Synthesis and fluorescence characterization of MEHPPV oligomers

Article abstract of DOI:10.1021/jo200336m

Trimer, tetramer, and pentamer oligomers based on the polymer backbone structure of poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene] (MEHPPV) have been synthesized by Horner-Wadsworth-Emmons reactions. The fluorescence spectra, emission quantum

Full text of DOI:10.1021/jo200336m

ARTICLE
pubs.acs.org/joc
Synthesis and Fluorescence Characterization of MEHPPV Oligomers
Andrew J. Tilley, Stephen M. Danczak, Christine Browne, Timothy Young, Tina Tan, Kenneth P. Ghiggino,*
Trevor A. Smith, and Jonathan White*
School of Chemistry and Bio 21 Institute, University of Melbourne, Victoria, Australia 3010
S Supporting Information
b
ABSTRACT: Trimer, tetramer, and pentamer oligomers based on the
polymer backbone structure of poly[2-methoxy-5-(20-ethylhexyloxy)-1,4-
phenylenevinylene] (MEHPPV) have been synthesized by Hor-
nerꢀWadsworthꢀEmmons reactions. The fluorescence spectra, emission
quantum yields, and lifetimes of the oligomers have been characterized in
dilute chloroform solutions. The oligomers exhibit a sequential increase in
absorption and emission wavelength maxima and a decrease in fluorescence
lifetime as the π conjugation length is increased. The shortening in excited
state lifetime is shown to be due to an increase in the rates of both radiative
and nonradiative processes. The absence of a mirror-image relationship for the absorption and fluorescence spectra of the
oligomers is attributed to the photoexcitation of a range of torsional configurations followed by relaxation to a more planar
arrangement that then emits.
’ INTRODUCTION
Conjugated polymers based on poly(phenylenevinylene)
(PPV) have been extensively studied as the key components in
a range of photoactive and electroactive materials.1ꢀ5 The
interest in these materials arises from their luminescent and
semiconducting properties that have seen them used in organic
light emitting diodes and in photovoltaic devices.6,7 PPV deriva-
tives that are substituted with methoxy and 2-ethylhexyloxy
substituents on the phenyl rings (e.g., poly[2-methoxy-5-
(20-ethylhexyloxy)-1,4-phenylenevinylene], MEHPPV) have
found particular application since they are more soluble and
more readily fabricated into useful materials than unsubstituted
derivatives.8,9 It has been proposed that in MEHPPV conforma-
tional defects along the polymer backbone break the extended π
conjugation, leading to light absorption by shorter conjugated
sequences with a distribution of lengths that constitute the
polymer chromophores. Following photoexcitation, energy
transfer among the chromophores that make up the chain
ultimately leads to the population of the lowest energy chromo-
phores made up of longer conjugated sequences, and it is these
that are thought responsible for the observed polymer
fluorescence.10 More recent studies have shown that this picture
is too simplistic and that the excited states of conjugated
polymers evolve over a broad range of time scales from femto-
seconds onward and involve exciton relaxation, localization, and
energy transfer processes that are influenced by dynamic polymer
chain conformations.11 In addition there is evidence quantum
coherence can contribute to energy transfer dynamics in con-
jugated polymers such as MEHPPV at room temperature.11,12
Rather than extended main chain conjugated polymers, we are
interested in the properties of polymers that contain shorter
chains of oligo-MEHPPV (from 3 to 5 units) as pendant
Figure 1. MEHPPV oligomers studied in this work.
chromophores on polymer chains, and how these chromophores
interact with each other, and with energy and electron acceptor
chromophores that may also be included. To understand the
photophysical properties of these polymers, however, we first
needed to prepare model MEHPPV oligomers that closely
resemble the chromophores present on the polymer chain so
that the photophysics of the individual chromophores are well
characterized. To this end we report here the preparation and full
characterization of the MEHPPV oligomers 1ꢀ3 (Figure 1) and
describe their fluorescence and other photophysical properties.
’ RESULTS AND DISCUSSION
Synthesis of Oligomers. The oligomers 1ꢀ3 were prepared
by sequential HornerꢀWadsworthꢀEmmons reactions accord-
ing to Scheme 1. This sequence began with the substituted
aldehyde 6 and the phosphonate 5, both of which were obtained
in a few steps from 4-methoxyphenol. Coupling of 5 and 6 was
followed by lithiation and formylation producing the aldehyde 8,
Received: February 15, 2011
Published: March 31, 2011
r
2011 American Chemical Society
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Scheme 1. Synthesis of Ethylhexyloligomers 1ꢀ3a
a Reagents and conditions: (a) (iPrO)3P; (b) KOBut, THF; (c) BuLi, THF, Me2NCHO.
which was either coupled with the phosphonate 13 to give the
trimer 1 or alternatively coupled with phosphonate 5 to give the
trimer 9. After lithiation and formylation of 9 the resulting
aldehyde 10 was coupled with either the phosphonate 13 to give
the tetramer 2 or alternatively with phosphonate 5 to give the
tetramer 11, which ultimately gave the pentamer 3 following a
similar sequence of reactions.
the tetramer of 431 and 493 nm in the same solvent. The
maximum molar absorption coefficients (ε), fluorescence life-
times (τf), and fluorescence quantum yields (φf) in chloroform
are provided in Table 1. The radiative (kr) and nonradiative (knr)
rate constants can be calculated from the quantum yield and
lifetime data by using eqs 1 and 2 and are also provided in
Table 1.
Photophysical Characterization. The absorption and fluor-
escence spectra of compounds 1ꢀ3 in chloroform are shown in
Figures 2 and 3. The absorption and emission spectra show a
sequential red-shift with increasing conjugation length. The
pentamer exhibits a broad absorption with maximum at
451 nm and a structured fluorescence with peak maximum at
518 nm. These may be compared to the corresponding absorp-
tion and emission maxima for the trimer of 397 and 452 nm, and
kr ¼ φf =τf
ð1Þ
ð2Þ
knr ¼ ð1 ꢀ φf Þ=τf
The observation of structured emission spectra compared to a
structureless broad absorption band has been noted previously
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Table 1. Selected Photophysical Data for the Oligomers in
Chloroform at 298 Ka
trimer 1
tetramer 2
pentamer 3
Φf
0.36
1.5
0.34
1.3
0.32
0.8b
3.6
τf (ns)
kr (108 sꢀ1
)
2.5
2.6
knr (108 sꢀ1
εmax (dm3 molꢀ1 cmꢀ1
)
4.4
5.1
8.7
)
39000
59000
87000
a Fluorescence lifetimes (τf) measured at 450 nm for 1 and 500 nm for 2
and 3. b Note: The fluorescence decay of the pentamer contained a
minor (10%) component with a lifetime of 1.2 ns (see text).
Figure 2. Room temperature absorption spectra of the oligomers in
chloroform.
Figure 4. Conformations of the trimers 14 and 15.
exists as a family of eight so-called “twistomers” where the four
dihedral angles θ1ꢀθ4 deviate from 0° by angles varying from
10° to 15°. These twistomers have similar energies and lie within
0.2 kcal/mol of one another, and therefore are all likely to be
populated at room temperature.
The qualitative predictions from molecular mechanics are
borne out in the crystal structure of the trimer derivative 15
(synthesized according to Scheme 2, with hexyloxy side chains
instead of ethylhexyloxy groups to remove stereoisomer hetero-
geneity). Thus trimer 15 adopts a conformation analogous to
that shown in Figure 4, and also shows a slight twist of the
aromatic rings with dihedral angles θ1ꢀθ4 all deviating from
planarity by ca. 10ꢀ15° (Figure 5).
