HEAT BLEACHABLE DYE SYSTEMS

Photothermographic elements containing heat bleachable acutance/antihalation dyes and thermographic elements employing heat bleachable dyes of the formula:in which:nis2,3,4 or 5,at least one of R1 to R4 represent hydrogen and the remainder of R1 to R4 independently represent a hydrogen atom, an optionally substituted cycloalkyl group, an optionally substituted alkenyl group, an optionally substituted alkyl group, an optionally substituted aryl group, an optionally substituted heterocyclic aromatic group, or R1 and R2 together or R3 and R4 together represent the necessary atoms selected from C, N, 0 and S to complete a non-aromatic type ring,X⊖ is an anion.