Complexation of 6-hydroxyquinoline with trimethylamine in polar and non-polar solvents

Spectral characteristics of 6-hydroxyquinoline (6-HQ) in presence of trimethylamine (TMA) were investigated in polar and non-polar solvents. The steady-state absorption, emission and excitation spectra along with the transient parameters reveal a strong ground state hydrogen-bonded complex formation between the 6-HQ and TMA molecules in both the media. A large Stokes shifted emission due to the formation of contact ion-pairs is observed in these media. However, in acetonitrile the longer decay time (≈12 ns) with relatively broadened emission spectra can be attributed to the presence of solvent separated ion-pairs in addition to contact ion-pairs. The ground state equilibrium constant for complex formation has been determined. The observed quenching behaviour of the fluorescence emission from the normal molecule with TMA appears to be static in nature.