CA1138875A - Thermolabile cyanine dyes - Google Patents

Abstract

Abstract of the Disclosure Images produced in photothermographic emulsions using silver halide as a light-sensitive material therein suffer from light scattering effects on the silver halide.
Acutance dyes are disclosed which can absorb scattered light and which are bleached at the development temperature of the photothermographic composition.

Description

FN 915,234 S

THERMOLA~ILE ACUTANC DYES FO~ DRY SILVER

This invention relates to compounds suitable for use as acutance dyes in photosensitive compositions, to the preparation of such compounds and to photosensitive compositions containing t,he compounds. The invention is particularly concerned with photosensitive compositions o-~the type known as r'dry silver" compositions.
` Dry silver photosensitive compositions comprise an intimate mixture of a light sensitive silver halide, a reducing agent for silver ions, and another silver compound such as a silver salt of an organic acid, e.g.
silver behenate or silver saccharine or a complexed silver salt, which upon reduction gives a visible change and whlch is substantially light-insensitive. Such a mixture is usually prepared in suspension and the resulting dispers~on spread as a layer on a suitable substrate. When dry~ the layer is exposed to a light image and thereafter a reproduction of the image can be developed by heating the layer in the presence of the reducing agent for silver ion such as hydroquinone or certain substituted phenols.

It is because the exposure and development of the layer occur without using water, that these photo-thermographic materials are often rererred to as dry silver light-sensitive materials. Such materials in which minor amounts of a photosensitive sil`ver halide catalyst-progenitor are associated in catalytic proximity with major amounts of a heat sensitive oxidation-reduction image forming reaction mixture which reacts more rapidly in the presence of the catalyst resulting upon exposure of 3~

3~ S

the silver halide are well known in the art. Examples of such materials are described in our British Patent No. 1,110,046 and in United States Patent ~os. 3,839,0L~9 and 3,457,075.
We believe, that when the mixture is exposed to light, a latent image is Pormed in the silver halide.
Thereafter, the silver compound can be reduced by heating with the reducing agent, this reduction belng catalyzed image-wise by the light exposed silver halide. By a suitable choice of temperature~ the reduction of the silver compound can be cataly~ed in the light exposed areas to give a visible darkening while any slight reduction which occurs in the non-light exposed areas is insufficient to give a marked change. Of course, because khe silver halide acts as a catalyst progenitor, only very small amounts of it can suffice, e.g. 0.1 to 10% by weight of the mixture. However, large amounts, e.g. up to 15 or even 20% may be desirable in some circumstances.
In order to improve the sharpness or definition of photographic images, a dye known as an acutance dye is often incorporated into photosensitive compositions. To be effective the acutance dye will absorb at the wavelengths at which the photosensitive composition is sensitive. The longer the path length of the light in the layer of light sensitive composition the greater the attenuation.
Therefore, scattered light is attenuated or absorbed to a larger extent than light which impinges dlrectly on a light-sensitive crystal. As a result therefore, although the overall speed of the composition is reduced slightly, ~388'~

scattered light and other light rays which are liable to produce a blurred image are preferentially absorbed and so the overall definition and sharpness of images produced in the layer are increased.
An acutance dye foruse in a dry silver composition is preferably heat labile, that is to say, that i-t is destroyed by the heat development of the dry silver composition to one or more compounds which are colorless.
It is therefore an object of this invention to provide dry silver compositions with acutance dyes, which absorb light at at least some of those wavelengths to which the composition is sensitive and which are rendered colorless upon heat development of the dry silver composition.
According to the invention there is provided a compound having the general formula: / R2 CII-CII~",C~

