GB2209169A - Polymer compound - Google Patents

Abstract

A siloxane polymer compound of the general structural formula: <IMAGE> has been observed to have nonlinear optical properties and may be deposited as a Langmuir-Blodgett film. The film may be used to produce planar and channel waveguides.

Description

POLYMER COMPOUND This invention relates to a polymer compound which has been found to be capable of use as an optical material. This can lead to the construction of an optical device, such as a planar or channel waveguide structure.

Organic materials are attractive for nonlinear optical devices due to their potentially large, fast-acting second and third order optical nonlinearities. For second-order nonlinear effects, such as frequency doubling and parametric amplification, ordered material structures are required. Additional benefits may be derived when the material can be formed as a thin film that can be used as an optical waveguide, in which high optical intensities can be achieved and maintained over long interaction lengths. Recent techniques for fabricating organic thin film structures have included single crystal growth and indiffusion. Langmuir-Blodgett (LB) multilayer deposition is an attractive alternative technique, enabling the fabrication of well controlled, highly ordered thin films, suitable for integrated waveguide and thin film optical devices.However, certain molecular design criteria have to be met to exploit this approach successfully. The molecular structure of most of the commonly reported nonlinear organic materials are unsuitable for deposition by the LB technique and molecular modifications are therefore necessary before they can be used. The present invention was devised to provide a new class of organic molecule, some examples of which can allow the fabrication of Langmuir-Blodgett films.

According to the present invention, there is provided a polymer compound of the following general structural formula:

where 1 = 1 to 99 ) The bars over 1, m and 1 + m m = 99 to 1 ) indicate mean values 1 + m = 2 to 100)

Q = -N=or-CH= G = -H or CH3 J = -H, o or -NO2 E = -H, o or -NO2 R = -H, -CN -NO2 or -CH3 Y = -H, -CN, -NO2 or -CH3,

nl = O to 18 (preferably 2 to 9) n2 = O to 6 In a first embodiment of the compound, X may be

with 1 = 24(+4) m = 10(+4) G,J & E -H Z = -CN nl =3 n2 = 0 In a second embodiment of the compound, X may be

with 1 = 24(t4) # = 10(#4) GJ#E = -H Z = -CN nl = 5 n2 = 0 In a third embodiment of the compound, X may be

with 1 = 24(#+4) # = 10 (+4) G,J & = -H Z = -CN nl = 10 n2 = 0 In a fourth embodiment of the compound, X may be

with 1 = 24(+4) m = 10(#4) GJ#E = -H Z = -CO2CH3 n1=5 n2 = 0 In a fifth embodiment of the compound, X may be

with 1 = 9(#2) # = 8(#2) G,J & = -H Z = -OH n1 =5 n2 = 2 In a sixth embodiment of the compound, X may be

with 1 = 9(+2) m = 8(#2) G,I & = -H

Z = -CO2H n1 = 5 n2 = 0 In a seventh embodiment of the compound, X may be

with 1 = 9(+2) m = 8(t2) G,J & = -H

z - #Cn3 nl = 5 D2 = 0 According to a feature of the invention, there is provided an optical element having non-linear optical properties comprising a substrate body supporting a layer of an organic material having the composition of any one of Compounds 1 to 7.

Preferably, the organic material is deposited on the substrate body by a technique which gives a high degree of control of the resulting film order and thickness. A deposition in the form of a multilayer coating may be used. One technique which has been found to be suitable is a dipping bath which enables a Langmuir Blodgett type of deposition to be effected. This allows the successive deposition of organised organic monolayers, the molecules of which have high nonlinear optical coefficients. Other possible techniques include crystal growth and a chemical vapour deposition process.

The invention further comprises a method for the preparation of an optical element having nonlinear optical properties, which comprises the step of passing a surface of a suitable substrate body into and out of a Langmuir trough containing a liquid carrying a superficial monomolecular layer of a material having the composition of any one of Compounds 1 to 7.

