Langmuir and Langmuir-Blodgett film characterization of a new amphiphilic coumarin derivative

In this paper, we report the synthesis and the monolayer behavior (surface pressure and surface potential) of a new amphiphilic coumarin dye, 7-aminoc oumarin-4-acetic acid octadecylamide (ACO), at the air-water interface. The spectroscopic characteristics (UV-vis, fluorescence, and fluorescence imag ing) of pure and mixed films (1:20, ACO/stearic acid and ACO/oleic acid) at the air-water interface as well as Langmuir-Blodgett (LB) films have been investigated and compared with the spectroscopic characteristics of ACO in solution. These experiments provide evidence of aggregate formation during compression of the monolayer at the air-water interface. Surface pressure d ependent in situ fluorescence imaging confirms that the fluorescent quenchi ng of the dye with increasing surface pressure originates as a result of fo rmation of nonfluorescent aggregates. Atomic force microscopy imaging of a pure ACO LB film shows that the size of these aggregates is in the nanomete r scale. This work provides information that ACO forms a stable monolayer a nd may be utilized as an efficient molecular probe for monolayer studies.