More Like this

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.

    

   more » « less
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. 

   more » « less
5. In silico prediction of annihilators for triplet–triplet annihilation upconversion via auxiliary-field quantum Monte Carlo

   https://doi.org/10.1039/d0sc03381b  

   Weber, John L. ; Churchill, Emily M. ; Jockusch, Steffen ; Arthur, Evan J. ; Pun, Andrew B. ; Zhang, Shiwei ; Friesner, Richard A. ; Campos, Luis M. ; Reichman, David R. ; Shee, James ( January 2021 , Chemical Science)

   null (Ed.)

   The energy of the lowest-lying triplet state (T1) relative to the ground and first-excited singlet states (S0, S1) plays a critical role in optical multiexcitonic processes of organic chromophores. Focusing on triplet–triplet annihilation (TTA) upconversion, the S0 to T1 energy gap, known as the triplet energy, is difficult to measure experimentally for most molecules of interest. Ab initio predictions can provide a useful alternative, however low-scaling electronic structure methods such as the Kohn–Sham and time-dependent variants of Density Functional Theory (DFT) rely heavily on the fraction of exact exchange chosen for a given functional, and tend to be unreliable when strong electronic correlation is present. Here, we use auxiliary-field quantum Monte Carlo (AFQMC), a scalable electronic structure method capable of accurately describing even strongly correlated molecules, to predict the triplet energies for a series of candidate annihilators for TTA upconversion, including 9,10 substituted anthracenes and substituted benzothiadiazole (BTD) and benzoselenodiazole (BSeD) compounds. We compare our results to predictions from a number of commonly used DFT functionals, as well as DLPNO-CCSD(T 0 ), a localized approximation to coupled cluster with singles, doubles, and perturbative triples. Together with S1 estimates from absorption/emission spectra, which are well-reproduced by TD-DFT calculations employing the range-corrected hybrid functional CAM-B3LYP, we provide predictions regarding the thermodynamic feasibility of upconversion by requiring (a) the measured T1 of the sensitizer exceeds that of the calculated T1 of the candidate annihilator, and (b) twice the T1 of the annihilator exceeds its S1 energetic value. We demonstrate a successful example of in silico discovery of a novel annihilator, phenyl-substituted BTD, and present experimental validation via low temperature phosphorescence and the presence of upconverted blue light emission when coupled to a platinum octaethylporphyrin (PtOEP) sensitizer. The BTD framework thus represents a new class of annihilators for TTA upconversion. Its chemical functionalization, guided by the computational tools utilized herein, provides a promising route towards high energy (violet to near-UV) emission. 

   more » « less