Monolayers and Langmuir–Blodgett films of optically active macrocyclic poly(esters) containing the 1,1′-bi-2-naphthol moiety at the air/water interface

Abstract

In order to fabricate chiral Langmuir–Blodgett (LB) films and expand the range of monolayer-forming materials, a new type of macrocyclic poly(aryl ester) containing the optically active 1,1′-bi-2-naphthol group, and which have no substituted alkyl chains, were investigated. The spreading behaviors and the fabrication of ultrathin films of the compounds were studied. Stable monolayers were formed with collapse surface pressures up to 40 mN m⁻¹ at the air/water interface, although these compounds have no substituted alkyl chains. It is suggested that in the monolayers the macrocyclic rings lie flat on the surface of the water, while the aromatic rings extended upwards out of the water surface. The monolayers can be transferred onto solid substrates uniformly using the horizontal lifting method. Transferred LB films were characterized by UV, polarized UV and circular dichroism (CD) spectra. In comparison with the corresponding solutions, the ¹B_b and ¹L_a bands of the compounds in LB films show a red shift. Both the UV and polarized UV spectra indicate a J-like aggregation of the chromophores in the LB films. In the CD spectra, splitting of the Cotton effect is observed both in solution and in LB films, indicating that interactions between the neighboring naphthalene chromophores take place. In the LB films, the exciton couplet shows a red shift in comparison with those in solution due to aggregation.