Mesomorphic properties of diesters with p-substituted-arylazomethine pendant groups

Article abstract of DOI:10.1080/154214090959984

The substituent steric and electronic effects on mesophase stability and glass-forming properties of a series of 1,4-bis-(4- n -alkyloxybenzoyloxy)-2- N -( p -Y-aryl)azomethinebenzenes were evaluated. The diesters showed a typical though mild dependence of the monotropic nematic-isotropic transition temperatures on the substituent size that was attributed to the conformational flexibility of the pendant azomethine group. In contrast, the dependence of the entropy change associated with the nematic-isotropic transition showed an atypical behavior ascribed to the extreme reduction of the mesogen axial ratio. The introduction of the bulky arylazomethine group on a lateral position originated significant crystallization supercooling. The appearance of glassy mesophases was detected in some of the diesters; the OEt and CF 3 groups were the more effective substituents to promote the formation of nematic glasses.

Full text of DOI:10.1080/154214090959984

Mol. Cryst. Liq. Cryst., Vol. 451, pp. 21–32, 2006
Copyright # Taylor & Francis Group, LLC
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/154214090959984
Mesomorphic Properties of Diesters with
p-Substituted-Arylazomethine Pendant Groups
ꢀ
Sandra A. Hernandez
Rau´ l O. Garay
ꢀ
´
Instituto de Investigaciones en Quımica Organica, Departamento de
´
´
Quımica, Universidad Nacional del Sur, Bahıa Blanca, Argentina
The substituent steric and electronic effects on mesophase stability and glass-
forming properties of a series of 1,4-bis-(4-n-alkyloxybenzoyloxy)-2-N-(p-Y-aryl)
azomethinebenzenes were evaluated. The diesters showed a typical though mild
dependence of the monotropic nematic–isotropic transition temperatures on the
substituent size that was attributed to the conformational flexibility of the pendant
azomethine group. In contrast, the dependence of the entropy change associated
with the nematic–isotropic transition showed an atypical behavior ascribed to
the extreme reduction of the mesogen axial ratio. The introduction of the bulky ary-
lazomethine group on a lateral position originated significant crystallization
supercooling. The appearance of glassy mesophases was detected in some of the
diesters; the OEt and CF3 groups were the more effective substituents to promote
the formation of nematic glasses.
Keywords: glassy mesophase; liquid crystal; nematic; substituent effects
INTRODUCTION
Understanding the structure–property relationships has been a major
driving force in liquid crystals research. It has been demonstrated that
even small structural changes of the mesogens lead to significant var-
iations in their physicochemical and electrooptical properties [1,2].
Among other structural modifications, the effect of lateral substitution
Financial support for this research was provided by Consejo Nacional de Investiga-
ꢀ
´
ciones Cientıficas (CONICET), Agencia Nacional para la Promocion Cientifica
y
ꢀ
´
´
Tecnologica (ANPCyT), and Secretarıa General de Ciencia y Tecnica-Universidad
Nacional del Sur (SGCyT).
´
Address correspondence to R. Garay, INIQO, Departamento de Quımica, Universidad
´
Nacional del Sur, Alem 1253, 8000 Bahıa Blanca, Argentina. E-mail: rgaray@criba.
edu.ar
21

ꢀ
S. A. Hernandez and R. O. Garay
22
SCHEME 1 Structures and acronyms of the diesters.
on the overall properties of many low-molecular-weight [3–5] and poly-
meric [6] nematic liquid crystals has been studied in the past decades.
Most of the studies refer to systems in which the substituent is directly
attached to the mesogenic unit. However, as Gray noted, the relative
effect of a lateral substituent on mesophase stability depends not only
on the size and polarity of the substituent but also upon the nature of
the molecule into which it is introduced [3]. The main purpose of this
study is to evaluate the electronic and steric effects on mesophase
stability of diesters bearing an N-arylazomethine pendant group with
a para-substituent. Because the substituent groups are not directly
attached to the central part of the mesogen but appended instead on
a lateral moiety that has conformational flexibility, the consequences
of the substitution on the mesomorphic properties are not apparent.
The mnemonic used for these compounds is nA[Y] where n denotes
the number of carbon atoms in the alkyl terminal chains, A the aryla-
zomethine lateral group and [Y] the substituent in the para position in
the arylazomethine group.
RESULTS AND DISCUSSION
The transitional properties of the compounds 4A[Y] and 6A[Y] are sum-
marized in Table 1 as well as those corresponding to the compound 6H.
Because only the transition temperatures of 6H are available in the
literature, this compound was synthesized to determine its transition
enthalpies [7]. The melting points and the liquid crystalline transition
temperatures listed are the peak maxima in the DSC traces. Each sam-
ple was treated in an identical manner, namely, ꢀheated at 10ꢀC minꢁ1
into the isotropic phase, then cooled to 30ꢀC at 10 C minꢁ1, held at that
temperature, and subsequently reheated into the isotropic phase. Many
of the compounds have a tendency to produce several solid modifications
and some of them show cold crystallization exotherms or no significant
melting endotherms in the second heating cycle. The compounds are
monotropic nematogens with the exception of 4A[NO2], 6A[NO2], and

