JP2002328349A - Optically responsive material and optically responsive element each using light induced electron transfer reaction - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optically functional element, capable of carrying out a high-density optical recording, a high-speed optical modulation or the like by changing the conditions of a waveguide mode by varying the complex refractive index of an optically responsive thin film through using the light induced electron transfer reaction of an ion pair charge transfer complex, which reaction causes a large absorption change and a fluorescent intensity change in a visible ray region or a near infrared region. SOLUTION: The optically responsive material has the general formula and forms an ion pair charge transfer complex between a substituted bipyridinium cation and a counter anion Y<-> . The ion pair charge transfer complex is exemplified by a polymer containing a 2,5-bis(4-bipyridinium)thiophene/ditetrakis[3,5- bis(trifluoromethyl)phenyl]borate in a dispersed state or a polymer having it in a part of the main chain thereof. The optically responsive thin film is formed of a polymer having the ion pair charge transfer complex in a part of the main chain or in the side chain or a polymer which is used as a dispersing or a fixing medium of the ion pair charge transfer complex.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light-responsive material and a light-responsive material suitable for optical recording and light modulation utilizing surface plasmon resonance or a waveguide mode observed in a dielectric thin film system formed on a metal thin film surface. Related to the element.

[0002]

2. Description of the Related Art Recording elements, modulation elements and the like have been conventionally manufactured by utilizing reversible color change caused by light irradiation. The recording element mainly has a drawback such as deterioration of recording caused by the readout light because the recording element mainly depends on an absorption spectrum or a change in reflectance in an ultraviolet to visible region. The response of the modulation element is very slow, from several tens of milliseconds to several seconds, due to thermal changes. On the other hand, there are few devices utilizing the photoinduced electron transfer reaction and those which absorb and change in the visible to near-infrared region with a strong change in fluorescence.
However, assuming future high-density optical recording and high-speed optical modulation, etc., a material exhibiting a large absorption change or fluorescence change in the visible or near-infrared region by irradiation with a violet semiconductor laser beam having a wavelength of about 400 nm, and a modulation capable of high-speed parallel processing. The development of devices is desired. That is, since the light collection limit is proportional to the wavelength and inversely proportional to the aperture ratio of the lens, the higher the wavelength, the higher the recording density becomes possible with the same optical system. However, there is a problem of light absorption of the optical component, and about 400 nm is considered to be a practical limit of a short wavelength. In this respect, high density recording and high speed modulation can be realized by providing a material that exhibits sufficient responsiveness to short wavelength light and causes absorption (imaginary part of refractive index) and fluorescence change. Also, assuming future ultra-high-speed parallel processing, light can be two-dimensionally manipulated by light. Considering compatibility with optical communication using quartz or plastic optical fibers, the refractive index in the visible to near-infrared region is extremely high. The development of materials that change at high speed is desired.

[0003]

SUMMARY OF THE INVENTION The present invention has been devised in order to meet such a demand, in which a photo-induced electron transfer reaction is caused by light of about 400 nm, and a visible light-induced electron transfer reaction is caused by the photo-induced electron transfer reaction. It is an object of the present invention to provide an optical functional element capable of changing absorption or fluorescence intensity at a very high speed in the near-infrared region and performing high-density optical recording, high-speed optical modulation, and the like.

In order to achieve the object, the photoresponsive material of the present invention is represented by the following general formula and is characterized by forming an ion-pair charge transfer complex between a substituted bipyridinium cation and a counter anion Y ^−. .

[0005] X: thiophenyl group, furyl group, bithiophenyl group, terthiophenyl group, fluorenyl group, pyrenyl group, perylenyl group or vinyl group bonded at the 4- or 2-position to the nitrogen atom of the bipyridinium group: R ₁ and R ₂ respectively independently an alkyl group, a poly (tetramethylene) group, a hydroxyalkyl group, an alkenyl group, an alkynyl group, an aralkyl group, an aryl group or a heterocyclic group Y ^-: chloride, bromide, iodide, aromatic molecules with anionic substituent Having one or more trifluoromethyl groups or other electron-withdrawing substituents

As an ion-pair charge transfer complex, for example,
2,5-bis (4-bipyridinium) thiophene / ditetrakis
A polymer containing [3,5-bis (trifluoromethyl) phenyl] borate salt in a dispersed state or a polymer having a part of the main chain is used. The photoresponsive thin film is formed using a polymer having an ion-pair charge transfer complex in a part or a side chain of a main chain, or a polymer acting as a dispersion / immobilization medium of the ion-pair charge transfer complex.

An optical recording element is manufactured by depositing a photoresponsive material as a fluorescent thin film on a substrate and further depositing an oxygen blocking polymer film on the fluorescent thin film. The fluorescence intensity is
It changes temporarily or constantly due to the photoinduced electron transfer reaction. In the light modulation element, a prism is arranged on the other surface of the glass substrate on which the metal thin film and the light-responsive thin film are deposited, in such a positional relationship that the modulated light transmitted through the prism is totally reflected by the surface facing the glass substrate. The modulated light forms a waveguide mode condition in the photoresponsive thin film, and the drive light source irradiates the photoresponsive thin film with the writing light in an arrangement steeply dependent on the incident angle of the reflectance.

