Photochromic organic compounds for optical memory

Article abstract of DOI:10.1007/s11172-008-0124-6

For the purpose of target syntheses of new photochromic compounds, a relationship between the structure and properties of a series of the known thermally irreversible photochromes was analyzed using the spectral kinetic data obtained by the authors.

Full text of DOI:10.1007/s11172-008-0124-6

Russian Chemical Bulletin, International Edition, Vol. 57, No. 4, pp. 867—875, April, 2008
867
Photochromic organic compounds for optical memory
V. A. Barachevskya✭ and M. M. Krayushkinb
aPhotochemistry Center, Russian Academy of Sciences,
7a ul. Novatorov, 119421 Moscow, Russian Federation.
Fax: +7 (495) 936 1255. Eꢀmail: barva@photonics.ru
bN. 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
For the purpose of target syntheses of new photochromic compounds, a relationship between
the structure and properties of a series of the known thermally irreversible photochromes was
analyzed using the spectral kinetic data obtained by the authors.
Key words: photochromism, optical memory, diarylethenes, fulgimides.
Progress in information technologies demands a sharp
increase in the informational capacity of information
carriers and in the rate of data processing.
wavelength (405 nm), an optical system with a digital aperꢀ
ture of 0.7/0.8, and the photosensitive layer with
a thickness of 0.1 mm.
An analysis of the modern state of research in this
area1 shows that the limiting density of information reꢀ
Prospects for increasing the informational capacity of
ODs are related to the creation of multilayer photosensiꢀ
tive coatings for bitwise information detection and thick
(>2 mm) photosensitive layers for holographic informaꢀ
tion detection. These ODs provide the threeꢀdimensionꢀ
al (3D) optical memory with the recording density higher
than 1 Tbit due to information recording and reproducꢀ
tion in various layers of a detecting medium (in the case
of the bitwise optical memory) or at different incident
angles of the activating and recovering laser radiation
(in the case of the holographic optical memory).
The prospects for improving ODs for optical memory
are associated with the use of photosensitive organic meꢀ
dia that experience photochemical transformations.
In principle, these media possess a higher resolving abilꢀ
ity than the presently used thermosensitive materials.
The purpose of the present study is the search for
thermally irreversible photochromic organic compounds
with two thermodynamically stable states for the develꢀ
opment of photochromic detecting media that provide
the creation of multilayer optical discs (Fig. 1). The pheꢀ
nomenon of twoꢀphoton photochromism is used to creꢀ
ate the 3D bitwise operative optical memory (WERM)2
based on the twoꢀphoton ODs.3
cording on magnetic discs can reach 230 Gbit inch–2
.
In this case, the informational capacity of magnetic discs
can be increased to 20 Gbit. The rate of data processing
can be 1 Gbit s–1
.
In addition to magnetic discs, optical discs (ODs) for
archive storage of information are widely popular. They
can be of the CD type (type I), providing multiple readꢀ
ing of an optical information recorded in a studio, and of
the WORM type (type II) with a single recording and
multiple reading directly in a personal computer. Reverꢀ
sive ODs of the WERM type (type III) were created for
operative multiple recording and repeated recording of
optical information and its multiple reading. Optical inꢀ
formation recording on the most part of known ODs is
based on thermoinduced processes of substance converꢀ
sion. In the case of ODs of types I and II, information
recording is performed due to the thermoinduced ablaꢀ
tion of deposited in vacuo layers of organic and inorganic
substances. Reversible recording — rewriting of optical
information in an OD of type III occurs due to the therꢀ
moinduced magnetization reversal of magnetic domains
in optical discs or reversible phase transformations of
metallic alloys. The informational capacity of these ODs
used for information reading from a semiconducting laꢀ
ser with a radiation wavelength of 650 nm is ~4.7 Gbit.
