Azo isocyanide gold(l) liquid crystals, highly birefringent and photosensitive in the mesophase

Article abstract of DOI:10.1021/ic9005295

Isocyanide ligands bearing an azo group and one alkoxy chain OC _nH_2n+1 have been synthesized. They are calamitic liquid crystals for n < 4 and display nematic (n = 8, 12) and SmA (n = 12) mesophases. Their gold(l) compounds [AuX(CNR)

Full text of DOI:10.1021/ic9005295

Inorg. Chem. 2009, 48, 6205–6210 6205
DOI: 10.1021/ic9005295
Azo Isocyanide Gold(I) Liquid Crystals, Highly Birefringent and Photosensitive
in the Mesophase
†
†
,†
§
‡
,§
ꢀ
ꢀ
´
´
Javier Arias, Manuel Bardajı, Pablo Espinet,* Cesar L. Folcia, Josu Ortega, and Jesus Etxebarrıa*
†
´
ꢀ
IU CINQUIMA/Quımica Inorganica, Facultad de Ciencias, Universidad de Valladolid, 47011-Valladolid,
‡
§
´
´
Spain, Departamento de Fısica Aplicada II and Departamento de Fısica de la Materia Condensada Facultad
´
´
de Ciencia y Tecnologıa, Universidad del Paıs Vasco, Apartado 644, 48080-Bilbao, Spain
Received March 18, 2009
Isocyanide ligands bearing an azo group and one alkoxy chain OCnH2n+1 have been synthesized. They are calamitic
liquid crystals for n > 4 and display nematic (n = 8, 12) and SmA (n = 12) mesophases. Their gold(I) compounds
[AuX(CNR)] (X = Cl, C6F5; R = C6H4NdNC6H4OCnH2n+1, n = 4, 8, 12) have been obtained by displacement of a weakly
coordinated ligand. The chloro gold(I) compounds exhibit nematic (n = 4) and SmA mesophases, and decompose at
temperatures higher than 200 °C, before reaching the clearing point. The pentafluorophenyl gold(I) compounds show
nematic and SmA (n = 12) mesophases. All the derivatives are photosensitive in solution because of trans to cis
isomerization of the azo group under UV light, which reverts photochemically or thermally to the trans isomer.
Irradiation in the mesophase also induces isomerization with consequent destabilization of the mesophase to
an isotropic liquid; the mesophase is recovered as soon as illumination stops. These azo mesogens show high
birefringence values, higher for the linear gold complexes than for the free azo ligand.
Introduction
liquid (favored by the bent shape cis isomer).3,6,8,9 Occasion-
ally more complicated results have been obtained.10,11
The reversible light induced trans-cis photoisomerization
of the azo group has been exploited to modify systems by
inducing chemical and physical changes under irradiation.
The phenomenon consists of the isomerization of the most
stable trans configuration, with an elongated rod-like molec-
ular form, to the bent cis configuration upon UV irradiation at
λ ≈ 365 nm (Scheme 1). The reverse transformation can be
brought about thermally, or by illuminating with visible light
at λ ≈ 450 nm.1 The application of this phenomenon to
compounds or mixtures displaying liquid crystal properties
has been envisaged to design optical switching materials based
on light-induced isothermal phase transitions,2-7 as the trans
to cis isomerization typically produces the collapse of the
mesophase (stable for the rod-like trans isomer) to an isotropic
4,40-Disubstituted azobenzene compounds with appropri-
ate substituents are liquid crystals that have been used to
prepare orthometalated liquid crystals by reaction, mostly
with palladium(II).12 In the cyclometalated mesogens ob-
tainedthe NdN fragment, being involved ina metallacycle, is
obviously blocked in its trans conformation, and the photo-
sensitivity is suppressed.13 The chemistry of goldwith any azo
ligand, including orthometalated gold(III) complexes,14 is
(9) Kubo, S.; Gu, Z. Z.; Takahashi, K.; Ohko, Y.; Sato, O.; Fujishima, A.
J. Chem. Soc., Chem. Commun. 1990, 1751.
(10) Prasad, S. K.; Nair, G. G. Adv. Mater. 2001, 13, 40.
(11) Krentzel, T. A.; Lavrentovich, O. D.; Kumar, S. Mol. Cryst. Liq.
Cryst. 1997, 304, 463.
(12) Ghedini, M.; Aiello, I.; Crispini, A.; Golemme, A.; La Deda, M.;
Pucci, D. Coord. Chem. Rev. 2006, 250, 1373.
(13) Donnio, B.; Guillon, D.; Bruce, D. W.; Deschenaux, R. Metallome-
sogens. 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; D., O'Hare, Ed.; Chapter 12.05, p 195.
(14) (a) Dell’Amico, D. B.; Calderazzo, F.; Marchetti, F.; Merlino, S.
Gazz. Chim. Ital. 1978, 108, 627. (b) Vicente, J.; Chicote, M. T. Inorg. Chim.
