Anti-Stokes Luminescence in Multi-Resonance-Type Thermally-Activated Delayed Fluorescence Molecules

Multichromatic Anti-Stokes Photon Upconversion through BNOSe Sensitization

Triplet-triplet annihilation upconversion (TTA-UC) has become an important sensing technique due to its ability to eliminate tissue autofluorescence interference. However, its quantitative application in oxygen sensing within complex systems remains fundamentally constrained. To overcome this limitation and explore synergistic anti-Stokes mechanisms, we developed a heavy-metal-free photosensitizer (BNOSe) via multiresonance architecture engineering. This innovation enables the creation of the first integrated platform capable of simultaneous TTA-UC and oxygen-resistant single-photon absorption upconversion (SPA-UC). The optimized system exhibits remarkable performance: it converts deep-red light (640 nm) into dual emissions at 617 nm (orange) and 412 nm (blue), achieving a record TTA-UC quantum yield of 19.3% with a 1.07 eV anti-Stokes shift, the largest value reported for visible-to-blue TTA-UC using metal-free sensitizers. Importantly, the oxygen-dependent TTA-UC and oxygen-resistant SPA-UC channels establish a self-calibrating sensing paradigm, showcasing multimodal capabilities in oxygen-probing bioimaging and multicolor analyte detection.

Anti-Stokes Emission Utilizing Reverse Intersystem Crossing

Photon-upconversion (PUC) processes in organic molecular systems, such as triplet-triplet upconversion and hot-band absorption, are promising technologies for future energy harvesting. Although these processes can generate high-energy excitons compared to excitation energy, a PUC process with a high yield and no energy loss has not been established and, therefore, is highly desired. Here, we propose an alternative PUC mechanism that uses reverse intersystem crossing on thermally activated delayed fluorescence (TADF) molecules. This process combines a triplet sensitizer and a TADF molecule, generating a triplet in the former and transferring it to the latter. Specifically, the triplet energy transfer from Ir(ppy)3 (sensitizer) to CzBSe (TADF) results in anti-Stokes emission with an anti-Stokes energy of 0.18 eV. We found that the triplet energy transfer rate strongly depends on the triplet radiative decay rate of TADF molecules and the difference in Gibbs energy between the energy acceptor and donor. Our findings will contribute to understanding triplet energy transfer dynamics in organic energy donor-acceptor systems and will lead to various applications, such as future optical cooling systems.

Organic Crystal with Anti-Stokes Photoluminescent Excitation and Thermally Activated Delayed Fluorescence Features

Thermal activation process utilizes environmental thermal energy to help supplement energy for the nonspontaneous energy-consuming upconversion physical transitions with positive free energy change (ΔG>0). Reverse intersystem crossing (rISC) and hot band absorption are two kinds of thermal activation transitions. Thermally activated delayed fluorescence (TADF) materials with rISC have significantly propelled advancements in organic semiconductors. Hot band absorption, enables anti-Stokes photoluminescence, offering a promising route for efficient photon upconversion. In this work, we constructed a crystal consisting of a donor-acceptor type TADF molecule, DPQ-DPAC, demonstrating dual thermal activation properties of hot band absorption with a notable 0.1 eV anti-Stokes shift emission and proficient TADF performance. Only in the crystal TADF efficiency facilitates and the photoluminescence quantum yield elevates to an impressive 90.8 %. Combining the extended absorption spectrum, these enhancements collectively realize anti-Stokes photoluminescence in crystal. Experimental and theoretical results on the DPQ-DPAC crystal indicate optimizations in its conformational and vibrational modes, resulting in enhancements to its properties. This finding provides insight into crafting organic materials with thermally activated functionalities and contributes to fully exploiting the potential of organic materials, further advancing versatile materials applications.

Reverse intersystem crossing mechanisms in doped triangulenes

Thermally activated delayed fluorescence (TADF) has emerged as one of the most promising strategies in the quest for organic light emitting diodes with optimal performance. This computational study dissects the mechanistic intricacies of the central photophysical step, reverse intersystem crossing (rISC) in N and B doped triangulenes as potential multi-resonance TADF compounds. Optimal molecular patterns conducive to efficient rISC, encompassing dopant atom size, number, and distribution, are identified. Additionally, we assess various electronic structure methods for characterizing TADF-relevant molecular systems. The findings identify the distinct role of the direct and mediated mechanisms in rISC, and provide insights into the design of advanced TADF chromophores for next-generation OLED technology.