[0008]

[Action] An electron-accepting bipyridinium cation compound is
Fluorescence can be enhanced by structural suppression of intramolecular motion. Although the photoexcited state is a cause of the generation of fluorescence, it is deactivated by various factors such as the movement of a substituent in a molecule. In ordinary bipyridinium, since two pyridinium groups are connected by a single bond, a rotational motion that deactivates a photoexcited state is likely to occur. On the other hand, when the pyridinium groups are linked by a group having a surface structure or the like effective for restricting rotation, the rotation is restricted and the fluorescence is improved. In the ion-pair charge transfer complex formed from the electron-accepting bipyridinium cation compound and the counter anion, one electron is completely transferred from the anion to the cation by photoexcitation (photoinduced electron transfer reaction). When the photoinduced electron transfer reaction occurs, a radical cation containing one electron is generated in the electron-accepting bipyridinium. As a result, the energy difference between the level where electrons exist and the empty level decreases, and a large absorption change occurs in the visible to near infrared region. Fluorescence also changes due to the appearance of new levels due to electron transfer. After the photoinduced electron transfer, electron transfer in the reverse direction from the radical cation to the oxidized form of the anion occurs, and the absorption / fluorescence change is restored. The reversion rate is determined by the oxidation-reduction potential of the bipyridinium cation and the counter anion. Therefore, by controlling the oxidation-reduction potential of the bipyridinium cation and the counter anion by a chemical method, the response speed of the absorption / fluorescence change can be controlled. The reverse electron transfer speed can be controlled from picoseconds to infinity according to the oxidation-reduction potential of anions and cations, and a photoresponsive material suitable as an optical recording element, an optical modulation element, or the like can be obtained.

Further, the waveguide mode condition of the system composed of the prism, the metal thin film, and the light responsive thin film changes according to the change in the complex refractive index of the light responsive thin film. , Both p-polarized light and s-polarized light can be used for light modulation. When manufacturing an optical recording element, an optical recording state is stabilized by laminating an oxygen-blocking polymer film 13 on a photoresponsive thin film 12 provided on a substrate 11 (FIG. 1). As the oxygen-blocking polymer film 13, polyvinyl alcohol having an oxygen permeability of 10 ⁻¹⁶ cm ³ · cm / cm ² · second · Pa or less is preferable. When an optical recording element 10 is irradiated with incident light L ₁ for writing or reading, photoinduced electron transfer reaction occurs, the intensity of the reflected light L ₂ and the fluorescence L ₃ for reading is changed. The fact that reading is possible with both the reflection intensity and the fluorescence intensity is a major difference from the conventional optical recording element.

As the light modulating element, a structure in which a light responsive thin film 23 is deposited on one surface of a glass substrate 21 via a metal thin film 22 and a prism 24 is disposed on the other surface (FIG. 2). A glass material having the same refractive index as the prism 24 is used for the glass substrate 21. When the under conditions photoresponsive thin film 22 was irradiated with writing light L ₄ enters the light modulation element 20 at an incident angle θ of the modulated light L _5, guiding the complex refractive index changes in the optical response thin film 22 by the writing light L ₄ The wave mode condition changes greatly, and light modulation in a wide wavelength range becomes possible. Specifically, the real part (Δn) and the imaginary part (Δk) of the complex refractive index change due to the photoinduced electron transfer reaction in 4,4-bipyridinium salt
Is shown in FIG.

[0011]

EXAMPLE 0.30 g of 2,5-di (4-pyridyl) thiophene,
Hexadecyl bromide (10 g) was placed in p-xylene (20 ml), and the mixture was heated and refluxed at 100 ° C. for 30 hours in a nitrogen atmosphere. The reaction produced a yellow precipitate. After cooling the reaction solution to room temperature, the precipitate was suction-filtered. The precipitate was repeatedly washed with hexane to remove hexadecyl bromide incorporated in the precipitate. Then, after purifying the precipitate using a HPLC (high performance liquid chromatography), sodium tetrakis [3,5-bis (trifluoromethyl) phenyl] borate ^- by ion-exchange in methanol with (TFPB) Thus, a target low molecular weight 2,5-bis (4-bipyridinium) thiophene ditetrakis [3,5-bis (trifluoromethyl) phenyl] borate salt was obtained.

[0012] Fully anhydrous tetrahydrofuran (TH
F) 23 ml was placed in a three-necked flask purged with nitrogen, the three-necked flask was cooled with ice water, 0.50 g of trifluoromethanesulfonic anhydride was added, and the mixture was stirred for about 15 minutes. Then, the mixture was cooled to -70 ° C with dry ice / acetone,
0.40 g of 2,5-di (4-pyridyl) thiophene dissolved in ml of anhydrous THF was added and stirred for about 1.5 hours. After the completion of the stirring, the reaction vessel was immersed in ice water, and left as it was overnight, to form a yellow suspension. The suspension is put into water, the produced solid substance is taken out, washed with water, and then dried under reduced pressure to give 2,5-bis (4-pyridinium).
A target polymer (photoresponsive material) having thiophene as a part of the main chain was synthesized. Further, the counter anion was ion-exchanged in the same manner as in the case of the synthesis of a low-molecular compound, to obtain a TFPB ^- salt.

