Photochromism is a well-known physical phenomenon that is observed with certain classes of chemical compounds. A detailed discussion of this phenomenon can be found in"Photochromism : Molecules and systems", Studies in Organic Chemistry 40, Eds. H. Durr and H. Bouas- Laurent, Elsevier, 1990.

The 2H-naphtho [1, 2-b] pyran system is known to be capable of exerting a photochromic effect as described, for example, in U. S. patent no. 3, 567, 605 and U. S. patent no. 4, 826, 977. U. S. patent no. 3, 567, 605 provides an example of a naphtho [1, 2-b] pyran which remains coloured at ambient temperatures for several hours, and U. S. patent no. 4, 826, 977 describes a series of yellow/orange colouring 2H-naphtho [1, 2-b] pyrans containing a spiro-adamantane group at the 2-position amongst other 2H-[1] benzopyran and isomeric naphthopyran systems. The basic structural unit of the 2H-naphtho [1, 2-b] pyran system, in this instance substituted at C-2 with a spiro-adamantane group, is illustrated below.

A range of purple/blue colouring 2 (4-aminophenyl)-2-alkyl-2H- naphtho [1, 2-b] pyrans have also been described in U. S. patent no. 4, 818, 096.

A series of photochromic 2H-naphtho [1, 2-b] pyrans, amongst other 2H [l] benzopyrans and isomeric naphthopyrans, bearing a cyclopropyl group as one of the substituents at the 2-position is described in patent publication W092/01959. It is also commented that the compound 2-cyclopropyl-2-p-methoxyphenyl-5-methyl-2H-naphtho [1, 2-b] pyran and several other analogues are of particular current interest, but no reasons are presented either to substantiate such interest or as to any significance of the 5-methyl group.

It is stated in U. S. patent no. 5, 066, 818 (1991) that"The compound, 2, 2-diphenyl-2H-naphtho [ 1, 2-bJpyran, also colours on exposure to near ultraviolet light at room temperature but does not bleach in a reasonable period of time. Substitution of the phenyl substituents in the meta and para positions have little effect on the rate of bleaching of these compounds." The very high optical density of 2, 2-diaryl-2H-naphtho [ 1, 2- b] pyrans achieved under irradiation and their slow attendant fade (bleaching) on removal of the source of irradiation relative to the photochromic properties displayed by the isomeric 3, 3-diaryl-3H-naphtho [2, 1-b] pyrans has been noted by B. van Gemert et al. (Mol. Cryst. Liq. Cryst. 1994, 246, 67).

The relatively slow attendant fade of the 2, 2-diaryl-2H-naphtho [ 1, 2- b] pyrans was rationalised by the absence of steric crowciing in the ring opened (coloured) quinoidal/zwitterionic forms. Such steric crowding is thought to be present for the ring opened form of the 3, 3-diaryl-3H- naphtho [2, 1-b] pyrans and accounts for their relatively rapid fade.

Pilkington Plc have also commented on the fading of photochromic materials in Research Disclosure {May (1994), No. 36144, p 267}. This disclosure reports that markedly improved rates of fade can be obtained for 2, 2-diaryl-2H-naphtho [ 1, 2-b] pyrans bearing substituents at both the 5-and 6-positions compared with 2, 2-diaryl-2H-naphtho [ 1, 2-b] pyrans that are unsubstituted at these sites. These substituents are reported to exert steric pressures upon the ring opened (coloured) forms and enhance the ring closure to the uncoloured naphthopyran system. However, these relatively fast fading materials described by Pilkington Plc with substituents at both the 5-and 6-positions are difficult to manufacture, requiring a long multi- stage process which renders them unattractive commercially. Thus the use of two substituents at the 5-and 6-positions to achieve rapid fade in these 2, 2-diaryl compounds has the disadvantage of manufacture complexities.

Two more recent U. S. patents no. 5, 458, 814 and no. 5, 514, 817 describe the synthesis of a range of fast fading intense yellow to red/purple colouring 2, 2-diaryl-2H-naphtho [ 1, 2-b] pyrans and phenanthropyrans which either possess a 5-substituent or are 5, 6-disubstituted.

