Synthesis of photochromic bisfulgimides by the condensation of (3Z)-3-[1-(2,5-dimethyl-3-thienyl)-ethylidene]-4-isopropylidene-2,5-furandione with aromatic diamines

Article abstract of DOI:10.1007/s10593-010-0589-8

The first representatives of thiophene derivatives with two fulgimide fragments in one molecule have been obtained by the condensation of (3Z)-3-[1-(2,5-dimethyl-3-thienyl)ethylidene]-4-isopropylidene-2,5-furandione with aromatic diamines. The photochromic properties of the obtained compounds have been investigated and the effect of a spacer, linking the two fulgimide fragments, on the reaction rates of photocoloration and photodecoloration of these compounds has been studied.

Full text of DOI:10.1007/s10593-010-0589-8

Chemistry of Heterocyclic Compounds, Vol. 46, No. 7, 2010
SYNTHESIS OF PHOTOCHROMIC BISFULGIMIDES BY THE
CONDENSATION OF (3Z)-3-[1-(2,5-DIMETHYL-3-THIENYL)-
ETHYLIDENE]-4-ISOPROPYLIDENE-2,5-FURANDIONE WITH
AROMATIC DIAMINES
S. I. Luyksaar1*, M. M. Krayushkin1, Yu. A. Pyankov2, and V. A. Barachevsky2
The first representatives of thiophene derivatives with two fulgimide fragments in one molecule have
been obtained by the condensation of (3Z)-3-[1-(2,5-dimethyl-3-thienyl)ethylidene]-4-isopropylidene-
2,5-furandione with aromatic diamines. The photochromic properties of the obtained compounds have
been investigated and the effect of a spacer, linking the two fulgimide fragments, on the reaction rates of
photocoloration and photodecoloration of these compounds has been studied.
Keywords: 3-acetyl-2,5-dimethylthiophene, fulgides, fulgimides, Stobbe condensation, photochromism.
Fulgimides of the thiophene series are considered at the present time as one of the promising classes of
photochromic compounds. They possess photochemical characteristics valuable in practice, such as thermal
irreversibility and high chemical stability, which enables these compounds to be considered as components for
constructing molecular switches, and also systems of recording, storage, and treatment of information [1-5].
The aim of the present work was the preparation of thiophene fulgimides, not reported in the literature,
containing two fulgimide fragments in one molecule linked by various aromatic bridges, and clarification of the
effect of the spacer on their photochromic properties.
The approach developed by us to the synthesis of this type of compounds includes the preparation of
(3Z)-3-[1-(2,5-dimethyl-3-thienyl)ethylidene]-4-isopropylidene-2,5-furandione (1) (Scheme 1), which is
described in the literature [6]. Compound 1 is then converted into the desired products by interaction with
aromatic diamines.
Hemiester 5 was obtained by the Stobbe condensation of 3-acetyl-2,5-dimethylthiophene (3), obtained
by the acylation of 2,5-dimethylthiophene (2) according to Friedel-Crafts, with diethyl isopropylidenesuccinate
(4) in the presence of t-BuOK as base. It should be noted that the use of t-BuOK as base in this reaction, in place
of NaOEt reported in the literature [7], enabled a purer product to be obtained. Subsequent alkaline
_______
* To whom correspondence should be addressed, e-mail: luyksaar@gmail.com.
1N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Moscow 119991, Russia.
2Photochemistry Center, Russian Academy of Sciences, Moscow 119421, Russia; e-mail: barva@photonics.ru.
__________________________________________________________________________________________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 1019-1026, July, 2010. Original
article submitted June 24, 2009.
822
0009-3122/10/4607-0822©2010 Springer Science+Business Media, Inc.

