Modulation of Supramolecular Interaction of Pt(II) Complexes Bearing Carbene Cyclometalate for Color-Tunable Luminescence

Abstract

Pt(II) complexes are known for their versatility in showing aggregation-induced emission. Herein, we report four Pt(II) complexes Pt-1, Pt-2, and Pt-3a/b featuring both the carbene cyclometalate (C<^>C) and chelating pyrazolate (N<^>N). We evaluated two synthetic methods: the first employed the carbene intermediate Pt-DMSO, followed by N<^>N coordination to give Pt-1-Cl and aryl cyclometalation, while the second involved sequential addition of C<^>C and N<^>N chelates to Pt(COD)Cl2. These Pt(II) complexes exhibited efficient sky-blue emission in a PMMA matrix at high dilution. Upon increasing the doping ratio, emission of Pt-1 and Pt-3a remained essentially unchanged, but Pt-2 and Pt-3b exhibited gradual emergence of a low-energy band at similar to 575 nm, which was attributed to the metal-metal-to-ligand charge transfer emission band. These aggregation propensities aligned well with the time-dependent density functional theory calculations based on the dimers and trimers. For applications, the organic light-emitting diode devices based on Pt-1 exhibited blue emission with a max. external quantum efficiency (EQE) of 11.7% at 50 wt %, while Pt-2-based devices gave concentration-dependent emission with max. EQEs of 9.4, 11.3, and 7.1% and CIE xy coordinates of (0.26, 0.45), (0.33, 0.47), and (0.45, 0.49) at 10, 50, and 100 wt %, respectively.