Synthesis and characterization of a new class of nematic photoluminescent oxadiazole-containing polyethers

Article abstract of DOI:10.1021/ma034382f

The synthesis and the characterization of a new class of segmented polyethers (PO) containing the oxadiazole unit are reported. Because of the anisotropic shape of oxadiazole-conjugated segment, the copolymers of the series show the monotropic nematic phase to be somewhat different from that observed in the case of the low molecular mass analogous compounds. In that case, high ordered liquid crystalline smectic phases are reported while the nematic phase is observed just in few cases. According to previous reports on oxadiazole-containing materials, PO show high photoluminescence activity in the blue region of the visible spectra. The good solubility in chlorinate solvents allows the preparation of films with homogeneous thickness by spin coating. A glass transition temperature in the range 100-120°C ensures good stability of film morphology at room temperature. For these features, polymers PO are potential candidate materials for fabricating blue-light-emitting devices.

Full text of DOI:10.1021/ma034382f

6410
Macromolecules 2003, 36, 6410-6415
Synthesis and Characterization of a New Class of Nematic
Photoluminescent Oxadiazole-Containing Polyethers
Dom en ico Acier n o,† Eu gen io Am en d ola ,‡ Sa lva tor e Bellon e,§ Sim on a Con cilio,
P io Ia n n elli,*, Hein r ich -Ch r istop h Neitzer t,§ Alfr ed o Ru bin o,| a n d F u lvia Villa n i|
Dipartimento di Ingegneria dei Materiali e della Produzione, Universita` di Napoli, P.le Tecchio,
I-80125 Napoli, Italy, Institute for Composite Materials and Biomaterials (IMCB)- CNR, P.le Tecchio,
I-80125 Napoli, Italy, Dipartimento di Ingegneria Elettronica, Universita` degli Studi di Salerno,
via Ponte Don Melillo, I-84084 Fisciano (Salerno), Italy, Dipartimento di Ingegneria Chimica ed
Alimentare, Universita` degli Studi di Salerno, via Ponte Don Melillo, I-84084 Fisciano (Salerno), Italy,
and ENEA C.R. Portici, v. Vecchio Macello - loc. Granatello, 80055 Portici (Na), Italy
Received March 26, 2003; Revised Manuscript Received J une 9, 2003
ABSTRACT: The synthesis and the characterization of a new class of segmented polyethers (P O)
containing the oxadiazole unit are reported. Because of the anisotropic shape of oxadiazole-conjugated
segment, the copolymers of the series show the monotropic nematic phase to be somewhat different from
that observed in the case of the low molecular mass analogous compounds. In that case, high ordered
liquid crystalline smectic phases are reported while the nematic phase is observed just in few cases.
According to previous reports on oxadiazole-containing materials, P O show high photoluminescence
activity in the blue region of the visible spectra. The good solubility in chlorinate solvents allows the
preparation of films with homogeneous thickness by spin coating. A glass transition temperature in the
range 100-120 °C ensures good stability of film morphology at room temperature. For these features,
polymers P O are potential candidate materials for fabricating blue-light-emitting devices.
1. In tr od u ction
unit promotes the appearing of high ordered smectic
phases and, only in a few cases, of the nematic phase.
The liquid crystalline (LC) order is particularly interest-
ing when optical active systems are required to be
anisotropic at the macroscopic level.
In this paper, we report on the synthesis and the
characterization of a new class of LC photoluminescent
segmented polymers having the formula P O(m ,a ).
The insertion of the flexible aliphatic segments along
and side attached to the chain moderates melting
temperature and promotes solubility in organic solvents
and the appearing of the nematic phase. The photo-
luminescence properties of polymers are also discussed.
In the last few years, new polymeric materials have
been synthesized and investigated for applications in
the field of organic light-emitting devices (OLEDs).1-31
For fabricating a LED, it is usually required to have
the presence of very thin layers of both hole-transport-
ing and electron-transporting molecules. The two layers
are confined between a hole-injection electrode and a
low work function electron-injection metal contact,
respectively. Photoemission is induced by the reciprocal
combination of holes and electrons at the interface,
under the action of a suitable potential difference.