Diesters with Arylazomethine Pendant Groups
23
TABLE 1 Calorimetric Investigation of the 4A and 6A Seriesa
1HC
1CC
Compound
Tm
DHm
Tm
TNI
(119)
(95)
DHNI DSNI=R
Tg
4A[H]
4A[NO2]
4A[CF3]
117b=128b=134 30.0
79–90c
49–64c
1.61
0.49
81b=95
5.4=34.2
89b=101 42.7=4.6
0.88
0.29
2.3
6H
6A[H]
125 32.9
124 32.8
123 53.2
115
215
(103)
(85)
2.30
1.62
1.25
1.21
0.57
0.52
0.42
0.40
74–86c
6A[Cl]
6A[CH3]
6A[CN]
6A[NO2]
6A[CF3]
6A[OEt]
6A[Ph]
97 42.4
(90)
127 90.2
73
105–110d
115b=144 52.5
122 48.6
(66)
(69)
(59)
0.90
0.73
0.42
0.32
0.26
0.15
6.0
ꢁ1.7
67b=87
5.0=30.4
102 43.4
aT ¼ ꢀC, DH ¼ KJ molꢁ1, DS ¼ J molꢁ1Kꢁ1
.
bTCC
.
cBroad exotherms with the main peak displaying one or more shoulders.
dDetected by optical microscope observations.
6A[CN] for which no mesophase is observed. The nematic phases were
assigned from their threaded optical textures.
The dependences upon the substituent van der Waals volumes, Vw,
of the transition temperatures as well as the entropy changes associa-
ted with the nematic–isotropic transition of the 6A series are shown in
Fig. 1. The transitional properties were plotted against Vw, instead of
van der Waals radii, rw, because the former account better for intermo-
lecular distance variations due to substituent changes [8]. The melting
points show no regular dependence on Vw. In contrast, the nematic–
isotropic transitions as well as the entropy associated with the
nematic–isotropic transition regularly decrease with increasing Vw.
The dependence of the TNI in 4A and 6A series is very typical of that
observed in nematogens [3]. Longer terminal chains lead to lower
nematic–isotropic transitions. Likewise, the TNI of 4A[H] and 6A[H]
are significantly lower than those reported for the unsubstituted anal-
ogous 4H (TNI ¼ 245ꢀC) and 6H (TNI ¼ 211ꢀC) as could be expected
from the decrease of the axial ratio of the mesogenic group caused by
the azomethine group attachment [7]. Because the DSNI=R remains
almost unchanged upon substitution (see entries 4 and 5 in Table 1),
the reduction of TNI reflects the decrease in the mesogenic core soft
interactions due to the increased biaxiality. Remarkably, even the
highly irregular 6A[Ph] displayed a nematic phase. The moderate

ꢀ
S. A. Hernandez and R. O. Garay
24
FIGURE 1 The dependence of the nematic–isotropic transition temperatures
on the van der Waals volumes of Y for the 6A series (&) and the dependence of
the entropy change associated with the nematic–isotropic transition on the
van der Waals volumes of Y for the 6A series (!).
response of TNI to substituent size can be attributed to the conforma-
tional flexibility of the pendant azomethine group that could allow the
p-aryl substituents to be partially aligned along the longitudinal axis
of the mesogenic unit, thus diminishing the effects due to the lateral
substituent size. Indeed, computer modeling studies have indicated
that the folded conformations (see Fig. 2) are predominant and that
their contribution to the conformational equilibria between folded and
extended conformations is significant [9]. On the other hand, the simi-
larity between the DSNI=R of 6H and 6A[H] as well as its reduction on
substitution at the para position in the 4A and 6A series are surprising
results if compared to structurally related compounds for which it is

