Synthesis, structures, and photochromic properties of N-aryl-3- indolylfulgides

Article abstract of DOI:10.1007/s11172-008-0186-5

New 3-indolylfulgides, viz., 3-[1-(1-aryl-5-methoxy-2-methyl-1H-indol-3-yl) ethylidene]-4-(1-methylethylidene)tetrahydro-2,5-furandiones, were synthesized. These compounds were obtained as E-isomers, as demonstrated by X-ray diffraction, electronic spectr

Full text of DOI:10.1007/s11172-008-0186-5

Russian Chemical Bulletin, International Edition, Vol. 57, No. 7, pp. 1435—1443, July, 2008
1435
Synthesis, structures, and photochromic properties
of Nꢀarylꢀ3ꢀindolylfulgides
S. K. Balenko,a V. P. Rybalkin,b N. I. Makarova,a S. O. Bezuglyi,b E. N. Shepelenko,b L. L. Popova,a
V. V. Tkachev,c S. M. Aldoshin,c A. V. Metelitsa,a V. A. Bren´,a,b and V. I. Minkina,b
aInstitute of Physical and Organic Chemistry, Southern Federal University,
194/2 prosp. Stachki, 344090 RostovꢀonꢀDon, Russian Federation.
Eꢀmail: dubon@ipoc.rsu.ru
bSouthern Scientific Center, Russian Academy of Sciences,
41 ul. Chekhova, 344006 RostovꢀonꢀDon, Russian Federation.
Eꢀmail: vpr53@ctsnet.ru
cInstitute of Problems of Chemical Physics, Russian Academy of Sciences,
1 prosp. Akad. Semenova, 142432 Chernogolovka, Moscow Region, Russian Federation.
Eꢀmail: sma@icp.ac.ru
New 3ꢀindolylfulgides, viz., 3ꢀ[1ꢀ(1ꢀarylꢀ5ꢀmethoxyꢀ2ꢀmethylꢀ1Hꢀindolꢀ3ꢀyl)ethylidene]ꢀ4ꢀ
(1ꢀmethylethylidene)tetrahydroꢀ2,5ꢀfurandiones, were synthesized. These compounds were obꢀ
tained as Eꢀisomers, as demonstrated by Xꢀray diffraction, electronic spectroscopy, and 1H NMR
spectroscopy. Fulgides exhibit photochromic properties in solution. The cyclic dihydrocarbazole
photoisomers of indolylfulgides show fluorescence properties and are characterized by high thermal
stability.
Key words: indoles, fulgides, synthesis, Xꢀray diffraction study, photochromism.
Bistable heteroaromatic fulgides generally have enꢀ
hanced resistance to photodegradation and are thermally
stable, due to which these compounds are considered as
photochromic systems suitable for use in optical memory
devices and as molecular switches.1,2 In some cases, phoꢀ
toinduced cyclic isomers of fulgides of the indole series
exhibit fluorescence, which is of great importance for the
design of materials for threeꢀdimensional data acquisiꢀ
tion.3—8 In this connection, we synthesized and characꢀ
terized the previously unknown fulgides of the indole
series containing aromatic substituents at the nitrogen
atom of the indole fragment.
thylamino)phenyl]ꢀ5ꢀmethoxyꢀ2ꢀmethylꢀ1Hꢀindolꢀ3ꢀ
yl}ethylidene)ꢀ4ꢀ(1ꢀmethylethylidene)tetrahydroꢀ2,5ꢀ
furandione (4c), were synthesized by the reactions of
acids 3a—c with acetyl chloride (4a,b) or acetic anhyꢀ
dride (4c).
The IR spectra of fulgides 4a—c show characteristic
1
bands of two exocyclic carbonyl groups. In the H NMR
spectra of 3ꢀ[1ꢀ(1ꢀarylꢀ5ꢀmethoxyꢀ2ꢀmethylꢀ1Hꢀindolꢀ3ꢀ
yl)ethylidene]ꢀ4ꢀ(1ꢀmethylethylidene)tetrahydroꢀ2,5ꢀ
furandiones 4a—c, the proton signals of the ethylidene
Me groups are observed at δ 2.80, 2.86, and 2.85, respecꢀ
tively, which indicates that these compounds have an E
configuration with respect to the indolylethylidene douꢀ
ble bond9 (Scheme 2).
Results and Discussion
With the aim of determining the geometric parameꢀ
ters and estimating the degree, for which the molecules
(in the solid state) are ready to have optical properties, we
prepared single crystals of compounds 4a,b and studied
them by Xꢀray diffraction.
The crystal structure of 4a contains two molecules per
asymmetric unit (the second molecule is denoted 4a´).
