Fast thermal evaporation in purification of 1,4-Di(pyren-1-ly)benzene

Article abstract of DOI:10.1002/jccs.201100557

This work presents a fast purification system that involves a vertical quartz tube and vacuum sublimation for separation without dilution. This system produced re-crystallized 1,4-di(pyren-1-yl)benzene (DPB) in a few hours following the synthesis of pyrene derivatives with a mole yield ratio of 1,4-di(pyrene-1-yl)benzene to 1-phenylpyrene (1PP) of 5:1. Differential scanning calorimetry (DSC) and X-ray diffractometry (XRD) were utilized to identify the products. Finally, the lifetimes of pyrene derivatives DPB and 1PP were determined by exponential regression to be 10.0 ± 0.14 and 3.3 ± 0.15 ns, respectively. From the lifetime measurements, the purity of the photo-responsive materials could be easily determined. To prevent red-shift of electro-luminescence (EL) spectra by the energy transfer mechanism, it has acquired to elect transfer layers for pure electroluminescence. Aco-catalytic reaction reduced the amount of impurities and eliminated the need for the use of a solvent in the purification step.

Full text of DOI:10.1002/jccs.201100557

JOURNAL OF THE CHINESE
CHEMICAL SOCIETY
Article
Fast Thermal Evaporation in Purification of 1,4-Di(pyren-1-ly)benzene
Chung-Yi Hsu,a Hung-Yin Lin,b Xuan-You Yan,a Tsung-Syun Huang,c
Yan-Kuin Suc,d and Thou-Jen Whanga,d*
aDepartment of Chemistry, National Cheng Kung University, Tainan 70101, Taiwan, R.O.C.
bDepartment of Chemical and Materials Engineering, National University of Kaohsiung,
Kaohsiung 81154, Taiwan , R.O.C.
cDepartment of Electrical Engineering, National Cheng Kung University, Tainan 70101, Taiwan, R.O.C.
dDepartment of Photonics, National Cheng Kung University, Tainan 70101, Taiwan, R.O.C.
(Received: Sept. 16, 2011; Accepted: Jan. 30, 2012; Published Online: Feb. 20, 2012; DOI: 10.1002/jccs.201100557)
This work presents a fast purification system that involves a vertical quartz tube and vacuum sublimation
for separation without dilution. This system produced re-crystallized 1,4-di(pyren-1-yl)benzene (DPB) in
a few hours following the synthesis of pyrene derivatives with a mole yield ratio of 1,4-di(pyrene-1-
yl)benzene to 1-phenylpyrene (1PP) of 5:1. Differential scanning calorimetry (DSC) and X-ray dif-
fractometry (XRD) were utilized to identify the products. Finally, the lifetimes of pyrene derivatives DPB
and 1PP were determined by exponential regression to be 10.0 0.14 and 3.3 0.15 ns, respectively. From
the lifetime measurements, the purity of the photo-responsive materials could be easily determined. To
prevent red-shift of electro-luminescence (EL) spectra by the energy transfer mechanism, it has acquired
to elect transfer layers for pure electroluminescence. A co-catalytic reaction reduced the amount of impu-
rities and eliminated the need for the use of a solvent in the purification step.
Keywords: Purity; Sublimation; Co-catalytic.
INTRODUCTION
Highly pure crystalline phases are required as new
ture.11,12 Recently, vacuum sublimation under temperature
gradients has been adopted to separate highly pure optical
materials by, for example, growing trans-stilbene and ben-
zophenone single crystals.13,14 For example, pure 2-(2-hy-
droxyphenyl)benzoxazolato lithium (LiPBO), pentacene
and sp2-hybridized bistriphenylenyls are purified by physi-
cal vapor transport in a horizontal glass tube.6,7 Although
several apparatus have been applied, an accurate under-
standing of the temperature difference between compounds
in the mixture is difficult to obtain, and the purified optical
materials are difficult to elucidate.
