JPH0445193A - Optical element - Google Patents

Abstract

PURPOSE:To obtain an optical element consisting of a composition containing a polymer in which a mesogen group exhibiting liquid crystal properties is introduced at a specific ratio and alpha-helix structure is formed, having good storage stability and capable of carrying out high-speed switching action. CONSTITUTION:The objective optical element consisting of a composition containing one or more kinds of polymer compounds consisting of a polypeptide derivative in which a mesogen group exhibiting liquid crystal properties is introduced on side chains at a ratio of 1-90% based on total side chains and alpha-helix structure is formed and preferably amino acid derivative residue is contained as an unit. Furthermore, a homopolymer containing L(D)-aspartic acid and L(D)-glutamine or glutamic acid as compositional units is especially preferably used as the above-mentioned polypeptide derivative.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an optical element using polymer liquid crystal.

[Conventional technology]

As seen in proteins in living organisms, polypeptide derivatives usually have extremely complex higher-order structures, thereby expressing various functions. α depends on the type of hydrogen bond formed by the amino acid residues that are its constituent units.
- They are roughly divided into three types: helices, β-sheets, and random coils. In other words, when amino acid residues form hydrogen bonds within the molecule, they form α-helices, when hydrogen bonds form between molecules, they form β-sheets, and when no hydrogen bonds are formed, they form random coil structures. Take.

Polyglutamic acid ester, a type of polypeptide derivative, has a secondary structure that differs depending on the side chain of each amino acid residue and surrounding environmental conditions (temperature, solvent, etc.), and is known to maintain its structure stably. There is. In particular, poly γ-benzyl monoglutamate (hereinafter referred to as P
(abbreviated as BLG) or poly γ-benzy-D-glutamate (hereinafter abbreviated as PBDG),
It is known to form a stable α-helical structure in many organic solvents such as dioxane, dimethylformamide, 1,2-dichloroethane, and tetrahydrofuran, and to exhibit a cholesteric liquid crystal phase.

The cholesteric liquid crystal phase has a layered structure, and within each layer, molecules are oriented in parallel in one direction. Further, the cholesteric liquid crystal phase has a twist axis (helix axis) in a direction perpendicular to this layer, and the orientation direction of molecules is shifted by a certain angle between each layer. The distance between layers whose orientation directions differ by 380° is called cholesteric pitch or simply pitch. Cholesteric liquid crystals are characterized by their large periodic structure, and the optical properties of cholesteric liquid crystals, such as their unusually large optical rotation power and the ability to selectively reflect right- or left-handed circularly polarized light in a narrow wavelength range, are derived from the above-mentioned helical structure. be. Due to the latter selective reflection ability, the cholesteric liquid crystal has circular dichroism (CD), and the reflection center wavelength λ■ has a relationship of λ■-nP with the helical pitch P and the refractive index n. This characteristic produces a vivid coloration effect ranging from red to blue when the λ ray is in the visible wavelength range.

As described above, cholesteric liquid crystals selectively reflect either right-handed or left-handed circularly polarized light in a wavelength range depending on the cholesteric pitch. When linearly polarized light enters such a liquid crystal, either the right or left circularly polarized light is selectively reflected, and the amount of transmitted light in that wavelength range is reduced by 1/2.
It becomes 2. Furthermore, when a right-handed circularly polarized light selective reflection film and a left-handed circularly polarized light reflective film are used in an overlapping manner, no light is transmitted.

The cholesteric pitch of the cholesteric liquid crystal phase formed by polyglutamic acid ester changes depending on various conditions such as the type of solvent, concentration, and temperature.

When converted to wavelength, the range of change corresponds to infinite wavelengths, from ultraviolet to far infrared. Therefore, by appropriately setting conditions, it is possible to selectively reflect right or left circularly polarized light components in any wavelength range.

When attempting to create an element utilizing such characteristics, a solid state, particularly a film form, is more preferable than a solution state in terms of handling properties, stability, and the like. Therefore, it is preferable to use a substance that forms a cholesteric liquid crystal phase in a solid state and whose cholesteric pitch changes depending on temperature or the like. However, PBLG (
or PBDG) forms a cholesteric liquid crystal phase only in a solution state, and does not show a cholesteric liquid crystal phase in a solid state, so that its use in devices is limited.

