Synthesis and properties of twin derivatives of triphenylamine and carbazole

Article abstract of DOI:10.1016/j.jphotochem.2017.03.004

Synthesis as well as thermal, optical, photophysical, and electrochemical properties of new carbazole and triphenylamine twin derivatives with high triplet energies are reported. The synthesized compounds exhibit ability of glass formation. Their glass transition temperatures are in the range of 32–37?°C. The triphenylamine and carbazole derivatives absorb electromagnetic irradiation in the range of 200–360?nm with the band gaps of 3.71 and 3.44?eV, respectively. DFT calculations show that HOMO and LUMO orbitals of compounds are localized separately on the substituents and central 4,4′-thiodibenzenthiol unit, respectively. The synthesized twin derivatives have triplet energies of 2.72 and 2.76?eV. The electron photoemission spectra of the films of the synthesized compounds reveal ionization potentials of 5.54 and 5.61?eV.

Full text of DOI:10.1016/j.jphotochem.2017.03.004

Accepted Manuscript
Title: Synthesis and properties of twin derivatives of
triphenylamine and carbazole
Authors: G. Simkus, A. Tomkeviciene, D. Volyniuk, V.
Mimaite, G. Sini, R. Budreckiene, J.V. Grazulevicius
PII:
S1010-6030(16)30834-6
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.jphotochem.2017.03.004
JPC 10555
To appear in:
Journal of Photochemistry and Photobiology A: Chemistry
Received date:
Revised date:
Accepted date:
29-9-2016
22-2-2017
2-3-2017
Please cite this article as: G.Simkus, A.Tomkeviciene, D.Volyniuk, V.Mimaite,
G.Sini, R.Budreckiene, J.V.Grazulevicius, Synthesis and properties of twin derivatives
of triphenylamine and carbazole, Journal of Photochemistry and Photobiology A:
Chemistry http://dx.doi.org/10.1016/j.jphotochem.2017.03.004
This is a PDF file of an unedited manuscript that has been accepted for publication.
As a service to our customers we are providing this early version of the manuscript.
The manuscript will undergo copyediting, typesetting, and review of the resulting proof
before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that
apply to the journal pertain.

Synthesis and properties of twin derivatives of triphenylamine and carbazole
a
a
a
a
b
c
G. Simkus , A. Tomkeviciene , D. Volyniuk , V. Mimaite , G. Sini , R. Budreckiene , J.V.
a
Grazulevicius *
a
Department of Polymer Chemistry and Technology, Kaunas University of Technology, Radvilenu
rd. 19, LT-50254, Kaunas, Lithuania
b
Laboratoire de Physicochimie des Polymères et des Interfaces, Université de Cergy-Pontoise, EA
2
528, 5 mail Gay-Lussac, Cergy-Pontoise Cedex, 95031, France.
c
Lithuanian University of Health Sciences, Veterinary Academy, Department of Biochemistry,
Tilzes Str 18, LT- 47181, Kaunas, Lithuania
*
Corresponding author. Tel.: +370 37 300193; fax: +370 37 300152.
E-mail address: juozas.grazulevicius@ktu.lt (J.V. Grazulevicius).

Graphical Abstract

Highlights:




Twin derivatives of carbazole and triphenylamine were synthesized.
The compounds can exist in solid amorphous state.
The solid layers of compounds showed ionization potentials of 5.54 and 5.61 eV.
The twin derivatives exhibited triplet energies of 2.72 and 2.76 eV.

Keywords: Click chemistry; Glass-forming; Thermal stability; Ionization potential; Charge
mobility.
Abstract
Synthesis as well as thermal, optical, photophysical, and electrochemical properties of new
carbazole and triphenylamine twin derivatives with high triplet energies are reported. The
synthesized compounds exhibit ability of glass formation. Their glass transition temperatures are in
o
the range of 32 – 37 C. The triphenylamine and carbazole derivatives absorb electromagnetic
irradiation in the range of 200 – 360 nm with the band gaps of 3.71 and 3.44 eV, respectively. DFT
calculations show that HOMO and LUMO orbitals of compounds are localized separately on the
substituents and central 4,4′-thiodibenzenthiol unit, respectively. The synthesized twin derivatives
have triplet energies of 2.72 and 2.76 eV. The electron photoemission spectra of the films of the
synthesized compounds reveal ionization potentials of 5.54 and 5.61 eV.
1
. Introduction
Organic semiconductors are currently used in different (opto)electronic devices such as organic
light-emitting diodes (OLED), photovoltaic cells, field-effect transistors, lasers [1-7]. The
development of inexpensive, reliable and effective organic electroluminescent materials is one of
the hottest research area of organic optoelectronics. The efficient OLEDs are mainly based on
phosphorescent transition metal complexes. With phosphorescent emitters the theoretical limit of
the internal quantum efficiency is 100% as a result of their harvesting of both singlet and triplet
excited states [8]. One of the reasons why the efficiency of phosphorescent materials is less than the
theoretical one is the concentration quenching effect which results in the decrease of the
photoluminescence quantum efficiency of the emitting material and hence can lead to the decrease
of the external quantum efficiency of phosphorescent OLEDs [9]. To avoid self-quenching it is
necessary to dope the emitters into an appropriate host. The ability to form stable amorphous films
guarantees that the emitter is uniformly dispersed in the host to minimize the concentration
quenching. In addition, it is required that the triplet energy of the host is higher than that of the
emitter in order to prevent energy back transfer from the phosphorescent guest to the host. Such
materials are characterized by confined conjugated systems. Due to the high triplet energies, wide
band gaps, efficient charge transport and excellent thermal stability, derivatives of carbazole and
triphenylamine are widely used in the design of host materials for emitting layers of OLEDs [10-
1
4]. In addition, these compounds are relatively inexpensive. They can be prepared from easily