Diesters with Arylazomethine Pendant Groups
25
FIGURE 2 PM3 geometry of the folded conformation of 6A[CF3].
often found that a lateral substituent in the central aromatic unit of the
triad increases DSNI=R [4]. According to Flory, small reductions in the
axial ratio would increase DSNI=R until a maximum is reached, and
then further reductions would result in a decrease of DSNI=R [10]. In
our case, it seems that the large axial ratio dwindling caused by the
bulky arylazomethine group leaves the mesogen in the regime where
further shortening of the axial ratio results in reductions of DSNI=R.
Both 4A[H] and 6A[H] showed strong supercooling, but eventually
they crystallize in the cooling cycle after revealing the metastable
mesophase. However, although the polar nature of the p-substituent
Y bears no effect on the nematic–isotropic transition, the substitution
with strong electronic-acceptor groups led to compounds with a higher
tendency to crystallize. Thus, no metastable mesophase was observed
for 4A[NO2], 6A[NO2], and 6A[CN]. Diesters 4A[NO2] and 6A[CN] dis-
tinctly showed only a crystallization exotherm in the cooling cycle with
less supercooling than those observed for 4A[H] and 6A[H]. However,
the DSC trace for 6A[NO2] was a flat line, and no transition of either
first or second order was recorded in the cooling cycle. However, we
were able to repeatedly visualize on the polarizing microscope a crys-
tallization transition at 110ꢀC. The remaining compounds of the 4A
and 6A series showed the transition to the metastable mesophase
but no crystallization exotherm above 30ꢀC in the cooling cycle. It
was possible to cycle repeated times between the isotropic and nematic
phases on the hot stage of the polarizing microscope without crystalli-
zation interference. Yet, some of them, 6A[Cl], 6A[CH3], and 6A[Ph],
crystallized shortly after they reached 20ꢀC in the hot stage of the
polarizing microscope. These diesters also displayed cold crystalliza-
tion exotherms in the DSC traces of the second heating cycle. Finally,
diesters 4A[CF3], 6A[CF3], and 6A[EtO] showed in the second heating
cycle the nematic–isotropic transition and either very small or no cold
crystallization exotherms and melting endotherms. Therefore, their
thermal behavior was also analyzed in a lower temperature range,

ꢀ
S. A. Hernandez and R. O. Garay
26
from ꢁ40ꢀC to 150ꢀC. At cooling rates of 10ꢀC, the DSC traces showed
a second-order transition indicating that all three diesters form glassy
nematic phases.
The glass transition temperatures quoted in Table 1 are the
inflexion points in the baseline. The DSC traces of the cooling and
second heating cycles for the glass-forming diesters 6A[CF3] and
6A[OEt] are shown in Fig. 3, together with the traces corresponding
to 6A[CH3], which crystallize at room temperature. On heating from
the glassy mesophase, 6A[CF3] showed significant melting transition
and cold crystallization only during and after isotropization, whereas
diester 6A[EtO] showed the glass transition, the nematic–isotropic
FIGURE 3 DSC traces for the first cooling and second heating cycles of a)
6A[CH3], b) 6A[CF3], and c) 6A[OEt].