*To whom correspondence should be addressed. E-mail: espinet@qi.uva.
es (P.E.), j.etxeba@ehu.es (J.E.).
(1) (a) Liu, Z. F.; Hashimoto, K.; Fujishima, A. Nature 1990, 347, 658.
(b) Willner, I.; Rubin, S.; Riklin, A. J. Am. Chem. Soc. 1991, 113, 3321.
(2) Urbas, A.; Tondiglia, V.; Natarajan, L.; Sutherland, R.; Yu, H.;
Li, J. H.; Bunning, T. J. Am. Chem. Soc. 2004, 126, 13580.
(3) Ikeda, T.; Tsutsumi, O. Science 1995, 268, 1873.
(4) Xie, S.; Natansohn, A.; Rochon, P. Chem. Mater. 1993, 5, 403.
(5) Newton, J.; Walton, H.; Coles, H.; Hodge, P. Mol. Cryst. Liq. Cryst.
1995, 260, 107.
ꢀ
Acta 1981, 54, L259. (c) Vicente, J.; Bermudez, M. D.; Escribano, J.; Carrillo,
M. P.; Jones, P. G. J. Chem. Soc., Dalton Trans. 1990, 3083. (d) Vicente, J.;
ꢀ
Bermudez, M. D.; Escribano, J.; Carrillo, M. P.; Jones, P. G. J. Organomet.
ꢀ
ꢀ
Chem. 1993, 456, 305. (e) Vicente, J.; Bermudez, M. D.; Carrion, F. J.;
(6) Tsutsumi, O.; Shiono, T.; Ikeda, T.; Galli, G. J. Phys. Chem. 1997,
101, 1332.
ꢀ
Martınez-Nicolas, G. J. Organomet. Chem. 1994, 480, 103. (f) McDonagh,
´
A. M.; Lucas, N. T.; Cifuentes, M. P.; Humphrey, M. G.; Houbrechts, S.;
Persoons, A. J. Organomet. Chem. 2000, 605, 184. (g) Alder, M. J.; Flower,
K. R.; Pritchard, R. G. J. Organomet. Chem. 2001, 629, 153. (h) Maiti, N.;
Dirghangi, B. K.; Chattopadhyay, S. Polyhedron 2003, 22, 3109.
(7) Furumi, S.; Akiyama, H.; Morino, S.; Ichimura, K. J. Mater. Chem.
1998, 8, 65.
(8) Kurihara, S.; Ikeda, T.; Sasaki, T.; Kim, H. B.; Tazuke, S. J. Am.
Chem. Soc. 1995, 268, 1873.
r
2009 American Chemical Society
Published on Web 06/08/2009
pubs.acs.org/IC

6206 Inorganic Chemistry, Vol. 48, No. 13, 2009
Arias et al.
Scheme 1
Scheme 2. (i) HCl(conc); T<5 °C, NaNO2; NH2Ph; NH2Ph+PhNH2
3
HCl; (ii) HCOOH, Reflux in Toluene; (iii) OC(OCCl3)2, NEt3; (iv) [AuX-
(tht)] (X=Cl, C6F5)a
comparatively scarce, and very little is known about their
photoisomerization behavior. To our knowledge, the poten-
tial photoisomerization behavior was only studied, in solu-
tion, for the interesting case of a tetranuclear macrocyclic
gold(I) alkynyl phosphine complex, in which the trans-cis
photoisomerization in solution can be locked by addition of
silver(I), which π-coordinates to the alkynyl groups and
precludes the breadth of the macrocycle associated to the
presence of a cis azo group.15
Only a few metallomesogens containing an uncomplexed
-NdN- function, and therefore keeping their potential for
photoisomerization, have been reported. These are some
calix[4]arene W(VI),16 enamino ketone Cu(II),17 azopyri-
dine silver(I)18,19 and salicyl Ni(II), Cu(II), and V(IV) com-
plexes.20-22 However, very few physical studies have been
made: for the salicylidenediaminato nickel complexes,22 and
for the silver derivatives,18,19 the photoisomerization in solu-
tion was studied by UV-vis absorption. Only for the
previous silver complexes used as dopant (3% mol) of
organic liquid crystals was the photoisomerization verified
on LC films formed by this eutectic mixture, at room
temperature, by their absorption spectra (reflectance) in the
doped mesophase.18 In summary, there is no previous report
of a metallomesogen being tested for photoisomerization in
the mesophase produced by the pure compound.