Polymers may be easily processed to thin stable films
by the spin-coating technique, which results in a fast
and versatile fabrication of devices. Moreover, chemical
architecture can be set up in order to promote the
specific required morphology of samples, when coupled
with a suitable thermal treatment. For applications in
the field of OLEDs, special polymeric materials can be
synthesized by inserting along or attaching side to the
chain short conjugated frames with electroluminescent
properties.
2. Exp er im en ta l Section
2.1. Ma ter ia ls. All reagents and solvents were purchased
from Aldrich and Carlo Erba. N,N-Dimethylacetamide (DMAc)
and N,N-dimethylformamide (DMF) were refluxed on calcium
hydride, distilled in a vacuum, and stored on 4 Å molecular
sieves. Other reagents were used without further purification.
According to Scheme 1, 4,4′-dicarboxy-1,n-diphenoxyalkane
dimethylester (2) and n-alkoxyterephthalic acid (1), with its
chlorinated derivative (3), were synthesized according to a
procedure previously reported.32,33
4,4′-Dica r boxy-1,n -d ip h en oxya lk a n e Dih yd r a zid es (4).
4,4′-Dicarboxy-1,n-diphenoxyalkane dimethylester 2 was pre-
pared according to the procedure described in ref 33. Com-
pound 4 was synthesized from compound 2 reacting with an
excess of hydrazine monohydrate in ethanol solution. The
procedure was the following: approximately 15 g of 2 was
stirred in boiling hydrazine monohydrate (160 mL) with
absolute ethanol (280 mL) for 4 h. At the end, the reaction
system was cooled, and the white crystalline dihydrazide 4
precipitated from the reaction solution. The solid was recov-
ered by filtration, repeatedly washed with cold ethanol, and
dried under vacuum at 60 °C. Final yields ranged between
80 and 90%. For 4,4′-dicarboxy-1,6-diphenoxyalkane dihy-
drazide: Tsolid-solid ) 172.7 °C, ∆Hsolid-solid ) 11.8 J /g; Tm ) 192.0
°C, ∆Hm ) 215.7 J /g. For 4,4′-dicarboxy-1,12-diphenoxyalkane
dihydrazide: Tm ) 214.0 °C, ∆Hm ) 179.4 J /g.
We have recently shown that new oxadiazole-contain-
ing low molecular mass compounds are blue-photo-
lumiscent materials,32 in agreement with that reported
by several authors for similar molecules.19,24-31 We
observed that the anisotropic shape of the conjugated
* Corresponding author. Fax: +39 089 964 057. E-mail:
piannelli@unisa.it.
† Dipartimento di Ingegneria dei Materiali e della Produzione,
Universita` di Napoli.
‡ Institute for Composite Materials and Biomaterials (IMCB)-
CNR.
§ Dipartimento di Ingegneria Elettronica, Universita` degli Studi
di Salerno.
Dipartimento di Ingegneria Chimica ed Alimentare, Univer-
sita` degli Studi di Salerno.
| ENEA C.R. Portici, v. Vecchio Macello - loc. Granatello.
10.1021/ma034382f CCC: $25.00 © 2003 American Chemical Society
Published on Web 07/24/2003

Macromolecules, Vol. 36, No. 17, 2003
New Class of Oxadiazole-Containing Polyethers 6411
P olym er Syn th esis (See Sch em e 1). Step 1: To a
suspension of 4,4′-dicarboxy-1,n-diphenoxyalkane dihydrazide
(4) (5.00 × 10-3 mol) in dry DMAc (50 mL) at room tempera-
ture, the stoichiometric amount of the appropriate n-alkoxy-
terephthalic dichloride (3) was added and the reaction was
allowed to take place overnight under stirring. The reaction
mixture was then poured into cold water and the resulting
solid product was filtered and washed twice with water. The
resulting polyazide P I was collected with a final yield of 58-
60%, purified by dissolving in boiling DMAc (30 mL) and DMF
(20 mL) and subsequent precipitation with water. The final
product was used in the subsequent intramolecular cyclization
reaction. The proton resonance data are in agreement with
the expected values. For example, P I(8,0.5) (CDCl3/CF3-
COOD): δ (ppm) ) 8.33 (d, 1H), 7.88 (d, 4H), 7.68 (s, 1H),
7.62 (d, 1H), 7.08 (d, 4H), 4.38 (t, 2H), 4.15 (m, 4H), 2.07 (m,
2H), 1.90 (m, 4H), 1.63-1.37 (m, 20H), 0.88 (t, 3H) (see Figure
1 for details).
