Synthesis and properties of photocross-linkable carbazole dimers

Article abstract of DOI:10.1016/j.reactfunctpolym.2016.12.004

New carbazole-based monomers with two reactive functional groups such as epoxypropyl, oxetanyl and vinyloxethyl were synthesized and their cationic photopolymerization was performed. The monomer containing epoxypropyl groups exhibited the highest conversion in photopolymerization (78%). The monomers and polymers exhibited ability of glass formation with the glass transition temperatures up to 98?°C for low-molecular-weight compounds and those observed for polymers ranging from 89 to 150?°C. The synthesized derivatives absorb electromagnetic irradiation in the range of 200–390?nm with the band gaps of 3.14–3.16?eV. The compounds exhibit blue photoluminescence with the intensity maxima at 400?nm. The compounds were found to have high triplet energies of ca. 2.78?eV. The electron photoemission spectra of the layers of the synthesized compounds revealed ionization potentials of 5.20–5.37?eV. The time-of-flight hole drift mobilities of the layers of the compounds exceed 10^??5?cm²/V?×?s at high electric fields.

Full text of DOI:10.1016/j.reactfunctpolym.2016.12.004

Accepted Manuscript
Synthesis and properties of photocross-linkable carbazole dimers
G. Simkus, A. Tomkeviciene, D. Volyniuk, S.V. Kostjuk, J.V.
Grazulevicius
PII:
S1381-5148(16)30230-9
DOI:
Reference:
doi: 10.1016/j.reactfunctpolym.2016.12.004
REACT 3778
To appear in:
Reactive and Functional Polymers
Received date:
Revised date:
Accepted date:
16 June 2016
9 November 2016
2 December 2016
Please cite this article as: G. Simkus, A. Tomkeviciene, D. Volyniuk, S.V. Kostjuk, J.V.
Grazulevicius , Synthesis and properties of photocross-linkable carbazole dimers. The
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ACCEPTED MANUSCRIPT
LISYNTHESIS AND PROPERTIES OF PHOTOCROSS-LINKABLE CARBAZOLE
DIMERS
G. Simkusa, A. Tomkevicienea, D. Volyniuka, S.V. Kostjukb, J.V. Grazuleviciusa*
aDepartment of Polymer Chemistry and Technology, Kaunas University of Technology, Radvilenu rd. 19, LT-50254, Kaunas,
Lithuania
bReaseach Institute for Physical Chemical Problems of the Belarusian State University, Leningradskaya st. 14 220030, Minsk,
Belarus
* Corresponding author. Tel.: +370 37 300193; fax: +370 37 300152. E-mail address: juozas.grazulevicius@ktu.lt (J.V.
Grazulevicius).
Abstract
New carbazole-based monomers with two reactive functional groups such as epoxypropyl, oxetanyl
and vinyloxethyl were synthesized and their cationic photopolymerization was performed. The
monomer containing epoxypropyl groups exhibited the highest conversion in photopolymerization (78
%). The monomers and polymers exhibited ability of glass formation with the glass transition
o
temperatures up to 98 C for low-molecular-weight compounds and those observed for polymers
o
ranging from 89 to 150 C. The synthesized derivatives absorb electromagnetic irradiation in the
range of 200 – 390 nm with the band gaps of 3.14 – 3.16 eV. The compounds exhibit blue
photoluminescence with the intensity maxima at 400 nm. The compounds were found to have high
triplet energies of ca. 2.78 eV. The electron photoemission spectra of the layers of the synthesized
compounds revealed ionization potentials of 5.20 – 5.37 eV. The time-of-flight hole drift mobilities of
the layers of the compounds exceed 10-5 cm2/V×s at high electric fields.
Keywords: Carbazole; Glass-forming; Cross-linking, Thermal stability; Charge mobility.
1. Introduction
The current level of development of organic light emitting diodes (OLEDs) enables their effective
application in the low-cost flat panel display technology and lighting [1]. Most of OLEDs are the
multilayer systems, which are composed of hole-transport, emitting, and electron-transport layers and
often some additional layers sandwiched between two electrodes [2,3]. Two methods are popular in their
fabrication. The most commonly used one is vacuum deposition. High quality multilayer devices are
fabricated by this method, but it is suitable only for low-molar-mass compounds, characterized by high
thermal stability. In addition, vacuum deposition also requires high instrumental expenses and time to

