Alignment of palladium complexes into columnar liquid crystals driven by peripheral triphenylene substituents

Article abstract of DOI:10.1021/ic402886t

A new triphenylene-imine (ImH) and its ortho-palladated complexes (μ-X)₂[Pd₂Im₂] (X = CH₃COO ^-, Cl^-, Br^-), (μ-Cl)(μ-SC _nH_2n+1)[Pd₂Im₂]

Full text of DOI:10.1021/ic402886t

Article
pubs.acs.org/IC
Alignment of Palladium Complexes into Columnar Liquid Crystals
Driven by Peripheral Triphenylene Substituents
Emiliano Tritto,† Ruben Chico,† Gerardo Sanz-Enguita,‡ Cesar L. Folcia,§ Josu Ortega,‡ Silverio Coco,*,†
́
́
and Pablo Espinet*,†
†
́
́ ́
IU CINQUIMA/Quımica Inorganica, Facultad de Ciencias, Universidad de Valladolid, 47071 Valladolid, Castilla y Leon, Spain
‡Department of Applied Physics II and Department of Condensed Matter Physics, University of the Basque Country, UPV/EHU,
§
48080 Bilbao, Spain
S
* Supporting Information
ABSTRACT: A new triphenylene-imine (ImH) and its ortho-
palladated complexes (μ-X)2[Pd2Im2] (X = CH3COO−, Cl−,
Br−), (μ-Cl)(μ-SCnH2n+1)[Pd2Im2] (n = 6, 12), [PdIm(acac)]
[ P d I m C l ( C N C 6 H 4 O C 1 2 H 2 5 ) ] , [ P d I m C l -
(CNC6H3(OC12H25)2)], and [PdImCl(CNC6H2(OC12H25)3)]
have been prepared. The free imine ligand is not a liquid
crystal, but most ortho-metalated dinuclear palladium
complexes and the mononuclear trialkoxyphenyl isocyanide
derivative display columnar mesophases at temperatures close
to ambient. For the dimeric complexes the mesophase
obtained is always columnar rectangular (Colr), with an uncommon structure: the dimeric triphenylene−Pd complex−
triphenylene molecules give rise to a triple-column stacking consisting of two columns of stacked triphenylene groups connected
to a central column formed by stacking of two ortho-palladated dimeric moieties. For the trialkoxyphenyl isocyanide derivative a
related polymer-like arrangement of columns alternating stacking of triphenylenes with stacking of two ortho-palladated dimeric
moieties is found. The mesophase structure is columnar oblique (Colob). The free imine and all palladium complexes exhibit
fluorescence at room temperature in dichloromethane solution, associated with the triphenylene core.
The utility of these systems could be limited by their relatively
low thermal stability because of the lability of the hydrogen bond.
Therefore, we decided to develop related systems based on
simpler and more robust molecules. The triphenylene moiety
looked like a good choice because it is a stable classical organic
system with many available procedures to modify and connect
different groups to the triphenylene core. This group is used
often to induce columnar mesophases in organic liquid
crystals,1d,3 and it is found also in a few nonconventional organic
liquid crystals arising from the chemical linkage of disc-like
triphenylenes and rod-shaped moieties,7 where phases other than
columnar can also arise. In addition, there have already been a
few reports of liquid crystalline metal−organic triphenylene
systems with covalently bonded Hg,8 Cr0,9 ZnII,10 CuII and NiII,11
and AgI complexes.12
With these precedents we considered that ortho-palladated
complexes (one of the most studied families in the field of
metallomesogens) should be easy to attach to the triphenylene
columnar core and would display good thermal stability.4 We
have obtained a family of interesting liquid crystalline mono- and
dinuclear ortho-metalated palladium complexes that display
unusual columnar mesophases close to ambient temperature.
