1,2,3-Triazabutadiene. VII. Untersuchungen zum Mechanismus der fotochemischen cis-trans-Isomerisierung von 1-Aryl-3[3-methyl-benzthiazolinyliden-(2)]-triazenen

1,2,3-Triazabutadienes. VII. Investigation of the Mechanism of the Photochemical cis-trans-Isomerization of 1-Aryl-3-[3-methyl-benzthiazolinyliden-(2)]-triazenes The direct photoisomerizations of substituted triazabutadienes are investigated. The quantum yields do not considerably depend on substituents in the phenyl-group of triazabutadienes, on the wavelength of irradiation light and on the solvent. The quantum yields of the cis→trans-transformation are always higher than the quantum yields of the back reaction. The sums of quantum yields approximate 1. At low temperatures the quantum yields of photoisomerization become smaller in a significant way. With flash photolysis it is not possible to prove triplet state of triazabutadienes. Triplet quenchers have no influence on photoisomerization. The mechanism of the photochemical cis-trans-isomerization of triazabutadienes is discussed.     

1,2,3-Triazabutadiene. V. Untersuchungen zum Mechanismus der thermischen cis-trans-Isomerisierung von substituierten 1-Aryl-3-[methylbenzthiazolinyliden-(2)]-triazenen

1,2,3-Triazabutadienes. V. Investigations of the Mechanism of the Thermal cis-trans Isomerisation of Substituted 1-aryl-3-[methylbenzthiazolinyliden-(2)]-triazenes The velocity of the thermal cis-trans-isomerisation of substituted 1-aryl-3-[methyl-benzthiazolinyliden-(2)]-triazenes was determined, varying the substituents in the aryl resp. benzo residue, the temperature and the solvent. Electron- withdrawing substituents in ortho- resp. para-position of the aryl residue and electron-releasing substituents in position 6 of the benzo residue increase the velocity of isomerisation as it do polar solvents and acid catalyst. In the aryl residue electron-releasing substituted and in meta-position electron-withdrawing substituted derivatives do not thermically isomerise in solution under the given conditions. From these results a polar rotation mechanism of the isomerisation around the NN-double bound of the triazabutadiene chain is concluded.     

1,2,3-Triazabutadiene. XX. Untersuchungen zur Fotoisomerisierung,Fotolyse, Protonierung und sauren Spaltung von 1-Aryl-3-[3-methyl-benzthiazolinyliden-(2)]-triazenen in mizellaren Lösungen

1,2,3-Triazabutadienes. XX. Investigations of the Photochemical Z-E-Isomerization, Photolysis, Protonation and Acidic Cleavage of 1-Aryl-3-3-methylbenzthiazolinyliden-(2)-triazenes in Micellar Solutions The E-isomers of the 1-Aryl-3-[3-methylbenzthiazolinyliden-(2)]-triazenes are soluble in aqueous micellar solutions of sodium dodecylsulfate (NDS) and cetyltrimethylammoniumbromide (CTAB). They are fixed in the Stern region of the micelles. The Z-isomers decompose in aqueous micellar solutions by acidic cleavage. They can be stabilized by the use of alkaline buffer solutions. The concentration of protons is higher by the factor 10³ in the Stern region of NDS-micelles than in the Stern region of CTAB-micelles. This difference is explained by electrostatic attraction and repulsion between the protons and the micelles. The quantum yields of the photochemical isomerization in micellar solutions and in organic solvents are the same. Water soluble ionic dyes with relatively low triplet energies sensitize the photoisomerization in micellar solutions and the photostationary state is on the side of the E-isomer.     

1,2,3-Triazabutadiene. VI. Untersuchungen zur cis-trans-Isomerie von 1-Aryl-1-äthyl-3-[3-methyl-benzthiazolinyliden-(2)]-triazeniumtetrafluoroboraten

1,2,3-Triazabutadiene. VI. Studies on the Cis-trans-Isomerisation of 1-Aryl-1-äthyl-3-(3-methylbenzthiazolin-2-ylidene) -triazeniumtetrafluoroborates Cis-trans-isomeric 1-aryl-3-[3-methylbenzthiazolinylidene-(2)]-triazenes will be alkylated under kinetic control stereospecifically to the corresponding cis-trans-isomeric 1-aryl-1-ethyltriazenium-tetraflouroborates 2 . By their n.m.r.(¹H and ¹³C)- and u.v.-vis.-spectroscopical as well as by their thermical and photochemical behavior the pairs of isomers are characterized as cis-trans-isomers about the N-1-N-2-bond. The rate of the thermal cis-trans-isomerisation depends from the substituents in 2 and from the solvent. Electron withdrawing substituents in para-position of the arylresidue and electron donors in the heterocycle increases the rate of the isomerisation. Morever it increases with an increasing DN-value of the solvent. The isomers can be changed into each other photochemically. The quantum yield of the cis-trans-isomerisation is evidently higher than of the trans-cis-transformation.     

