JPH03274545A - Wavelength multiplex recording medium - Google Patents

Abstract

PURPOSE:To allow the execution of good recording and reproducing without deterioration by dispersing a light absorptive dye and electron receptor or electron donor into a supporting material, specifying the free energy change of an electron transfer reaction and executing the recording by stepwise two photon stimulation. CONSTITUTION:The light absorptive dye and the electron receptor or electron donor are dispersed into the supporting material and the free energy change DELTAG of the electron transfer reaction is specified to >=-2.0eV; in addition, the recording is executed by the stepwise two photon stimulation. The recording is executed by the photochemical hole burning by the stepwise two photon stimulation if the free energy change DELTAG of the electron transfer reaction is specified to >=-2.0eV by adding the electron receptor or electron donor to the light absorbing dye in such a manner, then this material is cooled to a cryogenic temp. and is simultaneously irradiated with wavelength selecting light and gate light. The reading-out can be executed by the irradiation of only the wavelength selecting light, the photochemical burning is not generated by the irradiation with only the wavelength selecting light and the recording state is maintained as it is. The good recording and reproducing are executed in this way without deterioration.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is directed to the photochemical hole burning phenomenon (PHB phenomenon).
The present invention relates to a wavelength multiplexing recording medium that utilizes wavelength multiplexing, and particularly relates to a wavelength multiplexing recording medium that performs recording by stepwise two-photon excitation.

(Summary of the Invention) The present invention provides a wavelength multiplexing recording medium in which recording is performed by an electron transfer reaction caused by stepwise two-photon excitation. Optimizes the free energy change of , and enables good photochemical hole burning without recording deterioration.

[Prior Art] Wavelength multiplexing recording using photochemical hole burning is capable of ultra-high density recording, and research and development is being conducted with the aim of applying it to next-generation optical memories and the like.

The principle of wavelength multiplexing recording using photochemical hole burning is based on one broad absorption band ( in the non-uniform absorption band),
This method involves irradiating narrow-band laser light to form sharp holes. A large number of holes can be formed in the non-uniform absorption band by slightly changing the wavelength of the irradiated laser light. Theoretically, it is said that 101 to 10' holes can be formed in one nonuniform absorption band, and if the presence or absence of these holes is used for bit recording, the amount of information per spot can be dramatically increased. It is expected that this will be able to increase significantly.

(Problem to be solved by the invention) By the way, photochemical hole burning materials, on which much research has been done, perform recording by a photochemical reaction caused by one-photon excitation, so there is no threshold for recording and the readout light is used to record. The fundamental problem is that records are being destroyed.

To solve this problem, research is being carried out on photochemical hole burning materials using a stepwise two-photon excitation method (light gate type), which records photochemical reactions that occur from highly excited states generated by simultaneous irradiation with light of two wavelengths. In the second stepwise two-photon excitation method, the recording is not destroyed by light of one wavelength alone, and the recording is not deteriorated by the readout light.

As photochemical hole burning materials using the stepwise two-photon excitation method, materials in which recording is performed through electron transfer reactions are considered to have the greatest degree of freedom in material selection and are promising for improving recording characteristics. However, photochemical hole burning actually occurs only in materials with a specific molecular structure, and even though there is a degree of freedom, there are significant restrictions on the selection of material systems.

In addition, the actual situation is that the relationship between free energy changes that govern electron transfer reactions and photochemical hole burning, especially in stepwise two-photon excitation type photochemical hole burning materials, has not been elucidated at all.

Therefore, the present invention was devised in view of such conventional circumstances, and it clarifies the relationship between free energy changes that govern electron transfer reactions and photochemical hole burning, and uses stepwise two-photon excitation to suppress deterioration. An object of the present invention is to provide a wavelength multiplexing recording medium that is capable of performing good recording and reproducing operations.

[Means to solve the problem]

The inventors of the present invention have conducted intensive research over a long period of time to achieve the above-mentioned objective, and as a result, they added an electron acceptor or an electron donor to a light-absorbing dye to control the apparent energy change of the electron transfer reaction within a specific range. We have obtained the knowledge that photochemical hole panning occurs due to stepwise two-photon excitation when controlled to .

