Cyanine dyes have the general formula Cyanine dyes have the general formula <FORM:0604600/IV(b)/1> wherein R represents the methlene groups to complete a cyclopentylidene or cyclohexylidene ring, R1 and R2 are alkyl groups, Y represents S or Se, X represents an acid radical, and Z represents the atoms to complete a nitrogenous heterocyclic ring which heterocyclic ring may be substituted by alkyl, aryl (e.g. phenyl, naphthyl, or anthranyl), a hydrogenated ring system similar to that completed by R, alkoxy, or alkyl dioxy. The dyes are prepared by condensing quaternary ammonium salts of thiazoles and selenazoles containing an alicyclic dioxy ring with ethyl orthoformate or with 2 - (b - acetanilidovinyl) - 5 : 6 - methylenedioxybenzthiazole ethiodide, 2 - (b - acetanilidovinyl - 5 : 6 - cyclohexylidenedioxybenzthiazole ethiodide, or the corresponding seleno derivatives. 3 : 31-diethyl-5 : 6 : 51 : 61-dicyclohexylidenedioxybenzthiacarbocyanine iodide is prepared by reacting 2-methyl-5 : 6-cyclohexylidenedioxybenzthiazole ethyl p-toluenesulphonate with ethyl orthoformate in the presence of pyridine and triethylamine, and adding aqueous potassium iodide to the hot n-propyl alcohol solution of the product. 3 : 31-Diethyl-5 : 6 : 51 : 61-dicyclopentylidenedioxybenzthiacarbocyanine iodide is similarly prepared. 3 : 31-Diethyl-5 : 6-cyclohexylidenedioxy - 51 : 61 - methylenedioxybenzthiacarbocyanine iodide is prepared by refluxing together 2 - (b - acetanilidovinyl) - 5 : 6 - methylenedioxybenzthiazole ethiodide, 2-methyl-5 : 6-cyclohexylidenedioxybenzthiazole ethyl - p - toluenesulphonate, pyridine, and triethylamine. 3 : 31-Diethyl -5 : 6-cyclohexylidenedioxy-51 : 61-methylenedioxybenzthiabenzselenacarbocyanine iodide, 3 : 31-diethyl-5 : 6-cyclohexylidenedioxy-61 : 71-benzbenzthiacarbocyanine iodide, and 3 : 31-diethyl-5 : 6-cyclohexylidenedioxy-51 : 61-dimethoxybenzthiacarbocyanine iodide are similarly prepared. Alicyclic-dioxybenzenes are prepared by reacting catechol with cyclic ketones. Cyclohexylidenediozybenzene is prepared by treating a solution of catechol in hot anhydrous cyclohexanone with excess phosphoric anhydride. Cyclopentylidenedioxybenzene is similarly prepared. 1 : 2 - Dinitro - 4 : 5 - cyclohexylidenedioxybenzene is prepared by treating cyclohexylidenedioxybenzene with a mixture of glacial acetic and fuming nitric acids. 1 : 2-Dinitro-4 : 5-cyclopentylidenedioxybenzene is similarly prepared. 2 : 21-Dinitro-5 : 6 : 51 : 61-di-(cyclohexylidenedioxybenzene) disulphide is prepared by adding a fused mixture of sodium sulphide and sulphur to a boiling ethyl alcohol solution of 1 : 2-dinitro4 : 5 - cyclohexylidenedioxybenzene. 2 : 21 - Dinitro-5 : 6 : 51 : 61-di-(pentylidenedioxybenzene) disulphide is similarly prepared. 2 - Methyl - 5 : 6 - cyclohexylidenedioxybenzthiazole is prepared by adding zinc dust to a heated mixture of 1 : 2-dinitro-4 : 5-cyclohexylidenedioxybenzene disulphide, acetic anhydride, acetic acid, and acetyl chloride. 2-Methyl-5 : 6-cyclopentylidenedioxybenzthiazole and 2-methyl-5 : 6 - methylenedioxybenzselenazole are similarly prepared. The ethyl p-toluenesulphonates are prepared in the usual manner. 2 - (b - Acetanilidovinyl) - 5 : 6 - methylenedioxybenzthiazole ethiodide is prepared by heating together 2 - methyl - 5 : 6 - methylenedioxybenzthiazole ethiodide, diphenylformamidine and acetic anhydride. 2-(b -Acetanilidovinyl)-5 : 6 - cyclohexylidenebenzthiazole ethiodide is similarly prepared.ALSO:Cyanine dyes have the general formula <FORM:0604600/IV (c)/1> wherein R represents the methylene groups to complete a cyclopentylidene or cyclohexylidene ring, R1 and R2 are alkyl groups, Y represents S or Se, X represents an acid radical, and Z represents the atoms to complete a nitrogenous heterocyclic ring, which heterocyclic ring may be substituted by alkyl, aryl (e.g. phenyl, naphthyl, or anthranyl), a hydrogenated ring system similar to that completed by R, alkoxy, or alkyl dioxy. The dyes are prepared by condensing quaternary ammonium salts of thiazoles and selenazoles containing an alicyclic dioxy ring with ethyl orthoformate or with 2 - (b - acetanilidovinyl) - 5 : 6 - methylenedioxybenzthiazole ethiodide, 2 - (b - acetanilidovinyl - 5 : 6 - cyclohexylidenedioxybenzthiazole ethiodide, or the corresponding seleno derivatives. 3 : 31 - Diethyl - 5 : 6 : 51 : 61 - di - cyclohexylidenedioxybenzthiacarbocyanine iodide is prepared by reacting 2-methyl-5 : 6-cyclohexylidenedioxybenzthiazole ethyl p-toluenesulphonate with ethyl orthoformate in the presence of pyridine and triethylamine, and adding aqueous potassium iodide to the hot n-propyl alcohol solution of the product. 3 : 31 - Diethyl - 5 : 6 : 51 : 61 - dicyclopentylidene-dioxybenzthiacarbocyanine iodide is similarly prepared. 3 : 31 - Diethyl-5 : 6-cyclohexylidene-dioxy - 51 : 61 - methylenedioxybenzthiacarbocyanine iodide is prepared by refluxing together 2 - (acetanilidovinyl) - 5 : 6 - methylenedioxy - benzthiazole ethiodide, 2 - methyl - 5 : 6 - cyclohexylidenedioxybenzthiazole ethyl - p - toluenesulphonate, pyridine, and triethylamine 3 : 31-Diethyl- 5 : 6-cyclohexylidenedioxy-51 : 61 - methylenedioxybenzthiabenzselenacarbocyanine iodide, 3 : 31-diethyl-5 : 6-cyclohexylidenedioxy-61 : 71-benzbenzthiacarbocyanine iodide, and 3 : 31-diethyl-5 : 6-cyclohexylidenedioxy-61 : 71\h - benzbenzthiacarbocyanine iodide, and 3 : 31 - di - ethyl - 5 : 6 - cyclohexylidenedioxy - 51 : 61 - dimethoxybenzthiacarbocyanine iodide are similarly prepared.