Spectral and kinetic characteristics of formyl-substituted spiropyran in poly(methyl methacrylate) modified with elastomers

The efficiency of photochemical transformations of 1′,3′,3′-trimethyl-6′-formyl-8′-allylspiro[2H-1-benzopyran-2,2′-indoline] in PMMA modified with small amounts of poly(ethyl acrylates) of different structures is studied. It is shown that, in the presence of these additives, the quantum yield of the coloring reaction of the photochromic compound under UV irradiation and the rates of photochemical reactions (forward and back) increase. The maximum efficiency of photochemical parameters is observed for PMMA containing small amounts of linear poly(ethyl acrylate) occurring as a microphase in a glassy matrix.     

Intramolecular NH/pi complexes of 2-allylaniline derivatives in the ground and excited states

The photochemical and photophysical properties of three 8-allyl-1,2,3,4-tetrahydroquinolines (1a-c) have been studied. These compounds exhibit a 2-allylaniline-like photochemical behavior, undergoing photocyclization to lilolidines (3a-c). The absorption, emission, and excitation spectra of 1a-c, employing convenient model compounds for comparison, demonstrate the formation of a NH/pi intramolecular ground-state complex (AB). This species can absorb light at long wavelengths (330-340 nm), giving rise to the corresponding excited complex AB*. Emission from AB* is red-shifted (420 nm) with respect to that observed when the monomer A is excited (lambda(exc) = 300 nm). These experimental results have been rationalized by means of density-functional theory calculations.     

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.     

Identification of flurbiprofen and its photoproducts in methanol by gas chromatography-mass spectrometry

A sample of 10 mM flurbiprofen in methanol (or ethanol) was photoirradiated with sixteen 8 W low-pressure quartz mercury lamps irradiated at 306 nm in a Panchum PR-2000 photochemical reactor. In total, four major photoproducts derived from each sample were observed from the HPLC chromatogram. The photoproducts were separated and their structures elucidated by various spectroscopic methods. Alternatively, using GC-MS, 11 major photoproducts were observed. A reaction scheme of flurbiprofen in methanol is proposed: the photochemical reaction routes occur mainly via esterification and decarboxylation, followed by oxidation with singlet oxygen to produce a ketone, alcohols and other derivatives.     

Triggering DNAzymes with light: a photoactive C8 thioether-linked adenosine

Herein we report evidence for a light-inducible DNAzyme. In so doing, we also disclose the synthesis and photochemical properties of a novel nucleoside: 8-(2-(4-imidazolyl)ethyl-1-thio)-2'-deoxyriboadenosine (d1). The light sensitivity of (d1) was evaluated via an examination of the photoinduced reactivation of DNAzyme 8-17E from an inactive form that contained a single nucleotide (d1) modification. Restoration of DNAzyme activity results from a photoinduced reversion of (d1) to unmodified deoxyadenosine. Deuterium studies indicate that water is the source of hydrogen in the C8-H product and not the alkylthio group, suggesting that reversion of (1) to adenosine is not a consequence of simple homolysis of the C8-S bond but of an unprecedented photochemical conversion. This adenosine, which affords significant control of catalytic reactivation of a DNAzyme, may find general use in photodecaging other biological systems.     

钌钯氧化物涂层电极光电降解活性红3BS的研究

光电催化技术作为一种新型的高级氧化过程日益受到重视,并在废水处理中起到重要作用。目前光电降解技术的研究主要集中于半导体电极作为阳极的光电体系中。本文以活性红3BS为模型反应物,自行烧制钌钯氧化物涂层电极为阳极,进行了光电脱色染料的实验研究,并对其可能机理做了初步的探讨。     

Photoinduced hydrogen isotope exchange in anisole and toluene

Photochemical electrophilic aromatic substitution processes in deuterated and tritiated anisoles and toluenes have been examined. Valence isomerization did not occur in anisole on irradiation. The relative reactivities of the ortho, meta and para positions in toluene are 2:1:1·4 respectively, differing from those in the ground state. Up to 51% exchange has been observed for o-D-toluene and up to 30% exchange for o-D-anisole after 8 h irradiation. Extensive photodecomposition occurs under all conditions with anisole but is slower with toluene. Comparison of the observed substitution pattern of toluene with excited state electron distributions points to the involvement of the second excited singlet and first excited triplet states in the photochemical hydrogen exchange process.     

