7-OH quinoline Schiff bases: are they the long awaited tautomeric bistable switches?

Two novel, 7-hydroxyquinoline based, Schiff bases have been synthesized and their spectral properties have been investigated by combined use of optical and NMR spectroscopy and theoretical DFT calculations. The results indicate that 8-((phenylimino)methyl)quinolin-7-ol exists as a mixture of enol and two keto tautomers in solution, while 8-(((pentarfluorophenyl)imino)methyl)quinolin-7-ol is presented as a single enol form. Upon irradiation, in both compounds, through excited state intramolecular proton transfer mechanism, a rotation around the Cquin-CH bond occurs, indicating that they are suitable to be used as bistable switches. The back relaxation is faster comparing to the theoretical expectations, due to the additional flexibility around the azomethine bond. As a result of forming complexes with the acidic counter ion, no intramolecular rotation happens upon protonation with trifluoroacetic acid.

Automated summary

Two novel Schiff bases based on 7-hydroxyquinoline have been synthesized and studied for their spectral properties, indicating their potential as bistable switches. However, intramolecular rotation does not occur upon protonation with trifluoroacetic acid after forming complexes with the acidic counter ion.