Direct synthesis of 2,5-bis(dodecanoxy)phenyleneethynylene-butadiynes by sonogashira coupling reaction

Article abstract of DOI:10.1002/ejoc.201300230

The synthesis of a 2,5-bis(dodecanoxy)phenyleneethynylene-butadiyne series with 2, 4, 6 and 8 phenyl rings is reported. Sonogashira coupling reaction, rather than the Glaser/Eglinton/Hay reactions classically used for butadiyne formation was applied. The molecular structures of all compounds were confirmed by ¹H, DEPT-135, APT ¹³C, MALDI-TOF, FTIR and FT-Raman analyses. The linear and nonlinear optical properties were studied in solution by UV/Vis, static and time-resolved fluorescence, and by two-photon absorption (2PA) spectroscopy. With the exception of the dimer, for which intersystem crossing is very favoured due to the low energy gap between the singlet and triplet states as theoretically predicted, the other oligomers present high fluorescence quantum yields (0.77-0.82) and large cross-sections (up to 5000 GM for the octamer) that could be applied in multiphoton microscopy or nonlinear optics. An alternative strategy that can be used to obtain phenyleneethynylene- butadiynes through Sonogashira reaction is reported. A combined spectroscopic and theoretical study reveals that the dimer behaves like a diacetylene, whereas the longer oligomers present large quantum yield due to larger energy gaps between the singlet and triplet excited states. Copyright

Full text of DOI:10.1002/ejoc.201300230

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FULL PAPER
Highly Conjugated Systems
E. Arias, I. Moggio,* R. Torres,
R. F. Ziolo, J.-L. Maldonado, K. Green,
T. M. Cooper, G. Wicks, A. Rebane,
M. Drobizhev, N. S. Makarov,
M. Ottonelli, G. Dellepiane ............ 1–13
Direct Synthesis of 2,5-Bis(dodecanoxy)-
phenyleneethynylene-Butadiynes by Sono-
gashira Coupling Reaction
Keywords: Alkynes / Conjugation / Chain
structures / Nonlinear optics / UV/Vis spec-
troscopy
An alternative strategy that can be used to
obtain phenyleneethynylene-butadiynes
through Sonogashira reaction is reported.
A combined spectroscopic and theoretical
study reveals that the dimer behaves like a
diacetylene, whereas the longer oligomers
present large quantum yield due to larger
energy gaps between the singlet and triplet
excited states.
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I. Moggio et al.
FULL PAPER
DOI: 10.1002/ejoc.201300230
Direct Synthesis of 2,5-Bis(dodecanoxy)phenyleneethynylene-Butadiynes by
Sonogashira Coupling Reaction
Eduardo Arias,[a] Ivana Moggio,*[a] Román Torres,[a] Ronald F. Ziolo,[a]
José-Luis Maldonado,[b] Kirk Green,[c] Thomas M. Cooper,[d] Geoffrey Wicks,[e]
Aleksander Rebane,[e] Mikhail Drobizhev,[e] Nikolay S. Makarov,[e] Massimo Ottonelli,[f] and
Giovanna Dellepiane[f]
Keywords: Alkynes / Conjugation / Chain structures / Nonlinear optics / UV/Vis spectroscopy
The synthesis of a 2,5-bis(dodecanoxy)phenyleneethynyl-
ene-butadiyne series with 2, 4, 6 and 8 phenyl rings is re-
ported. Sonogashira coupling reaction, rather than the Gla-
ser/Eglinton/Hay reactions classically used for butadiyne for-
mation was applied. The molecular structures of all com-
and time-resolved fluorescence, and by two-photon absorp-
tion (2PA) spectroscopy. With the exception of the dimer, for
which intersystem crossing is very favoured due to the low
energy gap between the singlet and triplet states as theore-
tically predicted, the other oligomers present high fluores-
cence quantum yields (0.77–0.82) and large cross-sections
(up to 5000 GM for the octamer) that could be applied in
multiphoton microscopy or nonlinear optics.
1
pounds were confirmed by H, DEPT-135, APT 13C, MALDI-
TOF, FTIR and FT-Raman analyses. The linear and nonlinear
optical properties were studied in solution by UV/Vis, static
ents in the aryl groups have an important effect on the reac-
tion yield; electron-withdrawing rather than -donating
groups favour the cross-coupling, however, even when yields
of the desired product are always higher than 50%, usually
the amount of diacetylene formed as byproduct is not re-
ported. Butadiynes can also be formed in poly(phenyl-
enethynylene) compounds and are usually considered as
structural defects because they can polymerize in the solid
state, giving cross-linked insoluble materials.[2] Nevertheless,
oligo(p-phenylenebutadiynylene) and oligo(phenyleneethyn-
ylene-butadiyne) compounds have been reported as defined
molecular rods and interesting self-assembling properties
have been reported.[3] Diacetylenes are usually prepared by
Cadiot–Chodkiewicz coupling reaction for asymmetrical
butadiynes or oxidative dimerization of a terminal acetyl-
ene for symmetric diacetylenes by either Glaser, Eglinton
or Hay reactions; details on these reactions are reported in
a recent review by Diederich et al.[4] With the aim of provid-
ing novel materials with balanced hole and electron trans-
port properties, Klemm et al. reported in 2002 the synthesis
of highly luminescent hybrid phenyleneethynylene-phenyl-
enevinylene copolymers.[5] As part of the strategy, they syn-
thesized a central trimer by the Sonogashira cross-coupling
reaction between 1,4-diethynyl-2,5-bis(2-ethylhexyloxy)-
benzene and 4-bromobenzaldehyde, however, in addition to
the desired product, they also isolated the 1,4-bis{4-formyl-
phenylethynyl-[2,5-bis(octadecyloxy)phenyl]buta-1,3-diyne}
compound as a byproduct of the reaction, suggesting that
self-coupling of acetylenes of alkoxy phenyls gives rise to
the formation of butadiynes and, in particular, phenylene-
Introduction
Because phenyleneethynylene (PE) oligomers have poten-
tial applications in optoelectronics, new synthetic routes
have been explored to generate such compounds in fewer
steps and in higher yields; the routes are designed to en-
compass all types of molecular architecture such as linear,
cross, stars, hyperbranched, or dendritic types to obtain a
specific supramolecular order.[1] The Sonogashira reaction
is a well-known cross-coupling reaction that takes place
with an acetylene and a bromo or iodoaryl through the
catalytic action of a Pd0/CuI complex, whereby a small
amount of diacetylene as byproduct is always formed. Be-
cause the catalytic complex is rich in electrons, the substitu-
[a] Centro de Investigación en Química Aplicada,
Boulevard Enrique Reyna 140, 25294 Saltillo, Mexico
Fax: +52-844-4389839
E-mail: ivana.moggio@ciqa.edu.mx
Homepage: www.ciqa.mx
[b] Centro de Investigaciones en Óptica,
Loma del Bosque 115, Col. Lomas del Campestre, 37150 León,
México
[c] Department of Chemistry, McMaster University,
1280 Main St. W, Hamilton, Ontario, L8S 4M1, Canada
[d] Materials and Manufacturing Directorate, Air Force Research
Laboratory,
3005 Hobson Way, Wright-Patterson Air Force Base, Ohio
45433, USA
[e] Physics Department, Montana State University,
Bozeman, Montana 59717, USA
[f] Dipartimento di Chimica e Chimica Industriale, Universitá di
Genova,
Via Dodecaneso 31, Genoa 16146, Italy
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201300230.
