Synthesis, photonic characteristics, and mesomorphism of an oligo biphenylene vinylene π-electron system

Article abstract of DOI:10.1021/ol050161d

(Chemical Equation Presented) The synthesis and photonic and liquid-crystalline properties of a novel oligo biphenylene vinylene (OBV) chromophore with an extended π-electron system are reported; the compound exhibits high fluorescence, a large two-photon

Full text of DOI:10.1021/ol050161d

ORGANIC
LETTERS
2005
Vol. 7, No. 8
1505-1508
Synthesis, Photonic Characteristics, and
Mesomorphism of an Oligo Biphenylene
Vinylene
π-Electron System
Fre´de´ric Lincker,† Philippe Bourgun,† Patrick Masson,† Pascal Didier,‡
Luca Guidoni,‡ Jean-Yves Bigot,‡ Jean-Francois Nicoud,*,†
Bertrand Donnio,*,† and Daniel Guillon†
¸
Groupe des Mate´riaux Organiques (GMO) and Groupe d’Optique NonLine´aire et
d’Optoe´lectronique (GONLO), Institut de Physique et Chimie des Mate´riaux de
Strasbourg (IPCMS), UMR 7504 (CNRS-ULP), 23 rue du Loess,
67034 Strasbourg Cedex 2, France
nicoud@ipcms.u-strasbg.fr
Received January 24, 2005
ABSTRACT
The synthesis and photonic and liquid-crystalline properties of a novel oligo biphenylene vinylene (OBV) chromophore with an extended
-electron system are reported; the compound exhibits high fluorescence, a large two-photon absorption cross-section, and two- and three-
π
dimensional liquid-crystalline mesophases.
Conjugated organic materials have attracted considerable
attention in recent years due to numerous potential applica-
tions in various fields such as light-emitting diodes,1 pho-
tovoltaic cells,2 optical power limiting,3 three-dimensional
microfabrication,4 and two-photon laser scanning fluores-
cence imaging.5 To date, many types of organic materials
have been designed and fabricated for this purpose, most of
which have a linear molecular shape, such as oligo(phenyl-
enevinylene) (OPV),6 oligo(p-phenylene) (OPP),7 oligo-
(phenyleneethynylene) (OPE),8 and oligo(thiophene) (OT).9
Their particular electronic properties led us to the design of
a conjugated organic oligo biphenylene vinylene (OBV)
molecule based on biphenylene motifs linked together
† Groupe des Mate´riaux Organiques.
‡ Groupe d’Optique NonLine´aire et d’Optoe´lectronique.
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10.1021/ol050161d CCC: $30.25
© 2005 American Chemical Society
Published on Web 03/19/2005

through double bonds. Such a novel molecular structure may
lead to promising applications for light-emitting and non-
linear optical devices.
coupling is known to be efficient to form C-C connections
between two sp2 carbons and highly stereoselective (mainly
the (E)-stereoisomer is obtained) contrary to other methods
used for the preparation of stilbenyl compounds.
Scheme 2. Preparation of the OPV 10 and OBV 11
In this paper, we report on the synthesis of two hexacatenar
molecules (mesogens with a long rigid core bearing three
aliphatic chains at both extremities),10 the OBV-3 11 and
the OPV analogue 10, their one- and two-photon properties,
and their thermal behavior.
The synthetic approach for both OPV and OBV motifs
relies upon a symmetrical bis Heck reaction. Such a cross-
Scheme 1. Synthesis of the Building Block 8
Since the direct halogenation of 1, obtained from pyro-
gallol, did not lead to the expected compound 4, another
synthetic strategy for functionalization of pyrogallol deriva-
tive 1 in position 5 was envisaged. It started by the nitration
of 1 with sodium nitrite and nitric acid in a biphasic medium
H2O/CH2Cl2 (Scheme 1). Subsequent reduction of 2 using
the graphite-hydrazine system led to the corresponding
aniline derivative 3, which was then successfully converted
into the iodo derivative 3,4,5-tridodecyloxyiodobenzene 4
by a Sandmeyer reaction. Despite moderate yields (50%),
gram-scale materials could nevertheless be prepared. The
boronic acid 5 was prepared according to the classical “one-
pot” synthesis. To avoid spontaneous dehydration, leading
to trimerization,11 the acid was used immediately. To
facilitate the purification of the resulting biphenyl product
7, and thus to increase the reaction yield, in our hands it
appeared judicious, prior to the Suzuki coupling reaction, to
modify the polarity of the aldehyde adduct by converting
the aldehyde function in acetal. Coupling 5 and 1-(4-
bromophenyl)-4,4-dimethyl-2,6-dioxane in the presence of
Pd(PPh3)4 and K2CO3 in a C6H6/EtOH/H2O (2/1/1) mixture
at 90 °C led to intermediate 6 in high yield (90%). After
purification, 6 is hydrolyzed by treatment with TFA in the
(10) (a) Maltheˆte, J.; Nguyen, H. T.; Destrade, C. Liq. Cryst. 1993, 13,
171. (b) Nguyen, H. T.; Destrade, C.; Maltheˆte, J. AdV. Mater. 1997, 9,
375.
(11) Tokunaga, Y.; Ueno, H.; Seo, T.; Shimomura, Y. Heterocycles 2002,
57, 787.
1506
Org. Lett., Vol. 7, No. 8, 2005

