A photophysical and spectroelectrochemical study on N-phenyl-carbazoles and their oxidized species

Article abstract of DOI:10.1016/j.jphotochem.2018.07.039

A series of N-phenyl-carbazole derivatives namely TCz (N-tolyl-carbazol), TCz-TCz (a 3,3′-linked dimer), and CzPh-CH₂-PhCz (a methylene-bridged N-phenyl-carbazole), have been synthesized and studied by means of absorption and fluorescence spect

Full text of DOI:10.1016/j.jphotochem.2018.07.039

Accepted Manuscript
Title: A PHOTOPHYSICAL AND
SPECTROELECTROCHEMICAL STUDY ON
N-PHENYL-CARBAZOLES AND THEIR OXIDIZED
SPECIES
Authors: Cristina Luj a´ n Ram ´ı rez, Mar ´ı a In e´ s Mangione, Sonia
Graciela Bertolotti, Ernesto Maximiliano Arbeloa, Alejandro
Rub e´ n Parise
PII:
S1010-6030(18)30990-0
DOI:
Reference:
https://doi.org/10.1016/j.jphotochem.2018.07.039
JPC 11405
To appear in:
Journal of Photochemistry and Photobiology A: Chemistry
Received date:
Revised date:
Accepted date:
10-7-2018
23-7-2018
25-7-2018
Please cite this article as: Ram ´ı rez CL, Mangione MI, Bertolotti SG, Arbeloa
EM, Parise AR, A PHOTOPHYSICAL AND SPECTROELECTROCHEMICAL
STUDY ON N-PHENYL-CARBAZOLES AND THEIR OXIDIZED SPECIES,
Journal of Photochemistry and amp; Photobiology, A: Chemistry (2018),
https://doi.org/10.1016/j.jphotochem.2018.07.039
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A PHOTOPHYSICAL AND SPECTROELECTROCHEMICAL
STUDY ON N-PHENYL-CARBAZOLES AND THEIR OXIDIZED
SPECIES
1
2
3
Cristina Luján Ramírez, María Inés Mangione, Sonia Graciela Bertolotti,
3
1
Ernesto Maximiliano Arbeloa, * Alejandro Rubén Parise *
1
Departamento de Química, Facultad de Ciencias Exactas y Naturales, Universidad Nacional de
Mar del Plata. Funes 3350, Nivel II, Mar del Plata, Buenos Aires, Argentina. QUIAMM – INBIOTEC
–
CONICET
2
Instituto de Química Rosario, Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad
Nacional de Rosario-CONICET, Suipacha 531, S2002LRK Rosario, Argentina
3
Departamento de Quimica, FCEFQN, Universidad Nacional de Rio Cuarto, Ruta 36 Km 601, Río
Cuarto, Córdoba, Argentina. Instituto de Tecnologías Energéticas y Materiales Avanzados (UNRC-
CONICET)
Corresponding authors:
*
Ernesto M. Arbeloa
e-mail: earbeloa@exa.unrc.edu.ar
Alejandro R. Parise
e-mail: aparise@mdp.edu.ar
*

Graphical abstract
Highlights


Ground and singlet excited states of N-phenyl-carbazoles were characterized.
Properties of dicarbazoles are susceptible to electronic coupling between single
units.

The oxidized species were analyzed by cyclic voltammetry and
spectroelectrochemistry.


An electrochromic polymer was deposited by electropolymerization.
The studied compounds might be suitable as fluorescent sensors and hole
transporters.
Abstract
A series of N-phenyl-carbazole derivatives namely TCz (N-tolyl-carbazol), TCz-TCz
a 3,3´-linked dimer), and CzPh-CH -PhCz (a methylene-bridged N-phenyl-carbazole),
(
2
have been synthesized and studied by means of absorption and fluorescence spectra,
DFT calculations, cyclic voltammetry and spectroelectrochemistry. It is concluded that the
2
methylene bridge in CzPh-CH -PhCz isolates the two TCz units, whereas TCz-TCz allows
extending the electronic coupling along both carbazoles. Moreover, the phosphorescence

spectrum of TCz-TCz showed a high energy triplet state (2.61 eV). It was observed that
oxidation of CzPh-CH -PhCz generates an electrochromic polymer containing TCz-TCz
2
dimer units separated by methylene bridges. Oxidized TCz-TCz subunit was analyzed by
EPR spectroscopy, and found to be a Class III mixed valence ion in Robin and Day
classification. All results suggest that these molecules might be suitable as selective
probes in fluorescence sensing or as host materials in electroluminescent devices.
Keywords: Carbazole – Photophysics – Excited states – Mixed valence –
Electroluminescent materials
1
. Introduction
The study on the photophysical and photochemical properties of carbazole and
carbazole derivatives has attracted the attention of many researchers in the last decades
due to the implication of these molecules in photoinduced energy- and electron-transfer
reactions. After radiation absorption, the photoprocesses that occur from the excited states
of carbazole can find applications in areas of increasing current relevance such as
sensitizing, sensing chemistry, electrochemistry and optical materials among others.[1-6]
Since their relatively simple synthesis procedure and versatility in functionalization,
carbazoles are excellent fragments for the design of hole transporters materials because
they combine chemical robustness with electronically tunable properties.[7, 8] Nowadays,
the use of carbazoles in thermally activated delayed fluorescence (TADF) processes for
development of the third generation of OLED technology is a featured topic in the
optoelectronic devices field.[9]
Early reports deal with the synthesis and photophysical characterization of various
N- and C-substituted carbazoles.[10-13] The luminescent properties of these compounds
were highlighted from the high emission quantum yields obtained. Among the most
remarkable studies, the authors assessed the heavy atom effects on the singlet-to-triplet
intersystem crossing process from a series of halide-derivatives.[11, 12] Such results were
of practical interest in organic synthesis because the triplet excited states of carbazoles
promote the heterolytic cleavage of carbon-halide bonds, which leads to reactive
fragments capable of forming new C-C bonds with adequate substrates. The synthesis

