The excited-state interaction of resazurin and resorufin with amines in aqueous solutions. Photophysics and photochemical reactions

The photophysics and photochemical behavior of the phenoxazin-3-one dyes, resazurin and resorufin, have been studied in aqueous solutions. The irradiation of resazurin in the presence of amines leads to deoxygenation of the N-oxide group, giving resorufin. This photoreaction is highly dependent on the amine structure and is efficient only in the presence of tertiary aliphatic amines. The absorption and fluorescence properties of these dyes are dependent on pH. At pH above 7.5 both dyes are in their anionic form. For resorufin this form is highly fluorescent (phiF = 0.75). At lower pH the fluorescence is strongly reduced. The N-oxide dye presents a very weak fluorescence quantum yield (0.11), which also is reduced at low pH. Flash photolysis experiments allowed characterization of the triplet state and the transients formed after irradiation of these dyes in the absence and presence of amines. The triplet quantum yields are 0.08 for resazurin and 0.04 for resorufin. The photodeoxygenation of N-oxide in the presence of amines occurs from the triplet state.     

Heavy Atom Effects in Tellurapyrylium Dyes Useful in Photodynamic Therapy and Catalytic Generation of H2O2

Abstract

The large rate of intersystem crossing between singlet and triplet states of tellurapyrylium dyes leads to efficient generation of singlet oxygen in irradiated airsaturated aqueous solutions containing these dyes. One reaction of tellurapyrylium dyes with singlet oxygen and water is the formation of dihydroxy tellurane [tellurium(IV)] species. We have found that the photochemical generation of dihydroxy telluranes is reversible thermally. The tellurapyrylium dye is regenerated while a molecule of hydrogen peroxide is produced. The thermal generation of hydrogen peroxide coupled with a photochemical generation of singlet oxygen allows a catalytic cycle to be devised for the conversion of oxygen and water to hydrogen peroxide. The dihydroxy telluranes are efficient two-electron oxidizing agents and can be used as catalysts to accelerate reactions using hydrogen peroxide as a two-electron oxidizing agent. Examples of tellurapyrylium dye-mediated reactions of hydrogen peroxide include reactions of leucodyes normally oxidized by horseradish peroxidase and hydrogen peroxide. These processes lead to thermal and photochemical reactions that are potentially cytotoxic following the generation of singlet oxygen in photodynamic therapy. The regeneration of the original catalyst allows repeated treatment from a single dose.     

天线若丹明染料分子内能量与电荷传递的研究

染料三重态在染料激光的应用中起着重要作用，尤其是三重态一Z重态（T－T）吸收常常会造成谐振腔损耗＊．为了减少由基态吸收而造成的话振腔损耗，带有紫外吸收天线分子的三发色团染料已在研究问，2，5·二苯基螨喳（PP0）在紫外区（如308删）有很强的吸收，PPO－rhod．系列染料（见图1）在紫外区的吸收就很强，由PPO到若丹明母体的单线态一单线态（S功能量传递使这类三发色团染料具有较大的荧光量子效率，较小的基态重复吸收耗能卜，司．然而，在610N640nm区域中这些天线若丹明染料的激光输出效率远远小于若丹明Rh630＊，其原因正是…     

Intramolecular triplet energy transfer in multi-chromophoric dyes and its influence on the photostability

The photostability of organic dyes plays a very important role in practically all aspects of the development and applications of these dyes. In recent years, intramolecular transfer of triplet excitation energy between isolated chromophores on the same molecule has been a subject of intensive studies. Many multi-chromophoric organic dyes with covalent linkage between the chromophores, one of which can act as a triplet acceptor of the excess energy, have been synthesized and studied. The significant increases in photostability of such assembled dyes have been reported, suggesting that some chromophores can act as internal photostabilizers. These modified dyes have enhanced photostability and hence potential applications in a wide range of areas such as laser dyes, electroluminescent (EL) devices and solar cells.     

