THE INTERACTION OF ETHYL BENZOATE AND TRIFLUOROACETIC ACID IN EXCITED STATE

This paper is concerned with the interaction of ethyl benzoate (EBA) and trifluoroaceticacid (TFA) molecules in the excited state by measurements of steady--state and transient fluo-rescence spectra at room and low temperatures. The results show that not only the 1:1 exci-plex but also the 2:1 triplex between EBA and TFA was formed. The formation pathway ofthe triplex is that the exciplex formed at first, then by the interaction with the EBA mole-cule it transformed into triplex. But it could not be formed by the dimer of EBA by interac-tion with TFA. The dimer of EBA is confirmed in the concentrated solution. So there arefour components in EBA/TFA--concentrated solution and their fluorescence lifetimes aremeasured respectively.     

THE DECAY FUNCTION AND CONFORMATION OF 1,1''''-BINAPHTHYL (1,1''''-BIN)

The fluorescence lifetimes and emission spectra of 1,1'-BIN and some other compounds in different solvents, which should give some information concerning the conformational changes of 1,1'-BIN in the excited singlet state have been examined. The excited charge transfer properties of 1,1'-BIN have been examined as well. The results indicate that the two naphthyls in the excited binaphthyl molecule rotate around the connecting C—C bond very fast at room temperature in a fluid solvent since it occurs even in viscous solvents within 280 ps and that there is an exciplex formed between 1,1'-BIN and PDMP. The decay function of 1,1'-BIN is obtained.     

TBP"探针"法与荧光光谱法测定环己烷最低激发单态G值的比较

By using tri-Bu Phosphate (TBP) as an energy acceptor, G value of lowest excited singlet state of cyclohexane has been determine under g irradiation It was found that in N2 atmosphere when the dose approaches zero G(S1) equals 1.3 ?0.2. Which is in harmony with the G value determine by fluorescence method. Rate constant of energy transfer from lowest excited singlet state of cyclohexane to TBP was found to be 0.6 ?1010 mol-1譻-1, which is in harmony with kses. The influence factor on the determination of yields of excited states and rate constant of energy transfer was discussed. The excited triplet state of cyclohexane has been studied, G value of excited triplet state of cyclohexane is 0.26 ?0.04 and t x 6 ns.     

STUDIES ON BIO-ANTIOXIDANTS——PROOXIDATION OF VITAMIN E ON THE AUTOXIDATION OF LINOLEIC ACID IN SODIUM DODECYL SULFATE MICELLES

The reaction of vitamin E (α-tocopherol) with linoleic acid containing peroxidized linoleic acid has been studied. No significant reaction was found in ethanol solution, whereas in sodium dodecyl sulfate micelles vitamin E reacted rapidly with peroxidized linoleic acid, and thereby induced the peroxidation of linoleic acid, leading to oxygen absorption. The reaction kinetics was studied in detail by u. v. spectroscopy, HPLC and ESR spectroscopy. It was found that the main product was α-tocopherone with α-tocopheroxy radical as the reaction intermediate. A mechanism involving two consecutive bimolecular reactions between peroxidized linoleic acid and a-tocopherol and between peroxidized linoleic acid and a-tocopheroxy radical, with rate constant 2.93 and 6.21 mol/L-1s-1 respectively is proposed. The micellar effect on the reaction is discussed.     

Effects of Self—coiling of Organic Molecules on Intramolecular Exciplex Formation and Fluoresscence Quenching in DX—H2O Solvent System

Effects of self-coiling of organic molecules on intramolecular exciplex formation of compound I,in which the carbazole chromophore and terephthalic acid methylester acceptor group are linked by one (CH2)10 chain,and the decrease of the fluorescence intensities of compounds Ⅱ，Ⅲ，and Ⅳ,in which the carbazole chromophore and 3,5-dinitrobenzoate are connected by one aliphatic chain of (CH2)10 (Ⅱ），（CH2）12（Ⅲ）,or (CH2)4(Ⅳ）,have been studied in the dioxane (DX)-H2O binary system.The results show that self-coiling of organic molecules in DX-H2O facilitates intramolecular exciplex formation of I and induces the decrease of fluorescence intensities of Ⅱ,bacause of the proximity effect brought about by selfcoiling of organic molecules under hydrophobic-lipophilic interaction(HLI) between the excited carbazole chromophore and the acceptor.Since the similar effects are observed even when the concentration of the probes are less than their CAgCs(critical aggregate concentrations )in the DX-H2O mixture with the same φ values,formation of the intermolecular exciplex has been excluded.The effects are found to be strongly depended on φ values,indication that they are mainly driven by HLI.The properties of the acceptors can also affect the intramolecular exciplex formation.With terephthalic acid methylester moiety as the acceptor,the carbazole chromophore exhibits the fluorescence spectra of the exciplex,while with 3,5-dinitrobenzoate moiety as the acceptor,only the fluorescence spectra of excited carbazolyl chromophore are observed.     

