Synthetic control of excited states: New ancillary ligands for cyclometalated Ir(III) complexes

Due to the strong spin-orbit coupling of Ir atom, many cyclometalated Ir complexes are phosphorescent at room temperature, making these materials leading candidates for dopant emitters in OLEO applications. One method of modifying emission energies of Ir phosphors is to change the nature of cyclometalating ligand. This presentation will describe a new method of tuning the lowest excited state energy by employing high triplet energy ancillary ligands for Ir phosphors. Using different ancillary ligands, i.e., a family of pyrazolyl ligands and their analogues, and the same cyclometalating ligand, paratolylpyridine (tpy), it is possible to vary the emission color of Ir phosphors over a wide range. Electrochemical analysis shows that different ancillary ligands modify the emission energy by affecting the energy of HOMO while leaving the LUMO relatively unchanged. Meanwhile, the Ir complexes appear to have longer luminescence lifetime and slower radiative decay when their emission energies increase above some level