Synthesis of Linear and V-Shaped Carbazolyl-Substituted Pyridine-3,5-dicarbonitriles Exhibiting Efficient Bipolar Charge Transport and E-Type Fluorescence

Article abstract of DOI:10.1002/chem.201805323

With the aim of developing all-organic bipolar semiconductors with high charge mobility and efficient E-type fluorescence (so-called TADF) as environmentally friendly light-emitting materials for optoelectronic applications, four noble metals-free dyes with linear and V-shapes were designed using accepting pyridine-3,5-dicarbonitrile and donating carbazole units. By exploiting a donor-acceptor design strategy and using moieties with different donating and accepting abilities, TADF emitters with a wide variety of molecular weights were synthesized to achieve the optimum combination of charge-transporting and fluorescent properties in one TADF molecule. Depending on molecule structures, different TADF emitters capable of emitting in the range from 453 to 550 nm with photoluminescence quantum yields up to 98 % for the solutions in oxygen-free toluene were obtained. All compounds showed bipolar charge-transport. Hole mobility of 2.8×10^?3 cm²/Vs at 7×10⁵ V cm^?1 was observed for the compound containing two di-tert-butyl-substituted carbazole moieties. The compounds were tested in both non-doped and doped organic light-emitting diodes using different hosts. It was shown that the developed TADF emitters are suitable for different color devices with electroluminescence ranging from blue to yellow and with brightness, maximum current and external quantum efficiencies exceeding 10 000 cd m^?2, 15 cd/A, and 7 %, respectively.

Full text of DOI:10.1002/chem.201805323

A Journal of
Accepted Article
Title: Synthesis of linear and V-shaped carbazolyl-substituted
pyridine-3,5-dicarbonitriles exhibiting efficient bipolar charge
transport and E-type fluorescence
Authors: Brigita Vigante, Karolis Leitonas, Dmytro Volyniuk, Viktorija
Andruleviciene, Jurate Simokaitiene, Anna Ivanova, Audrius
Bucinskas, Juozas Vidas Grazulevicius, and Pavel Arsenyan
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using the Digital Object Identifier (DOI) given below. The VoR will be
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the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Chem. Eur. J. 10.1002/chem.201805323
Link to VoR: http://dx.doi.org/10.1002/chem.201805323
Supported by

Chemistry - A European Journal
10.1002/chem.201805323
FULL PAPER
Synthesis of linear and V-shaped carbazolyl-substituted pyridine-
,5-dicarbonitriles exhibiting efficient bipolar charge transport
and E-type fluorescence
3
[
a]
[b]
[b]
[b]
Brigita Vigante , Karolis Leitonas , Dmytro Volyniuk , Viktorija Andruleviciene , Jurate
[
b]
[a]
[b]
[b]
[a]
Simokaitiene , Anna Ivanova , Audrius Bucinskas , Juozas Vidas Grazulevicius* , Pavel Arsenyan
[
a]
Latvian Institute of Organic Synthesis, Aizkraukles 21, LV-1006, Riga, Latvia; e-mail: pavel@osi.lv
[
b]
Kaunas University of Technology, Department of Polymer Chemistry and Technology, Radvilenu pl. 19, LT-50254, Kaunas,
Lithuania; e-mail: juozas.grazulevicius@ktu.lt
Aiming to develop all-organic bipolar semiconductors with high
charge mobility and efficient E-type fluorescence (so-called TADF)
as environmentally-friendly light-emitting materials for optoelectronic
applications, four noble metals-free dyes with linear and V-shapes
were designed using accepting pyridine-3,5-dicarbonitrile and
donating carbazole units. Exploiting donor-acceptor design strategy
and using moieties with different donating and accepting abilities,
TADF emitters with wide variety of molecular weights were
synthesized for getting optimum combination of charge-transporting
and fluorescent properties in one TADF molecule. Depending on
molecule structures, different TADF emitters capable of emitting in
the range from 453 to 550 nm with photoluminescence quantum
yields up to 98% for the solutions in oxygen-free toluene were
obtained. All compounds showed bipolar charge-transport. Hole
which are always generated in electroluminescent devices under
electrical excitation [7]. As a result, TADF emitters can be as
efficient as phosphorescent emitters allowing to achieve 100 %
IQE of OLEDs [8]. Many TADF dyes showed high
photoluminescence quantum yields (PLQY), small singlet-triplet
energy splitting (ΔEST), emission ranging from deep-blue to infra-
red due to which they were utilized in all-colour OLEDs [9–11].
Among them, highly polar donor-acceptor type materials
containing electron-donating carbazole and strongly electron-
withdrawing carbonitrile moieties were demonstrated as highly
efficient TADF materials for various OLED applications [12, 13]
.
Since not only good exciton generation probability and high
PLQY but also good charge recombination probability are
required for light-emitting layers of OLEDs (all should be close to
unity for achieving the highest efficiency) [14], TADF emitters
-
3
2
5
mobility of 2.8×10 cm /Vs at 7×10 V/cm was observed for the
compound containing two di-tert-butyl-substituted carbazole moieties. have also to exhibit appropriate charge-transporting properties.
The compounds were tested in both non-doped and doped organic
light-emitting diodes using different hosts. It was shown that the
developed TADF emitters are suitable for different colour devices
with electroluminescence ranging from blue to yellow and with
brightness, maximum current and external quantum efficiencies
However, because of twisted donor-acceptor structures of
practically all TADF emitters, their charge mobilities are usually
low in comparison to those of other functional materials or
fluorescent emitters used in OLEDs [15]
.
In this work, aiming to develop TADF emitters with high charge
mobility, pyridine-3,5-dicarbonitrile and carbazole derivatives
were designed basing on theoretical study performed before
2
exceeding 10000 cd/m , 15 cd/A, and 7%.
their synthesis. Next, synthesis of
carbazolylphenyl-substituted, symmetrical and unsymmetrical
,5-dicyanopyridines is developed. It was found that carbazolyl
a
series of 4-
Introduction
3
groups in positions 2 and 6 are sensitive in basic media allowing
to obtain unsymmetrical 2,6-dicarbazolyl pyridines from
symmetrical ones in two steps. Finally, four linear or V-shaped
compounds were synthesized and their photophysical, thermal,
electrochemical electrooptical and charge transporting
properties were investigated. TADF origin of emission was
confirmed by steady-state and time-resolved luminescent
spectroscopy measurements at different temperatures. The
compounds were tested both in non-doped and doped OLEDs
Light-emitting devices are among the most required and used
devices in human society [1] . Recently, organic light emitting
diodes (OLEDs) entered to the global display and lighting
markets mainly due to the competitiveness with respect of
characteristics and because of environmental reasons 2].
