Fluorescence of alizarin complexone and its metal complexes

Abstract: Alizarin complexone (AC) in ethanol shows two fluorescence bands which originate from the lowest excited singlet before and after proton transfer. Upon addition of various metal ions (Ni2+, Zn2+, Gd3+, Th4+) to AC in ethanol the formation of well known AC complexes takes place. They are characterized by intense colours which are caused by IL (or ILCT) transitions. If low-energy LF states (Ni2+) are absent (Zn2+, Gd3+, Th4+) these complexes show a weak fluorescence. Even in the case of Gd and Th a heavy-atom effect is not apparent and fluorescence quenching is not observed. Moreover, AC complexes are not phosphorescent under any conditions. [Copyright &y& Elsevier]