More specifically, the present invention relates to photochromatic compounds belonging to the groups of chromenes and spiro-pyrans containing a 1, 3-oxazine-N- substituted ring in the molecule, a process for their preparation and their use in polymeric materials.

A further object of the present invention relates to polymeric compositions containing said photochromatic compounds and the photochromatic articles obtained from their processing.

Photochromatic compounds are substances which have the characteristic of reversibly changing colour and/or degree of light transmission when exposed to solar or ar- tificial light in the band ranging from W to visible, or

to some types of electromagnetic radiation, returning to their original state of colour and transmission when the initial light source is removed.

There are numerous substances with photochromatic characteristics, which belong to various groups of both organic and inorganic compounds such as, for example, those described in the texts"Photochromism", by G. H.

Brown (Ed.), Vol. III of the Weissberger series"Tech- niques of Organic Chemistry", Wiley Interscience, New York (1971) and in"Photochromism: Molecules and Systems", by H. Durer and H. Bouas-Laurent (Ed.), Vol. 40 of the series "Studies in Organic Chemistry"Elsevier (1990).

Among organic photochromatic compounds, those belong- ing to the groups of spiro-indolino-oxazines, spiro-pyrans and chromenes, are particularly known and used.

The above compounds are capable of giving photo- chromatic characteristics to polymeric organic materials used, for example, in the production of photochromatic lenses for eye-glasses, special inks, toys, and in many other applications.

As an example, the following patents can be men- tioned: USA 3,562,172, USA 3,578,602, USA 4,215,010, USA 4,342,668, USA 5,055,576, USA 5,110,922, USA 5,186,867, EP 146,135, EP 134,633, EP 141,407, EP 245,020, EP 0315,224 and IT 1,238,694.

The Applicant has now found photochromatic compounds belonging to the group of chromenes and spiro-pyrans con- taining a 1,3-oxazine-N-substituted ring in the molecule, which have excellent photochromatic characteristics, opti- mum wear resistance and high colourability characteris- tics.

An object of the present invention therefore relates to photochromatic compounds belonging to the group of chromenes and spiro-pyrans, having general formula (I): wherein: -R represents a linear or branched Cl-calo alkyl group, said alkyl group optionally substituted with 1-10 halogen atoms selected from fluorine, chlorine and bromine, aryl groups selected from phenyl, biphenyl and naphthyl, hetero-aromatic groups with 5-10 at- oms, heterocyclic groups with 5-6 atoms, hydroxyl groups, carboxyl groups, cyano groups, linear or branched C1-C6 alkoxyl groups, or with a 1,2,2,6,6- pentamethylpiperidine group; a vinyl group; a (meth) allyl group; a linear or branched C2-C6

alkenyl group; an aryl group selected from phenyl, biphenyl and naphthyl, said aryl group optionally substituted with linear or branched C1-C6 alkoxyl groups, carboxyl groups, N, N-dialkyl- (Cl-C6)-amine groups; a COOR'a ester group wherein R'a represents a linear or branched Cl-Cl0 alkyl group; a benzyl group, said benzyl group optionally substituted with 1-5 halogen atoms selected from fluorine, chlorine and bromine, or with C (X') 3 groups wherein X'is se- lected from fluorine, chlorine and bromine, linear or branched Cl-calo alkyl groups, linear or branched C1-C6 alkoxyl groups, carboxyl groups, cyano groups, or with a 1, 2,2,6,6-pentamethylpiperidine group ; or R represents a linear or branched Ci-Cio alkyl group substituted with an ORy group wherein Ry represents a linear or branched hydroxy- (Cl-C6)-alkyl group, a (meth) allyl group, a (meth) acrylic group, a linear or branched carboxy- (Cl-C6)-alkyl group, an acyloxyl group, a group having general formula (II): wherein R'1, R'2 and R'3, the same or different, rep-

