Pyrylocyanines. 21. Unsymmetrical α-pyrylo- and α-pyridocyanines

(2-Pyrylo)- and (2-pyrido)(indo)trimethinecyanines containing both electron donor and electron acceptor substituants in the heterocyclic rings have been synthesized. It has been shown that the 4,6-diphenyl-2H-pyran nucleus confers less basicity (electron donor characteristics) than the 1,3,3-trimethylindoline segment. It has also been shown that the introduction of substituents to the heterocyclic residues of unsymmetrical dyes allows one to manipulate their electronic asymmetry over a wide range up to a change in the distribution of charge from one ring to another.For Communication No. 20, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 44–48, January, 1985.