Synthesis and characterization of 1,3,5-triphenylamine derivatives with star-shaped architecture

Article abstract of DOI:10.1016/j.dyepig.2016.05.030

In this work we report the synthesis, electrochemical and optical properties of five new, star shaped compounds containing both carbazole and triphenylamine moieties, further endcapped with thiophene or 3,4-ethylenedioxythiophene units. Electrochemical, UV-visible spectroscopy and fluorescence methods were employed to study the properties of these compounds as well as their electropolymers. The basic characteristics such as the band gaps, HOMO and LUMO values, absorption and emission maximum wavelengths of the monomers and the polymers are reported and discussed.

Full text of DOI:10.1016/j.dyepig.2016.05.030

Dyes and Pigments 133 (2016) 25e32
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Synthesis and characterization of 1,3,5-triphenylamine derivatives
with star-shaped architecture
Alina Brzeczek a , Krzysztof Karon , Heather Higginbotham , Rafał G. J e˛ drysiak ,
,
**
a
,
*
c
a
a,
b
a
d
Mieczyslaw Lapkowski , Krzysztof Walczak , Sylwia Golba
Faculty of Chemistry, Silesian University of Technology, Strzody 9, 44-100 Gliwice, Poland
Centre of Polymer and Carbon Materials, Polish Academy of Science, Curie Sklodowska 34, 41-800 Zabrze, Poland
Durham University, Department of Physics, South Road, DH1 3LE Durham, United Kingdom
University of Silesia, Faculty of Computer Science and Materials Science, Institute of Materials Science, Bankowa 14, Katowice, Poland
a
b
c
d
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 25 February 2016
Received in revised form
In this work we report the synthesis, electrochemical and optical properties of five new, star shaped
compounds containing both carbazole and triphenylamine moieties, further endcapped with thiophene
or 3,4-ethylenedioxythiophene units. Electrochemical, UVevisible spectroscopy and fluorescence
methods were employed to study the properties of these compounds as well as their electropolymers.
The basic characteristics such as the band gaps, HOMO and LUMO values, absorption and emission
maximum wavelengths of the monomers and the polymers are reported and discussed.
17 May 2016
Accepted 19 May 2016
Available online 20 May 2016
©
2016 Elsevier Ltd. All rights reserved.
Keywords:
Carbazole
Triphenylamine
Star-shaped
Conducting polymers
Spectroelectrochemistry
1
. Introduction
[2e4]. Flattening the structure through the introduction of the rigid
core functionalized units that do not cause large steric hindrance or
elongation of arms, result in a shift in absorption and emission
spectra toward longer wavelengths [5,6]. Another approach for
better control of HOMO and LUMO energy levels and hence the
photophysical properties includes the introduction of both donor
and acceptor type units as the core or peripheral units of the star-
shaped molecules and thus shifting the spectra toward longer
wavelengths [7,8]. Among advantages of molecules with 3D archi-
tecture is the possibility of obtaining an amorphous material (i.e.
molecular glasses) due to non-planar molecular structure pre-
venting packing of molecules and hence ready crystallization [9].
Triphenylamine (TPA) possesses a flexible structure, which
together with bulky substituents enables some rotation in the star-
shaped molecule, thus it is successfully applied in materials
exhibiting aggregation induced emission enhancement (AIEE)
[10,6]. TPA also easily undergoes oxidation and forms stable radical
cations therefore it is commonly used as a hole transporting layer
Star-shaped low molecular weight compounds that possess
electroactive properties have been willingly applied in a variety of
applications such as organic light emitting diodes (OLEDs), organic
photovoltaics (OPVs) or organic field effect transistors (OFETs)
[1e3]. Depending upon the core and functionalization of the pe-
ripheral units it is possible to obtain star-shaped molecules with
different geometry and symmetry. A flat, inflexible central unit
with rigid arms usually provides an overall 2D geometry, whereas
non-planar centers provide a 3D architecture [1].
The structural orientation of the star-shaped molecules highly
affects their photophysical and electrochemical properties. A lack of
conjugation between the core and the peripheral arms can result in
a large energy band gap and hence absorption and emission of light
at shorter wavelengths. For this reason, carbazole and fluorene
functionalized star-shaped molecules are often used in blue OLEDs
[11,12]. Carbazole, due to its quite large planar structure can cause
some steric hindrance when functionalizing the TPA core and thus
it can enlarge the 3D molecular structure. Moreover, carbazole
exhibits good electron donating character and good hole
*
Corresponding author.
** Corresponding author.
E-mail addresses: alina.brzeczek@polsl.pl (A. Brzeczek), krzysztof.karon@polsl.pl
(
K. Karon).
http://dx.doi.org/10.1016/j.dyepig.2016.05.030
143-7208/© 2016 Elsevier Ltd. All rights reserved.
0

26
A. Brzeczek et al. / Dyes and Pigments 133 (2016) 25e32
transporting properties thus when substituted onto the TPA core
can be considered as a promising p-type material [13,14].
properties are gathered in Table 1. Absorption spectra of all mole-
cules exhibit three intense peaks located in the UV range of the
Herein we present a series of star-shaped molecules with C3
symmetry (Fig. 1) for potential application in organic electronics.
