光致噻吨酮与胺类、酚类、醇类的电子转移和氢转移反应

利用激光闪光光解方法研究了一系列胺类、酚类、醇类在脱氧乙腈中猝灭噻吨酮(TX)三重态的反应,得到了相应的瞬态吸收光谱和猝灭速率常数(kq).通过对光谱演变特性的分析,推断出三重态噻吨酮与不含有活泼氢的胺发生了电子转移反应,与含有活泼氢的胺发生了电子-质子转移反应.三重态噻吨酮与酚类、醇类反应中观察到噻吨酮加氢自由基的生成,据此推断出三重态噻吨酮与酚类、醇类发生了氢转移反应.胺类的猝灭速率常数随着反应自由能变(ΔG)的增大而减小,说明电子转移影响了噻吨酮三重态的猝灭.酚类的猝灭速率常数先随ΔG增大而减小,后随酚阳离子的酸性增强逐渐增大,可能是猝灭过程中电子转移影响减弱的同时氢转移影响逐渐增强.醇类的猝灭速率常数随着醇的α-C—H键能的增大而减小,说明α-C—H键能是影响噻吨酮三重态猝灭的关键因素.比较以前研究的胺类、酚类、醇类与三重态呫吨酮(XT)、芴酮(FL)反应的结果可知,由于分子结构差异性的影响,相关的猝灭速率常数按照呫吨酮、噻吨酮、芴酮的顺序逐渐减小.     

芳香氨基酸光敏化瞬态产物的光谱学及动力学表征

运用KrF激光闪光光解瞬态吸收光谱 ,以丙酮为光敏剂 ,研究了水溶液中芳香氨基酸的光化学反应 .通过动力学分析和猝灭实验 ,鉴别了光化学反应过程中的瞬态产物 ,获取了激发三重态的瞬态吸收光谱及动力学参数 .在丙酮存在下 ,色氨酸(Trp)和酪氨酸 (Tyr)的水溶液光解 ,分别观察到Trp激发三重态、N中心色氨酸自由基 (Trp/N·)和酪氨酸的酚氧自由基 (Tyr/O·) ,阐述了二者是丙酮三重态与Trp ,Tyr分别通过三重态 三重态 (T T)激发能转移和电子转移生成 ;苯丙氨酸 (Phe)不能与丙酮三重态进行激发能转移和电子转移 .进一步 ,在色氨酰酪氨酸 (Trp Tyr)敏化光解过程中 ,观察到分子内的电子转移 ,即Trp/N· Tyr→Trp Tyr/O·自由基的生成过程 .     

可见光诱导下喹喔啉酮与吡咯衍生物的氧化偶联（英文）

发展了一种区域选择性的喹喔啉酮3-位氧化偶联富电子吡咯衍生物的方法.以Mes-Acr-Me⁺ClO₄^-(3 mol%)为光敏剂,空气氧为氧化剂,高收率得到喹喔酮与吡咯衍生物的氧化偶联产物.该方法底物的官能团适用范围广,反应高效绿色,可快速构建基于喹喔啉酮-吡咯衍生物的药物分子库.相同测试条件下的Stern-Volmer荧光淬灭实验表明缺电子芳烃1-甲基喹喔啉酮对光敏剂的淬灭速率常数K_q=1.2×10⁹ L·mol^-1·s^-1,而富电子芳烃1-甲基吡咯/1-甲基吲哚的淬灭常数约为1.06～1.07×10¹⁰ L·mol^-1·s^-1,后者的荧光淬灭速率几乎是前者的10倍.     

2-蒽醌磺酸三重态与高聚鸟嘌呤核苷酸相互作用的激光光解

利用248 nm(KrF)激光光解技术研究了乙腈-水(97︰3)溶液中2-蒽醌磺酸激发三重态电子转移光氧化高聚鸟嘌呤核苷酸的原初过程.直接检测了上述电子转移氧化反应生成的阴阳离子自由基对的瞬态吸收光谱,分别获取了各自的表观反应速率常数,协同反应的自由能变化,阐明了电子转移反应的三重态机理.     

