB (60 nm)/Alq3: Rub: DCJTI (30:30:0.7 nm)/ETL DPQA
(30 nm)/LiF (0.5 nm)/Al at 500 cdmꢀ2
O
Lifetime studies (Fig. 27) were carried out on the red
devices at initial luminance of 500 cd mꢀ2 at constant current
and voltage drift plots for the same devices (drift voltage
normalised with respect to Alq3) are given in Fig. 28.
N
N
Figur
O
e
29
Energ
y level
diagra
Current efficiency
η /cd Aꢀ1 (b)
11.0 ± 0.5
6.0 ± 0.5
Power efficiency
CIE (x, y) (b)
Vt on /V (a)
Vop /V (b)
η /lm Wꢀ1 (b)
3.0 ± 0.2
2.0 ± 0.2
2.3 ± 0.2
3.0 ± 0.2
4.0 ± 0.2
Alq3
4.5 ± 0.1
3.9 ± 0.1
3.9 ± 0.1
3.5 ± 0.1
3.0 ± 0.1
3.2 ± 0.1
9.5 ± 0.1
8.5 ± 0.1
8.6 ± 0.1
8.5 ± 0.1
8.5 ± 0.1
10.5 ± 0.1
(0.321, 0.649)
(0.291, 0.654)
(0.297, 0.666)
(0.320, 0.647)
(0.288, 0.670)
(0.317, 0.651)
E278ꢀST
E278ꢀPhꢀST
E278ꢀThꢀST
E278ꢀNpꢀST
E278ꢀPyRꢀST
7.0 ± 0.5
7.5 ± 0.5
12.5 ± 0.5
11.0 ± 0.5
3.0 ± 0.2
This journal is © The Royal Society of Chemistry 2012
J. Name., 2012, 00, 1-3 | 13
(a) at 1 cd mꢀ2 (b) at 1000 cd mꢀ2

Alq3 (0.321, 0.649)
Journal of Materials Chemistry C
Page 14 of 17
VJieowuArrtnicalelONnlainme e
E278-ST (0.291, 0.654)
ARTICLE
DOI: 10.1039/C5TC00932D
E278-Ph-ST (0.297, 0.666)
E278-Th-ST (0.320, 0.647)
E278-Np-ST (0.288, 0.670)
E278-PyR-ST (0.317, 0.651)
m for device structure: ITO/ZnTpTP (50 nm)/
α
ꢀNPB (50
Figu
re
32
Lifet
ime
plots
of
the
gree
n
105
104
103
102
101
100
500
400
300
200
100
0
nm)/Alq3: DPQA (50:0.1 nm)/ETL (20 nm)/LiF (0.5 nm)/Al
Green devices were manufactured with DPQA as the dopant
and Alq3 as the host. The device structure was ITO/ZnTpTP (50
nm)/αꢀNPB (50 nm)/Alq3: DPQA (50 nm: 0.1 nm)/ETL (20
nm)/LiF (0.5 nm)/Al (See Fig. 33) where the ETL were E278ꢀ
ST, E278ꢀPhꢀST, E278ꢀThꢀST, E278ꢀNpꢀST, E278ꢀPyrꢀST and
Alq3 and their performance are shown in Table 10.
The current density vs voltage plot (Fig. 30) reveals that all
the E278ꢀX derivatives have higher current injection ability
than Alq3 and the differences among them is small, although a
trend of E278ꢀPhꢀST > E278ꢀThꢀST > E278ꢀNpꢀST > E278ꢀ
PyrꢀST > E278ꢀST > Alq3 can be gleaned. The luminance vs
devi
ces.
Devi
0
4
8
12
16
20
Voltage / V
voltage plot (Fig. 30) gives a slightly different order, but the ce structure: ITO/ZnTpTP (50 nm)/αꢀNPB (50 nm)/Alq3:
differences between the E278ꢀX derivatives are small. They all DPQA (50:0.1 nm)/ETL (20 nm)/LiF (0.5 nm)/Al at the initial
have considerably lower operating voltage than Alq3 as electron luminance of 1200 cd mꢀ2
transport layer.
