Single-Molecule Phosphorescence Resonance Energy Transfer for NIR Targeted Cell Imaging

Abstract

Abstract A single-molecule phosphorescence resonance energy transfer (PRET) system with a large Stokes shift of 367 nm and near-infrared (NIR) emission is constructed by alkyl-bridged methoxy-tetraphenylethylene-phenylpyridines derivative (TPE-DPY), cucurbit[n]uril (CB[n], n = 7,8), and β-cyclodextrin modified hyaluronic acid (HACD). The experiment results demonstrate that the high binding affinity and various stoichiometric ratios of CB[n] (n = 7, 8) to TPE-DPY not only regulate the topological morphology of supramolecular assembly but also induce different phosphorescence emissions. The assembly of TPE-DPY and CB[7] presents spherical nanoparticles, exhibiting an emerging phosphorescence emission at 525 nm via the macrocyclic confinement effect to phenyl-pyridine units. CB[8] with a larger hydrophobic cavity binds with TPE-DPY to form an n:n pseudorotaxane nanorod, which induces an efficient phosphorescence at 545 nm. Varying from the binary assembly of CB[7] or CB[8], an entirely distinct topological organic three-dimensional nanoplate is obtained by the co-assembly TPE-DPY with CB[7]/CB[8], accompanying enhanced phosphorescence at 540 nm. Uncommonly, the secondary assembly of HACD and TPE-DPY/CB[7]/CB[8] activates a single intramolecular PRET process derived from phenyl pyridines unit to methoxy-tetraphenylethylene function group, enabling an NIR delayed fluorescence at 700 nm excited by 333 nm, which ultimately applied to mitochondrial targeted imaging for cancer cells.