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Decoupling Intersystem Crossing and Radiative Rate in MR-TADF Emitters via High-Lying Triplet Channels
Ruiqi Wu1,2, Yanliang Zhao1,3, Haoran Wei2
1Shandong Provincial Engineering Research Center for Optoelectronic Sensing Materials and Device Micro-Nano Manufacturing, School of Integrated Circuits, Ludong University, Yantai264025, China.
The Journal of Physical Chemistry. A
|July 21, 2026
Summary
New theranostic agents overcome a key limitation in conventional thermally activated delayed fluorescence (TADF) emitters. This research demonstrates a novel approach using high-lying triplet states to enhance both imaging and therapeutic capabilities.
Area of Science:
- Materials Science
- Chemistry
- Biomedical Engineering
Background:
- Conventional thermally activated delayed fluorescence (TADF) emitters present a trade-off for theranostic applications, where improved charge transfer for intersystem crossing (ISC) reduces orbital overlap, hindering fluorescence radiative rates essential for imaging.
- This limitation restricts the simultaneous optimization of imaging and therapeutic functions in theranostic agents.
Purpose of the Study:
- To theoretically demonstrate a novel mechanism for overcoming the intrinsic trade-off in TADF emitters for theranostic applications.
- To decouple the efficiency of spin-flip processes from fluorescence rates, enabling simultaneous enhancement of imaging and photodynamic therapy efficacy.
Main Methods:
- Utilized multiple resonance TADF emitters, specifically CzBNPh and DABNA-2, for theoretical investigations.
- Employed nonadiabatic transition state theory combined with the Landau-Zener model to analyze intersystem crossing pathways.
- Investigated the role of high-lying triplet states in the TADF mechanism.
Main Results:
- Demonstrated that high-lying triplet states (specifically the S1 → T2 pathway) enable exceptionally fast ISC rates (∼107 s-1) with minimal activation barriers (0.09 kcal/mol).
- Showed that this upper-level ISC mechanism preserves significant frontier orbital overlap, crucial for maintaining rapid prompt fluorescence.
- Successfully decoupled spin-flip efficiency from fluorescence, resolving the intrinsic trade-off in conventional TADF emitters.
Conclusions:
- Established a new paradigm for designing theranostic agents by leveraging high-lying triplet state channels.
- This approach allows for the concurrent maximization of fluorescence imaging capabilities and photodynamic efficacy.
- The findings provide a robust strategy for developing advanced materials for integrated diagnostic and therapeutic applications.
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