F igu r e 1. 1H NMR spectra of P I(8,0.5) and P O(8,0.5)
dissolved in deuterated chloroform and trifluoroacetic acid.
F igu r e 2. IR spectra of powder samples of P I(8,0.5) and P O-
(8,0.5).
Sch em e 1. Tw o-Step Syn th esis of P O P olym er s

6412 Acierno et al.
Macromolecules, Vol. 36, No. 17, 2003
Ta ble 1. Th er m od yn a m ic Da ta of Vir gin Sa m p les of P I(m ,a )a
PI(m,a)
Tg (°C)
Tm (°C)
∆Hm (J /g)
Tan (°C)
∆Han (J /g)
Tiso (°C)
∆Hiso (J /g)
Td (°C)
η
inh (dL/g)
P I(5,1)
P I(5,0)
P I(5,0.5)
P I(8,1)
P I(8,0)
123.5
105.5
120.1
115.8
104.5
113.7
231.0
167.0
197.3
216.6
167.3
195.6
-5.4
-4.4
-4.6
-5.6
-3.2
-3.7
235.0
175.4
206.0
218.3
174.0
200.4
4.4
4.3
3.8
4.9
2.5
3.0
338.0
343.9
331.1
317.2
341.7
343.6
0.86
1.00
0.75
0.51
0.63
0.65
202.3
23.7
P I(8,0.5)
a
Tg ) temperature of glass transition; Tm/∆Hm ) melting temperature/enthalpy, second heating run; Tan/∆Han ) anisotropization
temperature/enthalpy, second cooling run; Tiso/∆Hiso ) isotropization temperature/enthalpy; Td ) 5% weight loss temperature; ηinh
inherent viscosities measured at 25.0 °C in 0.5 g/dL DMF.
)
Ta ble 2. Th er m od yn a m ic Da ta of Vir gin Sa m p les of P O(m ,a )d
P O(m ,a )
Tg (°C)
Tm (°C)
∆Hm (J /g)
Tc (°C)
223.0
210.6
198.3
∆Hc (J /g)
Tiso (°C)
∆Hiso (J /g)
Td (°C)
ηinhc (dL/g)
235.0
P O(5,1)
124.5
24.5a
-24.2a
365.9
0.35
224.0
211.4
173.7
P O(5,0)
P O(5,0.5)
P O(8,1)
96.9
97.3
27.6
-25.7a
362.5
357.4
375.0
0.49
0.17
0.33
164.6
168.0/ 156.0b
203.3b
-5.3b
-3.35b
178.0b
206.4b
6.2b
3.2b
210.0
218.2
116.2
20.2a
32.5
15.3
178.6
170.3
-14.5
P O(8,0)
105.5
101.1
200.0
195.7
-27.5a
394.6
380.8
0.12
0.39
165.5
191.3b
-4.9b
-3.6
194.7b
5.7b
P O(8,0.5)
136.3
a
Transition enthalpy, referring to the unresolved set of peaks. b Italicized data refer to the reversible nematic-to-isotropic liquid transition.
c Inherent viscosities were measured at 25.0 °C in 0.5 g/dL chloroform + 5% trifluoroacetic acid solutions, except for the less soluble
P O(5,1), which was dissolved in 0.5 g/dL chloroform + 50% trifluoroacetic acid. Tg ) temperature of glass transition; Tm/∆Hm ) melting
d
temperature/enthalpy, second heating run; Tc/∆Hc ) exothermic transition temperature/enthalpy, second cooling run; Tiso/∆Hiso
isotropization temperature/enthalpy, when resolved; Td ) 5% weight loss temperature.
)
F igu r e 3. Nematic optical texture of P I(8,0.5) taken at 195
°C in the cooling run. Crossed polarizers; 20× magnification.
