Abstract
Carminic acid which can be obtained as extract (cochineal) from certain scale insects is an important red dye with many applications. It shows a red fluorescence under ambient conditions. The lowest-wavelength absorption and the corresponding emission undergo a red shift when carminic acid interacts with metal cations such as Zn(2+), Al(3+), Gd(3+) and Th(4+) in aqueous solution. The Al(3+) ...
Abstract
Carminic acid which can be obtained as extract (cochineal) from certain scale insects is an important red dye with many applications. It shows a red fluorescence under ambient conditions. The lowest-wavelength absorption and the corresponding emission undergo a red shift when carminic acid interacts with metal cations such as Zn(2+), Al(3+), Gd(3+) and Th(4+) in aqueous solution. The Al(3+) complex of carminic acid which is isolated as Ca(2+) salt (carmine) displays this fluorescence also in the solid state while the Ni(2+) complex is not luminescent under any conditions owing to the presence of low-energy ligand field states. (C) 2011 Elsevier B.V. All rights reserved.
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