JP2000260063A - Near field optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a recording medium writable in a high density and with a high sensitivity and readable and reproducible many times without the destruction of recording by incorporating a photoacid generating agent and a fluorescent pH indicator into a part to be recorded and further, incorporating a sensitizer at need therein. SOLUTION: The photoacid generating agent is preferably at least one kind selected from among an onium salt, organic halogen compound, nitrobenzyl ester and sulfonate of polyvalent phenol. If the photoacid generating agent does not have absorption in a visible part or if the absorption is small, the sensitizer having the absorption in the visible part is combined. The fluorescent pH indicator emits fluorescence by the photoexcitation of the wavelength longer than the wavelength of the absorption peak of the sensitizer. Namely, the destruction of the recording does not occur even if the recording and reproducing of many times are executed even in the case of the fluorescent indicator having the absorption on the wavelength side longer than the wavelength of the sensitizer and not having photoreactivity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a near-field optical recording medium of photon mode utilizing photoreaction with high sensitivity.

[0002]

2. Description of the Related Art In recent years, along with the era of the demand for recording and transmitting a large amount of information, research on a high recording density and a high information transfer rate of a recording medium has been rapidly advanced. However, in the case of the optical recording medium, in the current system, there is a restriction that the spot diameter of the beam light for recording / reproducing information is reduced only to about the wavelength of the light, so that there is a limit to the high density.

As one means for solving this problem, near-field optical recording is receiving attention. As a recording medium for this near-field optical recording, a magneto-optical recording medium or a phase-change recording medium used as a usual optical recording medium has been mainly studied. For example, Bezig et al. (E. Bezig
Appl. Phys. Lett. 61 (1992) 142) has proposed using a Co / Pt multilayer film as a magneto-optical recording medium, while Hosaka et al. (S. Hosaka et al. Thin Solid). Fi
lms, 273 (1996) 122) attempts near-field optical recording on a phase-change recording medium.

However, all of these methods employ heat mode recording based on a recording principle of heating by near-field light, and thus have a drawback of insufficient sensitivity.
That is, since the near-field light uses light from an optical fiber or a micropipette having an opening diameter smaller than the wavelength as a light source, the light amount is extremely small. Therefore, a magneto-optical or phase-change recording medium that uses optical heating as a recording principle is essentially not suitable for a near-field optical recording medium, and in order to achieve high-sensitivity writing,
It is necessary to employ a light reaction. Under such circumstances, development of a highly sensitive photon mode optical recording medium utilizing a photoreaction is desired.

[0005] Photoreaction systems that can be used for near-field optical recording include:
Various light reactions are candidates, but from the viewpoint of sensitivity,
A system in which the fluorescence intensity changes by a light reaction is desirable. This is because fluorescence reading is more advantageous for increasing the transfer speed (writing and reproducing speed) than reading the change in absorption or reflection intensity (T. Tujioka, M. Irie, Appl. Opt. 37 (1)
998) 4419).

[0006] On the other hand, a number of fluorescent pH indicators whose fluorescent intensity changes greatly due to the generation of acid have already been developed. The fluorescent pH indicator has been used for a color dosimeter and the like used for radiation sterilization of medical instruments, management of radioactive waste, and the like by utilizing the property of discoloring by an acid generated by a radiation reaction.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional circumstances, and has as its object to provide a high-sensitivity, near-field optical recording of photon mode using photoreaction. To provide a medium.

[0008]

The near-field optical recording medium according to the present invention is characterized in that a portion to be recorded contains a photoacid generator, a fluorescent pH indicator and, if necessary, a sensitizer.

Thus, a fluorescent pH indicator,
By combining a photoacid generator that generates an acid by light irradiation and a sensitizer as required, a near-field optical recording medium with high sensitivity can be realized.

That is, the sensitizer is photoexcited by light irradiation or by light irradiation, and the photoacid generator generates an acid by its energy. The reaction of the acid with the fluorescent pH indicator makes the fluorescent pH indicator fluorescent, or changes the fluorescence intensity or wavelength. By using this light emission as a read physical quantity, recording and reproduction become possible.

In such a near-field optical recording medium of the present invention, not only can writing be performed with high sensitivity and high density, but also reading and reproduction can be performed many times without destroying the recording.

[0012]

Embodiments of the present invention will be described below in detail.

The near-field optical recording medium of the present invention contains a photoacid generator, a fluorescent pH indicator, and, if necessary, a sensitizer in the recording portion.

The photoacid generator used in the present invention includes:
Diazonium salts used for light amplification resists,
Onium salts such as iodonium salts and sulfonium salts;
Preferred are at least one compound selected from organic halides; nitrobenzyl esters; and sulfonic esters of polyhydric phenols. Specific examples of the photoacid generator include diphenyliodonium hexafluorophosphate (Ph ₂ IPF ₆ ), triphenylsulfonium triflate (Ph ₃ SCF ₃ SO ₃ ), and triphenylsulfonium hexafluoroantimonate (Ph ₃ SSbF _6). )
Alternatively, a compound represented by the following structural formula can be used.

[0015]

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When these photoacid generators have no absorption in the visible region or have a small absorption, it is preferable to combine a sensitizer having absorption in the visible region. As sensitizers, acridine yellow, acridine orange,
Wavelength 380, such as ethyl eosin and coumarin 153
One or more aromatic compounds having at least one absorption peak at 780 nm are preferred.

