Optical: systems and elements – Optical modulator – Light wave temporal modulation
Patent
1994-01-24
1996-05-28
Epps, Georgia Y.
Optical: systems and elements
Optical modulator
Light wave temporal modulation
359270, G02F 1153
Patent
active
055217451
DESCRIPTION:
BRIEF SUMMARY
This invention relates to electrochromic devices and is particularly concerned with such devices employing phthalocyanine-based electrochromic materials.
Electrochromism is the term used to describe the phenomenon of an electrochemically-induced spectroscopic change in a material, usually a change in colour. While the phenomenon has been known for some 50 years, it is only in recent years that practical applications have become apparent, for example in visual displays, antiglare mirrors and fields where colour changing filters are of use, e.g. windows. There have been proposed for use both inorganic materials such as tungsten oxide and organic materials such as viologens. Among the organic electrochromics, rare earth bisphthalocyanines have been proposed (see for example UK Patent 2177516 and Silver et al., Display, October 1988, 174-178 and 189). Certain transition metal monophthalocyanines have also been demonstrated to be electrochromic by Collins and Schiffrin, J. Electroanal. Chem., 139, (1982), 335-369. However, extension of their investigation to a non-transition metal, i.e. the p-block element tin, resulted in a compound (dichlorophthalocyaninato tin) which showed no electrochemical activity. While dichlorophthalocyaninato tin has been subsequently reported (UK Patent 2177516) as being capable of undergoing a colour change from blue to purple at 2.5 V, it was proposed for use only as a carrier to aid sublimation of a rare earth diphthalocyanine electrochromic material and as a spacer in the crystal lattice of the deposited rare earth diphthalocyanine.
It has now surprisingly been found that the p-block elements aluminium and silicon are capable of participating in phthalocyanine complexes exhibiting electrochromicity in response to both oxidizing and reducing voltages giving interesting colour change effects which in many cases are cyclable. In view of the fact that aluminium and silicon (unlike tin and also the transition metals) exist almost exclusively in their highest oxidation states (III and IV respectively), the metals themselves cannot be expected to take part in redox processes occurring at metallophthalocyanine-modified electrodes during electrochromic reactions. That aluminium and silicon phthalocyanine complexes could contribute usefully to the spectrum of colour effects obtainable with phthalocyanine electrochromics was an unexpected but pleasing finding.
According to the present invention, there is provided an electrochromic device comprising two electrodes separated by an electrolytic medium and means to permit the application of a potential between the electrodes, so as to create a circuit for charge transfer, and an electrochromic material in contact with the electrolyte and an electrode so that a change in spectral properties of the material is detectable from the exterior of the device, the electrochromic material comprising an aluminium and/or silicon containing monophthalocyanine or monotetrabenzoazaporphyrin complex. Aluminium and silicon complexes of phthalocyanine are known--see A. B. P. Lever "The Phthalocyanines" pages 27-114 of Advances in Inorg. Chem. and Radiochem. 7, 1965.
The aluminium and/or silicon containing complex comprises aluminium and/or silicon plus phthalocyanine suitably plus at least one inorganic ligand (such as chlorine, hydroxide or oxide) or organic ligand (such as acetoxy, benzyloxy, phenoxy or an anion of an organic acid). Alternatively the complex may be a silicon-containing phthalocyanine oligomer, for example, of general formula HO[pcSiO].sub.n H where n is, for example, from 2 to 5 and "pc" represents phthalocyanine. Yet again, the complex may be a mixed silicon/aluminiumoxyphthalocyanine, for example of general formula PcAlOSi(pc)OAlpc or PcAlOSi(pc)OSi(pc)OAlpc, which may also be in oligomeric form. While monophthalocyanine complexes are preferred because of their relatively easy preparation, it is contemplated that one or more of the bridging nitrogen atoms of the phthalocyanine may be replaced by carbon so as to give a mono-, di- or triazatet
REFERENCES:
patent: 4828369 (1989-05-01), Hotomi
patent: 5293546 (1994-03-01), Tadros et al.
Lukes Peter J.
Silver Jack
British Technology Group Ltd.
Epps Georgia Y.
Robbins Thomas
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