available raw materials. However, low-molar-mass glasses often suffer from poor morphological
stability, and facile crystallization, which limit their use in OLEDs. To prevent this problem
compounds with higher molecular weight, which do not readily crystallize, are required. The
synthesis of twin molecules from vinylcarbazole or vinyltriphenylamine linking them the fragment
of thiodibenzenthiol, thus preventing conjugation between the chromophores was the main synthetic
strategy.The limited conjugation between the chromophores is the precondition of high triplet
energy.The attachment of carbazole or triphenylamine moieties to the linkages with the limited
conjugation improve ability of the compounds to form morphologically stable solid amorphous
layers [15-18].
In this work we report on the synthesis and properties of two new carbazole and triphenylamine
twin derivatives with electronically separated chromophores. The derivatives were prepared by
thiol-ene click reactions [19,20]. The ecologically friendly nature of the coupling reaction (which
eliminate the use of toxic and expensive metal catalysts or organometallic reagents) is an attractive
feature that simplifies both the reaction processing and the product isolation. Even though it is
possible to synthesize a wide variety of organic compounds by employing inexpensive copper(I)-
catalyzed reactions [21,22], traces of copper may still remain at ppm levels in the product after
purification and affect the optoelectronic characteristics of the obtained compounds.
2
. Experimental
2
.1 Instrumentation
1
13
1
H and C NMR spectra were recorded using Bruker 700 MHz Avance III [700 MHz ( H), 175
1
3
MHz ( C)] spectrometer at room temperature. All the data are given as chemical shifts in δ (ppm).
CH Si (TMS, 0 ppm) was used as an internal standard. The courses of the reactions were
monitored by thin layer chromatography (TLC) using Silicagel 60 F254 plates and developed with
or UV radiation. Silica gel (grade 60, 63–200 mesh, 60 Å, Fluka) was used for column
(
3 4
)
I
2
chromatography. Melting points of the compounds were determined using Electrothermal Mel-
Temp melting point apparatus. Mass (MS) spectra were recorded on a Waters ZQ (Waters, Milford,
MA). Elemental analysis was performed with an Exeter Analytical CE-400 Elemental. Differential
scanning calorimetry (DSC) measurements were carried out using a DSC Q200 thermal analyser at
o
a heating rate of 10 C/min under nitrogen flow. Thermogravimetric analysis (TGA) was performed
on a TGA Q50 apparatus.
Absorption spectra of the dilute tetrahydrofuran (THF) solutions were recorded on Perkin Elmer
Lambda 35 spectrometer. Room temperature fluorescence spectra (PL) of the synthesized
compounds were taken by Perkin Elmer LS 55 spectrometer. For these measurements, the dilute

solutions of the investigated compounds were prepared by dissolving them in a spectral grade THF
-5
-5
at 10 M concentration. The phosphorescence spectra of dilute solution in THF (10 M) were
recorded at 77 K by Edinburgh Instruments FLS980.
The cyclic voltammetry (CV) measurements were carried out by a three-electrode assembly cell
from Bio-Logic SAS and a micro-AUTOLAB Type III potentiostat-galvanostat. The working
2
electrode was a glassy carbon of 0.12 cm surface. The reference electrode and the counter
+
-
electrode were Ag/Ag 0.01 M and Pt wire respectively. The solutions with the concentration of 10
3
M of the compounds in argon-purged dichloromethane with tetrabulthylammonium perchlorate
(TBAP; 0.1M) as electrolyte were used for the CV measurements. The CV curves were drawn
+
Fc
+
versus Fc/Fc as internal reference where the potential of the redox system E 1/2=0.216 V/Ag : Ag .
The ionization potentials (Ip(EP)) of the solid samples of the synthesized compounds were measured
by the electron photoemission in air method as reported earlier [23a,b]. The measurement error is
evaluated as 0.03 eV. The samples for the measurements were prepared by dissolving compounds in
THF and by casting on ITO coated glass plates. The samples were illuminated with the
monochromatic light when the negative voltage of -300 V was supplied to ITO. The counter-
electrode was placed at the distance of 3 mm from the sample surface and was connected to the
input of the 6517B Keithley electrometer for the photocurrent measurement. An energy scan of the
incident photons was performed while increasing the photon energy hv. In this scan direction, no
electrons were emitted until hv exceeded the ionization potential of the layer [24].
The charge carrier mobility (μ) measurements were carried by the time of flight method (TOF) as
reported earlier [25-27]. The sandwich-like cells (ITO/compound/Al) were fabricated for the
measurements. First, the layers of the compounds were prepared by drop casting their solutions in
THF onto cleaned ITO coated glass substrate. Finally, electrode Al (80 nm) was evaporated at 15
Å/s. The thickness of thin layers was measured using the method of carrier extraction in linearly
increasing voltage (CELIV) (ε~3.5) [28]. The charge carriers were generated at the layer surface by
illumination with pulses of Nd:YAG laser (pulse duration was 25 ps, wavelength 355 nm). The
transit time was determined from the kink point in the transient photocurrent curves. The transit
time t
t
with the applied bias (V) indicates the passage of holes through the entire thickness of the
2
cell (d) and enables determination of the hole mobility as μ=d /U·t
t
. The experimental setup
consisted of a delay generator Stanford Research DG 535 and a digital storage oscilloscope
Tektronix TDS754C.
2
.2 Computational details

The theoretical calculations were performed in the frame of density functional theory (DFT)
employing the B3LYP functional with Gaussian 09 program [29-31]. The 6-31G(d,p) basis set was
utilized for all calculations. The spectroscopic properties and of the molecules were calculated by
means of the method of time dependent density functional theory (TDDFT) [32,33]. Up to 40
excited states were calculated and the theoretical absorption bands were obtained by considering a
band half-width at half-maximum 0.15 and 0.3 eV. Natural transition orbital (NTO) calculations
were carried out to understand the nature of selected excited-states [34].
2
.3 Materials
Triphenylamine (TPA), phosphorus(V) oxychloride (POCl
3
), triphenylmethylphosphonium
bromide, potassium tert-butoxide (t-BuOK), 4,4′-thiodibenzenthiol (TBT) were purchased from
Aldrich and used without further purification. Triphenylamine-4-carbaldehyde (F-TPA) [35], 4-
vinyltriphenylamine (V-TPA) [34], 9-ethylcarbazole-3-carbaldehyde (F-CZ) [36], 9-ethyl-3-
vinylcarbazole (V-CZ) [36] were prepared according to the published procedures.
General procedure for the synthesis of TBT-2TPA and TBT-2CZ
A mixture of vinyl derivative (V-TPA or V-CZ, 2.2 equiv.) and 4,4′-thiodibenzenthiol (TBT, 1.0
equiv.) in dichloromethane was stirred for 1 h under argon atmosphere at room temperature. Then
the solvent was distilled and the crude product was purified by column chromatography.
Di(4-(2-(4-(N,N-diphenylamino)phenyl)ethyl)thio)phenylsulfide (TBT-2TPA) was prepared
according to the general procedure from 4-vinyltriphenylamine (V-TPA, 1.6 g, 5.9 mmol) and 4,4′-
thiodibenzenthiol (TBT, 0.5 g, 2.0 mmol). The crude product was purified by column
chromatography on silica gel using hexane/dichloromethane (8/1) as an eluent. The target
1
compound was obtained as white powder (fw=792 g/mol) in 38% yield (0.37 g). H NMR (700
MHz, CDCl
.06 (m, 8H, Ar), 7.07 – 7.11(m, 12H, Ar), 7.22– 7.30 (m, 16H, Ar). C NMR (175 MHz, CDCl
δ (ppm): 147.9, 146.3, 136.0, 134.4, 133.1, 131.5, 129.6, 129.3, 129.2, 124.4, 124.0, 122.6, 35.1 (S-
3
), δ (ppm): 2.91 (t, J = 8.3 Hz, 4H, S-CH
2
), 3.17 (t, J = 8.3 Hz, 4H, Ar-CH
2
), 7.00 –
1
3
7
3
),
+
+
CH
2
), 35.0 (Ar-CH
2
).MS (APCl , 20 V), m/z (%) = 793 ([M + H] , 100). Elemental analysis. Calcd
44 2 3
for C52H N S
(%): C 78.75, H 5.59, N 3.53, S 12.13; found (%): C 78.63, H 5.69, N 3.64.
Di(4-(2-(9-ethylcarbazol-3-yl)ethyl)thio)phenylsulfide (TBT-2CZ) was prepared according to the
general procedure from 9-ethyl-3-vinylcarbazole (V-CZ, 1.0 g, 4.48 mmol) and 4,4′-
thiodibenzenthiol (TBT, 0.31 g, 2.06 mmol). The crude product was purified by column