resent a hydrogen atom; a linear or branched Cl-Clo alkyl group, said alkyl group optionally substituted with 1-10 halogen atoms selected from fluorine, chlorine and bromine, linear or branched Cl-C6 alk- oxyl groups, carboxyl groups, cyano groups, or with an N, N-dialkyl- (Cl-C6)-amine group, or with a cyclic amine; a vinyl group; a (meth) allyl group; a linear or branched C2-Clo alkenyl group; a COOR'a ester group wherein R'a represents a linear or branched Cl-Cl0 alkyl group; a benzyl group, said benzyl group optionally substituted with 1-5 halogen atoms se- lected from fluorine, chlorine and bromine, or with C (X') 3 groups wherein X'is selected from fluorine, chlorine and bromine, linear or branched Cl-Cl0 alkyl groups, linear or branched Cl-C6 alkoxyl groups, carboxyl groups, cyano groups, or with a 1,2,2,6,6- pentamethylpiperidine group; a linear or branched C1-C6 alkoxyl group ; an N, N-dialkyl- (Cl-C6)-amide group; and n is an integer ranging from 0 to 11, ex- tremes included; or R represents one of the follow- ing groups having general formula (III), (IV) or (V):

wherein R'4, R's and R'6, the same or different, rep- resent a linear or branched Ci-Cio alkyl group; a linear or branched Cl-C6 alkoxyl group ; a hydroxyl group; a tri-alkyl-(Cl-C6)-siloxyl group; or a group having the formula :-0- (CH2) 2-0 (CH2) 2-OCH3; m is an integer ranging from 1 to 6, extremes included; Rl, R2, R3 and R4, the same or different, represent a hydrogen atom; a halogen atom selected from fluo- rine, chlorine, bromine and iodine; a linear or branched Cl-Cl0 alkyl group, said alkyl group option- ally substituted with 1-10 halogen atoms selected from fluorine, chlorine and bromine, linear or branched Cl-C6 alkoxyl groups, ORx groups wherein Rx represents a linear or branched hydroxy- (Cl-C6)- alkyl group, carboxyl groups, hydroxyl groups, cyano groups, or with a 1,2,2,6,6-pentamethylpiperidine

group; a benzyl group, said benzyl group optionally substituted with 1-5 halogen atoms selected from fluorine, chlorine and bromine, or with C (X') 3 groups wherein X'is selected from fluorine, chlo- rine and bromine, linear or branched Cl-Cl0 alkyl groups, linear or branched Cl-C6 alkoxyl groups, carboxyl groups, cyano groups, or with a 1,2,2,6,6- pentamethylpiperidine group; a hydroxyl group; a hy- droxy- (Cl-C6)-alkyl group; a linear or branched Cl-C6 alkoxyl group, said alkoxyl group optionally substi- tuted with hydroxyl groups; an N, N-dialkyl- (Cl-C6)- amine group ; a piperidine, piperazine or morpholine group; a Cl-C6 carboxyalkyl group; a C2-C6 car- boxyalkenyl group ; a carboxyamide group; an N, N- dialkyl- (Cl-C6)-carboxyamide group; a cyano group; a nitro group; a sulfonic group; an aryl group se- lected from phenyl, biphenyl and naphthyl, said aryl group optionally substituted with N, N-dialkyl- (Cl- C6)-amine groups, linear or branched C1-C6 alkoxyl groups, hydroxyl groups, linear or branched C1-C6 alkyl groups; an acyl group of the alkyl ketone, aryl ketone or benzyl ketone type; a vinyl group; a (meth) allyl group ; a (meth) acrylic group; a hetero- allyl group; a linear or branched C2-C6 alkenyl group, said alkenyl group optionally substituted

with one or two N, N-dialkyl- (Cl-C6)-4-aniline groups ; an N-2,3-dihydroindoline group; a linear or branched C1-C6 thioether group; two consecutive substituents between Ri, R2, R3 and R4 can represent the condensation points with other aromatic, heterocyclic or quinonic rings; P represents one of the following groups having gen- eral formula (VI) or (VII): wherein R5, R6, R7, R8, Rg, Rlo/Rll and R12, the same or different, have the same meanings as the Ri-R4 substituents described above; two consecutive sub- stituents between R5 and R12 can represent the con- densation points with other aromatic, heterocyclic or quinonic rings; Ra represents a methylene group; a vinylene group; a carbon-carbon bond; q is 0,1 or 2; B and B1 are selected from the following groups: (i) aryl, phenyl and naphthalene groups, said aryl, phenyl and naphthalene groups optionally mono-, di-

