Red and Deep-Red Phosphorescent Cyclometalated Platinum(II) Complexes with Variably Substituted 2-Picolinamide Ancillary Ligands.

The design of cyclometalated platinum(II) complexes with efficient red photoluminescence remains a significant challenge. Herein, we describe a total of 16 cyclometalated platinum(II) complexes supported by variably substituted 2-picolinamide ancillary ligands, an attractive class of supporting ligands that enables straightforward electronic and steric modification. 1-Phenylisoquinoline (piq) and 1-phenylisoquinoline-4-carbonitrile (piqCN) are used as the cyclometalating ligands, respectively, giving red and deep-red phosphorescence. The collection of compounds includes ten different 2-picolinamide derivatives bearing different substituent patterns. There are two possible isomers of these compounds, and in most cases, a single isomer is isolated, with the quinoline ring of the cyclometalating ligand and the pyridine ring of the 2-picolinamide ancillary ligand cis to one another. In the red region with piq as the cyclometalating ligand, most compounds exhibit photoluminescence quantum yields in the range of 0.11-22 when immobilized in poly(methyl methacrylate) films, and the photoluminescence profiles and the excited-state dynamics are minimally affected by the substituents on the ancillary ligands. In the deep-red region with piqCN as the cyclometalating ligand, quantum yields are similar or slightly higher at parity of ancillary ligand, and a significant increase in the radiative rate constant (k_r) is observed when augmenting the steric profile of the 2-picolinamide ligand.