Photochromatic composition and photochromatic articles which contain it

A photochromatic composition contains at least two photochromatic compounds, defined by the general formula: ##STR1## wherein the various substituents from R.sub.1 to R.sub.7 and X are as defined in the specification. In such a mixture, at least one photochromatic compound is defined by the general formula, wherein R.sub.7 represents a hydrogen atom, and at least one further compound is also defined by the general formula, wherein R.sub.7 represents an -NR.sub.8 R.sub.9, with R.sub.8 and R.sub.9 having the meaning as defined in the text.

The present invention relates to a photochromatic composition which 
contains at least two organic photochromatic compounds. 
The photochromatic compounds are substances which display the 
characteristics of reversibly changing in colour and/or degree of light 
transmission when they are exposed to some types of electromagnetic 
radiation, and to sun light, turning back into their original colour and 
transmission status when the initial light source is removed. 
The substances endowed with photochromatic characteristics known from the 
prior art are many, and belong to several classes of both inorganic and 
organic compounds, as described, e.g., in "Photochromism", G. H. Brown 
(Ed.), Vol. IV, from the Weisseberger Series "Techniques of Organic 
Chemistry", Wiley-Interscience, New York (1971). 
Among the organic photochromatic compounds, in particular those belonging 
to the class of the spiro-indolino-naphtho-oxazines are known, which are 
capable of conferring photochromatic characteristics on polymerized and 
transparent organic materials (organic glasses), for their use as sun 
filters and photochromatic optical articles, such as disclosed, e.g., in 
the following patents: U.S. Pat. Nos. 3,562,172; 3,578,602; 4,215,010; 
4,342,668; EP 146 135, WO 85/02619; EP 245 020; and in European patent 
applications publ. Nos. 134,633 and 141,407. 
The known photochromatic compounds belonging to the class of the 
spiro-indolino-naphtho-oxazines exhibit, as compared to other known 
organic photochromatic compounds (e.g., those belonging to the class of 
the spiro-piranes) the advantage of having a much higher fatigue strength, 
when they are submitted to repeated cycles of colouring and de-colouring; 
and a much higher ageing resistance when they are exposed to sun light, or 
to artificial ageing tests. This behaviour is very advantageous for the 
above set out uses. 
However, the organic photochromatic compounds known from the prior art are 
practically colourless in their deactivated status, both in solution in 
common organic solvents, as well as when they are incorporated in 
transparent polymeric materials, and turn to a generally blue colour when 
they are activated. This blue colour is a disadvantage for their use as 
optical photochromatic articles, in particular in the ophthalmic sector, 
for which more neutral colours please, e.g., the gray colour. 
Furthermore, the photochromatic effect obtained is in many cases of low 
intensity as regards the change in transmittance in the visible wavelength 
range. In other cases, such a change, although is satisfactory at low 
temperatures, is depressed down to unacceptedly low values with increasing 
temperature, even if within the values as required in practical use. 
Finally, the activation of the spiro-indolino-naphtho-oxazines, obtained 
under controlled laboratory conditions by irradiation with UV light of 
several wavelengths from about 320 to about 380 nm, is often not 
reproduced with the same satisfactory intensity when the exposure is 
carried out to the spectrum of frequencies and of relative intensities of 
sun light, as required for the ophthalmic use, and as sun filter. 
The purpose of present invention is overcoming the drawbacks which affect 
the prior art by means of a novel photochromatic composition containing at 
least two photochromatic compounds belonging to the class of the 
spiro-indolino-naphtho-oxazines. 