in which Rl represents an alkyl group containing 1 to 12 carbon atoms, R represents phenyl or nitrophenyl of molecular weight less than ' 2~ CH3C0_, C6H5, C6ll5CH~CO-, -COOC H CH ~ S02-, C6H5CH2-, NH2CO-, R NHCO-, or CH3SO2, wherein R3, R4 and R5 may be the same or different and are selected from the group of hydrogen, halogen, alkyl of 1 to 12 carbon atoms, alkoxy of 1 to 4 carbon atoms, alkenyl of 2 to 4 carbon atoms, -~CH2~nCOOH
where n is 0, 1, 2, or 3, -NO2, -NH2 or -NHCOCH3 or any two of R3, R4 and R5 together represent the carbon atoms needed to complete a fused on benzene ring, R6 represents an alkyl, aryl or aralkyl group, D represents -CH=CH-, 0, ~ NR7, ~ C(CH3)2, S or Se, '' `I
~ - 3 -R represents an alkyl group containing 1 to 4 carbon atoms or CH~CO-, Y represents -CN or -N02 Wit}l the exception that Y do~s not represellt -C~ when R- represents -CN, N is 1 when k is 0 or k is 1 when n is 0, and m is 0~ 1, 2 or 3, with the proviso tha~ when k - 0, n - 1, m = 0 and Y is -NO2, R2 is not a substituted phenyl group of the formula:

_ ~ z2 in which one of zl and z2 is N02 and the other represents a halogen atom, -N02~ -CN or a perfluoroalkyl group containing 1 to 4 carbon atoms.
It is preferred that Y represents -N02.
The invention also provides a light sensitive composition comprising an intimate mixture of a substantially light-insensitive silver compound which upon " ~13~S
--5~
reduction gives a visible change and sufficient of a silver halide to catalyze this reduction to give a visible change in those areas where the s:llver halide has been exposed to light when the mixture is heated in the presence of a reducing agen-t, and as an acutance dye a compound in accordance with the invention as described above.
The substituents R3, R4 and R5 may be the same as or different from one another and each represents a substituent which can be present in a cyanine dye type heterocyclic nucleus. Such substituents are known in the art and include hydrogen or halogen, e.g. chlorine, bromine or iodine, an alkyl group containing l to 12 carbon atorns, an alkoxy group containing l to 4 carbon atoms, an alkenyl group containlng 2 to 4 carbon atoms, -(CH2)nCOOH
where n is 0, l, 2 or 3, -N02, -NH2, or -NHCOCH3, or any two of R3 to R5 together represent the carbon atoms needed to complete a fused on benzene ring. Preferably at least one, more preferably at least two, of the substi~
tuents R3 to R5 represent hydrogen atoms. The most preferred substituents to be represented by each of R3 to R5 are hydrogen~ chlorine or bromine atoms, or methyl, ethyl, methoxy or ethoxy groups.
It is found that dry silver compositions containing one of the above noted acutance dyes can give excellent sharp images and that the acutance dye will be rendered colorless by the heating required to develop the composition. This is surprising in view of the fact that many of these dyes are found not to be decomposed to a colorless state when they are heated on their own to the temperature at which the dry silver compositions are heated ~or development.
According to a further embodiment o:~ the invention there is provided a method of preparing compounds of the formula:

' Dk--C=~ I~C/

in which Rl represents an alkyl group contalnillg l to 12 carbon atoms, R2 represents a substituted phenyl group o.~ molecular weight, less than 350, -CN, -NO2, CH3CO-~ C6H5-' C6H5CH2CO-~ ~Cc2Hs' 3 ~ 2~ 6 sC 2 ~ NH2CO , R NHCO , or CH3S02, each of R3, R an-l R5 independently represent a substituent which can be present in a cyanine dye type heterocyclic nucleus, R represents an alkyl, aryl or aralkyl group, 1 3 D represents -C=C-, 0, ~-NR7, - C(CH3)2, S or Se, R7 represents an alkyl group containing l to 4 carbon atoms or CH3CO-, Y represents -CN or NO2 with the exception that Y does not represent -CN

8 ~ 5 when R represents -CN, n is 1 when k is 0 or k is 1 when n is 0, and m is 0, 1, 2 or 3, comprising reacting ~ C~I=CH ~ Z3 Rl in which Z3 represents SR1 or -- N -'~ CO

15and ~ represents an anion, ~ /y with CH2 ~ \R2 - The reaction is carried out in the presence of a polar solvent, a base catalyst and an acid binding agent.
Suitable reagents are well known and fully exemplified in the cyanine/merocyanine dye literature.
The reaction is preferably carried out in the presence of C2H50H as a solvent and (C2H5?3N as both catalyst and acid binder. The preparation :Ls analogous to known processes used in the synthesis of merocyanine dyes.
Examples of compounds of the invention which may be used as acutance dyes are set out in the following Table.
.

