Preparation, characterization and optical properties of rare earth complexes with derivatives of N-phenylanthranilic acid

Abstract

N-phenylanthranilic acid and various derivatives (NPAs) can be employed to sensitize rare earth complexes, Gd3+ and Tb3+ in particular, for the excitation with UV-light in the range from 350 to 400 nm, where low cost, high power LEDs have become available during the last years. This range is of particular interest for applications in biophotonics or luminescent bioassays, which can exploit the unique features of the rare earth ions: large Stokes shifts, narrow line emissions and very long life times of the excited states. Among others, the 350–400 nm range allows the use of standard optics and closes the gap between numerous complexes known for wavelengths <350 nm and a plethora of organic dyes designed for the visible. Complexes of Gd3+, Tb3+ and Eu3+ were prepared and characterized with respect to chemical composition (elemental analyses, thermoanalysis) and spectroscopically (IR, phosphorescence, luminescence); quantum chemical calculations (DFT) accompanied the spectral interpretation.Several binary Tb3+ complexes were found to be excitable at wavelengths as high as 400 nm; quantum yields of 31% at decay times of 837 μs could be realized. Corresponding Eu3+ complexes were found to be essentially non-luminescent. The efficiencies can be enhanced substantially, if ancillary ligands are employed.