458
M. Ashraf et al. / Dyes and Pigments 95 (2012) 455e464
triethylamine added. The mixture was refluxed for the period of
time stated below, and resulted in a change in the colour of the
solution from red to either purple or green. After cooling, the solid
product was collected by filtration, washed with 3e4 times with
cold methanol and dried under vacuum to give 4def as coloured
solids.
128.9, 129.5, 131.3, 131.9, 140.9, 141.2, 143.0, 148.5, 171.2. lmax (DMF)
567, log10 4.48.
3
2.6.2. 2-[4-(2-{4-[(1,3,3-Trimethyl-1,3-dihydro-indol-2-
ylidenemethyl)-azo]-phenyl}-vinyl)-quinolin-1-yl]-ethanol iodide
(4h)
Dark brown solid (70%), m.p. 249e252 ꢀC (dec.). (Found: Mþ m/z
2.5.1. 2-{4-[(1,3,3-Trimethyl-1,3-dihydro-indol-2-ylidenemethyl)-
azo]-benzylidene}-malononitrile (4d)
475.2504 C31H31N4O requires Mþ m/z 475.2498;
D
¼ 1.3 ppm). 1H
NMR (d6-DMSO)
d 9.10 (d, J 9 Hz, 1H), 9.08 (d, J 9 Hz, 1H), 8.25 (d, J
Refluxed 20 min. Violet solid (85%), m.p. 226 ꢀC. (Found: MHþ m/z
15 Hz, 1H), 8.20 (m, 2H), 7.94 (d, J 9 Hz, 2H), 7.60 (d, J 9 Hz, 2H), 7.86
(m, 2H), 7.80 (s, 1H), 7.48 (d, J 6 Hz, 1H), 7.34 (t, J 5 Hz, 1H), 7.22 (d, J
6 Hz, 1H), 7.12 (t, J 6 Hz, 1H), 6.98 (d, J 15 Hz, 1H), 5.07 (t, J 5 Hz, 2H),
4.50 (t, J 5 Hz, 2H), 3.45 (s, 3H), 1.73 (s, 6H). 13C NMR (d6-DMSO)
354.1722 C22H19N5 requires MHþ m/z 354.1719;
D
¼ 0.8 ppm).
8.41 (s, 1H), 8.03 (d, J 9 Hz, 2H), 7.66 (d, J 9 Hz,
2H), 7.64 (s, 1H), 7.50 (d, J 9 Hz,1H), 7.36 (t, J 6 Hz,1H), 7.27 (d, J 9 Hz,
1H), 7.15 (t, J 6 Hz,1H), 3.73 (s, 3H),1.71 (s, 6H). 13C (d6-DMSO)
21.1,
1H NMR(d6-DMSO)
d
d
d
28.6, 29.9, 48.1, 109.0, 115.8, 121.4, 121.5, 122.1, 122.5, 122.8, 126.0,
128.0, 129.7, 130.9, 132.2, 132.3, 139.8, 143.8, 155.3, 158.1, 167.1,
168.0, 193.9. lmax (DMF) 555, log10 4.03.
29.0, 29.1, 30.3, 47.8, 48.6,108.4,109.5,121.0,121.2,121.8,122.4,123.2,
128.4, 130.0, 131.3, 134.2, 140.2, 144.1, 158.4, 168.9. lmax (DMF) 549,
3
log10 4.69.
3
2.7. Synthesis of 2-(3-dicyanomethylene-5,5-dimethyl-2-{4-[(1,3,3-
trimethyl-1,3-dihydro-indol-2-ylidenemethyl)-azo]-benzylidene}-
cyclohexylidene)-malononitrile (4i)
2.5.2. 3-(4-Hydroxy-phenyl)-2-thioxo-5-{4-[(1,3,3-trimethyl-1,3-
dihydro-indol-2-ylidenemethyl)-azo]-benzylidene}-thiazolidin-4-
one (4e)
Refluxed 4 h. Green solid (75%), m.p. 220 ꢀC. (Found: MHþ m/z
To a mixture of aldehyde 4a (10 mmol, 3.05 g) and dimedone
(10 mmol, 1.40 g) in toluene was added triethylamine (10 mmol,
1.0 mL). The reaction mixture was refluxed for 10 h and the water
generated removed using a DeaneStark trap. After all the starting
materials had been consumed (via TLC) malononitrile (20 mmol,
1.32 g) was added and the reaction mixture refluxed for a further
4 h resulted. This resulted in a colour change from red to brownish
red. The solvent was removed under reduced pressure, extracted
into dichloromethane, and washed with water. The organic phase
was then dried (MgSO4) and concentrated. The resultant solid was
purified by column chromatography (using dichloromethane as
eluent) to give a dark brownish-red solid. (45%), m.p. 136.2 ꢀC.
(Found: MHþ m/z 523.2533 C33H29N7 requires MHþ m/z 523.2538;
513.1413 C28H24N4O2S2 requires MHþ m/z 513.1419;
D
¼ 1.2 ppm).
