Molecular level optical information storage devices

Details Molecular level optical information storage devices Molecular level optical information storage devices

2000-04-07

2002-12-31

Kelly, Cynthia H. (Department: 1774)

Stock material or miscellaneous articles

Circular sheet or circular blank

C428S064200, C428S064400, C430S270160, C430S277100, C430S343000, C430S495100

Reexamination Certificate

active

06500510

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to the use of transition metal complexes as means to store information in optical information storage devices.
BACKGROUND OF THE INVENTION
Great interest is currently devoted to bistable molecular or supramolecular species presenting two forms whose interconversion can be modulated by an external stimulus. (Lehn J.-M., Supramolecular Chemistry, Concepts and Perspectives; VCH: Weiheim, (1995)). The design of such molecular-level switching devices is directly linked to the chemistry of signal generation, transfer, conversion, storage and detection.
Typical bistable species include photochromic compounds, which are molecules that can be interconverted between two forms exhibiting different visible light absorption (i.e., color). Photochromism occurs in a wide variety of materials, including both inorganic and organic compounds. Illustrative of the classes of organic compounds are anils, disulfoxides, hydrazones, oxazones, semicarbazones, stilbene derivatives, succinic anhydrides, camphor derivatives, syndromes and spiro compounds. A rather large variety of inorganic compounds show photochromism, including metal oxides, alkaline earth metal sulfides, titanates, mercury compounds, and copper compounds. These materials have been known for a long time and a description of these systems can be found in the literature. (“Photochromism” Glenn H. Brown Ed., Volume III, John Wiley & Sons, Publisher, 1971).
Because they interconvert between two different colors, photochromic compounds have the capability to function as a binary information storage system. One color represents 0, and the second color 1, to encode information in digital format. Molecular level optical memory devices incorporating these molecules should offer the possibility of packing an extremely large quantity of information into a small space, which can be read through a binary code with a resolution of the order of nanometers.
However, previously known photochromic compounds are unsuitable for long term information storage applications. Most photochromic compounds change their color by photoexcitation and revert, more or less slowly, to their initial state when kept in the dark. Compounds exhibiting this behavior are useless for information storage since the written information is spontaneously erased after a relatively short time.
Other prior photochromic compounds are more stable, but tend to undergo reversible photoisomerization. (Irie, M.; Mohri, M.
J. Org. Chem
. 53, 803 (1988); Hanazawa, M; Sumiya, R.; Horikawa, Y.; Irie, M;
J. Chem. Soc. Chem. Commun
. 206 (1992); Saika, T; Irie, M; Shimidzu, T;
J. Chem. Soc. Chem. Commun
. 2123 (1994)). Such compounds can be used for information storage optoelectronic devices, but do not provide a good long term storage solution, because the light used for reading the written data causes the back-conversion of the sampled molecules, and thus the gradual loss of information. Several attempts have been made to overcome this difficulty, including the use of photochemically inactive infrared light to read the status of the system.
Consequently, there is a need for improved photochromic molecules which will provide for stable, long-term storage of information.
SUMMARY OF THE INVENTION
The present invention overcomes the shortcomings of the prior art photochromic molecules by providing reactive species which undergo stable and irreversible color changes under controlled conditions.
