CA1321065C - Film comprising at least one unimolecular layer - Google Patents

Abstract

Abstract of the disclosure Film comprising at least one unimolecular layer A film for use in nonlinear optics comprises at least one Langmuir-Blodgett layer, the layer containing or comprising a dye of the formula

Description

hOECHST AK~IENGESELESCHAFT HOE 87~F Z14 K Dr. SP/fe Description Film comprising at least one uni~olecular layer The invention relates to a film comprising at least one uninolecular layer, which f;lm can be used for the pur-pose of nonlinear oPtics.

Nonlinear optics (NL0) is of great importance for the future development of ;nformation technology due to its potent;al for rapid s;gnal processing and transfer, and for ne~ methods ;n data process;ng. Spec;f;c organic sompounds are ~ore effect;ve and have faster switch-ing times than the customary inorganic substances for nonlinear optics.

A substance has nonl;near optical properties if the polarization P produced by the interaction between the substance and a strong electr;cal f;eld (a laser beam or a strong direct-current f;eld), is dependent on h;gher powers of the field strength, according to equat;an (1):
P = X(l) El + x(2) ElE2 ~ X(3) . ElE2E3 ~ ... (1) X(1)' X(2) and X(3) are the so-called 1st, 2nd and 3rd order suscePtibilities. E is the electrical field, which ~ay contain components of several frequencies. Due to NL0 interactions, fields of new frequencies can be genera-ted and the refractive ;ndices of the material can be altered. The susceptibilities x(2) and X(3) depend on 3û the so-called molecular hyperpolarizabilities B and y.

Inportant nonlinear optical effects which are dependent on x~2) are frequency doubling of a light beam, ;n par-t;cular a laser beam, parametr;c amplificat;on of a ~eak light signal and electroopt;cal convers;on of electrical signals. In order to ach;eve 2nd order effects, the active molecules must be al;gned non-centrosymmetrically since x(2) = 0 for centrosymmetric substances.

A process ~hich can produce an orclered alignment ~hich is particularly favorable for NL0 is the Langmuir-Llodgett (LE) process. In this process, molecules are spread on a ~ater surface, arranged parallel by reducing the area per molecule, and absorbed onto a substrate at constant shear by dipping and withdra~al of a base material. In each dipping operation, a unimolecular layer is trans-ferred ~hile retaining its order. In order to build up LY layers, amphiphilic molecules, i.e. molecules ~hich have a hydrophilic end (a "head") and a hydrophobic end (a "tail") are used.

In order to produce L~ layers having high 2nd order sus-ceptibilities, organ;c compounds are prepared which have both high 2nd order molecular hyperpolarizabilities and amphiphilic properties. A compound has a high value for B if ;t contains a conjugated electron system (for exam-ple a benzene ring) into vhich one or more electron-donor groups and one or more electron-acceptor groups are incorporated. A hydrophobic group is incorporated at the donor or acceptor end. The hyperpolarizability is in-creased if the molecule absorbs light in the ~avelength range of the incident electrical field or of the field produced by the NL0 (so-called resonance amplification).
However, absorption is undesired in many applications since it causes losses and adversely affects the optical stability ~the light intensity ~hich can be ~ithstood ~ithout permanent material damage). An ideal compound has a high hyperpolarizab;lity without absorbing exces-sively in the desired uavelength region.

It has been found that certain amphiphilic dyes havethese properties.

The invention thus relates to the film described in the claims.

The film according to the invention comprises at least one unimolecular layer ~hich contains or comprises an amphiphilic compound of the formula (I) R1 ~ CH~N-N~- ~ ~2 (I) in which R1 denotes the CH3- (CH2)m-0-CH3- (CH2)n~ ~ -o CH3 (C~2)nN(CH2)lH or CH3 (CH2)n(CO)N(CH2)lH radical and m i5 a number from 10 to 25, preferably 15 to 19, n is a number from 8 to 22, preferably 10-14, and l is a number from 0-25, preferably 0-4 or 14-22.

In the layer, the molecules of the compound of the formula (I) are oriented in the same direction, parallel to one another and non-centrosymmetrically. In many cases, they are essentially perpendicular to the layer plane, which is advantageous.
In order to build up relatively thick films while reta;n-ing the non-centrosymmetry, the film according to the invention comprises at least two unimolecular layers of different composition. In most cases, adjacent layers e~ch have different composition. However, the different co~position is not a basic prerequisite. For example, a layer ~hich contains or comprises a compound of the formula (I) alternates with a layer which does not contain or comprise a dye of the formula I but contains or comprises another amphiphilic compound, in particular ~ithout a chromophore. The layers which comprise a com-pound of the formula (I) may also contain small amounts of salts or the sub-phase used during spreading.

