Structure-properties relationship of the derivatives of carbazole and 1,8-naphthalimide: Effects of the substitution and the linking topology

Article abstract of DOI:10.1016/j.dyepig.2014.11.013

Nine compounds having electron-accepting 1,8-naphthalimide and electron-donating carbazole moieties were synthesized employing palladium-catalyzed C-N and C-C coupling reactions and characterized by the thermal methods, absorption and emission spectrometry, electrochemical and photoelectrical tools. The synthesized compounds possess high thermal stability with the 5% weight loss temperatures being in the range of 351-476 °C. Most of the synthesized compounds are capable of glass formation with glass transition temperatures ranging from 30 to 87 °C. The cyclic voltammetry measurements showed that the solid state ionization potentials values of the carbazole and 1,8-naphthalimide derivatives range from 5.46 eV to 5.76 eV and the electron affinities values range from -3.04 eV to -2.92 eV. Dilute solutions of the 3- and 3,6-naphthalimide-substituted derivatives of carbazole in polar solvents were found to emit in the green region with quantum yields ranging from 0.66 to 0.83, while in the solid state fluorescence quantum yields were found to be in the range of 0.01-0.45. ((E)-9-(((N-(2-ethylhexyl)-1,8-naphthalimide)-4-yl)ethenyl)-9H-carbazole) exhibited efficient fluorescence in the solid state with quantum yield as high as 0.45. The effects of the linking topology of the chromophores and of the incorporated alkyl substituents on the thermal, optical, and photoelectrical properties of the synthesized donor-acceptor compounds are analyzed. The impact of the ground state intramolecular twisting of the carbazole and naphthalimide moieties induced by the substituents resulting in significant variation in the rates of radiative and nonradiative excitation deactivation is revealed.

Full text of DOI:10.1016/j.dyepig.2014.11.013

Dyes and Pigments 114 (2015) 239e252
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Structure-properties relationship of the derivatives of carbazole and
1,8-naphthalimide: Effects of the substitution and the linking topology
a
a
,
*
a
a
Dalius Gudeika , Juozas Vidas Grazulevicius , Dmytro Volyniuk , Rita Butkute ,
b
c
d
c
Gytis Juska , Arunas Miasojedovas , Alytis Gruodis , Saulius Jursenas
a
Department of Polymer Chemistry and Technology, Kaunas University of Technology, Radvilenu pl. 19, LT-50254 Kaunas, Lithuania
Department of Solid State Electronics, Vilnius University, Sauletekio, aleja 9, LT-10222 Vilnius, Lithuania
Departmentof General Physics and Spectroscopy, Vilnius University, Sauletekio, aleja 9, LT-10222 Vilnius, Lithuania
Institute of Applied Research, Vilnius University, Sauletekio aleja 9, LT-10222 Vilnius, Lithuania
b
c
d
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 19 August 2014
Received in revised form
Nine compounds having electron-accepting 1,8-naphthalimide and electron-donating carbazole moieties
were synthesized employing palladium-catalyzed CeN and CeC coupling reactions and characterized by
the thermal methods, absorption and emission spectrometry, electrochemical and photoelectrical tools.
The synthesized compounds possess high thermal stability with the 5% weight loss temperatures being
12 November 2014
Accepted 14 November 2014
Available online 21 November 2014
ꢀ
in the range of 351e476 C. Most of the synthesized compounds are capable of glass formation with glass
ꢀ
transition temperatures ranging from 30 to 87 C. The cyclic voltammetry measurements showed that
the solid state ionization potentials values of the carbazole and 1,8-naphthalimide derivatives range from
Keywords:
Palladium-catalyzed
Molecular glass
Ionization potential
Photophysical properties
Intramolecular charge-transfer
Intramolecular twisting
5.46 eV to 5.76 eV and the electron affinities values range from ꢁ3.04 eV to ꢁ2.92 eV. Dilute solutions of
the 3- and 3,6-naphthalimide-substituted derivatives of carbazole in polar solvents were found to emit in
the green region with quantum yields ranging from 0.66 to 0.83, while in the solid state fluorescence
quantum yields were found to be in the range of 0.01e0.45. ((E)-9-(((N-(2-ethylhexyl)-1,8-
naphthalimide)-4-yl)ethenyl)-9H-carbazole) exhibited efficient fluorescence in the solid state with
quantum yield as high as 0.45. The effects of the linking topology of the chromophores and of the
incorporated alkyl substituents on the thermal, optical, and photoelectrical properties of the synthesized
donor-acceptor compounds are analyzed. The impact of the ground state intramolecular twisting of the
carbazole and naphthalimide moieties induced by the substituents resulting in significant variation in
the rates of radiative and nonradiative excitation deactivation is revealed.
©
2014 Elsevier Ltd. All rights reserved.
1
. Introduction
Derivatives of 1,8-naphthalimide are widely used for various
applications [5,6]. They were utilized in such fields as colouration
and brightening of polymers [7], as laser active media [8,9],
fluorescent markers in biology [10], anticancer agents [11], an-
algesics in medicine [12], fluorescence switchers and sensors
[13e16], as electron-transporting and emitting materials in light
emitting diodes [17e19]. They were also used in liquid crystal
displays [20] and as ion probes [21e23]. Derivatives of 1,8-
naphthalimide derivatives generally have high electron affinity
due to the existence of an electron-deficient centre [24] and
display good electron-transporting or hole-blocking capabil-
ities.1,8-Naphthalimide moiety can be easily functionalized [25].
By introducing different electron-donating substituents at C-4
position of 1,8-naphthalimide moiety the emission color of the
compounds can be readily tuned from near infrared to pure blue
Conjugated compounds containing both donor and acceptor
moieties have been extensively synthesized and studied because of
their potential applications in electronics and optoelectronics
[1e3]. The unique structure of donor-acceptor molecules allows
their optical and electrochemical properties to be tuned finely over
a wide range by appropriate chemical modification of the donor
and acceptor moieties [4]. The further progress in the design and
synthesis of the compounds containing both donor and acceptor
moieties depend to the great extent on the understanding the
structure-property relationship of such compounds.
*
Corresponding author. Tel.: þ370 37 300193; fax: þ370 37 300152.
E-mail address: juozas.grazulevicius@ktu.lt (J.V. Grazulevicius).
[
26e29].
http://dx.doi.org/10.1016/j.dyepig.2014.11.013
143-7208/© 2014 Elsevier Ltd. All rights reserved.
0

