Luminescence of fluorenes 2,7-conjugatively extended with pyrenylvinylene and pyrenylvinylene-phenylenevinylene

Article abstract of DOI:10.1039/b703180g

2,7-Bis(1′-pyrenylvinylene)-9,9-diethylfluorene (1) and 2,7-bis(1′-pyrenylvinylene-4″-phenylenevinylene)-9, 9-diethylfluorene (2) were synthesized and their static luminescence behavior assessed. They show solution photoluminescence (PL) maxima in chloroform at 475 nm and 467 nm, with quantum efficiencies of 54% and 52%, respectively. Double-layer LED devices with configuration ITO/PEDOT-PSS/(1 or 2)/Ca-Al emitted blue-green light with turn-on voltages of 2.5 V and emission maxima at 500 nm (2.48 eV); their luminance efficiencies were 0.36 and 0.30 cd A^-1, respectively. Blending of 1 at 20% (w/w) in PVK improved the luminance efficiency to 1.81 cd A^-1 for the same device configuration, with only a small increase in turn-on voltage to 3 V; the emission maximum was 497 nm (blue-green emission), the maximum luminance 7600 cd m^-2 with CIE color coefficients of (0.12, 0.45). For a 10% (w/w) blend of 2 in PVK using the same device configuration, the luminance efficiency was 1.47 cd A^-1, turn-on voltage 3 V, maximum luminance 2600 cd m^-2 with CIE coefficients of (0.13, 0.45). Simple π-MO calculations show that structural extension of the nominal conjugation length in 2 does not significantly decrease the effective band gap relative to 1, consistent with the observed lack of red shift in 2. The Royal Society of Chemistry.

Full text of DOI:10.1039/b703180g

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www.rsc.org/materials | Journal of Materials Chemistry
Luminescence of fluorenes 2,7-conjugatively extended with pyrenylvinylene
and pyrenylvinylene-phenylenevinylene
Ali Cirpan,a Hemali P. Rathnayake,b Paul M. Lahti*b and Frank E. Karasz*a
Received 6th March 2007, Accepted 26th April 2007
First published as an Advance Article on the web 18th May 2007
DOI: 10.1039/b703180g
2,7-Bis(19-pyrenylvinylene)-9,9-diethylfluorene (1) and 2,7-bis(19-pyrenylvinylene-40-
phenylenevinylene)-9,9-diethylfluorene (2) were synthesized and their static luminescence
behavior assessed. They show solution photoluminescence (PL) maxima in chloroform at 475 nm
and 467 nm, with quantum efficiencies of 54% and 52%, respectively. Double-layer LED devices
with configuration ITO/PEDOT-PSS/(1 or 2)/Ca–Al emitted blue-green light with turn-on
voltages of 2.5 V and emission maxima at 500 nm (2.48 eV); their luminance efficiencies were 0.36
and 0.30 cd A21, respectively. Blending of 1 at 20% (w/w) in PVK improved the luminance
efficiency to 1.81 cd A21 for the same device configuration, with only a small increase in turn-on
voltage to 3 V; the emission maximum was 497 nm (blue-green emission), the maximum
luminance 7600 cd m22 with CIE color coefficients of (0.12, 0.45). For a 10% (w/w) blend of 2 in
PVK using the same device configuration, the luminance efficiency was 1.47 cd A21, turn-on
voltage 3 V, maximum luminance 2600 cd m22 with CIE coefficients of (0.13, 0.45). Simple p-MO
calculations show that structural extension of the nominal conjugation length in 2 does not
significantly decrease the effective band gap relative to 1, consistent with the observed lack of
red shift in 2.
extension of the OFPV chromophore by attachment of
1. Introduction
pyrenylvinylene and pyrenylvinylene-phenylenevinylene to
Fluorene-based polymers and copolymers have been exten-
make 2,7-bis(19-pyrenylvinylene)-9,9-diethylfluorene and 2,7-
bis(19-pyrenylvinylene-40-phenylenevinylene)-9,9-diethylfluor-
ene, 1 and 2 respectively. We aimed to see whether conjugative
sively tested as prospective emitting layers for polymer light
emitting diodes (PLEDs).1 Some have high photoluminescence
(PL) efficiencies both in solution and in solid film, with emis-
extension of the OFPV unit would improve or degrade its
sion wavelengths tunable over much of the visible spectrum.
