Novel photochromic dithienylperfluorocyclopentenes with rhodanine fragments: Synthesis and spectroscopic properties

Article abstract of DOI:10.1007/s11172-010-0366-y

Novel photochromic dithienylperfluorocyclopentenes with rhodanine fragments 1a-c were obtained and their spectrokinetic characteristics were examined. The open-chain and cyclic forms of these compounds absorb at longer wavelengths compared to known symmetrical dithienylperfluorocyclopentenes. The influence of the substituent nature on the photochromism of these compounds was studied.

Full text of DOI:10.1007/s11172-010-0366-y

Russian Chemical Bulletin, International Edition, Vol. 59, No. 11, pp. 2126—2128, November, 2010
2126
Novel photochromic dithienylperfluorocyclopentenes
with rhodanine fragments: synthesis and spectroscopic properties
M. M. Krayushkin,a B. V. Lichitskii,a A. A. Dudinov,a O. Yu. Kuznetsova,a I. V. Platonova,b and V. A. Barachevskiib
aN. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences,
47 Leninsky prosp., 119991 Moscow, Russian Federation.
Fax: +7 (499) 135 5328. Eꢀmail: mkray@ioc.ac.ru
bPhotochemistry Center, Russian Academy of Sciences,
7a ul. Novatorov, 119421 Moscow, Russian Federation.
Fax: +7 (495) 936 1255. Eꢀmail: barva@photonics.ru
Novel photochromic dithienylperfluorocyclopentenes with rhodanine fragments 1a—c were
obtained and their spectrokinetic characteristics were examined. The openꢀchain and cyclic
forms of these compounds absorb at longer wavelengths compared to known symmetrical
dithienylperfluorocyclopentenes. The influence of the substituent nature on the photochromism
of these compounds was studied.
Key words: synthesis, photochromism, sulfurꢀcontaining diarylethenes, dithienylethenes,
rhodanines, photocoloration, photodecoloration, photodegradation.
Scheme 1
Photochromic dihetarylethenes undergoing UVꢀinꢀ
duced reversible cyclization are of considerable interest
for the design of photosensitive functional materials,1 opꢀ
tical storage devices,2 and various photoswitches.3
The goal of the present work was to obtain novel photoꢀ
chromic dithienylethenes 1a—c containing rhodanine fragꢀ
ments and study their spectrokinetic characteristics.
Results and Discussion
The target dithienylethenes 1a—c were obtained from
photochromic dialdehyde4 2 and various rhodanine derivꢀ
atives 3a—c (Scheme 1). It should be noted that with such
bases as sodium acetate in acetic anhydride or Nꢀmethylꢀ
morpholine, the reaction under study proceeded incomꢀ
pletely, giving a complex mixture of products. Good yields
of compounds 1a—c were achieved only in the presence of
catalytic amounts of ethylenediamine diacetate.
Products 1a—c are crystalline solids; their structures
were confirmed by elemental analysis and NMR spectroꢀ
1
scopy. The H NMR spectra show characteristic signals
for the equivalent protons at δ 7.70—7.72 for the thiophene
fragment and at δ 7.89—8.05 for the methine protons.
Photochromic dihetarylethenes are known1 to underꢀ
go UVꢀinduced reversible valence isomerization between
two thermally stable forms A and B (Scheme 2).
R = H (a), Me (b), Ph (c)
i. Ethylenediamine diacetate.
The results of a comparative spectrokinetic study of
the photochromic transformations of dithienylethenes
1a—c in acetonitrile for their equal concentrations
(C = 2•10–4 mol L–1) are given in Table 1 and Figs 1 and 2.
An analysis of the curves in Figs 1 and 2 shows that
these compounds undergo reversible phototransformations
when exposed to visible and UV radiation. It should be
noted that the absorption bands of the openꢀchain and
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2072—2074, November, 2010.
1066ꢀ5285/10/5911ꢀ2126 © 2010 Springer Science+Business Media, Inc.

