Introduction of two alkoxy/siloxy groups at the 2′ and 5′-positions of p-teraryls has been demonstrated to be an effective molecular design strategy for developing fluorophores that exhibit efficient solid-state ultraviolet (UV) emission. The designed p-teraryls emitted UV light in the solid state at wavelengths of 362–391 nm, with quantum yields of 0.20 to 0.46.

Abstract

Organic fluorophores that efficiently emit ultraviolet (UV) light in the solid state are expected to accelerate the development of potentially attractive UV-OLEDs. Herein, we demonstrate that 2′,5′-dialkoxy-, 2′,5′-bis(siloxy)-, and 2′-(alkoxy)-5′-(siloxy)-p-terphenyls and 2,5-dioxy-1,4-(1-naphthyl)benzenes are efficient UV-emitting solid fluorophores. The teraryls were prepared by a Pd-catalyzed Suzuki–Miyaura cross-coupling reaction of readily available 2,5-dialkoxy-1,4-diiodobenzenes with phenyl- and (1-naphthyl)boronic acid, followed by dealkylation–silylation. The dioxy-p-teraryls are thermally stable, with some having glass transition temperatures ranging from −8 to 47 °C. Single-crystal X-ray diffraction analysis of 2′,5′-bis(triphenylsiloxy)- and 2′-(hexyloxy)-5′-(triphenylsiloxy)-p-terphenyls revealed that the terphenyl moieties adopted twisted conformations, and there were no intramolecular π–π interactions in the crystal packing. The terphenyls in CH₂Cl₂ fluoresced at 370–386 nm with quantum yields of 0.30–0.44. Efficient UV emission (362–391 nm) of the teraryls was observed in the solid state, with quantum yields of 0.20–0.46. Density functional calculations suggest that the optical excitation of the terphenyls involves intramolecular charge transfer from the ethereal oxygen, with the moieties accepting the charge transfer depending on the substituents on the ethereal oxygen atoms.