In general, it is known that polypeptide derivatives having linear alkyl or aryl groups with a large number of carbon atoms in their side chain groups have long flexible side chain groups that act similar to solvents as the temperature rises. When such side chain groups occupy a certain amount of volume, a thermotropic cholesteric liquid crystal can be formed even in a solid state. Tokukai Shosetsu [12-
No. 116629 and No. 62-175939 disclose a material exhibiting a cholesteric liquid crystal phase obtained by changing the side chain group of a polyglutamic acid ester, and the application of this material to optical recording media, etc. ing.

[Problem to be solved by the invention]

However, the polypeptide derivatives disclosed in the above specification have a relatively low liquid crystal transition temperature and therefore have poor storage stability. Furthermore, it is difficult to fix the cholesteric phase during film formation, and an annealing process is required in which the film is heated to a temperature above -degree transition temperature and then cooled.

Therefore, an object of the present invention is to provide an optical element that has good storage stability, has a polymeric liquid crystal that does not require an annealing treatment during film formation, and is capable of high-speed switching operation.

[Means to solve the problem]

The polymer liquid crystal used in the optical element of the present invention selectively reflects only right-handed circularly polarized light or left-handed circularly polarized light in a specific narrow wavelength range, and the selective reflection wavelength range in parentheses is controlled by temperature, electric field, and magnetic field. , a polypeptide derivative that can be altered by applying external stress such as light, pressure, etc. This polypeptide derivative has an α-helical structure, and 1 to 90% of the side chain groups are mesogenic groups derived from a compound exhibiting liquid crystallinity.

Such polypeptide derivatives may be of any type as long as they express cholesteric liquid crystals, but are preferably polyamino acids having amino acids as constituent units,
Particularly preferred are homopolymers having L(D)-asparagine, L(D)-aspartic acid, L(D)-glutamine, or L(D)-glutamic acid as constituent units. On this occasion,
One molecule of a polypeptide derivative is formed of only one type of L-form or D-form. Furthermore, in the polymer matrix, L-form and D-form may coexist as long as they are not racemic, but a matrix consisting only of either isomer is preferred. This is because the helical structure of the cholesteric liquid crystal has reversed helical directions in the L-form and the D-form, and if these are present together, the liquid crystal structures cancel each other out, resulting in a defect.

Hereinafter, polypeptide derivatives used in the present invention will be explained using poly-L-glutamic acid ester as an example.
The same applies to other amino acids.

The poly-L-glutamic acid ester used in this invention is represented by the following general formula (I).

-← Listen-made - (fund) + "-1 + ■ - Carp - luster → -1CH2
CH2 C-0C-0 R, R2 In the above general formula (1), R1 is a side chain group containing at least one of the following (where i is an integer of 1 to 6 and j is an integer of 1 to 3), R2 is a mesogenic group.

The mesogenic group R2 in the above general formula (1) further includes:
It can be expressed by the formula. In the formula, A is either 10CH2-+-r- →CH2±1-0-1 or →CH2CH20+-r- (where k is an integer from 1 to 16), and B and C are each Any of the groups listed in Tables 2 and 3 below. In addition to the substituents listed in Table 2, B may be one in which one or both of the benzene rings contained in those substituents is substituted with a hetero ring such as It may be a combination of three or more benzene rings, cyclohexane rings, or heterocycles.

Furthermore, the mesogenic group R2 may be a substituent derived from a cholesterol derivative. Specific examples of the mesogenic group R2 are shown in Table 4 below, but the invention is not limited thereto. The above polyglutamic acid ester contains one or more of the above substituents as R2.

The content of mesogenic groups in polypeptide derivatives, as well as the structure of mesogenic groups and film formation conditions, is influenced by the temperature dependence of cholesteric pitch, the orientation behavior when voltage is applied, and the determination of the wavelength region of the pitch band during film formation. This is an important factor. In the polyglutamic acid ester represented by the above general formula (1), the proportion of glutamic acid residues having a mesogenic group R2 to the whole [1100X/(Ω10m)%
The optimum value of 0 varies depending on the structure of R1 and R2, but is usually 1 to 90%, preferably 2 to 50%. If this ratio is less than 1%, the effect of the mesogenic group will not be sufficiently exhibited. In addition, if this ratio exceeds 90%, phenomena such as crystallization and scooking occur due to the interaction between mesogenic groups, and cholesteric liquid crystal phase may not be expressed or the selected wavelength range may be fixed, resulting in optical This tends to reduce the performance of the element.

