GB2058114A - Electrochromic compounds - Google Patents

Abstract

The rare earth phthalocyanines are well-known for their electrochromic properties. Lutetium diphthalocyanine for example, can be persuaded (suitably arranged in an appropriate electrolytic cell) to display the colours from violet and deep blue, through various shades of green, to orange and red. Materials such as this have obvious possibilities in colour display systems of many sorts, and the invention provides novel and improved such materials, these being the polymeric rare earth diphthalocyanines of the empirical general formula <IMAGE> (wherein: "RE" represents the rare earth, "PC" represents the phthalocyanine ring system; and x is an integer greater than 1), especially the compound wherein RE is lutetium and x is 5. These polymeric diphthalocyanines may conveniently be made by reacting an appropriate rare earth organic derivative (such as the acetate) at elevated temperature with a suitable 1,2,4,5-tetracyanobenzene so as to produce the desired polymer.

Description

SPECIFICATION Electrochromic compounds This invention concerns electrochromic compounds, and relates in particular to certain novel phthalocyanines and processes for their preparation.

Phthalocyanines -- also known as benzoporphyrins -- are well-known as powerful colouring agents useful in the preparation of dyestuffs. Most of these phthalocyanines, both substituted and unsubstituted, are in the form of complexes with metals, and certain of these complexes -- those with the rare earth metals (the 1 5 elements from lanthanum to lutetium; particularly neodymium, praesodymium, erbium, yttrium and - especially - lutetium) - are wellknown for their electrochromic properties.A material is said to be electrochromic if it changes colour in response to changes in the magnitude or direction of the electric potential applied across it; lutetium diphthalocyanine, a material to which a considerable amount of study has been devoted, can be persuaded (suitably arranged in an appropriate electrolytic cell) to display the colours from violet and deep blue, through various shades of green, to orange and red. Materials such as this have obvious possibilities in colour display systems of many sorts, and the invention seeks to provide novel and improved such materials.

The rare earth diphthalocyanines are of the empirical general formula RE(PC)2H (I) wherein "RE" represents the rare earth, and "PC" represents the phthalocyanine ring system (phthalocyanine itself is shown in full in Formula II of the accompanying drawings). H - as normal -- represents hydrogen. The structure of the compounds is such that a single rare earth atom is "sandwiched" between two opposing phthalocyanine ring systems, and the structure of lutetium diphthalocyanine is represented in Formula III of the accompanying drawings.

Formula IV shows a simplified, general structure for complexes of this kind (RE is as defined hereinbefore, "BI" represents the individual benzoisoindole ring system making up the phthalocyanine system, and for clarity the bonds joining the two phthalocyanine systems to the rare earth atom have been omitted).

The present invention is concerned with novel rare earth phthalocyanines which may be regarded as polymeric versions of the currently-known materials, and which may be of considerable value in electrochromic display systems.

In one aspect, therefore, this invention provides a polymeric rare earth diphthalocyanine of the empirical general formula [RE(PC)zH]x (V) (wherein: "RE" and "PC" are as defined hereinbefore; and x is an integer greater than 1).

As might be expected the structure of this type of compound is quite complex. For convenience, however, it may be described as a "macrosandwich" version of the structure shown in Formulae III and IV, the individual RE(PC)2H units extending laterally in both possible directions, and may be pictured in grossly simplified form as shown in Formula VI of the accompanying drawings (in which the "Bl"s have, for clarity, not been shown at the line junctions).

The rare earth RE may be any of the 15 rare earth elements from lanthanum (Atomic Number 57) to lutetium (Atomic Number 71), but the lutetium macro complexes are preferred.

The phthalocyanine ring system is most preferably that of phthalocyanine itself (the presence of substituent groups in the benzoisoindole rings making up the basic phthalocyanine system causes as yet unpredictable changes in the electrochromic effect).

The value of integer x depends primarily upon the manner in which the inventive polymeric phthalocyanine is made (a particularly satisfactory preparative process is described hereinafter). It must be at least 2, and in certain cases may be as high as several hundred. Conveniently, however, x is a relatively low integer - in units rather than tens or hundreds, and an average value of about 5 seems most acceptable at present.

A particularly preferred polymeric rare earth diphthalocyanine V is thus the five unit macromolecule made with lutetium and unsubstituted phthalocyanine groups.

The polymeric diphthalocyanines of the invention may conveniently be made by a modification of the conventional method for making monomeric rare earth diphthalocyanines.

Accordingly, in another aspect this invention provides a process for the preparation of a polymeric rare earth diphthalocyanine V in which an appropriate rare earth organic derivative is reacted at elevated temperature with a suitable 1 ,2,4,5-tetracyanobenzene so as to produce the desired polymer.

The rare earth organic derivative may in essence be any such derivative capable of pyrolising to give the rare earth (probably in monatomic free radical form), but is most conveniently an ester - for example, an acetate (which is preferred) -- or a ketoate -- for example, an acetonyl acetonate.

The rare earth is itself conveniently lutetium, so that the preferred rare earth organic derivative is lutetium acetate.

The 1 ,2,4,5-tetracyanobenzene is most preferably the unsubstituted compound.