If A1, A2 and A3 denote different amphiphiles ~ithou~ a chromophore and if F1, F2 and F3 denote different dyes of the formula I, various ways of bu;ld;ng up the layer can be illustrated schemat;cally as follows:

1 32 1 06~

Fl/F2/Fl/F3 Al/Fl~Al/Fl Al/Fl/A2/A2 Fl/Al/A2/A3 Fl/Fl/Fl/Fl Fl/F2/Fl/F2 Fl/F2/Al/A2 Fl +Al/F2/Fl/F3 Al/Fl~Al/Al/F2+A2 Al +Fl/Al/A2/A3 Al +Fl/A2 +F2/Al +Fl/A2 +F2 Amphiphilic compounds simuttaneously contain at least one hydrophiLic and at least one hydrophob;c group in the molecule.

~he hydrophobic part of the second amphiphilic compound should have a certain minimum length. It is preferred for the second amphiphilic compound to contain at least one hydrophobic part containing at least 8 carbon atoms and at least one of the follo~ing polar groups: ether, hydroxyl, carboxylic acid, carboxylate, amine, carboxa-mide, ammonium salt, sulfate, sulfonic acid, phosphoric acid, phosphonic acid, phosphonate, phosphonamide, phos-phoric acid ester or phosphoramide group.

It is preferred for the amphiphilic compound to comprise t least one hydrophobic part having at least 8 carbon atoms and at least one polar part which ;s selected from the follo~ing groups -oR5 - CoOR3 ~R5 -N
~ R6 -N B
~J

' /~

\ R6 -N~ CoR4 ~ R5 ~ R7 _opotoR3)(oR4) -E
_0-E
-NR3-E, where R3 to R7, 0 and E have the following meanings:
R3 and R4, independently of one another, denote H or C1-C3-alkyl, R5, R6 and R7, independently of one another, denote H, C1-C4-alkyl, -C2H40H or -CH2-CHOH-CH3, in particular H or CH3 B denotes a divalent organic radical, so that -N 8 forms a nitrogen-containing hetero-cyclic ring, in part;cular a 5- or 6-mem-bered, saturated or unsaturated heterocyclic ring containing 1 to 3 carbon atoms or nitrogen and oxygen atoms or nitrogen and sulfur atoms~ and E denotes _P(O) R9 or p~o) 0~9, where R8 and R9, independently of one ancther, represent ~N
R

For example, the amphiphil;c compound may be a fatty acid of the general formula II
CH3(cH2)mco2H (II) ~here m denotes a number from 8 to 25, preferably 12 to 22.
The amphiphilic compound employed is advantageously an unsaturated acid amide of the general formula lII

H - (CH2)r N - C - C = CH - R2 (III) H - (CH2)s O R1 in ~hich R denotes H, Cl, F, CN or (CH2)tH, R2 denotes H, (CH2)UH or -CH=CH-(CH2)UH, r and s, independently of one another, denote a number from 0-22 and t and u, independently of one another, denote a number from û-24, in particular 0-18.
r is preferably a number from zero to 18 and s i5 pre-ferably zero.

Production of films and unimolecular layers by means of the LB technique usually takes place on water surfaces.
It is therefore preferred for the amphiphilic compound to have only low water solubility, in particular a water solubility of less than 5 g/l at 20C.

In order to achieve sufficiently low ~ater solubility of this amphiphilic compound, it is preferred that at least one of the values for r, s, t and u is at least 10. How-ever, ;t is not necessary that all the values are at least 10. A particularly preferred possibility is that one of the values for t and u is at least 10 and the other value is a maximum of 1. Another particularly pre-ferred possibility is that the value tor r is at least 10 and the values for t and u are a maximum of 1.
It is a~so possible to employ as amphiphilic compound saturated acid amides of the general formula IV

H - (CH2)r / N - C - (CH)tH (IV) H - (CH2)~

~here r and s, independently of one another, denote a number from 0-22 and t denotes a number from 0-24, and at least one of the values for r, s and t ;s at least 8.