The degree of polymerization (Dp-, 11+m) of the polyglutamic acid ester represented by the above-mentioned - Funazo (I) is from 50 to 2,000, more preferably from 75 to 700. Degree of polymerization is 50
If it is less than this, the film-forming properties of the polyglutamic acid ester deteriorate, and furthermore, the liquid crystal transition point tends to decrease, resulting in poor stability. In addition, if the degree of polymerization exceeds 2000, there is a risk that the liquid crystal transition point will become too high and the polyglutamic acid ester will decompose, and the viscosity will also increase, resulting in a slow response speed when an electric field is applied. There is a tendency.

Specific examples of polyglupolymic acid esters that can be suitably used in the optical element of the present invention are shown in Table 5 below.

The polypeptide derivative used in the optical element of the present invention has various characteristics such as response speed of pitch band shift due to external stress of cholesteric liquid crystal phase, sensitivity, fixed wavelength range of pitch band, etc., type and proportion of side chain groups, and film formation time. It varies greatly depending on factors such as the coating solvent, atmospheric conditions such as operating temperature, and the type of substrate.

Therefore, it is possible to create a variety of devices with different performances.

The above polypeptide derivatives can be prepared, for example, by conventional transesterification. In addition, methods for forming a film of the above polypeptide derivative include solution casting, spin cording, stretching, etc. in the same way as for ordinary polymers. From the viewpoint of maintenance, a solution casting method with less external pressure is preferable. That is, by dissolving a predetermined amount of the above polypeptide derivative in an organic solvent, applying the resulting solution uniformly onto a substrate by a day rubbing method, a roll coater method, a screen printing method, a doctor blade method, etc., and then drying it. Forms a film. The solvent used at this time may be any solvent as long as it can dissolve the polypeptide derivative and form an α-helical structure in the solution. Specifically, halogen-based solvents, -Dioxane, DMF.

Examples include THF. Further, as long as the above conditions are satisfied, a mixture of a poor solvent or a mixture of two or more good solvents may be used.

Since the fixed state of the cholesteric pitch band when forming a film of the above-mentioned polypeptide derivative varies greatly depending on the type of solvent, selection of the solvent is important in order to obtain a desired film-forming state.

The film obtained in this way already has a CD absorption property derived from the cholesteric liquid crystal phase. Therefore, there is no need for annealing. When this film is heated, it reaches a certain temperature (threshold temperature: 2 T,
Below h), the absorption peak of CD does not change; however, when this temperature is exceeded, the absorption peak of CD shifts to the longer wavelength side in proportion to the temperature.

Furthermore, if the film is rapidly cooled after the absorption peak has shifted, the absorption peak will be fixed in the shifted state, and the absorption peak will not shift for a long time even if it is left at room temperature. Furthermore, when a voltage is applied to the film while it is heated above the threshold temperature, the cholesteric liquid crystal phase collapses into a nematic liquid crystal phase, and the CD absorption peak disappears.

The following optical element according to the present invention will be explained with reference to the drawings.

FIG. 1 is a sectional view showing four embodiments of the optical element of the present invention. As shown in FIG. 1, this optical element includes a substrate 1, a heat generating layer 2, a total reflection layer 3, a polymer layer 4, and a total reflection layer 5.
are layered one after another. The heat generating layer 2 is made of, for example, tantalum nitride, is connected to a power source 7 via a switch 6, and generates heat when a voltage is applied thereto. The polymer layer 4 is a film of the polypeptide derivative obtained as described above, and is arranged so that the helical axis of the cholesteric liquid crystal phase is parallel to the substrate. The thickness of the polymer layer is at least 0.03 n. The total reflection layers 3 and 5 are films made of a material having a lower refractive index than the polymer layer 4. An optical signal is incident on this optical element from the direction of arrow A, which is parallel to the helical axis of the polymer layer 4.

When the heating layer 2 of this optical element is heated to raise the temperature of the polymer layer 4 above its threshold temperature, the CD absorption peak gradually shifts to the longer wavelength side. When the absorption peak reaches the wavelength of the signal light, the heating is stopped and the polymer layer 4 is rapidly cooled, so that the absorption peak is fixed at the wavelength of the signal light. In this state, if the polypeptide derivative forming the polymer layer 4 has the property of selectively reflecting left-handed circularly polarized light, and left-handed circularly polarized light is used for the signal light, this element It will be in the off state. Further, even if the signal light is linearly polarized light, if it passes through a circularly polarizing filter or the like before entering or after passing through this optical element and the right circularly polarized light component is removed, it will still be in the off state. When the optical element in the OFF state is reheated to a temperature corresponding to the fixed absorption peak and then the heat generating layer 2 is gradually cooled, the cholesteric pitch is gradually shortened and the optical element can be returned to the ON state. This on/off conversion operation can be repeated.

