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This invention relates to new compounds, new photographic elements and new
processes for forming image records in photographic elements. The
compounds of this invention that can be used in photographic elements and
processes are dye-providing materials and photographic reagents that
contain a cleavable substituent thereon. Generally, the cleavable moieties
of the compounds of this invention require acceptance of at least one
electron with subsequent intramolecular nucleophilic displacement to
cleave or displace the moiety from its original substituent position. The
cleavable substituents are useful in providing removable ballast groups,
removable inactivating groups, removable substituents which shift the
resonance of the molecule, and the like.
It is known in the art that certain blocking groups can be used on
compounds temporarily to immobilize or inactivate the compound in a
photographic element. Heavy counter ions, such as barium salts, have been
used to immobilize dyes, as disclosed by Yutzy, U.S. Pat. No. 2,756,142
issued July 24, 1956. Removable ballast groups on dyes or photographic
reagents are also described by Whitmore, Canadian Pat. No. 602,607 issued
Aug. 2, 1960, and U.S. Pat. Nos. 3,227,552, 3,628,952, 3,728,113,
3,725,062 and the like. Compounds that undergo intramolecular ring closure
upon oxidation to split off a dye are disclosed in U.S. Pat. Nos.
3,443,939, 3,443,940, 3,443,941 and 3,751,406. Compounds that are
initially immobile and undergo a redox reaction followed by alkali
cleavage to split off a dye are disclosed by Fleckenstein et al, Published
U.S. Ser. No. B351,673 filed Apr. 16, 1973.
It is also known in the prior art that intramolecular nucleophilic
displacement compounds containing an hydroxylamino nucleophile can be used
in photographic elements to release a diffusible image dye-providing
material or a photographic reagent, as shown by Hinshaw and Condit, U.S.
Ser. No. 534,966 filed Dec. 20, 1974, and Fields et al, U.S. Pat. No.
3,980,479 issued Sept. 14, 1976.
We have now discovered improved compounds that will undergo intramolecular
nucleophilic displacement and that offer certain advantages when used in
products such as photographic elements and the like in controlling the
release of a dye-providing moiety or a photographic reagent. Generally,
the compounds of this invention are aromatic nitro compounds which, upon
accepting electrons (reduction), undergo intramolecular nucleophilic
displacement to release an image dye-providing moiety or a photographic
reagent.
Aromatic nitro compounds have been known in the art for several years, for
example, as disclosed in U.S. Pat. Nos. 2,938,204 issued May 17, 1960, and
2,681,364 issued June 15, 1954; Biochemical J., 37, 326 (1943); Yakugaku
Zasshi, 89, 67 (1969); J. Chem. Soc., 2393 and 2398 (1971); etc. Aromatic
nitro compounds have also been suggested for use in photographic elements,
for example, as disclosed in U.S. Pat. No. 3,877,941, where an aromatic
nitro compound is used as an amine progenitor.
However, we have now found that certain aromatic nitro compounds in
accordance with this invention provide highly advantageous results in the
release of image dye-providing materials or the release of photographic
reagents. Generally, the useful compounds are based on an aromatic nitro
compound that contains at least one other group, which is an
electron-withdrawing group, in the aromatic ring or as a substituent of
the aromatic ring. Where the compounds are designed for photographic uses,
at least one substituent on the ring comprises an image dye-providing
moiety or a photographic reagent separated from the ring by an
electrophilic cleavage group that contains an electrophilic center and a
leaving group that is capable of being displaced by intramolecular
nucleophilic displacement upon the reduction of said nitro group.
In the broad concepts of this invention, we have discovered cleavable
moieties which can be put on any molecule through a linkage atom which is
an oxygen atom, a sulfur atom, a nitrogen atom or a selenium atom. The
cleavable moieties can be used to control the time and rate of release of
the compound, and upon reduction undergo intramolecular nucleophilic
displacement of the linkage atom, along with the moiety linked through the
atom. While this cleavage mechanism is particularly useful for
photographic reagents and image dye-providing moieties, it is also useful
for releasing pharmaceuticals, corrosion inhibitors and the like.
