JPH036539A - High-sensitivity mixed nonlinear optical material - Google Patents

Abstract

PURPOSE:To enhance a quadratic nonlinear optical effect by mixing a deriv. which is chemically modified in a part of the structure without changing the conjugation system of a pi conjugation compd. having high polarizability with the above-mentioned compd. CONSTITUTION:The org. nonlinear optical material having the large nonlinear molecular polarization and the deriv. which has the same conjugation system and has the resembling skeleton are mixed. The configuration of the molecules, therefore, changes in such direction where the polarization thereof is added like vector and the macroscopic nonlinear effect larger than in the case of the independent material is generated. Both the molecules are more easily mingled with each other by mixing the above-mentioned material with the deriv. having the resembling skeleton, by which strong influence is exerted to the mutual molecular configuration at an extremely short distance. In addition, the change in the configuration of both the molecules is contributed to the vector sum of the nonlinear molecular polarization as the deriv. has the same conjugation system. The nonlinear optical material having the large nonlinear effect is obtd. in this way.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention provides an optical device that is smaller, more sensitive, and less expensive than conventional devices.
In particular, it relates to materials from which optical second harmonic generation elements, optical modulation elements, optical switches, etc. can be made.

(Prior art) Recently, materials in which donor groups and acceptor groups are added to organic materials with delocalized pi electrons have shown an order of magnitude greater nonlinear effect on light waves than conventional inorganic materials, and electron clouds. It has been noted that the response is extremely fast, at sub-picoseconds, because it is caused by pure electronic polarization due to the displacement of . Furthermore, the light intensity threshold for optical damage is about three orders of magnitude higher than the maximum MW/cm2 order of inorganic materials, and the refractive index is 1.5 to 2.0, which is smaller than inorganic materials, and the input and output of light is Another feature of 2-methyl-4-nitroaniline (MNA) is that it is easy to use and can provide a high figure of merit when used in optical second harmonic generation devices, optical modulation devices, etc.0 For example, 2-methyl-4-nitroaniline (MNA) The figure of merit for second harmonic generation (SHG) is actually 20 for lithium niobate, an inorganic material.
It has been reported that the amount is 00 times higher. Therefore, if these materials can be effectively used in optical devices such as optical second harmonic generation elements, optical modulation elements, and optical switches, they can be expected to have the features of extremely high sensitivity, fast response, and low cost. Therefore, exploration and research into organic nonlinear materials with larger nonlinear effects is being actively conducted.

Among the physical phenomena caused by nonlinear effects, SHG experiments are
It is often used to estimate the magnitude of the second-order nonlinear effect of new synthetically developed materials. Generally, for organic nonlinear materials where large crystals are difficult to obtain, a powder sample is placed in a measurement cell and irradiated with a high-power optical pulse such as a Nd:YAG laser, and the generated second harmonic intensity is used as a reference sample. It is expressed as a multiple of that of urea powder, and is used as a rough guide for the magnitude of SHG activity (powder method).The above MNA is 22 times that of urea11 ) Lance −4°−
The salt of methyl sulfate of demethylamino-N-methylstilbuazolium is 250 times2), N-(4-nitrophenyl)-(L)-prolinol is 150 times3), and 4'nitrobenzylidene-3-acetamino -4-methoxyaniline is 230 times 4). In addition to the above, a composite material of balanitroaniline and a polymer with moderate interaction is also being researched, and when the polymer is polyhexamethylene speric acid, it is 3.7 times that of MNA5). There is a report.

In any case, the development of new materials with higher SHG activity is awaited.

Reference 1) B, F, Levine, et al+, Jour
al of Applied Physics, vol.
50. No, 4. p, 2523. April 1979
゜2) G, R, Meredith, Polymer P
reprint, vol, 23°p, 158.198
2゜3) J, Zyss, et, al, , J, C
hem, Phys, vol, 81. No,
9゜p, 4160. November 1984゜4
) Tetsuya Tsuneyoshi et al., Spring 1989 Applied Physics National Conference 2a
-G-1゜5) Kagami Mamoru et al., 1989 Spring National Conference on Applied Physics 2
a-G-3゜ (Problems to be solved by the invention) Materials with considerably high SHG activity have been reported in the above-mentioned papers, but the development of materials with even higher SHG activity harmonic generation element, optical modulation element,
In application to optical devices such as optical switches, further miniaturization and higher sensitivity can be expected.

Therefore, an object of the present invention is to present a method for obtaining a material with a higher SHG activity, that is, a larger second-order nonlinear effect.

(Means for Solving the Problems) The highly sensitive mixed nonlinear optical material according to the present invention is a nonlinear optical material obtained by mixing a certain organic nonlinear optical material and a derivative thereof having a similar skeleton and having the same conjugated system. By mixing, the arrangement of the molecules is changed so that their nonlinear molecular polarizations are added vectorially, and the macroscopic nonlinear effect is much larger than that of the non-mixing alone.

