Rhodamine 6G based molecular ion-active switches of optical and fluorescent properties

Abstract

A series of rhodamine 6G derivatives with o -hydroxyarylime substituents was synthesized. The obtained compounds in acetonitrile are capable of H+ induced transformation of the spirolactam form into open form. The process is accompanied by the formation of new long-wave absorption maxima at 527-529 nm and fluorescence bands at 557-560 nm. The compound containing 2-hydroxy-4-dimethylaminophenyl substituent in the presence of Zn2+ cations displays switching of emission at 429 nm. This fluorescence is quenched selectively by the CN- anion. Copper(II) cations cause the transformation of the spirostructure of rhodamine with a 2-hydroxy-3- tert -butylbenzofuran group into an open form. Isomerization occurs with a chromogenic naked-eye effect - a change in the color of the solution from pale yellow to pink and the appearance of fluorescence at 556 nm. The observed ion-induced spectral transformations can be used in design of optical and fluorescent chemosensors.