Fast and slow processes of thermal deactivation of excited stilbazolium merocyanine dyes

The long living triplet states play important role in sensitizing action in all photochemical reactions. The yield of generation of triplet states of dyes can be evaluated on the basis of measurements of their slow (microsecond) thermal deactivation (TD). All experiments were carried out in the oxygen presence, it means under quenching dye triplets. The pulse dye laser generates in the investigated solution pressure signal. The high of the amplitudes of first maximum of this pressure wave-form signal in the solution of the investigated dye and in the reference sample were measured. Reference sample exhibits only fast processes of TD. The comparison of the first maximum of wave-form photothermal signal of sample and of reference enable to calculate part of energy exchanged into heat in time longer than time resolution of arrangement. The fluorescence yields of investigated dyes were also established. On the basis of such data, using procedure described in literature, the yield of singlet–triplet intersystem crossing (ISC) was evaluated. It was shown that this yield depends on the length of stilbazolium merocyanine chain. The product of triplet state yield and energy was lower for merocyanines with longer chains. At lower temperatures the yield of fluorescence increases and amount of excitation exchanged in short time into heat decreases. The slow TD process increases in low temperature because of the decrease in the quenching of the dyes triplet states by oxygen. The amount of energy exchanged into heat in a time longer than time resolution of apparatus is due predominantly through TD of the dye triplet states.     

Synthesis and functional properties of green fluorescent poly(methylmethacrylate) for use in liquid crystal systems

The copolymerization of six 4-aminosubstituted-1,8-naphthalimide dyes comprising an allylic polymerizable group with methylmethacrylate has been investigated. The utility of the copolymers prepared as fluorescent component in polymer/liquid crystal systems has been examined. The photophysical and photochemical properties of the systems monomeric dye/liquid crystal and copolymer/liquid crystal have been also discussed. It has been shown that in a liquid crystal mixture 1,8-naphthalimide dyes and respective copolymer/liquid crystals have yellow–green fluorescent color with good photostability. Copyright © 2003 John Wiley & Sons, Ltd.     

Intramolecular interactions in the triplet excited states of benzophenone-thymine dyads

Time-resolved and product studies on the synthesized dyads 1 and 2 have provided evidence that the benzophenone-to-thymine orientation strongly influences intramolecular photophysical and photochemical processes. The prevailing reaction mechanism has been established as a Paterno-Büchi cycloaddition to give oxetanes 3-6; however, the ability of benzophenone to achieve a formal hydrogen abstraction from the methyl group of thymidine has also been evidenced by the formation of photoproducts 7 and 8. These processes have been observed only in the case of the cisoid dyad 1. Adiabatic photochemical cycloreversion of the oxetane ring is achieved upon direct photolysis to give the starting dyad 1 in its excited triplet state. The photobiological implications of the above results are discussed with respect to benzophenone-photosensitized damage of thymidine.     

Generation of oxynitrenes and confirmation of their triplet ground states

New sulfoximine- and phenanthrene-based photochemical precursors to oxynitrenes have been developed. These precursors have been used to examine the chemistry and spectroscopy of oxynitrenes. The first EPR spectra of oxynitrenes are reported and are consistent with their triplet ground states. Additional support for the triplet ground state of oxynitrenes is provided by trapping and reactivity studies, nanosecond time-resolved IR investigations, and computational studies.     

A LASER FLASH PHOTOLYSIS STUDY OF THE NATURE OF FLAVIN MONONUCLEOTIDE TRIPLET STATES AND THE REACTIONS OF THE NEUTRAL FORM WITH AMINO ACIDS

Abstract— Primary photochemical processes in aqueous solution have been characterised for FMN. The influence of pH on these processes is attributed to protonation of the neutral triplet and not to the presence of a dimeric species as postulated earlier. Second order rate constants for reaction between the neutral triplet and some naturally occurring amino acids are reported.     

