JP4936638B2 - Luminescence source by charge transfer complex molecule and method for producing the same - Google Patents

Description

The present invention relates to a light-emitting source based on the light-emitting function of a charge transfer complex molecule immobilized in an isolated state in the state of a single molecule formed by the interaction of an electron donor molecule and an electron acceptor molecule, and The present invention relates to a method of immobilizing a charge transfer complex molecule, which is a premise for producing a light emitting source, in a polymer matrix.

  Artificially controlled quantum two-level micro-quantum emitter (hereinafter referred to as micro-quantum emitter) as a component of minute light-emitting elements essential for next-generation optoelectronic technology and quantum information technology As an example in the process of development, semiconductor quantum dots are attracting attention.

  In the semiconductor quantum dot, electrons are confined in a three-dimensional space formed by microfabrication of a semiconductor compound, and the excited state of the electrons is discretized, so that the electrons just formed in the periphery of the nucleus A state similar to the discrete state of energy ranking is artificially created.

  Such a semiconductor quantum dot expresses a unique optical functionality that is different from the original state (bulk state) of the semiconductor compound itself. That is, it has been noticed that the function of controlling light in a quantum theory can be expressed by the interaction between the discretized electron level and the radiation field, and this function can be expressed by quantum cryptography using a single photon, It is indispensable in quantum information technology such as quantum relay that reads the quantum state of an electronic system as light.

  However, in order to apply the functions as described above, it is necessary to limit the size and arrangement of the quantum dots, but in practice, there are limited choices of materials for realizing the functions. Moreover, it has various problems such as low manufacturing costs.

  Furthermore, the operating temperature for exhibiting the above functions by quantum dots is as low as 4 to 77 K, and there is an urgent need to develop a system that operates at room temperature for practical use. Such room temperature operation has not been realized.

  In addition to the light emitting function such as the quantum dots, a method using molecular light emission from an organic compound has attracted attention as a micro quantum light emitter.

  In this method, organic molecules are not collected as a group, but a single molecule is fixed as an element unit in an isolated state and used as a micro quantum light emitter that acts as a quantum two level.

  In general, organic compound molecules have a wide selection range from existing compound groups, can synthesize new structures by molecular design, and are easy to process such as compatibilization with transparent matrix materials. Has the advantage of

  Reflecting this situation, several studies on single-molecule spectroscopy of organic fluorescent dyes and aromatic compounds have been reported.

  However, organic compound molecules generally have problems in chemical and physical stability, specifically inferior in light resistance, and in particular, deteriorate due to photochemical reaction due to light emitted by the molecules themselves. Overcoming it was an essential issue.

Patent Publication No. 2758898 (issued by the Japan Patent Office on May 28, 1998) W.E.Moerner and L.Kador, Phys. Lett., 62, 2535 (1989), M.Orrit and J. Bernard, Phys. Rev. Lett., 65, 2716 (1990), (E. Bezig and R. J. Chichester, Science, 262, 1422 (1993))

  Based on the above background, the present invention focuses on the charge transfer complex formed by the intermolecular interaction between the electron donor molecule and the electron acceptor molecule, and the charge transfer complex is isolated in a single molecule state. It is an object of the present invention to provide a basic technical idea that can be used as a light emission source after being fixed in the above.

In order to solve the above problems, the basic configuration of the present invention is as follows.
(1). An electron donor molecule and an electron acceptor molecule were uniformly dispersed at a concentration of 10 ⁻⁵ to 10 ⁻⁹ moles per gram of the resin solution in a resin solution that is scheduled to form a polymer matrix. single by the solution was applied to the thin film, and in the process of solidifying the thin film, a charge transfer complex molecule formed by the interaction of the electron donor molecules and electron acceptor molecules, in the polymer matrix A method for producing a light-emitting source that is immobilized in a molecularly isolated state,
(2). A light emitting source immobilized in a single molecular isolated state in the polymer matrix produced by the method of (1) ,
Consists of.