procedure and photophysical and electrochemical characterization of new extended -
systems based on carbazole-chromophore conjugates continue to be subject of constant
research, because of their application in optical and functional materials.[14, 15]
Due to the intrinsic fluorescent capacity of carbazoles, several carbazole derivatives
have been investigated for application as selective sensors for metal ions, anions and
compounds of biological interest in homogeneous solution.[16-18] Recently, studies on the
photophysics of several dye-carbazole couples demonstrated the relevance of these
chromophoric composites for optical and sensitizing processes.[19-21] For example, a
series of dye-carbazole derivatives has been recently synthesized to develop new
photoinitiating systems for free radical and cationic polymerizations, taking advantage of
their light absorption properties.[22-24] In order to obtain fluorescent nanoparticles for
lysosomal bioimaging in living cells, the synthesis and spectroscopic characterization of
BODIPY-carbazole dye were also reported.[25]
It is also known that the particular photophysics of carbazole-containing polymers is
responsible for its good electron donor capacity and outstanding photoelectrical
properties.[26-28] Among carbazole derivatives N-phenyl-carbazoles are of particular
interest due to display high thermal stabilities and tunable photoluminescence, which
directly influences their optical and electric properties.[29, 30] By attaching proper
substituents the dihedral angle between N-phenyl ring and carbazole moiety can be
modified, so affecting the grade of electron delocalization and the energy of the electronic
excited states. Furthermore, the pendant N-phenyl groups in the carbazole units of
copolymers reduce the rigidity and enhance the flexibility along polymer main chains, thus
resulting in good polymer solubility. Accordingly, N-phenyl-carbazoles are very interesting
building blocks to design soluble and thermally stable polymer with light-emitting
properties.[31, 32] Recently, new polycarbazole films based on N-phenyl derivatives were
electrochemically synthesized, which showed good electrochromic properties.[33]
Therefore, a knowledge of the photophysical and electrochemical behavior of carbazole-
based compounds is necessary prior to select the suitable derivatives for the synthesis of
new photosensitive polymers, optical devices or selective photosensors.
In this work, we describe the synthesis procedure and the photophysical,
electrochemical and spectroelectrochemical characterization of three N-phenyl carbazole
derivatives (Scheme 1), whose properties make them promising candidates as fluorescent
probes and charge carriers. Complementary electron paramagnetic resonance
spectroscopy (EPR) and DFT/TD-DFT molecular calculations were also carried out to help
the interpretation of the experimental data.

Scheme 1. Molecular structures of the N-(4-methyl-phenyl)-carbazole derivatives studied in this paper: 1)
2
TCz, 2) TCz-TCz, 3) CzPh-CH -PhCz, and 4) 3,6-ICz. (see the corresponding names in the text).
2
2
. Materials and methods
.1. Synthesis and characterization of carbazoles
All commercially available reagents used throughout this work were purchased from
Aldrich and used without further purification unless otherwise stated. When necessary,
reagents and solvents were purified according to standard procedures. The structures of
the compounds were assigned by means of nuclear magnetic resonance (NMR) and mass
1
13
spectrometry. The H and CNMR spectra were recorded on Bruker Avance-300
spectrometer with TMS as the internal standard and deuterated chloroform as solvent
(Abbreviations: s = singlet, d = doublet, t = triplet, and m = multiplet, expected but not
resolved). Mass spectra were performed by direct injection on a Shimadzu GCMS-
QP2100ULTRA-AOC20i CGL-MS spectrometer. The atom numbering for NMR
characterization is provided in Supplementary Material Information (SP01 and SP02 files).
Compound 1 [9-(4-methyl-phenyl)carbazole]: In a glass tube, 10 mL of dry
toluene were mixed with 4-iodotoluene (5.25 g, 24 mmol), carbazole (4.0 g, 24 mmol), CuI
(0.040 g, 0.2 mmol), 1,10-phenanthroline (0.041 g, 0.2 mmol) and potassium tert-butoxide
(3.5 g, 31 mmol). The container was sealed and heated to 120 °C for 24 h under argon
atmosphere with vigorous stirring. Then, 10 mL of toluene was added, the mixture was
filtered and the solid was washed with three aliquots of 10 mL of toluene. Combined
organic washings were concentrated under reduced pressure. Crude solid product was

purified by column chromatography (silica gel, hexane/ethyl acetate 9:1). Yield: 85%. m/z=
1
2
57.12. HNMR (300 MHz, CDCl
3
): δ 2.49 (s, 3H, CH ), 7.25 – 7.32 (m, 2H, H-3, H-6), 7.35
3
13
–
7.48 (m, 8H, H-1, H-8, H-2, H-7, H-2’, H-3’), 8.15 (d, 2H, J 7.7 Hz, H-4, H-5). CNMR
): δ 21.25 (CH ), 109.78 (C-1, C-8), 119.71 (C-3, C-6), 120.25 (C-4, C-5),
(75 MHz, CDCl
3
3
1
1
23.24 (Cq-C-4, Cq-C5), 125.84 (C-2, C-7), 127.01 (C-3’), 130.47 (C-2’), 135.01 (C-4’),
37.37 (C-1’), 141.07 (Cq-C-1, Cq-C-8).
Compound 2 [9, 9'-bis(4-methyl-phenyl)-9H, 9'H-3, 3'-bicarbazole]: 9-(4-methyl-
phenyl)carbazole (compound 1; 0.27 g, 1.0 mmol) was dissolved in dichloromethane (10
mL). Anhydrous FeCl (0.650 g, 4.0 mmol) was added and the resulting mixture turned
3
dark green color. The reaction mixture was stirred for 6 h at room temperature. Thin layer
chromatography (TLC) was used to monitor the reaction. After the reaction was
completed, the solution mixture was poured in methanol. A pale-yellow precipitate was
obtained, filtered and washed with methanol. The obtained pale-yellow crystals were dried
1
and crystallized from tetrahydrofuran. Yield: 98%. m/z=512.2. HNMR (300 MHz, CDCl
3
): δ
2
2
2
1
1
1
.51 (s, 6H, CH
3
), 7.27 – 7.34 (m, 2H, H-2), 7.40 – 7.45 (m, 8H, H-2’, H-1, H-H-3), 7.48 (d,
H, J 8.5 Hz, H-8), 7.50 (d, 4H, J 8.5 Hz, H-3’), 7.77 (dd, 2H, J 8.5, J 1.6 Hz, H-7), 8.24 (d,
13
H, J 7.7 Hz, H-4), 8.45 (d, 2H, J 1.6 Hz, H-5). CNMR (75 MHz, CDCl
3
): δ 21.27 (CH ),
3
09.91 (C-1), 110.03 (C-8), 118.86 (C-5), 119.80 (C-2), 120.39 (C-4), 123.48 (Cq-C-1),
23.86 (C-6), 125.78 (C-7), 125.94 (C-3), 126.95 (C-3’), 130.51 (C-2’), 134.26 (Cq-C-5),
35.09 (C-4’), 137.37 (C-1’), 140.20 (Cq-C-8), 141.53 (Cq-C-4).
Compound 3 [bis(4-(9H-carbazol-9-yl)phenyl)methane]: In a hermetically sealed
glass container, 15 mL of dry toluene were mixed with carbazole (4.0 g, 24 mmol), 4,4´–
diamino-diphenyl-methane (2.4 g, 12 mmol), CuI (0.080 g, 0.4 mmol), 1,10- phenanthroline
(0.081 g, 4.0 mmol) and potassium tert-butoxide (4.0 g, 36 mmol). The mixture was heated
at 120 °C for 24 h with stirring. Then, 10 mL of toluene was added, the mixture was filtered
and the solids were washed with three aliquots of 10 mL of toluene. Combined organic
washings were concentrated under reduced pressure. The obtained crude solid was
purified by column chromatography (silica gel, hexane/ethyl acetate 5:1) Yield: 75%.
1
m/z=498.2. HNMR (300 MHz, CDCl
3
): δ 4.24 (s, 2H, CH ), 8.16 (ddd, 4H, J 8.0 J 1.9 Hz,
2
H-3, H-6), 7.41 (dd, 4H, J 8.2 J 1.0 Hz, H-2, H-7), 7.45 (d, 4H, J 8.2 Hz, H-1, H-8), 7.52 (d,
1
3
4
1
H, J 8.5 Hz, H-2’), 7.56 (d, 4H, J 8.9 Hz, H-3’). CNMR (75 MHz, CDCl
3
): δ 41.34 (CH
2
),
09.81 (C-1, C-8), 119.89 (C-3, C-6), 120.32 (C-4, C-5), 123.35 (Cq-C-4, Cq-C-5), 125.91

