Photographic element containing a fragmentable electron donor for improved photographic response

A silver halide photographic element comprising a transparent support with low oxygen permeability and further comprising a cyan dye image-forming unit comprised of at least one red-sensitive silver halide emulsion layer having associated therewith at least one cyan dye-forming coupler, a magenta dye image-forming unit comprising at least one green-sensitive silver halide emulsion layer having associated therewith at least one magenta dye-forming coupler, and a yellow dye image-forming unit comprising at least one blue-sensitive silver halide emulsion layer having associated therewith at least one yellow dye-forming coupler wherein at least one silver halide emulsion layer contains a fragmentable electron donating compound of the formula:

• X—Y′ or a compound which contains a moiety of the formula —X—Y′, wherein:
• X is an electron donor moiety, Y′ is a leaving proton H or a leaving group Y, with the proviso that if Y′ is a proton, a base, β−, is present in the emulsion layer, and wherein:
• 1) X—Y′ has an oxidation potential between 0 and about 1.4 V;
• and
• 2) the oxidized form of X—Y′ undergoes a bond cleavage reaction to give the radical X• and the leaving fragment Y′;
• and, optionally,
• 3) the radical X• has an oxidation potential≦−0.7V (that is, equal to or more negative than about −0.7V).