Step 2: The freshly synthesized polyazide P I (1.0 g) was
poured into 40 mL of phosphorus oxychloride (POCl3); after 1
h the solution became clear, and the reaction was conducted
at the refluxing temperature for 5 h more. The clear solution
was cooled and dropped into water (500 mL), to which was
added crushed ice and potassium hydrogen carbonate. The
precipitate P O was filtered and washed with water, dried, and
purified by recrystallization from boiling DMAc. The yield is
approximately 65%. The proton resonance data are in agree-
ment with the expected values. For example, P O(8,0.5)
(CDCl3/CF3COOD): δ (ppm) ) 8.35 (d, 1H), 8.16 (d, 4H), 7.96
(m, 2H), 7.19 (d, 4H), 4.46 (t, 2H), 4.18 (m, 4H), 1.95 (m, 6H),
1.65-1.29 (m, 20H), 0.87 (t, 3H) (see Figure 1 for details).
2.2. Ch a r a cter iza tion . Fibers were extruded from the
isotropic phase and cooled to room temperature. The averaged
diameter of fibers was 200-300 µm.
F igu r e 4. X-ray diffraction pattern recorded at room tem-
perature on a fiber sample of P I(8,0.5). The pattern corre-
sponds to a cybotactic nematic phase.
Thermal measurements were performed by a DSC-7 Perkin-
Elmer calorimeter under nitrogen flow at 10 °C/min rate.
Thermogravimetric analysis was performed with a TA
Instruments SDT 2960 apparatus, in air at 20 °C/min.
Polarized optical microscopy was performed by a J enapol
microscope fitted with a Linkam THMS 600 hot stage.
An M2000 FTIR spectrometer (by Midac Co.) was adopted
to collect IR spectra.
X-ray diffraction spectra were recorded using a flat camera
with a sample-to-film distance of 90.0 mm (Ni-filtered Cu KR

Macromolecules, Vol. 36, No. 17, 2003
New Class of Oxadiazole-Containing Polyethers 6413
F igu r e 5. DSC traces of P I(8,0.5) powder sample: (a) second
heating showing the isotropization transition; (b) first cooling
showing the anisotropization transition.
F igu r e 7. Nematic optical texture of P O(8,0.5) taken at 190
°C in the cooling run. Crossed polarizers; 20× magnification.
F igu r e 8. X-ray diffraction pattern of a fiber sample of P O-
(8,0.5), taken at room temperature. The pattern corresponds
to the quenched nematic phase.
F igu r e 6. DSC traces of P O(8,0.5) powder sample: (a) first
heating showing the melting transition; (b) first cooling
showing the isotropic liquid-to-nematic transition, followed by
the nematic-to-mesophase transition; (c) second heating show-
ing the melting transition; (d, e) cooling run (d) and subsequent
fast heating run (e) for isolating the monotropic nematic-to-
isotropic liquid transition.
means of a CCD camera, model MTECCD1024x128-6 (1024
× 128 pixels by 26 µm; spectral range of 200-1000 nm).
Photoluminescence spectra were obtained by means of a
Perkin-Elmer LS50 spectrofluorometer on thin films spin
coated on quartz glasses (resolution 2.5 nm).
Measurements of polarization dependence on polymer fibers
have been performed using, for the excitation, an RLT370-10
highly directional GaN light emitting diode (optical output
power of 1 mW; emitting wavelength at 370 nm). For the
detection a Spindler and Hoyer polarizer, an UDT-PIN10
silicon photodiode, and a Stanford Research type “SR510” lock-
in-amplifier were used.
radiation). The Fujifilm MS 2025 imaging plate and a Fuji
Bioimaging analyzer system, model BAS-1800, were used for
recording and digitizing the diffraction patterns.
1H NMR spectra were recorded with a Bruker DRX/400
spectrometer. Chemical shifts are reported relative to the
residual solvent peak.
Inherent viscosities were measured at 25.0 °C with an
Ubbelohde viscometer. Viscosities of P O were performed in
0.5 g/dL chloroform + 5% trifluoroacetic acid solutions. Vis-
cosities of P I were measured in DMF solution.
Films of about 70 µm (evaluated by a KLA-TENCOR P10
surface profiler) have been prepared by spin coating (SET
Spinner TP6000 at 1000 rpm rate) from a solution of 3%
weight of PO in 1,1,2,2-tetrachloroethane and few drops of
trifluoroacetic acid. Films were then dried at 100 °C on a hot
plate for 30 min. Under this condition, transparent and
amorphous films are obtained.