(C-2, C-7), 127.29 (C-3’), 130.41 (C-2’), 135.96 (C-4’), 139.97 (C-1’), 140.94 (Cq-C-1, Cq-
C-8).
Compound 4 [9-(4-methyl-phenyl)-3,6-diiodo-carbazole]: A mixture of 9-(4-
methyl-phenyl)carbazole (5.0 g, 20 mmol), KI (7.3 g, 44 mmol), and KIO (4.7 g, 22 mmol)
3
in glacial acetic acid (200 mL) was heated at 110 °C for 6 h. The mixture was cooled and
the formed precipitate was collected by suction filtration. The crude product was
thoroughly washed with water and the solid was dissolved in CH
with aqueous NaHCO , dried with anhydrous Na SO and filtered. After solvent
evaporation, the pure compound was obtained by recrystallization from a mixture of
CH Cl /MeOH as a white solid. Yield: 95%. m/z=509.
2
Cl (200 mL) and washed
2
3
2
4
2
2
2
.2. Spectroscopic measurements
Absorption spectra were recorded on a Hewlett Packard 8453E diode array
spectrophotometer. Fluorescence measurements were carried out with a Horiba Jobin
®
Yvon FluoroMax -4P spectrofluorometer. The samples were analyzed on dichloromethane
solutions and a 1-cm-pathlength quartz cuvette was used in all spectroscopic assays. All
samples were adjusted to absorbance <0.1 at excitation wavelength (330 nm) for
recording the fluorescence spectra. Solutions of quinine sulphate in H
2
SO
0.5 mol L-1
4
were used as a recommended standard for fluorescence quantum yields
determination.[34] The absorbances of standard and sample were matched at the same
excitation wavelength, and were ≤0.05. Quantum yield was calculated according to
Equation 1:[34]
i
s
2
i
2
s
F A n
i
F
s
F
Φ =
Φ
(Eq. 1)
s
i
F A n
i
F
s
F
Φ
Φ
where
and
are the fluorescence quantum yield of the sample and that of the
i
s
standard, respectively. F and F are the integrated intensities (areas) of sample and
standard fluorescence spectra, respectively; A is the absorbed light at the excitation
wavelength; n
i
and n are the refractive index of the sample and reference solution,
s
respectively. Both the sample and the standard where excited at the same wavelength,
avoiding the introduction of an uncertainty in the relative photon flux. To minimize errors,

we use the same sample cell and the same absorbance at the excitation wavelength for
sample and reference.
Phosphorescence experiments were performed in the aforementioned FluoroMax®-
4
P spectrofluorometer, equipped with a phosphorimeter. A xenon flash lamp was used as
irradiation source and the emitted phosphorescence was measured using an R928P
photon-counting detector. Ethanolic solutions of the samples were analyzed at 77K.
The UV-Vis-NIR spectra for radical cation species were taken using a Shimadzu PC
3
101 spectrometer. The EPR spectra were measured in a Bruker EPR-ELEXSYS E500,
and simulated trace was calculated with Winsim 2002. Spectra of desired species were
checked spectrophotometrically before EPR measurements and the solutions were
degassed and sealed into capillary tubes.
2
.3. Electrochemical characterization
All electrochemical experiments were recorded with a TEQ-3 potentiostat.
Electrolysis and cyclic voltammetries were performed in a conventional three-electrodes
electrochemical cell. Acetonitrile (HPLC grade) was used as electrolysis solvent and
-1
TBAPF 0.1 mol L as supporting electrolyte after the crystallization from hot ethanol. The
6
working electrode was either indium-doped tin oxide covered glasses (ITO glasses,
VisionTeK Systems, Ltd., UK) or a 0.05 mm diameter platinum disc (99.99% purity). A
plate of pure gold was used as counterelectrode, and an Ag 99% purity wire was used as
pseudoreference electrode. The platinum electrode was polished with 1% alumina powder
in water over a piece of cloth, cleaned in an ultrasonic bath with absolute ethanol and dried
+
in air. All redox potentials were standardized using ferrocene/ferrocenium couple in
acetonitrile and referred to NHE.[35]
Bulk electrolysis was done in home-made cell composed by two small separate
compartments built with pipette tips. Two pieces of graphite felt were used as working and
counterelectrodes, and a silver wire as pseudoreference electrode.
The electropolymerization was performed on ITO covered glasses of 1 cm wide
-1
immersed in a 0.01 mol L sample solution, in electrolysis solvent and TBAPF . A constant
6
potential of 2000 mV was applied for 15 min and then reduced to 0 mV until the current
dropped to less than 1% of the initial value. The electrode was washed several times with
acetonitrile. After electropolymerization, the ITO glass was placed in a 3-mL glass cuvette

with acetonitrile and TBAPF
Teflon®) holder inside with Pt and Ag wires to be used as counter- and reference
electrodes, respectively.
6
0.1 mol L-1
The cuvette contained a polytetrafluoro-ethylene
.
(
Spectroelectrochemistry experiments were performed in solution with a three-
electrodes quartz thin layer cell using a graphite felt as counterelectrode, platinum woven
wire as working electrode (70 μm wires), and a silver pseudoreference electrode.
Absorption spectra were measured in the aforementioned Shimadzu UV-3101PC
spectrophotometer.
2
.4. Computational Methods
Density functional theory (DFT) calculations with the Coulomb attenuated CAM-
B3LYP exchange-correlation functional and a split valence 6-31G+* basis set were
performed to obtain the optimized ground state geometry.[36] SCRF model IEFPCM was
used for simulating the solvation effects.[37-40] Vibrational frequency calculations were
carried out to characterize the stationary points and no imaginary frequencies were found.
Excited state energies and optimized geometries were calculated with linear response
time-dependent density functional theory (TD-DFT). All calculations were performed with
Gaussian 09,[41] and Gabedit[42] was used to visualize molecular orbitals (MOs). The
VMD 1.8.9 program was used for graphics rendering.[43] Supplementary material SP03
shows output coordinates of DFT calculations.
3
3
. Results and discussion
.1. Synthesis of carbazoles and photophysical properties
The molecular structures of the N-(4-methyl-phenyl) carbazole derivatives
synthesized are depicted in Scheme 1. In order to highlight their distinctive structural
features, from now on the molecules will be renamed as follows: 1) TCz (N-tolyl-carbazol);
2
) TCz-TCz (3,3´-dimer); 3) CzPh-CH -PhCz (methylene-bridged N-phenyl-carbazole);
2
and 4) 3,6-ICz (3,6-iodide-carbazole). TCz-TCz was synthesized according to the
procedure described by Zhang et al. for analog derivatives,[44] yielding a very high
percentage of desired product (at around 100%). On the other hand, reported synthetic
2
pathways for TCz and CzPh-CH -PhCz[45, 46] were modified in order to apply milder
reaction conditions that improve yields. This optimization was based on the work of Kelkar

