Supramolecular Complex of Cucurbit[7]uril with Diketopyrrolopyrole Dye: Fluorescence Boost, Biolabeling and Optical...

New photostable and bright supramolecular complexes based on cucurbit[7]uril (CB7) host and diketopyrrolopyrole (DPP) guest dyes having two positively charged 4-(trimethylammonio)phenyl groups were prepared and characterized. The dye core displays large Stokes shift (in H₂O, abs./emission max. 480/550 nm; ϵ~19 000, τ_fl>4 ns), strong binding with the host (~560 nM K_d) and a linker affording fluorescence detection of bioconjugates with antibody and nanobody. Combination of protein-functionalized DPP dye with CB7 improves photostability and affords up to 12-fold emission gain. Two-color confocal and stimulated emission depletion (STED) microscopy with 595 nm or 655 nm STED depletion lasers shows that the presence of CB7 not only leads to improved brightness and image quality, but also results in DPP becoming cell-permeable.