Figure 1 shows the structure of 4a with displacement
ellipsoids of nonhydrogen atoms drawn at the 30% probꢀ
ability level, the atomic numbering scheme, and the secꢀ
ond molecule (indicated by dashed lines), which is suꢀ
perimposed with the former molecule by aligning the
N(1)C(10)C(11)C(13)C(19) fragments. The atomic
The Stobbe condensation of 3ꢀacetylꢀ1ꢀarylꢀ5ꢀmethꢀ
oxyꢀ2ꢀmethylindoles 1a—c with diethyl isopropylideneꢀ
succinate in the presence of sodium hydride and diisoꢀ
propylamine in THF afforded monoethyl esters of inꢀ
dolylꢀsubstituted isopropylidenesuccinic acids 2a—c,
which were hydrolyzed to acids 3a—c (Scheme 1). The
previously unknown fulgides, viz., (3E)ꢀ3ꢀ[1ꢀ(5ꢀmethꢀ
oxyꢀ2ꢀmethylꢀ1ꢀphenylꢀ1Hꢀindolꢀ3ꢀyl)ethylidene]ꢀ4ꢀ
(1ꢀmethylethylidene)tetrahydroꢀ2,5ꢀfurandione (4a),
(3E)ꢀ3ꢀ{1ꢀ[5ꢀmethoxyꢀ1ꢀ(4ꢀmethoxyphenyl)ꢀ2ꢀmethylꢀ
1Hꢀindolꢀ3ꢀyl]ethylidene}ꢀ4ꢀ(1ꢀmethylethylidene)tetraꢀ
hydroꢀ2,5ꢀfurandione (4b), and (3E)ꢀ3ꢀ(1ꢀ{1ꢀ[4ꢀ(dimeꢀ
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1409—1416, July, 2008.
1066ꢀ5285/08/5707ꢀ1435 © 2008 Springer Science+Business Media, Inc.

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Russ.Chem.Bull., Int.Ed., Vol. 57, No. 7, July, 2008
Balenko et al.
Scheme 1
R = Ph (a), 4ꢀMeOC6H4 (b), 4ꢀMe2NC6H4 (c)
numbering of molecule 4a´ is obtained by adding 30 to
the atoms of the molecule 4a. In the subsequent considerꢀ
ation of the structural details, the parameters of molecule
4a´ are given in parentheses. Molecule 4a differs from
4a´ in the orientation of the phenyl ring at the nitrogen
atom with respect to the plane of the indole fragment (after
superposition of their indole fragments and the C(20)
and C(50) atoms, the angle between the planes of the
phenyl rings is 34.6°), and these molecules have the opꢀ
posite orientation of the Me groups at the O(4) and O(34)
atoms (see Fig. 1).
In molecule 4a, the C(16) atom is in the syn orientaꢀ
tion with respect to the C(14) atom, resulting in an inꢀ
crease in the C(14)—C(15)—O(4) angle to 124.0(3)° and
a decrease in the C(17)—C(15)—O(4) angle to 114.0(3)°.
In molecule 4a´, the C(46) atom is turned about the
O(34)—C(45) bond in the opposite direction. The
C(44)—C(45)—O(34) angle in 4a´ (115.7(4)°) is smallꢀ
er than the analogous C(14)—C(15)—O(4) angle in 4a,
whereas the exocyclic C(47)—C(45)—O(34) angle is
larger (122.8(3)°). In addition, there is a substantial difꢀ
ference in the O(4)—C(15) bond length (1.390(4)
and 1.336(6) Å in 4a and 4a´, respectively) and
the C(15)—O(4)—C(16) bond angle (117.4(3) and
120.3(4)°). The distance between the C(7) and C(11)
atoms is 3.492 (3.513) Å; between the O(4) and H(14)
atoms, is 2.65 (2.48) Å; and between the O(4) and C(17)
atoms, is 2.45 (2.63) Å. This is accompanied by an inꢀ
tramolecular contact between the hydrogen atoms of the
Me groups and the H(14) atom in molecule 4a (2.29 and
2.36 Å) and the H(47) atom in molecule 4a´ (2.32 and
2.59 Å). The other geometric parameters of the indepenꢀ
dent molecules are identical within experimental error.
The packing modes of molecules 4a and 4a´ are shown in
Fig. 2. Molecules 4a are arranged in pairs one above
another (see Fig. 2, a), so that there are the intermolecuꢀ
Scheme 2

NꢀArylꢀ3ꢀindolylfulgides
Russ.Chem.Bull., Int.Ed., Vol. 57, No. 7, July, 2008
1437
O(2)
C(1)
C(6)
O(1)
C(16)
O(34)
C(4)
C(5)
C(14)
C(13)
C(46)
C(2)
C(3)
O(4)
O(3)
C(15)
C(10)
C(7)
C(9)
C(8)
C(19)
C(17)
C(11)
N(1)
C(12)
C(18)
C(20)
C(25)
C(55)
C(51)
C(21)
C(24)
C(54)
C(52)
C(22)
C(23)
Fig. 1. Molecular structures of compound 4a with displacement ellipsoids of nonhydrogen atoms drawn at the 30% probability level and
superimposed molecule 4a´ (indicated by dashed lines).
a
b
c
c
b
b
0
0
a
a
Fig. 2. Packing modes of molecules 4a (a) and 4a´ (b).

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Balenko et al.
O(3)
O(1)
gle to 114.7(2)°. The phenyl ring at the nitrogen atom is
turned with respect to the plane of the indole ring analogꢀ
osuly to molecule 4a´. The C(11)—N(1)—C(20)—C(21)
torsion angle is –68.2(4)°. The C(26) atom deviates
from the plane of the phenyl ring by 0.14 Å. The chaꢀ
racter of redistribution of the exocyclic bonds at the
C(23) atom remains unchanged (C(22)—C(23)—O(5),
O(2)
C(2)
C(16)
C(1)
C(3)
C(8)
C(4)
O(4)
C(15)
C(14)
115.5(2)°;
C(24)—C(23)—O(5),
125.1(2)°;
C(6)
C(7)
C(10)
C(24)—C(23)—O(5)—C(26), 9.2(3)°). In the crystal
structure, molecules 4b are packed so that the closest
contacts between atoms of the adjacent molecules are
longer than 2.60 Å.