The compounds of the present invention offer several advantages; for
example, the reduction prior to intramolecular displacement can be
accomplished with organic reducing agents under mild conditions such as
encountered in many photographic processes. In contrast, nitro compounds
are reduced according to several prior-art disclosures by hydrogenation in
the presence of a noble-metal catalyst.
In certain preferred embodiments, the compounds of this invention have the
formula:
##STR1##
where A represents a group containing the atoms necessary to form a 5- to
6-membered aromatic ring with the remainder of said formula, including
polycyclic aromatic ring structures, and wherein the aromatic rings can be
carbocyclic rings or heterocyclic rings such as groups containing aromatic
'onium groups in the ring, and A preferably represents the groups
necessary to form a carbocyclic ring system such as a benzene ring, a
naphthalene ring, etc.; W is an electron-withdrawing group having a
positive Hammett sigma value and includes groups such as cyano, nitro,
fluoro, chloro, bromo, iodo, trifluoromethyl, trialkylammonium, carbonyl,
N-substituted carbamoyl, sulfoxide, sulfonyl, N-substituted sulfamoyl,
ester and the like; R.sup.2 is a hydrogen atom, a substituted or
unsubstituted alkyl group preferably containing from 1-30 carbon atoms, or
a substituted or unsubstituted aryl group preferably containing from 6-30
carbon atoms; R.sup.1 is a bivalent organic group containing from 1-3
atoms in the bivalent linkage and can be alkylene groups, oxaalkylene,
thioalkylene, aminoalkylene, alkyl- or aryl-substituted nitrogen atoms and
the like; m and q are positive integers of 1 or 2; p is a positive integer
of 1 or greater and preferably 3-4, with [(R.sup.2).sub.q-1 W] being a
substituent on any portion of the aromatic ring structure of A, and p is 1
only when A contains an aromatic 'onium group, and when p is 2,
[(R.sup.2).sub.q-1 W] is ortho or para to the nitro group on said formula;
E and Q provide an electrophilic cleavage group where E is an
electrophilic center and is preferably a carbonyl group including carbonyl
(--CO--) and thiocarbonyl (--CS--) or it can be a sulfonyl group, and Q is
a bivalent group providing a monoatom linkage between E and X.sup.1
wherein said bivalent group can be an oxygen atom, a sulfur atom, a
selenium atom, a nitrogen atom which provides an amino group and the like,
and preferably Q is an amino group with an alkyl group substituent
containing from 1-20 atoms and preferably from 1-10 carbon atoms,
including substituted alkyl groups; n is an integer of 1-3 and is
preferably 1; and X.sup.1, together with Q, is either an image
dye-providing material such as an image dye or an image dye-precursor or a
photographic reagent such as an antifoggant moiety, a toner moiety, a
fixing agent, a development accelerator, a developing-agent moiety, a
hardener moiety, a development-inhibitor moiety and the like.
It is to be understood that, when multiple groups are present in the
compound as designated in the above formula, they may be identical or
different; for example, when p is 3, each [(R.sup.2).sub.q-1 -W] may be
selected from different substituents as specified, and it is understood
that R.sup.2 may be present on all or only some of said
electron-withdrawing groups; i.e., when p is greater than 2, q can be 2 on
some of the groups and 1 on some of the groups.
The formula above includes compounds where multiple cleavage groups are
located on an image dye-providing material or a photographic reagent,
i.e., when n is greater than 1. Compounds of this type are advantageous
where more than one cleavable group is used to shift a dye, prevent
reaction of the material or provide additional controls on the diffusion
of a diffusible moiety.