et al.[47] who developed a single-step catalytic synthesis of arylamines by using chelating
ligands, which enhanced the product yields significantly. In Scheme 2 are depicted the
synthesis of CzPh-CH -PhCz performed with a combination of 1,10-phenantroline (Phen)
2
and CuI as ligand/catalyst complex, in the presence of potassium tert-butoxide base (K+t-
–
but ). A yield at around 75% was obtained, a value over 3-fold greater than the 23%
previously reported by He et al.[46]
2
Scheme 2. Optimized procedure for the synthesis of CzPh-CH -PhCz (see Materials and methods section
for details)
The ground and singlet excited states of synthesized carbazole derivatives were
characterized in dichloromethane solutions by means of absorption and fluorescence
spectra (Figure 1). For the sake of comparison, some spectra were also recorded in
absolute ethanol. In Table 1 are summarized the photophysical parameters obtained along
with reported data for some related compounds.
Figure 1. Absorption (left, ordinates as shown) and fluorescence (right, ordinates normalized) spectra of the
compounds TCz, (black), TCz-TCz (red) and CzPh-CH
2
-PhCz (blue) in CH
2
Cl solution. The emission
2
spectra were recorded by exciting the samples at 330 nm.
Figure 1 shows that the studied compounds registered absorption in the UV region
with two main bands at around 290-300 and 330-350 nm, typical of carbazole moiety.[10]
In the case of TCz and CzPh-CH -PhCz almost identical absorption and fluorescence
2

spectra were recorded, and the data obtained for CzPh-CH -PhCz are in agreement with
2
those previously reported.[46] Also, the UV absorption spectrum of TCz-TCz in Figure 1
resembles that of the N-phenyl-carbazole dimer linked at 3, 3´positions, recently reported
by Tang et al.[30] As it can be seen on Table 1, only slight differences were observed in
the spectra recorded in ethanol with respect to those measured in CH
2
Cl . In spite of the
2
electron lone pairs on the nitrogen atoms, these results suggest that no specific
interactions (such as hydrogen bonds) are occurring between carbazoles and the protic
solvent. Similar results were reported by other authors with several N-substituted
carbazoles in polar and non-polar solvents (see Table 1 for some examples).[10, 48]
Table 1. Summary of spectroscopic properties of carbazoles derivatives in CH
ethanol are denoted with “‡”).
2
Cl
2
solution (some data in
λ
abs / nm
λ
em / nm
Δν / cm-1
354
Φ
F
(a)
Compound
Cz(b)
1
2
292, 334
338, 354
0.37
2
2
2
96, 346
94, 344
351, 365
350, 363
346, 359
347, 360
345, 359
348, 363
349, 363
350, 365
412
498
510
593
513
504
586
754
0.26
0.32
0.28
0.31
MeCz(b)
‡
‡
‡
‡
94, 340(
b)
(b)
‡(b)
‡(c)
(b)
‡(b)
‡(b)
3
PhCz
292, 340
92, 326, 339
293, 329, 342
‡
(c)
2
4
5
TCz
0.34
0.31
0.21
2
2
93, 329, 342
CzPh-CH
2
-PhCz
93, 328, 341(
d)
(d)
(d)
3
3
358
04, 342, 356
03, 341, 355
390, 407
385, 403
414
2449
2195
3543
0.12
-
6
7
TCz-TCz
‡
‡
EtCz-EtCz(e)
8
9
Biphenyl(f)
TMB(g)
248
310
349
305, 315
401
7536
7320
3653
0.18
0.13
0.73
1
0 TPB(h)
400
-
1
a) Relative to quinine sulphate in H
2
SO 0.5 mol L . Estimated error 10%.
4
b) Non-substituted carbazole (Cz), N-methyl-carbazole (MeCz), and N-phenyl carbazole (PhCz), Ref. [10]
c) Estimated from spectra of PhCz, Ref. [48]
d) Ref. [46]
e) Dimer of N-ethyl carbazole linked at 3, 3´positions in toluene, Ref. [49]
f) Ref. [50]
g) N,N,N′,N′-Tetramethyl-benzidine, Ref. [51]
h) N,N,N',N'-Tetraphenyl-benzidine, Ref. [52]

A close examination on Table 1 reveals that the spectroscopic features of
carbazoles seem to be independent on the substitution at the N position. This becomes
evident if the entries 2-5 are compared to each other (idem by comparing the dicarbazoles
6
-7 to each other). Such results can be explained by analyzing the MOs involved in the
electronic transitions that give rise to the absorption and emission spectra. Figure 2
depicts the optimized geometries and the highest occupied molecular orbitals (HOMOs)
corresponding to the ground and singlet excited state of TCz. It can be seen that both
HOMOs are localized on the carbazole planar rings, with the N-phenyl moiety twisted out
of the planarity and electronically uncoupled with the rest of the molecule. Therefore, such
twisted configuration is responsible for the spectral properties being insensitive to the
presence of either an alkyl- or phenyl- substituent at N position.
Figure 2. Optimized geometries and HOMOs for ground a) and singlet excited state b) of TCz.
Furthermore, although the twisted configuration of the N-phenyl moiety is also
present in both carbazole fragments of CzPh-CH -PhCz and TCz-TCz (Figure 3), the
2
spectroscopic behavior is very different when the linkage is on the planar rings of
carbazole structure. For TCz-TCz, average red shifts of 13 nm in absorption and 43 nm in
fluorescence bands with respect to those of TCz (and CzPh-CH -PhCz) is a clear sign of
2
increased conjugation. From Table 1, similar red shifts can be calculated (12 nm in
absorption and 49 nm in fluorescence bands) by analyzing the reported results for EtCz-
EtCz,[49] with respect to single MeCz[10] in non-polar solvents. Differences in conjugation
between CzPh-CH -PhCz and TCz-TCz are apparent in Figure 3, where HOMOs are
2
compared for both molecules. Note that localization of the HOMO in the ground state of
both dicarbazoles is on their planar -system (see Figure 3a-b), although conjugation only
extends when fragments are bound at 3,3’ position (TCz-TCz) and not when the linkage is
by methylene-bridged N-phenyl substituents (CzPh-CH -PhCz). Singlet excited states
2

follow the same behavior. Moreover, although free rotation around methylene bridge is
possible for CzPh-CH -PhCz, we have not found any orientation that promotes (through
2
space) an extension of the delocalized -system between both phenyl (close) or planar
rings (far) by orbital coupling. This observation suggests that not only N-phenyl- twisting
but also the methylene bridge disrupt any molecular orbital coupling between both TCz
fragments and therefore, they behave as two isolated chromophores. For these reasons,
the spectral features of CzPh-CH -PhCz match those of single TCz.
2
Figure 3. Optimized geometries and HOMOs for: TCz-TCz in the ground a) and singlet excited state b); and
CzPh-CH -PhCz in the ground c) and singlet excited state d).
2
Stokes shifts (energy gap between the longest wavelength absorption band and the
shortest emission one, Δν) are also shown in Table 1. It is clear that dicarbazoles bound at
3
,3’ position (entries 6-7) experience larger Stokes shifts than the others (entries 1-5),
diagnostic of difference in equilibrium geometry between ground and singlet excited states.
Optimized geometries for both states in TCz-TCz and CzPh-CH -PhCz are also shown in
2
Figure 3. Dihedral angle in TCz-TCz involving the 3,3´ bond shifts from 40 degrees in the
ground state to 12 degrees in the excited state, imposing near-coplanarity between the
adjacent carbazoles. This geometric rearrangement gives rise to the larger Stokes shift of
TCz-TCz and EtCz-EtCz compared to the emission from single carbazole rings.