or tri-substituted; (ii) heterocyclic aromatic groups such as, for example, pyridyl, furanyl, ben- zofuran-2-yl, benzofuran-3-yl, thienyl, benzothien- 2-yl, benzothien-3-yl, said heterocyclic aromatic groups optionally mono-or di-substituted; said aryl, phenyl, naphthalene and heterocyclic aromatic groups optionally being substituted with hydroxyl groups, piperidine groups, morpholine groups, pyr- role groups, linear or branched Cl-C6 alkyl groups, linear or branched Ci-C6 chloro-alkyl groups, linear or branched Cl-C6 fluoro-alkyl groups, linear or branched Cl-C6 alkoxyl groups optionally substituted with hydroxyl groups, linear or branched C1-C4 alkyl groups substituted with hydroxyl groups, linear or branched C1-C6 alkoxyl groups, acryloxyl groups, methacryloxyl groups, halogen atoms selected from chlorine and fluorine; (iii) groups represented by the following general formulae (VIII) or (IX):

wherein E represents a carbon atom or an oxygen atom; D represents an oxygen atom or a substituted nitrogen atom, on the condition that, when D repre- sents a substituted nitrogen atom, E represents a carbon atom, said nitrogen atom being substituted with linear or branched C1-C6 alkyl groups, or with C2-C6 acyl groups; R13 represents a linear or branched Cl-C6 alkyl group, a linear or branched Cl- C6 alkoxyl group, a hydroxyl group, a halogen atom selected from chlorine and fluorine; R14 and Ris each independently represent a hydrogen atom, a linear or branched Cl-C6 alkyl group; p'is 0,1 or 2; (iv) linear or branched Cl-C6 alkyl groups, lin- ear or branched Cl-C6 chloro-alkyl groups, linear or branched Cl-C6 fluoro-alkyl groups, linear or branched Cl-C4 alkyl groups substituted with linear or branched Cl-C6 alkoxyl groups, C3-C6 cycloalkyl groups optionally mono-substituted with a linear or branched Cl-C6 alkoxyl group or with a linear or branched Cl-C6 alkyl group, or with a halogen atom selected from chlorine and fluorine; (v) a group

having general formula (X): wherein F represents a hydrogen atom, a linear or branched Ci-C4 alkyl group; and Z is selected from the following groups: naphthyl, phenyl, furanyl, thienyl, said naphthyl, phenyl, furanyl and thienyl groups, optionally mono-or di-substituted with lin- ear or branched Cl-C4 alkyl groups, linear or branched Cl-C4 alkoxyl groups, halogen atoms se- lected from fluorine and chlorine; (vi) or, B and Bu considered jointly, represent a fluoren-9-ylidene group, said fluoren-9-ylidene group optionally mono- or di-substituted with linear or branched C1-C4 al- kyl groups optionally substituted with hydroxyl groups, linear or branched C1-C4 alkoxyl groups op- tionally substituted with hydroxyl groups, hydroxyl groups, halogen atoms selected from fluorine and chlorine, or they represent a group selected from spiro-monocyclic C3-Cl2 saturated hydrocarbon rings such as, for example, cyclopropylidene, cyclobu- tylidene, cyclopentylidene, cyclohexylidene, cyclo- heptylidene, cyclo-octylidene, cyclononylidene, cy- clodecylidene, cycloundecylidene, cyclododecylidene;

spiro-bicyclic C7-Cl2 saturated hydrocarbon rings such as, for example, bicyclo [2.2.1] heptylidene (norbornylidene), 1,7,7,-trimethyl- bicyclo [2.2.1] heptylidene (bornylidene), bicy- clo [3.2. lloctylidene, bicyclo- [3. 3.1] nonan-9- ylidene, bicyclo [4.3.2] undecane; spiro-tricyclic C7- Cl2 saturated hydrocarbon rings such as, for exam- ple, tricyclo [2.2.1.02w6Xheptylidene, tricyclo [3.3.1.13, 7] decylidene (adamantylidene), tricy- clo [5. 3.1.12'6] dodecylidene.

