CA1268034A - Photochromic composition resistant to fatigue - Google Patents

Abstract

PHOTOCHROMIC COMPOSITION RESISTANT TO PATIGUE
ABSTRACT OF THE DISCLOSURE
An organic photochromic composition comprising spiro [indoline-2,3'-[3H]-naphth [2,1-b] [1,4] oxazine] dye (spirooxazine dye) and unconventional ultraviolet stabilizers.
The ultraviolet stabilizers improve the light fatigue resistance of the spirooxazine (S.O.) dye and will not hinder the photocolorability of the photochromic composition. The unconventional ultraviolet stabilizers belong to the class of hindered amine light stabilizers (HALS) and excited state quenchers.

Description

D~CKGI~oU~D OF rllr, INvrNTIoN
The invel-tion relates to a photochromic composition, and more particularly to an organic photochromic composition comprisinq spiro [indo]ine-2,3'-[31l~-naphth [2,1-b] [1,4] oxa~ine]
(S.O.) dye and unconventional ultraviolet (UV) stabili~ers.

Compoullds which under-Jo reversible photo-induced color changes nre termed photochromic compounds. When subjected to ultraviolet light or visible irradiation, these pho~ochromic compounds change their transmission. They subsequently revert to their original color state when they are subjected to a difEerent wavelen~Jtl) oE radiation or when the initial light source is removed.

~ lthou~h the or~nnic photocl)romic n~ater;als hnve been known for over 50 yenrs, they have not had widespread industrial or commercial use. ~rhis is primarily due to the irreversible decomposition phenomenon, generally known as ~` ¢ ~L~6~

light Eatigue. Repeated expo.sure to light cnuses the photochromic material.s to lo.se l:heir pllol:ocllromism.

It is thoucJl~t l:hat ligl~t or heal: or both light and heAt are responsible Eor the photo(lecomposition oE organic photochromic compouncls. Tl~us, many people have tried to increase the ligl)t Eatigue resistance oE the compounds by adding numerous conventional antioxklant~s or ultraviolet light absorbers. For exalnple, U.S. Patent No. 3,212,898 teaches the use oE conventional UV ab.sorbers such as benzophenone and benzotriazole to increase the photochromic li Ee oE
photochromic benzosp;ropyran compounds. Similarly, U.S. Patent No. 3,666,352 teaches the use oE conventional UV 1ight absorbers in photochromic mercury thiocal-hazollate l.enses, transparent to radiation oE wavelengths greater than 4200 Angstrom units and opaque to radiation oE wavelengths less than 4200 Angstro~n units, in order to substantially increase the durability oE the lenses against photochemica1 degradation .

one class oE organic photochromic compounds, spiro [indoline-2,3'-[3~l]-naphth 12,1-b] [1,4] oxazine] dyes (S.O. dyes) are known to have good light Eatigue resistance. In general, the light Eatigue resistance oE the spirooxazine compounds is about 100 times better than the c].osely related spiropyrans.
This class oE photochromic compounds has been disclosed in I~.S. Patent Nos. 3,562,172; 3,578,602; 4,215,010; 4,342,66~;
and 4,440,672.

3V3'~
The precise mechanism Eor photodecomposition of S.O.
dyes is not yet fully understoocl. ~Ithough some eircumstantlal evidence indieates that oxyc~en is involved in the photodecomposition proces.q, the traditiollal antioxid~nts (aryl amines and hindered phenols~ do not improve the licJht Eatigue resistance oE S.O. dyes. The eonventional UV
stabilizers, substituted benæophenones and benzotriazoles, cause a small improvement in the l;ght Eatigue resistanee of S.O. dyes, but they cannot be used eEEectively since they create a sereening efEeet by absorbing UV radiation strongly in the region where the S.O. dyes absorb W radiation. By eompeting with the S.O. dyes to absorb W light, these conventional stabilizers substantially decrease the eEEeetive light intensity for S.O. dye aetivation. Furthermore, some oE
the eonventional ~V stabilizers are detrimental to S.O. dyes under eertain eonditions.

