Fotochemische Primärprozesse von Xanthenfarbstoffen. VIII. Zum Einfluß von gemischten Mizellen auf die fotochemischen Primärprozesse von Selenopyronin und Erythrosin sowie die sensibilisierte Diazoniumsalzfotolyse

Photochemical Primary Processes of Xanthene Dyes. VIII. Influence of Mixed Micelles on the Photochemical Primary Processes of Selenopyronine and Erythrosine and the Sensitized Photolysis of Diazonium Salts The influence of the nonionic detergent dodecyltriglycol (DTG) on the escape rate of dye ions from cationic and anionic micelles is investigated. The rate constant of the escape of selenopyronine ions (Sp^⊕) from mixed micelles of sodium dodecylsulfate (NDS) and DTG (1:1) (k_A ≈︁ 3,2 · 10⁴ s⁻¹) is, as a result of the lower charge density, higher by the factor 10 than that from clean NDS-micelles (k_A ≈︁; 2,8 · 10³ s⁻¹). Erythrosine ions (Et^2⊖) are tightly fixed to cetyltrimethylammoniumbromide (CTAB)-micelles (k_A ≈︁; 0,25 · 10³ s⁻¹) and to mixed micelles of CTAB and DTG (1:1). This may be a result of the twofold negative charge of the erythrosine ions. Properties of the mixed micelles (polarity, average aggregation numbers) are determined by using the dyes and pyrene as probes. The sensitized photolysis of diazonium salts by electron transfer from photoexited selenopyronine under aerobic conditions is more effective by a factor of 3–5 in the presence of anionic micelles than when in a water solution.     

Photochemische Primärprozesse von Xanthenfarbstoffen. II. Blitzlichtspektroskopische Untersuchungen zum Einfluß von anionischen Mizellen auf die photochemischen Primärprozesse von Selenopyronin

Photochemical Primary Processes of Xanthene Dyes. II. Investigations of the Influence of Anionic Micelles on the Primary Processes of Selenopyronine by Flash Excitation In aqueous solutions containing anionic micelles, the dye cations of selenopyronine are present at the micellar surface. If the concentration of the dye ions is much lower than the concentration of micelles, only monomolecular triplet decay (k₁^aM = 2 · 10⁻³s⁻¹) is observed. Under these conditions, the half-oxidized and half-reduced form of selenopyronin is not formed. If the concentration of the dye ions is much higher than the concentration of micelles, two or more dye ions are present at every micelle, and a fast bimolecular decay of the triplet state during the flash is observed. The quenching of the triplet state with p-benzoquinone (k₇^aM = 1,9 · 10⁹ l/mol s), DABCO (k₁₀^aM = 1,6 · 10⁷ l/mol s) and EDTA (k₁₁^aM = 1,3 · 10⁵ l/mol s) and the decay processes of the half-reduced and half-oxidized form in the micellar solution are investigated.     

Fotochemische Primärprozesse von Xanthenfarbstoffen. V. Untersuchungen zum Mizelleinfluß auf die fotochemischen Primärprozesse von Erythrosin

Photochemical Primary Processes of Xanthene Dyes. V. Investigations of the Influence of Micelles on the Photochemical Primary Processes of Erythrosine The triplet state of erythrosine decays in water solution mono- and bimolecularly (k₁ = 0,85 · 10⁴ s⁻¹; k_bi = 7,6 · 10⁸ l/mol s). As results of the bimolecular triplet decay a half-reduced and a half-oxidized form of the dye are observed. The dye ions are localized in the Stern layer of cationic micelles. The triplet state of those dye ions, which are localized individually at micelles, decays only monomolecularly (k = 2,1 · 10³ s⁻¹). If two or more dye ions are localized at a micelle, the bimolecular triplet decay takes place during the flash. Anionic micelles have no influence on the triplet decay processes of erythrosine.     

Photochemische Primärprozesse von Xanthenfarbstoffen. III. Blitzlichtspektroskopische Untersuchungen zum Einfluß von kationischen Mizellen auf die Photoredoxprozesse von Selenopyronin

Photochemical Primary Processes of Xanthene Dyes. III. Investigations of the Influence of Cationic Micelles on the Photoredox Processes of Selenopyronine by Flash Excitation Cationic micelles have no influence on the decay of the triplet state of selenopyronine (³F⁺). The products of photoredox reactions ³F⁺ + ³F⁺ (F⁺) → F^· + F and ³F⁺ + DABCO → F^· + DABCO live longer in the presence of the cationic micelles. The reason for the change of the lifetime is a separation of the photoredox products by micelles. F^. is stored in the interior of the micelles. The positively charged F and DABCO are repelled from the micelles and the electron back transfer is hindered.     

