The phosphorescent behaviors of 9-bromo- and 9-iodophenanthrene in crystals modulated by π–π interactions, C–H⋯π hydrogen bond and C–I⋯π halogen bond

• 9-Bromo- and 9-iodophenanthrene have remarkable different phosphorescent behaviors in crystals.
• 9-Bromo- and 9-iodophenanthrene emit monomer phosphorescence in CD and NaDC media.
• Different π–π interactions modulate their phosphorescent behaviors in crystals.
• The C–I⋯π halogen bond is more competitive to hydrogen bond in 9-IP crystal.
• The C–H⋯π hydrogen bond is more competitive to halogen bond in 9-BrP crystal.

XRD reveals the single crystal of 9-bromophenanthrene (9-BrP) with an infinite herringbone chain structure constructed by itself based on C–H⋯π hydrogen bond and additional edge-to-edge type π–π interaction between phenanthrenes. While, 9-iodophenanthrene (9-IP) possesses an infinite zigzag chain assembled via C–I⋯π halogen bond (XB) and its structure is extended to 3D by typical π–π stacking between phenanthrenes. The interaction energies were estimated by theoretical calculation. The phosphorescence maximum emission wavelengths of two single crystal samples have a significant difference between each other with the 640 nm for 9-BrP and 590 nm for 9-IP, respectively. To understand the effect of interactions between 9-halophenanthrenes in crystals on their phosphorescence, two strategies were utilized to keep them monomers, including 9-halophenanthrenes within hydrophobic cavity of cyclodextrin (CD) with space-regulation of cyclohexane, and sandwiching them in NaDC aggregates. The phosphorescence spectra and decay curves from isolated 9-BrP/9-IP monomers were successfully obtained. All results indicate that the C–H⋯π hydrogen bond and C–I⋯π halogen bond should have smaller effect to their luminescent behaviors while different π–π interactions are the main reason to lead to the obvious different phosphorescent properties between 9-BrP and 9-IP crystals and the largely red-shifted emission bands by approximately 100 nm compared with that of isolated monomers in cyclodextrin/NaDC media or dilute solution of 9-BrP/9-IP. The microcrystal particles separated from suspensions of 9-halophenanthrenes have almost consistent phosphorescent properties compared with their single crystals. Powder XRD confirms the homogeneity of the single crystals and microcrystal particles separated from suspensions of 9-halophenanthrenes and their consistency in structures.