Organic Binary and Ternary Cocrystal Engineering Based on Halogen Bonding Aimed at Room-Temperature Phosphorescence

Area of Science:

• Materials Science
• Solid-State Chemistry
• Organic Chemistry

Background:

• Organic room-temperature phosphorescence (ORTP) is crucial for advanced optical and electronic devices.
• Cocrystals offer tunable photophysical properties through controlled intermolecular interactions.
• Halogen bonding, particularly involving iodine, is an emerging strategy for designing functional organic materials.

Purpose of the Study:

• Investigate the relationship between crystal packing motifs and ORTP characteristics in binary cocrystals of 1,4-diiodotetrafluorobenzene (DITFB) and polycyclic aromatic hydrocarbons (PAHs).
• Explore the role of σ-hole···π and π-hole···π interactions in determining photoluminescence quantum yields (PLQYs).
• Examine the effect of crystal structure modification on ORTP properties using ternary cocrystals.

Main Methods:

• Synthesis and characterization of binary cocrystals: DITFB with phenanthrene (Phen), chrysene (Chry), and pyrene (Pyr).
• Crystallographic analysis to determine packing motifs and intermolecular interactions (σ-hole···π, π-hole···π).
• Preparation of ternary cocrystals by doping Pyr into Phen-DITFB cocrystals to study structural effects on PLQY.

Main Results:

• Binary cocrystals of Phen-DITFB and Chry-DITFB, featuring σ-hole···π interactions, exhibited higher PLQYs than Pyr-DITFB, which showed π-hole···π interactions.
• Ternary cocrystals retained the σ-hole···π interaction motif from Phen-DITFB.
• The ORTP emission in ternary cocrystals originated from Pyr, with a maximum PLQY exceeding 20% due to suppressed nonradiative decay.

Conclusions:

• Crystal packing motifs, dictated by σ-hole···π and π-hole···π interactions, significantly influence ORTP characteristics and PLQYs in DITFB-based cocrystals.
• Ternary cocrystal design, by modifying crystal packing, can enhance ORTP performance by minimizing nonradiative decay pathways.
• This study expands the potential of halogen bonding in designing high-performance organic phosphorescent materials.