In the light emitting source immobilized in a single molecule isolated state in the polymer matrix of the basic configuration (2), it is smaller than the intramolecular transition of a single molecule due to the two-level formation of the charge transfer complex molecule. Because it emits light with energy, it has better light resistance than single molecules such as organic dye molecules.

In addition, the wavelength, intensity, or polarization characteristics of the light emission from the charge transfer complex immobilized in a single molecule state in the polymer matrix depends on the electron donor and electron acceptor that form the charge transfer complex. The light-emitting source based on charge transfer complex molecules has a greater degree of freedom of state control than single-molecule light-emitting sources such as organic dye molecules, because it varies depending on the intermolecular distance of the body or the orientation state of both molecules. Therefore, it is possible to exhibit higher-order functions that cannot be realized with a single molecular light source such as an organic dye molecule.

That is, the light-emitting source in which the charge transfer complex molecules according to the present invention are immobilized in a single molecule isolated state is an external field such as a micro optical switch or an electric field that operates by a change in the spatial structure of the matrix due to external stress. It can be applied as a micro light source that can be controlled by a single light source, or as a single photon generation light source that is indispensable in quantum information technology such as quantum cryptography and quantum relay technology.

Emitting source that is immobilized in an isolated state in a single molecularly polymer matrix of the (2), the light source is in the overwhelmingly smaller state than the wavelength of light, those of the (2) Since the configuration of is derived from the manufacturing method of (1) , basic items related to the manufacturing method will be described first.

  A charge transfer complex is proposed as a reaction intermediate formed transiently by the interaction between an electron donor molecule and an electron acceptor molecule in the course of a chemical reaction, and its presence is confirmed by spectroscopic measurement of the reaction solution. (RSMulliken, J. Amer. Chem. Soc., 72, 600 (1950).

  Since the concentration of the charge transfer complex in the solution is proportional to the product of the concentration of the electron donor molecule and the electron acceptor molecule, so far a very dilute solution has not been measured.

Reflecting this situation, no attempt has been made to fix the charge transfer complex molecule in a single molecule state in an isolated state .

  Therefore, in order to perform spectroscopic measurement on a single molecule of a charge transfer complex formed from an electron donor and an electron acceptor and to use the isolated molecular pair as a micro quantum light source, it is not a solution state but a polymer or the like. It is necessary to fix and hold in an isolated state in a transparent matrix.

In the basic configuration (1) , a predetermined amount of the electron donor molecule solution and the electron acceptor molecule solution are added to a certain amount of the resin capable of forming the polymer matrix, and the system is homogenized. For example, a thin film is formed on the substrate by spin coating.

  The method for forming the light emitting source is not limited to the spin coating method, and any one of a dip coating method (a dip pulling method) and a polymer solution casting method may be used.

  Thus, as the resin for holding the charge transfer complex molecule, polystyrene and polymethyl methacrylate are suitable, but other polymethacrylates, polyacrylates, and polycarbonate are suitable.

The resin for forming the polymer matrix for immobilizing the light emitting source immobilized in a single molecule isolated state in the polymer matrix of the basic structure (2) is usually transparent (however, colored transparent Including resin.

When the resin is dissolved in the basic structure (1) , a solvent having good solubility, for example, for polystyrene, a polar solvent such as toluene, 1-methyl-2-pyrrolidone, dimethylformamide is used. .

Examples of the electron donor molecule in the light emitting source immobilized in a single molecule isolated state in the polymer matrix of the basic configuration (2) include anthracene, 9-methylanthracene, 9,10-dimethylanthracene, 9 -Hydroxymethylanthracene, phenanthrene, pyrene and perylene are preferred. As the electron acceptor molecule, tetracyanobenzene, dinitrobenzene, and pyromellitic dianhydride are preferable.

In the manufacturing method of the basic configuration (1) , when a transparent resin is employed, a single resin is fixed in the polymer matrix of the basic configuration (2) by being immobilized in the matrix formed of the transparent resin. A light-emitting source immobilized in a molecularly isolated state can be obtained.