Unveiling the Triplet State of a 4‐Amino‐7‐Nitrobenzofurazan Derivative in Cyclohexane

The nitrobenzofurazan (NBD) moiety has gained tremendous popularity over the last decades due to its fluorogenic nature. Indeed, upon interaction with aliphatic amines, it generates a stable fluorescent adduct, which has been used for protein and lipid labeling. In fact the 4‐amino substituted NBD belongs to the broad family of intramolecular charge transfer molecules, with the amino group acting as an electron donor upon photoexcitation, and the nitro group as an electron acceptor. Although the singlet excited state of 4‐amino NBD derivatives has been abundantly studied, investigation of its triplet manifold is scarce and even the absence of intersystem crossing for this type of molecules has been suggested. However, intramolecular charge transfer molecules are known to undergo intersystem crossing and high phosphorescence quantum yields have been reported in a nonpolar solvent. In the present paper, we have investigated the photophysical and photochemical properties of N‐hexyl‐7‐nitrobenzo[c][1,2,5]xadiazole‐4‐amine. We have shown the existence of a triplet state for this molecule in cyclohexane via nanosecond laser flash photolysis. Interestingly, deactivation of the triplet state leads to photoproducts formation, which are only present in the absence of oxygen.     

PHOTOCHEMICAL REACTIONS OF AROMATIC KETONES WITH NUCLEIC ACIDS AND THEIR COMPONENTS I—. PURINE AND PYRIMIDINE BASES AND NUCLEOSIDES*.

Abstract— The photochemical reactions of benzophenone and acetophenone with purine and pyrimidine derivatives in aqueous solutions have been investigated by flash photolysis and steady-state experiments. Upon excitation of these two ketones in aqueous solutions, two transient species are observed: molecules in their triplet state and ketyl radicals. The triplet state lifetimes are 65 μsec for benzophenone and 125 μsec for acetophenone. The ketyl radicals disappear by a second order reaction, controlled by diffusion. In the presence of pyrimidine derivatives, the triplet state is quenched and the ketyl radical concentration is decreased without any change in its kinetics of disappearance. Ketone molecules in their triplet state react with purine derivatives leading to an increase in the yield of ketyl radicals due to H-atom abstraction from the purines. Steady-state experiments show that benzophenone and acetophenone irradiated in aqueous solution at wavelengths longer than 290 nm undergo photochemical reactions. The rate of these photochemical reactions is increased in the presence of pyrimidine derivatives and even more in the presence of purine derivatives. Following energy transfer from the triplet state of benzophenone to diketopyrimidines, cyclobutane dimers are formed. The energy transfer rate decreases in the order orotic acid > thymine > uracil. Benzophenone molecules in their triplet state can also react chemically with pyrimidine derivatives to give addition photoproducts. All these results are discussed with respect to photosensitized reactions in nucleic acids involving ketones as sensitizers.     

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.     

Photoexcited triplets of dyes in zeolitic nanostructured channels. A time resolved EPR study

Two dyes (4-nitrostilbene, NST and 4-N,N-dimethylamino-4'-nitrostilbene, DANS) included in zeolites with nanometric channels and different Si : Al ratios have been photoexcited and their triplet state studied by time resolved EPR (TR-EPR). This is the first time that a TR-EPR spectrum of photoexcited triplet states of dyes in zeolites has been observed. The zeolites used were ZSM-5 and mordenite, with either protons or lithium as charge compensating ions, and the aluminium-free porosil. The ZFS parameters and the polarized spin populations have been obtained, and compared with those obtained in glassy solutions and in the organic nanostructured matrix perhydrotriphenylene (PHTP). For (3)DANS in neutral solvents and in PHTP the dimethylamino group is pi conjugated, whereas only its acid form is detected in all the zeolites. In the latter the spectra of the radical cations formed by spontaneous oxidation have also been observed both by cw-EPR and TR-EPR, the last spectra being spin polarized in emission. The mobility of the triplets is discussed, taking into account the spin polarization of the radical cations indicating a strong radical-triplet interaction.     

Mechanistic studies of photochemical reactions of N-ethylphthalmide with olefins

The primary processes in the photochemical reaction of N-ethylphthalmide with olefins in solution have been studied via absorption, fluorescence, phosphorescence, and triplet- triplet absorption spectroscopy. The lowest triplet state of N-ethylphthalimide is quenched by olefins such that its lifetime depends linearly upon the inverse of the olefin concentration.     

