Highly Efficient Supramolecular Aggregation-Induced Emission-Active Pseudorotaxane Luminogen for Functional Bioimaging

The direct tracking of cells using fluorescent dyes is a constant challenge in cell therapy due to aggregation-induced quenching (ACQ) effect and biocompatibility issues. Here, we demonstrate the development of a biocompatible and highly efficient aggregation-induced emission (AIE)-active pseudorotaxane luminogen based on tetraphenylethene conjugated poly(ethylene glycol) (TPE-PEG₂) (guest) and α-cyclodextrin (α-CD) (host). It is capable of showing significant fluorescent emission enhancement at the 400-600 nm range when excited at 388 nm, without increasing the concentration of AIE compound. The fluorescent intensity of TPE-PEG₂ solution was effectively enhanced by 4-12 times with gradual addition of 1-4 mM of α-CD. 2D NOSEY ¹H NMR revealed clear correlation spots between the characteristic peaks of α-CD and PEG, indicating the interaction between protons of ethylene glycol and cyclodextrin, and the structures are mainly based on threaded α-CD. The host-guest complex exhibits boosted fluorescent emission because the PEG side chains are confined in "nano-cavities" (host), thus, applying additional restriction on intermolecular rotation of TPE segments. In vitro cell experiments demonstrated the potential of AIE-active pseudorotaxane polymer as a biocompatible bioimaging probe.