Specific processes relating to the basic configuration (1) are as follows (a) and (b).
(A) Preparation of Polymer Solution Containing Charge Transfer Complex Molecule A certain amount of electron donor molecule or electron acceptor molecule is individually weighed with a precision balance, and a solution having a predetermined concentration is prepared using a measuring flask. Next, a certain amount of transparent resin is weighed in a glass bottle with a lid, and the electron donor molecule and the electron acceptor molecule prepared above are each adjusted to a concentration of 10 ⁻⁵ to 10 ⁻⁹ mole per 1 g of the resin solution. When a certain amount of the solution is injected together with the solvent using a measuring pipette and left overnight, a uniform polymer solution can be obtained. By the above operation, a polymer solution having a known concentration of electron donor molecules and electron acceptor molecules per unit weight of the matrix polymer is prepared. The charge transfer complex molecule is formed in a chemical equilibrium by the interaction of the electron donor molecule and the electron acceptor molecule and is uniformly dispersed in the polymer solution in the process in which the polymer dissolves into a homogeneous solution. .
(B) Preparation of polymer thin film containing charge transfer complex molecule The uniform polymer solution prepared in (a) above is dropped on a glass substrate mounted on a spin coater, and rotated at a predetermined rotation speed, whereby the dropping is performed. A thin film is prepared by gradually unfolding the part. In order to prepare a thin film having a thickness of 0.1 to 1.0 microns, the film is usually developed for 10 to 30 seconds at a rotational speed of 500 to 4,000 RPM. In the process of solidifying the prepared polymer thin film by natural drying, the charge transfer complex molecules are immobilized in the polymer matrix in a single molecular isolated state.

Using a polymer thin film sample containing a charge transfer complex molecule obtained by the processes of (a) and (b), the polymer matrix of the basic configuration (2) is immobilized in a single molecule isolated state. As a result of producing the emitted light source and measuring by laser scanning microspectroscopy, for example, when the concentrations of anthracene and tetracyanobenzene per gram of polystyrene are 10 ⁻⁵ moles or less, at room temperature, Although an emission spectrum unique to an isolated single molecule was observed, the emission source was overwhelmingly smaller than the wavelength of light, and showed a remarkable polarization characteristic.

Thus, it was realized that the charge transfer complex molecule was immobilized in a single molecule isolated state in the matrix, and the light emission characteristics showing the function as a quantum light source could be confirmed.

Examples that specifically support that the charge transfer complex molecules formed from a pair of electron donor molecules and electron acceptor molecules are immobilized in a single molecule state in isolation. The explanation will be given with reference to the drawings.

Weigh 0.100 g of polystyrene pellets into a glass bottle with a cap of 30 cc, add 5 ml each of anthracene and a solution of tetracyanobenzene in a concentration of 2 × 10 ⁻⁴ mole / l in toluene, and leave it overnight. A homogeneous polymer solution was prepared. When a few drops of this polymer solution are dropped on a glass substrate mounted on a spin coater and developed for 10 seconds at 4,000 revolutions per minute, an optically transparent polymer thin film with a thickness of 0.1 μm is formed. Is done. The concentration of the electron donor molecule and the electron acceptor molecule in the prepared sample was 10 ⁻⁶ mole per 1 g of the polystyrene matrix.

Similarly, by using solutions of anthracene and tetracyanobenzene having different concentrations, the concentrations of the electron donor molecule and the electron acceptor molecule in polystyrene are 10 ⁻² to 10 ⁻⁹ mole / g (polystyrene), respectively. As a result, it was possible to prepare a polymer thin film holding a charge transfer complex molecule at a concentration proportional to the product of the electron donor and electron acceptor concentrations.

  Instead of polystyrene as the matrix material, polymethyl methacrylate is selected, and pyrene, perylene, and phenanthrene are used as electron donor molecules, aromatic cyano compounds, and pyromellitic dianhydride as electron acceptor molecules, respectively. As for the combination system, a process similar to that of the method according to Example 1 was adopted. As a result, a polymer thin film holding the same charge transfer complex molecule as in Example 1 could be prepared.

