Abstract:
In this study steady state absorption, fluorescence excitation and emission spectra of
quinoline-i-carboxylic acid have been examined in non-polar and polar solvents and
computational calculation is also performed to achieve the goal of this research work in
finding the origin of dual fluorescence. The fluorescence spectra of quinoline-Z.
carboxylic acid are found to exhibit dual emission in polar solvent (dioxatie and DMSO)
at a shorter and at longer wctve length region corresponding to
I
Lb and
I
La state
respectively. The excitation wavelength dependence of the emission spectra has also been
studied, and strong dependence was observed in case of dioxane and Dlv!SO. Closer
examination of the absorption (excitation) spectra of the sample in these solvents
revealed the presence of two different absorptions (excitations) at shorter and longer
wavelength region indicating the sources of the two emissive states to be in the ground
state. The 3D emission spectra of the sample in these solvents indicate the
correspondence between the observed excitation spectra and the emission spectra.
Stepwise addition of solution of Zn (II ) ion i n to the solution o f the sample changed the
absorption position f r o m shorter wavelength to the longer wavelength region indicating
the presence of t wo absorbing species in the ground state. These results together with the
observation of t wo energy minima i n computational calculations of the PE S of quinoline-
2-carboxylic acid, indicated the presence of two different conformers of the same
molecule i n the ground state that lead to two close l ying excited state;
1
Lb and
I
La and
thereby results in the dual fluorescence of the compound. On the basis of the
experimental and theoretical results, it is suggested that the existence of tw o different
conformers of quinoline-i-carboxylic acid i n the ground state, which are at equilibrium
are the cause for the observed dual fluorescence.
