Compositions – Light transmission modifying compositions – Displaying color change
Patent
1988-02-19
1991-02-05
Maples, John S.
Compositions
Light transmission modifying compositions
Displaying color change
350266, 350353, 350354, 549 71, 549 70, G02B 523
Patent
active
049902873
DESCRIPTION:
BRIEF SUMMARY
This invention relates to optical devices, particularly optical resonant assemblies, which utilise photochromic compounds.
In our U.K. patent application No. 8519711 (Publication No. 2180360), we describe an optical resonant assembly in which a photochromic compound, which is reversibly convertible between coloured and bleached states, is used to provide a plurality of stable optical transmission states.
The device described in our above patent application employs a pair of light beams, i.e. a colouring beam and a bleaching beam whose relative intensities are varied to change the light transmittance of the device.
We have now found that it is possible to construct an optical resonant device which can be switched between bistable states using only one light beam of one or more wavelengths.
This is achieved by selection of a class of photochromic compounds which have a low quantum yield for bleaching with light in the visible region.
According to the present invention there is provided an optical resonant assembly which comprises a plurality of partially light-transmitting mirrors, a layer of photochromic material disposed between the mirrors, a light source providing a light beam of variable intensity incident on the layer of photochromic material and detecting means for determining transmittance values of said incident beam at different intensity levels, said photochromic material having a low quantum yield for bleaching with light of a wavelength corresponding to said light beam and being selected from pyran compounds of the general formula (I) below: ##STR2## wherein X and Y together represent a spiro-adamantylidene group or a spiro-carbocyclic or heterocyclic group or X and Y independently represent hydrogen, alkyl (preferably lower alkyl having 1 to 5 carbon atoms) or phenyl and R.sub.3 and R.sub.4 each independently represent hydrogen, alkyl, aralkyl, aryl, halogen or a heterocyclic group and R.sup.1 represents hydrogen, lower alkyl, aryl, alkoxy, alkyl- or dialkyl amino, halogen, or heterocyclic or R.sup.1 represents a fused benzene ring at the 5, 6 or 7, 8 positions.
Specific examples of compounds having the desired properties are described in our U.K. patent application No. 2180360A, which discloses a series of photochromic spiro-pyrans which are represented in general terms by the following general formulae (II), (III) & (IV). in which formula (II) represents the 2H-benzopyran series and formulae (III) and (IV) represent the isomeric naphthopyran series. ##STR3##
A wide variety of substituents are possible in the
benzopyran or napthopyran rings. For example, the rings can be substituted in the positions represented by R.sub.3 to R.sub.8 (or R.sub.3 to R.sub.10) with alkyl, aryl (including substituted phenyl, e.g. alkoxyphenyl and halophenyl), alkoxy, hydroxy, alkyl or dialkylamino (e.g. dimethylamino), alkylamino-phenyl, halogen or heterocyclic groups (e.g. furyl or thienyl), with the proviso that hydroxy or alkoxy or alkyl- or dialkylamino may not be a substituent in the R.sup.3 or R.sup.4 position. Preferred substituents are lower alkyl (e.g. methyl or ethyl), chlorine, bromine, hydroxy, phenyl, methoxy, or methoxy phenyl groups. It is also possible to produce related series of compounds in which the basic benzopyran or naphthopyran nuclei are annelated with aryl or heterocyclic rings, such as a thiophene or furan ring.
In addition to its beneficial effect in reducing fatigue reactions, the introduction of the spiro-2-adamantane group tends to cause an increase in the quantum yield for colouring in the U.V. region, whilst providing a fast thermal fade at ambient temperature.
The following procedure can be followed to prepare adamantylidene spiro pyrans of the above general formulae. It will be appreciated that chromene is an alternative name for benzopyran. Thus, 2H-chromene is an alternative name for 2H-1-benzopyran.
CONDENSATION
Adamantanone (1 mole), the o-hydroxyacetophenone (1.1 mole) and a cyclic secondary amine (1.2 mole) are dissolved in toluene (1 cm.sup.3 for each g of reactant) and
REFERENCES:
patent: 3565814 (1971-02-01), Pellon
patent: 4818096 (1989-04-01), Heller et al.
Brown, G. H. in Photochromism, Brown, G. H. ed., Wiley, New York, 1971, Chapter. 1.
Kirkby, C. J. H.; Cush, R.; Bennion, I. Optics. Comm. 56, (4) 288, 1985.
Mitsuhashi, Y. Optics Lett. 6(3) 111, 1981.
LeNoble, C.; Becker, R. S.; J. Photochem. 33 (1986) 187-197.
Bennion Ian
Cush Rosemary
Groves-Kirby Christopher J.
Trundle Clive
Maples John S.
The Plessey Company PLC
Treanor Richard
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