Novel charge transporting materials containing phenyl-1,2,3,4- tetrahydroquinoline moieties

Article abstract of DOI:10.1080/15421400701229727

New synthesized monohydrazone and dihydrazone containing 1-phenyl-1,2,3,4-tetrahydroquinoline moiety were investigated. The materials were examined by various techniques including differential scanning calorimetry (DSC), UV spectrometry, electron photoemi

Full text of DOI:10.1080/15421400701229727

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Novel Charge Transporting
Materials Containing
Phenyl-1,2,3,4-
Tetrahydroquinoline Moieties
Vytautas Getautis a , Maryte Daskeviciene a ,
Rimgaile Degutyte a , Jolanta Stumbraite a , Jonas
Sidaravicius b & Vygintas Jankauskas c
a Faculty of Chemical Technology, Kaunas University
of Technology , Kaunas, Lithuania
b Department of Polygraphic Machines , Vilnius
Gediminas Technical University , Vilnius, Lithuania
c Department of Solid State Electronics , Vilnius
University , Vilnius, Lithuania
Published online: 22 Sep 2010.
To cite this article: Vytautas Getautis , Maryte Daskeviciene , Rimgaile Degutyte ,
Jolanta Stumbraite , Jonas Sidaravicius & Vygintas Jankauskas (2007) Novel
Charge Transporting Materials Containing Phenyl-1,2,3,4-Tetrahydroquinoline
Moieties, Molecular Crystals and Liquid Crystals, 468:1, 131/[483]-140/[492], DOI:
10.1080/15421400701229727
To link to this article: http://dx.doi.org/10.1080/15421400701229727
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Mol. Cryst. Liq. Cryst., Vol. 468, pp. 131=[483]–140=[492], 2007
Copyright # Taylor & Francis Group, LLC
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421400701229727
Novel Charge Transporting Materials Containing
Phenyl-1,2,3,4-Tetrahydroquinoline Moieties
Vytautas Getautis
Maryte Daskeviciene
Rimgaile Degutyte
Jolanta Stumbraite
Faculty of Chemical Technology, Kaunas University of Technology,
Kaunas, Lithuania
Jonas Sidaravicius
Department of Polygraphic Machines, Vilnius Gediminas Technical
University, Vilnius, Lithuania
Vygintas Jankauskas
Department of Solid State Electronics, Vilnius University,
Vilnius, Lithuania
New synthesized monohydrazone and dihydrazone containing 1-phenyl-1,2,3,4-
tetrahydroquinoline moiety were investigated. The materials were examined by
various techniques including differential scanning calorimetry (DSC), UV spec-
trometry, electron photoemission and xerographic time of flight (XTOF) techni-
ques. The highest hole drift mobility 10ꢀ5 cm2Vꢀ1sꢀ1 at an electric field of
106 Vcmꢀ1 was observed for the dihydrazone.
Keywords: charge transport; electrophotography; hydrazone; 1-phenyl-1,2,3,4-
tetrahydroquinoline
INTRODUCTION
During recent years rapid development in the chemistry of
1,2,3,4-tetrahydroquinolines was observed. Traditionally they are of
Financial support of this research by the Lithuanian Science and Studies Foundation
(B-18=2006) are gratefully acknowledged.
Address correspondence to Vytautas Getautis, Faculty of Chemical Technology,
Kaunas University of Technology, Radvilenu pl. 19, Kaunas, 50270, Lithuania. E-mail:
vgetaut@ktu.lt
131=[483]

