Theoretical Study on the Tripletsensitized Photolysis of 2,5-Dimethylfuran

1 INTRODUCTION Photosensitization of the furans has once been a region of very active study in experiments[1～7]. As regards the reaction of 2,5-dimethylfuran in this work, however, it proceeds through carbene intermediate leading to the major product and also there are some minor reactions through diradical intermediate[2d]. Because of the symmetry of 2,5-dimethylfuran, the bond breakage between O atom and two adjacent carbon atoms are equal to each other. Thus there is only one bond br…     

2-甲基噻吩光异构化成3-甲基噻吩的理论研究

用CASSCF方法以6-31G基组研究了2-甲基噻吩光异构化为3-甲基噻吩的光化学反应和基态(S₀)及三重激发态(T₁)的相关势能面.反应主要发生在三重态(T₁)上,其间经历了两个双自由基,1个三元环中间体及4个过渡态.沿着反应路径找到了2个T₁/S₀势能面交叉点,其结构都类似于双自由基.在第二个T₁/S₀势能面交叉点附近由T₁向S₀的系间窜越(ISC)最为有利.     

A theoretical study on the low-lying excited states of 2,2':5',2'-terthiophene and 2,2':5',2':5',2'-quaterthiophene.

The nature and properties of the low-lying singlet and triplet valence excited states of 2,2':5',2'-terthiophene (terthiophene) and 2,2':5',2':5',2'-quaterthiophene (tetrathiophene) are discussed on the basis of high-level ab initio computations. The spectroscopic features determined experimentally for short alpha-oligothiophenes are rationalised on theoretical grounds. Special attention is devoted to the nonradiative decay process through intersystem crossing (ISC) from the singlet to the triplet manifold, which is known to be relatively less efficient in tetrathiophene. Along the geometry relaxation of the S1 state of terthiophene, the S1 and T2 states become degenerate, which leads to a favourable situation for the occurrence of ISC. The parallel process is expected to be less favoured in tetrathiophene because of the less efficient spin-orbit coupling and the increase of the S1-T2 energy gap.     

Ru催化N2与H2反应合成氨的两态反应机理

采用密度泛函理论(DFT)UB3LYP方法对Ru在单重态、三重态及五重态势能面上催化N_2与H_2反应合成氨的两态反应机理进行理论研究,发现该反应为典型的两态反应。计算得到最低能量交叉点(MECP)处自旋-轨道耦合常数(H_(soc))及双程系间窜越几率(P~(ISC)),MECP1:H_(soc)=508.34 cm~(-1),P_2~(ISC)=0.85,MECP9:H_(soc)=269.21 cm~(-1),P_2~(ISC)=0.27。运用能量跨度模型(energetic span model)确定Ru催化合成氨反应的转化频率(TOF)决速过渡态(TDTS)为~3TS2-3,TOF决速中间体(TDI)为~3IM9。     

Ab initio studies for the photodissociation mechanism of hydroxyacetone

The reaction pathways for CH(3)COCH(2)OH (hydroxyacetone) photodissociation on the low-lying electronic states have been studied with use of the CASSCF energy gradient techniques. The S(0)/S(1) and S(1)/T(1) intersection points were determined by the state-average CASSCF method. Two main reaction pathways, which are possible to the photodissociation, have been studied. It has been found that the mechanism is stepwise, and belongs to Norrish type-I reaction. The n --> pi* excitation leads to the first excited singlet state, followed by the intersystem crossing from S(1) to T(1). On the T(1) potential energy surface, the system can dissociate adiabatically to CH(3)(x) +COCH(2)OH( x) and CH(3)CO(x)+CH(2)OH(x). The COCH(2)OH(x) and CH(3)CO(x) radicals can further dissociate into CO, OH, and other fragments. Our calculated results are in good agreement with recent experimental results.     