Diesters with Arylazomethine Pendant Groups
27
transition, and very small cold crystallization exotherms and melting
endotherms. Analogously, 4A[CF3] showed only the glass and the
clearing transitions. Therefore, the ethoxy group, with moderate lipo-
philicity and larger VW, and the trifluoromethyl group, with very low
cohesive energy and low surface free energy (both with moderate
polarity but very low polarizability), are the substituents of choice to
avoid crystallization. As can be observed in Fig. 3, the substituent
groups are forced to lodge in the mesogen polar center even in the
folded conformations. Apparently, their lipophilicity and fluoro-
philicity interfere with the attractive interactions between the polar
centers of the mesogens. 6A[CF3] and 6A[CF3] showed higher glass
transition temperatures than 6A[OEt], though the variation is small.
It has been shown that enhanced molecular polarity results in increased
glass transition [11]. Though both groups are polar, the electron–
donating ethoxy group will oppose the dipole originated by the
azomethine group while the electron–withdrawing trifluoromethyl
group will reinforce it. Indeed, the molecular dipole moments calculated
at the semi-empirical level (PM3) for 6A[H], 6A[OEt], and 6A[CF3]
show the trend 2.11 D, 2.67 D, and 4.15 D, which is similar to the
trend reported for liquid crystal derivatives of 4-octyloxy-1-(p-Y-
arylazomethine)benzene with methoxy and trifluoromethyl groups [12].
In conclusion, we observed a typical though moderate dependence of
the monotropic nematic–isotropic transition temperatures on the van
der Waals volumes of the substituent that can be attributed to the con-
formational flexibility of the pendant azomethine group that could
allow them to be partially aligned along the mesogen longitudinal axis.
In contrast, the dependence of the entropy change associated with the
nematic–isotropic transition showed an atypical behavior ascribed to
the extreme reduction of the mesogen axial ratio. The introduction
on a lateral position of the bulky arylazomethine group originated sig-
nificant supercooling of the crystallization. The appearance of glassy
mesophases was detected in some of the compounds; the OEt and
CF3 groups were more effective in generating nematic glasses.
EXPERIMENTAL
All melting points are uncorrected. Elemental analysis were made in
the Universidad de Buenos Aires, INQUIMAE. 1H NMR and 13C
NMR spectra were recorded on a Bruker ARX300 spectrometer. Ther-
mal analysis was carried out on a Perkin-Elmer DSC7 instrument
equipped with a liquid nitrogen cooling system under a nitrogen flow
at scan rates of 10ꢀC=min with samples of about 10 mg. The melt beha-
vior was observed on an optical polarizing microscope (Leitz, Model

ꢀ
S. A. Hernandez and R. O. Garay
28
Ortolux) equipped with a pair of crossed polarizers and a hot stage
(Mettler).
Molecular Modeling
Molecular Modeling of the compounds and molecular dipole moments
calculation were carried out at the semi-empirical level using the PM3
MO program [14]. Modeling was assumed to be carried out in the gas
phase at 0 K. The minimization operations were performed using the
conjugate gradient method and halted by setting the gradient option
at 0.01 kcal=mol. The lowest potential energy conformations were
found by minimization of the energy function in conjunction with con-
formation searches around various bonds. Several close energy
minima, common to each of the 6A series members, were found as a
result of the high conformational flexibility of the molecules. Though
the dipole absolute values of a compound varied for each of the mini-
mum, the trend for each of the minima in the 6A series members
was similar.
Synthesis
The para-substituted anilines, 2,5-dihydroxybenzaldehyde and para-
n-hexyloxybenzoyl chloride, were obtained commercially (Aldrich).
4-n-Butoxybenzoic acid was prepared according to
a method
previously described [13], and then the acid was refluxed in thionyl
chloride to afford 4-n-Butoxybenzoyl chloride. With the exception of
the compound with Y ¼ Ph, the synthesis of N-(2,5-dihydroxy-
benzylidene)-p-substituted-anilines has been already reported [9].
N-(2,5-dihydroxybenzylidene)-p-biphenylaniline. [Y ¼ Ph]. A
mixture of 2,5-dihydroxybenzaldehyde (2.5 g, 18.1 mmol) was dis-
solved in dry methanol (5 ml) under argon, and then a solution of 40-
biphenylaniline (3.06 g, 18.1 mmol) in dry methanol (11 ml) was added
at room temperature. After 1 h the reaction mixture was cooled to
5ꢀC, and a yellow precipitate was isolated by filtration. The solid
washed with pentane and recrystallized from a mixture of benzene–
tetrachloroethane–acetonitrile (3:1:2). Yield: 59%; mp: 186–190ꢀC.
1H NMR (acetone-d6): 12.52 (s, 1H, OH), 8.86 (s, 1H, HC¼N), 8.02
0
(s, 1H, OH), 7.76 (d, 2H, Jo 8.8 Hz), 7.70 (d, 2Ho,o , Jo 7.3 Hz), 7.50 (d,
0
2H, Jo 8.8 Hz), 7.46 (d, 2Hm,m , Jo 7.3 Hz), 7.38 (t, 1Hp, Jo 7.3 Hz),
7.07 (d, 1H, Jm 2.9 Hz), 6.98 (dd, 1H, Jo 8.8 Hz and Jm 2.9 Hz), 6.84
(d, 1H, Jo 8.8 Hz). 13C NMR (acetone-d6): 162.9, 153.1, 149.6, 147.6,
139.4, 138.5, 128.9, 127.6, 127.5, 126.5, 121.4, 121.2, 119.3, 117.3,

