Synthesis and optical characterization of bipod carbazole derivatives

Article abstract of DOI:10.1515/hc-2020-0111

In this study, some new biscarbazole derivatives were synthesized for the purpose of being used in OLED technologies and related areas. The following compounds: {1,2-bis(2-(3,6-diphenyl-9H-carbazole-9-yl) ethoxy)ethane (C-1), bis[2-(2-(3,6- diphenyl-9H-carbazole-9-yl) ethoxy)etyl]ether (C-2), bis[2-(2-(3,6-di(naphthalene-1-yl)-9H-carbazol-9-yl)ethoxy)etyl]ether (C-3) and bis [2-(2-(3,6-di(naphthalene-2-yl)-9H-carbazol-9-yl)ethoxy) ethyl]ether (C-4) were synthesized by Suzuki-Miyaura Cross Coupling reactions. The structural properties of the synthesized compounds were characterized by FT-IR, 1H-NMR, 13C-NMR, and LC-MS. The maximum product yields of 81.6% were obtained for C-4 biscarbazole derivatives. The optical properties were studied using UV-visible and temperature/excitation power density dependent photoluminescence (PL) techniques. The emissions were observed at green and yellow-red color spectral bands. By applying Gaussian fitting to the measured spectra, the superposition of the broad peaks was deconvoluted into two peaks. The origin of emissions was attributed to π- π? transition in aromatic compounds caused by intramolecular charge transfer from host carbazole to these compounds.

Full text of DOI:10.1515/hc-2020-0111

Heterocycl. Commun. 2020; 26: 148–156
Research Article
Open Access
Baki Çiçek*, Merve Çağlı, Remziye Tülek and Ali Teke
Synthesis and optical characterization of bipod
carbazole derivatives
https://doi.org/10.1515/hc-2020-0111
List of abbreviations
Received May 23, 2019; accepted July 17, 2020.
Abstract: In this study, some new biscarbazole derivatives OLED
:
:
:
:
:
:
:
Organic Light Emitting Diodes
FourierTransformInfraredSpectroscopy
Proton Nuclear Magnetic Resonance
Carbon Nuclear Magnetic Resonance
Tetrabutylammonium iodide
Chemical Shift
were synthesized for the purpose of being used in FT-IR
1
OLED technologies and related areas. The following H-NMR
1
3
compounds: {1,2-bis(2-(3,6-diphenyl-9H-carbazole-9-yl)
C-NMR
ethoxy)ethane (C-1), bis[2-(2-(3,6- diphenyl-9H-carbazole- TBAI
9
-yl) ethoxy)etyl]ether (C-2), bis[2-(2-(3,6-di(naphthalene-
-yl)-9H-carbazol-9-yl)ethoxy)etyl]ether (C-3) and bis
2-(2-(3,6-di(naphthalene-2-yl)-9H-carbazol-9-yl)ethoxy)
δ
M
+
1
[
Molecular Ion Peak
ethyl]ether (C-4) were synthesized by Suzuki-Miyaura
Cross Coupling reactions. The structural properties of
the synthesized compounds were characterized by FT-IR,
Introduction
1
H-NMR, 13C-NMR, and LC-MS. The maximum product
Biscarbazoles as luminescent materials which include
two aromatic heterocyclic organic compounds have been
designed and synthesized for exploring some
applications. These include organic light-emitting
diodes (OLEDs) [1–3], organic photovoltaic and
electronic devices [4–10], studying biochemical
activities [11–18] and fundamental points of view
yields of 81.6% were obtained for C-4 biscarbazole
derivatives. The optical properties were studied using
UV-visible and temperature/excitation power density
dependent photoluminescence (PL) techniques. The
emissions were observed at green and yellow-red color
spectral bands. By applying Gaussian fitting to the
measured spectra, the superposition of the broad peaks
was deconvoluted into two peaks. The origin of emissions
was attributed to π- π* transition in aromatic compounds
caused by intramolecular charge transfer from host
carbazole to these compounds.