Here too, it is appropriate, in order to achieve adequate hydrophobicity, that at least one of the values for r, s and t is at least 10. A particularly preferred possibility is that the values for r and s are a maximum of 1 and the value for t ;s at least 10. Another particularly pre-ferred possibility is that the vaLue tor r is at least 10 and the value for t is a maximum of 1.

It is favorable if the chain lengths of the amphiphilic dyes and of the second amphiphilic compound employed are matched to one another. It is therefore preferred that the length of the alkyl chain of the amphiphilic phenyl-hydrazone ~dye) and of the hydrophobic part of the second amphiphil;c compound employed differ by a maximum of 1 nm.
If the second amphiphilic compound should contain tuo or more hydrophobic parts, the longest hydrophobic part is the decisive factor.

1 32 1 06~

ln order to produce the films according to the invention, the compounds of the formula I and/or the chromophore-free amphiphilic compounds are app~ied (spread) in a high-volatility solvent onto the surface of the sub-phase in a Langmuir-Blodgett film balance. The solvent evaporates and the compounds remain on the surface. The mean area per molecule is calculated from the dimensions of the surface, the spread volume and the concentration of the solution.
~he spread molecules are pushed together us;ng a barrier, the chains being oriented essentially perpendicular to the boundary layer as the density increases. Phase transitions during compression of the molecules can be detected in the shear area isotherms. Phase states can be detected in the shear area isotherms~ During compres-s;on, self-organ;zat;on of the molecules ;n the boundary layer causes production of a highly ordered, unimolecular tilm whose constant layer thickness is determined by the chain lengths of molecules. Typical thickness of a film of this type is bet~een 2 and 3 nm, ~hich corresponds approximately to the length of the longest molecules in the ~ayer.

Depending on the hydrophilicity of the substrate (= base material), the hydroph;lic or hydrophobic ends of the amph;philic molecules appl;ed (including the dye) face the substrate.

The unimolecular layer ;nitially formed on the ~ater sur-face is removed from the ~ater surface ~;th retention of the molecular order by immers;on and removal of a clean su;table base material. By repeating this process, several unimolecular layers can be applied successively, and the thickness of the film obtained can thus be varied.
Sù;table base materials are solids having clean surfaces, such as, for example, glass, ceramic or metal sheets, plastic sheets made of, for example, PMMA, polystyrene, po~ycarbonaee, po~yethylene, polypropylene or polytetra-f~uoroethylene, or metallic coatings on the substrates mentioned. Furthermore, meta~ foils can be used as base ~aterials. In this case, ho~ever, the nonlinear optical properties can only be observed in reflected light.

In order to experimentally determine the value for the 2nd order susceptibility tX(2)), the phenomenon of fre-quency doubling, in which incident light of frequency is converted in ar, active substance into light of fre-quency 2~.

The film according to the invention, in particular if it contains alternating layers of compounds of the formula (I) and other amphiphilic compounds, produces a stable multilayer having good nonlinear optical properties. It is therefore suitable, for example, for electrooptical switches, diode laser frequency doublers or optical para-metric ampl;fiers, for example as so-called boosters for ~eak light signals in optical signal communication net-works.

For specific applications, for example the construction of planar nonlinear optical fibers using light of certain polarization, it is advantageous for the chromophores of the dye (so-called active groups) to be oriented essen-tially perpendicular to the surface of the substrate (of the base ~aterial of the layer). In the case of some dyes, however, it is apparent that the chromophores are oriented essentially parallel to the surface, although the long hydrophobic alkyl chains are oriented essentially perpendicular.

This also applies to the above-described dyes of the formula (I) containing an acyloxyphenyl group.

It has been found that an essentially perpendicular orientation of the chromophores in these dyes can be achieved by depositing the dyes in mixtures with other -- ~o --amphiphilic substances in unimolecular oriented layers.

In this case, it is necessary, with respect to the con-sentration of the other amphiphilic compounds, that cer-S tain concentrations are observed. If their amount isless than 10 mol-%, only a weak orientation effect is observed, or none at all.

A preferred embodiment of the invention therefore con-cerns a film comprising at least one unimolecular layer vhich contains, besides the amphiphilic phenylhydrazone of the general formula (Ia) CH3(CH2)n ~ ~ ~ ~ -CH = N - NH ~ - N02 (Ia), at least one further a~phiphilic compound in a proportion from 10 to 90 mol-X. The sum of all amphiphilic com-pounds here is 100Z. In this case, phenylhydra~ones in vhose general formula n has a value trom 10-14 are pre-ferably used.

