Thermolabile acutance dyes for dry silver

A light sensitive composition comprising an intimate mixture of a substantially light-insensitive silver compound which upon reduction gives a visible change and sufficient amount of a silver halide to catalyse said reduction to give a visible change in those areas where the silver halide has been exposed to light when the intimate mixture is heated in the presence of a reducing agent, the intimate mixture including as an acutance dye a compound of the general formula:

• ##STR9## wherein:
• n is 1 when k is 0 or k is 1 when n is 0,
• m is 0, 1 or 2,
• Y is a member selected from the group consisting of --CN and NO.sub.2,
• R.sup.1 represents an alkyl group containing 1 to 12 carbon atoms,
• R.sup.2 is a member selected from the group consisting of a phenyl group, a substituted phenyl group of molecular weight less than 350, --COOR.sup.1 wherein R.sup.1 is an alkyl group of 1 to 12 carbon atoms, C.sub.6 H.sub.5 CO-- or R.sup.6 NHCO-- wherein R.sup.6 is a member of the group consisting of a hydrogen atom, alkyl, aryl or aralkyl group, and when m is 1 or 2, R.sup.2 may additionally represent a member of the group consisting of a hydrogen atom and an alkyl group having 1 to 4 carbon atoms,
• R.sup.3, R.sup.4 and R.sup.5 are cyanine dye compatible substituents,
• D represents a member of the group consisting of (CH.dbd.CH), O, S, Se,>C(CH.sub.3).sub.2 or >NR.sup.7, wherein R.sup.7 is selected from the group consisting of an alkyl group containing 1 to 4 carbon atoms and CH.sub.3 COO--,
• with the proviso that:
• when k=0, n=1, m=0 and Y is NO.sub.2
• R.sup.2 is not a substituted phenyl group of the formula:
• ##STR10##
• wherein one of Z.sup.1 and Z.sup.2 is NO.sup.2 and the other is a member of the group consisting of a halogen atom, --NO.sub.2, --CN and a perfluoroalkyl group containing 1 to 4 carbon atoms.