[0013] The polymer photo-responsive material has a concentration of 50 to 100 m.
g / ml was dissolved in THF, 1,2-dimethoxyethane or cyclohexanone, and a photoresponsive thin film of several hundred nm to several tens μm was prepared by spin coating or solvent evaporation. The obtained light-responsive thin film shows strong absorption at 370 to 400 nm from the absorption spectrum and the fluorescence spectrum of FIG.
Very strong fluorescence was observed at 0 to 530 nm. Wavelength 4
With the violet light irradiation of 00 nm, a large absorption change due to the photoinduced electron transfer reaction was observed in the visible region of 550 to 650 nm and the near infrared region of 800 to 1200 nm (FIG. 4). When TFPB ^- was used as the counter anion, the absorption spectrum was reversibly returned to the initial state by the reverse electron transfer reaction, the absorption was repeatedly changed, and the fluorescence intensity was also reversibly changed. When bromide was used as the counter anion, the reverse electron transfer reaction proceeded very quickly and returned in about 1 nanosecond. Further, unsubstituted tetra phenylalanine borate ^- Using, TPB (TPB) ^- there is no oxidation reverse electron transfer reaction for degradation, could be stored optical recording state semipermanently.

An Ag thin film having a thickness of 50 nm is deposited as a metal thin film 22 on a glass substrate 21, and a photoresponsive thin film 23 made of a 4,4'-bibipyridinium polymer TFPB ^- salt having a thickness of 1000 nm is further deposited on the metal thin film 22. Deposited on the glass substrate 2
The prism 24 was arranged on the opposite side of the prism 1. When the manufactured light modulation element 20 is excited by a pulse laser through a mask, an image can be modulated in a few tens of nanoseconds to a few microseconds, and application of the image information to ultrahigh-speed optical correlation is expected.

[0015]

As described above, the photoresponsive material of the present invention exhibits a large absorption or fluorescence change in the visible or near infrared region due to the photoinduced electron transfer reaction of the ion-pair charge transfer complex. When utilizing this property, for example, the wavelength 40
Irradiation of a violet semiconductor laser beam of about 0 nm causes an absorption change or a fluorescence change, so that high-density optical recording and high-speed optical modulation can be performed.

[Brief description of the drawings]

FIG. 1 shows an optical recording element using the photoresponsive material of the present invention.

FIG. 2 is a light modulation device using the photoresponsive material of the present invention.

FIG. 3 shows an absorption spectrum and a fluorescence spectrum of a photoresponsive thin film formed in an example.

FIG. 4 shows an absorption spectrum when the photoresponsive thin film formed in the example is irradiated with violet light.

[Explanation of symbols]

Reference Signs List 10: Optical recording element 11: Substrate 12: Photoresponsive thin film 13: Oxygen blocking polymer film 20: Optical modulation element 21: Glass substrate 22: Metal thin film 23: Photoresponsive thin film 24: Prism

Claims (5)

[Claims] 1. A photoresponsive material represented by the following general formula and forming an ion-pair charge transfer complex between a substituted bipyridinium cation and a counter anion Y ⁻ . X: thiophenyl group, furyl group, bithiophenyl group, terthiophenyl group, fluorenyl group, pyrenyl group, perylenyl group or vinyl group bonded at the 4- or 2-position to the nitrogen atom of the bipyridinium group: R ₁ and R ₂ respectively independently an alkyl group, a poly (tetramethylene) group, a hydroxyalkyl group, an alkenyl group, an alkynyl group, an aralkyl group, an aryl group or a heterocyclic group Y ^-: chloride, bromide, iodide, aromatic molecules with anionic substituent Having one or more trifluoromethyl groups or other electron-withdrawing substituents 2. A polymer or main chain in which the ion-pair charge transfer complex contains 2,5-bis (4-bipyridinium) thiophene / ditetrakis [3,5-bis (trifluoromethyl) phenyl] borate salt in a dispersed state. 2. The photoresponsive material according to claim 1, which is a polymer partially contained. 3. A polymer having the ion-pair charge transfer complex according to claim 1 or 2 in a part or a side chain of a main chain, or a polymer acting as a dispersion / immobilization medium of the ion-pair charge transfer complex. Photo-responsive thin film 4. An optical recording element comprising: a fluorescent thin film made of the photoresponsive material according to claim 1 deposited on a substrate; and an oxygen-blocking polymer film further deposited on the fluorescent thin film. 5. A prism disposed on one surface of a glass substrate and totally reflecting the modulated light transmitted therethrough on a surface facing the glass substrate; and a metal thin film deposited on the glass substrate on the opposite side of the prism. 3. A photoresponsive thin film made of the photoresponsive material according to claim 1 or 2, and the modulated light forms a waveguide mode condition in the photoresponsive thin film, and the photoresponsive thin film is arranged in such a manner that the incident angle dependence of the reflectance is steep. A light source that irradiates the thin film with writing light.