In certain embodiments and especially those embodiments where the compounds
are used in photographic elements, R.sup.2 is preferably present in the
compound as a ballasting group to render the compound immobile and
nondiffusible under alkaline processing conditions and (Q-X.sup.1)
represents a diffusible moiety. The nature of the ballasting group is not
critical, as long as the portion of the compound on the ballast side of E
is primarily responsible for the immobility. Generally, when R.sup.2 is a
ballast group, R.sup.2 will comprise long-chain alkyl radicals, as well as
aromatic radicals of the benzene and naphthalene series. Typical useful
groups for the ballast function contain from 8-30 carbon atoms and
preferably at least 12 carbon atoms.
The electron-withdrawing groups referred to for the compounds of the above
formulae generally are those groups which have a positive Hammett sigma
value and preferably a sigma value more positive than 0.2 or a combined
effect of more than 0.5 as substituents of the aromatic ring. The Hammett
sigma values are calculated in accordance with the procedures in Steric
Effects in Organic Chemistry, John Wiley and Sons, Inc., 1956, pp.
570-574, and Progress in Physical Organic Chemistry, Vol. 2, Interscience
Publishers, 1964, pp. 333-339.
Typical useful electron-withdrawing groups having positive Hammett sigma
values include cyano, nitro, fluoro, bromo, iodo, trifluoromethyl,
trialkylammonium, carbonyl, N-substituted carbamoyl, sulfoxide, sulfonyl,
N-substituted sulfamoyl, esters and the like. Where the term "aromatic
ring having an electron-withdrawing substituent" is used herein, it refers
to 'onium groups in the ring and to those groups substituted directly on
the ring which may be linkage for other groups such as ballast groups.
The electron-withdrawing groups include groups in the ring such as in a
compound of the formula:
##STR2##
wherein E, Q and X.sup.1 are as defined above.
Generally, the compounds of this invention are precursors for compounds
which function in the photographic element as intramolecular nucleophilic
displacement compounds. The nitro group on the compound undergoes
reduction to form a nucleophilic group. The term "intramolecular
nucleophilic displacement" is intended to refer to a mechanism where a
portion of the molecule is actually displaced rather than merely relocated
on the molecule; i.e., the electrophilic center must be capable of forming
a ring structure with said nucleophilic group. In the compounds of the
present invention, the nitro group on the aromatic ring becomes a
nucleophilic groups after it is reduced, i.e., after accepting at least
one electron. Generally, the intramolecular nucleophilic displacement
compounds are those compounds that have the nucleophilic group and the
electrophilic center juxtaposed by the three-dimensional configuration of
the molecule to promote close proximity of the groups whereby the
intramolecular nucleophilic displacement reaction can take place.
Generally, the respective electrophilic and nucleophilic groups can be
located in the compounds, including polycyclic compounds, where the groups
are held in the possible reaction positions. However, the nucleophilic
groups and electrophilic groups are preferably located on compounds
wherein a cyclic organic ring or a transient cyclic organic ring can be
easily formed by intramolecular reaction of the nucleophilic group at the
electrophilic center. Cyclic groups can be generally formed with 3-7 atoms
therein, and preferably in accordance with this invention the nucleophilic
group and the electrophilic group are positioned on a compound where they
can form a 5- to 7-membered ring, and more preferably a 5- or 6-membered
ring (4-membered rings are generally known to be difficult to form in
organic reactions). Intramolecular nucleophilic displacement occurs with
the compounds of this invention after the nitro group has accepted at
least one electron. The rate of nucleophilic displacement is very low or
substantially zero prior to reduction of the nitro group.
It should be understood that the compounds of this invention are stable
under the conditions of processing except where the primary cleavage of
the compound occurs as a direct function of the reduction of a nitro
group. The compound may contain other groups which ionize or hydrolyze,
but the primary imagewise release occurs by intramolecular nucleophilic
displacement where the nucleophilic group, provided by reduction of said
aromatic nitro group, reacts with the electrophilic center of the cleavage
group on the compound. It is understood that, where the aromatic nitro
compounds are to be used in highly alkaline conditions, the various groups
of the aromatic nitro compound are selected to provide compounds which are
relatively stable to external attack by alkali.
