Synthesis and optoelectronic properties of phenylenevinylenequinoline macromolecules

Article abstract of DOI:10.1039/c3nj01193c

A series of 3, 5 and 7 quinoline terminated arylenevinylene oligomers was selectively synthesized by applying two repetitive reactions at each cycle of oligomerization: a Wittig and Pd Heck cross-coupling. Oligomers were characterized by ¹H and homo-J-resolved, DEPT-135, APT, ¹³C NMR and MALDI-TOF spectrometry. A detailed characterization of the oligomers was performed by UV-Vis, static-dynamic fluorescence and Z-scan spectroscopy. The HOMO and LUMO levels were determined by cyclic voltammetry and compared with the theoretical ones. Effective conjugation is attained for the pentamer, whilst the molecular structure of the heptamer shows a pronounced torsion of the phenylenevinylene segment disrupting the degree of conjugation as revealed by theoretical simulation of the oligomer geometry. Furthermore, the theoretical simulation shows that the HOMO-LUMO frontier orbitals are mainly localized in the phenylenevinylene structure, while in the quinolines the spatial distribution is only located at the CN- group without any appreciable contribution of the adjacent phenyl group. The pentamer is the most fluorescent oligomer with a quantum yield in solution of = 0.62-0.68 depending on the solvent and a fluorescence lifetime of 1.07-1.28 ns, making this oligomer suitable for optoelectronic devices.

Full text of DOI:10.1039/c3nj01193c

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Synthesis and optoelectronic properties of
phenylenevinylenequinoline macromolecules†
Cite this: New J. Chem., 2014,
38, 974
Reyes Flores-Noria,a Rosa Vazquez,a Eduardo Arias,*a Ivana Moggio,a
´
Marlene Rodrıguez,a Ronald F. Ziolo,a Oliverio Rodrıguez,a Dean R. Evansb and
´
´
Carl Liebigbc
A series of 3, 5 and 7 quinoline terminated arylenevinylene oligomers was selectively synthesized by applying
two repetitive reactions at each cycle of oligomerization: a Wittig and Pd Heck cross-coupling. Oligomers
were characterized by 1H and homo-J-resolved, DEPT-135, APT, 13C NMR and MALDI-TOF spectrometry.
A detailed characterization of the oligomers was performed by UV-Vis, static-dynamic fluorescence and
Z-scan spectroscopy. The HOMO and LUMO levels were determined by cyclic voltammetry and compared
with the theoretical ones. Effective conjugation is attained for the pentamer, whilst the molecular structure of
the heptamer shows a pronounced torsion of the phenylenevinylene segment disrupting the degree of
conjugation as revealed by theoretical simulation of the oligomer geometry. Furthermore, the theoretical
simulation shows that the HOMO–LUMO frontier orbitals are mainly localized in the phenylenevinylene
structure, while in the quinolines the spatial distribution is only located at the CQN– group without any
appreciable contribution of the adjacent phenyl group. The pentamer is the most fluorescent oligomer
with a quantum yield in solution of f = 0.62–0.68 depending on the solvent and a fluorescence lifetime
of 1.07–1.28 ns, making this oligomer suitable for optoelectronic devices.
Received (in Porto Alegre, Brazil)
1st October 2013,
Accepted 25th November 2013
DOI: 10.1039/c3nj01193c
www.rsc.org/njc
shorter oligomers such as heptamers and pentamers. In quino-
line based oligomers for instance, it has been demonstrated
Introduction
The electron attracting character of the –CQN– group (A) of that even dimers exhibit efficient ICT. Whilst trimers, polymers
quinoline based materials1 generates a push–pull effect between or dendrimers may be used as active emitting layers in OLEDs,
an electron donor group (D), such as 2,5-di(alkoxy)benzene, their main application is as n-type materials for electrolumi-
through a p-conjugated connector (A–p–D–p–A) that in turn nescence (EL) efficiency enhancement layers in emitting poly-
provides efficient intramolecular charge transfer (ICT), which mers such as MEH-PPV.2–5 Because of our interest in obtaining
makes these materials suitable for linear, nonlinear optic (NLO) new materials with NLO and efficient ICT properties, we
and photovoltaic (PD) devices. Among the different architec- designed and synthesized odd numbered quinoline terminated
tures of quinoline based macromolecules, i.e., linear,2 asym- oligomers following the original idea of Wang,2 who found
metrical,3 polymer like4 or dendrimer,5 monodisperse excellent EL properties for similar trimers, in particular,
oligomers are of special interest as optoelectronic materials. for those bearing 2,5-di(methoxy)benzene as a donor and a
As such, they are models that help to understand the properties solubilizing group. In our design, we replaced the 2,5-di(methoxy)
of their polydisperse homologous polymers. Despite that, the group by 2,5-di(dodecanoxy) solubilizing chains and increased
synthesis of the monodisperse oligomers usually involves the phenylenevinylene segments in order to obtain a pentamer
numerous steps as well as a tedious purification workup. Their and a heptamer with both efficient ICT and emitting proper-
effective conjugation, however, is sometimes achieved with ties. However, we found minor optoelectronic differences
between the pentamer and the heptamer marked by
a
pronounced torsion of the conjugated chain that is dependent
on the oligomer’s length. In addition to our spectroscopic
and voltammetry study, theoretical calculations suggest that
quinoline as an electron acceptor (A) must be centered
as closest as possible to the electron donor (D) in order to
favor an ICT between D - A groups; a result that will be taken
into account for the design and synthesis of new n-type
a
´
´
Centro de Investigacion en Quımica Aplicada (CIQA), Boulevard Enrique Reyna
´
140, 25294 Saltillo, Mexico. E-mail: eduardo.arias@ciqa.edu.mx;
Fax: +52 844 438 98 39; Tel: +52 844 438 98 30
b Materials and Manufacturing Directorate, Air Force Research Laboratory,
3005 Hobson Way, Wright-Patterson Air Force base, OH, 45433, USA
c Azimuth Corporation, 4134 Linden Avenue, Suite 300, Dayton, OH, 45431, USA
† Electronic supplementary information (ESI) available: 1H, J-resolved 2D, APT,
DEPT-135, 13C NMR, UV-Vis spectra in solution, MALDI-TOF MS spectra and
molecular orbital simulations of selected oligomers. See DOI: 10.1039/c3nj01193c macromolecules.
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Results and discussion
Synthesis
solvents such as methanol, acetone and acetonitrile. Moreover,
7QPPV in its entirely (E) configuration is easily isolated from the
rest of the unreacted (Z) and (E,Z) mixtures of isomers, due to its
solubility only in hot CHCl3 or toluene; this behaviour made it
almost impossible to record its 13C NMR spectra; its molecular
structure was confirmed by MALDI-TOF spectrometry.
A central oligomer 3 was synthesized in order to grow oligomers in
odd number at each cycle, Scheme 1. By reacting one equivalent of
1 with 2 equivalents of 4-bromo styrene and using the modified
catalytic system reported in the literature, which in our case was
composed of Na(OAc2) (1.2 eq.), ꢀBr+NBu4 (0.2 eq.), POT (0.04 eq.)
and Pd(OAc2) (0.02 eq.) in DMF–Et3N (90/10 v/v), we could carry out
the reactions at 130 1C with bromoaryls, without promoting the
thermal decomposition of the catalyst and with a preferable all
E-isomer formation; 3 was obtained in 70% yield with a calculated
coupling constant of the vinylic protons of J = 16.5 Hz confirming
the AB system with an E isomerization.6
The oligomer synthesis consisted of applying the two repetitive
Wittig and Heck sets of reactions; the general pathway is depicted in
Scheme 2. The commercially available 2-quinolinecarboxaldehyde 4
is reacted with methyltriphenylphosphonium bromide under Wittig
conditions to give the 2-vinyl-quinoline 5 in 75% yields. Then 5 is
divided into three portions from which two equivalents of one
portion is reacted with one equivalent of 1,4-bis(dodecanoxy)-2,5-
diiodo-benzene 1 to afford the E-3QPV oligomer in 78% yields.