Isocyanide ligands are commonly used to prepare gold
mesogens because of theremarkable thermal stability of these
complexes.23-25 Here we report the synthesis of isocyanide
ligands containing an azo group (azo isocyanide ligands) and
an alkoxy chain, which provide the first gold(I) mesogens
bearing an azo group. As the azo group is not involved in
coordination, these colored gold-containing liquid crystals
are photosensitive, not only in solution but also in the
mesophase. This is the first time that the photoisomerization
has been demonstrated in a mesophase displayed by a pure
metallomesogen.
a Labels for aromatic hydrogen atoms are as shown in the amines.
with aniline, and isomerization of the diazoamine com-
pound. The corresponding crude formamides, made by
reaction with formic acid, were not analytically pure
but were used without further purification to obtain
the isocyanides 2 by dehydration with triphosgene in
the presence of triethylamine. The isocyanides were
purified by column chromatography and were used to
prepare the gold(I) complexes 3-4 by displacement of the
weakly coordinating tht (tetrahydrothiophene) ligand
from the adequate gold(I) precursor.
Compounds 1-4 are air-stable red (1) or orange (2-4)
solids at room temperature, which were characterized by
elemental analysis, and by IR and NMR spectroscopy
(see Experimental Section). The IR spectra of 2a-c in
dichloromethane show the characteristic ν(CtN) ab-
sorption at 2127 cm-1, which shift to 2220 cm-1 and
2216 cm-1, respectively, for the gold compounds 3a-c and
4a-c. In the 1H NMR spectra, the aromatic protons
display two pseudodoublets (AA0XX0 systems) at about
7 ppm for Hd (see Scheme 2 for labels), and in the range
7.78-7.95 ppm for Hc; and two pseudodoublets in the
range 6.74-7.69 for Ha, and 7.85-8.0 ppm for the Hb. In
addition, the resonances corresponding to the aliphatic
chain are observed. The 19F NMR spectra of compounds
4 display the three resonances typical of the pentafluor-
ophenyl group, at -116, -158, and -163 ppm.
Mesogenic Behavior. The thermal behavior of all the
compounds prepared was studied using polarized light
optical microscopy and differential scanning calorimetry.
The results are collected in Table 1 and in Figure 1. The
mesophases were identified as nematic (N) or smectic
A (SmA) by polarized optical microscopy, based on their
characteristic textures (Figure 2).
All the azo amine compounds are non-mesogenic. The
azo isocyanide ligands are enantiotropic calamitic liquid
crystals, except for the shortest aliphatic chain (2a). Com-
pound 2b shows a nematic marbled texture. Compound
2c exhibits a N mesophase observed as a Schlieren tex-
ture; it is observed by optical microscopy in a short-range
Results and Discussion
Synthesis and Characterization. The synthesis of the
ligands and their gold complexes is summarized in
Scheme 2. The amines 1 were readily prepared by diazo-
tization of the corresponding alkoxy amine, coupling
(15) Tang, H. S.; Zhu, N.; Yam, V. W. W. Organometallics 2007, 26, 22.
(16) Xu, B.; Swager, T. M. J. Am. Chem. Soc. 1993, 115, 1159.
(17) Szydlowska, J.; Pyzuk, W.; Krowczynsky, A.; Bikchantaev, I.
J. Mater. Chem. 1996, 6, 733.
(18) Antharjanam, P. K. S.; Mallia, V. A.; Das, S. Chem. Mater. 2002, 14,
2687.
(19) Antharjanam, P. K. S.; Mallia, V. A.; Das, S. Liq. Cryst. 2004, 31,
713.
(20) Aiello, I.; Ghedini, M.; La Deda, M.; Neve, F.; Pucci, D. Chem.
Mater. 1997, 9, 2107.
(21) (a) Rezvani, Z.; Nejati, K.; Seyedahmadian, M.; Divband, B. Mol.
Cryst. Liq. Cryst. 2008, 493, 71. (b) Nejati, K.; Rezvani, Z. New J. Chem.
2003, 27, 1665.
(22) Aiello, I.; Ghedini, M.; La Deda, M.; Pucci, D.; Francescangeli, O.
Eur. J. Inorg. Chem. 1999, 1367.
(23) Espinet, P. Gold Bull. 1999, 32, 127.
(24) Ballesteros, B.; Coco, S.; Espinet, P. Chem. Mater. 2004, 16, 2062.
ꢀ
(25) Bayon, R.; Coco, S.; Espinet, P. Chem.-Eur. J. 2005, 11, 1079.

Article
Inorganic Chemistry, Vol. 48, No. 13, 2009 6207
Table 1. Optical, Thermal, and Thermodynamic Data for Compounds 2-4
and mixed with the following transition. Moreover,
a monotropic SmA mesophase is observed upon cooling,
which appears as the focal-conic fan texture. There-
fore, the longer the alkoxy chain, the lower transi-
tion temperatures, the wider the LC temperature range,
and the more ordered the mesophases obtained. It is
comp.
n
transitiona
T (°C)b
ΔH (kJ mol-1
)
c
2a
4
Cr-Cr0
70.1
91.7
78.1
72.9
90.7
101.2
97
70.7
70.6
87.0
(83.3)
71.7
175.5
207
1.1
17.0
-12.9
2.0
18.8
0.1
Cr0-I
I-Cr
c
c
2b
2c
8
Cr-Cr0
Cr0-N
N-I
worth to remark that analogous ligands CNR are not
while for R=
26
liquid crystals for R=C6H4OCnH2n+1
,
I-N d
N-Cr
Cr-Cr0
C6H4C6H4CnH2n+1, C6H4-C(O)O-C6H4CnH2n+1 the
isocyanides are mesogens,27,28 with transition tempera-
tures lower than for compound 2, and display N and SmA
mesophases.
