. . . "-said compound with silver halide exposed to light; Y represents a divalent linking group; Z is a nucleophilic group, and it is able to attack the X, when the above-said compound is oxidized; n is 1 or 2, when X is --PO<, or n is 1, when X is another group; R1 and R2, or R3 and R4, or at least two kinds of atoms or substituents arbitrarily selected from Y1k, Z1k, and P may be independently linked" . .