Figure 3. Fluorescence spectra of the oligomers in chloroform with
excitation at the corresponding absorption maxima.
for MEHPPV polymers.13 The broad absorption has been
attributed to an inhomogeneous superposition of absorption
spectra arising from a distribution of chain segments with
different conjugation lengths, while the emission has been
thought to occur from low-energy conjugated sequences popu-
lated by energy transfer.10 However, the non-“mirror-image”
relationship between absorption and emission spectra observed
for dilute solutions of the oligomers of well-defined conjugation
length studied in this work suggests, instead, that this is an
inherent property of these molecules. Previous theoretical and
experimental studies of related phenylene vinylene polymers and
oligomers have suggested that the broad absorption spectra can
be attributed to the presence of a range of ground state torsional
configurations.14,15
To investigate this possibility analysis of the possible con-
formations of the simple model trimer 14 was carried out and
reveals that the molecule can plausibly exist as a mixture of six
different rotamers which differ by ca. 180° rotations about the
single bonds which separate the five π-systems (denoted as
θ1ꢀθ3 in Figure 4). Of these possible rotamers the structure
shown in Figure 4 is the lowest energy, with the next lowest being
ca. 0.88 kcal/mol higher in energy. Structure 14 is not planar but
The range of rotamers and torsional configurations can be
expected to have slightly different electronic arrangements and
transition energies that can lead to the spectral broadening
observed in the solution absorption spectra. Further evidence
is found by recording the absorption spectra of the representative
tetramer 2 as a function of temperature (see Figure 6). In this
case 2-methyltetrahydrofuran was used as the solvent to provide
an optically clear matrix as the solution was cooled. As the
temperature is lowered there is a marked red-shift and progres-
sive development of structure in the spectra consistent with
absorption by a restricted set of configurations.
Our interpretations are consistent with previous theoretical
studies of other phenylene vinylene oligomers that concluded the
asymmetry of absorption and fluorescence spectra at room
temperature can be associated with larger torsional flexibility in
the ground state compared to the excited state.14,15 The emission
arises from a restricted subset of low torsional angle configura-
tions leading to the structured emission observed. A previous
ultrafast spectroscopy study of related PPV trimers detected a
picosecond time-scale process (<40 ps) following excitation that
was also attributed by the authors to a rapid conformational
relaxation to more planar configurations.16
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Scheme 2. Synthesis of Hexyloxy Trimer 15a
a Reagents and conditions: (a) KOBut, THF; (b) BuLi, THF, Me2NCHO.
emitting rotamer configuration in this compound. Within the
time resolution of our time-correlated photon counting instru-
mentation we were unable to resolve the ultrafast component
(<40 ps) in the fluorescence decay profiles that has been reported
previously for related PPV trimers and assigned to excited state
torsional relaxation processes.16
In conclusion, MEHPPV type oligomers 1ꢀ3 have been
successfully synthesized by HornerꢀWadsworthꢀEmmons re-
actions. Their electronic absorption and fluorescence spectra can
be explained by the photoexcitation of a range of torsional
conformations followed by emission from more planar arrange-
ments. The incorporation of these chromophores as pendant
groups in polymers and the photochemistry of these materials
will be reported in a future communication.
’ EXPERIMENTAL SECTION
General Methods. All reactions were performed in oven-dried
glassware. Starting materials were used without further purification,
except for DMF, which was purified by stirring with CaSO4 for 24 h
followed by vacuum distillation over 4 Å molecular sieves. THF was
purified by refluxing over sodium and benzophenone until the solution
became dark, followed by distillation. Acetone was purified by distilla-
tion, followed by storage over 4 Å molecular sieves. CH2Cl2 was dried
with use of a solvent purification apparatus as described by Pangborn
et al.18 Thin layer chromatography was performed on aluminum sheets
precoated with silica gel, using mixtures of EtOAc/n-hexane, Et2O/
n-hexane, and CH2Cl2/n-hexane. Detection was achieved via irradiation
by UV light. Flash chromatography was performed by using the method
of Still et al., using silica gel grade 230ꢀ400 mesh.19 Automated column
chromatography was performed with a flash purification system. NMR
data was recorded on 400 and 500 MHz instruments. Chemical shifts are
expressed in parts per million (δ), using residual solvent (1H NMR δ
7.26 ppm for CDCl3; 13C NMR δ 77.16 ppm for CDCl3). Melting
points were obtained by using an automated melting point apparatus and
are uncorrected. Fourier transform infrared spectra and high-resolution
electrospray ionization mass spectra were recorded at The University of
Melbourne.
Figure 5. X-ray structure of the trimer 15 containing hexyloxy side
chains.
Extending the conjugation length of the oligomers leads to the
expected red-shift in absorption and emission spectra and an
increase in the absorption coefficient. There is a decrease in
fluorescence lifetime in order from trimer > tetramer > pentamer.
This trend is shown to arise from an increase in both the radiative
and nonradiative rate constants for the oligomers. It can be noted
from Table 1 that the relatively larger increase in nonradiative
rate compared to the radiative rate leads to the observed decrease
in fluorescence quantum yield with increasing conjugation
length. The results can be compared to published data on the
conjugated polymer MEHPPV where a fluorescence quantum
yield and lifetime in chloroform of 0.35 and 330 ps respectively
have been reported.17 While the fluorescence decay profiles for
the trimer and tetramer can be fitted adequately by single decay
components in each case, for the pentamer an additional minor
contribution (10% at 510 nm) of a component with a longer
lifetime of 1.2 ns was required. While the origin of this compo-
nent remains uncertain it may arise from a contribution by an
Photophysics. UVꢀvis absorption spectra were recorded on a
UVꢀvisꢀNIR spectrophotometer. All solution absorption spectra were
recorded against solvent blanks in matched 1.0 cm path length quartz
cells. Fluorescence spectra were recorded on a spectrofluorometer. The
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Figure 6. Absorption spectra of the tetramer 2 in 2-methyltetrahydrofuran as a function of temperature.
optical densities of the solutions were kept below 0.20 at the excitation
wavelength to minimize reabsorption effects. Fluorescence quantum
yield measurements were carried out by using the comparative method
against a known fluorescence standard (coumarin 343 in ethanol, φf =
0.63).20 The uncertainty in fluorescence quantum yield determinations
is estimated at (5%. Fluorescence decay profiles were recorded by the
time-correlated single photon counting technique, using the frequency
doubled (390 nm) output of a mode-locked and cavity-dumped Ti:
sapphire laser as the excitation source. Fluorescence lifetimes were
determined by analysis of the fluorescence decay profiles by iterative
reconvolution procedures. The uncertainty in fluorescence lifetimes
is (0.1 ns. Full details of the instrumentation can be found elsewhere.21
Low-temperature studies were carried out in a liquid nitrogen cryostat
fitted with a temperature controller.
residue (0.6 mbar, 150 °C) gave 2-bromo-1-(2-ethylhexyloxy)-4-meth-
1
oxybenzene as a pale yellow oil (18.87 g, 94%). H NMR (400 MHz,
CDCl3) δ 0.89ꢀ0.96 (6H, m), 1.30ꢀ1.35 (4H, m), 1.40ꢀ1.61 (4H, m),
1.70ꢀ1.79 (1H, m), 3.76 (3H, s), 3.84 (2H, d, J = 5.6 Hz), 6.79 (1H, dd,
J = 2.8, 9.0 Hz), 6.83 (1H, d, J = 8.9 Hz), 7.11 (1H, d, J = 2.8 Hz). 13C
NMR (500 MHz, CDCl3) δ 11.3, 14.2, 23.2, 24.0, 29.2, 30.6, 39.6, 56.0,
72.5, 112.9, 113.8, 114.4, 119.0, 150.2, 154.0. FT-IR (neat, cmꢀ1) 2928,
1492, 1462, 1439, 1380, 1270, 1210, 1181, 1040. HRMS (ESI)þ m/z
315.0954 (C15H24BrO2 [M þ H]þ requires 315.0960).