Their structure contains a triple stack of a central column of pairs
INTRODUCTION
■
Columnar liquid crystals have received considerable attention in
recent years as functional materials for application in nanoscale
conductive devices, field-effect transistors, or photovoltaic solar
cells.1,2 Many systematic studies on the influence of the
molecular constitution and stacking on the mesomorphism
have been reported, mostly on conventional organic liquid
crystals.1d,3 However, the number of studies on metal-containing
liquid crystals (metallomesogens) is comparatively lower.4,5
We have recently reported columnar hexagonal metal-
lomesogens based on supramolecular complexes formed from
metallo-organic acids hydrogen bonded to a substituted triazine
as proton acceptor. The metal fragments are dangling around the
central columnar triazine stacking.6 They are interesting soft
materials formally reminiscent of a polymeric backbone (the
column) supporting the organometallic fragments. However,
both the formation of the column and its connection to the
fragments are reversible upon heating or by dissolution. This
synthetic approach permits linking different metallic fragments
to the column. New or modified properties might appear in the
aggregate depending on the distribution of the metal fragments:
for instance, helical structures, interfragment interactions in the
columnar aggregate (e.g., metal−metal interactions along the
columnar direction), or properties associated with metal−metal
bonds (e.g., luminescence or electric one-dimensional con-
ductivity along the piled metal fragments).
Received: November 20, 2013
Published: March 17, 2014
© 2014 American Chemical Society
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Scheme 1. Synthesis of 2-(6-(4-Aminophenoxy)hexyloxy)-3,6,7,10,11-pentakis(dodecyloxy)triphenylene and the Imine Ligand
Scheme 2. Synthesis of Palladium Ortho-Metalated Complexes
of ortho-palladated dimeric moieties, flanked by two columns of
The cyclopalladated complexes were synthesized as depicted
in Scheme 2. Elemental analyses, yields, relevant IR data, and 1H
NMR spectra for the complexes are given in the Supporting
Information. The 1H NMR resonances associated with the ortho-
palladated imine moiety support the isomeric purity of the
complexes. The ortho metalation of the imine ligand to give the
acetato complex 1 was carried out as described elsewhere.15 The
typical structural features of complexes analogous to 1−3, but
triphenylene groups connected to it.
RESULTS AND DISCUSSION
■
Synthesis and Characterization. The Schiff base ImH was
synthesized by conventional methods as shown in Scheme 1.13,14
Details are given in the Supporting Information.
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without a triphenylene group, have been reported in detail in
previous papers.16 The acetato-bridged complexes are butterfly-
shaped at the Pd core, while the halogen-bridged complexes are
planar. In these dimers only the isomer with an anti arrangement
of the two imine fragments is detected by 1H NMR.
heating scan of all complexes shows the corresponding melting
and clearing transitions. However, in the cooling cycle no sign of
crystallization or glass transition was detected; the sample simply
becomes less fluid and looks frozen, suggesting that an
undetectable transformation to a glassy state has occurred. In
some compounds, unusually small enthalpy values were detected
for crystallization upon cooling and for the corresponding
melting transition in the second heating scan. This unusually
small enthalpy value is likely due to only partial crystallinity of the
sample, which is a frequent behavior in this type of system. It is
important to note that the melting and clearing points appear in
the DSC scans as broad transitions (Figures S1−S3, Supporting
Information). For this reason the significance and accuracy of
these data are probably low. The POM optical texture, when
formed on cooling from the isotropic melt, shows a mosaic
texture (Figure 1), which suggests a columnar mesophase, later
identified as Colr for complexes 2−5 and Colob for complex 9.
For the thiolato-bridged complex, a syn arrangement of the
imine moieties with the thiolato group trans to the imine
nitrogen atoms is proposed, as found in analogous palladium
complexes.17 The mononuclear species 6−9 show H NMR
1
spectra very similar to those of the dinuclear complexes, in
addition to the corresponding signals of the introduced ligand.
Thus, for the acetylacetonato (acac) complexes a singlet at ca. 5.4
ppm (acac CH group) and two singlets at 2.1 and 1.9 ppm (acac
nonequivalent Me groups) are observed.
The isonitrile derivatives display the signals of the substituted
aromatic ring and the signals corresponding to the respective
chains. A ROESY-1D (monodimensional rotating frame Over-
hauser effect spectroscopy) experiment on compound 9 showed
an ROE effect on the H signal of the imine ring upon irradiation
of the singlet of the aromatic ring of the isonitrile, supporting a
trans disposition of the isonitrile with respect to the imine
nitrogen.