The other two equivalents of the second portion of 5 is reacted
with one equivalent of 3 to yield the E,E-5QPV oligomer in 60%
yield. The third portion of 5 undergoes a Heck cross-coupling
with commercial 4-bromobenzaldehyde 8 to yield an aldehyde
terminated 9, which after a Wittig reaction generates the double
bonds, 10 was obtained in 88% yield. The E,E,E-7QPPV oligomer
is obtained in 47% yield by reacting two equivalents of 10 with
one equivalent of 3. It is worth mentioning that E,E,E-7QPPV is
soluble either in CHCl3, toluene or THF and precipitates in polar
The oligomers are symmetrical, so the 1H NMR spectra
could be accurately assigned, however as the molecule became
longer, the aromatic region became more complex as the
quinoline protons overlapped with those of the phenylenes
and vinylenes, while the aliphatic region of all of the oligomers
is well resolved showing the –O–CH2- a, b and g signals at 4.06,
1.89 and 1.56 ppm. The signals of –CH2– and –CH3 are centred
at 1.25 and 0.68 ppm, respectively. Since the spectroscopic and
optoelectronic properties of the oligomers depend in large
measure on their cis or trans configurations, unambiguous
1
assignment of vinylenes was carried out by recording their H
J-resolved spectra (JRES). As an example the JRES spectrum of
the E,E-5QPV is presented in Fig. 1. Two-dimensional JRES NMR
spectroscopy retains many of the benefits of 1D NMR, but
additionally disperses the overlapping of those with high signal
density regions into a second dimension, reducing congestion
and making easier the assignment of some signal; however
couplings to long distances are also present. Notice, for example,
that HB and HD protons resonate in a very complex region, but
are easily assigned in the 2D spectrum. Due to characteristic
equalities in coupling constants of J 16.23 Hz for HA (at 7.42 ppm),
HB (at 7.68 ppm) and of J 16.09 Hz for HC (at 7.15 ppm) and HD
(at 7.53 ppm), the E,E isomer of 5QPV is so confirmed. In
addition, signals of the phenyl protons H9 and H10 are easily
recognised with corresponding coupling constants of 8.3 Hz
because of the AB system. Furthermore, positive matrix-assisted
laser desorption ionization-time of flight mass spectrometry
(MALDI-TOF-MS) corroborated the oligomers’ molecular structure
by showing their expected molecular ion peak:6 for 3QPPV:
+
m/z 752.4 (Mꢁ , calcd for C64H106O4: 752.5); for 5QPPV: m/z 956.58
(Mꢁ+, calcd for C128H210O8: 956.62) and for 7QPPV: m/z 1160.72
Scheme 1 Reagents and conditions: (a) Pd(OAc)2, ꢀBr+NBu4, CH3COONa,
POT, DMF, 130 1C, 48 h.
(Mꢁ+, calcd for C192H314O12: 1160.72).
Scheme 2 Reagents and conditions: (a) MTPP-Br, t-BuOK, THF, rt, 24 h; (b) Pd(OAc)2, CH3COONa, ꢀBr+NBu4, POT, DMF, 130 1C, 72 h.
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All of the optical properties of the materials studied in this work
are summarized in Tables 1 and 2, while the UV-Vis spectra of the
nQPV family and those of model trimers in chloroform are shown in
Fig. 2. From this figure, several absorption features depending on
the molecular structure can be observed: (i) the electron donor
character of the 2,5-bis(dodecanoxy) chains increases the conjuga-
tion by a wavelength shift from 337 nm (sh 354 nm) (lit7 354 nm) for
the DSB to 388 nm (lit8 388 nm) for the 3C12DSB and (ii) to 391 nm
for the additional contribution of the electron donor of the bromine
atoms in the trimer 3BrPV, (iii) electronic absorption spectra of the
trimers with 2,5-bis(dodecanoxy) chains are characterized by an
intense broad band and a higher energy absorption peak at around
235 nm. According to theoretical calculations, the red shifted band
can be associated with the electronic transitions from the HOMO to
the LUMO, while the higher energy absorption to those between
lower lying occupied molecular orbitals (HOMO{ꢀ1}, HOMO{ꢀ2})
to LUMO, (iv) this energy band (235 nm) is red shifted but less
intense by both the presence of the quinoline and as a function of
the oligomer length.
The three spectra of the nQPV present a main peak due to the
p–p* electronic transition of the conjugated backbone, between 418
and 433 nm, in the same range of those reported for other OPVs.9
Along with the conjugation, the molar absorption coefficient of the
maximum increases while its wavelength red shifts, even if the
increase between the 5QPV and the 7QPV is of only three nm,
suggesting that the effective conjugation length is already gained
with 5 units. This is more evident by the trend in the band gap,
which is practically identical between 5QPV and 7QPV. It is worth
noting that no changes in the spectra were observed with concen-
tration or the solvent polarity, excluding ground state electronic
interactions.6 The calculated half height band width (HHBW)
increases as the oligomer chain increases, being 74, 84 and
116 nm for the 3QPV, 5QPV and 7QPV, respectively, and
suggesting a larger number of conformers in the ground state
as the length of the molecule increases. It is worth noting that,
in particular, when spectra were obtained in spectroscopic grade
chloroform, a drastic change of both the shape and wavelength
towards the blue was observed and was time dependent. After
many analyses, we discovered that the time dependent blue shift
was due to bleaching produced by the amylene stabilizer contained
in spectroscopic grade chloroform; this can be avoided by distilling
the solvent and eliminating the amylene. The fluorescence spectra,
Fig. 3, exhibit a main peak with a shoulder at higher wavelength;
similarly to OPV excitonic emission features.9a The maximum in
chloroform shifts from 476 nm for the 3QPV to 497 nm for both
5QPV and 7QPV; a few nanometers of difference is observed in THF
Fig. 1 1H and J-resolved NMR spectra of 5QPV in CHCl3.
Optical properties
In order to study the effect of the quinoline on the optoelectronic
properties of the nQPV oligomers, three other trimers were
incorporated in the discussion; 1,4-di(E)-styrylbenzene (DSB), 1,4-bis-
(dodecanoxy)-2,5-di(E)styrylbenzene (3C12DSB) and 1,4-bis((E)-4-
bromostyryl)-2,5-bis(dodecyloxy)benzene (3BrPV), Chart 1.
Chart 1 Molecular structure of trimers used as comparatives models in
the different characterization techniques: (DSB) 1,4-di(E)-styrylbenzene,
(3C12DSB) 1,4-bis(dodecanoxy)-2,5-di(E)styrylbenzene and (3BrPV)
1,4-bis((E)-4-bromostyryl)-2,5-bis(dodecyloxy)benzene.