chromatography on silica gel using hexane/acetone (6/1) as an eluent. The target compound was
1
obtained as yellow powder (fw=692 g/mol) in 15% yield (0.13 g). H NMR (70 MHz, CDCl
3
), δ
), 3.29 (t,J = 8.3 Hz, 4H, Ar-
), 7.14˗7.53 (m, 18H, Ar), 7.95 (s, 2H, Ar), 8.10 (d,J = 7.7 Hz,
(
ppm): 1.46 (t,J = 7.2 Hz, 6H, CH
CH ), 4.38 (q, J = 7.3, 4H, N-CH
H, Ar), 8.12 (d, J = 7.8 Hz,2H, Ar). C NMR (175 MHz, CDCl
3 2
), 3.15 (t, J = 8.2 Hz, 4H, S-CH
2
2
13
2
1
3
3
),δ (ppm):140.3, 138.9, 136.2,
33.0, 132.6, 131.5, 130.6, 130.4, 129.6, 126.3, 125.7, 123.1, 122.7, 120.4, 120.1, 118.7, 108.5,
+
7.6 (N-CH
2
), 35.8 (S-CH
2
), 35.7 (Ar-CH
2
), 13.8 (CH
3
).MS (APCl , 20 V), m/z (%) = 693 ([M +
+
H] , 100).Elemental analysis. Calcd for C44
H
40
N
2
S
3
(%): C 76.26, H 5.82, N 4.04, S 13.88; found
(%): C 76.12, H 5.91, N 4.08.
3
. Results and discussion
3
.1 Synthesis
TBT-2TPA and TBT-2CZ were synthesized by thiol-ene reaction as illustrated in Scheme 1.
Aldehydes F-TPA and F-CZ were obtained under the conditions of the Vilsmeier reaction [35,36].
Compounds V-TPA and V-CZ were prepared by Wittig reaction of the corresponding aldehydes in
the presence of methyltriphenylphosphonium bromide and potassium tert-butoxide. The reactions
of vinyl derivatives (V-TPA or V-CZ) and 4,4′-thiodibenzenthiol (TBT) in dichloromethane
yielded twin the molecules (TBT-2TPA and TBT-2CZ). The chemical structures of the
1
13
synthesized compounds were confirmed by H NMR, C NMR, mass spectrometries, and
elemental analysis. TBT-2TPA and TBT-2CZ were readily soluble in common organic solvents
like dichloromethane, chloroform, THF, acetonitrile, toluene.

Scheme 1. Synthesis of TBT-2TPA and TBT-2CZ
3
.2 Thermal properties
The thermal stability and morphological changes of the synthesized compounds were studied by
thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The glass transition
(
T
g
) and 5% weight loss (TID) temperatures of the derivatives are summarized in Table 1. TID for the
o
twin molecules is observed at 290 C, which is slightly lower to those of the common carbazole and
triphenylamine based compounds reported in the literature, such as 4,4′-bis(9-carbazolyl)biphenyl
o
derivatives [37,38] (310–365 C) or triphenylamine-based derivatives with different side groups
o
(
300 to 349 C) [39]. For the fabrication of devices, the temperatures of vacuum evaporation of
TBT-2TPA and TBT-2CZ have to be considerably lower than TID for avoiding of thermal
degradation of the compounds. The recent study showed that impurities in organic materials
decreased the lifetime of OLEDs even if the impurities did not contribute to the emission [40]. TGA
curves of the derivatives are shown in Fig. 1a. Two-stages are observed in the thermal degradation
of the synthesized compounds. The first step is apparently due to the degradation of the linkage
moiety. The onset of the second step for TBT-2TPA and TBT-2CZ is observed at approximately
o
the same temperature (355 C) which corresponds to the temperature of the onset of the thermal
degradation of carbazole [41] and triphenylamine [42] moieties.
Tg
100
TBT-2TPA
TBT-2CZ
TBT-2CZ
80
60
40
20
0
Tg
TBT-2TPA
[
a]
[b]
100
200
300
400
500
600
700
800
900
20
30
40
50o
60
70
o
Temperature ( C)
Temperature ( C)
Fig. 1. [a] TGA curves and [b] DSC curves (second heating scan) of TBT-2TPA and TBT-2CZ
o
(
heating rate 10 C/min, N
2
atmosphere)
Both the synthesized compounds were isolated as amorphous materials and only glass transitions
o
were observed in their DSC scans at 37 and 32 C, respectively, and no peaks due to crystallization
and melting appeared. Cooling down and following repeated heating revealed only glass transitions
(Fig. 1b).