[
19,20]. Such molecules are especially suited to
implementation in OLED technologies because of the
electron donation of nitrogen on the carbazole ring.
The efficient charge transfer from host carbazoles
to connected molecules is provided by a strong
Keywords: Bipod Carbazole, Suzuki-Miyaura Cross Cou- π-electron conjugation. Carbazoles have been used
pling, Optical Characterization, Photoluminescence, as host matrices in highly efficient blue, green, or red
OLED
electro-phosphorescent devices [6–8,16,21]. They also
have good thermal properties and structural stability,
allowing them to be used as a hole transport layer in
OLED technology [22–30]. Carbazole/thioxanthene-S,
S’-dioxide (EBCz-ThX) bipolar molecules synthesized by
electron accepting and electron donating groups with
a solvent-free green chemistry method were presented
as blue phosphorescent light emitting devices [31].
A green light with a peak maximum at 550 nm under
an applied external voltage was reported from a
diode based on 2,4-dicarbazolylquinoline [32]. Multi-
carbazole derivatives with twisted and zigzag-shape
structures were synthesized and used as sensitizers for
dye-sensitized solar cells [33].
*
Corresponding author: Baki Çiçek, Chemistry Department, Faculty
of Arts and Sciences, Balıkesir University, Balıkesir
E-mail: Turkey bcicek@balikesir.edu.tr; mervecagli@live.com
Merve Çağlı, Chemistry Department, Faculty of Arts and Sciences,
Balıkesir University, Balıkesir
E-mail: Turkey bcicek@balikesir.edu.tr; mervecagli@live.com
Remziye Tülek and Ali Teke, Physics Department, Faculty of Arts and
Sciences, Balıkesir University, Balıkesir
E-mail: Turkey baran@balikesir.edu.tr; ateke@balikesir.edu.tr
Open Access. © 2020 Çiçek et al., published by De Gruyter.ꢀ
Attribution alone 4.0 License.
ꢀThis work is licensed under the Creative Commons

Çiçek et al.: Synthesis and optical characterization of bipod carbazole derivativesꢁ
ꢁ149
To identify the potential use of newly synthesized Materials and methods
molecules in various applications, their photophysical
and electrochemical properties need to be investigated. As General
an example, Slodek et al. reported a strong dependence
of optical properties on the number of carbazole units All starting materials were purchased from Merck,
and length of alkyl chain on said carbazole units in Sigma-Aldrich and Fluka Co., and were used after
the molecule, as well as the position of substitution further analytical purifications using silica gel column
of carbazole for a donor-acceptor (D-A) system based chromatography. FT-IR spectra were taken using Perkin
1
on 2,4-dicarbazolyl-substituted quinolines. The low- Elmer BX2 FTIR Spectrometer. Both H-NMR (400 MHz)
1
3
temperature PL spectra were characterized by the spin- and C-NMR (100 MHz) spectra were obtained in CDCl
3
allowed fluorescence (400 nm) and spin-forbidden using an Agilent Tech. 400 NMR Spectrometer. LC-MS
phosphorescence (490–527 nm) bands [34]. The synthesis spectra were recorded on an Agilent Technologies-1260
and optical characterization of
a
salicylaldimine Infinity (LC) 6130 Quadropole (MS) Mass Spectrometer
difluoroboron complex with tert-butyl group was carried using acetonitrile as the solvent. Microanalyses
out by Zhang and co-workers. The maximal emission were performed with a Thermo Scientific Flash 2000
peak of the synthesized compound in THF at 514 nm elemental analyzer. The absorption spectra were
was ascribed to intramolecular charge transfer (ICT) recorded using a Perkin-Elmer Lambda 25 UV-Vis
emission. The peak positions of fluorescence emissions Spectrometer. The temperature and excitation power
were blue and red-shifted to 506 and 522 nm for crystal density dependent photoluminescence measurements
structure and ground powder respectively [32]. Complex were performed in the temperature range of 20–300 K
2
yellow (centered at ~574 nm) and red (centered at ~704 and excitation power densities between 2.6-330 mW/cm .