, ~3Z~

o ~ ,~
~D ~ N co In Ci CO C~
Ln :~ 3 IS~ ~ 3 i~ O O
r~ Ln ~) . .
: . ~ ~ ~ ~ ~ ~ ~ ~U
~; O O O O O O 0 2; }; Z ~ O O
~ Z Z Z Z; ~: Z

.~ ~ X X '-~ ~
~ ~ 11 0 C~ O li ~ V2 0 11 ~ O U2 : ~ ~ ~ V
~ I

a~ ~1 ~
Q
i ~ I ~10000 o o O O O O ~100 In~
Il P; ~:: ~ X ~: ~ X ~ ~ X
;

N ¦ [~ N V V ~ N ~i ~r; v ~ Ln v v Z O ~; Z; ~, ~~,' ~ Z Z Z Z O O
N 0 0 0 ~ ~ N N N N O O
OVVVVVVVOOOOC~V

~; X N N N ~1 N N ~ N N N N (\i t~l V V V ~) ~) VV C,7 V V C~ C ) V V
~1 ~I f\l '1 3 11~ ) ~ O ~I N ~rl 3 ~ - :
` `` .~

~3~ S
The acutance dyes can be incorporated into the dry silver compositions of the invention in an amount from 5 x 10 to 0.1 mole of acutance dye per kilogram of total dry solids ln the composition. Preferably, however, the dyes are incorporated in an amount of from 2 x 10 3 to 3 x 10 mole of acutance dye per kilogram of dry solids in the composition.
The light-sensitive compositions of the invention will nor~ally be spread for use on a support, suitable supports including, for example, paper, polymeric materials such as polyester or polyamide film bases, and glass~ The composition will normally be prepared as a solution or suspension which i~ spread as a layer on the support and then the solvent or vehicle is evaporated off to leave a dry photosensit:lve layer. If desired, a coating aid or binder such as polyvinyl butyral, polymethyl methacrylate 9 cellulose acetate, polyvinyl acetate, cellulose acetate-propionate and cellulose acetate butyrate, can be incorporated in the light-sensitive mixtureO
The substantially light-insensitive silver compound is suitably a silver salt of an organic acid.
The organic acid can preferably be a C12 to C2~ aliphatic acid and is more preferably a C16 to C25 aliphatic acid-Examples include silver behenate, silver caprate, silverlaurate, silver myristate, silver palmitate, silver stearate, silver arachidate and silver saccharine.
The reducing agent for this substantially light-insensitive silver compound can normally be quite .3~
--10-- , mild. Suitable examples include hydroquinone and substituted phenols such as l-methyl-4-hydroxy-naphthalene, methyl gallate~ catechol~ phenylene diamine, p-amino-phenol and l-phenyl-3-pyrazolidone. The reducing agent can be incorporated into the light-sensitive composition.
Alternatively, the composition can be placed in contact with the reducing agent after exposure to light. ~or example, a light-sensitive coating can be exposed to a light image, placed in contact with a layer containing the reducing agent and the image then developed by heating. Preferably, however, the reducing agent is incorporated in the light-sensitive composition before this is spread on the support. Then the storage stability of the composition can be improved by incorporating in the composition a small amount of a stabilizer such as an acid stabilizer, e.g. succinic acid~ benzoic acid or salicylic acid.
The silver halide can be present in amounts of up to 20% by weight of the mixture of silver compounds or can be present in small amounts, e.g. 0.1 to 10% by weight of the mixture of silver compounds. It can be added as such to the substantially light-insensitive compound or formed in situ by adding a soluble halide, e.g. a mercury or sodium halîde, to the substantially light-insensitive silver compound. The silver halide can, for example, be chloride, bromide or a mixture of them and/or other silver halides.
The light-sensitive compositions of the invention can include one or more sensitizing dyes to `" ` ~.~L3~