(Function) In organic optical nonlinear materials, an asymmetric potential distribution is formed within the molecule by adding a donor group or an acceptor group to a pi-electron system consisting of a conjugated double bond such as a benzene ring. It begins to exhibit large nonlinearity.

In order for the material to have macroscopically large nonlinear effects,
It is necessary to arrange the molecules so that the large nonlinear polarizations on the sides of the molecules add vectorially. However,
In general, as nonlinear molecular polarization increases, it tends to be arranged in such a way that it cancels out, and in the case of centrosymmetric crystals, macroscopic nonlinearity does not occur at all, and in other cases, macroscopic nonlinearity does not occur at all. Often exhibits slight nonlinearity.

The present invention combines an organic nonlinear optical material with large nonlinear molecular polarization with its derivatives having similar skeletons and having the same conjugated system, thereby adjusting the arrangement of molecules in such a way that their polarizations are added vectorially. It changes the direction of the material, creating a macroscopic nonlinear effect that is larger than that of a single material. The reason for this is not yet clear, but it is thought that, for example, when mixed with derivatives with similar skeletons, both molecules tend to mix with each other, and can have a strong influence on each other's molecular arrangement at a very close distance. Furthermore, since they are derivatives with the same conjugated system, it is conceivable that changes in the arrangement of both molecules may contribute together to the vector sum of nonlinear molecular polarization, resulting in an additively large Macroscopic nonlinear effects can be obtained. Having this same conjugated system and its effects are different from the mixed material of polymer and organic nonlinear material described in the (prior art) section.

As a result, in the example described in the next section, a large nonlinear effect that rewrites the record reported in the literature was observed in an experiment of second harmonic generation using the powder method, and an extremely sensitive organic nonlinear optical material was developed. It has been obtained. Therefore, in application to optical devices such as optical second harmonic generation elements, optical modulation elements, and optical switches, it is expected that the devices will be smaller and more sensitive. For example, if used in a second harmonic generation element using a low-output semiconductor laser as a fundamental wave light source, it would be possible to realize a four-fold improvement in recording density as a small and simple light source for optical recording.

(Example) As a specific example of the present invention, rose nitroaniline (hereinafter p
-NA) and its N-alkyl derivative.

p-NA has an amino group as a donor group and a nitro group as an acceptor group added to the para position of the benzene ring (
(see Figure 1), the susceptibility to second-order molecular nonlinearity is quite large, but in the crystalline state, this is vectorially canceled out due to central symmetry, so macroscopic second-order nonlinearity does not occur at all. Things are woven. The N-alkyl derivative of p-NA is one in which two or one hydrogen atom of the amino group of p-NA is replaced with an alkyl group (see Figure 1), and the macroscopic second-order nonlinearity is -) Similar to JA, most cases do not occur at all or are relatively small.

FIG. 1 shows the synthesis reaction of N-alkyl derivatives. That is, p-NA and a halogenated alkyl compound (
RX) to the solvent hexamethyl phosphorotriamide (HM
PA) and excess sodium bicarbonate (NaHC).
Oa ) and refluxed for an appropriate time, and the reaction was monitored by thin layer chromatography. The reaction product was extracted with ether, dried over magnesium sulfate, and extracted with ethanol for 3
Recrystallized ~4 times to obtain light yellow crystals. The structure of the obtained compound was confirmed and identified by proton nuclear magnetic resonance'H-NMR.

Here, four types of N-alkyl derivatives as shown in Table 1 were synthesized. That is, N-isopropyl-4-nitroaniline, N-normalpropyl-4-nitroaniline, N-normalbutyl-4-nitroaniline, and tothethyl-4-nitroaniline, each with compound numbers 1.2.
This will be shown below in Section 3.4. Table 1 shows the structure, yield, melting point, and absorption peak wavelength λ on the short wavelength side of each compound. , 8
．． Extinction coefficient ε, absorption edge wavelength λ on the short wavelength side. ,,. 2. The values of p-NA (compound no. 5) are shown in comparison with those of p-NA (compound no. 5).

A mixture of p-NA (5) and its synthesized N-alkyl derivatives (1 to 4) (I15.2/ff, respectively, !15.
415) was produced as follows. The amount of each compound corresponding to the mixing ratio (weight) was stirred and completely dissolved in the solvent ether, and then the solvent was evaporated to obtain a mixture.

As a simple method to find the magnitude of the second-order nonlinear effect,
A powdered measurement sample is irradiated with high-power pulsed laser light,
A method (powder method) in which the generated second harmonic (SHG) intensity is measured and expressed as a multiple of the SHG intensity generated by urea powder as a reference sample is often used. The mixture obtained as above was ground in a mortar, packed densely between the glass slides as shown in Figure 2, and SH
A sample cell (sample thickness: 1 mm) for G measurement was prepared.

FIG. 3 shows the apparatus used to measure the SHG intensity of powder samples. Pulsed laser has an oscillation wavelength of 1.
Q-switch Kd of 064 μm: Measured using a YAG laser with a repetition frequency of 1 kHz and a peak output of 11k11.

