Monolayer characteristics and spectroscopic study of benz(b)fluoranthene assembled in Langmuir Blodgett films mixed with stearic acid Original Research Article

Excellent Langmuir Blodgett (LB) films of benz(b)fluoranthene (B(b)F) have been prepared by mixing with stearic acid (SA). The surface pressure vs. area per molecule isotherms (π–A) of B(b)F mixed with SA at different mole fraction reveal that the area per molecule decreases with increasing mole fractions of B(b)F. The area per molecule vs. mole fraction shows that there is positive deviation of the experimental data to the idealized one. This indicates formation of aggregation of B(b)F molecules in the SA matrix. Spectroscopic properties of B(b)F in solution and in mixed LB films have been compared by absorption, steady state fluorescence, phosphorescence spectroscopy and lifetime measurements. Bathochromic shift in absorption and emission spectrum suggests the formation of some kind of aggregates in LB film. Decrease in fluorescence and phosphorescence lifetime is compared to that of pure B(b)F also supports the formation of different sized aggregates in the mixed film.