-19.4
1.9
12
Cr0-Nd-Ie
(I-Nd-SmAe)
SmA-Cr
32.2f
(-0.6f)
-30.8
8.3
Coordination to gold(I) leads to compounds with high-
er transition temperatures, more ordered mesophases and
longer mesophase ranges. In fact, all compounds 3 are
liquid crystals that exhibit SmA mesophases, identified by
a focal-conic fan texture. These chloro complexes have
clearing temperatures higher than 200 °C and decompose
before reaching the isotropic liquid. In addition, the
derivative with the shortest chain, 3a, displays a nematic
mesophase which is observed (Schlieren texture) accom-
panied by some decomposition. Increasing the alkoxy
chain length reduces the melting temperature, which leads
to a larger mesophase range: 31.5, 69, and 105.5 °C, for
compounds 3a-c respectively. For the pentafluorophe-
nyl derivatives 4, the transition temperatures are de-
pressed, and they exhibit shorter mesophase ranges and
less ordered mesophases, but the compounds are ther-
mally stable also in the isotropic liquid. All compounds 4
display a nematic mesophase characterized by a Schlieren
texture. Previous to the N phase, compound 4c exhibits a
SmA mesophase identified by its focal-conic fan texture.
For compounds 4 the longer the alkoxy chain, the lower
the melting point, whereas the clearing points follow the
order 4a > 4c > 4b. Again, increasing the chain length
leads to a more ordered mesophase (for 4c) and to a wider
mesophase range: 28.6, 47, and 62.8 °C, respectively,
for 4a-c. In comparison, analogous chloro and penta-
fluorophenyl gold(I) compounds with other isocyanides
3a
3b
3c
4a
4
8
Cr-SmA
SmA-N(dec.)d
Cr-SmA
151.0
220
144.5
250
5.7
7.4
SmA-dec.d
Cr-SmA
12
4
SmA-dec.d
c
Cr-Cr0
96.7
153.4
182
33.0
90.0
105.7
152.7
76.2
104.2
153
0.4
15.8
Cr0-N
N-Id
c
4b
4c
8
Cr-Cr0
14.8
3.7
14.6
1.3
19.7
15.3
c
Cr0-Cr00
Cr00-N
N-I
c
12
Cr-Cr0
Cr0-SmA
SmA-Nd
N-Id
167
a Cr, Cr0, Cr00=crystal; I=isotropic liquid. b Data for the first heating
scan. c Only observed by DSC. d Only observed by POM. e There are two
close consecutive transitions, and the melting point is not sharp.
f Combined enthalpies.
26
27,29
CNR (R = C6H4OCnH2n+1
,
C6H4C6H4CnH2n+1,
are mesogens, and
28,30
C6H4-C(O)O-C6H4CnH2n+1
)
they exhibit N and SmA phases, and even SmC meso-
phases for the latter.
Photosensitivity in Solution. As stated above, the azo
functional group can undergo isomerization from the
more stable trans isomer to the cis isomer, under UV
light illumination. Representative organometallic gold
derivatives were studied for this property. The UV-vis
spectra of the trans-cis isomers of the chloro gold
compound 3b in CH2Cl2 solution are shown in Figure 3.
Initially, the trans isomer shows a maximum at 365 nm
associated with an azo πfπ* transition. Besides there
is a shoulder at 290 nm related to an aromatic π-π*
transition, and an absorption at 460 nm due to an
Figure 1. Thermal behavior of compounds CNR (2), [AuCl(CNR)] (3),
and [Au(C6F5)(CNR)] (4) (upon heating; n=4, 8, 12).
ꢀ
(26) Coco, S.; Espinet, P.; Falagan, S.; Martı
J. Chem. 1995, 19, 959.
´
n-Alvarez, J. M. New
n-Alvarez, J. M.
(27) Benouazzane, M.; Coco, S.; Espinet, P.; Martı
´
J. Mater. Chem. 1995, 5, 441.
(28) Kaharu, T.; Ishii, R.; Takahashi, S. J. Chem. Soc., Chem. Commun.
1994, 1349.
Figure 2. (a) Nematic Schlieren texture (100ꢀ) observed for 4b,
obtained on cooling from isotropic liquid at 130 °C. (b) Focal-conic
SmA texture (100ꢀ) observed for 4c, obtained on cooling from isotropic
liquid at 120 °C.
