Ligand-centered luminescence and deactivation by ligand field states in alizarin complexes

Fluorescence of alizarin complexone and its metal complexes

“…The Ni(II) complex of AC does not show any emission. In analogy to previous studies of solid Ni(II), Co(II) and Cu(II) alizarin complexes [5] it is concluded that the IL excited state of the Ni(II) AC chelate is rapidly deactivated to a low-lying non-emissive LF state of Ni(II).…”

“…Since the lowest triplet is not populated these compounds are not phosphorescent under any conditions [9]. This applies also to solid alizarin complexes of Al(III) and Zn(II) [5] and the AC complexes of Zn(II), Gd(III) and Th(IV) which are all fluorescent but not phosphorescent. For the last two complexes this observation is really remarkable since both metal ions are known to speed up ISC in ligands.…”

“…In the present study we report initial observations about this subject. The emission behavior of some solid metal complexes of alizarin itself had been previously reported [5].…”

“…In the present study we report initial observations about this subject. The emission behavior of some solid metal complexes of alizarin itself had been previously reported [5].Owing to the low solubility of AC (sources: e.g. Alfa Aesar, Aldrich, Acros) in water all experiments were carried out in ethanol as solvent.…”

Absorption and luminescence spectra of cochineal

“…This is attributed to the presence of low-energy ligand field states of Ni 2+ which is are apparently rapidly populated from the emissive singlet of carminic acid. Other alizarin complexes of Ni 2+ show an analogous behavior [19,22]. Moreover, the appearance of the fluorescence in the case of Gd 3+ and Th 4+ is surprising since their heavy-atom effect should lead to a fluorescence quenching.…”