Table 1.Thermal characteristics of TBT-2TPA and TBT-2CZ.
Compound
TBT-2TPA
TBT-2CZ
32
a o
T
g
( C)
37
b o
T
ID ( C)
290
290
a
o
b
Determined by DSC, scan rate 10 C/min, N
2
atmosphere. 5% weight loss temperature
o
determined by TGA, heating rate 10 C/min, N
2
atmosphere.
3
.3 Geometrical structures and frontier orbitals
The theoretical optimized geometries of the twin derivatives of triphenylamine- and carbazole are
shown in Fig. 2. The propeller-like triphenylamine moieties have dihedral angles between phenyl
ring planes and C-N-C bonds of 41º – 43º in TBT-2TPA. In the structures of both compounds
TBT-2TPA and TBT-2CZ benzene rings of 4,4′-thiodibenzenthiol linker and substituents linked
through an alkyl chain are parallel to each other.
Fig. 2. Theoretical geometrical structures of TBT-2CZ and TBT-2TPA (B3LYP/6-31G(d,p) level)
Theoretical calculations revealed that the 4,4′-thiodibenzenthiol linker with alkyl chain in the
synthesized compounds TBT-2TPA and TBT-2CZ interrupt the conjugation between analogous
moieties. (Fig. 3) Therefore, the HOMO is localized on only one triphenylamine fragment, whereas
the HOMO delocalization on both carbazole moieties is an artefact due to the over delocalization
effect inherent to several DFT functionals. As expected, the LUMO is distributed on the central
4
,4′-thiodibenzenthiol unit. The small electron contribution of ethyl unit in HOMO and LUMO is
associated with the hyperconjugation effect between σ bonds with adjacent π orbital [43].

Fig. 3. Frontier orbitals of TBT-2CZ and TBT-2TPA (B3LYP/6-31G(d,p) level)
3
.4 Optical and photophysical properties
The optical and photophysical characteristics of the compounds are summarized in the Table 2. Fig.
-4
4
a displays the room temperature absorption spectra of 10 M THF solutions of TBT-2TPA and
TBT-2CZ. The spectra of pure triphenylamine (TPA) and 9-ethylcarbazole (CZ) compounds are
given for the comparison. Dilute THF solutions of the synthesized triphenylamine and carbazole-
based derivatives absorb electromagnetic radiation up to 360 nm. The positions of absorption bands
of TBT-2CZ and TBT-2TPA are almost identical compared to those of CZ and TPA, respectively.
The theoretical absorption spectra of these compounds are presented in Fig. 4b. It can be observed
that the experimental and the theoretical approaches produce different trends for the lowest energy
bands of triphenylamine- and carbazole-based compounds. Indeed, the weak lowest energy band in
the experimental spectra of TBP-2CZ is redshifted with respect to TBT-2TPA, whereas the
opposite can be observed from the theoretical spectra. The origin of this disagreement might reside
in combined effects: (i) solute-solvent interactions, carbazole is more prominent to these
interactions as compared to triphenylamine due to its planar geometry, and (ii) B3LYP functional
overestimates the effective conjugation length giving slight redshift of excitation energy of TPA
and TBT-2TPA [44]. Due to the donor-acceptor architecture, the band gaps of TBT-2TPA (4.00
eV) and TBT-2CZ (4.44 eV) are lower than those of TPA (4.65 eV) and CZ (4.69 eV) (Table S1)
[45]. Therefore, the experimental lowest energy bands of twin derivatives are shifted to longer
wavelengths with respect of that of the corresponding model compounds.

4
4
4
4
4
3
3
3
3
1.2
1
1
1
1
1
8
6
4
2
.8x10
.6x10
.4x10
.2x10
.0x10
.0x10
.0x10
.0x10
.0x10
[
a]
TBT-TPA
TBT-Cz
TPA
1.0
TBT-TPA
TBT-Cz
TPA
Cz
0.8
Cz
0.6
0.4
0.2
0
.0
0.0
2
50
300
350
250
300
350
400
Wavelenght (nm)
Wavelength, (nm)
Fig. 4. [a] Experimental and [b] theoretical UV absorption spectra of TBT-2TPA, TBT-2CZ, TPA
and CZ (ex = 310 nm)
In order to characterize electron transitions, induced by absorption of electromagnetic radiation, the
theoretical absorption spectra of analysed compounds were investigated (Fig. S1, Fig. S2, Fig. S3,
Table S2). Based on the theoretical results, the lowest energy absorption bands of TBT-2TPA and
TBT-2CZ are attributed to the combination of electronic transitions towards various excited states.
The transitions S
0
→S
1
, S
0
→S
9
for TBT-2TPA and S
0
3
→S for TBT-2CZ, with largest oscillator
strengths, are the dominant transitions which characterize the lowest energy absorption bands. In
order to identify the nature of transitions, the corresponding NTO were calculated. The hole and
electron localizations in the compounds received from NTOs are shown in Fig. 5. According to
these results, the lowest energy absorption band at 301 nm (S
TPA can be characterized as the charge transfer (CT) transition between the triphenylamine donor
part and the 4,4′-thiodibenzenthiol acceptor linker. In the case of TBT-2CZ, the lowest energy
absorption band at 351 nm (S →S ) is dominated by the donoracceptor CT transition, also
containing some contribution from the local acceptor excitations. The lowest transition S →S for
0
→S
1
, S
0
9
→S ) of compound TBT-
2
0
3
0
1
TBT-2CZ exhibits small oscillator strength, therefore it is hidden and does not appear as a separate
band (Fig. S1 and Table S2). The NTO results indicate that the lowest transition in TBT-2TCZ is
associated with the local electronic excitations in carbazole fragment (Fig. 5), involving HOMO-1,
HOMOLUMO+1 transitions (Table S2).

Fig. 5. Natural transition orbitals corresponding to hole- and electron localizations corresponding
to selected excited states of compounds TBT-2TPA and TBT-2CZ 2 (TD-B3LYP/6-31G(d,p)
level)
The bands of fluorescence spectra of TBT-2TPA and TBT-2CZ are shifted towards long
wavelength region in comparison with those of TPA or CZ, with Stokes shifts ranging from 23 to
7
0 nm. The TPA-based compounds exhibit larger Stokes shifts as compared to CZ-based
compound, probably due to the larger geometrical deformations happening in the TPA moiety.
TBT-2TPA
TBT-2CZ
TPA
CZ
3
50
400
450
500
Wavelenght (nm)
Fig. 6. Fluorescence spectra of the dilute THF solutions of TBT-2TPA, TBT-2CZ, TPA and CZ
ex = 310nm)
(