optical materials with high efficiency and electronic mobil-
ity for use in such applications as solar cells and infrared
photo-detectors.1,2 Frequently, an annealing process to
re-crystallize zinc sulfide (ZnS) has been utilized in the
manufacture of light emitting diodes (LEDs), lasers and
flat panel electroluminescent (FEL) displays.3,4 This an-
nealing process has also been applied to improve the trans-
port properties of single-wall carbon nanotubes by reduc-
ing the amount of impurities, which considerably affect the
electronic structure of the organic materials.5,6 Conjugation
with organic optical materials, in which the p-delocalized
electrons are responsible for the intra-molecular conduc-
tion, results in the formation of molecular crystals under
the influence of the relatively weak van der Waals interac-
tions among molecules. The electronic behavior is deter-
mined by the molecular packing7 and the design of transfer
layers.8 Furthermore, the purity and crystal shape of or-
ganic optical materials greatly influence the thermal stabil-
ity and photo-luminescence characteristics.9,10
A series of palladium (Pd)-catalyzed coupling proce-
dures have been developed by Heck, Hiyama, Kumada,
Negishi, Miyaura, Sonogashira, Suzuki and Stille.15-17 The
popular catalyzed method for forming aromatic carbon-
carbon (C-C, C=C, CºC) and carbon-nitrogen (C-N) or car-
bon-heteroatom bonds is of great importance in various
chemical syntheses.18 The catalyzed method can enhance
the yield of synthesized derivatives.19 To overcome practi-
cal limits of reactive efficiency, the Pd-catalyzed formation
of bonds is gradually becoming an accepted procedure.
Moreover, some related Pd-catalyzed assisted schemes
have applied to inactive functional groups and ascend-up
Chromatographic columns have been widely em-
ployed to separate particular products from a crude mix-
Dedicated to the memory of Professor Yung-Son Hon (1955–2011).
* Corresponding author. E-mail: twhang@mail.ncku.edu.tw
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Hsu et al.
of the transformations.20-22
were 16 to 25 degree, respectively. The difference between
the diffraction peaks of the re-crystallized and the original
Usually palladium in Suzuki coupling can be pre-cat-
alysts for popular reactions.23 Nevertheless, specially de-
signed catalysts are essential to the activation of steric hin-
drance or electronically un-activated compounds. The
Suzuki reaction with a catalytic cycling-mechanism in-
volves oxidative addition in advance, followed by a trans-
metallization step and then reductive elimination.24,25 The
catalytic quantity, reaction solvent environment, reaction
temperature and nontoxic nature in environmental applica-
tions are discussed.26,18 The activity of some catalysts is
completely determined from their reactive efficiency or ev-
idence of the yield of the reactions in which they partici-
pate.
Electroluminescence (EL) and quantum efficiency
are affected by the design of the devices and the emission
occurs through the doping effect or Förster energy transfer.
Of which emitting color will be determined by the excited
layer of the device. From the perspective of energy transfer,
di-molecular derivatives were frequently discussed.27 Es-
pecially for the di-molecular pyrene derivatives of polycy-
clic aromatic hydrocarbons, the capability to exhibit better
photophysical properties are influenced by the purity of the
derivatives.28 One thing worth to be noted is if heterocyclic
rings are not embedded into pyrene derivatives, such as the
1,4-di(pyrene-1-yl)benzene (DPB) while it is insoluble in
most of the solvents, it is a major drawback in column chro-
matography. Therefore, the thermal evaporator system can
be applied to cope with this dilemma.
Fig. 1. (a) Setup of the thermal evaporator purification
system with a vertical quartz-glass tube. The
setup consists of vacuum, cooling, heating sys-
tems, the controlling parameters are tuned by
vacuum degree, cooling temperature and the
temperature of heating tube. The size of cham-
ber is 38 cm in height, 25 cm in width, the ra-
dius of manual rotation plate is 8.5 cm and the
diameter of heating tube is 2~2.5 cm. (b) Vac-
uum pressure and temperature profile during
the thermal evaporation. To achieve the degree
of vacuum less than 1 ´10-3 torr, the tempera-
ture of warm-up stage was kept for a period of
time.
RESULTS AND DISCUSSION
TGA measurements were made by heating the mate-
rial at a rate 10 oC/min in gaseous nitrogen. The thermal de-
composition temperatures (Td) of the 1PP and DPB were
429 oC and 448 oC, respectively, indicating that they were
thermally stable at the deposition temperature in the vac-
uum system. The first DSC trace that was obtained at a
heating rate of 10 oC/min revealed that 1PP and DPB had
melting transition temperatures of 291.8 oC and 295.3, re-
spectively. In Table 2, DPB and 1PP of the melting temper-
atures differed by only 3.5 oC still can be completely sepa-
rated in the system shown on Fig. 1.
