Supramolecular Architecture in Langmuir Films of a Luminescent Ionic Liquid Crystal

A new luminescent ionic liquid crystal (ILC) with a positive charge in the aromatic central core and two hydrophobic alkyl chains at the ends, called Ipz, has been synthesized and its behavior at the air-liquid (NaCl 2 x 10(-6) M) interface has been characterized by combination of surface pressure and surface potential versus area per molecule (pi-A and Delta V-A) isotherms, Brewster angle microscopy (BAM) and UV-vis reflection spectroscopy. The results indicate the formation of a supramolecular architecture at the air-liquid interface formed by a head-to-head bilayer on top of a flat-core monolayer. Langmuir films were transferred onto solid substrates, and atomic force microscopy (AFM) and X-ray reflection (XRR) have confirmed that well-ordered multilayer films are obtained. Langmuir films supramolecular structure is different from the molecular organization of Ipz in lamellar liquid-crystalline phases. Furthermore, fluorescence emission spectra reveal a blue shift of the emission band of about 18 nm when compared to the solution spectra.