Structures of the complexes and proton transfer in the ground and excited states in aniline-acid systems

Mikheev, V. A.; Shraiber, V. M.

doi:10.1007/bf00661521

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“…24 It can be assumed that the second molecule of trifluoroacetic acid is tightly held by the anion of the same acid due to the hydrogen bond. 25 Ion pairs of the composition 1 : 2 are observed, for example, on protonation of 2,4,6 triarylpyridine with tri fluoroacetic acid in dioxane, 26 as well as on protonation of 7 aminocoumarins in acetonitrile with the same acid. 27 The reaction of dye 1a with sulfuric acid in ethanol can be described by the alternative scheme including forma Table 2.…”

Section: Resultsmentioning

confidence: 96%

Complexation of crown-containing butadienyl dyes with alkali and alkaline earth metal cations in the ground and excited electron states

et al. 2010

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Spectrophotometry and steady state fluorimetry were used for the study of complexation of crown containing butadienyl dyes with alkali and alkaline earth metal cations in acetonitrile, as well as protonation of these dyes with trifluoroacetic acid. Complexation of the compounds studied with the metal cations leads to the 1 : 1 product, whereas protonation with trifluoroace tic acid affords the 1 : 2 product containing 2 moles of the acid per 1 mole of the dye. Stability constants of the complexes are varied from 10 to 10 6 L mol -1 , basicity of the crown containing dyes in the reaction with trifluoroacetic acid increases with the increase in the macrocycle size. On complexation, the fluorescence spectra are shifted considerably less than the absorption spectra. This indicates that photorecoordination of the cation in the complex excited molecules occurred. Based on the correlation of the spectral shifts with the metal cation charge density, three types of complexes differing in the extent of influence of the cation charge on the spectral shifts can be singled out: "tight", "loose", and "solvent separated".The presence of crown ether fragments in dyes can sharply change their spectral luminescent properties on complexation and serve as optical molecular sensors for determination of a wide number of inorganic and organic cations. 1-6 Crown containing dyes can serve as a basis for the development of systems with a light controlled func tion of the cation bindings, capable upon irradiation to rapidly liberate necessary amount of free ions into solu tion. 2,5-7 Complexation with cations can serve as an in strument for the control of chromophore or acid base func tions of a dye, 2,5-9 including influence on the excited state intramolecular proton transfer. 10,11 Since all the va rieties in behavior of crown containing dyes are defined by their complexing ability, it is necessary to quantitatively characterize this ability by determination of stability con stants of the crown complexes with metal cations.In the present work, influence of the nature of a metal cation, a heterocyclic residue of the dye, and the size of a macrocycle cavity on the complexation of crown con taining butadienyl dyes 1b,c and 2 with alkali and alkaline earth metal perchlorates in acetonitrile have been studied. To find the limits of the complexation effects and a possi * Dedicated to Academician I. L. Eremenko on his 60th birthday. n = 1 (b), 2 (c)

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Section: Resultsmentioning

confidence: 96%