1,2,3-Triazabutadiene. IX. 15N-NMR-spektroskopische Untersuchungen an cis-trans-isomeren 1-Aryl-3-[3-methylbenzthiazolinyliden-(2)]-triazenen und -triazeniumsalzen

1,2,3-Triazabutadienes. IX. ¹⁵N-NMR-spectroscopic Investigations of Cis-Trans-Isomeric 1-Aryl-3-[3-methylbenzthiazolinyliden-(2)]-triazenes and -triazenium-salts The ¹⁵N-chemical-shifts and coupling constants of systematically ¹⁵N-labeled cis-trans-isomeric 1,2,3-triazabutadienes 1a–c and triazenium-salts were determined and discussed with respect to the steric and electronic structure of the compounds. The chemical shifts correlate with the π-electron density calculated in PPP-approximation. The similarity of the chemical shifts and coupling constants of the respective alkylated and protonated compounds proves the preferred protonation of the trans triazabutadien chain in N₁-position.     

1,2,3-Triazabutadiene. XI. Untersuchungen zur iod-sensibilisierten Fotoisomerisierung von 1-Aryl-3-(3-methyl-benzthiazolin-2-yliden) triazenen

1,2,3-Triazabutadienes. XI. Investigation of the Iodine-induced Photoisomerization of 1-Aryl-3-(3-methyl-benzthiazolin-2-yliden) triazenes cis-1-Aryl-3-(3-methyl-benzthiazolin-2-yliden)triazenes isomerize induced photo-chemically by iodine to the trans-isomer. The wavelength of the used irradiation light was 546 nm so that only I₂ absorb. The dependence of the quantum yields on the concentration of the cis-isomer and on the intensity of the irradiation light was investigated. The influence of the light intensity on the quantum yields shows, that the primary step is the dissoziation of I₂-molecules to I·- radicals, which induce the isomerization.     

1,2,3-Triazabutadiene. XIII. UV-vis-spektroskopische Untersuchungen zur Protonierung Z-E-isomerer 1-Aryl-3-[3-methylbenzthiazolinyliden-(2)]- und 1-Aryl-3-[1,3-dimethylbenzimidazolinyliden-(2)]-triazene

1,2,3-Triazabutadienes. XIII. U.V.-vis-Spectroscopic Investigations of the Protonation of Z-E-Isomeric 1-Aryl-3-[3-methylbenzthiazolinyliden-(2)]- and 1-Aryl-3-[1,3-dimethylbenzimidazolinyliden-(2)]-triazenes The u.v.-vis absorption spectra of Z-E-isomeric 1-aryl-3-[3-methylbenzthiazolinyliden-(2)]- and 1-aryl-3-[1,3-dimethyl-benzimidazolinyliden-(2)]-triazenes 1–3 resp. 4 show a pronounced halochromic effect in the presence of acids. The reason is the protonation of the N¹-atom of the triazabutadiene chain whereby the energetically favourable structure of a diazatrimethine is formed. The magnitude of the halochromic effect depends on the substituents in the aryl and benzo residue and on the Z-E-structure of the compounds.     

Photooxidation von Leukofarbstoffen. VIII. Kurzzeitspektroskopische Untersuchungen zum Mechanismus der Photooxidation von Leukokristallviolett

Photooxidation of Leuco Dyes. VIII. Time Resolved Investigations of the Mechanism of the Photooxidation of Leucocrystal Violet The photooxidation of leucocrystal violet has been reexamined by means of conventional and laser flash photolysis as well as spin trap experiments. Three radical transients have been observed and assigned to the cation radical (λ_max ≈ 490, 530 nm), the neutral radical with one NCH₃ CH₂ moiety (λ_max ≈ 480 nm) and the triphenyl methyl radical derivative (λmax ≈ 400 nm).     

1,2,3-Triazabutadiene. XII. Abhängigkeit der 13C-15N-Kopplungskonstanten von der Z/E-Isomerie der 1-Phenyl-3-[3-ethylbenzthiazolinyliden-(2)]-triazene und 1-Phenyl-1-ethyl-3-[3-ethylbenzthiazolinyliden-(2)]-triazenium- tetrafluoroborate

1,2,3-Triazabutadienes. XII. Dependence of the ¹³C- ¹⁵N Coupling Constants on the Z/E-Isomerism of the 1-Phenyl-3-[3-ethylbenzthiazolinyden-(2)]-triazenes and 1-Phenyl-1-ethyl-3-[3-ethylbenzthiazolinyliden-(2)]-triazenium-tetrafluoroborates ¹³C- and ¹⁵N spectra have been measured for the ¹⁵N-labelled triazene 1 and triazenium salt 2 . The ¹³C-¹⁵N coupling constants are discussed in the light of the Z/E-isomerism of the compounds. A significant nitrogen lone pair effect of the Z/E isomers on the magnitude of the coupling constant ¹J(¹⁵N₁ ¹³C₁·) was observed and discussed.     