hydrolysis of the hemiester with alcoholic KOH solution led to a mixture of (Z)- and (E)-isomers of 3-[1-(2,5-
dimethyl-3-thienyl)ethylidene]-4-isopropylidenesuccinic acid (6) in a ratio of approximately 1:1. Cyclization of
the diacid 6 formed with N,N'-carbonyldiimidazole at room temperature led to compound 1 in 77% yield
(Scheme 1).
Scheme 1
COOEt
O
COOEt
AcCl
4
t-BuOK
SnCl4
S
S
3
2
O
O
O
OH
O
OH
OH
O
KOH
CDI
O
O
O
S
S
S
5
1
6
CDI – N,N'-carbonyldiimidazole
The interaction of fulgide 1 and aromatic diamines 7a-d on boiling in benzene for 25-30 h led to the
preparation of a mixture of intermediately formed regioisomeric bisamido acids. Cyclization of the latter without
first purification by the method developed previously by us [8] using N,N'-carbonyldiimidazole under mild
conditions at room temperature, unlike the procedures applied previously [2, 4], led to the corresponding
bisfulgimides 8a-d in 36-52% yield (Scheme 2).
Scheme 2
O
O
1. H2N–X–NH2
N
X
N
7a–d
1
O
O
CDI
2.
S
S
8a–d
N N
O
c X =
a
b X =
X =
,
,
d X =
,
The structures of all the synthesized compounds were confirmed by the results of elemental analysis,
1
data of H NMR and IR spectroscopy, and also mass spectrometry. In the IR spectra of these compounds
characteristic bands were present for amide carbonyl groups at 1710 and 1755 cm-1, corresponding to the
alkylidenesuccinimide [9]. Signals were observed in the 1H NMR spectra for the 10 methyl groups as singlets in
the region δ 2.02-2.50 ppm, and signals appeared for the protons of the thiophene fragment as a singlet at
δ 6.56 ppm. The signals of the aromatic protons of phenyl substituents were present as doublets in the range
δ 6.59-7.49 ppm.
823

It is known that fulgides and fulgimides exist in three isomeric forms [1] (Scheme 3).
Scheme 3
Ar
Me
Me
O
O
O
UV
UV
UV
Vis
Me
Me
Ar
X
X
Ar
X
Me
O
O
Me Me
O
Me
Me
(Z)-isomer
(C)-isomer
(E)-isomer
X = O, NR4
All three isomers are in photochemical equilibrium although photochromic conversions only occur
between the open (E) and cyclic (C) forms. The (Z)-form cannot undergo cyclization because of its geometry,
and energy of UV radiation is consumed additionally in its conversion into the (E)-isomer, which is seemingly
an inevitable problem leading to a reduction in the quantum yield of cyclization when using fulgides and their
derivatives. The (Z)- or (E)-configuration of fulgides and fulgimides, containing an exocyclic isopropylidene
1
substituent, may readily be determined on the basis of H NMR spectra. This problem has been investigated in
detail in the literature [10, 11]. The configurations of similar fulgides and fulgimides are determined from the
chemical shift of the methyl groups of the isopropylidene fragment.
The (Z)-isomers of fulgides and fulgimides are characterized by the signals of CH3 groups of the
isopropylidene fragment displayed in the δ 1.9-2.5 ppm region. However the (E)-CH3 group of the
isopropylidene fragment of (E)-isomer gives a signal at δ 1.3-1.4 ppm, which is caused by the deshielding action
of the thiophene ring, displayed only in the (E)-isomers of fulgides and fulgimides. The signals of the methyl
groups of all the fulgimides synthesized by us (compounds 8a-d) lie in the range δ 2.02-2.50 ppm, which
indicates their (Z)-configuration.
Intense peaks were present in the mass spectra of compounds 8a-d for the molecular ion (I = 72-87%)
and for the [M-CH3]+ fragment (100%). Peaks with m/z 189 (72%) and 217 (64%) also had high intensity, but
their identification was unsuccessful due to the complex decomposition of these compounds under conditions of
electron impact for mass spectrometry.
TABLE 1. Spectral Kinetic Characteristics* of Fulgimides 8a-d in Toluene
max
Compound
λАmax, nm
λВmax, nm
ΔDB
kAB/kBA
8а
8b
8c
8d
330
335
335
310
528
530
530
530
1.2
0.9
1.5
1.1
0.7
0.6
0.4
0.4
max
max
*λA and λB are the wavelengths of the absorption band maxima of the
max
initial (open) A and photoinduced (cyclic) B form; DB
is the
photoinduced change of optical density at the wavelength of the absorption
band maximum of the photoinduced form B on UV irradiation through a
UVS-2 filter; kAB/kBA is the ratio of the rate constants of photocoloration
and photodecoloration of the photochromic compounds.
824

