Substitution controlled molecular orientation and nanostructure in the Langmuir–Blodgett films of a series of amphiphilic naphthylidene-containing Schiff base derivatives

Abstract

Three amphiphilic Schiff bases containing naphthylidene group, N-octadecyl-2′-hydroxy-naphthalenylideneamine (HNOA-1), N-(4′-octadecyloxy)-2′-hydroxy-naphthalenylideneaniline (HNOA-2), and N-(4′- N-octadecylbenzamide)-2′-hydroxy-naphthalenylideneaniline (HNOA-3), were designed and their interfacial assemblies were investigated. These amphiphiles have different substitution groups in the Schiff base moiety. It was observed that HNOA-1, being in lack of second aromatic ring, formed multilayer films at the air/water interface, while the other two compounds, with another aromatic ring and some hydrophilic groups, can be spread as monolayers on water surface. All of Schiff bases could coordinate with Cu(Ac) 2 in situ in the spreading films. Both the spreading films from water and aqueous Cu(Ac) 2 subphases were transferred onto solid substrates and their surface morphologies as well as molecular packing modes were investigated by a series of methods such as atomic force microscopy, Fourier transform infrared spectra and X-ray diffraction. Depending on the different substitutions, these amphiphiles showed different orientations in the Langmuir–Blodgett films. Particularly, during the process of complex formation at the air/water interface, great conformational change of the alkyl chain was observed for HNOA-2 in comparison with that of other compounds. In addition, nanofiber structures were observed for the Cu(II)-complexed HNOA-1 and HNOA-2 films.