ꢀ
ꢀ
(29) Bayon, R.; Coco, S.; Espinet, P.; Fernandez-Mayordomo, C.;
Martın-Alvarez, J. M. Inorg. Chem. 1997, 36, 2329.
(30) Ferrer, M.; Mounir, M.; Rodrıguez, L.; Rossell, O.; Coco, S.;
n, A. J. Organomet. Chem. 2005, 690, 2200.
´
´
ꢀ
Gomez-Sal, P.; Martı
´

6208 Inorganic Chemistry, Vol. 48, No. 13, 2009
Arias et al.
Figure 4. Aligned textures of compound 4b in the nematic phase (100ꢀ)
between crossed polarizers before (a) and after (b) 10 s of illumination
with light of 442 nm and 1 W cm-2. The different colors in (b) correspond
to different degrees of nematic order, the order increasing from black
(isotropic phase), to pink and green. The orange color in the original
texture (a) indicates even larger birefringence.
Figure 3. UV-vis absorption spectra of compound 3b (2.5ꢀ10-5
M
temperatures (hence it offers higher thermal stability)
than other complexes. Planar samples were easily aligned.
Upon illumination of a zone of the mesophase at 90 °C
(nematic on cooling) with the He-Cd polarized laser,
a decrease of the birefringence is observed initially; after
a few seconds, the samples undergo an isothermal transi-
tion to the isotropic phase (Figure 4). The speed of the
effect is maximal when the light polarization is parallel to
the nematic director. As soon as the laser light is removed,
the illuminated zone recovers the initial aligned nematic
mesophase, likely because of the treatment of the surface
cell, which facilitates this alignment. As far as kept within
the nematic mesophase range, the exact temperature is
not very important and the isotropic transition is always
observed. The isotropic transition upon laser irradiation
is again interpreted as a consequence of the trans-cis
photoisomerization of the azo moiety. Under suitable
light irradiation, the cis population increases, and the
material becomes isotropic. Once the light is switched off,
the cis population diminishes as it returns to the more
stable (and more suited for mesophase formation) trans
configuration. The cis-trans conversion takes place in
short times (less than 1 s) at these relatively high tem-
peratures where thermal isomerization is very efficient.32
Birefringence Studies in the Mesophase. We have also
studied the birefringence of compounds 2b, 3b, and 4b,
containing the same azo isocyanide ligand (alkoxy chain
n=8), to see the effect of coordination. The effect of the
metal fragment depends on the structure of the molecule,
in fact complexes with birefringence values higher, similar
or lower than the free ligands have been described.33
In our case the three compounds display very high
birefringence, which is characteristic of materials based
on azo molecules.34 The measured values of Δn are 0.32
for the free ligand 2b at 80 °C (N mesophase); 0. 59 for the
AuCl complex 3b at 200 °C (SmA mesophase); and 0.51
for the AuC6F5 complex 4b at 113 °C (N mesophase).
At lower temperatures the optical anisotropy is even
higher. Although birefringence measurements have
been carried out at different reduced temperatures
dichloromethanesolution). The intense peakat364 nmcorrespondstothe
trans isomer before irradiation. Arrows indicate how the band intensities
change upon irradiation.
nfπ* transition.31 After irradiation at 365 nm with an
UV lamp, the intensity of the absorptions at 290 and
460 nm rises, whereas that of the band at 365 nm
diminishes, because of the formation of the cis isomer.
The observation of two isosbestic points in the spectra,
located at 302 and 423 nm, confirms the participation
of only two compounds, the cis and trans isomers, as
expected. The highest photoisomerization is reached in
240 s for illumination intensities of 7 mW cm-2. Switch-
3
ing off the irradiation, the thermodynamically less stable
cis complex isomerizes to its trans isomer very slowly: it
takes around 4 days in the dark to return to the initial
point, although this isomerization can be accelerated by
using visible light. An analogous result was obtained for
the pentafluorophenyl derivative 4b. These studies show
that the photochemical trans-cis and the thermal and
photochemical cis-trans isomerizations still occur in our
azo gold complexes in solution and take place without
any decomposition of the complex.
Photoisomerization experiments in NMR tubes at
295 K and concentrations about 2 ꢀ 10-2 M were carried
1
out. The H NMR spectra for compounds 2b-4b, after
irradiation with 365 nm light for about 1 h show trans/cis
ratios of 55/45, 43/67, and 50/50, respectively.
The four resonances corresponding to the cis isomer
appear as two pseudodoublets (AA0XX0 systems) at
about 6.77 and 6.90 ppm, respectively, for Hd and Hc
(see Scheme 2 for labels); and, two pseudodoublets in
the range 7.30-7.50 for Ha, and 6.88-6.98 ppm for Hb.
Compared to the resonances of the trans isomer, Hb and
Hc (ortho to the azo group) are shifted around -1 ppm
by the paramagnetic anisotropic shielding of the other
phenyl ring, while Ha and Hd (meta to the azo group) are
shifted about -0.20 and -0.25 ppm. Besides the methy-
lene alkoxy protons are shifted -0.14 ppm.