Table 1 Optical properties of the oligomers studied in this work in different solvents
CHCl3
THF
Toluene
ES10 lAbs
lAbs
e ꢂ 104
Eg
lEm
ES10 lAbs
e ꢂ 104
Eg
lEm
e ꢂ 104
Eg
lEm
ES10
Oligomer
(nm) (Mꢀ1 cmꢀ1
)
(eV) (nm) (eV) (nm) (Mꢀ1 cmꢀ1
)
(eV) (nm) (eV) (nm) (Mꢀ1 cmꢀ1
)
(eV) (nm) (eV)
3C12DSB
3BrPV (3)
3QPV (6)
5QPV (7)
388
391
418
431
3.2
3.7
2.7
7.9
9.0
2.80 440
2.76 447
2.59 476
2.48 499
2.44 497
2.93 389
2.89 393
2.71 417
2.65 431
2.59 433
3.2
3.7
3.6
7.6
8.8
2.82 437
2.75 451
2.62 470
2.50 491
2.46 496
2.94 388
2.88 392
2.74 418
2.63 430
2.60 434
3.1
3.4
2.4
7.5
9.1
2.81 438
2.75 447
2.61 469
2.50 494
2.46 494
2.93
2.88
2.74
2.67
2.60
7QPV (11) 433
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Table 2 Fluorescence quantum yield (f), lifetime (t), radiative (krad), non radiative (knr) rate constants and Stokes shifts (Dn) of the oligomers in different
solvents
CHCl3
THF
Toluene
t (ns) krad (nsꢀ1) knr (nsꢀ1) Dn (cmꢀ1) f t (ns) krad (nsꢀ1) knr (nsꢀ1) Dn (cmꢀ1
)
Oligomer
f
t (ns) krad (nsꢀ1) knr (nsꢀ1) Dn (cmꢀ1) f
3C12DSB 0.76 1.51 0.50
3BrPV (3) 0.27 1.26 0.21
3QPV (6) 0.60 1.46 0.41
5QPV (7) 0.64 1.28 0.50
7QPV (11) 0.50 1.15 0.43
0.16
0.58
0.27
0.28
0.43
3019
3204
2793
2578
2193
0.81 1.72 0.47
0.27 1.36 0.20
0.53 1.68 0.31
0.68 1.23 0.55
0.56 0.98 0.57
0.11
0.54
0.28
0.30
0.45
2857
3272
2704
2215
2555
0.90 1.51 0.59
0.32 1.24 0.26
0.57 1.50 0.38
0.62 1.07 0.58
0.59 0.81 0.73
0.06
0.45
0.29
0.35
0.51
2924
3164
2579
2841
2433
an aromatic to quinoid structure after excitation10 and they
decrease with the conjugation, suggesting lower losses for internal
conversion when passing from the 3QPV to the 7QPV. The HHBW
of the emission spectra is of 58, 55, and 57 nm for the 3QPV, 5QPV
and 7QPV, confirming that molecules are more planar in the
excited state than in the ground state. Despite that, the higher
fluorescence quantum yield (f) is obtained for 5QPV (Table 2). In
the particular case of the trimers, the highest quantum yield (0.76)
is obtained for the hydrogen terminated trimer 3C12DSB, while the
lowest (0.27) is for the 3BrPV. A similar behavior has been reported
for phenyleneethynylene11 type oligomers and attributed to the
fact that bromine is an heavy atom that favors the triplet state
formation, which actually can be seen from the lower radiative
(krad) constant of 0.21 nsꢀ1 with respect to the nonradiative rate
constants (knr) of 0.58 nsꢀ1, Table 2. However, when quinoline is
the terminal group, a slight quenching of the quantum yield
emission is observed. This effect could be ascribed to the CQN–
electron withdrawing group that can produce a pathway for excita-
tion state decay, which leads to a radiative constant greater than the
nonradiative constant for this material.
Time correlated single photon counting measurements
(TSCPC), Fig. 4, give a typical monoexponential decay for the
three oligomers with lifetime t decreasing from 3QPV to 7QPV.
From f and t data, the radiative (krad) and nonradiative rate
constants (knr) are calculated; with the exception of 5QPV in
chloroform, krad increases with the conjugation according to
the Strickler–Berg expression.12 The trend of the lifetime with n
is mostly due to the corresponding increment of knr that is
related to internal conversion and intersystem crossing. As
previously observed, the losses due to internal conversion given
by the Stokes shift go in the opposite way and is lower for 7QPV.
Fig. 2 UV-Vis spectra and their corresponding molecular structure of the
different oligomers studied in this work in chloroform.
and toluene. As for the optical band gap, this is more evident from
the decrease of the first excited state energy, confirming that the
effective conjugation length is already attained for the 5QPV,
Table 1. The excitation and absorption spectra are practically
coincident; the Fig. 3 inset shows that of the 5QPV in chloroform
as an example. Moreover, it was found that the emission spectra are
not affected by the excitation wavelength.6 These two latter results
indicate that there is only one emitting state. The Stokes shift (Dn)
values are consistent with molecules that undergo a change from
Fig. 3 Fluorescence spectra of: dash dotted line 3C12DSB, dashed line
3QPV, solid line 5QPV, and short dotted line 7QPV. Inset: absorption (solid
line) and excitation (dash-dotted line) spectra of 7QPV in chloroform.
Fig. 4 TCSPC data for: ( ) 7QPV, (n) 5QPV, (J) 3QPV and (’) 3C12DSB
oligomers in toluene.
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Thus, the major nonradiative decay pathway is expected to be peak in the voltammograms of a conjugated molecule can be
intersystem crossing.
ascribed to the formation of polarons and bipolarons, or to the
separate contribution of the different functional groups of
the molecule,14 such as in this case, where the PV and the
2,5-bis(dodecanoxy) are electron donating groups, while quino-
lines are electron deficient groups. The oxidation potential of
3QPV is higher (+1.53 V) than that of trimers without quino-
lines, such as DSB (+0.96 V), 3C12DSB (+1.16 V) and 3BrPV
(+1.29 V). However, the reduction potential of 3QPV is much
lower (ꢀ1.62 V) than that of the references; DSB (ꢀ2.42 V),
3C12DSB (ꢀ2.35 V) and 3BrPV (ꢀ1.91 V). Certainly, the intro-
duction of quinolines into the p-conjugated structure promotes
sites for the reduction process, mainly because of the unbonded
pairs of electrons of the nitrogen, in accordance with the reported
work by Wang,2 who found similar values for both sides of quinoline
substituted trimers with 2,5-bis(methoxy) or phenyl or thiophenyl as
central aryls. Actually, the redox potentials of such trimers in DCM at
the onset are Eox (irreversible) between +1.16 and +1.39 V, while Ered
are between ꢀ1.35 and ꢀ1.57 V, with these results being consistent
with those found for trimer 3QPV. However, as the phenylene-
vinylene conjugated chain increases to 5QPV and 7QPV, the
maximal oxidation potential becomes similar for both oligo-
mers: Eox +1.17 V (quasi-reversible), but the reduction potentials
increase, the longer the oligomer chain length is. This tendency
is also consistent with the calculated electrochemical bands that
are actually close to those calculated from absorption spectra
gap (Eg) of 2.95, 2.79 and 2.77 eV for the 3QPV, 5QPV and 7QPV,
respectively, and that is related to the more extended p-electron
delocalization. It appears that the 5QPV and 7QPV behave more
as OPV materials and that the influence of the quinolines is
minimal; the quinoline effect is only reflected in shorter mole-
cules as the trimers of ref. 2 and 3QPV.
