Amphiphilic alkyl dimethylaminopyridinium compounds - on the design of SHGactive cationic amphiphiles and their adsorption behavior - Part 1. Synthesis of SHG-active alkyl dimethylaminopyridinium bromide, structure and physical properties

The aim of this work is to develop a homologous series of a novel model amp hiphile which resembles the characteristic features of a classical soluble amphiphile and provide in addition a sufficiently high hyperpolarizability in order to fully utilize the potential offered by second harmonic generati on (SHG). SHG is a non-linear optical techniques which is intrinsically sur face specific and allows new insights in the internal structure of the inte rphase and their corresponding static and dynamic properties. The molecular requirements for SHG-activity are polarizable pi -electrons further functi onalized by a electron donor or acceptor in order to break the inversion sy mmetry on a molecular scale. This was achieved within the homologous series of C-4-C-22 of 1-alkyl-4-dimethylaminopyridinium bromide with the headgrou p being the SHG active moiety. In the following we describe the synthesis a s well as the analysis and present furthermore a thermodynamic characteriza tion of the interfacial properties of these model compounds. A pronounced o dd-even effect in many interfacial properties was found. (C) 2001 Elsevier Science B.V. All rights reserved.