M.K. Paul et al. / Journal of Molecular Structure 1049 (2013) 78–89
87
(
d, 1H, J = 8.4 Hz, ArH), 7.37 (t, 1H, J = 8.0 Hz, ArH), 7.29 (d, 1H,
J = 7.8 Hz, ArH), 6.98 (d, 1H, J = 8.4 Hz, ArH), 6.44 (s, 1H, ArH),
.03 (t, 2H, J = 7.8 Hz, AOCH A), 2.68 (s, 3H, ArACH ), 1.68–1.21
m, 8H, J = 6.6 Hz, A(CH A), 0.91 (t, 3H, J = 6.6 Hz, ACH ). Ele-
mental analysis calculated for C21 : C, 70.96%; H, 7.09%; N,
.94% Found: C, 70.56%; H, 6.97%; N, 3.63%.
(400 MHz, CDCl
3
): (d
C
), 165.6, 163.8, 163.6, 162.5, 152.7, 151.0,
150.5, 149.5, 141.8, 134.5, 133.8, 130.5, 129.7, 129.3, 128.5,
126.5, 124.0, 123.0, 122.8, 122.3, 113.0, 107.5, 101.5, 77.3, 76.9,
76.7, 67.9, 31.0, 21.5, 19.2, 15.5, 13.8. Elemental Analysis calcu-
4
(
2
3
2
)
3
3
H25NO
4
31 3 3
lated for C32H N O : C, 76.02%, H, 6.18%, N, 8.31% Found: C,
3
76.00%, H, 6.08%, N, 8.21%.
0
0
(
4 -Methyl phenyl azo) phenyl-4-yl 3-[N-(4 -n-pentyloxy-2-
0
0
5
.9. 4-Hydroxy-4 -methyl azobenzene (4a) and 4-hydroxy-4 -methoxy
hydroxybenzylidene)amino]-2-methyl benzoate, 1b: Yellow solid,
ꢂ1
azobenzene (4b)
Yield: 0.074 g (70%). IR
735 ( C@O, ester), 1610 (
lated for C33 : C, 76.28%; H, 6.40%; N, 8.09% Found: C,
m
max in cm : 3194 (
mOAH, H-bonded),
1
m
mCH@N, imine). Elemental Analysis calcu-
0
4
-Hydroxy-4 -methyl (methoxy) azobenzene was prepared fol-
33 3 3
H N O
lowing the general procedure reported earlier [73,74]. An aqueous
solution of sodium nitrite (33 mmol) was added slowly with vigor-
ous stirring to a solution of p-toluidine (30 mmol) (or p-anisidine
76.00%; H, 6.11%; N, 7.88%.
1H and 13C NMR data of the compounds 1b, 1c, 1e and 1f have
been furnished in ESI.
0
0
3
0 mmol) in 3 M hydrochloric acid (50 ml) at 0 °C. The resulting
(4 -Methyl phenyl azo) phenyl-4-yl 3-[N-(4 -n-hexyloxy-2-
diazonium salt solution was then slowly added to a stirred solution
of phenol (33 mmol) in 10% aqueous sodium hydroxide (40 ml) at
hydroxybenzylidene)amino]-2-methyl benzoate, 1c: Yellow solid,
ꢂ1
Yield: 0.077 g (70.12%). IR
1743 ( C@O, ester), 1612 (
lated for C34 : C, 76.52%; H, 6.61%; N, 7.87% Found: C,
mmax in cm : 3196 (
mOAH, H-bonded),
0
°C. The dark brown suspension was acidified and the precipitate
m
mCH@N, imine). Elemental Analysis calcu-
was collected. The crude product was washed repeatedly with
large quantity of water and the final yellow solid was dried under
vacuum.
35 3 3
H N O
76.22%; H, 6.33%; N, 7.48%.