240
D. Gudeika et al. / Dyes and Pigments 114 (2015) 239e252
Carbazole-based compounds are known for their intense blue
Charge drift mobility measurements were performed using
charge extraction by linearly increasing voltage (CELIV) method
[49,50]. For the CELIV measurements the samples in configuration
ITO/compound/Al with the thickness of layers organic compound of
luminescence and electroluminescence [30,31]. Carbazole de-
rivatives are prefereable due to their rigid plane and good hole-
transporting properties [32]. Carbazole derivatives, consisting of
large planar aromatic systems possess enhanced thermal stability
2
100e200 nm and an active area of 7 mm were prepared. The layers
[
33e35]. Furthermore, carbazole moiety can easily be functional-
from 10 mg/mL THF solutions of the compounds were spin coated
onto glass/ITO substrates at 1000 rpm. Glass/ITO substrates were
sonicated in acetone, deionized water, and isopropanol for 10 min
before use. Al electrode of 60 nm of was thermally evaporated at
10 Å/s at a pressure below 5$10 mbar using a mask, to obtain
three top contact pixels. The light pulse was used to photogenerate
the charge carriers by exciting layers of compounds through the ITO
layer. The charge carriers were generated by illumination with
pulses of Nd:YAG laser (pulse duration was 25 ps, wavelength
355 nm). The experimental setup consisted of a delay generator
Tektronix AFG 3011 and a digital storage oscilloscope Tektronix
DPO 4032.
ized at its C-3 and C-6 [36], as well as at C-2 and C-7 [37] or N-
positions [38], allowing the fine-tuning of the electro-optical
properties of the molecules [39,40]. Many reported carbazole-
based materials are equipped with substituents at its C-3 and C-
ꢁ
5
6
-positions to enhance morphological and electrochemical stability
[41]. Recently, a series of carbazole derivatives with donor-acceptor
structures was reported as efficient emitting materials for organic
devices [42e44]. Such carbazole derivatives have a great potential
for the application as host materials in organic light emitting diodes
[
45], therefore the molecular design and synthesis of new carbazole
derivatives with donor-acceptor structure need to be further
developed by the structural modification in order to improve the
properties and to establish the relationship between structures and
properties.
In this paper we present the synthesis by stepwise palladium-
catalyzed CeN and CeC coupling reactions of a series of acceptor-
donor-(acceptor) compounds having electron-accepting 1,8-
naphthalimide moieties linked to electron-donating carbazole
species functionalized at three different positions (C-3, C-6 and N-
Absorption spectra of the dilute solutions of the investigated
compounds were recorded by UV-Vis-NIR spectrophotometer
Lambda 950 (Perkin Elmer). Fluorescence of dilute solutions,
compounds embedded in polystyrene (PS) matrix and of the neat
films was excited at a 365 and 420 nm wavelengths from 150 W
xenon arc lamp light source passed through a monochromator and
measured using back-thinned CCD spectrophotometer PMA-11
(Hamamatsu). For these measurements, the dilute solutions of
the investigated compounds were prepared by dissolving them in a
9
). One of the aims of this work was to explore the effects of the
ꢁ
6
linking topology of the chromophores and the nature of alkyl
substituents introduced at the carbazole nitrogen on the thermal,
optical, photophysical and photoelectrical properties of the com-
pounds. Basing on the results of the density-functional modeling
and detailed studies of the optical and photophysical properties of
the compounds embedded in various surrounding media the
impact of the conformational changes of the singly bonded
carbazole-naphthalimide systems is elucidated and its impact on
the nonradiative and radiative excited state deactivation is
discussed.
spectral grade solvent at 10 M concentration. The PS films with
the dispersed compounds with concentration of 1 wt% were pre-
pared by mixing the dissolved compounds and PS in THF and
casting the solutions on quartz substrates in an ambient air. The
ꢁ3
drop-casting from THF solutions (1 ꢂ10 M) was also employed to
prepare the neat films of the compounds. Fluorescence quantum
yields (QY) of the solutions were estimated by using integrated
sphere method [51]. Integrating sphere (Sphere Optics) coupled to
the CCD spectrometer via optical fiber was also employed to
measure
h of the neat films. Fluorescence transients of the samples
were measured using a time-correlated single photon counting
system PicoHarp 300 (PicoQuant) utilizing semiconductor diode
laser (repetition rate 1 MHz, pulse duration 70 ps, emission
wavelength 375 nm) as an excitation source.
2
. Experimental methods
2.1. Instrumentation
2
.2. Materials
1
13
Nuclear magnetic resonance ( H NMR and C NMR) spectra
1
were obtained using a Varrian Unity Inova (300 MHz ( H),
5.4 MHz (13C)). All the data are given as chemical shifts in
(ppm),
multiplicity, integration downfield from (CH Si. Mass (MS)
spectra were obtained on a Waters ZQ 2000 (Milford, USA).
Elemental analysis was performed with an Exeter Analytical CE-
4-Bromo-1,8-naphthalic anhydride and 2-ethylhexylamine
7
d
were purchased from TCI. Tri-o-tolylphosphine and 9H-carbazole
were purchased from Fluka and Reakhim respectively. 1-
Iodomethane, 1-bromobutane, 2-ethylhexylbromide, n-BuLi
(2.5 mol L in hexane), 2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-
dioxaborolane, bis(triphenylphosphine)palladium(II) dichloride
3 4
)
ꢁ
1
4
40 Elemental Analyser. Infrared (IR) spectra were recorded using
Perkin Elmer Spectrum GX spectrometer. DSC measurements were
(Pd(PPh
te(II) (Pd(OAc)
copper were obtained from Aldrich. The solvent, i.e. dime-
2
thylformamide (DMF, Lachema) was dried by distillation over CaH .
3
)
2
Cl
2
) and N-bromosuccinimide (NBS), palladium aceta-
carried out using a PerkineElmer DSC-7 series thermal analyzer at
2
), 18-crown-6, N-vinylcarbazole, triethylamine,
ꢀ
a heating rate 10 C/min under nitrogen flow. TGA measurements
e
were performed on a METTLER TOLEDO TGA/SDTA 851 . Melting
point (m.p.) of the material was determined using Electrothermal
Mel-Temp apparatus. Ionization potentials (IPEP) were established
by electron photoemission technique in air [46]. The samples for
the measurements were prepared by dissolving the compounds in
THF was dried and distilled over sodium and benzophenone.
Dichloromethane (POCH), ethyl acetate and n-Hexane (Penta) were
purified and dried using the standard procedures [52]. All other
reagents and solvents were used as supplied.
ꢀ
THF and by coating onAl plates precoated with ~0.5
mm thick
3,6-Dibromocarbazole (1a) [53] (m.p. 207e208 C, lit. [54] m.p.
ꢀ
ꢀ
methylmethacrylate and methacrylic acid copolymer adhesive
layer [47]. Electrochemical investigation was carried out using Bio-
Logic SAS and a micro-AUTOLAB Type III potentiostat-galvanostat.
The solutions of the synthesized compounds with the concentra-
209e210 C), 3-bromocarbazole (1b) [55] (m.p. 192e193 C, lit. [54]
ꢀ
m.p. 197e198 C), 3,6-dibromo-9-methyl-9H-carbazole (2a) [56]
(m.p. 136e137 C, lit. [56] m.p. 141 C), 3,6-dibromo-N-butylcar-
bazole (2b) [57] (m.p. 71e72 C, lit. [58] m.p. ¼ 74e75 C), 3,6-
dibromo-9-(2-ethylhexyl)carbazole (2c) [59] (colorless oil), 3-
bromo-9-methylcarbazole (2d) [53] (m.p. 74e75, lit. [56]
m.p. ¼ 78e79 ꢀC), 3-bromo-9-butylcarbazole (2e) [60] (colorless
ꢀ
ꢀ
ꢀ
ꢀ
ꢁ5
tion of 10 M were used for cyclic voltamperometry (CV) mea-
surements. The experiments were calibrated with the standard
ferrocene/ferrocenium redox system [48].

