Synthesis and Luminescent Properties of <i>cis</i> Bis-<i>N</i>-Heterocyclic Carbene Platinum(II) Bis-Arylacetylide Complexes

A series of luminescent N-heterocyclic carbene platinum(II) complexes, [(pmim)Pt(CC−R)2] (R = C6H5 (2), C6H4OMe (3), C6H2(OMe)3 (4), C6H4NMe2 (5), C4H3S (6), C6H4CCC6H5 (7), 1-pyrenyl (8), and C6H4F (9)), were successfully synthesized using the precursor (pmim)PtI2, 1 (pmim = 1,1′-dipentyl-3,3′-methylene-diimidazoline-2,2′-diylidene). The X-ray crystal structures of 1, 4, 5, and 7 have been determined. These complexes showed long-lived emission in solution at room temperature. The emission origin of the complexes is tentatively assigned to be from triplet states of predominantly intraligand (IL) character with some mixing of metal-to-ligand charge-transfer (MLCT) character. TD-DFT and DFT calculations have been performed on most of the complexes to ascertain the nature of the excited state. Changes in the alkynyl ligands lead to a change in the absorption and emission maxima seen for these complexes in a potentially predictable way.