Self-Restricted Green Fluorescent Protein Chromophore Analogues: Dramatic Emission Enhancement and Remarkable Solvatofluorochromism

The confinement effect of the beta-barrel defines the emission profiles of the chromophores of the green fluorescent protein (GFP) family. Here, we describe the design strategy and mimicking of confinement effects via the chromophore itself, termed the self-restricted effect. By systematically tailoring the GFP core, a family of 2,5-dialkoxy-substituted GFP chromophore analogues is found to be highly emissive and show remarkable solvatofluorochromism in fluid solvents. Fluorescence quantum yield (QY) and lifetime measurements, in combination with theoretical calculations, illustrate the mechanism relying on inhibition of torsional rotation around the exocyclic CC bond. Meanwhile, theoretical calculations further reveal that the electrostatic interaction between the solvent and the imidazolinone oxygen can contribute to suppress the radiationless decay channel around the exocyclic C=C double bond. Our findings put forward a universal approach toward unlocked highly emissive GFPc analogues, potentially promoting the understanding of the photophysics and biochemical application of GFP chromophore analogues.