Synthesis of some new lignans and the mechanism of intramolecular nonphenolic oxidative coupling of aromatic compounds

Treatment of cis-1,4-diaryl-2,3-epoxy butane with 2,3-dichloro-5,6-dicyano-1,4-benzo-quinone(DDQ) in trifluoroacetic acid(TFA) gave dibenzocycloheptadienes by pinacol rearrangement and intramolecular oxidative coupling of the aryl groups. Meanwhile, the benzofuran analogues were also formed by the same method. These new lignans have potent CNS inhibitory activities. It has been proven that the method is particularly useful when applied to the substrates in which the ring substituents are electron donating. The structures of these products were identified by the MS, UV, IR, NMR spectra, and elemental and X-ray crystallographic analyses.     

Interaction between hypocrellin and aliphatic amines

The interaction of hypocrellin, including hypocrellin A (HA) and hypocrellin B (HB), with aliphatic amines in deaerated solutions has been studied by ESR and nanosecond transient absorption spectra. In polar solvents, the acid-base interaction between hypocrellin and amines was observed without irradiation. The signals of semiquinone radical anions of hypocrellm and the spin-trapping adduct of α-phenyl-N-tertbutyl-ratrone (PNB) with the aminoalkyl radicals have been detected in photoinduced ESR studies. The transient absorption of excited triplet state of HA and semiquinone radical anion of HA have been observed in laser flash photolysis studies.     

STUDY ON THE PROTONATION MECHANISM OF 2,6-DIMETHYL NAPHTHALENE DICARBOXYLATE

By the study of absorption and fluorescence spectra and the lifetime of fluorescence at room and low temperatures of 2,6-dimethyl naphthalene dicarboxylate (DMN) in different concentrations of sulfuric acid, different interactions between molecules of DMN and sulfuric acid have been observed. These interactions have been revealed by the absorption spectra of charge transfer complex in the ground state, emission of exciplex, absorption spectra of hydrogen bonding interaction, absorption and emission spectra after proton transfer and different lifetimes before and after protonation. The interaction mechanism of DMN and sulfuric acid through first the CT complex and exciplex then hydrogen bonding and finally proton transfer is proposed.     

Theoretical Studies on the Mechanism of Photocycloaddition Reaction Between 6 Azauracil and Acetone

The mechanism of photocycloaddition reaction between 6-azauracll and acetone was studied by using semiemptrical SCFMO AMI method. It was found that this reaction is not a concerted one. The calculated results are as follows:(1) A T1 state exciplex is on the T1 state energy surface; (2) T exciplex as a reactant will proceed along the energy surface of T1 state to form a diradical intermediate. The energy barrier of this reaction step is 63. 6 kJ/mol; (3) The T1 state diradical intermediate happens to be close in energy to the ground state intermediate with a similar geometry. Such a situation turns out to be very favorable for an intersystem crossing (jump from the T, state to the ground state) ; (4) The final product will be formed from the ground S0 state intermediate via an energy barrier 88. 2 kJ/mol.     

STEADY-STATE AND TIME-RESOLVED FLUORESCENCE STUDY OF TRIPLE EXCIPLEX IN THE SYSTEM OF POLYACENAPHTHALENE AND TEREPHTHALIC DIMETHYLESTER

Triple exciplex formed between polyacenaphthalene and terephthalic dimethylester (TDE) has been studied by means of the steady-state and time-resolved fluorescence spectra. The theoretical model of the triple exciplex formation for a flexible polymer chain in a dilute solution has been proposed. The fluorescence decays of the monomer, the exciplex and the triple exciplex obey a double exponential rule in the pbotophysical processes of the triple exciplex formation. The association rate constant of the exciplex formation is k_3=6.0×10~9s~(-1)(mol/L)~(-1); the association rate constant of the triple exciplex formation is k_6=5.2×10~7s~(-1). A mechanism for the triple exciplex formation from the exciplex to the triple exciplex has been proved through the noncrystal films corresponding to the same concentrations of the solution systems and the fluorescence lifetimes of the intramolecular excimer.     