Fig. 2. (a) X-ray diffraction (XRD) spectrum of the de-
posited thin film. Note that diffracted degrees
from 16 to 25 of (2) and (3) appeared distinct
difference. Another, holding 250 oC in the vac-
uum for re-crystallization and original sample
o
(2) of deposited 350 C, was little variation in
the crystal morphology. (b) Optical microscope
images of the deposited crystallites. Note that 1
and 2 for BDP, 3 and 4 for 1PP, and before ther-
mal annealing for 1 and 3, and after thermal an-
nealing for 2 and 4.
An XRD spectrum was shown in Fig.2(a), the an-
nealed sample was held for 2 hrs to induce re-crystalliza-
tion and the original evaporated main products were com-
pared. The heterological diffraction angles of DPB and 1PP
290
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JOURNAL OF THE CHINESE
CHEMICAL SOCIETY
Fast Thermal Evaporation in Purification
material revealed the stability of the crystal lattice, without
the need to hold the temperature in the quartz column at
250 oC and 1 ´ 10-3 torr for a long time. Fig. 2(a) presents
the change in the pattern that was associated with anneal-
ing, and the enhanced signals were induced by the pre-
ferred orientation of the grown crystal. Figure 2(b) shows
the crystal morphology of optical microscopy which can
enhance the intensity of the XRD patterns in Figure 2(a).
The spectroscopic properties of DPB and 1PP in solu-
tion or as deposited films were measured and the homolo-
gous data were presented in Table 2. The maximum wave-
lengths of emission spectra were 459.3 nm and 455.7 nm
for 1PP and DPB, respectively. Comparing the photolumi-
nescence of the reference to the PL spectra from the dis-
solved solution or deposited film reveals that the spectrum
of the film that was prepared by vacuum vapor deposition
was red-shifted from that in the CHCl3 solvent. The major
reasons for that are the solvate-chromatic effect and intra-
molecular charge transfer.31-33 Photo-electrical materials
must be efficiently purified, and purities of over 99.98% by
elemental analysis (EA, Heraeus, Vario EL III).
nm of absorption wavelength with DPB and 1PP, and step
up 350 nm for excited wavelength placed in the above sort.
The maximum wavelength of the crude material lay be-
tween DPB and 1PP, while the full width at half maximum
(FWHM) of the crude and pure materials is almost twice of
DPB or 1PP. In the PL spectrum of Fig. 4(a). The maximum
of the peak in 1PP is red-shifted about 5 nm compared with
that of DPB. It is presumably ascribed to overture of that
the content of intra-molecular charge transfer (ICT) effec-
tively or aggregation of coplanar configuration. In the ul-
tra-violet photoelectron spectrum (UPS) measurements,
the investigation of the highest occupied molecular orbital
of energy level (EHOMO) in DPB and 1PP was 5.68 eV and
5.60 eV, respectively. Accordingly, the lowest non-occu-
pied molecular orbital of energy level (ELUMO) could be es-
timated from the optical band gap (Eg) of DPB (3.10 eV)
and 1PP (3.02 eV) to be the same 2.58 eV same in both DPB
and 1PP from the formula ELUMO = Eg + EHOMO.
The device was deposited in order of a patterned etch-
ing indium-tin-oxide (ITO) substrate as follows; (A) ITO /
Accordingly, lifetime can be measured to determine
the wave functions and distribution of electrons in a com-
plex molecule. Such a measurement is useful in studying
the dynamics of excited states and the mechanism of
quenching collisions. To evaluate the lifetime, the lifetime
decay apparatus was set at the photoluminescence wave-
length lmax = 455~460 nm. Fluorescence decay curves
were plotted using an oscilloscope and then exponential re-
gression fitting of the data was performed to determine the
lifetime. In Fig. 3(b), the fitted curves for the evaporated
materials had the equations, IiDPB = 4.46 exp(-t/tDPB) for
DPB with 1/tDPB= 1 × 108, Ii = 28.2 exp(-t/t1PP) for 1PP
with 1/t1PP= 3 × 108 and Ii = 56.4 exp(-t/tmix) for the equiva-
lent mixture of DPB and 1PP with 1/tmix= 3 × 108. There-
fore, the lifetime measurement method easily investigates
the purity and may be applied to the area of synthesized op-
toelectronic materials. In Figure 3(b) the more lifetime of
DPB and 1PP, the weaker intensities of the signal with
moderate decreasing trend will be. However, the intensity
of the mixture (1:1 mol%) has a deep decreasing tendency
with the lifetime because the intensity is not an additive
property. It means the purity will affect the lifetime pro-
foundly.
