Symmetrical azine-based polymers possessing 1-phenyl-1,2,3,4- tetrahydroquinoline moieties as materials for optoelectronics

Article abstract of DOI:10.1016/j.reactfunctpolym.2011.07.005

Glycidyl-terminated 3-hydroxy-1-phenyl-1,2,3,4-tetrahydroquinoline-6- carbaldehyde azine and its 4,4′-thiobisbenzenethiol, 2,5-dimercapto-1,3,4- thiadiazole, and 1,3-benzenedithiol copolymers were synthesized by multi-step synthetic route. The materials w

Full text of DOI:10.1016/j.reactfunctpolym.2011.07.005

Reactive & Functional Polymers 71 (2011) 1016–1022
Contents lists available at ScienceDirect
Reactive & Functional Polymers
journal homepage: www.elsevier.com/locate/react
Symmetrical azine-based polymers possessing
1-phenyl-1,2,3,4-tetrahydroquinoline moieties as materials for optoelectronics
Jolanta Ardaraviciene a,b, Brone Barvainiene a,c, Tadas Malinauskas a, Vygintas Jankauskas b,
Kestutis Arlauskas b, Vytautas Getautis a,
⇑
a Department of Organic Chemistry, Kaunas University of Technology, Radvilenu pl. 19, LT-50254 Kaunas, Lithuania
b Department of Solid State Electronics, Vilnius University, Sauletekio 9, LT-10222 Vilnius, Lithuania
c Kaunas University of Applied Sciences, Pramones pr. 20, LT-50468 Kaunas, Lithuania
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 4 May 2011
Received in revised form 1 July 2011
Accepted 2 July 2011
Available online 7 July 2011
Glycidyl-terminated 3-hydroxy-1-phenyl-1,2,3,4-tetrahydroquinoline-6-carbaldehyde azine and its
4,40-thiobisbenzenethiol, 2,5-dimercapto-1,3,4-thiadiazole, and 1,3-benzenedithiol copolymers were
synthesized by multi-step synthetic route. The materials were examined by various techniques including
differential scanning calorimetry, UV and fluorescence spectrometry as well as xerographic time of flight
technique. The ionization potentials of these materials are in the range of 5.40–5.61 eV as determined by
the electron photoemission method. The hole mobility, reaching 10ꢀ6 cm2/V s at the 106 V/cm electric
field, was observed in the polymer obtained in the polyaddition reaction of the above mentioned mono-
mer with 4,40-thiobisbenzenethiol.
Keywords:
Electroactive polymers
Azine
1-Phenyl-1,2,3,4-tetrahydroquinoline
Ionization potential
Charge transport
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
employed in the polyaddition reaction with bifunctional nucleo-
philic linking agents in the presence of triethylamine (TEA) to yield
Aromatic carbonyl compounds react easily with hydrazine form-
ing hydrazones, which could condense with a second molecule of
the carbonyl compound to yield an azine [1]. Due to fascinating
physical and chemical properties, azines and their derivatives have
been extensively applied in such areas as dyes [2–11], aggregation-
induced emission enhancement or nonlinear optical fluorophores
[12,13], biological [2,5,11,14–16], and pharmaceutical [17,18]
applications. Some of the azines have been also investigated as
liquid crystal compounds [19–23]. They have been studied for the
possible application in the twisted-nematic displays [24]. Further-
more, there are many papers on polyazines as highly conjugated
polymers in electronic, optoelectronic, and photonic applications
[25–29]. Additionally, a number of papers dedicated to the polya-
zines obtained by oxidative polymerization of various monomers
with chromophores connected via the azine linkage have been
published, and some of these polymers demonstrate high photoef-
ficienty [30,31].
the polymeric hole transporting materials (HTM). These HTM are
soluble in common organic solvents such as THF, chloroform,
dioxane, and exhibit hole drift mobility of 10ꢀ5 cm2/V s at strong
electric field [37,38].
