OPTICAL FILTER AND PROCEDURE FOR ITS PRODUCTION

(21) Application No. 45299/73 (22) Filed 27 Sept. 1973

(31) Convention Application No. 311 188 (32) Filed 1 Dec. 1972 in

(33) United States of America (US)

(44) Complete Specification published 17 Dec. 1975

(51) INT CL² C09K 9/02; C08K 5/34

(52) Index at acceptance

C4S 33Υ 650 670 717 735 76Υ C3 P 7D1A 8D2B2 Ε2 PC17 PC20C PC7 Τ2Χ

(54) PHOTOCHROMIC OPTICAL ELEMENTS

(71) We, AMERICAN OPTICAL CORPORATION, a corporation organized under the laws of the State of Delaware, United States of America, of 14 Mechanic Street, Southbridge, Massachusetts 01550, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed to be particularly described in and by the following statement;This invention is concerned with photo- .

chromic optical dements.

Various types of polychromic compounds are known and such compounds are known for use in ophthalmic devices, such as lenses, filters, screens, etc. These photochromic compounds change colour on exposure to certain types of light or electromagnetic radiation.

Photochromic compounds exhibit reversible changes, that is, they change to and from colours on exposure to or withdrawal from the light radiation. It is known that the photon chromic reaction is exhibited by compounds which contain atoms or molecules capable of changing back and forth between two distinct energy states. These compounds are induced into a higher energy state by absorption cf radiant energy and, in the absence of radiant energy, reduce to their unactivated stable state. In the coloured states, they absorb certain ranges of light rays and in the inactive state pass most visible wave lengths.

Some of the known photochromic substances are inorganic compounds, and whilst these are fairly resistant to breakdown upon continuing colour change reaction, such compounds react too slowly to provide a satisfactory optical screen or filter. Known' metalloorganic photochromic chemicals are prone to degrade under repeated reversing of the colour change. Furthermore, such mettallo-organic photochromic chemicals generally do not provide the absorption or the quality of screen or filter which is desired.

45 According to the present invention, we provide a photochromic synthetic plastics optical element which comprises, as the active photochromic substance, a compound of the formula^

[Pnc'

w

in which R, is hydrogen or a halogen atom, and R₂ and R₃, which may be the same or different, occupy the 5, 6, 7 or 8 positions and are hydrogen, halogen, nitro or alkoxy having up to 3 carbon atoms, at least one of R₂ and R₃ not being hydrogen, and which, on activation by ultraviolet light, becomes coloured, the compound of formula I having been inbibed into the synthetic plastics element by immersion of the latter in a solution of the compound.

As indicated, the photochromic compounds employed in optical dements of tire invention are compounds of formula I which possess the characteristic of becoming coloured on activation by ultraviolet light. Whilst substantially all the compounds falling within formula I possess the characteristic of becoming coloured on activation by ultraviolet light, there are a few compounds falling within formula I, such as 5,7 - dimethoxy - l',3',3'trimethylspiro(2H - 1 - benzopyran - 2£!indoline), which do not possess this characteristic. Whether or not a particular compound falling within formula I has this characteristic can be readily determined by a routine test by those skilled in the art; it will be understood that compounds which do not become coloured on U.V. activation, even though they are within formula I, are not employed in the optical elements of the present invention.

The parent compound of the compounds used according to the invention, that is the compound of the above formula in which each of Ri, R_? and R₃ is hydrogen, is l',3',3'-trimethylspiro (2Η - 1 - benzopyran - 2,2'indoline).

The invention also comprises a method of producing an optical dement of the invention which comprises immersing a synthetic plastics element in a concentrated solution of an indolino-benzospiropyran of formula I as defined above, heating the solution substantially to boiling temperature, maintaining the dement in the heated solution so that the compound of formula 1 is imbibed into the plastics dement, and then removing, washing and drying the dement.

Preferably, the imbibition is effected by immersing the plastics dement in a boiling, concentrated (preferably saturated or substantially saturated) solution of the spiropyran in a solvent therefor.

The unactivated dement containing the spiropyran is generally colourless or rdativdy weakly coloured; in the coloured or activated form, the dement has a broad absorption band at the red end of . the visible spectrum, the absorption maximum being in the region of 550-600 nanometers. The presence and position of the substituent groups in the compound of the above formula markedly influence its photochromic properties.

