Synthesis, crystal structure and photoluminescence of the salts Cation⁺ [M(caffeine)Cl]⁻ with Cation⁺=N ⁿ Bu₄ ⁺, AsPh₄ ⁺ and M==Zn(II), Pt(II)

Abstract 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.