In accordance therewith, the present invention relates to a photochromatic 
composition consisting of at least two photochromatic compounds, both of 
which can be represented by the following general formula (I): 
##STR2## 
wherein: R.sub.1 and R.sub.2 independently represent a hydrogen atom or a 
halogen atom (chlorine, bromine or fluorine), or a group selected from: 
(C.sub.1 -C.sub.5)-alkoxy; nitro; cyano; and a linear or branched (C.sub.1 
-C.sub.5)-alkyl either unsubstituted or substituted with one or more 
halogen (chlorine, bromine and fluorine) atoms, or (C.sub.1 
-C.sub.5)-alkoxy, (C.sub.1 -C.sub.5)-alkyl-thio, (C.sub.1 
-C.sub.5)-carboxy-alkyl and cyano groups; or 
R.sub.1 and R.sub.2, when are not hydrogen, can be linked to any of the 4-, 
5-, 6- and 7-positions of the indolinic moiety; 
R.sub.3 and R.sub.4 independently represent linear or branched (C.sub.1 
-C.sub.5)-alkyl group, phenyl or benzyl; or 
R.sub.3 and R.sub.4, when considered jointly together with the carbon atom 
to which they are linked, form a (C.sub.5 -C.sub.8)-cycloalkyl group; 
R.sub.5 is a phenyl; benzyl; allyl group; or a linear or branched (C.sub.1 
-C.sub.5)-alkyl group, either unsubstituted or substituted with one or 
more halogen (chlorine, bromine and fluorine) atoms, or (C.sub.1 
-C.sub.5)-alkoxy, (C.sub.1 -C.sub.5)-alkyl-thio, (C.sub.1 
-C.sub.5)-carboxy-alkyl and cyano groups; 
R.sub.6 represents a hydrogen atom, a halogen (chlorine, bromine or 
fluorine) atom, or a group selected from (C.sub.1 -C.sub.5)-alkoxy, 
(C.sub.1 -C.sub.5)-alkyl-thio, (C.sub.1 -C.sub.5)-carboxy-allyl and cyano 
groups; and a linear or branched (C.sub.1 -C.sub.5)-alkyl group, either 
unsubstituted or substituted with one or more halogen (chlorine, bromine 
and fluorine) atoms, or (C.sub.1 -C.sub.5)-alkoxy, (C.sub.1 
-C.sub.5)-alkyl-thio, (C.sub.1 -C.sub.5)-carboxy-alkyl and cyano groups; 
or represents a condensed aromatic or heterocyclic ring; 
R.sub.6, when it does not represent hydrogen, or a condensed aromatic or 
heterocyclic ring, can be in any one of the 7'-, 8'-, 9'-, 10'-positions 
of the naphthenic moiety; 
R.sub.7 represents either a hydrogen atom, or an 
##STR3## 
R.sub.8 and R.sub.9 represent, independently from each other, a hydrogen 
atom, or a linear or branched (C.sub.1 -C.sub.5)-alkyl group, phenyl or 
benzyl; or 
R.sub.8 and R.sub.9, when considered jointly together with the nitrogen 
atom to which they are linked, form a mono-cyclic or poly-cyclic 
structure, of from 5 to 12 members, possibly containing a further 
heteroatom selected from between oxygen and nitrogen; and 
X represents either --CH-- or N; 
in which composition at least one of the photochromatic compounds having 
formula (I) is characterized in that it has the R.sub.7 substituent 
constituted by hydrogen, and at least one of the photochromatic compounds 
having formula (I) is characterized in that it has the R.sub.7 substituent 
constituted by a group 
##STR4## 
wherein R.sub.8 and R.sub.9 have the above seen meanings. 
In the preferred form of practical embodiment, the photochromatic compounds 
of the composition according to the present invention, all of which can be 
defined by means of the general formula (I), and with the proviso that in 
at least one of them the R.sub.7 substituent represents a hydrogen atom 
and in at least one of them the R.sub.7 substituent represents the amino 
group 
##STR5## 
the R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, R.sub.6, R.sub.7, and, if 
present, R.sub.8 and R.sub.9, substituents, have the following meaning: 
R.sub.1 and R.sub.2 independently represent the hydrogen atom, or the 
methyl, methoxy or halogen groups; 
R.sub.3 and R.sub.4 represent each the methyl or ethyl group, or, when 
considered jointly, represent the cyclohexyl group; 
R.sub.5 represents a (C.sub.1 -C.sub.5)-alkyl group; 
R.sub.6 represents the hydrogen atom or the methoxy group; 
R.sub.8 and R.sub.9 jointly represent, together with the nitrogen atom to 
which they are linked, the piperidino, morpholino, pyrrolidinyl or 
hexamethyleneimino group; and 
X represents either --CH-- or N. 