C(5)
C(9)
C(17)
C(13)
C(19)
The principal structural difference between comꢀ
pounds 4a and 4b in the crystalline state is clearly illusꢀ
trated in Fig. 3, where the molecules are projected onto
the common plane of the indole fragment after superpoꢀ
sition of its atoms. Molecule 4b differs from 4a in
the torsion angle characterizing the orientation of the
fulgide fragment with respect to the C(5)—C(10) bond.
Thus, the C(11)—C(10)—C(5)—C(4) torsion angle is
52.7(4)° and –47.3(2)° in 4a and 4b, respectively. Thereꢀ
fore, the reaction centers C(7) and C(11) in molecule 4a
are in the syn orientation; in molecule 4b, in the anti
orientation. The distance between the C(7) and C(11)
atoms in molecules 4a and 4b is 3.492 (3.513) and
4.231 Å, respectively. After photocyclization, the reacꢀ
tion centers C(7) and C(11) in molecule 4a come closer
together from the side of the Me group at the C(12) atom;
in molecule 4b, from the opposite side. It can be concludꢀ
ed that in the crystal structure, molecule 4a adopts a conꢀ
formation structurally suitable for the electrocyclic rearꢀ
rangement, whereas the conformation of molecule 4b
is characterized by a large distance between the termiꢀ
nal carbon atoms of the hexatriene system. In the
latter case, a substantial rearrangement of the moleꢀ
cule is required for the electrocyclic reaction to be
completed.
C(11)
N(1)
C(18)
C(12)
C(20)
C(25)
C(24)
C(21)
C(22)
C(23)
O(5)
C(26)
Fig. 3. Molecular structures of 4a and 4b projected onto the comꢀ
mon plane of the indole ring.
lar O(32)...H(391)´ and O(32)´...H(391) (2.57 Å) conꢀ
tacts. Independent molecules 4a´ are located between
molecules 4a, do not form short contacts, and are orientꢀ
ed with respect to each other (see Fig. 2, b) in such a way
that their fulgide fragments are located one above another.
Figure 3 shows the molecular structure of 4b with
displacement ellipsoids of nonhydrogen atoms drawn at
the 30% probability level, the atomic numbering scheme,
and molecule 4a (indicated by dashed lines), which is
superimposed with the former molecule by aligning
the indole fragments.
In the crystal structures, molecules 4b and 4a (4a´)
have an E configuration. On the whole, except for
the details considered below, the distances and angles in
molecules 4a (4a´) and 4b are identical within experiꢀ
mental error. The C(16) atom in molecule 4b, like that in
molecule 4a, points toward the C(14) atom, which is
accompanied by a deviation of the MeO group in a counꢀ
terclockwise direction in the plane of the figure and leads
to an increase in the C(14)—C(15)—O(4) angle to
124.1(2)° and a decrease in the C(17)—C(15)—O(4) anꢀ
The electronic absorption spectra of Nꢀphenylꢀsubꢀ
stituted fulgide Eꢀ4a in toluene have longꢀwavelength
bands with a maximum at 386 nm and the molar extincꢀ
tion coefficient of 11600 L mol–1 cm–1 (Table 1).
The introduction of the phenyl substituent instead of the
methyl group at the nitrogen atom of the indole ring leads
to a hypsochromic shift (7 nm) of the longꢀwavelength
maximum of the Eꢀisomer compared to the Eꢀisomer of
the previously studied fulgide 5,6 which is characterized

NꢀArylꢀ3ꢀindolylfulgides
Russ.Chem.Bull., Int.Ed., Vol. 57, No. 7, July, 2008
1439
Table 1. Spectralꢀabsorption and spectralꢀfluorescent characteristics of the isomeric forms of fulgides 4a—c
in toluene at 293 K
Comꢀ
pound
Isomer
Absorption
ε/L mol–1 cm–1
Fluorescence
λ
max/nm
Excitation
Emission
λ
max/nm
4a
4b
4с
Е
С
386
611
11600
—
—
—
783
367 (S0 → S2),
610 (S0 → S1)
—
370 (S0 → S2),
615 (S0 → S1)
—
Е
С
389
616
10900
—
—
787
Е
С
396
633
11700
—
—
800
380 (S0 → S2),
640 (S0 → S1)
by the longꢀwavelength maximum at longer wavelengths
(393 nm, ε = 9530 L mol–1 cm–1).
4a at 343 K under irradiation using a mercury lamp
(λ = 365 nm) until the photostationary state is reached
and after the termination of irradiation is presented in
Fig. 5 (regions a and b, respectively). In the region b
(see Fig. 5), no changes in the absorbance of the colored
solution were observed within 40 min, which also indiꢀ
cates that no reverse dark reactions proceed.
The visible light irradiation (λ = 578 nm) of colored
solutions of fulgides 4a—c leads to their bleaching as
a result of the reverse ringꢀopening photoreaction C → E.
Cyclic isomers 4a—c show fluorescence properties with
the fluorescence quantum yields Φ = 10–3. The fluoresꢀ
cence maxima of solutions of the cyclic Cꢀisomers in
toluene are observed at long wavelengths, at 783 (4a),
787 (4b), and 800 nm (4c) (see Table 1). As can be
seen from the fluorescence excitation spectra of cyclic
isomers 4a—c, the transition absorption bands S0 → S2
(λmax = 367—380 nm) overlap with the transition abꢀ
The introduction of electronꢀreleasing groups at
the para position of the Nꢀphenyl fragment leads to a
small bathochromic shift (3 nm) of the longꢀwavelength
maximum for the 4ꢀmethoxy derivative (fulgide 4b)
(λmax = 389 nm, ε = 10900 L mol–1 cm–1) and a shift of the
maximum of this band by 10 nm for the 4ꢀdimethylamiꢀ
noꢀcontaining compound (fulgide 4c) (λmax = 396 nm,
ε = 11700 L mol–1 cm–1) compared to Nꢀphenylꢀ3ꢀinꢀ
dolylfulgide 4a (see Table 1).