2
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Synthesis of 2,5-Bis(dodecanoxy)phenyleneethynylene-Butadiynes
Figure 1. Chemical structure of (left side) 2,5-bis(dodecanoxy)phenyleneethynylene-butadiyne (pPEOC12-Dac) series of this work: dimer
4, tetramer 8, hexamer 12 and octamer 15 as per Scheme 1. (Right side) 2,5-bis(dodecanoxy)phenyleneethynylene (pPEOC12) series
studied in ref.[8] and here used as term of comparison for the discussion of the optical properties.
ethynylene-butadiyne structures are feasible by the Sonoga- 3%, whereas the diacetylene octamer was obtained in 89%
shira reaction. For this oligomer, the authors demonstrated yield. A physicochemical study by combining different spec-
that the diyne segment confers a stronger transition mo- troscopic techniques (NMR, UV, fluorescence and Raman)
ment, which results in a higher absorption coefficient and with theoretical simulations on the dimer and tetramer was
enhanced radiative rate constant. The major part of the also carried out in an attempt to explain the different pho-
work was devoted to a comparison of the electrochemical, tophysical properties of the dimer with respect to the longer
photophysical and photoconductivity properties of the re- oligomers. Quite large two-photon cross-sections (up to
sultant copolymers and concluded that the diyne-contain- 5000 GM for the octamer) were found that could be applied
ing polymers present higher photoconductivity and sta- in multiphoton microscopy or nonlinear optics.
bility, stronger electron-accepting properties and higher
quantum yields in the solid state. Other alkoxy-substituted
Results and Discussion
phenyleneethynylenes bearing central butadiynes were also
synthesized by Thomas’ group by combining the Glaser
oxidative reaction with the Sonogashira reaction. They
demonstrated by STM that these materials exhibit a very
Synthesis and Molecular Structure Characterization
The pathway used to synthesize the pPEOC12-Dac series
particular supramolecular arrangement when deposited on is depicted in Scheme 1. The convergent synthesis, in gene-
HOPG.[3c]
ral, involves only two repetitive reactions: a Pd/Cu cross-
In the present work, we report the synthesis of a series of coupling reaction and desilylation of the protected acetyl-
phenyleneethynylene-butadiynes (pPEOC12-Dac, Figure 1) ene groups.[6] In particular, the Pd/Cu cross-coupling reac-
for which the length of the phenyleneethynyene segment in- tions were carried out by adapting the Godt protocol,
creases from 1 to 4. Hereafter, these compounds will be whereby aryliodides are coupled to acetylenes at 0 °C,
referred to as dimer, tetramer, hexamer or octamer on the whereas for aryl bromides the solvent was heated to reflux
basis of the total number of phenyl rings. The phenylene- at ca. 80 °C.[7]
ethynylene-butadiynes were prepared in high yield by the
The oligomerization starts with the Pd/Cu cross-coupling
Sonogashira coupling reaction. In particular, we found that of one equivalent of 1 and 2 to generate the bromine-ter-
as the electron-donating character of the 2,5-bis(dodec- minated dimer 3 in 64% yield. From this reaction, the di-
anoxy)phenyleneethynylene-acetylene-terminated oligomer acetylene dimer 4 was isolated in 30% yield. We observed
increases by extension of the number of repetitive units, its that in all reactions for which the oligomers were acetylene-
cross-coupling with the halogen-aryl decreases, leading to terminated and a Pd/Cu cross-coupling reaction was in-
the formation of the diacetylene oligomer as the main prod- volved, the diacetylene was always isolated as a byproduct
uct. In this way, for instance, the Pd0/CuI cross-coupling of in large amounts. From this observation, we conducted an
an acetylene terminated tetramer with iodo-2,5-bis(do- exploratory reaction by adding the acetylene-terminated
decanoxy)benzene yields the expected pentamer in only ca. monomer 1 and the catalyst complex in a typical molar
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Scheme 1. Synthetic route for the pPEOC12-Dac series. Reagents and conditions: (a) [(Ph3P)2PdCl2] (2.5 mol-%), CuI (1.5 mol-%), NEt3,
THF, 0 °C; (b) [(Ph3P)2PdCl2] (2.5 mol-%), CuI (3.0 mol-%), NEt3, THF, 80 °C; (c) [(Ph3P)2PdCl2] (2.5 mol-%), CuI (1.5 mol-%), TMSA,
NEt3, THF, 60 °C; (d) TBAF, THF, room temp.
ratio of [[(C6H5)3P]2PdCl2] (2.5 mol-%)/CuI (1.5 mol-%) in 63% yield, which, after desilylation, gave acetylene-termin-
degassed Et3N, and obtained the diacetylene dimer 4 as the ated trimer 10. One equivalent of 10 then underwent Pd/
main product in 95% yield. A similar result was obtained CuI mediated cross-coupling to generate bromine-termin-
in the absence of CuI, although longer reaction times were ated tetramer 11 (46% yield) and diacetylene hexamer 12
necessary. No differences were observed by changing the (51% yield) as a byproduct. The self-coupling of 10 af-
palladium catalyst molar ratio or when the amount of CuI forded hexamer 12 in 87% yield. Finally, bromine-termin-
was increased to 3.0 mol-%; the self-coupling acetylene– ated tetramer 11 was subjected to another TMSA cross-
acetylene proceeded to completion in two hours. From coupling-desilylation cycle to form the acetylene-terminated
these results, for further reactions, 2 mol-% CuI was used, tetramer 14, from which, after acetylene-acetylene Pd/Cu
depending on the coupling type reaction; for instance, to coupling, octamer 15 was obtained in 89% yield.
favour the coupling between an acetylene and a bromoaryl
1H and 13C, DEPT-135 and APT 13C NMR spectroscopy
(ca. 80 °C) or iodoaryl (ca. 0 °C), a 1.5% molar ratio of CuI were essential to corroborate the molecular structures of the
1
was determined to be suitable, whereas for acetylene–acetyl- oligomers. Figure 2 (a) collects the H NMR spectra of the
ene coupling reactions the use of 3.0 mol-% CuI provided series with two expanded regions in Figure 2 (b and c). Fig-
quantitative yields when the palladium complex was kept at ure 2 (d) shows the 13C NMR spectrum of tetramer 8 with
a 2.5% molar ratio. Bromine-terminated dimer 3 was sub- the corresponding notations in the inserted chemical struc-
jected to Pd/Cu cross-coupling reaction with TMSA to af- ture, as an example. In Figure 2 (a), two different aromatic
ford dimer 5 in 66% yield. Desilylation of 5 gave acetylene- proton signals are identified in the series: those in the ortho
terminated dimer 6, which was subjected to Pd/Cu mediated position with respect to the triple bonds (Ho-ynes), and four
cross-coupling with one equivalent of 2 at 0 °C to generate protons that are meta and para to the triple bonds. The
bromine-terminated trimer 7 in 59% yield; the diacetylene latter four protons are positioned with two at each of the
tetramer 8 was also recovered as a byproduct in 37% yield. phenyl rings at the extremity of the oligomers and are lab-
Acetylene-terminated dimer 6 was acetylene-acetylene cou- elled as Hext. In the aliphatic region at ca. 4.0 ppm, two
pled to form diacetylene tetramer 8 in 93% yield. Sub- triplets appear corresponding to the protons α to the oxy-
sequently, bromine-terminated trimer 7 was subjected to an- gen of the two dodecanoxy chains, which are different one
other cycle of Pd/CuI coupling with TMSA to afford 9 in to the other; one set being the –CH2– in the δ position to
4
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Synthesis of 2,5-Bis(dodecanoxy)phenyleneethynylene-Butadiynes
Figure 2. NMR spectra in CDCl3: (a) 1H (300 MHz) of the pPEOC12-Dac series; (b) expansion of the corresponding aliphatic –O–CH2-
and (c) aromatic region, and (d) the conjugated region of the 13C NMR spectrum (75 MHz) of tetramer 8 with the corresponding
annotations on the chemical structure for assignment.