Tetrazolverbindungen. 4 [1]. Alkylierung von 1-Aryl-5-(2-dimethylamino-vinyl)-1 H-tetrazolen

Tetrazole Compounds. 4. Alkylation of 1-Aryl-5-(2-dimethylamino-vinyl)-1 H-tetrazoles Alkylation of 1-aryl-5-(2-dimethylamino-vinyl)-1 H-tetrazoles 1 with dialkyl sulfates or alkyl iodides yields mainly 4-alkyl-1-aryl-5-(2-dimethylamino-vinyl)-1 H-tetrazolium salts which can be isolated free from isomers by separation as perchlorates 2 . The reaction proceeds with retention of the E configuration of the vinyl group. In contrast to 1 the methyl groups of the dimethylamino substituent in 2 are magnetically non-equivalent indicating restricted rotation of this residue. On heating 2 with aqueous mineral acids the dimethylaminovinyl moiety undergoes degradation to a methyl group affording 4-alkyl-1-aryl-5-methyl-1 H-tetrazolium salts 4 , the structure of which was confirmed by independent synthesis. With hot aqueous alkali hydroxide 2 reacts under ring cleavage to give aryl azide. — ¹H n.m.r. and u.v. spectroscopic data of the tetrazolium salts 2 and 4 are reported.     

1,2,3-Triazabutadiene. XXII. Photochemie der 1-(Carbmethoxy-aryl)- und 1-(Carboxy-aryl)-3-(3-alkyl-benzthiazolinyliden-(2))-triazene als potentielle CEL-Farbstoffe

1,2,3-Triazabutadienes. XXII. Photochemistry of 1-(Carbmethoxy-aryl)- and 1-(Carboxy-aryl)-3-(3-alkyl-benzthiazolinyliden-(2))-triazenes as potential CEL-dyes 1-(Carbmethoxy-aryl)-3-(3-alkyl-benzthiazolinyliden-(2))-triazenes (ester-triazenes) ( 1 ) were synthesized by coupling of substituted 3-alkyl-2-imino-benzthiazolines-(1,3) with 2-, 3- and 4-carbmethoxy-benzenediazonium salts. The Z-isomers obtained can be transformed into the E-isomers 2 photochemically or by heating. In the presence of acids the E-ester-triazenes are protonated. From the E-ester-triazenes the potassium-salts ( 4 ) can be produced by alkaline ester hydrolysis. With hydrochloric acid the E-triazene-potassium salts ( 4 ) can be transformed into the protonated (at the N(1)-Atom) E-acid-triazenes ( 5 ). Their photochemical properties are identical with those of the protonated E-ester-triazenes ( 3 ). The 1-(carboxy-aryl)-3-(3-alkyl-benzthiazolinyliden-(2))-triazenes (E-acid-triazenes) ( 6 ) can be obtained from the protonated derivates by deprotonation in the presence of water. The photochemical behaviour of the E-acid-triazenes ( 6 ) and of the E-triazene-potassium-salts ( 4 ) depends on the position of the carboxy-group (2-position: photolysis, 3- and 4-position: photoisomerization). The uv/vis-spectroscopical and photochemical properties of the triazene-derivates in solution and in polymeric layers are discussed.     

1,2,3-Triazabutadiene XXI [1]. Zur Bestimmung des Oberflächenpotentials und des relativen pH-Wertes in der Sternregion anionischer Mizellen unter Verwendung von 1-(4′-Chlorphenyl)-3-(3-methylbenzthiazolinyliden-(2))-triazen als Sonde

1,2,3-Triazabutadienes. XXI. Determination of the Electrical Surface-potential and of the Relative pH Value in the Stern Region of Anionic Micelles by using 1-(4′-Chlorphenyl)-3-(3-methylbenzthiazolinyliden-(2))-triazene as Probe The title triazene is insoluble in water but it can be solubilized in the Stern region of micelles. It is used as pH indicator for the Stern region of anionic micelles. The relative pK_s-values for the triazene are determined in anionic micellar solutions of different detergents. The electrical potential at the surface of the charged micelles is calculated using the value of SDS-micelles for calibration. The dependence of the electrical potential and the pH value in the Stern region on the structure of the detergents is discussed.