OLED stability and color purity by comparison to the blue to
However fluorene-incorporating LEDs frequently have
unwanted longer wavelength green-emitting electrolumines-
cent (EL) bands (g-bands) variously attributed to excimers
derived from chromophoric p-stacking during device fabrica-
tion,2 and/or from adventitious oxidation.3 The variability of
color purity and reproducibility in such systems can depend
quite strongly on the nature and rate of energy transfer
between different exciton sites in a light emitting material. The
use of pyrene-containing units in various conjugated or
polychromophoric systems4 has been of particular interest to
us.5 For example, multifunctional EL materials incorporating
pyrene plus triarylamines or carbazoles pared by various
groups6 can show good thermal stability, high brightness and
high luminance efficiencies.
blue-green emission of OFPV itself, especially in view of
possible excimer formation in the solid state between pyrene
units. In addition, we wished to investigate the effect on the
emissive band gap of OFPV of these conjugation extensions.
The static solution phase and solid film photoluminescence
behaviors of the compounds are compared, as well as
characteristics of organic light emitting diode (OLED) test
devices made with both neat and PVK-blended 1 and 2 as
emissive layers.
2. Results and discussion
Synthesis and characterization of 1 and 2
Scheme 1 summarizes the syntheses of 1 and 2. 2,7-Dibromo-
9,9-diethylfluorene (3)7,8 was subjected to Heck coupling with
1-vinylpyrene 4, which itself was made by Wittig vinylation of
pyrene-1-carboxaldehyde 5. Product 1 was obtained in high
yield and purity having essentially all (E,E)-geometry, with no
visible (Z)-stilbene type olefinic protons in the d 6–7 range of
the proton NMR spectrum, and the presence of well-resolved
trans-ethenyl LC–H doublets at d 7.13–7.17 having J = 16 Hz.
Compound 4 was conjugation-extended by Heck coupling with
4-bromobenzaldehyde to make 6, vinylated to intermediate 7,
and coupled to core precursor 3 to give product 2. The
1H-NMR spectrum of 2 resembles that of 1 except for the
Recently we showed that small molecule phenylenevinylene-
fluorene-phenylenevinylene (OFPV) molecular chromophores
give good blue to blue-green PL and EL color purity and
OLED characteristics.7 This article describes conjugative
aDepartment of Polymer Science and Engineering, University of
Massachusetts, Amherst, Massachusetts 01003, USA.
E-mail: fekarasz@polysci.umass.edu; Fax: +1-413-253-5295;
Tel: +1-413-545-4783
bDepartment of Chemistry, University of Massachusetts, Amherst,
Massachusetts 01003, USA. E-mail: lahti@chem.umass.edu;
Fax: +1-413-253-5295; Tel: +1-413-545-4783
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Scheme 1 Syntheses of 1 and 2.
presence of para-phenylenevinylene resonances in the aromatic
region. As with 1, the 1H-NMR spectrum of 2 shows no
higher field (Z)-stilbenoid LCH resonances, so (E,E)-olefin
formation exclusively predominates, or nearly so. The
compounds are also resistant to thermal decomposition.
Compound 1 shows virtually no mass loss by thermogravi-
metric analysis at temperatures up to 400 uC; it loses y55% of
mass over 400–500 uC.
Multiple attempts to obtain diffraction quality single
crystals of 1,2 were unsuccessful, However, the compounds
are reasonably soluble in organic solvents, and form films on
glass that are quite adequate for use in fabricating test OLEDs.
poorly resolved pyrene absorption. Based on the spectral
onsets, the optical band gaps for 1 and 2 are nearly identical at
2.47–2.48 eV. The solid film absorption maxima and spectral
shapes for 1,2 are quite similar to the solution spectra,
indicating no major aggregation effects in the solid state.
The solution excitation spectra of 1 and 2 monitored at
525 nm essentially overlap their respective absorption spectra,
indicating that the absorbing chromophores are the only
significant emitters. Both compounds show very similar blue-
green solution photoluminescence (PL) bands in the 470–
520 nm region (Fig. 1), with no localized pyrene emission
peaks in the expected region of 360–425 nm. The fluorescence
quantum yields in chloroform at room temperature relative to
9,10-diphenylanthracence9 were 0.54 and 0.52, respectively.