Co encapsulated N-doped carbon nanotubes as robust catalyst for valorization of levulinic acid in aqueous media

The construction of an acid resistant catalyst for synthesis of γ-valerolactone from levulinic acid in aqueous media is an important but highly challenging goal.Herein,an efficient Co@NCNT-800(after 800℃ pyrolysis) catalyst was constructed by confining Co in N-doped carbon nano-tubes(NCNT) from low cost materials by a facile strategy.Combined with the characterization results and control experiments,the in situ formed Co and Co-Ox, but not Co-Nx, proved to be the main synergistic active sites of the catalyst.It was also found that Co species are completely isolated within the bamboo-like NCNT,which could protect the metal nanoparticles from agglomeration and leaching in the strong acid reaction system.The γ-valerolactone yield of no less than 99.9% can be obtained under a relatively mild condition,and the catalytic performance has not been significantly reduced within five cycles.Therefore,this work may pave a way for the design of robust non-noble catalyst,and has potential for the production of γ-valerolactone from biomass in large-scale industries.     

Effects of Hydrogen-bonding Interaction and Polarity on Emission Spectrum of Naphthalene-Triethylamine in Mixed Solvent

The effects of the protic and aprotic polar solvents on the emission spectrum of the naphthalene-triethyl-amine system in THF were studied under conditions of steady-state illumination. The fluorescence spectrum of the naphthalene-triethylamine system consists of two emission bands, the fluorescence band of naphthalene (band A, 329 nm) and the emission band of the exciplex(band B, 468 nm). The intensities of both the emission bands decrease with increasing the solvent polarity. The intensity of band B also decreases due to the hy-drogen-bonding interaction between triethylamine and protic solvent, while that of band A increases. It is thus suggested that the quenching of naphthalene fluorescence by triethylamine in THF occurs through the charge transfer and electron transfer reactions. The spectral changes upon the increase of solvent polarity can be explained by the dependences of the equilibrium constant between exciplex and ion-pair and the rate constant for the electron transfer reaction from triethyl.amine to the excited naphthalene on the rel.ative permittivity of solvent. It is shown that the formation of intermolecular hydrogen-bonding between triethylamine and protic solvent suppresses the quenching reaction by the decrease in free amine. Acetonitrile has only a polar effect and trichloroacetic acid only a hydrogen-bonding(or protonation) effect, while alcohols have both the effects. The effects of alcohols could be separated into the effects of solvent polarity and intermolecular hy-drogen-bonding interaction quantitatively.     

GENERATION OF RADICAL CATIONS——A FACILE GENERATION OF RADICAL CATIONS VIA THE ACTION OF AN OXOAMMONIUM TRIFLUOROACETATE

The reaction between a stable nitroxide, 2, 2, 6, 6-tetramethyl-4-chloropiperidinyl-1-oxy, la and aromatic amines and heterocycles, 3—9, in methylene chloride in the presence of trifluoroacetic acid, has been investigated. The corresponding radical cations of the amines and the heterocycles were readily generated by this reaction, which could persist for a long period of time in the system. Kinetic ESR studies were performed to elucidate the reaction mechanism and the results showed that the formation of the radical cations involves one-electron transfer reaction between the active oxidant, the oxoammonium trifluoroacetare, 2a, which results from the disproportionation of the nitroxide in the presence of trifluoroacetic acid, and the substrates studied. This affords a facile method for the generation of radical cations from aromatic amines and heterocyclics by the action of an organic oxidant.     

INVESTIGATION ON THE CONFORMATION OF THE MAIN-CHAIN NEMATIC POLYMER BY SMALL ANGLE X-RAY SCATTERING

The experimental investigation on the conformation of a thermotropic main-chain nematic polymer by small-angle X-ray scattering (SAXS) has been carried out. The average radius of gyration of the polymer has been determined in nematic and isotropic state respectively. The experiment shows that the boundary between domains is not sharp but diffuse, and the diffuse-boundary thickness of the polymer as a function of temperature has been given.     

Studies on the Interaction of 12-Tungstophosphoric Acid and Diethylene Glycol

The homogeneous system of 12-tungstophosphoric acid and diethylene glycol was studied using IR and NMR spectra. It was found that the protons in 12-tungstophosphoric acid formed proton oxonium ions with the hydroxyl oxygen in diethylene glycol by hydrogen-bonds, and the formed proton oxonium ions could react with the terminal oxygens of heteropoly anions. The dehydration-cyclization mechanism of diethylene glycol in the presence of heteropoly acid was also proposed.     