FIG. 1 shows a laser microspectrometer for observing the light emission characteristics of charge transfer complex molecules immobilized in a polymer matrix.

Continuous (CW) NdYVO ₄ laser second harmonic light (wavelength 532 nm) as the light source 10 (μm) × 10 ( The region of μm) was scanned two-dimensionally in about 3 minutes to record the emission from the charge transfer complex. The measurement temperature was room temperature, and the received light intensity on the sample surface was 30 μW.

  FIG. 2 shows a two-dimensional image of the emission state of polymer thin film samples prepared according to Example 1 and containing different concentrations of charge transfer complex molecules.

In the sample (A) in which the concentrations of anthracene as an electron donor molecule and tetracyanobenzene as an electron acceptor molecule are 10 ^-6 moles per gram of polystyrene, light emission is in a minute and isolated state. In the sample (B) in which the concentrations of anthracene and tetracyanobenzene are each 10 ⁻³ mole, it can be seen that light emission spreads over a larger area.

  FIG. 3 shows the results of measuring the time dependence of the emission intensity by specifying the emission points (A) and (B) of the sample.

  It was confirmed that the emission intensity of the sample (B) continuously decreases with time, whereas the sample (A) exhibits a so-called comb-like pattern characterizing the emission behavior of a single molecule.

  The general explanation for the emission of a single molecule in a comb shape is that the state in which excitation and rapid relaxation (fluorescence emission) between the ground state and the excited singlet state are repeated frequently is ON (bright). In this state, when an electron accidentally transits to a triplet excited state having a relatively long lifetime, this fluorescence is not generated, and an OFF (dark) state is assumed.

  On the other hand, when the concentration of the electron donor molecule and the electron acceptor molecule is large and the charge transfer complex molecule is considered to be in an aggregated state as in the sample (B), a certain molecule is excited. Even in the triplet state, since the other molecules are in the excited singlet state, the light emission source does not blink, but continuously emits light.

FIG. 4 shows the light emission mechanism of the single molecule described above. The light emission as shown in (A) is that the charge transfer complex molecule is immobilized in a single molecule state. Therefore, it can be understood that it functions as a minute quantum light emitter at room temperature.

  As a result of measuring the spectra of some of the minute isolated light emitting sources of the sample (A) described in Example 3, variation as shown in FIG. 5 was observed.

  Such measurement results show that the spectrum of a charge transfer complex molecule with a long intermolecular distance between the electron donor and the electron acceptor shifts to the short wavelength side, and that of the complex molecule with a short intermolecular distance shifts to the long wavelength side. This means that the individual charge transfer complex molecules immobilized in the polymer matrix exist in various spatial arrangements.

  FIG. 6 shows the results of comparing the light resistance of the light-emitting source based on the charge-transfer complex molecule prepared in Example 1 and the light-emitting source with various organic dye molecules under the same measurement conditions as in Example 3. .

  As in Example 1, the charge transfer complex molecule (A) based on anthracene and tetracyanobenzene has light resistance about twice that of cyanine dyes such as Nile Red (D) and PM 580 (C). Furthermore, it was confirmed that it has a light resistance that is slightly less than twice that of Lumogen Red 300 (B), which is a perylene imide dye that is considered to be excellent in durability.

  The reason why the charge transfer complex molecule is excellent in light resistance can be confirmed by a concrete experiment is that the charge transfer complex molecule forms two levels and is smaller than a single molecule system such as an organic dye molecule. This is because the light is emitted by energy, and the mechanism is schematically shown in FIG.

In FIG. 7, the excitation energy (hν _CT ) of the charge transfer complex can be expressed as hν _CT = (I−E) −Δc (where I is the ionization energy of the electron donor molecule, E is The electron affinity of the electron acceptor molecule, Δc is the Coulomb interaction.)