At ambient temperature, solutions of fulgides 4a—c
do not show fluorescence properties.
Under UV irradiation using a mercury lamp
(λ = 365 nm), solutions of fulgides 4a—c in toluene
acquire a color characteristic of the cyclization products
of the dihydrocarbazole isomers C (see Scheme 2), which
is accompanied5,6 by the appearance of bands in the specꢀ
tra at λ = 500—750 nm (Fig. 4).
The spectra of the photoinduced Cꢀisomers of fulgides
4a,b have absorption bands at 611 and 616 nm, respecꢀ
tively (see Table 1). In the case of 1ꢀ[4ꢀ(dimethylamino)ꢀ
phenyl]indolylfulgide 4c, the longꢀwavelength maximum
of the Cꢀisomer is shifted to longer wavelengths and is
observed at 633 nm.
An increase in the bathochromic shift of the longꢀ
wavelength maximum of both the Eꢀ and Cꢀisomers with
increasing electronꢀreleasing properties of the substituꢀ
ent in the para position of the Nꢀphenyl ring is consistent
with the concept of polarization of the Eꢀ and Cꢀisomers
of fulgides in the excited state due to a shift of the electron
density of the aromatic indole heterocycle to the anhyꢀ
dride group.10
A
0.7
0.6
0.5
0.4
0.3
0.2
0.1
The cyclic Cꢀisomers of fulgides 4a—c are characterꢀ
ized by high thermal stability in a toluene solution. Thus,
the thermal reverse reaction C → E is not detected at
293 K for 72 h. The time dependence of the absorbance at
the absorption maximum of the photoproduct C of fulgide
400
500
600
700
λ/nm
Fig. 4. Electronic absorption spectra of a solution of fulgide 4a in
toluene (c = 7.16•10–5 mol L–1, T = 295 K) under light irradiation
at λ = 365 nm recorded at 10 s intervals.

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Russ.Chem.Bull., Int.Ed., Vol. 57, No. 7, July, 2008
Balenko et al.
A
a
E
E
E
E
E
a
b
0.10
0.08
0.06
0.04
0.02
7
6
5
4
3
2
1
δ
15.74 25.56
15.99 15.25 15.38 15.00
C
b
0
10
20
30
40 t/min
C E + Z
C
Z
C
Fig. 5. Absorbance of the photoisomer Cꢀ4a (c = 3.5•10–5 mol L–1
T = 343 K) at the absorption maximum under light irradiation at
λ = 365 nm until the photostationary state is reached (region a) and
after termination of irradiation (region b).
,
Z
C
Z
E
E
Z
E
E
C
sorption bands S0 → S1 of the Eꢀisomeric forms
(λmax = 386—396 nm). As a result, due to the recyclizaꢀ
tion C → E in the electronic excitation state, the comꢀ
plete conversion of the starting Eꢀisomers of fulgides
4a—c into the colored products C cannot be achieved
(see Table 1).
7
6
5
4
3
2
δ
1.30 10.37 1.93
19.28 2.12
7.14 5.61 3.08
16.97 30.32
5.62
4.73
E
c
E + Z
E
E
In addition, the absorption bands of the Eꢀ and
Zꢀisomers strongly overlap (see Fig. 4), and both the
E→Z and Z→E photoisomerization reactions proceed
under irradiation at the absorption band of one of the
isomers.1 Hence, UV irradiation leads to the establishꢀ
ment of the stationary state, including three isomeric
forms (E, Z, and C), in solution (see Scheme 2). Actually,
E
Z
Z
Z
Z
1
the H NMR spectra of fulgide 4a in deuterotoluene
recorded upon successive irradition at λ = 365 and 578 nm
(Fig. 6) provide evidence that all three isomeric forms
are present in solution.
7
6
5
4
3
2
δ
1.30 10.37
19.28
7.14
3.08 16.97
30.32
4.73
1
The H NMR spectra of the starting solution show
Fig. 6. 1H NMR spectra of fulgide 4a in tolueneꢀd8 before irradiaꢀ
tion (Eꢀisomer) (a), after light irradiation at λ = 365 nm (E, Z, and
Cꢀisomers) (b), and after subsequent light irradiation at λ = 578 nm
(Eꢀ and Zꢀisomers) (c).
a set of signals characteristic of isomer Eꢀ4a (see Fig. 6, a).
After light irradiation at λ = 365 nm, the photostationary
state is reached. Thus, the proton signals of the Me groups
of all isomers (acyclic isomers Eꢀ4a and Zꢀ4a and cyclic
isomer Cꢀ4a) and the signal for the aromatic proton of
the Cꢀisomer (see Fig. 6, b) are observed. The ratio beꢀ
tween the starting fulgide Eꢀ4a and isomers Zꢀ4a and Cꢀ4a
is 5 : 6 : 9 (estimated from the integrated intensities of
the signals of the Me groups). Upon further visible light
Fulgides 4a—c are characterized by enhanced resisꢀ
tance to photodegradation. After the repeated photoꢀ
coloration—photobleaching cycle in toluene soluꢀ
tions (for example, of compound 4a; see Fig. 7),
the absorbance at the absorption maximum of the
Cꢀisomer (the photostationary state) remains virtually
unchanged.
