Highly efficient dual-channel doublet emission in lanthanide cerium(III) complex

Dual-channel luminescent materials are attractive due to their unique electronic structures and potential applications in various fields. Different from traditional dual-channel emitters with closed-shell structure showing singlet fluorescence and/or triplet phosphorescence, we demonstrate herein dual-channel cerium(III) complexes with open-shell structure showing doublet 5d-4f emission from the central Ce(III) ion. By systematically designing and studying a series of cerium(III) complexes Ce(Tp^4Me)(Bp^4Me)₂, Ce(Tp^4Me)₂(Bp^4Me) and Ce(Tp^4R)₃ (R = Me, Cl, I) with gradually varied coordination numbers from seven to eight and nine, respectively, it is found that the nine-coordinated complexes Ce(Tp^4R)₃ showed crowded coordination environments and longer coordination bonds, which underwent a coordination structural relaxation after high energy light excitation, resulting in a new channel emission. This work demonstrates an intriguing dual-channel doublet emission phenomenon in lanthanide Ce(III) complexes and will inspire new insights both into the design of novel lanthanide-based luminescent materials and dual-channel luminescent materials.