The invention further comprises an optical device, in which the optical element comprises multiple layers of a Langmuir-Blodgett deposited film having the composition of any one of Compounds 1 to 7, and which forms a region of high refractive index, which is supported on a substrate body formed of a lower refractive index material. The resulting device which provides defmition of a channel of high refractive index material will result in a two-dimensional confinement of the light which makes possible the construction of a range of planar waveguide structures. By using a photolithographic definition process, a channel waveguide structure can be produced which can have a width of a few microns.

Planar and channel waveguide structures provide a high degree of optical confinement which can be maintained over long lengths. This makes them very suitable for producing electro-opti and all-optical switching and signal processing devices with a low electrical or optical power consumption.

By way of example, some particular embodiments of the invention will now be described with reference to the accompanang drawings, in which: Figure 1 shows the chemical route used for synthesising Compounds 1 to 5, Figure 2 shows the route used for synthesising Compounds 6 and 7, Figure 3 is a sketch of a planar waveguide structure including a Langmuir-Blodgett deposited film of the invention; and, Figure 4 shows a channel waveguide structure including a similar film.

The evaluation of the polymer compounds and optical elements of the invention begins with the synthesis of the Compounds 1 to 7 which are derived from the aforementioned general structural formula.

The preparations of the compounds will first be described with reference to the chemical routes depicted in Figure 1 (for Compounds 1 to 5) and Figure 2 (Compounds 6 and 7) of the drawing.

SYNTHESIS OF COMPOUNDS 1 to 7 Alkvlations of 4-(4-hvdroxyphenviazo) benzonitrile (i) A mixture of 4-(4-hydroxyphenylazo) benzonitrile (2.23g, lOmmols), 4-brombut-l-ene (l.46g. limmols) and anhydrous potassium carbonate (1.51g, limmols) in dry butanone (5Oml) was stirred and heated under reflux for twentyfour hours. This mixture was then cooled and filtered and the residue washed with dry butanone (25ml). The filtrate was evaporated; flash chromatography of the residue (silica gel 2.8 x 10cm) elution with chloroform/petrol (2:1) gave orange elements which afforded 4-(4-but-3'-en- oxvphenylazo#benzonitrile, yellow needles from toluene solution, yield 1.665g (66%).

(ii) A mixture of 4-(4-hydroxyphenylazo) benzonitrile (2.23g, lOmmols), 6-bromohex-1-ene (l.79g, llmmols) and anhydrous potassium carbonate (l.51g, 1 immols) in dry butanone (50ml) was stirred and heated under reflux for twentyfour hours. This mixture was then cooled and filtered and the residue washed with dry butanone (24ml). The filtrate was evaporated; flash chromatography of the residue (silica gel 2.8 x 10cm) elution with chloroform/petrol (2:1) gave an orange eluate which afforded 4-(4-hex-5'-en oxvphenvlazo)benzonitrile. yellow plates from ethanol solution, yield 1.716g (61%).

(iii) A mixture of 4-(4-hydroxyphenylazo) benzonitrile (2.23g, 10mmols), 11-tosylundec-l-ene (3.57g, 1 immols) and anhydrous potassium carbonate (1.51g, llmmols) in dry butanone (50ml) was heated under reflux for twentyfour hours. This mixture was then cooled and filtered, the residue was washed with dry butanone (25ml). The filtrate was evaporated and flash chromatography of the residue (silica gel 2.8 x 10cm) elution with chloroform/petrol (2:1) gave an orange eluate which afforded 4-(4-undec-10'-en oxvphenvlazo)benzonitrile. yellow plates from ethanol solution, yield 2.541g, (72%).