Furthermore, still in the preferred form of practical embodiment, the 
R.sub.1, R.sub.2 and R.sub.6 groups, when they do not represent hydrogen, 
or, in case of R.sub.6 group, a ring structure, are respectively linked to 
the (4,5)- or (5,6)- and 9'-positions of the molecule. 
Specific examples of photochromatic compounds in which the R.sub.7 
substituent is different from hydrogen, are: 
A) 
1,3,3-Trimethyl-6'-piperidino-spiro-[indolino-2,3'-(3H)-naphtho-(2,1-b)-(1 
,4)-oxazine]. 
##STR6## 
B) 
1,3,3-trimethyl-6'-morpholino-spiro[indolino-2,3'-(3H)-naphtho-(2,1-b)-(1, 
4)-oxazine]. 
##STR7## 
C) 1,3,3,4,5,-(or 
1,3,3,5,6)-pentamethyl-6'-piperidino-spiro-[indolino-2,3'-(3H)-naphtho-(2, 
1-b)-(1,4)-oxazine]. 
##STR8## 
D) 
1,3,3-trimethyl-6'-piperidino-9'-methoxy-spiro-[indolino-2,3'-(3H)-naphtho 
-(2,1-b)-(1,4)-oxazine]. 
##STR9## 
Specific examples of photochromatic compounds in which the R.sub.7 
substituent is hydrogen are: 
E) 1,3,3,4,5- (or 1,3,3,5,6) 
pentamethyl-spiro-[indolino-2,3'-(3H)-naphtho-(2,1-b)-(1,4)-oxazine]. 
##STR10## 
F) 
1,3,3-trimethyl-spiro-[indolino-2,3'-(3H)-naphtho-(2,1-b)-(1,4)-oxazine]. 
##STR11## 
G) 
1,3,3-trimethyl-9'-methoxy-spiro-[indolino-2,3'-(3H)-naphtho-(2,1-b)-(1,4) 
-oxazine]. 
##STR12## 
The above listed photochromatic compounds have been incorporated into 
transparent organic polymers by means of techniques depending on the 
polymer used. 
In the photochromatic mixture of the present invention, the simultaneous 
presence of a photochromatic compound definable by means of formula (I) 
and having an --NR.sub.8 R.sub.9 in the 6'-position of the molecule, and 
of a photochromatic compound definable by means of said formula, but in 
which the substituent in 6'-position is hydrogen atom, is advantageous. 
In such a mixture, as said, both compounds act with a synergistic effect on 
the regulation of the sun light, generating a more intense colour, and 
with shorter response times, than the normal photochromatic organic 
compounds of the prior art, as well as than the individual components of 
the same mixture. 
The change in transmittance is furthermore maintained at satisfactory 
values with increasing room temperature, and much higher than as required 
by the practical application. Furthermore, the shades of colour which can 
be obtained by means of the use of the photochromatic mixture of the 
present invention are more neutral than the blue colour generally shown by 
individual components, and can be modulated within a wide range by means 
of a properly balanced dosage of both basic components, as well as of 
other components known from the prior art. 
Advantageously, this mutual mol ratio of the two photochromatic components 
defined by the general formula (I) and respectively bearing the --NR.sub.8 
R.sub.9 group and hydrogen in the 6'-position, is a number comprised 
within the range of from 0.1 and 9 and preferably from 0.2 to 1.5. 
As said, the photochromatic mixture of the present invention can be 
constituted by more than two compounds as defined by the general formula 
(I), provided that at least two of them are different from each other as 
to the 6'-substituent, as above said. 
Said mixtures can furthermore additionally contain other components, such 
as the U.V. stabilizers known from the prior art, capable of improving the 
duration of the photochromatic effect, without impairing the intensity of 
photocolourability of the same mixtures. Non-limitative examples of 
U.V.-stabilizers for the purposes of the present invention are the 
hindered ammines (HALS). 
The photochromatic mixture according to the present invention is useful in 
the production of photochromatic articles endowed with particular colour 
transitions, a high activation by exposure to sun light, a high fatigue 
and ageing resistance. 