The present invention has been completed based on this knowledge, and includes a light-absorbing dye, an electron acceptor, or an electron donor dispersed in a supporting material, and a free energy change ΔG of an electron transfer reaction of -2.0 eV. The above is now stage 2
It is characterized in that recording is performed by photon excitation.

Here, the free energy change ΔG of the electron transfer reaction is expressed by the following formula % formula % (1) E, , ; one-electron oxidation potential E r of the electron donor
, 4: It elemental potential Eo of the electron acceptor: It is given by the photoexcitation energy required to form a reaction state.

Therefore, when the light-absorbing dye is an electron donor, by adding an electron acceptor, and conversely, when the light-absorbing dye is an electron acceptor, by adding an electron donor, the above Δ
The value of G is set to be -2.0 eV or more.

The light-absorbing dye (photosensitive substance) and electron acceptor electron donor to be used are not restricted in any way, but examples of light-absorbing dyes include tetraphenylporphine zinc complex and tetraphenylporphine magnesium complex (both of which are electron donors). ) etc.

On the other hand, the support material (dispersion medium) in which these light-absorbing dyes, electron acceptors, and electron donors are dispersed is an optically transparent material that does not absorb in the absorption region of the light-absorbing dye, and
Any material can be used as long as it can uniformly disperse the light-absorbing dye and does not crack at extremely low temperatures, but in order to widen the width of the non-uniform absorption band, use an amorphous medium. In order to reduce the width of the hole, it is important to design the combination and structure of the light-absorbing dye and supporting material so that the interaction with phonons is reduced. Furthermore, in a system in which the interaction between the light-absorbing dye and the support material is strong, side holes are generated and the S/N ratio of the recorded signal is degraded, so it is necessary to select a system in which the interaction is as weak as possible.

The supporting material is selected after taking these conditions into consideration, and includes ethanol-methanol, tetrahydrofuran, organic glass such as glycerol, crystalline medium based on n-alkanes (Spolsky matrix),
polystyrene, polyethylene, polyvinyl alcohol,
Polymer resin materials such as polymethyl methacrylate can be used.

These supporting substances and light-absorbing dyes and electron acceptors.

Electron donors are mixed at a predetermined ratio to form a wavelength multiplexing recording material, but the concentration of the light-absorbing dye in this case is determined by the interaction between molecules of the light-absorbing dye when dispersed in a support material. It is sufficient to set the ratio to be negligible, and it can be selected appropriately depending on the type of light-absorbing dye and supporting material used.Normally, the light-absorbing dye accounts for 10 to 1 of the total amount.
0-! It is expressed as mol%.

The electron acceptor and electron donor need only be present in excess of the light-absorbing dye, and usually the volume ratio to the supporting material is about 1:1, which is in large excess with respect to the light-absorbing dye.

[Effect]

Adding an electron acceptor or electron donor to the light-absorbing dye reduces the free energy change ΔG of the electron transfer reaction to -2.0 eV
When the wavelength multiplexing recording medium described above is cooled to an extremely low temperature and simultaneously irradiated with wavelength selection light and gate light, recording is performed by a photochemical hole burning phenomenon caused by stepwise two-photon excitation.

Reading is performed by irradiating only the wavelength-selected light, and photochemical hole burning does not occur when only the wavelength-selected light is irradiated, and the recorded state is maintained as is.

[Example〕 The present invention will be explained below based on specific experimental results.

In this example, a tetraphenylporphine zinc complex was used as the light-absorbing dye, and polymethyl methacrylate (molecular weight 9XIO') was used as the support material (dispersion medium t).

A sample was prepared by adding ethyl bromide as an electron acceptor to this product.

The proportion of the tetraphenylporphine zinc complex contained in the sample was 10'□3 mol %, and the volume ratio of the electron acceptor to the supporting material was 1:1.

FIG. 1 shows the absorption spectrum of the tetraphenylporphine zinc complex (indicated by the solid line in the figure) and the absorption spectrum of the triplet state (T-T absorption spectrum).

Indicated by a broken line in the figure. ), the tetraphenylporphine zinc complex exhibits no absorption in the ground state for the 465 nm argon ion laser oscillation line, but the electronic transition from the lowest triplet state to a higher triplet state causes a large absorption. I know I have it.