The quantity of the spiropyran which diffuses into the surface of the plastics dement' is a function of the time of immersion. This, in turn, controls the extent of photocolouration that is obtained. The optimum concentration of photochromic compound in the plastics surface layer is generally obtained with immersion for at least 24 hours.

The optical element may be formed of any suitable synthetic plastics material of optical quality; suitable plastics indude, for example, polycarbonates, such as poly(allyl diglycol carbonate), which is commercially available under the designation CR--39, hydroxyl ated polyethylene, polymethylacrylates, such as polymethyl methacrylate, polyethylacrylates, polybuitylacrylates and other polyaciylates. The synthetic plastics material may contain' any of the usual additives thereto, such as plasticisers. In the following description, reference will be made to the accompanying drawings, in which:

Figure 1 is a graph showing the transmittance spectra of a plastics filter imbibed with 6 - nitro - l',3',3' - trimethylspiro(2H-

1 - benzopyran - 2,2' - indoline) before and after activation,

Figure 2 is a graph showing the transmittance spectra of a plastics filter imbibed with 6 - nitro - 8 - methoxy - 5' - chlorol',3',3' - trimethylspiro(2H - 1 - benzopyran-2,2'-indoline) both before and after activation, and

Figure 3 is a graph of the activation and recovery time, at room temperature, of the filter whose transmittance spectra are shown in Figure 2.

In order that the invention' may be more fully understood, the following examples are given by way of illustration only:Example 1. 65 A convex piano lens made of CR-39 was immersed for 24 hours in a saturated methanol solution of 6 - nitro - l',3',3' - trimethylspiro(2Η - 1 - benzopyran - 2,2' - indoline) which was maintained at the bailing point of the 70 solution. The lens was then removed, washed and dried. The dried lens was exposed to ultraviolet light and the transmittance spectra was found to include a developed broad absorption band centered at 555 nm. The acti- 75 vating light flux was 0.85 milliwatts per square centimeter. After a two minute irradiation of the lens at this power density, an optical density change of 1.4 at 555ηπΐ was noted. The transmittance spectra of the spiropyran in the 80 plastics lens is shown in Figure 1, where the wave length in nanometers is plotted against the percentage of transmission. The non-acticated state of the lens is shown by the solid line and the activated state by the dashed line; 85 the curves show that, the absorption change is.

centered at about the 555 nm band.

The following list of compounds have been effectively imbibed in a plastics element and the photochromic characteristics of the 90 resultant filter have been examined.

A, 6 - nitro - l',3',3' - trimethylspiro(2Η-l-benzopyran-2,2'-indoline)

Β. 6 - nitro - S' - chloro - l',3',3' - trimethylspiro(2H - 1 - benzopyran - 2,2' - indo- 95 line)

C. 8 - nitro - l',3',3' - trimethylspiro(2Η-l-benzopyran-2,2'-indolme)

D. 8 - nitro - 5' - chloro - l',3',3' - trimethylspiro (2# - benzopyran - 2,2'- 100 indoline)

Ε. 6 - nitro - 8 - methoxy - 5' - chlorol',3',3' - trimethylspiro(2/? - 1 - benzopyran-2,2'-indoline)

F. 7 - methoxy - 6 - nitro - l'£'£' - tri- 105 methylspiro(2H - 1 - benzopyran - 2,2'indoline)

G. 6 .- nitro - 8 - methoxy - l',3',3' - tri-

methylspiro (2Η - 1 - benzopyran - 2,2'indoline) Π0 Η. 7 - methoxy - 6 - nitro - 5' - chlorol',3',3' - trimethylspiro(2Η - 1 - bettzo-pyran-2,2'-iadoIine)

I. 5 - brorno - 8 - methoxy - l',3',3' - trimethylspiro(2H - 1 - benzopyran - 2,2'- 115 indoline)

J. 8 - nitro - 6 - methoxy - l',3',3' - trimethylspiro (2Η - 1 - benzopyran - 2,2'indoline)

Κ. 8 - nitro - 6 - methoxy - 5' - chloro- 120 l',3',3' - trimethylspiro(2H - 1 - benzopyran-2,2'-indoline)

