Abstract: The present invention provides heat-developable, photothermographic elements comprising a support bearing at least one photosensitive, image-forming layer comprising:(a) a photosensitive silver halide;(b) a non-photosensitive, reducible silver source;(c) a reducing agent for silver ions;(d) a binder; and(e) a spectrally sensitizing amount of a compound having the central nucleus: ##STR1## wherein: Z is S, O, Se or N--R.sup.3 ;R.sup.1 and R.sup.2 represent an alkyl group of from 1 to 20 carbon atoms other than carboxy-substituted alkyl, preferably an alkyl group of from 1 to 8 carbon atoms, and most preferably an ethyl group; andR.sup.3 is H or alkyl group;X and Y are thioalkyl groups of from 1 to 20 carbon atoms;n=0 to 4;m=0 to 4; the sum of n plus m equals at least 1;D.sup.1 to D.sup.7 each independently represents a methine group and adjacent methine groups selected from D.sup.2, D.sup.3, D.sup.4, D.sup.5 and D.sup.6 may form cyclic groups;p=0 or 1; andA.sup.- is an anion.