Solvent-activated fluorescent Eu(III) complex with carbazole-benzene-tripyridine D-π-A system for rapid identification of specific alcohols

In this work, we prepared a Carbazole-Benzene-Tripyridine ligand with a d -π-A structure and synthesized its corresponding Eu (III) and Tb (III) complexes. The structures of the complexes were analyzed by single crystal X-ray diffraction. It was surprisingly that the fluorescence emission intensity of the Eu(III) complex increases significantly once the solvent was added, indicating that the fluorescence could be activated by the solvent. However, it was confirmed that in the solid state, the complex molecules in the lattice were orderly arranged and there was a π-π stacking effect. The π-π stacking caused strong intermolecular interactions leading to emission quenching. The addition of solvent broke the π-π stacking and enhanced the fluorescence of the Eu(III) complex. The color of the fluorescence emission of the Eu(III) complex depended on the kind of added solvent. The results of nuclear magnetic resonance (NMR) and density functional theory (DFT) calculations suggested that the rotation of the C C single bond in the d -π-A structure ligand in different solvents caused a change in the spatial angle between the carbazole-benzene unit and the tripolypyridine unit in the ligand, thereby changing the excited state energy of the ligand. Hence, the varied emission colors of the complex reflect differences in the energy transfer efficiency of the ligand to rare earth ion. The solvent effect of the Eu(III) complex was then successfully applied in the rapid identification of specific alcohols.