Molecular J-aggregation for the Langmuir–Blodgett film of a novel tripodal dye

We investigated the arrangement of a tripodal dye, N1,N3,N5-tris(4-(5-(3,4,5-tridodecyloxyphenyl)-1,3,4-oxadiazol-2-yl)phenyl)benzene-1,3,5-tricarboxamide, A3O-3 (amide linkage), at the air–water interface by the Langmuir–Blodgett technique. The surface pressure (П) vs. surface area (A) isotherm for A3O-3 showed a sharp transition at 200 Å2/molecule. AT-IR and UV–visible spectrophotometry were employed to study the self-assembled structure of A3O-3 multilayers on the substrate. Comparisons with theoretical calculations of the molecular and extrapolated areas of the Π–A isotherm revealed that a change in the molecular arrangement of the A3O-3 monolayer took place under conditions of sharply increasing surface pressure. AT-IR data showed no hydrogen-bonding at high pressure and also demonstrated that the stability of the monolayer is due to π–π interactions. UV data displayed a maximum red shift as the surface pressure increased, which suggests that J-aggregation was initiated at the monolayer interface.