Bioinspired Fluorescent Dyes Based on a Conformationally Locked Chromophore of the Fluorescent Protein Kaede

A novel class of fluorescent dyes based on the conformationally locked heterocyclic core of the chromophore of the fluorescent protein Kaede was discovered. Introduction of a single conformational lock at the benzylidene fragment of the Kaede chromophore resulted in an increase in the fluorescence quantum yield (FQY) by one order of magnitude and a redshift of ca. 60 nm in the emission spectrum. Imposing the second lock at the ethylene fragment of the Kaede chromophore provided a further increase in the FQY. Locked analogues demonstrated bright and redshifted emission in a broad range of solvents, which makes them good candidates for a wide spectrum of fluorescent‐labeling applications.