The solid film PL spectra showed significant red shifts of
about 0.15 and 0.22 eV, respectively, by comparison to the
corresponding solution spectra (Table 1, Fig. 2). The shift of
the solid compared to the solution PL spectrum is presumably
due to different dielectric environment for emitting molecules
in the neat solid by comparison to solution, and/or p-cloud
interaction effects between proximal molecules in the solid
state sample.
Absorption and photoluminescence properties
The static photophysical behavior of 1,2 in dilute chloroform
solution and in spin-cast thin films is summarized in Table 1.
Absorption spectra in dilute chloroform (Fig. 1) and in the
solid state (Fig. 2) are very similar. Compound 1 shows main
absorption at 411 nm, with a weak set of absorptions that
include vibronic fine structure in the 270–350 nm region. The
latter region appears to be due to localized pyrene absorptions.
Compound 2 has its main absorption at 411 nm with a small
shoulder around 350 nm; the latter, again, appears to be a
Pyrene derivatives can form excimers in solution.10 The
excimer appears as a longer wavelength, featureless PL band at
Table 1 Optical properties of 1 and 2
Sample
l
max(abs)a/nm
l
max(abs)b/nm
Solutionc WPL
l
max(PL)a/nm
l
max(PL)b/nm
1
2
a
411
411
427
414
0.54
0.52
b
475 (503)
467 (495)
c
504
508
Chloroform solution. PL spectra obtained with 390 nm excitation wavelength. Neat film on quartz. Relative quantum yield compared to
9,10-diphenylanthracene standard (see ref. 9).
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Fig. 1 Solution UV-vis (a) and PL (b) spectra for 1 and 2 in chloroform at room temperature. PL spectra at 1 millimolar concentrations with
390 nm excitation.
Fig. 2 Solid film absorption, PL and EL spectra for 1 and 2. PL spectra at 390 nm excitation.
longer wavelengths than the monomer emission at shorter
wavelength; the monomer is seen readily in solution at lower
concentrations, and the emission becomes weaker relative to
the monomer emission at higher concentrations. For example,
some PPV derivatives with pyrene segments incorporated
into their main chains exhibit characteristic pyrene excimer
emission at 510–530 nm.4c However neither 1 nor 2 show
The OLEDs emit blue-green light, with EL spectra that are
virtually the same for both compounds. Both EL spectra show
poorly resolved vibronic structure, while the corresponding
solid film PL spectra are narrower and lack resolved fine
structure. The different lineshapes may be due to the different
exciton generation processes in PL and EL, and/or local
thermochromic effects by comparison to room temperature PL
spectra, which could occur because these simple OLEDs do
not have heat sinks.11 Table 2 summarizes OLED perfor-
mances using neat 1,2: compound 1 gave the best luminance
significant solution PL spectral shape changes over
a
1–1000 mM concentration range, so these appear to form no
significant concentrations of excimers.
efficiency of 0.36 cd A21 at a current density of 80 mA cm22
with a maximum brightness of 2600 cd m22 at a current
density of 740 mA cm22
,
Electroluminescent devices
.
Double-layer OLEDs with the configuration ITO/PEDOT-
PSS/(1 or 2)/Ca–Al were fabricated to investigate the
electroluminescence spectra of 1,2 (Fig. 2), as well as their
current–voltage and luminance–voltage characteristics (Fig. 3).
The addition of PVK to the emissive layer to aid hole
injection improves OLED performance significantly compared
to neat 1 or 2. The PVK-diluted PL and EL spectra are quite
similar as shown in Fig. 4, whereas the neat spectra show
Fig. 3 Current–voltage–luminance plots for ITO/PEDOT-PSS/(1 or 2)/Ca–Al LEDs.
