The unequivocal solid-state structure and stereochemistry of the hetaryl leuco-TAM dye, 2,2’-(2-phenyl propane-1,3-diylidene) bis(1,3,3-trimethylindoline) derivatives were established using X-ray single crystal analysis. The X-ray crystal analysis showed that the ZE-isomers only formed stereoselectively, with a so-called “three bladed propeller” conformation, from the reaction of a Fischer base and benzaldehyde derivatives.
However, the stability and steroselectivity are completely inversed in the formation of hetaryl LTAM derivatives, when the LTAM molecules contain an electron withdrawing groups such as p-NO2, p-(N), p-CHO, etc on the para position of the aryl group. In that situation, the EE-isomers unusually are formed mainly and later equilibriated to the mixture of EE, ZE and ZZ isomers. These EE isomers were stacked in a juxtaposition to form a dimer of a double dimer, adopting either a triclinic, with P-1, of monoclinic crystal system with a space group P21/n in the unit cell of the crystal.