Synthesis and Chiral Molecular Recognition of Phenylene-Bridged Bispyrrole Derivatives Having N-Substituted Imino Groups

Spectroscopic sensing of chiral substances with chemosensors has attracted much attentions in the field of supramolecular chemistry. We previously reported that p-phenylene-bridged bispyrrole bearing N-alkylimino groups becomes an acid-responsive single trichromatic BOG (blue, orange, and green) luminescent dye capable of emitting pure WL in solution.^[1]The observed variable emission originates from its trichromatic luminescent behavior upon protonation of the imino groups. As an extension of the study, we newly designed the m-phenylene-bridged bispyrrole bearing N-substituted imino groups as an acyclic chemosensor for carboxylic acids. We expected that the imino (Schiff base) groups specifically bind the carboxylic acid via acid-base hydrogen bonding interactions. This guest-binding might bring about the specific conformational changes of the host molecule to give the characteristic spectral changes in UV-Vis absorption, fluorescence, and CD spectroscopies.

In this poster presentation, we report synthesis and chemoseising behaviors of the three-types of m-phenylene-bridged bispyrrole bearing N-pyridyl, benzyl, or alkyl substituted imino groups. These bispyrrole derivatives showed spectral changes in the absorption and CD spectroscopy upon mixing with chiral dibenzoyl tartaric acid and mandelic acid. Especially, the pyridyl-substituted bispyrrole showed characteristic and relatively stronger Cotton effect in CD spectroscopy, which may originate from the multi-points and multi-step host-guest interactions.

[1] K. Imamura, Y. Ueno, S. Akimoto, K. Eda, Y. Du, C. Eerdun, M. Wang, K. Nishinaka, A. Tsuda, ChemPhotoChem 2017, 1, 427-431.