Despite the successful usage in highly efficient OLEDs of heavy-
metal-based emitters exhibiting phosphorescence which allowed
to achieve 100 % maximum internal quantum efficiency (IQE) [3,4]
high cost and harmfulness of noble metals based emitters limit
their applications in commercial OLEDs. On the other hand,
inexpensive and environmentally friendly emitters are vital for
OLED technologies. From this point of view, all-organic dyes
exhibiting E-type fluorescence (so-called thermally activated
delayed fluorescence (TADF)) are nowadays established as the
most attractive candidates for these technologies [5, 6]. Similarly,
to phosphorescent emitters, noble-metal-free TADF emitters can
produce light by harvesting both singlet and triplet excitons
[
,
Results and Discussion
Molecular design and synthesis
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Chemistry - A European Journal
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FULL PAPER
The target 2,6-dimethyl-pyridine-3,5-dicarbonitriles
5
and
6
According to the previously reported [19] procedure, 2,6-bis-(3,6-
di-tert-butylcarbazol-9-yl)-4-(4-fluorophenyl)-pyridine-3,5-
carbonitrile 9 was obtained by the treatment of 3,6-di-tert-butyl-
bearing carbazole and 3,6-bis-tert-butylcarbazole substituents at
the para positon of 4-phenyl group were obtained by oxidation of
appropriate 1,4-dihydropyridine derivatives
0
3
and
4
using
9H-carbazole sodium salt with 8 in THF solution at 0 to rt for 1 h.
sodium nitrite in glacial acetic acid. Whereas, 1,4-
dihydropyridine-3,5-carbonitriles 3 and 4 were synthesized by
cyclocondensation of 3-amino-butenenitrile with 4-(9H-
Surprisingly, the continuation of stirring of above mentioned
reaction mixture was extended to 24 h, 2-(3,6-di-tert-butyl-9H-
carbazol-9-yl)-4-(4-fluorophenyl)-6-hydroxy-pyridine-3,5-
dicarbonitrile (10) was obtained instead of 9 in 77% yield. In
other words, basic media promotes the cleavage of one of
carbazole moieties yielding 9. Further target 2,6-unsymmetrical
substituted pyridine 12 was obtained by routine procedure via
bromination of 10 following by the treatment of 11 with 3,6-
dicyanocarbazole [ in the presence of sodium hydride. Thus,
elaborated pathway (Scheme 2) allowed to obtain a new
pyridine-3,5-carbonitriles with different carbazole substituents at
the positions 2-and 6.
carbazole-9-yl) benzaldehyde
carbazole-9-yl)benzaldehyde 2 by analogy with the synthesis of
,4-dihydropyridine-3,5-carbonitriles reported previously [16]. It
1
or 4-(3,6-di-tert-butyl-9H-
1
should be noted that carbazolyl derivative 3 showed low
solubility in organic solvents, except of hot DMSO, however, the
introduction of two tert-butyl groups in positions C-3 and C-6 of
carbazole moiety led to considerable increase in solubility.
20]
X-ray analysis
The structure of compound 12 was additionally proved using X-
ray analysis. The ortep projection and crystal packing of 12 is
shown in Figure 1 and crystallographic data are listed in the
Table S1. From diluted solution (DCM/hexane) compound 12
formed yellow single crystals adopting monoclinic crystal system
Scheme 1. Preparation of linear 4-[4-(9H-carbazol-9-yl)phenyl]-2,6-
dimethylpyridine-3,5-dicarbonitrile 5 and 4-[4-(3,6-di-tert-butyl-9H-carbazol-9-
(
P21/n space group). As shown in Fig. 1a, 12 possess relatively
yl)phenyl]-2,6-dimethylpyridine-3,5-dicarbonitrile 6. Reaction conditions: (a)
o
carbazole or 3,6-di(tert-butyl)carbazole, K
amino-butenenitrile, AcOH, reflux, 15h; (c) NaNO
2
CO
3
, DMF, 160 C, 24h; (b) 3-
large dihedral angles (76° and 65°) between electron accepting
part ring and electron donating carbazolyl moieties proving
highly twisted molecular configuration required for TADF [21, 22].
Due to intermolecular forces in the crystal dihedral angles are a
little higher than calculated ones (53° and 45°) (Figure 1b).
o
2
, AcOH, 60 C, 10 min.
In continuation of or studies we moved to the elaboration of the
procedure for the preparation of 2,6-bis(3,6-di-tert-butyl-9H-
carbazol-9-yl)-4-(4-fluorophenyl)pyridine-3,5-carbonitrile
9.
Piperidinium 3,5-dicyano-6-hydroxy-4-(4-fluorophenyl)pyridin-2-
olate 7 was chosen as the starting material (Scheme 2). It was
prepared by cyclocondensation of 4-fluorobenzaldehyde with
cyanoacetamide in the presence of piperidine, modifying the
procedure described in literature [17]. The conversion of 7 into the
corresponding
2,6-dibromo-4-(4-fluorophenyl)pyridine-3,5-
carbonitrile (8) was carried out by the treatment with
phosphorous oxybromide in good yield by heating of 7 without
solvent at 170 C for 1h by analogue Di Rienzo procedure [18]
0
.
Figure 1. (a) X-ray structure of compound 12 and (b) the corresponding
optimized geometry obtained at the B3LYP/6-31G(d,p) level (in the absence of
medium effect). (c) Packing in the crystal structure of compound 12 viewed
along the a-axis (CCDC 1871379).
Scheme 2. Synthesis of V-shaped 2,6-bis-(3,6-di-tert-butylcarbazol-9-yl)-4-(4-
fluorophenyl)-pyridine-3,5-carbonitrile and 9-[3,5-Dicyano-6-(3,6-di-tert-
9
butylcarbazol-9-yl)-4-(4-fluorophenyl)-pyridin-2-yl]-9H-carbazole-3,6-
dicarbonitrile 12. Reaction conditions: (a) 3-amino-butenenitrile, methanol,
Photophysical properties
o
o
3
piperidine; (b) POBr , 170 C, 1h; (c) NaH, THF, 0 C to rt, 1h; (d) NaH, THF, rt,
o
o
2
3
4h; (e) POBr , 170 C, 3h; (f) 3,6-dicyanocarbazole, NaH, THF, 0 C to rt, 1h.
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Chemistry - A European Journal
10.1002/chem.201805323
FULL PAPER
Absorption spectra of the dilute toluene solutions (10-5 M) and
solid films of compounds 5, 6, 7 and 12 are shown in Figure 2a
and the wavelengths of maxima of the low-energy absorption
bands are collected in Table 1. The theoretical absorption
spectra (Figure S2) confirmed that low-energy absorption bands
mainly could be attributed to the intramolecular charge transfer
that of compound 5. This observation could be due to the band
gaps, i.e., the difference between ionization potential (IPCV) and
electron affinity (EACV), of the investigated compounds. The
band gaps decrease in the order 5 > 6 > 9 > 12 (2.97 eV > 2.92
eV > 2.85 eV > 2.71 eV). The slight differences between the
wavelengths of low-energy bands of the solutions in toluene and
of solid samples can be apparently explained by aggregation
effects in solid-state.
(
ICT) associated with electron transfer from carbazole to
pyridine-3,5-dicarbonitrile moiety. The low-energy absorption
bands of compounds 6, 9 and 12 are red shifted with respect to
Figure 2. Absorption spectra (top) of the dilute toluene solutions (10-5 M) and non-doped films and PL spectra (bottom) of the dilute toluene solutions (10-5 M),
non-doped films and doped films using the mCP host for compounds 5, 6, 9 and 12.
Emission spectra of the films of molecular mixtures 9:mCP and
Table 1. Photophysical data for the studied compounds.
12:mCP films were found to be blue-shifted even with respect to
Absorptio
n,
those of dilute toluene solutions. Previously observed unusual
blue-shift of emission spectra for TADF compounds in solid-state
were assigned to the intramolecular structural differences of
molecules in different media [24]. A further study shows that such
intramolecular structural differences were affected by aggregate-
PL,
nm
PLQY,
%
S
1
,
T
1
,
ΔES1T1,
Compo
und
eV
eV
eV
nm
a
b
THF/Hosted filmb
Toluene /Film/Hosted film
3
60/355/
75/372/
90/392/
00/403/
450/46
9/450
98/35
/31
3.145/
3.146
3.031/
3.005
2.883/
2.695
2.771/
2.625
2.767/
2.979
2.824/
3.014
2.735/
2.655
2.683/
2.635
0.378/
0.161
0.207/
0.009
0.148/
0.04
5
6
9
[23]
formation in host:guest systems . Apparently, in comparison to
PL spectra of non-doped films, the blue-shift of spectra of
-
3
-
475/49
1/475
93/18
/22
5:mCP, 6:mCP, 9:mCP and 12:mCP films are caused by both
solvatochromic-like and aggregation effects due to the specific
host-guest interactions.