To conclude, we synthesized photochromic fulgides,
viz., (3E)ꢀ3ꢀ[1ꢀ(1ꢀarylꢀ5ꢀmethoxyꢀ2ꢀmethylꢀ1Hꢀindolꢀ3ꢀ
yl)ethylidene]ꢀ4ꢀ(1ꢀmethylethylidene)tetrahydroꢀ2,5ꢀ
furandiones. New Nꢀarylindolylfulgides are characterꢀ
ized by resistance to photodegradation and high thermal
1
irradiation (λ = 578 nm) of this solution, the H NMR
spectrum shows the proton signals of acyclic isomers
Eꢀ4a and Zꢀ4a (see Fig. 6, c), which are present in soluꢀ
tion in a ratio of 7 : 3. Therefore, the analysis of the
1H NMR and electronic absorption spectra confirmed
the proposed mechanism of the photoinduced reactions
of new indolylfulgides 4a—c involving the E/Z photoꢀ
isomerization and the E→C photocyclization.

NꢀArylꢀ3ꢀindolylfulgides
Russ.Chem.Bull., Int.Ed., Vol. 57, No. 7, July, 2008
1441
A
ized with a 10% HCl solution (30 mL). The precipitate of dicarboxꢀ
ylic acid 3a was filtered off and dried in air. The yield was 92%,
colorless crystals, m.p. 245—246 °C. Found (%): C, 72.45; H, 6.22;
N, 3.45. C27H29NO5. Calculated (%): C, 71.58; H, 6.01; N, 3.34.
IR, ν/cm–1: 1750, 1780 (C=O). 1H NMR (CDCl3), δ: 0.90, 1.65,
2.00, and 2.20 (all s, 3 H each, Me); 3.65 (s, 3 H, OMe); 6.75—7.10
(m, 3 H, H arom.); 7.22—7.65 (m, 5 H, H arom.); 11.40—11.60
(br.s, 2 H, OH).
a b
0.30
0.25
0.20
0.15
0.10
0.05
0
(3E)ꢀ3ꢀ[1ꢀ(5ꢀMethoxyꢀ2ꢀmethylꢀ1ꢀphenylꢀ1Hꢀindolꢀ3ꢀyl)ꢀ
ethylidene]ꢀ4ꢀ(1ꢀmethylethylidene)tetrahydroꢀ2,5ꢀfurandione
(Eꢀ4a). Diacid 3a (2 g, 4.7 mmol) was dissolved under heating in
acetyl chloride (1.5 mL). The solvent was distilled off in vacuo.
The reaction product was purified by silica gel column chromaꢀ
tography using chloroform as the eluent. The yield was 97%, yelꢀ
low crystals, m.p. 182—184 °C (from MeCN). Found (%):
C, 78.80; H, 6.52; N, 3.35. C20H21NO4. Calculated (%): C, 78.21;
H, 6.28; N, 3.20. IR, ν/cm–1: 1790, 1760 (C=O). 1H NMR
(benzeneꢀd6), δ: 0.75, 1.60, 2.00, and 2.80 (all s, 3 H each, Me);
3.50 (s, 3 H, OMe); 6.70—6.90 (m, 5 H, H arom.); 7.00—7.05
(m, 3 H, H arom.).
(3Z)ꢀ3ꢀ[1ꢀ(5ꢀMethoxyꢀ2ꢀmethylꢀ1ꢀphenylꢀ1Hꢀindolꢀ3ꢀyl)ꢀ
ethylidene]ꢀ4ꢀ(1ꢀmethylethylidene)tetrahydroꢀ2,5ꢀfurandione
(Zꢀ4a) was synthesized in an NMR tube as a mixture with the Eꢀ and
Cꢀisomers from a solution of fulgide Eꢀ4a in deuterotoluene under
light irradiation at λ = 365 nm for 4 h (c = 2.4•10–2 mol L–1) .
1H NMR (benzeneꢀd6), δ: 1.30, 2.00, 2.10, and 2.15 (all s, 3 H each,
Me); 3.55 (s, 3 H, OMe); 6.70—6.90 (m, 5 H, H arom.); 7.00—7.20
(m, 3 H, H arom.).
0
2000 4000 6000 8000 10000
t/s
Fig. 7. Changes in the absorbance of a toluene solution of fulgide 4a
(c = 7.16•10–5 mol L–1, T = 295 K) at the absorption maxiꢀ
mum of the Cꢀisomer (λ = 610 nm) after repeated photocoloration
(λ = 365 nm) (a)—photobleaching (λ = 578 nm) (b) cycles.
stability of the photoinduced cyclic form showing fluoꢀ
rescence properties.
Experimental
8ꢀMethoxyꢀ4,4,4a,10ꢀtetramethylꢀ5ꢀphenylꢀ4a,5ꢀdihydroꢀ
1Hꢀfuro[3,4ꢀb]carbazoleꢀ1,3(4H)ꢀdione (Cꢀ4a) was synthesized in
an NMR tube as a mixture with the Eꢀ and Zꢀisomers from a solution
of fulgide Eꢀ4a in deuterotoluene under light irradiation at λ = 365
nm for 6 h (c = 2.4•10–2 mol L–1). 1H NMR (benzeneꢀd6), δ: 1.00,
1.15, 1.20, and 2.30 (all s, 3 H each, Me); 3.30 (s, 3 H, OMe);
5.85—5.90 (s, 1 H, H arom.); 6.55—6.65 (m, 1 H, H arom.);
6.90—7.20 (m, 6 H, H arom.).