不同极性溶剂中2-蒽醌磺酸钠三重态特征瞬态吸收谱及动力学研究

利用纳秒级激光光解瞬态吸收光谱装置－248nm(KrF）激光光解研究了水和乙腈溶液中2－蒽醌磺酸钠激发三重态的瞬态吸收光谱。水溶液中纯将的AQS激发三重态的特征吸收在580nm处；确定了AQS激发三重态的特征吸收普形、范围在水和乙腈溶液中的相似性；2－蒽醌磺酸钠激发三重态的半衰期在乙腈中为10.7μs，在水中却为为0.5μs；测定了2－蒽醌磺酸钠激发三重态衰减动力学参数。     

2(1H)-喹喔啉系列衍生物的质谱研究

2(1H)-喹喔啉衍生物是一类重要的杂环化合物,可应用于药物,如用作受体及受体拮抗剂、杀菌剂等;还可用作植物生长调节剂、荧光探针等诸多领域.本文研究了一系列喹喔啉衍生物的电子轰击质谱,得到了一些裂解规律.     

过硫酸铵促进喹喔啉-2(1H)-酮三氟甲基化反应

报道了温和条件下,过硫酸铵促进喹喔啉-2(1H)-酮与CF3SO2Na三氟甲基化制备3-三氟甲基喹喔啉-2(1H)-酮类的反应,开发了一种绿色、高效制备3-三氟甲基喹喔啉-2(1H)-酮衍生物的方法.该方法对不同取代的喹喔啉-2(1H)-酮衍生物具有较好的适用性,均以较高的产率得到相应的目标产物.与已有方法相比,本方法具有底物适用范围广、产率高、实验操作简便等优点,为3-三氟甲基喹喔啉-2(1H)-酮的制备提供了有效的路径.     

芘四磺酸钠水溶液激光闪光光解机理

采用激光闪光光解-瞬态吸收光谱技术研究了355nm激光作用下芘四磺酸钠(PyTS)水溶液的光化学反应机理及其产生水合电子的动力学行为.研究首次发现PyTS水溶液激发单线态(PyTS1*)在260nm、激发三线态(PyTS3*)在300nm及阴离子自由基(PyTS-?)在330nm处的特征吸收峰;分析了生成的水合电子(e-aq)的主要反应途径包括自猝灭反应及与PyTS的反应,得到水合电子与PyTS反应的准一级速率常数为2.7′105s-1;并计算得到在此实验条件下,PyTS水溶液经双光子吸收产生的水合电子量子产率为3.2′10-2.     

光/电催化喹喔啉酮官能团化反应研究进展

喹喔啉酮作为重要的含氮杂环骨架,广泛应用于抗菌化合物、抗肿瘤药物、半导体材料中.因此,开发新方法合成不同官能团化喹喔啉酮以丰富其结构多样性在近年来广受关注.在众多合成方法中,喹喔啉酮的直接C–H官能团化是一类步骤经济性较高、简便高效地构建喹喔啉酮衍生物的重要方法.近年来,光催化、电催化和光电催化技术已发展成为现代有机合成中强有力的绿色合成工具,可以有效利用光能或者电能促进有机化学转化,减少传统有机反应中的高能耗.过去几年,化学工作者在光/电催化喹喔啉酮的直接C–H官能团化反应方面进行了大量研究,开发了系列不同官能团化喹喔啉酮的绿色合成方法.本文系统总结了喹喔啉酮的光/电催化官能团化研究最新进展,重点讨论了光/电催化下自由基历程的喹喔啉酮C–H键直接官能团化反应,反应类型主要包括喹喔啉酮的3-芳基化、3-烷基化、3-氟烷基化、3-烷氧基化、3-酰化、3-氨基化、3-膦酰化、3-巯基化、3-硅烷基化和环化反应等方面,这将有助于理解光/电催化喹喔啉酮官能团化反应.反应在温和条件下可以成功产生各种碳中心或杂原子为中心的自由基,这些自由基进一步与喹喔啉酮的3-位进行加成反应,进而开发出众多有效的方法来合成不同官能团化的喹喔啉酮.这些条件温和的反应方法已经有部分成功应用于合成具有重要生物活性的喹喔啉酮化合物.此外,药物中常见的一些重要官能团,例如三氟甲基和二氟甲基等可以顺利地引入到喹喔啉酮骨架结构,这些研究为喹喔啉酮衍生物的生物活性相关研究奠定了基础.本文还对当前光/电催化喹喔啉酮官能团化反应所面临的挑战和未来发展作了展望和总结,期待在不久的将来,有机合成工作者能基于喹喔啉酮的C–H键直接官能团化开发更多不同类型的新反应.另一方面,需要进一步开发新型的非均相可见光催化剂,实现光催化剂的回收与再利用,进一步降低反应成本,促进其在药物开发、功能材料合成等应用方面的发展.     

