供电子能力对一类热活化延迟荧光分子反系间窜越速率的影响

本文基于第一性原理,研究了八个热活化延迟荧光分子的性质,揭示了基团供电子能力对分子几何构型、跃迁属性以及反系间窜越过程的影响.研究结果表明,对于咔唑和氧杂蒽酮组成的一类分子的最低三重激发态（T₁）而言,供体基团的二苯胺取代,几乎不会改变供体和受体之间的夹角,但却可以减小供体和受体间的键长.基团供电子能力越强,最高占据分子轨道（HOMO）和最低未占据分子轨道（LUMO）间的轨道重叠度越小,最低单重激发态S₁和T₁之间的能差（△E_S1-T1）越小.此外,供体基团上增加二苯胺能够增加HOMO的离域性,而且能够进一步地减小△E_S1-T1.通过计算S₁和T₁之间的旋轨耦合系数（H_so）,发现（<S₁|Ĥ_so|T₁>²）/（△E_S1-T1²）数值越大,反系间窜越速率越大.计算表明八个分子都可能是高效的热活化延迟荧光分子.本文提出了一条高效热活化延迟荧光分子的设计策略,即分离HOMO和LUMO的分布和增加HOMO的离域性能够有效地减小S₁-T₁能差.     

Investigation of magneto-optical effect in transverse magnetic field in He

The non-linear Voigt effect has been studied in He discharge under resonance laser interaction with the He transition. The range of non-linear signal existence was determined. The contribution of the lower and upper states to the overall signal was analyzed. The cross-section for depolarizing collisions with ground state He atoms was estimated for the 3³ D _2,3 He state. Received: 16 June 1998 / Received in final form: 14 December 1998     

The General Crossing Relation for Boundary Reflection Matrix

In this aper, we give the general crossing relation for boundary reflection matrix R(β) associated A_n-1⁽¹⁾ type S-matrix. We also use the first nontrivial extended crossing relation to determine the scalar factor of R(β) which is the rational diagonal solution to the boundary Yang-Baxter equation in the case of l=2 and n=3.     

YS-50阳离子色谱柱抑制电导法测定河水中阳离子

建立了ShodexICYS-50阳离子色谱柱测定河水中阳离子的离子色谱方法。以甲基磺酸(4mmol/L)为淋洗液,流速为1mL/min,抑制电导法检测,每个样品的分析时间为20min。在优化的实验条件下,Na+、NH4+、K+、Mg2+、Ca2+的检出限分别为1.30、1.44、3.18、2.31、5.17μg/L;加标回收率为91.24%～104.8%。并将此色谱柱与DionexIonpacCS12A进行分析比较,两根柱子的检测结果数据一致。研究结果表明,方法简便、快速、准确可靠,适合对河水此类复杂样品的检测。     

Bounding the crossing number of a graph in terms of the crossing number of a minor with small maximum degree

We show that if G has a minor M with maximum degree at most 4, then the crossing number of G in a surface Σ is at least one fourth the crossing number of M in Σ. We use this result to show that every graph embedded on the torus with representativity r ≥ 6 has Klein bottle crossing number at least ⌊2r/3⌋²/64. © 2001 John Wiley & Sons, Inc. J Graph Theory 36: 168–173, 2001     

Crossing numbers of graph embedding pairs on closed surfaces

We shall prove that any two graphs G₁ and G₂ can be embedded together on a closed surface of genus g with at most 4g · β(G₁) · β(G₂) crossing points on their edges if they are embeddable on the surface, where β(G) stands for the Betti number of G, and show several observations on crossings of graph embedding pairs. © 2000 John Wiley & Sons, Inc. J Graph Theory 36: 8–23, 2001     

Entropy-Based Shear Stress Distribution in Open Channel for All Types of Flow Using Experimental Data