According to the results of the photochemical investigations of the synthesized compounds, given in
Table 1, all the compounds have the same absorption maximum for the open (A) and cyclic (B) isomers, with
the exception of compound 8d (Fig. 1) in which the absorption maximum of the open form is displaced towards
the short wave region by 25 nm.
Fig. 1. Absorption spectra of fulgimide 8d in toluene before (1) and after irradiation at 313 nm for
1 (2), 2 (3), 4 (4), 8 (5), and 12 (6) min.
This indicates that the phenyl rings and the 1,3,4-oxadiazole ring do not in fact participate in
conjugation with the two fulgimide fragments.
Fig. 2. Kinetics of photocoloration under the action of 313 nm radiation (1), photodecoloration
under the action of 546 nm radiation (2), and photodecomposition under the action of unfiltered
mercury lamp radiation (3) of solutions of fulgimide 8d in toluene.
825

Judging by the change in optical density in the photoinduced state at the absorption maximum
wavelength of the cyclic isomer the light sensitivity of the compounds does not depend on the structure of the
spacer connecting the two fulgimide fragments, with the exception of structure 8c.
Analysis of the ratio of the photocoloration and photodecoloration constants of compounds 8a-d
indicates that an increase in the length of the spacer leads to an increase in the intensity of photodecoloration of
the compounds in comparison with the intensity of photocoloration of them, achieving maximum values for the
compound with the greatest length of spacer, viz. fulgimide 8d (Fig. 2).
In the course of the work carried out, previously unreported photochromic fulgimides of the thiophene
series containing two fulgimide fragments in one molecule, linked by bridges of various length, have been
obtained. The photochromic properties of the obtained compounds and the effect of the spacer linking the two
fulgimide fragments on the rate of the photocoloration and photodecoloration reactions of these compounds
have been investigated.
EXPERIMENTAL
1
The IR spectra were taken on a Perkin-Elmer-577 instrument (KBr disks). The H NMR spectra were
recorded on a Bruker WM-250 (250 MHz) spectrometer in CDCl3, the mass spectra (EI) were taken on a Kratos
MS-30 instrument with direct insertion of samples into the ion source, ionizing voltage 70 eV, emission current
0.1 mA, temperature in ionization chamber 250oC. Melting points were measured on a Boetius microscope
stage. Analysis of reaction mixtures and a check on the purity of isolated products was carried out by TLC on
Silufol UV-254 plates, eluent was ethyl acetate–petroleum ether (bp 40-70oC) in a 3:1 ratio.
Commercially available 2,5-dimethylthiophene, potassium tert-butylate, and N,N'-carbonyldiimidazole
(Acros) were used in the work. 3-Acetyl-2,5-dimethylthiophene (3) [12] and 2,5-di(p-aminophenyl)-1,3,4-oxa-
diazole (7d) [13] were obtained by known methods.
Investigation of the photochromic properties of compounds 8a-d was carried out in toluene solution.
The concentration of compounds in solution was 2·10-4 M. Measurement was carried out in a cuvette of 2 mm
thickness. Absorption spectra of the open and cyclic forms were measured on a Shimadzu UV-vis or Carey
(Varian) spectrophotometers over the spectral range 200-800 nm. The cyclic form was obtained after
photoexcitation of a solution with radiation from a DRSh-250 mercury lamp through a UV light filter isolating
radiation of λ 313 nm. Photodecoloration of a solution was achieved on irradiating with filtered radiation of
λ 546 nm. The kinetics of photocoloration of solutions of fulgimides were measured at the wavelength of the
absorption band maximum on irradiating previously decolored solutions of these compounds with the same
radiation. The kinetics of photodecoloration were measured on irradiation of previously colored solutions of
these compounds with irradiation by the mercury lines of a DRSh-250 lamp, isolated with the aid of the
appropriate glass filters.
Diethyl 3-Isopropylidenesuccinate (4). Potassium tert-butylate (31 g, 275 mmol) was dissolved with
heating in tert-butanol (300 ml) and a mixture of dry acetone (19 ml, 250 mmol) and diethyl succinate (52 ml,
313 mmol) was added during 1 h to the boiling solution. The reaction mixture was then boiled for 2 h, after
which the solvent was distilled off, water (200 ml) was added to the residue, and extracted with ether. The
aqueous layer was separated, acidified with hydrochloric acid to acid reaction, and extracted with ether. The
organic layer was separated, the ether distilled off, and ethyl alcohol (200 ml) and sulfuric acid (1 ml) were
added to the residue. The mixture was boiled for 12 h. After esterification, the ethyl alcohol was evaporated on a
rotary evaporator, water (200 ml) was added to the residue, and the mixture was extracted with methylene
chloride. The residual mobile oil after evaporation of the solvent was then vacuum distilled. Yield of compound
4 29.5 g (56%); bp 118-120oC (8 mm Hg), nD22 1.4538 (lit. bp 100-102oC (2 mm Hg), nD20 1.4550 [7]).
826

