The luminescent and photochemical properties of europium(III) cinnamates [Eu(Cin)3]n (I) and Eu(Cin)3·(phen) (II) were investigated in theoretical and experimental aspects. The high photostability of the complex I was explained. The complex II displays weak luminescence and low photostability in spite of the presence of a powerful antenna ligand 1,10-phenantroline in its coordination sphere. The unexpected