nm) colors were observed, with the relative intensities A frequency tripled Nd:YLFQ-switched pulse laser at 349
dependent on functional groups in PL spectra, for novel nm was used for the excitation. The luminescence was
carbazole derivatives synthesized using a condensation collected by suitable lenses and then dispersed with
reaction between carbazole amines and aromatic a 500 mm spectrometer using 1200 line/mm grating
aldehydes [35].
and detected by Intensified Charge Coupled Device
Although carbazoles have been synthesized with (ICCD) camera.
substitutions in all positions (on benzene rings and
nitrogen) [36], substitutions on 3- and 6- positions are
very common [30, 32–35]. Various methods with several Experimental
steps have been used for substitution on the aromatic
rings [36, 39]. The most common and successfully used Synthesis of 3,6-dibromocarbazole (B)
method is the Suzuki-Miyaura Cross Coupling Reaction
[
42–48]. The selection of groups expected to substitute Carbazole (A) (5 mmol, 0.835 g) was firstly dissolved in
on the desired positions is very important due to their 100 ml of dichloromethane. SiO (20 g) was then added
2
crucial effect on the optical properties of the final and stirred. A solution which contained NBS (10 mmol,
product.
1.78 g) dissolved in 150 ml of dichloromethane was
This study includes the synthesis and characteriza- added dropwise to the carbazole mixture, and was
tion of novel biscarbazole derivatives which were obtai- continuously stirred at room temperature for 24 hours in
ned by connection of two carbazole molecules through a dark environment [45]. The entire mixture was
their nitrogen positions and substitution of phenyl, then filtered and the residue was washed with
α-naphthyl and β-naphthyl on their 3- and 6- positions dichloromethane (3 x 30 ml). The combined organic
using the Suzuki-Miyaura Cross Coupling Reaction. The fractions were rinsed with water (200 ml) and, after the
formation of synthesized molecules was determined by phases were separated, the organic layer was collected.
infrared spectroscopy (FT-IR), nuclear magnetic reso- The solvent was evaporated after which a light green
nance spectroscopy (NMR), mass spectrometry (MS) powder was obtained (1.176 g, yield: 72%). FT-IR (γ cm-1):
and microanalysis methods. Their optical properties 3403 (N-H stretch), 3071 (aromatic C-H stretch), 1598
were studied using UV-Vis spectroscopy and tempera- (aromatic C=C stretch), 1459 (carbazole ring stretch),
ture/excitation power density dependent photolumine- 1127 (C-N bend), 802 (C-Br bend), 739 and 686 (aromatic
scence (PL).
C-H out-of-plane bend)

ꢁ
Çiçek et al.: Synthesis and optical characterization of bipod carbazole derivatives
150ꢁ
General Procedure-I for synthesis of bromine substituted Synthesis of Bis[2-(2-(3,6-dibromo-9H-carbazole-9-yl)
biscarbazoles ethoxy)etyl]ether (C-a2)
3
,6-dibromocarbazole (B) (2.0 equivalent), 1,2-bis(2- Synthesized using General Procedure-I with 3,6-dibromo-
chloroethoxy)ethane (1.0 equivalent), TBAI and 50% carbazole (2.8 mmol, 0.91 g), bis[2-(2-chloroethoxy)ethyl]
NaOH solution (10 ml) were added in 100 ml flask and ether (1.38 mmol, 0.27 ml), TBAI (0.50 g) to give the oily
-1
refluxed while it was stirring at 78 °C for 48 hours [49]. solid product (0.424 g, 37.5%). FT-IR (γ cm ): 3062 (aro-
After the reaction was complete, the mixture was cooled matic C-H stretch), 2956 and 2871 (aliphatic asymmetric
down to room temperature. The mixture was then filtered and symmetric stretch), 1471 (aliphatic asymmetric C-H
with dichloromethane (3x30 ml) and washed in water bend), 1435 (carbazole ring stretch), 1290 (aliphatic C-H,
(
200 ml). Organic phase was obtained after separating in-plane, symmetric bending), 1108 (C-O-C asymmetric
the layers and drying over Na SO . The solution was bend), 1057 (N-C bend), 1033 (C-O-C symmetric bend),
2
4
evaporated and the oily solid product was obtained by 1017 (C-H, aliphatic out-of-plane bending), 798 (C-Br
recrystallizing from a mixture of chloroform/n-hexane bend), 737 and 648 (aromatic C-H out-of-plane, symmetric
(
1:1) (see Figure 1).
