Modulating Room-Temperature Phosphorescence-To-Phosphorescence Mechanochromism by Halogen Exchange

Area of Science:

• Materials Science
• Solid-State Chemistry
• Photophysics

Background:

• Tuning the stimulus-responsiveness of luminescent crystals is complex due to interconnected factors like molecular structure and packing.
• Existing methods struggle to independently control these variables for precise mechanochromism modulation.

Purpose of the Study:

• To demonstrate a halogen-exchange strategy for disentangling factors controlling crystal mechanochromism.
• To achieve modulation of room-temperature phosphorescence-to-phosphorescence mechanochromism.

Main Methods:

• Synthesized isostructural crystals by replacing bromine with chlorine atoms in a thienyl diketone.
• Investigated molecular conformation, crystal packing, and amorphization behavior under mechanical stimulation.
• Analyzed phosphorescence properties of crystalline and amorphous states, considering heavy atom effects.

Main Results:

• Halogen exchange (Br to Cl) resulted in isostructural crystals with identical molecular conformation and packing.
• Amorphization behavior and the origin of amorphous state phosphorescence remained consistent.
• Phosphorescence properties of individual conformers were modulated by halogen identity, influencing mechanochromism.

Conclusions:

• Halogen exchange effectively isolates and modulates stimulus-responsive photofunctions in crystals.
• This method offers a promising route for designing tunable mechanochromic materials involving spin-forbidden processes.
• The heavy atom effect plays a crucial role in modulating phosphorescence upon halogen substitution.