Experimental and computational structural study of two hindered aminoanthraquinones in crystals and solutions

The crystal and molecular structures of 2-methyl-1-methylamino-anthraquinon e (I) and 1-methylphenylamino-anthraquinone (II) were studied by the X-ray single-crystal diffraction and the visible spectra of crystalline specimens and their solutions were recorded. The molecule I is closely planar, where as in the molecule II the amino,group is 58 degrees rotated out of the plan e of the anthraquinone skeleton. In both structures the molecules pack in s tacks. The comparison of experimental and calculated (on the DFT and AM 1 l evels) molecular structures, together with the comparison of experimental a nd INDO/S-calculated electronic spectra, give the evidence that molecular c onformations (especially for II) change upon transfer from the solid state to solutions, and the pi-delocalisation throughout the whole molecule enhan ces in the solid state.