Dithienylperfluorocyclopentenes
Russ.Chem.Bull., Int.Ed., Vol. 59, No. 11, November, 2010 2127
Table 1. Spectrokinetic characteristics of the photochromic transꢀ
formations of dithienylethenes 1a—c in acetonitrile
A
0.6
2
max
ph
max
Comꢀ
pound
λ
ΔDB
τ
1/2/s
λ
DA
B
A
1
/nm
/nm
3
0.4
0.2
1a
1b
1с
727
0.50
0.44
0.62
2000
284
390
405
284
392
407
288
393
407
0.73
1.72
1.72
0.51
1.32
1.33
0.80
2.01
2.01
734
740
2500 (37.5%)
2000 (28.5%)
4250
8500
12750
t/s
Note. Hereafter, λ(σ)max and λ max are the absorption peak waveꢀ
B
Fig. 2. Photocyclization kinetic curves of compound 1c in acetoꢀ
nitrile: (1) irradiation of the openꢀchain form with UV light
through a UFSꢀ1 light filter, (2) dark storage, and (3) photorecyclꢀ
ization upon irradiation of the cyclic form with visible light
through a KSꢀ10 light filter.
lengths for the openꢀchain (A) and cyclic forms (B), respectively;
DA is the peak optical densities of the openꢀchain form; ΔDBph is
the largest photoinduced change in the peak optical density for
the cyclic form in photoequilibrium; τ1/2 is the time required for
unfiltered radiation to halve the largest photoinduced change in
the peak optical density for the cyclic form in photoequilibrium.
metric derivatives.1 Such a considerable bathochromic
shift of the absorption band of the cyclic form has been
observed earlier only for some symmetric perfluorocycloꢀ
pentene4 and tetrahydrothiophene5 derivatives, as well as
for asymmetric diarylethenes containing an electronꢀreꢀ
leasing substituent in one thienyl fragment and an elecꢀ
tronꢀwithdrawing substituent in the other.1 Apparently,
these experimental results can be attributed to the conjuꢀ
gation between the electronꢀreleasing endocyclic S atom
of the rhodanine fragment in one part of the photoꢀ
chromic molecule and the electronꢀwithdrawing carbonyl
group in the other rhodanine ring. It is also worth noting
that the longꢀwavelength absorption bands of the openꢀ
chain form are very much the same as the UV spectra of
rhodanine derivatives of thiophene containing no photoꢀ
chromic fragment.6
Scheme 2
(especially) cyclic forms of these diarylethenes experience
bathochromic shifts compared to most other known symꢀ
A
2.1
It follows from Table 1 that introduction of a phenyl
fragment into rhodanine derivative 1a results in a bathoꢀ
chromic shift of the absorption band of the cyclic form,
which is due to the increased conjugation in the dithieꢀ
nylethene molecule.
1.4
All the compounds studied are comparably photosenꢀ
sitive to UV light, which is evident from numerically close
photoinduced changes in the optical density of the abꢀ
sorption peak of the cyclic form ΔDph. Data on the photoꢀ
degradation of diarylethenes exposed to unfiltered radiaꢀ
tion of an LCꢀ4 illuminator (Hamamatsu) show that they
are not easily prone to irreversible phototransformations.
Similar results were obtained for photochromic polyꢀ
mer films based on poly(methyl methacrylate) and the
aforesaid diarylethenes (C = 0.25 wt.% of the dry polymer
weight). The difference is that the absorption bands of
both the openꢀchain and cyclic forms experience addiꢀ
tional bathochromic shifts (Table 2).
0.7
2
4
3
1
300
400
500
600 700
800
λ/nm
Fig. 1. Electronic absorption spectra of compound 1c in acetoꢀ
nitrile: (1) no irradiation, (2) irradiation with UV light through
a UFSꢀ1 light filter, (3) further irradiation with visible light
through a KSꢀ10 light filter, and (4) reirradiation with UV light
through a UFSꢀ1 light filter.