improve their sensitivity to parts o~ the spectrum other than the shorter wavelengths. Thus dye sensitized dry silver compositions of the present invention can contain an additional acutance dye such as one o~' those described in Belgian Patent No. 866,202.
The invention will now be illustrated by the ~ollowing Examples.
Example 1 Preparation o~ l-methyl-4(cyano 4'-nitrophenylmethylene)-auinolane (Com~ound 1) l-Methyl-4-methylthioquinolinium toluene-4-sulphonate ~1.83 g) was placed in ethanol (20 ml) and 4-nitrophenylacetonitrile (0.81 g) added. The mixture was warmed, triethylamine (o.8 ml) added and the re~lulting mixture heat~d under reflux for 15 minutes. The dye wh~ch separate rrom the hot solution was f'iltered off and the crude compound (1.2 g) was twice crystalized ~rom toluene (200 ml) to give magenta needles (0.9 g) having a melting point o~ 203 to 204C. ~n methanolic solution the dye exhibited ~ = 2.0 x 104 at ~max 495 nm.
Example 2 Preparation o~ l-(benzoxazolinyl-2'-ene)-3-ethoxycarbonyl-3-nitro-~ro-2-ene (Com~ound 14)

2-Acetanilino-3-ethyl-benzoxazolium iodide (2.17 g) was placed in ethanol (10 ml) and ethyl nitroacetate (1.0 ml) added. The mixture was warmed, triethylamine (0.7 ml) added and the resulting mixture heated under re~lux ~or 7 minutes. The dye separa-ted upon cooling and a~ter ~iltration the crude product (1.2 g) was crystalized from toluene (17 ml) to give ~3~

yellow needles (1.05 g) having a melting point of 172 to 175C. In methanolic solution the dye exhibited ~ = 5.6 x 104 at ~max 452 nm.
Analysis:
Calculated: C = 59.21%; H = 5.26%; N = 9.21%
Found: C = 58.90%; H = 5.59%; N = 9.10%.

. . .

Claims (3)

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

1. A compound having the general formula:

in which R1 represents an alkyl group containing 1 to 12 carbon atoms, R2 represents phenyl or nitrophenyl of molecular weight less than 350, -CN, -NO2, CH3CO-, C6H5, C6H5CH2CO-, -COOC2H5, , C6H5CH2-, NH2CO-, R6NHCO-, or CH3SO2, wherein R3, R4 and R5 may be the same or different and are selected from the group of hydrogen, halogen, alkyl of 1 to 12 carbon atoms, alkoxy of 1 to 4 carbon atoms, alkenyl of 2 to 4 carbon atoms, -(CH2)n COOH
where n is 0, 1, 2 or 3, -NO2, -NH2 or -NHCOCH3 or any two of R3, R4 and R5 together represent the carbon atoms needed to complete a fused on benzene ring, R6 represents an alkyl, aryl or aralkyl group, D represents -CH=CH-, O, , , S or Se, R7 represents an alkyl group containing 1 to 4 carbon atoms or CH3CO-, Y represents -CN or -NO2 with the exception that Y does not represent -CN when R2 represents -CN, n is 1 when k is 0 or k is 1 when n is 0, and m is 0, 1, 2 or 3, with the proviso that when k = 0, n = 1, m = 0 and Y is -NO2, R2 is not a substituted phenyl group of the formula:

in which one of Z1 and Z2 is NO2 and the other represents a halogen atom, -NO2, -CN or a perfluoroalkyl group containing 1 to 4 carbon atoms.

2. A light-sensitive composition comprising an intimate mixture of a substantially light-insensitive silver compound which upon reduction gives a visible change and sufficient of a silver halide to catalyze this reduction to give a visible change in those areas where the silver halide has been exposed to light when the mixture is heated in the presence of a reducing agent, and as an acutance dye a compound as defined in claim 1.

3. A method of preparing the compound of claim 1 comprising reacting in which Z3 represents SR1 or and X? represents an anion, with .