In addition, the presenee of acids has a deleterious ëffeet on 5Ø eompounds. ~cids may be in the plastie host material from whicll the phol:ochromie artiele is made, such a.s PVC or cellulosics. The aeids are usually generated either thermally during the Eorrning proeess, or photoehemieally during u5e of the photoellrornic artiele. The S.O. dye solution b.eeomes a pinkish to reddish eolor in the presenee of even a minute alnount oE aeid, and the solution eeases to show a photoehromie eEfeet. The pinkish to reddish eolor is likely due to the formation of a complex between the S.O. compound and acid. A base must be usecl to neutralize the aeid and to restore the original colorless or light blue eolor.

3'~

U.S. Patent No. ~ 1(), 672 cl;scl.oses the use oE
organonickel complex stahilizers to improvt! the ~ ht fai:i~Ut!
resistance oE the photoch1 olnic compoul-c1s. Ilowever, these organonickel comploxes do not have the abill ity to neutralize acids which may be presenl: !

SUMM~I~Y Ol~ T111~ INVENTION
The problems oE the prior art are overcome by the discovery that a group of unconventional UV stabilizers will irnprove the light-Eatigue resistance oE S.O. dyes, while not affecting their photocolornbility. Tl-er;e unconventional UV
stabilizers belong to the class Oe hindere(1 amine litJht stabilizers (I~ ,S) and excited state quencl1ers. Ilindered amine light stabilizers of Eer an advanta~e over organometallic complex stabilizers in their ability to neutralize acid, and to thus improve the light-fatigue resistance and preserve the original color oE the S.O. dyes. It is preierable to use the hindered amine light stabilizers together with excited state quenchers in the organic photochromic compound of the invention; this combination has a synergetic effect in improving the light Eatigue resistance of the S.O. compounds.

These UV stabilizers will not hindt!r the photocolorability of S.O. dyes, since they have a minimal absorption in the UV region where S.O. dyes absorb. The S.O.
dye and UV stabil izers may be incorporatl?d within optically clear plastics to n~,a1ce a photochromic element suitable for a 3~

photochromic sunglass len,s, ski ~oggle, or other plastics to render them photochromi c Accordingly, it is an ob ject oE the present invention to improve the light Eatigue resistance Oe an organic photochromic composition containing S.O. dye.

It is another object oE the present invention to improve the light Eatigue resistance oE these pllotocllromic compositions without hinderillg their phol:ocolorability.

It is a Eurtller object oE the present invention to use such improved photochromic compositions to Eabricate photocllromlc artlcles such a9 sunglasses, ophthalmic lenses, ski goggles, window coating3, toys, fabrics, and the like.

Other objects and Eurtller scope oE applicability oE
the present invention wil l become apparent Erom the det~iled description to follow.

i f DEscn~ IoN O~ T1113 PRrA~`~11RED l:MBODIMENT
~ he o~--3anic p11otoc11ro111ic composition of the present invention comprise~: a~ spiro rindoline-2,3'-~3111-nnphth 12,l-_] [],~1 oxaz;ne1 (]ye ~spirooxazi11e 3ye), having t1~e structural Eormulfl C1t3 n~ ~ V= \~n2 'I
wherein one of Rl, R2 and n3 is hydrogen, halogen, lower ,alkyl, or lower alkoxy and the others are hydrogen; R4 and R5 1'are hydrogen, lower alkyl, lower alkoxy, halogen, or triEluoromethyl; and R6 is lower alkyl; and, b) an unconventional UV stabilizer or stabilizers. As used throughout the specification and claims, "lower" means up to 12 carbon atoms (n=1-12~ in the Eree alkyl or alkoxy radical group, wherein the alkyl Eree radical group has the structural formula of CnH2n+l, and the alkoxy Eree radical group has the structural Eormula of Cn1-12n+l0. PreEerallly~ the W stabilizer comprises a hindered amine light stabilizer ~11ALS~. The . .
preEerred hindered amine light stabilizers cornprise derivatives oE tetramethyl piperidine. Most preEerably, the UV
stabilizer comprises a combination oE a hindered amine light ~stabilizer and an excited state quenc1)er. PreEerably~ the excited state quencher comprises an organonickel complex light !

