Thermal-dye-bleach construction comprising a polymethine dye and a thermal carbanion-generating agent

A thermal-dye-bleach construction comprising a polymethine dye having a nucleus of formula:

• ##STR34## wherein:
• n is 0, 1, 2 or 3;
• W is selected from:
• hydrogen, alkyl groups of up to 10 carbon atoms, alkoxy and alkylthio groups of up to 10 carbon atoms, aryloxy and arylthio groups of up to 10 carbon atoms, NR.sup.1 R.sup.2, and NR.sup.3 R.sup.4 ;
• R.sup.1 to R.sup.4 are each independently selected from:
• alkyl groups of up to 20 carbon atoms, alkenyl groups of up to 20 carbon atoms, and aryl groups of up to 14 carbon atoms;
• or
• R.sup.1 and R.sup.2 together and/or R.sup.3 and R.sup.4 together may represent the necessary atoms to complete a 5-, 6-, or 7-membered heterocyclic ring group;
• or one or more of R.sup.1 to R.sup.4 may represent the atoms necessary to complete a 5- or 6-membered heterocyclic ring group fused to the phenyl ring on which the NR.sup.1 R.sup.2 or NR.sup.3 R.sup.4 group is attached;
• R.sup.5 and R.sup.6 are each independently selected from:
• hydrogen atoms, alkyl groups of up to 20 carbon atoms, aryl groups of up to 20 carbon atoms, heterocyclic ring groups comprising up to 6 ring atoms, carbocyclic ring groups comprising up to 6 carbon atoms and fused ring and bridging groups comprising up to 14 ring atoms;
• and, X.sup.- is an anion;
• in association with a thermal-carbanion-generating agent of general formula:
• ##STR35## wherein:
• R.sup.9 and R.sup.10 are individually selected from:
• hydrogen, an alkyl group, an alkenyl group, a cycloalkyl group, an aralkyl group, an aryl group, and a heterocyclic group;
• M.sup.+ is a cation which will not react with the carbanion generated from said thermal carbanion generating agent in such manner as to render said carbanion ineffective as a bleaching agent for said polymethine dye;
• p is one or two, and when p is one, Z is a monovalent group selected from:
• an alkyl group, a cycloalkyl group, an alkenyl group, an alkynyl group, an aralkyl group, an aryl group, and a heterocyclic group, and;
• when p is two, Z is a divalent group selected from:
• an alkylene group, arylene group, a cycloalkylene group, an alkynylene group, an aralkylene group, an alkenylene group, and a heterocyclic group.