Structural, Photophysical, and Electrophosphorescent Properties of Platinum(II) Complexes Supported by Tetradentate N2O2 Chelates

Abstract

We present an examination of the structural and photophysical characteristics of [Pt(N₂O₂)] complexes bearing bis(phenoxy)diimine auxiliaries (diimine=4,7‐Ph₂phen (1) and 4,4′‐tBu₂bpy (2)) that are tetradentate relatives of the quinolinolato (q) ligand. These neutral derivatives display high thermal stability (>400 °C in N₂). While the crystal lattice in 1 consists of (head‐to‐tail)‐interacting dimers, molecules of 2 are arranged into infinitely stacked planar sheets with possible π–π interactions but no close Pt⋅⋅⋅Pt contacts. Complexes 1 and 2 exhibit moderately intense low‐energy UV/Vis absorptions around λ=400–500 nm that undergo negative solvatochromic shifts. Both derivatives are highly luminescent in solution at 298 K with emission lifetimes in the μs range, and mixed ³[l→π*(diimine)] (l=lone pair/phenoxide) and ³[Pt(d)→π*(diimine)] charge‐transfer states are tentatively assigned. The excited‐state properties of 2 are also investigated by time‐resolved absorption spectroscopy and by quenching experiments with pyridinium acceptors to estimate the excited‐state redox potential. These emitters have been employed as electrophosphorescent dopants in multilayer OLEDs. Differences between the brightness, color, and overall performance of devices incorporating 1 and 2 are attributed to the influence of the diimine substituents.