Last column in Table 1 shows the fluorescence quantum yields (Φ
and some related compounds. As it can be seen, the data tend to two clearly different Φ
values. Firstly, Φ values at around 0.30 were obtained for TCz and CzPh-CH -PhCz and
agree with those reported for compounds with only one carbazole fragment (see entries 1-
). As described above, the two carbazoles of CzPh-CH -PhCz are electronically
uncoupled and, therefore, its Φ is analogous to those of single carbazole compounds. On
the other hand, a lower Φ value (less than half of the previous ones) was obtained for
F
) of analyzed
F
F
2
5
2
F
F
TCz-TCz. A close examination of Figure 3 reveals that the HOMOs in TCz-TCz expand
over a portion of the molecule that resembles a biphenyl-like or even a benzidine-like
structure. Table 1 shows that the Φ values for TCz-TCz, biphenyl and N,N,N',N'-
F
tetramethyl-benzidine are very similar, which suggests that the extra molecular rigidity
promoted by the -system extended favors the radiationless deactivation pathways. Note
the contrast with N,N,N',N'-tetraphenyl-benzidine (Table 1), which shows that fluorescence
deactivation is the preferred way when free-rotating arylamines are part of the biphenyl-
like skeleton. Therefore, the decreasing in Φ of TCz-TCz compared with electronically-
F
single carbazoles might be ascribed to an increase in the intersystem crossing quantum
yield, and not just to internal energy conversion from the singlet excited state to
surrounding solvent. This possible trend to triplet states formation is a relevant and
suitable characteristic for the application of this type of compounds as phosphorescent-
sensitizers in electroluminescence. To obtain some insights about this, phosphorescence
spectrum of TCz-TCz in solvent glass at 77K was recorded by exciting the sample at 330
nm (Figure 4). From the triplet emission maximum (476 nm) a S
0
-T energy gap of 2.61 eV
1
can be calculated for TCz-TCz, which is comparable to those reported for 3,3´-linked
dicarbazoles,[49, 53] and is near the limit value for a suitable host in blue
electroluminescent materials. Finally, although smaller than arylamines, the values of Φ
F
obtained for these carbazoles make them still appropriate to develop selective probes in
fluorescence sensing.

Figure 4. Normalized emission spectra of TCz-TCz in ethanol: fluorescence (black) in solution at
98K, and phosphorescence (red) in solvent glass at 77K.
2
3
.2. Electrochemical and spectroelectrochemical characterization
Figure 5 shows the absorption spectra of TCz-TCz recorded
spectroelectrochemically. The cyclic voltammetry of TCz-TCz (inset in Figure 5) showed
two reversible waves at 1280 y 1575 mV (vs. NHE) corresponding to the oxidation of the
nitrogen atoms in each carbazole fragment. At increasing potential, two simultaneous
absorption bands (one at 417 nm and a complex broad at 917 nm) are observed, which
are associated to the first oxidation potential. The near-infrared absorption band (917 nm)
can be ascribed to a mixed valence charge transfer, so the first monoxidized specie, TCz-
●+
TCz , would be a mixed valence ion.
Figure 5. Absorption spectra of TCz-TCz in Cl
2
CH obtained by spectroelectrochemistry from 0 to 1800 mV
2
-
1
vs. NHE. Inset: cyclic voltammetry in Cl
2
CH
2
with TBAPF 0.1 mol L .
6
In order to understand the electronic density distribution of this radical cation (either
localized or delocalized in both carbazole fragments), we performed the ESR spectrum of ex-situ

●+
electrogenerated TCz-TCz . The correlation between the theoretical simulated spectrum and the
experiment was 99.8% (Figure 6). Table 2 shows the hyperfine coupling constants fitted,
considering all nitrogen and hydrogen atoms. It is remarkable that both nitrogen atoms have the
same hyperfine coupling constant, a clear indication of a spin delocalized over the two redox
centers on the ESR time scale. This reinforces the mixed-valence character of the radical ion TCz-
●+
TCz , and strongly suggests a Robin and Day’s Class III (delocalized) classification.[54, 55]
Figure 6. Black: high resolution EPR spectrum (at 298 K, width = 50 Gauss) of TCz-TCz●+ in Cl
CH
0.1 mol L . Red: simulated spectrum with coupling
constants fitted using WINSIM 2002.
2
2
-
1
obtained by oxidation in an electrolytic cell with TBAPF
6
●
+
Table 2. Coupling constants found by simulation of ESR spectrum of TCz-TCz .
Atom
2N
2H
2H
4H
6H
Coupling constant/Gauss 8.77 3.06 2.90 0.95 0.90
●+
The spin density isosurface of TCz-TCz is showed in Figure 7. It can be inferred from the
spin distribution that the positive charge lies mostly on the two nitrogen and on the two sets of two
hydrogen atoms each, displaying a symmetric pattern on the biphenyl part of the molecule (a
delocalized hole), in agreement with the ESR experiment.

●+
Figure 7. CAM-B3LYP unpaired spin density (0.004 a.u.) obtained for Tcz-Tcz .
As the oxidizing potential increased another absorption band arose at 743 nm, whereas a
decrease in the NIR absorption was observed (see Figure 5). This resembles the spectrum
●+
measured for oxidized 3,6-ICz (Figure 8, discussion below) (see Figure S1 in Supplementary
material), in which there is no intervalence band. This fact is associated to the complete oxidation
2+
of both carbazole fragments to form the dication TCz-TCz . A similar behavior was observed in the
double oxidation of tetratolyl-benzidine, having two electronically coupled triarylamine units as
electroactive fragments.[56, 57]
On the other hand, CzPh-CH -PhCz showed a different electrochemistry. A complex
2
process was observed in the first voltammogram ( Figure 8a), with an first oxidation wave at 1510
mV and reduction waves around 1250 and 1450 mV. The different height and shape of the current
peaks suggest that a coupled chemical process takes place, in which the oxidized species
participates. In the successive cycles, two new reversible waves were observed at around 1300-
1
450 mV and 1500-1800 mV. The new shape of the voltammogram was typical of that registered
when a species is adsorbed and accumulated on the electrode. In order to verify this assignment,
the Pt electrode was rinsed with clean solvent to remove the soluble CzPh-CH -PhCz and
2
immersed in a fresh electrolysis solution. The voltammogram of this sample showed the
disappearance of the original waves at 1600 mV and the permanence of the recently formed peaks
at 1110 (cat.) and 1621 (an.) mV, and 1450 (cat.) and 1917 (an.) mV (Figure 9b Figure 8b).
-
1
2
Figure 8. a) Cyclic voltammetry of CzPh-CH -PhCz (0.01 mol L ) in electrolysis solution. Scan rate: 25 mV
-
1
s . b) Cyclic voltammetry of electrodeposited film on ITO glass in electrolysis solution (free of CzPh-CH
PhCz).
2
-
In order to obtain more insights about the adsorbed species, we performed a
spectroelectrochemical experiment on the film electrodeposited by oxidation using ITO as working
electrode. The absorption spectrum in Figure 9 shows that two successive species arise as the