(iv) Alkylations of methvl-4-(4-hvdroxvphenvlazo)benzoate A mixture of methyl-4-(4-hydroxyphenlazo)benzoate (2.56g, lOmmols), 6-bromohex-1-ene (l.79g, llmmols) and anhydrous potassium carbonate (1.51g, limols) in dry butanone (50ml) was heated under reflux for twentyfour hours. The mixture was then cooled and filtered and the residue washed with dry butanone (25ml). The filtrate was evaporated and flash chromatography of the residue (silica gel 2.8 x 10cm) elution with chloroformlpetrol (2:1) gave an orange eluate which afforded methyl-4-(4-hex-51-en- oxyphenylazo)benzoate, yellow microneedles from ethanol solution, yield 1.769g, (52%).

(v) Alkvlation of N-methylaniline 6-Bromohex-l-ene (16.30g, 100mmols) and N-methylaniline (10.7g, lOOmmols) were stirred at 100 C under nitrogen for twentysix hours. The mixture was then poured into water (lOOmI) and benzene (250ml) and sufficient saturated sodium bicarbonate solution added in order to basify the aqueous phase. The organic layer was then washed with water (x2) dried (MgSO4) and evaporated.Distillation of the residue afforded N-methyl-N-hex-5'- en-vlaniline, colourless oil, boiling point 1180C at 0.2mm Hg, yield 11.57g, (61%) (vi) Diazo Coupling Reaction of N-methyl-N-hex-5'-en-ylaniline Methyl-4-aminobenzoate (1.51 g, 1 Ommols) was dissolved in a mixture of concentrated hydrochloric acid (5ml) and water (20ml) and to the cooled solution (at a temperature below 5 C) was added sodium nitrite (0.76g, llmmols) in water (5ml). The solution was added to an ice cold mixture of N-methyl-N-hex-5'-en-ylaniline (1.89g, 10mmols), sodium acetate (2.5g). glacial acetic acid (2.5ml) and water (lOml) and the resulting solution was stirred overnight.

The mixture was poured into water and extracted with dichloromethane (200ml). The extracts were washed with saturated sodium bicarbonate solution, water, dried and evaporated. Flash chromatography of the residue (silica gel 2.8 x 10cm) and elution with chloroform gave orange-red eluates which afforded rnetbyl-4- (4-N-hex-5'-en-yl-N-methylaminophenylazo)benzoate as orange-red needles from methanol solution, yield 1.692g, (48%).

(vii) Esterification of 4-(4-N-hex-5'-en-yl-N-methylaminophenylazo)benzoic acid A solution of 4-(4-N-hex-5'-en-yl-N-methylaminophenylazo) benzoic acid (1.695g, 5mmols), imidazole (0.75g, llmmols) and tbutyldimethylchlorosilane (0.90g. 6mmols) in dimethyl formamide (25ml) was stirred overnight under nitrogen. The solution was then poured into water and extracted with petroleum ether (lOOml), the extract was washed with saturated sodium bicarbonate solution, water dried and evaporated. Flash chromatography of the residue petrolldichloromethane (2:1) gave red eluates which afforded t-butvldimethylsilvl-4-(4-N-hex-5'-en-vl-N-methvlaminophenylazo) benzoate. Red plates from aqueous ethanol, yield 1.875g (83%).

(viii) 4-Aminophenethylalcohol (6.86g, 50mmols) was dissolved in concentrated hydrochloric acid (1 8ml) and water (20ml) and to the cooled solution (at a temperature below 5OC) was added sodium nitric (lOg) in water (50ml) and the mixture was stirred overnight.

The solution was then acidified with 2M hydrochloric acid and the mixture extracted with chloroform (2 x 200ml). The extracts were washed with water (x2), dried and evaporated. Flash chromatography of the residue (silica gel 3.5 x 18cm) and elution with ethyl acetate gave yellow eluates which afforded 2-(4-(4-hydroxyphenylazo)phenyl)ethanol, yellow plates from aqueous ethanol, yield 9.464g (78%).