Mesomorphic Behavior. The free imine ligand used is not
mesogenic, but all of the dinuclear palladium complexes show
mesomorphic behavior, except for the acetato complex (usually
butterfly-shaped ortho-metalated acetato-bridged complexes are
not mesomorphic because of their unfavorable molecular
shape).4b,16d In contrast, the mononuclear derivatives do not
show liquid crystal behavior, except for the trialkoxyphenyl
isocyanide complex. Optical, thermal, and thermodynamic data
of the compounds, obtained by polarized optical microscopy
(POM), differential scanning calorimetry (DSC), and X-ray
scattering, are collected in Table 1.
In the five compounds that exhibit mesomorphic behavior
only one liquid crystalline phase is observed between the
isotropic state and the low-temperature crystal. The first DSC
Figure 1. POM texture (×100) of the mesophase of (μ-SC6H13)(μ-
Cl)[Pd2Im2] (compound 4) (chosen as a representative example, see
Figure S4 in the Supporting Information for more POM textures) near
the clearing point obtained on cooling. In the figure liquid crystalline
domains coexist with the isotropic state.
Table 1. Optical, Thermal, and Thermodynamic Data of
Ortho-Palladated Imine Complexes
b
b
The mesomorphic behaviors of the complexes with halogen
bridges (2 and 3) are very alike. The transition temperatures are
slightly lower for the bromo derivative, probably due to the larger
size of the bromo in comparison to the chloro ligand. For the
mixed chloro−thiolate derivatives (4 and 5), the introduction of
the additional chain of the thiolate group leads, as expected, to an
interesting decrease in melting temperatures. This decrease is
generally more pronounced as the length of the chain increases,
as observed here. For the mononuclear complexes, only the
trialkoxyphenyl isocyanide complex (9) displays liquid crystal
properties. The presence of the three additional alkoxy chains in
the molecule, which will certainly contribute to fill up a discotic
shape, must be the reason for this behavior.
In order to elucidate the structural properties of these
mesophases, X-ray diffraction measurements were carried out.
In all cases the diffraction diagram is typical of a liquid crystal
phase: a diffuse halo at wide angles, indicating the fluid character
of the phase, and a set of sharp peaks in the small-angle region
(see Figures 2 and 3 and Figures S5−S7 (Supporting
Information)). The peak positions of the different materials
under study are summarized in Table 2 together with their
relative intensities. In the case of compounds 2 and 3, the X-ray
diagram could be compatible with a simple lamellar structure,
temp
ΔH (kJ
a
compound
imine (ImH)
transition
(°C)
mol−1
)
C → C′
C → I
35
43
36
34
56
32
51
76
36
66
35
32
30
27.70
31.71
72.69
1.56
c
(μ-OAc)2[Pd2Im2] (1)
(μ-Cl)2[Pd2Im2] (2)
C → I
C → Colr
Colr → I
C → Colr
Colr → I
Colr → I
C → Colr
Colr → I
C → I
1.44
d
(μ-Br)2 [Pd2Im2] (3)
4.79
8.20
5.34
2.86
1.34
(μ-Cl)(μ-SC6H13) [Pd2Im2] (4)
(μ-Cl)(μ-SC12H25)[Pd2Im2] (5)
[PdIm(acac)] (6)
38.9
[PdImCl(CNC6H4OC12H25)] (7)
C → I
16.9
12.1
[PdImCl(CNC6H3(OC12H25)2)]
(8)
C → I
[PdImCl(CNC6H2(OC12H25)3)]
(9)
C → Colob
Colob → I
28
74
2.05
0.53
a
Abbreviations: Colr, columnar rectangular; Colob, columnar oblique;
I, isotropic liquid; C and C′, crystals. Data collected from the second
heating DSC cycle. The transition temperatures are given as peak
b
c
d
onsets. Data from the first heating scan. Combined transition.
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Figure 2. (a) X-ray diagram of compound 2 at 43 °C. q is the diffraction vector. (b) Detail of the small-angle region. In the figure the Miller indices of the
different peaks are indicated. (c) Corresponding charge-density map. The electron density distribution is compared to the molecular structure. Both
images are depicted at the same scale. In the figure the proposed model for the molecular packing is also schematized.
