Preparation and characterization of mixed monolayers and Langmuir−Blodgett films of merocyanine 540/octadecylamine mixture

Mixed monolayer of merocyanine 540 (MC540) dye and octadecylamine (ODA) at the air/water interface has been prepared using the co-spreading method. The pressure–area (π–A) isotherm studies revealed that the mixtures of MC540/ODA at a different ratio formed a stable monolayer at the air/water interface and these floating layers were easily transferred onto hydrophilic substrates as the Y-type Langmuir–Blodgett (LB) film. The specific area per molecule in the π–A isotherm of the mixed monolayer of MC540/ODA was larger than that of the pristine ODA. The area can also get increased up to 40 mN/m surface pressure by the increase of the dye concentration in the mixtures. The LB films of MC540/ODA mixture were formed at 30 mN/m surface pressure by transferring the mixed monolayer at the air/water interface on hydrophilic glass substrate via vertical dip-coating as mono- and multilayer films. The photophysical properties of MC540 in chloroform and LB films have been investigated using the absorption, steady-state and time-resolved fluorescence spectroscopy techniques. H-aggregate formation of MC540 both in chloroform and LB film were concluded from the spectroscopic results. The morphology of the one-layer mixed LB film of MC540/ODA on the glass substrate has been characterized by AFM (atomic force microscopy). The non-contact mode AFM image of the one-layer mixed LB film showed that the film surface consisted of MC540/ODA nanoclusters. In conclusion, our results contribute to understanding the strong interaction between MC540 and ODA at the air/water interface, and show the effects of some parameters on the mixed LB films of MC540.