Conformation-Locked Near-Infrared Probes for Real-Time Visualization of G Protein-Coupled Receptor Dimers in Living Systems

Visualizing G protein-coupled receptor dimerization in living systems remains a significant challenge due to the lack of activatable and biocompatible imaging tools. Here, we report a supramolecular near-infrared fluorophore based on a twisted intramolecular charge transfer (TICT) design whose emission is selectively activated by cucurbit[7]uril (CB[7]) complexation. The dye, DMA-BTZ, incorporates a strong electron donor (dimethylamino) and acceptor (benzothiazolium) pair to promote TICT-driven quenching in the free state. Upon CB[7] binding, TICT is suppressed via steric and electrostatic confinement, resulting in a dramatic 41.7-fold fluorescence enhancement. Spectroscopic measurements and excited-state quantum chemical calculations reveal that CB[7] binding restricts intramolecular twisting and stabilizes a planar, emissive excited-state geometry. This host-induced fluorescence turn-on enables selective imaging of μ-opioid receptor and δ-opioid receptor heterodimerization in mammalian cells and transgenic zebrafish models. The combination of modular donor-acceptor design, supramolecular activation, and biological applicability establishes a versatile strategy for developing high-contrast probes for real-time imaging of protein-protein interactions in vivo.