Saturated Deep Blue Organic Electrophosphorescence Using a Fluorine-Free Emitter

We demonstrate saturated, deep blue organic electrophosphorescence using the facial- and meridianal-isomers of the fluorine-free emitter tris(phenyl-methyl-benzimidazolyl)iridium(III) (f -Ir(pmb)3 and m-Ir(pmb)3, respectively) doped into the wide energy gap host, p-bis(triphenylsilyly)benzene. The study of blue organic electrophosphorescence has focused predominantly on the use of electron-withdrawing fluorine atoms to shift the molecular triplet state to the higher energies required. For example, external quantum efficiencies exceeding 10% have been demonstrated using fluorinated phenyl-pyridine complexes. There are drawbacks to using this technique, namely that the saturated blue phosphorescence required for many display applications may not be achievable through fluorination. In addition, the large electronegativity of the fluorine atom may destabilize the molecule, making it electrochemically reactive, leading to potentially short device operational lifetimes. Both of these challenges underscore the need for fluorine-free, deep blue emitting phosphors.