8-硝基-1-苯基-3, 3-二甲基吲哚苯骈螺吡喃的光化学

标题螺吡喃(Sp)甲醇溶液直接和二苯酮敏化光发色反应的量子产率分别是0.38和0.53.2,3-丁二酮首先猝灭三线态的光发色,然后,在较高浓度时,猝灭单线态的光反应.从敏化和猝灭反应的动力学分析,计算在直接光解中的初级光物理、光化学过程的量子产率.数据表明,Sp的三线态和单线态都有光反应活性,这与反应状态相关图分析结果相一致.三线态的参数是~3τ=2.2×10~(-3) ms,κ_r=9.13×10~4s~(-1),κ_(?)=8.27×10~4 s~(-1).而且,一旦生成激发三线态,它的光化学活性大约比激发单线态大2倍.     

单重态氧化学VII. 迷迭香中主要抗氧化成分对单重态氧的猝灭作用

本文研究了迷迭香酚和鼠尾草酚对单重态氧的猝灭作用。实验证明迷迭香酚和鼠尾草酚在甲醇中猝灭单重态氧的总速率常数K~A分别为2.51×10^7和7.19×10^6mol^1.dm^-3.s^-1, 其中化学猝灭的速率常数k~r分别为1.27×10^7和9.82×10^5mol.dm^-3.s^-1, 相应的半猝灭浓度β值为4.6×10^-3和1.6×10^-2mol.dm^-3。这是一类有实用价值的高效抗氧化剂。     

单重态氧化学 VI: 胶束中竹红菌甲素诱导的二苯基异苯并呋喃光敏氧化反应动力学

本文研究了增溶于胶束内部的HA诱导的DPBF光敏氧化动力学。测定了DPBF在不同胶束中光敏氧化总速率常数, 分别为5.12×10^9(SDS), 2.31×10^9(Triton X-100)和6.21×10^9L/mol.s(TDPB)。实验证明胶束可有效猝灭单重态氧却不猝灭HA的激发三重态, 从而导致DPBF光敏氧化双分子反应可按假一级动力学规律处理, 可求出表观速率常数为1.52×10^-^3s^-^1(SDS)或1.54×10^-^3s^-^1(Triton X-100), 相应的半寿命为7.5min, 这些结果为HA在水溶液中的光动态行为的研究提供了依据。     

单重态氧化学 VI: 胶束中竹红菌甲素诱导的二苯基异苯并呋喃光敏氧化反应动力学

本文研究了增溶于胶束内部的HA诱导的DPBF光敏氧化动力学。测定了DPBF在不同胶束中光敏氧化总速率常数, 分别为5.12×10^9(SDS), 2.31×10^9(Triton X-100)和6.21×10^9L/mol.s(TDPB)。实验证明胶束可有效猝灭单重态氧却不猝灭HA的激发三重态, 从而导致DPBF光敏氧化双分子反应可按假一级动力学规律处理, 可求出表观速率常数为1.52×10^-^3s^-^1(SDS)或1.54×10^-^3s^-^1(Triton X-100), 相应的半寿命为7.5min, 这些结果为HA在水溶液中的光动态行为的研究提供了依据。     

一种新的敏化/猝灭室温磷光: CTAB胶束中α-溴代萘敏化联乙酰的室温磷光猝灭

本文首次报道了将敏化和猝灭同时偶合在同一体系中的敏化/猝灭室温磷光新方法。体系中, CTAB胶束一方面增强α-溴代萘的室温磷光发射、α-溴代萘和联乙酰的三重态-三重态能量转移效率, 另一方面起到猝灭α-溴代萘敏化联乙酰发射的室温磷光的作用。CTAB对联乙酰的猝灭反应由三重态-三重态能量转移速率限制,求得α-溴代萘敏化联乙酰的三重态-三重态能量转移速率常数为1.76×10^9(mol.dm^-^3)^-^1s^-^1, CTAB对联乙酰的猝灭常数为7.82×10^7(mol.dm^-^3)^-^1s^-^1。详细研究了实验条件, 实现了猝灭法测定联乙酰,检测限达2.8×10^-^8mol.dm^-^3。     

