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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 × 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.

Photochemical behavior of calix[4]resorcinarenes (CRAs) and O-octaacetylated derivatives having four azobenzene residues at their lower rim in solutions and monolayers is described. UV irradiation of an O-octaacetylated CRA in homogeneous solution gave rise to a photostationary state consisting of a possible six isomers as a result of normal photoisomerization. The compound exhibited reversible precipitation/dissolution cycles in a diluted methanol solution upon alternate irradiation with UV and visible light owing to its scarce solubility of all-trans isomer. Wherease azobenzene chromophores tethered from the cyclic skeleton displayed marked intermolecular interactions in monolayers on a water surface, trans-to-cis photoisomerization took place even in compressed monolayers. The level of the photoisomerizability was dependent on the chemical structure and surface pressures. Monolayers of azobenzene CRAs exhibited the reversible alteration of their areas under a constant surface pressure upon UV and visible light irradiation because of the drastic shape change of the chromophores.

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