International patent application WO 95/05382, describes some neutral colouring, typically brown, photochromic heterocyclochromenes in which the hetero ring is fused to either thef-or g-face of the benzopyran unit. No examples or claims pertaining to the h-fused isomers were made.

A range oft-fused heterocyclic pyrans has been described in U. S. patent no.

5, 527, 911 (1996). The examples reported in this work all possess unsubstituted phenyl groups at C-2 in the pyran ring and provide orange or red colouring compounds. A subsequent U. S. patent no. 5, 552, 091 (1996) claims -, g-and h-fused benzofuro-, benzothieno-and indolo-benzopyrans.

In all examples, regardless of the mode of ring fusion, C-2 of the pyran ring is substituted with at least one of the following tricyclic moieties : fluorenyl, dibenzofuryl, dibenzothienyl or carbazolyl. No examples of C-2 (monocyclic) diaryl substituents are claimed in this work. An additional PCT, WO 94/20869, also describesf-, g-and h-fusions of benzothiophene and benzofuran to 2, 2-diaryl benzopyrans. None of the reported examples pertain to heterocyclic fused 2, 2-diaryl benzopyrans in which the pendant aryl groups possess one or more cyclic amino substituents located in the para position.

In International patent application no. PCT/GB98/00904, there are described the synthesis and applications of some neutral colouring (brown or brown/red) photochromic 2, 2-diaryl-2H-naphtho [1, 2-b] pyrans.

The brown or brown/red colouring is obtained by substituting the 2, 2-diaryl- 2H-naphtho [1, 2-b] pyrans in the 7-and/or 9-position with an amino function. The general formula in PCT/GB98/00904 also covers brown or brown/red compounds in which one or both of the 2, 2-diaryl groups may be unsubstituted, mono-, di-or poly-substituted and among the possible substitutents are amino, amino C,-C, alkyl, alkyl C,-Cs amino, dialkyl Cl-C5 amino and certain cyclic amino groups. However, there are no specific Examples of such compounds, but only of 2, 2-diaryl alkoxy substituted compounds.

We have now found that, surprisingly, photochromic 2, 2-diaryl- 2H-naphtho [1, 2-b] pyrans wherein at least one of the aryl groups is substituted with an amino function, preferably in the para position to the point of attachment to the pyran ring, in addition to amino function substitution at the 7-and/or 9-position, exhibit neutral non-brown, non- brown/red colouring which is quite different from the neutral brown or brown/red described in PCT/GB98/00904. The presence of a 5 substituent in these pyrans may also provide for rapid fading of the colour generated upon irradiation.

The neutral non-brown, non-brown/red colours observed in the photochromic compounds of the invention are typically various shades and hues of grey, blue grey, purple grey, green grey and, on occasion, approach black. They typically result from multiple absorption bands at about 460- 520 nm and about 550-650 nm upon irradiation with sunlight or a suitable artificial light source. The bands are often broad and may overlap.

The provision of grey colouring photochromic compounds is highly advantageous. Previously, to achieve, for example, grey colouring, it was necessary to mix two or more compounds. A disadvantage of mixing two or more compounds is that it is very difficult to obtain a uniform grey at all times in the bleach/fade cycle.

The neutral non-brown, non-brown/red, which we shall refer to hereinafter as grey, compounds of the present invention provide photochromic materials with good rates of fade over a broad range of temperatures and intense neutral colour generation accompanied by negligible background colour. These features render these compounds particularly useful as photochromic materials for incorporation into polymeric host materials since the amount of photochromic material required to impart a useful photochromic effect into the host material may be greatly reduced, thereby offering a considerable saving of synthetic effort and cost over conventional materials which do not possess the claimed substitutents.

Examples of applications of the polymeric host materials of the present invention include the manufacture of lenses for sunglasses and ophthalmic lenses, protective visors, screens, films,'plastic'sheeting, containers (e. g. bottles and other packaging vessels), mirrors, windows and screens for vehicles such as cars (including sunroofs), motorcycles, aircraft and ships, architectural uses e. g. glazing, and artistic'stained glass'windows and for use in novelty items. Additionally the materials may be used in vehicle body panels including fairings and spoilers, and related external surfaces and other embodiments where it may be deemed attractive to have said objects change colour in the presence of sunlight. A further use is their incorporation into inks and other such formulations for'printing'onto paper and fabrics and other suitable surfaces. This latter application may be particularly useful for the preparation of security markers (labels) on a broad range of objects e. g. cheques, bonds, bankers drafts, credit cards, charge cards and identity documents and cards. Such inks and other like formulations may be used for printing documents and greetings cards. The security/identity uses of these photochromic compounds may also extend to include the marking of fuels e. g. petrol and diesel and other oils.