Generally, symmetrical azines (Fig. 1a) are crystalline materials
which make them quite easy to purify by recrystallization. This fact
and one-step synthesis procedures, usually with quantitative yield
of the desired product, are two main advantages of the symmetrical
azines. However, this crystallinity is the key limiting factor for
applying various chromophores connected via azine linkage in the
optoelectronic devices. Unsymmetrical azines (Fig. 1b) prepared
from two different carbonyl compounds are more promising from
this point of view, as the tendency to crystallize is significantly
reduced; however, they are much more difficult to synthesize com-
pared to the symmetrical analogues. 3-Hydroxy-1,2,3,4-tetrahydro-
quinoline possesses flexible aliphatic chain and reactive hydroxyl
group, which can be exploited to further modify the molecule in
order to further enhance the solubility and decrease tendency to
crystallize. All these findings prompted us to synthesize new
symmetrical azine based polymers, containing phenyl-1,2,3,4-tetra-
hydroquinoline moieties, which could be used as HTM in optoelec-
tronic devices.
Recently, we have reported a new class of monomers [32] and
polymers [33–36] based upon hydrazone moieties. The monomers
were obtained in the reaction of various bifunctional hydrazones
with epichlorohydrin. The hydrazone containing monomers were
In the light of these findings, we designed a synthesis route to
azine chromophore-containing monomers and polymers with
⇑
Corresponding author.
E-mail address: vytautas.getautis@ktu.lt (V. Getautis).
1381-5148/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.reactfunctpolym.2011.07.005

J. Ardaraviciene et al. / Reactive & Functional Polymers 71 (2011) 1016–1022
1017
anhydrous magnesium sulfate and filtered off. Ethyl acetate and
excess of epichlorohydrin were removed. The residue was dis-
solved in methanol:THF = 3:1 and crystals formed when kept at
ꢀ5 °C. The crystalline product was filtered off and washed with
diethyl ether. Yield: 2.0 g (59%); mp: 132–134 °C (recrystallized
from ethyl acetate:2-propanol = 2:1).
Fig. 1. Chemical structure of symmetrical (a) and unsymmetrical (b) azines.
1H NMR (300 MHz, CDCl3, d, ppm): 8.51 (s, 2H, CH@N), 7.58 (s,
2H, 5-H of Ht), 7.47–7.14 (m, 12H, Ar), 6.67, 6.66 (2 d, J = 8.6 Hz,
2H, diastereomeric 8-H of Ht), 4.14–4.01 (m, 2H, CH of Ht), 3.94–
3.40 (m, 8H, NCH2 and OCH2), 3.27–3.09 (m, 4H, CH2Ar), 3.05–
2.90 (m, 2H, CH of epoxy gr.), 2.83–2.76 (m, 2H, one of CH2CH
protons from epoxy gr., HA), 2.61 (dd, JAB = 4.7 Hz, JBX = 2.7 Hz,
1H, HB of one diastereomer of CH2CH from epoxy gr.), 2.56 (dd,
charge transporting ability. To the best of our knowledge, the
charge drift mobility of the azine polymers has not been yet inves-
tigated. In this paper, we report the synthesis and the characteriza-
tion of new photoconductive polymers containing symmetrical
azine moieties obtained by polyaddition of glycidyl-terminated
3-hydroxy-1-phenyl-1,2,3,4-tetrahydroquinoline-6-carbaldehyde
azine and aromatic dimercapto compounds.
