Mutual Enrichment of the (Photo)Chemistry of Sydnones and Diarylethenes in Their Hybrids

Hybrids of mesoionic sydnone and photoswitchable diarylethene (SyDAEs) exhibited properties uncommon for either class of molecules. Their (photo)chemical reactivity is determined by the size of the central ring, unifying the two functional parts, and the substituents in the fused benzene ring. SyDAEs based on six-membered rings are photochromic yet undergo two novel irreversible photoreactions. A SyDAE with a seven-membered ring is photoinactive but readily undergoes (3+2) cycloaddition with diazacyclononyne provided by the favorable saddle-like conformation.