Furthermore, the materials may be used in optical data recording systems e. g. compact discs, and read/write optical data storage discs, as waveguides and laser dyes.

Typical host materials are optically clear or opaque polymer materials, such as polymers of polyol (alyl carbonate)-monomers, polyacrylates such as polymethylmethacrylates, poly (triethyleneglycol dimethylacrylate), polyperfluoroacrylates and cellulose acetate, cellulose triacetate, cellulose acetate propionate, cellulose acetate butyrate, poly (vinyl acetate), poly (vinyl alcohol), polyurethanes, polycarbonate, polyethylene terephthalate, polystyrene, polyfluorostyrene, poly (diethyleneglycol bis (alkyl carbonate)) and various copolymer mixes.

According to the present invention, there is provided a photochromic compound of the formula I In formula I above R'is selected from mono-, di-or poly- substituted aryl groups, mono-, di-or poly-substituted naphthyl groups and mono-, di-or poly-substituted heteroaryl groups (for example but not exclusively thienyl, benzothienyl, furyl, benzofuryl, pyrryl, indolyl, pyridyl, quinolyl, isoquinolyl, pyrimidyl, oxazolyl, isoxazolyl, thiazolyl, isothiazolyl, pyrazolyl, imidazolyl, benzimidazolyl, triazolyl, benzotriazolyl, tetrazolyl). The substituents for the aryl, naphthyl and heteroaryl groups representing R'are selected from the following nitrogen containing functionalities and are situated preferentially in a conjugating position, typically para to the point of attachment to the pyran ring : amino Cl-C2,, alkylamino, Cl-C2. dialkylamino, C2-C20 dialkenylamino, C2-C20 di (polyalkenyl) amino, arylamino, diarylamino, C1-C20 alkylarylamino, tetra (Ct-Cto linear or branched alkyl) guanidino and cyclic-amino groups (for example but not exclusively aziridino, pyrrolidino, piperidino, linear or branched C,-C2 alkylsubstituted piperidino, morpholino, thiomorpholino, indolino, piperazino, linear or branched C,-C2o N-alkylpiperazino, linear or branched Cl-C20 N- hydroxyalkylpiperazino, N-phenylpiperazino, N-arylpiperazino, homopiperidino). In addition to the above nitrogen containing function, R1 may also possess one or more additional substituents which are selected from hydrogen, linear or branched C1-C20 alkyl, C3-C20 cycloalkyl, C4-C20 bicycloalkyl (for example but not exclusively norbornyl), C5-C2o polycycloalkyl (for example but not exclusively adamantyl), linear or branched Ci-C2o haloalkyl, linear or branched C1-C20 perhaloalkyl, linear or branched C2-C20 alkenyl (E or Z isomers), linear or branched ¬2-020 polyalkenyl (any combinations of E or Z isomers), linear or branched C2-C20 alkynyl, linear or branched C4-C20 polyalkynyl, linear or branched Cl-C2o hydroxyalkyl, linear or branched Cl-C2o polyhydroxyalkyl, linear or branched C1-C20 alkoxy, linear or branched C1-C20 alkylthio, linear or branched C1-C20 (CI-C5 alkoxy) alkyl, linear or branched C1-C20 (C1-C5 alkylthio) alkyl, phenyl, aryl, heteroaryl, halogen, hydroxyl, formyl, acetyl, nitrile, carboxyl, C1-C5 alkoxycarbonyl, C1-C5 N-alkylamido, Cl-C5 N,N-dialkylamido, amido, nitro, amino, C,-C20 alkylamino, C1-C20 dialkylamino, C2- C20 dialkenylamino, C4-C20 di (polyalkenyl) amino, arylamino, diarylamino, Cl-C2o alkylarylamino, and cyclic-amino groups (for example but not exclusively aziridino, pyrrolidino, piperidino, linear or branched Cl-C20 alkylsubstituted piperidino, morpholino, thiomorpholino, indolino, piperazino, linear or branched Cl-C20 N- alkylpiperazino, linear or branched C1-C20 N-hydroxyalkylpiperazino, N- phenylpiperazino, N-arylpiperazino, homopiperidino), arylsulfanyl, aryloxy, arylsulfinyl, arylsulfonyl, linear or branched Cl-C20 alkylsulfonyl, di-(C1-C20 alkoxyalkyl) phosphonyl. Phenyl, aryl, naphthyl, and heteroaryl ring substituents may be located at the ortho-, meta-or para-positions. R'and or R2 may also be selected from the fused saturated heterocycles TI, ni and IV in which n and m are integers between 2 and 5 and may be the same or different.