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Table 2 EL characteristics of OLEDs made with neat 1 and 2 and with (1 or 2) : PVK blends
Composition (% w/w)
lmax(EL)/nm
Turn-on voltage/V
Maximum luminance/cd m22
Maximum luminance efficiency/cd A21
100% 1
100% 2
20% 1
10% 1
10% 2
5% 1
500
500
500
497
497
491
488
2.5
2.5
3
3
3
2600
2000
7600
4800
2600
1200
1300
0.36
0.30
1.81
2.10
1.47
0.60
0.48
4
5
1% 1
significantly narrower PL spectra with less fine structure than
the corresponding EL spectra. The OLED performance results
for the blend-based devices are shown in Fig. 5. The best
luminance efficiency of 2.1 cd A21 at 6 V was attained using a
10% (w/w) blend of 1 in PVK. The highest luminance of
7600 cd m22 was obtained using 20% (w/w) of 1 in PVK; this
OLED also has a relatively low 2.5 V turn-on voltage. There
was no noticeable difference in OLED performance stability
between those using neat 1 or 2 and those using the
PVK blends, over the timeframe of measurements made to
characterize the devices.
with 1, the CIE12 color coordinates are (0.12, 0.45); for the
10% blend with 2, they are (0.13, 0.45). The OLEDs with neat
1 and 2 have CIE coefficients of (0.23, 0.42) and (0.23, 0.41),
respectively. All these OLEDs emit light that is teal-colored,
blue-green to the eye.
Some recent work offers comparisons to other small
molecule systems incorporating conjugation between pyrene
and fluorene. Recently Zhao et al. described13 the synthesis
and photoluminescent properties of 8, which is similar to 1
save for having alkynyl instead of olefinic links between the
fluorene and pyrene units. The solution absorption spectral
maxima for 1 and 8 are nearly identical at 410–411 nm, but the
solution PL spectrum for 8 was strongly blue-shifted relative to
1, 431/457 nm versus 475/503 nm in solution (a difference of
0.27 eV). Diluted solid film PL spectra show a similar spectral
trend, with the PL maximum of 8 in PMMA at 460 nm
compared to 488 nm for 1 in PVK. The blue shift in the
emission spectra of 8 relative to that of 1 is consistent with a
The increase in turn-on voltages for the OLEDs made with
more dilute blends reflects the greater difficulty of hole/
electron transport across greater distances between emitter
sites. A small blue shift of 12 nm (60 meV) in the EL emission
spectral maxima as the fluorophore concentration decreases to
¡10% (w/w) concentration is presumably due to decreasing
aggregation of emitter sites. For the 10% (w/w) blend OLEDs
Fig. 4 PL of 10% blends of 1 or 2 with PVK, EL spectra for ITO/PEDOT-PSS/(10% 1 or 2 : PVK)/Ca–Al LEDs. PL spectra use 390 nm
excitation.
Fig. 5 Current–voltage and luminance–voltage plots for ITO/PEDOT-PSS/1 : PVK/Ca–Al LEDs.
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typically smaller conjugation linkage effect for alkynes by
comparison to alkenes. No EL experiments using 8 were
reported. Tao et al.14 described EL studies of pyrene-fluorene
systems 9–11 with shorter nominal conjugation lengths than
those in 1,2 and 8. Tang et al.15 described EL studies of similar
species 12,13. OLEDs made with these systems gave blue
emission with good intensities in the 450–470 nm range. Tang’s
systems showed impressively strong blue emission in some
multilayer OLEDs; these workers suggested that the non-
planarity of 9–11 contributes to their lack of longer wavelength
emission bands. However, the present systems 1,2 are much
more easily planarized than 9–11, and 1,2 also show no long
wavelength shoulders or excimer-like bands.
OLEDs with PEDOT-PSS hole-injection layer and 1 or 2 as
emitter layer give teal blue-green emission. OLEDs using
simple PVK blends with 1 and 2 show significantly higher
luminance than with neat 1 or 2, even for low weight
percentages of emitter, with only modest increases in LED
turn-on voltage and a small emission blue shift. Undesirable
excimer or impurity emitter bands are not observed under any
solution or solid state conditions used. The effective conjuga-
tion length for these systems is maximized in 1—an increase in
nominal conjugation length by insertion of a phenylenevinyl-
ene unit in 2 does not decrease the band gap or emission
energy. The simple fabrication methodology, high temperature
stability, and good color purity for OLEDs made from 1 make
it a good candidate for solid state luminescence applications.
4. Experimental
General
All commercially available materials were used as received
unless noted otherwise. Poly(3,4-ethylenedioxythiophene)/
poly(styrene sulfonate) (PEDOT-PSS) was obtained from
Bayer Corporation. Tetrahydrofuran (THF) was distilled first
from calcium hydride and then sodium/benzophenone under
argon. Spectroscopic grade solvents (Aldrich) were used as
received without further purification. Reported melting points
are uncorrected.