bending).
Synthesis of 1,2-bis(2-(3,6-dibromo-9H-carbazole-9-yl)
ethoxy)ethane (C-a1)
General Procedure-II for synthesis of bipod carbazole
derivatives
Synthesized
using
General
Procedure-I
with Brominated carbazoles (C-a1 or C-a2) (3.33 equivalent),
3
,6-dibromocarbazole (3 mmol, 0.970 g), 1,2-bis(2- PhB(OH) (13.33 equivalent) and Pd (dba) (1.0
2
2
3
chloroethoxy)ethane (1.5 mmol, 0.24 ml), TBAI (0.36 g) to equivalent) were placed in 100 ml flask. K CO (aq., 2M),
2
3
-1
give the oily solid product (0.585 g, 46.7%). FT-IR (γ cm ): toluene and two drops of Aliquot 336 were quickly
071 (Aromatic C-H stretch), 2956 and 2871 (symmetric and added. The mixture degassed with nitrogen was stirred
3
asymmetric aliphatic C-H stretch), 1624-1546 (carbazole at 80°C for 48 hours in a nitrogen atmosphere. The
ring stretch), 1471 (asymmetric aliphatic C-H bend), 1435 reaction was complete and allowed to cool to room
(
carbazole ring stretch), 1290 (symmetric aliphatic C-H temperature. It was then filtered in dichloromethane
bend), 1108 (C-O-C asymmetric bend), 1058 (N-C bend), (3 x 30 ml) and washed with water (200 ml). Organic
031 (C-O-C symmetric bend), 1017 (aliphatic C-H out-of- phase was obtained after separating the layers and
1
plane bending), 797 (C-Br bend), 750 and 648 (Aromatic drying over Na SO . The solution was evaporated and
2
4
C-H out-of-plane symmetric bending).
recrystallized from ethanol.
Br
Br
O
NBS, SiO2
2
DCM, 24 h
Cl
n
Cl
Synthesis of 1,2-bis(2-(3,6-diphenyl-9H-carbazole-9-yl)
ethoxy)ethane (C-1)
%50 NaOH, TBAI
78°C, 48 h
N
N
H
H
A
Br
B
Br
R
R
C-1 was obtained from 1,2-bis(2-(3,6-dibromo-9H-
carbazole-9-yl) ethoxy)ethane (C-a1) (0.2 mmol, 0.15 g),
PhB(OH) (0.8 mmol, 0.098 g) and Pd (dba) (0.06
N
N
2
2
3
OH
B
4
mmol, 0.055 g) and K CO (aq., 2M, 3 ml), toluene (6 ml)
R
OH
2
3
O
following the General Procedure-II. The yellow, slightly
oily solid product was achieved by recrystallization from
O
Pd2(dba)3 , 2M K2CO3 (aq.)
