NOVEL DEVELOPMENT ACCELERATOR-RELEASING COUPLERS

摘要

The invention provides a photographic element comprising a support bearing at least one silver halide emulsion layer and associated therewith (a) at least one coupler capable of releasing a development accelerator on colour development (DARC) and (b) at least one electron transfer agent-releasing coupler (ETARC), the DARC having the formula (I):- COUP-(T)n-X (I) wherein COUP is a coupler moiety; T is a timing group and n is 0, 1 or 2; and X is A-(L)1- -(Y)S-NR<SUB>1</SUB>NR2-CO-CO-R<SUB>3</SUB>; wherein A is a group capable of being adsorbed to the silver halide surface; L is a divalent linking group and r is 0, 1 or 2; Y is selected from the class consisting of an unsubstituted or substituted aryl or heterocyclic ring or ring system containing one or more O, N or S atoms and s is 0 or 1; R<SUB>1</SUB> and R<SUB>2</SUB> are independently selected from the class consisting of hydrogen, an unsubstituted or substituted acyl or alkyl- or aryl-sulfonyl group; and R<SUB>3</SUB> is selected from the class consisting of R, OR, NHR and NRR1; wherein R and R1 are independently selected from the class consisting of an unsubstituted or substituted alkyl, aryl or heterocyclic ring or ring system containing one or more O, N or S atoms; provided that (a) when s is 0, r is 0 and (b) the log Kow of XH is at least 3. The elements comprising the novel DARC(s) maintain the known synergistic speed improvement when combined with an ETARC(s), without however the high D<SUB>min</SUB> penalty.