content_image/927243.jpg content_image/927264.jpg content_image/927265.jpg
suitable solvent medium compnsmg one or more non› hydroxylic solvents (described below) at a general concen› tration of at least 0.1 mo!/! and up to and including 30 mo!/!; and at room temperature, adding either one or more primary alkylamines gradually to obtain a clear solution in the resulting reaction solution. Specific details for these syn› thetic methods are provided below in the Examples. 

Once prepared, the non-hydroxylic-solvent soluble silver complexes can be stored in the form of solid (after the solvent medium is removed by evaporative methods), or left in the reaction solution under conditions that are optimum for long-term stability (that is, negligible premature, non› photochemical reduction of silver ion to silver metal). 

Some particularly useful non-hydroxylic-solvent soluble silver complexes prepared according to the present invention are represented by formula (I): 

<img src='content_image/927243.jpg'>

wherein: 

a, b, and c are as defined above; 

L has a molecular weight of 250 or less, and is represented by either of the following formula (II) or (III): 

<img src='content_image/927264.jpg'>

<img src='content_image/927265.jpg'>

wherein R$_{1 }$ is hydrogen or an alkyl group having 1 or 2 carbon atoms, R$_{2 }$ and R$_{3 }$ are independently branched or linear alkyl groups having 1 to 8 carbon atoms, wherein any of the hydrogen atoms in the alkyl groups can optionally be replaced with a fluorine atom, and R$_{4 }$ is an alkyl group having 1 to 8 carbon atoms; 

Pis a 5- or 6-membered N-heteroaromatic compound that is selected from the group consisting of pyridine, 2-meth› ylpyridine, 4-methylpyridine, 2,6-dimethylpyridine, 2,3-di› methylpyridine, 3,4-dimethylpyridine, 4-pyridylacetone, 3-chloropyridine, 3-fluoropyridine, oxazole, 4-methylox› azole, isoxazole, 3-methylisoxazole, pyrimidine, pyrazine, pyridazine, and thiazole. 

Photosensitive Reducible Silver Ion-Containing Composi› tions 

An important characteristic of the present invention is to ensure its general absorption and use in the UV to visible part of the electromagnetic spectrum. Ideally, irradiating energy should have wavelengths in the UV to visible region (for example 350 nm to 450 nm) to allow selective excitation of the photosensitizer in the presence of a large variety of chromophores. 

The photosensitive reducible silver ion-containing com› positions according to the present invention contain only two essential components for purposes of providing silver metal during photo-irradiation in a rapid manner: (a) one or more non-hydroxylic-solvent soluble silver complexes according to the present invention; and (b) a solvent medium comprising one or more non-hydroxylic solvents as described below. However, the presence of a third compo- nent, ( c) one or more photosensitizers as described below, is very desirable in many embodiments, also can be considered 

essential to assure rapid photoreduction of silver ion at room or other low temperatures. No other components are pur› posely added to the photosensitive reducible silver ion› containing compositions according to the present invention so that the present invention provides simplified composi› tions that exhibit rapid silver metal formation for various methods and results. The incorporation of materials other than the three components (a) through (c) is likely to impede the generation of metallic silver. 

The (a), (b), and (c) components can be put together in general by mixing them under "safe light" (yellow light) conditions if desired. This mixing can occur in suitable solvent medium (as described below) comprising one or more of the (b) solvents. The resulting photosensitive reduc- ible silver ion-containing composition can be provided in liquid form having a viscosity of at least 1 centipoise and up to and including 1,000 centipoises at 25° C. 

The one or more non-hydroxylic-solvent soluble silver complexes can be present in an amount of at least 5 weight % and up to and including 90 weight %, based on the total weight of the photosensitive reducible silver ion-containing composition. 

Thus, in some embodiments, the photosensitive reducible silver ion-containing composition can comprise two or more different non-hydroxylic-solvent soluble silver complexes. Such embodiments can also include two or more different photosensitizers as described below. 

(II) 25 

The photosensitive reducible silver ion-containing com› position of claim 1 has exceptive long term stability as demonstrated by a silver stability test such that when the photosensitive reducible silver ion-containing composition is held at ambient temperature (20° C. to 25° C.) and under yellow safelight for 24 hours, less than 0.1 mo! % of its original silver ion content is reduced to silver metal. 

(III) 30 

Solvent Medium: 

The essential non-hydroxylic-solvent soluble silver com› plex (and photosensitizer if present) are generally solubi› lized in a suitable solvent medium that is predominantly non-hydroxylic organic solvents that include but are not limited to, acetonitrile, benzonitrile, acetone, methyl ethyl ketone, butyronitrile, propylene carbonate, propionitrile, isovaleronitrile, valeronitrile, and a mixture of two or more thereof. It is also desirable that the non-hydroxylic solvents do not participate in any redox reaction. That is, such non-hydroxylic solvents should not be capable under general preparation, storage, and use conditions to reduce silver ion by transferring electrons or to oxidize an a-oxy carboxylate by accepting electrons. Such reactions by non-hydroxylic solvents would negatively impact the thermal stability of photosensitive compositions according to the present inven› tion. 

Water is not purposely added to the solvent medium, and if water is present, it should be present at no more than 5 weight % based on the total weight of the solvent medium (not including the non-hydroxylic-solvent soluble silver complex and photosensitizer). 

Photo sensitizers: 

The photosensitizers useful in the present invention ini› tiate the electrochemical transformation of the non-hydrox› ylic-solvent soluble silver complexes. The photosensitizer must be capable of either reducing the silver ions or oxi› dizing the a-oxy carboxylates after the photosensitizer has absorbed light (that is, photoinduced electron transfer) at an electromagnetic radiation having a wavelength of at least 150 nm and up to and including 700 nm. Thus, the photo› sensitive compositions according to this invention are gen› erally sensitive to UV or visible electromagnetic radiation, 

