Nondestructive information reading method

Full text of DOI:10.1134/S0018143909070029

ISSN 0018-1439, High Energy Chemistry, 2009, Vol. 43, No. 7, pp. 527–528. © Pleiades Publishing, Ltd., 2009.
Nondestructive Information Reading Method
K. G. Dzhaparidze, L. V. Devadze, D. P. Maisuradze, and N. O. Sepashvili
Institute of Cybernetics, ul. Sanro Euli 5, Tbilisi, 0186 Georgia
e-mail: devadze2005@yahoo.com
Received September 1, 2009
DOI: 10.1134/S0018143909070029
Degradation of a photochromic material upon mul- media in molecular computers. The recording process
tiply repeated recording and partial erasure during is the transition from the first to the second thermody-
readout of information limit the potential use of spiro- namically stable state.
pyrans as switchers and memory recording/storage
NO2
CH3
H3C
H3C
CH3
NO2
hν1
N+
hν2, ΔT
O–
O
N
R
R
A
B
R = CH3; C2H5; …; C18H37
A is the colorless spiropyran form, and B is the col- tion: as the concentration decreases, the band undegoes
ored merocyanine form.
a bathochromic shift.
Reading is based on the determination of the spec-
The intermediate phase state is not formed in the
tral characteristics. During readout (i.e., the determina- aforementioned matrix when the dopant is a substance
tion of the optical density at the absorption band maxi- with the coplanar structure (naphthalene, anthracene,
mum), the recorded information is partially erased.
biphenyl mixture, etc.).
In this work, we consider the possibility of reducing
the partial erasure caused by information reading.
The erasure of information during readout is usually
precluded with the use of matrices in which the photo-
chromic transition is accompanied by changes detect-
able without destroying the recorded information [1, 2].
Spiropyran molecules change their configuration
upon UV irradiation: the bulky, colorless spiropyran
molecule transforms into the coplanar, colored merocy-
anine form with the corresponding absorption band in
the visible region. Consequently, it is possible to con-
trol the formation and disappearance of the intermedi-
ate phase state with the use of light in spiropyran-doped
system (figure).
We assume that the formation of the intermediate
phase state in a liquid-crystal composition in the pres-
ence of bulky spiropyran molecules is due to the special
arrangement of the system. Photoinduced changes in
the geometric characteristics of the molecule have an
effect on this arrangement, which is manifested in the
character of the Bragg reflection band. As has been
noted above, the wavelength at which the intermediate
phase state is formed depends on the spiropyran con-
centration.
In our case, a liquid-crystalline smectogenic mix-
ture of cholesteryl oleate and cholesteryl pelargonate
turned out to be a medium of this type. Studying the
influence of dopants with a bulky geometric structure,
such as terpenes (camphor, adamantine derivatives,
etc.), we have found that the normal pattern of the
Bragg reflection band dλ/dt < 0 changes the direction,
i.e., the sign dλ/dt > 0, at the cholesteric
smectic
(Ch Sm) phase transition boundary; the half width
of the corresponding band narrows; and the reflection
intensity dramatically increases under certain condi-
tions during cooling [3]. As a result, an intermediate
phase state (IPS) is formed. The wavelength of the
When the system is exposed to UV light, the con-
Bragg reflection band corresponding to the intermedi- centration of spiropyran decreases as a result of the for-
ate phase state correlates with the dopant concentra- mation of merocyanine molecules; consequently, the
527

528
DZHAPARIDZE et al.
absorption band appears in the visible region of the
A
1.4
spectrum. The wavelength of the absorption maximum
depends on the dopant nature and polarity of the sys-
tem, and its height depends on the merocyanine con-
centration. Thus, we observe two bands in the visible
region of the spectrum, the Bragg reflection band and
the absorption band of the colored form. The position
of the former band depends on the spiropyran concen-
tration, and the intensity of the latter band depends on
the merocyanine concentration. As merocyanine mole-
cules are formed, the Bragg band experiences a batho-
chromic shift and the absorption band is enhanced.
Information can be read according to the position of the
former band. Consequently, readout with the use of the
Bragg reflection band, rather than at the absorption
maximum, will provide for the storage of recorded
information without loss.
8
1.2
1.0
0.8
7
6
5
0.6
0.4
1
4
2
3
0.2
In conclusion, it should be noted that the method
proposed in this work makes it possible to measure the
extinction of the merocyanine form at the wavelength
of the absorption maximum.
400
500
600
λ, nm
Temperature dependence for the Bragg reflection band dur-
ing the formation of the intermediate phase state (A is the
apparent optical density): (1–3) the cholesteric phase and
(3) the formation of the intermediate phase state at T = (1)
31, (2) 30, and (3–8) 29°C.
REFERENCES
1. Feringa, B.L., Van Delden, R.A., Kaumura, N., and
Geerstema, E.M., Chem. Rev., 2000, vol. 100, p. 1789.
2. Shibaev, V.P., Bobrovsky, A.Ju., and Boiko, N.I., Prog.
Polym. Sci., 2005, vol. 28, no. 5, p. 729.
3. Dzhaparidze, K.G., Elashvili, Z.M., Devadze, L.V., Sep-
ashvili, N.O., and Katsiashvili, M.R., Kristallografiya,
2006, vol. 51, no. 3, p. 520.
Bragg band is shifted to longer wavelengths as com-
pared to the band observed before irradiation. As the
colored molecules are produced, the corresponding
HIGH ENERGY CHEMISTRY Vol. 43 No. 7 2009