Fig. 3. (a) Scheme of photon-path of lifetime measure-
ment, (b) Exponential fitting curve for lifetime
t value of purified sample evaporated at 350 oC,
mixing material (DPB: 1PP = 1:1) at 350 oC and
The crude and purity material related to photo-physi-
cal properties, as shown in the Fig. 4(a). Therefore, the trait
peak of absorption wavelength, in proper order near 350
o
the product evaporated at 330 C were 10.0
0.14, 3.3 0.15 and 3.3 0.08 ns, respectively.
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1931 chromaticity coordinates were (x = 0.23, y = 0.27)
and the maximum EL intensity was at 492 nm. For device
B, the CIE 1931 chromaticity coordinates were (x = 0.17, y
= 0.21) and the maximum EL intensity was at 461 nm.
When addition of an Alq3 layer in device A, the electrolu-
minescence spectrum was red-shift compared with device
B.34 Consequently, the electron transfer layer must be se-
lected very carefully to avoid the overlap and Förster en-
ergy transfer by the fluorescence excited from emitter in
the OLED device.
To improve the EL (electroluminescence) and quan-
tum efficiency in the range of visible light, a single layer of
PL (photoluminescence) dyes or doped emitted material
was used in an electron transfer layer. It is necessary to use
the doped material united with higher extinction (or ab-
sorption) coefficients and fluorescence of quantum yield to
be in accordance with the Förster energy transfer of emis-
sion. Of which emitting color will be determined by the ex-
cited layer of the device. From the perspective of energy
transfer, di-molecular derivatives formed from pyrene with
higher energy gap can appropriately excite a material with
lower energy gap to emit fluorescence. Di-molecular pyr-
ene derivatives of polycyclic aromatic hydrocarbons, ex-
hibit better photo-sensitivity, heat tolerance, electrical con-
ductivity, emissive capacity, stability and character of physi-
ology response, when purity of the derivatives has been
promoted.
Fig. 4. (a) The photoluminescence (PL) which the ex-
cited wavelength is 350 nm. (b) The electrical
characteristics of current–luminescence–volt-
age (I-L-V) curve measurements; (c) The elec-
troluminescence of the proposed devices.
For the conventional chromatographic columns, sil-
ica gel has to be chosen carefully and it is tedious to opti-
mize the ratio of solvents for elution efficiency. Even more,
it may take the risk of losing product since it is likely to be
adhered to silica gel. Generally, the best recycling ratio is
about 50% and the most of the byproducts are not retriev-
able so that it is unfavorable for investigating the reaction
mechanism. Therefore, it is impossible to recycle the mate-
rials because of contamination and it has huge impact on
environment. Thermal evaporator purification system not
only provides the solution to avoid the contamination dis-
cussed above and it is also time-saving in the process. The
purification yield can be improved especially for the com-
pounds that are not dissolvable in solvents, and the crystal-
lization will be greatly enhanced by adopting this system
for purification.
NPB (40 nm) / DPB (30 nm) / BCP (10 nm) / Alq3 (30 nm) /
LiF (1 nm) / Al and (B) ITO / NPB (40 nm) / DPB (30 nm) /
BCP (15 nm) / LiF (1 nm) / Al. The final deposited device
on a patterned etching ITO substrate included ten equal ef-
fective blocks of 3.6 mm2 each.34-36 Figure 4(b) is the plot
for the measurement of the I-L-V curve (current–bright-
ness–voltage) from the electrical characteristics of the de-
vice. When investigating the devices A and B, the initial
voltages of the characteristic features were 3.5 V and 4.0 V,
respectively. The current density can be distinguishable af-
ter 6.0 V, and 258 mA/cm2 and 500 mA/cm2 of 9.0 V in de-
vice A and B, respectively. The luminance of one device is
similar to that of the other, but device B was brighter in
terms of luminance at a given current density than was
device A.
Except a deposited layer of Alq3, several parameters
of the deposited layers, including deposition rate, substrate
temperature, and thickness were all the same between de-
vices A and B. As shown in Fig. 4(c), for device A, the CIE
EXPERIMENTAL
In this study, a vertical quartz-glass tube was used
with a thermal evaporator system to increase the efficiency
292
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Fast Thermal Evaporation in Purification
Scheme I
ronic ester yielded the target compound 1,4-di(pyrene-1-
yl)benzene (DPB) and the by-product 1-phenylpyrene
(1PP). The yield efficiencies of the two compounds were
affected by the catalytic diversity. Table 1 presents the rela-
tionship between the different catalysts and the yields. It
shows that the use of co-catalyst (PdCl2(PPh3)2
/
PdCl2(CH3CN)2) can attain to more possession with the
main products. Both pyrene derivatives can be purified by
thermal evaporization using a vertical quartz-glass tube.