DSC study of phase transition of anhydrous phospholipid DHPC and influence of water content

The phase transition behavior of 1,2-di-n-heptadecanoyl phosphatidylcholme (DHPC)with and without water has been studied by use of differential scanning calorimetry It was found by experiment that the glass transition occurred at first during the first heating of a sample of DHPC without water and then the sample underwent melting as an ordinary crystal.Therefore the sample of DHPC without water was a glassy crystal However,the DHPC sample crystallizing from melt was an ordinary crystal From the relationship between the total melting enthalpy Qf of freezable water and the water content h,it was concluded that the water contained in the DHPC samples might exist in three states recognizable thermodynamically.The water in the first state was an unfreezable water It was the water bound directly with the head groups of the phospholipid,i.e.the primary hydration water Every head group might bind seven such molecules of water.The water in the second state was the secondary hydration water,us melt ing point was     

SHG from centrosymmetric supermolecular crystal

Supermolecular crystal composed of p-nitrophenol, hexamethylenetetramine, phosphoric acid and water was obtained by supermolecular assembly. The crystal has a centrosymmetric structure with space group P21/c. The relative intensity and integral value of green frequency doubling of light from the crystal powder compared with that from KDP powder measured by pico-second Nd:YAG laser are 757.3 (KDP: 183.4) and 1771.7 (KDP: 423.98), respectively. In supermolecular crystal, due to the arrangement of centrosymmetric p-nitrophenol molecules in the inorganic-organic host framework formed by hexamethylenetetramine, phosphoric acid and water, the distances between the p-nitrophenol molecules with centrosymmetry are changed (N1A-O1A: 0.8158 nm, N1B'-O1B: 1.4450 nm, N1A-N1A': 0.5837 nm, N1B'-N1B: 0.6898 nm), and the interaction between the dipoles becomes weak, which is easy for the ground state to turn into the excited state charge separated form, and generate the stable asymmetrical distribution of π-electron clo     

PHOTOPHYSICS STUDIES OF ORCANIC COMPOUNDS (Ⅻ)——THE INVESTIGATION OF THE FLUORESCENCE SPECTRA OF N-SALICYLIDENE-p-(N,N-DIMETHYLAMINO)ANILINE

The fluorescence spectra of N--salicylidene-p-(N,N--dimethylamino)aniline have beeninvestigated in various solvents. Three kinds of fluorescence have been found in the solutionsof various concentrations. They are the excited intermediate (EI) which is formed when theproton transfer has occurred but essentially retains the geometry of the enol tautomer, theexciplex (EX) which consists of a ground monomer and an excited state intermediate and theexcited dimer (ED) which is caused by ground state aggregate. The fluorescence lifetimesof the fluorophores have been measured in tetrahydrofuran (THF). Luminescent mechanismhas been discussed based on the fluorescence spectra and the kinetic data of the compound.     

SYNTHESIS OF NOVEL SOLUBLE AROMATIC POLYPYROMELLITIMIDE CONTAINING ORDERED 1,2,4-TRIAZINE IN THE MAIN CHAIN

A new heat-resistant, soluble polymer, poly(phenyl-1,2,4-triazine imide), has been prepared via a two-step methodof polycondensation of N,N'-bis(4-benzil)pyromellitimide and terephthalamidrazone in cresol, followed by curing at highertemperature. The rigid 1,2,4-triazine group increases the solubility of the polyimide so that the polymer is soluble in cresol,N-methyl-2-pyrrolidone (NMP), trifluoroacetic acid and concentrated sulfuric acid, etc. Thermogravimetric analysis (TGA)indicates that this novel polyimide has good thermal stability with a high decomposition temperature of 447℃ in air and of423℃ in N_2. It has a tensile strength of 107.4 MPa with an elongation at break of around 7.6%.     

STUDIES ON THE MECHANISM OF VINYL PHOTOPOLYMERIZATION INITIATED BY CONDENSED AROMATIC HYDROCARBON-ANILINE SYSTEMS

Initiation mechanism of the photopolymerization of acrylonitrile and methyl methacrylate, usingbinary condensed aromatic hydrocarbon (CAH)-aniline systems as initiator, was studied. The strongerthe electron-donating ability of the aniline derivatives, the faster the the of photopolymerizationwill be. The radical intermediates produced by photoreaction between anthracene and anilinewere detected with ESR spectra. The initiation scheme involves the formation of exciplex betweenthe excited singlet state of CAH and the ground state of aniline as the first step, and then followedby proton transfer, leading to the generation of two kinds of radicals. From the end-group analysisof the polymers obtained, it is suggested that both kinds of radicals are involved in the initiation.