DE4219439A1 - Nonlinear optical mixtures - Google Patents

Abstract

Described are NLO mixtures whose matrix is made up of polymeric organo-silicon compounds as obtained by the so-called sol-gel method and which have embedded in the matrix an NLO compound.

Description

The invention relates to mixtures with non-linear optical (NLO) properties, consisting of an NLO-active connec tion and an SiO ₂ matrix. The SiO ₂ matrix is produced using the so-called sol-gel process, starting from pure or organically modified Si alkoxides or mixtures of the two.

Nonlinear optics is generally concerned with the interaction of electromagnetic fields and matter and can lead to a refractive index that is different from the light intensity is dependent. Detailed information on this can e.g. B. R.N. Prasad, D.J. Williams, Introduction to non linear optical effects in molecular and polymers, New York. be removed.

In summary, the following is important: A substance emits light when dipoles vibrate in it, the Frequency of the emitted light wave equal to the vibration frequency of the dipoles. Generate the vibrating dipoles multiple frequencies, these come in the of the concerned Fabric emitted light together before. Provided the spatial Expansion of the substance greater than the wavelength of the emit the light vibrating in the fabric should be iden dipoles in the same direction and with one Swing phase difference, which ensures that the egg No light emitted by a volume element due to interference with the light emitted by another volume element is wiped out.

In a polarisable substance, it is from the outside placed field E causes macroscopic polarization, which is defined as the dipole moment per unit volume.

The polarized material does not contain permanent molecules laren dipoles, the dipole moment results and thus the macroscopic polarization P from the shift of the elec tron by the amount d from their rest position, d. H. the heavy point of positive charge out. In contrast, are permanent  Containing dipoles, the field E changes that permanent dipole moment according to the same mechanism.

As long as the displacement d is proportional to the electrical Field remains, the polarization P is also proportional to electric field E, which in the known linear Equation 1

P = ε₀ _* chi _* E (Eq. 1)

is expressed. In the equation, ε ₀ denotes the absolute dielectric constant and chi (χ) the dielectric susceptibility.

If the field created from the outside is reinforced, it must of course any substance above a specific field strength a deviation from the linear law according to equation 1 demonstrate. The mechanical analogue is the deviation from Hooke's law when a spring is overloaded. Such Ab Deviations from linearity are mathematically represented by Ent treated in a power series, d. H. one develops the nonlinear function according to powers of the variable E, from which equation 2, the basic equation of not linear optics result.

P = ε₀ _* (chi ⁽¹⁾ _* E + chi ⁽²⁾ _* E² + chi ⁽³⁾ _* E³) (Eq. 2)

Here means:
chi ⁽¹⁾ the dielectric susceptibility of the first order, which is ultimately responsible for the linear behavior of the material in question, ie refractive index and absorption constant are independent of the field,
chi ⁽²⁾ the second order dielectric susceptibility, which is responsible for the second order nonlinear optical behavior of the substance in question, and
chi ⁽³⁾ the dielectric susceptibility of the third order, on which the non-linear optical behavior of the third order is based.
chi ⁽²⁾ and chi ⁽³⁾ are material constants that depend on the molecular structure, on the crystal structure, on the frequency of light and generally on temperature. As is known, you can use frequency doubling (SHG) or the determination of the Pockels effect (chi ⁽²⁾ ) or the "four-wave mixing method" (Degenerate Four Wave Mixing, DFWM) or the frequency tripling experiment (Third Har monic Generation, THG ; chi ⁽³⁾ ) can be determined. These methods are described in principle in the book by Prasad op. Cit.

Substances with a non-vanishing dielectric susceptibility chi ⁽³⁾ [chi ⁽³⁾ ≠ 0] have an intensity-dependent refractive index and are suitable, among other things, for the manufacture of purely optical switches and thus for use in optically operating computers. Further application possibilities for such materials are described by DR. Ulrich under the title "Nonlinear Optical Polymer Systems and Devices" in Molecular Crystals and Devices, Volume 180, pages 1 to 31, 1988.

For the use of nonlinear optical materials (here: materials based on a high chi ⁽³⁾ ) in optical components, a combination of different material properties is necessary. A high chi ⁽³⁾ alone is by no means sufficient for the requirements of an optical construction. In addition, the relaxation and thus the switching time should be very short (in the range of femtoseconds), the optical losses due to absorption, scattering, etc. should be minimal and, lastly, the materials should be easy to process in the form of layers, e.g. B. be given in optical fibers.

The current development of chi ⁽³⁾ materials mainly deals with the optimization of the amount of chi ⁽³⁾ and the relaxation time; good processability of the materials with small optical losses plays an increasingly important role. The previously known materials with NLO properties belong to both the class of low molecular weight organic compounds and the polymers.

So z. B. from DR Ulrich, Polymers for Nonlinear optical Applications, Mol, Cryst. Lig., Cryst. 1990, 189, 3-38 the following substance classes are known as NLO active:
Benzthiazoles e.g. B .:

Stilbene derivatives e.g. B .:

N-phenylbenzimidazole derivatives e.g. B .:

The following are known as NLO-active polymers: polyacetylene, polyenes, Polyphenylene, polythiophene, polyphenylene vinylidenes.

