Macrocyclic amphiphiles. 3. Monolayers of o-octacarboxymethoxylated calix[4]resorcinarenes with azobenzene residues exhibiting efficient photoisomerizability

O-Octacarboxymethoxylated calix[4]resorcinarenes having four azobenzene residues at the lower rim were prepared to study photoisomerizability in monolayers. UV irradiation of the amphiphilic macrocycles at 365 nm on a water surface resulted in the formation of about 60% of the Z-isomer even in densely packed monolayers while 99% of the Z-isomer was formed in solution photochemistry. Langmuir-Blodgett monolayered films deposited on a quartz substrate displayed about 72% of E-to-Z conversion at a photostationary state. The amphiphilic macrocycles adsorbed firmly on a quartz plate to give relatively densely packed monolayers. About 86% of Z-isomer was formed when these monolayers were exposed to 365 nm light. The efficient E-to-Z photoisomerizability in monolayers is ascribable to large difference in cross-sectional areas between the cylindrical framework of calix[4]resorcinarene (1.7 nm(2)) and azobenzenes (0.25 x 4 = 1.0 nm(2)) to ensure a two-dimensional free volume. The E-to-Z photoisomerization in adsorbed monolayers deviated from the first-order plots, indicating that steric constraint exists more or less.