New commercial ODs developed by the Bluꢀray Disc
Association have the recordꢀbreaking informational caꢀ
pacity: 25 Gbit for singleꢀsided and 50 Gbit for doubleꢀ
sided (DVD) information carriers, which is achieved by
the application of a semiconducting laser with a shorter
Photochromism is the ability of a substance to reversꢀ
ibly change (under optical irradiation) the visible abꢀ
sorption spectrum, i.e., the color and other properties
caused by the formation, in essence, of a different comꢀ
pound.4
During the photochromic process, a substance abꢀ
sorbs optical radiation and transits from the initial state А
to the soꢀcalled photoinduced state B characterized by a
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 853—861, April, 2008.
1066ꢀ5285/08/5704ꢀ0867 © 2008 Springer Science+Business Media, Inc.

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Russ.Chem.Bull., Int.Ed., Vol. 57, No. 4, April, 2008
4
Barachevsky and Krayushkin
cient and, hence, can provide nonꢀdestructive optical inꢀ
formation reading.9 These photochromic compounds
are few and mainly related to the classes of diarylethenes
I,10 fulgides and fulgimides II,11 and phenoxyꢀsubstituted
derivatives of quinones III.12
All compounds of the indicated types are subjected to
reversible photoinduced valence isomerization. Diꢀ
arylethenes I and fulgimides II undergo reversible phoꢀ
totransformations between the opened and cyclic forms,
and the phenoxyꢀsubstituted derivatives of quinones III
are characterized by reversible phototransformations beꢀ
tween the anaꢀ and paraꢀquinoid forms (Scheme 1).
1
2
3
5
Scheme 1
Fig. 1. Scheme of the multilayer detecting medium consisting
of consecutive layers: detecting (1), address (2), and isolating (3), as
well as the scheme of recording using one (4) or two beams (4 and 5)
of the same laser.
different absorption spectrum and a certain lifetime. The
backward transition from state B to state A occurs spontaꢀ
neously due to the internal energy and can considerably
be accelerated on heating of the substance or under
the action of the light absorbed by form B.
A
B
The photochromism phenomenon is inherent in many
organic and inorganic substances. Photochromism is
based on both the photophysical processes (triplet—triꢀ
plet absorption, singlet—singlet clarification) and nuꢀ
merous photochemical reactions accompanied by the reꢀ
arrangement of covalent bonds (during photodissociaꢀ
tion, redox photochemical reactions) or a change in the
configuration of molecules (cis—transꢀisomerization).4—6
Several materials for use in various areas of science and
technology have been developed on the basis of the orꢀ
ganic and inorganic photochromic substances.4—7
For some types of photochromes, the thermal relaxꢀ
ation of photoinduced form B becomes difficult because
of high thermodynamic barriers for the transition from
the ground state of form B to the ground state of form A.
Such photochromic compounds were named thermally
irreversible but photochemically reversible.8 Just these
products with two thermodynamically stable states are
appropriate for the creation of photochromic detecting
media for the operative 3D optical memory. In addition,
photochromes for these purposes should possess a low
efficiency of photodegradation, thus providing a high
fatigue resistance in optical information recording—reꢀ
peated recording and the twoꢀphoton absorption coeffiꢀ
In this work, we analyze the spectral kinetic properꢀ
ties of the recently synthesized thermally irreversible phoꢀ
tochromic compounds belonging to the classes of diꢀ
arylethenes and fulgimides.
Experimental
Photochromic diarylethenes13—30 and fulgimides23—31 used in
the work were synthesized according to known procedures.
Investigation was performed in solutions. The solvent was toluꢀ
ene (A.C.S. spectrophotometric grade). The concentration of

Photochromic compounds for optical memory
Russ.Chem.Bull., Int.Ed., Vol. 57, No. 4, April, 2008
869
the compounds in solution was 2•10–4 mol L–1. Measurements
were carried out in a cell 3 mm thick.
ly irreversible, because the storage of their irradiated soluꢀ
tions in dark for one month produced no substantial changꢀ
es in the UVꢀinduced absorbance in the absorption band
maximum of the cyclic form.
The results of a comparative spectral kinetic study of
diarylethenes 1—21 with similar structures of the thienyl
moieties but with different bridging fragments of 15 types
are presented in Table 1.
