Synthesis and X-ray crystal structure of isomeric pyridine-based leuco-TAM dyes, 2,2-(2-(pyridinyl)propane-1,3-diylidene)bis(5-chloro-1,3,3-trimethyl indoline) derivatives and unusual stability of 4-pyridinyl compound

- The X-ray crystal structures of isomeric pyridinyl leuco-dyes were established.
- The EE isomer was formed unusually for the 4-pyridinyl leuco-dye molecules.
- The 4- and 3-isomers have the Y-shaped and propeller conformations, respectively.