(3E)ꢀ4ꢀ[5ꢀMethoxyꢀ2ꢀmethylꢀ1ꢀ(4ꢀmethoxyphenyl)ꢀ1Hꢀinꢀ
dolꢀ3ꢀyl]ꢀ2ꢀ(1ꢀmethylethylidene)ꢀ3ꢀ(ethoxycarbonyl)pentꢀ3ꢀenoic
acid (Eꢀ2b) was synthesized analogously to monoethyl ester 2a
from 3ꢀacetylꢀ5ꢀmethoxyꢀ1ꢀ(4ꢀmethoxyphenyl)ꢀ2ꢀmethylindole
(0.01 mol). The yield was 55%, colorless crystals, m.p. 147—149 °C.
Found (%): C, 73.40; H, 6.52; N, 3.35. C28H31NO6. Calculatꢀ
ed (%): C, 72.46; H, 6.53; N, 3.13. IR, ν/cm–1: 1770, 1790 (C=O).
1H NMR (DMSOꢀd6), δ: 0.77 (t, 3 H, Me, J = 7.0 Hz); 1.94, 2.05,
2.13, and 2.22 (all s, 3 H each, Me); 3.74 and 3.86 (both s,
3 H each, OMe); 3.73—3.85 (m, 2 H, CH2); 6.50—6.65 (m, 1 H,
H arom.); 6.70—6.90 (m, 2 H, H arom.); 7.00—7.20 (m, 4 H,
H arom.); 11.90—12.00 (br.s, 1 H, OH).
The electronic absorption spectra were measured on an Agilent
8453 spectrophotometer. The fluorescence spectra were recordꢀ
ed on a Varian Eclipce spectrofluorimeter. Solutions were irradiatꢀ
ed using a DRShꢀ250 mercury lamp equipped with a kit of
light interference filters for isolation of mercury lines. The IR
spectra were measured on a Specord 75IR instrument in Nuꢀ
jol mulls. The 1H NMR spectra were recorded on a Varian
Unityꢀ300 instrument (300 MHz) using HMDS as the exterꢀ
nal standard.
(3E)ꢀ3ꢀ(Ethoxycarbonyl)ꢀ4ꢀ(5ꢀmethoxyꢀ2ꢀmethylꢀ1ꢀphenylꢀ
1Hꢀindolꢀ3ꢀyl)ꢀ2ꢀ(1ꢀmethylethylidene)pentꢀ3ꢀenoic acid (2a).
A solution of 3ꢀacetylꢀ5ꢀmethoxyꢀ2ꢀmethylꢀ1ꢀphenylindole (2.8 g,
0.01 mol), diethyl isopropylidenesuccinate (2.8 g, 0.013 mol), and
diisopropylamine (1.4 mL, 0.01 mol) in THF (20 mL) was added
with stirring to a suspension of sodium hydride (0.7 g, 0.03 mol) in
THF (10 mL) at room temperature. The reaction mixture was stirred
at 30 °C for 5 h. The solvent was distilled off using a water jet
vacuum pump. The residue was treated with 10% hydrochloric acid
(30 mL). The precipitate of monoethyl ester 2a was filtered off and
recrystallized from toluene. The yield was 52%, colorless crystals,
m.p. 162—163 °C. Found (%): C, 73.40; H, 6.52; N, 3.35.
C27H29NO5. Calculated (%): C, 72.46; H, 6.53; N, 3.13. IR,
(2E)ꢀ2ꢀ{1ꢀ[5ꢀMethoxyꢀ1ꢀ(4ꢀmethoxyphenyl)ꢀ2ꢀmethylꢀ1Hꢀ
indolꢀ3ꢀyl]ethylidene}ꢀ3ꢀ(1ꢀmethylethylidene)butanedioic acid
(Eꢀ3b) was synthesized analogously to acid 3a. The yield was 88%,
colorless crystals, m.p. 260—261 °C. Found (%): C, 70.45; H, 6.32;
N, 3.25. C26H27NO6. Calculated (%): C, 69.47; H, 6.05; N, 3.12.
1
ν/cm–1: 1760, 1790 (C=O). H NMR (CDCl3), δ: 0.65 (t, 3 H,
CH, J = 7.0 Hz); 1.96, 2.16, 2.18, and 2.21 (all s, 3 H each, Me);
3.83 (s, 3 H, OMe); 3.87 (q, 2 H, CH2, J = 7.0 Hz); 6.70—7.00
(m, 3 H, H arom.); 7.20—7.60 (m, 5 H, H arom.); 11.00—11.20
(br.s, 1 H, OH).
(2E)ꢀ2ꢀ[1ꢀ(5ꢀMethoxyꢀ2ꢀmethylꢀ1ꢀphenylꢀ1Hꢀindolꢀ3ꢀyl)ꢀ
ethylidene]ꢀ3ꢀ(1ꢀmethylethylidene)butanedioic acid (3a). Monoethyl
ester 2a (2.3 g, 5.2 mmol) was refluxed with a 10% methanolic KOH
solution (10 mL) in a flask equipped with a reflux condenser for 4 h.
The reaction mixture was cooled, diluted with water, and neutralꢀ
1
IR, ν/cm–1: 1760, 1785 (C=O). H NMR (DMSOꢀd6), δ: 1.95,
2.04, 2.15, and 2.22 (all s, 3 H each, Me); 3.74 and 3.86 (both s,
3 H each, OMe); 6.50—6.70 (m, 1 H, H arom.); 6.80—6.90
(m, 2 H, H arom.); 7.00—7.30 (m, 4 H, H arom.); 11.60—11.80
(br.s, 2 H, OH).