Photochemische Primärprozesse von Xanthenfarbstoffen. I. Blitzlichtspektroskopische Untersuchung der Primärprozesse von Selenopyronin

Photochemical Primary Processes of Xanthene Dyes. I. Investigations of the Primary Processes of Selenopyronine by Flash Excitation The triplet-state of selenopyronine absorbs light in the whole investigated spectral range (λ_max = 400 nm, 480 nm, 690 nm). As results of the bimolecular triplet decay a half-reduced (λ_max = 430 nm) and a half-oxidized (λ_max = 475 nm) form of the dye are observed. p-Benzoquinone quenches the triplet-state (k₇ = 1,5 · 10⁹ l/mol s) and the results are the half-oxidized form and the p-benzosemiquinone ion. For these two products different decay processes exist. The reducing agents DABCO, EDTA and Hydroquinone also quench the triplet state (k₁₀ = 1,2 · 10⁶ l/mol s, k₁₁ = 1,0 · 10⁶ l/mol s, k₁₂ = 1,0 · 10⁹ l/mol s) and as result the half-reduced form is observed. Measurements with thiopyronine give analogous results, which are in good agreement with investigations published in the literature.     

Einfluß von Weichmachern auf die Löschung der Lumineszenz von Pyronin B in Polymerfilmen

The effects of several plasticizers in layer-forming polymeric compounds are determined by means of the delayed fluorescence of Pyronine B to analyse the interactions between the plasticizers and polymers. It was found that small concentrations of the plasticizers harden the polymeric layers, with which, for instance, the oxygen permeability decreases. This phenomenon is marked especially for cellulose diacetate, for some plasticizers up to 30%.     

Löschung der Fluoreszenz aromatischer Urethane durch Ketone

Fluorescence Quenching of N-Arylurethanes by Ketones Fluorescence and photo-Fries reaction of N-aryl-urethanes can be quenched by diffusion-controlled energy transfer to biacetyl, acetone and other aliphatic ketones. Quenching of the photo reaction and fluorescence obeys the Stern- Volmer Equation. The efficiency of quenching may by influenced by solvents and substituents changing the S₁ energies of donors and acceptors. The identical rate constants determined by independent methods demonstrate that quenching of urethane fluorescence and photoreaction by aliphatic ketones occurs completely by singlet energy transfer.     

Desaktivierungsverhalten von Arenen und Heteroarenen. XVII. Löschung der Fluoreszenz von Kationen durch Anionen

Deactivation Behaviour of Arenes and Heteroarenes. XVII. Fluorescence Quenching of Cations by Anions Fluorescence quenching, caused by cation-anion interaction in the excited state, was investigated for the combinations of 13 acridinium and acridizinium ions (fluorophors) and chloride, bromide and iodide (quenchers). The obtained dependence of rate constants of dynamic quenching process on the acceptor properties of cations in the case of chloride is interpreted by the model of electron transfer in the encounter state. The resulting limit-rate constants of quenching are greater than those of diffusion of neutral molecules, caused by the Coulomb-interaction between cation and anion.     

Einfluß der Struktur auf die Unverträglichkeit von Polymergemischen in Lösung

The influence of polymer structure on the incompatibility in solution was investigated with combinations of 15 polyacrylates and polymethacrylates with different ester chain length. Small changes in polymer structure already cause an incompatibility in solution. In general it was found that the higher the difference in the carbon number the higher is the incompatibility. Furthermore there exists a dependence on the molecular weight of the polymer and on the nature of the solvent. Finally it was found that in contradiction to published data polyvinylacetate and polymethylacrylate are incompatible both, in dissolved and in solid state.     

