Phosphorescent Cocrystals Assembled by 1,4-Diiodotetrafluorobenzene and Fluorene and Its Heterocyclic Analogues Based on C–I···π Halogen Bonding

Three phosphorescent cocrystals were prepared by 1,4-diiodotetrafluorobenzene and fluorene (cocrystal <b>1</b>) and its heterocyclic analogues, dibenzofuran (cocrystal <b>2</b>) and dibenzothiophene (cocrystal <b>3</b>), based on C–I···π halogen bonding, and C–H···π, C–H···I, or C–H···F hydrogen bonding as well as F···F and S···S contacts. They were well characterized by X-ray crystallography, infrared, Raman spectroscopy, and differential scanning calorimetry and thermogravimetric analysis. The calculated halogen and hydrogen bonding energies indicate that the synergistic double C–I···π in cocrystal <b>3</b> or π···_XDI_HA···H patterns in cocrystal <b>2</b> really exist. 1,4-DITFB is a dual functional synthon: the cement to link luminescence molecules and a heavy atom perturber to enhance phosphorescence of emitters by spin–orbital coupling. Three cocrystals phosphoresce distinctively with well defined vibrational bands at 496 (0–0) and 531 nm (max) for <b>1</b>, 496 (0–0) and 529 nm (max) for <b>2</b>, and 520 (0–0) and 564 nm (max) for <b>3</b>, respectively. All the decays obey a monoexponential law with lifetimes 0.34, 0.51, and 2.50 ms, respectively. The phosphorescence spectra of fluorene, dibenzofuran, or dibenzothiophene in cocrystals are largely red-shifted by approximately 50–90 nm with respect to the free monomer in β-cyclodextrin aqueous solution, indicating modulatory phosphorescence emission by the molecular structure of emitters <i>per se</i>, weak bonding, and the cocrystal environment