Since compounds compounds 5, 6, 9 and 12 were designed as
3
-
518/52
8/500
27/36
/41
4
-
555/54
9/512
18/19
/36
0.088/
0.017
12
TADF emitters, their singlet and triplet energy splittings (ΔEST
were measured. The ΔEST values of 0.378, 0.207, 0.148 and
.088 eV for 5, 6, 9 and 12 were obtained from onsets of
)
[
a] Deoxygenated toluene. [b] mCP host was used.
0
fluorescence and phosphorescence spectra of the solutions in
THF at 77K, respectively (Figure 3a, Table 2). Time-dependent
density functional theory (TD-DFT) calculations for the
compounds at singlet and triplet excited states were performed
to study the overlap of frontier orbitals.[25] Figure 4 shows
theoretical results of the 5, 6, 9 and 12 which demonstrate
HOMO (HONTO) and LUMO (LUNTO) distribution. The smaller
overlap of the orbitals of compounds 9 and 12 compared to
those of 5 and 6 leads to the lower ΔEST. Additionally, ΔEST
values of the films of molecular mixtures 5:mCP, 6:mCP, 9:mCP
and 12:mCP were estimated and the values of 0.161, 0.009,
PL spectra of the solutions of compounds 5, 6, 9 and 12 in
toluene exhibited emission bands with the intensity maxima at
4
1
50, 475, 518 and 555 nm, respectively (Figure 2 bottom, Table
). Photoexcitation is followed by intramolecular and medium
relaxations which can be characterized by Stokes shift. The
Stokes shifts of dilute solutions of compounds originating from
the ICT and π-conjugation increased in the order 5 < 6 < 9 < 12.
PL spectra of spin-coated non-doped films of the compounds
were slightly red-shifted with respect to those of dilute solutions.
This observation can apparently be explained by the polarity
effect assuming higher values of dielectric constants of solid
samples of the compounds than dielectric constant of toluene
0.04 and 0.017 eV respectively were obtained. These values are
considerably lower than those observed for THF solutions
(Figure 3b, Table 2). Aggregate-formation is apparently the
(
ε=2.38). Because of low value of dielectric constant of mCP
[
23]
host (ε=2.84)
, the blue-shifted emission spectra were
reason of smaller ΔEST values of the studied compounds doped
expected for the films of host-guest molecular mixtures 5:mCP,
:mCP, 9:mCP and 12:mCP containing 10 wt% of emitters in
comparison to the PL of non-doped films (Figure 2 bottom).
in mCP [
.
23]
6
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Chemistry - A European Journal
10.1002/chem.201805323
FULL PAPER
Figure 3. Photoluminescence and phosphorescence spectra of the solutions of compounds 5, 6, 9 and 12 in THF recorded at 77K (a) and of the film of 9:mCP (b).
Emission intensities (c) and PL decays (d) of non-degased (as prepared) and deoxygenated toluene solutions of 5, 6, 9 and 12.
PL spectra and PL decay curves for non-degased and degased
toluene solutions of the compounds are shown in Figure 3 c,d.
Similar PL spectra were observed for non-degased and degased
toluene solutions of all the studied compounds displaying that
the emission originated from the same excited singlet state. The
stronger contribution of triplet excited states to the emission of
compounds 9 and 12 was evidenced by the increased PL
intensity and appearance of long-lived PL decay components as
compared to those of compounds 5 and 6 (Figure 3c,d). This
observation can be mainly explained by the smaller ΔEST values
observed for the solutions of 9 and 12 (Table 1).
calculated (Supporting Information). Compounds 5 and 6 with
relatively large ΔEST exhibited relatively high 푘푃퐹 and very low
푘푅퐼푆퐶 resulting in high PLQYs of their deoxygenated toluene
solutions (Table S1). Compounds 9 and 12 with lower PLQYs
and smaller ΔEST exhibited relatively low 푘푃퐹 and high 푘푅퐼푆퐶
which is comparable with that of highly efficient TADF emitters
[
26]. PLQYs of their solid samples were found to be higher than
those of dilute solutions. It should be noted that PLQY values for
solid-state samples were measured in air. Emission intensity
increased in vacuum due to TADF (Figure 5b, S3).
Delayed fluorescence of the studied compounds is attributed to
the TADF. This attribution is well-supported by the enhancement
of delayed fluorescence components in PL decay curves of host-
guest molecular mixtures mCP:5, mCP:6, mCP:9 and mCP:12
with increasing temperature from 77 to 300 K (Figure 5a, S3).
Very small differences between shapes of emission spectra of
the films of mCP:5, mCP:6, mCP:9 and mCP:12 at different
temperatures indicate similarity of fluorescence and
phosphorescence spectra resulting in small ΔEST and, hence,
efficient TADF. The PLQY values of the solutions of the studied
compounds in degassed toluene, non-doped and doped films
are collected in Table 1. High PLQY values were observed for
dilute solutions of 5 and 6, while compounds 9 and 12 exhibited
aggregation induced emission enhancement. To further
investigate the relative contribution of prompt and delayed
components to the whole relaxation processes, the rate
constants of prompt fluorescence 푘푃퐹 and TADF (푘푅퐼푆퐶 ) were
Figure 4. Distribution of orbitals of compounds 5, 6, 9 and 12 at singlet and
triplet excited states. Overlapping of orbitals are marked by red circles
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Chemistry - A European Journal
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Figure 5. PL decay curves of the film of compound 9 doped with mCP. recorded at different temperatures (a) PL spectra and PL decay curves of the molecular
mixture recorded in air and vacuum at room temperature (b).
melting. Meanwhile, no crystallization and melting peaks were
Thermal characterization
observed in the second heating scan of compound 12.
Electrochemical, photoelectrical and charge-transporting
properties
DSC and TGA curves of compounds 5, 6, 9 and 12 are shown in
Figure S4. Their thermal characteristics are collected in Table 2.
The studied samples exhibited 5% mass loss temperature (Td-
5%
) falling in the range from 305 to 423 °C. The Td-5% values
increased with the increase of molecular weight of the
compounds. All the compounds showed melting signals in the
Electrochemical analysis. Cyclic voltammetry (CV) curves of
compounds 5, 6,
9 and 12 are shown in Figure 6a.
Electrochemical characteristics of the solutions of the
compounds are collected in Table 2. The ionization potential
(I
P
CV) values of compounds were estimated from the onset
first DSC heating scans. Compounds
5 and 6 exhibited
crystallization signals in the cooling scans at 306 and 193 oC
potentials of the first oxidation event after calibration of the
respectively and only melting signals in the following repeated
heating scans.
CV
measurements against ferrocene. I
P
for 5, 6, 9 and 12 were
CV
found to be 5.75, 5.65, 5.85 and 5.89 eV, respectively. I
P
for 5,
6
, 9 and 12 were found to be 5.75, 5.65, 5.85 and 5.89 eV, respectively.