Table 10 Performance data of the green devices. Device
structure: ITO/ZnTpTP (50 nm)/αꢀNPB (50 nm)/Alq3: DPQA
1.2
Alq3, (0.321, 0.649)
E278-ST, (0.291, 0.654)
E278-Ph-ST, (0.297, 0.666)
E278-Th-ST, (0.320, 0.647)
E278-PyR-ST, (0.317, 0.651)
E278-Np-ST (0.317, 0.651)
(50: 0.1 nm)/ETL (20 nm)//LiF (0.5 nm)/Al
Figure 30 Current density and luminance vs voltage plots of
1.0
the green devices. Device structure: ITO/ZnTpTP (50 nm)/αꢀ
NPB (50 nm)/Alq3: DPQA (50:0.1 nm)/ETL (20 nm)/LiF (0.5
nm)/Al
0.8
0.6
0.4
0.2
0.0
0.8
0.6
0.4
0.2
0.0
Alq3, (0.321, 0.649)
Figur
E278-ST (0.291, 0.654)
e
31
E278-Ph-ST (0.297, 0.666)
E278-Th-ST (0.320, 0.647)
E278-Np-ST (0.288, 0.670)
E278-PyR-ST (0.317, 0.651)
20
15
10
5
15
12
9
Curre
nt
efficie
ncy
0
20
40
60
80
100
0
2000
4000
6000
t / h
8000
10000
12000
and
power
efficie
ncy vs
lumin
ance
Figure 33 Voltage drift plots of the green devices. Device
structure: ITO/ZnTpTP (50 nm)/ ꢀNPB (50 nm)/Alq3: DPQA
(50:0.1 nm)/ETL (20 nm)/LiF (0.5 nm)/Al
6
α
3
E278-X as blue emitters
plots
of the
green
device
s.
0
0
100 101 102 103 104 105
Since E278ꢀX are highly blue fluorescent in solvents such as
dichloromethane, chloroform and acetonitrile as well as in
thin films, we decided to investigate the properties of E278ꢀST,
-2
Luminance / cdm
and
E278ꢀPhꢀST
as
dopants
using
1,3ꢀbis(Nꢀ
Device structure: ITO/ZnTpTP (50 nm)/αꢀNPB (50 nm)/Alq3:
carbazolyl)benzene (mꢀCP) as a host. BAlq2 was used as the etl.
We fabricated devices of the structure ITO/MoO3 (10
nm)/αꢀNPB (40 nm)/mCP: E278ꢀx (50 nm: 1 nm)/BAlq2 (10
nm)/LiF (0.5 nm)/Al (Fig 34).
DPQA (50:0.1 nm)/ETL (20 nm)/LiF (0.5 nm)/Al
1.0
1.0
0.8
0.6
0.4
0.2
0.0
0.8
0.6
0.4
0.2
0.0
The EL spectra (λmax, 439 nm) of the devices with E278ꢀST
as the dopant overlaps completely with the PL of 2% doped
E278ꢀST in mꢀCP thin films produced by VTE (Figure 35).
This indicates that the excited state involved the EL is identical
to that in the PL. The devices emitted purplish blue colour
(CIE, (x,y): (0.156, 0.112). The current and power efficiencies
of the devices were 0.4±0.1 cd/A and 0.1 lm/W at 1000 cdmꢀ2
0
20 40 60 80 100
Alq3, (0.321, 0.649)
E278-ST, (0.291, 0.654)
E278-Ph-ST, (0.297, 0.666)
E278-Th-ST, (0.320, 0.3647)
E278-PyR-ST, (0.317, 0.651)
E278-Np-ST (0.288, 0.670)
respectively
.