Toluene, H2O, 80°C, N2, 48 h
n
n
-1
ethanol (0.020 g, 13.5%). FT-IR (γ cm ): 3058 and 3024
aromatic C-H stretch), 2926 and 2871 (C-H, symmetric
and asymmetric stretch), 1599 (Aromatic C=C stretch),
470 (C-H, aliphatic, in-plane, asymmetric bend), 1449
N
N
C
(
Br
Br
R
R
1
C-a
C-1 : R = Ph, n=2
C-2 : R = Ph, n=3
C-3 : R = -naphthyl, n=3
C-4 : R = -naphthyl, n=3
C-a1 : n=2
C-a2, : n=3
(carbazole ring stretch), 1340 (aliphatic C-H bend,
in-plane, symmetric), 1135 (C-O-C asymmetric bend),
1
111 (aliphatic C-H, out-of-plane bending), 1067 (C-N
Figure 1ꢀSynthesis of the original bipod carbazole derivatives (C-1,
C-2, C-3, C-4)
bend), 1018 (C-O-C symmetric bend), 748 and 702

Çiçek et al.: Synthesis and optical characterization of bipod carbazole derivativesꢁ
ꢁ151
(
aromatic C-H, out-of-plane, symmetric bending). stretch, naphthalene), 1600 (carbazole C=C stretch),
1
H NMR (CDCl , δ, ppm): 3.475 (2H, s), 3.832 (2H, t), 1467 (aliphatic C-H bend, asymmetric), 1454 (carbazole
3
4
.429 (2H, t), 7.526 (1H, d), 8.107 (1H, m), 7.612 (1H, m), ring stretch), 1291 (aliphatic C-H bend, symmetric), 1120
7
.612 (1H, d), 7.406 (1H, s), 7,412 (1H, d), 7.390 (1H, s). (C-O-C asymmetric bend), 1075 (aliphatic C-H bend,
1
3
C NMR (CDCl , δ, ppm): 69.323, 70.527, 58.602, 130.514, out-of-plane), 1057 (C-N bend), 1030 (C-O-C symmetric
3
1
23.191-110.632, 143.323, 139.551, 128.380, 128.959, 129.081. bend), 801 and 780 (aromatic symmetric C-H bending on
Anal. Calc. for C H N O (MW=752.34): C, 86.14; H, 5.89; α-substituted naphthalene, out-of-plane), 757 and 698
5
4
44
2
2
1
N, 3.72. Found: C, 86.00; H, 5.81; N, 3.77%. LC-MS (m/z): (aromatic symmetric carbazole bend, out-of-plane). H
7
+
53.30 (M , CH CN, Error % = 0.128).
NMR (CDCl δ, ppm): 3.388 (4H, s), 3.498 (2H, t), 3.635 (2H, t),
3
3,
7
.262 (1H, d), 7.590 (1H, d), 7.608 (1H, d), 7.539 (1H, d),
7
.281 (1H, s), 8.060 (1H, m), 7.222-7.135 (2H, m), 7.467 (1H,
1
3
Synthesis of Bis[2-(2-(3,6-diphenyl-9H-carbazole-9-yl)
ethoxy)etyl]ether(C-2)
m), 7.498 (1H, m), 7.377 (1H, d), 7.940 (1H, d). C NMR
(CDCl , δ, ppm): 74.010-72.125, 61.406, 133.150, 125.332,
3
125.759, 141.253, 126.505, 125.926, 138.408, 132.807, 128.106,
C-2 was obtained from bis[2-(2-(3,6-dibromo-9H-carbazole- 127.854, 133.485, 128.185, 127.786. Anal. Calc. for C H N O
9
72
56
2
3
-yl)ethoxy)etyl]ether (C-a2) (0.2 mmol, 0.16 g), PhB(OH) (MW=996.43): C, 86.72; H, 5.66; N, 2.81. Found: C, 86.68;
2
+
(
0.8 mmol, 0.098 g) and Pd (dba) (0.06 mmol, 0.055 g) H, 5.60; N, 2.90. %. LC-MS (m/z): 996.43 (M , CH CN,
2
3
3
and K CO (aq., 2M, 3 ml), toluene (6 ml) following the Error % = 0.003).
