Mid-green sensitizing dyes for photographic materials

A photographic element comprising a support having thereon a silver halide emulsion layer sensitized with a benzimidazolocarbocyanine dye according to the following formula I:

• ##STR12## wherein R1 and R3 are methyl or ethyl, at least one of R1 and R3 being methyl;
• R2 and R4 are substituted or unsubstituted C.sub.1 to C.sub.6 alkyl, provided that R2 and R4 are not both methyl;
• X1, X2, X3, and X4 are each independently methyl, methylthio, fluoro-substituted methyl or methylthio, or hydrogen, provided that at least one of X1 and X2 and at least one of X3 and X4 are not hydrogen;
• Y represents an ion as needed to balance the charge of the molecule;
• and wherein the adsorbed dye forms on the emulsion a J-aggregate with a maximum absorption between 540 to 556 nm, and the combination of substituents R1-R4 and X1-X4 are selected to fit the following equation (i);
• 0. 455.SIGMA..sigma..sub.i (R1-R4)+0.144.SIGMA..sigma..sub.p (X1-X4)+0.610>0.68 (i)
• where the small sigmas are electronic substituent constants, .sigma..sub.i being Taft's sigma (inductive) constant, and .sigma..sub.p being Hammett's sigma(para) constant.