Amphiphilic cup-shaped [(4-alkylphenyl)azo]-substituted calixarenes: Self-assembly and host-guest chemistry at the air-water interface

Chromophoric, amphiphilic [(4-alkylphenyl)azo]-substituted calixarenes 1-4 form stable monolayers at the air-water interface of a Langmuir trough. Monolayer limiting areas and collapse pressures are controlled with changes in pH and electrolyte concentration of the subphase. At pH = 8.2 or higher, deprotonation of the hydroxyls of the calixarene produces more polar headgroups, which result in larger mean molecular areas and increases in film collapse pressures. Similar effects result from increasing the concentration of electrolyte in the subphase. Effects of potential guests on monolayer assembly of [(4-alkylphenyl)-azo]-substituted calixarenes at the air-water interface were investigated. The limiting area of tetrakis-[(4-octylphenyl)azo]calix[4] arene decreases in the presence of N,N,N-trimethylanilinium iodide while no change is detected for tetramethylammonium iodide or N,N,N-trimethyl-N-(2-naphthyl)ammonium iodide. Interactions of the amphiphilic calixarenes and potential ammonium guests are discussed.