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The salts (N n Bu4)[Zn(caffeine)Cl3] and (AsPh4)[Pt(caffeine)Cl3] were prepared and their crystal structures determined by single crystal X-ray diffraction. The free ligand caffeine, as well as the complex anions [M(II)(caffeine)Cl3]− with M = Zn and Pt show an absorption spectrum with an intense band at λ max = 275 nm, which is attributed to an IL π–π* transition of the caffeine. A second band at ca. 300 nm is much weaker and largely obscured by the π–π* band. This second band is assigned to an IL n–π* transition. Both complex anions exhibit a photoluminescence (fluorescence), which originates from the n–π* state. The position of the n–π* state is recognized by the excitation band which distinctly overlaps with the fluorescence band.

The salt [NHEt3][Re(I)(quinaldate)(CO)3Cl] was obtained by the reaction of Re(CO)5Cl with quinaldic acid and triethylamine in toluene. The crystal structure analysis of this salt revealed the presence of the complex anion [Re(quinaldate)(CO)3Cl]−, with the d 6 Re(I) metal center in a pseudo-octahedral environment. The electronic spectra in absorption and emission exhibit bands which are attributed to quinaldate IL and CT transitions at comparable energies. The longest-wavelength emission originates from a Re(I) to quinaldate MLCT triplet, which can be quenched in solution by oxygen or triethylamine.

The complex Ag(I)(flavonolate)(PPh3)2 has been prepared and characterized including the crystal structure. This compound shows in degassed solution two emission bands, a fluorescence at λ max=505 nm and a phosphorescence at λ max=780 nm. Both emissions originate from lowest-energy flavonolate intraligand excited singlet and triplet states, respectively. In the presence of oxygen, the phosphorescence disappears and the complex becomes light-sensitive. The flavonolate ligand undergoes a photooxidation by oxygen.