Table 2. Thermal characteristics, energy levels and charge mobilities of
compounds 5, 6, 7 and 12
All the synthesized compounds exhibited oxidation peak
corresponding to the oxidation of carbazole moieties. Compound
μ
h
2
,
μ
e
2
,
CV
T
d-5%/ T
m
/
I
p
CV/I
OMO
eV
p
PE/H
E
A
CV/E
A
PE/
6 exhibited smaller I
P
value compared to that of compound 5
cm /Vs
cm /Vs
Compound
T
cr/ Tg,
C
LUMO,
due to the presence of electron-donating tert-butyl groups.
o
eV
CV
5
Comparable I
P
values of 9 and 12 reflect minor effect of cyano
at 7×10 V/cm
grpups attached to one carbazole moiety of compound 12.
Electron affinities (E
CV) of compounds were estimated from the
3
3
3
05/331/306
5.75/5.75/-
5.52
5.65/5.92/-
5.32
5.87/5.92/-
5.69
5.89/6.26/-
6.08
2.78/2.85/
-2.17
2.73/2.90/
-2.12
3.02/3.12/
-2.20
3.18/3.60/
-2.79
5
6
9
-
-
/-
A
24/353/193
onset potentials of the first reduction event after calibration of
the measurements against ferrocene. They ranged from 2.73 to
8.7×10-5
2.8×10-3
2.3×10-6
6.5×10-5
/-
78/416/274
208
23/354/-
229
1.2×10-4 3.18 eV. Reduction of 3,5-dicyanopyridine moieties in 5 and 6
/
CV
lead to the similar E
A
values of 2.78 and 2.73 eV, respectively.
4
12
8.3×10-6
/
Meanwhile, incorporation of electron withdrawing fluorine atoms
CV
Compounds 9 and 12 were obtained after purification as
crystalline substances. They could be transformed into the
glassy state and showed very high glass transition temperatures
of 208 and 229 °C respectively in the cooling and the second
heating scans. In the second DSC heating scan, compound 9
showed not only the glass transition but also crystallization and
in the structures lead to the increase of E
A
of compounds 9
CV
CV
and 12. I
P
and E
A
values (Table 2) demonstrate the similar
trend
(6 < 5 < 9 < 12), which is consistent with the trend of HOMO
and LUMO energies, respectively.
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Chemistry - A European Journal
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Figure 6. Cyclic voltammograms of the solutions of compounds 5, 6, 9 and 12 recorded at a scan rate of 50 mV/s (a) photoelectron emission spectra of vacuum-
deposited films of the compounds.
Photoelectron emission spectrometry. To characterize the
charge-injection properties of the studied compounds,
photoelectron emission measurements were performed for their
solid samples. Photoelectron emission spectra are shown in
butyl substituted carbazole units. Enhanced hole mobility of
compound 9 might be related to its HOMO which is well-
distributed within two tert-butyl substituted carbazole units thus
increasing HOMO-HOMO and keeping the same LUMO-LUMO
overlapping of the neighboring molecules of compound 9 in
comparison to those of compound 6 (Figure S2). Additionally,
Figure 6b. The values of ionization potentials (I PE
) are collected
p
in Table 2. The introduction of the strong electron-withdrawing
cyano-groups to the carbazole unit of compound 12 lead to the
hydrogen bonds formed by tert-butyl groups improve hole-
PE
[27]
increase of its I
P
value thus decreasing its hole-injection ability.
PE) of 5, 6, 9 and 12 were estimated to be
.85, 3.02, 3.12 and 3.6 eV. They were calculated as E = I
PE-E
is the optical band-gap energy, respectively. The
of 2.9, 3.02, 2.805 and 2.66 eV for 5, 6, 9 and 12
were taken from absorption spectra of their solid layers (Figure
).
transporting property of 9
. Attempting to increase electron
Electron affinities (E
A
mobility tert-butyl-substituted carbazole unit was replaced by
cyano-substituted carbazole moiety in the structure of compound
12. As it was previously shown, the introduction of the strong
electron-withdrawing cyano-groups in the carbazole core leads
to manifestation of electron-transporting ability in addition to
hole-transporting properties characteristic of carbazole
derivatives[28]. X-ray analysis showed that molecules of 12
interact by π-π interactions between antiparallelly arranged 3,6-
dicyano-9H-carbazolyl moieties (Fig. S7 a) with the distance of
3.55 Å. Additionally, the neighboring molecules are held by weak
N∙∙∙H-C hydrogen bonds (Figure S7 b, green, yellow, red,
magenta dashed lines) with the distances in the range of 2.530-
3.537 Å. The π-π stacking and hydrogen bonding can
apparently determine an effective molecular orientation and
packing in the solid state resulting in higher electron mobility
relative to hole mobility. However, its charge mobilities were
found to be much lower in comparison to those of compound 9.
The lower values of electron and hole mobilities observed for
compound 12 can be explained by increase in theoretical dipole
moment by roughly 5 D (3.2 D for 9 and 8.4 D for 12). In addition,
lower values of charge mobilities of compound 12 might be
related to small HOMO and LUMO distribution within molecule
12 in contrast to that of molecule 9. Further “perfect”
substitutions of compounds based on tert-butyl substituted
carbazole and pyridine-3,5-dicarbonitrile moieties may lead to
high and well-balanced both hole and electron mobilities.
Compound 9 exhibiting bipolar charge transport with hole
2
A
P
g
where E
g
values of E
g
6
Time-of-flight measurments. Charge-transporting properties of
the compounds were studied by time-of-flight (ToF) technique.
Transit times (ttr) were recorded for vacuum-deposited films of 6,
9
and 12 applying positive or negative electric fields (Figure 7
a,b, S5). Due to the shapes of the recorded charge transients,
the studied compounds are characterized by dispersive
transport of holes and electrons (Figure 7a,b, S5). Because of
strong tendency to crystallization of low-molar-mass compound
5, it was impossible to obtain the sample of sufficient quality for
TOF measurements of this compound (Figure S6). TOF
measurements showed that compounds 6, 9 and 12 are capable
to transport both holes and electrons (Figure 7 c). Relatively low-
molar-mass compound 6 containing pyridine-3,5-dicarbonitrile
and one tert-butyl substituted carbazole moieties showed well-
balanced hole and electron transport with charge mobilities
exceeding 5×10-5 cm /(Vs) at higher electric field than 7×105
V/cm. Apparently, the reason of the well-balanced hole and
electron transport of compounds 6 can be related to the similar
2
(
equal) spatial frontier orbital distributions resulting from the tert-
butyl substituted carbazole for HOMO and from the pyridine-3,5-
dicarbonitrile for LUMO as well as the similar (equal) HOMO-
HOMO and LUMO-LUMO overlapping of the neighboring
molecules in solid films (Figure S2). Similar electron mobilities
were observed for 9. This compound showed considerably
higher hole mobilities apparently due to the presence of two tert-
-3
2
mobility exceeding 10 cm /(Vs) and electron mobility exceeding
10-4 cm /(Vs) at electric fields higher than 7×105 V/cm can be
considered as promising candidate for optoelectronic
applications.
