π-Hole•••dz2[PtII] Interactions with Electron-Deficient Arenes Enhance the Phosphorescence of PtII-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 arenesF ring via pi-hole center dot center dot center dot 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 pi-hole center dot center dot center dot 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 pi-hole center dot center dot center dot d(z)(2)[Pt-II] contact that is dependent on the p-acidity of the arene(F) and its spatial characteristics.