Diesters with Arylazomethine Pendant Groups
29
116.9. Anal. calcd. for C19H15NO2: C, 78.87; H, 5.23; N, 4.84. Found: C,
79.31: H, 5.28: N, 4.46.
Diesters Synthesis
The Compounds 4A[Y] and 6A[Y], as well as 6H, were prepared by the
overnight reaction of the substituted hydroquinones (2.0 mmol) with
either p-n-hexyloxybenzoyl chloride or 4-n-butoxybenzoyl chloride
(4.1 mmol) in Cl2CH2 (40 ml) in the presence of Et3N (1.0 ml) at room
temperature and purified by several recrystallizations from ethanol.
Yields of purified model compounds: 40–70%. The diesters purity
1
was checked by TLC, and then they were fully characterized by H
and 13C NMR. The following numbering system to describe the proton
and carbons in the range of structurally similar compounds was
1
applied to the H and 13C NMR spectra.
0
4A[H]. 1H NMR (CDCl3): 6.97 (d, 4H2,2 , Jo 8.8), 8.15 (d, 2H3, Jo 8.8),
0
8.14 (d, 2H3 , Jo 8.8), 7.39 (dd, 1H7, Jo 8.8, Jm 2.7), 7.30 (d, 1H8, Jo 8.8),
8.08 (d, 1H11, Jm 2.7), 8.57 (s, 1H12), 7.34 (d, 2H14, Jo 8.0), 7.19–7.09
0
(m, 3H015,16), 4.05 (t, 2H17, J 6.6), 4.04 (t, 2H17 , J 6.6), 1.91–1.77 (m,
0
0
4H18,18 ), 1.64–1.46 (m, 4H19,19 ), 0.99 (t, 3H20, J0 6.9), 0.98 (t, 3H20
,
J 6.9). 13C NMR (CDCl3): 163.8 (C1), 163.6 (C1 ), 114.5 (C2), 114.3
0
0
0
0
(C2 ), 132.4 (C3), 132.3 (C3 ), 121.3 (C4,4 ), 164.6 (C5,5 ), 148.4 (C6),
125.5 (C7), 121.0 (C8), 148.8 (C9), 129.6 (C10), 124.0 (C11), 153.9 (C12),
0
151.8 (C13), 120.8 (C14), 129.0 (C15), 126.2 (C16), 68.0 (C17,17 ), 31.0
0
0
0
(C18,18 ), 19.1 (C19,19 ), 13.7 (C20,20 ). Anal. calcd. for C35H35NO6: C, 74.32;
H, 6.24; N, 2.48. Found: C, 74.17; H, 6.28; N,0 2.27.
0
4A[NO2]. 1H NMR (CDCl3): 6.97 (d, 4H2,2 , Jo 8.8), 8.16 (d, 4H3,3 , Jo
8.8), 7.45 (dd, 1H7, Jo 8.8, Jm 2.7), 7.33 (d, 1H8, Jo 8.8), 8.08 (d, 1H11,
Jm 2.7), 8.52 (s, 1H12), 7.13 (d, 2H14, Jo 8.0), 8.19 (d, 2H15,16, Jo 8.8),
0
0
4.06 (t, 2H17, J 6.6), 0 4.05 (t, 2H17 , J 6.6), 1.88–1.74 (m, 4H18,18 ),
0
1.61–1.42 (m, 4H19,19 ), 0.99 (t, 6H20,20 , J 6.9). 13C NMR (CDCl3):
164.9, 163.7, 114.5, 114.4, 132.4, 132.3, 120.8, 164.6, 148.8, 125.6,
121.4, 148.9, 128.8, 124.2, 156.5, 157.5, 121.1, 129.1, 145.6 (C16),
68.0, 31.0, 19.1, 13.7. Anal. calcd. for C35H34N2O8: C, 68.84; H, 5.61;
N, 4.59. Found: C, 68.68; H, 5.55; N, 4.35.