triple bonds (Hδ-ynes) centred at 4.0 ppm, whereas those in warming to completely dissolve), the oligomers have strong
the ε position to the triple bonds (Hε-ynes) appear at δ = intermolecular interactions that favour agglomeration. We
3.89 ppm, Figure 2 (b). As the oligomer length increased, confirmed this hypothesis when, after a few days at room
the integration of the Hδ-ynes also increased because of the temperature, a cotton-like precipitate was formed from a
large number of –CH2– groups. A similar behaviour was concentrated chloroform solution, which, in turn, could be
also observed in the aromatic region (Figure 2, c); the inten- redissolved upon gentle heating. However, despite this be-
sity of the Ho-ynes increases with oligomer length whereas haviour, attempts to grow single crystals failed.
the intensity of the Hext signal remained constant. The
In the 13C NMR spectra (illustrated in Figure 2 (d) for
theoretical factor for the integration ratio between the tetramer 8), two different acetylene carbon resonances were
Hδ-ynes and the total number of aromatic protons gives: clearly identified: the diacetylene signals that appear at ca.
1.33, 1.6, 1.71, 1.78 for dimer 4, tetramer 8, hexamer 12 79.1–79.9 ppm and the ethynes/phenyl signals that give sig-
and octamer 15, respectively, whereas the experimental val- nals centred at 88.9–92.5 ppm. It can be seen that all aro-
ues were 1.34, 1.74, 1.8 and 1.91. In the same way, the theo- matic and ethyne carbon resonances are chemically distinct,
retical factor of integration ratio between Ho-ynes/Hext gives including those of the ether substituted ring that appear as
0.5, 1.5, 2.5 and 3.5, which are values that match better four peaks at 150.3–155.2 ppm. The remaining eight aro-
with the observed values of 0.45, 1.7, 2.6 and 3.7, respec- matic carbon signals are centred at 114.0–118.77 ppm. A
tively, for the series. These factors are more useful indi- similar behaviour is observed for hexamer 12, for which two
cators of oligomer structure than the integration itself be- acetylene, two ethyne, six signals for the aromatic carbon
cause the number of protons obtained by integrating each atoms substituted with ethers, and twelve signals for the rest
individual peak does not match well with the expected of the aromatic carbon atoms are clearly identified. In the
structure as the oligomer length is increased, particularly spectrum of octamer 15 some signals overlap. The COSY
those corresponding to the aliphatic chains.
and HETCOR spectra confirm that all hydrogen–hydrogen
We believe that this behaviour could be due to the fact and carbon–hydrogen correlations match well with the cor-
that even in solution (most of these compounds require responding structures.
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Figure 3. MALDI-TOF MS (region of the molecular ion peak) for the pPEOC12-Dac series.
Positive Matrix-Assisted Laser Desorption Ionization symmetry of the molecules.[10] In contrast, both –CϵC–
Time-of-Flight Mass Spectrometry (MALDI-TOF-MS) stretching bands are expected to give a very intense Raman
analysis supported the molecular structure of the oligomers signal at almost the same wavenumber. In agreement with
by showing their expected molecular ion peak (Figure 3); this expectation, the IR spectrum presents a very weak sig-
For 4: m/z 938.6 (M+, calcd. for C64H106O4: 938.8), for 8: nal at around 2200 cm–1, whereas a very intense peak in the
m/z 1875.7 (M+, calcd. for C128H210O8: 1875.6), for 12: m/z Raman spectra appears at 2200Ϯ2 cm–1. Dimer 4 repre-
2812.4 (M+, calcd. for C192H314O12: 2812.4), for 15: m/z sents an exception, with no bands in the IR whereas the
3748.8 (M+, calcd. for C256H418O16: 3749.2). The isotopic Raman signal moves to 2220 cm–1.
resolution decreases along with the conjugation and its dis-
It should be noted that the oligomers do not exhibit to-
tribution pattern is consistent with the oligomer size, giving pochemical polymerization[11] either by UV irradiation or
more peaks for the octamer as there are more isotopic car- thermally, and are stable at air and at room temperature for
bon atoms present in the molecule. It should also be noted extended periods.
that the signals at higher molecular weight (molecular ion
weight +22.99) are attributed to Na+ cationization.[9]
Optical Properties and Theoretical Calculations
Figure 4 shows the IR spectra for monomer 1 and octa-
mer 15 as representative molecules of the pPEOC12-Dac
family. The monomer 1 clearly shows the intense ϵC–H
stretching band at 3286 cm–1 that, as expected, disappears
for octamer 15 as well as for the rest of the series. The most
interesting region is that related to the –CϵC– stretching
band, which should give a very weak signal at around
2200 cm–1 for the acetylenic triple bonds vibration and no
signal at all for the internal diacetylenic group, due to the
Figure 5 shows the absorption and fluorescence spectra
of the pPEOC12-Dac series in CHCl3; the optical proper-
ties are presented in Table 1.
Figure 5. Absorption and fluorescence (insert) spectra in CHCl3
for the pPEOC12-Dac series.
For comparison, relevant optical properties of 2,5-
bis(dodecanoxy)phenyleneethynylenes (pPEOC12, chemical
structure shown in Figure 1) are reported in this section.
Details on the synthesis and spectroscopic properties of
these molecules have been reported.[8] In general, the spec-
tral features of pPEOC12-Dac are very similar to those pre-
Figure 4. From bottom to top: infrared spectra (solid lines) of
monomer 1 and octamer 15, Raman spectrum (dotted line) of octa-
mer 15.
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Synthesis of 2,5-Bis(dodecanoxy)phenyleneethynylene-Butadiynes
Table 1. Optical properties of pPEOC12-Dac in CHCl3.