2
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Chemistry - A European Journal
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Figure 7. Time-of-flight current transients for electrons (a) and holes (b) in the layer of compound 9; electric field dependencies of hole and electron drift mobilities
for the vacuum-deposited layers of compounds 6, 9, 12 (c).
layer of compound 5 did not worked due to the crystallization of
Electroluminescent properties
the emitter. The EL maxima for the devices with the different
light-emitting layers were observed in range from 436 to 546 nm
being very similar to the wavelengths of PL maxima of the
corresponding non-doped or hosted solid-state layers based on
the investigated compounds series (Figure S8 a). Different
colour OLEDs (deep-blue, blue, green and yellow) were
fabricated depending on the structure of TADF emitters used
To test the electroluminescent (EL) properties of compounds 5,
6
, 9 and 12 as TADF emitters, organic light-emitting diodes with
the structure ITO/MoO (2nm)/NPB (40nm)/TCTA (8nm)/mCP
light-emitting layer (24nm)/TSPO1
3
(
(
(
(
8nm)/host:guest
8nm)/TPBi (40nm)/LiF:Al were fabricated and characterized
Figure 8). In the OLED structure, hole- and electron-injection
(
Table 3, Figure S11). Effect of hosts (mCP and TCz1) on EL of
doped devices was also observed due to the differences in
polarity and aggregation effects Table 3, Figure S8 [23]. Very
intensive EL was observed for green devices based on the
MoO
3
and LiF), hole- and electron-transporting (TCTA and
TPBi), exciton-blocking (mCP and TSPO1) layers were used for
providing good charge recombination probability in the emitting
layer.
2
emitter 9 reaching maximum brightness of 26700 cd/m (Figure
2
S9 b). Lower maximum brightness of 4600 and 890 cd/m were
obtained for yellow and blue devices based on the emitters 6
and 12 respectively partly due to the lower sensitivity of the
human eye in these regions in comparison to green one.
Relatively low turn-on voltages ranging from 3.8 to 6.25 V were
observed for the devices displaying good charge injection
properties of emitting layers. The maximum current, power and
external quantum efficiencies (EQE) of 15 cd/A, 5.1 lm/W, and
5.2% respectively were recorded for the device CI containing
emitting layer of 9:mCP (Table 3, Figure S9 c, d). Compound 9
showed overall the best performance in all types of the studied
devices. This observation can be mainly explained by good
combination of TADF and charge-transporting properties of
emitter 9.
Figure 8. Energy diagram of OLEDs containing compounds 5, 6,
9
and 12.
Depending on the light-emitting layer, non-doped (A, B, C, and D
using layers of compounds 5, 6, 9 and 12), and doped (AI, BI, CI,
DI and AII, BII, CII, DII using mCP and TCz1 as the host,
respectively and 10 wt% of the emitter in the host) OLEDs were
fabricated. The hosts mCP and TCz1 were chosen based on
their HOMO and LUMO levels, charge-transporting ability, and
high triplet-energy levels. The main output characteristics of the
devices are collected in Table 3. The corresponding plots are
placed in SI, Figures S8-S10. Non-doped OLED containing the
Table 3. Electroluminescent parameters of OLEDs.
V
on
Exter
nal
quant
um
efficie
ncy
[%]
CIE
1931
UCS
coordin
ates at
6V (x,
y)
[V]
Max
bright
ness
Curre
nt
efficie
ncy
Power
efficie
ncy
[lm/W
]
EL
at
set
2
maxi
mum
at 5V
[nm]
Devi
ces
0
at 10V
2
[cd/
[cd/m ]
[cd/A]
2
m ]
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Chemistry - A European Journal
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FULL PAPER
max
Non-doped devices
(0.677,
CIr
DIr
3.3
3.9
7700
1670
3.52
0.63
2.7
1.35
0.42
2.4
3.5
0.8
4.5
630
630
630
0.324)
A
B
-
-
-
-
-
-
-
(0.674,
.326)
0
(
(
(
0.19,
.29)
5.25
890
0.9
0.44
0.36
487
0
mCP
Ir
(0.676,
0.323)
3.9
10000
0.29,
.55)
C
D
5.0
6.0
26700
4600
10
3.65
0.92
2.9
521
544
0
Further optimization of OLEDs with 9 emitter doped in the mCP
host was performed. The structure of OLED was slightly
0.39,
.56)
2.3
0.69
0
3
simplified: ITO/MoO (2nm)/NPB (50nm)/Host:Guest (32nm)/
Doped devices using the mCP host with the same concentration of the
emitters
TPBi (50nm)/LiF:Al of these OLEDs (Figure 9a, insert). To
optimize the concentration of guest 9 in host:guest system,
devices CIa, CIb, CIc, and CId were fabricated with the
concentration of 9 emitter of 5 wt%, 10 wt%, 20 wt%, and 30
wt%, respectively. Being in green region, EL spectra were
slightly red-shifted with increasing concentration of the emitter
due to the solid-state polarity effects (Figure 9b).
(
(
(
(
0.15,
AI
BI
CI
DI
4.33
6.25
4.0
170
540
1.2
1.3
15
0.67
0.47
5.1
1.5
0.71
5.2
436
472
505
526
0.07)
0.16,
0.21)
0.23,
10100
5600
0.49)
0.30,
.56)
4.61
6.1
3.6
1.83
The best device performance was observed for OLED CIa
0
containing light-emitting layer with 5 wt% of 9 guest in mCP host.
Doped devices using the TCz1 host with the same concentration of the
emitters
2
Turn-on voltage of 3.95V and brightness of 14500 cd/m at 10 V
were obtained for these OLEDs (Table 3). In addition, these
OLEDs were characterized by enhanced maximum current
efficiency of 15.2 cd/A and external quantum efficiencies of 7.5%
(Figure 9 c,d). This value of maximum EQE for the device CIa is
far below of the best literature values reported for OLEDs with
the similar CIE coordinates which exceed 30 % in case of
OLEDs based on acridine and CN-substituted pyridine
derivatives [6, 9, 10, 29-33]. Predictably, these efficiencies can be
improved considerably when an appropriate bipolar host is
available for compound 9 instead of the mCP. In addition, to
demonstrate the importance of charge transporting properties,
(
(
(
(
0.16,
AII
BII
CII
DII
3.8
770
750
1.37
0.36
4.73
5.54
0.7
0.99
0.23
1.65
1.8
448
465
502
546
0.13)
0.16,
3.95
3.62
5.12
0.19
3.05
2.07
0.18)
0.22,
3400
1500
0.45)
0.37,
.55)
0
Doped devices using the mCP host with different concentrations of the
emitter 9
compounds
9
and 12 were tested as the hosts in
(
(
(
(
0.21,
CIa
CIb
CIc
CId
3.95
4.2
14500
11000
15000
6000
21.3
13.6
9.0
15.2
9.2
7.5
5.18
2.9
500
503
505
523
0.45)
phosphorescent OLEDs. EL spectra of the devices were related
to the emission of red phosphorescence guest used (Supporting
Information: paragraph “Red phosphorescent OLED.”, Figure
S12 a, S13) [34, 35]. Much higher maximum EQE of 3.5 % was
observed for device based on the host 9 relative to that of 0.8%
recorded for device based on the host 12 (Figure S12, Table 3).
We expect that our result will initiate further developments of
efficient TADF emitters taking to the account not only their TADF
but also charge-transporting properties.
0.20,
0.43)
0.23,
4.4
4.3
0.49)
0,29,
.45)
6.42
2.52
0.82
0.8
0
Red phosphorescent OLEDs based on the 9, 12 or mCP host
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Figure 1. Current density and brightness (a), EL spectra at 6V (b), EQE (c), and current efficiency (d) for devices CIa, CIb, CIc, and CId.
