Design of a fluorescent host for monitoring multiple hydrogen-bonding interaction directly by intramolecular charge-transfer emission

Abstract

The hosts 2-dodecanamido-4-methyl-N-[4-(dimethylamino)phenyl]quinoline-7-carboxamide 1 and 2-dodecanamido-4-methyl-N-(4-methoxyphenyl)quinoline-7-carboxamide 2 bearing an aromatic amide unit exhibit an anomalous fluorescence with a large Stokes shift at around 500–600 nm (LW emission) due to an intramolecular charge-transfer (ICT) process. The guests 3-ethyl-3-methylglutarimide (bemegride) 4 and 1-methyluracil 5 are associated with the hosts by forming three hydrogen bonds, and LW emission of the hosts largely increase. On the other hand, the guest 3-methyluracil 6 does not affect the emission of the hosts at all, though formation of two hydrogen bonds with the hosts is confirmed by ¹H NMR measurement. It is concluded that the hosts 1 and 2 can selectively detect the guests 4 and 5 that form hydrogen bonds both at the quinoline ring nitrogen and the amide proton (H_α) of the hosts simultaneously to affect rotation of the amide bond.