The intended effect occurs particularly clearly when theproportion of the second amPhiphilic compound is 40-75 ~no l -X .
Even the film according to the invention applied to the base naterial, vhose layers contain dyes of the formula Ia containing acyloxy groups and amphiphilic compounds, is stable and has good nonlinear optical properties.
The molecules are arranged parallel and in the same direc-tion, i.e. non-centrosymmetrically~ Ey adding this amphiphilic compound, tilms can be obtained in which not only the hydrophilic part, but also the chromophore, of the dye molecules is oriented perpendicular to the layer plane.

The dyes of the general formula I can be obtained as follows:

1) Ethers Alkyl bromide + p-hydroxybenzaldehyde -->
p-alkoxybenzaldehyde p-alkoxybenzaldehyde + p-nitrophenylhydrazine -->
the corresponding nitrophenylhydrazone.

2) Esters Acyl chloride + p-hydroxybenzaldehyde -->
p-acyloxybenzaldehyde.
p-Acyloxybenzaldehyde ~ p-nitrophenylhydrazine -->
the correspond;ng nitrophenylhydratone.

3) Monoalkylam;nes Carboxylic acid + aniline --> acylaniline.
Acylaniline + lithium aluminum hydride --> monoalkyl-aniline.
Monoalkylalanine + dimethylformamide/phosphorus oxy-chloride --> p-monoalkylaminobenzaldehyde (Vilsmeier) p-Monoalkylaminobenzaldehyde + p-nitrophenylhydrazine -->
Z0 the correspond;ng nitrophenylhydrazone.

4) Dialkylamines Excess of alkyl bromide + aniline --> N,N-dialkylaniline.
Introduction of an aldehyde group using dimethylforma-mide t= DMF)/phosphorus oxychloride --> p-dialkylamino-benzaldehyde.
p-Dialkylaminobenzaldehyde + p-nitrophenylhydrazine -->
the corresponding nitrophenylhydrazone.

5) Amide p-Monoalkylaminobenzaldehyde (cf. 3.) + acyl chloride --> p-(N-acyl-N-alkylamino)benzaldehyde.
From this, the corresponding nitrophenylhydrazone by means of p-nitrophenylhydraz ine.

6~ Dialkylamine containing different alkyl groups Alkylaniline + acyl chloride -->
N-a(kyl-N-acylaniline. Reduction using lithium aluminum hydride --~ p-(N-alkyl1-N-alkylz-amino)benzaldehyde~

From this, the corresponding nitrophenylhydrazone by means of p-nitrophenyLhydrazine.
The following Examples illustrate the invention.

Exa~ple 1 CH3- ~ CH2 ) 1 6-C ~ CH~N-NH ~ N2 6.11 9 of 4-hydroxybenzaldehyde ~ere dissolved in 200 cm3 of dry methylene chloride, 8 cm3 of tr;ethylam;ne ~ere added, and the solut;on was cooled to 5C in an ice bath.
15.1 9 of stearyl chloride, dissolved ;n 100 cm3 of dry methylene chlor;de, ~ere added drop~ise at this tempera-ture over the course of 20 minutes. The reaction solu-t;on ~as subse4uently ~ashed ~ith 1 M HCl, ~ater, 5X
strength Na2C03 solution and again ~;th water, the organ;c phase ~as dried using sodium sulfate, and the solvent ~as stripped off in vacuo. For purification, the product was recrystallized twice from methanol.
Melting range: 59.5-60.5C Yield: 12.74 9 3.89 9 of the stearate uere added to a solution of 1.53 9 of 4-nitrophenylhydraz;ne in a mixture of 10 cm3 of glacial acetic acid, 10 cm3 of uater and 100 cm3 of ethanol. ~he mixture uas stirred at room temperature for t~o hours, and the orange precipitate ~as filtered off under suction and recrystallized several times from methanol, ethyl acetate and acetone.
~elting range: 131-134C Yield: 1.28 9 Exa-ple 2 CH3-~cH2) 15-O~CH-N-lJH~No2 11.6 g of potassium carbonate vere ignited for 2 hours at 80~C and, after cooling, suspended in a solution of 9.77 g of 4-hydroxybenzaldehyde, 24.43 9 of 1-bromohexa-decane and 100 mg of potassium iodide in 600 cm3 of dry acetone. ~he suspension uas refluxed for 60 hours ~ith exclusion of moisture and subsequent~y filtered whilst hot. 600 cm3 of hexane were added to the filtrate, and the solution was washed with 10% strength Na2C03 solution and water. The organic phase was dried using sodium sul-fate, and the solvent was stripped off in vacuo. The product was subsequently recrystallized again from methanol.
Melting range: 51-59C Yield: 14~7 9 3.47 9 of the hexadecyl ether were added to a solution of 1.53 g of 4-nitrophenylhydrazine in a mixture of 10 cm3 of glacial acetic acid, 10 cm3 of water and 1ûO cm3 of ethanol, and the mixture was stirred at room temperature for 2 hours. The orange precipitate was fiLtered off under suction and recrystallized several times from ethyl acetate.
Melting range: 115-117C Yield: 3.16 9 Exa-ple 3 A silicon plate t4 cm x 1 cm) was cut out of a sil;con wafer and cleaned as follows:

1) Treatment for 1 hour in an ultrasound bath in a mix-ture comprising one part of 3û~ strength H202 and four parts of concentrated sulfuric acid. Subsequently rinse with clean water.

2) Dip for 20 setonds into an ammonium fluoride-buffered HF solution and subsequently rinse with clean water.
After this treatment, the silicon plates were hydrophobic ~contact an~le with water: 75C).

Layers of N-octadecylacrylamide were transferred onto the silicon plate by the method of Langmuir and ~lodgett by spreading 0.1 cm3 of a 10 4 molar solution of N-octadecyl-acrylamide in n-hexane on an aqueous sub-phase on the tank of a Langmuir film balance. By reducing the size of the monofilm-covered water surface, the shear was adjusted to 25 mN/m and kept constant at th;s value (area require-ment at this shear: 0.21 nm2/molecule). The s;Licon plate was then dipped vertically from above through the ~ater surface into the tank of the film balance ~dipping speed: 20 mm/min) and removed again after a short pause (10 seconds) at the lo~er reversal point (removal speed:
10 mm/min). Both during the dipping and removal opera-tion, a monolayer ~as transferred onto the sil;con plate.
~y repeating the dipPing operation and by varying the dipping depth, 10, 20, 30, 40 and 50 layers ~ere trans-ferred in this ~ay onto a base material. ey means of ellipsometer measurements, the thicknesses and refractive index of the L9 films ~ere subsequently measured.
(Result: layer thickness: 2.41 nm per monolayer; refrac-tive index 633 nm: 1.51) Ex~-ple ~

23.28 9 (0.25 mol) of freshly distilled aniline and 167.94 9 (0.55 mol) of 1-bromohexadecane uere combined and stirred for 3 days at 90C under a nitrogen atmos-phere. 700 ml of toluene uere then added, and the mix-ture Yas uashed by shaking uith 10% strength Na2C03 solu-tion. The ~ixture ~as subsequently acidified using 5%
strength HCl, and the precipitated hydrochloride ~as fil-tered off. A further 700 ml of toluene ~ere then added, the mixture was ~ashed by shaking uith 10X Na2C03, the organic phase was dried using Na2S04, and the solvent ~as r--oved under reduced pressure. After recrystallizing t~ice from ethanol, 56.5 9 (42X of theory) of colorless crystals ~ere obtained uhich melt at 48-49C.
A slurry of 10 9 (18.5 mol) of N,N-dihexadecylaniline in 20 9 of freshly distilled DMF uas cooled to 5C, and 2.8 9 ~18.5 mmol) of F'OCl3 ~ere added over the course of 5 minutes. ~hen the addition ~as complete, the mixture ~as stirred at 20C for one hour and at 80C for 3 hours.
After cooling, the reaction mixture was decomposed using 40 9 of ice ~ater and neutralized using 10 ml of 5 M
NaOH solution. The precipitate produced uas filtered off - , ~

under suction and recrystallized from methanol and hex-ane. 5.1 9 (48~ of theory) of colorless crystals of elting point 56-57C uere obtained.

0.1 9 (0.18 mmol) of N,N-dihexadecyLaminobenzaldehyde and 0.4 9 (2.6 mmol) of 4-nitrophenylhydrazine ~ere dissolved by warming briefly in a mixture of 5 ml of glacial acetic aeid, 3 ml of water and 30 ml of ethanol. After the mix-ture had been left to stand overn;ght, the dark red crys-tals produced uere filtered off ancl recrystallized from hexane and methanol. 50 mg (39~ of theory) of red crys-tals of melting point 47C uere obtained.

