GB2235449A

GB2235449A - Dinuclear complexes and methods of preparing optical fibres therefrom

Info

Publication number: GB2235449A
Application number: GB8919276A
Authority: GB
Inventors: George S Attard
Original assignee: University of Southampton
Current assignee: University of Southampton
Priority date: 1989-08-24
Filing date: 1989-08-24
Publication date: 1991-03-06
Also published as: GB8919276D0

Abstract

Dinuclear complexes of a divalent metal M with a bidentate ligand, are of formula <IMAGE> wherein R is an organic moiety containing at least one -C IDENTICAL C- group. Fibres have been drawn from their liquid crystalline melts. If R contains two conjugated -C IDENTICAL C- groups, the fibres may be polymerised. Both the pre-polymerised and the polymerised fibres exhibit non-linear electro-optical phenomena.

Description

NOVEL DINUCLEAR METALLIC CCMPLEXES AND ME'IHODS OF PREPARING OPTICAL FIBRES ?SIERFRaM The invention relates to new dinuclear metallic complexes, which can be formed into fibres, which fibres exhibit non-linear optical properties.

Optical fibres exhibiting non-linear phenomena, for example frequency doubling or trebling, have to date been made by doping conventional glass or silica optical fibres with metallic species.

It has been proposed that fibres formed from liquid crystalline melts of metallic compounds will show useful electro-optical properties.

Liquid crystal phases are fluids with orientational long-range order and varying degrees of spatial order. It has, however, proved difficult to form well-orientated fibres from the liquid crystalline melts of metallic compounds.

Desirable properties of a non-linear optical fibre are: flexibility; length of a few centimetres or more; molecular alignment over a macroscopic scale extending the entire length of the fibre; constant diameter of about 6 micrometres up to about 150 micrometres; a smooth fibre surface; and clean cleavage planes perpendicular to the fibre axis.

Certain transition metal complexes, soaps in particular, are knovzn to form discotic liquid crystalline phases, wherein the disc-shaped molecular complexes form columnar stacks arranged on a hexagonal lattice.

Attempts to obtain suitable fibres meeting the above criteria from these phases have not met any great success to date. J.

Phys. France 50 (1989) 513-519 describes attempts to melt-spin fibres from the discotic phase of copper laurate. The fibres were not of good quality.

The present invention provides a dinuclear complex of a divalent metal M with a bidentate ligand, the camplex being of formula

wherein R is an organic moiety containing at least one -C-C- group. R preferably contains two -C=C- groups, which groups may be conjugated.

M is preferably a transitionmetal and still preferably Cu(II), Mo(II) or Rh(II).

piety R preferably contains at least 8 carbon atoms, more preferably at least 11 carbon atoms, more preferably at least 16 carbon atoms, more preferably at least 24 carbon atoms and still more preferably 24 carbon atoms.

The invention further provides a polymerised complex according to the above formula, in which two -CtC- groups are conjugated.

The invention further provides optical fibres consisting substantially of a complex according to the above formula.

The invention further provides polymerised optical fibres consisting substantially of a complex according to the above formula, in which R contains two conjugated -r=r- groups.

The invention further provides a method of preparing an optical fibre, the method comprising drawing a fibre from a liquid crystalline melt of a complex according to the invention.

The invention further provides a method of preparing an optical fibre, in which R contains two conjugated -C=C- groups, the method comprising drawing, spinning or extruding a fibre from the liquid crystalline melt and further comprising polymerising the fibre, which polymerisation is preferably achieved by exposure of the fibre to ultra violet, X-ray or radiation.

Fibres prepared by the above methods are preferably drawn to a diameter of between 6 and 130 micrometres.

The invention further provides an optical fibre, which may be polymerised, consisting substantially of the complex accoring to the invention, or made by any of the above methods, having a coating of a lower refractive index than the fibre, which coating is preferably poly(methlymethacrylate).

It has been found that, for the complexes of the present invention, the fluidity of the discotic phase is conducive to forming fibres. Strands may be drawn from a reservoir of material. The liquid crystalline phase exists at temperatures above 850C. By varying the temperature of the phase and/or the drawing speed, fibres of varying diameter maybe prepared.

The fibre at room temperature is no longer a liquid crystalline phase. The room temperature fibre may be regarded as a glassy single crystal.

Characterisation of the individual fibres by both polarised light microscopy and X-ray diffraction shows a highly ordered internal structure along the length of the fibre.

Fibres consiting substantially of the complexes of the present invention may be poled by an electric field to exhibit second order optical effects, for example the doubling of radiation transmitted therethrough.

If moiety R contains two conjugated -CaC- groups, the fibres of the present invention may be topochemically polymerised on exposure to ultra violet, X-ray or d radiation. Polarised light microscopy of the polymerised fibres show that polymerisation results in little, if any, perturbation of the fibre's ultrastructure.

The polymerised fibres have been shown to exhibit third order optical phenomena, for example they will cause frequency trebling of light transmitted therethrough.

