Seven-membered ring excited-state intramolecular proton-transfer in 2-benzamido-3- (pyridin-2-yl)acrylic acid

Hydrogen bonding compound (E)-2-benzamido-3-(pyridin-2-yl) acrylic acid (1a) was synthesized and characterized by 1H NMR, FT-IR, and X-ray diffraction analysis in comparison to its analog. These analyses show the existence of seven-membered ring intramolecular hydrogen bonding in 1a. The hydrogen bonding results in the increasing of pKa comparing to its analog. Further investigation on the photophysical properties of 1a in selected solvents reveals that strong absorption appears at about 340 nm and dual emission at around 420 and 490 nm. The excited-state intramolecular proton-transfer in 1a is very sensitive to solvent polarity and fluoride ion. Theoretical studies also give evidence of excited-state intramolecular proton-transfer with quite low energy barrier.

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► 2-Benzamido-3-(pyridin-2-yl)acrylic acid has 7-membered ring intramolecular H-bond.
► Dual emissions are observed both in solution and solid states.
► Absorption and emission spectra are sensitive to solvents polarity, F− and base.
► Theoretical calculation shows low excited-state intramolecular H transfer barrier.