Synthesis and spectroscopic properties of cross-conjugated ketones and meso-substituted tridecamethine salts containing the pyran or pyridone fragment

The reactions of substituted 4H-pyrones and N-methyl-2,6-dimethylpyridone with dimethylformamide acetal and aminal acetals of conjugated -dimethylaminoaldehydes were studied. Cross-conjugated ketones and meso-ethoxy(dialkylamino)tridecamethine salts containing the pyran or pyridone fragment were synthesized and their spectroscopic properties were investigated. The replacement of the bridging O atom by the NMe group precludes an interaction between chromophores in cross-conjugated ketone and the related tridecamethine salt. In addition, the insertion of a meso-amino substituent into the polymethine chain of the salts containing the central pyrylium fragment leads to a sharp weakening of the chromophore interaction. In spite of the dramatic differences in the UV spectra of ketocyanines containing the bridging O or NMe fragments, these dyes have similar ¹³C NMR spectra.