Fast Triplet-Exciton Harnessing in Organic X-Ray Scintillators for Dynamic Radiography.

Area of Science:

• Materials Science
• Organic Chemistry
• Medical Imaging

Background:

• High-resolution dynamic X-ray imaging requires organic scintillators with high triplet-exciton utilization and rapid radioluminescence.
• Conventional thermally activated delayed fluorescence (TADF) scintillators face a trade-off between efficiency and decay lifetime due to slow reverse intersystem crossing (RISC).
• Minimizing the singlet-triplet energy gap (ΔE_ST) to accelerate RISC often reduces spin-orbit coupling (SOC), creating a design challenge.

Purpose of the Study:

• To develop a molecular design strategy for TADF scintillators that overcomes the efficiency-lifetime trade-off.
• To create novel TADF scintillators with accelerated RISC rates and enhanced performance for X-ray imaging.
• To enable high-resolution static and real-time dynamic X-ray imaging through improved scintillator properties.

Main Methods:

• Designed TADF scintillators by strengthening hybridization between charge-transfer (CT) and locally excited (LE) states to simultaneously reduce ΔE_ST and enhance SOC.
• Synthesized three TADF scintillators using a 2-chloro-7-fluoroquinazoline acceptor paired with phenoselenazine, phenothiazine, or phenoxazine donors.
• Characterized photoluminescence quantum yield, RISC rates, X-ray induced light yield, and radioluminescence lifetime.

Main Results:

• Achieved a high photoluminescence quantum yield of 96.3% and an accelerated RISC rate approaching 10⁷ s^-1.
• Demonstrated a high light yield of 26508 photons MeV^-1 under X-ray irradiation.
• Obtained a fast radioluminescence lifetime of 3 μs, suitable for dynamic radiography.

Conclusions:

• The developed molecular design strategy effectively overcomes the limitations of conventional TADF scintillators.
• The novel TADF scintillators exhibit excellent performance metrics for high-resolution static and dynamic X-ray imaging.
• This work provides a generalizable approach for designing high-performance TADF scintillators for advanced X-ray imaging applications.