Photosensitivity in the Mesophase. Since the gold com-
plexes display photosensitivity in solution, it is interesting
to check this behavior in the mesophase. The nematic
phase of compound 4b was chosen for these experiments
because it has lower viscosity and appears at lower
(32) (a) Ikeda, T.; Sasaki, T.; Ichimura, K. Nature 1993, 361, 428.
(b) Lansac, Y.; Glaser, M. A.; Clark, N. A.; Lavrentovich, O. D. Nature
1999, 398, 54.
(33) Ros, M. B. Other Physical Properties and Possible Applications of
Metallomesogens in Metallomesogens; Serrano, J. L., Ed.; VCH: Weinheim,
Germany, 1996; Chapter 11, p 424.
(31) (a) Kumar, S. K.; Hong, J. D.; Lim, C. H.; Park, S. Y. Macro-
molecules 2006, 39, 3217. (b) Astrand, P. O.; Sommer-Larsen, P.; Hvilsted,
S.; Ramanujam, P. S.; Bak, K. L.; Sauer, S. P. A. Chem. Phys. Lett. 2000,
325, 115.
(34) (a) Hagen, R.; Bieringer, T. Adv. Mater. 2001, 13, 1805. (b) Folcia, C.
´
L.; Alonso, I.; Ortega, J.; Etxebarrıa, J.; Pintre, I.; Ros, M. B. Chem. Mater.
2006, 18, 4617.

Article
Inorganic Chemistry, Vol. 48, No. 13, 2009 6209
(T/Tc=0.944, 0.959, 0.908 for 2b, 3b, and 4b, respectively)
and even in different phases in some cases (N and SmA),
which precludes rigorous comparison, the values are so
clearly larger in the gold compounds (3b and 4b) that it
seems safe to conclude that the presence of gold plays an
important role in increasing the molecular anisotropy.
Calcd (%): C, 75.55; H, 9.25; N, 11.01. Found: C, 75.15; H, 8.92;
1
3
N, 10.65. H NMR of 1b: δ 0.89 (t, JHH=6.8 Hz, 3H, CH3),
1.31-1.84 (m, 12H, CH3-(CH2)6-), 4.02 (brm, 4H, O-CH2-
3
(CH2)n and NH2), 6.74 (d, JHH = 8.3 Hz, 2H, Ha), 6.98 (d,
3JHH=9.0 Hz, 2H, Hd), 7.78 (d, 2H, Hc), 7.85 (d, 2H, Hb). UV-
vis in CH2Cl2 (nm; ε/M-1 cm-1): 377 (28234), 249 (12481).
Synthesis of the Formamide R-NHCHO and the Isocyanide
R-NtC (R=C6H4-NdN-C6H4-OCnH2n+1), n=4 (2a), 8
(2b), 12 (2c). They were prepared by adapting the general
method of Ugi.40 Yield of 2a: 86 mg, 61%. Anal. Calcd (%):
C, 73.10; H, 6.13; N, 15.04. Found: C, 73.43; H, 5.74; N, 15.32.
Yield of 2b: 245 mg, 50%. Anal. Calcd (%): C, 75.19; H, 7.51; N,
13.03. Found: C, 75.52; H, 7.12; N, 13.19. Yield of 2c: 347 mg,
61%. Anal. Calcd (%): C, 76.69; H, 8.49; N, 10.73. Found: C,
Conclusions
A new azo isocyanide ligand bearing an alkoxy chain has
been prepared. This polyfunctional ligand is suitable for
stable coordination to gold(I) fragments through the isocya-
nide function. These derivatives display liquid crystal beha-
vior and undergo azo trans-cis photoisomerization not only
in solution but also in the mesophase. As a consequence of
the structural change of the molecular shape associated to
azo trans-cis isomerization, the mesophases are destabilized
by laser irradiation and lead to an isotropic liquid. This
change is reversible, and the initial mesophase is quickly
recovered when the laser irradiation is switched off. The gold
complexes show noticeably higher birefringence than the free
ligands.