L. 6 - bromo - 8 - nitro - 5' - chloro -

l',3',3' - trimethylspiro(2ff - benzopyran-2,2'-indaline) 125

Whilst the detailed mechanism of the photochromism of the spiropyrans is not completely understood, it may be that photoeolouration

involves the rupturing of the spire carbon-

oxygen bond and a subsequent internal rota-

tion and electronic rearrangement yielding the

coloured form. The reversal from the coloured

to die colourless form requires return of the

molecule to the original -geometrical form for'

ring closing. Therefore, both the colour forma-

tion process and the thermal fading process

involve rotation of rather large molecular seg-

ments relative to each other and, accordingly,

both processes show some dependence of their

rates on the viscosity of die medium in which

the spiropyran is present.

Figure 3 shows the change in optical density

as a function of time for both a photocolauxa-

tion and a thermal decay. The dashed line

shows the results for compound Ε above in a

CR-39 matrix, and the solid line is the result

for the same compound in a hydroxylated

polyethylene matrix. The same activating con-

ditions were employed for each composition,

that is a General Electric CPR tungsten fila-

ment lamp (16ν, 18 amps) at a distance of 18

cm. In the. first case, it was monitored at 580

nm and in the second case it was monitored

at 600 nm. As may be seen from Figure 3,

both the rate of photoeolouration and the rate

of: thermal decay is greater in the softer

hydroxylated polyethylene matrix.

Example 2.

A convex-piano CR-39 lens* was immersed

for 24 hours in a saturated methanol solution

of compound Β above which was maintained

at the boiling point of the solution under re-

flux. The resulting lens having compound Β

imbibed therein was subjected to the same ex-

. \ posure as in Example 1 and a maximum opti-

cal density change of 0.52 at 572 nm was

observed.

Example 3.

Compound Ε above was incorporated in a first CR-39 lens by the procedure set out in Example 1 (the imbibition being carried out for 24 hours), and the resultant lens was essentially colourless before activation¹. On activation with ultraviolet light, the lens turned blue.

This composition showed no red fluorescence during irradiation. A second CR-39 lens was treated in a boiling saturated solution of compound Ε in methanol for 8 hours, was washed and dried and then irradiated with ultraviolet exposure for 2 minutes. The activating source was a black ray of 0.85 milliwatts per square centimeter. The percent transmittance of the " second lens dropped from 88.4% to 44.3% at 600 nm on activation.

Example 4.

A CR-39 lens imbibed with compound F above produced a light reddish purple in the unactivated state. The lens became a darW reddish purple when activated.

In the formation of such lenses, it has been found that the quantity of the spiropyran which diffuses into the surface of the plastic lens is a function of the time of immersion¹. This in turn controls the extent of photocolouration achieved in die lens. Thus, lenses which are immersed in a saturated boiling methanol solution of the compounds for periods of 48 hours or longer showed a greater photocolouration than lenses similarly treated for 24' hours.

A number of lenses were imbibed each with a different one of a number of indolinobenzospiropyrans listel below in Table I, which also shows the absorption maximum in both a CR-39 matrix and in a hydroxylated polyethylene matrix for the lenses obtained.

The absorption spectra of the coloured form is influenced by the type and position of the substituent groups. The absorption maximum is displaced to longer wave lengths when a nitro group is shifted from the 7-position to the 8-position. The introduction of a chlorine atom at the 5'-position in the indoline portion of the molecule also produces a bathochromic shift of the absorption maximum. The introduction of the methoxy group into the 8-position produces a bathochromic shift, whereas its introduction into the 7-position results in a hypsochromic shift. Furthermore, in general, the absorption maxima are shifted to shorter wave lengths in a hydroxylated polyethylene matrix.

Example 5.

The transmittance spectra of compound Ε in a CR-39 convex piano lens is shown in ' Figure 2. The spiropyran was imbibed into the matrix by immersion of the lens for 24 hours in a boiling saturated methanol solution of the compound. In this graph, the solid line shows the percentage transmittance of the non-activated lens, and the dashed line curve shows the transmittance after activation. This shows a maximum absorption at about 600 nm.

Example 6.

