Amphiphilic alkyl dimethylaminopyridinium compounds — on the design of SHG active 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 amphiphile 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 generation (SHG). SHG is a non-linear optical techniques which is intrinsically surface specific and allows new insights in the internal structure of the interphase and their corresponding static and dynamic properties. The molecular requirements for SHG-activity are polarizable π-electrons further functionalized by a electron donor or acceptor in order to break the inversion symmetry on a molecular scale. This was achieved within the homologous series of C4–C22 of 1-alkyl-4-dimethylaminopyridinium bromide with the headgroup being the SHG active moiety. In the following we describe the synthesis as well as the analysis and present furthermore a thermodynamic characterization of the interfacial properties of these model compounds. A pronounced odd-even effect in many interfacial properties was found.