132=[484]
V. Getautis et al.
interest for their physiological activity. Many relatively simple
synthetic of 1,2,3,4-tetrahydroquinolines are already used or have
been tested as potential drugs [1,2]. Besides pharmaceutical applica-
tions, tetrahydroquinoline derivatives are useful as corrosion inhibi-
tors [3], antioxidants [4], active components of various dyes [5] and
pesticides [6]. They are also widely used in modern recording technol-
ogies: as intermediates for photographic couplers [7], as highly sensi-
tive photosensitizers in photography [8] and as charge transporting
materials in electrophotographic photoconductors [9].
Compounds possessing hydrazone moiety are also well known for their
photoresponsible properties [10]. Due to high photosensitivity, simple
synthesis and low price they gain the advantage over other hole trans-
porting materials. Low molecular weight transporting materials (TM)
containing hydrazone moiety are usually crystalline substances, not cap-
able of forming thin neat homogenous layers, and therefore must be used
in combination with polymeric hosts, usually polycarbonate (PC). Aro-
matic hydrazone molecules dispersed in a binding polymer are used as
the main constituent of electrophotographic devices due to their excellent
hole transporting ability [11]. Recently, organic photoreceptors with
hydrazones possessing 1-phenyl-1,2,3,4-tetrahydroquinoline moiety were
recognized as hole transporting materials due to their rapid charge trans-
porting ability [12]. Unfortunately, the time and labour consuming multi-
step synthesis of starting 1-phenyl-1,2,3,4-tetrahydroquinoline limits the
development of organic photoreceptors with this promising moiety.
In the present article we report the synthesis, characterization
and photoconductive properties of hydrazones 4a and 4b possessing
1-phenyl-1,2,3,4-tetrahydroquinoline moiety. The molecules of these
TM include the large p-electron system conjugated through nitrogen
atoms and the flexible tetrahydroquinoline core with methoxy group
attached to it. These TM showed themselves as excellent hole trans-
porting materials: the measured mobilities of new 4a,b are high
enough for many practical applications.
EXPERIMENTAL
3-Hydroxy-1-Phenyl-1,2,3,4-Tetrahydroquinoline (1). Syn-
thesis of the starting 3-hydroxy-1-phenyl-1,2,3,4-tetrahydroquinoline
1 was carried out according to the procedure described in [13].
3-Methoxy-1-Phenyl-1,2,3,4-Tetrahydroquinoline (2). The
mixture of 3-hydroxy-1-phenyl-1,2,3,4-tetrahydroquinoline 1 (22.5 g,
0.1 mol), iodomethane (31.1 ml, 0.5 mol), potassium hydroxide (13.2 g,
0.02 mol) and potassium carbonate (13.8 g, 0.1 mol) was refluxed for
4 hours. At the end of the reaction potassium hydroxide, potassium

Materials Containing Phenyl-1,2,3,4-Tetrahydroquinoline
133=[485]
carbonate and potassium iodide were filtered off. The filtrate was
extracted with chloroform and washed with H2O until neutral. The
organic layer was dried over anhydrous MgSO4, and the solvent was
removed in vacuo together with the unreacted iodomethane. The
obtained compound 2 was used in the next step without purification.
3-Methoxy-1-Phenyl-1,2,3,4-Tetrahydroquinoline-6-Carbox-
aldehyde (3a). To a 250 ml 3-neck round bottom flask equipped with
thermometer, magnetic stirrer and addition funnel, was added DMF
(46.5 ml, 0.6 mol). The content was cooled down in a salt=ice bath,
and 18.5 ml of POCl3 (0.2 mol) were added portionwise, not allowing
the temperature of the mixture to rise above 5ꢁC. After the addition
was completed, the reaction mixture was allowed to warm to room
temperature. A solution of compound 2 (23.9 g, 0.1 mol) in 50 ml of
DMF was then added. The mixture was heated at 90ꢁC for 1 h. The
hot reaction mixture was poured into a 500 ml beaker containing
200 g ice. The mixture was neutralized by adding 40% NaOH and
allowed to stand at 5ꢁC for 24 hours. The precipitate was decanted, dis-
solved in ethyl acetate, the solution was washed with H2O until neu-
tral, dried over anhydrous MgSO4, and the solvent was removed. The
residue was purified by column chromatography on silica gel using
n-hexane=acetone ¼ 7:1 as the eluent. The pure product 3a was col-
lected and dried in vacuum at 30ꢁC (17.4 g, 65% yield). 1H NMR
(300 MHz, CDCl3, d, ppm): 9.70 (s, 1H, CHO); 7.62–7.23 (m, 7H, Ar);
6.54 (d, 1H, J ¼ 8.6 Hz, 8-H of quinoline ring); 3.95–3.87 (m, 1H,
CH); 3.86–3.64 (m, 2H, NCH2); 3.43 (s, 3H, CH3); 3.16 (dd, 1H,
JAB ¼ 16.0 Hz, JAX ¼ 4.1 Hz, HA of CH2CH); 3.00 (dd, 1H, JBX ¼ 6.3 Hz,
Hz, HB of CH2CH). IR, n=cmꢀ1: 3061, 3037 (CHAr); 2980, 2930, 2895
=
(CHaliph.); 1674 (CHO); 965, 818, 772, 701 (CH CH of mono- and trisub-
stituted benzenes). Found, %: C 76.25; H 6.35; N 5.16. C17H17NO2.
Calculated, %: C 76.38; H 6.41; N 5.24.
1-(4-Formylphenyl)-3-Methoxy-1,2,3,4-Tetrahydroquinoline-
6-Carboxaldehyde (3b). Compound 3b was prepared according to the
preparation procedure described above for 3a, except that much bigger
amounts of DMF (228 ml, 2.94 mol) and POCl3 (129 ml, 1.4 mol) were
used, and reaction time was prolonged to 24 hours. The crude product
was purified by column chromatography to give 12 g of compound 3b
1
(40% yield). H NMR (300 MHz, CDCl3, d, ppm): 9.95 (s, 1H, CHO in
Ph), 9.79 (s, 1H, CHO in quinoline ring); 7.94–7.21 (m, 6H, Ar); 7.02
(d, 1H, J ¼ 8.5 Hz, 8-H of quinoline ring); 3.98–3.66 (m, 3H, NCH2CH);
3.37 (s, 3H, CH3); 3.15 (dd, 1H, JAB ¼ 16.2 Hz, JAX ¼ 4.3 Hz, HA of
CH2CH); 3.01 (dd, 1H, JBX ¼ 5.6 Hz, HB of CH2CH). IR, n=cmꢀ1: 3064,
(CHAr); 2934, 2897, 2827 (CHaliph.); 1677 (CHO). Found, %: C 73.15; H
5.82; N 4.72. C18H17NO3. Calculated, %: C 73.20; H 5.80; N 4.74.