0
0
0
0
0
JA B = 4.7 Hz, JB X = 2.4 Hz, 1H, HB of other diastereomer of CH2CH
from epoxy gr.). IR selected bonds (KBr,
m
, cmꢀ1): 3060, 3032 (aro-
matic CH), 2943, 2864 (aliphatic CH); 1608 (CH@N), 1091
(CAOAC); 698 (CH@CH of monosubstituted benzene). 13C NMR
(75 MHz, CDCl3, d, ppm): 160.74, 146.73, 146.62, 146.47, 146.40,
129.93, 129.80, 129.66, 127.99, 127.86, 125.54, 125.43, 125.08,
125.01, 124.38, 124.28, 121.08, 121.01, 114.38, 114.25, 71.52,
71.39, 69.43, 69.22, 54.09, 53.55, 50.97, 50.90, 44.32, 33.83,
33.52. ESI-MS (20 V, m/z,%): 615 [M + 1]+ (95). Anal. calcd for
C38H38N4O4: C, 74.25; H, 6.23; N, 9.11. Found: C, 74.37; H, 6.38;
N, 8.92.
2. Experimental
2.1. Materials
Hydrazine hydrate, 4,4-thiobisbenzenethiol (TBBT), 2,5-dimer-
capto-1,3,4-thiadiazole (DMTD), and 1,3-benzenedithiol (BDT)
were purchased from Aldrich and used as received. 3-Hydroxy-1-
phenyl-1,2,3,4-tetrahydroquinoline (1), 3-acetyl-1-phenyl-1,2,3,
4-tetrahydroquinoline (2), and 3-acetyl-1-phenyl-1,2,3,4-tetrahy-
droquinoline-6-carbaldehyde (3) were synthesized according to
procedures described previously [39]. 3-Hydroxy-1-phenyl-
1,2,3,4-tetrahydroquinoline-6-carbaldehyde (4) was prepared
according to the published procedure [40].
2.2.3. General procedure for synthesis of polymers P1–P3
The polymers P1–P3 were prepared according to the general
procedure described below: monomer 6 (1.3 mmol), corresponding
dimercapto linking agent (1.3 mmol), and TEA (2.6 mmol) were re-
fluxed in THF (10 ml) under argon atmosphere for 45 h (TLC,
THF:n-hexane = 3:2). The reaction mixture was cooled to room
temperature and filtered through the 3–4 cm layer of silica gel
and the silica gel was washed with THF. Obtained solution was
concentrated to 10–15 ml by evaporation and then poured into
20-fold excess of n-hexane with intensive stirring. The resulting
precipitate was filtered off and washed repeatedly with n-hexane
and dried under vacuum at 40 °C.
2.2. Synthesis
2.2.1. 1,2-Bis(3-hydroxy-1-phenyl-1,2,3,4-tetrahydroquinoline-6-
ylmethylene)azine (5)
Aldehyde 4 (9.5 g, 0.04 mol) was dissolved in 10 ml of hot THF.
The solution was cooled to room temperature, hydrazine hydrate
(1 ml, 0.02 mol) was added and the reaction mixture was refluxed
for 1 h. The crystalline product formed during the reaction (TLC,
THF:n-hexane = 1:4) was filtered off and washed with 2-propanol.
Yield: 8 g (85%); mp: 224–226 °C (recrystallized from THF).
1H NMR (300 MHz, DMSO-d6, d, ppm): 8.45 (s, 2H, CH@N), 7.50–
7.17 (m, 14H, Ar), 6.54 (d, J = 8.6 Hz, 2H, 8-H of Ht), 5.12 (d, J =
3.9 Hz, 2H, OH), 4.21–4.10 (m, 2H, CH of Ht), 3.68 (dd, JAB = 11.7 Hz,
JAX = 2.2 Hz, 2H, one of NCH2 protons, HA), 3.44 (dd, JBA = 11.7 Hz,
JBX = 6.6 Hz, 2H, another of NCH2 protons, HB), 3.05 (dd,
JAB = 15.7 Hz, JAX = 4.1 Hz, 2H, one of CH2Ar protons, HA), 2.76 (dd,
JBA = 15.7 Hz, JBX = 7.2 Hz, 2H, another of CH2Ar protons, HB). IR se-
2.2.3.1. Poly[1,2-bis(3-oxiranylmethoxy-1-phenyl-1,2,3,4-tetrahydro-
quinoline-6-yl-methylene)azine-alt-4,40-thiobisbenzenethiol]
(P1). Polymer P1 was prepared according to the same procedure as
described above, except that 1.3 mmol of 4,40-thiobisbenzenethiol
was used. Yield: 0.65 g (56%).