ꢀ
30
S. A. Hernandez and R. O. Garay
0
0
4A[CF3]. 1H NMR (CDCl3): 6.98 (d, 4H2,2 , Jo 8.8), 8.15 (d, 4H3,3 , Jo
8.8), 7.44 (dd, 1H7, Jo 8.8, Jm 2.7), 7.31 (d, 1H8, Jo 8.8), 8.08 (d, 1H11,
Jm 2.7), 8.52 (s, 1H12), 7.57 (d, 2H14, Jo 8.0)0, 7.14 (d, 2H15,16, Jo 8.8),
0
0
4.06 (t, 2H17,17 , J 6.6), 1.91–1.77 (m, 4H18,18 ), 1.64–1.45 (m, 4H19,19 ),
0
0.99 (t, 6H20,20 , J 6.9). 13C NMR (CDCl3): 164.0, 163.7, 114.4, 114.3,
0
132.3, 132.2, 121.2 (C4), 121.1 (C4 ), 164.6, 148.6, 126.1, 121.2, 148.8,
129.1, 124.1, 155.8, 154.9, 120.9 (q, C14, J14 1.0), 126.2 (q, C15, J15
4
3
4.0), 127.9 (q, C16, J16 32.2), 68.0, 31.0, 19.1, 13.7, 123.8 (q, CF3,
2
1JCF3 273.0). Anal. calcd. for C36H34F3NO6: C, 68.24; H, 5.41; N, 2.21.
Found: C, 68.07; H, 5.35; N, 2.17.
0
0
1
6H. H NMR (CDCl3): 6.96 (d, 4H2,2 , Jo 8.9), 8.13 (d, 4H3,3 Jo 8.9),
0
0
7.25 (s, 4H7,8), 4.03 (0t, 4H17,17 J 6.6), 1.86–1.75 (m, 4H18,18 ), 1.53–
0
0
0
1.26 (m, 12H19,19 ,20,20 ,21,21 ), 0.91 (t, 6H22,22 J 7.0).13C NMR (CDCl3):
163.6, 114.3, 132.3, 121.4, 164.8, 148.4, 122.6, 68.3, 31.5, 25.6, 29.0,
22.6, 14.0.
0
6A[H]. 1H NMR (CDCl3): 6.98 (d, 4H2,2, Jo 8.8), 8.16 (d, 2H3, Jo 8.8),
0
8.15 (d, 2H3 , Jo 8.8), 7.40 (dd, 1H7, Jo 8.8, Jm 2.7), 7.31 (d, 1H8, Jo 8.8),
8.09 (d, 1H11, Jm 2.7), 8.58 (s, 1H12), 7.35 (d, 2H14, Jo 8.0), 7.20–7.10
0
(m, 3H15,160), 4.05 (t, 2H17, J 6.6), 4.04 0 (t, 2H17 , J 6.6), 1.89–1.76
0
0
(m, 4H18,18 ), 1.53–1.34 (m, 12H19,19 ,20,20 ,21,21 ), 0.92 (t, 3H22, J 6.9),
0
0
0.91 (t, 3H22 , J 6.9). 13C NMR (CDCl3): 163.9 (C1), 163.7 (C1 ), 114.5
0
0
0
(C2),0 114.4 (C2 ), 132.4 (C3), 132.3 (C3 ), 121.1(C4), 120.8 (C4 ), 164.6
(C5,5 ), 148.5 (C6), 125.5 (C7), 121.1 (C8), 148.9 (C9), 129.7 (C10), 124.0
(C11), 154.0 (C12), 151.8 (C13), 120.8 (C14),0 129.1 (C15), 126.2 (C16),
0
0
0
68.4=68.3 (C17,17 ), 31.5 (C18,18 ), 25.6 (C19,19 ), 29.1=29.0 (C20,20 ), 22.5
0
0
(C21,21 ), 13.9 (C22,22 ).
0
6A[Cl]. 1H NMR (CDCl3): 6.99 (d, 2H2, Jo 8.8), 6.98 (d, 2H2 , Jo 8.8),
0
8.16 (d, 2H3, Jo 8.8), 8.15 (d, 2H3 , Jo 8.8), 7.41 (dd, 1H7, Jo 8.8, Jm 2.7),
7.31 (d, 1H8, Jo 8.8), 8.07 (d, 1H11, Jm 2.7), 8.54 0(s, 1H12), 7.28 (d, 2H14,
Jo 8.8), 7.03 (m, 2H15, Jo 8.8), 40.05 (t, 4H17,17 , J 6.6), 1.90–1.76 (m,
0
0
0
0
4H18,18 ), 1.54–1.31 (m, 12H19,19 ,20,20 ,21,21 ), 0.92 (t, 6H22,22 , J 6.9).
13C NMR (CDCl3): 163.9, 163.7, 114.5, 114.3, 132.4, 132.3, 121.2,
121.1, 164.6, 148.5, 125.7, 121.1, 148.8, 129.3, 124.0, 154.2, 150.2,
122.1, 129.1, 131.8 (C16), 68.4=68.3, 31.5, 25.6, 29.0=28.9, 22.5, 13.9.
0
6A[CH3]. H NMR (CDCl3): 7.00 (d, 2H2, Jo 8.8), 6.98 (d, 2H2 , Jo
1
0
8.8), 8.15 (d, 2H3, Jo 8.8), 8.14 (d, 2H3 , Jo 8.8), 7.38 (dd, 1H7, Jo 8.8,
Jm 2.7), 7.30 (d, 1H8, Jo 8.8), 8.08 (d, 1H11, Jm 2.7), 8.58 (s, 1H12),
0
6.96 (d, 2H14, Jo 8.0),0 7.12 (m, 2H15, Jo 8.0), 4.05 (t, 4H17,17 , J6.6),
0
0
0
1.89–1.76 (m, 4H18,18 ), 1.54–1.32 (m, 12H19,19 ,20,20 ,21,21 ), 0.91 (t,
0
6H22,22 , J 6.9), 2.32 (s, 3H, CH3). 13C NMR (CDCl3): 163.8, 163.6,
114.5, 114.3, 132.4, 132.3, 121.1, 120.8, 164.6, 148.3, 125.3, 121.0,
148.9, 129.7, 123.9, 153.1, 149.2, 120.7, 129.6, 136.1 (C16),
68.3=ꢂ68.3, 31.5, 25.6, 29.0, 22.5, 13.9, 20.9 (CH3).