Rl3 may be selected from linear or branched C1-C20 alkyl, C3-C20 cycloalkyl, C4-C20 bicycloalkyl, CS-C2o polycycloalkyl, linear or branched Cl-C20 hydroxyalkyl, linear or branched Cl-C2o haloalkyl, linear or branched C1-C20 perhaloalkyl, phenyl, Cl-C20 linear or branched alkylsulfonyl, aryl, tosyl, arylsulfonyl, acyl, linear or branched Cl-C2o alkylcarbonyl, benzoyl, aroyl, substituted aroyl, butoxycarbonyl.

R2 is selected from phenyl, mono-, di-or poly-substituted aryl groups, unsubstituted, mono-, di-or poly-substituted naphthyl groups and unsubstituted, mono-, di-or poly-substituted heteroaryl groups (for example but not exclusively thienyl, benzothienyl, furyl, benzofuryl, pyrryl, indolyl, pyridyl, quinolyl, isoquinolyl, pyrimidyl, oxazolyl, isoxazolyl, thiazolyl, isothiazolyl, pyrazolyl, imidazolyl, benzimidazolyl, triazolyl, benzotriazolyl, tetrazolyl). The substituents, of which there may be one or more, for the aryl, naphthyl and heteroaryl groups representing R2 may be hydrogen, linear or branched C1-C20 alkyl, C3-C20 cycloalkyl, C4-C20 bicycloalkyl (for example but not exclusively norbornyl), C5-C2o polycycloalkyl (for example but not exclusively adamantyl), linear or branched Cl-C20 haloalkyl, linear or branched C1-C20 perhaloalkyl, linear or branched C2-C20 alkenyl (E or Z isomers), linear or branched C4-C20 polyalkenyl (any combinations of E or Z isomers), linear or branched C2-C20 alkynyl, linear or branched C4-C20 polyalkynyl, linear or branched C1-C20 hydroxyalkyl, linear or branched C1-C20 polyhydroxyalkyl, linear or branched C1-C20 alkoxy, linear or branched C1-C20 alkylthio, linear or branched C1-C20 (Cl-Clo alkoxy) alkyl, linear or branched Cl-C20 (CI-C5 alkylthio) alkyl, phenyl, aryl, heteroaryl, halogen, hydroxyl, formyl, acetyl, nitrile, carboxyl, Ci-Cio alkoxycarbonyl, Cl-Clo N-alkylamido, Cl-C5 N, N-dialkylamido, amido, nitro, amino, Ci-C2o alkylamino, C1-C20 dialkylamino, C2-C20 dialkenylamino, C4-C20 di (polyalkenyl) amino, arylamino, diarylamino, Cl-C2o alkylarylamino, and cyclic- amino groups (for example but not exclusively aziridino, pyrrolidino, piperidino, linear or branched C,-C2o alkylsubstituted piperidino, morpholino, thiomorpholino, indolino, piperazino, linear or branched Cl-C20 N-alkylpiperazino, linear or branched <BR> <BR> <BR> <BR> Cl-C2o N-hydroxyalkylpiperazino, N-phenylpiperazino, N-arylpiperazino, homopiperidino), arylsulfanyl, aryloxy, arylsulfinyl, arylsulfonyl, linear or branched C1-C20 alkylsulfonyl, di-(C1-C20 alkoxyalkyl) phosphonyl in addition to those substituents specified for R'. Phenyl, aryl, naphthyl, and heteroaryl ring substituents may be located at the ortho-, meta-or para-positions.