0
0
(4 -Methoxy phenyl azo) phenyl-4-yl 3-[N-(4 -n-butyloxy-2-
hydroxybenzylidene)amino]-2-methyl benzoate, 1d: Yellow solid,
0
ꢂ1
5
.10. 4-Hydroxy-4 -methyl azobenzene (4a)
Yield: 0.075 g (70.29%). IR
741 ( C@O, ester); 1610 (
(d ), 13.43 (s, 1H, AOH), 8.48 (s, 1H, ACH@NA), 8.03 (dd, 1H,
t
max in cm : 3192 (
t
OAH H-bonded);
1
1
t
t
C@N, imine
)
. H NMR (400 MHz, CDCl
3
):
ꢂ1
Yellow solid, m.p.: 148 °C, Yield = 3.1 g (67%). IR
t
max in cm
:
H
3
421 (
t
OAH), 1467(
tN@N, azo)
.
The 1H NMR data is furnished in
J = 1.2 Hz, J = 8.0 Hz, ArH), 8.00 (dd, 2H, J = 2.0 Hz, 6.8 Hz, ArH),
7.96 (dd, 2H, J = 2.0 Hz, J = 6.8 Hz, ArH), 7.42 (t, 1H, J = 7.6 Hz,
ArH), 7.40 (d, 1H, J = 6.4 Hz, ArH), 7.40 (dd, 1H, J = 2.4 Hz,
J = 6.4 Hz, ArH), 7.33 (d, 2H, J = 8.4 Hz, ArH), 7.05 (dd, 2H,
J = 2.0 Hz, J = 7.2 Hz, ArH), 6.61 (d, 1H, J = 2.0 Hz, ArH), 6.53 (dd,
12 2
ESI (Table S2). Elemental analysis calculated for C13H N O: C,
3.56%; H, 5.70%; Found: C, 73.06%; H, 5.28%.
-Hydroxy-4 -methoxy azobenzene (4b): Yellow solid. m.p.:
39 °C [139–141 °C, [74]], Yield = 2.8 g (66%). IR
421 ( OAH), 1467 (
7
0
4
ꢂ1
1
3
t
max in cm
:
t
t
N@N, azo)
.
The 1H NMR data is furnished in
: C,
1H, J = 2.4 Hz, J = 8.4 Hz, ArH), 4.05 (t, 2H, J = 6.8 Hz, AOCH
3.92 (s, 3H, AOCH A), 2.69 (s, 3H, ArACH ), 1.82 (q, 2H,
J = 7.2 Hz, ACH CH CH A), 1.53 (h, 2H, J = 7.2 Hz, ACH CH CH A),
.01 (t, 3H, J = 7.2 Hz, ACH ). C NMR (400 MHz, CDCl ): (d ),
165.7, 163.8, 162.6, 162.1, 152.3, 151.0, 150.5, 146.9, 141.8,
34.2, 133.8, 130.5, 129.7, 129.3, 128.5, 126.6, 124.8, 123.8,
122.7, 122.3, 114.2, 107.9, 101.5, 77.3, 77.0, 76.7, 68.1, 55.6, 31.0,
19.2, 15.4, 13.8. Elemental Analysis calculated for C32 : C,
73.68%; H, 5.99%; N, 8.06% Found: C, 73.03%; H, 5.31%; N, 7.98%.
2
A),
ESI (Table S2). Elemental analysis calculated for C13
12
H N
2
O
2
3
3
6
8.41%; H, 5.30%; Found: C, 68.02%; H, 5.23%.
.11. General procedure for the synthesis of compounds (1a–f)
Appropriate quantity of substituted benzoic acid (2 mmol) (2-
Methyl-3-N-(4-n-butyloxy-2-hydroxybenzylidene) amino benzoic
acid, 0.65 g; 2-Methyl-3-N-(4-n-pentyloxy-2-hydroxybenzylidene)
amino benzoic acid, 0.68 g; 2-Methyl-3-N-(4-n-hexyloxy-2-
2
2
2
2
2
3
1
3
1
3
3
C
5
1
31 3 4
H N O
0
0
(4 -Methoxy phenyl azo) phenyl-4-yl 3-[N-(4 -n-pentyloxy-2-
hydroxybenzylidene) amino benzoic acid, 0.71 g) and 4-hydroxy-
hydroxybenzylidene)amino]-2-methyl benzoate, 1e: Yellow solid,
0
ꢂ1
4
-methoxy azobenzene (0.456 g, 2 mmol) were dissolved in dry
Yield: 0.075 g (69.31%). IR
1737 ( C@O, ester); 1604 (
lated for C33 : C, 74.00%; H, 6.21%; N, 7.84% Found: C,
t
max in cm : 3186(
t
OAH H-bonded);
dichloromethane (DCM) (50 mL) and catalytic amount of 4-
dimethylaminopyridine (DMAP) (4 mg, 0.02 mmol) was added to
t
)
tC@N, imine . Elemental Analysis calcu-
33 3 4
H N O
0
the solution. A solution of N, N -dicyclohexylcarbodiimide (DCC)
73.93%; H, 6.11%; N, 7.78%.