Preferred photochromatic compounds having general formula (I) for the purposes of the present invention are those wherein: -R represents one of the following groups: methyl, ethyl, isopropyl, 2- (meth) allyl, 2-carboxymethyl, phenyl, 4-N, N-dimethylaminoaniline, 4-methoxy- benzene, 4-cyanobenzene, 2-methoxyethyl (-CH2CH2OCH3), hydroxyalkyl such as (-CH20H) or (-CH2CH20H), ; or it represents an alkyl group sub- stituted with an ORy group wherein Ry represents a (meth) acrylic group; a group having general formula (II) wherein R'1, R'2 and R'3, the same or different, represent a methoxyl group or an ethoxyl group and n is 3; or it represents a group having general for- mula (III), (IV) or (V), wherein R'd, R'5 and R'6,

the same or different, represent one of the follow- ing groups: methyl, hydroxyl, methoxyl, ethoxyl, an -0- (CH2) 2-O (CH2) 2-OCH3, group, or a tri-methylsiloxyl group and m ranges from 2 to 6, extremes included; Rl, R2, R3 and R4, the same or different, represent a hydrogen atom, a fluorine atom, a chlorine atom, a bromine atom, or one of the following groups: methyl, isopropyl, hydroxyl, 2-hydroxyethyl, meth- oxyl, N, N-dimethylamine, piperidine, morpholine, carboxyl, carboxymethyl, N, N-dimethyl-carboxyamide, cyano, nitro, methylketone, phenylketone, phenyl, ORx wherein Rx represents 2-hydroxyethyl; P represents one of the groups having general for- mula (VI) or (VII) wherein: -R5, R6, R7, R8, Rg, Rlo/Rll and Rl2, have the same meanings as Rl, R2, R3 and R4 described above; -two consecutive substituents between R3 and Rlo can represent the condensation point with other aromatic, heterocyclic or quinonic rings; -Ra represents a carbon-carbon bond; q is 0; -B and Bi, are each independently selected from the following groups: (i) phenyl groups option- ally mono-or di-substituted; (ii) heterocyclic aromatic groups such as, furanyl, benzofuran-2-

yl, thienyl, benzothien-2-yl, said heterocyclic aromatic groups optionally mono-or di- substituted; said phenyl and heterocyclic aro- matic groups being optionally substituted with hydroxyl groups, linear or branched Cl-C3 alkyl groups, Cl-C2 hydroxyalkyl groups, linear or branched C1-C3 alkoxyl groups, halogen atoms selected from chlorine and fluorine; (iii) groups represented by general formula (VIII) wherein E represents a carbon atom, D an oxygen atom; R13 represents a linear or branched C1-C3 alkyl group, a linear or branched Cl-C3 alkoxyl group; Ri4 and Ris each independently represent a hydrogen atom, a linear or branched Cl-C3 al- kyl group,; p'is 0 or 1; (vi) or, B and B' considered jointly, represent a fluoren-9- ylidene group, or a group selected from: ada- mantylidene, bornylidene, norbornylidene, bicy- clo [3.3.1] nonan-9-ylidene.

Specific examples of preferred compounds according to the present invention, but which should in no way be considered as limiting its scope, are: -The compound having formula (Ia) :

The compound having formula (Ib) : The compound having formula (Ic): The compound having the formula (Id) :

A further object of the present invention relates to a process for the preparation of the photochromatic com- pounds having general formula (I).

The photochromatic compounds having general formula (I) can be prepared by the condensation of photochromatic compounds having general formula (XI): wherein Ri, R2, R3, R4 and P have the same meanings de- fined above, with amines having general formula (XII): H2N-R (XII) wherein R has the same meanings described above, in the presence of formaldehyde, an inert organic solvent such as, for example, ethanol, acetonitrile, etc., at a tem- perature ranging from 50°C to 80°C, preferably at 60°C, for a time ranging from 1 hour to 15 hours, preferably from 1 to 6 hours.

The reaction product thus obtained, corresponding to one of the photochromatic compounds having general for- mula (I), is purified by means of crystallization, or by elution on a silica column.

Examples of amines having general formula (II) are: 2-hydroxyethylamine, 3-hydroxypropylamine, 3-aminoprop- ylmethyldiethoxysilane, p-aminophenyltrimethoxysilane, 3- (2-aminophenoxy) propyltrimethoxysilane, etc.