Cyclic voltammetry
Fig. 5 shows the first cycle of the voltammograms for each oligomer
and Table 3 summarizes all the calculated electrochemical
parameters. On the first anodic scan, two maxima oxidation
peaks: E1ox +1.53 V (irreversible) and Eo2x +2.03 V (quasi-reversible),
are observed for 3QPV, while in the cathodic scan two reduction
peaks at E1red ꢀ1.62 V (irreversible) and at Er2ed ꢀ2.10 V (quasi-
reversible) are also observed. The oxidation–reduction peaks are
related to the loss of two electrons, but the irreversibility
suggests that the resulting radical cations–anions are not
electrochemically stable. In other words and according to the
literature,13 the presence of more than one oxidative/reductive
Theoretical calculations
AM1 and DFT optimization. In order to better understand
the optical and electrochemical properties of the oligomers
and, in particular, to have a clearer idea of why the effective
conjugation of the series is attained with 5QPV, theoretical
simulations were performed first on the trimers and then on
the nQPV series. In this respect, we considered an all trans
configuration for all the oligomers as was confirmed by NMR.
After the DFT geometry optimization calculation, the trimer
that shows a completely planar geometry is the DSB model,
where all the atomic coordinates displayed a 0 Å value in Z-axis,
meaning that all the atoms are positioned on the X,Y plane
imparting an extended p-conjugation for this molecule.
Fig. 5 Voltammograms of nQPV series in 0.1 M of Bu4NPF6 in acetonitrile
at a scan rate of 50 mV sꢀ1
.
Table 3 Electrochemical properties of oligomers studied in this work (0.5 mmol) in CH2Cl2 solution, 0.1 M Bu4NPF6, at a scan rate of 50 mV sꢀ1
,
(V vs. Ag/AgCl)
onset
ox
max
ox
onset
red
max
red
1/2
ox
1/2
Oligomer
E
(V)
E
(V)
E
(V)
E
(V)
E
(V)
E (V)
red
HOMO1/2 (eV)
LUMO1/2 (eV)
Eg (eV)
DSB
0.63
0.98
1.11
1.38
1.05
0.90
0.96
1.16
1.29
1.53
1.17
1.17
ꢀ1.90
ꢀ1.95
ꢀ1.73
ꢀ1.37
ꢀ1.60
ꢀ1.66
ꢀ2.42
ꢀ2.35
ꢀ1.91
ꢀ1.62
ꢀ1.77
ꢀ1.80
0.80
1.07
1.20
1.46
1.11
1.04
ꢀ2.16
ꢀ2.15
ꢀ1.82
ꢀ1.49
ꢀ1.69
ꢀ1.73
ꢀ5.09
ꢀ5.36
ꢀ5.49
ꢀ5.75
ꢀ5.40
ꢀ5.33
ꢀ2.13
ꢀ2.14
ꢀ2.47
ꢀ2.80
ꢀ2.61
ꢀ2.56
2.96
3.22
3.02
2.95
2.79
2.77
3C12DSB
3BrPV (3)
3QPV (6)
5QPV (7)
7QPV (11)
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Fig. 6 Minimum energy (optimized) structure of nQPV series by DFT/6-311+G(d,p).
In contrast, both 3C12DSB and 3BrPV trimers show that, while phenylenevinylenes II and IV form an angle of 391 with respect
the 2,5-di(alkoxy) chains are in the same plane as that of to 2,5-di(alkoxy)benzene I, while this angle is of 44.61 between
the benzenoide, and upon increasing the conjugation by the the vinylenequinolines III and V with respect to I. Interestingly,
electron donor character of the two oxygens, a dihedral angle of 7QPV is a totally twisted structure with a pronounced dihedral
27.51 and 27.671, respectively, is formed. This angle is specifi- angle of 631 between quinolines IV and VII with respect to I. The
cally formed between planes I (central di(alkoxy)benzene) and II torsion is even more evident in Fig. 7 where the electrostatic
and I and III, while that of II and III is of 01.6 Interestingly, the potential is shown. The lack of planarity between the phenyl rings
dihedral angle displayed by 3QPV is reduced to only 4.01, Fig. 6. adjacent to the quinoline and those of the dialkoxy benzene I, as
According to Wang,2 who succeeded in obtaining single crystals evidenced by the dihedral angles, explains the enormous influence
of trimers related to 3QPV but without dialkoxy chains, the that makes changes to the p-conjugation, and thus, to the
molecule is co-planar: (i) because of the p–p interactions that electronic properties of this oligomer as determined by
promote the formation of ‘‘bricks’’ of molecules, and (ii) because UV-Vis and fluorescence spectroscopy.
the nitrogen of the quinoline in 1-position that is out of the
The molecular electrostatic potential (MEP). MEP predicted for
brick, interacts with the hydrogen in 8-position of the quinoline the trimers6 and the nQPV series is shown in Fig. 7. In particular,
intermolecularly, which means with another brick of molecules. the DSB trimer shows an homogeneous electron distribution map
In contrast, 5QPV is a rather twisted structure, since the all along the phenylenevinylene chain, while 3C12DSB and 3BrPV
Fig. 7 Molecular electrostatic potential (MEP) in gas phase of 3QPV, 5QPV and 7QPV oligomers.
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Fig. 8 Frontier molecular orbitals; spatial distribution for the HOMO{ꢀ1} - LUMO and HOMO - LUMO energy levels for the nQPV series obtained at
the B3LYP/6-31G(d) level.
trimers show in addition negative regions in red color because the oxygens unshared electron pairs. This behavior is also
of the oxygen unbounded pairs of electrons. Furthermore, in the observed for the 3QPV, where orbitals are located at the
nQPV series, it can be seen that both the oxygen of the dialkoxy 2,5-bis(dodecanoxy)benzene, however, for 5QPV and 7QPV the
chain as well as the nitrogen of the quinolines are surrounded by HOMO{ꢀ1} - LUMO orbitals are rather localized at the phenyl-
a great surface of negative charge, which can represent sites that enevinylene segments, which could explain why the theoretical
are susceptible to redox potentials; in contrast, low electron values decrease in energy from 0.88 to 0.5 and 0.29 eV for the
density is located around hydrogen bonds. The determined 3QPV, 5QPV and 7QPV, respectively; that differs in magnitude
MEP values for DSB, 3C12DSB, 3BrPV, 3QPV, 5QPV and 7QPV but not in trend to the experimental values of 0.64, 0.52 and
are ꢀ80.8, ꢀ137.2, ꢀ126.14, ꢀ179.1, ꢀ160.6 and ꢀ160.2 kJ molꢀ1
,
0.46 eV, respectively, because of the more delocalized orbitals to
respectively. Notice (i) that the less negative values are for the the phenylenevinylene segments; this difference is not as
quinoline terminated oligomers, in particular for 3QPV followed marked between 5QPV and 7QPV. In general, it can be seen that
by 5QPV that is almost the same as that of the 7QPV, and (ii) these the HOMO orbitals are localized mainly in the donor group of all
values have the same trend to those found in the reduction compounds, except in the case of 3QPV where it is distributed in
potentials, where the 3QPV can be more easily reduced than the the 2,5-di(alkoxy) benzene-vinylene segment, whilst in both
5QPV and 7QPV. This could likely be associated to the fact that 5QPV and 7QPV, the HOMO orbitals are distributed all along
those groups that promote the push–pull effect (A–D–A) are closer the central phenylenevinylene segment, which in the case of
in 3QPV, than for those in the other two oligomers that are 7QPV, the two external aryls on both sides of the quinoline do
separated by the p electron connectors (A–p–D–p–A) and that not show any spatial distribution. On the other hand, the LUMO
actually behave more like OPV materials.
