Three-coordinated Ce(III) complexes with long wavelength d–f emissions

Lanthanide luminescent materials have found a wide range of use in various fields. While most applications utilize intrashell f-f transitions, f-d transitions have recently emerged as a novel approach to develop molecular luminescent materials. Unlike Laporte-forbidden f-f transitions, f-d transitions are Laporte-allowed and thus not dependent on chromophoric ligands. Moreover, the involvement of 5d orbitals renders it possible to modulate the emission wavelength by tuning the lanthanide-ligand interaction. Herein, we report a series of three-coordinated cerium(III) complexes with a trigonal planar geometry supported by bulky 2,6-disubstituted phenoxide ligands. These complexes were fully characterized by X-ray crystallography and ¹H NMR spectroscopy. In addition, we investigated the photophysical properties of these compounds that reveal strong d-f emissions with the photoluminescent quantum yield up to 62% and the CIE value of (0.46, 0.51). This work opens a new avenue to regulate the emission wavelength of lanthanide luminescent molecules through ligand field engineering.