2
3
General Procedure-II. The yellow-green, slightly oily solid
was recrystallized from ethanol (0.127 g, 80.3%). FT-IR
-1
(
γcm ):3055(aromaticC-Hstretch),2924and2855(aliphatic Synthesis of Bis[2-(2-(3,6-di(naphthalene-2-yl)-9H-
C-H, symmetric and asymmetric stretch), 1596 (aromatic carbazol-9-yl)ethoxy)ethyl]ether(C-4)
C=C stretch), 1470 (aliphatic C-H bend, asymmetric),
1
448 (carbazole ring stretch), 1343 (aliphatic C-H bend, C-4 was obtained from bis[2-(2-(3,6-dibromo-9H-carba-
symmetric), 1139 (C-O-C asymmetric bend), 1112 (aliphatic zole-9-yl)ethoxy)etyl]ether (C-a2) (0.06 mmol, 0.048 g),
C-H bend, out-of-plane), 1055 (C-N bend), 1018 (C-O-C 2-naphthylboronic acid (0.24 mmol, 0.041 g) and
symmetric bend), 740 and 701 (aromatic C-H bend, out-of- Pd (dba) (0.0018 mmol, 0.0016 g) were placed in a
2
3
1
plane, symmetric). H NMR (CDCl , δ, ppm): 3.472 (4H, s), 100 ml flask, then quickly K CO (aq., 2M, 9 ml), toluene
3
3
2
3
.810 (2H, t), 4.291 (2H, t), 7.619 (1H, d), 8.074 (1H, d), 8.089- (18 ml) following the General Procedure-II. The light-
8
.106 (1H, d), 8.040 (1H, d), 7.601 (1H, s), 7.401 (1H, s), brown, slightly oily solid was recrystallized from
13
-1
7
.417 (1H, d), 7.333 (1H, m). C NMR (CDCl , δ, ppm): 70.535, ethanol (0.048 g, 81.6%). FT-IR (γ cm ): 3054 and 3022
3
6
9.301, 70.901, 60.644, 131.885, 110.831, 123.434 143.323, (aromatic C-H stretch), 2923 and 2854 (symmetric and
23.945, 123.023, 139.521, 128.395, 128.974, 127.237. Anal. asymmetric aliphatic C-H stretch), 1624, 1569 and 1494
1
Calc. for C H N O (MW=796.37): C, 84.39; H, 6.07; N, 3.51. (aromatic C=C stretch, naphthalene), 1594 (carbazole
56
48
2
3
Found: C, 84.36; H, 6.01; N, 3.55%. LC-MS (m/z): 796.40 C=C stretch), 1467 (aliphatic C-H bend, asymmetric),
+
(
M , CH CN, Error % = 0.004).
1454 (cbz ring stretch), 1290 (C-H aliphatic, in-plane,
symmetric), 1131 (C-O-C asymmetric bend), 1076 (ali-
phatic C-H bend, out-of-plane), 1031 (C-O-C symmetric
stretch), 811 and 737 (aromatic symmetric C-H bend on
β-substituted naphthalene, out-of-plane), 748 and 699
3
Synthesis of Bis[2-(2-(3,6-di(naphthalene-1-yl)-9H-
carbazol-9-yl)ethoxy)etyl]ether(C-3)
(
aromatic symmetric C-H bend on carbazole benzene,
1
C-3 was obtained from bis[2-(2-(3,6-dibromo-9H-carbazole- out-of-plane,). H NMR (CDCl , δ, ppm): 3.287 (4H, s),
3
9
-yl)ethoxy)etyl]ether (C-a2) (0.04 mmol, 0.032 g), 3.725 (2H, t), 4.379 (2H, t), 7.218 (1H, d), 7.927 (1H, s),
naphthalene-1-boronic acid (0.16 mmol, 0.028 g) and 7.900 (1H, d), 8.122-8.059 (1H, d), 7.258 (1H, s), 7.514 (2H,
1
3
Pd (dba) (0.0012 mmol, 0.001 g) were placed in a 100 ml m), 7.279 (2H, s), 7.952 (1H, d), 7.361 (1H, d). C NMR
flask, then quickly K CO (aq., 2M, 6 ml), toluene (12 ml) (CDCl , δ, ppm): 70.548, 70.650, 125.332, 125.759, 61.434,
2
3
2
3
3
following the General Procedure-II. The light-brown, 133.757, 125.718, 126.099, 143.210, 126.381, 126.030,
slightly oily solid was recrystallized from ethanol (0.024 g, 138.398, 127.684, 133.510, 128.537, 132.675, 128.233. Anal.