The tetraphenylporphine zinc complex is photoexcited by wavelength-selected light and undergoes an excited-multiplet state to form the lowest triplet Im
(excitation energy 1.59 eV). By irradiating gate light (465 nm) in this state, a transition to a high triplet state corresponding to the energy of gate light (2,79 eV) occurs.

FIG. 2 shows the results of irradiating this sample with laser light. In Fig. 2, only the wavelength-selected light is transmitted at the position 16761.8 cr' (the position indicated by arrow A in the figure).
．． Wavelength selective light and gate light (465 nm) were simultaneously irradiated at the 0CI-' position (the position indicated by arrow B in the figure). The intensity of the wavelength selective light is 450 mW/cj, the intensity of the gate light is 50@W/cii, and the irradiation time is 1 minute in both cases.

Photochemical hole burning does not occur when only wavelength-selected light is irradiated, and photochemical hole burning occurs only when gate light is present at the same time.

This indicates that holes are generated by an electron transfer reaction between the tetraphenylporphine zinc complex excited to a high triplet state and ethyl bromide. Note that the change ΔG in free energy of the electron transfer reaction in this sample is −1.57 eV.

FIG. 3 is an absorption spectrum showing the results when a sample of tetraphenylporphine zinc complex alone was irradiated with only wavelength-selected light or with wavelength-selected light and gate light simultaneously.

As is clear from Fig. 3, photochemical hole burning occurs in the sample containing the tetraphenylporphine zinc complex alone, whether it is irradiated with only wavelength-selected light or when simultaneously irradiated with wavelength-selected light and gate light. Not yet.

On the other hand, when chloroform (one-electron reduction potential - 1.67 eV) is used as the electron acceptor, as shown in Figure 4, when only the wavelength-selected light is irradiated, as in the case of the tetraphenylporphine zinc complex alone sample, as shown in Figure 4, Alternatively, when irradiating wavelength selective light and gate light simultaneously, photochemical hole burning does not occur, and when chloroform is used as the electron acceptor, the free energy change ΔG of the electron transfer reaction is -2.03 eV. be.

Therefore, various compounds were used as electron acceptors, and the free energy ΔG of the electron transfer reaction and the presence or absence of photogear I type photochemical hole burning reactivity (PHB reactivity) were investigated. The results are shown in the table below. In the following table, the one-electron reduction potential E red is the value for a saturated calomel electrode.

From the results shown in the table above, it was concluded that in order to cause photochemical hole burning due to an electron transfer reaction, the free energy ΔG of the electron transfer reaction needs to be ΔG≧−2°OeV.

〔Effect of the invention〕

As is clear from the above description, in the present invention,
We are elucidating the relationship between free energy changes that govern electron transfer reactions and photochemical hole burning, and optimizing free energy changes involved in electron transfer reactions by adding electron acceptors or electron donors to light-absorbing dyes. Step 2
It is possible to provide a wavelength multiplexing recording medium that can perform good recording and replaying without deterioration by photon excitation.

Furthermore, since the material does not necessarily have to be a single compound, the range of material selection for the wavelength multiplexing recording medium can be expanded.

[Brief explanation of drawings]

FIG. 1 is a characteristic diagram showing the absorption spectrum of the tetraphenylporphine zinc complex and the absorption spectrum of the triplet state. Figure 2 shows the absorption spectrum of tetraphenylporphine zinc complex when a sample containing ethyl bromide as an electron acceptor is irradiated with wavelength selective light or wavelength selective light and gate light simultaneously, and Figure 3 shows the absorption spectrum of tetraphenylporphine zinc complex. The absorption spectrum when a sample using a zinc complex alone is irradiated with wavelength-selected light or wavelength-selected light and gate light simultaneously. Figure 4 shows the absorption spectrum of a sample using a tetraphenylporphine zinc complex with chloroform added as an electron acceptor. This is an absorption spectrum when light or wavelength selective light and gate light are irradiated simultaneously.

Claims (1)

[Claims] A light-absorbing dye and an electron acceptor or an electron donor are dispersed in a supporting material, and the free energy change ΔG of the electron transfer reaction is set to -2.0 eV or more, and recording is performed by stepwise two-photon excitation. A wavelength multiplexing recording medium characterized by: