New thiophene-based glass-forming hydrazones for optoelectronic applications

Article abstract of DOI:10.1080/15421400701229685

A new series of thiophene-containing glass-forming hydrazones is synthesized. The thermal, photoelectrical, and optical properties of these compounds are examined. The synthesized hydrazones exhibit the thermal stability sufficient for their application i

Full text of DOI:10.1080/15421400701229685

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New Thiophene-Based Glass-
Forming Hydrazones for
Optoelectronic Applications
a
a
a
A. Michaleviciute , G. Buika , J. V. Grazulevicius
b
b
c
,
a
F. Tran-Van , C. Chevrot & V. Jankauskas
Department of Organic Technology , Kaunas
University of Technology , Kaunas, Lithuania
b
Laboratoire de Physicochimie des Polymères et
des Interfaces (LPPI) , Université de Cergy Pontoise,
Cergy Pontoise Cedex , France
c
Department of Solid State Electronics , Vilnius
University , Vilnius, Lithuania
Published online: 22 Sep 2010.
To cite this article: A. Michaleviciute , G. Buika , J. V. Grazulevicius , F. Tran-Van ,
C. Chevrot & V. Jankauskas (2007) New Thiophene-Based Glass-Forming Hydrazones
for Optoelectronic Applications, Molecular Crystals and Liquid Crystals, 468:1, 107/
[459]-118/[470], DOI: 10.1080/15421400701229685
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Mol. Cryst. Liq. Cryst., Vol. 468, pp. 107=[459]–118=[470], 2007
Copyright # Taylor & Francis Group, LLC
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421400701229685
New Thiophene-Based Glass-Forming Hydrazones
for Optoelectronic Applications
A. Michaleviciute
G. Buika
J. V. Grazulevicius
Department of Organic Technology, Kaunas University of Technology,
Kaunas, Lithuania
F. Tran-Van
C. Chevrot
Laboratoire de Physicochimie des Polym e` res et des Interfaces (LPPI),
Universit e´ de Cergy Pontoise, Cergy Pontoise Cedex, France
V. Jankauskas
Department of Solid State Electronics, Vilnius University,
Vilnius, Lithuania
A new series of thiophene-containing glass-forming hydrazones is synthesized.
The thermal, photoelectrical, and optical properties of these compounds are
examined. The synthesized hydrazones exhibit the thermal stability sufficient for
their application in optoelectronic devices. The values of ionization potential of
amorphous films of the newly synthesized hydrazones are from 4.43 to 5.79 eV.
The hole drift mobilities measured by the xerographic time-of-flight method in a
molecularly doped polymer containing 50 wt.% of one synthesized hydrazone
ꢀ6
2
ꢀ5
ꢀ1
exceed 10 cm =Vs at an electric field intensity of 6.4 ꢁ 10 V cm .
Keywords: hole-drift mobility; hydrazone; ionization potential; thiophene
The financial support from the Lithuanian Science and Studies Foundation and
the joint French-Lithuanian research program ‘‘Gilibert’’ is gratefully acknowledged.
Dr. habil. Valentas Gaidelis is thanked for the measurements of ionization potentials.
Address correspondence to J. V. Grazulevicius, Department of Organic Technology,
Kaunas University of Technology, Radvilenu pl. 19, Kaunas, LT 50254, Lithuania.
E-mail: Juozas.Grazulevicius@ktu.lt
107=[459]

1
08=[460]
A. Michaleviciute et al.
INTRODUCTION
Organic charge-transporting materials are used in optoelectronic and
electronic devices like electrophotographic photoreceptors, organic
light-emitting diodes, photovoltaic cells, field-effect transistors, and
other devices [1,2]. Hydrazones play an important role among organic
hole transport materials, especially those used in electrophotography,
because of their simple synthesis and high charge carrier mobilities
[
3,4]. Thiophene-based hydrazones are poorly studied up to now and
represent a relatively new family of organic hole transport materials
5]. Since the presence of sulphur or oxygen atoms in the molecules
[
of organic semiconductors improves their characteristics [7], we con-
tinue the work on the design and synthesis of hole-transporting
thiophene-based hydrazones. In this presentation, we report on the
synthesisand characterizationofnewthiophene-basedhole-transporting
glass-forming hydrazones, containing reactive and polymerizable
functional groups. The presence of reactive functional groups in
these structures makes them useful for the preparation of polymeric
charge-transporting materials.
EXPERIMENTAL
Materials
3
,4-ethylendioxythiophene (EDOT), butyllithium (2.5 M solution
in hexane), N-phenylhydrazine, 3-(bromomethyl)-3-methyl oxetane,
-chloroethyl vinyl ether, thiophene-2-carbaldehyde, phosphorus
2
oxychloride, potassium hydroxide, potassium carbonate, tetrabuty-
lammonium hydrogen sulphate, and sodium sulphate were purchased
from Aldrich and used as-received. The solvents were purified and
dried using standard procedures [8].
2
-(formyl)3,4-ethylenedioxythiophene (1a) was synthesized by
the Vilsmeier reaction of 3,4-ethylenedioxythiophene with POCl . The
3
synthesis and characteristics have been already reported in [6].
2
-(5-(5-(formyl)thiophene-2-yl)thiophen-2-yl)thiophene (1c)
was synthesized by the Vilsmeier formylation method [9]. Yielded
1
(
9
31%). H NMR (250 MHz, CDCl d, ppm): 7.01–7.69 (m, 7H, Ar),
3,
þ
þ
.84 (s, 1H, CHO). MS(APCI , 20 V), m=z (%): 277 ([M þ H] , 100).
-(N-phenylhydrazonemethyl)3,4-ethylenedioxythiophene (2a).
The characteristics of 2a have been already reported in [6].
-(N-phenylhydrazonemethyl)thiophene (2b). Thiophene
-dicarbaldehyde (2.0 g, 17.83 ꢁ 10 mol) was dissolved in 60 ml of
ethyl alcohol under mild heating. Then, a solution of 3.80 g
2
2
ꢀ3
2
ꢀ3
(
35.67 ꢁ 10 mol of N-phenylhydrazine in 5 ml of ethyl alcohol) was

New Thiophene-Based Glass-Forming Hydrazones
109=[461]
added. The reaction mixture was refluxed for 1.5 h. The precipitated
product was filtered and washed with methyl alcohol and dried. The
ꢀ1 1
yield of 2b was 87% (3.15 g). Yield (87%). FW ¼ 202 g mol . H NMR
(
250 MHz, CDCl , d, ppm): 6.88–7.62 (m, 8H, Ar), 7.80 (s, 1H, CH=N).
3
þ
þ
MS(APCI , 20 V), m=z (%): 203 ([M þ H] , 100).
-(5-(5-(N-phenylhydrazonemethyl)thiophene-2-yl)thiophen-
-yl)thiophene (2c) was synthesized by the same procedure as 2b.
2
2
ꢀ
1
1
The yield of 2c was 88%. FW ¼ 366 g mol . H NMR (250 MHz,
þ
CDCl , d, ppm): 6.90–7.62 (m, 8H, Ar), 7.82 (s, 1H, CH=N). MS(APCI ,
3
þ
2
0 V), m=z (%): 367 ([M þ H] , 100).
2
-(N-(3-methyloxetan-3-yl)N-phenylhydrazonemethyl)3,4-ethyl-
enedioxythiophene (3a). 2-(N-phenylhydrazonemethyl)3,4-ethyle-
ꢀ3
nedioxythiophene (2a) (0.5 g, 1.91 ꢁ 10 mol) was dissolved in 10 ml
ꢀ3
of ethyl methyl ketone and 0.6 g (3.82 ꢁ 10 mol) of 3-(bromomethyl)-
3
-methyl oxetane and tetrabutylammonium hydrogen sulphate
ꢀ3
were added. Then 0.32 g (5.73 ꢁ 10 mol) of KOH and 0.10 g
ꢀ3
(
0.76 ꢁ 10 mol) of Na SO were added by 3 portions. The reaction
2
4
mixture was refluxed for 15 h. After cooling, the inorganic components
were filtered off. The solvent was removed from the filtrate by rotary
evaporation. The product was purified by silica gel column chromato-
graphy using a mixture of acetone and hexane in a volume ratio of 1:6
as an eluent. The product was crystallized from eluent. Yield 0.28 g
ꢂ
ꢀ1
1
(
(
42%) of yellow crystals (mp: 80–81 C), FW ¼ 344 g mol . H NMR
250 MHz, CDCl , d, ppm): 1.55 (s, 3H, CH ), 3.87 (s, 2H, CH ), 4.22
3
3
2
(
(
d, 4H, CH ), 4.32, 4.40 (dd, 2H, CH ), 4.56, 4.72 (dd, 2H, CH ), 6.26
2
2
2
13
s, 1H, Ar), 7.08 (t, 1H, Ar), 7.27–7.45 (m, 5H, Ar).
C NMR
(
250 MHz, CDCl , d, ppm): 23.26 (CH ), 41.43 (C), 56.27 (CH ꢀN),
3
3
2
6
1
1
2
4.98 (CH ꢀO), 81.84 (CH ꢀO), 99.22 (CHꢀS), 116.28, 119.42,
2
2
23.22, 125.87 (Ar), 129.70 (CH=N, =CꢀS), 139.87 (NꢀC=), 141.844,
ꢀ1
47.35 (OꢀC=). IR (KBr), n=cm ): 3107, 3026 (CꢀH in Ar), 2976,
920, (CꢀH in Aliphat.), 1635 (C=N), 1599, 1497 (C=C in Ar), 1270
þ
(
3
CꢀN), 970 (CꢀS), 755, 698 (CꢀH in Ar). MS(APCI , 20 V), m=z (%):
þ
45 ([M þ H] , 100).
2
-(N-(3-methyloxetan-3-yl)N-phenylhydrazonemethyl)thio-
phene (3b) was synthesized by the same procedure as 3a. Yield 1.52 g
ꢂ
ꢀ1
1
(
54%) (mp: 78–79 C), FW ¼ 286 g mol . H NMR (250 MHz, CDCl , d,
3
ppm): 1.57 (s, 3H, CH ), 3.89 (s, 2H, CH ), 4.35 (d, 2H, CH ), 4.72 (d,
3
2
2
2
H, CH ), 6.99–7.02 (m, 2H, Ar), 7.13–7.31 (m, 4H, Ar), 7.40–4.47
2
1
3
(
(
(
(
m, 3H, Ar). C NMR (250 MHz, CDCl , d, ppm): 23.20 (CH ), 41.30
3 3
C), 57.53 (CH ꢀN), 81,47 (CH ꢀO), 120.88, 125.39, 125.84, 127.43
2
2
Ar), 128.73 (CꢀS), 129.83 (Ar CH, CꢀS), 142.43 (CH), 146.90
ꢀ1
C(Ar)ꢀN). IR (KBr, n=cm ): 3069, 3025 (CꢀH in Ar), 2955, 2930,
868 (CꢀH in Aliphat.), 1641(C=N), 1595, 1568, 1493, 1465 (C=C in
2

