Crystal Photodimerization Reactions of Spatially Engineered Isocoumarin Assemblies

We report the single-crystal-to-single-crystal (SCSC) photodimerization of a sulfonamide isocoumarin. When recrystallized, this material forms centrosymmetrically related supramolecular dimers that assemble via the complementary features of molecular shape and carboxyl···carboxyl contacts. This prescribed motif persists despite the presence of two-part whole-molecule disorder. Each disorder component is involved in a unique set of hydrogen-bonding interactions, N–H···OC versus N–H···OS, that propagate along the [111] and [110] directions of the crystal, respectively. Despite the observed disorder, the overall recognition profile of this supramolecular dimer remained intact, effectively promoting coplanar head-to-tail alignment with a separation of 3.4–4.1 Å between the neighboring CC groups. UV illumination studies using the tail-irradiation technique produced a single photodimer product in quantitative yield via a SCSC transformation.