In the field of NLO-active polymers, which are essentially those with conjugated π-electron systems, the processability to thin transparent layers has not yet been solved or has not been satisfactorily solved. The high molecular weight polymer systems, which show the greatest chi ⁽³⁾ effects, are very poorly soluble in solvents and can therefore not be processed from solution by so-called spin coating. The optical losses due to crystallization of the layers also impair their applicability (see Prasad, loc. Cit.).

One way to improve workability is the use of good film-forming polymers as auxiliary materials are used to produce layers. The so far Polymers used for this are not chemistry adapted to the NLO material and therefore cause, so to speak Dilution of the nonlinear optical effect. Besides, who slow crystallization processes in the Layers observed so that the optical losses ur materials that were originally satisfactory will later change worse.

The subject of the invention are NLO-active mixtures (composi tes), whose matrix of polymeric organosilicon compound is constructed as it is according to the so-called sol-gel process and are stored in the matrix. Contain NLO active connections.

These compounds can be of low or high molecular weight (Polymers).

As materials with non-linear optical properties come z. B. poly- or oligoheteroarenes of the general Formula Ia, their preparation u. a. in Houben-Weyl, volume 32, P. 1152. Doped are preferred Heteroarenes of the general formulas Ia and Ib

where n is the degree of polymerization and X = NR ¹ , where R ¹ = H, alkyl, phenyl, -SO ₂ aryl

R ² = R ³ = H or
R ² = -alkyl, -cycloalkyl, -phenyl, -halogen, -diphenylamine, -ester, -NH-phenyl or
X = S,
A⊖ = ClO ₄ ⊖, AsF ₆ ⊖, BF ₄ ⊖, FeCl ₃ ⊖, SbF ₆ ⊖.

As materials with NCO properties, poly or Oligoindophenins produced by the oxidative coupling of Verbin Type 11 are synthesized.

Furthermore, NLO-active composites can be run on Polyterpheny Lenen of the general formula IIIa or IIIb, as z. B. by Naarmann in Synthetic Metals, 44 (1991), 247-257, be be written, build up.

where R ¹ , R ² , R ³ and R ^{4 have} the following meanings:

• a) R ¹ = R ² = H; R ³ = R ⁴ = phenyl
• b) R ¹ = R ² = H; R ³ = R ⁴ = biphenyl
• c) R ¹ = R ² = R ³ = R ⁴ = phenyl
• d) R ¹ = R ² = thiophene; R ³ = R ⁴ = phenyl
• e) R ¹ = R ² = H; R ³ = R ⁴ = p-methoxyphenyl

By using oligomers or polymers of the general Formula IV, which is bifunctional through wittiganalogous implementation Aldehydes obtained with monofunctional carbonyl compounds composites with good nonlinear optical properties:

with R ¹ = phenyl, p-aminophenyl, p-nitrophenyl, biphenyl, p-methoxyphenyl, thiophene, pyrrole
and R ² = H or alkyl

Substituted as follows are of particular importance Polyene derivatives (Me = methyl):

Carotenoid derivatives with extensive konju are also suitable gation according to the formulas V-VII as in the Si matrix connections to be stored.

Good nonlinear optical effects are further enhanced by the Use of various phthalocyanines in general Formula VI achieved:

with R = alkyl  with Me = Al, Pb, Co, Ni, Mn, Cr, Ti, V, Sn, Zn

Particularly noteworthy are phthalocyanines with Fe, Si or V as the central atom.

Further conjugated systems of interest for SiO ₂ / NCO applications are substance classes such as perylenes, polyphenylene vinylidene and polyacetylenes.

The NLO-active mixtures can be obtained by subjecting solutions of compounds which build up the matrix SiO ₂ and nonlinearly optically active substance to the spin coat process. This process leads to homogeneous, transparent layers in which the NLO material is molecularly distributed. The layer thicknesses can be influenced by the speed of rotation of the rotor and are expediently in the range between 50 and 200 nm.

The matrix is expediently made in situ by the sol-gel method ren produced as a chemical-synthetic process. This Process for the production of layers of inorganic Po lymeric (e.g. silicates, glasses) or inorganic-organic polymers (e.g. organically modified silicates) known per se and z. B. by C.J. Brinker, G.W. clipper "Sol-Gel-Science - The Physics and Chemistry of Sol-Gel-Pro cessing ", Academic Press, 1990. The matrix poly mer can be adapted to the requirements of the NLO material will. By chemical modification of the inorganic Sol-gel material becomes a link that leads to a improved long-term stability and a homogeneous moleku laren distribution and so to low optical losses leads. By installing foreign metal atoms (e.g. Er substitution of Si by Ti or Zr) the refractive index of the sol Gel material can be adapted to the optical requirements.

