Silver halide light sensitive emulsion layer having enhanced photographic sensitivity

A compound of formula:

• Δ−(t)m−XY′
• wherein:
• Δ is protective group that is eliminated during development
• t is a timing group,
• m is an integer from 0 to 3,
• XY′ is a fragmentable electron donor moiety wherein:
• 1) X is an electron donor group
• 2) y′ is a leaving proton H or a leaving group Y
• 3) X—Y′ has an oxidation potential between 0 and about 1.4 V
• 4) the oxidized form of X—Y′ undergoes a bond cleavage reaction to give the radical X• and the leaving fragment Y′;
• and
• 5) the radical X• has an oxidation potential ≦−0.7V.

A compound of formula:

• XY′−(t)m−Δ
• wherein:
• Δ is protective group that is eliminated during development
• t is a timing group,
• m is an integer from 0 to 3,
• XY′ is a fragmentable electron donor moiety wherein:
• 1) X is an electron donor group
• 2) Y′ is a leaving proton H or a leaving group Y
• 3) X—Y′ has an oxidation potential between 0 and about 1.4 V
• 4) the oxidized form of X—Y′ undergoes a bond cleavage reaction to give the radical X• and the leaving fragment Y′;
• and
• 5) the radical X• has an oxidation potential ≦−0.7V.

A compound of formula:

• Δ−(t)m−XY′−(t)m−Δ
• wherein:
• Δ is protective group that is eliminated during development
• t is a timing group,
• m is an integer from 0 to 3,
• XY′ is a fragmentable electron donor moiety wherein:
• 1) X is an electron donor group
• 2) Y′ is a leaving proton H or a leaving group Y
• 3) X—Y′ has an oxidation potential between 0 and about 1.4 V
• 4) the oxidized form of X—Y′ undergoes a bond cleavage reaction to give the radical X• and the leaving fragment Y′;
• and
• 5) the radical X• has an oxidation potential ≦−0.7V.

A photographic element comprising at least one silver halide emulsion layer in which the silver halide is sensitized with a protected fragmentable electron donor compound represented by formula:

• ID Structure i Z-(L-X-Y′-(t)m-Δ)k ii iii iv A-(L-X-Y′-(t)m-Δ)k v vi vii (A-L)k-X-Y′-(t)m-Δ viii ix x Q-X-Y′-(t)m-Δ xi xii xiii A-(X-Y′-(t)m-Δ)k xiv xv xvi (A)k-X-Y′-(t)m-Δ xvii xviii xix Z-(X-Y′-(t)m-Δ)k xx xxi xxii (Z)k-X-Y′-(t)m-Δ xxiii or xxiv
• wherein Δ is a protective group that is eliminated during development of the photographic element, t is a timing group, m is an integer from 0 to 3, and X—Y′ is a fragmentable electron donor moiety in which X is an electron donor group and 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 or is covalently linked directly or indirectly to X, and wherein:
• 1) X—Y′ has an oxidation potential between 0 and about 1.4 V;
• 2) the oxidized form of X—Y′ undergoes a bond cleavage reaction to give the radical X• and the leaving fragment Y′;
• and
• 3) the radical X• has an oxidation potential ≦−0.7V;
• Z is a light absorbing group;
• k is 1 or 2;
• A is a silver halide adsorptive group;
• L represents a linking group containing at least one C, N, S, P or O atom;
• and
• Q represents the atoms necessary to form a chromophore comprising an amidinium-ion, a carboxyl-ion or dipolar-amidic chromophoric system when conjugated with X—Y′.