(iii) n-BuLi (1.6 M, 31 mL, 50 mmol) was added dropwise to a stirred
solution of 2-bromo-1-(2-ethylhexyloxy)-4-methoxybenzene (10.5 g,
9.38 mmol) in THF (200 mL) at ꢀ78 °C, and the resulting solution
was stirred at ꢀ78 °C for 10 min. DMF (4.6 mL, 60 mmol) was then
added dropwise and the resulting mixture was stirred at ꢀ78 °C for 45
min, then room temperature for 15 min. The reaction was then
quenched with sat. aq NaHCO3 (50 mL) and the THF removed under
reduced pressure. The residue was taken up in ether and washed with sat.
aq NaCl (3 ꢁ 50 mL) and H2O (3 ꢁ 50 mL), dried (MgSO4), filtered,
and concentrated under reduced pressure to give the aldehyde 6 as a
yellow oil (8.724 g, 100%). 1H NMR (CDCl3, 500 MHz) δ 0.88ꢀ0.96
(6H, m), 1.25ꢀ1.36 (4H, m), 1.38ꢀ1.59 (4H, m), 1.72ꢀ1.78 (1H, m),
3.80 (3H, s), 3.93 (2H, dd), 6.94 (1H, d, J = 9.1 Hz), 7.12 (1H, dd, J =
9.0, 3.3 Hz), 7.33 (1H, d, J = 3.3 Hz), 10.48 (1H, s). 13C NMR (CDCl3,
400 MHz) δ 11.05, 13.94, 22.92, 23.90, 29.01, 30.53, 39.45, 55.53, 71.28,
Synthesis
Preparation of 2-(2-ethylhexyloxy)-5-methoxy benzalde-
hyde, 6: (i) Bromine (6.8 mL, 21.1 g, 132 mmol) in CH2Cl2 (10 mL)
was added dropwise to a stirred solution of 4-methoxyphenol (14.92 g,
120 mmol) in CH2Cl2 (150 mL) at 0 °C. The mixture was brought to
room temperature and stirred for 2 h, then washed with sat. aq NaHCO3
(2 ꢁ 50 mL) and water (2 ꢁ 50 mL). The aqueous layers were then re-
extracted with additional CH2Cl2 (50 mL) and the combined organic
layers dried (MgSO4), filtered, and concentrated under reduced pres-
sure to give the product as a dark brown oil. The dark oil was further
purified by KugelꢀRohr distillation (0.6 mbar, 120 °C) to afford
2-bromo-4-methoxyphenol as a clear yellow oil, which solidified upon
cooling (23.56 g, 97%), mp 42ꢀ43 °C (lit.22 mp 43ꢀ44 °C). 1H NMR
(400 MHz, CDCl3) δ 3.75 (3H, s), 5.12 (1H, s), 6.80 (1H, dd, J = 2.9,
8.9 Hz), 6.95 (1H, d, J = 8.9 Hz), 7.01 (1H, d, J = 2.9 Hz). FT-IR
(neat, cmꢀ1) 3404, 2943, 1609, 1584, 1489, 1439, 1417, 1333, 1276,
1256, 1205, 1176, 1029.
(ii) 2-Ethylhexyl bromide (19.0 mL, 20.6 g, 107 mmol) was added to
a stirred solution of 2-bromo-4-methoxyphenol (12.95 g, 64 mmol) and
KOH (7.798 g, 139 mmol) in acetone (80 mL) and the resulting mixture
was stirred at reflux for 47 h. The mixture was then concentrated under
reduced pressure, taken up in ether, washed with H2O (3 ꢁ 80 mL), 10%
KOH (3 ꢁ 50 mL), sat. aq NaHCO3 (2 ꢁ 80 mL), and sat. aq NaCl (3 ꢁ
80 mL), dried (MgSO4), filtered, and concentrated under reduced
pressure to give a dark brown oil. Excess 2-ethylhexyl bromide was
removed by KugelꢀRohr distillation (0.6 mbar, 120 °C) to give a light
brown residue. Subsequent KugelꢀRohr distillation of the light brown
109.92, 114.15, 123.39, 153.36, 156.48, 189.24. FT-IR (neat, cmꢀ1
)
2958, 2928, 2560, 1638, 1613, 1585, 14949, 1463, 1422, 1388, 1276,
1216, 1158, 1040. HRMS (ESI)þ m/z 287.1617 (C16H24NaO3 [M þ
Na]þ requires 287.1618).
Diisopropyl 4-bromo-5-(2-ethylhexyloxy)-2-methoxy-
benzylphosphonate, 5: A solution of 2-bromo-1-(2-ethylhexyloxy)-
4-methoxy benzene (20.27 g, 64.3 mmol), p-formaldehyde (7.723 g,
257.2 mmol), concentrated HCl (36%, 22.1 mL, 257 mmol) and glacial
acetic acid (22.1 mL, 386 mmol) was heated at 80 °C for 24 h. After 24 h
the solution was cooled to room temperature and the mixture taken up
in n-hexane (100 mL). The organic layer was washed with sat. aq.
NaHCO3 (3 ꢁ 80 mL), sat. aq. NaCl (3 ꢁ 80 mL) and the combined
aqueous layers re-extracted with additional n-hexane (1 ꢁ 50 mL). The
organic layers were combined, dried (MgSO4), filtered and concentrated
under reduced pressure to give an inseparable 3:1 mixture of the desired
product 4 and its 6-chloromethyl isomer as a light brown oil (23.70 g,
100%) 1H NMR (signals for 4) (500 MHz, CDCl3) δ 0.87ꢀ0.96 (m, 6H),
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1.31ꢀ1.35 (m, 4H), 1.42ꢀ1.58 (m, 4H), 1.73ꢀ1.78 (m, 1H), 3.83 (s,
3H), 3.86 (d, 2H, J = 2.7 Hz), 4.59 (s, 2H), 7.08 (s, 1H), 7.26 (s, 1H).
13C NMR (CDCl3, 500 MHz) δ 151.4, 149.9, 125.6, 116.4, 115.5,
110.4, 72.4, 56.4, 41.1, 39.5, 30.5, 29.1, 23.9, 23.0, 14.06, 11.2. HRMS
(ESI)þ m/z 385.0541 (C16H24BrClNaO2 [M þ Na]þ requires
385.0546).
with sat. aq NaCl (3 ꢁ 50 mL) and H2O (3 ꢁ 50 mL), dried (MgSO4),
filtered, and concentrated under reduced pressure to give the aldehyde
1
as an orange oil (4.922 g, 100%). H NMR (500 MHz, CDCl3) δ
0.88ꢀ0.94 (12H, m), 1.28ꢀ1.40 (8H, m), 1.42ꢀ1.62 (8H, m),
1.76ꢀ1.83 (2H, m), 3.84 (3H, s), 3.88ꢀ3.93 (2H, m), 3.89 (3H, s),
4.00 (2H, d, J = 5.3 Hz), 6.82 (1H, dd, J = 2.9, 8.9 Hz), 6.86 (1H, d, J =
8.9 Hz), 7.20 (1H, d, J = 2.9 Hz), 7.23 (1H, s), 7.34 (1H, s), 7.49 (1H, d,
J = 16.7 Hz), 7.62 (1H, d, J = 16.7 Hz), 10.47 (1H, s). 13C NMR (CDCl3,
500 MHz) δ 11.3, 11.5, 14.20, 14.22, 23.17, 23.23, 24.2, 24.4, 29.27,
29.32, 30.8, 31.0, 39.8, 39.9, 56.0, 56.2, 71.4, 71.6, 109.0, 110.3, 112.0,
113.6, 114.8, 122.9, 124.1, 127.2, 127.4, 135.1, 151.3, 151.7, 153.8, 156.7,
189.2. FT-IR (neat, cmꢀ1) 1676, 972. HRMS (ESI)þ m/z 547.3393
(C33H48NaO5 [M þ Na]þ requires 547.3394).