R3 and R4, which may be the same or different, are selected from hydrogen, linear or branched C1-C20 alkyl, C3-C20 cycloalkyl, C4-C20 bicycloalkyl (for example but not exclusively norbornyl), C5-C20 polycycloalkyl (for example but not exclusively adamantyl), linear or branched Cl-C20 haloalkyl, linear or branched Cl- C20 perhaloalkyl, linear or branched C2-C20 alkenyl (E or Z isomers), linear or branched C4-C20 polyalkenyl (any combination of E or Z isomers), linear or branched C2-C20 alkynyl, linear or branched C4-C20 polyalkynyl, linear or branched Cl-C2o hydroxyalkyl, linear or branched CI-C2o polyhydroxyalkyl, linear or branched Cl-C2o alkoxy, linear or branched C1-C20 alkylthio, linear or branched C1-C20 (CI-Clo alkoxy) alkyl, linear or branched C1-C20 (CI-C5 alkylthio) alkyl, phenyl, aryl, heteroaryl, halogen, hydroxyl, formyl, acetyl, nitrile, carboxyl, Cl-C5 alkoxycarbonyl, Cl-C5 Nalkylamido, C1-C5 N,N-dialkylamido, amido, nitro, in addition to those groups specified for Rl and R2 above.

R5 is selected from linear or branched C1-C20 alkyl, C3-C20 cycloalkyl, C4-C20 bicycloalkyl (for example but not exclusively norbornyl), C5-C20 polycycloalkyl (for example but not exclusively adamantyl), linear or branched C,-C2o haloalkyl, linear or branched C,-C20 perhaloalkyl, linear or branched C2-C20 alkenyl (E or Z isomers), linear or branched C4-C20 polyalkenyl (any combination of E or Z isomers), linear or branched C2-C20 alkynyl, linear or branched C4-C20 polyalkynyl, linear or branched Cl-C20 hydroxyalkyl, linear or branched Cl-C20 polyhydroxyalkyl, linear or branched C1-C20 alkoxy, linear or branched C1-C20 alkylthio, linear or branched Cl-C2o (Ci-Cio alkoxy) alkyl, linear or branched C1-C20 (C1-C10 alkylthio) alkyl, phenyl, aryl, heteroaryl, halogen, hydroxyl, formyl, acetyl, linear or branched Cl-C2o alkanoyl, linear or branched C3-C20 alkenoyl, linear or branched C5-C20 polyalkenoyl, benzoyl, aroyl, heteroaroyl, nitrile, formyl, carboxyl, linear or branched Cl-C20 alkoxycarbonyl, C1-C20 N-alkylamido, C1-C20 N, N-dialkylamido, amido, nitro, amino, C1-C20 alkylamino, C1-C20 dialkylamino, C2-C20 dialkenylamino, C4-C20 di (polyalkenyl) amino, arylamino, diarylamino, C1-C20 alkylarylamino, and cyclic- amino groups (for example but not exclusively aziridino, pyrrolidino, piperidino, morpholino, thiomorpholino, indolino, piperazino, linear or branched C1-C20 N- alkylpiperazino, linear or branched C1-C20 N-hydroxyalkylpiperazino, N- phenylpiperazino, N-arylpiperazino, homopiperidino, Az-indolinyl) arylsulfanyl, aryloxy, arylsulfinyl, arylsulfonyl, linear or branched C,-C2o alkylsulfonyl, di- (Ci-C2o alkoxyalkyl) phosphonyl in addition to those substituents specified for R'and R2.

One or both of R7 and R9, which may be the same or different is selected from C1-C20 N-alkylamido, C,-C2o N, N-dialkylamido, amido, nitro, amino, C1-C20 alkylamino, C,-C2o dialkylamino, C2-C20 dialkenyiamino, C4-C20 di (polyalkenyl) amino, arylamino, diarylamino, C1-C20 alkylarylamino, and cyclic- amino groups (for example but not exclusively aziridino, pyrrolidino, piperidino, morpholino, thiomorpholino, indolino, piperazino, linear or branched C1-C20 N alkylpiperazino, linear or branched Cl-C20 N-hydroxyalkylpiperazino, N- phenylpiperazino, N-arylpiperazino, homopiperidino, N-indolinyl, N-1, 2, 3, 4- tetrahydrocarbazolyl, N-1, 2, 3, 4, 4a, 9a-hexahydrocarbazolyl, N-1, 2, 3, 4- tetrahydroquinolyl). Where only one of R7 or R9 is selected from the above nitrogen containing substituents, the other group R 7or R9 is selected from those substituents specified for R1, R2, R5, R6, R8 and R10.

