Size selective molecular recognition of calix[4]arenes in Langmuir–Blodgett monolayers

A stable and well-ordered monolayer of p-tert-butylcalix[4]arene (Cal-4) has been constructed at the air–water interfaces and transferred on solid substrates under an optimized condition. The surface pressure–area (Π–A) isotherm of Cal-4 on a basic subphase exhibits a limiting area of 160±10 Å2 per molecule, which is consistent with results obtained from CPK model and atomic force microscopic (AFM) study. The Π–A isotherms and AFM studies indicated that well ordered two-dimensional crystalline arrangement was obtained only on the basic subphase of pH 10 or higher. Electrostatic repulsion of adjacent phenolic anions at the lower rim and hydrophobic interactions among tert-butyl groups on the upper rim may be responsible for monomeric dispersion and well-aligned packing on the basic subphase. FT-IR and surface-enhanced Raman scattering (SERS) studies indicate that C4 axis of Cal-4 is oriented parallel to the surface normal at the interface. Size selective molecular recognition of Cal-4 through the hydrophobic upper cavity was demonstrated by using cyclic voltammetry and SERS studies of methyl viologen dication (MV2+).