1H NMR (d6-DMSO)
d 9.85 (s, 1H), 7.82 (s, 1H), 7.77e7.68 (m, 4H),
7.55 (s, 1H), 7.48 (d, J 9 Hz,1H), 7.33 (t, J 6 Hz, 1H), 7.22e7.16 (m, 3H),
7.10 (t, J 6 Hz, 1H), 7.68 (d, J 9 Hz, 2H), 3.45 (s, 3H), 1.73 (s, 3H). 13C
NMR (d6-DMSO)
122.5, 122.8, 126.0, 128.0, 129.7, 130.9, 132.2, 132.3, 139.8, 143.8,
155.3, 158.1, 167.1, 168.0, 193.9. lmax (DMF) 534, log10 4.67.
d 28.6, 29.9, 48.1, 109.0, 115.8, 121.4, 121.5, 122.1,
3
2.5.3. 2-[3-Cyano-5,5-dimethyl-4-(2-{4-[(1,3,3-trimethyl-1,3-
dihydro-indol-2-ylidenemethyl)-azo]-phenyl}-vinyl)-5H-furan-2-
ylidene]-malononitrile (4f)
Refluxed 2 h. Green solid (80%), m.p. 275 ꢀC. (Found: MHþ m/z
487.2247 C30H26N6O requires MHþ m/z 487.2246;
D
¼ 0.2 ppm). 1H
D
¼ 1.2 ppm). 1H NMR (d6-DMSO)
d 8.47 (s, 1H), 8.09 (d, J 9 Hz, 2H),
NMR (d6-DMSO)
d
7.98 (d, J 9 Hz, 2H), 7.94 (s, 1H), 7.65 (d, J 9 Hz,
7.70 (d, J 9 Hz, 2H), 7.64 (s,1H), 7.50 (d, J 9 Hz,1H), 7.36 (t, J 5 Hz,1H),
7.27(d, J 9 Hz, 1H), 7.15 (t, J 5 Hz, 1H), 3.73 (s, 3H), 1.90 (s, 4H), 1.71 (s,
2H), 7.62 (d, J 15 Hz, 1H), 7.48 (d, J 6 Hz, 1H), 7.34 (t, J 5 Hz, 1H), 7.22
(d, J 6 Hz, 1H), 7.17 (d, J 15 Hz, 1H), 7.12 (t, J 5.5 Hz, 1H), 3.47 (s, 3H),
6H), 1.50 (s, 6H). 13C (d6-DMSO)
d
21.1, 24.8, 27.7, 29.0, 29.1, 30.2,
1.81 (s, 6H), 1.72 (s, 6H). 13C NMR (d6-DMSO)
d
25.2, 28.4, 30.0, 48.2,
99.1, 109.1, 112.8, 113.9, 121.2, 122.0, 122.6, 123.1, 127.9, 131.0, 147.1,
175.0. lmax (DMF) 601, log10 5.04.
48.5, 77.4, 109.5, 114.9, 121.1, 121.5, 122.1, 123.1, 123.7, 128.0, 125.7,
132.5, 140.6, 158.2, 159.9, 168.9, 169.4. lmax (DMF) 441, log10
3. Results and discussion
3
4.33.
3
2.6. Preparation of compounds 4g,h. General procedure for the
coupling of acceptors 6g,h to 4a
3.1. Synthesis
Aldehyde 4a (1 eq) and the appropriate salt (1.1 eq) were dis-
solved in methanol and a catalytic quantity of triethylamine was
added. The reaction mixture was refluxed for 18 h and this resulted
in a change in the colour of the mixture from red to brown. After the
reaction was completed 75% of the solvent was removed at reduced
pressure and ether added until a solid appeared. This was collected
by filtration, washed with 3e4 times with cold ethanol and dried
under vacuum to give 4g,h as coloured solids.
The structures of the molecules prepared for this study are
shown in Fig. 1. The chromophores can be classified as one of two
types depending on the synthetic methodology used to prepare
them. The first type are chromophores 4aec, and which were ob-
tained in one step by simply coupling the corresponding diazonium
salt, 6aec, to Fischer’s base 5 (Scheme 1). The reactions employed
standard conditions for the diazotization of the appropriate aryl
amine in glacial acetic acid. These diazonium couplings proceeded
in high yield (72e88%) and this reinforces the strong electron
donating ability of the indoline ring system. Compound 4a is the
key synthon for the preparation of chromophores 4dei, and so was
synthesised in multi-gram quantities. Compounds 4deh could then
be obtained by refluxing 4a and the appropriate acceptor 6deh for
between 20 min and 24 h in methanol containing a catalytic
amount of triethylamine (Scheme 2). A key advantage of the
methodologies used to prepare 4aeh is that it was not necessary to
perform chromatography in order to obtain the final products pure.
Compound 4i was obtained by first condensing 4a with dimedone
in refluxing toluene and then adding malononitrile to the reaction
mixture and heating for an additional 5 h. The structures of all the
2.6.1. 2-[2-(2-{4-[(1,3,3-Trimethyl-1,3-dihydro-indol-2-
ylidenemethyl)-azo]-phenyl}-vinyl)-benzothiazol-3-yl]-ethanol
iodide (4g)
Greenish-red solid (72%), m.p. 259e63 ꢀC (dec.). (Found: Mþ m/z
481.2116 C29H29N4OS requires Mþ m/z 481.2113;
D
¼ 0.6 ppm). 1H
NMR (d6-DMSO)
d 8.25 (d, J 15 Hz, 1H), 7.98 (d, J 9 Hz, 2H), 7.82 (s,
1H), 7.62 (d, J 9 Hz, 2H), 7.51 (d, J 9 Hz, 1H), 7.38 (t, J 6 Hz, 1H),
7.26e7.22 (m, 3H), 7.15 (t, J 6 Hz,1H), 6.98 (d, J 15 Hz,1H), 6.82e6.78
(m, 2H), 5.07 (t, J 6 Hz, 2H), 4.50 (t, J 6 Hz, 2H), 3.45 (s, 3H), 1.73 (s,
6H). 13C NMR (d6-DMSO)
d
12.8, 14.2, 27.3, 32.1, 44.5, 45.8, 50.0,
54.9, 112.0, 113.8, 116.6, 118.4, 122.5, 124.2, 125.7, 128.2, 128.3, 128.5,