| 1. |
- Nishimura, Naoyuki, et al.
(författare)
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Photon upconversion utilizing energy beyond the band gap of crystalline silicon with a hybrid TES-ADT/PbS quantum dots system
- 2019
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Ingår i: Chemical Science. - : Royal Society of Chemistry (RSC). - 2041-6520 .- 2041-6539. ; 10:18, s. 4750-4760
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Tidskriftsartikel (refereegranskat)abstract
- The recent introduction of inorganic semiconductor quantum dots (QDs) as triplet sensitizers for molecular semiconductors has led to significant interest in harvesting low energy photons, which can then be used for photon upconversion (PUC), via triplet-triplet annihilation (TTA). A key goal is the harvesting of photons from below the bandgap of crystalline silicon 1.12 eV (approximate to 1100 nm) and their upconversion into the visible region. In practice, the systems demonstrated so far have been limited to harvesting photons with energies above 1.2 eV (approximate to 1 mu m), due to two reasons: firstly the need to use transmitter ligands which allow efficient energy harvesting from the QD but introduce an energy loss of larger than 200 meV in transmission from the QD to the annihilator, and secondly due to the use of molecules such as tetracene which cannot accept smaller energy than 1.2 eV. Here, we introduce a new strategy to overcome these difficulties by using a low energy triplet annihilator that also harvests excitations efficiently from QDs. Specifically, we show that 5,11-bis(triethylsilylethynyl) anthradithiophene (TES-ADT, triplet energy of 1.08 eV: ca. 1150 nm) functions as a triplet annihilator (20% TTA efficiency) while also rapidly extracting triplet excitons from lead sulfide (PbS) QDs with a rate constant of k = ca. 2 x 10(-8) s(-1) with an excitation at 1064 nm. This rate is consistent with an orbital overlap between TES-ADT and PbS QDs, which we propose is due to the thiophene group of TES-ADT, which enables a close association with the PbS surface, allowing this system to function both as annihilator and transmitter. Our results pave the way for the design of triplet annihilators that can closely associate with the QD surface and harvest low energy excitons with minute losses in energy during the TET process, with the ultimate goal of efficiently utilizing photon energy beyond the bandgap of crystalline silicon.
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| 2. |
- Pandya, Raj, et al.
(författare)
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Microcavity-like exciton-polaritons can be the primary photoexcitation in bare organic semiconductors
- 2021
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 12:1
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Tidskriftsartikel (refereegranskat)abstract
- Strong-coupling between excitons and confined photonic modes can lead to the formation of new quasi-particles termed exciton-polaritons which can display a range of interesting properties such as super-fluidity, ultrafast transport and Bose-Einstein condensation. Strong-coupling typically occurs when an excitonic material is confided in a dielectric or plasmonic microcavity. Here, we show polaritons can form at room temperature in a range of chemically diverse, organic semiconductor thin films, despite the absence of an external cavity. We find evidence of strong light-matter coupling via angle-dependent peak splittings in the reflectivity spectra of the materials and emission from collective polariton states. We additionally show exciton-polaritons are the primary photoexcitation in these organic materials by directly imaging their ultrafast (5 × 106 m s−1), ultralong (~270 nm) transport. These results open-up new fundamental physics and could enable a new generation of organic optoelectronic and light harvesting devices based on cavity-free exciton-polaritons.
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| 3. |
- Qin, Yi, et al.
(författare)
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Structural and Functional Study of D-Glucuronyl C5-epimerase
- 2015
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Ingår i: Journal of Biological Chemistry. - 0021-9258 .- 1083-351X. ; 290:8, s. 4620-4630
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Tidskriftsartikel (refereegranskat)abstract
- Heparan sulfate (HS) is a glycosaminoglycan present on the cell surface and in the extracellular matrix, which interacts with diverse signal molecules and is essential for many physiological processes including embryonic development, cell growth, inflammation, and blood coagulation. D-Glucuronyl C5-epimerase (Glce) is a crucial enzyme in HS synthesis, converting D-glucuronic acid to L-iduronic acid to increase HS flexibility. This modification of HS is important for protein ligand recognition. We have determined the crystal structures of Glce in apo-form (unliganded) and in complex with heparin hexasaccharide (product of Glce following O-sulfation), both in a stable dimer conformation. A Glce dimer contains two catalytic sites, each at a positively charged cleft in C-terminal alpha-helical domains binding one negatively charged hexasaccharide. Based on the structural and mutagenesis studies, three tyrosine residues, Tyr(468), Tyr(528), and Tyr(546), in the active site were found to be crucial for the enzymatic activity. The complex structure also reveals the mechanism of product inhibition (i.e. 2-O- and 6-O-sulfation of HS keeps the C5 carbon of L-iduronic acid away from the active-site tyrosine residues). Our structural and functional data advance understanding of the key modification in HS biosynthesis.
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