非血红素铁超氧化物活化丙烯分子多态反应机理的理论研究

采用密度泛函DFT-B3LYP理论对非血红素铁超氧化物活化丙烯分子多态反应机理进行了探讨. 研究结果表明氢原子抽取过程遵守单态反应机制,主要在基态高自旋七重态势能面进行,且具有较低活化能（ΔG^≠=65.6 kJ·mol^-1）,非血红素铁超氧化物可以作为有效氧化剂抽取氢原子。单态反应机制可能归因于近来建议的交换-加强反应原则（EER,铁中心具有较大交换稳定作用）。对于O-O键的活化,在CASSCF（10,8）/6-31+G（d）//TZVP水平下,势能面交叉区内,高自旋七重态（S₁）和五重态（Q₀）的自旋-轨道耦合（SOC）常数分别为2.26和2.19 cm^-1。轨道分析表明两条发生翻转自旋轨道具有相同空间组成（π_sub^*）,SOC禁阻,因此通过SOC作用反应体系不可能有效地从七重态（S=3）势能面系间穿越到五重态（S=2）势能面,系间穿越可能发生在反应最后的退出阶段。     

非血红素铁超氧化物活化丙烯分子多态反应机理的理论研究

采用密度泛函DFT-B3LYP理论对非血红素铁超氧化物活化丙烯分子多态反应机理进行了探讨.研究结果表明氢原子抽取过程遵守单态反应机制,主要在基态高自旋七重态势能面进行,且具有较低活化能（ΔG^≠=65.6 kJ·mol^-1）,非血红素铁超氧化物可以作为有效氧化剂抽取氢原子。单态反应机制可能归因于近来建议的交换-加强反应原则（EER,铁中心具有较大交换稳定作用）。对于O-O键的活化,在CASSCF（10,8）/6-31+G（d）//TZVP水平下,势能面交叉区内,高自旋七重态（S₁）和五重态（Q₀）的自旋-轨道耦合（SOC）常数分别为2.26和2.19 cm^-1。轨道分析表明两条发生翻转自旋轨道具有相同空间组成（π_sub^*）,SOC禁阻,因此通过SOC作用反应体系不可能有效地从七重态（S=3）势能面系间穿越到五重态（S=2）势能面,系间穿越可能发生在反应最后的退出阶段。     

Theoretical study of the photochemical reaction mechanism of bicyclo[4.1.0]hept‐2‐ene upon direct photolysis

Ab initio multiconfigurational CASSCF/MP2 method with the 6‐31G* basis set has been employed in studying the photochemistry of bicyclo[4.1.0]hept‐2‐ene upon direct photolysis. Our calculations involve the ground state (S₀) and excited states (S₁, T₁, and T₂). The ground‐state reaction pathways corresponding to the formation of the six products derived from bicyclo[4.1.0]hept‐2‐ene via two important diradical intermediates (D1 and D2) were mapped. It was found that there are various crossing points (conical intersections and singlet–triplet crossings) in the regions near D1 and D2. These crossing points imply that direct photolysis can lead to two possible radiationless relaxation routes: (1) S₁ → S₀, (2) S₁ → T₂ → T₁ → S₀. Computation indicates that the second route is not a competitive path with the first route during direct photolysis. The first route is initiated by barrierless cyclopropane bond cleavage to form two singlet excited diradical intermediates, followed by efficient decay to the ground‐state surface via three S₁/S₀ conical intersections in the regions near the diradical intermediates. All six ground‐state products can be formed via the three conical intersections almost without barrier after the decays. The barriers separating the diradical minima on S₁ from the S₁/S₀ conical intersections were found to be very small with respect to the vertical excitation energy, which can explain why the product distribution is independent of excitation wavelength. Triplet surfaces are not involved in the first route, which agrees with the fact that the product contribution was unchanged by the addition of naphthalene. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

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.     