We have recently reported on the star-shaped derivatives with a
benzene core decorated with carbazoles [15]. In this work benzene
is replaced with TPA in order to compare how this new core affects
the optical properties of the investigated star shaped molecules and
their electrochemical characteristics. The TPA core is further func-
tionalized with carbazole units end-capped with thiophene and
electromagnetic spectrum, with lmax at 241, 282 and 347 nm for Ia
and Ib; 264, 304 and 356 nm for IIa and IIb; 265, 317 and 346 nm for
III respectively.
Comparing the spectra of all compounds one can see that the
introduction of additional aromatic substituents increases the
conjugation length but only to a certain extent. Introduction of
thienyl units into the oligomer results in bathochromic shift of the
two first peaks of approximately 20 nm. The absorption maximum
of the last peak, and thus the absorption range is however shifted
only by 10 nm. The bathochromic shift is a result of the increased
effective conjugation length in IIa and IIb. The introduction of
ethylenedioxythienyl units do not cause any bathochromic shift in
the absorption maximum, which can be explained by larger steric
hindrance and poor conjugation between carbazole and EDOT
moieties. It seems that alkyl substituent at the nitrogen atom, have
a negligible effect on the absorption and emission spectra. However
if we compare appropriate pairs of compounds we can conclude
that peaks of compounds with longer chains are always 2e4 nm
blue shifted, proving a slight steric hindrance effect.
3
,4-ethylenedioxythiophene (EDOT) units that are known to easily
undergo electropolymerization. We report therefore electro-
oxidation induced polymerization of the investigated oligomers
and electrochemical and spectroelectrochemical characterization
of the obtained high molecular weight polymeric species.
2
. Synthesis
The star-shaped compounds with a TPA core were synthesized
by Suzuki-Miyaura coupling between triphenylamine boronic acid
pinacol ester and carbazolyl halides (Scheme 2). The triphenyl-
amine boronic acid pinacol ester (4) was prepared by the bromi-
nation of triphenylamine with NBS followed by borylation using 2-
To obtain insight into the electronic spectra, TDDFT calculations
were completed employing a B3LYP/6-31G(d) functional. Calcula-
tions were performed for molecules containing ethyl substituents
at the carbazole instead of long alkyl chains to shorten the calcu-
lation time. Chosen results of calculations are shown in supple-
mentary data.
isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane.
Carbazole
derivatives were prepared by monoiodination or dibromiantion
and followed by N-alkylation. Additional heterocyclic rings were
coupled with dibromocarbazole via Stille coupling as shown in
Scheme 1. Stille coupling obtained mono substituted products (4a/
The peak at 347 nm in the spectra of compounds Ia and Ib is
mainly attributed to
and TPA core (according to calculation the highest contribution in
this band having transitions HOMO/LUMO,
p-p* transitions in well conjugated carbazole
4
2 3 2
b) using PdCl (PPh ) as the catalyst. Products were, however,
obtained with a low yield of 20% after 72 h both when the reaction
was carried out in both DMF and THF solution. The addition of
cesium fluoride and copper(I) iodide as proposed by Mee et. al. [16]
reduced the reaction time to 2 h, however the yield of the product
was still a low 17%. Addition of 2-(tributylstannyl) derivative in
small portions throughout the whole reaction time allowed ob-
tained the mono substituted product with 35% yield. The synthe-
HOMO / LUMOþ1,3,4). The peak at 286 nm is strongly attributed
to transitions in which lone pair of nitrogen atoms (both from the
carbazole moieties as well as the central nitrogen atom) are
involved (highest contribution of transitions HOMO-3/LUMO,
HOMO-4 / LUMOþ2, HOMO-6 and HOMO-5 / LUMOþ1). The
absorption band at about 300 nm is also assigned to
tions in carbazole moieties.
pep* transi-
sized compounds were purified by column chromatography and
characterized by 1H NMR, 13C NMR and MALDI TOF analysis. The
For compounds IIa and IIb the peak at 356 nm is attributed to
* transitions in the highly conjugated core reaching TPA and
carbazole and also * transitions covering the thiophene moi-
data is in full compliance with expected chemical structures.
pep
pep
3
. Results and discussion
eties (according to calculation the highest contribution in this band
has transitions HOMO/LUMO, LUMOþ1,2,6,7). Between 300 and
3.1. Photophysical properties
3
25 nm there is a broad absorption band consisting of two over-
lapping bands with peaks at about 304 and 315 nm. The peak at
04 nm is strongly attributed to transitions in which lone pair of
The normalized absorption and emission spectra of the inves-
tigated TPA derivatives are shown in Fig. 2 and the optical
3
Fig. 1. Structures of investigated compounds with C3 symmetry.

A. Brzeczek et al. / Dyes and Pigments 133 (2016) 25e32
27
ꢀ
Scheme 1. Synthetic route for the preparation of carbazole halides. (i) NBS, DMF, 0.5 h (ii) NaH, C
8
H17Br/C16
H
33Br, DMF, 80 C, 17 h (iii) 2-(tributylstannyl)thiophene/2-(tribu-
ꢀ
tylstannyl)ethylenodioxythiophene, CsF, CuI, PdCl
2
(PPh
3
)
2
, DMF, 40 C, 2 h.
3 4 2 3 2
Scheme 2. Synthetic route for the preparation of carbazolyltriphenylamines Ia/Ib, IIa/IIb, III. Reagents and conditions: Pd(PPh ) , K CO , TBAB, toluene:H O (4:1), reflux, 92 h.