Korean river design standards set general design standards for rivers and river-related projects in Korea, which systematize the technologies and methods involved in river-related projects. This includes measurement methods for parts necessary for river design, but does not include information on shear stress. Shear stress is one of the factors necessary for river design and operation. Shear stress is one of the most important hydraulic factors used in the fields of water, especially for artificial channel design. Shear stress is calculated from the frictional force caused by viscosity and fluctuating fluid velocity. Current methods are based on past calculations, but factors such as boundary shear stress or energy gradient are difficult to actually measure or estimate. The point velocity throughout the entire cross-section is needed to calculate the velocity gradient. In other words, the current Korean river design standards use tractive force and critical tractive force instead of shear stress because it is more difficult to calculate the shear stress in the current method. However, it is difficult to calculate the exact value due to the limitations of the formula to obtain the river factor called the tractive force. In addition, tractive force has limitations that use an empirically identified base value for use in practice. This paper focuses on the modeling of shear-stress distribution in open channel turbulent flow using entropy theory. In addition, this study suggests a shear stress distribution formula, which can easily be used in practice after calculating the river-specific factor T. The tractive force and critical tractive force in the Korean river design standards should be modified by the shear stress obtained by the proposed shear stress distribution method. The present study therefore focuses on the modeling of shear stress distribution in an open channel turbulent flow using entropy theory. The shear stress distribution model is tested using a wide range of forty-two experimental runs collected from the literature. Then, an error analysis is performed to further evaluate the accuracy of the proposed model. The results reveal a correlation coefficient of approximately 0.95–0.99, indicating that the proposed method can estimate shear-stress distribution accurately. Based on this, the results of the distribution of shear stress after calculating the river-specific factors show a correlation coefficient of about 0.86 to 0.98, which suggests that the equation can be applied in practice.     

Unraveling the Efficiency of Thioxanthone Based Triplet Sensitizers: A Detailed Theoretical Study

Photochemical activation by triplet photosensitizers is highly expedient for a green focus society. In this work, we have theoretically probed excited state characteristics of thioxanthone and its derivatives for their triplet harvesting efficiency using density functional theory (DFT) and time-dependent density functional theory (TDDFT). Absorption and triplet energies corroborate well with the available experimental data. Our results predict that both the S₁ and T₁ states are π-π^* in nature, which renders a high oscillator strength for S₀ to S₁ transition. Major triplet exciton conversion occurs through intersystem crossing (ISC) channel between the S₁ (¹π-π^*) and high energy ³n- π^* state. Apart from that, there is both radiative and non-radiative channel from S₁ to S₀, which competes with the ISC channel and reduces the triplet harvesting efficiency. For thioxanthones with −OMe (Me=Methyl) or −F substitution at 2 or 2’ positions, the ISC channel is not energetically feasible, causing sluggish intersystem crossing quantum yield (Φ_ISC). For unsubstituted thioxanthone and for isopropyl substitution at 2’ position, the S₁-T₁ gap is slightly positive ( ), rendering a lower triplet harvesting efficiency. For systems with −OMe or −F substitution at 3 or 3’ position of thioxanthone, because of buried π state and high energy π^* state, the S₁-³nπ^* gap becomes negative. This leads to a high Φ_ISC (>0.9), which is key to being an effective photocatalyst.     

Theoretical studies on excited-state properties and luminescence mechanism of a Carbene–Metal–Amide Au(I) complex with thermally activated delayed fluorescence

Two-coordinate Carbene−Metal−Amide (CMA) complexes with thermally activated delayed fluorescence (TADF) have attracted much attention owing to their excellent luminescence properties and potential applications in organic light-emitting devices. However, the luminescence mechanism remains unclear. Herein, we took one CMA Au(I) complex as an example and investigate its relevant photophysics using both density functional theory (DFT) and time-dependent DFT methods with a polarizable continuum model. The calculated absorption and emission spectra agree with the experimental data and the S₁ and T₁ states show mixed ligand to ligand charge transfer (CT) and ligand to metal CT characters. Small spatial overlap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) minimizes the energy difference between the S₁ and T₁ states (ΔE_ST). Properly large spin-orbit coupling promotes the reverse intersystem crossing (rISC) process. At 300 K, the rISC process is much more efficient than the T₁ phosphorescent emission, which leads to the TADF emission.     

Sulfur Monoxide Release and Capture: A Computational Study

Thermolysis of thiirane oxide leads to production of highly reactive sulfur monoxide. The liberated SO can in turn be trapped with a diene scavenger forming dihydrothiophene oxide. Since the intermediate diatomic possesses a triplet ground state, the SO transfer can proceed on two spin-state surfaces. Here, we study the competition between singlet concerted and stepwise triplet diradical mechanisms utilizing the M06-2X density functional as well as CCSD(T) and MRCI+Q wavefunction theories. We find that the decomposition of thiirane oxide prefers to pass through a triplet diradical intermediate that becomes accessible from a nearby minimum energy crossing point (MECP). Hence, the thermolysis of thiirane oxide is expected to predominantly release triplet ground state sulfur monoxide in agreement with previous experimental reports. The addition of ³SO to 1,3-butadiene initially generates an allylic diradical, that ring-closes to a thiirane oxide through another MECP, and a subsequent rearrangement gives access to the final product.