Figure 3. (a) X-ray diagram of compound 9 at 45 °C. q is the diffraction vector. (b) Detail of the small-angle region. In the figure the Miller indices of the
different peaks are indicated. (c) Corresponding charge-density map. The electron density distribution is compared to the molecular structure. Both
images are depicted at the same scale. In the figure the scheme of the molecular packing is also represented.
assuming a certain degree of laxity in the angular position of the
second peak. However, this simple scheme of indexation is
clearly not applicable to the similar compounds 4 and 5.
Consequently, a 2D translation lattice is considered for all the
dinuclear materials (compounds 2−5). On the other hand, it is
important to note that the diffraction diagrams show a set of
reflections that correspond to different harmonics of a given
periodicity together with another peak that represents a different
periodicity, as can be deduced from Table 2. As a consequence,
the unit cell is not univocally determined. In view of this, it is clear
that some extra criterion is required to model the structures.
Therefore, we have indexed the X-ray diagrams assuming the
symmetry as high as possible, provided that suitable packing
conditions are fulfilled. Our strategy consisted of the
construction of electron density maps (Fourier maps) using
the diffracted intensities after selecting a given unit cell. These
maps allow us to obtain an image of the structure by positioning
the molecules in the unit cell.
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a
Table 2. Summary of the X-ray Scattering Results
compound
(μ-Cl)2[Pd2Im2] (2)
temp (°C)
cell param
peak position q/2π (Å−1)/normalized intensity
Miller index
43
a = 29.6 Å
0.0163/1
(02)
(11)
(06)
(08)
(02)
(11)
(06)
(08)
(02)
(04)
(11)
(06)
(08)
(20)
(02)
(11)
(06)
(01)
(11)
b = 122.7 Å
0.0347/0.383
0.0497/0.175
0.066/0.0189
0.017/1
(μ-Br)2[Pd2Im2] (3)
45
50
a = 29.45 Å
b = 117.6 Å
0.035/0.363
0.0514/0.400
0.068/0.045
0.016/1
(μ-Cl)(μ-SC6H13)[Pd2Im2] (4)
a = 26.1 Å
b = 125.0 Å
0.0320/0.016
0.0392/0.390
0.048/0.230
0.0641/0.011
0.0729/0.018
0.0156/1
(μ-Cl)(μ-SC12H25)[Pd2Im2] (5)
50
45
a = 26.9 Å
b = 128.2 Å
0.038/0.750
0.047/0.594
0.0224/0.969
0.0338/1
[PdImCl(CNC6H4(OC12H25)3)] (9)
a = 30.4 Å
b = 48.7 Å
β = 66.2°
0.0494/0.500
(11)
̅
a
Compounds 2−5 present a centered rectangular unit cell (Colr), whereas compound 9 shows a columnar oblique structure (Colob). The cell
parameters depend weakly on the temperature.
The procedure is based on the inverse Fourier transform of the
diffraction diagram. Briefly, the intensity of a given (hl) reflection
is proportional to the square modulus of the complex (hl)
Fourier component of the periodic electron density of the
structure. Accordingly, apart from the peak angular positions, the
intensity of the different reflections must also be considered. The
technical details of the procedure to obtain the charge-density
map can be found in ref 18. It is worth noting that the method has
some ambiguity, because the phases of the different Fourier
components are not experimentally accessible. As a consequence,
more than one map can be compatible with the X-ray pattern of a
compound. However, as in the present case, this ambiguity is
easily worked out in simple cases with a few reflections. For
example, only four essentially different maps result in the worst
case for the materials under investigation. The choice of the
correct electron charge distribution is made according to packing
conditions, molecular sizes, and optimization of the steric
interactions.
corresponding distances in the charge-density map. We can
therefore conclude that the proposed solution gives rise to a
reasonable structural model for compounds 2−5.
Additionally, the mass density of the different compounds has
been measured. In the case of the dinuclear palladium complexes
it is about 1.2 g/cm3 for all of the compounds. This fact implies
that four molecules per unit cell must be accommodated within
an average distance of about 5.5 Å in the direction parallel to the
column axis. A proposed arrangement for one pair of molecules is
presented in Figure 2c. As can be seen, the triphenylene groups
appear superimposed whereas the palladium fragments are
arranged in parallel in the plane of the figure, because their large
thickness (about 5−6 Å) is not compatible with their
superposition along the columnar axis.