2 2
Fig. 2. Absorption and emission spectra of studied compounds in CH Cl .
Table 1
nitrogen atom) are involved (highest contribution of transitions
Optical properties of compounds Ia, Ib, IIa, IIb and III.
HOMO-2,HOMO-3/LUMO and HOMO-1 / LUMOþ1). The peak at
Compound
labs [nm]
lem (lex) [nm]
F
315 nm on the other hand is mainly attributed to pep* transitions
in carbazole and tiophene moieties (HOMO / LUMOþ2,3,4
Ia
Ib
IIa
IIb
III
241, 282, 347
241, 280, 346
264, 304, 358
264, 304, 355
265, 317, 346
415 (347)
412 (347)
426 (356)
413 (356)
414 (346)
0.35
e
transitions).
e
For compound III the broad absorption band with maximum at
0.58
0.28
3
46 nm comprises bands corresponding mainly to
in Cz-Edot and in Cz-TPA core (HOMO/LUMO, LUMOþ3,5,8).
Bands corresponding to ne * transitions occur at 317 nm (HOMO-
/ LUMOþ3, HOMO / LUMOþ3,9,10).
All compounds are fluorescent. Photoluminescence spectra in
Cl are collected on Fig. 2. Compounds Ia, Ib, IIb and III have
pep* transitions
l
abs emaximum of absorbance,
wavelength,
lem maximum of emission,
l
ex e excitation
p
F
e fluorescence quantum yield.
1
CH
2
2
nitrogen atoms (both from carbazole moieties as well as central
almost the same shape, with emission band extending from 370 to

28
A. Brzeczek et al. / Dyes and Pigments 133 (2016) 25e32
5
00 nm, spectra of IIa is little red shifted. Peak maxima were found
at 415 nm for Ia, 412 nm for Ib, 426 nm for IIa, 413 nm for IIb and
14 nm for compound III (samples excited with light of a wave-
the three arms bearing carbazole and thiophene moieties and leads
to the formation of dications and reactive radicals in thiophene. The
increase of peak currents during the next voltammetric scans and
the resulting formation of a conducting film on the working elec-
trode is caused by the oligomerization process.
In case of compound III the oxidation begins at much lower
potential, Eonset, approximately 0.15 V, with the peak found at
0.293 V. Already this first oxidation step is an irreversible process
associated with rapid oligomerization. So low potential of oxidation
and ease of oligomerization resembles behavior of pure EDOT
which exhibits oxidation peak at 0.15 V [19].
4
length of 347 nm for Ia and Ib, 356 nm for IIa and IIb and 346 nm for
the III respectively). Quantum yields measured in toluene for de-
rivatives end-capped with carbazole, thiophene and EDOT are 0.53,
0
.58 and 0.28 for Ia, IIb and III respectively.
All spectra are evidently red shifted by approximately 60 nm
when compared to carbazole, which is assumed to be the most
emissive component in the investigated molecules. These star-
shaped compounds are also shifted 10 nm when compared to
previously described analogic compounds with a benzene core
Fig. 4 shows the multi-sweep cyclic voltammograms of all
[
15,17]. This bathochromic shift proves the interaction between TPA
investigated compounds (black line) in Bu
electrolyte and their electrodeposited films (red line) in monomer
free Bu NBF /dichloromethane electrolyte. Corresponding anodic
4 4
NBF /dichloromethane
and carbazole moieties. An additional shift in compound IIa, having
thienyl units, is related to yet more increased effective conjugation
length. Interestingly this effect isn’t observed in the case of analo-
gous compound with longer alkyl chain (IIb), nor in the compound
containing the EDOT unit (III), which is probably due to steric
hindrance.
4
4
and cathodic peaks (Ea and Ec) occurs on CV at potential (versus Fc/
þ
Fc ) for Ia: Ea1/Ec1 ¼ 0.314/0.288, Ea2/Ec2
¼
0.731/0.655,
Ea3 ¼ 0.954 V, for Ib: Ea1/Ec1 ¼ 0.421/0.349, Ea2/Ec2 ¼ 0.786/
0.720, Ea3 ¼ 1.010 V, for IIa: Ea1/Ec1 ¼ 0.267/0.200, Ea2 ¼ 0.517 V,
for IIb: Ea1/Ec1 ¼ 0.360/0.296, Ea2 ¼ 0.626 V, for III Ea1 ¼ 0.293 V.
For most of the investigated compounds oxidation is followed
by the consecutive oligomerization process, which is demonstrated
by the appearance of new peaks in the next scans. Only for
monomer Ib, a polymer film didn’t deposit well on the working
electrode under applied conditions. It was most likely caused by the
very good solubility of the formed oligomers in the electrolyte so-
lution due to the attached long alkyl chains. This supposition was
confirmed by the diffusion of a colorful species from the working
electrode surface into the bulk electrolyte during cyclic voltam-
metric scans.
3
.2. Electrochemical properties
Electrochemical properties of the compounds were investigated
using cyclic voltammetry (CV). All dyes undergo multistage
oxidation. The character of the oxidation process is different for
compounds terminated with carbazole units and for the ones
terminated with thiophene/EDOT units. Ia and Ib undergo a three
step oxidation in which the relative ratio of electrons involved in
each step is approximately 1:1:2 (data from DPV analysis), while
compounds IIa, IIb and III on the other hand undergo a two-step
oxidation with relative charge 1:3.