Diesters with Arylazomethine Pendant Groups
31
6A[CN]. 1H NMR (CDCl3): 6.97 (d, 4H2, Jo 8.8), 8.14 (d, 2H3, Jo 8.8),
0
8.13 (d, 2H3 , Jo 8.8), 7.43 (dd, 1H7, Jo 8.8, Jm 2.7), 7.30 (d, 1H8, Jo 8.8),
8.06 (d, 1H11, Jm 2.7), 8.49 (s0, 1H12), 7.10 (d, 2H14, Jo 8.0), 7.60 (m,
0
2H15, Jo 8.0), 4.05 (t, 4H10 7,17 , J 6.6), 1.89–1.76 (m, 4H18,18 ), 1.53–
0
0
0
1.31 (m, 12H19,19 ,20,20 ,21,21 ), 0.91 (t, 6H22,22 , J 6.9). 13C NMR (CDCl3):
163.9, 163.7, 114.3, 114.2, 132.3, 132.2, 121.0, 120.9, 164.6, 148.7,
125.3, 121.3, 148.9, 128.8, 124.2, 156.2, 155.6, 121.4, 133.3, 100.8
(C16), 68.3=ꢂ68.3, 31.4, 25.5, 28.9, 22.5, 13.9, 120.3 (CN).
0
1
6A[NO2]. H NMR (CDCl3): 6.98 (d, 4H2; Jo 8.8), 8.14 (d, 4H3,3 , Jo
8.8), 7.44 (dd, 1H7, Jo 8.8, Jm 2.7), 7.33 (d, 1H8, Jo 8.8), 8.09 (d, 1H11,
Jm 2.7), 8.51 (s, 1H12), 7.12 (d, 2H14, Jo 8.0), 8.18 (m, 2H15, 0Jo 8.0), 4.05
0
(t, 4H17, J 6.6), 4.04 (t, 4H17 , J 6.6), 1.89–1.78 (m, 4H18,180 ), 1.52–1.32
0
0
0
(m, 12H19,19 ,20,20 ,21,21 ), 0.92 (t, 6H22, J 6.9), 0.91 (t, 6H22 , J 6.9). 13C
NMR (CDCl3): 164.0, 163.7, 114.6, 114.4, 132.4, 132.3, 121.0, 121.0,
164.6, 148.8, 125.6, 121.4, 148.9, 128.8, 124.2, 156.5, 157.5, 121.1,
129.1, 145.6, 68.4=68.3, 31.4, 25.6, 29.0=28.9, 22.5, 13.9.
0
6A[CF3]. H NMR (CDCl3): 6.98 (d, 4H2; Jo 8.8), 8.15 (d, 4H3,3 , Jo
1
8.8), 7.43 (dd, 1H7, Jo 8.8, Jm 2.7), 7.32 (d, 1H8, Jo 8.8), 8.08 (d,
1H11, Jm 2.7), 8.53 (s, 1H12), 7.57 (d, 2H14, Jo 8.0), 7.13 (m, 2H15, Jo
0
8.0), 4.05 (t, 4H17, J 6.6), 4.04 (t, 4H17 , J 6.6), 1.89–1.76 (m,
0
0
0
0
4H18,18 ), 1.53–1.34 (m, 12H19,19 ,20,20 ,21,21 ), 0.92 (t, 6H22, J 6.9), 0.91
0
(t, 6H22 , J 6.9). 13C NMR (CDCl3): 164.0, 163.7, 114.6, 114.4, 132.4,
132.3, 120.9, 120.6, 164.6, 148.7, 126.2, 121.3, 148.9, 129.1, 124.2,
4
3