The photochromatic compounds having general formula (XI) are obtained by the condensation of compounds deriv- ing from propargyl alcohol having general formula (XIII), or of compounds deriving from a, ß-unsaturated aldehydes having general formula (XIV), with hydroxy-aryl compounds having general formula (XV), to give the photochromatic compounds having general formula (XI), indicated in Schemes 1-2: SCHEME 1

SCHEME 2 wherein the substituents Rl, R2, R3, R4 and P have the same meanings defined above.

Said condensation reaction is carried out in the presence of an inert organic solvent such as, for exam- ple, ethyl alcohol, isopropanol, toluene, or a mixture of said solvents, and in the presence of an amine such as, for example, triethylamine, methylmorpholine, piperidine, or an acid such as, for example, paratoluenesulfonic acid, sulfuric acid, acid alumina, or a metallic complex such as, for example, titanium (IV) tetra-ethoxide, as catalyst, at a temperature ranging from 50°C to 100°C, preferably from 60°C to 75°C, for a time ranging from 1 hour to 10 hours, preferably from 2 hours to 3 hours. The reaction product thus obtained is generally purified by means of elution on a silica column and subsequent crys- tallization from a solvent such as, for example, acetone, toluene, hexane, heptane, pentane, diethyl ether.

The compounds deriving from propargyl alcohol having general formula (XIII) can be prepared by the reaction of

ketone compounds with sodium acetylide in xylene or with a lithium acetylide/ethylenediamine complex as described, for example, in U. S. patent 5,585,042 and 5, 238,981.

The compounds deriving from a,-unsaturated alde- hydes having general formula (XIV) can be prepared ac- cording to processes known in the art as described, for example, in Japanese patent application JP 48/016482; or in"Organic Synthesis" (1970), Vol. 50, page 66.

The hydroxy-aryl compounds having general formula (XV) are usually products which are commercially avail- able such as, for example, 2,6-dihydroxynaphthol.

Specific examples of derivatives of propargyl alco- hol having general formula (XIII) are the following:

Specific examples of a, ß-unsaturated aldehydes hav- ing general formula (XIV) are the following: Specific examples of hydroxy-aryl compounds having gen- eral formula (XV) are the following:

The photochromatic compounds having general formula (I), object of the present invention, are colourless or lightly coloured powders.

Their solutions in common organic solvents, such as benzene, toluene, methanol, ethanol, for example, when not exposed to light sources, are colourless or slightly amber-coloured. When said solutions are exposed to a light source, either visible or ultraviolet, they become yellow-orange coloured, or pink. The colouring rapidly fades when the light source is removed.

The photochromatic compounds having general formula (I), object of the present invention, can be applied to the surface or incorporated in mass into the desired arti- cles, using techniques already known in the art and de- scribed hereunder.

Some polymeric photochromatic end-articles can be ob- tained with moulding techniques such as, for example, in- jection or compression moulding, starting from polymers in which one or more of the photochromatic compounds in the

solid state having formula (I) are homogeneously dispersed in mass.

Alternatively, the photochromatic compounds having general formula (I) can be dissolved in a solvent, to- gether with the polymeric material such as, for example, polymethyl methacrylate, polyvinyl alcohol, polyvinyl bu- tyral, cellulose acetate butyrate or epoxy, polysiloxane, urethane resin.

The mixture thus obtained is deposited on a transpar- ent base to form, after evaporation of the solvent, a pho- tochromatic coating.

The photochromatic compounds having general formula (I) described above, can also be added to a polymerizable monomer such as, for example, a meth (acrylic) or allyl carbonate monomer, so that, after polymerization carried out in the presence of a suitable initiator such as, for example, azo-bis (isobutyronitrile) in the case of the meth (acrylic) monomer, or a peroxyketal in the case of the allyl carbonate monomer, they are uniformly incorporated in the resin formed.

Finally, the photochromatic compounds having general formula (I) can be applied to a transparent substrate such as, for example, polycarbonate, polymethyl methacrylate or polydiethyleneglycol bis (allyl carbonate), by means of surface impregnation obtained by putting the substrate in

contact, at a suitable temperature, with a solution or dispersion containing one or more of the photochromatic compounds having general formula (I), operating according to a known method described, for example, in U. S. patent 5,130,353.