As can be seen from the data in Table 1, perfluorocyꢀ
clopentenes 1 and 17 and cyclopentene 18 possess
the highest stability toward irreversible phototransforꢀ
mations. The photoresistance increases sharply on going
from compound 1 with the thienyl moieties to derivative
17 with the benzothienyl moieties, which confirms
the earlier advanced concept on a higher fatigue resisꢀ
tance of dihetarylethenes in which the bridges are linked
with the condensed heterocycles or thiophenes with aryl
Absorption spectra of the opened and cyclic forms of the photoꢀ
chromes were recorded on a Shimadzu UV—VIS spectrophotomeꢀ
ter in a spectral range of 200—800 nm. The colored cyclic form was
obtained after the solution was photoexcited with the radiation from
a DRShꢀ250 mercury lamp passed through the UV light filter that
picked out the radiation with λ = 313 nm. The kinetics of photocolꢀ
orization of solutions of diarylethenes was measured at the waveꢀ
length of the absorption band maximum of the cyclic form appeared
upon the UV irradiation of solutions of these compounds prelimiꢀ
narily decolorized by the visible light.
The photodecolorization kinetics was studied upon the irradiaꢀ
tion of preliminarily colored solutions of these compounds by the
radiation of mercury lines from a DRShꢀ250 lamp in the visible
spectral region, which were picked out by glass filters that transmitꢀ
ted the radiation in the region of the absorption band of the cyclic
form. The kinetics of photocolorization and photodecolorization
processes before the beginning of efficient photodegradation was the
firstꢀorder reaction kinetics, because reversible phototransformaꢀ
tions occurred only between the opened and cyclic forms of diꢀ
arylethenes.
The kinetic curves of photodecomposition of the photochromic
compounds were used for the accelerated estimation of their fatigue
resistance in the photochromic transformations under the condiꢀ
tions of highꢀintensity irradiation. The photodecomposition of
the solutions was characterized by the time during which the absorꢀ
bance achieved in the photostationary state at the absorption band
maximum of the cyclic form halved upon continuous irradiation
with the nonꢀfiltered light from a DRShꢀ250 lamp.
The kinetics of thermal isomerization of the photoinduced form
of diarylethenes and fulgimides was studied by periodical (at an
interval of several days) measurement of absorption spectra of soluꢀ
tions. In intervals of the measurements, the solutions were stored
in dark.
Table 1. Spectral kinetic characteristics of phototransformations of
photochromic diarylethenes 1—21 in toluene
A
B
Comꢀ
pound
λ
λ
ΔDB
max
kAB/kBA t0.5/s
max
max
nm
1
2
3
4
5
6
7
290
300
365
400
<300
290
240,
300
300
325
<300
<300
625
515
550
505
450
455
>350
(sh)
515
585
470
420,
470
535
530
550
580
595
555
495
510
450
455
1.44
21.0
1.4
6.2
5.2
1.1
70
90
120
20
25
8
0.35
0.55
0.26
0.41
0.46
—*
1.9
—*
28
8
9
10
11
0.30
1.2
0.28
0.68
0.7
1.4
2.1
2.5
105
70
>300
100
All kinetic studies were carried out under the same experimental
conditions at comparable intensities of the incident UV and visible
radiation, which provided a possibility of comparative analysis of
the obtained results.
Special attention was given to the stability of the compounds to
irreversible phototransformation (photodegradation), which results
in their fatigue resistance in photochromic transformations between
the opened and cyclic forms during optical information recording—reꢀ
peated recording. In addition, a correspondence between the abꢀ
sorption band maxima of the both forms and wavelengths of
the existing lasers was determined. The photoinduced absorbance in
the absorption band maximum for the cyclic form in the equilibrium
state upon UV irradiation was also measured, which made it possiꢀ
ble to estimate a comparable photosensitivity of the compounds to
the recording UV radiation. The ratio of the photocoloration and
photodecoloration rate constants was used for the comparable estiꢀ
mation of the efficiency of these processes.
12
290
290
315
375
375
330
340
405
300
300
1.8
1.8
0.96
0.5
0.7
1.10
1.75
0.13
1.46
0.38
23.0
13.8
6.2
4.5
5.6
1.0
15
10
10
32
55
1040
750
360
60
13**
14**
15
16
17
18
19
20
21
1.3
0.2
0.6
—
24
A
B
Note. Here and in Tables 2—5 λ max and λ max are the maxima of
absorption bands of the opened (A) and cyclic (B) forms, respectiveꢀ
ly; ΔDBmax is the maximum photoinduced absorbance in the abꢀ
sorption band maximum of the cyclic form B in the photoequilibriꢀ
um state; kAB/kBA is the ratio of photocoloration and photodecolorꢀ
ation rate constants; t0.5 is the time during which the absorbance
achieved in the photostationary state at the absorption maximum of
the cyclic form is halved upon continuous irradiation with the nonꢀ
filtered light from a DRShꢀ250 lamp.
Results and Discussion
The objects of the study were dihetarylethenes 1—39
with various bridging fragments, as well as fulgimides
40—44 and bisfulgimides 45—49.
Diarylethenes. The preliminary studies show that all
the synthesized photochromic diarylethenes are thermalꢀ
* Fast photodegradation.
** In MeCN.

870
Russ.Chem.Bull., Int.Ed., Vol. 57, No. 4, April, 2008
Barachevsky and Krayushkin
Comꢀ
Comꢀ
Comꢀ
R
R
R
pound
pound
pound
1
COH
8
9
Me
15
16
Me
2
3
Me
Me
Me
Me
Me
10
11
17
18
COH
4
5
Me
Me
Me
Me
COH
12
19
H
6
7
Me
Me
13
14
Me
Me
20
21
H
H
Comꢀ
pound
R1
H
R2
R3
R4
Comꢀ
pound
R1
R2
R3
R4
Comꢀ
pound
R1
R2
R3
R4
22
Me
Me
Me
COH
COH
25
H
H
CH2OH Me
CH2OH Me
CH2OH
27
H
H
Me
Et
23
24
COH
H
Me
26
28
SEt
SEt
COH
Me CH2OH
or hetaryl substituents.12 The spectral characteristics of
the opened and cyclic forms of compound 17 are shown
in Fig. 2. The replacement of the thienyl moieties by the
benzothienyl ones results in the bathochromic shift of the
absorption band of the opened form and the hypsochroꢀ
mic shift of the absorption band of the cyclic form, as well
as an increase in the efficiency of the photodecoloration
process of the latter.
Depending on the structure of perfluorocyclopentene
derivatives of diarylethenes, the absorption band maxiꢀ

Photochromic compounds for optical memory
Russ.Chem.Bull., Int.Ed., Vol. 57, No. 4, April, 2008
871
Comꢀ
R1
R2
R3
Comꢀ
R1
R2
R3
Comꢀ
R1
R2
R3
pound
pound
pound
29
30
H
H
CH2OMe
Me
H
31
32
NO2 CH2OMe
NO2
33
H
Me
COH
H
H
Comꢀ
R
Comꢀ
R
Comꢀ
R
Comꢀ
Ar
pound
pound
pound
pound
34
CH(OH)Ph
C(O)Ph
38
42
NHCO2Bu
45
35
36
39
40
43
44
NPhCl
46
47
Ph
NPhNO2
37
41
NH2
48
mum of the cyclic form can vary in a wide range: from 515
to 580 nm (Table 2). These compounds are characterized
by a comparable sensitivity to the activating UV radiation
and an appropriate photoresistance. In this case, the effiꢀ
ciency of photocoloration insignificantly exceeds the efꢀ
ficiency of photodecoloration.
The spectral kinetic study of the benzothienyl derivaꢀ
tives of diarylethenes (Table 3) shows that the absorption
band maxima of their opened form exhibit the hypsoꢀ
chromic shifts compared to the thienyl derivatives.
