Cross-conjugated ω,ω′-bis(dimethylamino) ketones and dinitriles containing a cycloalkane or piperidine fragment: synthesis and study of spectroscopic properties

N-Substituted 4-piperidones react with β-dimethylaminoacrolein aminals to give keto-cyanines containing a piperidine ring. A reaction of 3-dimethylamino-1, 1,3-trimethoxypropane with 1-ethoxycarbonylpiperidin-4-ylidenemalononitrile produces a cross-conjugated ω,ω′-bis-(dimethylamino) dinitrile. Its yield is doubled when ionic liquids are used. The spectroscopic properties of the compounds obtained are highly sensitive to the structure: replacement of the C=O group in ketocyanines by the C=C(CN)₂ group results in a considerable bathochromic shift of the absorption spectra, while replacement of the central bridging fragment (CH₂)₃ by (CH₂)₄ results in a hypsochromic shift. All the compounds obtained exhibit positive solvatochromism.