Photochromism of an N-aminofulgimide-derived Schiff base

Article abstract of DOI:10.1007/s11172-009-0338-2

A Schiff base was synthesized from 5-methoxysalicylaldehyde and N-aminofulgimide, viz., 1-amino-3-[1-(2,5-dimethylthiophen-3-yl)ethylidene]-4- isopropylidenepyrrolidine-2,5-dione. The compound synthesized undergoes photochromic transformations typical of those of N-aminofulgimide studied earlier. A bathochromic shift of the absorption bands of the open and cyclic forms of the obtained Schiff base compared to the starting N-aminofulgimide was observed.

Full text of DOI:10.1007/s11172-009-0338-2

Russian Chemical Bulletin, International Edition, Vol. 58, No. 12, pp. 2423—2425, December, 2009
2423
Photochromism of an Nꢀaminofulgimideꢀderived Schiff base
L. D. Popov,a I. N. Shcherbakov,a V. A. Kogan,a S. I. Luiksaar,b M. M. Krayushkin,b
O. V. Venediktova,c A. M. Gorelik,c and V. A. Barachevskyc
aSouthern Federal University,
105 ul. B. Sadovaya, 344104 RostovꢀonꢀDon, Russian Federation.
Eꢀmail: shcherbakov@rsu.ru
bN. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences,
47 Leninsky prosp., 119991 Moscow, Russian Federation.
Eꢀmail: mkray@ioc.ac.ru
cPhotochemistry Center, Russian Academy of Sciences,
7a ul. Novatorov, 119421 Moscow, Russian Federation.
Eꢀmail: barva@photonics.ru
A Schiff base was synthesized from 5ꢀmethoxysalicylaldehyde and Nꢀaminofulgimide, viz.,
1ꢀaminoꢀ3ꢀ[1ꢀ(2,5ꢀdimethylthiophenꢀ3ꢀyl)ethylidene]ꢀ4ꢀisopropylidenepyrrolidineꢀ2,5ꢀdione.
The compound synthesized undergoes photochromic transformations typical of those of
Nꢀaminofulgimide studied earlier. A bathochromic shift of the absorption bands of the open
and cyclic forms of the obtained Schiff base compared to the starting Nꢀaminofulgimide was
observed.
Key words: photochromism, fulgimides, absorption spectra, phototransformations.
Fulgimide derivatives1—8 along with fulgides are reꢀ
garded as possible photosensitive components of the phoꢀ
tochromic optical memory devices.7,8 They usually unꢀ
dergo transformations that are irreversible thermally, but
reversible photochemically, between two forms, viz., the
colorless open (Еꢀisomer) and colored cyclic (Сꢀisomer)
forms (Scheme 1).
zation on exposure to UV light. In this case, the spectal
changes are generally exhibited in the UV region.
Photochromic fulgimides, viz., the earlier9 synthesized
Nꢀaminofulgimide 1 and a derived Schiff base 2 obtained
by the reaction with 5ꢀmethoxysalicylaldehyde, served
as the subjects of research.
The aim of the present work was to study the photoꢀ
chromic properties of the Schiff base 2 and their compariꢀ
son with those of the precursor Nꢀaminofulgimide 1.
However, as for some fulgides, these transformations
may be complicated by reversible E—Zꢀphotoisomeriꢀ
Scheme 1
EꢀIsomer
ZꢀIsomer
CꢀIsomer
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2345—2347, December, 2009.
1066ꢀ5285/09/5812ꢀ2423 © 2009 Springer Science+Business Media, Inc.