(ix) 2-(4-(4-hydroxyphenylazo)phenyl)ethanol (2.42g, 1 Ommols), 6bromohex-lene (1.79g, limmols) and anhydrous potassium carbonate (1.51g, llmmols) in dry butanone (some) was stirred and heated under reflux for twentyfour hours. The mixture was then cooled and filtered and the residue washed with dry butanone (25ml). The filtrate was evaporated and flash chromatography of the residue (silica gel 2.8 x 10cm) with chloroform/ethyl acetate (5:1) gave yellow eluates with afforded 2-(4-(4-hex-5'-en yloxvphenvl azo)phenvl )ethanol, yellow needles from toluene, yield 2.337g (72%).

(x) 2-(4-(4-hex-5'-en-yloxyphenylazo)phenyl)ethanol (1.62g, Smmols), (0.75g, 1 mmols) and t-butyldimethylchlorosilane (0.90g, 6mmols) in dimethylformamide (25ml) were stirred overnight under nitrogen. The solution was then poured into water and extracted with petroleum ether (100ml), the extract was washed with saturated sodium bicarbonate solution, water, dried and evaporated.

Flash chromatography of the residue (silica gel 2.8 x 30cm) and elution with petrol/dichioromethane (2:1) gave yellow eluates which afforded 2-(4-(4-hex-5'-en-yioxvphenvlazo)phenvl)ethvl-t- butyldimetbvlsilylether, orange plates from methanol, yield 1.878g (86%).

Standard Reaction Conditions for the hydrosilation of Poly(dimethvl.

bvdrogenmethylsil oxane) Copolymers ROUTEA To a solution of the chromophoric alkene (0.395g, 2mmols) and 65% polydimethyl 35 % polyhydrogenmethylsiloxane (2.2mmols) in toluene (50ml), heated under reflux under nitrogen, was added hexachloroplatinic acid (0.1 ml, 0.2% w/v in propan-2ol) and the solution heated for thirtysix hours. To the resulting solution was added oct-l-ene (0.Sml) and hexachloroplatinic acid (O.lml, 0 % w/v in propan-2-ol) and the solution was heated for a further twenty four hours. The purpose of the oct-l-ene addition was to 'mop-up' any unreacted silicon sites.The solution was then evaporated to dryness in vacuo and the residue dissolved in a minimum volume of dichloromethane. Methanol was then added to the solution until no further precipitation was noticed. The precipitation solution was centrifuged (5000 rpm) the supernatant liquid decanted and the precipitate dried.

This precipitation procedure was continued until no further unreacted chromophoric alkene could be detected by thin layer chromatography (t.l.c.) elution with dichloromethane.

At this point the precipitate was dried at 600C under high vacuum (0.2mmHg).

ROUTEB To a solution of the chromophoric alkene (0.134g, 4.4mmols) and 50% polydimethyl, 50% polyhydrogenmethylsiloxane (0.4 mmols) in toluene (50ml), heated under reflux under nitrogen, was added hexachloroplatinic acid (0.1 ml, 0.2% w/v in propan-2-ol) and the solution heated under reflux for thirtysix hours. To the resulting solution was added oct-l -ene (0.5ml) and hexachloroplatinic acid (O. lml, 0.2% w/v in IPA) and the solution heated for a further twentyfour hours. The purpose of the oct-lene addition was to 'mop up' any unreacted silicon sites. The solution was worked up as for Route A.

Removal of t-butvidimethvl silyl Protecting Group The protected polymer was dissolved in dichloromethane (50ml) and to the stirred solution under nitrogen was added borontrifluoride etherate (l.41g, lOmmols) and the resulting solution stirred for three hours. The solution was then poured into water and carefully neutralised with saturated sodium bicarbonate solution.

The organic phase was then dried (MgSO4) and evaporated and the resulting residue heated at 600C in vacuo (0.2mmHg).

mmols mmolsof backbone refers to mmols of SiH available in polydimethylipolyhydrogenmethylsiloxane.

Hexachloroplatinic acid was always freshly prepared, that is within four days.

All reactions under nitrogen/argon.

tl.c. plates: silica ROUTE A used for Compounds 1,2,3 and 4.

ROUTE B used for Compounds 5,6 and 7.

Physical data for products.