' I

c~

stabilizer. For a description o~ hindered ~mine light stabilizers and e~cltecl sta~e quenchers sec the ~ollowing four articles in Mode,-n Plastics ~nryclopedia:
1) Shute, ~aymond "Antioxidants," pp. 102-103 (19~3-1989); 2) Li, S.S., "Ultraviolet Stabilizers," pp. 174-177 tl983-1984); 3) Patel, A., "Antioxidants," pp. 106-107 (19~-19~5); and ~) Stretanski J.~ ltraviolet Stabilizers " pp 179-180 ~19~4-1985).

Between 0.1 anA about 15% by weight oE the S.O. dye and between 0.01 and about 5% by wei~ht oE the IWJS stabilizer or combined W .stal)ili7ers, depenclinc~ on their soLubility can be incorporated into a plastic article havinc~ enhanced light ~atigue resistance. rL~he SO clye and ~V stahilizers may be mixecl in a sGlution with an opticalLy clear polymer which is thereaEter cast as a Film, sheet, lens, or toy or a polymer WhiCIl iS injection molr3ed or otl~erwise sl~aped into a ~ilm or lens; or a prepolymerize(l ~ilm or lells containin(~ ti)e W
stabilizers may l~e immersed in a dye ~ath comprising S.O. dye dissolved in a solution o~ organic solvents such as alcollol toluene halogenal-e-l hydrocarbon or the like. otl~er methods o~
blending the W stabi:li%ers with the S.O. dye and polymers such as coating or laminating may also be employecl.

6~)3'~

One hinclered ~mine l.i~ht stabili7.er, use~ul in th~
~rganic photochroin.i.c c~mposi.tion oE the inventiorl, comprises the structuraL formula ~5 n~
~n7 ~3 ~\oc(cll2)n1l0~7r nl () () n~() 1' 2' ~ 5' ~6~ R7~ and Rlo are .lower alkyl; l~
and R8 are lower alkyl OL' h~-lr(.)c~en; and n=1-12; and in particular, the hindered am.ine li~3ht stabilizer is Bis ~2,2,6,6-tetramethy.l-4-piperidillyl) sebacate, wherein Rl, R2, R9~ R5, ~6~ R7, ~9 and Rlo are methyl, R3 and ~ are hydrogen, and n=8, sold under the trade~ar~ oE Tinuvin 770, and obtained from the C.iba-Geig~ Corporation; and also in particular, the hindered amine light stabilizer is Bis .(l,2,2,6,6-pentamethyl-4~piperidinyl) sebacate, wherein Rl, R2, R9, R5, R6, R7, Rg and Rld are methyl, R3 and R~ are methyl, and n=~, sold under the trademark of Tinuvin 765, and obtained from the Ciba-Geigy Corporation.

Another hinclered amine lic~ht stabilizer which is useful in the organic photocllrolnic composition oE the invention comprises tl~e structur~l Eormula n5 nh 11 r~
R3 N ~ I ~ N 1

2 ~ ~ ~ C - C 0 ~ 1 nl o I ~ nlo Cll,~

~7\J~c/ 12 16 1115 ol~ n/~ r~l3 wherein Rl, R2, R~, R5, R6, l~7~ Rg~ Rlo~ R12' R13' R14' R15, R16, and ~17 are lower ~lkyl; and R3 ~nd Ra are lower alkyl or hydroc~en; ana in particll].ar, the hindered amine light stabilizer is di~l,2,2,6,G-pentamethyl-4-piperidinyl)-butyl(3',5'-ditertbutyl-~-hydroxybenzyl) malon~te, wherein R1, R R , R5~ R6, R7~ l~9~ Rlo~ R12~ Rl~, Rl~' 15 16 17 are methyl, Rll is butyL, and ~ and R8 are methyl, sold under the trademark of Tinuvin 14~, an~1 obtained Eroln the Ciba-Geigy Corporation.

