Highly Photoluminescent Blue Ionic Platinum-Based Emitters

Abstract

New cycloplatinated N-heterocyclic carbene (NHC) compounds with chelate diphosphines (PP) as ancillary ligands: [Pt(R-CC∗)(PP)]PF6 (R = H, PP = dppm (1A), dppe (2A), dppbz (3A); R = CN, PP = dppm (1B), dppe (2B), dppbz (3B)) have been prepared from the corresponding starting material [{Pt(R-CC∗)(μ-Cl)}2] (R = H, A, R = CN, B) and fully characterized. The new compound A has been prepared by a stepwise protocol. The photophysical properties of 1A-3A and 1B-3B 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*(PP)] character. The electroluminescence of these materials in proof-of-concept solution-processed organic light-emitting diodes containing 3A and 3B as dopants was investigated. The CIE coordinates for devices based on 3A (0.22, 0.41) and 3B (0.24, 0.44) fit within the sky blue region.