Cladded fibres may be produced by coating the fibres, both pre-polymerised and polymerised, with a material of a lower refractive index than the fibre itself. Conventionally poly(methylmethacrylste) (PMMk) is used, and its application to the fibres of the present invention may be achieved by standard techniques.

EXAMPLE 1 Dicopper tetrakis (pentacosadiynoate) (CuPCD) of formula: [CH3-(CH2)ll-CFC-C-C-(CH2)8Coo]4Cu2 was prepared by either of the following methods.

Method 1. Pentacosadiynoic acid (l mol equivalent) was dissolved in absolute ethanol and added with stirring to a hot solution of 1.5 mol equivalents of sodium hydroxide (or potassium hydroxide) in absolute ethanol. Following reflux the reaction mixture was allowed to cool to room temperature whereupon the alkali metal sale of pentacosadiynoic acid was obtained as a light-sensitive white precipitate. The solid was collected and dried in vacuo. 2.5 mole equivalents of the alkali metal salt of pentacosadiynoic acid were dissolved in a small amount of absolute alcohol and the temperature of the solution raised to about 400C. Copper sulphate (1 mole equivalent) was dissolved in the minium quantity of distilled water. This solution was added to a stirred ethanol solution of the alkali metal carboxylate.The reaction mixture was stirred vigorously for 2-3 hours and allowed to cool to room temperature. The pale blue precipitate was filtered, dried in vacuo, and dissolved in boiling toluene. The toluene solution was filtered hot to remove insoluble impurities and the resulting clear solution was cooled in ice whereupon a pale blue precipitate was obtained. The was recrystallised twice more from toluene or heptane to yield a pale blue solid in ca.

70% yield after purification.

Method 2. Pentacosadiynoic acid (2.5 mole equivalents) was dissolved in absolute ethanol and the solution headed to about 600C. This was added to a hot solution of copper(II) acetate in absolute ethanol. The reaction mixture was ref fluxed for 2 hours and allowed to cool to room temperature.

The resulting precipitate was collected, dried in vacuo, and dissolved in boiling heptane. The heptane solution was filtered while hot and then cooled in ice. The pale blue solid was collected and recrystallised twice more from heptane, and dried in vacuo to yield ca. 85% of pure copper(II) pentacosadiynoate.

Products obtained by method 1 and method 2 are identical.

Method 2 is the preferred method of synthesis.

The thus prepared CCCCD was heated to 1300C. Fibres were drawn on a pin from the melt at a rate of lems 1.

The fibres were 80 micrometres in average diameter, and had lengths between 50rran and 600nun.

Scanning electron micrographs of the fibre are shown in Figures 1 and 2. These illustrate a smooth surface with few, if any, discernable surface features, and show clean cleavage planes perpendicular to the fibre axis.

Figure 3 shows a drawing of a typical X-Ray diffraction pattern of a CuPCD fibre. The sharp reflections in the pattern indicate a highly ordered internal structure.

It is envisaged that the non-linear electro-optical properties of both the pre-polymerised and the polymerised fibres according to the present invention will be exploited in the telecommunications field: such fibres can be joined to conventional optical fibres transmitting encoded light of a particular frequency, which frequency will be altered by transmission through the fibre of the present invention.

Claims

ClAIMS

1. A dinuclear complex of a diva lent metal M with a bidentate ligand, the complex being of formula

wherein R is an organic moiety containing at least one -C-=C- group.

2. A complex according to claim 1, in which R contains two -CsC- groups.

3. A complex according to claim 2, in which the -CtC- groups are conjugated.

4. A complex according to any preceding claim, in which M is a transition metal.

5. A complex according to any preceding claim, in which M is Cu(II), No(II) or Rh(II).

6. A complex according to any preceding claim, in which R contains at least 8 carbon atoms.

7. A complex according to any preceding claim, in which R contains at least 24 carbon atoms.

8. A complex according to any preceding claim, in which R contains 24 carbon atoms.

9. A complex according to any preceding claim, of formula [CH3-(CH2)11-C#C-C#C-(CH2)8COO]4CU2

10. A polymerised complex according to claim 3.

11. Optical fibre consisting substantially of a complex according to any of claims 1 to 9.

12. Polymerised optical fibre consisting substantially of a complex according to any of claims 1 to 9, in which R contains two conjugated -CEC- groups.

13. A method of preparing an optical fibre comprising drawing, spinning or extruding a fibre from a liquid crystalline melt of a complex according to any of claims 1 to 9.

14. A method according to claim 13, in which moiety R contains two conjugated -C=C- groups, further comprising polymerising the fibre.

15. A method according to claim 14, in which the polymerisation is achieved by exposure of the fibre to ultra violet, X-ray or X radiation.

16. A method according to any of claims 13 to 15 in which the fibre is drawn to a diameter of between 6 and 130 micrometres.

17. An optical fibre according to claim 11 or 12 or made by a method according to any of claims 13 to 16 having a coating of lower refractive index than the fibre.

18. An optical fibre according to claim 17, in which the coating is poly (methylmethacrylate).

19. A complex substantially as described with reference to Example 1.

20. An optical fibre substantially as described with reference to Example 1.

21. A method substantially as described with reference to Example 1.