Near-Unity Intersystem Crossing Efficiency and Bright Polymer Phosphorescence Enabled by Charge-Transfer...

Area of Science:

• Materials Science
• Photochemistry
• Organic Chemistry

Background:

• Bonding aromatic rings to carbonyl groups is key for intersystem crossing (ISC).
• The role of charge transfer (CT) in ISC and phosphorescence efficiency is often overlooked.
• Developing efficient room-temperature phosphorescence (RTP) materials is a significant challenge.

Purpose of the Study:

• To unveil a principle for producing highly-efficient RTP polymers using CT in diarylketone phosphors.
• To investigate the structure-property relationships governing RTP efficiency.
• To demonstrate the application of these phosphors in creating stable afterglow materials.

Main Methods:

• Design and synthesis of unsymmetrical diarylketones.
• Femtosecond transient absorption (fs-TA) spectroscopy to study ISC dynamics.
• Quantum yield measurements and analysis of excited states (singlet and triplet).

Main Results:

• Unsymmetrical diarylketones achieved RTP quantum yields exceeding 30% in copolymers.
• The mechanism involves a ¹CT→³LE transition with small energy gaps and strong spin-orbit coupling, leading to ultrafast ISC.
• Materials exhibited intense afterglow in 3D objects under ambient conditions, even at high temperatures and humidity.

Conclusions:

• Charge transfer is a critical prerequisite for highly efficient RTP in diarylketone phosphors.
• Molecular design controlling CT significantly impacts ISC speed and phosphorescence efficiency.
• This work provides a pathway for developing bright, stable, and versatile afterglow materials.