端基含4个丁氧基偶氮苯介晶基元光致变色液晶树状物的光化学研究

研究了新化合物含4个丁氧基偶氮苯介晶基元的零代(D0)光致变色液晶树状物在氯仿和四氢呋喃中的吸收光强、最大吸收波长、摩尔消光系数、量子产率、活化能、异构转换率、反-顺光异构化反应速率常数、热回复异构化反应速率常数、光回复异构化反应平衡常数及速率常数．D0的光致变色反应速率常数为10^-1s^-1,而含偶氮基元液晶聚硅氧烷的光致变色反应速率常数为10^-8s^-1,因此液晶树状物D0的光响应速度比后者快10^7倍．     

Photochemistry of α‐Diketones in Carbohydrates: Anomalous Norrish Type II Photoelimination and Norrish–Yang Photocyclization Promoted by the Internal Carbonyl Group

A series of four α‐diketones placed as 1α‐pyruvoyl tethers on D ‐glucopyranose and D ‐glucopyranosiduronic acid skeletons was prepared in order to determine the influence of captodative and stereoelectronic effects on the regioselectivity of the hydrogen atom transfer (HAT) in Norrish type II photochemical processes. We observed that the 1,5‐HAT regioselectivity can be switched between the two potentially abstractable syn‐1,3‐diaxial hydrogens at H6 and H8. Highly unusual photoproducts from Norrish type II photoelimination and Norrish–Yang photocyclization initiated by the excited internal carbonyl group were obtained, in some cases in excellent synthetic yield. The 1,5‐HAT transition state in the Norrish type II photoelimination was investigated by photochemical experiments in the crystalline state.     

Alkylation of amino acids and glutathione in water by o-quinone methide. Reactivity and selectivity.

o-Quinone methide (1) has been produced in water both thermally and photochemically from (2-hydroxybenzyl)trimethylammonium iodide (2). Michael addition reactions of 1 to various amines, and sulfides, including amino acids and glutathione have been carried out, obtaining alkylated adducts (3-16) in fairly good to quantitative yields. The reaction rate and selectivity of 1 toward nitrogen and sulfur nucleophiles, in competition with the hydration reaction, have been investigated at different pH by laser flash photolysis technique. The observed reactivity spans 7 orders of magnitude on passing from water (kNu = 5.8 M-1 s-1) to the most reactive nucleophile (2.8 x 10(8) M-1 s-1, 2-mercaptoethanol under alkaline conditions). These are the first direct reaction rate measurements of nucleophilic addition to the parent o-quinone methide (1). Competition experiments provided strong kinetic support to the involvement of free 1 as an intermediate in both thermal and photochemical reactions. Furthermore, several alkylation adducts regenerate 1 either by heating (9, 10, 13, and 14) or by irradiation (9, 11-13, 16). Such a thermal and photochemical reversibility of the alkylation process opens a new perspective for the use and application of such adducts as o-QM molecular carriers.     

Photochemical synthesis of 1,2,3,4,5,6,8,9-octamethyl-C2V-bishomocubane

1,2,3,4,5,6,8,9-Octamethyl-C_2V-bishomocubane was prepared by the photochemical cyclization of 1R,3S,4,5,6R,8S,9,10-octamethyltricyclo[6.2.0.0^3,6]deca-4,9-di-ene in benzene.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1440–1442, June, 1991.The authors express their gratitude to V. I. Eroshkin for a number of valuable suggestions for carrying out the photochemical experiments.     

Development of trityl-based photolabile hydroxyl protecting groups

A series of trityl-based photolabile hydroxyl protecting groups have been examined. These PPGs evolve from the traditional acid-labile trityl protecting group with proper electron-donating substituents. Structure-reactivity relationships have been explored. A m-dimethylamino group is crucial to achieve high photochemical deprotection efficiency. The o-hydroxyl group in 8 greatly improves the yield of the photochemical deprotection reaction, compared with the corresponding o-methoxyl-substituted counterpart 7. However, comparison between the photoreactions of 9 and 11 does not show similar structural relevance. The PPG in ether 1 (i.e., DMATr group) is structurally simple and easy to prepare and install. Its deprotection can be successfully carried out with irradiation of sunlight without requirement of photochemical devices.     