Generally, the nitro group and the electrophilic group are both attached to
the same aromatic ring structure, which can be a carbocyclic ring
structure or a heterocyclic ring structure and includes fused rings
wherein each group can be on a different ring; preferably, both groups are
attached directly to the same aromatic ring, which is preferably a
carbocyclic ring structure.
Generally, the intramolecular nucleophilic displacement compounds provided
by reduction of the compounds of this invention contain from 3 to about 5
atoms and preferably 3 or 4 atoms between the nucleophilic center of the
nucleophilic group and the atom which forms the electrophilic center,
whereby the nucleophilic center, taken together with the center of the
electrophilic group, is capable of forming a ring or a transient ring
having from 5-7 atoms therein and preferably 5 or 6 atoms therein.
The term "nucleophilic group" as used herein refers to an atom or group of
atoms that have an electron pair capable of forming a covalent bond.
Groups of this type are sometimes ionizable groups that react as anionic
groups. The compounds of this invention contain nitro groups which undergo
reduction to provide a nucleophilic group such as an hydroxylamino group.
The hydroxylamino nucleophilic group can contain more than one nucleophilic
center; i.e., either the nitrogen atom or the oxygen atom can be the
nucleophilic center. Where more than one nucleophilic center is present in
the nucleophilic group on the intramolecular nucleophilic displacement
compounds of this invention, the nucleophilic attack and displacement will
generally occur through the center which is capable of forming the most
favored ring structure; i.e., if the oxygen atom of the hydroxylamino
group would form a 7-membered ring and the nitrogen atom would form a
6-membered ring, the active nucleophilic center would generally be the
nitrogen atom.
The term "electrophilic group" refers to an atom or group of atoms that are
capable of accepting an electron pair to form a covalent bond. Typical
electrophilic groups are sulfonyl groups (--SO.sub.2 --), carbonyl
(--CO--) and thiocarbonyl (--CS--) and the like, where the carbon atom of
the carbonyl group forms the electrophilic center of the group and can
sustain a partial positive charge. The term "electrophilic cleavage group"
is used herein to refer to a group (--E--Q--) wherein E is an
electrophilic group and Q is a bivalent leaving group providing a mono
atom linkage between E and X.sup.1 wherein said mono atom is a nonmetallic
atom that has a negative valence of 2 or 3. The leaving group is capable
of accepting a pair of electrons upon being displaced from the
electrophilic group. Where the nonmetallic atom is a trivalent atom, it
can be monosubstituted by a group which can be a hydrogen atom, an alkyl
group including substituted alkyl groups and cycloalkyl groups, or an aryl
group including substituted aryl groups. Typical atoms useful in Q are the
nonmetallic atoms in groups VA and VIA of the periodic table which are
capable of having a negative valence of 2 or 3, such as nitrogen atoms,
sulfur atoms, oxygen atoms, selenium atoms and the like.
The compounds of the present invention include many types of dye-providing
materials and photographic reagents that benefit from the cleavage in
accordance with this invention. Immobile compounds can be prepared where
the ballasting portion is cleaved from a diffusible moiety which can then
diffuse to adjacent layers in a photographic element. A group can be
cleaved from the compound to render the compound active, such as on a
development inhibitor, or to shift the resonance such as on a shifted dye.
In still other embodiments, the group can be cleaved to enable the
compound to undergo subsequent reactions in the photographic element.
The compounds of the present invention offer several improvements over
those known in the prior art. Generally, the compounds provide the
advantage that they must accept electrons (undergo reduction) before any
cleavage will occur. Meanwhile, the compound remains relatively stable in
various liquid media such as alkaline solutions. In contrast, many related
compounds must be oxidized before they will undergo cleavage or they
hydrolyze to cleave the compound as a function of pH rather than as a
function of reduction.
In most uses contemplated for the aromatic nitro compounds of this
invention, they are reacted with an electron donor which reduces the nitro
compound providing a nucleophilic group on the compound for the subsequent
intramolecular nucleophilic displacement of the releasable moiety. The
electron donor can be provided to the aromatic nitro compound by spraying,
stencil, physical transfer, imbibition, imagewise transfer, etc. The term
"electron-donor" is understood to include those compounds or materials
which are capable of reducing the aromatic nitro compounds of this
invention.