D. Gudeika et al. / Dyes and Pigments 114 (2015) 239e252
241
ꢀ
1
oil), 3-bromo-9-(2-ethylhexyl)carbazole (2f) [61] (colorless oil), 9-
methyl-3,6-(4,4,5,5-tetramethyl[1,3,2]dioxaborolan-2-yl)-9H-
carbazole (3a) [62] (m.p. 249e250 C, lit. [62] m.p. 257e259 C), 9-
butyl-3,6-(4,4,5,5-tetramethyl[1,3,2]dioxaborolan-2-yl)-9H-carba-
zole (3b) [63] (colorless oil), 9-(2-ethylhexyl)-3,6-(4,4,5,5-
m.p. ¼ 177e178 C; H NMR spectrum (300 MHz, CDCl
3
,
d
, ppm):
8.72 (s, 1H, eHNaphthalene), 8.69 (s, 1H, eHNaphthalene), 8.68 (d, 1H,
J ¼ 1.2 Hz, eHNaphthalene), 8.66 (d, 1H, J ¼ 1.1 Hz, eHNaphthalene), 8.45
(d, 1H, J ¼ 1.2 Hz, eHNaphthalene), 8.42 (d, 1H, J ¼ 1.2 Hz,
eHNaphthalene), 8.30e8.29 (m, 2H, eHNaphthalene), 7.86 (d, 2H,
J ¼ 7.6 Hz, eHNaphthalene), 7.76 (s, 1H, eHNaphthalene), 7.73 (d, 2H,
J ¼ 1.2 Hz, eHCarbazole), 7.72e7.68 (m, 4H, eHCarbazole), 4.55e4.52
ꢀ
ꢀ
tetramethyl[1,3,2]dioxaborolan-2-yl)-9H-carbazole
(3c)
[64]
(
colorless oil), 9-methyl-3-(4,4,5,5-tetramethyl[1,3,2]dioxabor-
ꢀ
olan-2-yl)-9H-carbazole (3d) [59] (m.p. 142e144 C, lit. [62] m.p
1
(m, 2H, eNCH
eN(CH
1.91e1.86 (m, 2H, eNCH
18H, 9 ꢂ CH , eHaliphatic), 1.02e0.86 (m, 15H, 5 ꢂ CH
C NMR spectrum (75.4 MHz, CDCl , ppm): 164.7, 164.6, 148.7,
2
CH
, eHaliphatic), 2.06e2.01 (m, 2H, 2 ꢂ CH, eHaliphatic),
CH CH CH , eHaliphatic), 1.48e1.30 (m,
, eHaliphatic).
2
CH
2
CH
3
,
eHaliphatic), 4.23e4.15 (m, 4H,
ꢀ
47e149 C), 9-butyl-3-(4,4,5,5-tetramethyl[1,3,2]dioxaborolan-2-
2 2
)
yl)-9H-carbazole (3e) [65] (colorless oil), 9-(2-ethylhexyl)-3-
2
2
2
3
(
4,4,5,5-tetramethyl[1,3,2]dioxaborolan-2-yl)-9H-carbazole
(3f)
2
3
13
[61] (colorless oil), 4-bromo-N-(2-ethylhexyl)-1,8-naphthalimide
3
, d
(
2
4) [66] and 3,6-di-tert-butyl-9H-carbazole [67] (m.p.
142.7, 133.4, 132.2, 131.1, 130.8, 129.3, 129.0, 128.7, 127.2, 124.2,
123.4, 122.8, 121.6, 110.1, 61.0, 45.4, 37.8, 36.7, 35.9, 31.0, 28.7, 27.1,
ꢀ ꢀ
21e222 C, lit. [68] m.p. 228 C) were prepared according to the
ꢁ
1
published procedures.
25.7, 23.3, 15.0, 11.7. IR, (in KBr), cm : 3072
857 (C]Oanhydride); 1656, 1588, 1512, 1463
(C]Car); 1354, 1277
n (CHar); 2958, 2926,
2
n
(CHaliphatic); 1699
n
n
þ
2
.3. Synthesis
n
(CeN); 783, 759, 623
g
(CHar). MS (APCI ,
þ
20 V), m/z: 854 ([MþH] ). Anal. Calcd. for C57
63 3 4
H N O : C, 80.15; H,
2
9
.3.1. 3,6-((Di(N-(2-ethylhexyl)-1,8-naphthalimide)-4-yl)-9-metyl-
H-carbazole (5)
7.43, N, 4.92; O, 7.49%; found C 80.21, H 7.40, N 5.98%.
4
-Bromo-N-(2-ethylhexyl)-1,8-naphthalimide (4) (0.5 g,
.29 mmol) and 15 mL of dry THF and aqueous K CO solution
0.81 g, 5.85 mmol) in 2 mL H O were added via a syringe under
2.3.3. 3,6-((Di(N-(2-ethylhexyl)-1,8-naphthalimide)-4-yl)-9-(2-
ethylhexyl)-9H-carbazole (7)
The synthesis of 7 was carried out as described for 5 using 4-
bromo-N-(2-ethylhexyl)-1,8-naphthalimide (4) (0.5 g, 1.29 mmol),
9-(2-ethylhexyl)-3,6-(4,4,5,5-tetramethyl[1,3,2]dioxaborolan-2-
1
(
2
3
2
nitrogen to a three-necked round-bottomed flask (50 mL) equipped
with a magnetic stirrer, a reflux condenser and a nitrogen input
tube. 9-Methyl-3,6-(4,4,5,5-tetramethyl[1,3,2]dioxaborolan-2-yl)-
3 2 2
yl)-9H-carbazole (3c) (0.32 g, 0.59 mmol), (PPh ) Cl (0.02 g,
9
0
H-carbazole (3a) (0.25 g, 0.59 mmol) and Pd(PPh
3
)
2
Cl
2
(0.02 g,
0.02 mmol), K CO (0.81 g, 5.85 mmol). The crude product was
2
3
.02 mmol) were successively added and the reaction mixture was
purified by column chromatography on silica gel with ethyl acetate
and hexane (1:10, V:V) as an eluent and crystallized from the eluent
mixture of solvents to give 7 as yellow crystals. Yield: 63% (0.35 g),
ꢀ
refluxed at 80 C for 24 h under nitrogen atmosphere. After cooling
down to the room temperature methylene chloride (200 mL) was
added to the reaction mixture. Then it was washed three times with
distilled water, and dried with anhydrous magnesium sulfate. The
solution was filtered and concentrated. The crude product was
purified by column chromatography on silica gel with ethyl acetate
and hexane (1:9, V:V) as eluent and crystallized from the eluent
mixture of solvents to give 5 as yellow crystals. Yield: 66% (0.31 g),
ꢀ
1
3
m.p. 102e103 C; H NMR spectrum (300 MHz, CDCl , d, ppm): 8.73
(s, 1H, eHNaphthalene), 8.70 (d, 2H, J ¼ 1.5 Hz, eHNaphthalene), 8.68 (d,
1H, J ¼ 1.2 Hz, eHNaphthalene), 8.44 (d, 1H, J ¼ 1.2 Hz, eHNaphthalene),
8.41 (d, 1H, J ¼ 1.2 Hz, eHNaphthalene), 8.22 (d, 1H, J ¼ 1.6 Hz,
eHNaphthalene), 7.85 (s, 2H, J ¼ 7.6 Hz, eHNaphthalene), 7.77 (s, 1H,
eHNaphthalene), 7.75 (d, 2H, J ¼ 1.2 Hz, eHCarbazole), 7.68 (d, J ¼ 1.8 Hz,
eHCarbazole), 7.66e7.64 (m, 1H, eHCarbazole), 7.62e7.56 (m, 3H,
ꢀ
1
m.p. 147e148 C; H NMR spectrum (300 MHz, CDCl
s, 1H, eHNaphthalene), 8.69 (s, 1H, eHNaphthalene), 8.68 (d, 1H,
J ¼ 1.1 Hz, eHNaphthalene), 8.65 (d, 1H, J ¼ 1.1 Hz, eHNaphthalene), 8.42
3
, d, ppm): 8.71
(
eHCarbazole), 4.25e4.19 (m, 6H, eN(CH
2
)
3
, eHaliphatic), 2.06e1.98 (m,
, eCH,
3
, eHaliphatic). C NMR
2H, 2 ꢂ CH, eHaliphatic), 1.49e1.32 (m, 25H, 12 ꢂ CH
2
1
3
(
d, 1H, J ¼ 1.1 Hz, eHNaphthalene), 8.39 (d, 1H, J ¼ 1.1 Hz,
eHaliphatic), 1.03e0.91 (m, 18H, 6 ꢂ CH
eHNaphthalene), 8.33e8.28 (m, 2H, eHNaphthalene), 7.85 (d, 2H,
J ¼ 7.6 Hz, eHNaphthalene), 7.75 (s, 2H, eHNaphthalene, eHCarbazole), 7.72
spectrum (75.4 MHz, CDCl , ppm): 163.6,161.8,148.7,142.5,134.2,
3
, d
132.3, 131.2, 130.6, 130.3, 129.7, 128.4, 127.1, 124.7, 123.1, 122.2, 121.6,
111.7, 63.5, 43.3, 38.2, 37.8, 36.3, 32.2, 29.8, 26.1, 24.3, 23.3,14.3,11.9.
(
4
t, 3H, J ¼ 1.6 Hz, eHCarbazole), 7.70 (s, 2H, eHCarbazole), 4.22e4.16 (m,
ꢁ
1
H, eN(CH
2
)
2
,
eHaliphatic), 4.10 (s, 3H, eNCH
2
CH
2
CH
2
CH
3
),
IR, (in KBr), cm : 3071
n
(CHar); 2958, 2925, 2855
n (CHaliphatic);
2
.05e1.97 (m, 2H, 2 ꢂ CH, eHaliphatic), 1.47e1.32 (m, 16H, 8 ꢂ CH
2
,
1698 (C]Oanhydride); 1655, 1578, 1522, 1462 n
n
(C]Car); 1351, 1278
13
þ
eHaliphatic), 1.00e0.90 (m, 12H, 4 ꢂ CH
3
, eHaliphatic). C NMR
n
(CeN); 782, 759, 622
g
(CHar). MS (APCI , 20 V), m/z: 910
: C, 80.49; H, 7.86, N, 4.62; O,
þ
spectrum (75.4 MHz, CDCl
3
,
d
, ppm): 164.9, 164.8, 147.8, 141.6, 133.1,
([MþH] ). Anal. Calcd. for C61
71 3 4
H N O
131.4, 131.1, 130.7, 130.3, 129.1, 128.5, 127.0, 123.2, 123.1, 122.2, 121.6,
7.03%; found C 80.45, H 7.82, N 7.08%.
1
09.2, 44.4, 38.2, 31.0, 29.8, 29.0, 24.3, 23.3, 14.4, 10.9. IR, (in KBr),
ꢁ
1
cm : 3070
n
(CHar); 2955, 2924, 2856 (C]
n
(CHaliphatic); 1700
n
2.3.4. 3-((N-(2-ethylhexyl)-1,8-naphthalimide)-4-yl)-9-metyl-9H-
carbazole (8)
The synthesis of 8 was carried out as described for 5 using 4-
bromo-N-(2-ethylhexyl)-1,8-naphthalimide (4) (0.5 g, 1.29 mmol),
9-methyl-3-(4,4,5,5-tetramethyl[1,3,2]dioxaborolan-2-yl)-9H-
O
anhydride); 1654, 1586, 1510
n
(C]Car); 1352, 1279 n (CeN); 782,
þ
þ
7
54, 621
g
(CHar). MS (APCI , 20 V), m/z: 812 ([MþH] ). Anal. Calcd.
for C54
H
57
N
3
O
4
: C, 79.87; H, 7.08, N, 5.17; O, 7.88%; found C 79.92, H
7.03, N 5.15%.
carbazole (3d), (0.47 g, 1.55 mmol), (PPh
3 2 2
) Cl (0.02 g, 0.02 mmol),
2
9
.3.2. 3,6-Di((N-(2-ethylhexyl)-1,8-naphthalimide)-4-yl)-9-butyl-
H-carbazole (6)
The synthesis of 6 was carried out as described for 5 using 4-
K
2
CO (0.81 g, 5.85 mmol). The crude product was purified by
3
column chromatography on silica gel with ethyl acetate and hexane
(1:8, V:V) as an eluent and crystallized from the eluent mixture of
solvents to give 8 as yellow crystals. Yield: 65% (0.42 g), m.p.
122e123 C; H NMR spectrum (300 MHz, CDCl
1H, J ¼ 7.6 Hz, eHNaphthalene), 8.68 (dd, 1H, J ¼ 1.2 Hz, J
eHNaphthalene), 8.43 (dd, 1H, J
bromo-N-(2-ethylhexyl)-1,8-naphthalimide (4) (0.5 g, 1.29 mmol),
-butyl-3,6-(4,4,5,5-tetramethyl[1,3,2]dioxaborolan-2-yl)-9H-
carbazole (3b) (0.28 g, 0.59 mmol), Pd(PPh Cl (0.02 g,
.02 mmol), K CO (0.81 g, 5.85 mmol). The crude product was
ꢀ
1
9
3
,
d
, ppm): 8.71 (d,
3
)
2
2
1
2
¼ 7.3 Hz,
0
2
3
1
¼ 1.2 Hz, J ¼ 8.6 Hz, eHNaphthalene),
2
purified by column chromatography on silica gel with ethyl acetate
and hexane (1:8, V:V) as an eluent and crystallized from the eluent
mixture of solvents to give 6 as yellow crystals. Yield: 68% (0.34 g),
8.27 (d, 1H, J ¼ 2.3 Hz, eHNaphthalene), 8.16 (d, 1H, J ¼ 7.8 Hz,
eHNaphthalene), 7.86 (d, 1H, J ¼ 7.6 Hz, eHCarbazole), 7.73 (dd, 1H,
J
1
¼ 7.3 Hz, J
2
¼ 8.5 Hz, eHCarbazole), 7.66 (dd, 1H, J ¼ 1.7 Hz,
1