Emission and excitation spectra were obtained using a
Perkin-Elmer LS 50B spectrometer with a xenon lamp light
source. Emission quantum yields in spectrograde chloroform
were determined at an excitation wavelength of 380 nm using
external standard 9,10-diphenylanthracene (0.1 mmol L21 in
ethanol, WPL = 0.81) by a literature9 procedure. The maximum
absorbance of sample solution was less than 0.1 in order to
minimize errors due to internal filter effects. Solvent refractive
index and instrumental spectral response corrections were
made for quantum yield determination. The reported quantum
yields are averages of three independent measurements.
Structural elongation of the p-connectivity beyond that
of 1 does not extend the effective spectral conjugation length.
Torsional deconjugation of the pyrene units is likely in 9–13,
but seems less likely in 1 and 2, especially in solution. A
strongly twisted geometry for 1 or 2 should yield absorption
spectra that more resemble a sum of pyrene plus fluorene
components, with emission spectra resembling emission from
fluorene, assuming energy transfer from twisted pyrene
units to a nearly isolated, nonconjugated central fluorene.
Small amounts of twisted conformations in 1 and 2 may be
responsible for the small pyrene-like components in these
absorption spectra, and for their lower solution fluorescence
quantum yields (y50%) by comparison to those of 8 and 9–13
(68–78%).13–15 However, the luminescence of 1,2 seems
inconsistent with a deplanarized geometry.
2,5-Dibromo-9,9-diethylfluorene (3)
This compound was synthesized following previously pub-
lished7,8 procedures.
1-Pyrenecarboxaldehyde (4)
To a suspension of 1-pyrenylmethanol (1.0 g, 4.30 mmol) in
30 mL of dichloromethane, powdered manganese dioxide
(0.56 g, 6.45 mmol) was added and the mixture stirred at room
temperature overnight. The mixture was filtered, then evapo-
rated to give a yellow solid (0.85 g, 85%) that was used without
further purification. Mp 120–123 uC (lit.16 mp 125–127 uC);
1H-NMR (CDCl3): d 8.03 (s, 3 H), 8.11 (m, 1 H), 8.20 (d, 1 H,
J = 6 Hz), 8.31–8.28 (m, 2 H, J = 16 Hz), 9.37 (d, 2 H, J =
9 Hz), 10.73 (s, 1 H).
Rather, the similarities of PL and EL wavelengths for 1 and
2 appear to be due to their inherent effective conjugation
lengths. Simple Hu¨ckel p-MO computations that include all
p-C centers give a HOMO–LUMO gap for 1 of 0.575 b, while
that for 2 is 0.554 b. This small difference is consistent with the
similarities in their absorption spectra. Addition of the extra
phenylenevinylene units into 2 thus lengthens the structural
conjugation relative to 1, but does not significantly affect the
electronic conjugation.
1-Vinylpyrene (5)
3. Conclusions
To a suspension of triphenylphosphonium bromide (1.97 g,
5.53 mmol) in 25 mL of dry THF at 0 uC under argon
was added dropwise 2.21 mL (5.53 mmol) of n-butyllithium
Chromophores 1 and 2 exhibit solution phase bluish photo-
luminescence with moderate quantum yields. Double-layer
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1
solution (2.5 M in hexanes). The resulting orange solution was
allowed to warm to room temperature and stirred for an
additional 10 min. Next, 4 (850 mg, 3.69 mmol) in 10 mL of
THF was added to the reaction mixture dropwise over 30 min.
The resulting yellow suspension was stirred at room tempera-
ture overnight. The reaction mixture was then filtered, and the
filtrate was poured into 30 mL of water. The aqueous layer
was back-extracted with 2 6 15 ml of diethyl ether. The
combined organic layers were dried over anhydrous magne-
sium sulfate, filtered, and concentrated under vacuum. The
crude product was purified by column chromatography on
silica using diethyl ether as the eluent to yield 530 mg (62%) of
5 as a yellow solid. For multiple determinations with samples
obtained in this manner. Mp 120–123 uC (lit.17 mp 82–84 uC,
lit.18 mp 87–89 uC); 1H-NMR (CDCl3) d 5.64 (d, 1 H, J =
11 Hz), 6.03 (d, 1 H, J = 17 Hz), 7.83 (dd, 1 H, J = 11,17 Hz),
8.03 (t, 1 H, J = 8 Hz), 8.09 (s, 2 H), 8.2 (m, 4 H), 8.35 (d, 1 H,
J = 8 Hz), 8.52 (d, 1 H, J = 8 Hz).