A similar study was also carried out for compound 9. In this
case the X-ray diffraction pattern was indexed on the basis of an
oblique lattice. In Figure 3a the X-ray pattern is depicted. The
small-angle region with the indexation scheme is shown in Figure
3b. The electron density distribution proposed for this
compound appears in Figure 3c with the corresponding
comparison to the molecular structure. In this case two regions
of high charge density can be observed per unit cell. These
maxima correspond to the palladium fragments (the highest) and
to the triphenylene groups, respectively. A good agreement
between the corresponding molecular length and the distance
between charge density maxima is observed as well. The density
mass is in this case 1.08 g/cm3, which implies, as in the previous
example, that two molecules per unit cell must be placed within a
distance of 5.4 Å along the column. Therefore, the two
triphenylene groups can be superimposed to accommodate
two thicker palladium fragments in the plane of the figure. The
proposed structure appears sketched in Figure 3c and features a
polymer-like arrangement of columns alternating stacking of
triphenylenes with stacking of two ortho-palladated dimeric
moieties.
In the case of dinuclear palladium complexes, we considered
the simplest case of a rectangular centered structure.
Accordingly, we indexed the diffraction diagrams as indicated
in Table 2.
The dinuclear palladium complexes (compounds 2−5)
present similar charge-density maps. As an example, Figure 2a
shows the X-ray scattering pattern for compound 2. In Figure 2b
the small-angle region is detailed and the proposed indexation
scheme is presented. The corresponding electron density
distribution is shown in Figure 2c. In the figure the molecule
has been drawn on the left-hand side at the same scale. The
highest density areas (the brightest ones) correspond to the
palladium fragments, since these groups are expected to
concentrate the most important charge density. The two
secondary maxima in the unit cell can be attributed to the
triphenylene groups that also present a remarkable charge
density. As can be seen, the molecular length between the
palladium fragments and the triphenylene groups (23 Å,
calculated with ACD Laboratories Chemsketch) matches the
Photophysical Studies. The UV−vis absorption and
fluorescence spectra of the free imine and the palladium
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complexes in dichloromethane solution are all summarized in
Table 3.
Table 3. UV−Visible and Luminescence Data for the Free
Imine and for Their Ortho-Palladated Complexes in
Dichloromethane Solution at 298 K (10−5 M)
λex/
nm
λem/
nm
compound
ImH
λ/nm (ε/mol−1 cm−1
)
10−3Φf
344 (16414), 308 (32427), 279 (110993),
270 (73662), 261 (51844)
278
267
288
288
281
285
288
279
279
279
385
7.02
1
2
3
4
5
6
7
8
9
342 (30387), 307 (74714), 278 (262353),
270 (178111), 261 (128368)
385
386
385
385
385
385
385
385
385
4.95
1.16
1.24
3.56
1.68
0.91
7.85
5.67
5.48
346 (25730), 307 (68980), 279 (227063),,
269 (172901), 260 (134156)
346 (25334), 308 (67425), 279 (230400),
270 (178237), 260 (148015)
Figure 5. Normalized luminescence excitation and emission spectra of 2
in dichloromethane solution at different concentrations.
347 (15608), 308 (44122), 279 (150877),
270 (107455), 260 (79840)
346 (32968), 308 (73805), 278 (249502),
270 (197709), 261 (158366)
344 (35079), 308 (78098), 279 (265253),
270 (200221), 262 (156900)
than that for 2,3,6,7,10,11-hexadodecyloxytriphenylene under
the same conditions (0.17). Therefore, although the imine and
the ortho-metalated fragment are not directly connected
electronically, they enhance nonradiative deactivation process
in these systems.