The structures of these compounds were elucidated by 1H
NMR, mass spectrometry and elemental analysis.
Synthesis process of 1,4-di(pyrene-1-yl)benzene, including (a)
bromination, (b) pyrene boronic ester and (c) suzuki coupling re-
action. a The yield is shown on Table 1. aAbbreviations: NBS =
n-bromo succinimide, DMF = dimethylformamide, THF =
tetrahydrofuran, and n-BuLi = n-butyllithium.
Figure 1(a) shows the setup of the thermal evaporator
purification system with a vertical quartz-glass tube. The
overall apparatus includes vacuum, cooling, thermal evap-
orator and detector systems, the control parameters were
tuned by vacuum value, cooling and heating tube tempera-
ture of material sector. The vacuum system contains a ro-
tary pump and a diffusion pump, when the vacuum value
less than 5 ´ 10-2 torr was achieved by the rotary pump and
the diffusion pump reached warming up to 100 oC the sys-
tem keeps vacuuming until less than 1 ´ 10-3 torr. The evap-
orating only proceeds at this stage. The cooling water starts
circulating to keep thermostated at 24 °C when the diffu-
sion pump went into working. The control temperature of
thermal evaporator system, as shown in Figure 1(b) pres-
ents the use of temperature gradient and vacuum evapora-
tion to separate impurities from pyrene derivatives. After
the synthesis process, the residue reactant and impurities
of purification of pyrene derivatives. Scheme I represents a
protocol for synthesizing pyrene derivates by the bromina-
tion of pyrene, which was the main reactant in the forma-
tion of N-bromosuccinimide (NBS) in N,N-dimethylform-
amide (DMF) solvent; the corresponding pyrene boronic
acid was formed by the re-crystallization of 1-bromopyr-
ene to substitute a halogen-lithium salt, which can react
with n-BuLi at -78 oC in anhydrous tetrahydrefuran (THF).
Following the reaction, B[(CH3)2CHO]3 was esterified
with pinacol, yielding the boronic ester after purification
by acid pickling (~75% yield). Finally, the Suzuki coupling
reaction between the 1,4-diiodobenzene and pyrene bo-
Table 1. The yield of synthesized pyrene derivatives from various catalysta
PdCl2(PPh3)2 /
PdCl2(CH3CN)2
Pd(PPh3)4
5~10
PdCl2(PPh3)2
3~5
PdCl2(CH3CN)2
3~5
Catalyst /mol % /
Derivatives yield %
1~2
1~2
1PP
DPB
20%
50%
25%
60%
10%
50%
10%
85%
a The yields of derivatives determined with quantity of decomposition temperature (Td) as an
internal standard.
Table 2. Photoluminescence and thermal properties of synthesized pyrene derivatives
Photoluminescence (nm)
Thermal properties (oC)
Evaporation
Temperature (oC)
a
d
e
Tm
wF
lfb
lsc
Td
Tcf
330 oC
350 oC
58.5 0.5 459.3 0.6 450.7 0.6 429.3 0.6 291.8 0.3 166.0 1.0
62.7 0.3 455.7 0.6 453.3 0.6 448.0 1.0 295.3 0.5 180.6 0.6
a wF, full width at half maximum (FWHM); b lf , maximum of emitted wavelength in the deposited
film; c ls, maximum of emitted wavelength in the solvent of CHCl3; d Td, decomposition temperature;
e Tm, melting temperature; f Tc, crystallization temperature.
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which has low-decomposition points were sublimed when
temperature (Tc) and, melting temperature (Tm) were deter-
mined with a differential scanning calorimeter (DSC,
PerkinElmer DSC-7) at a heating rate of 5 °C/min. Decom-
position temperature (Td) was obtained from TGA mea-
surements using a PYRIS Diamond TG/DTA-10 with a
heating rate of 20 °C/min. Highest occupied molecular or-
bital (HOMO) levels of the new compound were measured
directly by using ultraviolet photoelectron spectroscopy
(UPS, Riken Keiki AC-2), while the lowest unoccupied
molecular orbital (LUMO) values were determined from
the HOMO and the lowest energy absorption edge of the
UV absorption spectra. Absorption and fluorescence spec-
tra were recorded using a Hitachi-U3010 UV–Visible
spectrophotometer and a Hitachi-F4500 Luminescence
spectrophotometer, respectively.
