Peter Magdolen

Ultrasound effect on the aromatic nucleophilic substitution reactions on some haloarenes

The sonochemical nucleophilic aromatic substitutions on haloarenes with different amines have been studied. A beneficial ultrasound effect was observed and high yields of the products were obtained after 15-30 min sonication. The reaction course of the nucleophilic aromatic substitution was found to be strongly dependent on nucleophilicity, bulkiness, and boiling point of amines as well as on the electron-withdrawing property of the substituents on the haloarenes.

New conjugated benzothiazole-N-oxides: synthesis and biological activity.

Eleven new 2-styrylbenzothiazole-N-oxides have been prepared by aldol – type condensation reactions between 2-methylbenzothiazole–N-oxide and para-substituted benzaldehydes. Compounds with cyclic amino substituents showed typical push-pull molecule properties. Four compounds were tested against various bacterial strains as well as the protozoan Euglena gracilis as model microorganisms. Unlike previously prepared analogous benzothiazolium salts, only weak activity was recorded.

Spectroscopic study of 2-[2-(4-cyclaminophenyl)ethen-1-yl] benzothiazoles and their N-allylbenzothiazolium bromides. Solvent and substituent effects on their ultraviolet–visible and fluorescence spectra

UV-vis and fluorescence spectra of 2-[2-(4-cyclaminophenyl)ethen-1-yl] benzothiazoles 1 and their N-allylbenzothiazolium bromides 2 have been measured and interpreted. The substitution and solvent effects on electronic structure and spectra have been investigated. The benzothiazolium salts substituted with saturated cyclamines show strong push-pull character and can be used as potential NLO materials. Formation of aggregated structures was observed at higher concentrations of the benzothiazolium bromides.

Conjugated push-pull salts derived from linear benzobisthiazole: preparation and optical properties

A series of novel monomethylated salts derived from linear benzobisthiazole was prepared. The push-pull attributes of these new compounds are represented by a quaternised azolium cycle as the acceptor part at one end of the structure and the dialkylamino- or diarylamino-substituted benzene ring as the donor part at the opposite end. Both moieties are connected by a conjugated linker consisting of one or two double bonds. Such dipolar structures are promising candidates for non-linear optical materials. The quantum-chemical indices describing linear and non-linear optical properties were obtained from semi-empirical calculations. The relationships between the chemical structure and non-linear optical properties of the cations studied were obtained. Effective conjugation was confirmed by measuring the optical properties in the UV-VIS region.

On the 3-Aminophenothiazine Synthesis

Abstract Investigation of the key step of 3-aminophenothiazine (5) synthesis, that is thiation of N-(4-phenylaminophenyl)-phthalimid (3) was carried out. The best results were achieved using microwave irradiation, when 55% of the pure thiation product 3-phalimidophenothiazine (4) were isolated in 10–20 min reaction time.

Photophysical properties and photostability of novel benzothiazole-based D-π-A-π-D systems.

The photophysical properties and photochemical stability of two novel D-π-A-π-D systems based on a benzothiazole core and terminal N,N-dimethylaminophenyl and N,N-diphenylaminophenyl groups were investigated. The quantum yield of photoreactions (Φ) was determined for various oxygen concentrations in the solvent (CH2Cl2) and various irradiation wavelengths. Trans-cis photoisomerization is proposed as a photobleaching mechanism during irradiation at longer wavelength due to charge-transfer transitions. Solution deoxygenation led to an unusual decrease in the photostability of the compounds investigated, most likely because of cation radical formation. The population of higher excited states for short-wavelength irradiation opened another degradation pathway and the overall degradation percentage decreased in comparison with long-wavelength irradiation. We assume that photoisomerization of the second double bond and electron transfer to CH2Cl2 (and subsequent oxidation reactions) contribute to this slower degradation branch. Singlet oxygen contributes significantly, albeit to the smallest values of Φ, to the overall photodegradation for both types of irradiation.