COMPOUNDS 1. IR vmax = 2220cm-1 (C = N); CT = 78 C 2. IR vmax = 2220cm-1 (C = N); K-N = 47 C, N-I = 78 C 3. IR vmax = 2220cm-1 (C = N); K-S = 40 C, S-N = 530C, N-I = 1070C 4. IR Vmax = 1710cm-1 (C = O); CT = 94"C 5. IR Vmax = 3320cm-1 (0 - H); CT = 800C 6. IR Vmax = 1680cm-1 (C = O); CT = 1480C 7. IR Vmax = 1710cm-1 (C = 0); compound an oil - no differential scanning calorimetry (DSC) information available.

Notes on transition temperatures: K = crystalline S = smectic liquid crystal S, -= phase type A of the polymorphic smectic state N = nematic liquid crystal I = isotropic liquid Cr = clearing temperature (it was not determined whether the material has a liquid crystal phase or not) Hence, a transition at w C from smectic to nematic liquid crystal is given as:S-N = x C (Also note m.p. = C-I) Physical data for intermediates COMPOUND PREPARED BY STEP: (i) Mass ion, M+ = 253; IR vrnax - 2200cm-1 (C=N); m.p. = 116 C (cooling I-N = 98 C, N-K =84 C) (ii) M+ = 281; IR vmax = 2200cm-1 (C=N); m.p. = l24 C (cooling I-N = l09 C, N-K = l05 C) (iii) M+ = 351; IR vmax - 2200cm-1 (C=N); m.p. = 132-4 C (iv) M+ = 338; K-SA = 1130C, SA-I = 1190C Heating K-SA = 115.6 , SA-I = 1190 ) by differential scan Cooling S-K = I-SA = 1160 ) ning calorimetry (DSC) (v) M+ = 189;; b.p. = 118 C at 0.2mmHg (vi) when X' = -CH3 M+ = 351; IR vmax = 1710cm-1 (C=O); m.p. = 63-5 C when X' = -H , = 337; IR Vmax = 1680cm-1 (C=O) and vmax = 2500 2690cm-1 (O-H); K-N = 1850C N-I = 200 C (decomp) (vii) M+ = 451; IR Vmax = 1695cm-1 (C=O); m.p. = 62-4 C (viii) M+ = 242; IR vmax = 3400 and 3060cm-1 (O-H); p. = 195-7"C (ix) Me = 324; IR vmax = 3340cm-1 (O-H); mp. = 81-3"C (x) Me = 438;; mp. = 380C Following synthesis and purification of each compound, a solution of known concentration of the material under test is made up using a suitable solvent, for example chloroform.

By use of the Langmuir Trough unit it is possible to form a monomolecular layer on a substrate base and this operation is capable of being carried out under accurately reproducible conditions. The organic material to form the monomolecular layer in a suitable solution is first deposited on the surface of a suitable liquid subphase (usually highly purified water), the temperature and pH of which have been correctly optimised The liquid subphase is contained in the trough of the Langmuir unit and the accurately measured amount of organic material solution is deposited within part of the subphase surface that is capable of being confined within a movable surface barrier which defines a working area on the liquid surface. Upon evaporation of the solvent, individual molecules of the organic material are left floating on the subphase surface. By suitably moving the surface barrier, the working surface area may be compressed and the molecules can be made to form a quasi-solid layer one molecule in thickness.

The stability of the test monolayer is capable of being monitored by measuring the change in surface area with time at a preset surface pressure under given subphase conditions.

To form a multilayer of the material of the test monolayer requires the use of a dipping mechanism which is part of the Langmuir unit and which is normally housed on a gantry located above the trough. The mechanism includes a screw thread drive arrangement to which an appropriate body of a selected substrate material can be attached. Examples of common substrates are silicon wafers (n- type or p- type), glass or evaporated metals, the surfaces of which have been chemically treated to ensure cleanliness and the presence of a hydrophilic or hydrophobic surface condition. The substrate is lowered and raised through the subphase-monolayer interface such that a transfer of the monolayer material from the subphase to the substrate surface takes place. By repeating this cycle, a multilayer deposit of the organic material can be built up upon the substrate body.

