The unusual visible fluorescence violating the Kasha's rule suggests the aggregation of guanidinium carbonate in its aqueous medium

Guanidinium salt solutions are one of the important electrolytes which have been extensively used for understanding the folding/unfolding mechanism of proteins. The structure of aqueous Gdm2CO3 has been controversial as some studies suggest that the hetero ion pairing takes place which leads to the aggregation whereas other studies does not support the idea of ion pairing. In this paper, we have used the steady state, time resolved fluorescence methods and density functional theory to understand the structure of guanidinium carbonate (Gdm2CO3) in terms of ion pairing as well as aggregation. The structure of the aqueous Gdm2CO3 has been controversial as some studies suggests that the Interestingly, Gdm2CO3 does not have any aromatic chromophore but it shows the broad visible fluorescence in the aqueous medium. Moreover, the fluorescence spectrum depicts a strong excitation dependent feature violating the Kasha's Rule. The concentration dependent emission, excitation, lifetime fluorescence along the density functional theory studies clearly suggests the formation of different size of aggregated clusters of Gdm2CO3 which causes the visible fluorescence of aqueous Gdm2CO3 violating the Kasha's rule.