Langmuir monolayer and langmuir-blodgett films formed by a melamine-headed azobenzene-derived amphiphile: Interfacial assembly affected by host-guest interaction

A novel azobenzene-derived amphiphile with a melamine head, 2Azo-2C ₁₂H ₂₅-melamine, has been synthesized. π-A isotherm measurements displayed that this amphiphile is able to form a stable Langmuir monolayer on both pure water and barbituric acid (BA)- or thymine (T)-containing subphases. The collapse surface pressure and limiting molecular area of its Langmuir monolayer on pure water are 40 mN/m. and 0.56 nm ², respectively. However, when barbituric acid or thymine was introduced into the subphase, the corresponding π-A isotherms of the monolayers exhibited a lower collapse surface pressure (22 m.N/m for BA, 21 mN/m. for T) and smaller limiting molecular area (0.54 nm ² for BA and 0.52 nm ² for T). UV-vis and FT-IR studies of the LB films formed by 2Azo-2C ₁₂H ₂₅-melamine have also been carried out. The results indicated that the LB films of 2Azo-2C ₁₂H _25--melamine deposited from pure water undergo distinct collapse of the H-aggregate upon UV irradiation, while the LB films deposited from a BA or T-containing subphase retain the H-aggregate. The host-guest-interaction-induced blockage of azobenzene photoisomerization should be responsible for the stabilized H-aggregate. A 1:1 host/guest binding mode to form a linear supramolecular polymeric chain has been proposed in the Langmuir monolayers formed on a B A- or T-containing subphase. The current results suggest that the host-guest interaction should be an effective means to manipulate the interfacial assembly of azobenzene-derived amphiphiles.