Photochemical behaviour of a discoid, cinnamoyl-substituted azacrown derivative Isomerization and crosslinking in the ordered state

The photochemistry of a discoid, mesogenic hexa-cinnamoyl-substituted hexacyclen, which is mainly determined by the competition between E Z-photoisomerization and (2 4-2)-photocycloaddition, is investigated in solution and in bulk. In a poor solvent, such as cyclohexane, columnar aggregates are supposed to be formed, due to the amphiphilic structure of the hexacyclen. Upon irradiation, these preformed aggregates undergo intracolumnar photocycload-dition between the photoreactive sites of the adjacent molecules. In the columnar mesophase, the liquid-crystalline order is disturbed by the E/Z-photoisomerization. It turns out that a highly fluid-like environment, which is present in aggregates formed in a poor solvent, is important to provide the required population of reactive sites in order to obtain a defined photocycloaddition reaction.