MACROCYCLIC AMPHIPHILES - 3 - MONOLAYERS OF O-OCTACARBOXYMETHOXYLATEDCALIX[4]RESORCINARENES WITH AZOBENZENE RESIDUES EXHIBITING EFFICIENT PHOTOISOMERIZABILITY

O-Octacarboxymethoxylated calix[4]resorcinarenes having four azobenzen e residues at the lower rim were prepared to study photoisomerizabilit y 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 film s deposited on a quartz substrate displayed about 72% of E-to-Z conver sion 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 t o 365 nm light. The efficient E-to-Z photoisomerizability in monolayer s is ascribable to large difference in cross-sectional areas between t he cylindrical framework of calix[4]resorcinarene (1.7 nm(2)) and azob enzenes (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 t he first-order plots, indicating that steric constraint exists more or less.