242
D. Gudeika et al. / Dyes and Pigments 114 (2015) 239e252
J
J
2
¼ 8.4 Hz, eHCarbazole), 7.63e7.49 (m, 3H, eHCarbazole), 7.33 (dd, 1H,
13C NMR spectrum (75.4 MHz, CDCl
, d, ppm): 162.9, 14.2, 140.7,
3
134.3, 131.3, 131.1, 130.7, 129.7, 129.1, 128.5, 127.9, 126.9, 126.5, 123.2,
123.1, 122.7, 122.2, 121.4, 120.6, 119.7, 109.1, 108.9, 102.2, 63.1, 46.4,
1
¼ 1.5 Hz, J
2
¼ 7.4 Hz, eHCarbazole), 4.27e4.15 (m, 2H, eNCH
2
,
eHaliphatic), 3.99 (s, 3H, eNCH
.51e1.29 (m, 8H, 4 ꢂ CH , eHaliphatic), 1.04e0.90 (m, 6H, 2 ꢂ CH
eHaliphatic). C NMR spectrum (75.4 MHz, CDCl
48.2, 141.7, 133.6, 131.4, 131.1, 130.7, 129.7, 129.1, 128.5, 127.9, 126.9,
26.6,123.3,123.1,122.7,122.1,121.4,120.7,119.6,109.0,108.8,100.2,
3
), 2.07e2.00 (m, 1H, CH, eHaliphatic),
1
2
3
,
38.2, 35.8, 31.0, 29.5, 29.1, 26.6, 24.2, 23.3, 14.3, 10.9. IR, (in KBr),
13
ꢁ1
3
,
d
, ppm): 164.9,
cm : 3072
n
(CHar); 2958, 2926, 2847 (C]
n
(CHaliphatic); 1699
n
1
O
anhydride); 1652, 1588, 1512, 1453
n
(C]Car); 1357, 1276 n (CeN);
þ
þ
1
4
3
783, 759, 621
g
(CHar). MS (APCI , 20 V), m/z: 603 ([MþH] ). Anal.
: C, 81.69; H, 8.36, N, 4.65; O, 5.31%; found C
81.63, H 8.40, N 4.58%.
ꢁ1
4.4, 38.2, 31.0, 29.5, 29.0, 24.2, 23.3, 14.4, 10.9. IR, (in KBr), cm
:
50 2 2
Calcd. for C41H N O
070 (CHar); 2957, 2923, 2851 n (CHaliphatic); 1703 n (C]Oanhy-
n
dride); 1648, 1569, 1511
n
(C]Car); 1354, 1277
n
(CeN); 782, 756, 622
þ
þ
g
(CHar). MS (APCI , 20 V), m/z: 505 ([M þ H] ). Anal. Calcd. for
2.3.7. 9-((N-(2-ethylhexyl)-1,8-naphthalimide)-4-yl)-9H-carbazole
C
34 36 2 2
H N O : C, 80.92; H, 7.19, N, 5.55; O, 6.34%; found C 80.85, H
(
11)
4
7.15, N 5.58%.
-Bromo-N-(2-ethylhexyl)-1,8-naphthalimide (4) (0.5 g,
.29 mmol), copper powder (0.32 g, 5.15 mmol), 18-crown-6
0.06 g, 0.26 mmol), K CO (1.42 g, 10.31 mmol), 9H-carbazole
1
(
(
2
.3.5. 3-((N-(2-ethylhexyl)-1,8-naphthalimide)-4-yl)-9-butyl-9H-
2
3
carbazole (9)
0.94 g, 5.14 mmol) and o-dichlorobenzene (15 mL) were placed
The synthesis of 9 was carried out as described for 5 using 4-
bromo-N-(2-ethylhexyl)-1,8-naphthalimide (4) (0.5 g, 1.29 mmol),
ꢀ
into a round-bottom flask and vigorously stirred at 180 C for 24 h
under nitrogen. When the reaction was finished, the inorganic
components were removed by filtration. The solvent was removed
by distillation under reduced pressure. The crude product was
purified by column chromatography using the mixture of ethyl
acetate and hexane (1:9, V:V) as an eluent and crystallized from the
eluent mixture of solvents to obtain 11 as yellow crystals. Yield: 58%
9
-butyl-3-(4,4,5,5-tetramethyl[1,3,2]dioxaborolan-2-yl)-9H-carba-
zole (3e) (0.54 g, 1.55 mmol), (PPh Cl (0.02 g, 0.02 mmol), K CO
0.81 g, 5.85 mmol). The crude product was purified by column
3
)
2
2
2
3
(
chromatography on silica gel with ethyl acetate and hexane (1:8,
V:V) as an eluent and crystallized from the eluent mixture of sol-
ventsto give
9
as yellow crystals. Yield: 68% (0.48 g),
ꢀ
1
(
0.36 g), m.p. 110e111 C; H NMR spectrum (300 MHz, CDCl3, d,
ꢀ
1
m.p. ¼ 115e116 C; H NMR spectrum (300 MHz, CDCl
3
, d, ppm):
ppm): 8.83 (d, 1H, J ¼ 7.7 Hz, eHNaphthalene), 8.72 (d, 1H, J ¼ 1.2 Hz,
eHNaphthalene), 8.69 (d, 1H, J ¼ 1.2 Hz, eHNaphthalene), 8.25 (d, 2H,
J ¼ 2.6 Hz, eHCarbazole), 7.95 (d, 1H, J ¼ 7.8 Hz, eHNaphthalene), 7.83
8
.73 (s, 1H, eHNaphthalene), 8.71 (s, 1H, eHNaphthalene), 8.69 (dd, 1H,
J
J
1
¼ 1.1 Hz, J
2
¼ 7.3 Hz, eHNaphthalene), 8.46 (dd, 1H, J ¼ 1.1 Hz,
1
2
¼ 8.5 Hz, eHNaphthalene), 8.28 (dd, 1H, J ¼ 1.3 Hz, eHNaphthalene),
.16 (dd, 1H, J ¼ 7.8 Hz, eHCarbazole), 7.87 (d, 1H, J ¼ 7.6 Hz,
(
dd, 2H, J
1
¼ 1.2 Hz, J
2
¼ 8.5 Hz, eHCarbazole), 7.66 (t, 1H,
8
eHNaphthalene), 7.45e7.35 (m, 4H, eHCarbazole), 4.31e4.15 (m, 2H,
eCH , eHaliphatic), 2.09e1.99 (m, 1H, eCH, eHaliphatic), 1.56e1.24 (m,
H, 4 ꢂ CH
NMR spectrum (75.4 MHz, CDCl3,
32.3, 131.9, 130.3, 129.2, 127.9, 127.6, 126.6, 124.0, 123.0, 120.9,
20.8, 110.2, 44.5, 38.2, 31.0, 28.9, 24.3, 23.4, 14.4, 10.9. IR, (in KBr),
eHCarbazole), 7.74 (dd, 1H, J
1
¼ 7.3 Hz, J ¼ 8.5 Hz, eHCarbazole),
2
2
7.67e7.61 (m, 2H, eHCarbazole), 7.60e7.52 (m, 2H, eHCarbazole),
13
8
2
, eHaliphatic), 1.09e0.82 (m, 6H, 2 ꢂ CH
3
, eHaliphatic).
C
4
4
.48e4.41 (m, 2H, eNCH
H, eN(CH , eHaliphatic), 2.01e1.96 (m, 1H, CH, eHaliphatic),
, eHaliphatic), 1.09e0.87 (m, 9H, 3 ꢂ CH
eHaliphatic). C NMR spectrum (75.4 MHz, CDCl , ppm): 163.9,
47.2, 140.7, 135.3, 132.0, 131.1, 130.7, 129.7, 129.5, 128.5, 127.8, 126.4,
26.2, 123.2, 123.1, 122.6, 122.5, 121.3, 120.7, 119.5, 109.0, 108.7,
07.2, 62.1, 43.4, 39.2, 35.2, 31.1, 29.9, 29.1, 24.2, 23.3, 15.4, 13.5, 10.8.
2 2 2 3
CH CH CH , eHaliphatic), 4.26e4.17 (m,
d
, ppm): 164.6,164.2,142.0,140.4,
2 2
)
1
1
1.57e1.24 (m, 12H, 6 ꢂ CH
2
3
,
13
3
, d
ꢁ1
cm : 3055
n
(CHar); 2958, 2923, 2878, 2856
n
(CHaliphatic); 1699
n
1
1
1
(
(
(
C]Oanhydride); 1634, 1652, 1587
n
(C]Car); 1457; 1333, 1235
n
þ
CeN); 782,789, 753, 746
[MþH] ). Anal. Calcd. for C33
g
(CHar). MS (APCI , 20 V), m/z: 490
H N O : C, 80.78; H, 6.98, N, 5.71; O,
34 2 2
þ
ꢁ
1
IR, (in KBr), cm : 3069
n
(CHar); 2954, 2924, 2838
n (CHaliphatic);
6
.52%; found C 80.86, H 6.76, N 5.84%.
1701 (C]Oanhydride); 1656, 1577, 1523, 1466 n
n
(C]Car); 1357, 1267
(CHar). MS (APCI , 20 V), m/z: 547
: C, 81.28; H, 7.74, N, 5.12; O,
þ
n
(CeN); 789, 761, 619
g
þ
(
5
[MþH] ). Anal. Calcd. for C37
H
42
N
2
O
2
2.3.8. (9-((N-(2-ethylhexyl)-1,8-naphthalimide)-4-yl)-3,6-di-tert-
butyl-9H-carbazole (12)
.85%; found C 81.33, H 7.68, N 5.88%.
(9-((N-(2-ethylhexyl)-1,8-naphthalimide)-4-yl)-3,6-di-tert-
2
.3.6. 3-((N-(2-ethylhexyl)-1,8-naphthalimide)-4-yl)-9-(2-
butyl-9H-carbazole (12) was prepared by the same procedure as 11
using 4-bromo-N-(2-ethylhexyl)-1,8-naphthalimide (4) (0.5 g,
1.29 mmol), 3,6-di-tert-butyl-9H-carbazole (1.52 g, 5.15 mmol). The
crude product was purified by column chromatography using the
mixture of ethyl acetate and hexane (1:9, V:V) as an eleuent to give
almost pure 12. Recrystallization from eluent gave pure 12 as yel-
ethylhexyl)-9H-carbazole (10)
The synthesis of 10 was carried out as described for 5 using 4-
bromo-N-(2-ethylhexyl)-1,8-naphthalimide (4) (0.5 g, 1.29 mmol),
9
9
0
purified by column chromatography on silica gel with ethyl acetate
and hexane (1:9, V:V) as an eluent and crystallized from the eluent
mixture of solvents to give 10 as yellow crystals. Yield: 71% (0.55 g),
-(2-ethylhexyl)-3-(4,4,5,5-tetramethyl[1,3,2]dioxaborolan-2-yl)-
H-carbazole (3f) (0.63 g, 1.55 mmol), (PPh Cl (0.02 g,
.02 mmol), K CO (0.81 g, 5.85 mmol). The crude product was
3
)
2
2
ꢀ
1
2
3
low crystals. Yield: 71% (0.55 g), m.p. 133e134 C; H NMR spec-
trum (300 MHz, CDCl3,
d
, ppm): 8.81 (d, 1H, J ¼ 7.8 Hz,
eHNaphthalene), 8.72 (d, 1H, J ¼ 1.2 Hz, eHNaphthalene), 8.70 (d, 1H,
J ¼ 1.2 Hz, eHNaphthalene), 8.26 (d, 2H, J ¼ 1.9 Hz, eHCarbazole), 7.90 (d,
1H, J ¼ 7.8 Hz, eHNaphthalene), 7.67 (t,1H, eHNaphthalene); 7.48 (dd, 2H,
ꢀ
1
m.p. 108e109 C; H NMR spectrum (300 MHz, CDCl
d, 1H, J ¼ 7.5 Hz, eHNaphthalene), 8.69 (dd, 1H, J ¼1.2 Hz, J
eHNaphthalene), 8.46 (dd, 1H, J ¼ 8.5 Hz, eHNaphthalene),
¼ 1.2 Hz, J
.27 (d, 1H, J ¼ 2.2 Hz, eHNaphthalene), 8.16 (d, 1H, J ¼ 7.7 Hz,
3
,
d, ppm): 8.72
(
1
2
¼ 3.4 Hz,
J
1
¼ 2.0 Hz, J
4.31e4.19 (m, 2H, eCH
eHaliphatic), 1.52 (s, 18H, 6 ꢂ CH
eHaliphatic), 1.05e0.95 (m, 6H, 2 ꢂ CH
trum (75.4 MHz, CDCl3, , ppm): 144.0, 142.4, 140.4, 138.2, 132.2,
2
¼ 3.1 Hz, eHCarbazole), 7.38e7.34 (m, 2H, eHCarbazole),
1
2
2
, eHaliphatic), 2.09e2.02 (m, 1H, eCH,
, eHaliphatic), 1.49 (s, 8H, 4 ꢂ CH
8
3
2
,
13
eHNaphthalene), 8.08 (d, 1H, J ¼ 7.9 Hz, eHCarbazole), 7.87 (dd, 1H,
3
, eHaliphatic). C NMR spec-
J
J
J
1
2
1
¼ 1.9 Hz, J
¼ 8.5 Hz, eHCarbazole), 7.64e7.51 (m, 3H, eHCarbazole), 7.32 (dd, 1H,
¼ 1.2 Hz, J ¼ 6.8 Hz, eHCarbazole), 4.25e4.18 (m, 2H, eNCH
, eHaliphatic), 2.22e2.14 (m, 1H,
CH, eHaliphatic), 2.04e1.96 (m, 1H, CH, eHaliphatic), 1.50e1.30 (m,
6H, 8 ꢂ CH , eHaliphatic), 1.03e0.89 (m, 12H, 4 ꢂ CH , eHaliphatic).
2
¼ 7.4 Hz, eHCarbazole), 7.74 (dd, 1H, J
1
¼ 7.3 Hz,
d
131.9, 130.6, 129.1, 127.6, 127.1, 124.2, 123.7, 122.5, 116.7, 116.4, 110.2,
109.7, 44.5, 38.2, 35.0, 32.2, 31.0, 29.0, 24.3, 23.4, 14.4, 10.9. IR, (in
2
2
,
ꢁ
1
eHaliphatic), 4.17e4.11 (m, 2H, eNCH
2
KBr), cm : 3053
1701, 1699 (C]Oanhydride); 1623, 1651, 1587
1235 (CeN); 779,789, 751, 742
n (CHar); 2955, 2921, 2874, 2856 n (CHaliphatic);
n
n
(C]Car); 1457; 1333,
þ
1
2
3
n
g
(CHar). MS (APCI , 20 V), m/z: 602