The fluorescent pH indicator used in the present invention desirably emits fluorescence when excited by light having a wavelength longer than the absorption peak of the sensitizer. That is, if the fluorescent pH indicator has absorption on the longer wavelength side than the sensitizer and has no photoreactivity, the recording will not be destroyed even if recording and reproducing are performed many times. As such a pH indicator, for example, at least one kind of compound selected from fluorescein, a fluorescein derivative, hydroxypyrene and a hydroxypyrene derivative is preferable. As the fluorescent pH indicator, specifically, Seminaphtho Rhodafluoro-1,
Examples thereof include those represented by the following structural formula, such as carboxyseminaphthofluorescein-1 and the like.

[0018]

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[0019]

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There are no particular restrictions on the content of the photoacid generator, the sensitizer added as needed, and the fluorescent pH indicator in the recorded portion. It is preferable that the sensitizer be 5 to 50 parts by weight and the fluorescent pH indicator be 0.01 to 0.1 parts by weight.

The method of producing the near-field optical recording medium of the present invention is not particularly limited. For example, a photoacid generator, a fluorescent pH indicator, and a sensitizer added as necessary may be polyvinyl alcohol, polyN -Disperse in a binder such as vinylpyrrolidone, PMMA, polycarbonate or the like so that the total concentration of the photoacid generator, sensitizer and fluorescent pH indicator is about 50 to 200 mg / ml, and this dispersion is made of glass or acrylic resin. , A methacrylic resin, a polyester resin, a polyolefin resin, a polycarbonate resin or the like by spin coating on a substrate, for example, about 10 to 1000 nm, preferably 50 to 6 nm.
There is a method of forming a thin film having a thickness of about 00 nm.

[0022]

EXAMPLES Next, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples unless it exceeds the gist of the present invention.

Example 1 5 mg of diphenyliodonium hexafluorophosphate (Ph ₂ IPF ₆ , manufactured by Tokyo Kasei) as a photoacid generator, 1 mg of acridine yellow (manufactured by Aldrich) as a sensitizer, and fluorescein as a fluorescent pH indicator Derivative Seminaphtho Rhodafluoro-1 (Molecula
r Probes, C-1270, 10 ^-6 mol / l aqueous solution)
ml of polyvinyl alcohol (10% by weight).
(Aqueous solution) was dispersed in 1 ml, and the dispersion was spin-coated on a glass substrate to form a thin film (thickness: 300 nm), thereby producing an optical recording medium. The film formation portion of this optical recording medium was irradiated with near-field light (488 nm light, optical fiber having an aperture diameter of about 100 nm) from an optical fiber, and optically recorded. Thereafter, this record was read out based on the change in the fluorescence intensity of the optical recording portion when scanning the entire recording surface with 514 nm light.

As a result, at the time of optical recording, 488 nm
Acridine yellow was photoexcited by the light, the energy was transferred to the photoacid generator, an acid was generated, and the generated acid reacted with Seminaphtho Rhodafluoro-1 to decrease its fluorescence intensity. For this reason, upon irradiation with 514 nm light, the optical recording portion was observed as a dark spot (about 100 nm in diameter).

The change in the fluorescence spectrum of Seminaphtho Rhodafluoro-1 used as a fluorescence pH indicator in Example 1 is as shown in FIG.

Example 2 An optical recording medium was prepared in the same manner as in Example 1 except that carboxyseminapthofluorescein-1 (C-1255, manufactured by Molecular Probes) was used as a fluorescent pH indicator, and optical recording was performed in the same manner. Was performed, and then the recording was read.

As a result, at the time of optical recording, 488 nm
By light, acridine yellow is photoexcited, the energy is transferred to the photoacid generator, an acid is generated, and the generated acid reacts with carboxyseminaphthofluorescein-1,
The fluorescence intensity increased. For this reason, upon irradiation with 514 nm light, the optical recording portion was observed as a bright spot (about 100 nm in diameter).

[0028]

As described above in detail, according to the present invention, a near-field optical recording medium of a photon mode utilizing a photoreaction, capable of high-sensitivity, high-density writing, and non-destructive repetitive reading. And a near-field optical recording medium having a reproducing function.

[Brief description of the drawings]

FIG. 1 is a graph showing a fluorescence spectrum of Seminaphtho Rhodafluoro-1 used as a fluorescence pH indicator in Example 1.

Claims (5)

[Claims] A photo-acid generator and a fluorescent pH are applied to a portion to be recorded.
A near-field optical recording medium containing an indicator. 2. The photoacid generator according to claim 1, wherein the photoacid generator is at least one compound selected from the group consisting of onium salts, organic halides, nitrobenzyl esters, and sulfonates of polyhydric phenols. Near-field optical recording medium. 3. The near-field optical recording medium according to claim 1, further comprising a sensitizer. 4. The near-field optical recording medium according to claim 3, wherein the sensitizer is an aromatic compound having at least one absorption peak in a wavelength range of 300 to 780 nm. 5. The fluorescent pH indicator according to claim 1, wherein the fluorescent pH indicator is at least one compound selected from the group consisting of fluorescein, fluorescein derivatives, hydroxypyrene and hydroxypyrene derivatives.
Item 6. The near-field optical recording medium according to item 1.