The isomeric mixture of 4 in triisopropyl phosphite (27.14 g, 29.9 mL,
130.3 mmol) was then stirred at reflux for 16 h. Removal of the excess
triisopropyl phosphite by KugelꢀRohr distillation gave a mixture of 4-
and 6-diisopropyl phosphonates as a brown oil. The brown oil was
separated by flash chromatography (EtOAc/petroleum spirit as eluent)
to give the desired product 5 as a light brown oil (25.08 g, 78% over two
steps). 1H NMR (500 MHz, CDCl3) δ 0.89ꢀ0.94 (6H, m), 1.20 (6H, d,
J = 6.2 Hz), 1.28 (6H, d, J = 6.2 Hz), 1.30ꢀ1.35 (4H, m), 1.38ꢀ1.58
(4H, m), 1.70ꢀ1.79 (1H, m), 3.14 (2H, d, J = 21.8 Hz), 3.77 (3H, s),
3.85 (2H, d, J = 5.6 Hz), 4.58ꢀ4.68 (2H, m), 6.99 (1H, d, J = 2.7 Hz),
7.03 (1H, d, J = 1.0 Hz). 13C NMR (500 MHz, CDCl3) δ 11.1,
14.0, 23.0, 23.8 (d, J = 5.0 Hz), 23.9, 24.1 (d, J = 3.7 Hz), 27.4 (d, J =
141 Hz), 29.0, 30.5, 39.5, 56.2, 70.5 (d, J= 6.9 Hz), 72.3, 110.4 (d, J=4.5Hz),
115.9, 116.6, 120.7 (d, J = 8.2 Hz), 149.6, 151.5 (d, J = 7.5 Hz). FT-IR
(neat, cmꢀ1) 1211. HRMS (ESI)þ m/z 515.1532 (C22H38BrNaO5P -
[M þ Na]þ requires 515.1538).
(E,E)-1-Bromo-2-(2-ethylhexyloxy)-4-(20-(2-ethylhexyloxy)-
40-(200-(2-ethylhexyloxy)-500-methoxystyryl)-50-methoxystyryl)-
5-methoxybenzene, 9: A solution of aldehyde 8 (0.762 g, 1.45
mmol) and phosphonate 5 (1.073 g, 2.17 mmol) in THF (15 mL) was
added to a stirred solution of potassium tert-butoxide (0.651 g, 5.80
mmol) in THF (15 mL) at 0 °C. The mixture was brought to room
temperature and stirred for 4 h. The reaction was then quenched with
sat. aq NH4Cl (10 mL) and the THF removed under reduced pressure.
Ether was added and the organic phase was washed with sat. aq NH4Cl
(3 ꢁ 50 mL) and sat. aq. NaCl (3 ꢁ 50 mL), dried (MgSO4), filtered,
and concentrated under reduced pressure to give a light brown oil. The
light brown oil was purified by column chromatography (ether/petro-
leum spirit as eluent) to give the product as an orange oil (1.021 g, 84%).
1H NMR (500 MHz, CDCl3) δ 0.88ꢀ1.00 (18H, m), 1.27ꢀ1.42 (12H,
m), 1.44ꢀ1.66 (12H, m), 1.76ꢀ1.82 (3H, m), 3.83 (3H, s), 3.86 (3H, s),
3.87ꢀ3.97 (9H, m), 6.78 (1H, dd, J = 3.0, 8.9 Hz), 6.84 (1H, d, J = 8.9
Hz), 7.09 (1H, s), 7.15 (1H, s), 7.17 (2H, s), 7.22 (1H, d, J = 3.0 Hz),
7.41 (1H, d, J = 16.6 Hz), 7.46ꢀ7.53 (3H, m). 13C NMR (500 MHz,
CDCl3) δ 11.4, 11.5, 14.23, 14.24, 23.22, 23.25, 24.1, 24.4, 29.3, 29.4,
30.7, 30.98, 31.01, 39.8, 39.95, 40.01, 56.0, 56.55, 56.63, 71.4, 71.7, 72.5,
109.4, 110.1, 111.2, 111.5, 111.6, 113.6, 113.9, 116.7, 122.5, 123.5, 123.7,
124.4, 126.8, 127.2, 127.5, 128.1, 150.3, 151.4, 151.45, 151.49, 151.6,
153.9. FT-IR (neat, cmꢀ1) 971. HRMS (ESI)þ m/z 835.4497
(C49H72BrO6 [M þ H]þ requires 835.4512).
Diisopropyl 4-methylbenzylphosphonate, 13: A solution of
p-methylbenzyl bromide (5.061 g, 27.35 mmol) in triisopropyl phos-
phite (14.5 mL, 58.8 mmol) was refluxed for 24 h. The unreacted
triisopropyl phosphite was then removed by KugelꢀRohr distillation
1
to give the product as a clear oil (6.479 g, 89%). H NMR (CDCl3,
500 MHz) δ 1.17 (6H, d, J = 6.2 Hz), 1.27 (6H, d, J = 6.2 Hz), 2.31 (3H,
s), 3.06 (2H, d, J = 21.5 Hz), 4.55ꢀ4.62 (2H, m), 7.09 (2H, d, J = 8.1
Hz), 7.18 (2H, dd, J = 2.4, 8.1 Hz). 13C NMR (500 MHz, CDCl3) δ 20.8,
23.59, 23.63, 23.86, 23.89, 33.6, 34.7, 70.1, 70.2, 128.6, 128.81, 128.83,
129.5, 129.6, 135.9. FT-IR (neat, cmꢀ1) 1236. HRMS (ESI)þ m/z
293.1278 (C14H23NaO3P [M þ Na]þ requires 293.1283).
(E)-1-Bromo-2-(2-ethylhexyloxy)-4-(20-(2-ethylhexyloxy)-
50-methoxystyryl)-5-methoxybenzene, 7: A solution of alde-
hyde 6 (1.593 g, 6.03 mmol) and phosphonate 5 (1.985 g, 4.03 mmol) in
THF (20 mL) was added to a stirred solution of potassium tert-butoxide
(1.844 g, 16.4 mmol) in THF (30 mL) at 0 °C. The mixture was brought
to room temperature and stirred for 2.5 h. The reaction was then
quenched with sat. aq NH4Cl (15 mL) and the THF removed under
reduced pressure. Ether was added and the organic phase was washed
with sat. aq NH4Cl (3 ꢁ 50 mL) and sat. aq NaCl (3 ꢁ 50 mL), dried
(MgSO4), filtered, and concentrated under reduced pressure to give a
light brown oil. The light brown oil was purified by flash chromatogra-
phy (CH2Cl2/petroleum spirit as eluent) to give the product as a lime
(E,E)-2-(2-Ethylhexyloxy)-4-(20-(2-ethylhexyloxy)-40-(200-(2-
ethylhexyloxy)-500-methoxystyryl)-50-methoxystyryl)-5-meth-
oxybenzaldehyde, 10: n-BuLi (1.6 M, 6.2 mL, 9.9 mmol) was added
dropwise to a stirred solution of bromide 9 (5.367 g, 6.42 mmol) in THF
(120 mL) at ꢀ78 °C, and the resulting dark solution was stirred
at ꢀ78 °C for 10 min. DMF (0.9 mL, 11.7 mmol) was then added
dropwise and the resulting mixture was stirred at ꢀ78 °C for 30 min,
then room temperature for 1.5 h. The reaction was then quenched with
sat. aq NaHCO3 (50 mL) and the THF removed under reduced
pressure. The residue was taken up in ether and washed with H2O
(4 ꢁ 100 mL), dried (MgSO4), filtered, and concentrated under reduced
pressure to give the aldehyde as an orange oil (5.040 g, 100%). 1H NMR
(500 MHz, CDCl3) δ 0.83ꢀ1.01 (18H, m), 1.28ꢀ1.39 (12H, m),
1.42ꢀ1.66 (12H, m), 1.75ꢀ1.87 (3H, m), 3.83 (3H, s), 3.85ꢀ4.01
(12H, m), 6.78 (1H, dd, J = 3.0, 8.9 Hz), 6.84 (1H, d, J = 8.9 Hz), 7.16
(1H, s), 7.17 (1H, s), 7.21 (1H, d, J = 3.0 Hz), 7.24 (1H, s), 7.34 (1H, s),
7.46ꢀ7.54 (3H, m), 7.65 (1H, d, J = 16.6 Hz), 10.46 (1H, s). 13C NMR
(500 MHz, CDCl3) δ 11.4, 11.5, 14.21, 14.22, 14.24, 23.2, 23.3, 24.2, 24.4,
24.5, 29.29, 29.34, 30.9, 30.98, 31.02, 39.8, 39.9, 40.0, 56.0, 56.2, 56.6, 71.4,
71.7, 109.0, 109.6, 110.0, 110.1, 111.7, 113.6, 114.0, 122.2, 123.3, 124.1,
124.2, 126.2, 127.4, 128.0, 128.4, 135.3, 151.2, 151.4, 151.5, 151.8, 153.8,
156.8, 189.1. FT-IR (neat, cmꢀ1) 1675, 971. HRMS (ESI)þ m/z 785.5353
(C50H73O7 [M þ H]þ requires 785.5356).
