Structural Effects on the Langmuir Monolayers of Calix[4]arene Induced by Lower Rim Aromatic Substitution

The Langmuir monolayer properties of lower rim aromatically substituted calix[4]arenes, 5,11,17,23-tetra-tert-butyl-25,27-bis(2-naphth-1′-ylacetylaminoethoxy)-26,28-dihydroxylcalix[4]arene (BNAEC), 5,11,17,23-tetra-tert-butyl-25,27-bis(2-benzoylamino ethoxy)-26,28-dihydroxylcalix[4]arene (BBAEC) and 5,11,17,23-tetra-tert-butyl-25,27-bis(2-cinnamoylaminoethoxy)-26,28-dihydroxylcalix[4]arene (BCAEC), have been studied. Film balance measurements and Brewster angle microscopy (BAM) observation demonstrate that all the compounds can form Langmuir monolayers with different molecular limiting areas. BNAEC or BBAEC monolayer is able to form condensed domains during compression, while BCAEC monolayer can never form condensed domain. BNAEC monolayer is more readily to form condensed domain than BBAEC monolayer. Moreover, BNAEC monolayer can form the total condensed phase during compression even when T=28 °C, while BBAEC monolayer can not when T>10 °C. The results imply that different lower rim aromatic substitutions affect essentially the intermolecular interaction and molecular packing in the monolayer at air/water interface.