Probing the decay coordinate of the green fluorescent protein: Arrest of cis-trans isomerization by the protein significantly narrows the fluorescence spectra

A study of the fluorescent spectra of the green fluorescence protein (GFP) and the anionic form of p-hydroxybenzylidenemethylimidazolone (p-HBDI) reveals a well-resolved vibronic structure but broad and structureless chromophore spectra at lower temperatures. The results show that the cis-trans isomerization exhibited by the protein significantly narrows the fluorescence spectra, which is otherwise consistent with the decay of the torsional deformation (TD).