Fluorescence Spectra Of Solutions Research Articles

Prospects for using photoinduced intramolecular proton transfer to study the dynamics of conformational changes in flexible molecular chains

Photoinduced excited-state intramolecular proton transfer in 2-hydroxy-1-(N-morpholinomethyl)naphthalene (HMMN) and in 7-hydroxy-8-(N-morpholinomethyl)quinoline (HMMQ) has been studied by means of stationary and time-resolved fluorescence. Both molecular systems have an intramolecular hydrogen bond. This causes a very fast ESIPT process to occur directly upon excitation with a rate constant >2 × 1011 s–1. HMMN is known to show dual fluorescence; however, HMMQ in neat polar solvents is found to exhibit three fluorescence bands. The bands at the short- and long-wavelength side of the spectrum are assigned, respectively, to emission from the excited initial tautomeric form (enol form) and the adiabatically produced excited keto form. This agrees with the fact that these two bands are also observed in the fluorescence spectrum of solutions of 7-hydroxyquinoline in neat alkanols, in which the excited keto form is known to be formed adiabatically as a result of active solvent participation in the ESIPT process. The third band originates from an excited zwitterionic species in which the proton is located on the N atom in the morpholino group. The side group acts as a molecular crane, picking up the proton from the initial binding-site and depositing it at the final proton binding-site. The rate constant for the transport of the proton from the initial to the final location is determined by the rate constant for the required motion of the free end of the side group. This rate constant has been studied as a function of viscosity η of the solvent and is found to be proportional to η–c, with c= 0.6 and 0.4 in the case of n-alkanols and alkanenitriles as solvents, respectively. A process consisting of two sequential ESIPT processes, as in HMMQ, offers precise control of initial and final conformation in the study of the dynamics of flexible molecular chains. The prospects for using such a double ESIPT process as a tool to study chain dynamics are discussed.

New organic luminophores on the basis of cyano- and dicyanopyridines

Absorption and fluorescence spectra of solutions of cyanopyridine derivatives of polyphenylene type, II-VIII, were investigated. The spectral characteristics determined are interpreted in relation to the probable conformational structure of the investigated substances in the states S0 and S1. The relationship between the Stokes shift and the solvent effect on the fluorescence spectra is discussed.

Inhibition of replicative DNA synthesis and induction of DNA repair by intercalating drugs in human fibroblasts

A novel acrylic monomer bearing acridinyl group, acridine-9-N-acrylamide (Ac-9AA) was synthesized from 9-aminoacridine (9AA) and acryloyl chloride in the presence of triethylamine in dry dichloromethane (CCl2) at room temperature. The synthesized Ac-9AA was identified by IR, MS and 1H NMR spectra. Homopolymer of Ac-9AA was obtained using AIBN as a thermal initiator in THF under 65–70 °C and the average molecular weights (Mw) of poly(Ac-9AA) obtained was very low, being in the order of ca. 103. Copolymer of Ac-9AA and acrylamide was synthesized with thermal initiator and poly(Ac-9AA-co-AM) was characterized by the method of IR, UV–vis and DSC. The photophysical behaviors of Ac-9AA and its polymers were explored by recording the fluorescence spectra in solution, solid and film. In addition, the pH and temperature dependence on fluorescence of the water-soluble poly(Ac-9AA-co-AM) were investigated in detail. The results showed that the relative fluorescence intensity of poly(Ac-9AA-co-AM) had an excellent linear response to temperature in the range of 0–60 °C. Moreover, the fluorescence intensity increased continuously from low pH to high pH while the excitation maxima at 388 nm and emission maxima at 400 nm had redshift after the addition of HCl or NaOH, which results from the fact that the predominance of tautomeric forms of Ac-9AA changed at different medium. This investigation may provide a convenient way to prepared multifunctional macromolecule biomaterial bearing aminoacridine to probe pH and temperature in biological system.

An improved acriflavine-Feulgen reagent for quantitative DNA cytofluorometry.

We have modified the acriflavine-Feulgen histochemical method for the quantitative determination of DNA by performing the staining of hydrolyzed cells affixed to cover slips with acriflavine dissolved in 90% ethanol. Compared to conventional techniques, in which the acriflavine is dissolved in aqueous HCl plus potassium metabisulfite, this method not only decreased non-Feulgen (background) staining in both the nucleus and the cytoplasm, but also increased the fluorescent intensity of Feulgen stained nuclei more than four-fold. Cells stained by our modified method exhibited a fluorescence maximum of 507 nm, which is similar to the 500 nm fluorescence maximum obtained with acriflavine bound to apurinic acid solution by a modification of the acriflavine-Feulgen method. These fluorescence maxima are in contrast to the 510 nm to 625 nm fluorescence maxima which are obtained when cells are stained according to conventional protocols. The fluorescence intensities of nuclei of synchronized cells stained by the modified method were proportional to DNA content. Thus, by the criteria of staining specificity, in situ and in solution fluorescence spectra agreement and quantitative staining, we conclude that our modified acriflavine-Feulgen method is more satisfactory for quantitatively measuring DNA in situ by cytofluorometry than the usual acriflavine-Feulgen method.