品红甲亚胺染料光褪色机理研究（Ⅰ）：—与活性氧的反应能力

用紫外－可见吸收光谱和高效液相色谱研究了品红甲亚胺染料（MAD）的光褪色过程，结果表明：MAD本身不是产生活性氧（^O2,O^-2)的敏化剂，而是一个良好的活性氧的受体。敏化剂亚甲基兰（MB）孟加拉玫瑰 （RB）所产生的活性氧都对MAC的褪色有贡献，用竞争动力学实验，以二苯基苯并呋喃为竞争反应的标准物质，测定了MAD与活性氧反应的总反应速率常数（k=8.50×10^7L/mol.s)和化学反应速率常数（kR=1.49×10^7L/mol.s)结果发现猝灭过程以物理猝灭为主，RB工MB敏化MAD光氧化实验表明，^1O2是导致MAD光氧化色的主要原因。     

曙红敏化1-苄基-1,4-二氢吡啶菸酰胺光还原二苯乙二酮的反应

本文研究了曙红敏化NAD(P)H的模型化合物-1-苄基-1,4-二氢吡啶菸酰胺(BNAH)光还原二苯乙二酮的反应机制及光敏剂曙红的激发态行为。用三重态猝灭剂蒽猝灭反应的结果表明,曙红的激发单重态与激发三重态都参与了敏化反应。计算了单重态与三重态反应的量子产率及它们的反应速率常数。从氧化还原电位及激发能的数据可以预计,能量转移敏化不可能反生,而受激发的曙红将电子转移至受体二苯乙二酮这一步则很可能是光敏还原反应的起始过程。     

单重态氧化学VII. 迷迭香中主要抗氧化成分对单重态氧的猝灭作用

本文研究了迷迭香酚和鼠尾草酚对单重态氧的猝灭作用。实验证明迷迭香酚和鼠尾草酚在甲醇中猝灭单重态氧的总速率常数K~A分别为2.51×10^7和7.19×10^6mol^1.dm^-3.s^-1, 其中化学猝灭的速率常数k~r分别为1.27×10^7和9.82×10^5mol.dm^-3.s^-1, 相应的半猝灭浓度β值为4.6×10^-3和1.6×10^-2mol.dm^-3。这是一类有实用价值的高效抗氧化剂。     

金属酞菁敏化光还原硝基化合物的反应

本文研究了各种金属酞菁以及带有不同取代基的锌酞菁敏化光还原硝基化合物的反应。确定了光敏还原反应的主要产物是氨基和羟氨基化合物;羟氨基化合物与亚硝基化合物通过暗反应缩合生成偶氮N-氧化物。测定了它们的氧化还原电位和荧光量子产率。从敏化光还原反应的量子产率及荧光猝灭与硝基化合物浓度的依赖关系,计算出各种金属酞菁激发单重态与三重态的敏化效率。受激发金属酞菁将电子转移至硝基化合物是敏化光还原反应的起始过程。电子转移生成离子自由基对后,电荷分离与逆电子转移过程相互竞争。由于自旋选择规则的限制,激发三重态的敏化效率一般比激发单重态的敏化效率高。为了提高敏化光还原反应的效率,除选择三重态产率较高的敏化剂外,改变敏化剂的结构可提高敏化剂激发单重态的敏化效率,从而提高敏化光还原反应的量子产率.     

一种新的敏化/猝灭室温燐光法——CTAB胶束中α-溴代萘敏化联乙酰的室温燐光猝灭

本文首次报道了将敏化和猝灭同时偶合在同一体系中的敏化/猝灭室温烘燐新方法.体系中,CTAB胶束一方面增强α-溴代萘的室温燐光发射、α-溴代萘和联乙酰的三重态-三重态能量转移效率,另一方面起到猝灭α-溴代萘敏化联乙酰发射的室温燐光的作用.CTAB对联乙酰的猝灭反应由三重态-三重态能量转移速率限制,求得α-溴代萘敏化联乙酰的三重态-三重态能量转移速率常数为1.76×10~9(mol·dm~(-3)~(-1)S~(-1),CTAB对联乙酰的猝灭常数为7.82×10~7(mol·dm~(-3)~(-1)S~(-1).详细研究了实验条件,实现了猝灭法测定联乙酰,检测限达2.8×10~(-8)mol·dm~(-3).     

Laser induced photochromic mechanism of 3-phenyl-3-[1,2-dimethylindol-3-YL]-3H-naphtho[2,1-B]pyran

The photochromic process of 3-phenyl-3-[1,2-dimethylindol-3-yl]-3H-naphtho[2,1-b]pyran [I] has been examined with nanosecond laser flash photolysis techniques in cyclohexane and acetonitrile respectively. Both excited singlet state and triplet state are involved in the photocoloration process. The decay kinetics of photoproducts are also studied. The maximum absorption wavelength and lifetime of the transient species are solvent dependent.     