UV-visible absorption measurements were performed with
a Hamamatsu deuterium lamp L2D2 and an Osram HLX
Xenophot lamp equipped with two monochromators (a J obin-
Yvon SPEX 1681 monochromator, model 1681B, with a resolu-
tion of 0.25 nm, for the incident beam and a J obin-Yvon ISA
TRIAX 320 monochromator, with a resolution of 0.06 nm, for
the transmitted beam, respectively). Data were recorded by
3. Resu lts a n d Discu ssion
3.1. Syn th esis. The two-steps synthetic path given
in Scheme 1 ensures high molecular weights and good
quality of final products. This is the consequence of the
good solubility of both P I and P O in POCl3, which
avoids the segregation, by precipitation, of the unreacted
azide segments along the chain. Consequently, the
cyclization is complete according to the 1H NMR spectra
(Figure 1) and the disappearing of the characteristic
signals of N-H bond (hydrogen bond) in the IR spectra
(Figure 2). The single-step procedure based on the direct
reaction between the dihydrazide compound 4 and the
acid compound 1 in POCl3 was tried, but only oligomeric
products were obtained. Moreover the acid compound
1 is low soluble in POCl3, thus the cyclization process
is only partial. In the thermogravimetric P I trace, a

6414 Acierno et al.
Macromolecules, Vol. 36, No. 17, 2003
low angle (Figure 4). This reflection, associated with the
absence of higher order spots, corresponds to the lay-
erlike packing of chains in a nematic-cybotactic struc-
ture (d-spacing of 34 Å). The broad halo at high angle
corresponds to the chain-chain distance (d-spacing of
4.4 Å).
When virgin samples of P I(8,0.5) are heated on
isotropization, the subsequent cooling and heating
traces show only the sharp peak corresponding to the
isotropization and to the anisotropization (Figure 5),
respectively.
Also P O show the nematic phase, but in a monotropic
way. According to Table 2, the isotropization transition
can be isolated only in the case of P O(8,1) and copoly-
mers P O(5,0.5), P O(8,0.5). The flat shape of the
conjugated bis(oxadiazole) segment, inserted along the
macromolecular chain, promotes the intermolecular
packing and, consequently, stabilizes the crystalline
phase respect to the nematic phase. In the case of
copolymers, the statistical insertion of flexible segments
along the chain destabilizes the crystalline order and
the nematic phase can be reversibly observed (see
Figures 6 and 7).
F igu r e 9. UV-visible absorption and emission spectra of a
thin film sample of P O(8,0.5). Emission spectra were recoded
by irradiating the sample at 340 nm.
shoulder is observed starting at a temperature of about
290 °C, which corresponds to the loss of water related
to the cyclization process (Table 1). P O are stable at
temperature lower than about 300 °C, while a degrada-
tion process occurs at about 320-350 °C, related to
thermal decomposition of the less stable aliphatic seg-
ments (Table 2).
In a previous paper some of us reported on a class of
fully conjugated polymers analogous to P O and having
the formula34
3.2. P h a se Beh a vior . Thermodynamic properties of
P I and P O polymers are given in Tables 1 and 2,
respectively. Hereinafter P I(8,0.5) and P O(8,0.5) are
taken as representative terms of the two series.
P I are liquid crystalline nematic polymers, according
to the optical texture shown in Figure 3 and the fluid
nature of the anisotropic phase. The X-ray diffraction
pattern of a fiber sample of P I(8,0.5) recorded at room
temperature shows a strong out-meridian reflection at
R(m ) do not melt and do not show any liquid crystal-
line phase. In the case of P O the nematic phase is
F igu r e 10. (a) Photoluminescence of P O(8,0.5) fiber sample irradiated at 370 nm in the dark. (b) Comparison between the
polarized photoluminescence and the polarized X-ray equatorial spot, taken from the pattern shown in Figure 8.

Macromolecules, Vol. 36, No. 17, 2003
New Class of Oxadiazole-Containing Polyethers 6415
promoted by the combined effects of both the flexible
segments inserted along the chain and side ones at-
tached to the chain. In this case, polymers can be
extruded from the melt and highly orientated fiber
samples can be easily prepared especially in the case of
copolymers, taking advantage of the nematic nature of
the molten phase (see Figure 8).