2424
Russ.Chem.Bull., Int.Ed., Vol. 58, No. 12, December, 2009
Popov et al.
A
Results and Discussion
0.3
Photoinduced spectral changes for a solution of comꢀ
pound 1 in toluene are presented in Fig. 1. The open form
of fulgimide 1 is characterised by a longꢀwavelength
absorption band with a maximum at 327 nm (see Fig. 1,
curve 1). Under UV excitation, the intensity of this abꢀ
sorption band is lowered and, at the same time, the
absorption band in the visible region at 518 nm appears
(see Fig. 1, curve 2). This is evidence of the formation of
a cyclic form, which has been shown by the examples
of other fulgimides.7 We established that this form is
thermally stable. On storage of the irradiated solutions
for 5 days in the dark, the absorption band intensity is
decreased by 16% for a solution in toluene and by 1.4%
for a solution in acetonitrile. However, on exposure to
light, the cyclic form is again transformed into the open
one (see Fig. 1, curve 3). One isosbestic point is observed,
which suggests the occurence of interconversions between
two isomeric forms, i.e., between the open (Е) and cyclic
(С) forms. Possible E—Zꢀphotoisomerization was not
spectroscopically observed.
The spectral characteristics of compound 2 signifiꢀ
cantly differ from those of the aboveꢀconsidered fulgimide
(Fig. 2). The absorption band of the open form is shifted
to longꢀwavelengths by 38 nm, its absorption maximum
is 365 nm (see Fig. 2, curve 1). The absorption band of
the photoinduced cyclic form that is observed in the
visible region, is also bathochromically shifted by 25 nm
(λmax = 543 nm) (see Fig. 2, curve 2). As with comꢀ
pound 1, the absorption band intensity of the open form
(365 nm) decreases with simultaneous appearance of the
absorption band of the cyclic form at 543 nm (see Fig. 2,
curve 2). However, in contrast to compound 1, the
0.2
0.1
1
2, 3
2
3
4
1
4
300
400
500
600 λ/nm
Fig. 2. Absorption spectra of a solution of compound 2 in
toluene prior to (1) and after irradiation for 20 s with a mercuryꢀ
xenon lamp through a UFSꢀ8 light filter (2), as well as after
irradiation for 6 (3) and 40 s (4) through a ZhSꢀ10 light filter.
absorption band intensity of the open form of compound
2 is not restored, but decreases upon irradiation of the
photocolored solutions with visible light (see Fig. 2, curves
3 and 4). In the case of compound 2, two isosbestic points
are observed.
A small value of the bathocromic shift of the longꢀ
wavelenth absorption bands of the open and cyclic forms
of Schiff base 2 is determined by the weak conjugation
between the πꢀsystems of the salycilic and fulgimide fragꢀ
ments through the nitrogen atom of the fiveꢀmembered
maleimide ring. This is evidenced by the minor, as against
compound 1, decrease in the absorption band intensity
of the open form upon UV irradiation.
The thermal stability of the cyclic form of Schiff base
2 is lower than that of compound 1, which is evidenced
by somewhat faster, spontaneous decoloration of the
cyclic form of compound 2 in both toluene (by 85.87% in
12 days) and acetonitrile (by 14.5% in 10 days). As in the
case of compound 1, the rate of spontaneous decoloration
in toluene is higher than that in acetonitrile.
The fact that the absorption band intensity of the open
form in the case of solution of compound 2 is not restored
to the initial value on exposure to visible light, taking into
account the presence of two isosbestic points in a series of
the photoinduced absorption spectra, can be explained
not only by the photocyclization processes, but also by
the E—Zꢀphotoisomerization reaction, apparently, of the
fulgimide and/or imine fragment, as well as by irreversꢀ
ible photodecomposition of compound 2, which requires
further studies.
A
0.14
0.12
0.10
0.08
1
0.06
3
2
0.04
0.02
3
2
1
300
400
500
600 λ/nm
Thus, as a result of this work, a novel representative
of fulgimides is synthesized, which exhibits the photoꢀ
chromical properties close to those of Nꢀaminofulgimide
with the bathochromically shifted absorption bands of the
open and cyclic forms.
Fig. 1. Absorption spectra of a solution of compound 1 in
toluene prior to (1) and after irradiation for 30 s with a mercuryꢀ
xenon lamp through a UFSꢀ8 light filter (2), as well as after
irradiation for 45 s with the same lamp through a ZhSꢀ10 light
filter (3).

Photochromism of a fulgimide Schiff base
Russ.Chem.Bull., Int.Ed., Vol. 58, No. 12, December, 2009 2425
Experimental
This work was financially supported by the Division of
Chemistry and Materials Science of the Russian Academy
of Sciences (Program No. 1) and Southern Federal Uniꢀ
versity.
1ꢀAminoꢀ3ꢀ[1ꢀ(2,5ꢀdimethylthiophenꢀ3ꢀyl)ethyllidene]ꢀ
4ꢀisopropylidenepyrrolidineꢀ2,5ꢀdione (1) was synthesized
according to a known procedure.9
1ꢀ[(2ꢀHydroxyꢀ5ꢀmethoxybenzylidene)amino]ꢀ3ꢀ[1ꢀ(2,5ꢀ
dimethylthiophenꢀ3ꢀyl)ethylidene]ꢀ4ꢀisopropylidenepyrrolidineꢀ
2,5ꢀdione (2). To a boiling solution of compound 1 (0.29 g,
0.001 mol) in ethanol (5 mL), a hot solution of 5ꢀmethoxyꢀ
salicylaldehyde (0.152 g, 0.001 mol) in ethanol (2 mL) was
added. The solution was refluxed for 2 h and left for 24 h. The
yellow crystalline precipitate that formed was separated, washed
with a minimum amount of cold ethanol and recrystallized
from ethanol. The yield was 0.39 g (80%), m.p. 160—161 °C.
Found (%): C, 65.2; H, 5.5; N, 6.7. С23H24N2O4S. Calculꢀ
References
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1
ated (%): С, 65.12; H, 5.66; N, 6.60. H NMR (DMSOꢀd6), δ:
2.00, 2.08, 2.28, 2.42, 2.49 (all s, 3 H each, Me); 3.73 (s, 3 H,
OMe); 6.57 (s, 1 H, H of thienyl); 6.81 (d, 1 H, H(3) arom.,
J = 8.93 Hz); 6.88 (dd, 1 H, H(4) arom., J = 2.93 Hz,
J = 8.93 Hz); 7.10 (d, 1 H, H(6) arom., J = 2.93 Hz); 9.29 (s,
1 H, CH=N); 10.33 (s, 1 Н, ОН). MS, m/z (Irel (%)): 424 [М]+
(35), 409 [M – CH3]+ (35), 274 [fulgimide]+ (35), 260 (50), 246
(12), 231 (43), 217 (43), 203 (50), 193 (28), 189 (100), 174 (35),
161 (48), 149 (88), 136 (85), 115 (18), 111 [thiophenyl]+ (28),
106 (31).
Spectral studies for solutions were performed on a Cary 50
Bio (Varian) spectrophotometer in the range of 200—800 nm in
a 2ꢀmm cell (KUꢀ1 quartz glass). Toluene (Scharlau, analyt.
grade) was used as the solvent. The concentration of compounds
in solution was 1•10–4 mol L–1. The 1H NMR spectra of
solutions of compounds in DMSOꢀd6 were recorded on a Varian
Unityꢀ300 (300 MHz) spectrometer using Me4Si as the internal
standard.
Photocoloration of solutions was induced by UV irradiation
with the mercuryꢀxenon lamp (Hamamatsu) through UFSꢀ5
and UFSꢀ8 light filters. Photodecoloration of the colored
solutions was performed by irradiation of the solution with visible
light through a ZhSꢀ10 light filter.
Received September 10, 2007;
in revised form March 26, 2008