Neocyanin

The dye was first discovered by Ogata in 1924 as a by-product in the synthesis of cryptocyanin , but was only isolated from the mixture in 1925 by T. Clark. The chemical structure of the compound was proposed by König and later confirmed by Kendall, Mayer and F. Hamer. Subsequently, the dye gave rise to a large group of related compounds, called “ neocyanins ” ^{[2] [3]} .

The maximum sensitization of unsubstituted neocyanin with quinoline nuclei is 824 nm, the maximum absorption is 760 nm ^[2] .

Compared with other sensitizing dyes of the time, neocyanins turned out to be very stable, which allowed them to be used without difficulty as part of photographic emulsions. Neocyanin derivatives allowed to sensitize for medium exposures in the range from 680 to 880 nm, while increasing the exposures up to 900 nm. The absolute maximum of sensitization was achieved using hypersensitization and was 1160 nm ^[2] .

The dye is synthesized according to the general method of obtaining cyanine dyes. To do this, use the condensation reaction of ethyl iodide lepidine in triethyl orthoformate in the presence of pyridine . As a result of the reaction, 42% of cryptocyanin and 17% of neocyanin are formed. To increase the yield of neocyanin, the reaction can be carried out with lepidine para-sulphonate, while the yield will be 7% of cryptocyanin and 26% of neocyanin. If the dye is precipitated using ammonium bromide , the yield of neocyanin can be increased up to 37%, and the yield of the methyl derivative in such conditions will be 41% ^[2] .

• Venkataraman K. Chemistry of synthetic dyes. - L .: State Scientific and Technical Publishing House of Chemical Literature, 1957. - Vol. 2.
• Glafkides P. Photographic chemistry. - London: Fountain Press, 1958. - Vol. 2.