1H NMR (300 MHz, CDCl3, d, ppm): 8.48 (s, 2H, CH@N), 7.53 (s,
2H, 5-H of Ht), 7.45–6.98 (m, 20H, Ar), 6.63 (d, J = 8.4 Hz, 2H, 8-H
of Ht); 4.01–3.35 (m, 12H, NCH2CH and OCH2CH); 3.17–2.69 (m,
8H, CH2Ar and SCH2), 2.10–1.51 (m, 2H, OH). IR selected bonds
lected bonds (KBr, m
, cmꢀ1): 3600–3200 (OH), 3058, 3033 (aro-
(KBr, m
, cmꢀ1): 3600–3200 (OH), 3035 (aromatic CH), 2864 (ali-
matic CH), 2930, 2865 (aliphatic CH), 1606 (CH@N), 824, 795
(CH@CH of 1,2,4-trisubstituted benzene), 765, 701 (CH@CH of
monosubstituted benzene). 13C NMR (75 MHz, DMSO-d6, d, ppm):
159.78, 146.46, 146.08, 130.18, 129.68, 126.96, 125.50, 125.39,
124.89, 123.46, 121.61, 113.21, 66.96, 62.00, 56.72, 35.76, 25.08.
ESI-MS (20 V, m/z,%): 503 [M + 1]+ (1 0 0). Anal. calcd for
phatic CH), 1608 (CH@N); 1268 (CAN), 1114 (CAOAC), 813, 698
(CH@CH of 1,4-disubstituted benzene, 1,2,4-trisubstituted ben-
zenes and monosubstituted benzenes). 13C NMR (CDCl3, 75 MHz,
d, ppm): 160.69, 146.59, 146.55, 146.41, 135.06, 133.24, 131.40,
129.97, 129.69, 127.92, 125.41, 125.34, 125.11, 124.20, 120.88,
120.83, 114.40, 114.34, 75.06, 71.36, 70.62, 70.48, 68.89, 53.55,
36.87, 33.40.
C32H30N4O2: C, 76.47; H, 6.02; N, 11.15. Found: C, 76.59; H, 5.91;
N, 11.28.
2.2.2. 1,2-Bis(3-oxiranylmethoxy-1-phenyl-1,2,3,4-
tetrahydroquinoline-6-ylmethylene)azine (6)
2.2.3.2. Poly[1,2-bis(3-oxiranylmethoxy-1-phenyl-1,2,3,4-tetrahydro-
quinoline-6-yl-methylene)azine-alt-2,5-dimercapto-1,3,4-thiadiazole]
(P2). Polymer P2 was prepared according to the same procedure as
described above, except that 1.3 mmol of 2,5-dimercapto-1,3,4-
thiadiazole was used. Yield: 0.33 g (32%).
A mixture of 5 (2.8 g, 0.0045 mol) and epichlorohydrin (25 ml,
0.3 mol) was stirred vigorously for 5 h at 35–40 °C. During the
course of the reaction anhydrous Na2SO4 (3 g, 0.02 mol) and 85%
powdered KOH (6.7 g, 0.1 mol) were added in six equal portions
every hour with prior cooling of the reaction mixture to 30 °C. After
termination of the reaction (TLC, THF:n-hexane = 1:4), the mixture
was extracted with ethyl acetate, the organic layer was dried over
1H NMR (300 MHz, DMSO, d, ppm): 8.42 (s, 2H, CH@N), 7.60–
7.12 (m, 14H, Ar), 6.52 (d, 2H, J = 8.4 Hz, 8-H of Ht), 5.42–5.33
(m, 2H, OH), 4.21–2.72 (m, 20H, NCH2CH, OCH2CH, CH2Ar and
SCH2). IR selected bonds (KBr, m
, cmꢀ1): 3600–3200 (OH), 2969,

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J. Ardaraviciene et al. / Reactive & Functional Polymers 71 (2011) 1016–1022
2868 (aliphatic CH), 1608 (CH@N), 1270 (CAN), 1112 (CAOAC),
The strong (10ꢀ15–10ꢀ12 A) photocurrent was flowing in the circuit
699 (monosubstituted benzene).