All obtained polymers exhibit slightly different electrochemical
properties to those of the corresponding monomers. Poly-Ia un-
dergoes a three step oxidation, with corresponding peaks found at
potentials of Ea1/Ec1 ¼ 0.279/0.283, Ea2/Ec2 ¼ 0.612/0.506, Ea3/
Fig. 3 shows example voltammograms of Ia, IIa and III registered
during oxidation at various potentials. On the CV of Ia, the first
oxidation step is
a
reversible process (peak separation
þ
D
pp ¼ 0.06 V), which can be attributed to the oxidation of the tri-
Ec3 ¼ 0.992/0.915 V versus Fc/Fc . In case of poly-Ib, four peaks are
phenylamine core and formation of a stable radical cation, pro-
posed previously by this group [18]. Further oxidation leads to the
formation of reactive radicals in the carbazole moieties and dica-
tions are generated by their recombination (second and third peaks
respectively). Oxidation to potentials above 0.9 V versus Fc/Fc
(
observed using CV, Ea1/Ec1 ¼ 0.350/0.320, Ea2/Ec2 ¼ 0.610/0.560,
Ea3/Ec3 ¼ 0.813/0.787, Ea3/Ec3 ¼ 1.054/0.965 V.
Films of poly-IIa and poly-IIb exhibit three oxidation peaks. For
poly-IIa peaks occur at Ea1/Ec1 ¼ 0.287/0.284, Ea2/Ec2 ¼ 0.638/
þ
þ
0.548, Ea3/Ec3 ¼ 1.073/0.985 V vs. Fc/Fc , while for poly-IIb Ea1/
third peak on the cyclic voltammogram) initiates the
Ec1 ¼ 0.390/0.374, Ea2/Ec2 ¼ 0.732/0.651, Ea3/Ec3 ¼ 1.191/1.081 V.
CV of poly-III displays four peaks, Ea1/Ec1 ¼ ꢁ0.232/ꢁ0.271,
Ea2/Ec2 ¼ ꢁ0.037/ꢁ0.130, Ea3/Ec3 ¼ 0.305/0.258, Ea3/Ec3 ¼ 0.943/
oligomerization.
Analogously in the case of IIa the initial oxidation of Ib is
accompanied by the formation of stable radical cations on the TPA
unit. Further oxidation above 0.65 V is associated with oxidation of
þ
0.877 V vs. Fc/Fc . All received polymer films are stable under
oxidation up to approximately. 1.3 V versus ferrocene.
Fig. 3. Cyclic voltammogram (CV) registered during electrochemical oxidation of oligomers Ia, IIa and III to various potentials. Potential sweep rate 0.1 V/s; 1 mM monomer solution
in 0.1 M Bu4NBF4/CH Cl
2
2
.

A. Brzeczek et al. / Dyes and Pigments 133 (2016) 25e32
29
3.3. Spectroelectrochemistry of polymers
Spectroelectrochemical properties of the electro-deposited
carbazole containing polymer films were investigated by
UVeviseNIR analysis. The absorption spectra of polymers Ia, Ib, IIa,
IIb, and III, on an ITO coated glass electrode, recorded as a function
of increasing applied electrode potentials are shown in Fig. 5.
The oxidation process proceeds in a different way for each group
of polymers.
In the case of Ia and Ib the absorption bands corresponding to
the electro-deposited polymers, gradually decrease with the
increasing applied voltage. At the same time during the doping
Fig. 4. Cyclic voltammograms of star-shaped derivatives: black lines demonstrate CV
curves of compounds in 0.1 M Bu NBF /dichloromethane electrolyte and red lines
display CV curves of electrodeposited polymers on a platinum working electrode in
monomer free 0.1 M Bu NBF /dichloromethane electrolyte. Measurement conditions:
4
4
4
4
scan rate 0.1 V/s; Ag/AgCl reference electrode calibrated against Fc/Fcþ. (For inter-
pretation of the references to colour in this figure legend, the reader is referred to the
web version of this article.)
The electrochemical data were used to determine the energy of
the HOMO levels. Each HOMO level was calculated using the
oxidation onset potential according to the equation
HOMO ¼ ꢁ(5.1 þ Eoxonset). The LUMO level, which is accompanied
with the reduction process, couldn’t be determined due the limi-
tation of the supporting electrolyte. Subsequently this value was
then calculated from the difference between the HOMO and the
band gap, determined from the optical band gap (Egopt). The optical
band gap was calculated from the Planck equation for photon en-
ergy. All parameters are displayed in Table 2.
Fig. 5. Set of UVevis absorption spectra of poly-Ia, Ib, IIa, IIb and III thin films on an ITO
electrode, recorded at gradually stepped potentials.
Table 2
Electronic properties of compounds Ia, Ib, IIa, IIb and III and their polymers.
Compound
Monomer
Egopt [eV]
Polymer
EHOMO [eV]
ELUMO [eV]
Egopt [eV]
EHOMO [eV]
ELUMO [eV]
Ia
Ib
IIa
IIb
III
3.15
3.14
3.06
3.15
3.13
ꢁ5.34
ꢁ5.39
ꢁ5.26
ꢁ5.36
ꢁ5.25
ꢁ2.19
ꢁ2.25
ꢁ2.20
ꢁ2.21
ꢁ2.12
2.31
3.07
2.58
2.57
2.61
ꢁ5.27
ꢁ5.28
ꢁ5.24
ꢁ5.09
ꢁ4.79
ꢁ2.96
ꢁ2.21
ꢁ2.66
ꢁ2.52
ꢁ2.18
þ
Electrochemical data of Ia, Ib, IIa, IIb, III obtained from cyclic voltammetry (Potentials vs Ag/AgCl calibrated against Fc/Fc ).
