Luminescent 2-phenylbenzothiazole cyclometalated Pt^II and Ir^III complexes with chelating P^O ligands

Abstract

Two series of cyclometalated Pt^II and Ir^III complexes with general formulas [Pt(pbt){PPh₂(R)-κ<i>P</i>,<i>O</i>}] (2a-2c) and [Ir(pbt)₂{PPh₂(R)-κ<i>P</i>,<i>O</i>}] (3a-3c), where Hpbt is 2-phenylbenzothiazol and PPh₂(R) is a diphenylphosphino donor functionalized deprotonated acid (R = <i>o</i>-C₆H₄CO₂a, <i>o</i>-C₆H₄SO₃b, CH₂CH₂CO₂c) are presented. The structures of 1, 2a-2c, 3a and 3b were confirmed by single X-ray diffraction analyses, and the intermolecular interactions in 2a were studied using Hirshfeld surface analysis and non-covalent interaction (NCI) methods on its X-ray structure. Their photophysical properties were investigated by absorption and emission analyses [CH₂Cl₂, solid (298, 77 K) and doped polystyrene (PS) films], supported by TD-DFT calculations on 1, 2a-2c and 3a. The Pt^II complexes exhibit bright phosphorescence in the region 525-542 nm, ascribed to a mixed ³IL/³MLCT excited state with a predominant ³IL contribution. The Ir^III derivatives (3a-3c) show orange photoluminescence (535-584 nm, 298 K), blue shifted at 77 K (527-560 nm), originated from the admixture of ³IL/³MLCT/³LLCT excited states. Interestingly, the photoluminescence quantum yields of the Pt complexes 2a-2c (<i>ϕ</i> = 46.5-66.5%) in PS films are remarkably higher than those of the corresponding iridium complexes (<i>ϕ</i> = 17.3-32%) and the precursor 1 (<i>ϕ</i> = 17%). The calculated ³MC-³IL/³MLCT energy gap for 2a and 3a accounts for the higher quantum yield of the Pt in relation to the Ir complex.