Photochemical Fluorescence Enhancement of Terbuium-Fleroxacin System and Determination of Fleroxacin

ABSTRACT

The sensitized fluorescence of the terbium ion (Tb³⁺) can be observed when excited in the presence of fleroxacin (FLRX) in the aqueous solution because a Tb³⁺ -FLRX complex was formed. The sensitised fluorescence was greatly enhanced after the complex system was irradiated by 365nm ultraviolet light. The irradiation makes the complex system undergo photochemical reactions and a new terbium complex which is more favourable to the intramolecular energy transfer is formed. On this basis a new sensitive and selective photochemical fluorimetric method for the determination of FLRX was developed. Under the optimum experimental conditions, the linear range of the determination is 1.0—200×10^?7 mol 1^?1 for FLRX, and the detection limit is 1.2×10^?8mol 1^?1. Without any pre-treatment the recoveries of FLRX in human urine samples were determined with satisfaction.     

The photochemical reaction between 1,4-dicyanonaphtalene and methylbenzenes: Electron transfer and formation of benzylic radicals

The photochemical reaction of 1,4-dicyanonaphtalene (1) in the presence of methylbenzenes (2a–c) in acetonitrile affords 1 - benzyl - 4 - cyanonaphtalenes (3), 1 - benzyl - 1,4 - dicyano - 1,2 - dihydronaphtalenes (4), 2 - benzyl - 1,4 - dicyano - 1,2 - dihydronaphtalenes (5 and 6) and the tetracyclic derivatives 7 and 8. Compounds 3, 7 and 8 are not the products of subsequent transformations of compound 4. No photochemical reaction is observed in non-polar media, in which, on the contrary, exciplex emission is detected. Experiments in the presence of electron acceptors, electron donors and strong acids support the idea that the reaction is initiated by electron transfer from the methylbenzenes to singlet excited 1, followed by protolytic equilibrium of the benzylic radical cation to the corresponding radical, which is the attacking species.     

Polarisation nucleaire induite chimiquement: etude comparative de la decomposition thermique et photochimique de peroxydes d'acyle benzoyle

A comparative CIDNP study of the thermal and photochemical decomposition of acyl benzoyl peroxides PhCO₂O₂CR (R = methyl and isobutyl) has provided an explanation of the effect of the mode of initiation on the course of the decomposition of this class of peroxides and on the product distribution. The observed variations result from an important decrease (from 10^?8 sec to less than 10^?10 sec) in the lifetime of the benzoyloxy radical on changing from thermal to photochemical initiation.     

Conformations and reactions of bicyclo[3.2.1]oct-6-en-8-ylidene

Bicyclo[3.2.1]oct-6-en-8-ylidene (1) can assume either the conformation of "classical" carbene 1a or that of foiled carbene 1b in which the divalent carbon bends toward the double bond. Oxadiazoline precursors for the generation of 1 were prepared, followed by photochemical and thermal decomposition as well as flash vacuum pyrolysis (FVP) of a tosyl hydrazone sodium salt precursor, to give a number of rearrangement products. Matrix isolation experiments demonstrate the presence of a diazo intermediate and methyl acetate in all photochemical and thermal precursor reactions. The major product from rearrangements of "classical" bridged carbene 1a is bicyclo[3.3.0]octa-1,3-diene as a result of an alkyl shift, while dihydrosemibullvalene formed from a 1,3-C-H insertion. In contrast, thus far unknown strained bicyclo[4.2.0]octa-1,7-diene formed by a vinyl shift in foiled carbene 1b. The experimental results are corroborated by density functional theory (DFT), MP2, and G4 computations.     

端基含36个己氧基偶氮苯基元的二代碳硅烷光致变色液晶树状高分子的光化学研究

研究了含36个己氧基偶氮苯介晶基元的二代(G2)光致变色液晶树枝状高分子在氯仿和四氢呋喃溶液中的最大吸收波长,摩尔消光系数,反顺光异构化反应速率常数,光化学回复异构化正逆反应速率常数及其平衡常数,G2和G1的光致变色反应速率常数kp为10-1s-1,而含偶氮基元光致变色液晶聚硅氧烷的kp为10-8s-1,因此液晶树状高分子的光响应速率比后者快107倍.     

