Geometric Isomers of Merocyanine Forms

To understand the mechanism of photochromism in SPs and to account for the spectroscopic behavior of MCs, in particular, the positions and nature of the 

X-ray diffraction analysis ofMCl-MC6 showed that only planar trans-cisoid and trans-transoid isomers exist in the crystalline state. The former occurs in crystals ofMCl-MC4, MC6, and the open form ofabenzothiazoline MC studied by Miler-Strenger and Gugliemetti.44 The latte occurs together with the trans-cisoid isomer in crystals of MC3, MC4, and MC5, which have two nitro substituents in the phenolate fragment. 

The lowering of the rotation barrier about the C(4)-C(4a) bond when two electron-acceptor nitro groups are introduced into the phenolate moiety is evidently due to the increased contribution of form E to the structure of this 

Nature of the Molecular Packing and Ehergy of Intermolecular Interactions in Merocyanine Crystals 

In the trans-transoid isomers, the substituents on the N(l ) atom do not hinder the solvation. A solvated trans-transoid MC isomer can form both head-to-tail aggregates and aggregates with solvating molecules. In MCI crystals, the 

---