Supramolecular Self-Assembly and Metal–Ligand-Enhanced Organic Room-Temperature Phosphorescence for Live Cell Imaging

A purely organic supramolecular assembly emitting room-temperature phosphorescence (RTP) was constructed from 1-(3-(bis(pyridin-2-ylmethyl)amino)propyl)-4-(4-bromophenyl)pyridin-1-ium bromide (BP-DPA) by complexing with cucurbit[8]uril (Q[8]) and Zn²⁺ through a supramolecular assembly. Benefiting from the strong affinity and the macrocyclic restriction effect of Q[8], phosphorescence emission was achieved by encapsulating BP-DPA in the Q[8] cavity. Notably, secondary assembly with Zn²⁺ formed the supramolecular complex BP-DPA@Q[8]⊂Zn²⁺, which greatly contributed to the enhancement of the phosphorescence quantum yield and lifetime from 1.75% to 6.25% and from 0.48 to 1.25 ms, respectively. Meanwhile, BP-DPA@Q[8] specifically recognizes Zn²⁺ with a low detection limit without interference from common metal ions, anions, and biomolecules. It permeates the plasma membrane of cells and emits a specific phosphorescence response signal in the presence of Zn²⁺. In addition, this material can also be utilized for the development of portable indicator papers, enabling the rapid and visualized detection of Zn²⁺. This work provides a route for constructing multilevel supramolecular assemblies of RTP, extending the biological applications of purely organic RTP materials and offering additional possibilities for the potential utilization of cucurbit[n]uril-based room-temperature phosphorescence materials.