The photochromatic compounds having general formula (I), object of the present invention, have the charac- teristic of being able to be incorporated in mass, or us- ing one of the techniques described above, into various organic polymers such as, for example, high density poly- ethylene (HDPE), low density polyethylene (LDPE), ethyl- ene-vinylacetate copolymer, polyether amides, polypropyl- ene, polymethyl methacrylate, polyvinyl alcohol, polyvinyl butyral, cellulose acetate butyrate, epoxy, polysiloxane or urethane resins, polycarbonate, polydiethylene glycol bis (allyl carbonate), polyamides, polyesters, polystyrene, polyvinylchloride, polyethylacrylate, siliconic polymers.

A further object of the present invention therefore relates to polymeric compositions comprising the above polymeric materials and the above photochromatic compounds having general formula (I) and the photochromatic articles obtained from their processing.

The photochromatic compounds having general formula (I), object of the present invention, are added to the above polymeric compositions in a quantity ranging from

0.01% to 5% by weight, preferably between 0.1% and 2% by weight, with respect to the weight of said polymeric com- positions.

The photochromatic compounds having general formula (I), object of the present invention, can also be added to coating compositions, such as for example, paints, lac- quers, paints or lacquers based on hybrid polysiloxanes and/or silica gel, compositions based on plastic materi- als.

A further object of the present invention therefore relates to coating compositions, such as for example, paints, lacquers, paints or lacquers based on hybrid poly- siloxanes and/or silica gel, compositions based on plastic materials, comprising said photochromatic compounds.

The photochromatic compounds having general formula (I), object of the present invention, are added to the above coating compositions in a quantity ranging from 0.01% to 12% by weight, preferably between 0. 1% and 4% by weight, with respect to the weight of said coating compo- sitions.

Paints or lacquers based on hybrid polysiloxanes and/or silica gel are obtained by means of the"sol-gel" process described, for example, by M. Nogami, Y. Abe in: "Journal of Materials Science" (1995), Vol. 30, pages 5789-5792.

The above coating compositions can be applied to the substrate (metal, plastic, wood, etc.) using the conven- tional methods such as, for example, brushing, spraying, pouring, dipping or electrophoresis.

The photochromatic compounds having general formula (I), object of the present invention, can optionally be used in the presence of the usual additives for organic polymers such as, for example, phenolic antioxidants, sterically hindered amines, benzotriazoles, benzophenones, phosphites or phosphonites, enamines.

The photochromatic compounds having general formula (I), object of the present invention, which, as already specified above, are colourless or have a light colouring, can be used as such, mixed with each other, or in a combi- nation with other suitable organic photochromatic com- pounds in order to obtain, after activation, the formation of colourings such as brown and grey. Particularly useful for this purpose are photochromatic compounds belonging to the group of spiro-indoline-oxazines or spiro-pyrans de- scribed in the art, for example, in U. S. patent 5,066,818.

Some illustrative examples are provided for a better understanding of the present invention and for its em- bodiment but should in no way be considered as limiting the scope of the invention itself.

EXAMPLE 1

Preparation of the Compound having formula (XIII)-1 48 g of 4,4'-dimethoxybenzophenone and 90 ml of tet- rahydrofuran are charged into a 250 ml flask, equipped with a reflux cooler and mechanical stirrer. 80 g of a suspension of sodium acetylide in xylene at 18% are added, under stirring, to the solution, obtaining a mix- ture which is saturated with gaseous acetylene and left at 40°C for 16 hours.

The above mixture is subsequently cooled to room temperature and 125 ml of water and 250 ml of toluene are added. The toluene phase is separated and concentrated, obtaining 50 g of a white crystalline precipitate corre- sponding to the compound having formula (XIII)-1 which is identified by means of gas-mass (molecular weight: 242.27).

EXAMPLE 2 Preparation of the Compound having formula (XI)-1.

10 g of 2,6-dihydroxynaphthalene having formula (XV)-1, 17 g of the Compound having formula (XIII)-1 ob- tained as described in Example 1,90 ml of methylethylke- tone and 1 ml of trifluoroacetic acid are charged into a 200 ml flask equipped with a reflux cooler and mechanical stirrer: the mixture is left, under stirring, at 25°C for 6 hours.