orbitals are distributed all along the conjugated chain up to the
Molecular orbitals. HOMO and LUMO energy conformations nitrogen of the quinoline for 3QPV and 5QPV, but particularly,
are depicted in Fig. 8 for the nQPV series. Sudeep et al.15 found that the distribution is not homogenous for 7QPV, which is located in
the high energy peak observed by UV-Vis for 2,5-di(alkoxy)phenylene- the five phenylenevinylene segments without participation of the
ethynylene oligomers is generated by the HOMO{ꢀ1} - LUMO quinoline. It is worth noting that in the three cases, the aryls of
transitions, because the 2,5-di(alkoxy) groups modify the central the quinolines do not play an important electronic distribution,
arene-ring’s p-orbital through the resonance interaction with just the nitrogen. The theoretical HOMO–LUMO gap of 3.09, 2.84
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Table 4 Measured values of the nonlinear absorption coefficient b and
the two photon absorption cross-section s for the nQPV series. These
values are used as a relative comparison between samples
Concentration
(M)
s (cm4 ꢂ s per photon ꢂ
Oligomer
b (CM/GW)
molecule)
3QPV (6)
5QPV (7)
2.2 ꢂ 10ꢀ2
7QPV (11) 1.1 ꢂ 10ꢀ4
0.18 ꢃ 0.06 2.48 ꢃ 0.8 ꢂ 10ꢀ48
0.40 ꢃ 0.05 5.68 ꢃ 0.7 ꢂ 10ꢀ48
0.14 ꢃ 0.02 4.04 ꢃ 0.7 ꢂ 10ꢀ46
2.2 ꢂ 10ꢀ2
family with respect to other phenylenevinylenes, in which there
is a two photon absorption resonance contribution.17
Fig. 9 Experimental and fit Z-Scan data for 5QPV at a concentration of
2.2 ꢂ 10ꢀ2 M and a laser intensity of 228 MW cmꢀ2. For this measurement a Conclusions
value of 0.39 cm GWꢀ1 was extracted for b from the fit data. An average
1
value of 0.40 ꢃ 0.05 cm GWꢀ1 was extracted for measurements made at The H J-resolved (JRES) 2D NMR spectroscopy is a method to
several intensities.
unambiguously identify the E isomer in OPV type oligomers that
usually present a high signal density in the aromatic-vinyl region.
Our investigation of OPV oligomers bearing quinolines at both
extremities disclosed that: (1) effective conjugation is attained with
the 5QPV as was demonstrated by UV-Vis and fluorescence spectro-
scopies, (2) 7QPV is not more conjugated than 5QPV because the
largeness of the molecule leads to torsion of the phenylenevinylene
structure, reducing the degree of conjugation as was determined by
theoretical calculations, (3) a possible push–pull effect is clear only
for the trimer 3QPV, where the 2,5-di(dodecanoxy) donor groups are
and 2.9 eV is very consistent with those found electrochemi-
cally, 2.95, 2.79 and 2.77 eV, for the series, which decreases as a
function of the oligomer’s length, due to the p-extended con-
jugation up to the effective conjugation attained with the 5QPV.
Z scan measurements. The Z-scan was utilized to investigate
the nonlinear parameters in the nQPV series. As a representa-
tive measurement, Fig. 9 shows that of 5QPV with the fit used to
extract the nonlinear absorption coefficient. An average of the
close to the quinoline electron deficient groups, while for 5QPV and
measured values b and s for the nQPV series is shown in
7QPV no considerable effect of the quinolines was observed either
Table 4. These values have been extracted from the Z-scan
spectroscopically, electrochemically or theoretically, (4) the HOMO
measurements assuming both a Gaussian pulse width and
spatial profile. It is to be pointed out that the excitation
wavelength was chosen to be 1064 nm, instead of 532 nm, in
order to avoid the linear absorption contribution that could be
important in particular for 7QPV. The ns laser pulse can induce
nonlinear optical and thermal effects, which are not distinguish-
able from one another in the ns regime. However, as no
orbitals are localized mainly in the 2,5-di(dodecanoxy)benzene donor
group of the trimer 3QPV, but in the three central phenylenevinylene
groups of the 5QPV and 7QPV oligomers, while the LUMO orbitals
are distributed all along the conjugated chain up to the nitrogen of
the quinoline.
significant difference was observed in the nonlinear properties
Experimental section
over an intensity range of 0.77 to 2.77 MW cmꢀ2, we can assume
General
that free carrier and thermal effects are minimal.
The following chemical reagents: 4-bromobenzaldehyde, 2-quino-
linecarboxaldehyde, methyltriphenylphosphonium bromide
(MTPP-Br), potassium tert-butoxide (t-BuOK), palladium(II)
acetate, tri-o-tolylphospine (POT), anhydrous sodium acetate, and
tetrabutylammonium bromide (ꢀBr+NBu4) were purchased from
Aldrich and used without further purification. Electrochemical
grade tetrabutylammonium hexafluorophosphate (Bu4NPF6) was
purchased from Fluka. DMF, CHCl3, CH2Cl2 and hexanes were
purchased from J. T. Backer. Triethylamine (Et3N) (Aldrich) was
distilled from KOH, THF was first distilled from KOH and then
from sodium benzophenone until a typical blue complex was
formed. Acetonitrile was passed through a plug of silica gel and
then distilled from NaH. All solvents used for optical characteriza-
tion were of spectroscopic grade and obtained from Aldrich.
It can be seen that s increases with an increased conjugation
length of the molecules. This behavior has been observed in other
molecular systems, and has been attributed to an increased dipole
moment that typically accompanies the increased conjugation
length.16 Despite the fact that the concentration of 7QPV is less
than that of the other two molecular systems studied, the value of
s can be compared, as it should be independent of the concen-
tration (this is not the case for comparing the values of b). The
measured two-photon absorption cross-section for 7QPV is
expected to be significantly larger than that for 3QPV and 5QPV
due to its increased conjugation length and the corresponding
shift in the linear absorption shown in Fig. 2. In fact, due to the
red-shifted linear absorption spectrum of 7QPV, compared to the
spectra of the other molecules, the two-photon absorption for
1064 nm light is in resonance with the HOMO–LUMO transition,
whereas in the case of 3QPV and 5QPV absorption at 1064 nm is
Theoretical studies
towards the lower energy side of the resonance. This could also All calculations were performed using the Spartan10 and Gaussian
explain the difference in the value range measured for this 09W programs. Lateral propoxy chains were used in place of the
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dodecanoxy chains in order to shorten the computational time; This method was utilized to investigate these nonlinear para-
this approximation is usually accepted.15 Optimization of meters in the nQPV molecule series using a q-switched YAG:Nd
the geometry of the structures was carried out by AM1 semi- laser with a pulse width of 15 ns (at 1064 nm). For 3QPV and
empirical calculations. The coordinates thus obtained were 5QPV in THF a concentration of 2.2 ꢂ 10ꢀ2 M is used. For 7QPV,
further optimized through density functional theory (DFT) the concentration was 1.08 ꢂ 10ꢀ4 M due to the saturation limit
calculations at the restricted B3LYP (Becke 3-parameters Lee– of the solvent; therefore, a comparison with the other molecular
Yang–Parr exchange correlation function) level with a 6-31G(d) systems cannot be directly made. The sample length was 1 cm;
mixed basis set.
this path length was chosen in order to obtain a detectable signal
in the weakest sample of the three samples (3QPV). For each
material, the nonlinear absorption is measured at several input
Equipment
1H (300 MHz), Homo-J-Resolved, DEPT-135, APT, and 13C NMR intensities between 0.77 to 2.77 MW cmꢀ2
.