D. Gudeika et al. / Dyes and Pigments 114 (2015) 239e252
243
þ
(
5
[MþH] ). Anal. Calcd. for C41
H
50
N
2
O
2
: C, 81.69; H, 8.36; N, 4.65; O,
7.90e7.83 (m, 4H, eHCarbazole
eHCarbazole), 7.46e7.39 (m, 2H, eHCarbazole), 4.23e4.14 (m, 2H, eCH
eHaliphatic), 1.91e1.86 (m, 1H, eCH, eHaliphatic), 1.49e1.33 (m, 8H,
,
-vinylic), 7.62e7.55 (m, 2H,
.31%; found C 81.45, H 8.28, N 4.43%.
2
,
13
4
ꢂ CH
spectrum (75.4 MHz, CDCl3,
32.3, 131.9, 130.3, 129.4, 129.2, 127.9, 127.6, 126.6, 124.1, 123.0,
20.9, 120.4, 110.3, 45.5, 37.8, 32.1, 28.8, 25.4, 23.5, 14.3, 10.9. IR, (in
2
, eHaliphatic),1.03e0.88 (m, 6H, 2 ꢂ CH
3
, eHaliphatic). C NMR
2
9
.3.9. ((E)-9-(((N-(2-ethylhexyl)-1,8-naphthalimide)-4-yl)ethenyl)-
H-carbazole (13)
A round bottom flask was charged with a mixture of 4-bromo-
d
, ppm): 164.6,164.1,141.7,140.6,139.8,
1
1
N-(2-ethylhexyl)-1,8-naphthalimide (4) (0.5 g, 1.29 mmol), N-
vinylcarbazole (0.40 g, 1.93 mmol), Pd(OAc) (0.005 g, 0.016 mmol),
P(o-tolyl) (0.016 g, 0.071 mmol), DMF (8 mL) and triethylamine
2 mL). The flask was degassed and purged with N . The reaction
mixture was heated at 90 C for 24 h under nitrogen. Then, it was
filtered and the filtrate was poured into methanol. The yellow
precipitate was filtered, washed with methanol and dissolved in
methylene chloride. After evaporation of the solvent, the crude
product was purified by silica gel column chromatography using
the mixture of ethylacetate and n-hexane (1:9, V:V) as an eluent
and crystallized from the eluent mixture of solvents to give 13 as
ꢁ
1
KBr), cm : 3052
n
(CHar); 2956, 2924, 2878, 2856
n (CHaliphatic);
(C]Car); 1457; 1333,1235
2
1
700 (C]Oanhydride); 1634,1652,1587 n
n
3
n
(CeN); 955
g
(trans, CH]CH); 782,789, 753, 746
g
(CHar). MS
(
2
þ
þ
ꢀ
(APCI , 20 V), m/z: 500 ([MþH] ). Anal. Calcd. for C34H N O : C,
32 2 2
8
1.57; H, 6.44; N, 5.60; O, 6.39%; found C 81.76, H 6.58, N 5.48%.
3. Results and discussion
3.1. Synthesis and characterization
ꢀ
1
yellow crystals. Yield 32% (0.21 g), m.p. ¼ 214e215 C. H NMR
Compounds 5e13 were synthesized as shown in Scheme 1 by
Suzuki-Miyaura coupling reactions of compound 4 with 1.1 equiv.
spectrum (300 MHz, CDCl3,
d
, ppm):8.71 (d, 1H, J ¼ 1.1 Hz,
eHNaphthalene), 8.69 (d, 1H, J ¼ 1.1 Hz, eHNaphthalene), 8.57 (d, 1H,
J ¼ 1.1 Hz, eHNaphthalene), 8.55 (d, 1H, J ¼ 1.1 Hz, eHNaphthalene), 8.17
of
carbazole or 2.2 equiv. of 9-alkyl-3,6-(4,4,5,5-tetramethyl[1,3,2]
dioxaborolan-2-yl)-9H-carbazole catalyzed by Pd(PPh
9-alkyl-3-(4,4,5,5-tetramethyl[1,3,2]dioxaborolan-2-yl)-9H-
(
d, 2H, J ¼ 7.7 Hz, eHCarbazole), 8.06 (d, 1H, J ¼ 2.5 Hz, eHNaphthalene),
3 4
) .
Scheme 1. The synthetic routes to compounds 5e13. Reagents and conditions: (a) 9H-carbazole or 3,6-di(tert-butyl)-9H-carbazole, Cu, 18-crown-6, K
2
CO
3
, o-dichlorobenzene,
ꢀ
ꢀ
ꢀ
1
80 C, 24 h; (b) N-vinylcarbazole, Pd(OAc)
2 3
, P(o-tolyl) , DMF, TEA, 90 C, 24 h; (c) aromatic boronic acid pinacol ester, Pd(PPh
3
)
2
Cl
2
, THF/H
2
O, K
2 3
CO , 80 C, 24 h.