LUMO ¼ EHOMO þ Eg), Energy of band-gap calculated from UVevis spectroscopy.
E
HOMO
¼
ꢁ(Eoxonsetþ5.) where,
E

30
A. Brzeczek et al. / Dyes and Pigments 133 (2016) 25e32
process new defined absorption bands appear at ca. 470 and
beyond 900 nm. While further doping proceeds, these peaks
slightly shift hypsochromically and later diminish. Simultaneously
a new, broad absorption band grows in at approximately 700 nm.
The absorption peak located at ca. 700 nm is apparently due to the
formation of bipolarons, whereas the spectral bands appearing at
lower and higher energy regions might be due to the formation of
polaronic species [20,21].
3.14 eV for the monomer). This unusual behavior is probably caused
by steric hindrances that also cause difficulties in polymerization.
Both compounds with carbazole-thiophene linkages reach
similar Eg 2.58 and 2.57 eV for poly-IIa and poly-IIb respectively.
The Eg value of III monomer equals to 3.13 eV and after polymeri-
zation this value decreases to 2.61 eV.
4. Experimental
Oxidation of poly-IIa, IIb and III occurs in a different way. During
oxidation, two peaks representing two various polarons appear
simultaneously at approximately 450 and 650 nm (and beyond
4.1. Methods
9
00 nm). When the applied potential is raised the bipolaron band
The structure of the synthesized compounds were analyzed
1
13
increases in the range of 800e1000 nm. This observation might be
explained by the formation of charged species such as two different
polarons and later bipolarons. Potentials, at which bands corre-
sponding to polarons and dipolarons appear, on the spectra are
consistent with peak potentials in the cyclic voltammograms. As a
result of p-doping, the color of the electrodeposited films changes
from yellowish (in the undoped state) to black (in the fully oxidized
state at app. 1.5 V potential) which implies that these polymeric
films have potential for application in electrochromic devices. An
example of this color change within electrodeposited films can be
seen in Fig. 6 whereby photos of poly-IIa film on ITO in the neutral
and oxidized state (yellowish and black respectively) are shown.
Other compounds exhibit similar colors in neutral and oxidized
forms.
with NMR at 600 MHz for H NMR and 151 MHz for C NMR on a
1
Varian 600 MHz System spectrometer or at 400 MHz for H NMR
13
and 100 MHz for C NMR on an Agilent 400 MHz spectrometer;
values are in parts per million (ppm) relative to tetramethylsilane
d
(TMS) as an internal standard. MALDI-TOF spectra were recorded
on a Shimadzu AXIMA Performance instrument without additional
matrix.
Electrochemical measurements were carried out using a CH
Instruments 660C potentiostat. The experiments were carried out
in the conventional three electrode system. Briefly, a platinum disc
of 1 mm diameter was used as the working electrode, Pt wire
served as the counter electrode, and Ag wire was used as a pseudo-
reference. Additionally, in each experiment the reference electrode
potential was monitored using ferrocene as an internal standard.
All cyclic voltammetry measurements were carried out at the scan
rate of 0.1 V/s at room temperature. All solutions were purged with
Ar for 10 min prior to each experiment. A typical sample concen-
tration was 1 mM in the dried dichloromethane containing 0.2 M of
3.4. Electronic properties of monomers vs polymers
The band gaps (Eg) of the materials films were calculated from
Bu
4
4
NBF (Aldrich, 98% purity).
the optical absorption edge and were significantly dependent upon
chemical structure (see Table 2).
UVevis spectroelectrochemical measurements were completed
with an AutoLab PGSTAT 20 electrochemical complex, Ocean Optics
QE6500 and NIRQuest apparatus. In spectroelectrochemical ex-
periments an ITO/quartz transparent electrode was used in the
cuvette-type cell.
Fluorescence spectra were recorded using Jobin Yvon Horiba
f
Spectrofluorimeter Fluoro Max-3. Fluorescence quantum yields (F )
were determined using a comparison method using 9,10 dipheny-
lanthracene (0.95 in ethanol) as the solution standard [22]. The
reference and unknown samples were prepared with their absor-
bance maxima reading less than 0.1 in order to reduce internal filter
effects. Samples were deoxygenated in a clean degassing cell,
immediately prior to measurement of the fluorescence emission.
The emission spectrum of each sample was corrected for detector
efficiency before data analysis.
All monomers have similar Eg values which varies from 3.06 eV
for compound IIa to 3.15 eV for Ia and IIb. From these values it
appears that the Eg is mainly determined by the carbazole
etriphenylamine core. In almost all cases after polymerization the
Eg value decreased significantly, providng evidence of the increase
in conjugation length. The most significant decrease in Eg is
observed for poly-Ia, where the Eg is equal to 2.31 eV (versus
3
.15 eV for the monomer). Interestingly, in the case of its analog
structure Ia, which differs by the alkyl chain length attached to the
carbazole, the Eg decreases the least, reaching 3.07 eV (versus
The quantum-mechanical calculations were performed for both
investigated compounds using density functional theory (DFT)
using U-B3LYP/6-31G level of theory and basic set; calculations
were performed on Gaussian software using the PL-Grid
infrastructure.
