Cucurbit[8]uril-based non-covalent heterodimer realized NIR cell imaging through topological transformation from nanowire to nanorod

In recent years, multicolor cascade supramolecular assemblies with controllable topological morphology have become a research hotspot due to their wide application in light-emitting materials, cell imaging and other fields. Herein, several kinds of macrocycles including cucurbiturils, calixarene and cyclodextrins are used as building blocks to construct fluorescent assemblies with anthryl-conjugated phenylpyridine (G), wherein cucurbit[8]uril (CB[8]) and G can form nanowires at a stoichiometric ratio of n:n through host-guest encapsulation to form a non-covalent heterodimer. Significantly, the macrocycle confinement effect drastically enhances the fluorescence emission of G and emission peak generated bathochromic shift from 500 nm to 600 nm. When the supramolecular polymer is further assembled with amphiphilic calix[4]arene (SC4A8), the fluorescence emission of G⊂CB[8] further increases to 1.4 times, accompanied by the morphological transformation from linear structure to nanorod structure. Subsequently, a very small amount of dye Cy5 is added to the assembly solution as an energy receptor, and the negatively charged G⊂CB[8]@SC4A8 system is regarded as an energy donor. The efficient energy transfer process enables near-infrared (NIR) emission at 675 nm with 71% energy transfer efficiency (ΦET) at a donor/receptor ratio of 100:1. Finally, the cascade supramolecular assembly has been successfully applied to targeted imaging in the nucleus of HeLa and A549 cancer cells.