film oxidizes with the applied potential, from 0 to 2000 mV. The first one with absorption band
centered at 432 and another with a broad band at around 1400 nm, the latter being ascribed to an
intervalence compound similar to TCz-TCz described above (bands at 417 y 917 nm in Figure 5).
Figure 9. Absorption spectra obtained by spectroelectrochemistry of electropolimerized film deposited on
ITO glass, at applied potentials from 0 to 1800 mV.
This electrochemical behavior, along with the formation of a NIR absorbing species
resembles that of methylene-bridged phenylamines previously reported by our group,[58] in which
phenylamine moieties form (by oxidative coupling) a benzidine fragment. It was observed that the
film did not remained adsorbed on the ITO surface beyond 9 potential step cycles spanning 1000
seconds from an all-reduced to an all-oxidized state ( Figure 10). This behavior is contrary to that
of methylene-bridged phenylamine polymer,[58] which showed to be highly insoluble and stable.
The formation of this polymer can be understood by comparison with the electrochemistry of both
TCz and 3,6-ICz in acetonitrile solution.
Figure 10. Absorbance of the electropolymerized film at 420 nm (red), 790 nm (black) and 900 nm (blue),
from 0 to 2000 mV during 1000 seconds.

TCz has a complex behavior showing an irreversible oxidation wave at 1500 mV and a
reduction process at 1200 mV (inset in Figure 11). According to Figure 12 Figure 11, several
absorption bands were observed from the spectroelectrochemistry experiments, which can be
ascribed to two different species: the first one with bands at 410 and 909 nm, and the second one
with absorption at around 693 nm. Although it was not possible to isolate the species formed after
●+
the electrochemical oxidation, the sequence in spectra resembles that of TCz-TCz , so it suggests
that this fragment appears during the voltammetry. Similar results were reported for analogous
compounds.[59]
Figure 11. Absorption spectra of TCz in Cl
2
CH obtained by spectroelectrochemistry, with applied potential
2
-
1
from 0 to 2000 mV vs. NHE. Inset: cyclic voltammetry in Cl
2
CH with TBAPF6 0.1 mol L .
2
Since carbazole derivatives having free 3 and 6 positions are reported to form dimers when
oxidized (actually, it is the way by means TCz-TCz was synthesized in the present work), we
performed an electrochemical study of 3,6-ICz, which is substituted with iodine at the 3 and 6
positions, so preventing any coupling. As expected (figure S1 in Supplementary material), the
cyclic voltammetry of 3,6-ICz (inset) Figure 8 (inset) shows a reversible wave at 1650 mV without
any coupled homogeneous processes and from espectroelectrochemistry only two bands at 350
●
+
and 590 nm ascribed to the radical 3,6-ICz were observed. These bands have also been
recorded with other 3,6-disubstituted carbazoles, whose electronic structure were described
elsewhere.[60] Moreover, no absorptions were detected in NIR, as expected for a non dimeric
species.
In contrast to TCz-TCz (whose monooxidized cation is not further reactive for
2
polymerization), each redox fragment in CzPh-CH -PhCz behaves as a single TCz forming
independent –CH -TCz-TCz-CH – subfragments by coupling with other oxidized molecules in
2
2
solution, no matter the state of the aliphatically bound (and beyond the metylene bridge) TCz in the
same molecule. Polymerization, then, generates high amounts of electronically disconnected units,
responsible for the electrochromic response, each one electronically very similar to TCz-TCz (see
analogy between Figure 10 Figure 9 and Figure 12 Figure 11). As seen in the related phenylamine

polymer,[60] the absence of delocalization between the redox centers on both ends of the
methylene bridge forces electronic hopping as the main electron transport mechanism in the (now)
TCz-TCz methylene bridged film.
4
. Conclusions
Based on a combination of reported procedures, a series of N-(4-methylphenyl)-
carbazole derivatives were synthesized and purified with high yields. Absorption and
fluorescence spectra of these molecules were recorded, which showed spectroscopic
features analogous to those of some related compounds previously reported. DFT and TD-
DFT calculations showed that the N-(4-methylphenyl) ring is not electronically coupled to
the rest of the system, unlike triphenylamine compounds previously studied by our group.
Furthermore, by analyzing the molecular orbitals could be seen that the methylene bridge
in CzPh-CH
at 3,3´-position in TCz-TCz extends the -system along of both fragments.
Oxidation of CzPh-CH -PhCz yields TCz-TCz units separated by methylene bridges
2
-PhCz promotes the uncoupling of the two carbazole units, whereas linkage
2
in a polymeric form that resulted in less stable film on the ITO surface than those formed
by benzidine units. The near-infrared band at around 1000 nm (either in soluble TCz-TCz
or in polymer) is assigned to the intervalence charge transfer between carbazole subunits
of TCz-TCz fragments. It should be noted that although intervalence transitions in
delocalized molecules do not transfer net charge between redox centers (it resembles a 
→
* transition), they are usually classified as “charge transfers” because are a special
case of them under the same theory.
The radical cation of TCz-TCz is electronically delocalized, allowing that the positive
charge (hole) is symmetrically distributed on the molecule. This compound (either as a
single molecule or as part of the polymer) behaves as Class III in Robin and Day
classification. The lower fluorescence quantum yield of TCz-TCz compared to single
carbazoles suggests a favorable intersystem crossing to triplet state, which was found at
2
.61 eV above ground state. This value suggests that the fragment //-CH
2
-TCz-TCz-CH -//
2
is a suitable candidate for green-blue electroluminescent host polymer material. Also, the
still decent values of fluorescence quantum yields obtained shows that this family of
compounds may be interesting for selective probes in fluorescence sensing.
Acknowledgments

This paper is based on a project supported by ANPCYT (research project PICT
439/2013). E. M. A. thanks to Universidad Nacional de Río Cuarto and CONICET for
1
financial support. A. R. P and C. L. R. thank to Universidad Nacional de Mar del Plata for
financial support and INBIOTEC-CONICET. M. I. M thanks to IQUIR - Universidad
Nacional de Rosario for financial support. All authors are research staff at CONICET.