Desaktivierungsverhalten von Arenen und Heteroarenen. XXXIII. Zur statischen Löschung der Fluoreszenz von Azinium-Anthracenen in Lösungsmitteln mit n-Donatoreigenschaften

Deactivation Behaviour of Arenes and Heteroarenes. XXXIII. Static Fluorescence Quenching of Azinium-Anthracenes by Solvents of n-Donor Properties The fluorescence of azinium-anthracenes is quenched by solvents of n-donor properties. A model of static quenching by electron transfer is developed analogous to the dynamic process. The rates of quenching correlate with the donor properties of the solvent (ionization potential) and the acceptor properties of the fluorophor (reduction potential). In the same way as in the case of dynamic quenching this static process is characterized by a high free enthalpy of activation. The existence of a thermally induced step in the process of the electron transfer affects the temperature dependence of the fluorescence quantum yields. The analysis of this temperature dependence on the basis of an Arrhenius equation shows a linear relationship.     

Bestimmung der Dimerisationskonstanten kationischer Farbstoffe in festen Schichten von Polyvinylalkohol durch Eigenlöschung der Fluoreszenz

Determination of Dimerization Constants of Cationic Dyes in Solid Layers of Polyvinyl Alcohol by Means of Fluorescence Self-Quenching The concentration-dependent quenching of the fluorescence of cationic dyes (acridine orange, methylene blue, rhodamine B, and rhodamine 6G, respectively) has been used to evaluate the monomerdimer equilibrium constants of these dyes.     

Zum Verhalten von Polyamidcarbonsäuren aus Pyromellithsäuredianhydrid und Benzidin in Lösung. II. Einfluß von Triäthylamin auf die Viskosität der Lösungen von Polyamidcarbonsäure in Dimethylacetamid

By addition of triethylamin (TEA) to a dilute solution of poly(amic acid) in dimethylacetamide (DMA) a strong increase of the reduced specific viscosity (η_sp/c) was observed. This can be explained by coil-widening caused by electrostatic forces between -COO^?-groups on the polymer chains. The ions are formed by the following proton transfer reaction: The dependence of the η_sp/c-values on the polymer concentration and the slope of the (η_sp/c)/c-curves (measured in DMA) are principially similar to those observed with polyelectrolytes in aqueous solutions. In contrast to the aqueous systems the η_sp/c-values in DMA do not pass through a maximum with increasing addition of base, but move asymptotically toward certain limiting values. The characteristic run of the viscosity-titration-curves is due to the fact, that in this case the neutralisation of the poly(amic acid) is carried out in an aprotic solvent with a base (TEA) which is incapable to dissociate itself. Therefore an excess of TEA favours the formation of ions according to the above equilibrium but does not increase the ionic strength of the solution. The ionic character of the discussed mechanisms is confirmed by corresponding electrolytic conductivity measurements. A comparison of the viscosity-titration-curves of poly(amic acid) and polymethacrylic acid shows the strong effect of the primary chain structure (stiffness of the chain) on the degree of coil widening.     

Zum Einfluß von Polyvinylsulfat auf die Photodimerisierung von Acridiziniumperchlorat

The Influence of Sodium Polyvinylsulfate on the Photodimerization of Acridizinium Perchlorate During the irradiation of aqueous solutions of acridizinium perchlorate (λ_exc = 405 nm) a photodimer of this compound is formed. The quantum yield of the reaction depends on the concentration of the acridizinium ion. In 10⁻⁴ m solutions the quantum yield of dimerization is π = 0.0054 ± 0.0005. Addition of the anionic polyelectrolyte sodium polyvinylsulfate leads to a considerable increase of the quantum yield (up to π = 0.6) in dependence on the concentration of the polyion. A kinetic model is developed, including the electrostatic interaction of the acridizinium cation and the polyanion. The influence of diazonium cations as competitive agent is investigated and dicussed.     

Zum abbau von polymerlösungen durch kapillarscherung. Einfluß der kapillarlänge und strömungsform auf den abbau

The dependence of shear degradation of polymer solutions on capillary length at constant shear stress is investigated with solutions of poly(isobutylene) (M_vis=6,1 · 10⁶) in toluene. We examined concentrations of 0.1, 0.25, 1 and 4% and found the degradation to increase with capillary length. In 0,1% solution we found a decreased efficiency of degradation, due to a change in the structure of solution. Flow instabilities, which appear above a critical shear rate D in polymer solutions and pretend a loss in viscosity, are not caused by shear degradation. This result supports our interpretation of unstable flow of polymer solutions as slip flow (spurt).