The introduction of substituents of different nature into
the benzothienyl moieties exerts virtually no effect on the
position of the absorption band maximum of the cyclic
form. The photosensitivity and the ratio of the photocolꢀ
oration and photodecoloration rate constants for the maꢀ
jority of substances are comparable with the correspondꢀ
ing parameters for the thienyl derivatives. The exceptions
are compounds 32 and 33 with the bulky substituents,
which are characterized by lower photosensitivity and
efficiency of the photocoloration reactions compared to
those of the photodecoloration process. All compounds
of this type are more photosensitive than the thienyl deꢀ
rivatives of diarylethenes.
Cyclopentene derivative 18 is also characterized by
an appropriate photoresistance (see Table 1). Its parameꢀ
ters determining the photosensitivity and efficiency of

872
Russ.Chem.Bull., Int.Ed., Vol. 57, No. 4, April, 2008
A
Barachevsky and Krayushkin
A
1.2
1.2
1.0
0.8
0.6
0.4
0.2
1.0
0.8
0.6
0.4
0.2
7
6
5
4
3
2
6
5
4
3
2
1
300
400
500
600 λ/nm
1
Fig. 2. Absorption spectra of perfluorocyclopentene diarylethene 17
in toluene before (1) and after consecutive UVꢀirradiation with the
light at the wavelength 313 nm (2—6).
300
400
500
λ/nm
Fig. 3. Absorption spectra of cyclopentene diarylethene 18 in toluꢀ
ene before (1) and after consecutive UVꢀirradiation with the light at
the wavelength 313 nm (2—7).
photocoloration and photodecoloration processes are
comparable with those for perfluorocyclopentene analog
17. The sharp difference is observed in the position of
the absorption band of the cyclic form of this compound,
whose absorption maximum exhibits a shortꢀwavelength
shift by 60 nm (Fig. 3).
The spectral kinetic study of other cyclopentene deꢀ
rivatives (Table 4) shows that the photochromic properꢀ
ties of these compounds are determined, to a substantial
extent, by their structure. The replacement of the hyꢀ
droxyꢀcontaining substituent in compound 34 by the carꢀ
bonylꢀcontaining substituent (compounds 35 and 36) inꢀ
duces the bathochromic shift of the absorption bands of
both opened and cyclic forms. Compound 35 manifests
the highest photosensitivity. The introduction of nitro
groups into the benzene fragments (compound 36) deꢀ
creases the photosensitivity and somewhat increases
the photoresistance. Compound 37 turned out to be least
photostable.
photochromic transformations, which can be due to
the cis—transꢀphotoisomerization of the azine fragments.
Benzothienyl maleimide derivative 19 possesses an
increased photostability compared to thienylꢀcontaining
analog 4 (see Table 1). As compared to the perfluorocyꢀ
clopentene and cyclopentene derivatives, compound 19
is characterized by a lower photosensitivity, a higher
efficiency of photocoloration, and a sharp bathochromic
shift of the absorption band of the opened form.
Compounds 3, 8, 10, and 11 are also among photoreꢀ
sistant diarylethene derivatives (see Table 1).
For other compounds under study, as well as for those
considered above, a stabilizing effect of the benzothienyl
moieties compared to the thienyl fragments is pronounced
(see Table 1, cf. compounds 5 and 20, 6 and 21). However,
these compounds and other substances listed in Table 1 are
inferior to the above considered diarylethenes in photoꢀ
stability and, hence, they have no special practical interest.