新型三重态光敏剂——3-芳甲酰基香豆素光物理和光化学性质的研究

本工作合成了一系列新型的三重态光敏剂——3-芳甲酰基香豆素。测定了它们的吸收光谱和磷光光谱,研究了它们的光物理和光化学行为,包括如磷光量子产率的测定以及比较了它们对反式茋敏化异构化的能力。结果表明,这是一类很有效的三重态光敏剂。     

Aminium cation radical of glycylglycine and its deprotonation to aminyl radical in aqueous solution

The photochemical reaction between glycylglycine and triplet 4-carboxybenzophenone has been investigated using time-resolved chemically induced dynamic nuclear polarization (CIDNP). It is shown that the mechanism of the peptide reaction with triplet excited carboxybenzophenone is electron transfer from the amino group of the peptide, leading to the formation of an aminium cation radical that deprotonates to a neutral aminyl radical. Simulation of the CIDNP kinetics leads to an estimation of the paramagnetic relaxation time for the alpha-protons at the N-terminus at 20 to 40 mus with the best-fit value of 25 mus.     

Absorption spectra of 2,3-dihydrothionaphthen-3-one and its derivatives

A number of new thioindigoid dyes have been synthesized. They have been subjected to photochemical isomerization. The absorption spectra of the dyes synthesized have been compared with the absorption spectra of analogous dyes not containing bromine. The spectra of the cis forms are less sensitive to the introduction of a bromine atom than those of the trans forms.For Communication XI, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, Vol. 6, No. 8, pp. 1031–1033, August, 1970.     

Etude theorique (cndo/s) des etats excites et des transitions electroniques de 2h-chromenes representant la partie responsable de l'ouverture photochimique de spiropyrannes

The excited states and electronic transitions of some 2H-chromenes (considered responsible for photochemical opening of photochromic spiropyrans) have been studied. The relative positions of nπ^* and ππ^* singlet and triplet energy levels of these compounds allow a satisfactory interpretation of their optical properties. Also highly localized electronic charge transfers are demonstrated in the case of 2H-chromenes substituted by a nitro group.     

ELECTRON PARAMAGNETIC RESONANCE OF SOME TRIPHENYLMETHANE DYES IN THE TRIPLET STATE

Abstract— Electron paramagnetic resonance spectra of the triplet states of several triphenylmethane dyes in glassy solutions at 90 K have been measured and their zero-field splitting parameters estimated. Crystal violet and para rosaniline do not possess trigonal symmetry in their triplet states, and the unusually broad absorptions in the Δ M ₈= 1 region of the spectra have been attributed to the presence of different rotational isomers of the dye cations. A number of malachite green derivatives were investigated, but absorption of the triplet states of these dyes was only observed in the low field Δ M ₈= 2 region of the spectrum.     

高效液相色谱-柱后在线光化学衍生荧光检测法测定辣椒油中4种苏丹红染料

建立了在线光化学衍生、荧光检测、高效液相色谱(HPLC)测定辣椒油中苏丹红I、II、III和B的方法。以乙腈-水为流动相,采用梯度洗脱方式在SB-C18色谱柱上分离。用实验室自制的程序控制时间/光强光化学反应器作为在线衍生装置,优化了光衍生反应的条件和荧光检测条件。3种不同加标浓度下,辣椒油样品中4种苏丹红染料的加标回收率为81.3%～100.4%。加标水平为0.8 mg/kg下荧光信号强度的相对标准偏差(RSD,n=6)为2.6%～3.8%。苏丹红I、II、III和B的检出限(LOD)和定量限(LOQ)范围分别为0.009～0.054 mg/kg和0.030～0.181 mg/kg,优于传统的HPLC分离、二极管阵列检测器检测方法。该方法具有简单、灵敏、选择性好的特点,适用于食品样品中苏丹红的常规分析。