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

Abstract

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.