(Sensitized) photolysis of diazonium salts as a mild general method for the generation of aryl cations. Chemoselectivity of the singlet and triplet 4-substituted phenyl cations

The photolysis of a series of 4-X-benzenediazonium tetrafluoroborates is studied in MeCN. Loss of nitrogen occurs from the singlet excited state with X=H, t-Bu, and NMe2 and leads to the singlet aryl cation. This adds to the solvent yielding the corresponding acetanilides. With other substituents, ISC competes with (X=Br, CN) or overcomes (X=COMe, NO2) fragmentation and the aryl cation is formed in part or completely in the triplet state. In neat MeCN, this either abstracts hydrogen from the solvent (in most cases inefficiently) or undergoes intersystem crossing to the more stable singlet that reacts as above. In the presence of pi nucleophiles (allyltrimethylsilane or benzene), the triplet aryl cation is efficiently trapped giving substituted allylbenzenes and biphenyls, respectively. By triplet sensitization by xanthone, the triplet cation and the products from it are obtained from the whole series considered. The direct or sensitized photodecomposition of diazonium fluoroborates, substituted with both electron-donating and -withdrawing substituents, in the presence of alkenes and arenes offers an access to an alternative arylation procedure.     

Intramolecular triplet energy transfer via higher triplet excited state during stepwise two-color two-laser irradiation

We studied the energy transfer processes in the molecular array consisting of pyrene (Py), biphenyl (Ph2), and bisphthalimidethiophene (ImT), (Py-Ph2)2-ImT, during two-color two-laser flash photolysis (2-LFP). The first laser irradiation predominantly generates ImT in the lowest triplet excited state (ImT(T1)) because of the efficient singlet energy transfer from Py in the lowest singlet excited state to ImT and, then, intersystem crossing of ImT. ImT(T1) was excited to the higher triplet excited state (Tn) with the second laser irradiation. Then, the triplet energy was rapidly transferred to Py via a two-step triplet energy transfer (TET) process through Ph2. The efficient generation of Py(T1) was suggested from the nanosecond-picosecond 2-LFP. The back-TET from Py(T1) to ImT was observed for several tens of microseconds after the second laser irradiation. The estimated intramolecular TET rate from Py(T1) to ImT was as slow as 3.1 x 104 s-1. Hence, long-lived Py(T1) was selectively and efficiently produced during the 2-LFP.     

Triplet Excited States and Singlet Oxygen Production by Analogs of Red Wine Pyranoanthocyanins

During the maturation of red wines, the anthocyanins of grapes are transformed into pyranoanthocyanins, which possess a pyranoflavylium cation as their basic chromophore. Photophysical properties of the singlet and triplet excited states of a series of synthetic pyranoflavylium cations were determined at room temperature in acetonitrile solution acidified with 0.10 mol dm^?3 trifluoroacetic acid (TFA, to inhibit competitive excited state proton transfer) and at 77 K in a rigid TFA‐acidified isopropanol glass. In solution, the triplet states of these pyranoflavylium cations are efficiently quenched by molecular oxygen, resulting in sensitized formation of singlet oxygen, as confirmed by direct detection of the triplet‐state decay by laser flash photolysis and of singlet oxygen monomol emission in the near infrared. The strong visible light absorption, the relatively small singlet‐triplet energy differences, the excited state redox potentials and the reasonably long lifetimes of pyranoflavylium triplet states in the absence of molecular oxygen suggest that they might be useful as triplet sensitizers and/or as cationic redox initiators in polar aprotic solvents like acetonitrile.     

