TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preparation (disclosed): The merocyanine-based organic dye (II) is obtained by condensing merocyanine compound of formula (IV) and bipyridium-based compound of formula (III). SPECIFIC COMPOUNDS - 42 Merocyanine-based organic dyes are disclosed e.g. 1-(2-((2E)-2-cyano-3-(4-(4-(2,2-diphenylethenyl)phenyl)-1H,2H,3H,3aH,4H,8bH-cyclopenta(b)indol-7-yl)prop-2-enamido)ethyl)-4-(1-(2-((2E)-2-cyano-3-(4-(4-(2,2-diphenylethenyl)phenyl)-1H,2H,3H,3aH,4H,8bH-cyclopenta(b)indol-7-yl)prop-2-enamido)ethyl)pyridin-1-ium-4-yl)pyridin-1-ium dibromide of formula (IA), 1-(2-(2-cyano-3-(4-(4-((E)-2-(4-(methoxycarbonyl)phenyl)ethenyl)phenyl)-1H,2H,3H,3aH,4H,8bH-cyclopenta(b)indol-7-yl)prop-2-enamido)ethyl)-4-(1-(2-(2-(5-((4-(4-(2,2-diphenylethenyl)phenyl)-1H,2H,3H,3aH,4H,8bH-cyclopenta(b)indol-7-yl)methylidene)-2-((5E)-3-methyl-4-oxo-2-sulfanylidene-1,3-thiazolidin-5-ylidene)-4-oxo-1,3-thiazolidin-3-yl)acetamido)ethyl)pyridin-1-ium-4-yl)pyridin-1-ium dibromide, 1-(2-(2-cyano-3-(4-(4-(2,2-diphenylethenyl)phenyl)-1H,2H,3H,3aH,4H,8bH-cyclopenta(b)indol-7-yl)prop-2-enamido)ethyl)-4-(1-(2-(2-(5-((4-(4-(2,2-diphenylethenyl)phenyl)-1H,2H,3H,3aH,4H,8bH-cyclopenta(b)indol-7-yl)methylidene)-2-((5E)-3-methyl-4-oxo-2-sulfanylidene-1,3-thiazolidin-5-ylidene)-4-oxo-1,3-thiazolidin-3-yl)acetamido)ethyl)pyridin-1-ium-4-yl)pyridin-1-ium dibromide, 1-(2-(2-((5E)-5-((4-(4-((E)-2-(4-carboxyphenyl)ethenyl)phenyl)-1H,2H,3H,3aH,4H,8bH-cyclopenta(b)indol-7-yl)methylidene)-4-oxo-2-sulfanylidene-1,3-thiazolidin-3-yl)acetamido)ethyl)-4-(1-(2-(2-(5-((4-(4-(2,2-diphenylethenyl)phenyl)-1H,2H,3H,3aH,4H,8bH-cyclopenta(b)indol-7-yl)methylidene)-2-((5E)-3-methyl-4-oxo-2-sulfanylidene-1,3-thiazolidin-5-ylidene)-4-oxo-1,3-thiazolidin-3-yl)acetamido)ethyl)pyridin-1-ium-4-yl)pyridin-1-ium sulfate and 4-(1-(2-(2-cyano-3-(4-(4-methylphenyl)-1H,2H,3H,3aH,4H,8bH-cyclopenta(b)indol-7-yl)prop-2-enamido)ethyl)pyridin-1-ium-4-yl)-1-(2-(2-cyano-3-(4-(4-(2,2-diphenylethenyl)phenyl)-1H,2H,3H,3aH,4H,8bH-cyclopenta(b)indol-7-yl)prop-2-enamido)ethyl)pyridin-1-ium dibromide.    EXAMPLE - 2-cyano-3-(4-(4-(2,2-diphenylethenyl)phenyl)-1H,2H,3H,3aH,4H,8bH-cyclopenta(b)indol-7-yl)prop-2-enoic acid, 2-(5-((4-(4-(2,2-diphenylethenyl)phenyl)-1H,2H,3H,3aH,4H,8bH-cyclopenta(b)indol-7-yl)methylidene)-2-((5E)-3-methyl-4-oxo-2-sulfanylidene-1,3-thiazolidin-5-ylidene)-4-oxo-1,3-thiazolidin-3-yl)acetic acid, 2-bromo-ethylamine and hydrobromide were reacted, to obtain 1-(2-(2-cyano-3-(4-(4-((E)-2-(4-(methoxycarbonyl)phenyl)ethenyl)phenyl)-1H,2H,3H,3aH,4H,8bH-cyclopenta(b)indol-7-yl)prop-2-enamido)ethyl)-4-(1-(2-(2-(5-((4-(4-(2,2-diphenylethenyl)phenyl)-1H,2H,3H,3aH,4H,8bH-cyclopenta(b)indol-7-yl)methylidene)-2-((5E)-3-methyl-4-oxo-2-sulfanylidene-1,3-thiazolidin-5-ylidene)-4-oxo-1,3-thiazolidin-3-yl)acetamido)ethyl)pyridin-1-ium-4-yl)pyridin-1-ium.