Material Properties This section relates to the Langmuir-Blodgett and optical properties of the materials. It is to be noted that Compounds 1,6 and 7 have been prepared but not yet assessed.

Compound 2 A stable monolayer is not formed, film instability (possibly collapse of the monolayer) occurring at 15-18mNm-1. The monolayer is expanded (not condensed) and changing the subphase pH (from 2.0 to 12.0) causes little change in the isotherm (it-A behaviour), apart from a tendency to slightly more expanded behaviour at high pH when # < 10mNm-1.

Compound 3 Similar behaviour to Compound 2 with it = 15-18mNm-1, although no pH effects are observed over the range 2.0-12.0.

Compound 4 Expanded monolayer produced with itc = 23mNTm-l. At it 20mNm-1 30% monolayer is lost in one hour. Monolayers were transferred to glass substrates and their optical properties assessed.

Although monolayer instability is 30% in one hour the loss accelerates with time and amounts to only 3% approximately within the initial ten minutes of compression. Monolayers can be deposited within this time, so that film instability here is considered negligible.

The deposition conditions used were: subphase pH = 5.5 (pure water) it = 20mNm-1 T = 200C Deposition rate = SOpLms- Substrate = glass Substrate pretreatment = general clean with lens tissue, ultrasonic clean in water thirty minutes, nitrogen dry, clean in refluxing propan-2-ol (thirty minutes), nitrogen dry, then either (i) hydrophobic treatment: reflux in Cl2Si(CH3)2 thirty minutes, wash with propan-2-ol, wash with dichloromethane, wash with propan-2-ol, nitrogen dry; or, (ii) hydrophilic treatment: immerse in an aqueous solution of ammonia and hydrogen peroxide (as outlined) for thirty seconds, wash with water, nitrogen dr.

Solution for {30% ammonium hydroxide 25ml hydrophilic (30% hydrogen peroxide looms pre-treatment (water 500ml Monolayer samples were examined for Second Harmonic Generation (SHG) using a standard technique as described in I.

Girling, N. Cade, P. V. Kolinsky and C. M. Montgomery, Elec. Lett., 21, 164 (1985). Linearly polarised light from a Nd: YAG laser was focussed onto the film surface at an angle of incidence of 450 and the reflected light monitored using an Sl photocathode photomultiplier tube. The pump wavelength was removed with absorbing filters and a narrow band-pass filter centred at a wavelength of 530 nanometres. The laser was passively Q-switched using a dye, to give smooth pulses and significantly reduced noise levels on the detected signal. A clear signal was observed with pulse energies greater than a few hundred CLJ. These were confirmed to be SHG by varying the centre frequency of the narrow band filter away from 530 nanometres, when no signal was detected.The signal was observed to vary quadratically with energy of the 1.06 micrometre pump beam; this is characteristic of SHG. No 'signal was observed from uncoated areas of the substrate and there was no evidence of film anisotropy.

The SHG signal was predominantly p-polarised (parallel to plane of incidence) for both p- and s-polarised (perpendicular to plane of incidence) pump radiation, indicating that the polarisation field driving the generation is aligned perpendicular to the substrate, that is, along the molecular long axis.

The intensity of the SHG signal (ç') was compared with that of a monolayer of the material 4-carboxy-4'-decylmethylamino-2'methylazobenzene (CAMAB), for which the second order polarisability is known. The monolayer of Compound 4 was measured at different points within the film area to yield an average SHG efficiency of 15% relative to CAMAB.If packing factors are considered negligible and the refractive indices for the two materials are assumed to be equivalent then using the fact that ss(CAMAB) = 9 x 10-49C3m3J-2 and B2 (Compound 4) = 12W (Compound 4) B2 (CAMAB) pw (CAMAB) then B (Compound 4) = 3.5 x 1049C3m3J-2 This compound therefore represents the first known example of a specifically prepared L-B preformed polymer to exhibit nonlinear optical effects.