-
1
6
1.3%). FT-IR (γ cm ): 3062 and 3026 (aromatic C-H Calc. for C H N O (MW=996.43): C, 86.72; H, 5.66; N,
72 56 2 3
stretch), 2923 and 2854 (aliphatic C-H stretch, asymmetric 2.81. Found: C, 86.65; H, 5.63; N, 2.85 %. LC-MS (m/z):
and symmetric), 1656, 1579 and 1496 (aromatic C=C 996.43 (M , CH CN, Error % = 0.003).
+
3

ꢁ
Çiçek et al.: Synthesis and optical characterization of bipod carbazole derivatives
152ꢁ
Results
possible ions (supplementary materials). The results
of microanalysis also support successful synthesis of
In this work 1,2-bis(2-(3,6-diphenyl-9H-carbazole-9-yl) compounds.
ethoxy)ethane (C-1), bis[2-(2-(3,6- diphenyl-9H-carbazole- In UV-vis spectra, the absorption bands were observed
-yl) ethoxy)etyl]ether (C-2), bis[2-(2-(3,6-di(naphthalene- in the range of 225-380 nm for all samples. This range is
-yl)-9H-carbazol-9-yl)ethoxy)etyl]ether (C-3) and suitable for our PL measurement using 349 nm laser.
bis[2-(2-(3,6-di(naphthalene-2-yl)-9H-carbazol-9-yl) The PL spectra are shown in Figure 2 together
9
1
ethoxy)ethyl]ether (C-4) were synthesized. The syntheses with reference sample containing only carbazole for
of these compounds were started by brominating the 3- comparison. The reference sample has several relatively
and 6- position of the carbazole ring. During this process, narrow peaks over the spectral range between 370 and
SiO was used as an efficient-reusable catalyst [42]. Then, 500 nm with the most intense peak situated at 420 nm.
2
two molar equivalents of bromo carbazole were led to react
In the work done by Zhang et al. [32], three
with dichloroether derivatives via S 2 reaction. The oily absorption peaks located at 294, 354 and 379 nm were
N
solid product was obtained by recrystallizing the mixture observed for salicylaldimine difluoroboron complex
of chloroform/n-hexane (1:1). Finally, the bromines were with tert-butyl group. They were attributed to carbazole,
*
replaced by phenyl boronic acid, α-naphthyl boronic acid π-π and intramolecular charge transfer (ICT) transitions
and β-naphthyl boronic acid moieties via the Suzuki- respectively. The emission peak of the synthesized
Miyaura Cross Coupling Reaction. The oily solid products compound in THF mixure present at 514 nm was ascribed
were re-crystallized from ethanol. The yields of C-1, C-2, to ICT emission. The peak positions of fluorescence
C-3 and C-4 bipod carbazole derivatives were obtained as emissions were blue and red-shifted to 506 and 522 nm
1
3.5, 80.3, 61.3 and 81.6%, respectively.
for crystal structure and ground powder respectively.
In FT-IR spectra, the N-H stretch peak of The optical properties of two 2,4-difluorenylquinoline
secondary amines which is only seen in carbazole derivatives with different lengths of alkyl chain at the
and 3,6-dibromocarbazole, disappeared due to the fluorene unit (one with methyl and other with octyl
reaction between 3,6-dibromocarbazole and 1,2-bis(2- chain) of donor-acceptor (D-A) type were reported
chloroethoxy)ethane. Therefore, the N-H stretch by Slodek et al [50]. They observed bright emission
peak was not observed in FT-IR spectra of C-a1, a2, in the blue spectral region at 406 nm, whereas the
1
, 2, 3, and 4. The C-Br stretch peak was observed in replacement of fluorine with carbazole unit resulted in
,6-dibromocarbazole, C-a1 and C-a2 but not in C-1, a bathochromic shift of peak wavelength with emission
, 3, and 4. These results indicate that no Br atoms bands at 425 and 530 nm.
