Raman, ROA, and luminescence spectra of chiral lanthanide complexes with L- and D-alanine

The Raman spectra of lanthanide [Ln(H2O)4(Ala)2]2(ClO4)6 crystals were measured with 488, 532, 633, and 1064 nm laser lines, and ROA of complexes in water were collected using 532 nm excitation. As in IR and VCD, nu(C--O) stretching and (3(OCO) bending vibration bands showed a tendency typical to the lanthanide contraction effect. However, in Raman, the effect is less pronounced than the IR spectrum because it is strongly perturbed by lanthanide ion luminescence, which comes from the 4f -> 4f transitions. The lower the energy of the excitation line, the less the bands are perturbed by the luminescence. On the other hand, some ROA spectra taken in water revealed strong circularly polarized luminescence signals (Eu, Sm, and Er complexes). Yet, for the non- luminescing systems, it was impossible to see lanthanide ions' influence as the signals were too slight and hidden in noise.