R6, R R10, R11, R12, R14, R15, R17 and R18 which may be the same or different, are selected from hydrogen, linear or branched Cl-C2o alkyl, C3-C20 cycloalkyl, C4-C20 bicycloalkyl (for example but not exclusively norbornyl), C5-C20 polycycloalkyl (for example but not exclusively adamantyl), linear or branched C1-C20 haloalkyl, linear or branched C1-C20 perhaloalkyl, linear or branched C2-C2o alkenyl (E or Z isomers), linear or branched ¬4-020 polyalkenyl (any combination of E or Z isomers), linear or branched C2-C2o alkynyl, linear or branched C4-C20 polyalkynyl, linear or branched C1-C20 hydroxyalkyl, linear or branched Cl-C2o polyhydroxyalkyl, linear or branched C1-C20 alkoxy, linear or branched Cl-C20 alkylthio, linear or branched C1-C20(C1-C10 alkoxy) alkyl, linear or branched C1-C20 (Ci-CIO alkylthio) alkyl, phenyl, aryl, heteroaryl, halogen, hydroxyl, formyl, acetyl, linear or branched C1-C20 alkanoyl, linear or branched C3-C20 alkenoyl, linear or branched C5-C2o polyalkenoyl, benzoyl, aroyl, heteroaroyl, nitrile, carboxyl, formyl, Cl-C-20 alkoxycarbonyl, C1-C20 N- alkylamido, C1-C20 N, N-dialkylamido, amido, nitro, amino, C1-C20 alkylamino, C1-C20 dialkylamino, C2-C20 dialkenylamino, C4-C20 di (polyalkenyl) amino, arylamino, diarylamino, Cl-C2o alkylarylamino, and cyclic-amino groups (for example but not exclusively aziridino, pyrrolidino, piperidino, morpholino, thiomorpholino, indolino, piperazino, linear or branched C1-C20 N-alkylpiperazino, linear or branched Cl-C20 N- hydroxyalkylpiperazino, N-phenylpiperazino, N-arylpiperazino, homopiperidino, N- indolinyl), arylsulfanyl, aryloxy, arylsulfinyl, arylsulfonyl, linear or branched C,-C20 alkylsulfonyl, di-(C,-C, o alkoxyalkyl) phosphonyl in addition to those substituents specified for R'and R2 and R5.

Rl6 of which there may be one or more, the same or different, are selected from hydrogen, linear or branched C1-C20 alkyl, C3-C20 cycloalkyl, C4-C20 bicycloalkyl (for example but not exclusively norbomyl), C5-C20 polycycloalkyl (for example but not exclusively adamantyl), linear or branched Cl-C20 haloalkyl, linear or branched C1-C20 perhaloalkyl, linear or branched C2-C20 alkenyl (E or Z isomers), linear or branched C4-C20 polyalkenyl (any combination of E or Z isomers), linear or branched C2-C20 alkynyl, linear or branched C4-C20 polyalkynyl, linear or branched C1-C20 hydroxyalkyl, linear or branched Cl-C20 polyhydroxyalkyl, linear or branched Cl-C20 alkoxy, linear or branched Cl-C2o alkylthio, linear or branched C1-C20 (Ci-Cio alkoxy) alkyl, linear or branched C1-C20 (CI-C5 alkylthio) alkyl, phenyl, aryl, heteroaryl, halogen, hydroxyl, formyl, acetyl, linear or branched Cl-C20 alkanoyl, linear or branched C3-C2o alkenoyl, linear or branched C5-C20 polyalkenoyl, benzoyl, aroyl, heteroaroyl, nitrile, carboxyl, formyl, C1-C20 alkoxycarbonyl, C1-C20 N alkylamido, C1-C20 N,N-dialkylamido, amido, nitro, amino, C1-C20 alkylamino, C1-C20 dialkylamino, C2-C20 dialkenylamino, C4-C20 di (polyalkenyl) amino, arylamino, diarylamino, C1-C20 alkylarylamino, and cyclic-amino groups (for example but not exclusively aziridino, pyrrolidino, piperidino, morpholino, thiomorpholino, indolino, piperazino, linear or branched C1-C20 N-alkylpiperazino, linear or branched C1-C20 N- hydroxyalkylpiperazino, N-phenylpiperazino, N-arylpiperazino, homopiperidino, N- indolinyl), arylsulfanyl, aryloxy, arylsulfinyl, arylsulfonyl, linear or branched Cl-C20 alkylsulfonyl, di-(CI-Clo alkoxyalkyl) phosphonyl in addition to those substituents specified for R'through to and including Rl8.