(3Z)-3-[1-(2,5-Dimethyl-3-thienyl)ethylidene]-4-isopropylidenesuccinic
Acid
(6).
Potassium
tert-butylate (11 g, 100 mmol) in dry toluene (250 ml) was placed into a round-bottomed flask fitted with a
reflux condenser, a dropping funnel, and a magnetic stirrer. A solution of compound 4 (20 g, 90 mmol) and
3-acetyl-2,5-dimethylthiophene (3) (14.4 g, 90 mmol) in dry toluene (50 ml) was added dropwise during 30 min
to the resulting suspension. The reaction mixture was stirred at room temperature for 8 h. The solvent was then
distilled, water (250 ml) was added to the residue, and the mixture was extracted with ether (2×100 ml). The
aqueous layer was separated, and acidified with HCl to a weakly acidic reaction, and then extracted with
chloroform (3×70 ml). The organic layer was separated, dried over CaCl2, and the solvent evaporated on a rotary
evaporator. The residue, hemiester 5, was dissolved in 10% ethanolic KOH solution (100 ml), and hydrolyzed
for 7 h. The solvent was then distilled off to dryness, water (100 ml) was added to the residue, and the solution
acidified to weakly acidic reaction. Diacid 6 was extracted with chloroform, the solvent removed, dried over
CaCl2, and the solvent distilled on a rotary evaporator. The residue was a dark-brown viscous oil. Petroleum
ether (200 ml) and diethyl ether (30 ml) were added to it. The precipitated crystals were filtered off, washed on a
Schott filter with petroleum ether, and dried in a vacuum desiccator. Diacid 6 (11.98 g, 44%) was obtained as
white crystals; mp 203-205oC (lit. mp 204-205oC [6]).
(3Z)-3-[1-(2,5-Dimethyl-3-thienyl)ethylidene-4-isopropylidene-2,5-furandione (1). Diacid 6 (11.98
g, 41 mmol) was dissolved with stirring in dry THF (50 ml) and N,N'-carbonyldiimidazole (120 mmol) was
added to the resulting solution. The reaction mixture was stirred at room temperature for 3 h. The solvent was
then distilled off on a rotary evaporator, water (100 ml) was added to the residue, and the mixture extracted with
methylene chloride. The solvent was evaporated, petroleum ether (20 ml) was added to the residue, and the
mixture placed in the refrigerator (0-5oC) for 1 h. The precipitated crystals were filtered off on a Schott filter,
and washed with petroleum ether. After recrystallization from a chloroform–petroleum ether (1:2) mixture,
anhydride 1 (8.72 g, 77%) was obtained as pale-yellow crystals; mp 155-156oC (lit. mp 155-156oC [6]).
Interaction of (3Z)-3-[1-(2,5-Dimethyl-3-thienyl)ethylidene]-4-isopropylidene-2,5-furandione (1)
with Aromatic Diamines (General Method). Fulgide 1 (1 g, 3.6 mmol) was added to a solution of diamine
7a-d (1.8 mmol) in dry benzene (30 ml) and the reaction mixture was boiled for 25-30 h. At the end of boiling
the precipitated crystals of amido acid were filtered off and used further without additional purification. The
isolated crystals were suspended in dry tetrahydrofuran (30 ml) and N,N'-carbonyldiimidazole (8 mmol) was
added. The reaction mixture was stirred for 5 h at room temperature. The solvent was then distilled off on a
rotary evaporator, water (100 ml) was added to the residue, and the mixture was extracted with ethyl acetate.
After distilling off the solvent, the obtained amorphous solid was purified by column chromatography on silica
gel with a petroleum ether–ethyl acetate (2:1) mixture.
(Z)-1,4-Phenylenebis{3-[1-(2,5-dimethyl-3-thienyl)ethylidene]-4-isopropylidene}pyrrolidine-
2,5-dione (8a). Light-yellow crystals of compound 8a (0.43 g, 38%) were obtained; mp 258-260oC
(chloroform–petroleum ether). 1H NMR spectrum, δ, ppm (J, Hz): 2.04 (6H, s, 2CH3); 2.12 (6H, s, 2CH3); 2.34
(6H, s, 2CH3); 2.41 (6H, s, 2CH3); 2.49 (6H, s, 2CH3); 6.56 (2H, s, 2H-4 thioph.); 7.40 (4H, s, H arom.). Mass
spectrum, m/z (Irel, %): 624 [M]+ (87). Found, %: C 69.20; H 5.81; S 10.26. C36H36N2O4S2. Calculated, %:
C 68.91; H 5.80; S 10.17.
(Z)-1,3-Phenylenebis{3-[1-(2,5-dimethyl-3-thienyl)ethylidene]-4-isopropylidene}pyrrolidine-
2,5-dione (8b). Light-yellow crystals of compound 8b (0.4 g, 36%) were obtained; mp 174-178oC (chloroform–
1
petroleum ether). H NMR spectrum, δ, ppm (J, Hz): 2.02 (6H, s, 2CH3); 2.11 (6H, s, 2CH3); 2.33 (6H, s,
2CH3); 2.41 (6H, s, 2CH3); 2.48 (6H, s, 2CH3); 6.56 (2H, s, 2H-4 thioph.); 7.31-7.47 (4H, m, H arom). Mass
spectrum, m/z (Irel, %): 624 [M]+ (72). Found, %: C 69.20; H 5.81; S 10.26. C36H36N2O4S2. Calculated, %:
C 68.97; H 5.78; S 10.19.
(Z)-4,4'-Biphenylenebis{3-[1-(2,5-dimethyl-3-thienyl)ethylidene]-4-isopropylidene}pyrrolidine-
2,5-dione (8c). White crystals of compound 8c (0.61 g, 49%) were obtained; mp >260oC (chloroform–petroleum
1
ether). H NMR spectrum, δ, ppm (J, Hz): 2.04 (6H, s, 2CH3); 2.12 (6H, s, 2CH3); 2.34 (6H, s,
827