For the possible application of compounds TBT-2TPA and TBT-2CZ as host materials for the
phosphorescent emitters the triplet energies are of major interest. For efficient phosphorescence
1 0
from triplet guests in a host matrix, the triplet energy E(T -S ) of a host must be larger than that of

a guest to facilitate exothermic energy transfer from a host to a guest and to prohibit reverse energy
transfer from a guest back to a host [8,46].
Phosphorescence spectra of the solutions of TBT-2TPA and TBT-2CZ in THF were recorded at 77
K by applying delay time of 100 μs after excitation. The triplet energies estimated from the first
phosphorescence emission peak were found to be 2.72 and 2.76 eV for TBT-2TPA and TBT-2CZ,
respectively. These values are higher than that of common blue phosphorescent emitter
2
’
iridium(III)bis[(4,6-difluorophenyl)-pyridinato-N,C ]picolinate (FIrpic,
T
E =2.65 eV) [46].
Consequently, efficient energy transfer from the host materials to the FIrpic dopant is expected,
indicating that TBT-2TPA and TBT-2CZ can be suitable as the host materials for blue OLEDs.
Table 2. Optical and photophysical characteristics of TBT-2TPA, TBT-2CZ, TPA and Cz.
Compound
TBT-2TPA
301
TBT-2CZ
298, 337, 351
239, 275, 302
357, 374
455
TPA
299
300
352
408
53
Cz
294, 335, 346
233, 273, 308
359
a
λ
λ
λ
λ
ab.max (nm)
b
ab.teor (nm)
305
c
fl.max (nm)
371
d
phos.max (nm)
449
409
Stokes Shift (nm)
70
23
13
opt
e
3.71
3.44
3.75
3.52
E g (eV)
f
E
S
(eV)
(eV)
3.34
2.72
3.31
3.52
3.45
g
*
*
E
T
2.76
3.04
3.03
a
-5
b
Wavelengths of absorption peaks of solutions (10 M in THF). Theoretical wavelengths of
c
-5
d
absorption peaks. Wavelengths of fluorescence peaks of solutions (10 M in THF). Wavelengths of
opt
g
-
5
e
phosphorescence peaks of solutions (10 M in THF, 77 K). The optical band gaps E
estimated from
f
g
the edges of absorption spectra. Singlet energy estimated from the highest-energy fluorescence peak.
*
Triplet energy estimated from the highest-energy phosphorescence peak. The values taken from the
literature [47,48].
3
.5 Electrochemical and photoelectrical properties
To elucidate the energetic conditions for energy and electron transfer in dilute solutions, the
ionization potentials and electron affinities were established by cyclic voltamperometry (CV). The
measurements were carried out with a glassy carbon electrode in dichloromethane solutions
3
containing 0.1M tetrabutylamonium perchlorate (TBAP) as electrolyte, Ag/AgNO as the reference
electrode and a Pt wire counter electrode. The experiments were calibrated with the standard
ferrocene/ferrocenium redox system [49]. The electrochemical characteristics are summarized in

Table 2. The CV curves of TBT-2TPA and TBT-2CZ are shown in Fig. 7. In the first redox cycle
the oxidation of TBT-2TPA started at 0.73 V (Table 3) and resulted in the formation of cation
radicals. As the CV scans continued, a new oxidation peak appeared at 0.63 V. A possible
explanation can be related to the oxidation of new compounds formed after the initial CV cycle.
Indeed, further to the first oxidation cycle, the cation radicals reacted with each other or with the
neutral molecules, leading to the formation of dimmers. The dimmers are more easily oxidized than
TPA moieties [50]. The intensity of this peak increased gradually with the number of continued
scans. Furthermore, during the each CV cycle, TBT-2TPA exhibited consequently two reduction
peaks in the region of 0.55 – 0.80 V, which can be ascribed to the reduction of the oxidized species
present in the solution.
TBT-2CZ exhibited the similar electrochemical behaviour (Fig. 7). The oxidation of TBT-2CZ
started at 0.68 V in the first cycle, which was somewhat lower than the corresponding value
observed for TBT-2TPA (Table 3). TBT-2CZ exhibited two oxidation peaks in the region of 0.30
–
0.8 V by continued scanning, one of which was absent in the first cycle. It seems that the
carbazole moieties were oxidized in the first scan, followed by irreversible formation of new
carbazolyl compound [51].
2
1
1
0
5
0
5
0
5
th
5
th
1
,0
4
rd
3
nd
2
st
1
0,5
0,55
0,60
0,65
0,70
Potential (V)
TBT-2TPA
-
0,0
0,2
0,4
0,6
0,8
1,0
Potential (V)
0,5
20
15
10
5
0
TBT-2CZ
0
,0
-0,5
0,3
0,4
Voltage (V)
0,0
0,2
0,4
0,6
0,8
Voltage (V)
Fig. 7. Cyclic voltammograms of TBT-2TPA and TBT-2CZ in argon-purged
-1
dichloromethane solution (scan rate of 50 mV s )

Taking 4.8 eV [52] as the ionization potential (Ip(CV)) value for the ferrocene redox system related to
the vacuum level, the Ip(CV) values of TBT-2TPA and TBT-2CZ were estimated and were found to
opt
be 5.39 and 5.48 eV, respectively (Table 3). With the band gap (E g ) values obtained from the
absorption spectra, the electron affinity (EA(CV)) values of 1.68 and 2.04 eV were estimated for
TBT-2TPA and TBT-2CZ respectively.
In the design and fabrication of organic devices, it is very important to have energy levels of the
materials used [53]. The solid-state ionization potentials (Ip(EP)) of organic materials are usually
estimated by ultraviolet photoelectron spectroscopy (UPS) in deep vacuum [54,55]. For organic
materials which possess Ip(EP) lower than 6.0 eV (the value related to absorbance of oxygen) Ip(EP)
can be estimated by UPS in air [56,57]. Taking into account the potential application of the studied
compounds in organic devices, the ionization potentials Ip(EP) of the solid layers of the compounds
were also estimated by photoelectron emission spectrometry in air. The results are presented in Fig.
8
and Table 3. In the agreement with the CV results, Ip(EP) of triphenylamine-based compound
(
TBT-2TPA) was found to be slightly higher than that of carbazole derivative (TBT-2CZ). Having
I
p(EP) of 5.54 and 5.61 eV and the optical band-gap energy of ca. 3.71 and 3.44 eV, the electron
opt
affinity (EA(EP)) of 1.83 and 2.17 eV was calculated by a formula EA(EP)=Ip(EP)- E g for TBT-2TPA
and TBT-2CZ. The energy levels Ip(EP) and EA(EP) are related to the values of HOMO of -5.54 and -
5
.61 eV and LUMO of -1.83 and -2.17 eV, respectively. These values should be taken into account
in the case of application of TBT-2TPA and TBT-2CZ in solid-state devices.
TBT-2TPA
TBT-2CZ
4
3
2
1
0
5,4
5,5
5,6
5,7
5,8
5,9
6,0
6,1
6,2
Photon energy (eV)
Fig. 8. Electron photoemission spectra of the layers of TBT-2TPA and TBT-2CZ recorded in air at
o
2
5 C
Table 3. Electrochemical and photoelectrical characteristics of TBT-2TPA and TBT-2CZ.

a
b
c
d
o
e
Compound
TBT-2TPA
Eonset
V)
0.73
0.68
I
p(CV)
E
(eV)
1.68
2.04
A(CV)
I
p(EP)
  
