Acyclic and Cyclic Di- and Tri(4-oxyphenyl-1,2-phenyleneethynylene)s:  Their Synthesis and Ferromagnetic Spin Interaction

A new set of π-conjugated and alternant but non-Kekulé-type di- and tri(1,2-phenyleneethynylene)s pendantly substituted with phenoxyl radicals at the 4 positions ( 1a, 2a, and 3a ) was synthesized. The synthesis of these acyclic and cyclic compounds was achieved through the head-to-tail coupling of 2-bromo(or -iodo)-4-[3‘,5‘-di- tert -butyl-4‘-trimethylsiloxyl(or -hydroxy)phenyl]-1-ethynylbenzenes. The di- and triphenoxyl compounds ( 1a, and 2a and 3a ) were triplet and quartet at the ground state, respectively, which was ascribed to a ferromagnetic coupling effect of the diphenyl ethynylene bridge for the pendant phenoxyls' spins. The cyclic π-conjugation in 3a exhibited a stronger effect on the spin alignment.