2,5-Dimethoxy-1,4-bis[2-(2,4-dimethoxyphenyl) ethenyl]benzene studied by quantum chemical calculations and single crystal X-ray diffraction

The configurational isomers of 2,5-dimethoxy-1,4-bis-[2-(2,4-dimethoxyphenyl)ethenyl]benzene have been investigated by ab initio (4-21G level) and MOPAC-AM1 semiempirical methods. The calculations were guided by and compared with single crystal X-ray results of the trans,trans-isomer determined at 298 K and 103 K. The barriers of rotation of the latter isomer in the free and the solid state were enumerated. A comparison with related molecules, in particular 1,4-bis[2-(3,4,5-trimethoxyphenyl)ethenyl]benzene, is made. The positioning of substituents is shown to be of importance for ring rotational movements and NMR shifts, as well as for UV /Vis spectroscopy.