 
2
2
(
(eV)
5.39
5.48
(eV)
5.54
5.61
(cm /V·s) (cm /V·s)
-
-
-9
-7
TBT-2CZ
2.8×10
2.3×10
a
b
Ionization potentials Ip(CV) and electron affinities EA(CV) were estimated by cyclic voltamperometry according
opt
c
to Ip(CV) = 4.8 + Eonset and EA(CV)= Ip(CV)˗E g . Ionization potentials Ip(EP)of the solid samples were measured by
d
electron photoemission spectrometry. Zero field mobility in the films of the synthesized compounds
e
molecularly doped in bisphenol Z polycarbonate (PC-Z). Hole mobility value in the films of the synthesized
6
compounds molecularly doped in PC-Z) at electric field E = 1.5×10 V/cm.
Time-of-flight technique was used to characterize hole drift mobilities in the films of the
synthesized compounds. To run TOF, we have prepared non-doped layers of TBT-2TPA and TBT-
2
CZ by thermal evaporation of the compounds. Next, the top Al electrode was deposited. However,
the quality of Al electrode was not sufficient, most probably, due to low glass transition
o
temperatures of 37 and 32 C for TBT-2TPA and TBT-2CZ, respectively. This result shows that
TBT-2TPA and TBT-2CZ can not be used for the preparation non-doped layers in organic devices,
but the compounds can be used as dopants depending on future device design. In addition, the TOF
technique was used to characterize hole drift mobilities in the films of the synthesized compounds
molecularly doped in polymeric host bisphenol Z polycarbonate (PC-Z). Because of the relatively
low solubility of TBT-2TPA in PC-Z we were not able to prepare the solid solutions of high
enough concentration for the time-of-flight measurements. Only TBT-2CZ showed good enough
solubility for the preparation of 50 wt.% solid solution in PC-Z. The solid solution of TBT-2CZ in
-7
2
6
PC-Z demonstrated hole drift mobility of 2.3 × 10 cm /V·s at electric field E= 1.5 × 10 V/cm
-6
2
(
Table 3). Hole drift mobility of the order of 10 cm /V·s can be predicted for amorphous films of
the pure compounds.
4
. Conclusions
Carbazole and triphenylamine twin derivatives with high triplet energies were synthesized by thiol-
ene click reactions. The molecular structures allow the synthesized compounds to exist in solid
amorphous state with high enough thermal stability. The glass transition temperatures of the
o
synthesized compounds were observed at 37 and 32 C. Results obtained by means of TDDFT
calculations showed charge transfer character in the excited state of the carbazole- and
triphenylamine-based derivatives. The triplet energies of the solid samples of the compounds were
found to be 2.72 and 2.76 eV. The electron photoemission spectra of the films of the compounds
revealed ionization potentials of 5.54 and 5.61 eV. Meanwhile, the cyclic voltammetry

measurements showed slightly lower ionization potentials of 5.39 and 5.48 eV. Hole drift mobility
-7
in the solid solution of carbazole twin derivative in bisphenol Z polycarbonate reached 2.3×10
2
6
cm /V·s at electric field of 1.5×10 V/cm, as established by time-of-flight technique.
Acknowledgments
This work was supported by the Horizon 2020 ICT29-2014 project PHEBE (grant No 641725).
References
[
1] K. S. Yook, J. Y. Lee, Organic materials for deep blue phosphorescent organic light-emitting
diodes, Adv. Mater. 24 (2012) 3169–3190.
[
2] A. J. Ward, A. Ruseckas, M. M. Kareem, B. Ebenhoch, L. A. Serrano, M. Al-Eid, B.
Fitzpatrick, V. M. Rotello, G. Cooke, I. D. W. Samuel, The impact of driving force on electron
transfer rates in photovoltaic donor-acceptor blends, Adv. Mater., 27 (2015) 2496–2500.
3] A. Pron, P. Gawrys, M. Zagorska, D. Djurado, R. Demadrille, Electroactive materials for
organic electronics: preparation strategies, structural aspects and characterization techniques,
Chem. Soc. Rev. 39 (2010) 2577–2632.
[
[
[
[
[
[
4] P. Bujak, I. Kulszewicz-Bajer, M. Zagorska, V. Maurel, I. Wielgus, A. Pron, Polymers for
electronics and spintronics, Chem. Soc. Rev. 42 (2013) 8895–8999.
5] D. S. Weiss, M. Abkowitz, Advances in organic photoconductor technology, Chem. Rev. 110
(2010) 479–526.
6] A. W. Hains, Z. Liang, M. A. Woodhouse, B. Gregg, Molecular semiconductors in organic
photovoltaic cells, Chem. Rev. 110 (2010) 6689–6735.
7] A. Pivrikas, B. Philippa, R. D. White, G. Juska, Photocarrier lifetime and recombination losses
in photovoltaic systems, Nat. Photonics 10 (2016) 282–283
8] M. A. Baldo, D. F. O’Brien, Y. You, A. Shoustikov, S. Sibley, M. E. Thompson, S. R. Forrest,
Highly efficient phosphorescent emission from organic electroluminescent devices, Nature
3
95 (1998) 151–154.
[
9] C. Adachi, M. A. Baldo, M. E. Thompson, S. R. Forrest, Nearly 100% Internal
Phosphorescence Efficiency in an Organic Light-Emitting Device. J. Appl. Phys. 90 (2001)
5
048–5051.
[10] Y. J. Cheng, S. H. Yang, C. S. Hsu, Synthesis of conjugated polymers for organic solar cell
applications, Chem. Rev. 109 (2009) 5868–5923.

