Optisch sensibilisierte Halogensilberemulsion

The invention relates to cyanine dyes of the formula wherein R1 represents alkyl; y represents sulphur or selenium; A represents an alkyl radical where y stands for selenium and A represents an alkyl or b -hydroxypropyl-g -sulphonic acid group which may be in salt form, e.g. an alkali metal or ammonium salt where y stands for sulphur, and in which the fused benzene rings can be substituted, e.g. with an alkyl, alkoxy halogen, phenyl, cyclohexyl, phenylalkyl, thienyl or 5,6-dioxy methylene substituent or have an additional benzene ring fused thereon, which are prepared by the usual methods from heterocyclic quaternary ammonium salts of the formula and their appropriately substituted derivatives.ALSO:Compounds of the formula wherein the fused benzene ring may contain 5-methyl; 6-methyl; 5-methoxy; 6-methoxy; 5,6-dimethyl; or 5-chloro substituents are prepared by reacting 3-chloro-2-hydroxy propane sulphonic acid with the appropriately substituted benzothiazole. These compounds are used to prepare cyanine dyes (see Division C4).