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(N-butylimidazol-2-ylidene)­phenylene)­(chloro)­platinum­(II)
(1) and its bromo analogue 2 were synthesized
and characterized. X-ray crystal structure determinations revealed
complexes 1 and 2 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 1, 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 1 had a significant distortion,
mostly about the Caryl–Pt–Cl angle. These
complexes were congeners of materials for organic light emitting diodes
(OLEDs).