This laser light is weakly focused by the lens L1 and irradiated onto the sample surface. Since the second harmonic generated from the sample is also radiated backward, a reflecting mirror is provided, and a lens L2. L, so that as much light as possible enters the photomultiplier tube, which is a photodetector. A filter made of an aqueous solution of copper sulfate and an interference filter capable of passing only the second harmonic were inserted between the sample and the laser beam so as not to enter the photodetector. The electrical signals from the photomultiplier tubes were averaged using a digital storage scope to remove noise.

Table 2 shows the SHG intensities of powder samples of the various mixtures mentioned above as relative values based on the values of urea powder samples (thickness 1 mm, particle size 88-105 μm). The first column of the table is the mixing ratio (weight). Therefore, the values in the first and last rows indicate the SHG intensities of only N-alkyl derivatives and only p-NA, respectively. From this table, it can be seen that the N-alkyl derivatives synthesized this time have weak SHG activity (
115,315 1.5.0.24) or p-
It can be seen that although it does not show this at all like HA (215, 415), it shows an extremely large maximum value of SHG intensity at a certain mixing ratio. That is, the mixture 175.215.315.
4'5 has a mixing ratio of 0.5 and 0.5 to p-NA, respectively.
1,0.05゜l, the SHG intensity reaches its maximum value of 416.
It became 270,271°134. 416 of this urea.
The value of 270.271 times is a large value that has been reported in the literature, for example, it is 250 times that of the methyl sulfate salt of trans-4-demethylamino-N-methylstilbuazolium, and N-(4 -nitrophenyl)-(L)-
150 times more than prolinol, 4°-nitropenzylidene-
This breaks the record of 230 times that of 3-acetamino-4-methoxyaniline. In other words, it has become clear from the above examples that the mixed nonlinear optical material of the present invention provides a method for producing extremely large macroscopic nonlinear effects.

In the above example, a mixture of p-NA and its N-alkyl derivative was used, but even for a material having larger nonlinear molecular polarization instead of p-NA, a mixture with the derivative can cause even larger macroscopic nonlinear polarization. It is expected that it will be effective.

(Effects of the Invention) As explained above, according to the present invention, by mixing an organic nonlinear optical material with large nonlinear molecular polarization and a derivative thereof having a similar skeleton and having the same conjugated system, the arrangement of molecules can be changed. It is possible to change the orientation so that their polarizations add up vectorially, producing a macroscopic nonlinear effect larger than that of a single material. When mixed with derivatives with similar skeletons, both molecules can easily mix with each other, and can have a strong influence on each other's molecular arrangement at a very close distance, and since they have the same conjugated system, both molecules Since changes in the arrangement of can contribute together to the vector sum of nonlinear molecular polarizations, an additively large macroscopic nonlinear effect is obtained.

[Brief explanation of the drawing]

Figure 1 shows the N of rose nitroaniline (p-HA).
-A drawing showing the reaction for synthesizing an alkyl derivative; Fig. 2 is a drawing showing the structure of a sample cell for measuring the second harmonic generated from a powdered nonlinear material; Fig. 3 is a drawing showing the structure of a sample cell for measuring the second harmonic generated from a powdered nonlinear material; Diagram showing a measuring device for measuring the generated second harmonic (S: sample, R: reflecting mirror, Ll, L2.L3: lens, LPF: filter that absorbs laser light and does not transmit it, IF: second harmonic Table 1 shows the compound number, structure, yield, melting point, and absorption on the short wavelength side of the N-alkyl derivative of p-NA that was actually synthesized in the example. Peak wavelength λ60. ．． Extinction coefficient ε, absorption edge wavelength λ on the short wavelength side. ,. Table 2 shows the SHG intensities of mixtures of p-NA and various toalkyl derivatives relative to the urea reference sample, and describes the cases of various mixing ratios. Table 2 Compound Table Substituent Yield Melting Point 2 (1) iso-Pr. n-Pr. -But 1) Measured in ethanol (°C) λ, - λ20,. l. N-R/p-N^ (nm) (m2/mol) 980 440 320 880 470 (nm) 10 1 10.1 1 10.5 1 /1 0.5/1 0.2/1 0.1/ 1 0.08/1 0.06/1 0.05/1 0.04/ 1 0.02/1 0.01/1 0ha mixture 115 0.0 soG (X urea) 15 0.0 19.0 25.0 77.9 O0 70 63 60,0 49 93,0 7,7 0,0 15 0,24 22,5 18,3 22,7 40,6 17 22 70 36 71 45, O 17゜0 20 .0 0.0 15 54.0 Figure 1 Figure A N-alkyl derivative

Claims (1)

[Claims] 1. A π-conjugated compound (parent compound) with high polarizability,
It is a highly sensitive nonlinear optical material obtained by mixing derivatives whose structures are partially chemically modified without changing the conjugation system, and is characterized by producing a significantly more nonlinear effect than a single derivative or parent compound that is not mixed. do.