Compound 5 This material produces a highly stable monolayer (no significant film loss is observed when maintained at it = 30mNm-1 for several tens of hours) with #c # 40mNm-1 and a condensed monolayer within the range it = 20-40mNm-1. Deposition has taken place using the following conditions: subphase pH = 5.5 (pure water) it = 30mNm-1 T = 200C Deposition rate = 50 ms-1 Substrate = glass Substrate pretreatment= hydrophilic (as for Compound 4) Number layers = (i) 1 (monolayer); (ii) 12; (iii) 47; (iv) 210 These samples have been assessed with the following results: (i) Monolayer. Optical examination by the technique outlined for the monolayers of Compound 4 was able to detect SHG from the monolayer.The level of SHG intensity was estimated at about 20% relative to that of CAMAB.

(ii) 12 and (iii) 47 layers. Deposition occurred by the Y-mode.

Materials of the alcohol family have generally been found, by workers in the L-B field, to be extremely difficult to deposit as multilayers. This compound represents one of the rare examples of alcohol multilayers and illustrates that the alchohol head-group is not the sole consideration but the system into which it is incorporated is critical; the latter is represented here by the siloxane copolymer system.

Examination of these multilayers by optical microscopy (x 500) revealed few defects and imperfections. When viewed in reflected light the films appeared smooth and featureless.

(iv) 210 layers. In this case a surface relief grating (period = 0.4467 micrometre) was defined in the glass substrate by standard holographic photolithographic techniques. Again the multilayer structure was observed to be of good quality when examined by optical microscopy (x 500). The grating was used to couple 0.6328 micrometre radiation from a He-Ne laser into the waveguide modes of the film. Waveguiding was confirmed by scratching the multilayer and observing an abrupt termination of the guided light. Accurate determination of waveguide attenuation on a film of 2.0 micrometres is consistent with a loss figure of the order lOdBcm-l. The refractive index of the 2.0 micrometre film has been measured as no = 1.5529 + 0.0028, ne = 1.5732 + 0.0044. In addition, the thickness per layer has been measured as 22.0 Angstrom Units.

From the SHG intensity value given above relative to that for CAMAB it is possible to calculate ss in the same way as for Compound 4. Hence, neglecting the packing density and assuming a similar refractive index for CAMAB and Compound 5: (3(Compound 5) = 4 x 1e49c3m 3J 2 As for Compound 4, this material represents the first known example of nonlinear optical effects being exhibited by L-B films of a preformed polymer. In addition this material represents the first known example of waveguiding in a L-B multilayer of a nonlinear optical preformed polymer.

The data for the above Compounds 2-5 indicate that conventional head-groups (-CN, -C02CH3, -OH) are acting as the hydrophilic group, and the polysiloxane backbone (which can have hydrophilic tendencies) is not in direct contact with the aqueous subphase.

The substrate body carrying a mono or multilayer deposit of the organic compound according to the invention formed an optical element having nonlinear optical properties. The element can be used to construct various optical devices as depicted in Figures 3 and 4.

Figure 3 shows a planar waveguide formed from a substrate body 1 which supports a Langmuir-Blodgett film 2 multilayer of one of the aforementioned Compounds 1 to 7. The substrate 1 had a lower refractive index than that of the film 2, and the provision of a high refractive index region bounded by a lower refractive index region thus gave the necessary confinement to provide the required waveguide effect.

A typical thickness for the material of the film 2 for use in guiding visible and near infrared light was of the order of one micron.

From the planar waveguide construction, the definition of a narrow channel in the high refractive index material will result in a two-dimensional confinement of the light and make possible the construction of a range of channel waveguide structures. One such construction is shown in Figure 4 where the substrate body 1 supports a Langmuir-Blodgett deposited film 2 multilayer which bv photolithographic definition has been cut away to leave a width of only a few microns.