References
[
[
1] Joanna O, Mateusz G, Roman P, Dariusz B. Pol J Chem Technol. 2014;16(1):75-80.
2] He T, Gao Y, Chen R, Ma L, Rajwar D, Wang Y, et al. Multiphoton Harvesting in an Angular Carbazole-
Containing Zn(II)-Coordinated Random Copolymer Mediated by Twisted Intramolecular Charge Transfer
State. Macromol. 2014;47(4):1316-24.
[
3] Cao P-F, Rong L-H, de Leon A, Su Z, Advincula RC. A Supramolecular Polyethylenimine-Cored Carbazole
Dendritic Polymer with Dual Applications. Macromol. 2015;48(19):6801-9.
[
(
4] Venkatesh Y, Rajesh Y, Karthik S, Chetan AC, Mandal M, Jana A, et al. Photocaging of Single and Dual
Similar or Different) Carboxylic and Amino Acids by Acetyl Carbazole and its Application as Dual Drug
Delivery in Cancer Therapy. J Org Chem. 2016;81(22):11168-75.
5] Higginbotham H, Karon K, P. L, Data P. Carbazoles in Optoelectronic Applications. Disp Imaging.
017;2(3-4):207-16.
6] Shin BS, Yoon CW, Kwak SK, Kang JW. Thermodynamic assessment of carbazole-based organic polycyclic
compounds for hydrogen storage applications via a computational approach. Int J Hydrogen Energy.
018;43(27):12158-67.
7] Wang H, Sheikh AD, Feng Q, Li F, Chen Y, Yu W, et al. Facile Synthesis and High Performance of a New
Carbazole-Based Hole-Transporting Material for Hybrid Perovskite Solar Cells. ACS Photonics.
015;2(7):849-55.
8] Wu J, Xie Y, Chen X, Deng GJ. Transition Metal‐Free Carbazole Synthesis from Arylureas and
Cyclohexanones. Adv Synth Catal. 2016;358(20):3206-11.
9] Wex B, Kaafarani BR. Perspective on carbazole-based organic compounds as emitters and hosts in TADF
applications. J Mater Chem C. 2017;5(34):8622-53.
10] Bonesi SM, Erra-Balsells R. Electronic spectroscopy of carbazole and N- and C-substituted carbazoles in
homogeneous media and in solid matrix. J Lumin. 2001;93(1):51-74.
11] Bonesi SM, Erra-Balsells R. Electronic spectroscopy of N- and C-substituted chlorocarbazoles in
homogeneous media and in solid matrix. J Lumin. 2002;97(2):83-101.
12] Ponce María B, Cabrerizo Franco M, Bonesi Sergio M, Erra‐Balsells R. Synthesis and Electronic
[
2
[
2
[
2
[
[
[
[
[
Spectroscopy of Bromocarbazoles. Direct Bromination of N‐ and C‐Substituted Carbazoles by
N‐Bromosuccinimide or a N‐Bromosuccinimide/Silica Gel System. Helv Chim Acta. 2006;89(6):1123-39.
[
13] Bonesi SM, Mesaros M, Cabrerizo FM, Ponce MA, Bilmes GM, Erra-Balsells R. The photophysics of
nitrocarbazoles used as UV-MALDI matrices: Comparative spectroscopic and optoacoustic studies of
mononitro- and dinitrocarbazoles. Chem Phys Lett. 2007;446(1):49-55.
[
14] Kato S-i, Yamada Y, Hiyoshi H, Umezu K, Nakamura Y. Series of Carbazole–Pyrimidine Conjugates:
Syntheses and Electronic, Photophysical, and Electrochemical Properties. J Org Chem. 2015;80(18):9076-90.
15] Damit EF, Nordin N, Ariffin A, Sulaiman K. Synthesis of Novel Derivatives of Carbazole-Thiophene, Their
Electronic Properties, and Computational Studies. J Chem. 2016;2016:14.
16] You J, Shan Y, Zhen L, Zhang L, Zhang Y. Determination of peptides and amino acids from wool and
[
[
beer with sensitive fluorescent reagent 2-(9-carbazole)-ethyl chloroformate by reverse phase high-
performance liquid chromotography and liquid chromotography mass spectrometry. Anal Biochem.
2
[
003;313(1):17-27.
17] Shao J, Lin H, Lin H. Rational design of a colorimetric and ratiometric fluorescent chemosensor based
on intramolecular charge transfer (ICT). Talanta. 2008;77(1):273-7.
18] Yang L, Zhu W, Fang M, Zhang Q, Li C. A new carbazole-based Schiff-base as fluorescent chemosensor
for selective detection of Fe3+ and Cu2+. Spectrochim Acta Part A: Mol Biomol Spectrosc. 2013;109:186-92.
19] Gupta VD, Padalkar VS, Phatangare KR, Patil VS, Umape PG, Sekar N. The synthesis and photo-physical
properties of extended styryl fluorescent derivatives of N-ethyl carbazole. Dyes Pigments. 2011;88(3):378-
4.
20] Konidena RK, Thomas KRJ, Kumar S, Wang Y-C, Li C-J, Jou J-H. Phenothiazine Decorated Carbazoles:
Effect of Substitution Pattern on the Optical and Electroluminescent Characteristics. J Org Chem.
015;80(11):5812-23.
[
[
8
[
2