1
green oil (2.065 g, 90%). H NMR (500 MHz, CDCl3) δ 0.81ꢀ0.97
(12H, m), 1.27ꢀ1.40 (8H, m), 1.41ꢀ1.62 (8H, m), 1.74ꢀ1.81 (2H, m),
3.82 (3H, s), 3.83 (3H, s), 3.91 (4H, m), 6.78 (1H, dd, J = 2.9, 8.9 Hz),
6.83 (1H, d, J = 8.9 Hz), 7.08 (1H, s), 7.15 (1H, s), 7.18 (1H, d, J = 2.9
Hz), 7.38 (1H, d, J = 16.6 Hz), 7.46 (1H, d, J = 16.7 Hz). 13C NMR (500
MHz, CDCl3) δ 11.3, 11.5, 14.2, 23.20, 23.22, 24.1, 24.4, 29.2, 29.3, 30.7,
31.0, 39.8, 39.9, 56.0, 56.5, 71.6, 72.5, 111.2, 111.6, 111.7, 113.6, 114.0,
116.7, 123.1, 124.3, 127.1, 127.8, 150.2, 151.4, 151.5, 153.8. FT-IR
(neat, cmꢀ1) 971. HRMS (ESI)þ m/z 385.0541 (C32H47BrNaO4 [M þ
Na]þ requires 385.0540).
(E)-2-(2-Ethylhexyloxy)-4-(20-(2-ethylhexyloxy)-50-meth-
oxystyryl)-5-methoxybenzaldehyde, 8: n-BuLi (1.6 M, 8.80 mL,
14.1 mmol) was added dropwise to a stirred solution of bromide 7
(5.399 g, 9.38 mmol) in THF (130 mL) at ꢀ78 °C, and the resulting
dark solution was stirred at ꢀ78 °C for 10 min. DMF (1.35 mL, 17.5
mmol) was then added dropwise and the resulting solution was stirred
at ꢀ78 °C for 45 min, then room temperature for 15 min. The reaction
was quenched with sat. aq NaHCO3 (50 mL) and the THF removed
under reduced pressure. The residue was taken up in ether and washed
(E,E,E)-1-Bromo-2-(2-ethylhexyloxy)-4-(20-(2-ethylhexyloxy)-
40-(200-(2-ethylhexyloxy)-400-(2000-(2-ethylhexyloxy)-5000-meth-
oxystyryl)-500-methoxystyryl)-50-methoxystyryl)-5-meth-
oxybenzene, 11: A solution of aldehyde 10 (0.402 g, 0.512 mmol)
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and phosphonate 5 (0.382 g, 0.774 mmol) in THF (10 mL) was added
to a stirred solution of potassium tert-butoxide (0.256 g, 2.28 mmol) in
THF (10 mL) at 0 °C. The mixture was brought to room temperature
and stirred for 3 h. The reaction was then quenched with sat. aq NH4Cl
(5 mL) and the THF removed under reduced pressure. Ether was added
and the organic phase was washed with sat. aq NH4Cl (2 ꢁ 50 mL) and
sat. aq NaCl (2 ꢁ 50 mL), dried (MgSO4), filtered, and concentrated
under reduced pressure to give an orange solid. The orange solid was
purified by passing it through a plug of silica (CH2Cl2 as eluent) to give
the product as a bright orange solid (0.494 g, 88%), mp 97ꢀ98 °C. 1H
NMR (500 MHz, CDCl3) δ 0.84ꢀ1.01 (24H, m), 1.29ꢀ1.42 (16H, m),
1.43ꢀ1.67 (16H, m), 1.76ꢀ1.86 (4H, m), 3.83 (3H, s), 3.86 (3H, s),
3.89ꢀ3.99 (14H, m), 6.77 (1H, dd, J = 3.0, 8.9 Hz), 6.84 (1H, d, J = 8.9
Hz), 7.08 (1H, s), 7.16ꢀ7.18 (5H, m), 7.22 (1H, d, J = 3.0 Hz), 7.41
(1H, d, J = 16.6 Hz), 7.45ꢀ7.56 (5H, m). 13C NMR (500 MHz, CDCl3)
δ 11.4, 11.5, 14.3, 23.2, 23.3, 24.1, 24.4, 24.5, 29.3, 29.4, 30.7, 31.0, 31.0,
39.8, 39.95, 40.03, 40.04, 56.0, 56.55, 56.62, 56.64, 71.4, 71.5, 71.7, 72.5,
109.3, 109.4, 110.0, 110.1, 111.1, 111.5, 111.6, 113.7, 113.9, 116.7, 122.5,
122.9, 123.5, 123.6, 123.8, 124.4, 126.8, 127.2, 127.25, 127.34, 127.6,
128.2, 150.3, 151.4, 151.45, 151.48, 151.5, 151.6, 153.9. FT-IR
(neat, cmꢀ1) 968. HRMS (ESI)þ m/z 1094.6206 (C66H95BrO8 [M]þ
requires 1094.6210).
3.91 (3H, s), 3.94 (2H, d, J = 5.6 Hz), 6.77 (1H, dd, J = 3.0, 8.9 Hz), 6.83
(1H, d, J = 8.9 Hz), 7.11ꢀ7.18 (5H, m), 7.21 (1H, d, J = 3.0 Hz),
7.39ꢀ7.52 (5H, m). 13C NMR (500 MHz, CDCl3) δ 11.4, 11.5, 14.3,
21.4, 23.25, 23.26, 24.39, 24.42, 29.35, 29.40, 31.0, 31.1, 39.9, 40.0, 56.0,
56.5, 71.7, 71.8, 109.3, 110.3, 111.6, 113.6, 113.9, 122.7, 123.5, 123.6,
126.5, 126.9, 127.2, 128.1, 128.7, 129.2, 129 0.5, 129.7, 135.4, 137.4,
151.38, 151.40, 151.6, 153.8. FT-IR (neat, cmꢀ1) 966. HRMS (ESI)þ
m/z 612.4173 (C41H56O4 [M]þ requires 612.4179).