Primary photophysical properties of ofloxacin

Steady-state fluorescence has been used to study the excited singlet state of ofloxacin (OFLX) in aqueous solutions. Fluorescence emission was found to be pH dependent, with a maximum quantum yield of 0.17 at pH 7. Two pKa*s of around 2 and 8.5 were obtained for the excited singlet state. Laser flash photolysis and pulse radiolysis have been used to study the excited states and free radicals of OFLX in aqueous solutions. OFLX undergoes monophotonic photoionization from the excited singlet state with a quantum yield of 0.2. The cation radical so produced absorbs maximally at 770 nm with an extinction coefficient of 5000 +/- 500 dm3 mol-1 cm-1. This is confirmed by one-electron oxidation in the pulse radiolysis experiments. The hydrated electron produced in the photoionization process reacts with ground state OFLX with a rate constant of 2.0 +/- 0.2 x 10(10) dm3 mol-1 s-1, and the anion thus produced has two absorption bands at 410 nm (extinction coefficient = 3000 +/- 300 dm3 mol-1 cm-1) and at 530 nm. Triplet-triplet absorption has a maximum at 610 nm with an extinction coefficient of 11,000 +/- 1500 dm3 mol-1 cm-1. The quantum yield of triplet formation has been determined to be 0.33 +/- 0.05. In the presence of oxygen, the triplet reacts to form both excited singlet oxygen and superoxide anion with quantum yields of 0.13 and < or = 0.2, respectively. Moreover, superoxide anion is also formed by the reaction of oxygen with the hydrated electron from photoionization. Hence the photosensitivity due to OFLX could be initiated by the oxygen radicals and/or by OFLX radicals acting as haptens.     

THE PHOTOSENSITIZERS BENZOPHENOXAZINE and THIAZINES: COMPREHENSIVE INVESTIGATION OF PHOTOPHYSICAL and PHOTOCHEMICAL PROPERTIES

Eight differently substituted title dye compounds have been investigated regarding intersystem crossing, triplet state, fluorescence and singlet excited state pKa properties. In general, non-halogenated oxazines and thiazines as well as a mono bromooxazine show very low triplet quantum yields, phi tau (less than 0.03) and relatively long triplet lifetimes (approximately 40 microseconds) in acidic methanol. The phi tau data correlate well with known singlet oxygen yields. In basic methanol no triplet transient is observed but a significant yield of a ground state transient protonated (base dye) form is produced with a short lifetime, approximately 400 ns. Fluorescence can be seen simultaneously from both the excited base and the protonated base dye forms in basic methanol. For iodinated oxazine or thiazines, the triplet yield increases and can be as high as 0.5 (diiodo case) in acidic methanol. The triplet lifetimes are further shortened to approximately 10 microseconds compared to the non-iodinated derivatives above. The triplet yields of the iodo compounds are higher or equal to known singlet oxygen yields. In basic methanol triplet yields up to 0.2 can be seen, the triplet lifetime are shortened still further to 1 microsecond but no observable protonated form is produced (in distinction to the non-iodinated cases). Consideration is given to the correlation of triplet and singlet oxygen yields, ground and excited pKa properties, spin-orbit coupling and internal conversion properties, solvent effects, and phototherapeutic activity of these dyes.     

Ligand-Localized Triplet-State Photophysics in a Platinum(II) Terpyridyl Perylenediimideacetylide

The synthesis, electrochemistry, and photophysical behavior of a Pt(II) terpyridyl perylenediimide (PDI) acetylide (1) charge-transfer complex is reported. The title compound exhibits strong (ε ≈ 5 × 10(4) M(-1)cm(-1)) low-energy PDI acetylide-based π-π* absorption bands in the visible range extending to 600 nm, producing highly quenched singlet fluorescence (Φ = 0.014 ± 0.001, τ = 109 ps) with respect to a nonmetalated PDI model chromophore. Nanosecond transient absorption spectroscopy revealed the presence of a long excited-state lifetime (372 ns in 2-methyltetrahydrofuran) with transient features consistent with the PDI-acetylide triplet state, ascertained by direct comparison to a model Pt(II) PDI-acetylide complex lacking low-energy charge-transfer transitions. For the first time, time-resolved step-scan FT-IR spectroscopy was used to characterize the triplet excited state of the PDI-acetylide sensitized in the title compound and its associated model complex. The observed red shifts (～30-50 cm(-1)) in the C═O and C≡C vibrations of the two Pt(II) complexes in the long-lived excited state are consistent with formation of the (3)PDI acetylide state and found to be in excellent agreement with the expected change in the relevant DFT-calculated IR frequencies in the nonmetalated PDI model chromophore (ground singlet state and lowest triplet excited state). Formation of the PDI triplet excited state in the title chromophore was also supported by sensitization of the singlet oxygen photoluminescence centered at ～1275 nm in air-saturated acetonitrile solution, Φ((1)O(2)) = 0.52. In terms of light emission, only residual PDI-based red fluorescence could be detected and no corresponding PDI-based phosphorescence was observed in the visible or NIR region at 298 or 77 K in the Pt(II) terpyridyl perylenediimideacetylide.     