134=[486]
V. Getautis et al.
3-Methoxy-1-Phenyl-1,2,3,4-Tetrahydroquinoline-6-Carbox-
aldehyde N,N-Diphenylhydrazone (4a). To a solution of N,N-
diphenylhydrazine hydrochloride (2.4 g, 11 mmol) in 80 ml of meth-
anol was added a solution of compound 3a (2 g, 7 mmol) in 15 ml of
methanol. The mixture was refluxed for 1 h. Then the reaction mix-
ture was extracted with ethyl acetate. The organic layer was dried
over anhydrous MgSO4, and organic solvents were removed. The
residue was purified by column chromatography on silica gel using
n-hexane=ethyl acetate ¼ 7:1 as the eluent. The pure product was
crystallized from the eluent, filtered off and recrystallized from ethyl
ꢁ
1
acetate=methanol ¼ 1:1 to yield 1.6 g (49%). m.p.: 140.5–142 C. H
NMR (300 MHz, CDCl3, d, ppm): 7.43–7.07 (m, 18H, Ar and
=
CH N); 6.69 (d, 1H, J ¼ 8.6 Hz, 8-H of quinoline ring); 3.88–3.77
(m, 1H, CH); 3.77–3.50 (m, 2H, NCH2); 3.39 (s, 3H, CH3); 3.12 (dd,
1H, JAB ¼ 16.1 Hz, JAX ¼ 4.6 Hz, HA of CH2CH); 3.00 (dd, 1H,
JBX ¼ 7.0 Hz, HB of CH2CH). Found, %: C 80.26; H 6.32; N 9.72.
C29H27N3O. Calculated, %: C 80.34; H 6.28; N 9.69.
1-(4-Formylphenyl)-3-Methoxy-1,2,3,4-Tetrahydroquinoline-
6-Carboxaldehyde bis(N,N-Diphenylhydrazone) (4b). To a sol-
ution of N,N-diphenylhydrazine hydrochloride (2.6 g, 12 mmol) in 50 ml
of methanol was added a solution of compound 3b (1.5 g, 5 mmol) in
10 ml of THF. The mixture was refluxed for 1.5 h, cooled down and
extracted with ethyl acetate. The organic layer was dried over anhydrous
MgSO4, and organic solvents were removed. The residue was purified by
column chromatography (n-hexane=ethyl acetate ¼ 12:1). The product
was crystallized from toluene=methanol ¼ 2:1. The crystalline 4b was
filtered off, washed with small amount of cold methanol (5ꢁC) and recrys-
tallized from toluene=methanol ¼ 2:1 (2 g, 61% yield). m.p.: 216–218ꢁC.
1
=
H NMR (300 MHz, CDCl3, d, ppm): 7.62–7.07 (m, 28H, Ar, CH N);
6.81 (d, 1H, J ¼ 8.6 Hz, 8-H of quinoline ring); 3.88–3.79 (m, 1H,
NCH2CH); 3.78–3.52 (m, 2H, NCH2); 3.37 (s, 3H, CH3); 3.12 (dd, 1H,
JAB ¼ 16.2 Hz, JAX ¼ 4.8 Hz, HA of CH2CH); 2.87 (dd, 1H, JBX ¼ 6.9 Hz,
Hz, HB of CH2CH). IR, n=cmꢀ1: 3061, 3035 (CHAr); 2989, 2888, 2821 (CHa-
=
liph.); 1590, 1522 (C C, CꢀN). Found, %: C 80.32; H 5.89; N 11.19.
C42H37N5O. Calculated, %: C 80.36; H 5.94; N 11.16.
Measurement
1
The H NMR spectra were taken on Varian Unity Inova (300 MHz)
spectrometer in CDCl3. The IR spectra were taken for samples in
KBr pellets on a Perkin Elmer Spectrum BX II FT-IR System spec-
trometer. The UV spectra were recorded on a Spectronic Genesys 8
spectrometer in THF (10ꢀ4 M) in a microcell with an internal width

