Bright persistent luminescence from pure organic molecules through a moderate intermolecular heavy atom effect

Area of Science:

• Organic Chemistry
• Materials Science
• Photophysics

Background:

• Strong phosphorescence typically correlates with short luminescence lifetimes, limiting exploration of persistent organic phosphors.
• Pure organic molecules with strong room-temperature phosphorescence are rare due to inherent photophysical constraints.

Purpose of the Study:

• To develop novel carbazole derivatives with strong persistent room-temperature phosphorescence.
• To investigate the effect of intermolecular moderate heavy atom effect on phosphorescence properties.
• To explore strategies for enhancing luminescence lifetime and quantum yield in organic materials.

Main Methods:

• Synthesis of carbazole derivatives with flexible alkyl chains linking heavy atoms and carbazole moieties.
• Analysis of photoluminescence properties in crystal states, focusing on molecular stacking.
• Characterization of phosphorescence quantum yield (ΦP) and luminescence lifetime.

Main Results:

• Seven out of eight carbazole derivatives exhibited persistent room-temperature phosphorescence.
• Three compounds showed phosphorescence quantum yields exceeding 9.5%.
• A specific derivative achieved a 39.5% phosphorescent quantum yield and a 200 ms lifetime, emitting white light with 72.6% luminescent efficiency.

Conclusions:

• The strategy of using an intermolecular moderate heavy atom effect with flexible linkers successfully induces strong persistent room-temperature phosphorescence in carbazole derivatives.
• Molecular stacking in crystal states significantly influences photoluminescence properties.
• The developed materials show potential for applications requiring efficient and long-lasting light emission, including white light generation.