Photochemistry of kynurenine, a tryptophan metabolite: properties of the triplet state

Photolysis of aqueous kynurenine (KN) solutions results in the formation of triplet kynurenine TKN. In low pH solutions, triplet formation occurs with almost 100% efficiency, while in neutral solutions the triplet quantum yield is PhiT = 0.018 +/- 0.004. The dissociation constant of TKN, which is attributed to deprotonation of the anilino group, has a pKa value of 4.7. Similar triplet absorption spectra were obtained under direct and acetone-sensitized photolysis. The large difference in quantum yields as a function of pH is attributed to excited-state properties of the first excited singlet state of KN. The rate constant quenching for TKN by oxygen is kq = 2 x 10(9) M(-1) s(-1).     

Change in spin state and enhancement of redox reactivity of photoexcited states of aromatic carbonyl compounds by complexation with metal ion salts acting as Lewis acids. Lewis acid-catalyzed photoaddition of benzyltrimethylsilane and tetramethyltin via photoinduced electron transfer

The lowest excited state of aromatic carbonyl compounds (naphthaldehydes, acetonaphthones, and 10-methylacridone) is changed from the n,pi triplet to the pi,pi singlet which becomes lower in energy than the n,pi triplet by the complexation with metal ions such as Mg(ClO(4))(2) and Sc(OTf)(3) (OTf = triflate), which act as Lewis acids. Remarkable positive shifts of the one-electron reduction potentials of the singlet excited states of the Lewis acid-carbonyl complexes (e.g., 1.3 V for the 1-naphthaldehyde-Sc(OTf)(3) complex) as compared to those of the triplet excited states of uncomplexed carbonyl compounds result in a significant increase in the redox reactivity of the Lewis acid complexes vs uncomplexed carbonyl compounds in the photoinduced electron-transfer reactions. Such enhancement of the redox reactivity of the Lewis acid complexes leads to the efficient C-C bond formation between benzyltrimethylsilane and aromatic carbonyl compounds via the Lewis-acid-promoted photoinduced electron transfer. The quantum yield determinations, the fluorescence quenching, and direct detection of the reaction intermediates by means of laser flash photolysis experiments indicate that the Lewis acid-catalyzed photoaddition reactions proceed via photoinduced electron transfer from benzyltrimethylsilane to the singlet excited states of Lewis acid-carbonyl complexes.     

A photochemical study of (E,E,E,E)-2-[9-(2-hydroxyethyl)imino-3,7-dimethyl-1,3,5,7-decatrien-1-yl]- 1,3,3-trimethylcyclohexene, a derivative of all-trans-retinal and ethanolamine

A derivative of all-trans-retinal (RAL) and ethanolamine, A2-E, is the main fluorescent component of human retinal lipofuscin. The accumulation of lipofuscin has been correlated with exposure to ambient radiation and loss of photoreceptors. A possible precursor to A2-E is the imine formed from RAL and ethanolamine. This compound, (E,E,E,E)-2-[9-(2-hydroxyethyl)imino-3,7-dimethyl-1,3,5,7- decatrien-1-yl]-1,3,3-trimethylcyclohexene (HIDD), has been synthesized and structurally characterized. The photophysical and photochemical properties of HIDD and its protonated form, HIDD-H+, have been investigated using steady-state and time-resolved methods. Both HIDD and HIDD-H+ are weakly fluorescent, and the fluorescence lifetime and quantum yield for HIDD are ca 0.6 ns and 4.0 +/- 0.5 x 10(-4), respectively. HIDD forms a triplet excited state on direct excitation that decays with kd = 3.4 x 10(4) s-1. The extinction coefficient and quantum yield of intersystem crossing for the HIDD triplet are measured as 7.6 +/- 1.3 x 10(4) M-1 cm-1 and 0.055 +/- 0.006, respectively. The triplet excited state of HIDD-H+ can be sensitized by triplet energy transfer and has a decay rate constant of 1.6 x 10(4) s-1. The lifetime of the HIDD triplet excited state is observed to decrease with increasing concentration of the well-known electron or hydrogen atom donors, 2,3,5,6-tetramethyl-1,4-phenylenediamine and 2,3,5-trimethylhydroquinone, and the bimolecular rate constants for these reactions are approximately 5.4 x 10(6) M-1 s-1 and 1.7 x 10(8) M-1 s-1, respectively. These types of reactions may model photooxidative mechanisms of damage in the retina.