3q3~

~ nother 11inderecl alliine light sl:al~ilizer which is useEul in the orgallic pllotochrolnlc compo.~ition o~ the inverl~ion compl.ise~ 1:l)(? .c;trLIotlllal Eorlllu].n N - (Cll2)n - _N

nl3 ~ n9 ~ n~

Rl, R4, R5, Rll, and R16 are lower alkyl or llydrogen;

R2, R3, R6, R7, R~ 9, l~lo, R12' R13' R14' 15 17 18 are lower alkyl; nl=1-12; and n2-1-15; and in particular, the hindered amine light stabi].izer is poly[(6-[~1,1,3,3-tetra-methylbutyl)amino]-1,3,5-triazine-2,4-diyl)(1,6-12,2,6,6-tetra-methyl-4-piperi-linyl]amino-hexamethylene)], wherein R2, R3, R6, 7' 8' Rg~ R~ R12~ 3~ Rl~ Rls, R17, and Rl~ are meth~
Rl, R4, R5, Rll, and ~16 are hydrogen, and nl=6, sold under the tradern~rk Chimassorb 9~4, and obtained ~rom the Ciba-Geigy Corporation.

--1 .1.--~L~6~03'~

Another hinlerec~ am;.ne light stabilizer which is useful in the organic pholocllrolllic compos.ition of the invention comprises the strllcturl~l. Eormul.a ; ~ n ~ 2 Rl~ R2~ R5~ R6, 1~7~ ~91 and Rlo are lower alkyl;
R3 and R8 are 1ower alkyl or l~ydrogen; n~ 12; an(l n2=1-15;
and in partic~llar, the llinclered ami.lle li.gllt sta~il.i%er is poly[~6-tmorpholino)-s-tr.iazine-2,~-diyl][l,6-(2,2,6,6-tetra-methyl-4-piperidyl)amino]llexclmetllylene], wherein Rl~ ~2~ R4, R5, R6, R7, 1~9, and Rlo are methyl, 1~3 and ~ are hydroc~en, ancl nl=6, sold uncler tlle tr~demark Cyasorh 33~fi, alld ohtained from the American Cyanalmicd Cor.poration.

~ nother hill~ler.ed ~mine light stabili~er which is use~l in the or~anic phot~cllrolnic compo~;t;on ~E the invention compri.ses ~llc 5~ lo~ur~l. Eo~m nl ... ~ 2 - .

., _ o ~ 11 cll~ C112 u ~ 2 C~2 C _ wherein Rl, R2, R3, an(l 1~ are lower alkyl; and n-1-15; and in particular, the hindered amine ].igllt stabil.izer is a dimethyl sllccinate polymer with ~-hydroxy-2,2,6,6-tetrarnethyl-1-piper-idineethanol, where;n l~l R2, 1~3 and ~4 are metllyl., sold under the trademark Tinuvin 622 ancl obta.ined Erom the Ciba-Geigy Corporation.

Other hindered amine liq11t stabilizers which are use~ul in the orgarlic photochromic compo.si tion of the invention include a hindered alnine light stabilizer having the structural formula (C26H52N~)n, wherein n=1-15 sold under the trademark Of Spinuvex A-36 and obtained Eroln the Borg-Warner Corporation; and a hindered amine li~ht stabili2er sold under the trademark of Mostavin TMN20, and obtained Erom tile American Hoechst Corporation.

Ultraviolet stabil.i%ers, belonqinq to the class oE
excited state quenchers, which are useful in the organic photocllromic compound oE the invention, include colnplexes of i~ Ni ion with some orqanic ligand cobalt (III) tris-di-n-butyldithiocarbamate, cobalt (II) diisopropylditi~iocarbamate (Co DIPDTP), and nickel diisopropyldithiophosi?l)~te (Ni DIpD~rp)~

The preEerred excited state quellcl)ers are singlet oxygen c~uenchers, and in partic-llar, complexes oF Ni2 ion ~ith some organic ligancl. rhese i~ii2~ complexes are normal~y used in polyole~ins l:o provitle protection irom photo-degradation Most preEerably, the Ni2i c~olnplexe~ are:
[2,2 -Thiobis ['~i-(1,1,3,3-tetralnt-~thyLbut:yl) phenolato]
~butylamine)~ nickel, havinci the structuraL ormuLa CH~ 1 - C''2 c,l3~ C~3 S . . . . . . ~.i . . . NH2 ( CH2 ) 3CH3 CH3 C--C~2 ~--~ -C/
CH3 Cil3 sold under the trademarkoE Cyasorb UV 10~, and obtained from the American Cyanalnid Company;

. .
- - .