Elemental analysis: C H N
15 calculated: 76.65Z 10.86~ 7.95 found: 76.14X 10.78X 7.80 Exa-ple S

~ silicon plate ~as cleaned as in Example 3 and coated, - analogously to Example 3, vith 10, 20, 40 and 60 mono-l~yers of the dye from Example 2 by the Langmuir-Blodgett proeess (sub-phase: water; temperature: 20C; shear:
35 mN/m; area requirement: 0.26 nm2/molecule; d;pping speed: 20 mm/min; removal speed: 10 mm/min). The layers ~ere investigated ellipsometrically as in Example 3. The layer thickness determined therefrom ~as 2.75 nm per onolayer and the refractive index at 633 nm uas 1.58.

Exa-ple 6 .
~s in Example 5, 10, 20, 40 and 60 monolayers of the dye synthesized according to Example 1 were transferred onto a silicon plate and the ellipsometric layer thickness and refract;ve index at 633 nm were determined. The layer thickness per monolayer uas 2.75 nm and the refractive index uas 1.58.

Exaople 7 A glass speciTen slide (76 mm x 26 mm) was cleaned by the following method:
The glass was subjected to ultrasound for one hour in a mixture comprising one part of 30X strength hydrogen per-oxide and four parts of concentrated sulfuric acid. The specimen slide was then rinsed with water and treated with ultrasound for 15 minutes at 50C in a cleansing solution (2-4 g/l). The slide was subsequently again rinsed thoroughly with clean water.
The specimen slide thus treated was dipped into the aqueous sub-phase in a Langmuir film balance~ the dye synthesized in Example 1 ~as spread on the water surface and compressed, and the glass slide was removed from the sub-phase (sub-phase: water; temperature: 20C; shear:
35 oN/m; area requirement: 0.24 nm2/molecule; removal speed: 10 mm/min). During this operation, a monolayer vas transferred onto both the front and back of the glass plate.
The coated glass plate was clamped into the sample cham-ber of an apparatus for determining the nonlinear opti-cal susceptibility and was measured. The 2nd order sus-ceptibility was 0.56 x 10 6 esu and the nonlinear polari-zation uas 108 x 10~3 esu.

The apparatus for determining the nonlinear optical susceptibility uorks as follows:

An Nd:YAG laser generates a pulsed laser beam of wave-lcngth 1,064 nanometer ~ ~ 9,398 cm 1), which is split into 2 sub-beams by a semi-transParent mirror. The first ; sub-beam is converted, by frequency doubling in a refer-ence samPle~ into a reference beam of wavelength 532 nano-meters ~2w = 18,796 cm 1), which is measured by a photo-multiplier. The second sub-beam hits a glass slide, on both sides of which the Langmuir-81Odgett layer to be investigated has been applied. The direction of the laser beam forms an angle ~ with the perpendiculars to the glass slide p(ane. After irradiation of the Langmuir-~lodgett layer, the light beam Likewise contains light of frequency 2~. The basic wave (w) remaining is then absorbed by filters. The intensity of the ~frequency-doubled) beam remaining is measured by a second photo-multiplier. The intensity is divided by the intensity of the reference signal in order to be able to compensate for variations in the laser power in the calculat;ons.
The dependency of the standardized signal on the angle of rotation 6 is observed or calculated. The second order susceptibility and the orientation of the chromo-phores on the surface can be determined from the amplitude and angle dependency of the fre~uency-doubled signal.
The thickness and refractive inde~ of the LB layer, which are likewise involved in the calculation, can be deter-mined by ellipsometry.

Exa-ple 8 A glass sPecimen sl;de was coated as in Example 7 with a monolayer of the dye synthesized in accordance with Example 2, and the susceptibility and the nonlinear polar;zation were measured. The 2nd order susceptibility was 1.7 x 10 6 esu and the nonlinear polarization ~as 325 x 10 30 esu.

Exa-ple 9 A glass specimen slide was cleaned as in Example 7 and coated with a monolayer of N-octadecylacrylamide ~sub-phase: water; temperature: 20C; shear: 25 mN/m;
removal speed: 10 mm/min). The film was then absorbed from the water surface of the film balance, the dye syn-thesized in accordance with Example 2 was spread, and a dye monolayer was transferred by dipping in the base material (shear: 35 mN/m; dipping speed: 20 mm/min).
The dye film ~as subsequently absorbed from the water sùrface, N-octadecylacrylamide was spread, and a mono-layer was again transferred on removal after dipping.

