Synthesis, spectral properties, and conformations of nonlinear cross-conjugated polyenes containing pyrane or dihydropyridine fragment

Abstract

New cross-conjugated ω,ω′-dimethylaminopolyenes containing the central pyrane or N-methyldihydropyridine fragment were synthesized. In new compounds, the interaction of the aminopolyene chromophores occurs through the dicyanomethylidene, 1-cyano-1-(4-nitrophenyl)methylidene, or 1,3-dioxoindan-2-ylidene groups in position 4 of the heterocycle. The conformation of the synthesized compounds was determined by 2D 1H NMR spectroscopy (NOESY and ROESY): the chromophores are arranged at an acute or obtuse angle in the structures with the pyrane or dihydropyridine fragment, respectively. The conformational differences in polyenes result in a drastic change in their spectral properties: for the dyes with an acute angles between the chromophores, the long-wavelength absorption band is less intense, as a rule, than the shorter-wavelength band, while the situation is opposite for the compounds with an obtuse angle. The absorption spectra of the synthesized compounds with dinitrile and other acceptor groups lie in a longer-wavelength region than the absorption spectra of the corresponding compounds with carbonyl acceptor groups. The central bridging substituent NMe decreases the energy of interaction of the chromophores.