(E,E,E)-200-(2-Ethylhexyloxy)-100-(20-(2-ethylhexyloxy)-50-
methoxy-10-(1-methylstyryl)styryl)-400-(2000-(2-ethylhexyloxy)-
5000-methoxystyryl)-500-methoxybenzene, 2: A solution of alde-
hyde 10 (0.228 g, 0.290 mmol) and phosphonate 13 (0.169 g, 0.625
mmol) in THF (5 mL) was added to a stirred solution of potassium tert-
butoxide (0.130 g, 1.16 mmol) in THF (5 mL) at 0 °C. The mixture was
brought to room temperature and stirred for 3 h. The reaction was then
quenched with sat. aq NH4Cl (5 mL) and the THF removed under
reduced pressure. Ether was added and the organic phase was washed
with sat. aq NH4Cl (2 ꢁ 30 mL) and sat. aq NaCl (2 ꢁ 30 mL), dried
(MgSO4), filtered, and concentrated under reduced pressure to give a
light brown solid. The light brown solid was purified by flash chroma-
tography (ether/n-pentane as eluent) to give the product as a bright
1
yellow oil (0.126 g, 50%), mp 101ꢀ103 °C. H NMR (500 MHz,
(E,E,E)-2-(2-Ethylhexyloxy)-4-(20-(2-ethylhexyloxy)-40-(200-(2-
ethylhexyloxy)-400-(2000-(2-ethylhexyloxy)-5000-methoxystyryl)-
500-methoxystyryl)-50-methoxystyryl)-5-methoxybenzalde-
hyde, 12: n-BuLi (1.6 M, 4.7 mL, 7.5 mmol) was added dropwise to a
stirred solution of bromide 11 (4.626 g, 4.22 mmol) in THF (75 mL)
at ꢀ78 °C, and the resulting dark solution was stirred at ꢀ78 °C for
10 min. DMF (0.7 mL, 9.1 mmol) was then added dropwise and the
resulting mixture was stirred at ꢀ78 °C for 30 min, then room
temperature for 1.5 h. The reaction was then quenched with sat. aq
NaHCO3 (50 mL) and the THF removed under reduced pressure. The
residue was taken up in ether and washed with H2O (3 ꢁ 80 mL), dried
(MgSO4), filtered, and concentrated under reduced pressure to give the
CDCl3) δ 0.88ꢀ1.01 (18H, m), 1.28ꢀ1.42 (12H, m), 1.43ꢀ1.68 (12H,
m), 1.75ꢀ1.88 (3H, m), 2.37 (3H, s), 3.83 (3H, s), 3.85ꢀ3.99 (12H, m),
6.77 (1H, dd, J = 3.0, 8.9 Hz), 6.84 (1H, d, J = 8.9 Hz), 7.13 (1H, m),
7.15ꢀ7.18 (6H, m), 7.22 (1H, d, J = 3.0 Hz), 7.42ꢀ7.53 (6H, m), 7.54
(1H, d, J = 16.6 Hz). 13C NMR (500 MHz, CDCl3) δ 11.45, 11.53, 14.3,
21.4, 23.25, 23.26, 24.40, 24.42, 24.5, 29.36, 29.42, 30.98, 31.02, 31.1,
39.96, 40.01, 40.1, 56.0, 56.5, 56.6, 71.5, 71.7, 71.8, 109.2, 109.3, 110.1,
110.2, 111.6, 113.7, 113.9, 122.7, 122.9, 123.53, 123.56, 123.7, 126.5,
126.9, 127.2, 127.28, 127.31, 128.2, 128.7, 129.5, 135.4, 137.4, 151.39,
151.44, 151.47, 151.52, 151.6, 153.9. FT-IR (neat, cmꢀ1) 969. HRMS
(ESI)þ m/z 872.5949 (C58H80O6 [M]þ requires 872.5955).
(E,E,E,E)-200-(2-Ethylhexyloxy)-100-(20-(2-ethylhexyloxy)-50-
methoxy-10-(1-methylstyryl)styryl)-400-(2000-(2-ethylhexyloxy)-
4000-(20000-(2-ethylhexyloxy)-50000-methoxystyryl)-5000-meth-
oxystyryl)-500-methoxybenzene, 3: A solution of aldehyde 12
(0.423 g, 0.405 mmol) and phosphonate 13 (0.168 g, 0.622 mmol) in
THF (15 mL) was added to a stirred solution of potassium tert-butoxide
(0.097 g, 0.864 mmol) in THF (15 mL) at 0 °C. The mixture was
brought to room temperature and stirred for 19 h. The reaction was then
quenched with sat. aq NH4Cl (10 mL) and the THF removed under
reduced pressure. Ether was added and the organic phase was washed
with H2O (3 ꢁ 50 mL), dried (MgSO4), filtered, and concentrated
under reduced pressure to give an orange solid. The orange solid was
purified by flash chromatography (ether/n-hexane as eluent) to give the
product as an orange solid (0.418 g, 91%), mp 149ꢀ150 °C. 1H NMR
(500 MHz, CDCl3) δ 0.88ꢀ1.02 (24H, m), 1.29ꢀ1.43 (16H, m),
1.44ꢀ1.70 (16H, m), 1.75ꢀ1.86 (4H, m), 2.37 (3H, s), 3.83 (3H, s),
3.85ꢀ4.02 (17H, m), 6.77 (1H, dd, J = 3.0, 8.9 Hz), 6.84 (1H, d, J = 8.9
Hz), 7.13 (1H, m), 7.16ꢀ7.19 (7H, m), 7.22 (1H, d, J = 3.0 Hz),
7.42ꢀ7.46 (3H, m), 7.48ꢀ7.56 (7H, m). 13C NMR (500 MHz, CDCl3)
δ 11.4, 11.5, 14.2, 21.4, 23.3, 24.4, 24.5, 29.34, 29.36, 29.40, 29.41, 30.97,
31.02, 31.11, 39.94, 40.0, 40.05, 56.0, 56.5, 56.6, 71.4, 71.5, 71.7, 71.8,
109.19, 109.23, 110.0, 110.1, 110.2, 111.5, 113.6, 113.8, 122.7, 122.8,
122.9, 123.50, 123.54, 123.60, 123.63, 126.5, 126.9, 127.2, 127.26,
127.29, 127.4, 128.2, 128.7, 129.5, 135.4, 137.4, 151.37, 151.43,
1
aldehyde as an orange solid (4.371 g, 99%), mp 91ꢀ93 °C. H NMR
(400 MHz, CDCl3) δ 0.82ꢀ1.02 (24H, m), 1.28ꢀ1.42 (16H, m),
1.43ꢀ1.68 (16H, m), 1.74ꢀ1.86 (4H, m), 3.83 (3H, s), 3.86ꢀ4.02
(17H, m), 6.77 (1H, dd, J = 3.0, 8.9 Hz), 6.84 (1H, d, J = 8.9 Hz),
7.17ꢀ7.19 (4H, m), 7.22 (1H, d, J = 3.0 Hz), 7.24 (1H, s), 7.35 (1H, s),
7.46ꢀ7.53 (4H, m), 7.57 (1H, d, J = 16.4 Hz), 7.66 (1H, d, J = 16.5 Hz),
10.47 (1H, s). 13C NMR (500 MHz, CDCl3) δ 11.4, 11.5, 14.2, 23.2,
23.3, 24.2, 24.4, 24.5, 29.3, 29.4, 30.8, 30.97, 31.02, 39.8, 39.9, 40.0, 56.0,
56.2, 56.6, 71.35, 71.43, 71.7, 109.0, 109.3, 109.5, 109.9, 110.1, 111.5,
111.6, 112.2, 112.5, 113.6, 113.9, 114.6, 122.1, 122.7, 122.9, 123.2, 123.4,
123.5, 123.6, 123.7, 124.0, 124.18, 124.23, 126.1, 127.0, 127.17, 127.23,
127.3, 127.4, 127.5, 128.0, 128.1, 128.2, 128.5, 135.3, 151.2, 151.4,
151.46, 151.50, 151.6, 151.8, 153.8, 156.8, 189.1. FT-IR (neat, cmꢀ1
)
1676, 967. HRMS (ESI)þ m/z 1044.7041 (C67H96O9 [M]þ requires
1044.7054).
(E,E)-10-(2-Ethylhexyloxy)-50-(200-(2-ethylhexyloxy)-500-meth-
oxystyryl)-40-methoxy-20-(4-methylstyryl)benzene, 1: A solu-
tion of aldehyde 8 (0.286 g, 0.545 mmol) and phosphonate 13 (0.273 g,
1.311 mmol) in THF (7 mL) was added to a stirred solution of
potassium tert-butoxide (0.288 g, 2.54 mmol) in THF (8 mL) at 0 °C.
The mixture was brought to room temperature and stirred for 24 h. The
reaction was then quenched with sat. aq NH4Cl (5 mL) and the THF
was removed under reduced pressure. Ether was added and the organic
phase was washed with sat. aq NH4Cl (2 ꢁ 50 mL) and sat. aq NaCl
(2 ꢁ 50 mL), dried (MgSO4), filtered, and concentrated under reduced
pressure to give a yellow oil. The yellow oil was purified by flash
chromatography (CH2Cl2/n-pentane as eluent) to give the product as a
bright yellow oil (0.255 g, 76%). 1H NMR (500 MHz, CDCl3) δ
0.83ꢀ1.00 (12H, m), 1.26ꢀ1.42 (8H, m), 1.43ꢀ1.65 (8H, m),
1.75ꢀ1.84 (2H, m), 2.37 (1H, s), 3.83 (3H, s), 3.84ꢀ3.90 (2H, m),
151.46, 151.49, 151.51, 151.56, 151.60, 153.8. FT-IR (neat, cmꢀ1
)
968. HRMS (ESI)þ m/z 1132.7729 (C75H104O8 [M]þ requires
1132.7731).
