Photothermographic materials containing co-developers with phosphonium cation

A photothermographic material comprising a support having on at least one side thereof, one or more photothermographic imaging layers comprising in reactive association:

• a. a photosensitive silver halide,
• b. a non-photosensitive source of reducible silver ions,
• c. a reducing agent composition for said reducible silver ions comprising a trisphenol reducing agent represented by the following Structure (I),
• d. a polymeric binder, and
• e. a substituted olefinic co-developer that is represented by the following Structure (IV):
• wherein L1 and L2 are independently sulfur or a mono-substituted or unsubstituted methylene group,
• R1 and R2 are independently primary or secondary substituted or unsubstituted alkyl groups having 1 to 12 carbon atoms,
• R3, R4, and R5 are independently substituted or unsubstituted alkyl groups having 1 to 12 carbon atoms, substituted or unsubstituted alkoxy groups having 1 to 12 carbon atoms, or halo groups, and
• R6, R7, R8, R9, R10, and R11 are independently hydrogen or any substituent that is substitutable on a benzene ring,
• wherein V and W are independently aromatic or electron withdrawing groups, provided that at least one of V and W is an electron withdrawing group, or V and W can represent the atoms necessary to form a ring containing an electron withdrawing group,
• R is an —O−A+ or —S−A+ group, and
• A+ is a quaternary phosphonium cation.