Fluorene-based oxadiazoles: thermally stable electron-transporting materials for light-emitting devices

We have synthesized and characterized a series of fluorene-based oxadiazole derivatives, in each of which two identical oxadiazole moieties are linked to a fluorene unit via an sp3-hybridized carbon atom (C-9) to form a rigid, nonplanar structure. This structural feature leads to a reduction in the tendency to crystallize and an increase in the glass transition temperature. Electrochemical studies revealed that these materials undergo reversible reductions and have high electron affinities. Each fluorene-based oxadiazole exhibited reasonably good performance when it was used as the electron-transporting layer in a multi-layer organic EL device.