含不同基团偶氮苯化合物的合成及其光致异构化性质

以苯胺或对硝基苯胺为起始原料,通过重氮偶合法合成了4种分别含有硝基、氨基和不同数目偶氮基的偶氮苯化合物(1~4),其结构经¹H NMR和FT-IR确证。研究了1~4在紫外灯(12 W)照射下随时间变化的UV-Vis谱图。结果表明：含有给电子基团(NH₂)偶氮苯的光致异构化速率较含有吸电子基团（NO₂）时更快,NO₂对分子的异构化有一定抑制作用;分子中偶氮基的数目增加时,顺反异构化过程也受到影响。     

Theoretical Investigation of the Reaction Mechanism of the Photoisomerization of 1,2‐Dihydro‐1,2‐azaborine

The photoisomerization of 1,2‐dihydro‐1,2‐azaborine was investigated by high‐level multireference ab initio and density functional theory calculations. The intermediates (IMs) and transition states (TSs) on the S₀ and S₁ states were optimized using the state‐averaged complete active space self‐consistent field method. The multireference configuration interaction method with the Davidson correction was used to obtain accurate energetics. Moreover, the conical intersections (CIs), which play a crucial role in photoisomerization, were also optimized. On the basis of the calculation results, the most favorable proposed reaction pathway is as follows: reactant→Franck‐Condon region→TS₁→CI→IM₀→TS_0P→product. The product was not directly formed through the CI, and the IM₀ existed on the S₀ state. These results show that the isomerization of 1,2‐dihydro‐1,2‐azaborine involves both photoreactions and thermal reactions. The calculated results clarify recent experimental observations.     

Theoretical Study of the Photochemical Reaction Mechanism of Bicyclo [4.1.0 ] heptane

IntroductionPhotochemical reactions, which involve a three-membered ring, have been of great interest to experi-mental photochemists[1—10]. A main reason for thisphenomenon is that the cyclopropane ring exhibits somereaction characteristics of double bon…     

气相中Ir＋循环催化N2O与CO反应机理的理论研究

采用密度泛函UB3LYP方法和Stuttgart赝势基组, 计算研究了气相中循环催化N2O ＋CO →N2 ＋CO2 反应的微观机理. 通过对相关物种亲氧性的计算, 证明了Ir＋循环催化作用在热力学上是可行的. 不同自旋态反应势能面的计算结果表明, 循环催化的两步反应均为自旋禁阻反应, 各存在不同自旋态势能面的交叉, 并运用Yoshizawa的内禀坐标单点垂直激发计算的方法找出了势能面交叉点; 两步反应均为放热反应, 总放热量为358.9 kJ•mol－1.     

Theoretical Study on Photoisomerization Mechanisms of Diphenyl-Substituted N,C-Chelate Organoboron Compounds

N,C-chelate organoboron compounds are widely employed as photoresponsive and optoelectronic materials due to their efficient photochromic reactivity. It was found in experiments that two diphenyl-substituted organoboron compounds, namely B(ppy)Ph₂ (ppy=2-phenylpyridyl) and B(iba)Ph₂ (iba=N-isopropylbenzylideneamine), show distinct photochemical reactivity. B(ppy)Ph₂ is inert on irradiation, whereas B(iba)Ph₂ undergoes photoinduced transformations, yielding BN-cyclohepta-1,3,5-triene via a borirane intermediate. In this work, the complete active space self-consistent field and its second-order perturbation (CASPT2//CASSCF) methods were used to investigate the photoinduced reaction mechanisms of B(ppy)Ph₂ and B(iba)Ph₂. The calculations showed that the two compounds isomerize to borirane in the same way by passing a transition state in the S₁ state and a conical intersection between the S₁ and S₀ states. The energy barriers in the S₁ state of 0.54 and 0.26 eV for B(ppy)Ph₂ and B(iba)Ph₂, respectively, were explained by analyzing the charge distributions of minima in S₀ and S₁ states. The results provide helpful insights into the excited-state dynamics of organoboron compounds, which could assist in rational design of boron-based photoresponsive materials.     