The photochromatic mixture according to the present invention is applied to 
the surface of, or is incorporated into, the desired articles, generally 
constituted by transparent polymeric materials, by means of suitable 
techniques. Photochromatic polymeric articles can be obtained by means of 
moulding techniques (e.g., injection-moulding, press-moulding, and so 
forth;) by homogeneously dispersing throughout the mass the photochromatic 
mixture. 
According to an alternative route, the mixture can be dissolved in a 
suitable solvent, together with a polymeric material (e.g., 
poly-methyl-methacrylate, polyvinyl-alcohol, poly-vinyl-butyral, cellulose 
acetate-butyrate or epoxy resin, polysiloxane resin or urethane resin, and 
so forth), and deposited on a transparent support in order to form, after 
the evaporation of the solvent, a photochromatic coating. 
According to an alternative route, the photochromatic mixture can be added 
to a polymerizable monomer, e.g., methyl-methacrylate, so that after a 
polymerization carried out in the presence of a suitable polymerization 
initiator, e.g., azo-bis(isobutyronitrile), it results to be evenly 
incorporated to the formed resin. 
According to an alternative route, the photochromatic mixture can be 
dissolved in a suitable solvent, in the presence of a resin, as above 
disclosed, and from this solution, by evaporating the solvent, a 
photochromatic film or sheet can be formed, which contain the uniformly 
dispersed photochromatic mixture. 
According to an alternative route, the photochromatic mixture can be 
applied to a transparent substrate (e.g., a polycarbonate substrate, a 
polymethyl-methacrylate substrate or a poly-diethylene-glycol-bis(allyl 
carbonate) substrate) by means of a surface impregnation obtained by 
placing the substrate into contact, at a suitable temperature, with a 
solution or dispersion which contains the mixture. 
In particular, by means of the above disclosed techniques, photochromatic 
articles can be obtained, such as photochromatic ophthalmic lenses and 
photochromatic sun filters, that is to say, which are capable of 
constituting an at least partial screen towards the sun radiation, in a 
reversible way. 
Such articles can be advantageously used, e.g., as lenses for sun glasses, 
prescription-lenses, contact lenses, glasses for cars or transport means 
in general, and windows in the building sector. 
The following experimental examples are reported in order to illustrate the 
present invention without limiting it. The compounds reported in the 
Examples were prepared according to methods known from the prior art. 
In particular, optical photochromatic articles of polymethyl-methacrylate 
(PMMA) were obtained by adding the photochromatic compound and the 
polymerization initiator azo-bis(isobutyro-nitrile) (AIBN) to the monomer 
and then carrying out the polymerization by casting into moulds of a 
suitable shape. 
Optical articles of poly-diethylene-glycol-bis(allyl-carbonate) were made 
photochromatic by means of a surface impregnation technique. For that 
purpose, a solution or suspension is prepared of the photochromatic 
compound in a suitable solvent or dispersant, normally selected from among 
the usual organic solvents, silicone oils, fluorinated oils, and the like, 
and the photochromatic compound is transferred on to the polymeric 
substrate by dipping the polymeric article in said solution or suspension, 
for suitable times and at suitable temperatures.

A more detailed description of the application processes used is given in 
the hereinunder reported experimental examples. 
On the optical photochromatic articles obtained, the following 
characteristics are determined: 
The U.V.-visible spectrum in the deactivated status (optical density at 
.lambda..sub.max), as determined by the Cary 2300 spectrophotometer. 
The change in light transmittance (.DELTA.Y) at 23.degree. C., as 
determined by the MACBETH spectrophotometer, after a 120-second activation 
with an UV-A lamp of 9 W/m.sup.2 of irradiance. The values of .DELTA.Y 
were also measured after a 4-minute exposure to sun light, by using the 
Gardner's Hazemeter XL 211. 
Kinetics of return to the deactivated form (time for recovery of 50% of the 
initial transmittance, t.sub.1/2), by means of a MACBETH 
spectrophotometer, under the same activation conditions as hereinabove 
disclosed. 