Using the measurement apparatus shown in FIG. 8, the polarization characteristics of the charge transfer complex molecules prepared in Example 1 and immobilized in a single molecule isolated state in the matrix were measured. Shown in When the fluorescence intensity is observed while rotating the polarizer at a constant speed, the light-emission point repeats in a cycle of 180 °, confirming that the individually immobilized charge-transfer complex molecules have strong polarization characteristics. I was able to.

The present invention enables a point light source beyond the concept of a micro optical element typified by a conventional quantum dot or the like, that is, an ultimate single photon source. The charge transfer complex molecule pair immobilized in a single molecule isolated state according to the present invention has light resistance superior to a single molecule system such as an organic dye molecule due to the formation of two levels, As a single photon generation source stable at room temperature, it can be used as a probe for measuring a nanoscale space.

  In addition, as a single photon generation source capable of controlling the emission intensity, wavelength, polarization characteristics, and the like, it can be used for quantum information processing techniques such as quantum cryptography.

A laser scanning microspectrophotometer for measuring the emission behavior of charge transfer complex molecules in an isolated state is shown. The photographic image which observed the light emission state of the polymer thin film sample containing the charge transfer complex molecule | numerator of different density | concentration by the scanning microspectroscopy method is shown. (A) corresponds to the case where the concentrations of the electron donor molecule (anthracene) and the electron acceptor molecule (tetracyanobenzene) are each 10 ⁻⁶ mole / g (polystyrene), and (B) is the concentration described above. Are 10 ^-3 mole / g (polystyrene). The time dependence of the luminescence intensity of polymer thin film samples containing different concentrations of charge transfer complex molecules is shown. (A) corresponds to the case where the concentrations of the electron donor molecule (anthracene) and the electron acceptor molecule (tetracyanobenzene) are each 10 ⁻⁶ mole / g (polystyrene), and (B) is the concentration described above. Are 10 ^-3 mole / g (polystyrene). The transition energy level of a molecule and the mechanism by which a single molecule flashes and emits light in a binary manner, light (ON) and dark (OFF). The variation state of emission spectra of charge transfer complex molecules (anthracene / tetracyanobenzene) having different spatial arrangements immobilized in a single molecule isolated state in a matrix is shown. Comparison of light resistance between charge transfer complex molecules (anthracene / tetracyanobenzene) and organic fluorescent dye molecules is shown. Indicates the excitation energy level of the charge transfer complex molecule. An apparatus for measuring polarization characteristics of charge transfer complex molecules is shown. The polarization characteristics of a charge transfer complex molecule (anthracene / tetracyanobenzene) immobilized in a single molecule isolated state are shown.

Claims (7)

An electron donor molecule and an electron acceptor molecule were uniformly dispersed at a concentration of 10 ⁻⁵ to 10 ⁻⁹ moles per gram of the resin solution in a resin solution that is scheduled to form a polymer matrix. single by the solution was applied to the thin film, and in the process of solidifying the thin film, a charge transfer complex molecule formed by the interaction of the electron donor molecules and electron acceptor molecules, in the polymer matrix A method for producing a light-emitting source that is immobilized in a molecularly isolated state. As the film-forming process, a spin coating method, a dip coating method, a manufacturing method of a light emitting source for the charge transfer complex molecule of claim 1, wherein immobilized in a polymer matrix, which comprises employing one of the casting. A light-emitting source immobilized in a single molecule isolated state in the polymer matrix produced by the method according to claim 1 . 4. The luminescent source according to claim 3 , wherein any one of anthracene, 9-methylanthracene, 9,10-dimethylanthracene, 9-hydroxymethylanthracene, phenanthrene, pyrene and perylene is employed as the electron donor molecule. 4. The luminescent source according to claim 3 , wherein any one of tetracyanobenzene, dinitrobenzene, and pyromellitic dianhydride is used as the electron acceptor. 4. The light emitting source according to claim 3 , wherein a transparent resin is employed as the polymer matrix. 4. The light emitting source according to claim 3, wherein a thin film made of a polymer matrix resin is formed on a glass substrate.

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