0
2000
4000
6000
8000 10000 12000
t / h
14 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 2012

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Journal Name
Journal of Materials Chemistry C
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ARTICLE
DOI: 10.1039/C5TC00932D
similar to that of PL (
λ
max, 456 nm, shoulder 470 nm), but the
PL has an additional shoulder at 410 nm, akin to the features of
the PL obtained from pure (neat) E278ꢀPhꢀST films produced
by VTE (Figure 36). We therefore conclude that the excited
states involved in both cases are same. E278ꢀPhꢀSt devices
show higher efficiencies (1 cd/A, 0.2 lm/W at 1000 cdmꢀ2), but
dark blue emission (CIE, x,y: 0.164, 0.186) (Figure 37). We
believe that the optimisation of the thickness of the hole
transporter, emissive layer and the dopant level should result in
higher efficiency. This work is ongoing and will be published
elsewhere.
Figure 36 The EL spectra of devices where E278ꢀPhꢀST is the
dopant and the PL spectra with 2 % E278ꢀPhꢀST as dopant
Table 11 Performance data of the blue devices. Device
Figure 34 Energy level diagram for the device structure: structure: ITO/MoO3 (10 nm)/αꢀNPB (40 nm)/mꢀCP: E278ꢀX
ITO/MoO3 (10 nm)/αꢀNPB (40 nm)/mCP: E278ꢀX (50: 1 (50: 1 nm)/BAlq2 (10 nm)//LiF (0.5 nm)/Al
Dopant
CIE colour
coordinates (x, y)
Current efficiency
/cd Aꢀ1
Power
efficiency
/lm Wꢀ1
E278-ST / Thin film /PL
mCP / Thin film / PL
1.0
E278ꢀST
(0.156, 0.112)
(0.164, 0.186)
0.mCP:E278-ST(50:1nm) / Thin film / PL
m4C±P0+.E1278-ST(50:1n0m.1),0(0±.105.60,02.112)
0.8
E278ꢀPhꢀST
1 ±0.1 0.20±0.02
0.6
0.4
0.2
0.0
Figure 37 CIE
coordinates of
EL of the blue
350
400
450
500
λ/nm
550
600
650
the
devices
of
nm)/BAlq2 (10 nm)/LiF (0.5 nm)/Al
ITO/MoO3 (10
nm)/αꢀNPB (40
nm)/mCP:
Figure 35 The EL spectra of devices where E278ꢀST is the
dopant and the PL spectra with 2 % E278ꢀST as dopant
E278ꢀ
X
(50:
1
nm)/BAlq2 (10
O
nm)/LiF (0.5 nm)/Al
N
N
Al
O
N
2
CIE colour coordinate diagram in Figure 36 illustrates the
colour obtained from the E278ꢀST (purple blue) and E278ꢀPhꢀ
ST (blue) devices.
mCP
BAlq2
The EL spectra of the devices based on E278ꢀPhꢀST is
E278 Ph-ST/ Thin film / PL
mCP/ Thin film / PL
mCP+E278-Ph-ST (50:1nm) Thin film / PL
mCP+E278-Ph-ST (50:1), (0.164, 0.186)
Conclusions
A number of thermally stable, conjugated, blue emitting
vinylene bis(vinyl quinolinyl)benzene derivatives were
prepared and three of them were characterised by singleꢀcrystal
Xꢀray crystallography. They exhibit blue to bluishꢀgreen
emission (fluorescence and electroluminescence) depending on
their substituents. We have demonstrated that band gaps,
HOMOꢀLUMO levels and the mobilities can be tuned by
appropriate choice of substituents. Some derivatives namely
E278ꢀST, E278ꢀPhꢀST and E278ꢀThꢀST leave no residues on
vacuum thermal evaporation.