1
10=[462]
A. Michaleviciute et al.
Ar), 1259 (CꢀN), 1139 (CꢀOꢀC) 976 (CꢀS), 753, 707, (CꢀH in Ar).
þ
þ
MS(APCI , 20 V), m=z (%): 287 ([M þ H] , 100).
-(5-(5-(N-(3-methyloxetan-3-yl)-N-phenylhydrazonemethyl)
thiophene-2-yl)thiophen-2-yl)thiophene (3c) was synthesized by
2
ꢀ1
the same procedure as 3a. Yield (40%) of 3c. FW ¼ 450 g mol .
1
H NMR (250 MHz, CDCl , d, ppm): 1.45 (s, 3H, CH ), 4.03 (s, 2H,
3
3
CH ), 4.11 (d, 2H, CH ), 4.50 (d, 2H, CH ), 7.11–7.18 (m, 2H, Ar),
2
2
2
7
.28–7.38 (m, 9H, Ar), 7.55 (d, 1H, Ar, CH), 7.79 (s, 1H, Ar). IR
ꢀ1
(
1
1
KBr), n=cm ): 3065 (CꢀH in Ar), 2958, 2931 (CꢀH in Aliphat.),
665 (C=N), 1596, 1571, 1497, 1462 (C=C in Ar), 1272, 1260 (CꢀN),
þ
127 (CꢀOꢀC), 977 (CꢀS), 748, 693 (=CꢀH). MS(APCI , 20 V), m=z
þ
(
%): 451 ([M þ H] , 100).
2
-(N-vinyloxyethyl-N-phenylhydrazonemethyl)3,4-ethylene-
dioxythiophene (4a). To a 250-ml three-neck round bottom flask
equipped with a reflux condenser and a magnetic stirrer, 3,4-ethylene-
dioxythiophene-2-carbaldehyde-N-phenylhydrazone (4) (2 g, 7.69 ꢁ
ꢀ3
1
0 mol) was added and dissolved in 10 ml of ethyl methyl ketone.
ꢀ3
Then 1.35 ml (15.38 ꢁ 10 mol) of 2-chloroethyl vinyl ether, 0.86 g
ꢀ
3
ꢀ3
(
15.38 ꢁ 10 mol) of KOH and 1.06 g (7.69 ꢁ 10 mol) of K CO were
2
3
added into the reaction mixture. The reaction mixture was refluxed
for 17 h. After cooling, the inorganic components were filtered off.
The solvent was removed from the filtrate by rotary evaporation.
The product was purified by silicagel column chromatography using
a mixture of acetone and hexane in a volume ratio of 1:7 as an eluent.
The product was crystallized from the eluent. Yield 1.29 g (50%) of
ꢂ
ꢀ1
1
yellow crystals (mp: 79–80 C), FW ¼ 330 g mol . H NMR (250 MHz,
CDCl , d, ppm): 3.98 (t, 2H, CH ), 4.08–4.11 (m, 1H, =CH ), 4.20–
3
2
2
4
.31 (m, 7H, CH ), 6.29 (s, 1H, Ar), 6.50–6.57 (m, 1H, Ar), 6.95–7.00
2
ꢀ1
(
m, 1H, Ar), 7.32–7.41 (m, 4H, Ar), 7.80 (s, 1H, Ar). IR (KBr, n=cm ):
3
106, 3028 (CꢀH in Ar), 2979, 2921, 2880, (CꢀH in Aliphat.),
1
670(C=N), 1622, 1597, 1497 (C=C in Ar), 1275 (CꢀN), 1105
þ
(
CꢀOꢀC), 745, 690 (CꢀH in Ar). MS(APCI , 20 V), m=z (%): 331
þ
(
[M þ H] , 70).
2-(N-vinyloxyethyl-N-phenylhydrazonemethyl)thiophene (4b)
was synthesized by the same procedure as 4a. Yield (46%)
ꢂ
ꢀ1
1
(
mp: 74–75 C), FW ¼ 272 g mol . H NMR (250 MHz, CDCl , d,
3
ppm): 3.99 (t, 2H, CH ), 4.09–4.12 (m, 1H, =CH ), 4.21–4.28 (m, 3H,
2
2
CH ), 6.50–6.57 (m, 1H, Ar), 6.98–7.07 (m, 2H, Ar), 7.16–7.27 (m,
2
ꢀ1
2
3
1
H, Ar), 7.34–7.44 (m, 4H, Ar), 7.86 (s, 1H, Ar). IR (KBr, n=cm ):
098, 3069, 3042 (CꢀH in Ar), 2979, 2918, 2878, (CꢀH in Aliphat.),
648(C=N), 1594, 1568, 1500, 1478 (C=C in Ar), 1276 (CꢀN), 1171
þ
(
CꢀOꢀC), 995 (CꢀS), 755, 709 (CꢀH in Ar). MS(APCI , 20 V), m=z
þ
(
%): 273 ([M þ H] , 65).