Photochemical Hydrogen Evolution at Metal Centers Probed with Hydrated Aluminium Cations,Al+(H2O)n,n=1–10

Hydrated aluminium cations have been investigated as a photochemical model system with up to ten water molecules by UV action spectroscopy in a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. Intense photodissociation was observed starting at 4.5 eV for two to eight water molecules with loss of atomic hydrogen, molecular hydrogen and water molecules. Quantum chemical calculations for n=2 reveal that solvation shifts the intense 3s–3p excitations of Al⁺ into the investigated photon energy range below 5.5 eV. During the photochemical relaxation, internal conversion from S₁ to T₂ takes place, and photochemical hydrogen formation starts on the T₂ surface, which passes through a conical intersection, changing to T₁. On this triplet surface, the electron that was excited to the Al 3p orbital is transferred to a coordinated water molecule, which dissociates into a hydroxide ion and a hydrogen atom. If the system remains in the triplet state, this hydrogen radical is lost directly. If the system returns to singlet multiplicity, the reaction may be reversed, with recombination with the hydroxide moiety and electron transfer back to aluminium, resulting in water evaporation. Alternatively, the hydrogen radical can attack the intact water molecule, forming molecular hydrogen and aluminium dihydroxide. Photodissociation is observed for up to n=8. Clusters with n=9 or 10 occur exclusively as HAlOH⁺(H₂O)_n-1 and are transparent in the investigated energy range. For n=4–8, a mixture of Al⁺(H₂O)_n and HAlOH⁺(H₂O)_n-1 is present in the experiment.     

CRYSTAL AND MOLECULAR STRUCTURE OF A PHOTOSENSI-TIZER 3-BENZOYLCOUMARINE

<正> 3-Benzoylcoumarine C16H10O3, Mr = 250. 26, monpclinic, space group P21/n, a =11. 744(1), 6 = 16.837(2), c=12. 525(2)A , β= 100. 00(1)°, Z = 8, Dc =1. 363g/cm3, Do = 1. 382g/cm3, F( 000) = 1040, μ(MoKa) = 0. 880cm-1. R and Rw were 0. 048 and 0. 049, respectively, for 2490 observed reflections. X-ray structural analysis reveals that the title compound contains 3 planes intersecting each other with different dihedral angles and thus the whole molecule displays non-planar configuration. This result is consistant with the previous conclusion from photochemical study.     

Photochemisches Verhalten von 1- und 2-alkylierten 1, 2-Dihydronaphthalinen bei tiefen Temperaturen

The irradiations of 1, 1-dimethyl- (8), 1, 1-di-(tri-deuteriomethyl)- (d₆– 8 ), 1, 1, 2, 2-tetramethyl- ( 9 ) and cis- and trans-1, 2-dimethyl-1, 2-dihydronaphthalenes (cis- and trans- 10 ) were investigated in 2, 2-dimethylbutane/pentane at ?100° using a mercury high-pressure lamp, and with mercury high- and low-pressure lamps at room temperature. The results were compared with one another, and those of the individual compounds are collected in schemes 2 and 4–7. The most important results are the following: 1. The 1, 2-dihydronaphthalenes undergo a conrotatory ring opening to the o-quinodimethanes on irradiation with high- or low-pressure lamps at room temperature or at ?100°. Thermal reactions ([1, 7a]H-shifts, electrocyclisations) are suppressed at ?100°. The o-quinodimethanes formed from 8 (scheme 2), 9 (scheme 5) or cis- 10 (scheme 6) undergo on irradiation with the high-pressure lamp, [1, 5]H-shifts or photochemical Diels-Alder reactions after renewed photochemical excitation, to yield the benzobicyclo[3.1.0]hex-2-ene derivatives. These Diels-Alder reactions do not proceed stereospecifically, and therefore are not orbital symmetry controlled reactions. 2. If the 1, 2-dihydronaphthalenes are irradiated at room temperature with either a high- or a low-pressure lamp, then the initially formed o-quinodimethanes undergo thermal [1, 7a]H-shifts, in preference to all other reactions, as long as this is sterically possible; the resulting products can undergo secondary photochemical transformations. Such o-quinodimethanes are formed on irradiation of 8, 9 and cis- 10 . From trans- 10 , an o-quinodimethane mixture is formed, of which one component (cis, cis- 22 ) undergoes thermal [1, 7a] H-shifts, while the other (trans, trans- 22 ) suffers a thermal disrotatory electrocyclisation to give cis- 10 . If a high-pressure lamp is used in the last experiment, then the competing photochemical Diels-Alder cyclisation to bicyclic compounds of the type 23 (scheme 7) can result in the trans, trans- 22 . As was shown by Salisbury [3], and confirmed by ourselves in other cases [2], photochemical Diels-Alder reactions or [1, 5]H-shifts in the o-quinodimethanes require light of wavelength ? 400 nm (high-pressure lamp). The present photochemical investigations amplify and confirm our earlier conclusions concerning the photochemistry of the 1, 2-dihydronaphthalenes [2].