[b]
pPEOC12-Dac
λabs
[nm]
HHBWabs
[nm][a]
ε ϫ104
[m–1 cm–1] [nm]
λem
Stokes’ shift HHBWfluo
ΦF
τ
[ns]
kF ϫ109
knr ϫ109
[cm–1]
[nm][a]
[s–1]
[s–1]
Dimer 4
350
400
425
435
64
68
74
77
1.68
7.39
11.60
16.99
387
444
463
470
2732
2477
1931
1712
49
23
23
24
0.07
0.77
0.78
0.82
0.42Ϯ0.2%
0.87Ϯ0.2%
0.72Ϯ0.3%
0.69Ϯ0.4%
0.18
0.88
1.08
1.19
2.20
0.26
0.30
0.26
Tetramer 8
Hexamer 12
Octamer 15
[a] Half height band width. [b] Ϯ10%.
viously reported for the pPEOC12. (1) The absorption spec-
The fluorescence decays obtained by time-correlated sin-
tra are very broad (half-height band width (HHBW) gle-photon counting (TCSPC) can be well-fitted with a
around 70 nm), whereas the fluorescence spectra are of the monoexponential curve, supporting the conclusion that
excitonic type with smaller HHBW because the planariz- there is only one emitting state. Figure 6 illustrates the de-
ation of the geometry in the excited state reduces the con- cay and fit for octamer 15 as an example, together with the
formation distribution with respect to the ground state. The weighted residuals. The TCSPC results for the other oligo-
change in the geometry from ground to excited state is con- mers are reported in the Supporting Information.
firmed also for this series with the Stokes’ shift ranging
from the value of aromatic systems (around 1430 cm–1) to
those of biphenyls, which assume a more planar conforma-
tion after excitation (ca. 3310 cm–1).[12] In this respect, di-
mer 4 has the higher value for the Stokes’ shift. (2) The
absorption spectra present an intense peak due to the
HOMO–LUMO transition, which redshifts along with an
increase in the oligomer length. The corresponding molar
absorption coefficient ε increases in accordance with the
higher chromophore content. Higher energy peaks can be
observed in the 300–320 nm range and ascribed to elec-
tronic transitions from lower lying occupied orbitals.[13]
(3) The absorption spectra do not change with concentra-
tion or solvent polarity, excluding the possibility of any
ground-state interactions such as aggregation[13a] (see the
Figure 6. TCSPC data for tetramer 8 in chloroform.
Supporting Information). (4) The fluorescence spectra are
independent of the excitation wavelength, and the excitation
The corresponding lifetimes are in the same range as
spectra are the same when the emission peak is fixed at the those reported for alkoxy phenyleneethynylenes[14] and the
more intense peak or to the shoulder, confirming that only diyne oligomer reported by Klemm.[5] The value decreases
one emitting state exists (see the Supporting Information). from tetramer 8 to octamer 15 along with an increase in
It can be observed that dimer 4 absorbs at lower wavelength the radiative rate constant Kf, in agreement with the higher
than dodecanoxy trimer 3PEOC12-H[8] (350 vs. 380 nm) extinction coefficient. The nonradiative constant Knr is
and tetramer 8 absorbs at wavelengths between 3PEOC12- practically constant. A particular case is dimer 4, for which
H and the dodecanoxy phenyleneethynylene pentamer the lifetime is lower, giving a Knr much higher than the
5PEOC12-H (412 nm),[8] in accordance with the level of other oligomers. This suggests stronger nonradiative losses.
conjugation. However, hexamer 12 and octamer 15 present As previously discussed, this oligomer presents a larger Sto-
absorption maxima at higher wavelength than heptamer kes’ shift, which implies higher internal conversion losses.
7PEOC12-H and even the pPEOC12 homopolymer and However, the large decrease in the fluorescence quantum
have higher molar absorption coefficient,[8] suggesting that yield and large nonradiative constant could also be due to
the presence of the central diacetylene group increases the intersystem crossing to the triplet state, as reported for dif-
π-π overlap in the ground state with respect to the phenyl- ferent types of diphenylpolyynes.[15]
eneethynylenes. Similar behaviour was found by Klemm et
To investigate the possibility of intersystem crossing, mo-
al. in a study that compared the optical properties of a lecular mechanics theoretical simulations were performed
phenyleneethynylene aldehyde tetramer with those of the on dimer 4 and tetramer 8. Figures 7 and 8 report some
corresponding diyne containing oligomer, i.e., the maxi- representative conformers obtained within this study for the
mum absorption wavelength and relative molar absorption two oligomers. For dimer 4 (Figure 7), a negligible energy
coefficient were higher for the diyne oligomer with respect difference of about 0.3 kcal/mol is predicted between the
to the phenyleneethynylene.[5] (5) Fluorescence quantum conformers with the phenyl rings dihedral angles near 0°
yields are very high for tetramer 8, hexamer 12 and octamer (D1) and 80° (D2), respectively. Nevertheless, the strong de-
15, and are in the same range as those reported for H-ter- pendence of the relative conformational energy on the “ran-
minated phenyleneethynylenes.[8] In contrast, dimer 4 pres- domization” of the aliphatic tails should be emphasized and
ents a very low quantum yield.
this could be strongly correlated with the environment in
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Figure 7. Some representative examples of conformer geometries of dimer 4. Relative stability (kcal/mol) and the value of the dihedral
angles of the phenyl rings are reported in parentheses.
Figure 8. Some representative examples of conformer geometries of tetramer 8. Relative stability (kcal/mol) and the values of the dihedral
angles of the phenyl rings between the internal and external rings are reported in the parentheses.
which the oligomers are embedded (solution, solid state).
The results of the time dependence (TD) calculations are
In contrast, for tetramer 8 (Figure 8), an energy difference summarized in Table 2.
of 32 kcal/mol is found between the conformer with di-
hedral angles of the phenyl rings equal to 0° (T1) and 64°
Table 2. Calculated (TD-B3LYP/6-311G**) wavelength (nm) and
(T2), respectively. In this case, there are more significant
alignment effects on the aliphatic chains with respect to the
dimer because the “external” phenyl rings are spaced by a
single triple bond, which reduces their randomization.
These results imply that for dimer 4, at room temperature,
almost all the conformational isomers are present with a
comparable population weight, whereas for tetramer 8 the
dominant conformations should be those with all the
phenyl rings lying on the same plane (see T1 in Figure 8).
On the basis of this analysis, we refined the structure of D1,
D2, T1 and T2 at the B3LYP/6-311G** level. With respect
to the molecular mechanics (MM/UFF) results, the dihe-
oscillator strengths for the first optical allowed (S) and triplet (T)
excited state and their energy difference ΔES–T (cm–1), for the
model systems.
Structure[a] S [nm] Oscillator strength T [nm] ΔES–T [cm–1]
D1
D2
T1
T2
376.1
351.1
459.8
404.1
1.147
0.830
2.959
2.037
412.1
351.4
504.7
412.4
2307
24
1936
500
[a] ab initio geometry.
Comparison between Table 1 and Table 2 reveals good
dral angle between the phenyl rings increases from 0° to 18° agreement with the experimental results: (1) for dimer 4, the
for D1, decreases from 80° to 53° for D2, and does not main absorption peak is experimentally observed at 350 nm
change for T1, whereas for T2 it decreases to 44° from 64°. and calculated to be 351 nm for D2; for tetramer 8 at
Finally, as expected, for the oligomer backbones, the ab ini- 400 nm (calculated 404 nm for T2). (2) Because the singlet
tio calculated bond length of the triple bonds becomes more and triplet excited states for the conformer D2 have practi-
relaxed 1.210–1.220 Å (vs. 1.200–1.205 Å of MM/UFF) and cally the same energy, a high probability of intersystem
those of the single bonds more compressed 1.350–1.360 Å crossing between these states could occur, with the conse-
(vs. 1.411–1.415 Å of MM/UFF) as a consequence of a bet- quence of a luminescence quenching, as experimentally ob-
ter description, with the ab initio calculations of the conju- served. On the other hand, the energy gap between the sing-
gation effects on these oligomers, which plays an important let and triplet excited state for tetramer 8 is greater. Conse-
role in the description of the electronic transitions.
quently, this quenching channel is unfavourable and the
8
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Synthesis of 2,5-Bis(dodecanoxy)phenyleneethynylene-Butadiynes
Table 3. Two-photon spectroscopy data for pPEOC12-Dac in CHCl3.