(3E)ꢀ3ꢀ{1ꢀ[5ꢀMethoxyꢀ1ꢀ(4ꢀmethoxyphenyl)ꢀ2ꢀmethylꢀ1Hꢀ
indolꢀ3ꢀyl]ethylidene}ꢀ4ꢀ(1ꢀmethylethylidene)tetrahydroꢀ2,5ꢀ
furandione (Eꢀ4b). Fulgide Eꢀ4b was synthesized analogously to

1442
Russ.Chem.Bull., Int.Ed., Vol. 57, No. 7, July, 2008
Balenko et al.
3
fulgide Eꢀ4a. The yield was 95%, greenishꢀyellow crystals, m.p.
166—168 °C. Found (%): C, 70.25; H, 6.41; N, 2.83. C26H25NO5.
Calculated (%): C, 70.42; H, 6.54; N, 2.97. IR, ν/cm–1: 1755,
β = 64.54(2)°, γ = 89.89(2)°, V = 2104.8(6) Å , Z = 4,
–
dcalc = 1.267 g cm–3, μ(MoꢀKα) = 0.086 mm–1, space group P1.
The intensities of 5734 reflections were measured (2θ < 45°)
from a single crystal of dimensions 0.1×0.22×0.28 mm using
the ω/2θ scanning technique. After the merging of equivalent reflecꢀ
tions (Rint = 0.0242), a total of 5445 observed reflections
1
1810 (C=O). H NMR (CDCl3), δ: 1.08, 2.06, 2.24, and 2.86
(all s, 3 H each, Me); 3.82 and 3.90 (both s, 3 H each, OMe);
6.70—6.90 (m, 3 H, H arom.); 7.10—7.30 (m, 4 H, H arom.).
(3Z)ꢀ3ꢀ{1ꢀ[5ꢀMethoxyꢀ1ꢀ(4ꢀmethoxyphenyl)ꢀ2ꢀmethylꢀ1Hꢀ
indolꢀ3ꢀyl]ethylidene}ꢀ4ꢀ(1ꢀmethylethylidene)tetrahydroꢀ2,5ꢀ
furandione (Zꢀ4b) was synthesized in an NMR tube as a mixture
with the Eꢀ and Cꢀisomers from a solution of fulgide Eꢀ4b in
deuterotoluene under light irradiation at λ = 365 nm for 4 h
(c = 2.4•10–2 mol L–1). 1H NMR (tolueneꢀd8), δ: 1.20, 2.10, 2.15,
and 2.20 (all s, 3 H each, Me); 3.30 and 3.50 (both s, 3 H each,
OMe); 6.60—7.20 (m, 7 H, H arom.).
(F2 > σ(F2)) were obtained, of which 3855 reflections with
hkl
F2 > 4σ(F 2) were used in calculations (in the final step, 3807
reflections were used).
The Xꢀray data for the structure of 4b were collected on an
automated Bruker Pꢀ4 diffractometer (MoꢀKα radiation, graphite
monochromator). Paleꢀyellow transparent crystals are triclinic,
C26H30NO5, M = 436.51, a = 9.659(1) Å, b = 10.030(2) Å,
c = 13.418(1) Å, α = 89.59(1)°, β = 78.25(1)°, γ = 62.76(1)°,
3
8ꢀMethoxyꢀ5ꢀ(4ꢀmethoxyphenyl)ꢀ4,4,4a,10ꢀtetramethylꢀ
4a,5ꢀdihydroꢀ1Hꢀfuro[3,4ꢀb]carbazoleꢀ1,3(4H)ꢀdione (Cꢀ4b) was
synthesized in an NMR tube as a mixture with the Eꢀ and Zꢀisomers
from a solution of fulgide Eꢀ4b in deuterotoluene under light irradiꢀ
V = 1126.0(2) Å , Z = 2, dcalc = 1.287 g cm–3, μ(MoꢀKα) =
–
0.089 mm–1, space group P1. The intensities of 4331 reflections
were measured (2θ < 50°) using the ω/2θ scanning technique from
a single crystal of dimensions 0.16×0.20×0.22 mm. After the mergꢀ
ing of equivalent reflections (Rint = 0.0211), a total of 3601 observed
reflections (F2 > σ(F2)) were obtained, of which 3041 reflecꢀ
1
ation at λ = 365 nm for 6 h (c = 2.4•10–2 mol L–1). H NMR
(tolueneꢀd8), δ: 0.40, 1.05, 1.20, and 2.30 (all s, 3 H each, Me);
3.35 and 3.45 (both s, 3 H each, OMe); 6.60—7.20 (m, 7 H,
H arom.).
hkl
tions with F2 > 4σ(F2) were used in calculations. The strucꢀ
tures of 4a (4a´) and 4b were solved by direct methods using the
SHELXSꢀ97 program package11 and refined by the fullꢀmaꢀ
trix leastꢀsquares method based on F2 with anisotropic displaceꢀ
ment parameters for nonhydrogen atoms using the SHELXLꢀ97
program package.11 In the crystal structures of 4a (4a´) and 4b, all
hydrogen atoms were located in difference Fourier maps. Then the
atomic coordinates and the isotropic temperature factors for all
H atoms were refined by the leastꢀsquares method using a riding
model.11 In the last cycle of the fullꢀmatrix refinement, the absolute
shifts of all variable parameters of the structures (571 for 4a (4a´)
and 290 for 4b) were <0.001σ. The final R factors for 4a (4a´) were
R1 = 0.056, wr2 = 0.14 based on 3807 observed reflections with
I > 2σ(I); R1 = 0.080, wr2 = 0.16 based on all 5445 measured
reflections, GOF 1.032. After the completion of the refinement,
the maximum and minimum residual electron densities were
0.42 and –0.32 e Å–3, respectively. The final R factors for 4b were
R1 = 0.046, wr2 = 0.13 based on 3041 observed reflections with
I > 2σ(I); R1 = 0.053, wr2 = 0.13 based on all 3601 measured
reflections, GOF 1.042. After the completion of the refinement, the
maximum and minimum residual electron densities were 0.16
and –0.17 e Å–3, respectively.