Fluorescence spectra of solutions of halide salts with an admixture of seo 3 2? anions

Fluorescence spectra of solutions of halide salts with an admixture of seo 3 2? anions

Energy transfer by chlorophyll b in detergent micelles

The concentration-dependent depolarization, concentration-dependent quenching, absorption and fluorescence spectra in solutions of chlorophyll b-containing detergent micelles with Triton X-100 were studied in a concentration range of c = 0.4 μM–0.6mM chlorophyll b and c d = 0.4–7.0mM Triton X-100. The concentration-dependent depolarization obeys Fo¨rster's theory of depolarization of fluorescence with a transfer distance parameter R 0 = 43 ± 2A˚. The concentration-dependent quenching is described by an empirical formula for the relative fluorescence yieldη/η 0=sol1[1 + (cc 1/2) 2] given by Kelly and Porter (Kelly A. R. and Porter, G. (1970) Proc. R. Soc. Lond. Ser. A. 315, 149–161). With increasing chlorophyll b concentration the red absorption band at 650 nm is shifted toward a longer wavelength and its width increases by 10 nm, the intensity of the long wave fluorescence band increases about 720 nm. The results analysed in terms of these findings lead to the conclusions that chlorophyll b molecules are (a) locally concentrated in the micelles up to the concentration range of in vivo conditions, (b) partly in an aggregated state capable for fluorescence, (c) the chlorophyll b →chlorophyllb homotransfer may be about 3–26 % of the homotransfer chlorophyll a →chlorophyll-a depending on the ratio of their concentrations.

Investigation of the dependence of the quantum yield with respect to the fluorescence spectrum of solutions

On the basis of the theory of universal intermolecular interactions a general equation was obtained describing the dependence of the relative quantum yield on the frequency of the light of the fluorescence of solutions in the presence of quenching of the second kind. The spectral dependence of the quantum yield in the case of quenching of the fluorescence by contaminant nonlight-absorbing substances is considered in detail. Measurements carried out on aqueous glycerine solutions of 4-aminophthalimide and 1-, 3-, 5-triphenylpyrazoline quenched by potassium iodide confirmed the theoretical conclusions.

The effect of dye concentration upon the degree of polarization in the fluorescence spectra of solutions

The effect of dye concentration upon the degree of polarization in the fluorescence spectra of solutions

Auto-association of tetracene in solution

A systematic study of the absorption and fluorescence spectra of solution of tetracene led us to the discovery of two auto-associated species: microcrystals, improperly called a dimer by several authors and another species, which could be the true dimer.

Dependence of the fluorescence spectra of solutions of complex molecules on the exciting light

Dependence of the fluorescence spectra of solutions of complex molecules on the exciting light

Excimer Formation in Vinyl Polymers. I. Temperature Dependence in Fluid Solution

The fluorescence spectra of solutions of poly (2-vinyl naphthalene) in both fluid and glassy solvents have been studied at room temperature and at liquid-nitrogen temperature. Excimer emission was observed at all temperatures in glassy solution, but this emission is quenched at lower temperature in fluid solution. This behavior is interpreted in terms of excimer-forming main chain conformations which are of higher energy than the most favored conformation and maintain thermal equilibrium in fluid solution only. The temperature dependence of monomer chromophore emission in fluid solution is accurately fit with a kinetic model of intrachain excimer formation in which the chain conformer lifetime is limited by collision with solvent molecules. In n-propyl benzene solution, the energy barrier to excimer formation above the lowest-energy chain conformation was found to be 3608 cal/mole.

Excited molecular complexes of aromatic hydrocarbons

Measurements of fluorescence spectra of solutions at room temperature have been used to study the nature of intermolecular interaction in excited molecular complexes that are unstable in the ground state. It was concluded that (a) when the two molecules are unsubstituted aromatic hydrocarbons or their alkyl derivatives (mixed excimers), the type of inter action seems to be the same as in excimers, i.e., the complex is formed only when resonance interaction is possible and it has zero dipole moment; (b) when one of the hydrocarbons has a donor or acceptor substituent group (exciplexes), the main interaction has a charge-transfer character to which a dipole-dipole interaction may contribute if there is an overlap between the emission spectrum of the excited molecule and the absorption spectrum of the other.

Fluorescence spectra of solutions of europium chelates

The fluorescence spectra at different stages in the dissociation indicate the composition of the chelates and also the instability constants of some.