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prepare solid films which leads to relatively high costs [4]. An alternative method to fabricate multilayer
systems is spin-coating. It requires less investments and enables to coat larger areas. However, most of
organic semiconductors are soluble in the same organic solvents. Therefore during preparation of
multilayer systems it is important to ensure insolubility of a bottom layer onto which a top layer has to be
cast. The approach that is used to solve this problem is to render the material insoluble after spin-coating.
In order to get insoluble layer soluble functionalized precursor polymers, crosslinkable side-chain
polymers or monomers are used [5]. The crosslinking process for obtaining insoluble polymer layers can
be carried out using thermal [6,7], photochemical [8-10], or chemical treatment [11,12].
It is well know that carbazole-based darivatives are characterized by high triplet energies, ET (up to
3.05 eV), excellent hole-transporting properties, wide bang gap and thermal stability which are the main
requirements for host materials used in blue phosphorescent OLEDs [13,14]. In this work we report on
the synthesis and properties of several photocross-linkable carbazole based monomers and demonstrate
their photocross-linking.
2. Experimental
2.1. Instrumentation
1H and 13C NMR spectra were recorded using Bruker Avance III [400 MHz (1H), 100 MHz (13C)]
spectrometer at room temperature. All the data are given as chemical shifts in δ (ppm). (CH3)4Si (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 I2 or UV radiation. Silica gel
(grade 60, 63–200 mesh, 60 Å, Fluka) was used for column chromatography. Melting points (m.p.) of the
compounds were determined using Electrothermal Mel-Temp melting point apparatus. Mass (MS) spectra
were recorded on a Waters (ACQUITY UPLC®). Elemental analysis was performed with an Exeter
Analytical CE-400 Elemental. Differential scanning calorimetry (DSC) measurements were carried out
using a DSC Q2000 thermal analyzer at a heating rate of 10 oC/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 photoluminescence (PL) spectra 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 at 10-4 M
concentration. The phosphorescence spectra of dilute solution in THF (10-4 M) were recorded at 77 K by
Edinburgh Instruments FLS980.

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The kinetics of the photopolymerization were monitored by real-time FT-IR spectroscopy using Bruker
Vertex 70 spectrometer. The samples were exposed by UV radiation with the wavelength range of 250–
450 nm using UV/Visible spot curing system OmniCure S2000 (Lumen Dynamics Group Inc). The
intensity of the UV radiation was 9.3 W∙cm-2 (high pressure 200 W mercury vapor short arc).
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 electrode was a
glassy carbon of 0.12 cm2 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 versus Fc/Fc+ as internal reference where the
potential of the redox system EFc1/2=0.210 V/Ag:Ag+.
The ionization potentials (Ip(EP)) of the solid samples of the synthesized compounds were measured by the
electron photoemission spectrometry in air as reported earlier [15]. 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 experimental setup consisted of deep UV deuterium light source
ASBN-D130-CM, CM110 1/8m monochromator, and electrometer 6517B Keithley.
The charge carrier mobility (μ) measurements were carried by the time of flight method (TOF) [16]. 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, Al electrode (80 nm) was evaporated at 15 Å/s. The thickness of thin layers was measured using
the method of carrier extraction by linearly increasing voltage (CELIV) (ε~3) [17]. The charge carriers
were generated at the layer surface by illumination with pulses of Nd:YAG laser(EKSPLA NL300, a
wavelength of 355 nm, pulse duration 3-6 ns). The transit time was determined from the kink point in the
transient photocurrent curves. The transit time tt with the applied bias (V) indicates the passage of holes
through the entire thickness of the cell (d) and enables determination of the hole mobility as μ=d2/U×tt.
The experimental setup consisted of a Keithley 6517B electrometer, and a Tektronix TDS 3052C
oscilloscope.
2.2 Materials
3-Iodo-9H-carbazole (1) [18], 3,6-dibromo-9H-carbazole (3) [19] and 3,6-dimethoxy-9H-carbazole (4)
[20] were synthesized according to procedures described in literature. 3-Iodo-9-isopentyl-9H-carbazole
(2) was prepared by alkylation of 3-iodocarbazole in the presence of phase transfer catalyst [21].

