Benzofuran trimers for organic electroluminescence

Four linear benzofuran trimers have been prepared by a two-stage synthetic procedure. They were tested as materials for organic electroluminescence (OEL). Precursor phenylene ethynylene oligomers were formed in the first stage, then after removal of the phenolic hydroxyl protecting groups, a base was used to promote the cyclization of ortho-hydroxy phenylene ethynylenes to benzofurans. Both acetate esters and tert-butyl carbonates were employed as protecting groups. tert-Butyl and n-hexyl substituents on the benzofurans were used to modulate solubility, aggregation, and film-forming properties; two tert-butyl groups prevented aggregation in the solid state, thus maintaining emission in the blue region of the visible spectrum. The OEL characteristics of the tert-butyl-substituted benzofuran trimer were explored, and blue emission was observed. The two-stage synthetic procedure employed for the preparation of these benzofuran trimers may be applied to a wide variety of benzofuran oligomer and polymer targets.