[a]
pPEOC12-Dac
Nπ
νio [cm–1][b]
νf0 [cm–1][c]
Γ [cm–1][d]
σ2 [GM][e]
S [GMcm–1][f]
Dimer 4
32
64
96
28600
25000
23500
23000
29850
29400
28600
26700
2050
2050
2050
2050
8
360
2100
5000
1.38ϫ104
3.62ϫ105
1.80ϫ106
5.37ϫ106
Tetramer 8
Hexamer 12
Octamer 15
128
[a] Number of π electrons per oligomer. [b] 1PA-allowed transition frequency. [c] 2PA-allowed transition frequency. [d] 2PA bandwidth.
[e] 2PA cross-section. [f] Conjugation signature.
oligomer (and those with a greater number of repeat phen- C is a constant, μ01 is the transition dipole moment of the
ylenethynylene units) should be fluorescent, as experimen- 1PA transition and μif is the transition dipole moment be-
tally observed.
tween the 1PA and 2PA transitions. A fit to a power law
gives:
k
S = ANπ
Two-Photon Absorption
where Nπ is the number of π electrons in the oligomer. The
dependence of S on Nπ reveals the extent of conjugation.
When there is strong conjugation through the oligomer, μ
Two-photon absorption (2PA) is a nonlinear optical pro-
cess that can be used in fluorescence microscopy, optical
data storage, nonlinear optics and microfabrication.[16] Due
to the large fluorescence quantum yield obtained for the
oligomer series, 2PA spectroscopy was carried out in
chloroform (Figure 9) using the fluorescence technique.[17]
The data are summarized in Table 3.
4
≈ Nπ, giving S ≈ Nπ . When k Ͻ 4, the excited states are
more localized. A plot of S vs. Nπ (the number of π elec-
trons in the oligomer) is presented in Figure 10. The value
of k is calculated to be 4.3, suggesting strong conjugation
to the oligomers resulting from a rod-like shape. Hexamer
12 and, particularly, octamer 15 present quite large cross
sections in the red region (between 650 and 750 nm).
Figure 10. Plot of conjugation signature S vs. the number of π elec-
trons in the pPEOC12-Dac series (N).
Figure 9. Two-photon spectra in CHCl3 for the pPEOC12-Dac
series. The 1PA spectrum shifted by 2λ is also shown.
All the spectra show a rather weak peak or shoulder co-
incident with the S0ǞS1 transition. This result indicates
that the centre of symmetry is broken sufficiently to give a
slight permanent dipole moment. A much stronger transi-
tion just above the S0ǞS1 band is likely a g-g transition
that is forbidden in the corresponding 1PA. The 2PA fea-
tures shift to the red with increasing chain length in a sim-
ilar way to the 1PA spectrum shift.
Conclusions
A facile route by Sonogashira reaction is reported for the
synthesis of 2,5-bis(dodecanoxy)phenyleneethynylene-buta-
diynes having 2, 4, 6 and 8 phenyl rings. The electron-donor
character of the dodecanoxy chains favour acetylene-acetyl-
ene coupling, which proceed in quantitative yields, whereas
the yields are rather modest for the cross-coupling between
iodo or bromo aryl acetylenes. The molecular structure of
the series was corroborated by 1H, 13C, DEPT-135, and
APT 13C NMR studies and by FTIR and FT-Raman spec-
The spectra behave according to a three-level model, so
we calculated the conjugation signature S:[18]
νio
S = σ2mΓf(2
– 1)2 = C|μ01|2|μif|2
νfo
where σ2m is the 2PA cross-section, Γf is the 2PA bandwidth troscopy. The optical properties in solution were observed
(cm–1), νio is the energy of the 1PA transition (cm–1), and to be very similar to those of the corresponding phenylenee-
νfo is the energy of the 2PA transition (cm–1). The quantity thynylene moieties with the exception of the dimer, in which
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I. Moggio et al.
FULL PAPER
General Procedure for the Cross-Coupling of an Acetylene with
Bromo or Iodo Aryls: To a two-necked round-bottomed flask con-
taining [(Ph3P)2PdCl2] (2.5 mol-%), CuI (1.5 mol-%) and the aryl
halide was added dry and degassed 95:5 (v/v) Et3N/THF by using
a cannula. The mixture was heated at 60 °C for 5 min (by Goldt’s
method, it was cooled to ca. 0 °C). The acetylene monomer dis-
solved in degassed Et3N was then added by using a syringe and the
mixture was stirred vigorously for 16 h at 60 °C (by the Goldt
method after adding the acetylene, the reaction was left to reach the
room temperature and stirred for 48 h). The mixture was filtered to
remove the ammonium salt and the organic phase was ready for
the next purification process.
intersystem crossing is more favoured due to the low energy
gap between the singlet and triplet states as revealed by
theoretical calculations. The hexamer and octamer, in par-
ticular, show a large quantum yield of 0.78 and 0.82, respec-
tively, and 2PA cross-sections of 103 GM, which make them
good candidates for multiphoton microscopy applications.
Experimental Section
General Procedure for the Homocoupling of an Acetylene: To a two-
necked round-bottomed flask containing [(Ph3P)2PdCl2] (2.5 mol-
%), CuI (3.0 mol-%) and the acetylene compound was added dry
and degassed 95:5 (v/v) Et3N/THF by using a cannula. The reac-
tion was then heated to 80 °C and stirred under nitrogen overnight.
The mixture was filtered to eliminate the ammonium salt and the
organic phase was ready for the next purification process.
Materials: The following materials were obtained from Aldrich and
used without further purification: hydroquinone, 1-bromo-
dodecane, copper(I) iodide, dichlorobis(triphenylphosphane)palla-
dium(II), tetrabutylammonium fluoride (TBAF; 1.0 m in THF), tri-
methylsilyl acetylene (TMSA) and NaH. CH2Cl2, CHCl3, meth-
anol, hexanes and toluene were purchased from Aldrich and Baker.
THF and triethylamine (Et3N) were distilled from KOH, and THF
then from sodium/benzophenone complex. Solvents used for the
optical characterization were spectroscopic grade from Aldrich.
General Procedure for Trimethylsilyl (TMS) Cleavage: A round-
bottomed flask was charged with the (trimethylsilyl)ethynyl com-
pound, THF, and two drops of water and stirred until total dissol-
ution of the compound. TBAF was added (0.2 equiv. per silyl
group, 1 m solution in THF) and the mixture was stirred at room
temperature for 30 min. The reaction was stopped by passing it
thought a plug of silica gel. After THF evaporation, the product
was dried in vacuo for 2 h and then used without further purifica-
tion.
1
Molecular Characterization: H and 13C NMR spectroscopic data
were obtained at room temperature with a JEOL (300 MHz) or a
BRUKER AVANCE III (500 MHz) spectrometer using CDCl3 as
solvent and internal reference. MALDI-TOF-MS was carried out
with a Waters/Micromass MALDI micro MX mass spectrometer
operated in reflection mode using α-cyano-4-hydroxycinnamic acid
as a matrix. Raman scattering spectra were obtained on powders
with an 830 nm diode Laser and a Renishaw system. Infrared spec-
tra were obtained with a Nicolet Magna 550 spectrophotometer
(FTIR) on KBr crystals.