The aromatic nitro compounds can be used in combination with organic
electron donors in photographic elements. In a photographic element
containing a layer of silver halide having an aromatic nitro compound
associated therewith, the electron donor is destroyed as a function of
silver halide development. In the remaining areas, the electron donor
reduces the aromatic nitro compound whereby intramolecular nucleophilic
displacement can take place. Where the electron donor is also a good
silver halide developer, an electron donor is used which has a faster
reaction rate with the silver halide than it does with the aromatic nitro
compound. Typical useful electron donors which are also silver halide
developers include ascorbic acid, trihydroxypyrimidines such as
2-methyl-4,5,6-trihydroxypyrimidine, hydroxylamines such as diethyl
hydroxylamine, and the like.
The aromatic nitro compounds of this invention can also be used in
photographic elements in combination with organic electron donors which
are relatively poor silver halide developers or do not develop silver
halide, as disclosed by Chasman, Dunlap and Hinshaw, U.S. Ser. No. 775,025
entitled PHOTOGRAPHIC ELEMENTS CONTAINING BALLASTED ELECTRON-ACCEPTING
NUCLEOPHILIC DISPLACEMENT COMPOUNDS, filed on even date herewith and which
is incorporated herein by reference. The electron donors can be present in
the photographic element as a hydrolyzable precursor for the electron
donor, an immobile electron donor or a diffusible electron donor.
Generally, the electron donor is destroyed imagewise, and where it has not
been destroyed it reacts with the aromatic nitro compound to transfer
electrons whereby the aromatic nitro compound can undergo cleavage. In one
embodiment in a photographic element, the aromatic nitro compounds are
used in combination with a substantially immobile hydrolyzable
electron-donor precursor and an electron-transfer agent. The electron
transfer agent, such as a 3-pyrazolidone compound, reacts with developable
silver halide to provide oxidized electron-transfer agent. The oxidized
electron transfer agent reacts with the electron donor as it is made
available by hydrolysis to destroy an imagewise pattern of the electron
donor. The remaining electron donor can react with the aromatic nitro
compound whereby it can undergo cleavage. Where a diffusible dye is
released, it will be made available for diffusion to an adjacent
image-receiving layer.
Alkali-labile electron donors which are preferably used according to
Chasman, Dunlap and Hinshaw, supra, include those compounds which have a
finite rate of hydrolysis under processing conditions and include
benzisoxazolones, lactones, blocked hydroquinones and the like.
Typical electron donors which can be used in combinations with the aromatic
nitro compounds of this invention include:
##STR3##
In certain preferred embodiments, the cleavable group is used as a
substituent on a shiftable dye to control the resonance of the dye. Upon
cleavage of the aromatic nitro group from the dye, it will undergo a
bathochromic or hypsochromic shift. Shiftable dyes are generally known in
the prior art, including those disclosed by Weyerts, U.S. Pat. No.
3,260,597 issued July 12, 1966, wherein an acyl group is used to shift the
absorption of the dye. Generally, the cleavage moieties of the present
invention can be used on any dye where there is an ionizable nitrogen
atom, oxygen atom, sulfur atom or selenium atom which affects the
resonance of the dye. In accordance with this invention, the cleavable
moiety is substituted on the dye so that the ionizable group is the
leaving group in the electrophilic cleavage group.