1.0
0.8
0.6
0.4
0.2
This journal is © The Royal Society of Chemistry 2012
J. Name., 2012, 00, 1-3 | 15
0.0
350
400
450
500
550
600
650
λ/nm

Journal of Materials Chemistry C
Page 16 of 17
VJieowuArrtnicalelONnlainme e
ARTICLE
DOI: 10.1039/C5TC00932D
Their effectiveness as electron transporters in red and green 7. S. Reinnke, F. Lindner, G. Schwartz, N. Seidler, K. Walzer, B.
OLEDs has been explored. The phenylꢀ and naphthylꢀ Lussem and K. Leo, Nature, 2009, 459, 234.
substituted compounds were found to be superior to Alq3 as 8. H. Sasabe, T. Chiba, S. J. Su, YꢀJ. Pu, K. Naayama and J. Kido,
electron transporters in organic light emitting diodes (OLEDs). Chem., Commun., 2008, 5821.
The electron mobility of the parent molecule and its phenylꢀ, 9. J. J. Brown, IMID, OLED Workshop, Korea, 2007.
thienylꢀ and naphthylꢀsubstituted compounds were determined 10. (a) J. Endo, T. Matsumoto and J. Kido, Jpn. J. Appl. Physics.,
to be 8 x 10ꢀ7, 3.3 x 10ꢀ6, 5.5 x 10ꢀ6 and 8 x 10ꢀ6 respectively.
2002, 41, L358; (b) P. Kathirgamanthan, S. Surendrakumar, S.
The dark blue electroluminescence from the E278ꢀST and Ravichandran, R.V. Reddy, J. Antipan Lara, S. Ganeshamurugan, M.
E278ꢀPhꢀST derivatives opens up an area of colour tuning from Kumaraverl, G. Paramaswara and V. Arkley, Chem Letts., 2010,
simple molecular modification.
122ꢀ124; (c) A. P. Kulkarni, C. J. Tonzole, A. Babel and S. A.
Jeneke, Chem. Mater., 2004, 16, 4556; (d) G. Hughes and M. R.
Bryce, J. Mater. Chem., 2005, 15, 94ꢀ107
Supplementary information
11. I. D. Parker, J. Appl. Phys., 1994, 75, 1656.
The 6ꢀsubstituted 2ꢀmethylꢀ8ꢀhydroxyquinoline was
synthesised by Suzuki coupling reaction from 6ꢀbromoꢀ2ꢀ
methylquinolines and the corresponding boronic acids.
Bis(vinyl quinolinyl)benzene derivatives were made by
refluxing benzeneꢀ1,4ꢀdicarboxaldehyde (terephthalaldehyde)
with the 2ꢀmethylquinolinyl derivative in acetic anhydride and
subsequent purification by sublimation. The synthetic details of
the compounds presented are given in the Supplementary
Information.
12. (a) A. J. Heeger, I. D. Parker and Y. Yang, Synthetic Metals.,
1994, 67, 23; (b) D. R. Baigent, N. C. Greenham, J. Gruner, R. N.
Marks, R. H. Friend, S. C. Moratti and A. B. Homes, Synthetic
Metals., 1994, 67, 3ꢀ10
13. R. Partridge, US Patent. 1976/ 3995299
14. C. W. Tang, US Patent. 1982/ 4356429
15. C. W. Tang and S. A. VanSlyke, Appl. Phys. Lett., 1987, 51,
913.
16. J. H. Burroughes, D. D. C. Bradley, A. R. Brown, R. N. Marks,
K. Mackay, R. H. Friend, P. L. Burn and A. B. Holmes, Nature,
1990, 347, 539.
17. J. Kido, K. Nagai and Y.Okamoto, IEEE Trans. Electron
Devices, 1997, 44, 1245.
18. T. Wakimoto, Y. Fukuda, K. Nagayama, A. Yokoi, H. Nakada
and M. Tsuchida., IEE Trans. Electron Devices, 1997, 44, 1245.
19. P. Kathirgamanathan and D. R. Rosseinsky, J. Chem. Soc.,
Chem. Commun., 1980, 839.