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3-(3,6-Dimethoxycarbazol-9-yl)-9-isopentylcarbazole (5)
A mixture of 3-iodo-9-isopentyl-9H-carbazole (3.84 g, 10 mmol), 3,6-dimethoxy-9H-carbazole (2 g, 8.8
mmol), 18-crown-6 (0.44 mmol, 0,12 g), potassium carbonate (9.73 g, 71 mmol), and copper powder
(2.24 g, 35 mmol) in o-dichlorbenzene (30 ml) was refluxed under argon at 180 oC. After 4 h the reaction
was stopped, copper powder and inorganic salts were removed by filtration. The solvent was distilled
under reduced pressure and the crude product was purified by column chromatography on silica gel using
hexane/dichloromethane (3/1) as an eluent. The target compound was obtained as brownish powder
(fw=462g/mol) in 72 % yield (3.52 g). 1H NMR (400 MHz, CDCl3), δ (ppm): 8.20 (s, 1H, Ar), 8.05 (d, J
= 7.8 Hz, 1H, Ar), 7.60 (d, J = 2.4 Hz, 2H, Ar), 7.56 – 7.54 (m, 2H, Ar), 7.50 (dd, J = 7.0, 1.2 Hz, 1H,
Ar), 7.45 (d, J = 8.2 Hz, 1H, Ar), 7.29 (d, J = 8.9 Hz, 2H, Ar), 7.27 – 7.21 (m, 1H, Ar), 7.04 (dd, J = 8.9,
2.5 Hz, 2H, Ar), 4.38 (t, J = 7.1 Hz, 2H, NCH2), 3.96 (s, 6H, OCH3), 1.86 – 1.69 (m, 3H, CH2, CH), 1.07
(d, J = 6.3 Hz, 6H, CH3). 13C NMR (100 MHz, CDCl3), δ (ppm): 153.8, 140.9, 139.2, 137.5, 130.6, 129.3,
127.8, 126.3, 125.1, 123.7, 123.2, 122.5, 120.7, 119.3, 119.2, 115.2, 110.8, 109.5, 108.9, 102.9, 56.2 (2C,
OCH3), 41.6 (NCH2), 37.6 (CH), 26.2 (CH2), 22.7 (2C, CH3). MS (APCl+, 20 V), m/z (%) = 463 ([M +
H]+, 100). Elemental analysis. Calcd for C31H30N2O2 (%): C 80.49, H 6.54, N 6.06, O 6.92; found (%): C
80.54, H 6.56, N 6.09.
3-(3,6-Dihydroxycarbazol-9-yl)-9-isopentylcarbazole (6)
Compound 5 (1 g, 2.2 mmol) was dissolved in dry dichloromethane (DCM, 15 ml) at room temperature
o
and cooled to -80 C. Boron tribromide (1 M in DCM, 11.2 ml, 11.2 mmol) was added slowly. After the
o
addition, the homogeneous mixture was stirred at -80 C for 30 min and then it was allowed to warm
slowly to room temperature overnight. The reaction mixture was poured into water (200 ml), stirred for
30 min, and extracted with DCM. The combined organic phase was dried over Na2SO4, filtered, and
concentrated. The crude product was purified by column chromatography on silica gel using
hexane/acetone (4/1) as an eluent. The target compound was obtained as white crystals (fw=434 g/mol,
o
m.p.: 131 – 132 C) in 85 % yield (0.80 g). 1H NMR (400 MHz, DMSO-d6), δ (ppm): 9.06 (s, 2H, OH),
8.34 (s, 1H, Ar), 8.23 (d, J = 6.8 Hz, 1H, Ar), 7.79 (d, J = 8.6 Hz, 1H, Ar), 7.63 (d, J = 8.0 Hz, 1H, Ar),
7.56 (dd, J = 8.6, 2.1 Hz, 1H, Ar), 7.51 (t, J = 7.1 Hz, 1H, Ar), 7.44 (d, J = 2.4 Hz, 2H, Ar), 7.21 (t, J =
7.7 Hz, 1H, Ar), 7.14 (d, J = 8.8 Hz, 2H, Ar), 6.89 (dd, J = 8.7, 2.4 Hz, 2H, Ar), 4.47 (t, J = 7.1 Hz, 2H,
13
NCH2), 1.77 – 1.65 (m, 3H, CH2, CH), 1.01 (d, J = 6.1 Hz, 6H, CH3). C NMR (100 MHz, DMSO) δ
(ppm): 151.3, 140.9, 138.9, 136.4, 129.5, 126.8, 125.1, 123.5, 123.4, 122.3, 121.5, 119.4, 119.3, 115.7,
110.7, 110.5, 109.8, 105.5, 41.4 (NCH2), 37.7 (CH), 26.0 (CH2), 23.0 (2C, CH3). MS (APCl+, 20 V), m/z
(%) = 435 ([M + H]+, 100). Elemental analysis. Calcd for C29H26N2O2 (%): C 80.16, H 6.03, N 6.45, O
7.36; found (%): C 80.22, H 6.08, N 6.48.