Ageing resistance, as determined by means of an Atlas Weather-O-Meter 
equipped with a continuous-irradiation xenon lamp of 6,500 W, operating at 
a temperature of 63.degree. C. on the reference black panel, and at a 
relatively humidity of 50%. The ageing resistance is evaluated by 
measuring, after various times of exposure in the Weather-O-Meter, the 
values of optical density at .lambda..sub.max of the deactivated form, and 
the residual value of .DELTA.Y after activation with the UV-A lamp. 
EXAMPLE 1 
Photochromatic lenses of poly-diethylene-glycol-bis(allyl-carbonate) are 
prepared by means of surface impregnation with mixtures of (A) and (E) 
photochromatic compounds in the following proportions: 
______________________________________ 
Photochromatic Mixture 
(a) (b) (c) 
______________________________________ 
(A) Compound (% by weight) 
20 30 40 
(E) Compound (% by weight) 
80 70 60 
______________________________________ 
In particular, a dispersion of 2% by weight of said (a), (b) or (c) mixture 
in silicone oil is prepared. 
In order to transfer the photochromatic compound, the lens is dipped into 
the siliconic dispersion for times ranging from 30 to 90 minutes, and at 
temperatures comprised within the range of from 170.degree. to 190.degree. 
C., as a function of the desired value for optical density. At the end of 
the impregnation, the lens is washed with petroleum ester, and the 
characteristics as listed hereinabove in the specification are evaluated. 
The results relevant to the (a), (b) and (c) photochromatic mixtures are 
reported in Table (I), as compared to those obtained on a lens obtained, 
under the same conditions, by using the (A) photochromatic compound alone. 
TABLE 1 
______________________________________ 
Photochromatic 
Optical Optical t.sub.1/2 
Compound/ Density Status .DELTA.Y 
(23.degree. C. 
Composition (.lambda..sub.max) 
Colour (23.degree. C.) 
sec.) 
______________________________________ 
(a) Composition 3,807 gray-blue 
32.2 44 
(348 nm) 
(b) Composition 3,699 gray-blue 
36.1 50 
(350 nm) 
(c) Composition 4,116 gray- 34.9 45 
(350 nm) violet 
(A) Photochromatic 
2,796 violet 36.8 56 
Compound (362 nm) 
(E) Photochromatic 
2,455 light 18.7. 60 
Compound (346 nm) blue 
______________________________________ 
In Table II, the results obtained from the accelerated ageing tests in 
W-O-M are reported. 
TABLE II 
__________________________________________________________________________ 
Photochromatic Compound/ 
Exposure in W-O-M (hours) 
Composition O.D. 
(23.degree. C.) 
O.D. 
(23.degree. C.) 
O.D. 
(23.degree. C.) 
__________________________________________________________________________ 
(a) Composition 
3.137 
29.3 2.960 
28.9 2.680 
25.1 
(b) Composition 
3.097 
32.2 2.845 
32.2 2.530 
26.9 
(c) Composition 
3.154 
32.0 2.883 
34.0 2.538 
26.8 
(A) Compound 1.610 
33.0 0.800 
21.8 0.380 
9.0 
(E) Compound 1.800 
18.2 1.604 
18.0 1.403 
18.1 
__________________________________________________________________________ 
From an examination of these results, it is clear that the (a), (b) and (c) 
mixtures, with the photochromatic activity (.DELTA.Y), and the return 
times back to the deactivated status (t.sub.1/2), being the same, show, as 
compared to the individual photochromatic (A) and (E) products, the 
advantages of a colour of the activated status which is more neutral, and 
can be modulated 
as a function of their ratio by weight; a considerably higher ageing 
strength and photochromatic activity then the pure (A) product, and the 
pure (E) product, respectively. 
EXAMPLE 2 
The photochromatic response to sun light exposure is evaluated of a neutral 
lens of poly-diethylene-glycol-bis(allyl carbonate) impregnated with the 
(b) photochromatic mixture of Example 1, as compared to a similar lens 
impregnated with the spiro-oxazinic photochromatic compound known from the 
prior art, having the formula: 
##STR13## 
wherein the two methyl groups on the benzene-indolinic ring are in the 
4,5- and 5,6-positions. 
