Synthesis, Air Stability, Photobleaching, and DFT Modeling of Blue Light Emitting Platinum CCC-N-Heterocyclic Carbene Pincer Complexes

The recently reported metalation/transmetalation route for the synthesis of CCC-bis­(NHC) pincer ligand supported transition-metal complexes was extended to Pt. 2-(1,3-Bis­(<i>N</i>-butylimidazol-2-ylidene)­phenylene)­(chloro)­platinum­(II) (<b>1</b>) and its bromo analogue <b>2</b> were synthesized and characterized. X-ray crystal structure determinations revealed complexes <b>1</b> and <b>2</b> to have distorted-square-planar configurations around the metal. Photophysical and thermal properties of these complexes are reported, and their extended photostability in air is discussed and contrasted. Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) computations of the ground state and various low-lying excited states have revealed admixing of Pt 5d orbitals and the ligand π* orbitals for both the ground state and the low-lying excited states of complex <b>1</b>, indicating the low-lying states to be a mixture of metal-to-ligand charge-transfer and ligand-centered transition (MLCT-LC). Somewhat surprisingly, the computed gas-phase geometry of the excited state of complex <b>1</b> had a significant distortion, mostly about the C_aryl–Pt–Cl angle. These complexes were congeners of materials for organic light emitting diodes (OLEDs)