Effect of positional substitution of methyl group on the fluorescence properties of quinolinium ion

In the present study we have investigated the effect of methyl substitution at various positions on the spectral and decay behavior of some quinolinium ions. The spectra reveal marked differences when methyl group is present at 7th and 8th positions. The non-radiative deactivation is also considerably affected by the substituent position. The results are explained by considering the modulation (decrease as compared to the unsubstituted quinolinium) in nonradiative rate (intersystem crossing) due to substitution.