Efficient Visible-to-UV Photon Upconversion Systems Based on CdS Nanocrystals Modified with Triplet Energy Mediators

Developing high-performance visible-to-UV photon upconversion systems based on triplet–triplet annihilation photon upconversion (TTA-UC) is highly desired, as it provides a potential approach for UV light-induced photosynthesis and photocatalysis. However, the quantum yield and spectral range of visible-to-UV TTA-UC based on nanocrystals (NCs) are still far from satisfactory. Here, three different sized CdS NCs are systematically investigated with triplet energy transfer to four mediators and four annihilators, thus substantially expanding the available materials for visible-to-UV TTA-UC. By improving the quality of CdS NCs, introducing the mediator via a direct mixing fashion, and matching the energy levels, a high TTA-UC quantum yield of 10.4% (out of a 50% maximum) is achieved in one case, which represents a record performance in TTA-UC based on NCs without doping. In another case, TTA-UC photons approaching 4 eV are observed, which is on par with the highest energies observed in optimized organic systems. Importantly, the in-depth investigation reveals that the direct mixing approach to introduce the mediator is a key factor that leads to close to unity efficiencies of triplet energy transfer, which ultimately governs the performance of NC-based TTA-UC systems. These findings provide guidelines for the design of high-performance TTA-UC systems toward solar energy harvesting.     

Photon Upconversion Hydrogels for 3D Optogenetics

The ability to optically induce biological responses in 3D has been dwarfed by the physical limitations of visible light penetration to trigger photochemical processes. However, many biological systems are relatively transparent to low-energy light, which does not provide sufficient energy to induce photochemistry in 3D. To overcome this challenge, hydrogels that are capable of converting red or near-IR (NIR) light into blue light within the cell-laden 3D scaffolds are developed. The upconverted light can then excite optically active proteins in cells to trigger a photochemical response. The hydrogels operate by triplet–triplet annihilation upconversion. As proof-of-principle, it is found that the hydrogels trigger an optogenetic response by red/NIR irradiation of HeLa cells that have been engineered to express the blue-light sensitive protein Cry2olig. While it is remarkable to photoinduce the clustering of Cry2olig with blanket NIR irradiation in 3D, it is also demonstrated how the hydrogels trigger clustering within a single cell with great specificity and spatiotemporal control. In principle, these hydrogels may allow for photochemical control of cell function within 3D scaffolds, which can lead to a wealth of fundamental studies and biochemical applications.     

Reducing the Singlet−Triplet Energy Gap by End-Group π−π Stacking Toward High-Efficiency Organic Photovoltaics

To improve the power conversion efficiencies for organic solar cells, it is necessary to enhance light absorption and reduce energy loss simultaneously. Both the lowest singlet (S1) and triplet (T1) excited states need to energertically approach the charge-transfer state to reduce the energy loss in exciton dissociation and by triplet recombination. Meanwhile, the S1 energy needs to be decreased to broaden light absorption. Therefore, it is imperative to reduce the singlet−triplet energy gap (ΔE_ST), particularly for the narrow-bandgap materials that determine the device T1 energy. Although maximizing intramolecular push−pull effect can drastically decrease ΔE_ST, it inevitably results in weak oscillator strength and light absorption. Herein, large oscillator strength (≈3) and a moderate ΔE_ST (0.4−0.5 eV) are found for state-of-the-art A−D−A small-molecule acceptors (ITIC, IT-4F, and Y6) owing to modest push−pull effect. Importantly, end-group π−π stacking commonly in the films can substantially decrease the S1 energy by nearly 0.1 eV, but the T1 energy is hardly changed. The obtained reduction of ΔE_ST is crucial to effectively suppress triplet recombination and acquire small exciton dissociation driving force. Thus, end-group π−π stacking is an effective way to achieve both small energy loss and efficient light absorption for high-efficiency organic photovoltaics.     

Spirobifluorene Dimers: Understanding How The Molecular Assemblies Drive The Electronic Properties

Spirobifluorene (SBF) is one of the most important scaffolds used in the design of organic semi-conductors (OSCs) for electronics. In recent years, among all the structures developed for these applications, SBF dimers have been highlighted due to their great potential in thermally activated delayed fluorescence and in phosphorescent organic light-emitting diodes. Attaching two SBF units generate 10 dimers, each possessing its own structural specificity, which in turn drives its electronic properties. These ten SBF dimers are gathered herein. Understanding how the molecular assembly determines the electronic properties has been one of the pillars of organic electronics. This is the goal of this article. As positional isomerism is a key tool to design OSCs, defining the design guidelines for the SBF scaffold appears of interest for the future of this building block. Herein, the importance of the two main parameters involved in the electrochemical and photophysical properties, namely the nature of the phenyl linkages and the steric congestion between the two SBF units is discussed. The combination of these two parameters drives the electronic properties but their respective weight is different as a function of the regioisomer involved or of the property considered (frontier orbitals energy level, absorption, fluorescence, phosphorescence).     