(75.4 MHz) spectra were recorded at room temperature on a Jeol
Eclipse spectrometer using CDCl3 as solvent and internal
Synthesis
reference. FAB+ mass spectra were recorded on a JEOL JMS
1,4-Bis((E)-4-bromostyryl)-2,5-bis(dodecyloxy) benzene 3 (3BrPV).
AX505 HA instrument. Optical properties were studied in A mixture of 1,4-bis(dodecanoxy)-2,5-diiodo-benzene 1 (1000 mg,
spectroscopic grade THF, toluene and chloroform (Aldrich). 14.32 ꢂ 10ꢀ2 mmol), Pd(OAc2) (32 mg, 0.14 mmol), anhydrous
UV-Vis spectra were recorded on a Shimadzu 2401PC and on an sodium acetate (352 mg, 4.29 mmol) and ꢀBr+NBu4 (461 mg,
Agilent 8453 spectrophotometer in the 200–1100 nm range. 1.43 mmol) were placed in a two neck round bottom flask.
Band gaps (Eg) were obtained at the onset of the normalized Then, 20 mL of degassed Et3N were added via a cannula, stirred
UV-Vis spectra (absorbance of 0.1). Static fluorescence studies and heated for 1 h. Later, 4-bromostyrene 2 (524 mg, 2.86 mmol)
were performed on a Perkin Elmer LS50B spectrometer. dissolved in 80 mL of DMF (previously bubbled with nitrogen
Emission spectra were obtained by exciting at 10 nm before for 15 min) was added dropwise (very important) and heated at
the maximum absorption spectra, while excitation spectra were 130 1C for 72 h. After removing the solvents, the crude product
obtained by fixing the maximum emission wavelength. Fluores- was washed with a solution of H2O–NaHCO3, then the organic
cence quantum yield was obtained according to ref. 18 and by phase was extracted with CHCl3 and the solvent evaporated. The
using quinine sulfate in 0.1 M H2SO4 as standard. Measure- crude product was taken up in 3 mL of CHCl3 and precipitated
ments were performed by controlling the temperature at 25.0 ꢃ twice in methanol. The resulting product was purified: (1) in a SiO2
0.3 1C using a water circulating bath. Values were averaged column first using hexane to eliminate the remaining 1 and then by
from four samples. The first excited state energy (ES10) was a mixture of hexane:CH2Cl2 (3 : 1 v/v, Rf = 0.4) and (2) by pre-
calculated from the wavelength at which the normalized absor- parative GPC chromatography (Biorads, Bio-beds SX1, toluene) to
bance and fluorescence spectra cross. Lifetime t was obtained afford a yellow fluorescent powder in 70% yield. m.p. = 95–105 1C.
by a single photon counting technique (10 000 counts) in a 1H NMR (CDCl3, 300 MHz): d(ppm) 7.46(d, 4H, J = 8.35 Hz, Ar–H1),
Horiba TemPro instrument at 370 nm NanoLED excitation 7.44(d, 2H, J = 16.51 Hz, QCH4), 7.37(d, 4H, J = 8.80 Hz, Ar–H2),
(1 MHz repetition rate) and by using a 0.01% ultrapure water 7.08(s, 2H, Ar–H5), 7.05(d, 2H, J = 16.51 Hz, QCH3), 4.03(t, 4H,
dispersion of Ludox AS40 (Aldrich) for the prompt signal. The J = 6.46 Hz, CH2–a–O), 1.85(m, 4H, CH2–b–O), 1.52(m, 4H,
electrochemical properties of oligomers were investigated by CH2–g–O), 1.25(br s, 32H,–CH2–), 0.87(t, 6H, CH3). 13C NMR (CDCl3,
cyclic voltammetry in a C3 cell stand from Basi coupled to a 75 MHz): d(ppm) 151.22, 136.98, 131.84, 128.05, 127.74, 126.82,
potentiostat/galvanostat ACM Gill AC. All the experiments were 124.29, 121.19, 110.73, 69.62, 32.02, 29.77, 29.55, 29.47, 26.38, 22.79,
performed at room temperature in acetonitrile containing 14.23. UV-Vis (CHCl3); lmax (330 nm) e (5.11 ꢂ 104 Mꢀ1 cmꢀ1),
Bu4NPF6 (0.1 M) as the supporting electrolyte, glassy carbon (394 nm) e (6.75 ꢂ 104 Mꢀ1 cmꢀ1).
as a working electrode (GCE), Pt wire electrode as the counter
2-Vinyl-quinoline 5. A mixture of 2-quinolinecarboxaldehyde
electrode, Ag/AgCl electrode as the reference electrode and 4 (1 g, 6.36 mmol) and methyltriphenylphosphonium bromide
ferrocene/ferrocenium (FOC) as internal reference (Eox = 5.1 V, (2.5 g, 6.97 mmol) in dry THF (40 mL) was stirred at 0 1C for 15
Ered = 3.05 V); value of ꢀ4.8 eV below the vacuum level. The min under Ar. Then, t-BuOK (0.78 g, 6.97 mmol) was added in
experiments were carried out under a nitrogen atmosphere at a portions and the reaction was stirred at room temperature for
scanning rate of 50 mV sꢀ1 between ꢀ3.0 and +3.0 V. In all the 24 h. After this time, 50 mL of water was added and the organic
experiments a redox signal was detected at Bꢀ0.8 V, which was layer extracted twice with CH2Cl2. The combined organic layers
assigned to the electrolyte solution. The molecular orbital ener- were washed twice with water, dried over anhydrous Na2SO4
gies HOMO and LUMO were calculated from the first oxidation and the solvent evaporated under vacuum. The resulting crude
(Eox) and reduction (Ered) potentials using the relationship:19 product was purified using a neutral alumina chromatographic
EHOMO[LUMO] = [ꢀexp(E1/2(Ox[red]vs.Ag/AgCl) ꢀ Eonset(FOCvs.Ag/AgCl))] ꢀ column using hexane as eluent to obtain a yellow oil in 75%
4.8. In our electrochemical experiments, ferrocene exhibited an yield. 1H NMR (CDCl3, 300 MHz): d(ppm) 8.06(dd, 1H,
(E) oxidation potential of 0.51 V. The electrochemical energy J = 9.08 Hz, QnH8), 8.03(dd, 1H, J = 8.80 Hz, QnH5), 7.71(d,
gap (Eg) was the difference between LUMO–HOMO. The open 1H, J = 7.98 Hz, QnH4), 7.65(t, 1H, J = 6.80 Hz, QnH7),
aperture Z-scan can be used to measure the nonlinear absorp- 7.54(d, 1H, J = 8.53 Hz, QnH3), 7.44(t, 1H, J = 7.153 Hz, QnH6),
tion coefficient and two-photon absorption cross-section.17 7.00(q, 1H, QC–HC), 6.23(d, 1H, J = 17.61 Hz, QC–HB),
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5.62(d, 1H, J = 10.73 Hz, QC–HA). 13C NMR (CDCl3, 75 MHz): 8 (2 g, 10.88 mmol), Pd(OAc2) (7.27 mg, 0.324 mmol), and POT
d(ppm) 156.52, 146.21, 136.54, 132.80, 130.11, 128.92, 127.91, (664 mg, 0.54 mmol) in Et3N : THF (56 : 14 mL) was stirred under Ar
126.82, 120.0, 118.73.
at reflux for 48 h. After cooling, the resulting mixture was filtered and
2,20-(1E,10E)-2,20-(2,5-Bis(dodecanoxy)-1,4-phenylene)bis(ethene- the solvent evaporated. The residue was taken up in CHCl3 (150 mL).