In addition to the 2H-naphtho [1, 2-b] pyran compounds of formula I, the present invention includes the pyrans of the general formula V, VI, VII and VIII In addition to the 2H-naphtho [1, 2-b] pyran compounds of formula I, the substituents R5 and R6 or R7 and Rg or Rg and R9 or R9 and Rl° may each be conjoined by a four carbon unit containing one or more substituents represented by R16 to provide benzo fused naphthopyrans of the general formula IX and X and XI and XII.

In addition to the 2H-naphtho [1, 2-b] pyran compounds of formula I, the present invention includes the heterocyclic fused pyrans of the general formula XHI and XIV and XV and XVI and XVII and XVIII and XIX.

The function (X) in the structures MIT-EX is selected from a single bond, O, S, SO, SO2, Se, NH, N-O, N-linear or branched C1-C20 alkyl, N-C3-C20 cycloalkyl, N-C4-C20 bicycloalkyl, N-C5-C20 polycycloalkyl, N-linear or branched Ci-Cio hydroxyalkyl, N-linear or branched C1-Clo haloalkyl, N-linear or branched Ci-Cio perhaloalkyl, N-phenyl, N-C1-C10 linear or branched alkylsulfonyl, N-aryl, N-tosyl, N- acyl, N-benzoyl, N-aroyl, N-butoxycarbonyl, P-linear or branched C1-Clo alkyl, P- phenyl, P-aryl, P-substituted aryl, P (O)-linear or branched C1-C10 alkyl, P (O) O-linear or branched C1-C10 alkyl, P (O) O-phenyl, P (O) O-aryl, C=S, C=O, C=NR16, CH2, CHR16, C (OH)R16, CR17R18, The function (Y) in the structures XVII - XIX is selected from a single bond, O, S, SO, SO2, Se, NH, N-O, N-liner or branched C1-C20 alkyl, N-C3-C20 cycloalkyl, N-C4-C20 bicycloalkyl, N-C5-C20 polycycloalkyl, N-linear or branched C1-C10 hydroxyalkyl, N-linear or branched CI-Clo haloalkyl, N-linear or branched Ci-Cio perhaloalkyl, N-phenyl, N-C1-C10 linear or branched alkylsulfonyl, N-aryl, N-tosyl, N- acyl, N-benzoyl, N-aroyl, N-butoxycarbonyl, P-linear or branched C1-C10 alkyl, P- phenyl, P-aryl, P-substituted aryl, P (O)-linear or branched C1-C10 alkyl, P (O) O-linear or branched Cl-calo alkyl, P (O) O-phenyl, P (O) O-aryl, C=S, C=O, C=NR16, CH2, CHR, C (OH)R16, CR17R18.

The 1-naphthols and related hydroxy compounds are either commercially available or obtained by known synthetic methods, or derived by such methods by persons skilled in the art of organic synthesis. In particular, the application of the Stobbe condensation to prepare numerous substituted 1-naphthols has been discussed (see Organic Reactions, Wiley, New York, 1951, volume 6, p. 1). Other routes to useful hydroxy compounds include the application of Bradsher cycloaddition methodology e. g. R F. Frank et al., J. Chem. Soc., Chem. Commun., 1984, 761.

The synthesis of the propargyl alcohols has been described in the scientific literature, see for example T. F. Rutledge in'Acetylenic Compounds,'Reinhold, New York, 1968.