3.3. Op tica l P r op er ties a n d P h otolu m in escen ce.
As already pointed out, the use of the oxadiazole frame
in the synthesis of new materials, suitable for the
fabrication of OLED, has been widely investigated. The
main reason is the possibility to extend the electron-
transport character of this molecular frame to new
materials and to set emission in the blue region of the
visible spectra.
Refer en ces a n d Notes
(1) Burroughes, J . H.; Bradley, D. D. C.; Brown, A. R.; Marks,
R. N.; Mackay, K.; Friend, R. H.; Burns, P. L.; Holmes, A. B.
Nature (London) 1990, 347, 539.
(2) Holmes, A. B.; Bradley, D. D. C.; Brown, A. R.; Burn, P. L.;
Burroughes, J . H.; Frien, R. H.; Greenham, N. C.; Gymer, R.
W.; Halliday, D. A.; J ackson, R. W.; Kraft, A.; Martens, J . H.
F.; Pichler, K.; Samuel, I. D. W. Synth. Met. 1993, 55-57,
4031.
(3) Berggren, M.; Ingana¨s, O.; Gustafsson, G.; Rasmusson, J .;
Andersson, M. R.; Hijertberg, T.; Wennerstrom, O. Nature
(London) 1994, 372, 444.
(4) Brown, B.; Bradley, D. D. C.; Burroughs, J . H.; Friend, R.
H.; Greenham, N. C.; Burn, P. L.; Holmes, A. B.; Kraft, A.
Appl. Phys. Lett. 1992, 61, 2793.
(5) Grem, G.; Leditzky, G.; Ulrich, B.; Leising, G. Adv. Mater.
1992, 4, 36.
(6) Adachi, C.; Tsutsui, T.; Saito, S. Appl. Phys. Lett. 1990, 56,
799.
(7) Hedrick, J . L.; Tweig, T. Macromolecules 1992, 25, 2021.
(8) Strukelj, M.; Papadimitrakopoulos, F.; Miller, T. M.; Roth-
berg, L. J . Science 1995, 267, 1969.
(9) Li, X. C.; Holmes, A. B.; Kraft, A.; Moratti, S. C.; Spencer, G.
C. W.; Cacialli, F.; Gru¨ner, J .; Friend, R. H. J . Chem. Soc.,
Chem. Commun. 1995, 2211.
(10) Li, X. C.; Spencer, G. C. W.; Holmes, A. B.; Moratti, S. C.;
Cacialli, F.; Friend, R. H. Synth. Met. 1996, 76, 153.
(11) Pei, Q.; Yang, Y. Chem. Mater. 1995, 7, 1568.
(12) Buchwald, R.; Meier, M.; Karg, S.; Po¨sch, P.; Schmidt, H. W.;
Strohriegl, P.; Riess, W.; Schwoerer, M. Adv. Mater. 1995, 7,
839.
Polymers P O are quite transparent in the visible
range and strongly absorb in the UV range as shown
in Figure 9. There are two strong and broad absorption
bands peaked at about 340 and 250 nm, which obviously
depends only on the oxadiazole moiety and is indepen-
dent of the aliphatic insertions.
When film samples are exposed to UV radiation, P O
show a strong photoluminescence in the blue region of
the spectrum. When a sample is irradiated at 340 nm,
the emission spectrum shows a broad peak located at
about 430 nm with a shoulder at about 460 nm (Figure
9), similar to that reported for analogous oxadiazole-
containing compounds.
(13) Huang, W.; Yu, W. L.; Meng, H.; Pei, J .; Li, S. F. Y. Chem.
Mater. 1998, 10, 3340.
P O copolymers can be easily extruded to give oriented
fiber samples due to the nematic nature of the material.
The consequence is the parallel packing of chains in a
macrodomain. The reciprocal alignment of the oxadia-
zole units in a macroscopic array influences the response
to the UV irradiation in the two directions parallel and
perpendicular to the fiber axis, respectively. As a
consequence, polymers give in emission a polarized
photoluminescence (see Figure 10) with the same period
of the X-ray diffraction. Compared to the polarization
of the nematic halo in the diffraction pattern shown in
Figure 8, photoluminescence profile is broader as con-
sequence of the scatter due to sample anisotropy.
(14) Lee, J . I.; Klaerner, G.; Miller, R. D. Chem. Mater. 1999, 11,
1083.