FIG. 2 is a cross-sectional view of the optical element shown in FIG. 1, which is further provided with electrodes. As shown in FIG. 2, this optical element includes a substrate 1, a heat generating layer 2, an electrode 8, and a total reflection layer 3.
, a polymer layer 4, a total reflection layer 5, and an electrode 9 are sequentially laminated. A power source 7 is connected to the heat generating layer 2 via a switch 6, and electrodes 8 and 9 are connected to a power source 11 via a switch 10. Electrodes 8 and 9 are made of aluminum, for example. The helical axis of the polypeptide derivative film forming the polymer layer 4 is arranged parallel to the substrate 1, and the optical signal enters the device from the direction of arrow A, which is parallel to this helical axis.

This optical element can also be turned off for signal light by fixing the absorption peak of the polypeptide derivative film at a desired wavelength by the same operation as the optical element shown in FIG. However, in the optical element shown in FIG. 2, it is only necessary to apply a voltage to the electrodes 8 and 9 in order to turn this state back on. By applying voltage to electrodes 8 and 9, α-
This is because the long axis of the helix main chain is oriented perpendicularly to the substrate l, and the cholesteric liquid crystal phase changes to the nematic liquid crystal phase. When the voltage application to the electrodes 8 and 9 is stopped, the polypeptide derivative immediately forms a cholesteric layer by its own orientation ability and returns to the OFF state again. This operation can also be repeated.

In the optical element shown in FIGS. 1 and 2, the heat generating layer 2 is not limited to the position adjacent to the substrate 1;
It may be arranged adjacent to the second total reflection layer 5, or it may be arranged such that two heat generating layers are provided and the polymer layer 4 is sandwiched therebetween. Further, the method of heating the polymer layer is not limited to heating using a heating layer, but heating can also be performed by infrared irradiation or the like. In the device shown in FIG. 2, the electrodes 8 and 9 are not limited to aluminum, but may also be made of copper, silver, gold, organic conductors, or the like. It is also possible to further simplify the structure of the device by using a film that has both the functions of an electrode and a total reflection layer.

[Function] The polypeptide derivative used in the optical element of the present invention has a mesogenic group introduced into the side chain.

Due to the action of this mesogenic group, polypeptide derivatives
The liquid crystal transition point becomes higher, the storage stability of the cholesteric pitch band improves, and the liquid crystal transition point shows a clearer threshold temperature. Furthermore, the rotational movement of the mesogenic group increases the mobility of the α-helical main chain in the matrix, improving the response speed and sensitivity to external stresses such as temperature, electric field, magnetic field, light, and mechanical pressure. In addition, if the mesogenic group introduced into the side chain has a permanent dipole moment,
The permanent dipole moment of the entire polypeptide derivative molecule also increases, further improving the response speed to electric fields and the like. In addition, mesogenic groups have a stronger solvent-like effect than other substituents such as alkyl groups and aryl groups, so they already exhibit a cholesteric liquid crystal phase at the time of film formation, eliminating the need for annealing treatment for initialization. Become.

〔Example〕

Example 1 Polyγ-benzyl-monoglutameth (P) of Dp300
BLG) 10 g, 12 g of a liquid crystal compound represented by the following formula, and P-)luenesulfonic acid 4 as a catalyst.
5 g was dissolved in 1,2-dichloroethane/1,4-dioxane (1/l) mixed solvent 1,000 ml, and heated at 60°C for 3
After stirring for 4 hours, the polypeptide derivative shown as (5-1) in Table 5 was obtained by precipitation from methanol. The ratio of mesogenic groups to the total side chains in this polypeptide derivative was about 25%.

The obtained polymer was dissolved in a tetrahydrofuran solution to obtain a solution having a concentration of 10 .mu./wJ, and the solution was coated on a quartz plate to prepare a cast film. The thickness of the obtained cast film was about 6,7-.