Though there are various other factors involved (specifically, a large number of different types of by-product impurity, including the unwanted polymeric rare earth monophthalocyanine), nevertheless it is reasonable to say that the primary factor deciding the value of x (in Formula V) is the proportion of the two reactants (the rare earth organic derivative and the tetracyanobenzene). In a macromolecular product of infinite molecular weight the proportion of rare earth to benzoisoindole groups is 1: 4, so a similar proportion of reactants would be expected to result in a product corresponding to Formula V where x is very large. A change in either direction -- say, to 1: 2 or to 1: 6 - would result in a much smaller macromolecule (x is smaller) and a greater quantity of by-products.In practice, to obtain acceptable quantities of the 5-unit version (x = 5) of the desired polymeric rare earth diphthalocyanine V it is preferred to use molar proportions of rare earth organic derivative to tetracyanobenzene of about 1 5.

The reaction is carried out at an elevated temperature, and indeed is advantageously effected, under pyrolytic conditions, at a temperature of several hundred degrees Centigrade (for example, 3000 C). Moreover, the reaction is very preferably effected under completely anhydrous conditions.

As state above, the immediate product of the reaction is a mixture of the desired polymer V and various by-products. The mixture can generally be separated by conventional methods (such as column chromatography) to give the desired compound.

The invention extends, of course, to a polymeric rare earth diphthalocyanine V whenever prepared by a process as described herein.

The polymeric rare earth diphthalocyanines of the invention, which appear to be chemically more stable than their corresponding monomeric analogues, exhibit interesting electrochromic properties, and may therefore be of use in the provision of multi-colour electro-optical display systems (for which purpose they can be vacuum evaporated, or rf sputtered, into thin film form, and suitably disposed -- with appropriate electrodes -- in an electrolytic cell) in accordance with the techniques used or suggested for use for that purpose. The invention extends, therefore, to such a display system when made using a polymeric diphthalocyanine V.

The following Examples are now given, though only by way of illustration, to show details of the invention.

EXAMPLE 1 Preparation of poly(lutetium diphthalocyanine) (V; RE = Lu, x = 5) 0.325 g (0.001 mole) of lutetium acetate and 0.8448 g (0.01 mole) of 1,2,4,5tetracyanobenzene were thoroughly mixed by grinding together in a mortar. The resultant powder was introduced into a strong walled quartz tube of length 60 mm and diameter 25 mm, and the tube was evacuated (to 0.01 Torr), sealed, placed in a rotating tube furnace, and heated at3150C for three hours.

The reaction product was ground and successively washed on a sinter with methanol and acetone to give a dark blue-black powder.

This was then chromatographed on alumina (using dimethyl formamide as eluent), the required fraction being azure blue in colour. Evaporation of the solvent left the desired compound as a dark blue-black powder which was vacuum dried at 2500C to constant weight.

The product, which took the form of an amorphous powder, slowly sublimed (at 1 x 10-6 Torr) at 4500 C. It was soluble in dimethyl formamide, but insoluble in methanol and ether. Its structure was confirmed (by IR and visible light spectra) by comparison with that of the known material monomeric lutetium diphthalocyanine.

IR Spectrum in cm~1 (Nujol) Peaks at: 2220 (-CN); and 1300, 1000 and 720 (typical of monomeric rare earth phthalocyanines).

Visible Spectrum in my (DMF) Peaks at: 710 and 625.

The material so prepared showed enhanced stability over the corresponding lutetium diphthalocyanine monomer in respect of both electrochemical stability and stability during vacuum deposition.

Claims (15)

1. A polymeric rare earth diphthalocyanine of the empirical general formula [RE(PC)2H]X (V) (wherein: "RE" represents the rare earth; "PC" represents the phthalocyanine ring system; and x is an integer greater than 1).

2. A polymeric rare earth diphthalocyanine V as claimed in claim 1, wherein the rare earth is lutetium.

3. A polymeric rare earth diphthalocyanine V as claimed in either of the preceding claims, wherein the phthalocyanine ring system is that of phthalocyanine itself.

4. A polymeric rare earth diphthalocyanine V as claimed in any of the preceding claims, wherein the value of integer x is about 5.

5. A polymeric rare earth diphthalocyanine V as claimed in any of the preceding claims which is the five unit macromolecule made with lutetium and unsubstituted phthalocyanine groups.

6. A process for the preparation of a polymeric rare earth diphthalocyanine V as claimed in any of the preceding claims, in which an appropriate rare earth organic derivative is reacted at elevated temperature with a suitable 1,2,4,5tetracyanobenzene so as to produce the desired polymer.

7. A process as claimed in claim 6, in which the rare earth organic derivative is an ester.

8. A process as claimed in claim 7, in which the ester is an acetate.

9. A process as claimed in claim 8, in which the rare earth organic derivative is lutetium acetate.

10. A process as claimed in any of claims 6 to 9, in which the 1 ,2,4,5-tetracyanobenzene is the unsubstituted compound.

11. A process as claimed in any of claims 6 to 10, in which there is used molar proportions of rare earth organic derivative to tetracyanobenzene of about 1: 5.

12. A process as claimed in any of claims 6 to 11, in which the reaction is carried out, under pyrolytic conditions, at a temperature of several hundred degrees Centigrade.

13. A process as claimed in any of claims 6 to 12, in which the immediate product is a mixture of the desired polymer V and various by-products, and this mixture is then separated to give the desired compound.

14. A process as claimed in any of claims 6 to 13 and substantially as described hereinbefore.

1 5. A polymeric rare earth diphthalocyanine V as claimed in any of claims 1 to 5 whenever prepared by a process as claimed in any of claims 6to 14.

1 6. A multi-colour electro-optical display system when made using a polymeric diphthalocyanine V as claimed in any of claims 1 to 5 and

15.