155.8, 154.9, 120.9 (q, C14, J14,F 1.0), 126.3 (q, C15, J15,F 4.0), 127.3
(q, C16, J16,F 32.7), 68.4=68.3, 31.5=31.4, 25.6, 29.0=ꢂ29.0, 22.5,
2
1
13.9, 123.8 (q, CF3, JCF3 272.0).
0
6A[OEt]. H NMR (CDCl3): 6.98 (d, 2H2; Jo 8.8), 6.97 (d, 2H2 ; Jo
1
0
8.8), 8.16 (d, 2H3, Jo 8.8), 8.14 (d, 2H3 , Jo 8.8), 7.36 (dd, 1H7, Jo 8.8,
Jm 2.7), 7.28 (d, 1H8, Jo 8.8), 8.06 (d, 1H11, Jm 2.7), 8.58 (s, 1H12),
0
7.10 (d, 2H14, Jo 8.8), 0 6.82 (m, 2H15, Jo 8.8), 4.05 (t, 0 4H17,17, J 6.6),
0
0
1.89–1.76 (m, 4H18,18 ), 1.53–1.34 (m, 12H19,19 ,20,20 ,21,21 ), 0.91 (t,
0
6H22,22 , J 6.9), 4.00 (c, CH2, J 6.9), 1.37 (t, CH3, J 6.9). 13C NMR
(CDCl3): 163.8, 163.6, 114.5, 114.3, 132.3, 132.2, 121.3, 121.3, 164.6,
148.2, 125.0, 120.9, 148.8, 129.9, 123.9, 151.5, 144.4, 122.2, 114.9,
157.9, 68.3=ꢂ68.3, 31.5=31.5, 25.6, 29.0=ꢂ29.0, 22.5, 13.9, 63.6
(CH2), 14.9 (CH3).
0
6A[Ph]. 1H NMR (CDCl3): 6.98 (d, 2H2, Jo 8.8), 6.97 (d, 2H2, Jo 8.8),
0
8.16 (d, 2H3, Jo 8.8), 8.15 (d, 2H3 , Jo 8.8), 7.41 (dd, 1H7, Jo 8.8, Jm 2.7),
7.32 (d, 1H8, Jo 8.8), 8.10 (d, 1H11, Jm 2.7), 8.64 (s, 1H12), 7.56 (d, 2H14,
0
Jo 8.8), 7.18 (m, 2H15, Jo 8.8), 4.05 (t, 2H17, J 6.6), 4.04 (t, 20H17 , J6.6),
0
0
0
1.88–1.76 (m, 4H18,18 ), 1.54–1.32 (m, 12H19,19 ,20,20 ,21,21 ), 0.92 (t,
0
3H22, J 6.9), 0.91 (t, 3H22 , J 6.9), 7.56 (d, Jo 8.8, 2H o, o0), 7.44–7.26
(m, 3H m, m0, p). 13C NMR (CDCl3): 163.8, 163.6, 114.5, 114.3, 132.3,

ꢀ
S. A. Hernandez and R. O. Garay
32
132.2, 121.0, 120.7, 164.6, 148.7, 125.5, 121.2, 148.8, 129.6, 124.0,
153.7, 150.8, 121.3, 126.8, 139.1, 68.3=ꢂ68.3, 31.4=ꢂ31.4, 25.5,
29.0=ꢂ29,0, 22.5, 13.9, 140.4 (Ph, ipso), 126.8 (Ph, o, o0), 128,7 (Ph,
m, m0), 127.7 (Ph, p). Anal. calcd. for C45H47NO6: C, 77.45; H, 6.79;
N, 2.01. Found: C, 77.38; H, 6.80; N, 1.90.
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