The moiety represented by (Q-X.sup.1) in the above formula can be a silver
halide development inhibitor including triazoles and tetrazoles such as a
5-mercapto-1-phenyltetrazole, a 5-methylbenzotriazole, a
4,5-dichlorobenzotriazole and the like, and it can also be an antifoggant
including azaindenes such as a tetrazaindene and the like. The compounds
that contain releasable silver halide development inhibitors or
antifoggants can generally be used in the photographic elements in
association with silver halide layers wherein said compound can be
incorporated in amounts such as 0.1 to 30.0 mg./m..sup.2 dissolved in a
coupler solvent such as diethyl lauramide. When these compounds are
incorporated in photographic elements in association with negative silver
halide emulsions, a positive imagewise distribution of inhibitor or
antifoggant will be produced upon development. Thus, silver development is
inhibited or restrained in the low-exposure toe as seen on the Density/Log
E curve, but not in the more fully exposed shoulder as seen on the
Density/Log E curve. Development inhibition of the unexposed areas is
thereby achieved selectively. When the silver halide emulsions also have
dye releasers in accordance with this invention associated therewith, the
overall effect of the inhibitor or antifoggant is to release more dye in
the unexposed regions, improving maximum image dye density to the
image-receiving layer without increasing the amount of dye released in the
exposed regions.
In certain peferred embodiments, cleavable groups of this invention are
used to ballast a moiety which is a diffusible dye-providing material.
Preferably, the image dye-providing moiety is a preformed dye or a shifted
dye. Dye materials of this type are well-known in the art and include dyes
such as azo dyes including metallizable azo dyes and metallized azo dyes,
azomethine (imine) dyes, anthraquinone dyes, alizarin dyes, merocyanine
dyes, quinoline dyes, cyanine dyes and the like. The shifted dyes include
those compounds wherein the light absorption characteristics are shifted
hypsochromically or bathochromically when subjected to a different
environment such as a change in pH, reaction with a material to form a
complex such as with a metal ion, removal of a group such as a
hydrolyzable acyl group connected to an atom of the chromophore as
mentioned by Weyerts, U.S. Pat. No. 3,260,597 issued July 12, 1966, and
the like. The electrophilic cleavage group and other groups on the
molecule should, of course, be selected to provide stable compounds when
used under highly alkaline conditions, and preferably the cleavable moiety
is attached to an amino group when the compound is used under highly
alkaline conditions. In certain embodiments, the shifted dyes are highly
preferred and especially those containing a hydrolyzable group on an atom
affecting the chromophore resonance structure, because the compounds can
be incorporated directly in a silver halide emulsion layer or even on the
exposure side thereof without substantial reduction in the recording light
exposure. After exposure, the dye can be shifted to the appropriate color
such as, for example, by hydrolytic removal of the acyl group to provide
the respective image dye.
In another embodiment, the cleavage groups of this invention are used to
provide a temporary ballast on a moiety which is a diffusible image-dye
precursor. The term "image-dye precursor" is understood to refer to those
compounds that undergo reactions encountered in a photographic imaging
system to produce an image dye, such as color couplers, oxichromic
compounds, and the like.
The aromatic nitro compounds described herein have particular application
in a photographic process where it is desired to have a diffusible entity
such as a dye transferred to an adjacent layer or a receiving element.
However, in certain embodiments this invention relates to the release of
an imagewise distribution of a diffusible photographically useful compound
which is a photographic reagent. Typical useful photographic reagents are
known in the art, such as in U.S. Pat. Nos. 3,227,551, 3,698,898,
3,379,529 and 3,364,022, for example, a silver complexing agent, a silver
halide solvent, a fixing agent, a toner, a hardener, an antifoggant, a
fogging agent, a sensitizer, a desensitizer, a developer or an oxidizing
agent. In other words, --Q-X.sup.1 in the above formula may represent any
moiety which, in combination with a hydrogen atom, provides a photographic
reagent upon cleavage.