Both of them were activated by a 4-minute exposure to sun light, and were 
evaluated for the change in light transmittance (.DELTA.Y) shown by the 
two lenses following said exposure, and measured by means of the Gardner's 
Hazegard XL 211. 
The results are reported in Table III. 
TABLE III 
______________________________________ 
Photochromatic 
(b) Spiro-Oxazine 
Compound/ Photochromatic 
from the Prior 
Composition Mixture Art 
______________________________________ 
Optical density 
3.482 1.792 
(.lambda..sub.max) 
(350 nm) (347 nm) 
Activated status 
gray-blue blue 
colour 
Deactivated status 
88 90 
transmittance (%) 
Activated status 
45 54 
transmittance (%) 
.DELTA.Y (%), at 23.degree. C. 
43 54 
t.sub.1/2 (23.degree. C., sec.) 
50 110 
______________________________________ 
As compared to the lens with the spiro-oxazine known from the prior art, 
the lens obtained with the (b) photochromatic mixture of the present 
invention shows a more neutral colour of the activated status, a higher 
photochromatic activity (.DELTA.Y), and a twice as high return rate to the 
deactivated status 
EXAMPLE 3 
With the (b) photochromatic mixture of the previous example, a neutral 
photochromatic lens of poly-(methyl-methacrylate) is prepared, which has 
the following composition: 
______________________________________ 
(b) photochromatic mixture 
10 mg 0.066 
parts 
Methyl-methacrylate 
15 g 100 parts 
Azo-bis(isobutyro-nitrile) 
0.15 g 0.100 
parts 
______________________________________ 
The polymerization of the lens is carried out by casting, maintaining the 
mould in a temperature-controlled water bath at 55.degree. C. for 80 
hours. 
At the end of the polymerization, by opening the mould, a photochromatic 
lens of poly(methyl methacrylate) is obtained, which has the 
characteristics as reported in Tables IV and V. 
In the same tables, also the characteristics are reported for comparison 
purposes, of lenses obtained, with the other conditions being the same, by 
separately using the individual (A) and (E) photochromatic compounds. 
TABLE IV 
______________________________________ 
Photochromatic 
Optical Activated t.sub.1/2 
Compound/ Density Status .DELTA.Y 
(23.degree. C. 
Composition 
(.lambda..sub.max) 
Colour (23.degree. C.) 
sec.) 
______________________________________ 
(b) Composition 
3.490 gray-blue 26.0 28 
(349 nm) 
(A) Compound 
3.620 violet 30.2 29 
(363 nm) 
(E) Compound 
3.020 light 4.2 11 
347 nm) blue 
______________________________________ 
TABLE V 
__________________________________________________________________________ 
Exposure in W-O-M (hours) 
Photochromatic Compound/ 
.DELTA.Y .DELTA.Y .DELTA.Y 
Composition (O.D.) 
(23.degree. C.) 
(O.D.) 
(23.degree. C.) 
(O.D.) 
(23.degree. C.) 
__________________________________________________________________________ 
(b) Composition 
3.312 
20.9 3.306 
19.5 3.268 
17.6 
(A) Compound 3.412 
27.9 3.304 
26.4 3.234 
24.0 
(E) Compound 2.402 
3.8 1.620 
3.0 
__________________________________________________________________________ 
These results demonstrate that in poly-(methyl methacrylate), the (b) 
composition according to the present invention unexpectedly shows 
photochromatic characteristics as well a stability, which are similar t o 
those of the pure (A) photochromatic compound, even if it is constituted 
for its major portion by the (E) photochromatic compound, which, in the 
pure state, displays very bad photochromatic characteristics and ageing 
resistance. 
EXAMPLE 4 
A mixture is prepared, which is constituted by a polypropylene powder of 
MOPLEN FLF 20 type, having a fluidity degree of 11, manufactured by 
HIMONT, and by the (b) photochromatic mixture of Example 1, in the mutual 
ratio by weight to each other of respectively 100:0.25. 
For comparison purposes, mixtures of polypropylene with the individual (A) 
and (E) photochromatic compounds in the same weight ratios are prepared. 
Said polymeric mixtures are transformed into films of 50 m of thickness by 
extrusion at the temperature of 215.degree. C. The photochromatic 
characteristics of the so-obtained films, and the relevant resistances 
under such conditions as reported in the text, are reported in Table VI. 