New Thiophene-Based Glass-Forming Hydrazones
111=[463]
Measurements
1
The H NMR spectra were obtained on Bruker AC 250 (250 MHz) and
Bruker DPX 250 (250 MHz) instruments. IR-spectroscopy was per-
formed on a Perkin Elmer Spectrum GX spectrophotometer, using
KBr pellets. The mass spectra were obtained on a Waters ZQ 2000.
The UV-vis spectra were recorded with a Spectronic Unicam
TM
Genesys
8 spectrophotometer. The fluorescence emission spectra
were recorded with a Hitachi MPF-4 luminescence spectrometer.
The differential scanning calorimetry (DSC) measurements were per-
ꢂ
ꢀ1
formed on a Mettler DSC-821e at a heating rate of 20 C min in the
N atmosphere. The thermogravimetric analysis (TGA) was fulfilled
2
using a NETZSCH STA 409 thermogravimeter at a heating rate of
ꢂ
ꢀ1
1
0 C min in the N atmosphere.
2
The ionization potential (I ) was measured by the method of elec-
p
tron photoemission in air as described before [10]. The samples for
the measurements were prepared by casting the solutions of the com-
pounds on Al plates pre-coated with methylmethacrylate and meth-
acrylic acid copolymer as the adhesive layer. The hole drift
mobilities of the solid solutions of the synthesized hydrazones in
bisphenol Z polycarbonate were measured by the xerographic time-
of-flight method [11].
RESULTS AND DISCUSSION
3
,4–ethylenedioxythiophene-, thiophene- and terthiophene-based
dihydrazones having oxetane and vinyloxyethyl groups were synthe-
sized by the two- or three-step synthetic route as shown in Scheme 1.
The first step was the formylation by the Vilsmeier method to produce
compound 1a and 1c. The second step was the condensation of alde-
hydes 1a–c with N-phenylhydrazine to produce compounds 2a–c.
The last step was the alkylation of hydrazones obtained with 3-(bro-
momethyl)-3-methyl oxetane in the presence of potassium hydroxide
to obtain 2-(N-(3-methyloxetan-3-yl)N-phenylhydrazonemethyl)3,
4
-ethylenedioxythiophene 3a, 2-(N-(3-methyloxetan-3-yl)N-phenylhy-
drazonemethyl)thiophene 3b and 2-(5-(5-(N-(3-methyloxetan-3-yl)-N-
phenylhydrazonemethyl)thiophene-2-yl)thiophen-2-yl)thiophene3c.The
alkylation with 2-chloroethyl vinyl ether in the presence of potassium
hydroxide and potassium carbonate gave 2-(N-vinyloxyethyl-N-
phenylhydrazonemethyl)3,4-ethylenedioxythiophene 4a and 2-(N-
vinyloxyethyl-N-phenylhydrazonemethyl)thiophene 4b. All the final
products, i.e., hydrazones 3a–c and 4a,b, were purified by column
chromatography to obtain pure and well-defined compounds. The

1
12=[464]
A. Michaleviciute et al.
SCHEME 1 Synthesis of compounds 3a–c and 4a,b.
1
structures of the synthesized compounds were confirmed by H NMR,
IR spectroscopy, and mass spectrometry. Hydrazones 3a–c and 4a,b
are soluble in common organic solvents such as tetrahydrofuran,
chloroform, and acetone.
1
The signals in the H NMR spectra of all the newly synthesized
hydrazone compounds can be exactly assigned to the characteristic
hydrogen atoms of these compounds. The proton signal of the formyl
group at 9.84 ppm, which is present in the spectra of aldehydes 1a–c,
disappears completely in the spectra of hydrazones 2a–c. The new
characteristic signals at 7.80–7.82 ppm due to the protons of N=CH

New Thiophene-Based Glass-Forming Hydrazones
113=[465]
group appear in the spectra of hydrazones 2a–c. Compounds 3a–c
show signals at 4.11–4.40 ppm and 4.50–4.72 ppm typical of the oxeta-
nyl group and at 3.87–4.03 ppm, for which the protons of =NꢀCH ꢀC
2
group are responsible. The signals of the CH group in the spectra of
3
compounds 3a–c are observed at 1.45–1.57 ppm. The signals of =CH2
group protons of the ethyl vinyl ether moiety in the spectra of com-
pounds 4a,b are observed at 4.08–4.31 and 4.09–4.28 ppm, respect-
ively. The signals at 6.50–7.86 ppm in the spectra of all the
synthesized hydrazones can be assigned to the aromatic protons and
to the protons of ꢀCHꢀN groups.
The mass spectra of new hydrazone compounds show the corre-
sponding molecular ion peaks.
ꢀ
1
In the synthesis of hydrazones 2a–c, the strong IR 1650-cm
absorption band typical of formyl groups disappears. In the synthesis
ꢀ1
of 3a–c and 4a,b, the IR absorption band at around 3300 cm which
is specific to the absorption of NꢀH disappears completely. All the
final compounds have the characteristic absorption bands of aromatic
ꢀ
1
groups at 3025–3107 cm
1
(CꢀH stretch), at 1568–1599 and 1462–
ꢀ1
ꢀ1
500 cm (C=C stretches), 693–755 cm (CꢀH), and the characteristic
ꢀ
1
absorption bands of aliphatic groups at 2918–2979 and 2868–2880 cm
CꢀH stretches). The IR spectra of compounds 3a–c and 4a,b have
(
ꢀ1
the characteristic absorption bands of ether groups at 1105–1171 cm
ꢀ1
(
CꢀOꢀC stretches) and the bands at 1203–1276 cm due to the CꢀN
stretching.
The thermal properties of vinyloxyethyl substituted hydrazones
were studied by DSC and TGA in the nitrogen atmosphere. The thermal
stability of the synthesized compounds is predetermined by the pres-
ence of hydrazone moieties [12]. Their 5% weight loss temperatures
ꢂ
range from 234 to 279 C, the values of glass transition temperatures
T and melting points T of compounds 3a,b and 4a,b are summarized
g
m
in Table 1.
TABLE 1 Thermal Characteristics of
Compounds 3a,b and 4a,b
ꢂ
ꢃ
ꢂ
m
T , [ C]
Compound
T
g
, [ C]
3a
3b
4a
4b
40
ꢀ3
15
–
80
79
79
75
ꢃ
st
1
heating only.