Since it is necessary to enhance the thermal stability
of recorded optical information caused by the diffusion
Unlike the above considered compounds, substances
38 and 39 are characterized by the low efficiency of
Table 2. Spectral kinetic characteristics of phototransformations of
thienyl perfluorocyclopentene diarylethenes 22—28 in toluene
Table 3. Spectral kinetic characteristics of phototransformations
of benzothienyl perfluorocyclopentene diarylethenes 29—33
in toluene
A
B
Comꢀ
pound
λ
λ
ΔDB
kAB/kBA t0.5/s
max
max
max
nm
A
B
22
23
24
295
290
290
380, 580
385, 565
365, 380,
580
345, 515
345, 520
1.15
0.76
1.40
2.1
2.4
3.3
70
90
80
Comꢀ
pound
λ
λ
ΔDB
kAB/kBA t0.5/s
max
max
max
nm
29
30
31
320
290, 330
300, 340
(sh)
330
315
520
365, 545
545
0.9
1.24
2.0
1.5
0.9
1.3
160
480
600
25
26
300 (sh)
285,
300 (sh)
285
0.98
1.10
2.5
3.7
160
190
27
28
345, 525
540
0.65
0.77
3.6
1.2
220
50
32
33
550
540
0.26
0.46
0.5
0.4
200
220
<300

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Russ.Chem.Bull., Int.Ed., Vol. 57, No. 4, April, 2008
A
873
Table 4. Spectral kinetic characteristics of phototransformations of
benzothienyl cyclopentene derivatives of diarylethenes 34—39
in toluene
A
B
Comꢀ
pound
λ
λ
ΔDB
max
kAB/kBA
t0.5/s
max
max
0.15
0.10
0.05
2
nm
34
35
36
37
38
39
300
340
350
320
370
385
455
495
490
500
500
500
0.47
0.5
0.6
2.6
5.7
—
120
150
180
60
—
—
1.8
0.39
1.07
—
—
—
3
1
of photochromic molecules in the polymer layer and in
order to increase the concentration of photosensitive
components in the polymer layer, the photochromic polyꢀ
mers were prepared,21,22 and among them product 50 was
studied in most detail.
400
500
600
λ/nm
Fig. 4. Absorption spectra of photochromic polymer 50 before (1)
and after consecutive irradiation with the UV (2) and visible (3) light.
The spectral characteristics of the opened and cyclic
forms of the photochromic fragment of this polymer are
presented in Fig. 4.
Fulgimides. As in the case of diarylethenes, the study
of the kinetics of thermal relaxation of photoinduced
cyclic form B to the initial opened form A shows that the
both forms are thermally stable for at least one month
when storing the solutions in well closed vessels in dark.
The spectral kinetic characteristics of the studied
monofulgimides are presented in Table 5.
The absorption spectra of opened forms A of comꢀ
pounds 40—44 in toluene exhibit a band with a maꢀ
ximum at 290—330 nm. The absorption spectra of
the initial and photoinduced forms of monofulgimide 41
irradiated with different doses of UV radiation are shown
in Fig. 5. The series of the spectra contain an isosꢀ
bestic point, indicating the absence of side processes
in the mutual transformation of the both forms of this
photochrome. It can be assumed that the Е—Zꢀisoꢀ
merization process typical of fulgides is inefficient in
this case.
The results in Table 5 show that the position of the
absorption band maximum of the opened form depends
insignificantly on the structure of the compound, in parꢀ
ticular, an increase in the electronꢀwithdrawing properꢀ
ties of the R substituent results in a small hypsochromic
spectral shift (cf. compound 40 and compounds 43 and
44). Substances 40—42 are characterized by the longestꢀ
wavelength absorption bands of the opened form.
The cyclic forms of all the compounds absorb in the
visible spectral region at 520—540 nm (see Fig. 5 and
Table 5). However, unlike the opened form, the absorpꢀ
tion band of the cyclic form shifts to the longꢀwavelength
region compared to compound 40 with an increase in the
electronꢀwithdrawing properties (compounds 43 and 44).
Compounds 40 and 41 are characterized by the shortestꢀ
wavelength absorption of the cyclic form. An analysis of
the kinetics of photocoloration of solutions of fulgimides
in toluene (see Table 5) shows that the efficiency of this
process decreases upon the introduction of electronꢀwithꢀ
drawing substituents into the phenyl fragment (comꢀ
pounds 43 and 44) with the simultaneous increase in the
photoresistance of these compounds.
Synthesized bisfulgimides 45—48 are similar in their
spectral kinetic properties to monofulgimides and
characterized by the same absorption band maxima of
both the opened and photoinduced forms (see Table 5).
