Langmuir monolayers from functionalized amphiphiles with epoxy terminal groups

We studied Langmuir and Langmuir-Blodgett monolayers from amphiphiles with traditional (carboxylic) and bulky functionalized (epoxy) terminal groups at the air-water and air-solid interfaces. We demonstrated that the molecules with a central azobenzene fragment and carboxylic (AA-1 molecule) and bulky epoxy (AE-1 molecule) polar groups formed orthorhombic unit cells with larger than expected area per alkyl tail. The higher order of symmetry indicated by the appearance of higher Qxy peaks revealed that the alkyl tails formed a herringbone structure with limited long range ordering. In the condensed monolayer, the azobenzene group of the AA-1 molecules was oriented vertically in contrast to the AE-1 molecule that was significantly tilted. In addition, the presence of the bulky epoxy focal groups caused a less dense lateral packing of the azobenzene groups. We suggest that the bulky focal group causes intramonolayer packing which can enhance the ability of the chemically grafted azobenzene groups for photoisomerization.