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3-(3,6-Di((2,3-epoxypropyl)oxy)carbazol-9-yl)-9-isopentylcarbazole (7a)
Compound
6
(0.5 g, 11.5 mmol), 3-chloro-1,2-epoxypropane (8.5 g, 92 mmol) and
benzyltrimethylammonium chloride (BTMA, 0.1 g, 0.58 mmol) were placed in a 250 ml round-bottomed
flask. The mixture was heated at reflux for one hour. The excess of 3-chloro-1,2-epoxypropane was
removed at reduced pressure, and the resin obtained was dissolved in DCM, washed several times with
water and dried over magnesium sulfate. The solvent was evaporated and the residue was purified by
column chromatography on silica gel using hexane/ethyl acetate (4/1) as an eluent. The target compound
was obtained as yellowish powder (fw=546 g/mol) in 74 % yield (0.47 g). 1H NMR (400 MHz, CDCl3), δ
(ppm): 8.19 (s, 1H, Ar), 8.06 (d, J = 7.7 Hz, 1H, Ar), 7.61 (d, J = 2.5 Hz, 2H, Ar), 7.57 – 7.42 (m, 4H,
Ar), 7.33 – 7.21 (m, 3H, Ar), 7.07 (dd, J = 8.9, 2.5 Hz, 2H, Ar), 4.40 (t, J = 7.5 Hz, 2H, NCH2), 4.36 (dd,
one of CH2O protons in oxirane ring (HA’), JA’M’ = 3.2, JA’X’ = 11.0 Hz, 2H), 4.11 (dd, one of another
CH2O protons in oxirane ring (HM’), JM’A=5.6, JM’X = 11.0 Hz, 2H), 3.47 – 3.42 (m, 2H, CHO), 2.95 (dd,
another CH2O protons in oxirane ring (HM), JMA=4.8, JMX = 9.2 Hz, 2H), 2.83 (dd, one of another CH2O
protons in oxirane ring (HA), JAX =2.7, JAM = 5.0 Hz, 2H), 1.89 – 1.72 (m, 3H, CH2, CH), 1.07 (d, J = 6.3
13
Hz, 6H, CH3). C NMR (100 MHz, CDCl3) δ (ppm): 152.7, 140.9, 139.3, 137.9, 129.0, 126.3, 125.0,
123.7, 123.1, 122.5, 120.7, 119.3, 119.2, 115.9, 110.8, 109.5, 108.9, 104.5, 70.1 (2C, OCH2), 50.5 (2C,
OCH), 44.9 (2C, OCH2 in oxirane ring), 41.6 (NCH2), 37.6 (CH), 26.2 (CH2), 22.7 (2C, CH3). MS
(APCl+, 20 V), m/z (%) = 547 ([M + H]+, 100). Elemental analysis. Calcd for C35H34N2O4 (%): C 76.90,
H 6.37, N 5.12, O 11.71; found (%): C 79.96, H 6.40, N 5.15. IR (KBr), , (cm-1): 3061, 3014 (C-H, Ar);
2960, 2923, 2875 (C-H, Alif); 1603, 1577, 1494, 1485 (C=C, Ar); 1327 (C-N); 915, 845 (C-O-C); 749
(C-H, Ar).
3-(3,6-Di(3-methyloxetane-3-yl-methoxy)carbazol-9-yl)-9-isopentylcarbazole (7b)
Compound 6 (0.2 g, 0.46 mmol) was dissolved in ethylmethylketone (5 ml) and 3-bromomethyl-3-
methyloxetane (0.46 g, 2.8 mmol) was added dropwise. After adding NaH (0.06 g, 2.8 mmol) the reaction
o
was carried out at 60 C for three hours. The excess of 3-bromomethyl-3-methyloxetane was removed at
the reduced pressure and the obtained resin was dissolved in ethyl acetate, washed several times with
water and dried over magnesium sulfate. The solvent was evaporated under vacuum and the crude
product was purified by column chromatography on silica gel using hexane/ethyl acetate (1/8) as an
eluent. The target compound was obtained as yellowish crystals (fw=602 g/mol, m.p.: 160 – 161 oC) in 64
1
% yield (0.18 g). H NMR (400 MHz, CDCl3), δ (ppm): 8.20 (s, 1H, Ar), 8.06 (d, J = 7.7 Hz, 1H, Ar),
7.65 (d, J = 2.4 Hz, 2H, Ar), 7.58 – 7.43 (m, 4H, Ar), 7.34 – 7.20 (m, 3H, Ar), 7.07 (dd, J = 8.8, 2.5 Hz,
2H, Ar), 4.73 (d, J = 5.9 Hz, 4H, CH2O in oxetane ring), 4.51 (d, J = 5.9 Hz, 4H, CH2O in oxetane ring),