[
[
[
[
[
11] R. J. Thomas, J. T. Lin, Y. T. Tao, C. W. Ko, Light-emitting carbazole derivatives: potential
electroluminescent materials, J. Am. Chem. Soc. 123 (2001) 9404–9411.
12] J. Y. Li, D. Liu, Y. Q. Li, C. S. T. Lee, A high Tg carbazole-based hole-transporting material
for organic light-emitting devices, Chem. Matter. 17 (2005) 1208–1212.
13] J. F. Morin, M. Leclerc, D. Adès, A. Siove, Polycarbazoles: 25 years of progress, Macromol.
Rapid Commun. 26 (2005) 761–778.
14] S. Grigalevicius, 3,6(2,7),9-Substituted carbazoles as electroactive amorphous materials for
optoelectronics, Synth. Met. 156 (2006) 1–12.
15] C. Adachi, R. C. Kwong, P. Djurovich, V. Adomovich, M. A. Baldo, M. E. Thompson, S. R.
Forrest, Endothermic energy transfer: a mechanism for generating very efficient high-energy
phosphorescent emission in organic materials, Appl. Phys. Lett. 79 (2001) 2082–2084.
16] S. Tokito, T. Iijima, Y. Suzuri, H. Kita, T. Tsuzuki, F. Sato, Confinement of triplet energy on
phosphorescent molecules for highly-efficient organic blue-light-emitting devices, Appl. Phys.
Lett. 83 (2003) 569–571.
[
[
[
17] R. J. Holmes, B. W. D‘Andrade, S. R. Forrest, X. Ren, J. Li, M. E. Thompson, Efficient, deep-
blue organic electrophosphorescence by guest charge trapping, Appl. Phys. Lett. 83 (2003)
3
818–3820.
18] S.-J. Yeh, M.-F. Wu, C.-T. Chen, Y.-H. Song, Y. Chi, M.-H. Ho, S.-F. Hsu, C.-H. Chen, New
dopant and host materials for blue-light-emitting phosphorescent organic electroluminescent
devices, Adv. Mater. 17 (2005) 285–289.
[
[
[
19] C. N. Bowman, C. E. Hoyle, Thiol-ene click chemistry, Angew. Chem. Int. Ed. 49 (2010)
1
540–1573.
20] A. Dondoni, The emergence of thiol-ene coupling as a click process for materials and
bioorganic chemistry, Angew. Chem. Int. Ed. 47 (2008) 8995–8997.
21] V. V. Rostovtsev, L. G. Green, V. V. Fokin and K. B. Sharpless, A stepwise Huisgen
cycloaddition process: Copper(I)-catalyzed regioselective "ligation" of azides and terminal
alkynes, Angew. Chem., Int. Ed. 41 (2002), 2596–2599.
[
22] C. W. Tornoe, C. Christensen and M. Meldal, Peptidotriazoles on solid phase: [1,2,3]-triazoles
by regiospecific copper(I)-catalyzed 1,3-dipolar cycloadditions of terminal alkynes to azides,
J. Org. Chem. 67 (2002) 3057–3064.
[
23] a)N. A. Kukhta, D. Volyniuk, L. Peciulyte, J. Ostrauskaite, G. Juska, J. V. Grazulevicius,
Structure-property relationships of star-shaped blue-emitting charge-transporting 1,3,5-
triphenylbenzene derivatives, Dyes Pigm. 117 (2015) 122–132; b) D. Gudeika, J. V.
Grazulevicius, D. Volyniuk, G. Juska, V. Jankauskas, G. Sini, Effect of Ethynyl Linkages on

the Properties of the Derivatives of Triphenylamine and 1, 8-Naphthalimide, J. Mater. Chem.
C 119 (2016) 28335–28346;
[
[
[
[
24] Y. Nakayama, S. Machida, D. Tsunami, Y. Kimura, M. Niwano, Y. Noguchi, H. Ishii,
Photoemission Measurement of Extremely Insulating Materials: Capacitive Photocurrent
Detection in Photoelectron Yield Spectroscopy, Appl. Phys. Lett. 92 (2008) 153306–153308.
25] C. A. Amorim, M. R. Cavallari, G. Santos, F. J. Fonseca, A. M. Andrade, S. Mergulhão,
Determination of carrier mobility in MEH-PPV thin-films by stationary and transient current
techniques, J. Non-Cryst. Solids 358 (2012) 484–491
26] V. Mimaite, J. V. Grazulevicius, R. Laurinaviciute, D. Volyniuk, V. Jankauskas, G. Sini, Can
hydrogen bonds improve the hole-mobility in amorphous organic semiconductors?
Experimental and theoretical insights, J. Mater. Chem. C. C 3 (2015) 11660–11674.
27] R. R. Reghu, J. V. Grazulevicius, J. Simokaitiene, A. Miasojedovas, K. Kazlauskas, S.
Jursenas, P. Data, K. Karon, M. Lapkowski, V. Gaidelis, V. Jankauskas, Glass-forming
carbazolyl and phenothiazinyl tetra substituted pyrene derivatives: photophysical,
electrochemical, and photoelectrical properties, J. Phys. Chem. C 116 (2012) 15878−15887.
28] G. Juska, K. Genevicius, M. Viliunas, K. Arlauskas, H. Stuchlõkova, A. Fejfar, J. Kocka, New
method of drift mobility evaluation in lc-Si:H, basic idea and comparison with time-of-light, J.
Non-Cryst. Solids 266-269 (2000) 331–335.
[
[
29] W. Kohn and L. Sham, Self-consistent equations including exchange and correlation effects,
Phys. Rev. 140 (1965) A1133–A1138
[
30] C. T. Lee, W. T. Yang and R. G. Parr, Development of the Colle-Salvettl correlation-energy
formula into a functional of the electron density, Phys. Rev. B: Condens. Matter Mater. Phys.
3
7 (1988) 785–789.
[
31] M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, G.
Scalmani, V. Barone, B. Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H. P.
Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng, J. L. Sonnenberg, M. Hada, M. Ehara, K.
Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T.
Vreven, J. Montgomery, J. E. Peralta, F. Ogliaro, M. Bearpark, J. J. Heyd, E. Brothers, K. N.
Kudin, V. N. Staroverov, T. Keith, R. Kobayashi, J. Normand, K. Raghavachari, A. Rendell, J.
C. Burant, S. S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene, J. E. Knox, J.
B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev, A. J.
Austin, R. Cammi, C. Pomelli, J. W. Ochterski, R. L. Martin, K. Morokuma, V. G.
Zakrzewski, G. A. Voth, P. Salvador, J. J. Dannenberg, S. Dapprich, A. D. Daniels, O. Farkas,

