Photobehavior of crystalline 4-styrylcoumarin dimorphs: structure-reactivity correlations

Abstract

4-Styrylcoumarin crystallizes from chloroform and hexane mixture in two morphologically different modifications. The monoclinic form (needles, P2₁/c) undergoes stereospecific photodimerization producing anti head-to-tail dimer across pyrone double bond, whereas the triclinic modification (prisms,) dimerizes yielding photodimer of the same configuration, but across styrenic double bond. Single crystal X-ray analyses of the dimorphs reveal the packing differences permitting rationalization of the regio- and stereochemistry of the photoproducts. The significantly low dimer yield from the prismatic crystals is rationalized.