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4.39 (t, J = 7.6 Hz, 2H, N-CH2), 4.18 (s, 4H, CH2O), 1.88 – 1.72 (m, 3H, CH, CH2), 1.51 (s, 6H, CH3),
1.07 (d, J = 6.0 Hz, 6H). 13C NMR (101 MHz, CDCl3), δ (ppm): 153.3, 140.9, 139.3, 137.8, 129.1, 126.4,
125.0, 123.8, 123.1, 122.5, 120.7, 119.3, 119.2, 115.7, 110.8, 109.5, 108.9, 104.1, 80.0 (4C, OCH2 in
oxetane ring), 74.1 (2C, OCH2), 41.6 (NCH2), 39.9 (2C, CH in oxetane ring), 37.6 (CH), 26.2 (CH2), 22.7
(2C, CH3), 21.5 (2C, CH3). MS (APCl+, 20 V), m/z (%) = 603 ([M + H]+, 100). Elemental analysis. Calcd
for C39H42N2O4 (%): C 77.71, H 7.02, N 4.65, O 10.62; found (%): C 77.76, H 7.05, N 4.67. IR (KBr), ,
(cm-1): 3056, 3031 (C-H, Ar); 2957, 2950, 2872 (C-H, Alif); 1606, 1575, 1494, 1471 (C=C, Ar); 1325 (C-
N); 981, 935, 841 (C-O-C); 746 (C-H, Ar).
3-(3,6-Di(2-(vinyloxy)ethoxy)carbazol-9-yl)-9-isopentylcarbazole (7c)
Compound 6 (0.16 g, 0.37 mmol), 2-chloroethylvinylether (0.16 g, 1.5 mmol) and tetrabutylammonium
hydrogen sulfate (TBAHS, 0.006 g, 0.02 mmol) were dissolved in acetone (15 ml). The mixture was
heated to reflux and potassium hydroxide (0.12 g 2.2 mmol) as well as sodium sulfate (0.1 g, 0.72 mmol)
were added. After refluxing for 2 hours, acetone was removed and the reaction product was dissolved in
ethyl acetate and washed with water. The crude product was purified by column chromatography on silica
gel using hexane/ethyl acetate (1/8) as an eluent. The target compound was obtained as white crystals
(fw=574 g/mol, m.p.: 103 – 104 oC) in 52 % yield (0.11 g). 1H NMR (400 MHz, CDCl3), δ (ppm): 8.19 (s,
1H, Ar), 8.06 (d, J = 7.6 Hz, 1H, Ar), 7.62 (d, J = 2.4 Hz, 2H, Ar), 7.55 – 7.45 (m, 4H, Ar), 7.32 – 7.23
(m, 3H, Ar), 7.07 (dd, J = 8.9, 2.5 Hz, 2H, Ar), 6.60 (dd, J = 14.4, 6.8 Hz, 2H, OCH), 4.43 – 4.34 (m, 6H,
NCH2, OCH2), 4.29 (dd, J = 14.4, 2.2 Hz, 2H, CH=CH2), 4.15 – 4.07 (m, 6H, CH=CH2, OCH2 ), 1.87 –
13
1.71 (m, 3H, CH, CH2), 1.07 (d, J = 6.3 Hz, 6H, CH3). C NMR (100 MHz, CDCl3), δ (ppm): 152.7,
140.9, 139.2, 137.8, 129.1, 126.3, 125.0, 123.7, 123.1, 122.5, 120.7, 119.3, 119.2, 115.9, 110.8, 109.4,
108.9, 104.5, 86.9 (2C, CH=), 67.7 (4C, OCH2), 66.6 (2C, CH2=), 41.6 (NCH2), 37.6 (CH), 26.2 (CH2),
22.6 (2C, CH3). MS (APCl+, 20 V), m/z (%) = 575 ([M + H]+, 100). Elemental analysis. Calcd for
C37H38N2O4 (%): C 77.33, H 6.66, N 4.87, O 11.14; found (%): C 77.39, H 6.69, N 4.90. IR (KBr), ,
(cm-1): 3058 (C-H, Ar); 2956, 2945, 2875 (C-H, Alif); 1606, 1573, 1490, 1463 (C=C, Ar); 1323 (C-N);
1151 (C-O-C), 1107, 962, 846 (CH=CH2); 748 (C-H, Ar).
General procedure of photocross-linking of monomers 7a–c
Silicon glass slides were used as the substrates. The slides were carefully cleaned and dried before use.
Solutions of the monomers 7a–c in 1,2-dichloroethane (10 %) were prepared, and 3 mol% of
diphenyliodonium hexafluorphosphate was added shortly before drop-casting. After drop-casting the
samples were dried and then irradiated by UV lamp for 1 hour.

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Polymer P1 was obtained from monomer 7a after photorosslinking. IR (KBr), , (cm-1): 3061, 3014 (C-H,
Ar); 2960, 2923, 2875 (C-H, Alif); 1603, 1577, 1494, 1485 (C=C, Ar); 1327 (C-N); 1106 (C-O-C); 749 (
C-H, Ar).
P2 was obtained from monomer 7b after photorosslinking. IR (KBr), , (cm-1): 3056, 3031 (C-H, Ar);
2957, 2950, 2872 (C-H, Alif); 1606, 1575, 1494, 1471 (C=C, Ar); 1325 (C-N); 1047 (C-O-C); 746 (C-H,
Ar).
P3 was obtained from monomer 7c after photorosslinking. IR (KBr), , (cm-1): 3058 (C-H, Ar); 2956,
2945, 2875 (C-H, Alif); 1606, 1573, 1490, 1463 (C=C, Ar); 1323 (C-N); 1151 (C-O-C); 748 (C-H, Ar).
3. Results and discussions
3.1. Synthesis
The cross-linkable monomers were synthesized by multi-step synthetic route as shown in Scheme 1. The
first step was Tucker iodination of 9H-carbazole using KI and KIO3. 3-Iodo-(9-isopentyl)carbazole (2)
was obtained by alkylation of 3-iodocarbazole (1) with 1-bromo-3-methylbutane (BrMeBu). Ullman
coupling reaction of iodocarbazole 2 with an excess of 3,6-dimethoxycarbazole (4) led to 3-(3,6-
dimethoxycarbazol-9-yl)-9-isopentylcarbazole (5). Compound 4 was synthesized by bromination of 9H-
carbazole with N-bromosuccinimide (NBS) in chloroform, followed by the direct methoxide
displacement of bromine in 3,6-dibromo-9H-carbazole (3). Demethylation of methoxy groups of
o
compound 5 using boron tribromide at -80 C, gave compound 6 which was used for the synthesis of
monomers 7a–c.
Compound 7a was obtained by the reaction of compound 6 with 3-chloro-1,2-epoxypropane using
BTMA, whereas by interaction of 6 with 3-bromomethyl-3-methyloxetane or 2-chloroethylvinylether in
the basic conditions gave 7b and 7c, respectively.
Scheme 1.
The structures of synthesized compounds were confirmed by 1H and 13C NMR, mass spectrometries, and
elemental analysis. The cross-linkable compounds 7a, 7b, and 7c were used for the preparation of the
cross-linked materials P1, P2, and P3 (Scheme 2).
Scheme 2.