1
14=[466]
A. Michaleviciute et al.
All the synthesized hydrazones, which were isolated as crystalline
materials, can be transformed into the amorphous state. Unfortu-
nately, only 3a showed T well above room temperature. The first
g
DSC heating runs of hydrazones 3a,b and 4a,b revealed the melting
ꢂ
at 75–80 C. The recooling and second heating run revealed no peaks
due to the crystallization and melting, and only the glass-transition
ꢂ
temperatures were observed in the DSC heating scans at 40 C for 3a,
ꢀ
ꢂ ꢂ
3 C for 3b, and 15 C for 4a. The DSC apparatus used did not allow
us to fix the glass-transition temperature of 4b. We can only state that
this compound can exist in the solid amorphous state.As an example,
the DSC thermograms of compound 3a are shown in Figure 1.
The DSC results show that 3,4-ethylendioxythiophene-based
hydrazone 3a has higher T than the corresponding thiophene-based
g
compound 3b. The vinyloxyethyl-substituted hydrazone 4a has lower
T than the corresponding oxetanyl-substituted hydrazone 3a.
g
The newly synthesized hydrazones were also characterized by
UV=vis and fluorescence (FL) spectrometry. Terthiophene-based
hydrazone 3c absorbs the electromagnetic radiation in the range
2
00–500 nm, while 3,4-ethylendioxythiophene- and thiophene-based
derivatives absorb in the range 200–400 nm (Fig. 2).
It is evident that the chromophore has a substantial influence on
the spectra of the synthesized hydrazones. The low-energy absorption
bands of 3,4-ethylenedioxythiophene-based hydrazones 3a, 4a show a
ꢂ
FIGURE 1 DSC curves of compound 3b. Heating rate 20 C=min.

New Thiophene-Based Glass-Forming Hydrazones
115=[467]
ꢀ5
FIGURE 2 UV=vis absorption spectra of dilute THF solutions (10 ) of
compounds 3a–c and 4a,b.
bathochromic shift of 8 nm with respect of the corresponding absorp-
tion bands of thiophene-based hydrazones 3b, 4b. The low-energy
absorption band of terthiophene-based hydrazone 3c exhibits a batho-
chromic shift of 71 nm with respect of the corresponding absorption
bands of thiophene-based hydrazones. This observation shows that
the effective delocalization of electrons over the hydrazone and terthio-
pene moieties takes place in a molecule of hydrazone 3c. The lower
ionization potential can be expected for hydrazone 3c relative to the
other newly synthesized hydrazones. The substituent at the nitrogen
atom of a hydrazone moiety has small effect on the absorption spectra
of hydrazones. The lowest energy absorption band of vinyloxyethyl-
substituted hydrazones 4a,b show a bathochromic shift of ca. 2 nm
with respect of the lowest energy absorption band of the corresponding
oxetanyl substituted hydrazones 3a–c. The maxima of the UV absorp-
tion and the fluorescence emission spectra of dilute THF solutions of
compounds 3a–c and 4a,b are summarized in Table 2.
The fluorescence maximum of terthiophene-based hydrazone 3c is
considerably red-shifted as compared with the fluorescence maxima
of thiophene- and 3,4-ethylenedioxythiophene-based hydrazones.
An important characteristic of electronically active compounds used
in optoelectronic devices is the ionization potential I which charac-
p
terizes the electron releasing work under illumination. The ionization