96–99 uC; H-NMR (CDCl3) d 7.41 (d, 1 H, J = 16 Hz), 7.85,
7.95 (AA9BB9 quartet, 4 H, J = 7 Hz), 8.05 (t, 1 H, J = 7 Hz),
8.10 (s, 2 H), 8.2 (m, 4 H), 8.36 (s, 1 H), 8.38 (d, 1 H, J =
16 Hz), 8.52 (d, 1 H, J = 8 Hz), 10.06 (s, 1 H); MS(EI) calc. for
C25H16O m/z = 332.1, found 332.1.
1-Vinyl-4-(1-pyrenylvinylene)benzene (7)
This compound was synthesized by following the same
procedure used for 5. Mp 136–137 uC; 1H-NMR (CDCl3) d
5.31 (d, 1 H, J = 8 Hz), 5.82 (d, 1 H, J = 18 Hz), 6.97 (dd, 1 H,
J = 8,18 Hz), 7.37 (d, 1 H, J = 16 Hz), 7.52, 7.67 (AA9BB9
quartet, 4 H, J = 8 Hz), 8.03 (t, 1 H, J = 7 Hz), 8.08 (s, 2 H),
8.2 (m, 5 H), 8.34 (d, 1 H, J = 8 Hz), 8.52 (d, 1 H, J = 8 Hz);
MS(EI) calc. for C26H18 m/z = 330.1, found 330.1.
2,7-Bis(19-pyrenylvinylene-40-phenylenevinylene)-9,9-
diethylfluorene (2)
To a three-necked round bottom flask were added 7 (258 mg,
780 mmol), 3 (148 mg, 0.390 mmol), tri-o-tolylphosphine
(23 mg, 0.075 mmol) and a catalytic amount of palladium
acetate (2.0 mg, 0.008 mmol). The flask was flushed with
argon, 20 mL of dry DMF was added, the solution was heated
to 90 uC and stirred for 30 min. Then triethylamine (2.05 g,
1.8 mL, 20.27 mmol) was added and heating continued at 90 uC
for two days. The reaction was then cooled and poured into
30 mL of water, the mixture chilled with an ice bath, and 5 mL
of 10% aq. HCl added dropwise. The resultant yellow solid
was vacuum-filtered, dissolved in chloroform, and filtered
through Celite. The filtrate was concentrated in vacuum and
purified by column chromatography on silica using hexane and
chloroform (2 : 5) as eluent. The solid product was collected to
yield 225 mg (65%) of 2 as a yellow powder. Mp 275–277 uC;
1H-NMR (CDCl3): d 0.39 (broadened mult., 6 H, J = 7 Hz),
2.21 (broadened mult., 4 H), 7.41 (d, 2 H, J = 16 Hz), 7.57 (s,
4 H), 7.5–7.8 (overlapping m, 12 H), 8.04 (t, 2 H, J = 7 Hz),
8.11 (s, 4 H), 8.2–8.3 (overlapping m, 12 H), 8.42 (d, 2 H, J =
8 Hz), 8.65 (d, 2 H, J = 8 Hz); HR-MS(FAB) calc. for C69H50
m/z = 878.3913, found 878.3972.
2,7-Bis(19-pyrenylvinylene)-9,9-diethylfluorene (1)
To a three-necked round bottom flask were added 5 (280 mg,
1.22 mmol), 3 (236 mg, 0.613 mmol), tri-o-tolylphosphine
(60 mg, 0.197 mmol) and a catalytic amount of palladium
acetate (4.5 mg, 0.002 mmol). The flask was flushed with
argon, 20 mL of DMF was added, and solution was heated to
90 uC and stirred for 30 min. Then triethylamine (1.14 g,
1.0 mL, 11.26 mmol) was added and heating continued at 90 uC
for two days. The reaction was cooled and poured into 30 mL
of water, the mixture chilled with an ice bath, and 5 mL of 10%
aq. HCl added dropwise. The resultant yellow solid was
vacuum-filtered, dissolved in chloroform, and filtered through
Celite. The filtrate was concentrated in vacuo and purified by
column chromatography on silica using hexane and chloro-
form (1 : 3) as eluent. The solid product was collected to yield
230 mg (55%) of 1 as a yellow powder. Mp 278–280 (decomp.)