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The kinetics of consumption of reactive functional groups of 7a–c were monitored by real-time FT-IR
spectrometry. The samples were simultaneously exposed to UV irradiation beam and to the analyzing IR
beam, which monitored the resulting drop of absorbance. The degree of conversion were calculated from
the decrease of IR absorption bands of reactive functional groups according to equation:
Degree of conversion (%) = ((A0 – At)/A0)×100;
where A0 and At are optical density of absorption bands before and after UV irradiation for a certain
period of time.
The IR absorption bands at 845 cm-1, 981 cm-1, 962 cm-1 were used to estimate the degree of conversion
of epoxypropyl, oxetanyl and vinyloxyethyl groups, respectively. Fig 1 shows a stacked plot of IR spectra
of the photopolymerization mixture of monomer 7a over the reaction time period of 1 hour. The decrease
of intensity of absortion bands at 845 and 910 cm-1 as function of time represents the rate of the
consumption of the epoxypropyl groups, while the increase of the optical density of absorption band
centered at 1100 cm-1 throughout the reaction period, identifies the increased number of C-O-C linkages.
The similar trends were observed for polymerization of monomers 7b and 7c, where changes in optical
density of characteristic absorbtion bands of epoxypropyl groups centered at 835, 941, 981 cm-1 and of
vinyloxyethyl moieties at 844, 962, 1103 cm-1 were monitored in IR spectra (Figure S7 and S8 in ). The
optical density of the peak of absorption band of aromatic group at ca. 1460 cm−1 was used as internal
standard for all kinetic calculations.
Fig 1.
High initial rate of cross-linking was observed during UV irradiation. After 5 min of irradiation, the
degrees of conversion of epoxypropyl, oxetanyl and vinyloxyethyl groups reached ca. 48, 51 and 39 %,
respectively. After 1 h, the highest conversion (ca. 78 %) was observed for epoxypropyl groups (Fig 2).
Fig 2.
3.2. Thermal properties
The thermal properties of the synthesized compounds were studied by DSC and TGA. The values of glass
transition temperatures (Tg), melting point (Tm), and temperatures at which 5% loss of mass (TID) were
observed are summarized in Table 1. All the synthesized compounds demonstrated relatively high
o
thermal stability. The values of TID were found to be higher than 328 C as confirmed by TGA at the
o
heating rate of 10 C/min. The increased molecular weight of polymers determined higher thermal
stability compared to that of the corresponding monomers and TID values are higher by ca 40 oC.

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Table 1
Formation of the glassy state of all synthesized compounds was confirmed by DSC analysis. The
synthesized compounds 6, 7b and 7c were obtained as crystalline materials. However, they readily
formed glasses when their melt samples were cooled down. For the illustration of above stated the DSC
o
curves of compound 6 are shown in Fig 3. The sample showed endothermic melting signal at 133 C
during the first heating cycle. It did not subsequently crystallize when cooled down, and exhibited a glass
transition temperature of 98 oC during the second heating scan.
Fig 3.
Compounds 5, 7a and polymers P1–P3 were isolated as amorphous materials. Only glass transition were
observed in their DSC scans, and no peaks due to crystallization and melting appeared. Cooling and the
following heating scans revealed only glass transition. The DSC curves of the second heating scans of
polymers P1–P3 and monomers 7a–c are presented in Fig 4.
Fig 4.
Tg values of polymers P1–P3 were found to be higher than those of the corresponding monomers. This
observation can be explained by the increased molecular size of polymers. Among the low-molecular-
weight compounds the highest Tg was observed for compound 6 containing hydroxyl groups (Tg = 98 oC),
which apparently take part in hydrogen bonding. Replacement of hydrogen atoms by the epoxypropyl,
oxethanyl or vinyloxethyl groups changes the lead to decreased packing density of the molecules. These
conformational changes and the effect of the additional aliphatic chains of the functional groups
apparently determined the lower Tg values of the monomers by 22 – 56 oC compared to that of compound
6.
3.3. Optical and photophysical properties
The synthesized low-molecular-weight compounds exhibit similar photophysical properties because of
their similar structures. UV absorption and fluorescence spectra of monomer 7a are presented in Fig 5.
The absorption spectrum covers the near-ultraviolet region (200 – 390 nm) and shows a narrow
absorption band at 311 nm corresponding to the local π–π∗ electron transition of a single carbazole moiety
[22]. The carbazole moiety also contributes to the absorption bands at longer wavelengths (354 and