2CH3); 2.41 (6H, s, 2CH3); 2.49 (6H, s, 2CH3); 6.56 (2H, s, 2H-4 thioph.); 7.38 (4H, d, J = 8.2, H arom.); 7.60
(4H, d, J = 8.2, H arom). Mass spectrum, m/z (Irel, %): 700 [M]+ (81). Found, %: C 71.97; H 5.75; S 9.15.
C42H40N2O4S2. Calculated, %: C 71.84; H 5.71; S 8.98.
(Z)-4,4'-(2,5-Diphenylene-1,3,4-oxadiazolyl)bis{3-[1-(2,5-dimethyl-3-thienyl)ethylidene]-4-iso-
propylidene}pyrrolidine-2,5-dione (8d). White crystals of compound 8d (0.72 g, 52%) were obtained;
mp 180-183oC (chloroform–petroleum ether). 1H NMR spectrum, δ, ppm (J, Hz): 2.04 (6H, s, 2CH3); 2.12 (6H,
s, 2CH3); 2.34 (6H, s, 2CH3); 2.40 (6H, s, 2CH3); 2.49 (6H, s, 2CH3); 6.56 (2H, s, 2H-4 thioph.); 7.58 (4H, d,
J = 8.8, H arom); 8.16 (4H, d, J = 8.8, H arom.). Mass spectrum, m/z (Irel, %): 768 [M]+ (76). Found, %:
C 68.73; H 5.24; S 8.34. C44H40N4O5S2. Calculated, %: C 68.61; H 5.30; S 8.17.
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