The combination of the substituted 1-naphthols and the propargyl alcohols to afford the naphthopyran is well established (Scheme), see for example L. Merlini in Advances in Heterocyclic Chemistry,'Academic Press, 1975, vol. 18, p. 159 ; R Guglielmetti in'Photochromism : Molecules and Systems,'Studies in Organic Chemistry 40, eds. H. Durr and H. Bouas-Laurent, Elsevier, 1990. chp. 8 ; J. D.

Hepworth, C. D. Gabbutt, B. M. Heron in'Comprehensive Heterocyclic Chemistry II,'eds. A R Katritzky, C. W. Rees, E. E. V. Scriven, Pergamon, 1996, vol. 5, p.

351. H ( w I I acid catalyst (Ar ci-i + 0-Ar i HO Ar, Au Scheme The acid catalyst may be selected from alumina (e. g.

Brockmann 1), acetic acid, trifluoroacetic acid, silica, clays (e. g. montmorillonite, tonsil), acidic exchange resins, alkylbenzene sulfonic acids (e. g. toluenesulfonic acid).

Organic solvents frequently employed for the reaction include benzene, toluene, xylene, and relatively high boiling alkanes and ethers.

In order that the invention may be more fully understood, reference will now be made to the following Examples, by way of illustration only.

Examples The following examples have been selected to illustrate the claimed effect, but in no way limit the claim.

1. Methyl 9-dimethylamino-2-phenyl-2-(4-piperidinophenyl)-2H-naphthof l, 2- b] pyran-5-carboxylate A solution of methyl 6-dimethylamino-4-hydroxy-2-naphthoate (5 mmol) and 1- phenyl-1- (4-piperidinophenyl) prop-2-yn-1-ol (5 mmol) in toluene (60 cm3) containing acidic alumina (Brockmann 1) (5g) was refluxed for 90 minutes. The cooled solution was filtered and the alumina residue washed well with ethyl acetate (5 x 40 cm3).

Removal of the dried solvent gave a brown gum which was flash chromatographed using 30% ethyl acetate in hexane as the eluent to give an off-white solid.

Recrystallisation from ethyl acetate and hexane gave the title compound (m. p. = 155- 156. 5 °C).

The following compounds were obtained in a similar fashion from the requisite starting materials : 2. Methyl 9-dimethylamino-2v2-di (4-piperidinophenyl)-2H-naphtho [lv2-b] pyran- 5-carboxylate (m. p. = 187-189 °C) from methyl 6-dimethylamino-4-hydroxy- 2-naphthoate and 1, l-di (4-piperidinophenyl) prop-2-yn-1-ol.

3. Methyl 9-morpholino-2-(4-dimethylaminophenyl)-2-(4-methoxyphenyl)-2 H- naphtho [1, 2-b] pyran-5-carboxylate (m. p. = 208. 5 - 211 °C) from methyl 6- morpholino-4-hydroxy-2-naphthoate and 1- (4-dimethylaminophenyl)-1- (4- methoxyphenyl)-prop-2-yn-1-ol.

4. Methyl 9-dimethylamino-2, 2-di (4-dimethylaminophenyl)-2H-naphtho [1, 2- b] pyran-5-carboxylate (m. p. = 224. 5-226 °C) from methyl 6-dimethylamino- 4-hydroxy-2-naphthoate and 1,1-di (4-dimethylaminophenyl) prop-2-yn-1-ol.

5. 2-Phenyl-2-(4-piperidinophenyl)-2H-pyrano [2, 3-a] xanthen-12-one (m. p. = 153-155 °C) froyn l-hydroxyxanthone and 1-phenyl-1- (4-piperidinophenyl)- prop-2-yn-l-ol.

6. 2-Phenyl-2- (4-piperidinophenyl)-2H-1-benzothieno [2, 3-h]-1-benzopyran (m. p. = 144 - 146 °C) from 4-hydroxydibenzothiophene and 1- (4- piperidinophenyl)-1-phenylprop-2-yn-1-ol.

7 Methyl 9-dimethylamino-2-phenyl-2- (4-pyrrolidinophenyl)-2H-naphtho [1, 2- b] pyran-5-carboxylate (. p. = 176-178 °C) from methyl 6-dimethylamino-4- hydroxy-2-naphthoate and 1-phenyl-1- (4-pyrrolidinophenyl) prop-2-yn-1-ol.