Spectroscopic characterizations of the mixed Langmuir-Blodgett (LB) films of 2,2′-biquinoline molecules: Evidence of dimer formation

This communication reports the π-A isotherms and spectroscopic characterizations of mixed Langmuir and Langmuir-Blodgett (LB) films of non-amphiphilic 2,2′-biquinoline (BQ) molecules, mixed with polymethyl methacrylate (PMMA) and stearic acid (SA). The π-A isotherms and mole fraction vs. area per molecule studies indicate complete immiscibility of sample (BQ) and matrix (PMMA or SA) molecules. This immiscibility may lead to the formation of microcrystalline aggregates of BQ molecules in the mixed LB films. The scanning electron micrograph gives the visual evidence of microcrystalline aggregates of BQ molecules in the mixed LB films. UV-vis absorption, fluorescence and excitation spectroscopic studies reveal the nature of these microcrystalline aggregates. LB films lifted at higher surface pressure indicate the formation of dimer or higher order n-mers.