Photophysical properties of 4-methyl 3-phenyl coumarin organized in Langmuir-Blodgett films: Formation of aggregates

Langmuir-Blodgett (LB) films of 4-methyl 3-phenyl coumarin (MPC), a non-amphiphilic derivative of coumarin mixed with stearic acid (SA) are studied. The surface pressure-area (π-A) isotherm study at air-water interface reveals a repulsive type of interaction between the MPC and SA molecules resulting in the formation of aggregates of MPC molecules. Absorption, fluorescence and phosphorescence studies indicate the formation of J-type aggregate in LB film. Low temperature (77 K) phosphorescence lifetime is found to be decreased due to aggregate formation. Micro structured aggregates are observed after examining the surface morphology of LB film by scanning electron microscopy (SEM).