This invention provides a photographic element comprising at least one silver halide emulsion layer in which the silver halide is sensitized with a compound of the formula (a):
&Dgr;−(t)m−XY′ (a)
XY′−(t)m−&Dgr; (b)
&Dgr;−(t)m−XY′−(t)m−&Dgr; (c)
wherein &Dgr; is 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 XY′ 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, &bgr;−, 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.
该发明提供了一种摄影元素,其中至少包含一个
银卤化物乳剂层,其中
银卤化物被化合物(a)的敏化作用所敏化:&Dgr;−(t)m−XY′ (a);XY′−(t)m−&Dgr; (b);&Dgr;−(t)m−XY′−(t)m−&Dgr; (c);其中&Dgr;是保护基,在摄影元素的显影过程中被消除,t是时间基团,m是从0到3的整数,XY′是可分解的电子给体基团,其中X是电子给体基团,Y′是离去质子H或离去基团Y,但如果Y′是质子,则乳剂中存在碱&bgr;−,或者&bgr;−直接或间接地与X共价连接,且:1) X—Y′的氧化电位在0到约1.4 V之间;2) X—Y′的氧化形式经历键裂解反应,形成自由基X•和离去基团Y′;3) 自由基X•的氧化电位≦−0.7V。