76.85; H, 8.59; N, 11.02. 1H NMR of 2b (trans): δ 0.89 (t, 3JHH
=
6.8 Hz, 3H, CH3), 1.31-1.86 (m, 12H, CH3-(CH2)6-), 4.06 (t,
3JHH=6.6 Hz, 2H, O-CH2-(CH2)n), 7.02 (d, 3JHH=9.0 Hz, 2H,
Hd), 7.51 (d, 3JHH=8.8 Hz, 2H, Ha), 7.90 (d, 2H, Hb), 7.92 (d,
2H, Hc). IR (CH2Cl2): 2127 ν(CtN) cm-1. IR (KBr): 2118
ν(CtN) cm-1. IR (Nujol): 2118 ν(CtN) cm-1. UV-vis in
CH2Cl2 (nm; ε/M-1 cm-1): 356 (19885), 260 (12227), 229
1
(15429). H NMR of 2b (cis): δ 0.89 (m, 3H, CH3), 1.31-1.86
3
(m, 12H, CH3-(CH2)6-), 3.92 (t, JHH =6.6 Hz, 2H, O-CH2-
=
3
3
(CH2)n), 6.76 (d, JHH = 9.0 Hz, 2H, Hd), 6.88 (d, JHH
8.6 Hz, 2H, Hb), 6.89 (d, 2H, Hc), 7.30 (d, 2H, Ha).
Experimental Section
In the photosensitivity studies in solution (on 2.5ꢀ10-5
Synthesis of [AuCl(CNR)] R = C6H4-NdN-C6H4-OCn-
2n+1; n=4 (3a), 8 (3b), 12 (3c). To a dichloromethane solution
M
dichloromethane solutions), the UV-vis spectra were mea-
sured every 60 s, and the irradiation was carried out with
H
(20 mL) of [AuCl(tht)] (67 mg, 0.21 mmol) was added the
stoichiometric amount of the corresponding isocyanide 2b
(70 mg, 0.21 mmol). The resulting suspension was stirred for
15 min, and compound 3 was obtained as an insoluble orange
solid. Yield of 3a: 85 mg, 79%. Anal. Calcd (%): C, 39.90; H,
3.35; N, 8.21. Found: C, 39.51; H, 2.98; N, 8.08. Yield of 3b:
95 mg, 80%. Anal. Calcd (%): C, 44.42; H, 4.44; N, 7.40. Found:
C, 44.40; H, 4.07; N, 7.43. Yield of 3c: 113 mg, 86%. Anal. Calcd
(%): C, 48.12; H, 5.33; N, 6.73. Found: C, 48.16; H, 5.10; N,
7.06. 1H NMR of 3b (trans): δ 0.89 (t, 3JHH=6.8 Hz, 3H, CH3),
1.31-1.86 (m, 12H, CH3-(CH2)6-), 4.06 (t, 3JHH=6.6 Hz, 2H,
an UV lamp at λ=365 nm (I=7 mW cm-2). The same lamp
3
was used for the NMR photoisomerization studies on 2 ꢀ
10-2 M CDCl3 solutions. Planar samples were prepared in
commercially available cells (Linkam) of nominal thickness
of 5 μm. The inner glass surfaces were coated with polyimide
and rubbed unidirectionally. The induced alignment was
rather good in the nematic phases. Samples were illuminated
with polarized laser light, and the textures were simulta-
neously observed in the polarizing microscope. We employed
a He-Cd laser emitting at 442 nm, and the average inten-
sity of irradiation on the samples was about 1 W/cm2. The
birefringence was measured using a Berek compensator.
The optical path difference was determined through the
rotation angle of a calcite plate cut perpendicular to the
polarizing microscope axis.35 Transition temperatures and
enthalpies were measured by differential scanning calorime-
try, with a Perkin-Elmer DSC-7 (heating rate of 10 K min-1),
using aluminum crucibles. The apparatus was calibrated with
indium (156.6 °C, 28.45 J g-1) as standard. Other technical
detailswereaspreviouslyreported.36 Literature methods were
used to prepare [AuX(tht)] (X=Cl, C6F5).37,38 Only example
proceduresandIRandNMRdata(1HNMRkeyinScheme2)
for n=8 are described here, as the syntheses and the IR
and NMR data were similar for the rest of the compounds.
Yields and analytical data are given for all the compounds.
Synthesis of the Amine R-NH2 (R=C6H4-NdN-C6H4-
OCnH2n+1), n=4 (1a), 8 (1b), 12 (1c). They were prepared by
a standard procedure,39 but starting with p-alkoxyaniline com-
pounds. Yield of 1a: 348 mg, 67%. Anal. Calcd (%): C, 71.45; H,
7.11; N, 15.60. Found: C, 71.80; H, 6.95; N, 15.43. Yield of 1b: 63
mg, 26%. Anal. Calcd (%): C, 73.81; H, 8.36; N, 12.91. Found:
C, 74.15; H, 7.96; N, 12.81. Yield of 1c: 783 mg, 17%. Anal.
3
O-CH2-(CH2)n), 7.02 (d, JHH = 8.8 Hz, 2H, Hd), 7.66 (d,
3JHH=8.3 Hz, 2H, Ha), 7.95 (d, 2H, Hc), 7.98 (d, 2H, Hb). IR
(CH2Cl2): 2221 ν(CtN) cm-1. IR (KBr): 2238 ν(CtN) cm-1
.