This procedure was continued until an alternating film comprising 3 layers of acrylamide and 2 layers of dye had been built up. The 2nd order susceptibility was oeasured on this film as in Example 7. Its value was 0.27 x 10-6 esu.

Exa~ple 10 CH3-(CH2)14~ o- ~ -CH=N-NH- ~ -No2 6.11 9 of 4-hydroxybenzaldehyde were dissolved in 200 ml of dry ~ethylene chloride, 8 ml of triethylamine were added, and the solution was cooled to 5C in an ice bath.
13.7 9 of palmityl chloride, dissolved in 100 ml of dry methylene chloride, were added dropwise at this tempera-ture over the course of 30 minutes. The reaction solution was subsequently washed with 1 M hydrochloric acid, water, 5X strength Na2C03 solution and again with water, the orgamic phase was dried using sod;um sulfate, and the solvent ~as str;pped off in vacuo. For purification, the p-palmitoyloxybenzaldehyde was recrystallized fro~
nethanol.
Melting range: 6O-71C
Yield: 14.02 9 3.16 9 of the palmitate were added to a solution of 1.53 9 of 4-nitrophenylhydrazine in a mixture of 10 ml of glacial acetic acid, 10 ml of water and 100 ml of ethanol. The mixture was stirred at room temperature for two hours, and the orange precipitate was filtered off under suction and recrystallized twice from methylene chloride and once from methanol.
Melting range: 129-132C
Yield: 2.51 9 Exa-ple 11 Six glass specimen slides (76 mm x 26 mm) were cleaned .

_ 19 _ by the following method:
The glass was treated with ultrasound for one hour in a mixture comprising one part of 30~ strength hydrogen per-oxide and four parts by volume of concentrated sulfuric S acid. The specimen slide was subsequently rinsed with water and treated with ultrasound for 15 minutes at 50C
in a soLution of alkaline cleanser (4 g/l of Extran(R) liquid from Merck AG). The slide was subsequently rinsed thoroughly with clean water.
~ixtures of the dye synthesized in Example 10 and N-octa-decylacrylamide in the molar ratios 95:5, 90:10, 80:20, 60:40 and 40:60 were prepared.

For each mixture, a cleaned object slide was dipped into the aqueous sub-phase in a Langmuir film balance, the dye/N-octadecylacrylamide mixture was spread c,n the sur-tace and compressed, and the base material was removed from the sub-phase. During this procedure, a monolayer 2~ was transferred onto both the front and back of the glass plate. ~Absorption conditions: sub-phase water, tempera-ture 20C, shear 30 mN~m, removal speed 1.5 cm/min).

The coated glass plates were clamped into the sample chamber of an apparatus ~or determining the nonlinear optical susceptibility and ~easured as described in Example 7. From the measurement results, it was possible to determine that the chromophores ;n the layers of the oixtures having the ratios 95:5, 90:10 and 80:20 (dye/N-octadecylacrylamide) ~ere essentially parallel to thesurface. However, the chromophore is oriented essentially perpendicular to the surface in layers of mixtures con-taining an N-octadecylacrylamide proportion of 40 mol-%
or more.
Exa-ple 12 Five glass speci0en slides were cleaned as in Example 11.
~ixtures of the dye synthesized in Example 10 and paLmitic . ' ~

1 32 1 ()65 acid were prepared in the mo~ar ratios 95:5 90:10 80:20 60:40 and 40:60.

For each mixture a monolayer ~as absorbed onto a base material as in ExampLe 11 tsame absorption conditions).
The coated glass plates were clamped into the specimen chamber of the apparatus for determining the nonl;near optical susceptibiLity and measured. From the measure-ment results it was possible to determine that the chro-mophores were essentially parallel to the surface in thelayers of the mixtures having the molar ratios 95:5 90:
10 and 80:20 (dye/palmitic acid) but were oriented essentially perpendicular to the surface in the layers of the mixtures having a palmitic acid content of 40% or more.

Claims (23)

1. A film comprising at least one unimolecular layer of an amphiphilic compound, wherein the layer contains or com-prises a compound of the formula (I) (I) in which R1 denotes the CH3-(CH2)m-O- , , CH(CH2)nN(CH2)1H or CH3(CH2)n(CO)N(CH2)1H radical and m denotes a number from 10 to 25, n denotes a number from 8 to 22 and l denotes a number from 0-25, the molecules thereof being oriented in the same direc-tion, parallel to one another and non-centrosymmetrically.