4.2. Materials
Carbazole, triphenylamine, 2-isopropoxy-4,4,5,5-tetramethyl-
1,3,2-dioxaborolane and other synthetic materials were purchased
from Sigma-Aldrich and used as received. 3-Iodo-9H-carbazole was
synthesized according to the procedure described by Tucker [23].
3,6-dibromo-9H-carbazole was prepared according to the proce-
dure described by Cheng-Hsiu Ku et al. [24]. Alkylated carbazoles
were prepared by previously reported procedures [15]. Tris(4-
(
4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)amine
prepared according to the procedure described by Cremer et. al
25]. Solvents were used without further purification except from
DMF (HPLC grade) which was dried with 4 Å molecular sieves prior
was
[
Fig. 6. The photo showing a film of poly-IIa on ITO in the neutral state i.e. undoped
(
left) and the fully oxidized state, at a potential approx. 1.5 V (right).

A. Brzeczek et al. / Dyes and Pigments 133 (2016) 25e32
31
to use. Toluene Rotidry was taken for the coupling reactions. Col-
umn chromatography was performed using silica gel 60
tetrakis(triphenylphosphine)palladium(0) (18 mg, 0.016 mmol)
was added to the reaction mixture. The reaction mixture was
refluxed for 92 h under nitrogen, cooled to r.t. and poured onto
(
0.040e0.063 mm) purchased from Merck.
water (50 mL). The resulting mixture was extracted with CH
2 2
Cl
4
.2.1. 3-Bromo-9-hexadecyl-6-(thiophen-2-yl)-9H-carbazole (4a)
(4 ꢂ 20 mL) and dried over anhydrous Na
2
SO . The solvent was
removed under reduced pressure and the residue was purified by
4
3
,6-Dibromo-9-hexadecyl-9H-carbazole 5 (5.0 g, 9.1 mmol) was
dissolved in anhydrous DMF (100 mL) and purged with nitrogen.
column chromatography (n-hexane: toluene 3:1 v/v for Ib and Ia, n-
Cesium fluoride (2.8 g, 18 mmol), copper(I) iodide (0.17 g,
hexane: CH
2
Cl
2
5:3 v/v for IIa, n-hexane: CH
2 2
Cl 2:1 v/v for IIb and
0
.91 mmol) and PdCl
2
(PPh
3
)
2
(0.32 g, 0.46 mmol) were then added
n-hexane: CH
2
Cl 1:1 v/v and CH Cl for III were used as eluents).
2
2
2
to the reaction mixture. 2-(tributylstannyl)thiophene (3.4 g,
9
4
3
.1 mmol) was added dropwise to the reaction mixture for 2 h at
0 C, while stirring. The reaction mixture was stirred for a further
4.3.1. Tris{4-[9-butyl-9H-carbazol-3-yl]phenyl}amine Ia (57 mg,
39%)
ꢀ
0
min until the 2-(tributylstannyl)thiophene substrate was
1H NMR (600 MHz, acetone-d6)
d
8.35 (d, J ¼ 1.2 Hz, 3H),
completely consumed (progress of reaction was monitored by TLC
n-hexane: CHCl 5:1, v/v)). The reaction mixture was poured into
water (200 mL), extracted with CH Cl
(4 ꢂ 40 mL) and dried over
anhydrous Na SO . The solvent was removed under diminished
pressure and the residue was purified by silica gel packed column
hexane: CHCl 5:1, v/v) to an afford light yellow solid (1.8 g, yield:
8.14e8.11 (m, 3H), 7.68 (dd, J ¼ 8.5, 1.8 Hz, 3H), 7.67e7.64 (m, 6H),
7.52 (d, J ¼ 8.5 Hz, 3H), 7.46 (d, J ¼ 8.5 Hz, 3H), 7.36e7.33 (m, 3H),
7.19e7.16 (m, 6H), 7.11e7.08 (m, 3H), 4.34 (t, J ¼ 7.2 Hz, 6H),
1.80e1.72 (m, 6H), 1.33e1.28 (m, 6H), 0.83 (t, J ¼ 7.4 Hz, 9H).
(
3
2
2
2
4
13
C NMR (151 MHz, acetone-d6) d 149.00, 143.64, 142.51, 139.23,
(
3
134.19, 130.46, 128.43, 127.26, 127.07, 126.03, 125.58, 123.01, 121.45,
3
5%).
120.74, 112.02, 111.78, 45.12, 33.71, 22.82, 15.92. MALDI-TOF-MS m/z
calcd for C66H N , 909,21; found, 908.2.
60 4
1H NMR (400 MHz, CDCl
)
d
8.23 (dd, J ¼ 1.8, 0.6 Hz, 1H),
3
8
2
.22e8.21 (m, 1H), 7.72 (dd, J ¼ 8.4, 1.6 Hz, 1H), 7.53 (dd, J ¼ 8.8,
.0 Hz, 1H), 7.36 (dd, J ¼ 8.8, 1.6 Hz, 1H), 7.32 (dd, J ¼ 3.6, 1.2 Hz, 1H),
4.3.2. Tris{4-[9-hexadecyl-9H-carbazol-3-yl]phenyl}amine Ib
(83 mg, yield: 38%)
7
2
.26e7.23 (m, 2H), 7.09 (dt, J ¼ 6.0, 3.0 Hz, 1H), 4.23 (t, J ¼ 7.2 Hz,
1
H), 1.87e1.79 (m, 2H), 1.38e1.17 (m, 10H), 0.89e0.81 (m, 3H).