244
D. Gudeika et al. / Dyes and Pigments 114 (2015) 239e252
Compounds 11 and 12 were synthesized by Ullmann type
between the naphthalimide and carbazole moieties. For the up-
ward transitions from S , the maximum accessible dihedral angle is
condensation of compound 4 with 9H-carbazole or 3,6-di(tert-
butyl)carbazole, respectively. Compound 13 was obtained by Heck
reaction of bromo derivative 4 with N-vinylcarbazole in the pres-
ence of palladium(II) acetate and tri-o-tolylphosphine. All the crude
products were purified by silica gel column chromatography to
obtain compounds 5e13 in the yields of 32e71%. All the target
0
limited by the molecule energy, which is of the order of the thermal
energy. The broad energy minimum of the D-A type derivatives of
ꢀ
carbazole and naphthalimide extending over the angles of 40e130
implied molecules with a large variety of twist angles available in
the ground state at room temperature. This also indicates weak
steric effects between the fragments for the dihedral angles within
this range. There is also interplay between the lowest S S and S
1 2 3
transitions that involve different molecular orbitals within allowed
1
13
compounds were characterized by HNMR, C NMR, IR and
elemental analysis. They exhibited good solubility in common
organic solvents such as dichloromethane (DCM), chloroform,
tetrahydrofuran (THF), chlorobenzene, dioxane, toluene.
range of the twisting angles. For the C-3 linked compound 8
(
Fig. 2(b)) the largest oscillator strength of 0.75 shows S
transition which is formed by of molecular orbitals. Note, that
and S states is small, >0.1 eV
state becomes the lowest en-
0 2
eS
3.2. Theoretical calculations
p-p
the energy distance between the S
and for rotation angle of 43 this S
1
2
ꢀ
Quantum chemical calculations of the carbazole and naph-
2
thalimide derivatives were performed using density functional
theory (DFT) as implemented in the Gaussian 09 [69] software
package. Ground-state geometries of the molecular structures were
optimized at the B3LYP functional level with the 6-31G(d) basis set
supplemented with polarization functions. Singlet transition en-
ergies, the corresponding oscillator strengths, and spatial distri-
butions of electron density for the highest occupied molecular
orbital (HOMO) and the lowest unoccupied molecular orbital
ergy state. For N-9 linked compound 11 (Fig. 2(b)) the allowed S
2
state shows remarkably smaller oscillator strength of 0.33 for S
0
eS
2
ꢀ
transition at the optimized twisting angle of 61 . The reduction of
the oscillator strength of the lowest allowed transition is typical
feature of N-9 linked carbazole moieties due to enhanced impact of
n-
oscillator strength of 0.004. The energy separation between S
states is of 0.13 eV. Owing to the almost flat configuration
p
orbitals [40]. The lowest energy S
0
eS
1
transition is of low
1
and
S
2
(
LUMO) were obtained by means of the semi empirical ZINDO
compound 13, having ethenyl-containing linkage between N-9
calculations. The DFT calculations revealed similar electronic en-
ergy spectra, and electron density distributions for the mono-
position of carbazole and C-4 position of 1,8-naphthalimide shows
allowed S eS transition with the oscillator strength of 0.95.
0 1
3
substituted and bisubstituted compounds 5e12 up to the S state.
Higher-lying states will not be considered in the further discussion.
Fig. 1 shows optimized geometries and charge density distri-
butions in the HOMO and LUMO states for compounds 5, 8, 11 and
3.3. Thermal properties
The thermal transitions of compounds 5e13 were studied by
13 (for more details on the calculated electron density distributions
DSC and TGA under a nitrogen atmosphere. The values of glass
for HOMO and LUMO molecular orbitals of carbazole and 1,8-
naphthalimide derivatives (6, 7, 9, 10 and 12) see in the
Supplementary Information (SI)).
g m
transition temperatures (T ), melting points (T ), crystallization
temperatures (Tcr) and 5% weight loss temperatures (Tdec-5%) are
summarized in Table 1.
The compounds show significant variation in the rotation angle
between the planes of naphthalimide and carbazole moieties (here
The synthesized derivatives exhibit high thermal stability. Their
5% weight loss temperatures exceed 351 C. Compounds 5e13 were
isolated after the synthesis as crystalline materials. Their first DSC
ꢀ
ꢀ
0
angle denote planar configuration). Compounds 5e10 in which
carbazole is linked to 1,8-naphthalimide moiety at C-3 position
show rotation angle of 51 , while compounds 11, 12 in which
heating scans revealed endothermal melting signals in the range of
108e224 C. No crystallizations were observed during the cooling
ꢀ
ꢀ
carbazole is linked to 1,8-naphthalimide at N-9 position show
larger angle of 60 , while compound 13 having ethenyl-containing
linkage between N-9 position of carbazole and C-4 position of 1,8-
scans, which indicated direct transitions from the melt to glassy
states. In the second DSC heating scans, the compounds exhibited
glass transitions with glass transition temperatures ranging from
ꢀ
ꢀ
naphthalimide shows almost flat configuration with rotation angle
30 to 101 C. Glass transition temperature of compounds 9 and 10
ꢀ
of only 14 . It is evident that the HOMO state comprises charge
were found to be below the room temperature, therefore these
compounds cannot be classified as molecular glasses. The DSC
thermograms of compound 8 are given in Fig. 3.
redistribution from the naphthalimide and carbazole moieties,
where the impact of carbazole orbitals is governed by the rotation
angle. Derivatives of carbazole having two 1,8-naphthalimide
moieties (5e7) show broader electron density distribution
extending on both naphthalimide moieties (compound 5). The
charge density in the LUMO state is predominantly localized on the
naphthalimide moieties for all the compounds.
To obtain the information on the states of different conformers
of the singly bridged multichromophoric compounds, the optimi-
zation was performed for various dihedral angles between the
planes of neighboring carbazole and naphthalimide units. Fig. 2
ꢀ
The first DSC scan of compound 8 revealed melting at 127 C,
whereas after cooling the second heating scan revealed glass
ꢀ
transition at 47 C. Compounds 11 and 12 in which carbazolyl
groups are directly linked via N-9 position to the 1,8-naphthalimide
moiety form glasses with the glass transition temperatures of 40
ꢀ
and 48 C, respectively. Compound 13 in which carbazolyl group is
linked to 1,8-naphthalimide moiety via the bridge containing
double C]C bond, exhibiting almost flat geometry did not form
ꢀ
glass upon cooling from the melt. It only showed melting at 224 C.
shows calculated energies of the ground S
0
and excited S
1
, S
2
and
Nevertheless, amorphous films of compound 13 can be obtained by
processing from solution. Compounds 5e7 having two 1,8-
S
3
states and of the corresponding oscillator strengths of the
transitions, for compounds 8 and 11, in which carbazole moiety is
linked to 1,8-naphthalimide species via its C-3 and N-9 positions,
correspondingly.
g
naphthalimide moieties exhibited considerably higher T than
monosubstituted derivatives 8e10 with the corresponding alkyl
substituents, apparently, because of their larger molecular weights,
which result in the stronger intermolecular interactions. Incorpo-
ration of methyl, butyl and ethylhexyl nonconjugated substituents
at the carbazole N-9 position progressively lead to the remarkable
The energies and oscillator strengths exhibited some angular
ꢀ
asymmetry with respect to a 90 angle due to asymmetry intro-
duced by orientation of the alkyl chains. The optimization of the
total energies revealed flat energy minima of the ground S
0
and
g
decrease in the T values both for monosubstituted (8e10) and
excited S , S and S states with respect to the dihedral angle
1
2
3
bisubstituted (5e7) carbazole derivatives. Apparently, the flexible

D. Gudeika et al. / Dyes and Pigments 114 (2015) 239e252
245
Fig. 1. Optimized geometries and calculated electron density distributions for HOMO and LUMO molecular orbitals of compounds 5, 8, 11 and 13.
alkyl chains especially the branched ones, act as internal plasti-
cizers of the molecular glasses preventing compact molecular
packing.
solutions in polystyrene matrix and the solid films of the pure
compounds are shown in Figs. 4 and 5. The photophysical charac-
teristics are summarized in Table 2.
First we will discuss optical properties of the compounds in
which 1,8-naphthalimide moieties are linked at C-3 and C-6-posi-
tions of carbazolyl groups (compounds 5e10). Dilute THF solutions
of 3-monosubstituted and 3,6-disubstituted carbazole compounds
exhibited two broad absorption bands at 344 nm and 398 nm
3
.4. Optical and photophysical properties
The absorption and normalized fluorescence spectra of the
dilute solutions of compounds 5e13 in dilute THF, of the solid

246
D. Gudeika et al. / Dyes and Pigments 114 (2015) 239e252
Fig. 3. DSC thermograms of compound 8 recorded at a heating/cooling rate of
ꢀ
ꢁ1
2
0 C min under N .
1
substituents at the carbazole nitrogen atom results in the signifi-
cant alteration of the intensity of the lowest energy absorption
band in respect to the higher-energy naphthalimide absorption
band. With the increase of the molecular weight of the alkyl sub-
stituent for monosubstituted compounds 8e10 the intensity of
low-energy band decreases, while that of higher energy band in-
creases. This observation can be attributed to the intramolecular
twisting of the singly bonded donor-acceptor system. One can
suggest that smaller substituents result in flatter geometry of the
donor-acceptor system and thus, stronger absorbance of the lowest
energy band.
Dilute solutions of mono- and disubstituted carbazole com-
pounds 5e10 exhibited efficient fluorescence in the green spectral
region with the bands peaking at 520e534 nm (Fig. 4). The Fluo-
rescence spectra of the dilute solutions in polar THF are unstruc-
tured, broadened and strongly Stokes-shifted (by more than
0 1 2 3
Fig. 2. Calculated energies of the ground S and excited S , S and S states and of
corresponding oscillator strengths of the transitions, for compounds 8 (a, b) and 11 (c,
d).
which are typical for naphthalimide based donor-acceptor systems
120 nm). This observation indicates the pronounced intramolecular
[
29,70]. The absorption band at 344 nm can be attributed to the
naphthalimide moiety [71], while the lowest energy absorption
band can be attributed to the extended -conjugated state
charge-transfer character of the excited states, which is typical for
naphthalimide based donor-acceptor systems [72,73]. Generally,
fluorescence spectra of compounds 5e10 exhibit similar fluores-
cence spectral properties which are in agreement with the results
of DFT modeling showing delocalised orbitals in the HOMO state
and almost similar localization of the excitation on the naph-
thalimide moiety in the LUMO state (see Fig. 4). The wavelengths of
intensity maxima of fluorescence spectra of 3-monosubstituted
carbazole derivatives are red-shifted by 10 nm in comparison
with those of 3,6-disubstituted compounds. The significant red
shift of ca. 60 nm of the fluorescence spectra of the dilute solutions
in THF as compared to the spectra of the solid solutions in poly-
styrene matrix can be attributed to the polarity of the surrounding
media. Pronounced positive solvatochromic effects are typical for
naphthalimide based donor-acceptor systems [29,70]. Efficient
fluorescence of the solid solutions of compounds 5e10 in nonpolar
PS media correlate with the intensity of the lowest energy ab-
sorption band in accordance with variation of the radiative relax-
ation rate (see below). Relatively short radiative decay time of
p
involving the electron-donor carbazole and the electron-acceptor
naphthalimide moieties. In accordance with the quantum chemi-
cal modeling, the values of oscillator strength of the lowest energy
transitions of the bisubstituted carbazole compounds 5e7 are
nearly twice as large as those of the monosubstituted counterparts
8
e10 as a result of extended p-conjugation to the two naph-
thalimide moieties. Interestingly, increase of the length of alkyl
Table 1
Temperatures of the thermal transitions of compounds 5e13.
ꢀ
ꢀ
ꢀ
ꢀ
Tdec-5% [ C]
Compound
T
g
[ C](2nd heating)
T
m
[ C]
T
cr [ C]
5
6
7
8
9
101
96
30
47
15
ꢁ5
40
48
e
154
184
108
127
121
110
117
140
224
e
476
457
383
434
385
351
373
417
422
e
e
e
e
6
e8 ns observed for the compounds in which 1,8-naphthalimide
moieties are linked at C-3 and C-6-positions of carbazolyl groups
indicate on allowed transitions involving the lowest energy pep
10
11
12
13
e
e
e
176
orbitals, that can be further stabilized by the interaction with the
solvent, what is in line with the results of DFT modeling.
ꢀ
Determined by DSC, scan rate 10 C/min, N
2
atmosphere. T
m
g
is melting point, T is
Fluorescence quantum yields (
h) of the compounds in polar THF
glass transition temperature, Tcr is crystallization temperature. Tdec-5%e5% weight
ꢀ
loss temperatures; scan rate 20 C/min, N
2
atmosphere.
solutions were determined to be in range of 0.66e0.83 for 5e10,