The obtained cast film was heated while controlling the temperature, and the CD was measured at an appropriate temperature. The results are shown in FIGS. 2 and 3. Figures 2 and 3 are graphs showing the shift of the absorption peak of CD due to temperature rise. In Figure 2, the vertical axis represents the absorption of CD, the horizontal axis represents the wavelength of light, and in Figure 3, , the vertical axis represents the reciprocal of the wavelength showing the absorption peak in FIG. 2, and the horizontal axis represents the temperature. As is clear from these figures, a clear threshold temperature (T, )
Below, the absorption peak of CD does not change, and when TIL is exceeded, the absorption peak shifts to the longer wavelength side in proportion to the temperature. Furthermore, in a cast film that was heated above Tlb and rapidly cooled after the absorption peak shifted, no peak shift was observed for a long time even when the film was left at room temperature.

In addition, electrodes were provided on both sides of this cast film, and Tl
When a voltage is applied while the film is heated to a temperature higher than h, the cholesteric liquid crystal phase collapses into a nematic reflux liquid crystal phase, and the CD absorption peak disappears.

Example 2 PBLG of Dp200 and a liquid crystal compound represented by the following formula were reacted in the same manner as in Example 1, and as shown in Table 5 (5-2
) was obtained.

The ratio of mesogenic groups to all side chain groups in this polypeptide derivative was about 32%.

This polypeptide derivative was dissolved in a tetrahydrofuran solvent to obtain a solution having a concentration of losg/-, and the solution was coated on a quartz plate to prepare a cast film. The thickness of this cast film was 5.21.

Using the obtained cast film, CD was measured in the same manner as in Example 1. The results are shown in FIGS. 4 and 5. FIGS. 4 and 5 are graphs showing the shift of the absorption peak of CD due to temperature increase, and correspond to FIGS. 2 and 3 in Example 1, respectively.

In FIG. 4, the vertical axis represents CD absorption, and the horizontal axis represents the wavelength of light. In FIG. 5, the vertical axis represents the reciprocal of the wavelength showing the absorption peak in FIG. 2, and the horizontal axis represents temperature. As in Example 1, as is clear from these figures, the absorption peak of CD does not change below a clear threshold temperature (T, , ), and Tl
When b is exceeded, the absorption peak shifts to the longer wavelength side in proportion to the temperature. Furthermore, in a cast film that was heated above Tlk and rapidly cooled after the absorption peak shifted, no peak shift was observed for a long time even when the film was left at room temperature.

Examples 3 to 8 Using the same method as in Example 1, the results shown in Table 5 below (5-
Polypeptide derivatives shown as 3) to (5-8) were prepared. Example 1 for each polypeptide derivative obtained
Table 1 shows the results of CD measurements conducted in the same manner as above.

Comparative Examples 1 and 2 The polypeptide derivatives shown as (6-1) and (6-2) in Table 6 were respectively formed into films in the same manner as in Example 1, and the CD was measured.

Here, the polypeptide derivative (P
BLG) has a mesogenic group substitution rate of 0%, and the polypeptide derivative represented by (6-2) has a mesogenic group substitution rate of 10%.
Corresponds to 0%. As a result of the measurement, no CD absorption peak corresponding to the cholesteric pitch band appeared even when the temperature was increased.

The symbols listed in the column "Applicability as an element" in Table 1 above have the following meanings.

O... Suitable for the device △... Suitable for the device ×... Not suitable for the device Example 9 An optical element having the structure shown in FIG. 1 was made using the cast films prepared in Examples 1 to 8. Created. That is, an optical element was prepared by sequentially laminating a heat generating layer made of tantalum nitride, a total reflection layer, a cast film, and a total reflection layer on a substrate.

The heat generating layer is connected to a power source and can generate heat by applying a voltage. The cast film was arranged so that the helical axis of the cholesteric liquid crystal phase was parallel to the substrate, and the film thickness was set to 10.5-. For the total reflection layer, a film made of a substance having a lower refractive index than the cast film was used.

An optical signal is incident on this optical element from a direction parallel to the helical axis of the cast film.

The heating layer of each of the produced optical elements was heated to heat the cast film above Tlh, and the absorption peak of CD was shifted to the wavelength of the signal light. By stopping the heating of the heating layer in this state and rapidly cooling it, the cholesteric pitch band was fixed at the wavelength of the signal light. That is, each optical element was turned off with respect to the signal light.

The heating layer of each optical element that had been turned off was heated again to raise the temperature of the cast film to the temperature required to set it in the off state. Then, by gradually cooling the heating layer, the cholesteric pitch of the cast film was gradually shortened, and each optical element was turned on again.