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370nm); however, these bands in the UV spectra of compounds 5–7c are significantly wider and red-
shifted indicating optical transitions, which involve electron charge redistribution over the whole
molecules consisting of two carbazole moieties [23].
Dilute THF solutions of the synthesized compounds exhibited blue emission with the intensity maxima at
ca. 400 nm. The materials showed small Stokes shifts (30 nm) indicating low energy loss during the
relaxation process.
Fig 5.
The phosphorescence spectra of the monomers were recorded at 77 K by applying delay time of 100 µs
after excitation on purpose to evaluate the potential of the carbazole derivatives 5–7 and polymers P1–P3
to be exploited as the host materials in phosphorescent OLEDs. Triplet state energies (ET) estimated from
the highest-energy peak of the phosphorescence spectra were found to be 2.78 eV. This value is higher
than that of common blue phosphorescent emitter iridium(III)bis[(4,6-difluorophenyl)-pyridinato-
N,C2’]picolinate (FIrpic, ET=2.65 eV) [24] and efficient energy transfer from the host to FIrpic dopant can
be predicted, suggesting that the synthesized monomers 5–7 and polymers P1–P3 can be suitable as the
host materials for blue phosphorescent OLEDs.
3.4. Electrochemical and photoelectrical properties
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 containing
0.1 M tetrabutylamonium perchlorate (TBAP) as electrolyte, Ag/AgNO3 as the reference electrode and a
Pt wire counter electrode. The experiments were calibrated with the standard ferrocene/ferrocenium redox
system [25]. The cyclic voltammograms of all the studied compounds showed quasi-reversible oxidation
couples. The electrochemical characteristics are summarized in Table 2. The synthesized carbazole
derivatives have an open reactive C-6 position, however they exhibited stable redox properties and the
formation of radical cations in the solutions did not lead to the creation of dimeric derivatives as it was
earlier observed for 3-monosubstituted carbazole compounds [26]. This means that the substituent at the
C-3 position of carbazole moity stabilizes radical cation [27]. As an example, several cyclic
voltammogram scans of compound 5 are presented in Fig 6.
Fig 6.
The ionization potentials (Ip(CV)) of the synthesized monomers were found to be in the short range of 5.11
– 5.30 eV. The lowest value of Ip(CV) was showed by compound 5 containing methoxy groups. With the

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band gap (E ogpt ) values obtained from the absorption spectra, the electron affinity (EA(CV)) values of 5–7
were calculated which range from 1,95 to 2,14 eV (Table 2).
The ionization potentials (Ip(EP)) of the solid layers of the monomers were estimated by the electron
photoemission in air method. Compound 6 containing hydroxyl groups showed the highest ionization
potential value of 5.37 eV. The ionization potential values of the other compounds (5 and 7a–c) were
found to be comparable i.e. 5.20 – 5.29 eV (Table 2).
Table 2
The time-of-flight technique was used to characterize hole drift mobility in the amorphous films of 5, 6
and 7a–c. Compound 5 having methoxy groups exhibited slightly better charge-transporting properties.
Hole drift mobility in solid film of 5 reached 1.3 × 10-5 cm2/V, while films of other compounds
demonstrated hole drift mobility in the range of 1.2 × 10-6 – 4.8 × 10-6 cm2/V·s at electric field E = 3.6 ×
105 V/cm (Table 2). The hole drift mobilities of the studied compounds show linear dependencies on the
square root of the electric field (E1/2) with the good agreement to Poole–Frenkel relationship
µ=µ0×exp(α×E1/2) (Figure 6) [28]. The values of the zero electric field charge mobility (µ0) and the field
dependence parameter (α) are given in Table S1 showing strong dependencies of µ on electric field.
Compound 6 containing hydroxyl groups showed the lowest hole drift mobility, while the cross-linkable
compounds 7a, 7b, and 7c presented slightly higher mobilities (Figure 7). Distinctive plateau in the TOF
transients is not clearly seen showing that hole transports of the compounds are dispersive (Figures S9-
S13).
Fig 7.
4. Conclusions
New glass-forming carbazole dimers with reactive functional groups were synthesized. Their cationic
photocross-linking was monitored by FT-IR spectrometry. The highest degree of conversion of reactive
functional groups was observed for the monomer containing epoxypropyl groups. The molecular structure
of the synthesized compounds allows them to exist in solid amorphous state. Their glass transition
temperatures depend on the nature of the functional group. The highest glass transition temperature was
o
observed for the compound containing hydroxyl groups (98 C). Polymers exhibited considerably higher
o
glass transition temperatures than monomers (89–150 C). Dilute THF solutions of the synthesized
compounds exhibited blue emission with the intensity maxima at ca. 400 nm. The electron photoemission

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spectra of the solid layers of the monomers revealed ionization potentials of 5.54–5.61 eV. Hole drift
mobility of the materials reached 1.3×10-5 cm2/V·s at electric field of 3.6 × 105 V/cm, as established by
time-of-flight technique.
Aknowledgement
This research was funded by a grant No. TAP LB-03/2015 from the Research Council of Lithuania.

