FRET‐Based In‐Cell Detection of Highly Selective Supramolecular Complexes of <i>meso</i> ‐Tetraarylporphyrin with Peptide/BODIPY‐Modified Per‐ <i>O</i> ‐Methyl‐β‐Cyclodextrins

Artificial supramolecular systems capable of self-assembly and that precisely function in biological media are in high demand. Herein, we demonstrate a highly specific host-guest-pair system that functions in living cells. A per-O-methyl-β-cyclodextrin derivative (R8-B-CD Me) bearing both an octaarginine peptide chain and a BODIPY dye was synthesized as a fluorescent intracellular delivery tool. R8-B-CD Me was efficiently taken up by HeLa cells through both endocytosis and direct transmembrane pathways. R8-B-CD Me formed a 2 : 1 inclusion complex with tetrakis(4-sulfonatophenyl)porphyrin (TPPS) as a guest molecule in water, from which fluorescence resonance energy transfer (FRET) from R8-B-CD Me to TPPS was observed. The FRET phenomenon was clearly detected in living cells using confocal microscopy techniques, which revealed that the formed supramolecular R8-B-CD Me /TPPS complex was maintained within the cells. The R8-B-CD Me cytotoxicity assay revealed that the addition of TPPS counteracts the strong cytotoxicity (IC 50 = 16 μM) of the CD cavity due to complexation within the cells. A series of experiments demonstrated the bio-orthogonality of the supramolecular per-O-methyl-β-CD/tetraarylporphyrin hostguest pair in living cells