Synthesis,Photoisomerization, Antioxidant Activity,and Lipid-Lowering Effect of Ferulic Acid and Feruloyl Amides

The Ugi four-component reaction employing naturally occurred ferulic acid (FA) is proposed as a convenient method to synthesize feruloyl tertiary amides. Applying this strategy, a peptoid-like derivative of ferulic acid (FEF77) containing 2 additional hydroxy-substituted aryl groups, has been synthesized. The influence of the configuration of the double bond of ferulic acid and feruloyl amide on the antioxidant activity has been investigated thanks to light-mediated isomerization studies. At the cellular level, both FA, trans and cis isomers of FEF77 were able to protect human endothelial cord vein (HECV) cells from the oxidative damage induced by exposure to hydrogen peroxide, as measured by cell viability and ROS production assays. Moreover, in steatotic FaO rat hepatoma cells, an in vitro model resembling non-alcoholic fatty liver disease (NAFLD), the molecules exhibited a lipid-lowering effect, which, along with the antioxidant properties, points to consider feruloyl amides for further investigations in a therapeutic perspective.     

多共振热激活延迟荧光过程的理论研究

本工作借助第一性原理和动力学演化,系统地研究了四个叔丁基-咔唑及吩噻嗪取代的硼-氮化合物(BCz-BN、2PTZ-BN、Cz-PTZ-BN和2Cz-PTZ-BN)的多共振热激活延迟荧光的高效发光机制.结果表明上述分子T₁与T₂间的内转换速率远大于其它辐射与非辐射速率,同时T₂到S₁的反向系间窜越速率也高于T₁到S₁的反向系间窜越速率,因此其多共振热激活延迟荧光过程应遵循T₁→T₂→S₁→S₀的路径.进一步动力学演化表明,T₁与T₂之间的内转换主要发生在演化初期,随着时间的推移,能量逐渐由T₂向S₁转移,并最终在S₁完成荧光发射.上述研究揭示了多共振延迟荧光的微观本质,为未来设计及合成新的多共振热激活延迟荧光分子提供了理论依据.     

Theoretical study of lanthanide-based in vivo luminescent probes for detecting hydrogen peroxide

The 4f-4f emissions from lanthanide trication (Ln³⁺) complexes are widely used in bioimaging probes. The emission intensity from Ln³⁺ depends on the surroundings, and thus, the design of appropriate photo-antenna ligands is indispensable. In this study, we focus on two probes for detecting hydrogen peroxide, for which emission intensities from Tb³⁺ are enhanced chemo-selectively by the H₂O₂-mediated oxidation of ligands. To understand the mechanism, the Gibbs free energy profiles of the ground and excited states related to emission and quenching are computed by combining our approximation—called the energy shift method—and density functional theory. The different emission intensities are mainly attributed to different activation barriers for excitation energy transfer from the ligand-centered triplet (T1) to the Tb³⁺-centered excited state. Additionally, quenching from T1 to the ground state via intersystem crossing was inhibited by intramolecular hydrogen bonds only in the highly emissive Tb³⁺ complexes. © 2018 Wiley Periodicals, Inc.     

Mechanistic Investigations on the Photoisomerization Reactions of 1,2‐Dihydro‐1,2‐Azaborine

The mechanisms of the photochemical isomerization reactions were investigated theoretically by using a model system of 1,2‐dihydro‐1,2‐azaborine with the CAS(6,6)/6‐311G(d,p) and MP2‐CAS‐(6,6)/6‐311++G(3df,3pd)//CAS(6,6)/6‐311G(d,p) methods. Three reaction pathways, which lead to three kinds of photoisomers, have been examined. The structures of the conical intersections, which play a decisive role in such photorearrangements, were obtained. The thermal (or dark) reactions of the reactant species have also been examined by using the same level of theory to assist in providing a qualitative explanation of the reaction pathways. The model investigations suggest that the preferred reaction route for 1,2‐dihydro‐1,2‐azaborine, which leads to the Dewar 1,2‐dihydro‐1,2‐azaborine photoproduct, is as follows: reactant→Franck–Condon region→conical intersection→photoproduct. The results obtained allow a number of predictions to be made.