under illumination. Photocurrent I is strongly dependent on the
incident light photon energy hm m) dependence was
. The I0.5 = f(h
2.2.3.3. Poly[1,2-bis(3-oxiranylmethoxy-1-phenyl-1,2,3,4-tetrahydro-
quinoline-6-yl-methylene)azine-alt-1,3-benzenedithiol] (P3). Poly-
mer P3 was prepared according to the same procedure as
described above, except that 1.3 mmol of 1,3-benzenedithiol were
used. Yield: 0.88 g (86%).
plotted. Usually the dependence of photocurrent on incident light
quanta energy is well described by the linear relationship between
I
0.5 and h
m
near the threshold [42,43]. The linear part of this depen-
dence was extrapolated to the h axis and Ip value was determined
m
as the photon energy at the interception point.
1H NMR (300 MHz, CDCl3, d, ppm): 8.51 (s, 2H, CH@N), 7.56 (s,
2H, 5-H of Ht), 7.46–7.07 (m, 16H, Ar), 6.67 (d, J = 8.6 Hz, 2H, 8-H of
Ht), 4.03–3.39 (m, 12H, NCH2CH and OCH2CH), 3.20–2.80 (m, 8H,
The hole drift mobility was measured by the XTOF technique
[43–45]. The samples for mobility measurements were prepared
from solutions in THF of neat HTM. The layer thickness was in
CH2Ar and SCH2), 1.80–1.60 (m, 2H, OH). IR (KBr,
m
, cmꢀ1): 3600–
the range of 1.5–2 lm. The sample substrate was polyester film
3200 (OH); 3057, 3036 (aromatic CH); 2897, 2864 (aliphatic CH);
1608 (CH@N); 1268 (CAN); 1114 (CAOAC); 698 (monosubstituted
benzene). 13C NMR (CDCl3, 75 MHz, d, ppm): 160.74, 146.61,
146.42, 136.90, 129.98, 129.69, 129.34, 127.93, 126.52, 125.41,
125.35, 125.08, 124.22, 120.97, 120.92, 114.41, 114.37, 71.43,
71.40, 70.66, 70.50, 69.03, 68.98, 53.59, 36.74, 33.46.
with a conductive Al layer. Positive corona charging created an
electric field inside the HTM layer. Charge carriers were generated
at the layer surface by illumination with pulses of a xenon flash
(pulse duration 1 ls, used UV filter). The layer surface potential de-
crease as a result of pulse illumination was up to 5–10% of the ini-
tial potential before illumination. The capacitance probe that was
connected to the wide frequency band electrometer measured
the rate of the surface potential decrease, dU/dt. The transit time
tt was determined by the kink on the curve of the dU/dt transient
in a double logarithmic scale. The drift mobility was calculated
2.3. Measurement
The 1H NMR spectra were taken on a Varian Unity Inova
(300 MHz for 1H and 75 Hz for 13C) spectrometer. Elemental anal-
yses were performed with an Exeter Analytical CE-440 Elemental
Analyzer. The UV spectra were recorded on a PerkinElmer Lambda
35 UV/VIS spectrometer in THF. Solution (10ꢀ4 M) of investigated
HTM and microcell with an internal width of 1 mm were used.
