Highly Photoluminescent Blue Ionic Platinum-Based Emitters

Abstract

New cycloplatinated <i>N</i>-heterocyclic carbene (NHC) compounds with chelate diphosphines (P^P) as ancillary ligands: [Pt(R-C^C*)(P^P)]PF₆ (R = H, P^P = dppm (<b>1A</b>), dppe (<b>2A</b>), dppbz (<b>3A</b>); R = CN, P^P = dppm (<b>1B</b>), dppe (<b>2B</b>), dppbz (<b>3B</b>)) have been prepared from the corresponding starting material [{Pt(R-C^C*)(μ-Cl)}₂] (R = H, A, R = CN, B) and fully characterized. The new compound <b>A</b> has been prepared by a stepwise protocol. The photophysical properties of <b>1A</b>-<b>3A</b> and <b>1B</b>-<b>3B</b> have been widely studied and supported by the time-dependent-density functional theory. These compounds show an efficient blue (dppe, dppbz) or cyan (dppm) emission in PMMA films (5 wt %), with photoluminescence quantum yield (PLQY) ranging from 30% to 87% under an argon atmosphere. This emission has been assigned mainly to transitions from ³ILCT [π(NHC) → π*(NHC)] excited states with some ³LL'CT [π(NHC) → π*(P^P)] character. The electroluminescence of these materials in proof-of-concept solution-processed organic light-emitting diodes containing <b>3A</b> and <b>3B</b> as dopants was investigated. The CIE coordinates for devices based on <b>3A</b> (0.22, 0.41) and <b>3B</b> (0.24, 0.44) fit within the sky blue region.