Synthesis, Langmuir and Langmuir-Blodgett films of a calix[7]arene ethyl ester. AFM characterization, subphase influence and molecular modelling

Abstract

Calixarenes are promising compounds to be used as ionophores and for molecular recognition. Their ability to form Langmuir and Langmuir–Blodgett (LB) films is of great interest in order to obtain small sensor devices which incorporate an active nanometric film. The p-tert-butylcalix[7]arene ethyl ester compound has been synthesised and its ability to form Langmuir and LB films has been shown. This macrocycle forms monolayers but it tends to form multilayers at higher compressions, as corroborated by AFM. BAM images show a uniform layer till the multilayer process occurs and a good correspondence with the features of the surface pressure–area isotherm. AFM images reveal that, in water subphase, films are quite homogeneous but the presence of small islands has also been observed. The presence of ions in the subphase, as sodium, potassium, rubidium, cesium, calcium, barium, cadmium and tin chloride salt solutions, leads to some changes in the surface pressure–area isotherms, but the more important changes are observed by AFM. More uniform films are observed for rubidium, cesium, cadmium and tin ions. A very different nanometric structure has been observed for tin ions. Some characteristics of the films, molecular area and height, are correlated with molecular modelling calculations.