π-Hole···dz2[PtII] Interactions with Electron-Deficient Arenes Enhance the Phosphorescence of PtII-Based Luminophores

Two phosphorescent PtII-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 arenesF to give infinite reverse sandwich structures. In four out of six structures, a dz2 orbital of PtII is directed to the arenesF ring via π-hole···dz2[PtII] interactions, whereas in the other two structures, the filled dz2 orbital is directed toward the arene C atoms. Computed molecular electrostatic potential surfaces of the arenesF and the complexes, noncovalent interaction indexes for the co-crystals, and natural bond orbital calculations indicate that π-hole···dz2[PtII] 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···dz2[PtII] contact that is dependent on the π-acidity of the areneF and its spatial characteristics.