One of the most important steps of fundamental characterization of ILs based on acidochromic indicators is to evidence their form, i.e. to show the molar ratio between cations and anions in the composition of the IL, as well as to confirm their purity. In the case of organic ions this can be achieved using NMR-techniques as shown further.
In this work, a series of ion pairs with tetra(decyl)ammonium (TDA+) as a cation was synthesized for the first time with a conventional method described in [3]. The following water-soluble acido- and metallochromic dyes served as anions: bromophenol blue (BPB2–), bromothymol blue (BTB2–), fluorescein (FL2–), thymolphthalein (TPT2–), methyl red (MR–), ethyl orange (EO–) and eriochrome black T (EBT2–).
All the novel compounds were comprehensively characterized by methods of NMR: 1H and 13C relaxation, COSY and NOESY spectroscopy. In this contribution, we pay special attention to peculiarities of NMR application relative to the mentioned class of ionic liquids: acquisition and analysis of 1H and 13C NMR spectra, relaxation data processing, and interpretation of COSY and NOESY spectra.