2,1-diyl)bisquinoline 6 (3QPV). A mixture of 5 (50 mg, 0.322 mmol), The organic layer was washed with water (100 mL), dried with
1,4-bis(dodecanoxy)-2,5-diiodo-benzene 1 (110 mg, 0.161 mmol), Na2SO4, filtered, and evaporated to dryness. The resulting residue
Pd(OAc2) (3 mg, 0.0135 mmol), and POT (7 mg, 0.023 mmol) in was purified by column chromatography by using neutral alumina
Et3N : DMF (80 : 20 mL) was stirred under Ar at reflux for 72 h. and hexane–CH2Cl2 (1/1 v/v, Rf = 0.3) as an eluent to obtain a pale
After cooling, the resulting mixture was filtered and the solvent yellow powder in 76% yield. m.p. = 108–112 1C. 1H NMR (CDCl3, 300
evapored. The orange residue was taken up in CHCl3 (100 mL). MHz): d(ppm) 10.0(s, 1H, CHO), 8.13(dd, 1H, J = 8.5 Hz, QnH8),
The organic layer was washed with water (100 mL), dried with 8.07(dd, 1H, J = 8.5 Hz, QnH5), 7.87(d, 1H, J = 8.5 Hz, Ar–H10),
Na2SO4, filtered, and evaporated to dryness. The resulting 7.86(d, 1H, J = 6.05 Hz, QnH4), 7.76(dt, 2H, J = 8.25 Hz, QnH7, H6),
residue was purified by column chromatography by using 7.72(d, 1H, J = 16.23 Hz, –CQCHB), 7.64(d, 1H, J = 8.5 Hz, Ar–H9),
neutral alumina and hexane–CHCl3 (8 : 2 v/v) as eluent to afford 7.52(d, 1H, J = 7.15 Hz, QnH3), 7.51(d, 1H, J = 16.23 Hz, –CQCHA).
an orange powder in 78% yield. m.p. = 87–90 1C. 1H NMR 13C NMR (CDCl3, 75 MHz): d(ppm) 191.67, 155.12, 148.28,
(CDCl3, 300 MHz): d(ppm). 8.05(d, 2H, J = 8.53 Hz, QnH8), 142.52, 136.69, 136.04, 132.92, 132.15, 130.30, 130.06, 129.37,
8.004(d, 2H, J = 16.5 Hz, –CQHB), 7.75(2d, 4H, QnH5, H4), 127.73, 127.66, 126.71, 119.67. UV-Vis (CHCl3); lmax (295 nm) e
7.68(2t, 4H, J = 8.25 Hz, QnH7, H6), 7.49(d,2H, J = 8.25 Hz, (1.73 ꢂ 104 Mꢀ1 cmꢀ1), (344 nm) e (3.04 ꢂ 104 Mꢀ1 cmꢀ1
)
QnH3), 7.46(d, 2H, J = 16.23 Hz, –CQHA), 7.29(s, 2H, Ar–H), (356 nm) e (2.94 ꢂ 104 Mꢀ1 cmꢀ1).
4.06(t, 4H, J = 6.60 Hz, CH2–a–O), 1.90(q, 4H, J = 6.88 Hz,
(E)-2-(4-Vinylstyryl)quinoline 10. A mixture of 9 (1 g, 3.86 mmol)
CH2–b–O), 1.56(q, 4H, CH2–g–O), 1.24(br s, 32H,–CH2–), and methyltriphenylphosphonium bromide (1.6 g, 4.26 mmol)
0.86(t, 6H, CH3). 13C NMR (CDCl3, 75 MHz): d(ppm) 156.73, in dry THF (50 mL) was stirred at 0 1C for 15 min under N2. Then,
151.47, 148.29, 136.24, 129.75, 129.59, 129.18, 128.97, 127.57, t-BuOK (0.5 g, 4.26 mmol) was added portion wise and the reaction
127.35, 127.03, 126.16, 118.67, 110.52, 69.47, 32.03, 29.78, 29.61, was stirred at room temperature for 24 h. After this time, 50 mL of
29.56, 29.48, 26.36, 22.79, 14.22. UV-Vis (CHCl3); lmax (418 nm), water were added. The organic phase was extracted twice with
+
e (2.7 ꢂ 104 Mꢀ1 cmꢀ1). MALDI-TOF (Mꢁ ): m/z calcd for CH2Cl2. The combined organic layers were washed with water, dried
C52H68N2O2: 752.53, found, 752.44.
over anhydrous Na2SO4, filtered and the solvent vacuum evaporated.
The resulting residue was purified by column chromatography by
2,20-(1E,10E)-2,20-(4,40-(1E,10E)-2,20-(2,5-Bis(dodecanoxy)-1,4-
phenylene)bis(ethene-2,1-diyl)bis(4,1-phenylene))bis(ethene-2,1- using neutral alumina and hexane–CH2Cl2 (5/5 v/v) as an eluent to
diyl)diquinoline 7 (5QPV). A mixture of 3 (300 mg, 0.37 mmol), 5 obtain a pale yellow solid in 88% yield. m.p. = 112–116 1C. 1H NMR
(173 mg, 1.11 mmol), Pd(OAc2) (8 mg, 0.03 mmol), anhydrous (CDCl3, 300 MHz): d(ppm) 8.12(d, 1H, J = 8.5 Hz, QnH8), 8.09(dd,
sodium acetate (73 mg, 0.89 mmol), and ꢀBr+NBu4 (48 mg, 1H, J = 8.5 Hz, QnH5), 7.78(dd, 1H, J = 8.25 Hz, QnH4), 7.69(t,
0.149 mmol) in DMF : Et3N (90 : 10 mL) was stirred under N2 and 1H, J = 8.8 Hz, QnH7), 7.64(d, 1H, J = 17.33 Hz, –CQCHB), 7.61(t, 1H,
heated at 130 1C for 72 h. After cooling, 100 mL of H2O–NaHCO3 J = 8.25 Hz, QnH6), 7.49(dd, 1H, J = 7.15 Hz, QnH3), 7.42(d, 4H,
was added and the organic phase was extracted with CHCl3, then J = 8.25 Hz, Ar–H), 7.40(d, 1H, J = 16.51 Hz, –CQCHA), 6.72(q, 1H,
dried with MgSO4, filtered and the solvent evaporated under –CQCHC), 5.79(d, 1H, J = 17.61 Hz, –CQCHD), 5.28(d, 1H, J = 10.73
reduced pressure. The resulting residue was dissolved in 1 mL Hz, –CQCHE). 13C NMR (CDCl3, 75 MHz): d(ppm) 156.01, 148.33,
of CHCl3 heated until its total dissolution and precipitated in 137.96, 136.48, 136.41, 136.13, 134.09, 129.85, 129.26, 128.93, 127.60,
methanol three times. The desired product was obtained as an 127.42, 126.77, 126.25, 119.37, 114.42. UV-Vis (CHCl3); lmax (294 nm)
1
orange solid in 60% yield. m.p. = 155–163 1C. H NMR (CDCl3, e (2.97 ꢂ 104 Mꢀ1 cmꢀ1), (346 nm) e (4.89 ꢂ 104 Mꢀ1 cmꢀ1) (359 nm)