1
uC; H-NMR (CDCl3) d 0.52 (t, 6 H, J = 7 Hz), 2.25 (q, 4 H,
J = 7 Hz), 7.51 (d, 2 H, J = 16 Hz), 7.71 (s, 2 H), 7.76, 7.82
(AA9BB9 quartet, 4 H, J = 8 Hz), 8.05 (t, 2 H, J = 8 Hz), 8.11
(s, 4 H), 8.2 (m, 8 H), 8.31 (d, 2 H, J = 16 Hz), 8.40 (d, 2 H, J =
8 Hz), 8.61 (d, 2 H, J = 8 Hz); HR-MS(FAB) calc. for C53H38
m/z = 674.2974, found 674.3013.
EL device fabrication
Double-layer light-emitting diode test devices (LEDs) were
fabricated on indium/tin oxide (ITO) coated glass slides (OFC
Corporation, 20 ohm sq21) using the configuration ITO/
PEDOT-PSS/EM/Ca-Al. EM was the emissive material: 1 or 2
or blends of 1 with PVK. A hole injection layer of PEDOT-
PSS was first spin-coated on top of the ITO, and then dried at
100 uC for 1 h under vacuum. Chloroform solutions of 1 or 2
or % (w/w) blends of them with PVK were then spin-coated
onto the PEDOT-PSS layer under a nitrogen atmosphere. A
Ca cathode about 400 nm thick was vapor-deposited, followed
by a protective layer of aluminium. Typical device areas were
6 mm2. The devices were characterized using methods and
instrumentation that have been previously described.19
4-(19-Pyrenylvinylene)benzaldehye (6)
To a three-necked round bottom flask were added 4-bromo-
benzaldehyde (740 mg, 3.99 mmol), 1-vinylpyrene, 5 (820 mg,
3.59 mmol), tri-o-tolylphosphine (244 mg, 0.80 mmol) and a
catalytic amount of palladium acetate (60 mg, 0.13 mmol). The
flask was flushed with argon, 30 mL of dry DMF was added,
the solution was heated to 85 uC and stirred for 30 min. Then
triethylamine (0.7 ml, 7.99 mmol) was added and heating
continued at 85 uC for two days. The reaction was then cooled
and poured into 50 mL of water, the mixture chilled with an
ice bath, and 15 mL of 10% aq. HCl added dropwise. The
resultant yellow solid was vacuum-filtered, dissolved in
chloroform, and filtered through Celite. The filtrate was
concentrated in vacuo and purified by column chromatography
on silica using diethyl ether as eluent. The solid product was
collected to yield 800 mg (50%) of 6 as a yellow powder. Mp
Acknowledgements
AC and FEK acknowledge support from the U.S. Air Force
Office of Scientific Research. HR and PML acknowledge
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Chem. B, 2004, 108, 8689; (k) K. Becker, J. M. Lupton,
support from U.S. Department of Energy grant DE-FG02-
05ER15695. Support from the U.S. National Science
Foundation for the University of Massachusetts Amherst
Mass Spectrometry Facility is acknowledged.
J. Feldmann, B. S. Nehls, F. Galbrecht, D. Gao and U. Scherf,
Adv. Funct. Mater., 2006, 16, 364; (l) X.-H. Zhou, Y. Zhang,
Y.-Q. Xie, Y. Cao and J. Pei, Macromolecules, 2006, 39, 3830.
4 (a) U. Oertel, D. Appelhans, P. Friedel, D. Jehnichen, H. Komber,
B. Pilch, B. Hanel and B. Voit, Langmuir, 2002, 18, 105; (b)
J. A. Mikroyannidis, Synth. Met., 2005, 155, 125; (c) J. A.
Mikroyannidis, P. G. Persephonis and V. G. Giannetas, Synth.
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3036 | J. Mater. Chem., 2007, 17, 3030–3036
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