Compounds 1–3, 5 and 6: Synthesized as reported in Ref.[8]
1,4-Bis{[2,5-bis(dodecanoxy)phenyl]buta-1,3-diyne} (4): Applying
the procedure for the homocoupling of acetylenes: In a flask con-
taining [(Ph3P)2PdCl2] (18.63 mg, 0.02655 mmol), CuI (6.07 mg,
0.032 mmol) and 1 (500 mg, 1.06 mmol) was added by using a can-
nula triethylamine (80 mL) and THF (8 mL). The mixture was
heated at 80 °C for 16 h. After filtering the ammonium salt and
removal of the solvent, the crude product was first precipitated in
methanol, purified by column chromatography (SiO2; hexanes–
CH2Cl2, 1:1; Rf = 0.7) and then by preparative gel permeation
chromatography column (Biorad; Bio-Beads SX1, toluene) to af-
ford, after solvent evaporation, 4 (95% yield) as a white powder;
m.p. 83–87 °C. 1H NMR (300 MHz, CDCl3): δ = 6.98 (d, J =
2.7 Hz, 2 H, Ar-Ho-ynes), 6.83 (dd, J1 = 9.0, J2 = 2.7 Hz, 2 H, Ar-
Hext), 6.78 (d, J = 9.0 Hz, 2 H, Ar-Hext), 3.97, 3.87 (2ϫt, J =
6.6 Hz, 8 H, CH2-α-O), 1.76 (m, 8 H, CH2-β-O), 1.45 (m, 8 H,
UV/Vis absorption spectra were measured with a Shimadzu
2401PC spectrophotometer. The emission spectra were recorded
with a Perkin–Elmer LS 50B spectrofluorimeter by exciting at
10 nm below the lower energy peak. Fluorescence quantum yields
in solution (φF) were determined by using a reported procedure[19]
and using quinine sulfate (0.1 m in H2SO4; φ = 0.54 at 347 nm)
as standard. The experiments were conducted by controlling the
temperature at 25.0Ϯ0.5 °C with a water circulating bath. Four
solutions with absorbance of lower than 0.1 at the excitation wave-
length were analyzed for each sample. Fluorescence lifetimes were
obtained at room temperature by the TCSPC technique with a
Horiba Jobin Yvon TemPro instrument with nanoLED excitation
at 370 nm for tetramer 8, hexamer 12 and octamer 15. For dimer
4, a nanoLED of 295 nm was used because this oligomer emits
near 370 nm. Fits were performed with DAS6 software available in
the instrument. Two-photon (2PA) spectra were measured at ambi-
ent conditions according to published methods.[20]
CH2-γ-O), 1.26 (br. s, 64 H, CH2), 0.87 (br. m, 2 H, CH3) ppm. 13
C
NMR (75 MHz, CDCl3): δ = 14.22 (CH3), 22.80 (CH2), 26.09 (C-
γ-O), 29.36 (C-β-O), 29.48 (CH2), 29.75 (CH2), 32.01 (CH2), 68.78
and 70.01 (C-α-O), 77.91, 78.76 (CϵC), 112.49, 114.17, 115.48,
117.66, 119.18 (Ar), 152.78, 153.39, 155.53 (ArC-O) ppm. UV/Vis
(CHCl3): λmax (ε, m–1 cm–1) = 350 nm (1.68ϫ104). MALDI-TOF:
m/z calcd. for C64H106O4 [M]·+ 938.8; found 938.6.
Theoretical Studies: Theoretical simulations were carried out on di-
mer 4 and tetramer 8, using the Gaussian 09 software.[21] To reduce
the computational time required, we investigated the phenyl ring
torsional barriers of the two model systems in the framework of
the molecular mechanics approach using the UFF force field.[22]
The geometry of the most stable conformers was then further opti-
mized at the B3LYP/6-311G** level. Electronic transitions were
computed by using the TD-B3LYP/6-311G** approach and taking
into account solvent effects with the polarizable continuum model
(PCM). Moreover, because the aliphatic tails should not make a
significant contribution to the electronic nature of the excitations
(at least for the lowest levels) they were replaced by a –OCH3
group.[23]
Dodecanoxy Mono Bromine Terminated Trimer 7: Applying the
procedure used for the cross-coupling of a bromo aryl with an
acetylene: In
0.0103 mmol), CuI (1.96 mg, 0.0103 mmol) and
a
flask containing [(Ph3P)2PdCl2] (7.25 mg,
(324 mg,
6
0.345 mmol) was added Et3N (100 mL) and THF (10 mL) under
nitrogen. The mixture was heated at 50 °C for 15 min and then
cooled to 0 °C. Compound 2 (224.48 mg, 0.345 mmol) in anhy-
drous and degassed Et3N (5 mL) was added by using a syringe. The
mixture was allowed to reach room temperature and stirred for
48 h. After filtering the ammonium salt and evaporating the sol-
vent, the crude product was purified first by precipitation in meth-
10
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Synthesis of 2,5-Bis(dodecanoxy)phenyleneethynylene-Butadiynes
anol, then by silica gel chromatography (hexanes–CHCl3, 2:1; Rf =
0.4) and finally passed through a preparative gel permeation
chromatography column (Biorad; Bio-Beads SX1, toluene) to af-
ford, after solvent evaporation, 7 (59% yield) as a yellow powder;
Compound 11: Applying the procedure for the cross-coupling of a
bromo aryl with an acetylene: In a flask containing [(Ph3P)2PdCl2]
(17 mg, 0.230 mmol), CuI (3 mg, 0.014 mmol) and 2 (601 mg,
0.923 mmol) was added triethylamine (100 mL) and THF (10 mL)
under nitrogen. The mixture was heated at 50 °C for 15 min, then
1
m.p. 76–80 °C. H NMR (500 MHz, CDCl3): δ = 7.09 (s, 1 H, Ar-
H), 7.02–6.99 (m, 4 H, Ar-H), 6.81 (s, 2 H, Ar-H), 4.04–3.95 (m, 10 (1300 mg, 0.923 mmol) in dry and degassed Et3N (5 mL) was
10 H, CH2-α-O), 3.90 (t, J = 6.4 Hz, 2 H, CH2-α-O), 1.98–1.70 (m, added by using a cannula. The mixture was allowed to react at
12 H, CH2-β-O), 1.49–1.38 (m, 12 H, CH2-γ-O), 1.38–1.15 (br. s,
80 °C for 16 h. After filtering the ammonium salt and evaporation
108 H, -CH2-; theoretical value 96 H), 0.90–0.76 (br. m, 20 H, CH3; of the solvent, the crude product was purified first by precipitation
theoretical value 18 H) ppm. 13C NMR (125.6 MHz, CDCl3): δ = in methanol, then by silica gel chromatography (hexanes–CHCl3,
14.15 (CH3), 22.74 (CH2), 25.99–26.07 (C-γ-O), 29.31 (C-β-O),
29.42–29.55 (CH2), 29.72–31.98 (CH2), 68.74–69.83 (C-α-O), 89.86,
90.74, 90.76, 91.66 (-CϵC-), 113.16, 113.26, 114.04, 114.08, 114.46,
114.75, 116.64, 117.43, 117.80, 118.35, 118.62 (Ar), 149.56, 152.95,
153.57, 154.07, 154.10 (ArC-O) ppm. UV/Vis (CHCl3): λmax (ε,
1:1; Rf = 0.4) and finally by preparative gel permeation chromatog-
raphy (Biorad; Bio-Beads SX1, toluene) to afford, after solvent
evaporation, 11 (46% yield) as a yellow powder; m.p. 84–87 °C. 1H
NMR (500 MHz, CDCl3): δ = 7.09 (br. s, 1 H, Ar-H), 7.02–6.98
(br. s, 6 H, Ar-H), 6.81(br. s, 2 H, Ar-H), 4.05–3.94 (m, 14 H, CH2-
α-O), 3.90 (t, J = 6.3 Hz, 2 H, CH2-α-O), 1.90–1.70 (m, 16 H, CH2-
β-O), 1.55–1.42 (m, 16 H, CH2-γ-O), 1.41–1.18 (br. s, 136 H,
CH2-; theoretical value is 128 H), 0.92–0.84 (br. m, 26 H, CH3;
theoretical value is 24 H) ppm. 13C NMR (125.6 MHz, CDCl3): δ
= 14.20 (CH3), 22.78 (CH2), 25.95–26.12 (CH2-γ-O), 29.35 (CH2-
β-O), 29.55–29.80 (CH2), 32.02 (CH2), 68.76, 69.76, 70.03, 70.08,
70.16 (CH2-α-O), 89.93, 90.76, 90.93, 91.45, 91.74 (-CϵC-), 113.13,
113.33, 114.15, 114.26, 114.46, 114.55, 114.76, 116.66, 117.38,
117.45, 117.81, 118.35, 118.65 (Ar), 149.58, 152.97, 153.60, 154.12
(ArC-O) ppm. UV/Vis (CHCl3): λmax (ε, m–1 cm–1) = 400 nm
(6.87ϫ104).
