π-Hole··· d z 2 [Pt II ] Interactions with Electron-Deficient Arenes Enhance the Phosphorescence of Pt II -Based Luminophores.

Two phosphorescent Pt ^II -based cyclometalated complexes were co-crystallized with perfluorinated arenes to give 1:1 co-crystals. The X-ray study revealed that each of the complexes is embraced by arenes ^F to give infinite reverse sandwich structures. In four out of six structures, a d _z ² orbital of Pt ^II is directed to the arenes ^F ring via π-hole··· d _z ² [Pt ^II ] interactions, whereas in the other two structures, the filled d _z ² orbital is directed toward the arene C atoms. Computed molecular electrostatic potential surfaces of the arenes ^F and the complexes, noncovalent interaction indexes for the co-crystals, and natural bond orbital calculations indicate that π-hole··· d _z ² [Pt ^II ] contacts (and, generally, the stacking) are of electrostatic origin. The solid-state photophysical study revealed up to 3.5-fold luminescence quantum yield and 15-fold lifetime enhancements in the co-crystals. This increase is associated with the strength of the π-hole··· d _z ² [Pt ^II ] contact that is dependent on the π-acidity of the arene ^F and its spatial characteristics.