维生素K3的激发三重态与色氨酸、酪氨酸电子转移氧化反应的激光闪光光解研究

利用时间分辨的激光闪光光解技术研究了乙腈-水混合溶液(1:1,V/V)中2-甲基萘醌(通常称为维生素K3)的激发三重态对色氨酸、酪氨酸的光敏氧化机理.通过瞬态吸收光谱的变化可以推断维生素K3的激发三重态可以与色氨酸、酪氨酸发生电子转移反应,反应形成的维生素K3阴离子自由基的吸收峰可以直接从瞬态吸收谱图中观察到.维生素K3与色氨酸、酪氨酸的电子转移反应的速率分别为1.1×109和0.6×109L·mol-1·s-1.吉布斯自由能(ΔG)的计算结果表明维生素K3的激发三重态与色氨酸、酪氨酸电子转移反应在热力学上是可行的.     

Triplet excimers of fluoroquinolones in aqueous media

Generation of triplet eximers of 6-fluoro-7-piperazinyl-quinolone-3-carboxylic acids (FQs) have been detected in aqueous media using laser flash photolysis (LFP). These transient species (SS) are generated by self-quenching reactions of FQ triplet excited states such as pefloxacin (PFX), norfloxacin (NFX), the N-acetylated form of NFX (ANFX), and its methyl ester (EANFX) with their ground states. In this context, self-quenching rate constants in the range of (1-7) × 10(8) M(-1) s(-1) were determined. The triplet excimers show transient absorption spectra with λ(max) ca. 710 nm for SS(NFX), 740 nm for SS(PFX), and 620 nm for SS(ANFX) and E(ANFX), which are red-shifted with respect to their predecessors triplet excited states. These excimers can be also observed in the presence of phosphate buffer (PB). Experiments performed with NFX and ANFX at different PB concentrations showed that deprotonation processes are not involved in the generation of SS. The triplet multiplicity of the FQ excimers was confirmed by energy transfer reactions with naproxen. The correlation between fluorescence, intersystem crossing, excimer and photodegradation quantum yields of (A)NFX indicated that FQ self-quenching reactions are mainly a deactivation pathway. On the other hand, generation of FQ radical anions absorbing at λ(max) ca. 620 nm has been observed by an efficient electron transfer reaction from Trp to NFX, PFX, and ANFX (rate constants ca. 1 × 10(9) M(-1) s(-1)).     

Proton and electron transfer in the excited state quenching of phenosafranine by aliphatic amines

The quenching of the excited singlet and triplet states of phenosafranine by aliphatic amines was investigated in acetonitrile and methanol. The rate constants for the quenching of the excited singlet state depend on the one-electron redox potential of the amine suggesting a charge transfer process. However, for the triplet state, quenching dependence on the redox potential either is opposite to the expectation or there is not dependence at all. Moreover, in MeOH the first-order rate constant for the decay of the triplet state, k(obs) presents a downward curvature as a function of the amine concentration. This behavior was interpreted in terms of the reversible formation of an intermediate excited complex, and from a kinetic analysis the equilibrium constant K(exc) could be extracted. The log K(exc) shows a linear relationship with the pKb of the amine. On the other hand, for the triplet state quenching in acetonitrile k(obs) varies linearly with the amine concentration. Nevertheless, the quenching rate constants correlate satisfactorily with pKb and not with the redox potential. The results were interpreted in terms of a proton transfer quenching, reversible in the case of MeOH and irreversible in MeCN. This was further confirmed by the transient absorption spectra obtained by laser flash photolysis. The transient absorption immediately after the triplet state quenching could be assigned to the unprotonated form of the dye. At later times the spectrum matches the semireduced form of the dye. The overall process corresponds to a one-electron reduction of the dye mediated by the deprotonated triplet state.     