m
–1 cm–1) = 381 nm (5.86ϫ104).
Compound 8: Applying the procedure for the homocoupling of
acetylenes: In flask containing [(Ph3P)2PdCl2] (6 mg,
a
8.0ϫ10–3 mmol), CuI (2 mg (8.0ϫ10–3 mmol) and 6 (250 mg,
0.142 mmol) was added by using a cannula Et3N (40 mL) and THF
(4 mL). The mixture was heated at 80 °C for 16 h. After filtering
the ammonium salt and evaporation of the solvent, the crude prod-
uct was precipitated in methanol, purified by column chromatog-
raphy (SiO2; hexanes–CH2Cl2, 2:1; Rf = 0.3) and then by prepara-
tive gel permeation chromatography (Biorad; Bio-Beads SX1, tolu-
ene) to afford, after solvent evaporation, 8 (93% yield) as a yellow
powder; m.p. 83–85 °C. 1H NMR (300 MHz, CDCl3): δ = 7.00,
6.97 (2ϫs, 6 H, Ar-Ho-ynes), 6.81 (s, 4 H, Ar-Hext), 3.98, 3.89 (2ϫt,
J = 3 Hz, 16 H, CH2-α-O), 1.81 (br. m, 16 H, CH2-β-O), 1.47
(br. m, 16 H, CH2-γ-O), 1.23 (br. s, 128 H, CH2), 0.87 (br. m, 24
H, CH3) ppm. 13C NMR (75 MHz, CDCl3): δ = 14.19 (CH3), 22.78
(CH2), 26.09 (C-γ-O), 29.36 (C-β-O), 29.46 (CH2), 29.75 (CH2),
32.01 (CH2), 68.76, 69.82 and 70.05 (C-α-O), 79.30, 79.64
(DacCϵC), 89.73, 92.32 (ynesCϵC), 112.40, 113.91, 114.42,
115.80, 116.82, 117.19, 118.05, 118.62 (Ar), 152.94, 153.39, 154.13,
155.06 (ArC-O). UV/Vis (CHCl3): λmax (ε, m–1 cm–1) = 400 nm
(7.39ϫ104). MALDI-TOF: m/z calcd. for C128H210O8 [M]·+
1875.6; found 1875.7.
Compound 12: Applying the procedure for the homocoupling of
acetylenes: In
a
flask containing [(Ph3P)2PdCl2] (3 mg,
0.0036 mmol), CuI (1 mg, 0.004 mmol) and 10 (200 mg,
0.142 mmol) was added by using a cannula Et3N (25 mL) and THF
(2.5 mL). The mixture was heated at 80 °C for 16 h. After filtering
the ammonium salt and evaporation of the solvent, the crude prod-
uct was first precipitated in methanol, then purified by column
chromatography (SiO2; hexanes–CH2Cl2, 1.5:1; Rf = 0.4) and fi-
nally passed through a preparative gel permeation chromatography
column (Biorad; Bio-Beads SX1, toluene) to afford, after solvent
evaporation, 12 (87% yield) as a yellow powder; m.p. 108–112 °C.
1H NMR (300 MHz, CDCl3): δ = 7.01, 7.0, 6.99, 6.98 (4ϫs, 10 H,
Ar-Ho-ynes), 6.81 (s, 4 H, Ar-Hext), 3.99, 3.90 (2ϫt, J = 6.3 Hz, 24
H, CH2-α-O), 1.82 (br. m, 24 H, CH2-β-O), 1.46 (br. m, 24 H, CH2-
γ-O), 1.23 (br. s, 192 H, CH2), 0.86 (br. m, 36 H, CH3) ppm. 13C
NMR (75 MHz, CDCl3): δ = 14.18 (CH3), 22.77 (CH2), 26.09 (C-
γ-O), 29.26 (C-β-O), 29.45 (CH2), 29.75 (CH2), 32.01 (CH2), 68.77,
69.82 and 70.04 (C-α-O), 79.42, 79.69 (DacCϵC), 89.89, 91.28,
91.78, 92.38 (ynesCϵC), 112.60, 113.97, 114.09, 114.48, 114.92,
115.63, 116.71, 117.16, 117.26, 117.45, 118.01, 118.64 (Ar), 152.96,
153.40, 153.57, 153.66, 154.10, 155.08 (ArC-O) ppm. UV/Vis
(CHCl3): λmax (ε, m–1 cm–1) = 425 nm (11.6ϫ104). MALDI-TOF:
m/z calcd. for C192H314O12 [M]·+ 2812.4; found 2812.4.