IR (Nujol): 2238 ν(CtN) cm-1. UV-vis in CH2Cl2 (nm;
ε/M-1 cm-1): 364 (27229), 273 (16915), 227 (19118). 1H NMR
3
of 3b (cis): δ 0.89 (t, JHH=6.8 Hz, 3H, CH3), 1.31-1.86 (m,
3
12H, CH3-(CH2)63-), 3.92 (t, JHH = 6.5 Hz, 2H, O-CH2-
(CH2)n), 6.77 (d, JHH = 9.0 Hz, 2H, Hd), 6.92 (d, 2H, Hc),
6.98 (d, 3JHH=8.7 Hz, 2H, Hb), 7.49 (d, 2H, Ha).
Synthesis of [Au(C6F5)(CNR)] R = C6H4-NdN-C6H4-
OCnH2n+1; n=4 (4a), 8 (4b), 12 (4c). To a dichloromethane
solution (20 mL) of [Au(C6F5)(tht)] (88 mg, 0.19 mmol) was
added the stoichiometric amount of the isocyanide 2b (64 mg,
0.19 mmol). The resulting suspension was stirred for 15 min.
Then it was filtered through Kiesselgur (unreacted isocyanide if
any) and concentrated to dryness. Compound 4 was obtained as
an orange solid. Yield of 4a: 82 mg, 65%. Anal. Calcd (%): C,
42.94; H, 2.66; N, 6.53. Found: C, 42.58; H, 2.69; N, 6.55. Yield
of 4b: 92 mg, 67%. Anal. Calcd (%): C, 46.36; H, 3.60; N, 6.01.
Found: C, 45.97; H, 3.31; N, 5.82. Yield of 4c: 128 mg, 89%.
Anal. Calcd (%): C, 49.28; H, 4.40; N, 5.56. Found: C, 48.91; H,
4.22; N, 5.65. 1H NMR of 4b (trans): δ 0.89 (t, 3JHH=6.8 Hz, 3H,
CH3), 1.31-1.86 (m, 12H, CH3-(CH2)6-), 4.06 (t, 3JHH=6.6 Hz,
2H, O-CH2-(CH2)n), 7.03 (d, 3JHH=8.8 Hz, 2H, Hd), 7.69 (d,
3JHH=8.3 Hz, 2H, Ha), 7.95 (d, 2H, Hc), 8.00 (d, 2H, Hb). 19
F
(35) Wahlstrom, E. E. Optical crystallography with particular reference to
the use and theory of the polarizing microscope; John Wiley: New York, 1960.
NMR: δ -116.41 (m, 2F, Fo), -157.73 (m, 1F, Fp),
(36) Arias, J.; Bardajı
4990.
(37) Uson, R.; Laguna, A.; Laguna, M. Inorg. Synth. 1989, 26, 85.
´
, M.; Espinet, P. J. Organomet. Chem. 2006, 691,
-162.73 (m, 2F, Fm). IR (CH2Cl2): 2216 ν(CtN) cm-1. IR
(KBr): 2221 ν(CtN) cm-1. IR (Nujol): 2220 ν(CtN) cm-1
.
ꢀ
ꢀ
(38) Uson, R.; Laguna, A.; Vicente, J. Chem. Commun. 1976, 353.
(39) Vogel, A. I.; Tatchell, A. R.; Furnis, B. S.; Hannaford, A. J.; Smith,
P. W. G. Vogel’s Textbook of Practical Organic Chemistry, 5th ed.; Longman
Group: London, 1989.
(40) Weber, W. P.; Gokel, G. W.; Ugi, I. K. Angew. Chem., Int. Ed. Engl.
1972, 11, 530.

6210 Inorganic Chemistry, Vol. 48, No. 13, 2009
Arias et al.
UV-vis in CH2Cl2 (nm; ε/M-1 cm-1): 366 (27354), 280 (18952),
=
and MAT2006-13571-C02; Consolider Ingenio 2010, Grant
ꢀ
INTECAT, CSD2006-0003), the Junta de Castilla y Leon
254 (20820), 231 (27375). 1H NMR of 4b (cis): δ 0.89 (t, 3JHH
6.8 Hz, 3H, CH3), 1.31-1.86 (m, 12H, CH3-(CH2)6), 3.93
(Projects VA012A08 and GR169) and the Gobierno Vasco
(Project IT-484-07) for financial support. J. Arias thanks the
3
3
(t, JHH = 6.6 Hz, 2H, O-CH2-(CH2)n), 6.78 (d, JHH
=
3
9.2 Hz, 2H, Hd), 6.92 (d, 2H, Hc), 6.98 (d, JHH = 9.0 Hz,
Ministerio de Educion y Ciencia (Spain) for a grant.
ꢀ
2H, Hb), 7.50 (d, 2H, Ha).
Supporting Information Available: IR and NMR data for
compounds with n = 4, 12. This material is available free of
charge via the Internet at http://pubs.acs.org.
ꢀ
Acknowledgment. We thank the Spanish Comision Inter-
ministerial de Ciencia y Tecnologıa (Projects CTQ2008-03954
´