Features of cation packing in crystal forms of a 18-crown-6-containing styryl dye iodide and feasibility of the solid phase [2+2]-autophotocycloaddition reaction in it

X-ray structure determinations of three crystal forms of a 18-crown-6-containing styryl dye of the pyridine series in iodide form (1), containing various solvate molecules, namely water (1a), 2,6-dihydroxyoaphthalene (1b), 1,4-hydroquinone (1c), and analysis of crystal packings of these crystals, together with the previously investigated non-solvated form (crystal 1) and the solvates with benzene and water (crystal 1d) has been carried out. Crystal packing in 1a, 1b, 1c, and 1d involves a stacking leading to dimers of the dye cations, structurally preorganized for the [2+2]-photocycloaddition (PCA) reaction. On irradiation of with visible light, the PCA reaction with the centrosymmetric rctt isomer leads to the cyclobutane derivative formation. In the case of 1a and 1b the PCA proceeds with the retention of crystallinity, while with other solvates crystals are transformed into a glass. The glasses keep the form and the shine of the initial crystals, nevertheless. In the cases of the non-solvated crystal form (1), translation-related stacks form, with the geometry inconsistent with that of the preorganized dimer. These crystals are stable in visible light.