Compound 9: Applying the procedure for the cross-coupling of a
bromo aryl with an acetylene: In a flask containing [(Ph3P)2PdCl2]
(4.2 mg, 0.006 mmol), CuI (1.5 mg, 0.0072 mmol) and 7 (350 mg,
0.239 mmol) was added triethylamine (50 mL) and THF (5 mL)
under nitrogen. The mixture was heated at 50 °C for 15 min, then
TMSA (0.12 mL, 0.72 mmol) was added by using a syringe. The
mixture was stirred and heated overnight at 80 °C. After filtering
off the ammonium salt and evaporating the solvent, the crude
product was purified by chromatography (SiO2; hexanes–CH2Cl2,
2:1; Rf = 0.4) to give, after solvent evaporation, 9 (63% yield) as a
1
yellow powder; m.p. 64–71 °C. H NMR (300 MHz, CDCl3): δ =
Compound 13: Applying the procedure for the cross-coupling of a
7.03–6.92 (br. s, 5 H, Ar-H), 6.81 (br. s, 2 H, Ar-H), 4.06–3.93 (m,
bromo aryl with an acetylene: In a flask containing [(Ph3P)2PdCl2]
12 H, CH2-α-O), 3.89 (t, J = 6.4 Hz, 2 H, CH2-α-O), 1.90–1.70 (m, (4 mg, 6.2114ϫ10–3 mmol), CuI (ca. 1 mg, 3.1057ϫ10–3 mmol)
12 H, CH2-β-O), 1.56–1.42 (m, 12 H, CH2-γ-O), 1.40–1.15 (br. s,
114 H, CH2-; theoretical value is 96 H), 0.92–0.83 (br. m, 19 H,
CH3; theoretical value is 18 H), 0.26 (s, 7.5 H, SiMe3; theoretical
value is 9 H) ppm. 13C NMR (75.4 MHz, CDCl3): δ = 0.06 (SiMe3),
and 11 (400 mg, 0.207 mmol), was added triethylamine (70 mL)
and THF (7 mL) under nitrogen. The mixture was heated at 50 °C
for 15 min, then TMSA (0.10 mL, 0.621 mmol) was added by using
a syringe. The mixture was stirred and heated overnight at 80 °C.
14.20 (CH3), 22.78 (CH2), 25.69–26.14 (CH2-γ-O), 29.46 (CH2-β- After filtering off the ammonium salt and evaporating the solvent,
O), 29.52–29.58 (CH2), 29.60–29.80 (CH2), 32.02 (CH2), 68.06, the crude product was purified by chromatography (SiO2; hexanes/
68.75, 69.51, 69.77, 70.02 (CH2-α-O), 89.90, 90.77, 91.33, 91.71, CH2Cl2, 1:1; Rf = 0.4) to give, after solvent evaporation, 13 (52%
100.09, 101.32 (-CϵC-), 113.68, 114.08, 114.45, 114.75, 116.66,
yield) as a yellow powder; m.p. 73–77 °C. 1H NMR (500 MHz,
CDCl3): δ = 7.04–6.98 (br. s, 5 H, Ar-H), 6.96 (br. s, 1 H, Ar-H),
117.08, 117.41, 117.55, 118.62 (Ar), 152.95, 153.40, 153.56, 154.08,
154.27 (ArC-O) ppm. UV/Vis (CHCl3): λmax (ε, m–1 cm–1) = 389 nm 6.95 (br. s, 1 H, Ar-H), 6.83 (br. s, 2 H, Ar-H), 4.06–3.96 (m, 14 H,
(3.90ϫ104).
CH2-α-O), 3.92 (t, J = 6.4 Hz, 2 H, CH2-α-O), 1.90–1.73 (m, 16 H,
Eur. J. Org. Chem. 0000, 0–0
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I. Moggio et al.
FULL PAPER
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CH2-β-O), 1.56–1.42 (m, 16 H, CH2-γ-O), 1.41–1.21 (br. s, 142 H,
CH2-; theoretical value is 128 H), 0.92–0.84 (br. m, 26 H, CH3;
theoretical value is 24 H), 0.28 (s, 7 H, SiMe3; theoretical value is 9
H) ppm. 13C NMR (125.6 MHz, CDCl3): δ = –0.02 (SiMe3), 14.10
(CH3), 22.69 (CH2), 25.94–26.12 (CH2-γ-O), 29.38 (CH2-β-O),
29.44–29.54 (CH2), 29.55–29.80 (CH2), 31.93 (CH2), 68.70, 69.47,
69.60–69.80, 69.98 (CH2-α-O), 89.85, 91.40, 91.61, 91.68, 100.03,
101.26 (-CϵC-), 113.71, 114.08, 114.12, 114.24, 114.44, 114.49,
114.69, 116.59, 117.08, 117.35, 117.41, 117.54, 118.58 (Ar), 152.90,
[3]
[4]
153.37, 153.53, 154.07, 154.03, 154.23 (ArC-O) ppm. UV/Vis [5]
(CHCl3): λmax (ε, m–1 cm–1) = 405 nm (10.217ϫ104).
[6]
Compound 15: Applying the procedure used for the homocoupling
of acetylenes: In
a flask containing [(Ph3P)2PdCl2] (2.0 mg,
0.0026 mmol), CuI (ca. 1.0 mg, 0.0031 mmol) and 14 (193 mg,
0.10271 mmol) was added by using a cannula, Et3N (25 mL) and
THF (2.5 mL). The mixture was heated at 80 °C for 16 h. After
filtering the ammonium salt and evaporation of the solvent, the
crude product was precipitated in methanol, purified by column
chromatography (SiO2; hexanes/CH2Cl2, 1.5:1; Rf = 0.3) and then
by preparative gel permeation chromatography (Biorad; Bio-Beads
SX1, toluene) to afford, after solvent evaporation, 15 (89% yield)
as a yellow powder; m.p. 124–127 °C. 1H NMR (300 MHz, CDCl3):
δ = 7.01–6.98 (4ϫbr. s, 14 H, Ar-Ho-ynes), 6.81 (s, 4 H, Ar-Hext),
4.02 (br. s, 16 H, CH2-α-O), 3.90 (t, J = 6.3 Hz, 16 H, CH2-α-O),
1.83 (br. m, 32 H, CH2-β-O), 1.50 (br. m, 32 H, CH2-γ-O), 1.24
(br. s, 256 H, CH2), 0.86 (br. m, 48 H, CH3) ppm. 13C NMR
(75 MHz, CDCl3): δ = 14.17 (CH3), 22.76 (CH2), 26.11 (C-γ-O),
29.27 (C-β-O), 29.46 (CH2), 29.76 (CH2), 32.01 (CH2), 68.78, 69.82
and 70.05 (C-α-O), 79.44, 79.70 (DacCϵC), 89.92, 91.44, 91.70,
91.83, 92.36 (ynesCϵC), 112.64, 114.15, 114.50, 114.72, 114.79,
115.61, 116.67, 117.18, 117.46, 118.02, 118.65 (Ar), 152.97, 153.43,
153.60, 153.67, 154.10, 155.09 (ArC-O). UV/Vis (CHCl3): λmax (ε,
[7]
[8]
[9]
[10]
[11]
[12]
[13]
m
–1 cm–1) = 435 nm (16.99ϫ104). MALDI-TOF: m/z calcd. for
C256H418O16 [M]·+ 3749.2; found 3748.8.
[14]
[15]
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Supporting Information (see footnote on the first page of this arti-
cle): DEPT-135, APT, 13C NMR spectra for the oligomers in
CDCl3; MALDI-TOF MS; Additional absorption and fluores-
cence spectra of tetramer 8 and TCSPC data for dimer 4, hexamer
12 and octamer 15 in chloroform.
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M. Drobizhev, Y. Stepanenko, A. Rebane, C. J. Wilson, T. E. O.
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Acknowledgments
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A. T. R. Williams, S. A. Winfield, J. N. Millar, Analyst 2003,
The authors wish to acknowledge the Mexican National Council
for Science and Technology (CONACYT) for financial support
through project 98513R and the United States Air Force Office for
Scientific Research (AFOSR) through grant FA9550-10-1-0173.
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12
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Date: 08-07-13 10:59:34
Pages: 13
Synthesis of 2,5-Bis(dodecanoxy)phenyleneethynylene-Butadiynes
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Received: February 12, 2013
Published Online: ᭿
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