Synthesis and Characterization of Mono-, Bis-, and Trissubstituted Pyridinium and Pyrylium Dyes

A series of mono-, bis-, and trissubstituted pyridinium and pyrylium dyes have been synthesized by the condensation of methylpyridinium and methylpyrylium salts with aldehydes or nitroso compound. Large bathochromic shifts were observed in the following order, both in substituted azomethine pyridinium and pyrylium dyes, mono < bis < tris. The magnitude of the shift appeared in the order of multiple bonds, –CH=CH– < –CH=CH–CH=CH– < –CH=N–.