In one aspect of the invention, a binary data recording medium is provided which includes a substrate and a recording layer on the substrate. The recording layer includes an organometallic transition metal complex which absorbs at a first wavelength. When the complex is subject to a light-induced excited state resulting in a reaction product in the recording layer, it absorbs light having a second, different wavelength. The light absorption of the first wavelength is assigned a first value, and light absorption of the second wavelength is assigned a second value, the first and second values corresponding to binary code.
The transition metal complex in one aspect of the present invention includes at least one of the following formulas: [M(N—N)
2
L
2
]
n
, [M(N—N)L
4
]
n
, [M(N—N—N)L
3
]
n
, and [M(N—N—N)
2
]
n
. M is a transition metal; N—N is a chromophoric polypyridine ligand incorporating from one to two substituents selected from the group consisting of —COOH, —B(OH)
2
, —PO
3
H
2
, and —R—PO
3
H
2
, where R is a saturated or aromatic hydrocarbon group; N—N—N is a chromophoric terpyridyl ligand incorporating from one to three substituents selected from the group consisting of —COOH, —B(OH)
2
, —PO
3
H
2
, —R—PO
3
H
2
, and phenyl, where the phenyl incorporates one or more substituents selected from the group consisting of —COOH, —B(OH)
2
, —PO
3
H
2
, —R—PO
3
H
2
, where R is a saturated or aromatic hydrocarbon group; and L is a nonchromophoric monodentate or polydentate ancillary ligand.
In other aspects of this particular embodiment, M is selected from cobalt, nickel, copper, iridium, palladium, platinum, rhenium, osmium, iron, ruthenium and rhodium; N—N is selected from substituted and unsubstituted 2,2′-bipyridyl, substituted and unsubstituted 1,10-phenanthroline and substituted or unsubstituted 2,2′-biquinoline; N—N—N is substituted by a phenyl, and where the phenyl incorporates a substituent in a para position; and L is selected from NC—(CH
2
)
2
—CN, NC—(CH
2
)
3
—CN, NC—(CH
2
)
4
—CN, halide, NCS
−
, N
3
−
, —CH
3
−
, H
−
, oxalate, CO, CN
−
, NO, H
2
O, OH
−
, NH
3
, triazole, pyridine, pyrazine, 4,4′-bipyridine, 4,4′-bipyridylethane, 4,4′-bipyridylethylene, 4-cyanopyridine, dicyanobenzene, diethylenediamine, NO
2
−
, and acetylacetone; or L may include a coordinating solvent selected from the group consisting of acetylacetone, methanol, acetonitrile, acetone, tetrahydrofuran, ethanol, dimethylformamide, and dimethylsulfoxide. The substrate may be amorphous, nanocrystalline or a semiconductor.
In a further aspect of the present invention, the transition metal complex includes at least one of the following formulas: [M(N—N)
2
(Y-nor-Y)(L)]
n
, [M(N—N)
2
(Y-nor-Y)
2
]
n
, [M(N—N)
2
(X)(Y-nor-Y)M(N—N)
2
(L)]
n
, [M(N—N—N)(Y-nor-Y)(L)
2
]
n
, [M(N—N—N)
2
(Y-nor-Y)
2
(L)]
n
, and [M(N—N—N)
2
(L)
2
(Y-nor-Y)M(N—N—N)
2
(L)
2
]
n
. Y is selected from cyano, pyridine, and pyridine methylene and nor is norbomadiene; M is a transition metal; N—N is a substituted or unsubstituted chromophoric polypyridine ligand; N—N—N is a substituted or unsubstituted chromophoric terpyridyl ligand; L is a nonchromophoric monodentate or polydentate ancillary ligand; and X is a ligand selected from the group consisting of polyaza macrocyclic group and polythio macrocyclic group.
In a further aspect of the present invention, the transition metal complex includes at least one of the following formulas: [trans-HOOCpyRu
II
(X)
4
—NC-nor-CN]
2+
, ([trans-HOOCpyRu
II
(X)
4
—NC]
2
-nor)
4+
, [trans-CH
3
—OOCpyRu
II
(X)
4
—NC-nor-CN]
2+
, ([trans-CH
3
—OOCpyRu
II
(X)
4
—NC]
2
-nor)
4+
, [trans-CH
3
CH
2
—OOCpyRu
II
(X)
4
—NC-nor-CN]
2+
, and ([trans-CH
3
CH
2
—OOCpyRu
II
(X)
4
—NC]
2
-nor)
4+
. HOOCpy is the isonicotinic acid; NC-nor-CN is the dicyanonorbomadiene ligand; X is selected from polyaza macrocyclic group, polythio macrocyclic group, and NH
3
; and trans is the configuration of the Ru center.
In a further aspect of the present invention, the transition metal complex includes a molecular sensitizer. The molecular sensitizer has a photoabsorption spectrum and is capable of injecting an electron into an empty conduction band of the substrate upon absorption of visible light to form oxidized molecular sensitizer having a photoabsorption spectrum different from the unoxidized molecular sensitizer. An electron accep

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