IR-spectroscopy was performed on Perkin Elmer Spectrum BX II
FT-IR System using KBr pellets. Fluorescence emission and excita-
tion spectra were recorded with a Hitachi MPF-4 luminescence
spectrometer in THF. Solution (10ꢀ4 M) of investigated HTM and
microcell with an internal width of 1 cm were used. The average
molecular weight and the molecular weight distribution were esti-
mated by gel permeation chromatography (GPC) using a Waters
GPC system including a Waters 410 UV detector (254 nm), four col-
umns (300 ꢁ 7.5 mm) filled with PL-Gel absorbent (pore sizes: 106,
105, 104 and 5000 nm) using THF as eluant. Polystyrene standards
were used for column system calibration.
Simultaneous thermogravimetric analysis and differential scan-
ning calorimetry (TGA–DSC) was performed with a Netzch STA 409
PC Luxx. Samples of 5–8 mg were heated in aluminium pans at a
scan rate 10 K/min under a nitrogen flow. During the first heating
the melting point was determined for the monomer. The glass
transition temperatures (Tg) for all investigated compounds were
determined during the second run.
by the formula
l
= d2/U0tt, where d is the layer thickness and U0
is the surface potential at the moment of illumination. XTOF inte-
gral transients are measured with charge integrator connected to
the capacitance probe.
3. Results and discussion
The key monomer 1,2-bis(3-oxiranylmethoxy-1-phenyl-1,2,3,4-
tetrahydroquinolin-6-ylmethylene)azine (6) was synthesized
according to the Scheme 1. 3-Hydroxy-1-phenyl-1,2,3,4-tetrahy-
droquinoline (1) was obtained by a one-pot reaction of diphenyl-
amine with epichlorohydrin. In order to protect hydroxyl group,
1 was converted to the acetyl derivative 2, which in turn was
formylated and the hydroxyl group was deprotected to yield 3-hy-
droxy-1-phenyl-1,2,3,4-tetrahydroquinoline-6-carbaldehyde (4).
The reaction between 4 and hydrazine hydrate yielded a symmet-
rical azine 5, which was then alkylated with epichlorohydrin, and
the glycidyl-terminated 3-hydroxy-1-phenyl-1,2,3,4-tetrahydro-
quinoline-6-carbaldehyde azine 6 was isolated.
In the 1H NMR spectra (Fig. 2a) of 6, the epoxy groups give a
double set of signals of the AB part of an ABX system at 2.85–
2.50 ppm, indicating that due to the presence of two stereogenic
centers, the monomer was isolated as a mixture of diastereomers.
Finally, the symmetrical azine based polymers P1–P3, contain-
ing 1-phenyl-1,2,3,4-tetrahydroquinoline moieties, were synthe-
sized by the nucleophilic oxirane ring opening reaction of
monomer 6 with 4,4-thiobisbenzenethiol (TBBT), 2,5-dimercapto-
1,3,4-thiadiazole (DMTD), or 1,3-benzenedithiol (BDT), respec-
tively, in the presence of a catalyst TEA (Scheme 2).
Purity and structure of the synthesized polymers P1–P3 were
confirmed by IR, UV, and 1H NMR spectroscopy. 1H NMR spectra
(Fig. 2b) show the characteristic signals associated with the reso-
nance of the hydrogen atoms of phenyl-1,2,3,4-tetrahydroquino-
line core and confirm the molecular structure. Additionally, some
individual downfield peaks have been assigned to characteristic
protons: a singlet of protons of CH@N group appears in the region
of 8.51–8.42 ppm, as well as a singlet and a doublet of 5-H and 8-H
of tetrahydroquinoline in the regions of 7.56–7.53 ppm and 6.67–
6.52 ppm, respectively. In the FTIR spectra of the azine-based com-
pounds the imine vibration at about 1606 cmꢀ1 was recorded
(Fig. 3). Furthermore, IR and NMR analyses have indicated that
polymers P1–P3 do not possess thiol end groups as characteristic
signals attributed to these groups are absent. The IR spectra exhibit
The samples for the ionization potential measurement were
prepared by dissolving materials in THF and were coated on Al
plates pre-coated with ꢂ0.5
methacrylic acid copolymer adhesive layer. The thickness of the
transporting material layer was 0.5–1 m. The ionization potential
lm thick methylmethacrylate and
l
(Ip) was measured by the photoemission in air method [41], similar
to the one used in [42]. Usually, photoemission experiments are
carried out in vacuum and high vacuum is one of the main require-
ments for these measurements. If vacuum is not high enough, the
sample surface oxidation and gas adsorption are influencing the
measurement results. In our case, however, the organic materials
investigated are stable enough towards oxygen and the measure-
ments may be carried out in the air.
