Photoacoustic and Fluorescence Spectroscopy of Metallomesogens Containing Lanthanide Ions

Metallomesogens Ln(bta)3L2 (Ln3+: La3+, Eu3+, and Ho3+; bta: benzoyltrifluoroacetonate; L: Schiff base) were prepared. Photoacoustic (PA) spectroscopy was used to study physicochemical properties of the liquid crystalline metal complexes. In the region of ligand absorption, PA intensity increases for Eu(bta)3L2, La(bta)3L2, and Ho(bta)3L2, in that order. It is found that the PA intensity of the ligand bears a relationto the intramolecular energy transfer process. For the first time, phase transitions of Eu(bta)3L2 from glass state to smectic A (SmA) phase and SmA phase to isotropic liquid are monitored by PA and fluorescence (FL) spectroscopy from two aspects: nonradiative and radiative transitions. The results show that PA technique may serve as a new tool for investigating the spectral properties and phase transitions of liquid crystals containing metal ions.