Temperature‐Triggered Structural Dynamics of Non‐Coordinating Guest Moieties in a Fluorescent Actinide Polyrotaxane Framework

Abstract We present here the synthesis of a novel fluorescent actinide polyrotaxane compound URCP1 through the utilization of an end‐cutting pseudorotaxane precursor with only the cucurbit[6]uril (CB[6]) macrocyclic components acting as linking struts. The non‐coordinating guest motif in the obtained polyrotaxane, with increased freedom and structural flexibility, can display intriguing temperature‐triggered conformational variations inside the cavity of CB[6], which was clearly evidenced by crystallographic snapshots at different temperatures. Notably, this observation of temperature‐triggered structural dynamics in URCP1 represents the first report of actinide polyrotaxane with such feature in solid‐state. Moreover, URCP1 has a high photoluminescence quantum yield (PLQY) of 49.8 %, comparable to other luminescent uranyl compounds, and can work as a fluorescent probe to selectively detect Fe 3+ over other eight competing cations in aqueous solution, with the limit of detection being as low as 4.4×10 −3 ppm.