Example 10 An optical element having the structure shown in FIG. 2 was created using the cast films prepared in Examples 1 to 8. That is, these optical elements are formed by sequentially laminating on a substrate a heat generating layer made of tantalum nitride, an electrode made of aluminum, a total reflection layer, a cast film, a total reflection layer, and an electrode made of aluminum. The heat generating layer and the picture electrode are connected to a power source and voltage can be applied thereto. When a voltage is applied to the heat generating layer, the heat generating layer is heated, and when applied to the electrode, a voltage can be applied to the cast film. The helical axis of the polypeptide derivative film forming the cast film is arranged parallel to the substrate, and the optical signal enters the device from a direction parallel to this helical axis.

Each of the produced optical elements was turned off for signal light in the same manner as in Example 9. In this state, by applying a voltage to the electrodes, the cholesteric liquid crystal phase of the cast film was changed to a nematic liquid crystal phase, and each optical element was turned on for signal light. Then, when the voltage was stopped from being applied to the electrodes, each optical element immediately returned to its off state.

No. table spear table -CN.

()C,, Ton++ (n-1 to 6).

N02 -NH2, -Cf:I.

-COOCnH2n+t (n-1 to 6).

-Br.

I.

-oCo-C,,H2,,+1(n-1 to 6).

H3 H3 H3 H3 (* represents asymmetric carbon) 1←Kan-CH-Co→--111← CH2 CH2 −←NH−CH (a) →−−−−−← CH2 CH2 No. table NH-CH-(a)→- CH2 CH2 N)(-CH (sword→− CH2 CH2 1←God-CH-(4)→----← CH2 CH2 1←NH-CH-■→----1000 CH2 CH2 CH3 table (continuation) Stamp - CH - mark → - CH2 CH2 NH-CI-CCLner CH2 CH2 -O ← Listen-CH-CO→--m-← CH2 CH2 -O CH2 table (continuation) NH-CH-Co→- CH2 CH2 CH2 CH2 -O H3 table -+NH-Cil-CO→- Cil,.

CI, 2 -(-N11 Cil (to) → - C1(2) [Effects of the Invention] As described above, according to the present invention, cholesteric pitch can be reduced by using a polypeptide derivative in which a mesogenic group is introduced into the side chain. Increased storage stability, temperature, electric field,
An optical element is provided that has improved response speed and sensitivity to external stresses such as magnetic fields, light, and mechanical pressure.

Furthermore, the polypeptide derivative used in the optical element according to the present invention forms a cholesteric liquid crystal phase even in a solid state, and since the cholesteric liquid crystal phase is formed at the time of film formation, it is necessary to anneal for initialization. No processing is required. Thus, an optical element is provided that is easier to manufacture.

[Brief explanation of drawings]

FIG. 1 is a diagram schematically showing a cross section of an optical element according to one embodiment of the present invention, FIG. 2 is a diagram schematically showing a cross section of an optical element according to another embodiment of the present invention, and FIG. is C of the polypeptide derivative film prepared in Example 1.
A graph showing the D absorption characteristics according to temperature. FIG. 4 is a graph showing the relationship between the absorption peak and temperature of the polypeptide derivative film prepared in Example 1. FIG. 5 is a graph showing the relationship between the absorption peak and temperature of the polypeptide derivative film prepared in Example 2. A graph showing the CD absorption characteristics according to temperature, and FIG. 6 is a graph showing the relationship between the absorption peak and temperature of the polypeptide derivative film 7r prepared in Example 2.

Claims (4)

[Claims] (1) Optical device with a cell structure that selectively reflects only right-handed circularly polarized light or left-handed circularly polarized light in a specific wavelength range, and can change the wavelength range by applying external stress An element comprising a composition containing at least one polymer compound in which mesogenic groups exhibiting liquid crystallinity are introduced into side chains in a proportion of 1 to 90% of all side chains, and which form an α-helical structure. optical element. (2) The optical element according to claim 1, wherein the polymer compound is a polypeptide derivative having amino acid derivative residues as constituent units. (3) A polymer layer made of either a film made of the polymer compound or a cell sealed with the polymer compound solution, and a heat generating layer that heats the polymer layer are laminated on the substrate in sequence or in reverse order. The optical element according to claim 1, comprising a structure. (4) The optical element according to claim 1, comprising a polymer layer made of the polymer compound and two electrodes laminated on both sides of the polymer layer.