Ortho green fluorescence protein synthetic chromophore; Excited-state intramolecular proton transfer via a seven-membered-ring hydrogen-bonding system

A structural isomer of the core chromophore (p-HBDI) in green fluorescence protein, o-HBDI, is synthesized. o-HBDI possesses a seven-membered-ring hydrogen bond, from which the excited-state intramolecular proton transfer takes place, resulting in a remarkable tautomer emission of similar to 605 nm.