The samples were illuminated with monochromatic light from
the quartz monochromator with deuterium lamp. The power of
the incident light beam was (2–5) ꢃ 10ꢀ8 W. The negative voltage
of –300 V was supplied to the sample substrate. The counter-elec-
trode with the 4.5 ꢁ 15 mm2 slit for illumination was placed at
8 mm distance from the sample surface. The counter-electrode
was connected to the input of the BK2–16 type electrometer, work-
ing in the open input regime, for the photocurrent measurement.

J. Ardaraviciene et al. / Reactive & Functional Polymers 71 (2011) 1016–1022
1019
Scheme 1. Synthesis route to the symmetrical azine based monomer 6.
Fig. 2. 1H NMR spectra (CDCl3) of the monomer 6 (a) and polymer P3 (b).

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J. Ardaraviciene et al. / Reactive & Functional Polymers 71 (2011) 1016–1022
Scheme 2. Synthesis route to the azine-based polymers P1–P3.
Fig. 4. DSC first heating, cooling, and second heating curves for monomer 6.
Fig. 3. FTIR absorption spectra of monomer 6 and polymer P2.
curve of 6 reveals melting at 115 °C, no crystallization takes place
during cooling, and only glass transition at 57 °C is registered dur-
ing the second heating. The material remains in glassy state after
melting, therefore, compound 6 can be considered as a molecular
glass. Formation of the glassy state in azine-based polymers P1,
P2 and P3 was observed at 114 °C, 120 °C and 94 °C, respectively
(Table 1 and Fig. 5). Influence of varying flexible spacers and
molecular weight is clearly noticeable. Although P2 is just an olyg-
omer, its Tg is similar to that of P1. On the other hand, P3 and P1
possess somewhat similar molecular weights, but their Tg differ
by 20 °C. This difference could be attributed to more loose packing
of the polymeric chains in case of P3, as metha-substituted linking
agent BDT clearly introduces more structural disorder compared
with more symmetrical para-substituted TBBT.
a broad absorption band in 3600–3200 cmꢀ1, which demonstrates
strong hydrogen bonding in the target polymers P1–P3.
The average molecular weights and their distribution of the
synthesized polymers P1–P3 were detected by GPC and are pre-
sented in the Table 1. As seen from the GPC results, the relatively
high molecular weight polymers P1 and P3 were obtained using
TBBT and BDT as linking agents. On the other hand, low molecular
weight of oligomer P2 most likely could be explained by unfavor-
able conformation of resulting oligomeric chains, which, in turn,
inhibit further reaction between these segments.
Thermal stability of the investigated compounds was examined
by TGA under the nitrogen atmosphere. The data obtained is pre-
sented in Table 1. The 5% weight loss temperatures (Tdec-5%) for
polymers PI–P3 are close to that obsorved for monomer 6
(314 °C) and are in the range of 305–310 °C. The thermal degrada-
tion of these compounds proceeds, apparently, by the breakage of
azo bond of azine moiety. Formation of the glassy state of mono-
mer 6 and azine-based P1–P3 was confirmed by DSC analysis.