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Figure captions
Scheme 1. Synthesis of monomers 7a-c.
Scheme 2. Photocross-linking of monomers.
Fig 1. Progress of photopolymerization of 7a and the spectral changes in the range 800-1600 cm-1 of the
reaction mixture monitored by FT-IR.
Fig 2. Conversion of reactive functional groups versus time curves for photopolymerization of monomers
7a–c initiated with DFIF. [DFIF] = 3 mol% of monomer.
Fig 3. DSC curves of 6 (scan rate 10 oC/min, N2 atmosphere).
Fig 4. DSC curves of [A] monomers 7a–c and [B] polymers P1–P3 (scan rate 10 oC/min, N2 atmosphere).
Fig 5. UV absorption and PL (ex = 310 nm) spectra of dilute solution of compound 7a (10-4 mol L-1) in
THF.
Fig 6. Cyclic voltammogram of 5 in argon-purged DCM solution (scan rate of 50 mV s-1).
Fig 7. Hole drift mobilities as a function of E1/2 for the layers of 5, 6 and 7a–c.

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Scheme 1. Synthesis of monomers 7a-c.

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Scheme 2. Photocross-linking of monomers.

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110
0 min
100
90
80
70
60
50
40
30
20
10
0
45 min
800
900
1000
1100
1200
1300
1400
1500
160
-1
Wavenumber, cm
Fig 1. The spectral changes in the range of 800-1600 cm-1 of the photopolymerization mixture of 7a
monitored after the different periods of time (from 0 to 45 min) of irradiation by FT-IR.

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80
70
60
P1
P2
P3
50
40
30
20
10
0
0
500 1000 1500 2000 2500 3000 3500 4000 4500
Time, s
Fig 2. Conversion of reactive functional groups versus time curves for photopolymerization of monomers

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Tg = 98 o
C
Tm = 133 o
C
-20
0
20
40
60
80
100 120
140
160
Temperature (oC)
Fig 3. DSC curves of 6 (scan rate 10 oC/min, N2 atmosphere).

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[A]
[B]
P1
P2
P3
7a
7b
7c
Tg= 150 oC
Tg=49 o
C
Tg= 97 oC
Tg=56 o
C
Tg= 89 oC
Tg=22 o
C
0
20
40
60
80
100
120
50
100
150
200
Temperature, oC
Temperature, oC
Fig 4. DSC curves of [A] monomers 7a–c and [B] polymers P1–P3 (scan rate 10 oC/min, N2 atmosphere).

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120000
100000
80000
60000
40000
20000
0
250
300
350
400
450
500
Wavelenghtnm)
Fig 5. UV absorption and PL (ex = 310 nm) spectra of dilute solution of compound 7a (10-4 mol L-1) in
THF.

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1,5
1,0
0,5
0,0
-0,5
-1,0
0,40
0,45
0,50
0,55
0,60
0,65
0,70
0,75
Voltage, V
Fig 6. Cyclic voltammogram of 5 in argon-purged DCM solution (scan rate of 50 mV s-1).

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10-3
6
5
10-4
7a
7b
7c
10-5
10-6
10-7
10-8
0
200
400
600
800
1000
E1/2 (V1/2/cm1/2
)
Fig 7. Hole drift mobilities as a function of E1/2 for the layers of 5, 6 and 7a–c.

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Table 1. Thermal characteristics of compounds 5-7c and polymers P1-P3.
Compound
Tm, oC
5
-
24
335
6
133
98
7a
-
49
328
7b
161
56
7c
103
22
P1
-
150
375
P2
-
97
382
P3
-
89
379
Tg, oC
TID, oC
360
337
355

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Table 2. Electrochemical and photoelectrical characteristics of 5, 6 and 7a–c.
a
b
c
d
Egopt
Compound
E1/2
Ip(CV)
EA(CV)
Ip(EP)
(eV)
3.16
3.14
3.16
3.15
3.16
(V)
(eV)
5.11
5.26
5.24
5.21
5.30
(eV)
1.95
2.12
2.08
2.06
2.14
(eV)
5.28
5.37
5.28
5.29
5.20
(cm2/V·s)
1.3·10-5
1.2·10-6
2.4·10-6
4.8·10-6
4.7·10-6
0.31
0.46
0.44
0.41
0.50
5
6
7a
7b
7c
a
b
Ionization potentials Ip(CV) and electron affinities EA(CV) were estimated by cyclic voltamperometry according to
opt
g
c
Ip(CV) = 4.8 + E1/2 and EA(CV) = ˗(Ip(CV) ˗ E
). Ionization potentials Ip(EP) were measured by electron photoemission
spectrometry in air. d Hole mobility value at electric field E = 3.6 × 105 V/cm.