attached on carbazole were left. Br atoms were replaced Due to stronger π-conjugation and efficient
3
2
by substitution of boron acid molecules via the Suzuki- intramolecular charge transfer from carbazole to aromatic
Miyaura Cross Coupling reaction. Symmetric and
asymmetric peaks of aliphatic C-H and C-O-C were
observed in C-a1, a2, 1, 2, 3 and 4, but not in carbazole
or 3,6-dibromocarbazole. This indicates the presence of
ether and aliphatic groups. As a result, the syntheses of
intermediate and final products were confirmed with
FT-IR data.
The 1H-NMR and 13C-NMR spectra data also
support successful synthesis of C-1, C-2, C-3 and C-4
1
(
supplementary materials). For example, in H-NMR
spectra of C-3 molecule, ether peaks labeled as 1, 2, and 3
were observed at δ 3.472-4.291 ppm and aromatic peaks at
1
3
δ 7.619-8.106 ppm (supplementary materials). In C-NMR
spectra of the same molecule, ether peaks were observed
at δ 60.644-70.901 ppm, and aromatic peaks at δ 110.831-
1
43.323 ppm (supplementary materials).
The molecular ion peaks of C-1, C-2, C-3, and C-4 were
obtained from LC-MS spectra taken in dichloromethane.
The spectra contain peaks of molecular ions and other Figure 2ꢂPL spectra for all samples at room temperature

Çiçek et al.: Synthesis and optical characterization of bipod carbazole derivativesꢁ
ꢁ153
compounds, the PL spectra of C-1, C-2, C-3 and C-4 depict of PL spectra, as observed. The change of integrated
completely different character compared to carbazole. As intensity within a temperature range of 20-300 K for C-3
first seen, all spectra were dominated with a broad peak at is approximately three times, while for C-4 it is about 2.3
about ~513, 523, 553, 565 nm for samples C-1, C-2, C-3 and times. This is probably due to the difference in stereo-
C-4, respectively. However, these peaks were decomposed electronic effect of compounds attached to the alpha
into two peaks using Gauss fitting as shown in and beta positions.
the inset.
Figure 5 shows the excitation power density depen-
Figures 3 and 4 show temperature dependent PL dent normalized integrated intensities for all samples. As
peak positions (the one at high energy side of spectrum) seen from the figure integrated intensity increases with
and normalized integrated intensities deduced from the excitation power density as expected. At high excitation
Gauss fitting to the experimental data. From figures, the density, a small degree of saturation is realized.
peak wavelengths and integrated intensities are appro-
ximately temperature independent for C-1 and C-2. This
is consistent with the spatial configuration of structures
C-1 and C-2, where the most stable formation is expected
at the anti-position of the carbazole and benzene rings.
Within the temperature range studied in PL measure-
ment, no changes are expected for both structures. On
the other hand, for the samples (C-3 and C-4), in which
the α-naphthyl and β-naphthyl are attached to carbazole,
the peak wavelengths and integrated intensities incre-
ase as the temperature increases. At low temperatures,
the rotation around the sigma bond is weak and prefers
to be at the most stable anti-position. As the tempera-
ture increases the rotation of the sigma bond is expected
to increase. A resonance occurs when the electrons of p
orbital of carbazole that do not participate in hybridiza-
tion and p orbital of naphthyl group come to the same
parallel plane. This provides a complete resonance on
the molecule that causes redshift in the peak wave- Figure 4ꢂThe normalized integrated intensity versus temperature for
length positions and increases in integrated intensities all samples
Figure 5ꢀThe normalized integrated intensity versus excitation
density for all samples
Figure 3ꢀTemperature dependent peak positions

ꢁ
Çiçek et al.: Synthesis and optical characterization of bipod carbazole derivatives
154ꢁ
Conclusions
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