Materials Containing Phenyl-1,2,3,4-Tetrahydroquinoline
135=[487]
of 1 mm. The course of the reactions and the purity of the products
were monitored by TLC on Silufol UV-254 plates (eluent:
n-hexane=acetone ¼ 3=1) and development with I2 or UV light. Silica
˚
gel (grade 62, 60–200 mesh, 150 A, Aldrich) was used for column chro-
matography. Elemental analyses were performed with an Exeter
Analytical CE-44 Elemental Analyzer. Thermal transition data for
synthesized compounds 4a and 4b was collected using a TA Instru-
ments Model 2929 apparatus (New Castle, DE) at a heating rate of
10 K=min under nitrogen atmosphere. The glass transition tempera-
tures (Tg) were determined from the second heating. Ionization poten-
tial was measured by the photoemission in air method described in [14].
The samples for mobility measurements were prepared from 1:1 mass
proportion compositions of 4a and 4b with polycarbonate-Z (PC) (Iupi-
lon Z-200 from Mitsubishi Gas Chemical Co.). The sample substrate
was polyester film with conductive Al layer. The layer thickness was
in the range of 7–11 mm. The hole drift mobility was measured by XTOF
technique [15]. Positive corona charging created electric field inside the
TM layer. Charge carriers were generated at the layer surface by
illumination with pulses of N2 laser (pulse duration was 2 ns, wave-
length 337 nm). The layer surface potential decrease as a result of pulse
illumination was up to 1–5% of the initial potential before illumi-
nation. The capacitance probe that was connected to the wide fre-
quency 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 linear scale. The drift mobility
was calculated by the formula l ¼ d2=U0tt, where d is the layer thick-
ness and U0 is the surface potential at the moment of illumination.
RESULTS AND DISCUSSION
A practical route for the synthesis of hydrazones 4a and 4b possessing
1-phenyl-1,2,3,4-tetrahydroquinoline moiety is shown in Scheme 1. Dif-
ferently to the multi-step synthesis of the widely used 1-phenyl-1,2,3,
4-tetrahydroquinoline, the starting 3-hydroxy-1-phenyl-1,2, 3,4-tetrahy-
droquinoline (1) was obtained by one-pot reaction of diphenylamine with
epichlorohydrin as described in [13]. Alkylation of 1 with iodomethane in
the presence of KOH and K2CO3 gave phenyltetrahydroquinoline 2 sub-
stituted with methoxy group. The next step was a Vilsmeier formylation
followed by condensation of the resulting monoaldehyde 3a and dialde-
hyde 3b with N,N-diphenylhydrazine to get final products-hydrazones
4a and 4b. The chemical structures of the new hole transporting com-
1
pounds 4a and 4b were confirmed by IR, UV, H NMR spectrometry
and elemental analysis.

136=[488]
V. Getautis et al.
SCHEME 1 Synthesis of researched material.
The formation of the glassy state in 4a and 4b was confirmed by
DSC. The melting points (Tm) and glass transition temperatures (Tg)
of the synthesized TM are presented in Table 1. These investigations
revealed, that products 4a,b exist both in crystalline and amorphous
state. Figure 1 shows, that the DSC curve for 4a at first heating
reveals two peaks, corresponding to two eutectic melting points at
125ꢁC and 142ꢁC. Thus, hydrazone 4a is distinguished by
polymorphism with the predominant second crystalline phase at
142ꢁC. No crystallization takes place during second heating, only glass
transition is revealed at 44ꢁC. The material remains in glassy state
after melting and subsequent cooling. This is also common for
TABLE 1 Characteristics of 4a and 4b
Compound
Tm=ꢁC
Tg=ꢁC
Ip=eV
l0=cm2Vꢀ1sꢀ1
l=cm2Vꢀ1sꢀ1
4a
4b
142
214
44
81
5.29
5.21
2 ꢂ 10ꢀ7
7.2 ꢂ 10ꢀ6
2.2 ꢂ 10ꢀ5
5.6 ꢂ 10ꢀ7