Compound G listed above was synthesized by reacting 2 grams of 5-mtro-3-methoxy salicylaldehyde with 1.75 grams of 1,3,3-tri-methyl-2-methylene-indoline in 40 grams of absolute alcohol. The reaction mixture was refluxed for li hours. The precipitated product was recovered, washed and dissolved in benzene. This compound, when imbibed into a plastics matrix, exhibits a blue photocolourization.

Example 7.

Compound Η was synthesized by reacting 2.0 grams of 5-nitro-4-methoxy salicylaldehyde with 2.0 grams of l,3,3-trimethyl-2-methylene - 5 - chloro - indoline in 40 grams of absolute ethanol. The reaction solution is a reddish purple. The recovered, precipitated compound was washed, dried and dissolved in benzene. The benzene solution of the compound was colourless, but was purple when irradiated with ultraviolet and its recovery time was about 45 seconds. The compound, when imbibed into a CR-39 matrix, exhibits a purple photocolorisation.

Example 8.

Compound J above was prepared by reacting stoichiometric amounts of l,3,3-trimethyl-2-methylene indoline and 3-nitro-5-methoxysalicylaldehyde in refluxing ethanol for about 2 hours. A tan coloured crystalline material was recovered, and after washing with cold ethanol, was air dried. A dilute ethanol solution of the compound exhibited a light green photocolouration when cooled with dry ice (solid carbon dioxide). A chloroform solution containing this spiropyran and dissolved polymethylmethacrylate was yellow. A polymethyl methacrylate film haying the spiropyran imbibed therein was yellow in colour and became a darker yellow when irradiated with ultraviolet light.

Example 9.

Compound Κ above, in a dilute ethanol solution, exhibited a green photocolour when cooled with dry ice. A chloroform solution was yellow in colour, and when imbibed into a polymethyl methacrylate film the latter was also yellow. The film showed a green photocolouration when irradiated with ultraviolet light. The recovery time of the film at room temperature was about 5 minutes.

Example 10.

A convex piano lens was immersed in a boiling saturated methanol solution of compound Κ above for 74 hours. The treated lens was washed and dried; It had a light yellowgreen colour. After irradiation with ultraviolet, it became a green-blue colour. The thermal recovery appears to be faster than the other spiropyran compounds in CR-39.

Example 11.

Compound L above was prepared by interacting 1 g of 3-nim>-5-bromosalicyialdehyde in 30 ml of ethanol with 0.8 g of 1,3,3-tri-rnethyl-2-methylene-5-chloroindoline. The reaction mixture was refluxed for two hours. After standing overnight at room temperature, the product crystallized. The crystals were recovered by filtration and washed with cold ethanol. The crystals were light yellow. A benzene solution of the crystals, irradiated with ultra violet light, turned from colourless to greenish-blue.

This compound, when imbibed into a CR-39 matrix, exhibits a greenish-blue photocolorisation.

In addition to the absorption spectra of the coloured form, the photocolouration efficiency is also markedly influenced by the type and position of the various substituent groups. A qualitative indication of the photocolouration efficiency of the indolinobenzospiropyrans in a CR-39 plastic matrix was obtained by measuring the optical density change (at the wave length of the maximum absorption of the coloured form) before and after a sixty second irradiation with an ultraviolet source. The activating source consisted of two 15-watt lamps (black light) which are ultraviolet lights. The activating light flux was 0.7 milliwatts per square centimeter. All measurements were made at 23 °C. The values, set out in covery during the 60 second irradiation period, Table 2 below in column 3, do not reflect which loss did not, however, exceed 10% of the loss in optical density due to thermal re- the observed optical density change.

With regard to the above table, the follow-

ing observations may be made: (1) spiro-

pyrans with a nitro group substituted in the 6-

position are more light sensitive titan those

with the nitro group in the 8-position, (2) the

introduction of a methoxy group in either the

7-position or the 8-position reduces the photo-

sensitivity, and (3) the effect of a chlorine

atom in the 5-position is ambiguous.

In addition to photocolouration by ultra-

violet light, many of the spiropyrans listed in

Table 2 above exhibit photo bleaching of the

coloured form when irradiated with white light.

Accordingly, a valid assessment of the useful-

ness of a given photochromic composition must

include an evaluation of the relative efficiencies

of the photocolouration and photobleaching. In

this reagard, it has been observed that the two

derivatives with methoxy groups in the 8-

position exhibit no detectable photo bleaching.