J Phys Chem B 2013 Feb 15;117(8):2300-13. Epub 2013 Feb 15.
Division of Molecular Imaging and Photonics, Department of Chemistry, Katholieke Universiteit Leuven, Celestijnenlaan 200F, 3001 Heverlee, Belgium.
Green-to-red photoconversion is a reaction that occurs in a limited number of fluorescent proteins and that is currently mechanistically debated. In this contribution, we report on our investigation of the photoconvertible fluorescent protein Dendra2 by employing a combination of pump-probe, up-conversion and single photon timing spectroscopic techniques. Our findings indicate that upon excitation of the neutral green state an excited state proton transfer proceeds with a time constant of 3.4 ps between the neutral green and the anionic green states. In concentrated solution we detected resonance energy transfer (25 ps time constant) between green and red monomers. The time-resolved emission spectra suggest also the formation of a super-red species, first observed for DsRed (a red fluorescent protein from the corallimorph species Discosoma) and consistent with peculiar structural details present in both proteins.