Synthesis, crystal structure and photoluminescence of the salts Cation(+) [M(caffeine)Cl](-) with Cation(+) = (NBu4+)-Bu-n, AsPh4+ and M = Zn(II), Pt(II)

摘要

The salts ((NBu4)-Bu-n)[Zn(caffeine)Cl-3] and (AsPh4) [Pt(caffeine)Cl-3] 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)Cl-3](-) with M=Zn and Pt show an absorption spectrum with an intense band at lambda(max) = 275 nm, which is attributed to an IL pi-pi* transition of the caffeine. A second band at ca. 300 nm is much weaker and largely obscured by the pi-pi* band. This second band is assigned to an IL n-pi* transition. Both complex anions exhibit a photoluminescence (fluorescence), which originates from the n-pi* state. The position of the n-pi* state is recognized by the excitation band which distinctly overlaps with the fluorescence band.