[
21] Gawale Y, Adarsh N, Kalva Sandeep K, Joseph J, Pramanik M, Ramaiah D, et al. Carbazole‐Linked
Near‐Infrared Aza‐BODIPY Dyes as Triplet Sensitizers and Photoacoustic Contrast Agents for Deep‐Tissue
Imaging. Chem – Eur J. 2017;23(27):6570-8.
[
22] Yilmaz G, Tuzun A, Yagci Y. Thioxanthone–carbazole as a visible light photoinitiator for free radical
polymerization. J Polym Sci, Part A: Polym Chem. 2010;48(22):5120-5.
23] Al Mousawi A, Garra P, Dumur F, Bui T-T, Goubard F, Toufaily J, et al. Novel Carbazole Skeleton-Based
Photoinitiators for LED Polymerization and LED Projector 3D Printing. Mol. 2017;22(12).
24] Al Mousawi A, Arar A, Ibrahim-Ouali M, Duval S, Dumur F, Garra P, et al. Carbazole-based compounds
[
[
as photoinitiators for free radical and cationic polymerization upon near visible light illumination.
Photochem Photobiol Sci. 2018;17(5):578-85.
[
25] Lv H-j, Zhang X-t, Wang S, Xing G-w. Assembly of BODIPY-carbazole dyes with liposomes to fabricate
fluorescent nanoparticles for lysosomal bioimaging in living cells. Analyst. 2017;142(4):603-7.
26] Grazulevicius JV, Strohriegl P, Pielichowski J, Pielichowski K. Carbazole-containing polymers: synthesis,
properties and applications. Prog Polym Sci. 2003;28(9):1297-353.
27] K. N, H. M. Novel Complex Polymers with Carbazole Functionality by Controlled Radical Polymerization.
Int J Polym Sci. 2012;2012(ID 170912).
28] Ates M, Uludag N. Carbazole derivative synthesis and their electropolymerization. J Solid State
Electrochem. 2016;20(10):2599-612.
29] Bagnich SA, Rudnick A, Schroegel P, Strohriegl P, Köhler A. Triplet energies and excimer formation in
meta- and para-linked carbazolebiphenyl matrix materials. Phil Trans R Soc A. 2015;373:20140446.
30] Tang G-M, Chi R-H, Wan W-Z, Chen Z-Q, Yan T-X, Dong Y-P, et al. Tunable photoluminescent materials
based on two phenylcarbazole-based dimers through the substituent groups. J Lumin. 2017;185:1-9.
31] Chen JP, Natansohn A. Synthesis and Characterization of Novel Carbazole-Containing Soluble
Polyimides. Macromol. 1999;32(10):3171-7.
32] H. L, Y. Z, Y. H, D. M, L. W, X. J, et al. Novel Soluble N‐Phenyl‐Carbazole‐Containing PPVs for
[
[
[
[
[
[
[
Light‐Emitting Devices: Synthesis, Electrochemical, Optical, and Electroluminescent Properties. Macromol
Chem Phys. 2004;205(2):247-55.
[
33] Hsiao S-H, Lin S-W. Electrochemical synthesis of electrochromic polycarbazole films from N-phenyl-3,6-
bis(N-carbazolyl)carbazoles. Polym Chem. 2016;7(1):198-211.
34] Brouwer AM. Standards for photoluminescence quantum yield measurements in solution (IUPAC
Technical Report). Pure Appl Chem. 2011;83(12):2213-28.
35] Noviandri I, Brown KN, Fleming DS, Gulyas PT, Lay PA, Masters AF, et al. The
[
[
Decamethylferrocenium/Decamethylferrocene Redox Couple:ꢀ A Superior Redox Standard to the
Ferrocenium/Ferrocene Redox Couple for Studying Solvent Effects on the Thermodynamics of Electron
Transfer. J Phys Chem B. 1999;103(32):6713-22.
[
36] Yanai T, Tew DP, Handy NC. A new hybrid exchange–correlation functional using the Coulomb-
attenuating method (CAM-B3LYP). Chem Phys Lett. 2004;393(1):51-7.
37] Mennucci B, Tomasi J. Continuum solvation models: A new approach to the problem of solute’s charge
distribution and cavity boundaries. J Chem Phys. 1997;106(12):5151-8.
38] Mennucci B, Cancès E, Tomasi J. Evaluation of Solvent Effects in Isotropic and Anisotropic Dielectrics
[
[
and in Ionic Solutions with a Unified Integral Equation Method:ꢀ Theoretical Bases, Computational
Implementation, and Numerical Applications. J Phys Chem B. 1997;101(49):10506-17.
[
39] Tomasi J, Mennucci B, Cancès E. The IEF version of the PCM solvation method: an overview of a new
method addressed to study molecular solutes at the QM ab initio level. J Mol Struct: THEOCHEM.
999;464(1):211-26.
1
[
[
40] Chipman DM. Reaction field treatment of charge penetration. J Chem Phys. 2000;112(13):5558-65.
41] Frisch MJ, Trucks GW, Schlegel HB, Scuseria GE, Robb MA, Cheeseman JR, et al. Gaussian 09W, Revision
A. 1. Wallingford (CT): Gaussian. Inc; 2009.
42] Allouche A-R. Gabedit—A graphical user interface for computational chemistry softwares. J Comput
Chem. 2010;32(1):174-82.
[
[
[
43] Humphrey W, Dalke A, Schulten K. VMD: Visual molecular dynamics. J Mol Graph. 1996;14(1):33-8.
44] Zhang Q, Zhuang H, He J, Xia S, Li H, Li N, et al. Improved ternary memory performance of donor-
acceptor structured molecules through cyano substitution. J Mater Chem C. 2015;3(26):6778-85.

[
45] Kim SH, Cho I, Sim MK, Park S, Park SY. Highly efficient deep-blue emitting organic light emitting diode
based on the multifunctional fluorescent molecule comprising covalently bonded carbazole and anthracene
moieties. J Mater Chem. 2011;21(25):9139-48.
[
46] He J, Liu H, Dai Y, Ou X, Wang J, Tao S, et al. Nonconjugated Carbazoles: A Series of Novel Host
Materials for Highly Efficient Blue Electrophosphorescent OLEDs. J Phys Chem C. 2009;113(16):6761-7.
47] Kelkar AA, Patil NM, Chaudhari RV. Copper-catalyzed amination of aryl halides: single-step synthesis of
triarylamines. Tetrahedron Lett. 2002;43(40):7143-6.
48] Sarkar A, Chakravorti S. A solvent-dependent luminescence study on 9-phenyl carbazole. J Lumin.
998;78(3):205-11.
49] Tsai MH, Hong YH, Chang CH, Su HC, Wu CC, Matoliukstyte A, et al. 3-(9-Carbazolyl)carbazoles and 3,6-
[
[
1
[
Di(9-carbazolyl)carbazoles as Effective Host Materials for Efficient Blue Organic Electrophosphorescence.
Adv Mater. 2007;19(6):862-6.
[
1
[
50] Berlman IB. Handbook of Fluorescence Spectra of Aromatic Molecules. Academic Press, Inc (London)
971;2nd Ed.(United Kingdom ).
51] Costero AM, Sanchis J, Gil S, Sanz V, Williams JAG. Poly(amine) biphenyl derivatives as fluorescent
sensors for anions and cations. J Mater Chem. 2005;15(27-28):2848-53.
52] Arce R, Kevan L. Photochemical behaviour of N,N,N´,N´-tetramethylbenzidine and its protonated forms
[
in sodium dodecyl sulphate anionic micelles under 337 nm laser irradiation. J Chem Soc, Faraday Trans 1:
Phys Chem Condensed Phases. 1985;81(7):1669-76.
[
53] Brunner K, van Dijken A, Börner H, Bastiaansen JJAM, Kiggen NMM, Langeveld BMW. Carbazole
Compounds as Host Materials for Triplet Emitters in Organic Light-Emitting Diodes:ꢀ Tuning the HOMO Level
without Influencing the Triplet Energy in Small Molecules. J Am Chem Soc. 2004;126(19):6035-42.
[
54] Robin MB, Day P. Mixed Valence Chemistry-A Survey and Classification. In: Emeléus HJ, Sharpe AG,
editors. Advances in Inorganic Chemistry and Radiochemistry: Academic Press; 1968. p. 247-422.
55] Crutchley RJ. Intervalence Charge Transfer and Electron Exchange Studies of Dinuclear Ruthenium
Complexes. In: Sykes AG, editor. Advances in Inorganic Chemistry: Academic Press; 1994. p. 273-325.
56] Seo ET, Nelson RF, Fritsch JM, Marcoux LS, Leedy DW, Adams RN. Anodic Oxidation Pathways of
Aromatic Amines. Electrochemical and Electron Paramagnetic Resonance Studies. J Am Chem Soc.
966;88(15):3498-503.
57] Chiu KY, Su TX, Li JH, Lin T-H, Liou G-S, Cheng S-H. Novel trends of electrochemical oxidation of amino-
substituted triphenylamine derivatives. J Electroanal Chem. 2005;575(1):95-101.
58] Ramírez CL, Parise AR. Solvent resistant electrochromic polymer based on methylene-bridged
arylamines. Org Electron. 2009;10(5):747-52.
59] Chiu S-K, Chung Y-C, Liou G-S, Su YO. Electrochemical and Spectral Characterizations of 9-
Phenylcarbazoles. J Chin Chem Soc. 2012;59(3):331-7.
60] Xu B, Sheibani E, Liu P, Zhang J, Tian H, Vlachopoulos N, et al. Carbazole-Based Hole-Transport
Materials for Efficient Solid-State Dye-Sensitized Solar Cells and Perovskite Solar Cells. Adv Mater.
014;26(38):6629-34.
[
[
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