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Chemistry - A European Journal
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recorded at 77 K with the delay time after excitation exceeding
50 ms. Photoluminescence decay curves were taken exploiting
Conclusions
the PicoQuant LDH-D-C-375 laser (wavelength 374 nm) as the
excitation source. Photoluminescence quantum yields (PLQY)
were measured using an integrated sphere (inner diameter of
120 mm) on Edinburgh Instruments FLS980 spectrometer. To
estimate hole and electron mobilities of vacuum-deposited
layers of the studied compounds, time-of-flight (TOF) method
was used. TOF experiments were performed using samples with
Derivatives of non-substituted or tert-butyl-substituted carbazole
and pyridine-3,5-dicarbonitrile
were synthesized and
characterized as efficient TADF emitters. Their potential for
optoelectronic applications was proved by photophysical,
thermal, electrochemical, photoelectrical, charge-transport and
electroluminescence experiments some of which were
supported by theoretical calculations. Derivative of di-tert-butyl-
substituted carbazole and fluorophenyl-substituted pyridine-3,5-
dicarbonitrile showed the best combination of TADF and charge-
transporting properties. Its solid sample showed singlet-triplet
energy splitting of 0.04eV. Its molecular mixture with host
material showed potoluminescence quantum yield of 41 %. The
a
structure indium-tin-oxide (ITO) /few μm thick organic
layer/aluminium. In TOF setup, a laser (EKSPLA NL300, 355 nm
wavelength) was used as the excitation source. To check hole
and electron transport in the layers at different electric fields,
different positive and negative external voltages (U) were
applied to the samples employing 6517B electrometer (Keithley).
TDS 3032C oscilloscope (Tektronix) was used to record the
photocurrent transients of holes or electrons. Charge mobilities
-3
2
2
layer of compound 9 showed hole mobility of 2.8×10 cm /(Vs)
were estimated by the formula μ=d /(U×t ), where t is a transit
tr
tr
and electron mobility of 1.2×10-4 cm /(Vs) at electric field of
2
time, d is the thickness of a layer and U is applied voltage.
Electroluminescent devices were fabricated by vacuum
deposition of organic and metal layers onto pre-cleaned ITO
coated glass substrates under vacuum higher than 2×10−6 mBar.
ITO-coated glass substrates with a sheet resistance of 15 Ω/sq
were pre-patterned getting seven independent devices with area
5
.2∙105 V/cm. Compound 9-based electroluminescent device
showed maximum external quantum efficiency of 7.5 %.
2
Experimental Section
6 mm . Density-voltage and luminance-voltage characteristics
were recorded utilizing certificated photodiode PH100-Si-HA-D0
together with the PC-Based Power and Energy Monitor 11S-
LINK (from STANDA) and Keithley 2400C source meter.
Electroluminescence (EL) spectra were taken by the Avantes
AvaSpec-2048XL spectrometer. Device efficiencies were
calculated using the luminance, current density, and EL spectra.
Density Functional Theory (DFT) calculations were carried out
using B3LYP functional together with 6-31G(d,p). Absorption
spectra of the molecules and their optimized geometries at
excited state were calculated using time-dependent DFT (TD-
DFT). Natural transition orbital (NTO) calculations were carried
Materials
3
To fabricate devices, materials (molybdenum trioxide (MoO ),
N,N′-di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine
(
NPB), tris(4-carbazoyl-9-ylphenyl)amine (TCTA), 1,3-bis(9-
carbazolyl)benzene
(mCP),
diphenyl-4-triphenylsilyl-
phenylphosphineoxide (TSPO1) and 2,2’,2’’-(1,3,5-benzinetriyl)-
tris(1-phenyl-1-H-benzimi-dazole) (TPBi)) were purchased from
Sigma Aldrich or Lumtec and used as received (Figure S1). 3,6-
Di(9-carbazolyl)-9-(2-ethylhexyl)carbazole
(TCz1)
was
synthesized according to the published procedure (Figure S1) [36]. out to visualize orbitals of some compounds. All calculations
were carried out with Gaussian 16 program. The single crystal of
Instrumentation
compound 12 was obtained by slow evaporation from the
mixture of solvents (DMC/hexane). Yellow single crystal was
mounted on the glass capillary using glue. The crystallographic
analysis was performed employing XtaLAB mini diffractometer
(Rigaku) with graphite monochromated Mo Kα (λ = 0.71075 Å)
X-ray source. The measurements were performed at the
temperature of 293 K. The crystallographic data for structure of
compound 12 reported in this paper have been deposited in
Cambridge Crystallographic Data Centre with CCDC no
1871379. The copies of data can be obtained free of charge on
application to CCDC. (The Cambridge Structural Database
(CSD) - The Cambridge Crystallographic Data Centre (CCDC),
(http://www.ccdc.cam.ac.uk/solutions/csd-
Thermal properties of the compounds were characterized by
differential scanning calorimetry (DSC) and thermogravimetric
analysis (TGA). DSC measurements were carried out by using a
TA Instruments Q2000 calorimeter. The samples were examined
at
a heating/cooling rate of 10 C°/min under nitrogen
atmosphere. TGA was performed on a TA Instruments Q50
analyser. The heating rate was 20 C°/min. The measurements
were perfomed under nitrogen atmosphere. Electrochemical
properties of the solutions of the compounds in dichlormethane
with 0.1
M
tetrabutylammonium hexafluorophosphate as
supporting electrolyte were studied by cyclic voltammetry (CV)
+
using Ag/Ag as the reference electrode and a Pt wire counter
system/components/csd/).
performed using the OLEX2
Calculations/visualizations
were
[
37]
electrode. The measurements were performed under argon
atmosphere at 50 mV/s potential rate at room temperature.
crystallographic software
package except for refinement, which was performed using
SHELXL [38]. Anisotropic thermal parameters were assigned to
all non-hydrogen atoms. The hydrogen atoms were included in
the structure factor calculation at idealized positions by using a
riding model and refined isotropically.
Ionization potential (I CV
potential using the relationship I CV
affinity (E ) values were obtained from the reduction potential
using the approximation E = 4.8 + Ered vs Fc. Emission and
) was estimated from the onset oxidation
= 4.8 + Eox vs Fc,. Electron
p
p
A
A
UV/Vis absorbance spectra of the compounds were recorded
using the Edinburgh Instruments FLS980 and Avantes
spectrometers, respectively. Phosphorescence spectra were
Synthesis
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Chemistry - A European Journal
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Unless otherwise stated, all reagents were purchased from
commercial suppliers and used without further purification. Thin
layer chromatography (TLC) was performed using MERCK Silica
gel 60 F254 plates and visualized by UV (254 nm) fluorescence.
ZEOCHEM silica gel (ZEOprep 60/35-70 microns – SI23501)
was used for column chromatography. H and 13C NMR spectra
were recorded on a Varian 400 Mercury spectrometer at 400.0
dihydropyridine-3,5-dicarbonitrile 3 (0.62 g, 1.55 mmol) was
suspended in glacial acetic acid (10 mL) and sodium nitrite
0
(1.035 g, 15 mmol) was added at 60 C. The mixture was heated
at mentioned t for 10 min. After cooling the mixture was poured
onto ice and the precipitates were filtered. The crude product
was purified by column chromatography (silica gel, eluent
DCM:petroleum ether, 4:1 ) yielding 5 (0.51 g, 82%) as pale
1
0
1
and 100.58 MHz correspondingly at 298 K in CDCl
High resolution copies of the H NMR spectra of the new
emitters were shown in the ESI (Appendices 2).
3
or DMSO-d
6
.
