Phosphorescent Ir(III) complexes bearing double benzyldiphenylphosphine cyclometalates; strategic synthesis, fundamental and integration for white OLED fabrication

A new Ir(III) complex [Ir(bdp)₂(OAc)] (1) was prepared by the treatment of IrCl₃(tht)₃ with approx. two equivalent of benzyldiphenylphosphine in refluxing decalin solution, bdpH = benzyldiphenylphosphine and tht = tetrahydrothiophene. Complex 1 proves to be a versatile precursor, which could further react with various triazolate chelates such as 5-pyridyl-3-trifluoromethyl-1,2,4-triazole (fptzH), 3-tert-butyl-5-(2-pyridyl)-1,2,4-triazole (bptzH), 5-(1-isoquinolyl)-3-tert-butyl-1,2,4-triazole (iqbtzH) and 5-(1-phenanthridinyl)-3-tert-butyl-1,2,4-triazole (pbtzH) to afford the emissive complexes [Ir(bdp)₂(fptz)] (2), [Ir(bdp)₂(bptz)] (3), [Ir(bdp)₂(iqbtz)] (4), and [Ir(bdp)₂(phbtz)] (5), respectively. Single crystal X-ray diffraction studies of 1 and 5 revealed a distorted octahedral Ir(iii) metal core, both possess two mutually orthogonal bdp cyclometalates, and the respective PPh₂ donors reside at the cis-orientation. Formation of complexes 2-5 can be envisioned as simple replacement of acetate with the incoming N-heterocyclic triazolate chelates. As for photophysical properties, the structural variation leads to salient difference in emission features among complexes 2-5. Combining theoretical approaches, the results are rationalized by the contribution from the degree of ligand π-conjugation, together with the occurrence of ligand-to-ligand charge transfer (LLCT) and intra-ligand ππ* transition in the lowest lying excited state. The orange-red and white light-emitting OLEDs were then fabricated using 5 as dopant, for which the respective devices gave peak efficiencies of 13.6% photons/electron, 33.3 cd A^-1, 29.8 lm/W and with CIE_x,y = 0.530, 0.467 at 100 cd m^-2, and peak efficiencies of 13.0% photons/electron, 28.0 cd A^-1, 22.8 lm/W, and with CIE_x,y = 0.356, 0.348 at 1000 cd m^-2.