The constructions of the planar and channel waveguide structures which have just been described can lead to other electro optic and all-optical switching and signal processing devices which make use of the organic compounds of the invention.

The foregoing description of embodiments of the invention has been given by way of example only and a number of modifications may be made without departing from the scope of the invention as defined in the appended claims.

For instance, it is not essential that the polymer compound of the invention should be deposited by the dipping bath technique that has been specifically described. In a different embodiment the technique of film assembly might use processes such as crystal growth, chemical vapour deposition etc.

Before the deposit of polymer compound is placed on the substrate body, the body might be given an initial coating such as one of silicon nitride or to form a reflecting surface on the body. The layers of polymer compound on the substrate body also might be provided with intervening layers of different substances.

It will be noted that this specification has disclosed the use of siloxane polymers as materials that can be depostied by the Langmuir-Blodgett technique. A range of siloxane polyners including specifically the Compounds 1 to 7 has been described.

The use of the t-butyldimethylsilyl group as a protecting group in the synthesis of compounds such as Compounds 5 and 6 has also been disclosed.

Langmuir-Blodgett films prepared according to the present specification are likely to be more mechnically robust and temperature stable than those films when made of monomer and non-polymerisable materials.

The specification gives examples of specifically prepared preformed polymers exhibiting non-linear optical properties from Langmuir - Blodgett films. There is also an example of waveguiding in a specifically prepared preformed polymer Langmuir - Blodgett multilayer of a non-linear optical material, and relatively low loss waveguiding in thick (about 2.0 micrometre) multilayers has been demonstrated.

Claims (13)

1. A polymer compound of the following general structural formula:

where 1 = 1 to 99 ) The bars over 1, m and 1 + m # = 99 to 1 ) indicate mean values 1 + m =

2 to 100)

Q = -N= or -CH= G = -H or -CH3 J = -H, -CN or -NO2 E = -H,-CN or-NO2 R = -H, -CN, -N02 or -CH3 Y = -H, -CN, -NO2 or -CH3,

-SH, -SCH3, or -S03H nl = O to 18 (preferably 2 to 9) n2 = O to 6 2. A polymer compound as claimed in Claim 1, in which,

and 1 = 24(#4) m = 10(+4) GJ#E = -H Z = -CN n1

3 n2 = 0 3.A polymer compound as claimed in Claim 1, in which,

and I = 24(+4) # = 10(#4) G,I & = -H Z = -CN nl =5 n2 = 0

4. A polymer compound as claimed in Claim 1, in which,

and -I = 24(+4) m = 10(+4) G@J # E = -H A = # Z = -CN n1 = 10 n2 = 0

5. A polymer compound as claimed in Claim 1, in which,

and 1 = 24(#4) m = 10(+4) G@J # E = -H A = # Z = -CO2CH3 n1 =5 n2 = 0

6. A polymer compound as claimed in Claim 1, in which,

and 1 = 9(+2) #=8(#2) G,I & = -H Z = -OH n1=5 n2 = 2

7.A polymer compound as claimed in Claim 1, in which,

and 1 = 9(+2) m = 8(±2) G,J & = -H

Z = -C02H n1 = 5 n2 = 0

8. A polymer compound as claimed in Claim 1, in which,

and 1 = 9(#2) m = 8(+~) G,J & = -H

Z = -C02CH3 n1 = 5 n2 = 0

9. An optical element having non-linear optical properties, the element comprising a substrate body supporting a layer of a polymer compound having the composition of any one of the compounds claimed in Claims 1 to 8.

10. An optical element as claimed in Claim 9, in which the substrate body supports multiple layers of said polymer compound, the layers constituting a film of high refractive index material.

11. An optical element as claimed in Claim 9 or 10, in which the polymer compound layer is formed by deposition from a liquid subphase surface.

12. An optical device, such as a planar or channel waveguide structure, including an optical element as claimed in any one of Claims 9 to 11.

13. An optical device, substantially as hereinbefore described with reference to the accompanying drawings.