Materials Containing Phenyl-1,2,3,4-Tetrahydroquinoline
137=[489]
FIGURE 1 DSC curves for 4a (heating rate to 10 K=min).
monocrystalline material 4b, except that this molecular glass exhibits
higher Tg ¼ 81ꢁC.
Since p-electrons are very important for the charge transporting
process in the TM structures, the absorption spectra of 4a and 4b were
recorded. Figure 2 demonstrates that electron transitions to the
higher energy states in the investigated derivatives give two main
absorption maxima at ca. 210 nm and 380 nm. The comparison of 4a
and 4b with the starting 1 showed, that the second absorption band
is bathochromically shifted by 72 nm and 98 nm respectively, because
of the p-electron conjugation including the lone electron pair on the
nitrogen atom. Furthermore, dihydrazone 4b, as compared to mono-
hydrazone 4a, showed additional 26 nm shift to longer wavelengths
due to expanded conjugated p-electrons system.
The results of the electron photoemission in air are presented in
Figure 3. There is a little ionization potencial (Ip) difference
between monohydrazone 4a and dihydrazone 4b (Table 1). The
ionization potential value for compound 4a is 5.29 eV. As expected,
Ip ¼ 5.21 eV for the compound 4b is lower if compared to 4a. It is
known, that the Ip values for charge transporting materials, includ-
ing those widely used with pigments in electrophotographic photo-
receptors, such as titanyl phthalocyanines [16], are in the range of
5.1–5.6 eV. Thus, Ip values of the newly synthesized 4a,b are suf-
ficient for these compounds to be used as charge transporting
materials.

138=[490]
V. Getautis et al.
FIGURE 2 Absorption spectra (THF, c ¼ 10ꢀ4 M) of 4a, 4b and starting
compound 1.
Investigative 1-phenyl-1,2,3,4-tetrahydroquinoline based hydrazones
4a,b are soluble in common organic solvents such as acetone, chloroform,
THF, dioxane etc. This really good solubility is mainly due to the
flexible tetrahydroquinoline core in 4a and 4b. Clear, transparent and
FIGURE 3 Photoemission (in air) spectra of the TM.

Materials Containing Phenyl-1,2,3,4-Tetrahydroquinoline
139=[491]
FIGURE 4 Field dependencies of the hole drift mobilities of 4a and 4b.
homogeneous films were obtained by the casting technique. The hole drift
mobility for the investigative TM 4a and 4b was measured by XTOF
technique.
Figure 4 shows the room temperature dependencies of hole drift
mobility on electric field for 4a and 4b in the composition with PC.
The mobility defining parameters l0 and the mobility value at the
6.7 ꢂ 105 Vcmꢀ1 field are given in Table 1. Mobility value in amorphous
film of the composition of 4b with PC exceeds 10ꢀ5 cm2Vꢀ1sꢀ1 at an
electric field of 106 Vcmꢀ1. As seen from these results, hole drift
mobility of 4b is by one order of magnitude higher than mobility of
4a. This is presumable because conjugated p-electron system is larger
in the compound 4b. It should be noted, that the measured mobility of
the TM compositions with a binder is high enough for many
practical applications and it remains approximately in the same
range as was reported for compound 1-phenyl-1,2,3,4-tetrahydroqui-
noline-6-carboxaldehyde-1,10-diphenylhydrazone [17].
CONCLUSIONS
A simple synthesis procedure of 3-hydroxy-1-phenyl-1,2,3,4-tetrahy-
droquinoline allows to develop and evaluate novel hole transporting
materials possesing phenyl-1,2,3,4-tetrahydroquinoline moiety for
electrophotography. DSC investigations revealed, that the newly
synthesized hydrazones 4a and 4b can exist both in crystalline and

140=[492]
V. Getautis et al.
amorphous state. The measured mobilities of the TM are high enough
for many practical applications. The highest hole mobility exceeding
10ꢀ5 cm2Vꢀ1sꢀ1 at an electric field of 106 Vcmꢀ1 was observed in the
case of 4b.
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