(3E)ꢀ4ꢀ{1ꢀ[4ꢀ(Dimethylamino)phenyl]ꢀ5ꢀmethoxyꢀ2ꢀmethylꢀ
1Hꢀindolꢀ3ꢀyl}ꢀ3ꢀ(ethoxycarbonyl)ꢀ2ꢀ(1ꢀmethylethylidene)pentꢀ
3ꢀenoic acid (Eꢀ2c) was synthesized from 3ꢀacetylꢀ1ꢀ(4ꢀdiꢀ
methylamino)phenylꢀ5ꢀmethoxyꢀ2ꢀmethylindole (0.01 mol) analꢀ
ogously to monoethyl ester 2a. The yield was 47%, colorless crysꢀ
tals, m.p. 173—175 °C. Found (%): C, 70.95; H, 6.92; N, 5.35.
C29H34N2O5. Calculated (%): C, 71.00; H, 6.99; N, 5.71.
IR, ν/cm–1: 1760, 1790 (C=O). 1H NMR (CDCl3), δ: 0.67 (t, 3 H,
Me, J = 7.0 Hz); 1.95, 2.15, 2.16, and 2.19 (all s, 3 H each,
Me); 3.04 (s, 6 H, NMe2); 3.82 (s, 3 H, OMe); 3.70—3.95
(m, 2 H, CH2); 6.60—7.20 (m, 7 H, H arom.); 11.05—11.25 (br.s,
1 H, OH).
(2E)ꢀ2ꢀ(1ꢀ{1ꢀ[4ꢀ(Dimethylamino)phenyl]ꢀ5ꢀmethoxyꢀ2ꢀmethꢀ
ylꢀ1Hꢀindolꢀ3ꢀyl}ethylidene)ꢀ3ꢀ(1ꢀmethylethylidene)butanedioic
acid (Eꢀ3c) was synthesized analogously to acid 3a. The yield was
84%, colorless crystals, m.p. 224—225 °C. Found (%): C, 70.95;
H, 6.92; N, 5.35. C27H30N2O5. Calculated (%): C, 71.11; H, 6.54;
N, 6.06. IR, ν/cm–1: 1760, 1790 (C=O). 1H NMR (DMSOꢀd6), δ:
1.95, 2.03, 2.14, and 2.21 (all s, 3 H each, Me); 3.02 (s, 6 H,
NMe2); 3.74 (s, 3 H, OMe); 6.50—7.20 (m, 7 H, H arom.),
11.60—11.80 (br.s, 2 H, OH).
This study was financially supported by the Russian
Foundation for Basic Research (Project No. 06ꢀ03ꢀ32988),
the Ministry of Education and Science of the Rusꢀ
sian Federation (Research Program "Development of
the Scientific Potential of Higher School," Grant RNP
2.1.1.1938), and the Council on Grants of the President
of the Russian Federation (Program for State Support of
Leading Scientific Schools of the Russian Federation,
Grant NShꢀ4849.2006.3).
(3E)ꢀ3ꢀ(1ꢀ{1ꢀ[4ꢀ(Dimethylamino)phenyl]ꢀ5ꢀmethoxyꢀ2ꢀmeꢀ
thylꢀ1Hꢀindolꢀ3ꢀyl}ethylidene)ꢀ4ꢀ(1ꢀmethylethylidene)tetrahydroꢀ
2,5ꢀfurandione (Eꢀ4c). Diacid 3c (1.7 g, 3.9 mmol) was dissolved
under heating in acetic anhydride (2 mL). The solvent was distilled
off in vacuo. Fulgide 4c was purified by silica gel column chromaꢀ
tography using chloroform as the eluent and recrystallized from
MeCN. The yield was 91%, yellow crystals, m.p. 190—192 °C.
Found (%): C, 70.25; H, 6.41; N, 2.83. C26H25NO5. Calculatꢀ
ed (%): C, 70.42; H, 6.54; N, 2.97. IR, ν/cm–1: 1755, 1810 (C=O).
1H NMR (CDCl3), δ: 1.08, 2.06, 2.23, and 2.86 (all s, 3 H each,
Me); 3.00 and 3.05 (both s, 6 H each, NMe2); 3.90 (s, 3 H, OMe);
6.70—7.30 (m, 7 H, H arom.).
Xꢀray diffraction study. The unit cell parameters were measured
and the threeꢀdimensional Xꢀray diffraction data set for the structure
of 4a (4a´) was collected on an automated Enraf—Nonius CADꢀ4
diffractometer (MoꢀKα radiation, graphite monochromator). Light
transparent crystals are triclinic, C25H23NO4, M = 401.44,
a = 13.044(2) Å, b = 13.405(2) Å, c = 13.523(3) Å, α = 81.26(2)°,
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Received June 21, 2007;
in revised form February 5, 2008