CH2Cl2/H2O mixture to generate the corresponding aldehyde
7. Despite the strong acidity of the reaction mixture, no
secondary product formation was observed. The key precur-
sor 3,4,5-tridodecyloxy-p-phenylstyrene 8 was formed by
reaction of 7 in THF with phosphorus ylide formed in situ
by addition of t-BuOK on commercially available methyl-
triphenylphosphonium bromide.
Both the OBV-3 (11) and OPV-3 (10) compounds were
prepared from Heck coupling between 8 and 4,4′-dibromo-
biphenyl and between 912 and 1,4-diiodobenzene, respectively
(Scheme 2).
Table 1. Photophysical Data of 10 and 11 in CH2Cl2
photophysical data
λabs [nm]a
stilbene-420
10
11
348
373
369
log ꢀ
4.80
361
429
4.81
379
442
4.95
396
424 (444)
λex [nm]a
λem [nm]b
fwhmabs (width)[nm]c
fwhmem (width)[nm]c
Φfd
Stokes shift [nm]
â [cm/GW]e
σ2TPA [10-20 cm4 GW-1
σ2′ TPA [GM]f
61.2 (55.5)
83.8 (79.0)
0.64
81
0.3
63.4 (60.5) 71.0 (63.0)
68.8 (74.0) 68.2 (60.0)
0.77
69
2.0
0.93
55 (75)
4.8
The UV absorption/emission properties of these com-
pounds were investigated, and the typical one-photon absorp-
tion and fluorescence spectra of 10 and 11 are shown in
Figure 1.
]
5.0
124
33.4
832
80.0
1992
a Only the largest absorption maxima are listed. b Wavelength of emission
maximum when excited at the absorption maximum. c Full widths at half
maximum. d Quantum efficiencies using fluorescein in 0.1 N NaOH as a
standard.16 e â ) σ2NAd × 10-3 where NA is the Avogadro constant and
d the concentration of the TPA compound in the solution.17 f σ′ [GM] ≈
2
24.9σ2 [10-20 cm4 GW-1]. 1GM (Goppert-Mayer) ) 10-50 cm4 s photon-1
molecule-1
.
particular, stilbene-420 has been shown to present good
optical limiting properties in concentrated solutions due to
multiphoton absorption.14 We have investigated the TPA
properties of the OBV and OPV derivatives using 150 fs
pulses delivered by a Ti:sapphire amplified laser operating
at a wavelength of 790 nm with a repetition rate of 5 kHz.
The typical measured nonlinear transmission curves obtained
for the stilbene-420 reference, 10, and 11 are shown in
Figure 2.
With basic theoretical considerations and taking into
account the spatial (transverse) Gaussian distribution and a
Gaussian temporal shape for the pulse, the TPA coefficient
â and the corresponding σ2 can be obtained from the curves
of Figure 2.15 The nonlinear photophysical data of 10 and
11 are summarized in Table 1 and compared to stilbene-
420. It appears clearly that the new OBV derivative 11 leads
to an improved σ2 in comparison with the OPV analogue
10. This result supports our molecular engineering strategy
for finding new and very efficient TPA chromophores.
Due to their structures and with respect to criteria
compatible for LC-phase formation, the thermal behavior of
compounds 10 and 11 was investigated using thermal optical
polarized microscopy, DSC, and X-ray diffraction.
Due to the longer size of the biphenylene building units,
the molecular anisotropy necessary for mesophase induction
is more readily attainable with OBV compound 11 than with
OPV compound 10. And indeed, only the polycatenar
triblock molecule 11 exhibits mesophases over wide tem-
perature ranges, whereas 10 melts directly into the isotropic
Figure 1. Linear absorption (A) and fluorescence (I) spectra of
commercially available stilbene-420 (black) reference in water, 10
(blue), and 11 (green) in CH2Cl2 (c ) 10-5 mol L-1).
Both hexacatenars 10 and 11 are highly fluorescent in
solution and in the solid state. The absorption maximum of
11 (λmax ) 369 nm) is slightly blue-shifted (4 nm) with
respect to that of 10 (λmax ) 373 nm) (Table 1). The
absorption and emission bands of 11 are broadened and
intense. It is also interesting to note that 11 has an inherently
higher solution fluorescence quantum yield than 10 and emits
with a clear deep blue light. Given this, such systems may
be regarded as potentially promising candidates for blue-
emitting layers in electroluminescent devices.
It has been observed by various groups recently that
symmetrical linear conjugated molecules bearing donor
groups at each end, so-called “push-push”, can display high
nonlinear absorption behavior characterized by large two-
photon absorption (TPA) cross-section σ2 values.13 In
Bre´das, J.-L.; Ehrlich, J. E.; Fu, J.-Y.; Heikal, A. A.; Hess, S. E.; Kogej,
T.; Levin, M. D.; Marder, S. R.; McCord-Maughon, D.; Perry, J. W.; Ro¨ckel,
H.; Rumi, M.; Subramaniam, G.; Webb, W. W.; Wu, X.-L. Science 1998,
281, 1653. (c) Ventelon, L.; Moreaux, L.; Mertz, J.; Blanchard-Desce, M.
Chem. Commun. 1999, 2055. (d) Ventelon, L.; Charier, S.; Moreaux, L.;
Mertz, J.; Blanchard-Desce, M. Angew. Chem., Int. Ed. 2001, 40, 2098.
(14) Chollet, P. A.; Dumarcher, V.; Nunzi, J. M.; Morel, Y.; Baldeck,
P. L. Nonlinear Optics 1999, 21, 299.
(12) 9 was prepared according to literature procedures: (a) Donnio, B.;
Bruce, D. W. New J. Chem. 1999, 275. (b) Gehringer, L.; Guillon, D.;
Donnio, B. Macromolecules 2003, 36, 5593.
(13) (a) Cumpston, B. H.; Ananthavel, S. P.; Barlow, S.; Dyer, D. L.;
Ehrlich, J. E.; Erskine, L. L.; Heikal, A. A.; Kuebler, S. M.; Lee, I.-Y. S.;
McCord-Maughon, D.; Qin, J.; Ro¨ckel, H.; Rumi, M.; Wu, X.-L.; Marder,
S. R.; Perry, J. W. Nature 1999, 398, 51. (b) Albota, M.; Beljonne, D.;
(15) Oulianov, D. A.; Tomov, I. V.; Dvornikov, A. S.; Rentzepis, P. M.
Opt. Commun. 2001, 191, 235.
Org. Lett., Vol. 7, No. 8, 2005
1507