Synthesis of n-Hexyl Derivatives
2-Bromo-1-hexyloxy-4-methoxybenzene, 16: KOH (14.34 g,
255.6 mmol) was added to a stirred solution of 2-bromo-4-methoxy-
phenol (26.02 g, 128 mmol) and 1-bromohexane (27.0 mL, 31.7 g,
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ARTICLE
192 mmol) in acetone (125 mL) at room temperature. The reaction
mixture was then stirred at reflux for 70 h. After 70 h, the acetone was
removed under reduced pressure and the dark residue was taken up in
ether. The organic layer was washed with H2O (1 ꢁ 80 mL), 10%
KOH (2 ꢁ 80 mL), and sat. aq NaHCO3 (2 ꢁ 80 mL), dried
(MgSO4), filtered, and concentrated under reduced pressure to give
a dark brown oil. Excess 1-bromohexane was removed by KugelꢀRohr
distillation (0.6 mbar, 155 °C) to give a light brown residue. Subsequent
KugelꢀRohr distillation of the light brown residue (0.6 mbar, 190 °C)
gave the product as a pale yellow oil (34.831 g, 95%). 1H NMR (500 MHz,
CDCl3) δ 0.89ꢀ0.93 (3H, m), 1.32ꢀ1.38 (4H, m), 1.46ꢀ1.52 (2H, m),
1.77ꢀ1.83 (2H, m), 3.76 (3H, s), 3.96 (2H, t, J = 6.5 Hz), 6.79 (1H, dd, J =
2.9, 8.9 Hz), 6.84 (1H, d, J = 9.0 Hz), 7.11 (1H, d, J = 2.9 Hz). 13C NMR
(500 MHz, CDCl3) δ 14.2, 22.7, 25.8, 29.4, 31.7, 56.0, 70.4, 113.0, 113.9,
114.9, 118.9, 150.1, 154.2. HRMS (ESI)þ m/z 392.9613 (C13H19AgBrO2
[M þ Ag]þ requires 392.9619).
(d, J = 4.9 Hz), 120.8 (d, J = 9.1 Hz), 149.4 (d, J = 3.4 Hz), 151.7 (d, J =
7.5 Hz). FT-IR (neat, cmꢀ1) 1211. HRMS (ESI)þ m/z 487.1219
(C20H34BrNaO5P [M þ Na]þ requires 487.1225).
(E)-1-Bromo-2-hexyloxy-4-(20-hexyloxy-50-methoxystyryl)-
5-methoxybenzene, 19: A solution of aldehyde 17 (1.199 g, 5.07
mmol) and phosphonate 18 (3.554 g, 7.64 mmol) in THF (15 mL) was
added to a stirred solution of potassium tert-butoxide (2.275 g, 20.27
mmol) in THF (10 mL) at 0 °C. The mixture was brought to room
temperature and stirred for 3 h. The reaction was then quenched with
sat. aq NH4Cl (10 mL) and the THF removed under reduced pressure.
Ether was added and the organic phase was washed with H2O (3 ꢁ
50 mL) and sat. aq NH4Cl (1 ꢁ 50 mL), dried (MgSO4), filtered, and
concentrated under reduced pressure to give a yellow solid. The yellow
solid was purified by automated column chromatography (SNAP 50G
cartridge, ether/petroleum spirit as eluent) to give the product as a
yellow solid (2.507 g, 95%), mp 53ꢀ55 °C. 1H NMR (500 MHz,
CDCl3) δ 0.88ꢀ0.93 (6H, m), 1.30ꢀ1.41 (8H, m), 1.49ꢀ1.56 (4H, m),
1.79ꢀ1.86 (4H, m), 3.82 (3H, s), 3.83 (3H, s), 3.97 (2H, t, J = 6.4 Hz),
4.03 (2H, t, J = 6.5 Hz), 6.77 (1H, dd, J = 3.0, 8.9 Hz), 6.83 (1H, d, J = 8.9
Hz), 7.07 (1H, s), 7.16 (2H, m), 7.38 (1H, d, J = 16.6 Hz), 7.43 (1H, d,
Jtrans = 16.6 Hz). 13C NMR (500 MHz, CDCl3) δ 14.2, 22.7, 22.8, 25.8,
26.0, 29.4, 29.6, 31.7, 31.8, 55.9, 56.5, 69.6, 70.4, 111.7, 111.8, 111.9,
114.0, 116.6, 123.3, 124.4, 127.2, 127.9, 150.0, 151.2, 151.6, 153.9. FT-
IR (neat, cmꢀ1) 971. HRMS (ESI)þ m/z 519.2110 (C28H40BrO4 [M þ
H]þ requires 519.2110).
2-Hexyloxy-5-methoxybenzaldehyde, 17: n-BuLi (1.5 M,
9.0 mL, 13.5 mmol) was added dropwise to a stirred solution of bromide
16 (2.595 g, 9.04 mmol) in THF (50 mL) at ꢀ78 °C, and the resulting
solution was stirred at ꢀ78 °C for 15 min. DMF (1.3 mL, 16.9 mmol)
was then slowly added and the resulting mixture was stirred at ꢀ78 °C
for 45 min, then room temperature for 15 min. The reaction was then
quenched with sat. aq NaHCO3 (15 mL) and the THF was removed
under reduced pressure. The residue was taken up in ether and washed
with H2O (3 ꢁ 80 mL) and sat. aq NaCl (1 ꢁ 80 mL), dried (MgSO4),
filtered, and concentrated under reduced pressure to give a yellow oil.
The yellow oil was purified by automated column chromatography
(SNAP 50G cartridge, ether/petroleum spirit as eluent) to give the
(E)-2-Hexyloxy-4-(20-hexyloxy-50-methoxystyryl)-5-meth-
oxybenzaldehyde, 20: n-BuLi (1.6 M, 6.4 mL, 10.3 mmol) was
added dropwise to a stirred solution of bromide 19 (3.540 g, 6.814
mmol) in THF (95 mL) at ꢀ78 °C, and the resulting dark solution was
stirred at ꢀ78 °C for 10 min. DMF (1.1 mL, 14.2 mmol) was then added
dropwise and the resulting solution was stirred at ꢀ78 °C for 45 min,
then room temperature for 15 min. The reaction was quenched with sat.
aq NaHCO3 (25 mL) and the THF removed under reduced pressure.
The residue was taken up in ether and washed with H2O (3 ꢁ 50 mL),
and the aqueous layer was extracted with additional ether. The com-
bined organic layers were dried (MgSO4), filtered, and concentrated
under reduced pressure to give an orange solid. The orange solid was
purified by flash chromatography (ether/n-hexane as eluent) to give the
aldehyde as a yellow solid (2.450 g, 77%), mp 66ꢀ67 °C. 1H NMR (500
MHz, CDCl3) δ 0.88ꢀ0.93 (6H, m), 1.32ꢀ1.38 (8H, m), 1.47ꢀ1.56
(4H, m), 1.81ꢀ1.88 (4H, m), 3.82 (3H, s), 3.88 (3H, s), 3.98 (2H, t, J =
6.4 Hz), 4.11 (2H, t, J = 6.4 Hz), 6.81 (1H, dd, J = 2.9, 8.9 Hz), 6.85 (1H,
d, J = 8.9 Hz), 7.18 (1H, d, J = 2.9 Hz), 7.21 (1H, s), 7.33 (1H, s), 7.48
(1H, d, J = 16.6 Hz), 7.56 (1H, d, J = 16.6 Hz), 10.45 (1H, s). 13C NMR
(CDCl3, 500 MHz) δ 14.1, 14.2, 22.7, 22.8, 25.9, 26.1, 29.4, 29.6, 31.7,
31.8, 56.0, 56.2, 69.3, 69.6, 109.0, 110.7, 112.1, 114.0, 114.8, 123.2, 124.2,
127.38, 127.43, 135.1, 151.3, 151.5, 153.9, 156.5, 189.2. FT-IR
(neat, cmꢀ1) 1668, 983. HRMS (ESI)þ m/z 469.2948 (C29H41O5
[M þ H]þ requires 469.2954).
