THEORETICAL AND SPECTROSCOPIC INVESTIGATIONS OF INDIGO DYES .23. LIGHT-ABSORPTION AS WELL AS CRYSTAL AND MOLECULAR-STRUCTURE OF N,N'-DIMETHYLINDIGO - AN EXAMPLE OF THE USE OF SYNCHROTRON RADIATION

The determination of physically meaningful thermal ellipsoids for hydrogen from X-ray diffraction data was achieved in the X-ray structure analysis of N,N'-dimethylindigo (1) by synchrotron radiation. Owing to the steric interactions of the CH3 groups with the carbonyl O atoms, the molecule is slightly twisted. This explains the bathochromic absorption of 1 in comparison to that of indigo and was also predicted from calculations.