Thermally developable infrared sensitive imaging materials containing heat-bleachable antihalation composition

A photothermographic material that is sensitive at a wavelength of at least 700 nm and comprises a support having thereon one or more thermally-developable imaging layers comprising a hydrophobic binder and in reactive association, a photosensitive silver halide, a non-photosensitive source of reducible silver ions, and a reducing composition for said non-photosensitive source reducible silver ions,

• and on the backside of said support, an antihalation layer comprising a heat-bleachable antihalation composition comprising:
• a) a hexaarylbiimidazole, and
• b) an infrared radiation-absorbing compound having the following Structure I:
• A1—L1—A2 (I)
• wherein A1 represents a group derived from a dye base, a heterocyclic group, or an electron-donating aromatic group, A2 represents a group derived from a dye base, a heterocyclic group, a group derived from a dye acid, or an electron-donating aromatic group, and L1 represents a conjugated linking group that maintains electron delocalization between A1 and A2 to provide infrared absorbance.