300 MHz): d(ppm). 8.09(2d, 2H, J = 8.80 Hz, QnH8), 8.08(d, 2H, e (4.84 ꢂ 104 Mꢀ1 cmꢀ1).
J = 8.80 Hz, QnH5), 7.98(d, 2H, J = 7.98 Hz, QnH4), 7.71(2t, 4H,
Compound 11 (7QPV). A mixture of 3 (235 mg, 0.291 mmol),
J = 8.5 Hz, QnH6, H7), 7.68(d, 2H, J = 16.23, –CQHB), 7.66(d, 4H, 10 (225 mg, 0.874 mmol), Pd(OAc2) (14 mg, 0.058 mmol),
J = 8.53 Hz, Ar–H10), 7.62(d, 2H, J = 9.90 Hz, QnH3), 7.55(d, 4H, anhydrous sodium acetate (72 mg, 0.874 mmol), and ꢀBr+NBu4
J = 8.25 Hz, Ar–H9), 7.53(d, 2H, J = 16.51, –CQHD), 7.42(d, 2H, (94 mg, 0.292 mmol) in DMF : Et3N (90 : 10 mL) was stirred under
J = 16.23, –CQHA), 7.15(d, 2H, J = 15.68, –CQHC), 7.13(s, 2H, Ar–H), N2 and heated at 130 1C for 72 h. After cooling, 100 mL of H2O–
4.06(t, 4H, J = 6.60 Hz, CH2–a–O), 1.89(q, 4H, J = 6.88 Hz, CH2–b–O), NaHCO3 was added and the organic phase was extracted with
1.56(q, 4H, CH2–g–O), 1.25(br s, 32H,–CH2–), 0.86(t, 6H, CH3). 13
C
CHCl3, dried with MgSO4, filtered and the solvent evaporated under
NMR (CDCl3, 75 MHz): d(ppm) 156.09, 151.29, 148.26, 138.56, reduced pressure. The resulting residue was dissolved in 1 mL of
136.52, 135.67, 134.33, 131.00, 129.92, 129.16, 128.90, 128.55, CHCl3, heated until total dissolution and precipitated in methanol
128.40, 127.70, 127.61, 127.41, 127.03, 126.28, 124.12, 119.37, three times. Later, the residue was re-dissolved in 5 mL of hot
110.71, 69.65, 32.04, 29.80, 29.60, 29.50, 26.43, 22.80, 14.23. toluene and left standing until the desired product precipitated
UV-Vis (CHCl3); lmax (435 nm), e (7.9 ꢂ 104 Mꢀ1 cmꢀ1). MALDI- during two days; it was then filtered and dried. The desired
+
TOF (Mꢁ ): m/z calcd for C68H80N2O2: 956.62, found, 956.58.
product was obtained as a deep orange solid in 47% yield.
(E)-4-(2-(Quinolin-2-yl)vinyl)benzaldehyde 9. A mixture of m.p. = 175–182 1C. 1H NMR (CDCl3, 300 MHz): d(ppm)
2-vinyl-quinoline 5 (1.84 g, 11.88 mmol), 4-bromobenzaldehyde 8.15(d, 2H, J = 8.08 Hz, QnH8), 8.12(d, 2H, J = 8.08 Hz,
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Paper
3 G. S. Chen, R. S. Talekar, K.-T. Wong, L.-C. Chi and J.-W.
Chern, J. Chin. Chem. Soc., 2007, 54, 1387.
4 Y. Zhu, M. M. Alam and S. A. Jenekhe, Macromolecules, 2003,
36, 8958.
5 T. W. Kwon, M. M. Alam and S. A. Jenekhe, Chem. Mater.,
2004, 16, 4657.
QnH5), 7.78(dd, 2H, J = 8.16 z, QnH4), 7.71(2t, 4H, J = 8.40 Hz,
QnH7, H6), 7.72(d, 2H, J = 16.5, –CQHA), 7.66(d, 2H, J = 8.71 Hz,
Ar–H11), 7.64(d, 2H, J = 8.4 Hz, QnH3), 7.54(d, 4H, J = 8.56 Hz,
Ar–H12), 7.49(d, 2H, J = 16.46, –CQHE), 7.46(d, 2H, J = 8.6 Hz,
Ar–H10), 7.42(d, 2H, J = 17.60, –CQHB), 7.37(d, 2H, J = 6.40 Hz,
Ar–H9), 7.17(d, 2H, J = 16.0 Hz, –CQHD), 7.13(d, 2H, J = 16.53 Hz,
–CQHC), 7.14(s, 2H, ArO–H13), 7.05(d, 2H, J = 16.30 Hz, –CQHF),
4.06(t, 4H, J = 6.60 Hz, CH2–a–O), 1.89(q, 4H, J = 6.88 Hz, CH2–bO),
1.56(q, 4H, CH2–g–O), 1.25(br s, 32H,–CH2–), 0.86(t, 6H, CH3) UV-Vis
6 ESI†.
7 T. Jiu, Y. Li, X. Liu, H. Liu, C. Li, J. Ye and D. Zhu, J. Polym.
Sci., Part A: Polym. Chem., 2007, 45, 911.
+
(CHCl3); lmax (440 nm), e (19.5 ꢂ 104 Mꢀ1 cmꢀ1). MALDI-TOF (Mꢁ ):
´
8 S. Leroy-Lhez, M. Allain, J. Oberle and F. Fages, New
m/z calcd for C80H92N2O2: 1160.72, found, 1160.76.
J. Chem., 2007, 31, 1013.
1,4-Bis(dodecanoxy)-2,5-distyrylbenzene, model compound 128
(3C12DSB). A mixture of 1,4-bis(dodecanoxy)-2,5-diiodo-benzene 1
(550 mg, 0.787 mmol), Pd(OAc2) (7 mg, 0.031 mmol), and tris-
(o-toly1)phosphine (10 mg, 0.031 mmol) were placed in a two neck
round bottom flask. Then 20 mL of Et3N–DMF (1 : 4 v/v) were added
via a cannula, stirred and heated for 1 h. Later, freshly distilled
styrene (172 mg, 0.19 mL, 1.65 mmol) dissolved in 5 mL of DMF
(previously bubbled with nitrogen for 15 min) was added and heated
at 120 1C for 72 h. After removing the solvents, the crude product
was washed with brine solution, then the organic phase was
extracted with CH2Cl2, dried over MgSO4 and the solvent evaporated.
The crude product was purified by preparative GPC chromatography
(Biorads, Bio-beds SX1, toluene) and then recrystallized in hexane to
afford a pale orange powder in 78% yield. m.p. = 75–78 1C. 1H NMR
(CDCl3, 300 MHz): d(ppm) 7.54(dd, 4H, J = 7.15 Hz, Ar–H), 7.50(d,
2H, J = 16.51 Hz,QCH–), 7.38(t, 4H, J = 7.70 Hz, Ar–H), 7.26(m, 2H, J
= 7.43 Hz, Ar–H), 7.15(d, 2H, J = 16.51 Hz,QCH–), 7.14(s, 2H, Ar–H),
4.07(t, 4H, J = 6.46 Hz, CH2–a–O), 1.89(m, 4H, CH2–b–O), 1.56(m,
4H, CH2–g–O), 1.28(br s, 32H,–CH2–), 0.89(t, 6H, CH3).
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Acknowledgements
¨
Z. Hu, D. McCord-Maughon, T. C. Parker, H. Rockel,
We wish to acknowledge CONACYT-American Air Force Office of
Scientific Research for the financial support through the initia-
tive (1010/189/10C-286-10)-(FA5990-10-1-0236). The authors also
thank Gabriela Padron for technical assistance.
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S. Thayumanavan, S. R. Marder, D. Beljonne and J.-L. Bredas,
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Notes and references
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984 | New J. Chem., 2014, 38, 974--984
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