344 (9592), 308 (30291), 279 (119449),
269 (85321), 261 (66136)
345 (12656), 307 (42587), 279 (138509),
269 (102149), 261 (80052)
345 (13235), 308 (41696), 279 (144292),
269 (103592), 261 (78714)
In the solid state, the luminescent behavior of these derivatives
is lost. The luminescence spectra of 2 in dichloromethane
solution, as a function of concentration, are shown in Figure 5. As
the concentration is gradually increased from 10−6 to 10−3 M, the
intensity of the emission bands decreases and the emission is lost
at higher concentration. This behavior suggests the formation of
nonemissive excimer or excimer-like adducts.21
The electronic spectra are all very similar, displaying a very
structured spectral pattern with absorption bands and extinction
coefficients typical of triphenylene chromophores (Figure 4),
In summary, mesomorphic mono and dinualear ortho-
palladated complexes with an unusual luminescent imine,
containing a substituted triphenylene motif, have been prepared.
Although the free imine ligand obtained is not mesogenic, most
of the dinuclear palladium compounds, and the mononuclear
trialkoxyphenyl isocyanide complex, give rise to mesophases with
very interesting columnar arrangements. The discoid tripheny-
lene moieties, having a strong tendency to stack as columns, force
the metal-containing moieties to also stack in columnar zones.
Due to the greater thickness of the latter, they arrange themselves
in pairs of two parallel dimeric Pd cores, so as to better match the
thickness of two stacked disks of triphenylene. Thus, in the LC
structure the columnar Pd zones are flanked by two columns of
triphenylenes, keeping the triphenylene/Pd = 1/1 ratio. In
contrast, in the monomeric complex, where the Pd atom bears a
discoid isocyanide ligand attached to it, a polymer-like structure
is adopted in which the triphenylene and the Pd-containing
zones alternate, again keeping the triphenylene/Pd = 1/1 ratio.
This original accumulation, in a fluid material, of Pd-containing
columnar zones supported by fully organic columns, although
not associated with Pd−Pd bonds at the moment, merits further
investigation and elaboration.
Figure 4. Absorption spectrum of (μ-Cl)2[Pd2Im2] (2), recorded in
CH2Cl2 solution (10−6 M) at room temperature.
which are assigned to triphenylene π−π* transitions.19 In the
complexes described here the imine group is located too far from
the triphenylene core to expect any significant influence on its
electronic transitions. Indeed, the imine and the palladium
complexes display similar electronic spectra. It is also well-known
that the presence of long chains in hexakis(n-alkyloxy)-
triphenylenes does not significantly affect the spectroscopic
properties of the chromophore in solution.19a
The fluorescence spectroscopic data for the free imine and the
orthometalated complexes are given in Table 3. The free imine
and the palladium complexes are luminescent at room
temperature in dichloromethane solution. As for the electronic
spectra, all of the emission spectra are similar, with a very
structured pattern with the maximum at ca. 385 nm (Figure 5),
typical of fluorescent 2,3,6,7,10,11-hexaalkoxytriphenylenes.19a
The quantum yields for the complexes, Φ, measured in
dichloromethane solution at room temperature,20 are smaller
ASSOCIATED CONTENT
■
S
* Supporting Information
Text and figures giving full details of the synthetic methods
together with the spectroscopic and analytical data for the
prepared compounds, DSC scans, X-ray diffractograms, and
POM textures. This material is available free of charge via the
Internet at http://pubs.acs.org.
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(7) (a) Kreuder, W.; Ringsdorf, H.; Hermann-Schonherr, O.;
̈
AUTHOR INFORMATION
■
Wendorff, J. H. Angew. Chem., Int. Ed. Engl. 1987, 26, 1249−1252.
(b) Mahlstedt, S.; Janietz, D.; Strake, A.; Wendorff, J. H. Chem. Commun.
2000, 15−16. (c) Kouwer, P. H. J.; Pourzand, J.; Mehl, G. H. Chem.
Commun. 2004, 66−67. (d) Kouwer, P. H. J.; Mehl, G. H. J. Mater. Chem.
2009, 19, 1564−1575. (e) Tanaka, D.; Ishiguru, H.; Shimizu, Y.; Uchida,
K. J. Mater. Chem. 2012, 22, 25065−25071.
(8) Kumar, S.; Varshney, S. K. Liq. Cryst. 2001, 28, 161−163.
(9) Schulte, J. L.; Laschat, S.; Schulte-Ladbeck, R.; von Arnim, V.;
Schneider, A.; Finkelmann, H. J. Organomet. Chem. 1998, 552, 171−176.