Primary processes in the photosensitized polymerization of cationic monomers

A detailed time-resolved laser spectroscopy investigation has been carried out on the electron transfer reactions of substituted thioxanthone derivatives with diphenyliodonium (Ph-I⁺) salts having different metal halide counterions (MX^?_n). Quenching of thioxanthones' triplet state has been followed under various conditions, by changing the number and nature of substituents on the thioxanthone skeletone, using anion with different nucleophilicity and employing different solvents, namely methanol and acetonitrile. A Photosensitization mechanism is proposed involving an electron transfer from thioxanthone to diphenyliodonium salt. The absorption spectra of the thioxanthone's excited state and the formed new transient are recorded and the rate constants of the excited state processes are measured. The triplet state of thioxanthone derivatives has been quenched by cationically polymerizable monomers and the quantum yield of the major processes has been evaluated. Photolytic experiments have been performed to measure the extent of acid formation. Form photopolymerization experiments using different photoinitiating systems, the rate of polymerization and percentage of monomer conversion have been determined. Both the reactivity in the excited states and the nucleophilicity of the anions affect the efficiency of the photopolymerization reaction.     

Evaluation of Transient Absorption Spectra of N, N, N′, N′- Tetra - ( p -methylphenyl ) - 4, 4′- diamino - 1, 1′- diphenyl Ether ( TPDAE ) for Electron Transfer from TPDAE to Fullerenes ( C60 / C70 ) by Laser Flash Photolysis

Photoinduced electron transfer processes between fullerenes (C60 / C70) and N, N, N′, N′- tetra - ( p-methylphenyl ) - 4, 4′- diamino - 1, 1′- diphenyl ether ( TPDAE ) have been studied by nanosecond laser flash photolysis. Quantum yields and rate constants of electron transfer from TPDAE to excited triplet state of fullerenes (C60 / C70 ) in benzonitrile have been evaluated by observing the transient absorption bands in the near-IR region where the excited triplet state, radical anion of fullerenes ( C60 / C70 ) and radical cations of TPDAE appear.     

Evaluation of Transient Absorption Spectra of N, N, N, N- Tetra - ( p -methylphenyl ) - 4, 4- diamino - 1, 1- diphenyl Ether ( TPDAE ) for Electron Transfer from TPDAE to Fullerenes ( C_(60) / C_(70) ) by Laser Flash Photolysis

Fullerenes C60 and C70 have high electron affinity ( 2.6 - 2.8 ev ) and readily form anions on electronchemical reduction1, which were famous as electron acceptor in photo-excitation because of symmetrical shape, large size, and properties of its p - electron system2. After observation of molecular ferromagnetism3 in the tetrakis (dimethylamino ) ethylene salt of C60 as well as the occurrence of ultra-fast photoinduced electron transfer within the dimethyl aniline - C60 complex4, prompted us…     

Generation and decay dynamics of triplet excitons in Alq3 thin films under high-density excitation conditions

We studied the generation and decay dynamics of triplet excitons in tris-(8-hydroxyquinoline) aluminum (Alq3) thin films by using transient absorption spectroscopy. Absorption spectra of both singlet and triplet excitons in the film were identified by comparison with transient absorption spectra of the ligand molecule (8-hydroxyquinoline) itself and the excited triplet state in solution previously reported. By measuring the excitation light intensity dependence of the absorption, we found that exciton annihilation dominated under high-density excitation conditions. Annihilation rate constants were estimated to be gammaSS = (6 +/- 3) x 10(-11) cm3 s(-1) for single excitons and gammaTT = (4 +/- 2) x 10(-13) cm3 s(-1) for triplet excitons. From detailed analysis of the light intensity dependence of the quantum yield of triplet excitons under high-density conditions, triplet excitons were mainly generated through fission from highly excited singlet states populated by singlet-singlet exciton annihilation. We estimated that 30% of the highly excited states underwent fission.     