2. A film as claimed in claim 1, which comprises at least two unimolecular layers of different composition, in each case one layer containing or comprising a compound of the formula (I) alternating with a layer containing or com-prising another amphiphilic compound.

3. A film as claimed in claim 2, which comprises at least two unimolecular layers of different composition, in each case one layer containing or comprising a compound of the formula (I) alternating with a layer containing or com-prising an unsaturated amphiphilic compound.

4. A film as claimed in claim 3, wherein the unsaturated amphiphilic compound has the formula III

(III) in which R1 denotes H, Cl, F, CN or (CH2)tH, R2 denotes H, (H2)uH or -CH=CH-(CH2)uH, r and s, independently of one another, denote a number from 0-22 and t and u, independently of one another, denote a number from 0-24.

5. A film as claimed in claim 1, wherein the unimolecular layer additionally contains at least one second amphi-philic compound in a proportion of 10 to 90 mol-%, the sum of all amphiphilic compounds being 100% and R1 in the formula I denoting CH3(CH2)nCO2- where n = 8-22.

6. A film as claimed in claim 5, wherein n is 10 to 14.

7. A film as claimed in claim 5, wherein the proportion of the second amphiphilic compound is 40 to 75 mol-%.

8. A film as claimed in claim 5, wherein the second amphi-philic compound contains a hydrophobic part containing at least 8 carbon atoms and at least one of the following polar groups: ether, hydroxyl, carboxylic acid, carboxy-late, amine, carboxamide, ammonium salt, sulfate, sul-fonic acid, phosphoric acid, phosphonic acid, phosphon-ate, phosphonamide, phosphoric acid ester or phosphoramide group.

9. A film as claimed in claim 8, wherein the second amphi-philic compound comprises at least one hydrophobic part containing at least 8 carbon atoms and at least one polar part which is selected from the following groups -OPO(OR3)(OR4) -PO(OR3)(OR4) -E
-O-E
-NR3-E, where R3 to R7, B and E have the following meanings:
R3 and R4, independently of one another, denote H or C1-C3-alkyl, R5, R6 and R7, independently of one another, denote H, C1-C4-alkyl, -C2H4OH or -CH2-CHOH-CH3, B denotes a dlvalent organic radical, so that forms a nitrogen-containing hetero-cyclic ring, and or E
, where R8 and R9, independently of one another, represent

10. A film as claimed in claim 9, wherein the second amphi-philic compound is a fatty acid of the formula II

CH3(CH2)mCO2H (II), where m denotes a number from 8 to 25.

11. A film as claimed in claim 8, wherein the second amphi-philic compound has the formula III
(III) in which R1 denotes H, Cl, F, CH or (CH2)tH, R2 denotes H, (CH2)uH or -CH=CH-(CH2)uH, r and s, independently of one another, denote a number from 0-22, find t and u, independently of one another, denote a number from 0-24.

12. A film as claimed in claim 11, wherein at least one of the values for r, s, t and u is at least 10.

13. A film as claimed in claim 12, wherein one of the values for t and u is at least 10 and the other value is a maxi-mum of 1.

14. A film as claimed in claim 12, wherein the value for r is at least 10 and the values for t and u are a maximum of 1.

15. A film as claimed in claim 8, wherein the second amphiphilic compound has the formula IV
(IV) where r and s, independently of one another, denote a number from 0-22 and t denotes a number from 0-24, and at least one of the values for r, s and t is at least 8.

16. A film as claimed in claim 15, wherein at least one of the values for r, s and t is at least 10.

17. A film as claimed in claim 16, wherein the values for r and s are a maximum of 1 and the value for t is at least 10.

18. A film as claimed in claim 16, wherein the value for r is at least 10 and the value for t is a maximum of 1.

19. A film as claimed in claim 8, wherein the length of the alkyl chain in the amphiphilic phenylhydrazone and of the hydrophobic part of the second amphiphilic compound employed differ by a maximum of 1 nm.

20. A film as claimed in claim 5, wherein the second amphiphilic compound has a water solubility at 20°C of less than 5 g/l.

21. A film as claimed in claim 10, wherein m denotes a number from 12 to 22.

22. A film as claimed in claim 9, wherein R5, R6 and R7, independently of one another, denote H or CH3.

23. A film as claimed in claim 9, wherein forms a 5- or 6-membered saturated or unsaturated heterocyclic ring having 1 to 3 carbon atoms or N and O atoms or N and S atoms.