Guest-Driven Luminescence: Lanthanide-Based Host–Guest Systems with Bimodal Emissive Properties Based on a Guest-Driven Approach

Graphical Abstract

Nanoscopic cage molecules: A series of lanthanide-based (Ln=Nd^III, Ho^III, Er^III, Tm^III, and Yb^III) discrete closed, semi-opened, and polymeric cage-like host–guest systems with bimodal emissive properties based on the guest-driven approach are reported (see figure). The photoinduced solid-state emission spectrum could be a good diagnostic technique for monitoring the solid-state guest-exchange process.

Abstract

A series of discrete closed, semi-closed, and polymeric lanthanide-based [{Ln(H₂O)₈}³⁺⊂Ln^III₂L₄] host–guest systems with tetragonal prism-like structure have been designed and synthesized through the ligand-dominated approach. These nanoscopic cages are robust and can be maintained upon guest exchange. Within the restricting space, the luminescence intensity of the encapsulated [Ln(H₂O)₈]³⁺ species is dramatically enhanced due to the vibrational movements originating from the OH oscillators in the coordinated water molecules being effectively reduced by the host–guest H-bonding interactions. Based on the guest-driven approach, tunable emission and bimodal emission (UV/Vis/NIR) of these [{Ln(H₂O)₈}³⁺⊂Ln^III₂L₄] supramolecular systems are successfully realized. Moreover, the strong luminescence originating from [{Ln(H₂O)₈}³⁺⊂Ln^III₂L₄] host–guest system can be quenched by encapsulation of d-block metal quenchers, such as Fe³⁺ and Cu²⁺, through solid-state f–d metal exchange. Additionally, this study demonstrates that the photoinduced solid-state guest-independent emission spectrum could be one of the most diagnostic techniques for monitoring the solid-state guest-exchange process.