(10) Cammidge, A. N.; Gopee, H. Chem. Commun. 2002, 966−967.
(11) Mohr, B.; Wegner, G.; Ohta, K. Chem. Commun. 1995, 995−996.
(12) Yang, F.; Bai, X.; Guo, H.; Li, C. Tetrahedron Lett. 2013, 54, 409−
413.
Corresponding Authors
*E-mail for P.E.: espinet@qi.uva.es.
*E-mail for S.C.: scoco@qi.uva.es.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was sponsored by the Ministerio de Ciencia e
Innovacion
́
(Project CTQ2011-25137), the Junta de Castilla y
Leon
́
(Project VA302U13), MICINN-FEDER of Spain-UE
(13) (a) Ros, M. B.; Ruiz, N.; Serrano, J. L.; Espinet, P. Liq. Cryst. 1991,
9, 77−96. (b) Coco, S.; Cordovilla, C.; Espinet, P.; Gallani, J.-L.;
Guillon, D.; Donnio, B. Eur. J. Inorg. Chem. 2008, 1210−1218.
(14) Kumar, S.; Manickam, M. Synthesis 1998, 1119−1122.
(15) Baena, M. J.; Espinet, P.; Ros, M. B.; Serrano, J. L. J. Mater. Chem.
1996, 6, 1291−1296.
(Project MAT2012-38538-C03-02), and the Basque Country
Government (Project GI/IT-449-10). E.T. and G.S.-E. thank the
European Commission (Erasmus Mundus) and the Basque
Country University, respectively, for grants. The authors thank
one of the reviewers for helpful suggestions about the structural
́
characterization of the mesophases and Prof. Jesus Etxebarria
́
(16) (a) Onoue, H.; Minami, K.; Nakagawa, K. Bull. Chem. Soc. Jpn.
1970, 43, 3480−3485. (b) Nakamoto, N. IR and Raman Spectra of
Inorganic and Coordination Compounds, 3rd ed.; Wiley-Interscience:
New York, 1978. (c) Baena, M. J.; Buey, J.; Espinet, P.; Kitzerow, H.-S.;
Heppke, G. Angew. Chem., Int. Ed. 1993, 32, 1201−1203. (d) Baena, M.
J.; Buey, J.; Espinet, P.; García-Prieto, C. E. J. Organomet. Chem. 2005,
690, 998−1010.
(Basque Country University) for valuable discussions on the
paper.
REFERENCES
■
(1) (a) Kaafarani, B. R. Chem. Mater. 2011, 378−396. (b) Pisula, W.;
Zorn, M.; Chang, J. C.; Mullen, K.; Zentel, R. Macromol. Rapid Commun.
̈
́
́
(17) Buey, J.; Diez, G. A.; Espinet, P.; Garcıa-Granda, S.; Perez-
2009, 30, 1179−1202. (c) Kato, T.; Yasuda, T.; Kamikawa, Y. Chem.
Commun. 2009, 729−739. (d) Sergeyev, S.; Pisula, W.; Geerts, Y. H.
Chem. Soc. Rev. 2007, 36, 1902−1929. (e) Laschat, S.; Baro, A.; Steinke,
N.; Giesselmann, F.; Hagele, C.; Scalia, G.; Judele, R.; Kapatsina, E.;
Sauer, S.; Schreivogel, A.; Tosoni, M. Angew. Chem., Int. Ed. 2007, 46,
Carreno, E. Eur. J. Inorg. Chem. 1998, 9, 1235−1241.
̃
(18) Folcia, C. L.; Alonso, I.; Ortega, J.; Etxebarria, J.; Pintre, I.; Ros, M.
B. Chem. Mater. 2006, 18, 4617−4626.
̈
́ ́
(19) (a) Markovitsi, D.; Germain, A.; Millie, P.; Lecuyer, P.; Gallos, L.
K.; Argyrakis, P.; Bengs, H.; Ringsdorf, H. J. Phys. Chem. 1995, 99,
1005−1017. (b) Marguet, S.; Markovitsi, D.; Millie, P.; Sigal, H.; Kumar,
S. J. Phys. Chem. B 1998, 102, 4697−4710.
4832−4887.