o
heating up to 200 C from room temperature. When the
vacuum value was reduced obviously the temperature main-
tained constant until the vacuum value was reduced further
for a period of time. Then the separation of compounds
which has lower sublimation points was accomplished
through sublimation when heating up to 300 oC. Therefore,
by manipulating the vacuum value parameter through ris-
ing and maintaining temperature the following heating
stages up to 300 and 350 oC can be completed. Impurities
are usually separated effectively from solid crude if their
vaporization pressures differ sufficiently. The pyrene de-
rivatives were placed in a steel boat (sample container) un-
der a vertical quartz tube, which was thoroughly cleaned
with acetone, and then heated in steps in a dynamic vac-
uum, which was produced by a diffusion pump (ANELVA
Model-300), in a vacuum chamber, to temperatures of 200,
300, 330 and 350 oC. Three heating coils around the quartz
tube and under the crucible provided the temperature gradi-
ent. Impurities first sublimed on top of the substrate panel
when it was heated to 300 oC, and then the 1PP (by-prod-
An X-ray powder diffraction (XRD, Shimadzu XRD-
700) spectrum of the deposited film on the Corning glass-
substrate was obtained at room temperature with a 2q range
from 5 to 50 with Cu Ka radiation with a wavelength of
1.5418 Å. Each diffraction peak in the spectrum from 5o to
50o corresponds to two pyrene derivates. X-ray diffraction
was used to identify the crystal lattice of the organic optical
material.
o
uct) was evaporated at 330 C. After the fore-mentioned
impurities and by-products had been removed, the system
was cooled to room temperature. Four heaters (three lo-
cated in the quartz tube, one located in the crucible) were
attached to the side of the quartz column and their tempera-
tures were set to 350, 250, 350, and 25 oC, respectively. The
DPB (main product) was introduced to the middle level of
the quartz tube from the crucible at an evaporation temper-
ature of 350 oC. The sample was re-crystallized on the sur-
face of the quartz column by maintaining the temperatures
of the second and third heater for two hours. The separated
impurities, 1PP and purified DPB were collected either by
rotating the Corning glass substrate on the top of the quartz
column or on the inner surface of the quartz column when
the sample was in contact with a colder surface.
The fluorescence lifetime investigation can be ap-
plied to characterize a pure material from its spectral time
profile on the solution and the solid film.29 According to the
spontaneous emission transition probability formula (1)
Ni (t) = Ni0 exp(-Ait),
(1)
where the Ni0 is photon counting of fluorescence at t = 0,
Ni(t) is photon counting of fluorescence at t = t and Ai is the
Einstein coefficient. Because the population is propor-
tional to the fluorescence intensity, formula (1) could be
changed to Ii(t) = Ii0 exp(-t/t), where Ii0 is the fluorescence
intensity at t = 0, Ii(t) is the fluorescence intensity at t = t
and t = 1/Ai defined as lifetime is the time which the popu-
lation Ni decays to 1/e of the original value at t = 0.30 In Fig.
3(a) a pulse excitation source, which is the third harmonic
oscillation from an Nd-YAG laser with a wavelength of 355
nm, was used to excite the samples and to obtain the life-
time information.
Thermo-gravimetric analysis (TGA, Perkin-Elmer
Pyris 1) and differential scanning calorimetry (DSC,
Perkin-Elmer Pyris Diamond) were employed to evaluate
the thermal properties of materials. According to experi-
ence value and approximate calculation, 80~100 oC below
the decomposition temperature for the material is the maxi-
mum reference point for gradient temperature, and thereby
characterize the product of the reaction and the compounds
that were separated each other by temperature gradient
vacuum evaporation.
The lifetime of the wavelength that was emitted by
the pyrene derivatives was measured and electrical charac-
terization was performed to ensure optical performance.
Materials of optoelectronic device were thermally de-
posited in a thermal evaporator (ULVAC, model TU02-
Glass transition temperatures (Tg), crystallization
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2. Naito, M.; Ishimaru, M.; Hirotsu, Y.; Valdez, J. A.; Sickafus,
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dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP), and
lithium fluoride (LiF). They played the roles as holes trans-
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brightness–voltage).
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ACKNOWLEDGEMENTS
The first author was grateful to Prof. Franklin Chau-
Nan Hong that leading Nanodevices and Nanotechnology
Lab, Department of Chemical Engineering, National
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