10 g of activated carbon and 50 ml of toluene are added to the reaction raw product obtained: the mixture is heated to 60°C for 1 hour. The organic phase is subse- quently filtered and concentrated and the raw product ob- tained is recrystallized twice with 100 ml of toluene ob- taining 11.2 g of a product corresponding to the Compound having formula (XI)-1 which is identified by means of gas-mass (molecular weight = 410).

EXAMPLE 3 Preparation of the Compound having formula (Ia).

4.10 g of the Compound having formula (XI)-1 ob- tained as described in Example 2,0.84 g of formaldehyde, 25 ml of ethanol and 0.84 g of 2-hydroxyethylamine are charged into a 50 ml flask equipped with a bubble cooler and magnetic stirrer: the mixture is heated to reflux temperature for 2 hours.

A white precipitate is obtained, which is cooled to room temperature, filtered and washed with ethanol (20 ml) obtaining 3.25 g of a product corresponding to the Compound having formula (Ia) which is identified by means of gas-mass (molecular weight = 495).

EXAMPLE 4 Preparation of the Compound having formula (Ib).

2.05 g of the Compound having formula (XI)-1 ob- tained as described in Example 2,0.32 g of formaldehyde, 20 ml of acetonitrile, 1. 1 g of 3-aminopropyl- methyldiethoxysilane and 4 g of calcium sulfate are charged into a 50 ml flask equipped with a bubble cooler and magnetic stirrer: the mixture is heated to reflux temperature for 4 hours.

A reaction raw product is obtained, which is cooled to room temperature, washed with toluene (10 ml), fil- tered and dried under vacuum obtaining a powder.

The above powder is recrystallized with 30 ml of toluene obtaining 0.5 g of a precipitate having a slightly amber-colouring corresponding to the Compound having formula (Ib) which is identified by means of liq- uid chromatography on a column (HPLC) coupled with a gas- mass (molecular weight = 625).

EXAMPLE 5 Evaluation of the photochromatic activity.

The photochromatic activities of Compounds (Ia) and (Ib) are evaluated according to the following procedure.

Solutions are prepared at a concentration equal to 10-4 M (the exact concentrations are indicated in Table 1) of Compounds (Ia) and (Ib) in toluene and 1.3 ml of each solution is subsequently placed in a 1 cm quartz cell hav- ing an inlet with a square base.

The quartz cell containing the solution is introduced into a Peltier temperature control system (HP accessory- Nr. HP 89090A), with the possibility of magnetic stirring during the measurement, and is radiated from above with a Philips WA lamp with irradiation equal to 9 Watt/cm2 resting on the cell itself. The irradiation time is 60'' in order to ensure that the maximum colouring degree of the solution is reached.

The spectrum of the solution is registered before and after irradiation between 400 nm and 700 nm with a Hewlett Packard HP 8452A spectrophotometer with photodiodes.

The following data are determined by means of a mathematical calculation effected with the Lotus 123v5w program based on the tristimulus theory: (a) (AY) which indicates the difference between the light transmittance (Y) of the solution before and after irradiation and represents the photochromatic activ- ity of the compound analyzed at the concentrations

indicated in Table 1; (b) AL*, Aa* and Ab which correspond to the variation in the colourimetric coordinates of the above solutions CIE 1976 (L*, a* and b*), corresponding to the gloss or luminosity (L*), to the red-green coordinate (a*) and yellow-blue coordinate (b*), before and after ir- radiation.

The data obtained are indicated in Table 1.

A further explanation of the above values and infor- mation relating thereto can be found, for example, in "Color Science: Concepts and Methods, Quantitative data and Formulae" (1982). G. Wyszecki and W. S. Stiles, 2ni Ed., New York.

TABLE 1 PHOTOCHROMATIC ACTIVITY AND COLOURIMETRIC DATA AT 20°C IN METHANOL Photochromatic Conc. AY ALt Aa Ab Compound (10-4 M) (Ia) 1.040 14.01-6.01 10.75 1.28 (Ib) 1.011 14. 20-6. 09 10.76 0.66