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 Fe3+ over other eight competing cations in aqueous solution, with the limit of detection being as low as 4.4×10−3 ppm.

Proximity Effect in Uranyl Coordination of the Cucurbit[6]uril-Bipyridinium Pseudorotaxane Ligand for Promoting Host–Guest Synergistic Chelating

“…For instance, once the binding constant is too weak, the pseudorotaxane linker might dissociate into two independent components during the assembly process with metal cations. 28 Alternatively, another possible way to enhance the metal coordination capability of the pseudorotaxane ligand is changing the molecular configurations of well-bonded pseudorotaxane linkers. In most previous work, the binding motifs (commonly carboxylate) in the pseudorotaxane ligands usually are located at the para-positions of the guest molecules bridged by alkyl chains, while those with meta-substituent groups are relatively few.…”

“…It should be mentioned that this strategy must be well-designed to balance the host–guest inclusion and metal–organic coordination. For instance, once the binding constant is too weak, the pseudorotaxane linker might dissociate into two independent components during the assembly process with metal cations …”

Modular Assembly of Isostructural Mixed-Ligand Uranyl Coordination Polymers Based on a Patterning Strategy

“…The selection of metal centers plays a crucial role in the exploration of new kinds of coordination polymers. Given the recent developments and breakthroughs in actinide-based materials, chemists have made significant progress in the exploration of actinide coordination polymers because of their novel topology and interesting electronic properties. − As a representative of the actinide series, uranium is the most widely studied and shows rich coordination chemistry and structural diversity due to the unique 5f electronic orbital participating in bonding and hydrolysis. Uranium has a variety of oxidation states, from +2 to +6 valence, among which hexavalent uranium, always in the form of uranyl with a linear structure, is the most common state.…”

Impact of the proximity effect on uranyl coordination of conformationally variable weakly-bonded cucurbit[6]uril-bipyridinium pseudorotaxane

“…Among all the available organic linkers, pseudorotaxanes have been demonstrated to be versatile precursors which can endow the prepared materials with unique topologies 17,18 and molecular dynamics. 19–21 In a typical pseudorotaxane, the macrocyclic host and the string guest bond with each other through weak interactions between these two components. This provides an important platform for designing new organic ligands through non-covalent binding, which can produce richer variations in the linkers than direct chemical modification.…”