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1. Revealing the Contest between Triplet–Triplet Exchange and Triplet–Triplet Energy Transfer Coupling in Correlated Triplet Pair States in Singlet Fission

   https://doi.org/10.1021/acs.jpclett.1c03217  

   Abraham, Vibin ; Mayhall, Nicholas J. ( November 2021 , The Journal of Physical Chemistry Letters)
2. Triplet-triplet annihilation photon-upconversion in hydrophilic media with biorelevant cholesteryl triplet energy acceptors

   https://doi.org/10.1016/j.jphotochem.2021.113412  

   Yun, Young Ju ; Isokuortti, Jussi ; Laaksonen, Timo ; Durandin, Nikita ; Ayitou, A. Jean-Luc ( September 2021 , Journal of Photochemistry and Photobiology A: Chemistry)
3. Efficient Triplet–Triplet Annihilation Upconversion in an Electroluminescence Device with a Fluorescent Sensitizer and a Triplet‐Diffusion Singlet‐Blocking Layer

   https://doi.org/10.1002/adma.201804850  

   Chen, Chia‐Hsun ; Tierce, Nathan T. ; Leung, Man‐kit ; Chiu, Tien‐Lung ; Lin, Chi‐Feng ; Bardeen, Christopher J. ; Lee, Jiun‐Haw ( October 2018 , Advanced Materials)

   Solid‐state triplet–triplet annihilation upconversion (TTAUC) blue emission in an electroluminescence device (i.e., an organic light‐emitting diode (OLED)) is demonstrated. A conventional green fluorophore, tris‐(8‐hydroxyquinoline)aluminum (Alq₃), is employed as the sensitizer that generates 75% triplet under electrical pumping for the blue triplet–triplet annihilation emitter, 9,10‐bis(2′‐naphthyl) anthracene (ADN), with the heterojunction bilayer structure. The operation lifetime is elongated both for ADN blue (4.1x) and Alq₃green (34.8%) emission due to efficient use of excitons and separation of recombination and emission zone. To reduce the singlet quenching (SQ) of blue TTAUC signal by the Alq₃sensitizer with lower bandgap, 1‐(2,5‐dimethyl‐4‐(1‐pyrenyl)phenyl)pyrene (DMPPP) is inserted between the Alq₃and ADN as a triplet‐diffusion‐and‐singlet‐blocking layer. DMPPP exhibits triplet energy close to Alq₃and higher than ADN, as well as higher singlet energy than both Alq₃and ADN. It allows triplet diffusion from Alq₃to ADN, but blocks the SQ of the blue TTAUC signal by Alq₃. 86.1% intrinsic efficiency of TTAUC is demonstrated in this trilayer (Alq₃/DMPPP/ADN) OLED.

    

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4. An energetics assessment of benzo[ a ]tetracene and benzo[ a ]pyrene as triplet–triplet annihilation emitters

   https://doi.org/10.1039/D2ME00004K  

   Wang, Xiaopeng ; Marom, Noa ( April 2022 , Molecular Systems Design & Engineering)

   Optical upconversion (UC) of low energy photons into high energy photons enables solar cells to harvest photons with energies below the band gap of the absorber, reducing the transmission loss. UC based on triplet–triplet annihilation (TTA) in organic chromophores can upconvert photons from sunlight, albeit with low conversion efficiency. We utilize three energy-based criteria to assess the UC potential of TTA emitters in terms of the quantum yield (QY) and the anti-Stokes shift. The energy loss in the singlet pathway of an emitter encounter complex, where a high energy photon is emitted, determines whether a chromophore may undergo TTA. The energy loss in the triplet pathway, which is the main competing process, impacts the TTA QY. The energy difference between the lowest singlet and triplet excitation states in TTA emitters sets an upper bound for the anti-Stokes shift of TTA-UC. Using the energetic criteria evaluated by time-dependent density functional theory (TDDFT) calculations, we find that benzo[ a ]tetracene, benzo[ a ]pyrene, and their derivatives are promising TTA emitters. The energetics assessment and computer simulations could be used to efficiently discover and design more candidate high-performance TTA emitters. 

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5. Transforming Triplet Vinylnitrene into Triplet Alkylnitrene at Cryogenic Temperatures

   https://doi.org/10.1021/acs.orglett.9b01950  

   Shields, Dylan J. ; Sarkar, Sujan K. ; Sriyarathne, H. Dushanee ; Brown, Jocelyn R. ; Wentrup, Curt ; Abe, Manabu ; Gudmundsdottir, Anna D. ( July 2019 , Organic Letters)