These investigations (Fig. 4) have revealed that monomer 6 can ex-
ist both in crystalline and amorphous phase. The DSC first heating
The UV absorption spectra of aldehyde 4, monomer 6, and tar-
get polymers P1–P3 are presented in Fig. 6. The absorption spec-
trum of the 6 is batochromically (ꢄ55 nm) and hyperchromically
shifted with respect to the spectrum of aldehyde 4 as a conse-
quence of the increased conjugated
based monomer 6. On the other hand, difference in
conjugation between monomer 6 and corresponding polymers is
p-electron system of azine-
p-electron
not significant (ꢄ2 nm) what proves that conjugated
p-electron
Table 1
Characteristics of polymers P1–P3.
ꢀ
Mn; (g molꢀ1
)
M
w; (g molꢀ1
)
Mw Mw
Compound
Tg (°C)
Tdec-5% (°C)
Reaction time (h)
Yield (%)
Ip (eV)
P1
P2
P3
11,716
5842
12,768
65,205
16,280
38,658
5.6
2.8
3.0
114
120
94
305
304
310
45
45
45
56
32
86
5.61
5.40
5.42

J. Ardaraviciene et al. / Reactive & Functional Polymers 71 (2011) 1016–1022
1021
of charge transport layer. The Ip values for charge transporting
materials, including those widely used with pigments in electro-
photographic photoreceptors, such as titanyl phthalocyanines,
are in the range of 5.1–5.7 eV [46].
The important advantage of P1–P3 is the lack of excimer form-
ing sites in these polymers. Fig. 6 shows normalized fluorescence
spectra of dilute THF solutions of azine-based polymers P1–P3.
For comparison, the spectrum of a dilute solution of monomer 6
is presented. The spectra of P1–P3 are almost identical to that of
monomer 6 and only the structureless monomer fluorescence with
a blue luminescence peaking at 460 nm is observed.
Clear, transparent, and homogeneous films of P1 and P3 were
obtained by the casting technique, while in the case of P2 the ob-
tained film was mat. For the sample of P1, XTOF measurements
have revealed that small charge transport is not Gaussian (stochas-
tic), however well-defined transit time is seen on log–log plots
(Fig. 8). The mobility field dependence is presented in Fig. 9. Inves-
Fig. 5. DSC second heating curves for polymers P1–P3.
tigated mobility
l may be well approximated by the formula
pffiffiffi
l
¼
l
0 expð
a
EÞ
ð1Þ
a is Pool–Frenkel parameter,
Here, l0 is the zero field mobility,
and E is electric field strength. Such mobility dependence is
explainable by terms of the Borsenberger and Weiss [47] and Bor-
senberger et al. [48] disorder formalism.
Unfortunately, we were unable to measure the charge drift
mobility of P3 because of too dispersive charge carrier transport.
However, XTOF integral transients (Fig. 10) indicate a rapid charge
transfer of holes through the sample thickness at positive surface
charging; practically all charge is transferred in ꢂ0.02 s. It should
Fig. 6. UV absorption and fluorescence spectra (kex = 330 nm) of 4, 6 and P1–P3 in
THF solutions.
system remains intact during polyaddition reaction. Moreover, the
presence of the linking fragment TBBT in the molecule of polymer
P1 can be observed in 270 nm region of the UV spectrum due to the
lone electron pairs of the sulfur atoms between phenyls.
The electron photoemission spectra of the films of polymers
P1–P3 are shown in Fig. 7 and Table 1. The Ip for P1 is 5.6 eV,
the Ip values for polymeric TM P2 and P3 are 5.4 and 5.42 eV,
respectively. The Ip values of these compounds indicate that they
are suitable for the application in electrographic photoreceptors,
as it is widely known that holes are easily injected into the charge
transport layer from the charge generation layer with Ip close to Ip
Fig. 8. XTOF transients for P1. Insert shows the one transient curve in linear plot.
Fig. 7. Photoemission in air spectra of the polymers P1–P3.
Fig. 9. Field dependence of the hole drift mobility of P1.

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Acknowledgments
Jolanta Ardaraviciene acknowledges EU Structural Funds
project ‘‘Postdoctoral Fellowship Implementation in Lithuania’’
for funding her postdoctoral fellowship.
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