Synthesis and properties of photochromic bisindolinospiropyrans

Bisspiropyrans were obtained by reaction of diquaternary salts — 1,1-polymethylenebis-(2,3,3-trimethylindoleninium) halides — or the corresponding methylene bases with 5-nitro-salicylaldehyde in the presence of piperidine. Bisspiropyrans of another type were obtained by reaction of 1-propyl-2,3,3-trimethylindoleninium iodide with 5,5-methylenedisalicylaldehyde and 5,5-methylenedi(3-nitrosalicylaldehyde). The photochemical and spectral properties of the bisspiropyrans were compared with those of the corresponding monospiropyrans.Communication VII from the series Photochromism of Organic Substances. See [1] for communication VI.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1631–1638, December, 1973.