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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. Triplet vinylnitrenes

   https://doi.org/10.1002/9780470682531.pat0925  

   Banerjee, U.; Thenna-Hewa, K.; Gudmundsdottir, A. D. (June 2019, Patai’s chemistry of functional groups)

   This chapter describes how intramolecular sensitization has been used to successfully form triplet vinylnitrene intermediates from vinyl azide, isoxazole, and azirine compounds. Triplet vinylnitrenes have been thoroughly characterized in cryogenic matrices using UV/vis absorption, infrared, and electron spin resonance spectroscopies. Electron spin resonance spectroscopy shows that vinylnitrenes have a significant 1,3‐biradical character, which is further supported by density functional theory calculations. Laser flash photolysis, which has allowed the direct detection of triplet vinylnitrenes in solution, reveals that they are short‐lived intermediates with lifetimes on the order of a few microseconds. Vinylnitrenes decay efficiently by intersystem crossing to form products because their 1,3‐biradical character renders their vinylic CC bond flexible, which enhances intersystem crossing. At cryogenic temperatures, flexible triplet vinylnitrenes are not stable and intersystem cross to form products. Nevertheless, triplet vinylnitrenes can be stabilized by limiting the flexibility of the vinylic CC bond, which renders them stabile in cryogenic matrices. Thus, they are promising building blocks for high‐spin assemblies. Furthermore, as stabilized vinylnitrenes can also be employed in bimolecular reactions, they have potential for use in various synthetical applications. 

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4. 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)
5. Spin-Correlated Radical Pairs as Magnetic Switches for Controlling Emissive Triplet States via Triplet–Triplet Energy Transfer

   https://doi.org/10.1021/acs.jpclett.5c01512  

   Lin, Neo; Zagajowski, Madalyn J; Esipova, Tatiana V; Mani, Tomoyasu (July 2025, The Journal of Physical Chemistry Letters)

   Magnetic fields offer a powerful means to control molecular emission, enabling quantum sensing and spin-level control of chemical reactions. Here, we demonstrate a strategy to magnetically control red to near-infrared phosphorescence via triplet–triplet energy transfer (TTET) from donor–chiral bridge–acceptor (D−χ–A) molecules that generate spin-correlated radical pairs (SCRPs) upon photoexcitation. These SCRPs yield non-emissive triplet excited states whose formation is sensitive to magnetic fields. By transferring this energy to emissive Pt- and Pd-based π-extended porphyrins, we enable magnetic control over phosphorescence that would otherwise be unresponsive to weak magnetic fields (<1 T). This approach establishes a platform for quantifying magnetic field effects on silent triplet states while extending magnetically responsive emission into the near-infrared. Coupling SCRP-based molecular magnetic switches to long-wavelength emissive acceptors offers a new way for probing and modulating spin-dependent processes and triplet-state populations in molecular systems. 

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