The exception is compound 48 for which the absorption
band maximum of the opened form is shifted by 25 nm to
the shortꢀwavelength region. This means that the phenyl
cycles and the heterocycle arranged between them are not

874
Russ.Chem.Bull., Int.Ed., Vol. 57, No. 4, April, 2008
Barachevsky and Krayushkin
A
Table 5. Spectral kinetic characteristics of phototransformations of
monofulgimides 40—44 and bisfulgimides 45—49 in toluene
0.6
A
B
Comꢀ
pound
λ
λ
ΔDB
max
kAB/kBA t0.5/s
0
0.4
0.3
0.2
0.1
max
max
nm
40
41
42
250, 325
325
230, 280,
330
290
305
250, 330
285, 335
(sh)
522
520
530
0.75
0.9
0.70
1.2
1.0
0.9
25
70
40
6
5
4
3
2
1
43
44
45
46
540
540
528
530
0.61
0.65
1.2
0.3
0.4
0.8
0.4
95
100
30
1.5
50
47
285, 335
(sh)
530
1.5
0.4
50
300
400
500
600
λ/nm
Fig. 5. Absorption spectra of monofulgimide 41 before (1) and
after consecutive UVꢀirradiation with the light at the wavelength
313 nm (2—6).
48
49
310
335
530
495
1.1
0.75
0.4
0.1
50
220
An analysis of the presented results of the spectral
kinetic study of thermally irreversible photochromic diꢀ
arylethenes and fulgimides makes it possible to reveal the
most promising directions of the synthesis of photochroꢀ
mic compounds that satisfy the requirements of using
them as photosensitive components of photochromic deꢀ
tecting media for ODs of the threeꢀdimensional bitwise
operative optical memory of superlarge informational
capacity. According to the whole body of the properties,
the most promising for this application are perfluorocyꢀ
clopentene and cyclopentene derivatives of diarylethenes.
Photochromic fulgimides satisfy the requirements imꢀ
posed on the spectral characteristics and photosensitivity
but are inferior to the chosen diarylethenes in the fatigue
resistance to photochromic transformations.
The samples of photochromic detecting media have
been developed on the basis of the synthesized thermally
irreversible photochromic perfluorocyclopentene diꢀ
arylethenes and fulgimides that mostly satisfy the condiꢀ
tions of application.32
The revealed large diversity of spectral characteristics
of the opened and cyclic forms of the synthesized diꢀ
arylethenes allows the fourꢀdimensional (4D) optical
memory to be created, providing information recording
and reproduction in different regions of the detecting
medium volume and also at different wavelengths of laser
radiation and, hence, leading to an increase in the inforꢀ
mational capacity of ODs.
virtually involved in the conjugation of two fulgimide resꢀ
idues.
The value of the photoinduced change in the absorꢀ
bance at the wavelength of the absorption band maximum
of the cyclic form shows that the photosensitivity of
the compounds is virtually independent of the structure
of the spacer between the fulgimide moieties.
Unlike photochromes 45—48, the absorption band of
the cyclic form of product 49 is shifted to the shortꢀ
wavelength spectral region (by 32 nm compared to anaꢀ
log 45) (Fig. 6, Table 5). The photodecoloration rate
increases and the photoresistance of the compound is
enhanced. By analogy to diarylethenes, it can be assumed
that this occurs due to the replacement of the thienyl
fragments by the benzothienyl ones.
A
0.7
0.6
0.5
0.4
0.3
0.2
0.1
7
6
5
4
3
2
This work was financially supported by the Internaꢀ
tional Scientific Technical Center (Grant 2117) and the
Presidium of the Russian Academy of Sciences (Program
of Fundamental Research "Development of Methods for
Synthesis of Chemical Substances and Creation of Novel
Materials," Subprogram "Polyfunctional Materials for
Molecular Electronics").
1
300
400
500
600 λ/nm
Fig. 6. Absorption spectra of bisfulgimide 45 before (1) and afꢀ
ter consecutive UVꢀirradiation with the light at the wavelength
313 nm (2—7).

Photochromic compounds for optical memory
Russ.Chem.Bull., Int.Ed., Vol. 57, No. 4, April, 2008
875
Spektrosk., 2007, 103, 975 [Opt. Spectroscopy, 2007, 103, 936
(Engl. Transl.)].
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Received February 13, 2008