Structure, Z/E photoisomerization and an effect of (phenylene-)vinylene conjugation extension on absorption and fluorescence of methylidene-pyrrolinones

Six methylidene-pyrrolinones with a conjugation chain extended by vinylene and phenylene-vinylene groups were studied; five of them were synthesized for the first time. Their structures were estimated theoretically by density functional theory (DFT) and proved by X-ray diffraction techniques in two cases. Structural changes upon Z/E photoisomerization in solution were studied by a combination of 1H NMR spectroscopy and DFT GIAO method. Both types of conjugation extension caused a bathochromic shift in absorption. Vinylene extension produced the compounds fluorescent in solution. N-methylated derivatives have shown solid-state fluorescence.