0
0
(
0.49 g, 2.4 mmol) was added to the reaction mixture and the mix-
(4 -Methoxy phenyl azo) phenyl-4-yl 3-[N-(4 -n-hexyloxy-2-
ture was stirred for 48 h under inert atmosphere at room temper-
ature. The precipitate of N, N -dicyclohexylurea was removed by
hydroxybenzylidene)amino]-2-methyl benzoate, 1f: Yellow solid,
0
ꢂ1
Yield: 0.079 g (69.91%). IR
1739. ( C@O, ester); 1610 (
for C34 : C, 74.29%; H, 6.42%; N, 7.64% Found: C, 73.07%; H,
t
max in cm : 3246(
t
OAH H-bonded);
filtration and the solvent DCM was evaporated to get crude prod-
uct. The crude product was purified by column chromatography
using silica gel (60–120 mesh) with hexane/ chloroform (9:1) as
eluent. The yellow solid was recrystallized several times from
absolute ethanol to get the pure product.
t
tC@N,imine). Elemental Analysis calculated
35 3 4
H N O
6.31%; N, 7.38%.
0
0
(
4 -Methyl phenyl azo) phenyl-4-yl 3-[N-(4 -n-butyloxy-2-
6. Conclusions
hydroxybenzylidene)amino]-2-methyl benzoate, 1a: Yield:
ꢂ1
1
0
.072 g (69%). IR
ester), 1610 (
s, 1H, AOH), 8.44 (s, 1H, ACH@NA), 8.00 (dd, 1H, J = 2.0 Hz,
m
max in cm : 3170 (
m
OAH, H-bonded), 1743 (
m
C@O
,
For all future applications in the field of BLCs, it is important to
draw from a wide range of compounds and different classes of sub-
stances, in order to optimize the criteria for selecting appropriate
materials. Since future priorities for the specific properties cannot
yet be foreseen, realization of new classes of materials remains of
high importance. Achiral four ring unsymmetrical bent-core liquid
crystals derived from 3-amino-2-methylbenzoic acid with imine,
ester and photochromic azo linking moieties have been designed,
synthesized and characterized. All the compounds exhibit wide
thermal range of enantiotropic N phase. The compounds exhibit
photochromic behaviour due to presence of azo group in the
m
CH@N, imine). H NMR (400 MHz, CDCl
3
): (d ), 13.49
H
(
J = 6.8 Hz, ArH), 7.99 (dd, 2H, J = 2.8 Hz, 8.0 Hz, ArH), 7.84 (d, 2H,
J = 8.4 Hz, ArH), 7.39 (dd, 2H, J = 2.0 Hz, J = 6.8 Hz, ArH), 7.37 (d,
H, J = 7.6 Hz, ArH), 7.32 (d, 1H, J = 8.8 Hz, ArH), 7.31 (t, 1H,
J = 9.6 Hz, ArH), 7.27 (d, 2H, J = 7.6 Hz, ArH), 6.52 (dd, 1H,
J = 2.4 Hz, J = 8.4 Hz, ArH), 6.50 (d, 1H, J = 2.0 Hz, ArH), 4.02 (t,
1
2
1
ACH
H, J = 6.4 Hz, AOCH
.80 (q, 2H, J = 6.8 Hz, ACH
CH CH A), 0.99 (t, 3H, J = 7.6 Hz, ACH
2
A), 2.68 (s, 3H, ACH
3 3
A), 2.44 (s, 3H, ArACH ),
2
CH CH A), 1.51 (h, 2H, J = 7.2 Hz,
2
2
13
2
2
3
3
).
C
NMR