Molecular aggregation behavior of perylene-bridged bis(beta-cyclodextrin) and its electronic interactions upon selective binding with aromatic guests.

A novel water-soluble perylene bisimide derivative 1 was synthesized with two permethyl-beta-cyclodextrin grafts at the imide nitrogens, and its structure was identified by NMR, Fourier transform infrared spectroscopy (FT-IR), matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS), and elemental analysis. Its aggregation behavior in water and organic solutions was further investigated by UV-vis, fluorescence, and (1)H NMR spectra, showing that 1 exhibits strong pi...pi aggregation in water. Especially, the aggregation and optical properties were comprehensively compared between the neutral form 1 and protonated form 1H(2) through concentration- and temperature-dependent UV-vis experiments. The aggregation constant of 1H(2) is almost 1 order of magnitude lower than that of 1 owing to electrostatic repulsion. On the other hand, 1H(2) exhibits better fluorescence than 1 by overcoming the photoinduced electron transfer process from imino groups to perylene backbone. Furthermore, by employing the binding sites of grafted cyclodextrins to aromatic guests, pronounced electronic interactions between perylene and anthracene/pyrene guests were observed.