6
yellow powder, Mp: > 200 C. H NMR (400 MHz, DMSO-d ) δ
1
8.29 (d, J = 7.7 Hz, 2H), 7.98-7.91 (m, 4H), 7.54-7.46 (s, 4H),
7.39-7.30 (s, 2H), 2.84 (s, 6H). IR νmax (KBr): 2224, 1605, 1570,
1514, 1445, 1375, 1336, 1221, 1175, 828, 746, 726. HRMS:
4
-(9H-carbazole-9-yl) benzaldehyde (1).
fluorobenzaldehyde (1.27 mL, 12 mmol, 1.2 eq), K
0 mmol, 3 eq) and 9H-carbazole (1.67 g, 10 mmol, 1 eq) in
A
mixture of 4-
2
CO (4.15 g,
3
18 4
[M]+ calcd for C27H N 398.1531, found 398.1526.
3
DMF (20 mL) was refluxed for 18 h. After cooling the mixture
was poured into ice-water and extracted with DMC (3x50 mL).
4-[4-(3,6-Di-tert-butyl-9H-carbazol-9-yl)phenyl]-2,6-dimethyl-
3,5-dicarbonitrile (6). 4-[4-(3,6-Di-tert-butyl-9H-carbazol-9-
The organic phase was dried with anhydrous Na
2
SO
4
and
yl)phenyl]-2,6-dimethyl-1,4-dihydropyridine-3,5-dicarbonitrile
4
evaporated. The crude product was purified by column
chromatography (silica gel, eluent DCM:petroleum ether 1:1)
affording aldehyde 1 ( 2.22 g, 82%) as a pale yellow powder.
(0.51 g, 1 mmol, 1 eq) was suspended in glacial acetic acid (10
mL) and sodium nitrite (0.69g, 10 mmol, 10 eq) was added at 60
C. The mixture was heated at mentioned t for 10 min. After
0
Mp=133-135 oC (lit. 134-136 oC). 1H-NMR corresponds to
cooling the mixture was poured onto ice and the precipitate was
filtered. The crude product was purified by column
chromatography (silica gel, eluent DCM:petroleum ether, 4:1 )
literature [
.
39]
4
-(3,6-di-tert-butyl-9H-carbazole-9-yl) benzaldehyde (2).
mixture of 4-fluorobenzaldehyde 1 (1.27 mL, 12 mmol, 1.2 eq),
CO (4.15 g, 30 mmol, eq) and 3,6-di-tert-butyl-9H-
A
0
yielding 6 (0.38 g, 75%) as pale yellow powder, Mp: > 200 C.
1
K
2
3
3
3
H-NMR (400 MHz, CDCl ): 8.15 (t, J = 1.3 Hz, 2H), 7.85-7.74
carbazole (2.79 g, 10 mmol, 1 eq) in DMF (20 mL) was refluxed
for 18 h. After cooling the mixture was poured into ice-water and
extracted with DMC (3x50 mL). The organic phase was dried
(m, 4H), 7.50 (d, J= 1.3 Hz, 4H), 2.92 (s, 6H), 1.48 (s, 18H). 13
NMR (CDCl ): δ 165.36, 143.62, 138.55, 130.48, 126.59, 123.86
C
3
116.33, 115.25, 109.33, 107.25, 34.76, 31.96, 24.77. IR νmax
with anhydrous Na
2
SO
4
and evaporated. The crude product was
(film): 2223, 1607, 1552, 1516. HRMS: [M]+ calcd for
purified by column chromatography (silica gel, eluent
C
35
H
34
N
4
510.2783, found 510.2773. Anal. Calcd. for C35
34 4
H N :
DCM:petroleum ether 1:1) affording aldehyde 2 (2.42 g, 63%) as
C, 82.32; H, 6.71; N, 10.97; Found: C, 81.98; H, 6.70 ; N, 10.93.
o
o
1
a pale yellow powder. Mp=162-165 C (lit. 159-160 C). H-NMR
corresponds to literature [40]
-[4-(9H-carbazol-9-yl)-2,6-dimethyl-1,4-dihydropyridine-3,5-
dicarbonitrile (3). The mixture of 4-(9H-carbazole-9-
yl)benzaldehyde (0.542 g, mmol, eq) and 3-
.
Piperidinium
3,5-dicyano-6-hydroxy-4-(4-
4
fluorophenyl)pyridin-2-olate (7). A mixture of cyanoacetamide
(6.0 g, 71 mmol, 2 eq), piperidine (7.01 mL, 71 mmol, 2 eq) and
MeOH (45 mL) was heated until complete dissolution. The
mixture was cooled to rt and 4-fluorobenzaldehyde (3.75 mL,
35.5 mmol, 1 eq) was added. The mixture was vigorously stirred
at rt for 24 h. The solvent was evaporated to a half of volume
and after cooling the precipitate was filtered. The crude product
was washed with cold MeOH and EtOAc and dried in vacuo,
1
2
1
aminocrotononitrile (0.36 g, 4.4 mmol, 2.2 eq) in acetic acid (20
mL) was refluxed for 15 h. After cooling the precipitate was
filtered and washed with acetic acid and methanol yielding 0.62
g (78%) of 3 as pale yellow solid. The substance is used in the
0
1
next step without further purification. Mp: > 200 C. H NMR (400
MHz, DMSO-d ) δ 9.63 (s, 1H), 8.25 (dd, J = 7.8, 1.2 Hz, 2H),
.74 – 7.65 (m, 2H), 7.64 – 7.53 (m, 2H), 7.50 – 7.36 (m, 4H),
.30 (ddd, J = 8.0, 6.7, 1.2 Hz, 2H), 4.61 (s, 1H), 2.10 (s, 6H).
6
yielding 7 (4.23 g, 35%) as white powder, which was used in the
1
7
7
next reaction without purification. H-NMR (400 MHz, DMSO-d
6
):
7.48-7.42 (m, 2H), 7.31 (t, J= 8.9 Hz, 2H), 3.02-2.98 (m, 4H),
1.67-1.51 (m, 6H). 13C NMR (DMSO-d
): 164.08, 163.72, 161.63,
61.35, 133.21, 133.18, 130.70, 130.62, 119.12, 115.75, 115.53,
-
-
MS (ES ) m/z: 399.3 ([M-H] , 100).
6
1
-
-
4
1
-[4-(3,6-Di-tert-butyl-9H-carbazol-9-yl)phenyl]-2,6-dimethyl-
,4-dihydropyridine-3,5-dicarbonitrile (4). The mixture of 4-
82.23, 44.31, 22.78, 22.13. MS (ES ) m/z: 254 ([M-H-piperidine] ,
100).
(
3,6-di-tert-butyl-9H-carbazole-9-yl )benzaldehyde 2 (0.77 g, 2
mmol, 1 eq) and 3-aminocrotononitrile (0.36 g, 4.4 mmol, 2.2 eq)
in acetic acid (20 mL) was refluxed for 15 h. After cooling the
precipitate was filtered and washed with acetic acid and
methanol yielding 0.90 g (88%) of 4 as pale yellow solid. The
substance is used in the next step without purification. Mp: > 200
2,6-Dibromo-4-(4-fluorophenyl)pyridine-3,5-dicarbonitrile (8).
