GB411811A - Improved process of sensitising silver halide emulsion layers - Google Patents

Abstract

Photographic silver halide emulsions are sensitized to light of 500--720 mm by the addition of a benzothiocarbocyanine or benzo seleno-carbocyanine dye in which the benzene rings are substituted by amino or substituted amino groups, and the hydrogen of the central carbon atom of the trimethine chain is replaced by an alkyl or alkoxy group. Examples of suitable dyes are (1) 1:1<1>-diethyl-6:6<1>-bisdiethylaminobenzthio - b - methyl - carbocyanine iodide made by boiling 2-methyl-5-diethylamino - benzthiazole ethyl iodide with ethyl ortho-acetate in dry pyridine; (2) 1:1<1>-diethyl - 6 : 6<1> - bisdiethylaminobenzthio - b - ethyl-carbocyanine perchlorate made by boiling the base of example 1 with ethyl ortho-propionate in pyridine and precipitating the dye with sodium perchlorate; (3) 1:1<1>-diethyl-5: 5<1>-dimethyl - 6 : 6<1>-bisdiethylamino - benzthio b -methyl-carbocyanine iodide made by boiling 2 : 6 - dimethyl - 5 - diethylaminobenzthiazole ethyl iodide with ethyl ortho-acetate in pyridine; (4) 1 : 1<1> - diethyl : 5 : 5<1> - bisdiethylaminobenzthio - b - methyl carbocyanine perchlorate made by heating 6-diethylamino - 2 - methylbenzthiazole ethyl iodide in pyridine with ethyl-orthoacetate and precipitating the dye with sodium perchlorate; (5) 1 : 1<1> - diethyl - 6 : 6<1> - bisdiethylamino - benzthio - b - ethoxy - carbocyanine perchlorate made by heating 2 - methyl - 5 - diethylaminobenzthiazole ethyl iodide in pyridine with orthocarbonic acid ethyl ester; (6) 1 : 1<1> - diethyl - 5 : 5<1> - bisacetylamino - benzseleno - b - methyl - carbocyanine bromide stated to be made by heating 6-acetylaminobenzthiazole ethyl sulphate in dry pyridine with ethyl-orthoacetate and precipitating the dye with potassium bromide; (7) 1 : 1<1> - dimethyl - 5 : 5<1> - bispropionylamino - benzseleno - b - ethyl carbocyanine bromide made by heating 6 - propionylamino - 2 - methyl - benzselenazole dimethyl sulphate and ethylortho-propionate in pyridine, and precipitating the dye with potassium bromide. The dyes are applied in the manner described in Specification 400,951.