TABLE VI 
__________________________________________________________________________ 
Polypropylene film - Thickness 50 m - Photochromatic product 
concentration 0.1% 
Photochromatic/Compound 
0 .DELTA.Y 
t.sub.1/2 
15 .DELTA.Y 
t.sub.1/2 
30 .DELTA.Y 
t.sub.1/2 
Composition (O.D.) 
23.degree. C. 
seconds 
(O.D.) 
23.degree. C. 
seconds 
(O.D.) 
23.degree. C. 
seconds 
__________________________________________________________________________ 
(b) Composition 
0.124 
16.3 
21 0.097 
11.8 
18 0.077 
3.9 29 
(A) Compound 0.169 
18.4 
22 0 0 / 
(E) Compound 0.100 
4.2 10 0.08 
0 / 
__________________________________________________________________________ 
EXAMPLE 5 
A mixture of the (D) and (G) photochromatic compounds in the weight ratio 
of 60/40 is prepared. 
Said mixture is applied by surface impregnation to neutral lenses of 
poly-diethylene-glycol-bis(allyl carbonate), and is evaluated as disclosed 
at Example 1. 
The results are reported in Table VII. 
TABLE VII 
______________________________________ 
Optical density (.lambda..sub.max) 
2.944 (345 .mu.m) 
Colour in the activated status 
violet 
.DELTA.Y (23.degree. C.) 
31.7 
t.sub.1/2 (23.degree. C., seconds) 
55 
Ageing in W-O-M: 
52 hours, O.D. 1.728 
.DELTA.Y (23.degree. C.) 
24.8 
85 hours, O.D. 1.450 
.DELTA.Y (23.degree. C.) 
19.2 
158 hours, O.D. 1.077 
.DELTA.Y (23.degree. C.) 
18.1 
______________________________________ 
EXAMPLE 6 
The following mixtures with a different weight ratio between the 
photochromatic compounds (A) and (F) are prepared: Photochromatic 
______________________________________ 
Composition 1 2 3 4 5 
______________________________________ 
(A) Compound 
0 30 50 70 100 
(F) Compound 
100 70 50 30 0 
______________________________________ 
The mixtures Nos. 1 and 5, are reported for comparative purposes. 
Said mixtures were applied to the surface of neutral lenses of 
poly-diethylene-glycol-bis(allyl carbonate) according to the same 
technique as reported in Example 1. 
The resulting properties are reported in Table VIII. 
TABLE VIII 
__________________________________________________________________________ 
Composition No. 
1 2 3 4 5 
__________________________________________________________________________ 
Optical density (.lambda..sub.max) 
1.274 
&gt;4.500 
2.600 1.378 2.006 
Colour of the activated state 
light blue 
blue-violet 
blue-violet 
blue-violet 
violet 
.DELTA.Y 23.degree. C. 
18.8 29.4 29.7 32.7 35.4 
t.sub.1/2, 23.degree. C., seconds 
20 32 34 40 42 
__________________________________________________________________________ 
The reported data shows the synergistic effect of the two (A) and (F) 
products, in that the photochromatic activity of their mixtures is very 
close to the photochromatic activity displayed by the more active (A) 
compound alone, and the times of return back to the deactivated form are 
considerably shorter. 
The structures of a few photochromatic compositions of the invention are 
graphically illustrated in the accompanying drawings, wherein: 
FIG. 1 is an NMR.sup.1 H spectrogram of the photochromatic compound (A) at 
10-5 .delta.; 
FIG. 2 is a spectrogram similar to that of FIG. 1, but taken at 5-0 
.delta.; 
FIG. 3 is an NMR.sup.1 H spectrogram of the photochromatic composition (B); 
FIG. 4 is an NMR.sup.1 H spectrogram of the photochromatic composition (C), 
and 
FIG. 5 is an NMR.sup.1 H spectrogram of the photochromatic spectrogram of 
the photochromatic composition (D). 
For all the NMR.sup.1 H spectrograms shown in FIGS. 1-5, the substances to 
be tested were dissolved in deuterated chloroform.