A mixture of 7 (2.00 g, 5.88 mmol, 1 eq) and POBr (4.21 g,
3
14.69 mmol, 2.5 eq) was heated with stirring in an oil bath at 170
0
C for 1 h. After cooling, the reaction mixture was quenched by
the addition of ice and the precipitate was filtered. The crude
product was purified by silica gel column chromatography
(eluent: DCM/lpetroleum ether, 2:1) yielding 8 (1.52 g, 68%) as
0
1
C. H-NMR (400 MHz, DMSO-d
6
): 9.62 (s, 1H), 8.29 (dd, J= 2.0,
0
7
.6 Hz, 2H), 7.66 (d, J= 8.4 Hz, 2H), 7.55 (d, J= 8.4 Hz, 2H),
.47 (dd, J= 8.7, 2.0 Hz, 2H), 7.33 (dd, J= 8.7, 0.6 Hz, 2H), 4.59
white powder. Mp: > 200 0C. 1H-NMR (400 MHz, DMSO-d
6
):
):
+
13
(
s, 1H), 2.10 (s, 6H), 1.41 (s, 18H). MS (ES ) m/z: 513 ([M+H],
7.76-7.65 (m, 2H), 7.54-7.44 (m, 2H). C NMR (DMSO-d
6
100).
164.07, 163.73, 161.63, 161.36, 133.12, 133.09, 130.69, 130.61,
19.07, 115.76, 115.55, 82.32. Anal. Calcd. for C13 Br FN : C,
1
H
4
2
3
4
-[4-(9H-Carbazol-9-yl)phenyl]-2,6-dimethyl-3,5-
40.98; H, 1.06; N, 11.03; Found: C, 40.58, H, 1.05, N, 10.84.
GC/MS: 381 (calcd. 381).
dicarbonitrile (5). 4-[4-(9H-carbazol-9-yl)-2,6-dimethyl-1,4-
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Chemistry - A European Journal
10.1002/chem.201805323
FULL PAPER
1
24.23, 117.04, 116.82, 116.78, 114.50, 113.30, 111.88,
+
+
2
,6-Bis(3,6-di-tert-butyl-9H-carbazol-9-yl)-4-(4-
fluorophenyl)pyridine-3,5-dicarbonitrile (9). Sodium hydride
60% oil dispersion, 0.43 g, 12.8 mmol, 3.2 eq) was added to
110.08102.68, 34.93, 31.77. MS (ES ) m/z: 580 ([M+H] , 100).
(
2-(3,6-di-tert-butyl-9H-carbazol-9-yl)-6-(3,6-dicyano-9H-
THF (15 mL) under argon. 3,6-Di-tert-butyl-9H-carbazole (3.35 g, carbazol-9-yl)-4-(4-fluorophenyl)pyridine-3,5-dicarbonitrile
0
1
2 mmol, 3 eq) was added at 0 C and suspension was stirred
(12). Sodium hydride (60% oil dispersion, 83.6 mg, 1.75 mmol,
2.12 eq)was added to THF (5 mL) under argon. 3,6-di-tert-butyl-
9H-carbazole (359 mg, 1.66 mmol, 2 eq) was added at 0 C,
for 30 min and then a THF (10 mL) solution of 8 (1.52 g, 4 mmol,
eq) was added. The mixture was stirred at rt for 1 h (TLC)
before it was poured into ice-water. The suspension was
extracted with chloroform (5x30 mL), dried over Na SO . After
the solvent was removed, the crude yellow product was carefully
washed twice with acetonitrile to remove the 3,6-di-tert-butyl-9H-
carbazole. Further purification was achieved using column
chromatography (silica gel, eluent: DCM/ petroleum ether, 1:2)
and 9 (1.94 g, 62%) as bright yellow powder was obtained. Mp>
00 C. H-NMR (400 MHz, CDCl
H), 7.89 (dd, J = 8.8, 5.0 Hz, 2H), 7.70 (dd, J = 8.7, 0.6 Hz, 4H), Hz, 2H), 8.11 (dd, J = 2.0, 0.6 Hz, 2H), 7.92- 7.87 (m, 2H), 7.83-
.47 (dd, J = 8.8, 2.0 Hz, 4H), 7.40 (dd, J = 8.8, 8.2 Hz, 2H), 7.77 (m, 4H), 7.66 (dd, 8.7, 0.6 Hz, 2H), 7.51-7.41 (m, 4H), 1.45
.46 (s, 36H). 13C NMR (CDCl ): 163.85, 163.27, 154.93, 152.77, (s, 18H). 13C NMR (CDCl
): 163.85, 163.27, 154.93, 152.77,
47.51, 141.11, 136.49, 131.92, 131.83, 131.18, 128.13, 128.09,
26.18, 125.67, 124.28, 124.05, 118.65, 117.34, 117.12, 116.94,
13.30, 113.26, 113.15, 112.15, 107.30, 102.11, 101.21,34.95,
0
1
suspension was stirred for 30 min and then a THF (5 mL)
solution of 11 (0.48 g, 0.83 mmol, 1 eq) was added. The mixture
was stirred at rt for 1 h (TLC) before it was poured into ice-water.
The yellow precipitates were filtered off and further purification of
crude product was achieved using column chromatography
(silica gel, eluent: EtOAc/petroleum ether, 20%→ 50% EtOAc).
Desired 12 (199 mg, 67%) was obtained as bright yellow powder.
2
4
0
1
0
1
2
4
7
1
1
1
1
3
7
3
): 8.09 (dd, J = 2.0, 0.6 Hz,
3
Mp> 200 C. H-NMR (400 MHz, CDCl ): 8.46 (dd, J = 1.5, 0.8
3
3
147.51, 141.11, 136.49, 131.92, 131.83, 131.18, 128.13, 128.09,
126.18, 125.67, 124.28, 124.05, 118.65, 117.34, 117.12, 116.94,
113.30, 113.26, 113.15, 112.15, 107.30, 102.11, 101.21,34.95,
31.71, 31.68. IR νmax (film): 2222, 1630, 1602, 1546. HRMS:
1.71, 31.68. HRMS: [M]+ calcd for C53
77.4180. IR νmax (film): 2228, 1603, 1540, 1506. Anal. Calcd.
: C, 81.82; H, 6.76; N, 9.00; Found: C, 81.73, H,
5
H52FN 777.4207, found
[M]+ calcd for C47
m/z: 716 ([M+H] , 80). Anal. Calcd. for C47H34FN7: C, 78.86; H,
H
34FN
7
715.2860, found 715.2851. MS (ES+)
+
for C53
H52 FN
5
6.97, 8.90.
4.79; N, 13.70; Found: C, 78.59; H, 4.72; N, 13.50.
2-(3,6-Di-tert-butyl-9H-carbazol-9-yl)-4-(4-fluorophenyl)-6-
hydroxy-pyridine-3,5-dicarbonitrile (10). Sodium hydride (60%
oil dispersion, 0.68 g, 16.45 mmol, 4.12 eq) was added to THF
Acknowledgements
(
1
10 mL) under argon. 3,6-Di-tert-butyl-9H-carbazole (4.11 g,
4.69 mmol, 4 eq) was added at 0 C and suspension was
0
This work was supported by the project of scientific co-operation
program between Latvia, Lithuania and Taiwan “Synthesis and
studies of high-triplet-energy materials for blue OLEDs” (grant
No. TAP-LLT-2/2017, No LV-LT-TW/2018/11)
stirred for 30 min and then a THF (10 mL) solution of 8 (1.40 g,
.67 mmol, 1 eq) was added. The mixture was stirred at rt for 24
3
h (TLC) before it was poured into ice-water. The yellow
precipitates were filtered and carefully washed with acetonitrile
to remove the starting 3,6-di-tert-butyl-9H-carbazole. Then the
crude product was boiled with mixture of solvents
Keywords: delayed fluorescence, electroluminescence, OLED,
substituent.
(
7
DCM/petroleum ether, 1:1). Obtained compound 10 (1.47 g,
7%) as bright yellow powder was used in the next reaction
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without additional purification. Mp. > 200 C. H-NMR (400 MHz,
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