Brightly Luminescent Pt(II) Pincer Complexes with a Sterically Demanding Carboranyl-Phenylpyridine Ligand: A New Material Class for Diverse Optoelectronic Applications

A series of three
Pt­(II) complexes with a doubly cyclometalating
terdentate ligand L1, L1H2 = 3,6-bis­(p-anizolyl)-2-carboranyl-pyridine, and diethyl sulfide (1), triphenylphosphine (2), and t-butylisonitrile (3) as ancillary ligands were synthesized.
X-ray diffraction studies of 1 and 2 show
a coordination of the L1 ligand in a C–N–C
mode in which the bulky and rigid o-carborane fragment
is cyclometalated via a C atom. Importantly, no close intermolecular
Pt–Pt contacts occur with this ligand type. The new Pt­(II)
pincer complexes display very high luminescence quantum yields at
decay times of several tens of μs even in solution under ambient
conditions. On the basis of the low-temperature (T = 1.3 K) emission decay behavior, the emission is assigned to a
ligand centered triplet excited state 3LC with small 1,3MLCT admixtures. Because the phosphorescence is effectively
quenched by molecular oxygen, optical sensors operating in a wide
range of oxygen pressure can be developed. Owing to the very high
luminescence quantum yields, the new materials might also become attractive
as emitter materials for diverse optoelectronic applications.