D. Gudeika et al. / Dyes and Pigments 114 (2015) 239e252
247
Fig. 4. Absorption and normalized fluorescence spectra of 1
mM solutions in THF (solid line), of the solid solutions in PS matrix at 1 wt% concentration (dotted line), and of the solid
films (dashed line) of compounds 5e7 (thick line) and 8e10 (thin line). Fluorescence quantum yields (
h) are indicated.
while for compounds 5e10 embedded in nonpolar PS matrices the
values of were found to be lower. They varied from 0.40 to 0.67.
The enhancement of in polar solvents was attributed to the
reduction of the influence of nonradiative recombination processes
involving intersystem crossing [70,73]. Fluorescence spectra of the
solid films of compounds 5e10 are slightly broadened and the
constant from 6.4 to 12 ns and synchronous decrease in the non-
radiative decay constant from 12.3 to 8 ns of their solid solutions
in PS. This observation can be attributed to the twisted conforma-
tion of the molecules in the ground state. Flatter molecular ge-
ometry results in stronger radiative transitions and lower rate of
the non-radiative relaxation.
h
h
values of
h
of the films were found to be lower from 5 to 76 times
The decay transients of the solid films of compounds 5e10
exhibited non-exponential behavior with average decay times
shorter than those observed for the dilute solutions. Since the
decay curves of the solid solutions in PS are single exponential, one
can attribute the shortening of the lifetimes in the wet casted solid
films to the dispersive exciton hopping [76].
The absorption and normalized fluorescence spectra of dilute
THF solutions, solid solutions in polystyrene matrix and of solid
films of the investigated carbazole and 1,8-naphthalimide de-
rivatives 11e13 are shown in Fig. 5. The photophysical charac-
teristics of compounds 11e13 are summarized in Table 2.
Generally the absorption spectra of the compounds (11e13) in
which carbazolyl groups are linked via N-9 position to the 1,8-
naphthalimide moiety show two similar bands as the absorp-
tion spectra of 1,8-naphthalimide derivatives with the carbazolyl
groups linked at C-3 and C-6 carbazole positions, however the
lowest energy absorption band of the former compounds is
significantly red-shifted (up to 38 nm). The red shift can be
due to exciton migration quenching.
Excited state relaxation for the dilute solutions of compounds
5
e10 in THF was found to follow the single exponential decay
profile with estimated fluorescence lifetimes from 5.2 ns to 5.9 ns.
The estimated fluorescence decay times for mono-substituted
carbazole compounds were longer by 0.5e0.6 ns than those
observed for bi-substituted derivatives (see Fig S2, (SI)). The
incorporation of the compounds into solid PS matrix usually leads
to restriction of the intramolecular vibrations and thus to reduction
of the rate of non-radiative relaxation [74,75]. However in the case
of compounds 5e10 the non-radiative decay rate was estimated to
be 2e3 times higher in THF liquid media compared to the values
estimated for the solid PS matrix. At the same time, the radiative
decay rates of the dilute THF solutions and of the solid solutions in
PS of the compounds showed only slight differences. Thus the in-
crease of
h in THF solutions occurs mainly due to the reduction of
the non-radiative relaxation rate induced by the polarity of the
surrounding media. The similar results were observed for naph-
thalimide systems possessing fluorene substituents and were
attributed to the reduction of the intersystem crossing rate [70].
The alteration of the recombination rate constants, induced the
increase of alkyl substituents at the nitrogen atom carbazole moi-
ety, correlates well with the intensity of lowest energy absorption
bands. For instance, the increase in molecular weight of compounds
attributed to the low lying ne
p states of carbazole moiety [40].
The optical properties of compounds 11 and 12 significantly
differ from those of compound 13. As revealed by DFT modeling,
the singly bonded compounds 11 and 12 exhibit significantly
twisted molecular geometry, while compound 13 with ethenyl-
containing linkage between the chromophores possesses
almost flat geometry. This is in line with almost 6-fold
enhancement of the low-energy band oscillator strength of
8
e10 results in the continuous increase of the radiative decay

248
D. Gudeika et al. / Dyes and Pigments 114 (2015) 239e252
0.07e0.09. These values were found to be more than 10-fold lower
than those estimated for the derivatives 5e10 in which 1,8-
naphthalimide moieties are linked at C-3 or C-3,6-positions of
carbazole ring. Fluorescence decay times for compounds 11 and 12
were 7 and 7.7 ns respectively, while compound 13, possessing
ethenyl-containing linkage, demonstrated 10-fold faster fluores-
cence decay. In accordance with the variation of the oscillator
strength of the lowest energy absorption band, the radiative decay
time of compounds 11 and 12 is 5e6 times larger than that of
compound 13. This is in line with the results of DFT modeling,
1 0
indicating on forbidden S eS transition for strongly twisted
compound 11 in contrast to compound 13 possessing almost flat
geometry. Interestingly, the rate of non-radiative recombination is
also significantly faster for compound 13. In case of the linkage via
N-9 position of carbazole moiety the impact of polarity of the
surrounding media has opposite effect as compared to C-3 linked
compounds. The rate of non-radiative relaxation is decreasing by a
factor of 2e3 in a nonpolar media. We attribute this observation to
the peculiarities of the intersystem crossing rate of the compounds
in which carbazolyl group is linked via N-9 position.
The solid films of the carbazole derivatives substituted at N-9
position demonstrated fluorescence spectra with the band peaks at
501, 537 and 563 nm for compounds 11, 12 and 13, respectively.
Fluorescence spectra of the solid films of compounds 11 and 12
were found to be significantly blue shifted in comparison with the
spectra of THF solutions. Solid state spectra exhibit well expressed
vibronic structures indicating the regular packing of the molecules.
It should be stressed that compound 13, possessing almost flat
geometry, exhibited very efficient fluorescence in the solid state
with
h as high as 0.45, which is significantly higher than that of
isolated molecules in liquid solution in THF and in solid solution in
PS. The significant red shift and narrowing of the fluorescence
spectrum indicate the ordered packing and enhanced excitonic
interaction in the film of compound 13. The enhancement of the
average fluorescence lifetime in the film and the increase of
h
Fig. 5. Absorption and normalized fluorescence spectra of 1
line), of the solid solutions in PS matrix at 1 wt% concentration (dotted line), and of the
solid films (dashed line) of compounds 11e13. Fluorescence quantum yields (h) are
indicated.
m
M solution in THF (solid
indicate significant reduction of the non-radiative relaxation rate.
The similar tendency was observed for anthracene crystals, where
the significant reduction of the intersystem crossing rate was
attributed to the increased exciton coupling in the crystal [77,78].
3
.5. Electrochemical and photoelectrical properties
compound 13 with respect respect to those of compounds 11 and
2 (see Fig. 1).
Dilute solutions of compounds 11e13 exhibited broad unstruc-
tured fluorescence bands peaking at 540e579 nm. The estimated
fluorescence quantum yields of the solutions were in the range of
1
The electrochemical properties of compounds 5e13 were
examined by cyclic voltammetry (CV). The measurements were
carried out at 25 C in CH
tylammonium hexafluorophosphate (Bu
ꢀ
2
Cl
2
solution containing 0.1 M tetrabu-
NPF as supporting
4
6
)
Table 2
Photophysical properties of the dilute THF solutions, solid films and 1 wt% solid solutions in PS matrixes of compounds 5e13.
Compound Liquid solution in THF
Neat film
Solid solution in PS
a
b
max
max
max
l
abs(nm) (ε ,
l
F
h
t
t
R
t
NR
l
F
h
t
(ns)
l
F
h
t
t
R
t
NR
ꢁ
1
ꢁ1
c
d
d
c
c
d
d
L mol cm
)
(nm)
(ns) (ns)
(ns)
(nm)
(nm)
(ns) (ns)
(ns)
5
6
344 (25,061) 397 (24,643) 522
345 (24,256) 398 (25,014) 520
0.69 5.4
0.83 5.2
7.8
6.3
17.4
30.6
541
522
<0.01 0.2 [57%], 1.1 [30%], 6.4 [13%] 468
0.45 3.8 8.4
6.9
12.1
0.17 4.4 [52%], 1.2 [27%], 17.7 461
21%]
0.67
4
5.9
[
7
8
9
343 (21,113) 395 (14,277) 522
345 (10,833) 398 (12,202) 533
344 (12,413) 398 (10,505) 534
0.73 5.2
0.76 5.9
0.78 5.8
7.1
7.8
7.4
19.3
24.6
26.4
513
522
533
0.06 1.8 [56%], 0.4 [28%], 5.9 [16%] 461
0.01 0.3 [46%], 1.1 [39%], 4.3 [15%] 465
0.48 3.7
0.66 4.2
0.55 4.1
7.7
6.4
7.5
7.1
12.3
9.1
0.07 2.3 [47%], 0.5 [34%], 11.4
19%]
466
[
10
11
12
13
342 (16,553) 398 (8296)
336 (15,253) 413 (3660)
344 (14,647) 432 (3167)
433 (18,078)
529
540
579
542
0.66 5.7
0.09 7
0.08 7.7
0.07 0.7
8.6
58.3
51.3
10
16.8
7.9
9.1
519
501
537
563
0.06 1.0 [62%], 0.3 [31%], 3.5 [7%] 462
0.10 4.9 [49%], 9.8 [45%], 1.1 [6%] 474
<0.01 0.3 [47%], 1.0 [43%], 3.3 [10%] 496
0.40 4.8 12
0.32 13.8 43.1
0.15 13.8 92
0.15 2.6 17.3
8
20.3
16.2
3.1
0.8
0.45 4.5 [83%], 1.9 [17%]
495
a
b
c
Peak wavelength of absorption bands.
Molar extinction coefficient.
Wavelength of fluorescence band maximum.
Radiative and non-radiative decay time constants calculated as
d
t
/h
and
t/(1ꢁh), respectively.