1
product as a light brown oil (1.494 g, 70%). H NMR (500 MHz,
CDCl3) δ 0.89ꢀ0.92 (3H, m), 1.33ꢀ1.38 (4H, m), 1.45ꢀ1.51 (2H, m),
1.79ꢀ1.85 (2H, m), 3.80 (3H, s), 4.03 (2H, t, J = 6.5 Hz), 6.93 (1H, d,
J = 9.1 Hz), 7.12 (1H, dd, J = 3.3, 9.0 Hz), 7.32 (1H, d, J = 3.3 Hz), 10.48
(1H, s). 13C NMR (500 MHz, CDCl3) δ 14.1, 22.7, 25.9, 29.3, 31.7,
55.6, 69.4, 110.2, 114.6, 123.8, 125.3, 153.7, 156.6, 189.8. FT-IR
(neat, cmꢀ1) 1682. HRMS (ESI)þ m/z 237.1485 (C14H21O3 [M þ
H]þ requires 237.1491).
Diisopropyl 4-bromo-5-hexyloxy-2-methoxybenzylpho-
sphonate, 18: A solution of bromide 16 (24.64 g, 85.80 mmol),
p-formaldehyde (10.31 g, 343.3 mmol), concentrated HCl (32%, 34 mL,
347 mmol), and glacial acetic acid (30.0 mL, 31.5 mmol) was heated at
80 °C for 23 h. After 23 h the solution was cooled to room temperature
and the mixture was taken up in n-hexane (100 mL). The organic layer
was washed with sat. aq NaHCO3 (3 ꢁ 100 mL) and sat. aq NaCl (3 ꢁ
100 mL) and the combined aqueous layers were re-extracted with
additional n-hexane (2 ꢁ 100 mL). The organic layers were combined,
dried (MgSO4), filtered, and concentrated under reduced pressure to
give a 3:1 mixture of the desired product and its 6-chloromethyl
1
regioisomer as a dark brown oil (28.75 g, 100%). H NMR of the
desired 4-chloromethyl regioisomer (500 MHz, CDCl3) δ 0.90ꢀ0.92
(3H, m), 1.33ꢀ1.37 (4H, m), 1.47ꢀ1.52 (2H, m), 1.77ꢀ1.86 (2H, m),
3.83 (3H, s), 3.98 (2H, t, J = 6.5 Hz), 4.59 (2H, s), 6.94 (1H, s), 7.08
(1H, s). The isomeric mixture in triisopropyl phosphite (35.7 g, 39.4 mL,
171.4 mmol) was then stirred at reflux for 19 h. Removal of the excess
triisopropyl phosphite by KugelꢀRohr distillation gave a mixture of
4- and 6-diisopropyl phosphonates as a brown oil. The brown oil was
purified by flash chromatography (EtOAc/n-hexane as eluent) to give
the desired product as a light brown oil (22.72 g, 57% over two steps). 1H
NMR (400 MHz, CDCl3) δ 0.90 (3H, t, J = 7.1 Hz), 1.19 (6H, d, J = 6.2
Hz), 1.27 (6H, d, J = 6.2 Hz), 1.32ꢀ1.36 (4H, m), 1.45ꢀ1.50 (2H, m),
1.76ꢀ1.82 (2H, m), 3.13 (2H, d, J = 21.8 Hz), 3.77 (3H, s), 3.97 (2H, t,
J = 6.6 Hz), 4.57ꢀ4.67 (2H, m), 7.01 (1H, d, J = 2.7 Hz), 7.03 (1H, d, J =
1.0 Hz). 13C NMR (500 MHz, CDCl3) δ 14.1, 22.6, 23.7 (d, J = 5.1 Hz),
23.9 (d, J = 5.0 Hz), 24.1 (d, J = 3.7 Hz), 25.7, 27.4 (d, J = 142 Hz), 29.3,
31.6, 56.3, 70.2, 70.6 (d, J = 6.8 Hz), 110.6 (d, J = 4.6 Hz), 116.0, 117.0
(E,E)-10-Hexyloxy-50-(200-hexyloxy-500-methoxystyryl)-40-
methoxy-20-(4-methylstyryl)benzene, 15: A solution of alde-
hyde 20 (0.210 g, 0.448 mmol) and phosphonate 13 (0.193 g, 0.714
mmol) in THF (7 mL) was added to a stirred solution of potassium tert-
butoxide (0.104 g, 0.927 mmol) in THF (3 mL) at 0 °C. The mixture
was brought to room temperature and stirred for 5 h. The reaction was
then quenched with sat. aq NH4Cl (20 mL) and the THF removed
under reduced pressure. Ether was added and the organic phase was
washed with H2O (3 ꢁ 50 mL), dried (MgSO4), filtered, and concen-
trated under reduced pressure to give a yellow solid. The yellow solid
was purified by flash chromatography (ether/n-hexane as eluent) to give
the product as a yellow solid (0.203 g, 81%), mp 70ꢀ72 °C. 1H NMR
(500 MHz, CDCl3) δ 0.87ꢀ0.94 (6H, m), 1.31ꢀ1.44 (8H, m),
1.51ꢀ1.58 (4H, m), 1.81ꢀ1.89 (4H, m), 2.37 (3H, s), 3.83 (3H, s),
3.92 (3H, s), 3.97 (2H, d, J = 6.4 Hz), 4.04 (2H, d, J = 6.5 Hz), 6.77 (1H,
3379
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The Journal of Organic Chemistry
ARTICLE
dd, J = 3.0, 8.9 Hz), 6.84 (1H, d, J = 8.9 Hz), 7.11ꢀ7.14 (2H, m), 7.16
(2H, s), 7.18 (1H, s), 7.20 (1H, d, J = 3.0 Hz), 7.43ꢀ7.50 (5H, m). 13C
NMR (CDCl3, 500 MHz) δ 14.17, 14.20, 21.4, 22.8, 29.08, 29.12, 29.62,
29.66, 31.8, 55.9, 56.5, 69.7, 69.8, 109.2, 111.0, 111.7, 113.8, 114.1, 122.7,
123.7, 123.8, 127.1, 127.2, 128.3, 128.8, 129.5, 135.4, 137.4, 151.2, 151.7,
153.9. FT-IR (neat, cmꢀ1) 965. HRMS (ESI)þ m/z 556.3546
(C37H48O4 [M]þ requires 556.3553).
(18) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Organometallics 1996, 15, 1518–1520.
(19) Still, W. C.; Kahn, M.; Mitra, A. J. Org. Chem. 1978, 43,
2923–2925.
(20) Reynolds, G. A.; Drexhage, K. H. Opt. Commun. 1975, 13,
222–225.
(21) Bell, T. D. M.; Ghiggino, K. P.; Haynes, A.; Langford, S. J.;
Woodward, C. P. J. Porphyrins Phthalocyanines 2008, 11, 455.
(22) (a) Kajigaeshi, S.; Kakinami, T.; Okamoto, T.; Nakamura, H.;
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’ ASSOCIATED CONTENT
S
Supporting Information. Crystallographic information
b
file for 15, details of the molecular mechanics calculations for
the rotamer and twistomer conformations of 14, and 1H and 13
C
NMR spectra for all new compounds. This material is available
free of charge via the Internet at http://pubs.acs.org. The crystal-
lographic coordinates for 15 have been deposited with the Cam-
bridge Crystallographic Data Centre; deposition no. 818656.
These data can be obtained free of charge from the Cambridge
Crystallographic Data Centre, 12 Union Rd., Cambridge CB2 1EZ,
UK or via www.ccdc.cam.ac.uk/conts/retrieving.html.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: whitejm@unimelb.edu.au.
’ ACKNOWLEDGMENT
We thank Dr. Xiaoming Wen for assistance with the fluores-
cence lifetime measurements. Financial support from the Austra-
lian Research Council Discovery Grant Program is acknowledged.
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