In general, the coating sols are targeted by Hydrolysis and condensation of reactive Si alkoxides poses. In general, pure alkoxides, such as. B. Tetraethoxysilane (TEOS) or organically modified Alkoxides in which an alkoxide function by an orga African radical is substituted.  

The organically modified Si alkoxides are by the general formula VII described:

R ¹ - (CH ₂ ) _n -Si (OR ² ) ₃ ,

with R ¹ = -Me, -CN, -NH ₂ -NCO, -SH,
R ² = alkyl such as B. -Et, -Me, -n-propyl, -i-propyl and n = 1-8.

Particularly suitable organically modified alkoxides are e.g. B. n-propyltrimethoxysilane (PTNS) or cyanopropyltriethoxysilane (CNTPES). By means of acidic or alkaline-catalyzed hydrolysis and condensation of the silicon alkoxides or mixtures thereof, SiO ₂ -containing coating sols can be produced in various solvents. Suitable solvents are very generally alcohols, alkanes, cyclic tertiary amines, secondary aliphatic amines, sulfur-containing solvents, ether diols or mixtures thereof. Particularly noteworthy is EtOH, MeOH, N-methylpyrrolidone, dimethylamide, sulfolane, diethylene glycol diethyl ether or toluene. If a solvent is unsuitable for the sol-gel reaction, the reaction can be carried out in a typical "sol-gel solvent" (EtOH or the like). After the end of the reaction, a solvent exchange can then follow, with which the incorporation of the nonlinear optical substance into the SiO ₂ matrix is possible again.

Due to the range of variation of the solvent polar activity is the homogeneous introduction of the NLO materials, which are often only poorly soluble in common solvents are given great flexibility.

The introduction of the NLO materials into the sol-gel approach takes place either at the beginning of the actual hydrolysis u. Condensation reaction or after completion of the reaction and subsequent homogenization. The decisive factor is the solution NLO compound in the solvent of the sol- Gel approach or in the exchanged solvent.

Through the targeted cocondensation of the Si alkoxides with the network work-changing metal atoms that have the corresponding Metal alkoxides can be introduced, the refraction  index of the coating to the optical requirements fit.

example 1

0.025 mol CNPTES are dissolved in 19 ml EtOH. 1.25 · 10 ^-4 mol HCl are added to the mixture and it is heated to 78 ° C. 0.15 mol of H ₂ O are added dropwise in the course of 15 minutes, and the mixture is subsequently stirred at 80 ° C. for 3 hours. The mixture is cooled to room temperature with stirring within 1 h. 1.5 g of β-apo-8'-carotenal is added to the resulting solution with stirring and homogenized for 1 h. The sol obtained is applied at 10,000 rpm to quartz glass by means of spin coating and then annealed at 120 ° C. under N ₂ for 12 h. Layers with a thickness of 90 nm are obtained.

(UV _max = 283 nm; χ ³ (THG) = 2.9 · 10 ^-12 esu).

Example 2

0.1 mol of PTMS is dissolved in 52 ml of N-methylpyrrolidone. 5 × 10 ^-4 ml of HCl are added to the mixture and it is heated to 80 ° C. 0.3 mol of H ₂ O is added dropwise in the course of 15 minutes, and the mixture is subsequently stirred at 80 ° C. for 3 hours. With further stirring, 4 g of β-apo-8'-carotenal are added to the solution and stirred at 80 ° C for 1 h. The mixture is cooled to room temperature with stirring. Spin coating on a glass substrate at 10000 rpm produces transparent yellowish layers with a layer thickness of 95 nm

(UV _max = 285 nm; χ ³ (THG) = 4 · 10 ^-12 esu).

Example 3

0.025 ml of CNPTES are dissolved in 32 ml of diethylene glycol diethyl ether and 0.15 mol of H ₂ O and 1.24 · 10 ^-4 mol of HCl are added. The mixture is stirred at 80 ° C for 3 h. Then 1.5 g of vanadium oxide phthalocyanine are added. The mixture is stirred at 80 ° C for 1 h and the mixture is cooled. Spincoating at 8000 rpm on quartz glass gives a blue-colored transparent layer (layer thickness: 135 nm).

(UV _max = 750 nm; χ ³ (THG) = 9 · 10 ^-12 esu).

Example 4

In a N ₂ atmosphere, a mixture of 0.02 mol CNPTES and 0.005 mol TEOS in N-methylpyrrolidone (NMP) is HCl-catalyzed (1.24 · 10 ^-4 mol) with the addition of 0.15 mol H ₂ O within 3 h co-condensed at 80 ° C. Then 1.5 g of a C ₄₀ astaxanthin dissolved in NMP were added and the mixture was stirred at 50 ° C. for 1 h. Transparent purple, 135 nm thick layers are obtained after coating a quartz substrate.

UV _max = 330 nm; χ ³ (THG) = 5.9 · 10 ^-11 esu).

Claims (1)

NLO-active mixture, the matrix of polymeric silicon or ganic connections is established, as it is after the so-called. Sol-gel processes can be obtained and stored in the matrix containing an NLO active connection.