1
16=[468]
A. Michaleviciute et al.
TABLE 2 UV Absorption and FL Emission (in THF solutions,
c ¼ 10ꢀ mol l ) Maxima of Compounds 3a–c and 4a,b
5
ꢀ1
b
Compound
UV:kmax [nm]
FL :kmax [nm]
3
3
3
4
4
a
b
c
a
b
359
351
422
361
353
422
421
496
424, 472
415, 450
a
a
a
Shoulder.
b
For 3a–c and 4a, the excitation wavelength was 310 nm, for
b – 290 nm.
4
potentials I of the hydrazone films 3a–c, 4a,b were established from
p
their electron photoemission spectra shown in Figure 3.
The I values are summarized in Table 3.
p
The lowest Ip value of 5.43 eV was observed for compound 3c.
3
,4-Ethylenedioxythiophene-based hydrazones 3a, 4a show somewhat
higher ionization potentials but lower than that of thiophene-based
hydrazones 3b, 4b. These observations are consistent with the data of
UV=vis spectroscopy. Terthiophene and 3,4-ethylenedioxythiophene-
based hydrazones 3a,c and 4a seem to be suitable for the application
FIGURE 3 Electron photoemission spectra in air of the films of compounds
4a–c, 4a,b.

New Thiophene-Based Glass-Forming Hydrazones
117=[469]
TABLE 3 Ionization Potentials of the Films of Hydrazones 3a–c and 4a,b
Compound
p, eV
3a
3b
3c
4a
4b
I
5.66
5.76
5.43
5.60
5.79
as charge-transporting materials for electrophotographic photorecep-
tors. Holes are easily injected into the charge-transporting layer from
a charge-generating layer with I close to that of the transport layer.
p
The values of Ip for the conventional charge-generating materials
are in the range 5.1–5.6 eV [13].
3,4-Ethylenedioxythiophene- and terthiophene-based hydrazones
were subjected to the charge mobility studies by the xerographic
time-of-flight technique. Figure 4 shows the electric field dependences
for the 50% solid solutions of hydrazones 3c and 4a in PC-Z. The
linear dependences of the hole drift mobilities on the square root of
the electric field intensity are observed.
The room-temperature hole drift mobilities of 50% solid solutions of
ꢀ
6
2
ꢀ1 ꢀ1
3
1
6
c and 4a in bisfenol Z polycarbonate are 2.3 ꢁ 10 cm V
s
and
ꢀ
8
2
ꢀ1 ꢀ1
.1 ꢁ 10 cm
V
s , respectively, at an electric field intensity of
ꢀ
5
ꢀ1
.4 ꢁ 10 V cm .
FIGURE 4 Electric field dependences of the hole drift mobilities in the
charge-transporting layers of compounds 3c and 4a molecularly doped in
PC-Z (50% wt.).

1
18=[470]
A. Michaleviciute et al.
CONCLUSIONS
We have synthesized new glass-forming thiophene-based hydrazones
containing functional oxetanyl and vinyloxyethyl groups. Their chemical
1
structures were confirmed by H NMR, IR spectroscopy, and mass spec-
trometry. Their optical, thermal, and photoelectrical properties are stud-
ied. The hydrazones synthesized can be transformed into the amorphous
ꢂ
ꢂ
phase with glass-transition temperatures ranging from ꢀ3 C to 40 C.
The synthesized compounds exhibit the thermal stability typical of
hydrazones. Their 5% weight loss temperatures are in the range from
ꢂ
2
34 to 279 C. The ionization potentials, measured by the method of
electron photoemission in air, are from 5.43 to 5.78eV. The best hole
transport properties were showed by terthiophene-based hydrazone.
The time-of-flight experiment showed that the hole drift mobility in
molecularly doped bisphenol Z polycarbonate containing 50 wt.% of
2
-(5-(thiophen-2-yl)thiophen-2-yl)thiophene-5-carbaldehyde-N-phenyl-N-
ꢀ6
2
ꢀ1 ꢀ1
(3-methyloxetan-3-yl-methyl)hydrazone is 2.3 ꢁ 10 cm V
s
at an
ꢀ5
ꢀ1
electric field intensity of 6.4 ꢁ 10 V cm .
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