Figure 3. Representative optical textures of the three-dimensional
body-centered tetragonal mesophase of 11 at 147 °C obtained by
cooling from the Colh mesophase.
Figure 2. Nonlinear transmission of stilbene-420 (black circle)
reference in water, 10 (blue square), and 11 (green triangle) in
CH2Cl2 (c ) 10-2 mol L-1). The continuous lines are the best fit
to a TPA law (see Supporting Information).
another mesophase, Mtet, characterized by a three-dimen-
sional body-centered tetragonal space group (a ) 59.3 Å,
c ) 83.8 Å). The presence of the large 4-fold symmetry
defects observed all over the Mtet texture (Figure 3) is indeed
compatible with a three-dimensional tetragonal symmetry.18
For the Colh phase, the classical model is proposed, involving
the piling of clusters made of a few molecules.10,19 In contrast,
the supramolecular organization of the Mtet phase is more
complicated and may resemble the micellar model proposed
in rod-coil systems.20 It would then consist of the formation
of clusters containing a few molecules, these aggregates
being localized at the nodes of a three-dimensional tetragonal
lattice (one in the center and one on the corner).
In summary, a new conjugated organic material based on
biphenylene vinylene motifs has been synthesized. In contrast
to the OPV-3 analogue, the OBV-3 hexacatenar 11 exhibited
a columnar hexagonal phase and an unusual three-dimen-
sional phase with a body-centered tetragonal symmetry. The
good one- and two-photon optical properties of 11 strongly
suggest that such materials can be considered as attractive
components for the elaboration of photoactive materials.
liquid at 59 °C. The transition temperatures and the corre-
sponding enthalpy changes determined from DSC scans are
recorded in Table 2.
Table 2. Thermal Behavior of 11
11
transition temperatures (°C) [∆H (kJ mol-1)]
heating
cooling
Cr 64.4 [2.4], Mtet 143.2 [0.8], Colh 155.6 [0.1]
I 157.1 [0.1], Colh 148.5 [0.8], Mtet 31.0 G
Cr, crystalline phase; G, glassy state; I, isotropic liquid; Colh, hexagonal
columnar phase; Mtet, three-dimensional body-centered tetragonal phase.
The liquid-crystalline behavior was probed by the observa-
tion under polarized optical microscopy of unusual textures
showing birefringent and fluid domains, coalescing into a
uniform monodomain on increasing the temperature, and by
small-angle X-ray diffraction studies. A typical texture
exhibited by 11 is shown in Figure 3. On slow cooling from
the isotropic liquid, a homeotropic texture is developed for
the columnar hexagonal phase. On further cooling, the
formation of beautiful fernlike domains growing from the
latter along two or three preferential directions was observed.
These domains then merged into an unusual hexagonal shape
mosaic texture with perfectly defined edges. On cooling, this
phase is frozen into a glassy state. X-ray diffraction analysis
confirmed the presence of two mesophases: at high tem-
perature, a columnar phase with a two-dimensional hexagonal
lattice, the Colh phase (a ) 46.4 Å), and at lower temperature,
Supporting Information Available: Experimental pro-
cedures and characterization for all new compounds. This
material is available free of charge via the Internet at
http://pubs.acs.org.
OL050161D
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