气提式三重循环生物膜反应器用于制药废水的处理

采用气提式三重循环生物膜反应器（TLABR）处理制药废水，稳定阶段对COD和NH4^＋-N的去除率分别为73％和70％。当温度为27～30℃、pH=8．5时，反应器内形成了稳定的NO2^--N积累。同时，考察了不同HRT下高效反应器的处理效果，探讨了pH对反应器内发生的短程硝化效果的影响以及亚硝化菌对游离氨浓度的适应性。结果表明：在HRT为3、6、9h下，对COD和氨氮的去除率分别为65．3％、73．9％、75．1％和48．9％、68．4％、72．8％；NO2^--N积累率分别为92．7％、76．2％、69．7％；反应器出水水质稳定，体现了高效性和抗冲击负荷能力。     

Recent research on stimulated emission depletion microscopy for reducing photobleaching

Stimulated emission depletion (STED) microscopy is a useful tool in investigation for super‐resolution realm. By silencing the peripheral fluorophores of the excited spot, leaving only the very centre zone vigorous for fluorescence, the effective point spread function (PSF) could be immensely squeezed and subcellular structures, such as organelles, become discernable. Nevertheless, because of the low cross‐section of stimulated emission and the short fluorescence lifetime, the depletion power density has to be extremely higher than the excitation power density and molecules are exposed in high risk of photobleaching. The existence of photobleaching greatly limits the research of STED in achieving higher resolution and more delicate imaging quality, as well as long‐term and dynamic observation. Since the first experimental implementation of STED microscopy, researchers have lift out variety of methods and techniques to alleviate the problem. This paper would present some researches via conventional methods which have been explored and utilised relatively thoroughly, such as fast scanning, time‐gating, two‐photon excitation (TPE), triplet relaxation (T‐Rex) and background suppression. Alternatively, several up‐to‐date techniques, especially adaptive illumination, would also be unveiled for discussion in this paper. The contrast and discussion of these modalities would play an important role in ameliorating the research of STED microscopy.     

Realization of triplet–triplet annihilation in planar heterojunction exciplex-based organic light-emitting diodes

Triplet–triplet annihilation (TTA) for enhancement of luminous efficiency occurs with difficulty in exciplex-based organic light-emitting devices (OLEDs) because it is an interaction among several neighboring donor and acceptor molecules. However, TTA has been realized in our planar-heterojunction (PHJ) exciplex-based OLEDs by using a thin recombination zone to enhance the interfacial density of the triplet states. The TTA process, which is characterized by a high-field decrease (HFD) in the magneto-electroluminescence from the PHJ OLEDs, appears at approximately 150 K and becomes stronger with decreasing temperature. At a given temperature, the higher the injected current is, the stronger HFD is observed. Additionally, we find that TTA could even happens at room temperature with appropriate selection of the donor molecule, which may be attributed to the favorable electron-donating ability of the methoxy group (–OCH₃) in the donor molecule and the matched overlaps of the intermolecular conformation of the donor and the acceptor.     

High triplet energy Al complex as a host material for blue phosphorescent organic light-emitting diodes

An Al complex, tris((2-(pyrazol-1-yl)pyridin-3-yl)oxy)aluminum (Al(pypy)₃), was synthesized as a high triplet energy host material for blue phosphorescent organic light-emitting diodes. A high triplet energy ligand, 2-(1H-pyrazol-1-yl)pyridin-3-ol, was coordinated to the Al to develop the high triplet energy host material derived from Al. The Al(pypy)₃ host showed a high triplet energy of 2.86 eV for efficient energy transfer to blue triplet emitter. A maximum quantum efficiency of 20.5% was achieved in blue device using the Al(pypy)₃ host material.     

Synthesis and photophysical properties of host materials with high triplet energy based on dibenzofuran and triphenylamine functionalities

A host material with high triplet energy based on dibenzofuran and triphenylamine interconnected through diphenylmethylene linkage was synthesized and photophysical properties of the host material were investigated. A high triplet energy of 2.90 eV was obtained due to complete separation of an electron donating triphenylamine and accepting dibenzofuran by diphenylmethylene linkage. It was found out that intermolecular charge transfer dominated the light emission of the host material.     

新型三线态喹喔啉铱(Ⅲ)配合物的微波合成及其光致发光

在微波辅助加热下,4,4'-二氟-2,3-二苯基喹喔啉(DPQF)与水合三氯化铱(IrCl3·H2O)反应,合成了一种新型三环喹喔啉铱配合物[Ir(DPQF)3],通过1HNMR、元素分析和质谱方法对配合物结构进行了表征,并研究了配合物的吸收光谱和光致发光光谱.结果表明,配合物Ir(DPQF),在391和453 nm处...