The art of acetylenic scaffolding: rings,rods, and switches

Acetylenic scaffolding with derivatives of tetraethynylethene (TEE, 3,4-diethynylhex-3-ene-1,5-diyne) and (E)-1,2-diethynylethene (DEE, (E)-hex-3-ene-1,5-diyne) provides carbon-rich compounds with interesting physicochemical properties. Thus, these modules are building blocks for monodisperse, linearly pi-conjugated oligomers [polytri(acetylene)s, PTAs] extending in length beyond 10nm, and for large, macrocyclic, all-carbon cores (dehydroannulenes and expanded radialenes) exhibiting strong chromophoric properties. The advanced materials' properties were strongly influenced by the presence of electron-donating substituents at the lateral positions, decreasing the decreasing the (HOMO-LUMO) gap in both PTAs and expanded radialenes. Arylated TEEs were found to undergo photochemically induced cis-trans isomerization, paving the way for applications as light-driven molecular switches in optoelectronic devices. Derivatives of 1,3-diethynylallene are new modules that offer the prospect of scaffolding in an orthogonal manner; that is, they represent precursors for helical oligomers.