D. Gudeika et al. / Dyes and Pigments 114 (2015) 239e252
249
electrolyte with a glassy carbon working electrode. The oxidation
potentials were measured vs Ag/AgNO as the reference electrode.
Taking 4.8 eV as the ionization potential (IPCV) value for the ferro-
cene redox system related to the vacuum level, the IPCV and elec-
tron affinity (EACV) values of compounds 5e13 were calculated. The
results of the CV measurements are shown in Table 3.
Compounds 5e13 exhibited irreversible oxidation/reduction
processes, which could be assigned to one-electron oxidation of
carbazole moiety at positive potential range (localized at
Compound 13 also has active 3,6-positions of the carbazole moiety
and the repeated CV scans resulted in electrochemical polymeri-
zation of the compound (Fig. 6(e)). The CV curve of compound 12
shows two quasi-reversible oxidation peaks in the positive poten-
tial range (Fig. 6(f)). The first peak with the onset potential of 0.66 V
can be ascribed to the oxidation of the electron-rich nitrogen atom
in the carbazole core. The second peak, with the onset potential of
0.88 V can be attributed to oxidation of tert-butyl groups, which
causes radical recombination and formation of a quinoid structure
[80]. Repeated oxidation cycles did not change the redox potential
what is an evidence of the electrochemical stability of the
compound.
The ionization potential values, the layers of the synthesized
compounds were also established by electron photoemission
technique in air. Electron photoemission spectra of the amorphous
films of compounds 5e13 are shown in Fig. 7. The values of the
ionization potentials (IPEP) are presented in Table 4.
3
0
.66e0.96 V) and quasi-reversible reduction/reoxidation processes
at negative potential range (localized at ꢁ1.76 to ꢁ1.88 V). 3,6-
Disubstituted carbazoles 5e7 showed much higher oxidation po-
tentials (0.88 V (for 5), 0.87 V (for 6) and 0.95 V (for 7)) compared to
3
0
-substituted carbazoles 8e10 (0.77 V (for 8), 0.77 V (for 9) and
.78 V (for 10)) (Table 3). The similar positions of cathodic reduction
peaks indicate that naphthalimide moieties are responsible for
these processes. The solid state ionization potentials established by
CV (IPCV) range from 5.45 to 5.76 eV. In the 3-substituted carbazoles
The IPEP values of amorphous layers of the synthesized com-
pounds range from 5.57 to 6.01 eV. The values of solid state ioni-
zation potentials established by electron photoemission technique
are by ca. 0.2e0.3 eV higher than those estimated by CV. However
the trend of the IPEP values is in agreement with that of IPCV. 3,6-
Disubstituted compounds 5e7 and 9-substituted derivatives 11,
8
e10 the donoric fragment apparently has stronger influence on
the electrochemical properties as compared to 3,6-disubstituted
carbazoles 5e7. For this reason, 3-substituted carbazoles 8e10
show lower IPCV values as compared to those of 3,6-disubstituted
carbazoles 5e7.
Since C-3- and C-6-positions of carbazole moieties in com-
pounds 5e7 are occupied, repeated 5 oxidation cycles of the solu-
tions of these compounds do not show any changes in the CV
curves. This is an evidence of the electrochemical stability of the
12 exhibit
a
little higher ionization potentials than 3-
monosubstituted compounds 8e10 and 9-substituted compound
13.
Charge-transporting properties of carbazole and 1,8-
naphthalimide derivatives were studied by CELIV technique at
room temperature in air. The samples for CELIV measurements
were prepared in the diode configuration by spin coating. Before
the CELIV measurements using integral mode TOF technique we
defined the holes as majority charge carriers of the studied carba-
zole and 1,8-naphthalimide derivatives. Fig. 8 shows photo-CELIV
current transients of the amorphous layer of 5 for the different
maximum voltage of the triangle pulse.
3
,6-disubstituted carbazoles (5e7). Meanwhile the electron-rich
and highly activated 6-positions of 3-substituted carbazoles 8e10
are very sensitive towards electrochemical oxidation, which may
lead to dimerization reactions [79] and dimer formation in the
potential range 0e1 V, and hence to a lower electrochemical sta-
bility (Fig. 6(aec)).
Among 9-substituted carbazoles 11e13 the oxidation potentials
are in the order: 11 > 12 > 13. The EACV levels of compounds 5e13,
which are related to the onset reduction potentials, are close to
each other (Table 3).
The capacitive charging current was found to be much higher
than the current related to the conductivity of the derivative. The
2
9
-Substituted carbazole derivative 11 has active 3,6-positions of
charge carrier mobilities were estimated by the formula
m
¼ Kd /
2
the carbazole moiety and therefore undergoes electrochemical
polymerization and the film formation on the electrode surface
Atmax, where K ¼ 2/3 for volume photogeneration charge carrier,
d is the sample thickness, A ¼ U(t)/t is the voltage rise rate, tmax is
extraction time when the maximum in the current transients is
observed. The maximum was not clearly observed for the layer of 5
(Fig. 6(e)). The polymeric film formation is evidenced by the suc-
cessive growth of the current within the potential range ꢁ2 to 1.3 V.
(Fig. 8) therefore for the estimation of tmax we subtracted the curves
of the dark-CELIV current transients from the curves of the photo-
CELIV current transients (Fig. 8, insert). The extraction time values
(tmax) for the amorphous layer of compound 5 decreased from
Table 3
ꢁ ꢁ5
5
2.2$10 to 1.45$10 s with the increase of the maximum voltage
Electrochemical characteristics of 5e13.
of the pulse from 10 to 20 V. This observation shows the increase of
the mobility of charge carriers with the increase of the electric field.
The CELIV current transients of the amorphous layers of other
studied derivatives were similar to those of compound 5. It was not
possible to measure charge motilities for derivatives 9 and 10 since
their glass transition temperatures are lower than the room tem-
perature and it was difficult to get a top Al electrode on the layers of
these derivatives.
Compound Eox vs
E
Fc/V
red
onset
a
vs
IPCV
[eV]
EACV
[eV]
E
elc
g
[eV]c
E
opt
g
[eV]
IPEP,
[eV]
onset
a
b
b
d
e
Fc/V
5
6
7
8
9
1
1
1
1
0.88
0.87
0.95
0.77
0.77
0.78
0.96
ꢁ1.87
ꢁ1.85
ꢁ1.86
ꢁ1.87
ꢁ1.88
ꢁ1.88
ꢁ1.76
5.68
5.67
5.75
5.56
5.55
5.58
5.76
5.46
5.45
ꢁ2.94 2.75
ꢁ2.95 2.72
ꢁ2.94 2.81
ꢁ2.94 2.61
ꢁ2.93 2.63
ꢁ2.92 2.66
ꢁ3.04 2.72
ꢁ3.01 2.45
ꢁ3.00 2.46
2.57
2.55
2.78
2.40
2.75
2.58
2.73
2.50
2.51
5.95
5.98
6.00
5.78
5.76
5.93
6.09
5.81
5.69
0
1
2
3
The hole mobility data for compounds 5e7 and 11e13 estab-
lished by CELIV are summarized in Table 4. All the studied de-
rivatives of carbazole and 1,8-naphthalimide display the hole
0.66, 0.86 ꢁ1.79
0.66
ꢁ1.80
a
ox
red
E
and E
are measured vs. ferrocene/ferrocenium.
onset
onset
ꢁ6
2
b
mobility values of the order of 10 cm /V$s at the electric fields of
Ionization potentials and electron affinities estimated according to
5
ox
red
ox
red
the range of (3.6e8.1)$10 V/cm, with only a minor effect of the
IPCV ¼ ðE
þ 4:8Þ [eV]. EACV ¼ ꢁðE
þ 4:8Þ [eV] (where, E
and E
are
onset
onset
onset
onset
þ
the onset reduction and oxidation potentials versus the Fc/Fc ).
substitution pattern and the linking topology on the hole mobil-
ities. These mobility values are lower compared to those of
donorꢁacceptor molecules consisting of triphenylamine core and
c
elc
elc
E
¼ jIPCVj ꢁ jEACVj, whereEg is the electrochemical band gap.
g
d
The optical band gap estimated from the onset wavelength of optical absorption
edge, in which the edge is the onset
according to the empirical formula: E
value of absorption spectrum in long wave direction.
g
¼ 1240/
l
l
1,8-naphthalimide arms [81], and of naphthalimide-substituted
e
Established from electron photoemission in air spectra.
fluorene derivatives [70]. The charge mobilities of the earlier

250
D. Gudeika et al. / Dyes and Pigments 114 (2015) 239e252
Fig. 6. Cyclic voltammograms of compounds 5e13 (10 5 M solutions, scan rate of 50 mV s vs Ag/Ag ) in 0.1 M solution of Bu
ꢁ
ꢁ1
þ
4 6 2 2
NPF in CH Cl .
4. Conclusions
A series of 1,8-naphthalimide and carbazole derivatives with
different substitution patterns and different linking topologies
were synthesized via palladium-catalyzed reactions. These com-
pounds exhibit high thermal stability with 5% weight loss tem-
ꢀ
perature up to 476 C. Most of the synthesized compounds are
capable of glass formation with glass transition temperatures from
ꢀ
3
0 to 87 C. Optical properties of the singly bonded carbazole
electron-donor and naphthalimide electron-acceptor systems were
rationalized in the frames of the model of intramolecular charge-
transfer states, which is confirmed by DFT modeling and analysis
of the excited state properties in the media of various polarity and
viscosity. Naphthalimide and carbazole donor-acceptor systems
show broad unstructured fluorescence spectra peaking at
460e580 nm. Singly bonded 3-C-monosubstituted and 3,6-C-
disubstituted compounds show pronounced positive sol-
vatochromic effects with the reduction of the non-radiative
recombination rate in polar solvents which results in high photo-
luminescence quantum yields up to 0.83. Increase of the length of
alkyl substituents at N-9 position carbazole ring induces twisted
conformation of the singly bonded naphthalimide and C-3-
carbazole system. Strong intermolecular coupling of the flat de-
rivative of 1,8-naphthalimide and carbazole possessing ethenyl-
containing linkage in the solid state results in the significant
enhancement of fluorescence quantum yield (up to 0.45) due to
Fig. 7. Electron photoemission spectra of the layers of compounds 5e13.
reported derivatives were estimated by xerographic time of flight
XTOF) technique. The charge mobility values of the films of com-
pounds 5e8, 11e13 could be higher if measured it by time of flight
(
(
[
TOF) [82] or by organic field effect transistor (OFET) technique
83].
Table 4
The charge carrier mobility data for the layers of the derivatives of carbazole and 1,8-naphthalimide established from CELIV transients at 20 V.
Compound
5
6
7
8
11
12
13
Thickness (d), nm
150
1.43$10
100
2.37$10
110
0.87$10
240
1.6$10
100
3$10
160
0.47$10
75
2
ꢁ6
ꢁ6
ꢁ6
ꢁ6
ꢁ6
ꢁ6
ꢁ6
0.14$10
Mobility (
m
), cm /V s

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