J. B. Foresman, J. V. Ortiz, J. Cioslowski and D. J. Fox, Gaussian 09, Revision B.01, Gaussian
Inc., Wallingford CT, 2009.
[32] M. E. Casida, C. Jamorski, K. C. Casida, D. R. Salahub, Molecular excitation energies to high-
lying
bound
states
from
time-dependentꢀdensity-functionalꢀresponseꢀtheory:
Characterizationꢀand correctionꢀofꢀtheꢀtime-dependentꢀlocalꢀdensityꢀapproximation ionization
threshold, J. Chem. Phys. 108 (1998) 4439–4449.
[
33] R. Bauernschmitt, R. Ahlrichs, Treatment of electronic excitations within the adiabatic
approximation of time dependent density functional theory, Chem. Phys. Lett. 256 (1996)
4
54–464.
[34] R. L. Martin, Natural transition orbitals, J. Chem. Phys. 118 (2003) 4775–4777.
[
35] D. Gudeika, A. Michaleviciute, J. V. Grazulevicius, R. Lygaitis, S. Grigalevicius, V.
Jankauskas, A. Miasojedovas, S. Jursenas, G. Sini, Structure properties relationship of donor–
acceptor derivatives of triphenylamine and 1,8-naphthalimide, J. Phys. Chem. C 116 (2012)
1
4811–14819.
[
[
[
[
[
[
36] L. Leijing, G. Qing, L. Jiyang, Y. Bin, T. Wenjing, Synthesis, characterization and properties
of novel star-shaped π-conjugated oligomers with triphenylamine core, Chin. J. Chem. 31,
(2013) 456–464.
37] P. Schrögel, A. Tomkeviciene, P. Strohriegl, S. T. Hoffmann, A. Köhler, C. Lennartz, A
series of CBP derivatives as host materials for blue phosphorescent organic light-emitting
diodes, J. Mater. Chem. 21 (2001) 2266–2273.
38] P. Schrögel, N. Langer, C. Schildknecht, G. Wagenblast, C. Lennartz, P. Strohriegl, Meta-
linked CBP derivatives as host materials for a blue iridium carbene complex, Org. Electron.
1
2 (2011) 2047–2055.
39] P. Liu, P. Zhang, D. Cao, L. Gan, Y. Li, New side groups-tuned triphenylamine-based
chromophores: Synthesis, morphology, photophysical properties and electronic structures, J.
Mole. Struct. 1050 (2013) 151–58.
40] H. Fujimoto, M. Yahiro, S. Yukiwaki, K. Kusuhara, N. Nakamura, T. Suekane, H. Wei, K.
Imanishi, K. Inada, C. Adachi, Influence of material impurities in the hole-blocking layer on
the lifetime of organic light-emitting diodes, Appl. Phys. Lett. 109 (2016) 243302.
41] S. Gong, X. He, Y. Chen, Z. Jiang, C. Zhong, D. Ma, J. Qina, C. Yang, Simple CBP isomers
with high triplet energies for highly efficient blue electrophosphorescence, J. Mater. Chem. 22
(2012) 2894–2899.

[
42] C. He, Q. He, Y. Yi, G. Wu, F. Bai, Z. Shuai, Y. Li, Improving the efficiency of solution
processable organic photovoltaic devices by a star-shaped molecular geometry, J. Mater.
Chem. 18 (2008) 4085−4090.
[
[
[
[
43] J. E. McMurry. Organic chemistry with biological applications 2 edition, Cengage Learning,
Canada, 2010.
44] B. Milian-Medina, J. Gierschner, π-Conjugation, WIREs Comput. Mol. Sci. 2 (2012) 513–
5
24.
45] J. Roncali, Molecular engineering of the band gap of p-conjugated systems: facing
technological applications, Macromol. Rapid Commun. 28 (2007) 1761–1775.
46] R. J. Holmes, S. R. Forrest, Y.-J. Tung, R. C. Kwong, J. J. Brown, S. Garon, M. E. Thompson,
Blue organic electrophosphorescence using exothermic host-guest energy transfer, Appl. Phys.
Lett. 82 (2003) 2422−2424.
[
47] Z. Xiaguang, S. Whei, S. Xuili, Y. Pei, H. Rongxing, L. Ming, The DFT study on non-
conjugated polymer host materials based on styrene derivatives for phosphorescent polymer
light-emitting diodes, J. Phys. Org. Chem. 28 (2015) 554−563.
[
48] K. Brunner, A. van Dijken, H. Borner, J. J. A. M. Bastiaansen, N. M. M Kiggen,, B. M. W.
Langeveld, Carbazole compounds as host materials for triplet emitters in organic light-
emitting diodes:ꢀ Tuning the HOMO level without influencing the triplet energy in small
molecules, J. Am. Chem. Soc. 126 (2004) 6035−6042.
[
49] M. Thelakkat, J. Ostrauskaite, A. Leopold, R. Bausinger, D. Haarer, Fast and stable
photorefractive systems with compatible photoconductors and bifunctional NLO-dyes, Chem.
Phys. 285 (2002) 133−147.
[
50] O. A. Negru, M. Grigoras, Grafted polytriphenylamines synthesized by atom transfer radical
polymerization in tandem with oxidative polycondensation, Iran. Polym J. 22 (2013) 647−651.
51] J. Qu, Y. Suzuki, M. Shiotsuki, F. Sanda, T. Masuda, Synthesis and electro-optical properties
of helical polyacetylenes carrying carbazole and triphenylamine moieties, Polymer 48 (2007)
[
4
628−4636.
[
[
[
52] M. Thelakkat, H. W. Schmidt, Synthesis and properties of novel derivatives of 1,3,5-
tris(diarylamino)benzenes for electroluminescent devices, Adv. Mater. 10 (1998) 219−223.
53] Y. Gao, Surface analytical studies of interfaces in organic semiconductor devices, Mat. Sci.
Eng. R 68 (2010) 39−87.
54] M. A.-Berger, R. Trattnig, T. Qin, R. Schlesinger, M. V. Nardi, G. Ligorio, C. Christodoulou,
N. Koch, M. Baumgarten, K. Müllen, E. J. W. List-Kratochvil, All-solution-processed
multilayer polymer/dendrimer light emitting diodes, Org. Electron. 35 (2016) 164−170.

[
55] X. Zhang, F. You, Q. Zheng, Z. Zhang, P. Cai, X. Xue, J. Xiong, J. Zhang, Solution-processed
MoOx hole injection layer towards efficient organic light-emitting diode, Org. Electron. 39
(2016) 43−49.
[
56] K. Ivaniuk, V. Cherpak, P. Stakhira, Z. Hotra, B. Minaev, G. Baryshnikov, E. Stromylo, D.
Volyniuk, J. V. Grazulevicius, A. Lazauskas, S. Tamulevicius, B. Witulski, M. E. Light, P.
Gawrys, R. J. Whitby, G. Wiosna-Salyga, B. Luszczynska, Highly Luminous Sky-Blue
Organic Light-Emitting Diodes Based on the Bis [(1, 2)(5, 6)] indoloanthracene Emissive
Layer. J. Phys. Chem. C 120 (2016) 6206−6217.
[
57] E. Angioni, M. Chapran, K. Ivaniuk, N. Kostiv, V. Cherpak, P. Stakhira, A. Lazauskas, S.
Tamulevičius, D. Volyniuk, N. J. Findlay, T. Tuttle, J. V. Grazulevicius, P. J. Skabara, A
single emitting layer white OLED based on exciplex interface emission, J. Mater. Chem. C 4
(2016) 3851−3856.