Phase transitions in Langmuir monolayer of long chain attached fluorescein studied by second harmonic generation technique

Optical second harmonic generation (SHG) measurements coupled with Π-A isotherms have been shown to be helpful, for the following and comprehension of orientational orders and phase transitions in Langmuir monolayers. Using the SHG-(Π-A) measurements, monolayers of 5-hexadecanoylaminofluorescein on the water surface were examined by monolayer compression. The phase transitions were noticeably revealed. Dependence of the square root of the intensities polarizations quotient in the molecules surface density, allowed establishing tilting orientation alignment phases. In addition, change in the monolayer symmetry C_∞v→C_2v as it goes through the LE–LC phase transition, was clearly recognized. It was concluded that a possible change in β is taking place due to aggregate formation.