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-Kekule-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.