́
(2) (a) Hains, A. W.; Liang, Z.; Woodhouse, M. A.; Gregg, B. A. Chem.
Rev. 2010, 110, 6689−6735. (b) Oukachmih, M.; Destruel, P.; Seguy, L.;
Ablart, G.; Jolinat, P.; Archambeau, S.; Mabiala, M.; Fouet, S.; Bock, H.
Sol. Energy Mater. Sol. Cells 2005, 85, 535−543. (c) Schmidt-Mende, L.;
Fechtenkotter, A.; Mullen, K.; Moons, E.; Friend, R.; MacKenzie, J.
Science 2001, 293, 1119−1122.
(20) Velapoldi, R. A.; Tønnesen, H. H. J. Fluoresc. 2004, 14, 465−472.
(21) (a) Turro, N. J. Modern Molecular Photochemistry; University
Science Books: Mill Valley, CA, 1991. (b) Birks, J. B. Photophysics of
Aromatic Molecules; Wiley-Interscience: New York, 1970.
(3) (a) Shimizu, Y.; Kurobe, A.; Monobe, H.; Terasawa, N.; Kiyohara,
K.; Uchida, K. Chem. Commun. 2003, 1676−1677. (b) Bushby, R. J.;
Boden, N.; Kilner, C. A.; Lozman, O. R.; Lu, Z.; Liu, Q.; Thornton-Pett,
M. A. J. Mater. Chem. 2003, 13, 470−474. (c) Kato, T.; Mizoshita, N.;
Kishimoto, K. Angew. Chem., Int. Ed. 2006, 45, 38−68. (d) Kumar, S.
Chem. Soc. Rev. 2006, 35, 83−109. (e) Kumar, S. Liq. Cryst. 2005, 32,
1089−1113. (f) Kumar, S. Liq. Cryst. 2004, 31, 1037−1059. (g) Gupta,
S. K.; Raghunathan, V.; Kumar, S. New. J. Chem. 2008, 33, 112−117.
(h) Bisoyi, H. K.; Kumar, S. Tetrahedron Lett. 2008, 49, 3628−3631.
(i) Feng, X.; Marcon, V.; Pisula, W.; Hansen, M. R.; Kirkpatrick, J.;
Grozema, F.; Andrienko, D.; Kremer, K.; Mullen, K. Nat. Mater. 2009, 8,
̈
421−426. (j) Tahar-Djebbar, I.; Nekelson, F.; Heinrich, B.; Donnio, B.;
Guillon, D.; Kreher, D.; Mathevet, F.; Attias, A.-J. Chem. Mater. 2011,
23, 4653−4656. (k) Sauer, S.; Steinke, N.; Baro, A.; Laschat, S.;
Giesselmann, F.; Kantlehner, W. Chem. Mater. 2008, 20, 1909−1915.
(4) (a) Espinet, P.; Esteruelas, M. A.; Oro, L.; Serrano, J. L.; Sola, E.
Coord. Chem. Rev. 1992, 117, 215−274. (b) Metallomesogens; Serrano, J.
L., Ed.; VCH: Weinheim, Germany, 1996. (c) Donnio, B.; Guillon, D.;
Bruce, D. W.; Deschenaux, R. Metallomesogens. In Comprehensive
Organometallic Chemistry III: From Fundamentals to Applications;
Crabtree, R. H., Mingos, D. M. P., Eds.; Elsevier: Oxford, U.K., 2006;
Vol. 12 (Applications III: Functional Materials, Environmental and
Biological Applications), Chapter 12.05, pp 195−294. (d) Donnio, B.
Inorg. Chim. Acta 2014, 409, 53−67.
(5) Bruce, D. W. In Inorganic Materials, 2nd ed.; Bruce, D. W.; O’Hare,
D., Eds.; Wiley: Chichester, U.K. 1996; Chapter 8.
(6) (a) Coco, S.; Cordovilla, C.; Domínguez, C.; Donnio, B.; Espinet,
P.; Guillon, D. Chem. Mater. 2009, 21, 3282−3289. (b) Domínguez, C.;
Heinrich, B.; Donnio, B.; Coco, S.; Espinet, P. Chem. Eur. J. 2013, 19,
5988−5995.
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