H NMR (400 MHz, CDCl
3
)
d
8.32 (s, 3H), 8.14 (d, J ¼ 7.6 Hz, 3H),
13
C NMR (101 MHz, CDCl
28.00, 126.10, 124.97, 124.47, 123.82, 123.22, 122.21, 122.16, 117.94,
11.78, 110.29, 109.22, 43.31, 31.75, 29.31, 29.13, 28.92, 27.24, 22.58,
4.04.
3
)
d
145.40, 140.19, 139.49, 128.55,
7.72 (d, J ¼ 8.2 Hz, 3H), 7.66 (d, J ¼ 8.0 Hz, 6H), 7.50e7.43 (m, 6H),
7.41 (d, J ¼ 8.2 Hz, 3H), 7.36e7.30 (m, 6H), 7.25e7.21 (m, 3H), 4.30 (t,
J ¼ 7.0 Hz, 6H), 1.93e1.85 (m, 6H), 1.43e1.14 (m, 78H), 0.87 (t,
J ¼ 6.8 Hz, 9H).
1
1
1
13
3
C NMR (101 MHz, CDCl ) d 140.89, 139.75, 131.84, 128.99,
4
.2.2. 3-Bromo-6-(3,4-ethylenedioxythiophen-2-yl)-9-octyl-9H-
127.95, 125.70, 124.85, 124.50, 123.35, 123.00, 120.40, 118.81, 118.42,
110.37, 108.87, 108.78, 43.22, 31.92, 29.70, 29,69, 29.67, 29.66, 29.65,
29.61, 29.58, 29.52, 29.43, 29.36, 29.03, 27.34, 22.69, 14.11. MALDI-
carbazole (4b)
3
,6-Dibromo-9-octyl-9H-carbazole 5 (2.0 g, 4.6 mmol) was
dissolved in anhydrous DMF (45 mL) and purged with nitrogen.
Cesium fluoride (1.4 g, 9.2 mmol), copper(I) iodide (90 mg,
132 4
TOF-MS m/z calcd for C102H N , 1414,17; found, 1414.96.
0
.46 mmol) and PdCl
reaction mixture.
-(Tributylstannyl)-3,4-(ethylenedioxy)thiophene
2
(PPh
3
)
2
(0.16 g, 0.23 mmol) were added to the
4.3.3. Tris{4-[9-butyl-6-(thiophen-2-yl)-9H-carbazol-3-yl]phenyl}
amine IIa (78 mg, yield: 42%)
1
2
(2.0
g,
H NMR (600 MHz, acetone-d6)
d
8.59 (d, J ¼ 1.6 Hz, 3H),
4
4
.6 mmol) was added dropwise to the reaction mixture for 2 h at
0 C. The reaction mixture was stirred for another 30 min until the
7.83e7.78 (m, 15H), 7.64 (d, J ¼ 8.5 Hz, 3H), 7.62 (d, J ¼ 8.5 Hz, 3H),
7.48 (dd, J ¼ 3.6, 1.1 Hz, 3H), 7.38 (dd, J ¼ 5.1, 1.1 Hz, 3H), 7.32e7.29
(m, 6H), 7.13 (dd, J ¼ 5.1, 3.6 Hz, 3H), 4.47 (t, J ¼ 7.2 Hz, 6H),
1.93e1.88 (m, 6H), 1.48e1.36 (m, 6H), 0.95 (t, J ¼ 7.4 Hz, 9H).
ꢀ
stannyl derivative substrate was consumed (TLC: n-hexane: CHCl
:2, v/v). The reaction mixture was poured into water (100 mL),
extracted with CH Cl
(4 ꢂ 30 mL) and dried over anhydrous
Na SO . The solvent was removed under diminished pressure and
the residue was purified by silica gel packed column (n-hexane:
CHCl 5:2, v/v) to an afford light yellow solid (0.84 g, yield: 37%).
H NMR (400 MHz, CDCl
8.37 (d, J ¼ 1.6 Hz, 1H), 8.24 (d,
3
5
13
2
2
C NMR (151 MHz, acetone-d6) d 149.03, 148.15, 143.17, 143.02,
2
4
139.06, 134.48, 130.72, 130.47, 128.41, 127.64, 127.08, 126.78, 126.32,
126.12, 126.01, 124.71, 121.09, 120.31, 112.29, 45.27, 33.74, 22.81,
15.92. MALDI-TOF-MS m/z calcd for C78H N S , 1155,58; found,
66 4 3
3
1
3
)
d
1154.9.
J ¼ 1.6 Hz, 1H), 7.81 (dd, J ¼ 8.6, 1.6 Hz, 1H), 7.52 (dd, J ¼ 8.6, 1.6 Hz,
1
4
H), 7.37 (d, J ¼ 8.6 Hz, 1H), 7.26 (d, J ¼ 8.6 Hz, 1H), 6.32 (s, 1H),
.38e4.26 (m, 4H), 4.26e4.21 (m, 2H), 1.86e1.82 (m, 2H), 1.31e1.22
4.3.4. Tris{4-[9-hexadecyl-6-(thiophen-2-yl)-9H-carbazol-3-yl]
phenyl}amine IIb (0.11 g, 40%)
1
(
m, 10H), 0.91e0.84 (m, 3H).
