More Like this

1. The magnet: With more power comes more annihilation

   https://doi.org/10.1016/j.matt.2023.06.026  

   Sullivan, Colette M.; Nienhaus, Lea (August 2023, Matter)

   Probing the underlying attributes of triplet-triplet annihilation-based upconversion systems is necessary to enable future practical applications. Through a combination of excitation power-dependent upconversion measurements under applied magnetic fields and molecular dynamics simulations, Schmidt and coworkers have recently demonstrated a quantitative approach for extracting critical parameters detailing the intricate upconversion process. 

   more » « less
2. Naphtho[2,3- a ]pyrene Thin Films – H, I, or J? Aggregate Alphabet Soup Served over Triplet Pair States

   https://doi.org/10.1021/acs.jpcc.4c05675  

   Sullivan, Colette M; Szucs, Adrienn M; Siegrist, Theo; Nienhaus, Lea (November 2024, The Journal of Physical Chemistry C)

   Photon upconversion in the solid state has the potential to improve existing solar and infrared imaging technologies due to its achievable efficiency at low power thresholds. However, despite considerable advancements in solution-phase upconversion, expanding the library of potential solid-state annihilators and developing a fundamental understanding of their solid-state behaviors remains challenging due to intermolecular coupling affecting the underlying energy landscape. Naphtho[2,3-a]pyrene has shown promise as a suitable solid-state annihilator. However, the origin of its multiple underlying emissive features remains unknown. To this point, here, we investigate NaPy/poly(methyl methacrylate) thin films at varying concentrations to tune the intermolecular coupling strength to determine its photophysical properties at a range of temperatures between 300–50 K. The results suggest that the multiple emissive features present in the NaPy thin film emission at room temperature arise from a multidimensional I-aggregate (520 nm), an excimer (550 nm), and a strongly coupled J-dimer (620 nm). In addition, we find that at low temperatures, the emission spectrum is dominated by direct emission from the 1(TT) state. 

   more » « less
3. Expanding the synthetic toolbox to access pristine and rare-earth-doped BaFBr nanocrystals

   https://doi.org/10.1039/D1DT02694A  

   Dhanapala, B. Dulani; Munasinghe, Hashini N.; Dissanayake, K. Tauni; Suescun, Leopoldo; Rabuffetti, Federico A. (November 2021, Dalton Transactions)

   A new synthetic route to access pristine and rare-earth-doped BaFBr nanocrystals is described. Central to this route is an organic–inorganic hybrid precursor of formula Ba 5 (CF 2 BrCOO) 10 (H 2 O) 7 that serves as a dual-halogen source. Thermolysis of this precursor in a mixture of high-boiling point organic solvents yields spherical BaFBr nanocrystals (≈20 nm in diameter). Yb:Er:BaFBr nanocuboids (≈26 nm in length) are obtained following the same route. Rare-earth-doped nanocrystals display NIR-to-visible photon upconversion under 980 nm excitation. The temperature-dependence of the green emission from Er 3+ may be exploited for optical temperature sensing between 150 and 450 K, achieving a sensitivity of 1.1 × 10 −2 K −1 and a mean calculated temperature of 300.9 ± 1.5 K at 300 K. The synthetic route presented herein not only enables access to unexplored upconverting materials but also, and more importantly, creates the opportunity to develop solution-processable photostimulable phosphors based on BaFBr. 

   more » « less
4. CdSe nanocrystal sensitized photon upconverting film

   https://doi.org/10.1039/D1RA06562A  

   Rigsby, Emily M.; Miyashita, Tsumugi; Fishman, Dmitry A.; Roberts, Sean T.; Tang, Ming L. (September 2021, RSC Advances)

   Here, films using CdSe nanocrystal (NC) triplet photosensitizers in conjunction with diphenylanthracene (DPA) emitters were assembled to address several challenges to practical applications for solution-based photon upconversion. By using poly(9-vinylcarbazole) as a phosphorescent host in this film, volatile organic solvents are eliminated, the spontaneous crystallization of the emitter is significantly retarded, and ∼1.5% photon upconversion quantum yield (out of a maximum of 50%) is obtained. Transient absorption spectroscopy on nanosecond-to-microsecond time scales reveals this efficiency is enabled by an exceptionally long triplet lifetime of 3.4 ± 0.3 ms. Ultimately, we find the upconversion efficiency is limited by incomplete triplet–triplet annihilation, which occurs with a rate 3–4 orders of magnitude slower than in solution-phase upconversion systems. 

   more » « less
5. Upconversion of Reductants

   https://doi.org/10.1002/anie.201807247  

   Syroeshkin, Mikhail_A; Kuriakose, Febin; Saverina, Evgeniya_A; Timofeeva, Vladislava_A; Egorov, Mikhail_P; Alabugin, Igor_V (February 2019, Angewandte Chemie International Edition)

   Abstract The many applications of photon upconversion—conversion of low‐energy photons into high‐energy photons—raises the question of the possibility of “electron upconversion”. In this Review, we illustrate how the reduction potential can be increased by using the free energy of exergonic chemical reactions. Electron (reductant) upconversion can produce up to 20–25 kcal mol⁻¹of additional redox potential, thus creating powerful reductants under mild conditions. We will present the two common types of electron‐upconverting systems—dissociative (based on unimolecular fragmentations) and associative (based on the bimolecular formation of three‐electron bonds). The possible utility of reductant upconversion encompasses redox chain reactions in electrocatalytic processes, photoredox cascades, design of peroxide‐based medicines, firefly luminescence, and reductive repair of DNA photodamage. 

   more » « less