Photochromic crown ethers .1. Formation of ion pairs, trans-cis-isomerization, and metal ion binding in a nonpolar mediumстатья
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Дата последнего поиска статьи во внешних источниках: 18 июля 2013 г.
Аннотация:An amphiphilic crown-containing styryl dye (1) was synthesized, and the effects of irradiation, temperature, and alkali and alkali-earth metal ions on the conductivity and optical spectra of its solutions in dioctyl phthalate were studied. Compound 1 in the transform almost completely exists as ion pairs (IF). Irradiation at a long-wavelength absorption maximum (lambda(max)) results in a reversible increase in the conductivity and, hence, a degree of dissociation of IP (alpha); these parameters decrease when complexes with metal ions are formed. The relaxation times for the photoinduced conductivity coincide with a decrease in the extinction within experimental error in the 20-60 degrees C temperature range. The photoinduced increase in alpha is caused by trans-cis-isomerization and an increase in steric hindrances for the interaction of the ClO4- anion with the N+ atom of benzothiazolium in the cis-form of 1. The activation energies for the dark cis-trans-relaxation, absolute alpha values, and thermodynamic parameters of dissociation of IP in the trans-form, as well as the alpha values in a photostationary mixture of cis-trans-isomers, were estimated. The decrease in alpha after binding with metal ions is likely caused by the redistribution of the positive charge to benzothiazolium through the conjugated system of 1. Correlations between the decrease in conductivity (decrease in alpha) and the hypsochromic shift Delta lambda(max) after the formation of complexes between 1 and metal ions were observed.