Enhancing the photoluminescence quantum yields of blue-emitting cationic iridium(III) complexes bearing bisphosphine ligands

Herein we present a structure-property relationship study of thirteen cationic iridium(III) complexes of the form of [Ir(C<^>N)(2)(P<^>P)]PF6 in both solution and the solid state through systematic evaluation of six bisphosphine (P<^>P) ligands (xantphos, dpephos, dppe, Dppe, nixantphos and isopropxantphos). All of the complexes are sky-blue emissive, but their photoluminescence quantum yields (Phi(PL)) are generally low. However, strong and long-lived blue luminescence (lambda(cm) = 471 nm; Phi(PL) = 52%; tau(c) = 13.5 mu s) can be obtained by combining the reduced bite angle of the 1,2-bis-diphenylphosphinoethene (dppe) chelate with the bulky 2-(4,6-difluorophenyl)-4-mesitylpyridinato (dFmesppy) cyclometalating ligand. To the best of our knowledge this is the highest Phi(PL) and the longest tau(e) reported for cyclometalated iridium(III) complexes bearing bisphosphine ligands. Light-emitting electrochemical cells (LEECs) were fabricated using lead complexes from this study, however due in part to the irreversible electrochemistry, no functional LEEC was achieved. Organic light-emitting diodes were successfully fabricated but only attained maximum external quantum efficiencies of 0.25%.