Synthesis and Fluorescent Properties of Alkynylated 3‑Methylidenephthalides with Extended π‑Systems.

The iodocyclization of (iodoethynyl)-benzoate via the 5-exo-dig pathway affords (diiodomethylene)-isobenzofuran-1-(3H)-one. The Sonogashira cross-coupling of the diiodide proceeds stereoselectively by the substitution of one iodine atom and protodeiodination of the second one, giving Z-isomers of alkynylated derivatives. The arylacetylenes coupling products exhibit fluorescence with an aggregation-induced emission enhancement. The coupling products of Z-3-(TMS-ethynyl)-methylenephthalid and 1,4-diiodo-2,5-bis-(octyloxy)-benzene with extended π-systems underwent fast isomerization, giving equilibrium mixtures of isomers and exhibiting strong fluorescence in nonaggregating solvents.