The effect of alkyl substituent length on receptor properties of dithiaaza-crown - Hemicyanine monolayers

Abstract

Planar supramolecular systems based on Langmuir monolayers of chromoionophores are widely used for sensor applications, and crown ether ionophoric groups are intensively studied. However, almost no attention is devoted to investigation of effect of alkyl moieties onto receptor properties of such systems. In the present work, we carry out a comparative study of Langmuir monolayers of three alkylated dithiaaza-crown substituted hemicyanine chromoionophores differing only in number of carbon atoms (12, 16, 21) in the hydrophobic alkyl substituent. A dependence of receptor properties of the studied monolayers on the length of alkyl chain is revealed. It is shown that the efficiency of mercury cations binding by both liquid-expanded and compressed monolayer of dithiaaza-crown substituted hemicyanine dyes formed on pure water subphase is identical for all three compounds with various length of alkyl chain substituent due to the key role of the interactions between chromoionophore fragments of neighboring molecules at the interface. Degree of system sensitivity enhancement due to barium cation-induced preorganization increases with increase of number of carbon atoms in the alkyl chain.