‘Excimer’ fluorescence VII. Spectral studies of naphthalene and its derivatives

The fluorescence spectra of solutions of naphthalene and fourteen of its methyl, ethyl, dimethyl and trimethyl derivatives were observed as a function of molar concentration c at 20 °C and as a function of temperature from 20 to -70 °C. All the compounds show similar excimer fluorescence characteristics with mean values of the excimer binding energy B = 0.28 ± 0.03 eV and of the excimer interaction energy V' m = 0.765 ± 0.03 eV, with the exception of 1,8-dimethyl naphthalene (B = 0.14 eV) in which excimer formation is sterically hindered. The monomer fluorescence quantum efficiencies and ionization potentials were also determined. The fluorescence spectra of liquid 1,6-dimethyl naphthalene and its solutions in three solvents were observed, and the rate parameters and the entropy change ∆ S on excimer formation were determined, B and ∆ S (= -19.1 cal mole -1 deg -1 ) have similar values in the pure liquid and in cis -decalin and dilute ( c ≤ 1 m) cyclohexane solutions, but slight differences occur in n -heptane and concentrated (c > 1 m ) cyclohexane solutions.

The Chemiluminescence, Fluorescence and Absorption Spectra of 2,4,5-Triphenylimidazole

Abstract The chemiluminescence spectra of 2,4,5-triphenylimidazole (lophine) in 1n ethanolic potassium hydroxide exhibited with oxygen and with hydrogen peroxide at 70°C have been measured. Both spectra spread, over about 470–660 mμ; the maximum wavelengths are 545 mμ and 555 mμ respectively. The fluorescence spectra of solutions of lophine have been measured at 70°C. The maximum wavelengths are as follows: 371 mμ, 388 mμ (ethanol), 441 mμ (1n KOH–C2H5OH) and 391 mμ (1 n CH3COOH–C2H5OH). The absorption spectra of lophine have also been measured: λmax 303 mμ (ε= 2.56× 1O4) in ethanol: λmax 326 mμ (ε=3.33×104) 1n ethanol potassium hydroxide, and λmax 295 mμ (ε=2.03×104) in a 1n solution of acetic acid in ethanol.

'Excimer’ fluorescence. IV. Solution spectra of polycyclic hydrocarbons

The fluorescence spectra of solutions of the following compounds which show excimer fluorescence are recorded: 5-ethyl, 5-butyl, 5-propyl, 5-amyl and 6-isopropyl 1:2-benzanthracene; 1:2:3:4-dibenzanthracene, perylene, 1:12-benzperylene and anthanthrene; and 2,5-diphenyloxazole. The spectra of these and other compounds showing excimer fluorescence are analyzed and discussed in terms of the potential energy of the dimer in its excited and ground states. A consideration of the molecular structure and energy levels of further compounds which do not show excimer fluorescence in solution indicates various factors which may inhibit excimer formation, namely (i) chemical combination, (ii) steric hindrance, and (iii) weakness of interaction.

‘Excimer’ fluorescence I. Solution spectra of 1:2-benzanthracene derivatives

Observations have been made of the concentration dependence of the fluorescence spectra of solutions of 1:2-benzanthracene and fifteen of its hydrocarbon derivatives. All of the compounds, except the 9,10-dim ethyl derivative, exhibit dim er emission at higher concentrations. The lower excited states, 1 L b and 1 L a , satisfy Förster’s conditions for fluorescent dim er formation. The factors determining the relative quantum yield of excimer fluorescence are discussed. The different types of crystal fluorescence spectra shown by the compounds are explained in terms of excimer formation in the crystal lattice.

Excimer fluorescence spectra of pyrene derivatives

Results are given for the effect of concentration on the fluorescence spectra of solutions of pyrene and a number of its derivatives, and the mechanism involved in this effect is discussed.

The connection of the absorption and fluorescence spectra of solutions

The connection of the absorption and fluorescence spectra of solutions

Fluorescence spectra of solutions of uranyl nitrate at liquid air temperature

Photometric studies on the fluorescence spectra of rapidly cooled aqueous and alcoholic solutions of uranyl nitrate are reported. Five distinct series of bands, designated asα, β′, γ, δ andα′ appear, depending upon concentration, pH, solvent, etc. From their conditions of enhancement and suppression and close analogy with corresponding room temperature spectra reported earlier, theα andγ-bands are shown to be due to the species UO 2 ++ (hydrated) and UO3UO 2 ++ . Higher hydrolysed species give δ-bands. Theα′-bands, which appear in alcoholic solutions also, are attributed to UO2(NO3)2 ·xH2O. The assignment ofβ′-bands is not certain. The intensity distribution in various series is studied and it is found that relative toα series the distribution is largely shifted away from the (0, 0) band inα′ series and towards the (0, 0) band inγ series. Theα′ andγ bands disappear around −60° C. which corresponds with the transformation temperature of ice structure. Various characteristics in the spectra are discussed on the basis of environmental differences in the species.