A heat-developable light-sensitive material is described, characterized by containing a polymer having a functional group releasing a basic component upon thermal decomposition in the side chain thereof. This polymer is a new base precursor which when added to heat-developable light-sensitive materials increases their storage stability and permits them to form an image of high density and decreased in fog even after storage. Preferred examples of such polymers are polymers having a repeating unit represented by the general formula (I): ##STR1## wherein R.sub.1, R.sub.2 and R.sub.3 are each a univalent group, L is a divalent connecting group having from 1 to 20 carbon atoms, M is a cation and x is a number equivalent with the valence of M.

A bisguanidine salt selected from the group consisting of a 4-(phenylsulfonyl)phenylsulfonylacetic acid salt of N,N'-bis(1,3-diethylguanyl)ethylenediamine, a 4-(phenylsulfonyl)phenylsulfonylacetic acid salt of N,N'-bis(1,3-diisopropylguanyl)ethylenediamine, a 4-(phenylsulfonyl)phenylsulfonylacetic acid salt of N,N'-bis-(imidazoline-2-yl)ethylenediamine, a 4-(phenylsulfonyl)-phenylsulfonylacetic acid salt of 1,4-bis(1,3-diisopropylguanyl)piperazine, a 4-(phenylsulfonyl)phenylsulfonylacetic acid salt of 1,4-bis(1,3-diethylguanyl)piperazine, a 4-(4-methylphenylsulfonyl)phenylsulfonylacetic acid salt of N,N'-bis(1,3-diethylguanyl)ethylenediamine and a 4-(4-ethylphenylsulfonyl)phenylsulfonylacetic acid salt of 1,4-bis(1,3-diethylguanyl)piperazine which can be used as a base precursor which is rapidly decomposed by heat treatment at 120.degree. C. or less to release a base.

A thermal-dye-bleach construction comprising a thermal nucleophile-generating agent in association with a polymethine dye having a nucleus of general formula (I): ##STR1## in which: n is 0, 1, 2 or 3; R.sup.1 and R.sup.4 are independently selected from the group consisting of hydrogen atoms, optionally substituted alkyl groups of up to 30 carbon atoms, optionally substituted alkenyl groups of up to 30 carbon atoms and optionally substituted aryl groups of up to 14 carbon atoms; and 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 or 6-membered optionally substituted heterocyclic ring; or one or more of R.sup.1 to R.sup.4 may represent the necessary atoms to complete an optionally substituted 5 or 6-membered heterocyclic ring 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 independently selected from the group consisting of hydrogen atoms, tertiary amino groups, optionally substituted alkyl groups of up to 10 carbon atoms, optionally substituted aryl groups of up to 10 carbon atoms, optionally substituted heterocyclic rings comprising up to 6 ring atoms, optionally substituted carbocyclic rings comprising up to 6 carbon atoms and optionally substituted fused ring systems comprising up to 14 ring atoms, and, X.sup..crclbar. is an anion.

Improved compounds and base precursors that undergo thermal decomposition are disclosed. Thermal-dye-bleach agents, and in particular, a novel class of salts of arylsulfonylacetic acids as bleaching agents for photothermographic use are disclosed. Photothermographic elements employing these thermal-dye-bleach agents are suitable for use as acutance and antihalation systems, bleachable filter dye materials, and in promoting unblocking of various components such as blocked developers, especially in in photothermographic elements.

A base precursor in the form of a salt of an organic base with a carboxylic acid is disclosed. The organic base is a diacidic to tetraacidic base which is composed of two to four guanidine moieties and at least one linking group for the guanidine moities. The organic base is such a hydrophilic compound that the number of carbon atoms contained in the organic base is not more than six times the number of the guanidine moieties. The linking group is a residue of a hydrocarbon or a heterocyclic ring. The guanidine moiety corresponds to an atomic group formed by removing one or two hydrogen atoms from a compound having the following formula (I): ##STR1## where each of R.sup.1, R.sup.2, R.sup.3, R.sup.4 and R.sup.5 independently is hydrogen, an alkyl group, an alkenyl group, an alkynyl group, a cycloalkyl group, an aralkyl group, an aryl group or a heterocyclic group, each of which may have one or more substituent groups, and any two of R.sup.1, R.sup.2, R.sup.3, R.sup.4 and R.sup.5 may be combined together to form a five-membered or six-membered nitrogen-containing heterocyclic ring. A process for formation of an organic base from the base precursor and a light-sensitive material containing the base precursor are also disclosed.