Ni cke 1 [ 0 -e thy l ( 3, 5-d i - te r t-bu ty l - Il-hyd ro~:ybe n zy L ) ]
pho~;phonate, havin~l th~ r~lcl:ural. Eormu].a _ (C113) 3C

. l~o~ 2 IP Mi (C~3~ 3~ C~t~5 o sold under the trademark of Irgastab 2002, and obtained Erom the Ciba-Geigy Corporat:ion; Nickel dibutyldithiocarbamate, having the structural Eormula ._ CH3 ~ CH2 ) 3 ~ S
/NC\ Ni CH3 ( C}l2 ) 3/ \S
_ __ 2 sold under the trademark oE nylex NBC, and ol>ta.ined Erom E.l.
duPont de Memours ~ Company;

Bis [2,2'-thiobis-4-(1,1,3,3-tetramethy1buty1~ pheno1ato]

nickel, having the structural formu1a C~13_ClU3C~t2~ Ho~?}Cl3cll2-cl-c~3 ~13~ C113 \ C,l3 c,~3 s ~ s CH5~ 2 1 ~DII O_~ C--Cll--Ci_C~l t ~l3 Cil3 C~13 sold under the trademark o~ UV-Chek ~M 101, and obtained from the Ferro Corporal:ion; Nickel di-lsopropyl clitl~iopllosphate (Ni DIPDTP~, having the structural ~ormula l(CH3)2CI~0]2 p~ ~ Ni'~ ~ [Cll(cll3)2]2 and other Ni2 coml?lexes so]d under the trademark~ of W -chek AM 105, UV-Chek ~M 12fi, and ~V-Chelc ~M 205 which can also be obtained from the Ferro Corporat:ion.

The pre~errecl S.O. dyes ~or use in accc)rd~nce with the invention are 1,3,3,~,5-pentamethy1-~'-methoxy-spiro [indo1ine-2,3'-[3ll]-naphtll [2~1-b] ~1,4] oxa~ine;
1,3,3,5,6-pentamethy1-9'-met)loxy-spirooxazine;
1,3,3-trimethy1-5'-methoxy spirooxa~ine;
1,3,3-trimethy1-5-methoxy spirooxazine;
1,3,3t4,5-pentamethyl-8'-bromo spirooxazine;
1,3,3,5,6-pentamethy1-8'-bromo spirooxazine;

. .

1,2,3,3,4,5-hexAInetllyl-9'-metlloxy spirooxazine;
i,2,3,3,5,6-hexame l:hyl -9 ' -me ~:hoxy spiroox;l7.ine;
l~3~3-trimethyl-~-triEluorome~hy~ -mel:hoxy g~irooxa7.ine;
1,3,3-trimetllyl-6-lriEluorom~-3tllyl-9'-metlloxy spirooxazine;
'1,3,3-trimethyl~4-tr;Eluorolnethyl-5'-mel:lloxy .spirooxazine; and 1,3, 3-trimethyl-6-triEl~lorolllethyl-5'-metl~oxy spirooxa~ine.

The preferred plastic hosts are cellulose acetate butyrate (CAB); CR-39'~, a diethylene glycol bis (allyl carbonate) obtained from PPG Industries, Inc.; Lexan'~, a polycarbonate resin conclensation product oE bisphenol-A and phosgene, obtained Erom General Electric; Plexi(Jla3l~ a polymethyl methacrylate obtained Erom the Rohlll and lla~s Company; polyvinyl c!lloride; and polyolefins.

'rl-e invention is Eurther illustrated by the EolLowing non-limiting example~s.

!j - Rxamples 1-B
Eight cellulose acetate butarate (CAB) samples ~having a thickness oE 17-19 m1s., containing 0.4% by weight oE
a mixture of 1,2,3,3,4,5- and 1,2,3,3,5,6-hexamethyl-9'-methoxy SØ isomers, with and witl-ollt hindered amine light stabilizers (H~T..S) were prepared by castin<J a methylene .chloride solution of C~B. Four successive castings were needed to obtain the desire(l thickness with good optical appearance.
The control sample containe-1 no ll~I.S. ~rhe seven other samples contained variou.s hindered amine ligllt stal~ilizers in an . ~

1~6~03'~
arhi.trary amount o~ 1% by wei-3hl~ e sn~ le.s were suhjected to a 20-llour cycle lia(leollleter exl-osu~e tesl:ing. ~r~er Civ~
cycl.e.s, the control. .3alllL)l.e wil:hollt ll7~T,'`, .lo~sl: al.l. its photochromisln whi.l.e t:hl? salllr].es with Tl7~r.~S still. sllowed good photocllromi~m. ~ lt-~ specil~ic II~I.S usecl and l:he percerltage ot residual photocoloral~i:Lity o~ the CA13 salnL~les aftc!r 100 hours of Fadeometer exposure is sllown in Table 1.

Tab.l.e 1 Percentacle oE l~esidual Photocolorabi].;.l:y Example ~I~LSPercent Residual Phc ocolorability Control None * 0 2 Tinuvin 770 6~1

3 Tinuvin 765*84

4 Tinuvin 622 31 Tinuvin 14'tG7 6 Chimassorb 9~14* 76 7 Spinuvex ~36* 90 8 Hostavin N2U71 Examples 9-10 Two CAB sheet samples (60 mls.) were nnade by - injection molding. One o~ the C~B sheet samples had 0.2~ by weight Oe a mixture oE 1,2,3,3,~t,5- and 1,2,3,3,5,6-hexa-methyl-9'-methoxy s~;.rooxazine .isomers and 0.2~ hy weight o~
UV-Chek AM-205 as an excited state quencher. q~he other sample . . also had 0.2~ by weigllt Tinuvin 622 as a hindered amine ligllt stabilizer in addition to the S.O. dye and the W~Chek ~M-205*
The sample witllout the ll~LS lost all oE its photochrolnism after 15 20-hour Fa(leometer exposure cycles. ~lowever, the sample with the 117~L', still. had ~10~i o~ thc original photocolora~ilit:y ].eEt.
.0 ,~
~` *Trade Mark ~L2~

_xampl.es 11-13 7~ colltroL salllple Wrl~; cast at .l.G()" in r~n oven Eor 20 minu~:es Eroln a pl.asti.~ol. SOl.UI:ion COllSi.C.~:i.llfl 0E 3~
d.iisodecylphtllalate~ 3r~ octyl epoxy t:allate 3% mark stal~ilizer 63% PVC and 0. l-rh 1~ 3~ 3 1~ 5- and 1 31 3 5 6-penta-methyl-9 -methoxy S.O. ~.tye mixture Two more samples were prepared as follows: One sample had in addition to the ingredients in the control sample 0 2~ by weight: UV-Chek AM-205 and the other sample llad 0.2r~ by weight w-chek AM-205 and 1.0r~ by weight Tinuvin 622. rrhe control sample lost all oE
its photochromic eE~ect aEter 20 hours o~ Fadeomet:er exposure;
the sample with UV-CIlek r~M-205 lasted ~0 hours be~ore losinq its photochromic e~Eect and the sample witll both UV-Chek AM-205 and Tinuvin 622 lastecl 1~0 hours beEore losing its photochromic eE~ect.

Examples 14-18 An ethanol solution oE 1 3 3-trimel:llyl S.O. dye was prepared by dissolving 13.1 mg oE dye in 100.0 ml oE ethanol.
Two milliters of the .sol.ution was placed in each of Eive 10.0 ml volumetric Elasks. lllen 0.1)1 ml oE 1 N IICl w IS added to each Elask and eacll solut:.ion was ~lilute(-l with etl~nnol to 10.Q
ml. Each so].ution wa.s originaJ.ly col.orle.ss b~ becarne pinki.sh and lost its pl-otochl-oln.ic eEEect once the IICl wrls addcd. To Eour oE the solutions wa.r, added about 3 mg oE eit:her Tinuvin 770 Tinuvin 765 Cyasorb 10~3~1 or uV-Chek ~M-205. The solutions containing l:he li.nuvin and Cyasorl~ compounds reverted to color].ess solut:iol)s ancl regained their ., ~ ~

*Trade Mark , . . ..

~ 26~

photochromic eEEecl, while the other solutions remained pinkish and showed no photocllrolnic efeect.

Although the inventi.on has be~n described with reference to its pre~erre.l embodimellt, otller eml>odimellts call achieve the same resul~s. Variations and moclieications o~ thc present invention wil.l he obvious to thc):ie skil.Led in the art and it is intended to cover in tlle apuellcled claims all such modifications ~nd eq~livalents.

.: -.`.'~. '' ~, .
.

Claims (18)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR
PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of increasing the light fatigue resistance of a spirooxazine photochromic composition which comprises incorporating in said composition a hindered amine light stabilizer.

2. A method according to claim 1 wherein said photochromic composition additionally contains a singlet oxygen quencher ultraviolet stabilizer.

3. A method according to claim 2 wherein said singlet oxygen quencher ultraviolet stabilizer is a Ni2+ ion complex with an organic ligand.

4. A method according to claim 2 wherein said singlet oxygen quencher ultraviolet stabilizer is selected from [2,2' -thiobis [4 -(1,1,3,3-tetramethylbutyl) phenolato] (butylamine)] nickel, nickel [0-ethyl (3,5-di-tert-butyl-4-hydroxybenzyl)] phosphonate, nickel dibutyldithiocarbamate, nickel di-isopropyl dithiophosphate, bis [2,2' -thiobis-4-(1,1,3,3-tetramethylbutyl) phenolato] nickel, cobalt (III) tris-di-n-butyldithiocarbamate, and cobalt (II) diisopropyldithio-carbamate.

5. A method according to claim 4 wherein said photochromic composition comprises a polymer containing about 0.1% to about 15% by weight spirooxazine photochromic dye.

6. A method aecording to claim 5 wherein said hindered amine light stabilizer and said singlet oxygen quencher ultraviolet stabilizer are incorporated in said photochromic composition in a total amount of about 0.01% to about 5% by weight.

7. A method according to claim 6 wherein said hindered amine light stabilizer is a tetramethyl piperidine derivative.

8. A method according to claim 1, wherein said hindered amine light stabilizer is selected from one or more compounds of the following formutae:
wherein R1, R2, R4, R5, R6, R7, R9, and R10 are lower alkyl, R3 and R8 are selected from lower alkyl and hydrogen, and n is 1-12;

wherein R1, R2, R4, R5, R6, R7, R9, R10, R11, R12, R13, R14, R15, R16 and R17 are lower alkyl, and R3 nnd R8 are selected from lower alkyl and hydrogen;

Claim 8 con't 2 wherein R1, R4, R5, R11 and R16 are selected from lower alkyl and hydrogen, R2, R3,?R7,R8, R9, R10, R12, R13, R14, R15, R17 and R18 are lower alkyl; n1 is 1-12, and n2 is 1-15;
wherein R1, R2, R4, R5, R6, R7, R9, and R10 are lower alkyl, R3 and R8 are selected from lower alkyl and hydrogen, n1 is 1-12 nnd n2 is 1-15;
wherein R1, R2, R3, and R4, are lower alkyl, and n is 1-15;
and (C26 H52 N4)n wherein n is 1-15.

9. A method according to claim 8 wherein said photochromic composition contains one or more of a spironxazine photochromic dye of the formula wherein one of R1, R2 and R3 is selected from the group consisting of hydrogen, halogen, lower alkoxy, and lower alkyl and the others are hydrogen; R4 and R5 are selected from the group consisting of hydrogen, lower alkyl, lower alkoxy, halogen, and trifluoromethyl; and R6 is lower alkyl.