Typical useful photographic reagents containing the cleavage group
according to this invention are as follows:
##STR4##
The diffusible moiety represented by Q-X.sup.1 can also be a silver halide
development accelerator such as a benzyl alcohol, a benzyl
.alpha.-picolinium bromide and the like, a fogging agent or nucleating
agent, or an auxiliary developer such as a 1-phenyl-3-pyrazolidone, and
the like. When these compounds are used in photographic elements in
association with silver halide emulsions which also have associated
therewith image dye-providing materials in accordance with this invention,
the released dye density of all dyes in the unexposed regions would be
somewhat reduced by fog development. If, however, one layer was unexposed
while the other two were given an imagewise exposure, the amount of
foggant or development accelerator reaching the unexposed layer from the
other two layers would be less where those layers were exposed. Hence, the
Dmax of the unexposed layer would increase as a function of exposure of
the other two layers. This greatly enhances the saturation of single
colors in a photograph.
When color couplers are present in the compounds of this invention, the
couplers can be released or made available in areas where no development
occurs and can be reacted with an oxidized color developer such as a
primary aromatic amine to form the image dye. Generally, the color coupler
and the color developer are so chosen that the reaction product is
immobile. Typical useful color couplers include the pyrazolone couplers,
pyrazolotriazole couplers, open-chain ketomethylene couplers, phenolic
couplers and the like. Further reference to the description of appropriate
couplers is found in U.S. Pat. No. 3,620,747 by Marchant issued Nov. 16,
1971, which is incorporated herein by reference.
The compounds of this invention containing oxichromic moieties can also be
advantageously used in a photographic system because they are generally
colorless materials due to the absence of an image-dye chromophore. Thus,
they can also be used directly in the photographic emulsion or on the
exposure side thereof without competitive absorption. Compounds of this
type are those compounds which undergo chromogenic oxidation to form the
respective image dye. The oxidation can be carried out by subsequent
aerial oxidation or incorporation of oxidants into the imagereceiving
layers of the film unit. Compounds of this type have been referred to in
the art as leuco compounds, i.e., compounds which have no color. Typical
useful oxichomic compounds include leuco indoanilines, leuco indophenols,
leuco anthraquinones and the like. In certain preferred embodiments, the
compounds of this invention contain oxichromic moieties as described by
Lestina and Bush, U.S. Pat. No. 3,880,658, which is incorporated herein by
reference.
In those embodiments of this invention where the aromatic nitro compounds
contain an image dye-providing moiety, they are generally used in a layer
on a support in sufficient quantity to produce a discernible image record.
The concentration needed will depend on the thickness of the layer and
absorption characteristics of the dye. However, where a visible image
record is desired, the aromatic nitro compound is generally used in
concentrations of at least 1 .times. 10.sup.-5 moles/m..sup.2 and
preferably from about 1 .times. 10.sup.-4 to 2 .times. 10.sup.-3
moles/m..sup.2.
The compounds of this invention are particularly useful in photographic
elements and in photographic processes to provide an imagewise
distribution of a photographically useful compound. The photographic
element can contain the immobile compounds in association with any
photographic material that produces an imagewise distribution of electron
donor during development which in turn can react with the nucleophile
precursor group on said aromatic nitro compound. In certain preferred
embodiments, where silver halide emulsions are used as the recording
means, the emulsion can be a negative, direct-positive or reversal
emulsion and the like which undergo development with a silver halide
developing agent to produce oxidized silver halide developer. The
unexhausted silver halide developing agent can react with the nucleophile
precursor group by a simple redox reaction or electron transfer to provide
the nucleophilic group, whereby intramolecular nucleophilic displacement
of the diffusible moiety can take place.
Black-and-white or one-color systems can be made that employ as few as one
silver halide emulsion and compounds according to this invention that
comprise the required image dye-providing moieties to providethe desired
net color effect. Preferably, the compounds of this invention are used in
three-color systems such as, for example, photographic elements containing
a layer comprising a redsensitive silver halide emulsion having associated
therewith an aromatic nitro compound comprising a cyan image dyeproviding
moiety, a layer containing a green-sensitive silver halide emulsion having
associated therewith an aromatic nitro compound that comprises a magenta
image dyeproviding moiety, and a layer containing a blue-sensitive silver
halide emulsion having associated therewith an aromatic nitro compound
that comprises a yellow image dyeproviding moiety.
The photographic element can be designed to provide an image record in
either the image | | |