Study of acyl group migration by femtosecond transient absorption spectroscopy and computational chemistry

The primary photophysical and photochemical processes in the photochemistry of 1-acetoxy-2-methoxyanthraquinone (1a) were studied using femtosecond transient absorption spectroscopy. Excitation of 1a at 270 nm results in the population of a set of highly excited singlet states. Internal conversion to the lowest singlet npi* excited state, followed by an intramolecular vibrational energy redistribution (IVR) process, proceeds with a time constant of 150 +/- 90 fs. The 1npi* excited state undergoes very fast intersystem crossing (ISC, 11 +/- 1 ps) to form the lowest triplet pipi* excited state which contains excess vibrational energy. The vibrational cooling occurs somewhat faster (4 +/- 1 ps) than ISC. The primary photochemical process, migration of acetoxy group, proceeds on the triplet potential energy surface with a time constant of 220 +/- 30 ps. The transient absorption spectra of the lowest singlet and triplet excited states of 1a, as well as the triplet excited state of the product, 9-acetoxy-2-methoxy-1,10-anthraquinone (2a), were detected. The assignments of the transient absorption spectra were supported by time-dependent DFT calculations of the UV-vis spectra of the proposed intermediates. All of the stationary points for acyl group migration on the triplet and ground state singlet potential energy surfaces were localized, and the influence of the acyl group substitution on the rate constants of the photochemical and thermal processes was analyzed.     

富勒烯(C60／C70)与N，N，N’，N’-四-(对甲苯基)-4，4’-二胺-1，1’-二苯硒醚(TPDASe)间光诱导电子转移过程的激光光解研究

富勒烯(C60／C70)与N，N，N’，N’-四-(对甲苯基)-4，4’-二胺-1，1’-二 苯硒醚(TPDASe)间在激光光诱导条件下，发生了分子间的电子转移过程．在可见- 近红外区(600-1200nm)，观测到了TPDASe阳离子自由基、富勒烯(C60／C70)激发三 线态和阴离子自由基，在苯腈溶液中，观测瞬态谱测定了电子从TPDASe转移到富勒 烯(C60／C70)激发三线态的量子转化产率(Φet^T)和电子转移常数(Ket)．     

Reactivity of aromatic amines with triplet 1,8-dihydroxyanthraquinone: a laser flash photolysis study

The property of the lowest excited triplet states of 1,8-dihydroxyanthraquinone (DHAQ) was investigated by using time-resolved laser flash photolysis at 355nm in organic solvents, i.e. acetonitrile and cyclohexane. The transient absorption spectra of the excited triplet DHAQ were obtained in acetonitrile, which have an absorption maximum at 480nm and two broad absorption bands around 350 and 650nm. 3DHAQ(*) is efficiently quenched by triphenylamine (TPA) via photoinduced electron transfer pathway, which was testified by the finding of TPA radical cation. In addition, aniline derivatives such as N,N-dimethylaniline (DMA), 3,5,N,N-tetramethylaniline (TMA), 4-dimethylaminobenzoic acid (DMABA) and dimethyl-p-toluidine (DMT) could also quench 3DHAQ(*) rapidly. Evidence for electron transfer interaction with anilines in acetonitrile was obtained from transient spectral characterization of formed radicals. Experimental k(q) values approach the diffusion-controlled rate limit, and decrease significantly from DMT (1.85x10(10)M-1s-1) to DMABA (1.95x10(9)M-1s-1). These k(q) values depend on the charge density on the "N" atom of anilines, which could be quantified by Hammett sigma constant.     

Stepwise laser photolysis studies of beta-bond cleavage in highly excited triplet states of biphenyl derivatives having C-O bonds

Photochemical profiles of beta-bond dissociation in highly excited triplet states (Tn) of biphenyl derivatives having C-O bonds were investigated in solution, using stepwise laser photolysis techniques. The lowest triplet states (T1) were produced by triplet sensitization of acetone (Ac) upon 308-nm laser photolysis. The molar absorption coefficients of the T1 states were determined using triplet sensitization techniques. Any photochemical reactions were absent in the T1 states. Upon 355-nm laser flash photolysis of the T1 states, they underwent fragmentation, because of homolysis of the C-O bond in the Tn states from the observations of the transient absorption of the corresponding radicals. The quantum yields (Phidec) for the decomposition of the T1 states upon the second 355-nm laser excitation were determined. Based on the Phidec values and the bond dissociation energies (BDEs) for the C-O bond fission, the state energies (ERT) of the reactive highly excited triplet states (TR) were determined. It was revealed that (i) the Phidec was related to the energy difference (DeltaE) between the BDE and the ERT, and (ii) the rate (kdis) of beta-cleavage in the TR state was formulated as being simply proportional to DeltaE. The reaction mechanism for beta-bond cleavage in the TR states was discussed.