On a possible excited state proton transfer in N-formylkynurenine derivatives

It is shown that intramolecular hydrogen bonding between the

and the ortho carbonyl on the side chain of N'formylkynurenine and some parent compounds plays an important role on their spectroscopic properties. The fluorescence emissionλ_max is shifted by about 4000 cm^?1 in going from polar to non-polar solvents. This abnormally red-shifted fluorescence is attributed to an excited state proton transfer from the formamido to the ortho carbonyl of the side chain.