Notes and references
a
Organic Electronics, Wolfson Centre, Brunel University
London, Kingston Lane, Uxbridge, UB8 3PH, UK.
p.kathirgamanathan@brunel.ac.uk
b
School of Chemistry, University of Nottingham, University
Park, Nottingham, NG7 2RD, UK.
a.j.black@nottingham.ac.uk
20. L. B. Valdes, Proc. I.R.E., 1954, 42, 420.
1. (a) H.Sasabe and J. Kido, J of Mater. Chem C., 2013, 1, 1699ꢀ
707; (b) J. W. Kwon, T. J. Park, W. S. Jeon, S. H. Jeon, J. J. Park, Y.
K. Lee and J. Jang, SID Symposium Digest of Tech. Papers, 2007,
38(1), 888ꢀ891; (c) P. Kathirgamanathan, S. Surendrakumar, J.
21. L. J. Van der Pauw, Philips Research Reports., 1958, 13, 1.
22. L. J. van der Pauw, Philips Tech. Reviews, 1959, 20, 220.
23. L. J. Van der Pauw, Philips Research Reports, 1961, 16, 187.
24. P. Kathirgamanathan, Ph. D Thesis (Exeter)ꢀ(1980)
25. Physics and Chemistry of the Organic Solid State, Editors: D.
Fox, M.M. Labes, A. Weissberger, Interscience Publishers, New
York (1967).
26. B. W. D’Andrade, S. Datta, S. R. Forrest, P. Djurovich, E.
Polikarpov and M. Thmpson, Organic Electronics, 2005, 6, 11.
27. M. Cole and W. Brutting, Physics of Organic Semiconductors,
pages 95ꢀ128, WileyꢀVCH Verlag GmBH, ISBNꢀ13: 978ꢀ3ꢀ527ꢀ
40550ꢀ3 (2005).
28. S. J. Su, H. Sasabe, Y.J Pu, K.Nakayama and J. Kido, Adv.
Mater., 2010 22,3311.
29. K. T. Kamtekar, A. P. Monkman and M. R. Bryce, Adv.
Materials., 2010, 22(5), 572ꢀ582
30. (a) S. Hyun Kim, J. Jang and J Y. Lee, Appl. Phys. Letts., 2007,
91, 083511; (b) S. Ok Jeon, K S. Yook, C, W, Joo and J. Y. Lee,
Adv. Materials., 2010, 22(16), 1872
32. (a) J. Antipan Lara and P. Kathirgamanathan, IEEE Proc.
Optoelectron., 2000, 147, 369; (b) D. R. Lamb, Electrical
conduction Mechanisms in Thin Insulating Films., 1967, Methuen
and Co. Ltd, 11, New Felter Lane, London EC4
33. D. Yokahama, J. Mater. Chem, 2011, 21, 19187ꢀ19202
34. Agilent Technologies, 10 Mead Road, Yarnton, Oxfordshire
OX5 1QU, United Kingdom
35. G. M. Sheldrick, Acta Crystallogr., Sect. A 2008, 64, 112.
36. G. M. Sheldrick, Acta Crystallogr., Sect. A 2015, 71, 3.
37. L. J. Bourhis, O. V. Dolomanov, R. J. Gildea, J. A. K. Howard
and H. Puschmann, Acta Crystallogr., Sect. A 2015, 71, 59.
38. C. F. Macrae, P. R. Edgington, P. McCabe, E. Pidcock, G. P.
Shields, R. Taylor, M. Towler and J. van de Streek, J. Appl.
Crystallogr. 2006, 39, 453.
AntipanꢀLara,
S. Ravichandran, V.R. Reddy, S.
Ganeshamurugan, M. Kumaraverl, V. Arkley, A. J. Blake and D.
Bailey, J. Mater. Chem., 2011, 21, 1762ꢀ1771; (d) P.
Kathirgamanathan, S. Surendrakumar, S. Ravichandran,
R. R.
Vanga, J.AntipanꢀLara, S. Ganeshamurugan, M. Kumaraverl, G.
