Spectral and fluorescent properties of cross-conjugated polyene ketones with terminal N-methylpyrrole residues

The spectral and fluorescent properties of a number of cross-conjugated ketones with one or two terminal N-methylpyrrole residues and those of polyene bis-omega,omega'-dimethylamino ketones with methyl substituents in the polyene chain and of some related compounds were studied. The photophysical properties of cross-conjugated ketones with terminal N-methylpyrrole residues are similar to those of the corresponding polyene bis-omega,omega-dimethylamino ketones studied in detail previously. In both series of compounds, the absorption and fluorescence spectra undergo a bathochromic shift following an increase in the length of the polyene chains or introduction of alpha,alpha'-trimethylene or alpha,alpha'-dimethylene bridges into these chains; the same trend is observed on passing from less polar solvents to more polar solvents (positive solvatochromism). Thermochromism (long-wavelength shift of the absorption spectra upon cooling the solutions) is observed in both series of compounds. The introduction of methyl substituents into the polyene chains of bis-omega,omega'-dimethyiamino ketones results in a decrease in the fluorescence quantum yield.