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Krayushkin et al.
Table 2. Spectrokinetic characteristics of the photochromic transꢀ
formations of dithienylethenes 1a—c in a poly(methyl methꢀ
acrylate) film (C = 0.25 wt.% of the dry polymer)
The organic layer was dried over Na2SO4 and concentrated; the
residue was recrystallized from ethanol.
(5E,5´E)ꢀ5,5´ꢀ[(3,3,4,4,5,5ꢀHexafluorocyclopentꢀ1ꢀeneꢀ
1,2ꢀdiyl)ꢀ4,4´ꢀbis(5ꢀmethylthiophenꢀ2ꢀylmethylidene)]bis(2ꢀthiꢀ
oxoꢀ1,3ꢀthiazolidinꢀ4ꢀone) (1a). Yield 78%, m.p. >300 °C.
1H NMR (DMSOꢀd6), δ: 2.08 (s, 6 H, 2 Me); 7.70 (s, 2 H,
CHHet); 7.89 (s, 2 H, CH); 13.85 (s, 2 H, NH). Found (%):
C, 42.84; H, 2.05; N, 4.78. C23H12F6N2O2S6. Calculated (%):
C, 42.19; H, 1.85; N, 4.28.
(5E,5´E)ꢀ5,5´ꢀ[(3,3,4,4,5,5ꢀHexafluorocyclopentꢀ1ꢀeneꢀ
1,2ꢀdiyl)ꢀ4,4´ꢀbis(5ꢀmethylthiophenꢀ2ꢀylmethylidene)]bis(3ꢀmeꢀ
thylꢀ2ꢀthioxoꢀ1,3ꢀthiazolidinꢀ4ꢀone) (1b). Yield 65%, m.p. >300 °C.
1H NMR (DMSOꢀd6), δ: 2.11 (s, 6 H, 2 Me); 3.39 (s, 6 H,
2 Me); 7.72 (s, 2 H, CHHet); 8.05 (s, 2 H, CH). Found (%):
C, 44.70; H, 2.56; N, 4.78. C25H16F6N2O2S6. Calculated (%):
C, 43.98; H, 2.36; N, 4.10.
max
ph
max
Comꢀ
pound
λ
ΔDB
τ
1/2/s
λ
DA
B
A
/nm
/nm
1a
1b
1c
745
0.40
3650
285
392
410
283
393
412
290
396
412
0.52
1.25
1.29
0.86
1.31
1.32
0.51
1.21
1.24
747
750
0.71 4150 (40%)
0.30
3250
(5E,5´E)ꢀ5,5´ꢀ[(3,3,4,4,5,5ꢀHexafluorocyclopentꢀ1ꢀeneꢀ
1,2ꢀdiyl)ꢀ4,4´ꢀbis(5ꢀmethylthiophenꢀ2ꢀylmethylidene)]bis(3ꢀpheꢀ
nylꢀ2ꢀthioxoꢀ1,3ꢀthiazolidinꢀ4ꢀone) (1c). Yield 65%, m.p. >300 °C.
1H NMR (DMSOꢀd6), δ: 2.11 (s, 6 H, 2 Me); 7.42 (d, 4 H,
H arom., J = 7.2 Hz); 7.50—7.60 (m, 6 H, H arom.); 7.72 (s, 2 H,
CHHet); 8.05 (s, 2 H, CH). Found (%): C, 52.43; H, 2.69; N, 3.89.
C35H20F6N2O2S6. Calculated (%): C, 52.10; H, 2.50; N, 3.47.
Preparation of films. Poly(methyl methacrylate) (10%, 100 mg)
was added to a solution of a photochrome (0.25 mg) in chloroꢀ
form (1 mL). The resulting formulation (0.25% photochrome
with respect to the dry polymer) was placed in a Dacron tub
(2.5×2.5 cm) and allowed to dry completely. The Dacron subꢀ
strate was removed from the dried film. The film thickness was
100—150 μm.
To sum up, we obtained for the first time novel
dithienylperfluorocyclopentenes with rhodanine fragments
that undergo photochromic transformations in acetoꢀ
nitrile. The spectrokinetic characteristics of the photoꢀ
chromic transformations depend on the structures of the
rhodanine substituents.
Experimental
1
H NMR spectra were recorded on Bruker AMꢀ300 instruꢀ
ments (300 MHz) in DMSOꢀd6. Melting points were measured
on a Boetius hot stage and are given uncorrected. The course of
the reactions was monitored and the purity of the compounds
obtained was checked by TLC (Silica gel 60 F254 plates (Merck),
ethyl acetate—hexane (1 : 3)).
This work was financially supported by the Russian
Foundation for Basic Research (Project No. 08ꢀ03ꢀ00660).
References
Spectrokinetic studies were performed in acetonitrile (Krioꢀ
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1
182 °C). H NMR (CDCl3), δ: 1.20 (s, 6 H, Me); 7.20 (s, 2 H,
CH); 10.10 (s, 2 H, CHald). Rhodanines 3b (see Ref. 8) and 3c
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Synthesis of rhodanine derivatives of dithienylperfluorocycloꢀ
pentenes 1a—c (general procedure). A mixture of dialdehyde 2
(0.174 g, 0.41 mmol), rhodanine 3 (0.82 mmol), and ethylenediꢀ
amine diacetate (2 mg, 0.01 mmol) in a mixture of benzene
(15 mL) and acetic acid (4 mL) was refluxed with a Dean—Stark
trap for 10 h. After the reaction was completed (monitoring by
TLC, Rf 0.60), the solvent was removed and the residue was
dissolved in ethyl acetate (50 mL) and washed with water (2×50 mL).
Received June 17, 2010;
in revised form September 28, 2010