Ionically self-assembled terephthalylidene-bis-4-n-alkylanilines/n-decanesulfonic acid supramolecules: Synthesis, mesomorphic behaviour and optical properties

This paper describes the preparation, mesomorphic and photophysical studies of a two type of calamitic molecules derived from azomethines, N,N'-(1,4-phenylenebis(methan-1-yl-1-ylidene)bis(4-pentyl-benzenamine) (LCBAZ1) and N,N'-(1,4-phenylenebis(methan-1-yl-1-ylidene)bis(4-decylbenzenamine) (LCBAZ2) before and after protonation with the n-decyl sulfonic acid (DSA). The lengths of the outer spacers are four or nine methylene units connected with the imine group by phenyl ring in the para position. Liquid crystal properties of the undoped and doped azomethines are studied by differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). Wide-angle X-ray diffraction (WAXD) technique is used to probe the structural properties of the azomethines as well as its complexes. The lengths of the outer flexible spacers have an effect on the mesomorphic properties of the azomethines. The compound LCBAZ2 with nine methylene units exhibit smectic phases (Sm C and Sm X), while the LCBAZ1 with four methylene units exhibit nematic and smectic phases (N and Sm C). The effects of protonation on the phase transitions of the azomethines are investigated. The structure formation of (LCBAZx)(1) (DSA)2 complexes are discussed on the basis of FTIR spectroscopy. Additionally, the azomethines before and after protonation with DSA are investigated by UV-vis and photoluminescence (PL) spectroscopy. With the exception of LCBAZ1 in its undoped state, the chloroform solution of the doped or undoped azomethines exhibit greenish fluorescence when the solutions are subjected to 400 nm excitation wavelength. It are concluded that the combination of the molecular and supramolecular engineering concepts stabilized the smectic phase. (C) 2008 Elsevier B.V. All rights reserved.