Dye-forming compositions

In an activating radiation-sensitive imaging composition comprising (1) a leuco form of a dye having one or more removable hydrogen atoms the removal of which forms a compound colored differently from the leuco form and (2) a photooxidant capable of converting said leuco dye to said differently colored form when said composition is exposed to activating radiation,

• the improvement wherein said photooxidant has the structural formula ##STR19## wherein R.sup.1 is a carbocyclic or heterocyclic ring containing from 5 to 10 ring atoms, and
• Z represents the non-metallic atoms necessary to complete 1 or more rings containing from 5 to 17 ring atoms,
• said photooxidant being present in an amount effective to provide an improved difference density of said colored form compared to the difference density produced by the same composition lacking said photooxidant.

In an imaging element useful to obtain a lithographic printing plate, comprising a support, and on the support, a composition comprising a negative-working photopolymer, a photosensitizer, a leuco form of a dye having one or more removable hydrogen atoms the removal of which forms a compound colored differently from the leuco form and a photooxidant capable of converting said leuco dye to said differently colored form when exposed to activating radiation,

• the improvement wherein said photooxidant has the structural formula ##STR20## wherein R.sup.1 is a carbocyclic or heterocyclic ring containing from 5 to 10 ring atoms, and
• Z represents the non-metallic atoms necessary to complete 1 or more rings containing from 5 to 17 ring atoms,
• said photooxidant being present in an amount effective to provide an improved difference density of said colored form compared to the difference density produced by the same composition lacking said photooxidant.

In an imaging element useful to obtain a lithographic printing plate, a comprising a support, and on the support, a composition comprising a negative-working photopolymer, a photosensitizer, a leuco form of a dye having one or more removable hydrogen atoms the removal of which forms a compound colored differently from the leuco form and a photooxidant capable of converting said leuco dye to said differently colored form when said composition is exposed to activating radiation,

• the improvement wherein said photooxidant has the structural formula ##STR21## wherein R.sup.1 is a carbocyclic or heterocyclic ring containing from 5 to 10 ring atoms, and
• Z represents the non-metallic atoms necessary to complete 1 or more rings containing from 5 to 17 ring atoms,
• said photooxidant being present in an amount effective to provide an improved difference density of said colored form compared to the difference density produced by the same composition lacking said photooxidant.

In a method of forming an image, comprising the step of imagewise exposing to activating radiation a composition comprising a print-out leuco dye having one or more removable hydrogen atoms the removal of which forms a compound colored differently from the leuco form,

• the improvement wherein the print-out density of said leuco dye is increased by means of a photooxidant having the structural formula ##STR22## wherein R.sup.1 is a carbocyclic or heterocyclic ring containing from 5 to 10 ring atoms, and
• Z represents the non-metallic atoms necessary to complete 1 or more rings containing from 5 to 17 ring atoms,
• said photooxidant being present in an amount effective to provide an improved difference density of said colored form compared to the difference density produced by the same composition lacking said photooxidant.

In a method of forming an image, comprising the step of imagewise exposing to activating radiation a composition comprising a print-out leuco dye having one or more removable hydrogen atoms the removal of which forms a compound color differently from the leuco form,

• the improvement wherein the print-out density of said leuco dye is increased by means of a photooxidant having the structural formula ##STR23## wherein R.sup.1 is a carbocyclic or heterocyclic ring containing from 5 to 10 ring atoms, and
• Z represents the non-metallic atoms necessary to complete 1 or more rings containing from 5 to b 17 ring atoms,
• said photooxidant being present in an amount effective to provide an improved difference density of said colored form compared to the difference density produced by the same composition lacking said photooxidant.