(15) Li, X. C.; Liu, Y.; Liu, M. S.; J en, A. K. J . Chem. Mater. 1999,
11, 1568.
(16) Liu, Y.; Liu, M. S.; Li, X. C.; J en, A. K. J . Chem. Mater. 1998,
10, 3301.
(17) Liu, Y.; Ma, H.; J en, A. K. J . Chem. Mater. 1999, 11, 27.
(18) Peng, Z.; Zhang, J . Chem. Mater. 1999, 11, 1138.
(19) Bao, Z.; Peng, Z. Chem. Mater. 1998, 10, 1202.
(20) Lu, J .; Hlil, A. R.; Sun, Y.; Hay, A. S.; Maindron, T.; Dodelet,
J . P.; D’Iorio, M. Chem. Mater. 1999, 11, 2501.
(21) Casu, M. B.; Imperia, P.; Schrader, S.; Schulz, B.; J andke,
M.; Strohriegl, P. Synth. Met. 2001, 121, 1397.
(22) Xu, B.; Pan, Y.; Zhang, J .; Peng, Z. Synth. Met. 2000, 114,
337.
(23) Wang, Z.; Yang, X.; Chen, X.; Xu, Z.; Xu, X. Thin Solid Films
2000, 363, 94.
4. Con clu sion s
(24) Meier, M.; Buchwald, E.; Karg, S.; Po¨sch, P.; Greczmiel, M.;
Strohriegl, P.; Riess, W. Synth. Met. 1996, 76, 95.
(25) Paik, K. L.; Baek, N. S.; Kim, H. K.; Lee, J . H.; Lee, Y. Opt.
Mater. 2002, 21, 135.
(26) J ousseaume, V.; Maindron, T.; Wang, Y.; Dodelet, J . P.; Lu,
J .; Hlil, A. R.; Hay, A. S.; D’Iorio, M. Thin Solid Films 2002,
416, 201.
(27) Ding, J .; Tao, Y.; Day, M.; Roovers, J .; D’Iorio, M. J . Opt. A:
Pure Appl. Opt. 2002, 4, S267.
(28) Zheng, S.; Shi, J . Chem. Mater. 1999, 13, 4405.
(29) Paik, K. L.; Baek, N. S.; Kim, H. K.; Lee, Y.; Lee, K. J . Thin
Solid Films 2002, 417, 132.
(30) Song, S. Y.; J ang, M. S.; Shim, H. K.; Song, L. S.; Kim, W. H.
Synth. Met. 1999, 102, 1116.
(31) Bettenhausen, J .; Greczmiel, M.; J andke, M.; Strohriegl, P.
Synth. Met. 1997, 91, 223.
(32) Li, X. C.; Spencer, G. C. W.; Holmes, A. B.; Moratti, S. C.;
Cacialli, F.; Friend, R. H. Synth. Met. 1996, 76, 153.
(33) Acierno, D.; Concilio, S.; Diodati, A.; Iannelli, P.; Piotto Piotto,
S.; Scarfato, P. Liq. Cryst. 2002, 29, 1383.
According to our previous contribution about low
molecular mass compounds containing oxadiazole unit32
and to several reports on similar systems,19,24-31 P O are
blue photoluminescent materials. Taking advantage of
the nematic phase, P O can be easily oriented to make
fiber samples from the molten state. Oriented samples
emit polarized photoluminescence.
Thanks to the flexible spacers along the chain and
the side pendant segments, P O are soluble in common
chlorinate solvents. Thin films obtained by spinning
technique show strong emission in the blue region of
the visible spectra.
All these features make P O suitable to be used as
active material in the fabrication of blue-emitting
OLED. The study of electronic properties of P O and the
realization of an electroluminescent device using P O as
the electron transport component are under scrutiny.
(34) Caruso, U.; Iannelli, P.; Roviello, A.; Sirigu, A. J . Polym. Sci.,
Polym. Phys. 1997, 36, 2371.
(35) Gillo, M.; Iannelli, P.; Laurienzo, P.; Malinconico, M.; Roviello,
A.; Mormile, P.; Petti, L. Chem. Mater. 2002, 14, 1539.
Ack n ow led gm en t. Support by FIRB “Micropolys”
Project financed by the Ministero dell’Istruzione, dell’Uni-
versita` e della Ricerca (MIUR) is gratefully acknowl-
edged.
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