Paramaswara and V. Arkley, Chem. Lett., 2010, 39, 1222ꢀ1224; (e)
P. Kathirgamanathan, S. Surendrakumar, R. R. Vanga, S.
Ravichandran, J. AntipanꢀLara, S. Ganeshamurugan,M. Kumaraverl,
G. Paramaswara and V.Arkley, Organic Electronics, 2011, 12, 666ꢀ
676; (f) S. Chen, J. Wei, K. Wang, D. Chen, Y. Liu and Y. Wang, J.
Mater. Chem., 2013, 1, 6594ꢀ6602; (g) P. Kathirgamanathan and S.
Surendrakumar, Patent (PCT)., WO2009/112854 A1 (17ꢀ09ꢀ2009)
2. (a). P. Kathirgamanathan, V. Arkley, S. Surendrakumar, G.
Paramaswara,
J
AntipánꢀLara,
S.
Ravichandran,
S.
Ganeshamurugan, M. Kumaraverl and Y. F. Chan, Asian Soc. for
Information Display, 2007, ISBN: 978ꢀ981ꢀ05ꢀ8143ꢀ5. (2b). P.
Kathirgamanathan, S. Surendrakumar, Juan AntipanꢀLara, S.
Ravichandran, Y.F.Chan, V. Arkley, S. Ganeshamurugan, M.
Kumaraverl, G. Paramaswara, A. Parteepan, V. R. Reddy, D. Bailey
and A. J. Blake, J. Mater. Chem.,2012, 22, 6104ꢀ6116.
3. K. Ueno, A. Senoo and S. Mashmo, US Patent. 6436559B1, 20ꢀ
08ꢀ2002.
4. S. H. Son, O. K. Kim, S. H. Yoon, K. K. Kim., Y. G. Lee and J.
S. Bae, US Patent. 6720573B2, 13ꢀ04ꢀ2004.
5. K. P. Klubeck and D. Y. Kondakov, US Patent. 2007/0122657,
31ꢀ05ꢀ2007.
6. P. Kathirgamanathan, V. Kandappu, S. Hara, K. Chandrakumar,
S. L. Marianesan, S. Selvaranjan, S. Surendrakumar and M. J.
Toohey, Mater. Lett., 1999, 40, 285.
16 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 2012

Page 17 of 17
Journal Name
Journal of Materials Chemistry C
View ArticAle ROnTliInCeLE
DOI: 10.1039/C5TC00932D
39.
a. S. R. Butter, Ph. D. Thesis, “Effects of Conformation on
the Electronic and Optical Properties of Aryleneethylenes”
Durham University (2007).
b. L. D. Bozano, B. W. Kean, V. R. Deline, J. R. Salem and
J. C. Scott, Appl. Phys. Letters, 84 (4), 607 (2004).
c. Z. S. Su, M. K. Fung, C. S. Lee, W. L. Li and S. T. Lee,
Appl. Phys. Letters, 93, 083301 (2008).
d. M. A. Mohd Sarjidan, S. H. Basri, N. K. Zaaba, M. S.
Zainin and W.H. Abd Majid, Bulletin of Materials
Science, 2015, 38(1), 235ꢀ239.
e. Y.K. Fang, Y.T. Chiang, S.F. Chen, C.Y. Lin, S.C. Hou,
C.S. Hung, T.W. Tsai, S.H. Chang and T. H. Chou, J.
Physics and Chemistry of Solids, 69 (2008) 738ꢀ741
f. T.Y. Chang, Y. W. Cheng and P.T. Lee, Appl. Phys.
Letters, 96, 043309 (2010).
g. Y. S. Kim, S.Y. Jung, K. H. Koh and S. Lee, J. Korean
Physical Society, 53 (6), 3563 (2008)
This journal is © The Royal Society of Chemistry 2012
J. Name., 2012, 00, 1-3 | 17