Control of Photochemical Properties of Monolayers and Langmuir-Blodgett Films of Amphiphilic Chromoionophores
Résumé
Control of the structure of ultrathin films that determine the steric conditions of the passing of intermolecular interactions is one of the most promising methods of implementing the advantages of planar supramolecular systems as basic elements of nanosize information devices. This work studies the behavior of Langmuir monolayers of a new amphiphilic crown-substituted chromoionophore I on a water subphase. It is found that dithiaazacrown ether in molecule I selectively binds Hg2+ cations both in organic solvents and from aqueous subphase. The electronic absorption spectra of the monolayer showed that H-aggregation occurs actively in the course of two-dimensional compression on deionized water, which hinders the complexation process, while the presence of Na+ and Ba2+ cations in the subphase results in the effective inhibition of this aggregation. This conclusion is confirmed by spectral fluorimetric studies of monolayers of a dye with a similar structure that contains a chromophoric group with a much higher fluorescence quantum yield. Monolayer aggregation on deionized water at the surface pressure values of just 4-6 mN/m leads to the three to fourfold fluorescence quenching, while in the case of subphases containing inert (noncomplementary to the dye ionophoric fragment) cations, the compression of the monolayer to pressures of 25-30 mN/m reduces the fluorescence intensity by no more than 25-35%. It was thus found that variations in the subphase composition allows one to monitor the degree of aggregation of the monolayer and the efficiency of cation recognition.