H NMR (400 MHz, CDCl
3
)
d
8.59 (d, J ¼ 1.6 Hz, 3H), 7.84e7.78
13
C NMR (101 MHz, CDCl
28.36, 125.14, 124.64, 124.63, 123.28, 122.07, 118.39, 111.64, 110.23,
09.02, 99.63, 96.48, 64.81, 64.58, 43.29, 31.75, 29.31, 29.12, 28.90,
3
)
d
142.30, 139.61, 139.45, 137.11,
(m, 12H), 7.66 (d, J ¼ 8.6 Hz, 6H), 7.63 (d, J ¼ 8.6 Hz, 3H), 7.48 (dd,
J ¼ 3.6, 1.1 Hz, 3H), 7.38 (dd, J ¼ 5.1, 1.1 Hz, 3H), 7.32 (d, J ¼ 8.6 Hz,
6H), 7.12 (dd, J ¼ 5.1, 3.6 Hz, 3H), 4.48 (t, J ¼ 7.2 Hz, 6H), 1.96e1.92
(m, 6H), 1.43e1.16 (m, 78H), 0.86 (m, 9H). MALDI-TOF-MS m/z calcd
1
1
2
7.23, 22.58, 14.11.
138 4 3
for C114H N S , 1660,54; found, 1661.83.
4.3. General procedure for the preparation of Ia/Ib, IIa/IIb and III
4.3.5. Tris{4-[9-octyl-6-(3,4-ethylenedioxythiophen-2-yl)-9H-
Tris(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)
carbazol-3-yl]phenyl}amine III (0.11 g, yield: 45%)
1
amine (0.10 g, 0.16 mmol) and corresponding aryl halide (3a, 3b or
-Iodo-9H-carbazole) (4,5 eq.) were dissolved in solvent mixture of
toluene (20 mL) and H O (5 mL). Powdered anhydrous potassium
carbonate (1.4 g, 100 mmol) and tetrabutylammonium bromide
10 mg, 0.03 mmol) were added and the reaction mixture was
purged with nitrogen for 10 min and degassed. Next
H NMR (400 MHz, CDCl
3
)
d
8.40 (d, J ¼ 1.6 Hz, 3H), 8.28 (d,
3
J ¼ 1.2 Hz, 3H), 7.75 (dd, J ¼ 8.6, 1.6 Hz, 3H), 7.66 (dd, J ¼ 8.8, 1.6 Hz,
3H), 7.60 (d, J ¼ 8.4 Hz, 6H), 7.47 (d, J ¼ 8.4 Hz, 3H), 7.38 (d,
J ¼ 8.4 Hz, 2H), 7.32 (d, J ¼ 8.8 Hz, 2H), 7.26 (d, J ¼ 8.8 Hz, 6H), 6.21
(s, 3H), 4.25 (m, 18H), 1.85e1.77 (m, 6H), 1.37e0.93 (m, 30H),
0.82e0.76 (m, 9H).
2
(

32
A. Brzeczek et al. / Dyes and Pigments 133 (2016) 25e32
13C NMR (101 MHz, CDCl
36.93, 136.48, 131.99, 127.97, 124.99, 124.71, 124.57, 124.45, 124.41,
24.21, 123.43, 123.22, 118.75, 118.67, 118.30, 114.01, 108.98, 108.86,
6.24, 64.78, 64.56, 43.27, 31.76, 29.35, 29.14, 29.02, 27.28, 22.65,
4.07. MALDI-TOF-MS m/z calcd for C96 , 1498,01; found,
)
d
146.34, 142.26, 140.09, 139.81,
processable phosphonate functionalized deep-blue fluorescent emitter for
efficient single-layer small molecule organic light-emitting diodes. Chem
Commun 2012;48:8970e2.
3
1
1
9
1
[
4] Moonsin P, Prachumrak N, Rattanawan R, Keawin T, Jungsuttiwong S,
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5
. Conclusions
The synthetic route and properties of a series of star-shaped
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discussed. UVevis and fluorescence studies have shown only slight
changes in the optical properties depending on the groups
appended to the carbazoles as well as the length of the alkyl chains
attached. All compounds exhibited strong fluorescence approxi-
mately red shifted when compared to carbazole. The chemical
structure very strongly influenced the electrochemical properties
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potential of oxidation but also in polymerization. All compounds
were successfully polymerized, producing electroactive oligomers.
The thin films of the resulting polymers were investigated by
means of UVevis-spectroelectrochemistry. The spectroelec-
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cations and dications in all polymers even at high doping level. All
polymers exhibit similar electrochromic effects giving color
changes from yellowish in the neutral form to almost black in the
oxidized form what makes them promising candidates for elec-
trochromic displays. Moreover, good luminescent properties and
the capacity of tuning their electrochemical characteristic renders
oligomers for application in OLED field.
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[
[
[
[
[
[
[
Acknowledgements
18] Karon K, Lapkowski M, Dabuliene A, Tomkeviciene A, Kostiv N,
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This work was financed by Polish National Science Centre,
Project No. 2012/05/B/ST5/00745. This research was supported in
part by PL-Grid Infrastructure. Alina Brzeczek is grateful to National
Science Center 2015/16/T/ST5/00525 for the financial support.
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Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.dyepig.2016.05.030.
[
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