10. A method according to claim 9 wherein said hindered amine light stabilizer is selected from one or more of bis (2,2,6,6-tetramethyl-4-piperidinyl) sebacate;
bis (1,2,2,6,6-pentamethyl-4-piperidinyl) sebacate;
di(1,2,2,6,6-pentamethyl-4-piperidinyl) - butyl(3',5' -ditertbutyl-4-hydroxybenzyl) malonate; poly[(6-[(1,1,3,3-tetramethylbutyl) -amino]-1,3,5-triazine-2,4-diyl) (1,6-[2,2,6,6-tetramethyl-4-piperidinyl]
amino-hexamethylene)]; poly[[6-(morpholino)-s-triazine-2,4-diyl] [1,6-(2,2,6,6-tetramethyl-4-piperidyl) amino] -hexamethylene];
and dimethyl succinate polymer with 4-hydroxy-2,2,6,6-tetramethyl-1-piperidineethanol.

11. A photochromic composition comprising at least one photochromic compound having the structural formula wherein one of R1, R2 and R3 is selected from the group consisting of hydrogen, halogen, lower alkoxy, and lower alkyl and the others are hydrogen; R4 and R5 are selected from the group consisting of hydrogen, lower alkyl, lower alkoxy, halogen, and trifluoromethyl; and R6 is lower alkyl; and a hindered amine light stabilizer.

12. A composition according to claim 11 additionally comprising a singlet oxygen quencher ultraviolet stabilizer.

13. A composition according to claim 12 wherein said singlet oxygen quencher ultraviolet stabilizer is a Ni2+ ion complex with an organic ligand.

14. A composition according to claim 12 wherein said singlet oxygen quencher ultraviolet stabilizer is selected from [2,2'-thiobis [4 -(1,1,3,3-tetramethylbutyl) phenolato] (butylamine)] nickel, nickel [0-ethyl(3,5-di-tert-butyl-1-hydloxybenzyl)] phosphonate, nickel dibutyldithiocarbamate, nickel di-isopropyl dithiophosphate, bis[2,2 -thiobis-4-(1,1,3,3-tetramethylbutyl) phenolato] nickel, cobalt (III) tris-di-n-butyldithiocarbamate, and cobalt (II) diisopropyldithio-carbamate.

15. A composition according to claim 11, wherein said hindered amine light stabilizer is selected from one or more compounds of the following formulae:

wherein R1, R2, R4, R5, R6, R7, R9, and R10 are lower alkyl, R3 and R8 are selected from lower alkyl and hydrogen, and n is 1-12;

wherein R1, R2, R4, R5, R6, R7, R9, R10, R11, R12, R13, R14, R15, R16 and R17 are lower alkyl, and R3 and R8 are selected from lower alkyl and hydrogen;

Claim 15 con't 2 wherein R1, R4, R5, R11 and R16 are selected from lower alkyl and hydrogen, R2, R3 , , R9, R10, R12, R13, R14, R15, R17 and R18 are lower alkyl; n1 is 1-12, and n2 is 1-15;

wherein R1, R2, R4, R5, R6, R7, R9, and R10 are lower alkyl R3 and R8 are selected from lower alkyl and hydrogen, n1 is 1-12 and n2 is 1-15;

wherein R1, R2, R3, and R4 are lower alkyl, and n is 1-15;
and (C26 H52 N4)n wherein n is 1-15.

16. A composition according to claim 15 wherein said hindered amine light stabilizer is selected from one or more of bis (2,2,6,6-tetramethyl-4-piperidinyl) sebacate;
bis (1,2,2,6,6-pentamethyl-4-piperidinyl) sebacate;
di(1,2,2,6,6-pentamethyl-4-piperidinyl) - butyl(3',5'-ditertbutyl-4-hydroxybenzyl) malonate; poly[(6-[(1,1,3,3-tetramethylbutyl)-amino]-1,3,5-triazine-2,4-diyl) (1,6-[2,2,6,6-tetramethyl-4-piperidinyl]
amino-hexamethylene)]; poly[[6-(morpholino)-s-triazine-2,4-diyl] [1,6-(2,2,6,6-tetramethyl-4-piperidyl)amino]-hexamethylene];
and dimethyl succinate polymer with 4-hydroxy-2,2,6,6-tetramethyl-1-piperidineethanol.

17. A composition according to claim 15 additionally comprising a plastic host.

18. A composition according to claim 17 containing about 0.1% to about 15% by weight of said photochromic compound and about 0.01% to about 5% by weight of said stabilizer or stabilizers.