Rigidification or interaction-induced phosphorescence of organic molecules

Area of Science:

• Materials Science
• Organic Chemistry
• Photophysics

Background:

• Phosphorescent materials traditionally rely on metal complexes.
• Metal-free organic molecules typically exhibit phosphorescence only at low temperatures (77 K) and in rigid matrices.
• Achieving both long-lived and intense room-temperature phosphorescence in organic molecules is challenging due to conflicting properties.

Purpose of the Study:

• To review recent advancements in designing organic molecules with room-temperature phosphorescence (RTP).
• To highlight molecules that are weakly phosphorescent in solution but become highly phosphorescent upon aggregation.
• To categorize the mechanisms responsible for switching on RTP in these systems.

Main Methods:

• Reviewing literature on aggregation-induced room-temperature phosphorescence (AIRPT) in metal-free organic molecules.
• Classifying systems based on the mechanism of phosphorescence enhancement: rigidification (crystallization, encapsulation) and intermolecular interactions (self-aggregation, heavy-atom effects).
• Analyzing examples of molecules exhibiting switched-on phosphorescence upon aggregation.

Main Results:

• Identified two primary mechanisms for switching on RTP in organic molecules: rigidification and intermolecular interactions.
• Demonstrated that aggregation can overcome the limitations of solution-phase phosphorescence for organic emitters.
• Showcased novel organic molecules with significant RTP intensity and longevity achieved through aggregation.

Conclusions:

• Aggregation is a powerful strategy to achieve efficient room-temperature phosphorescence in metal-free organic molecules.
• The design of organic materials for RTP can be guided by understanding rigidification and intermolecular interaction mechanisms.
• Further research into aggregation-induced phosphorescence holds promise for advanced optoelectronic applications.