Synthesis and characterization of the fluorescence utility of two Visible-Light-Absorbing tryptophan derivatives

[Display omitted] •4-Dicyanovinyltryptophan (4DCV-Trp) was synthesized.•4DCV-Trp is a visible-light-absorbing fluorophore that emits yellow fluorescence in water.•The fluorescence spectrum of 4DCV-Trp is sensitive to solvent polarity.•4NO2-tryptophan (4NO2-Trp) can be used as a FRET quencher of biological blue fluorophores, such as 4CN-tryptophan (4CN-Trp).•A fluorescence assay based on 4NO2-Trp and 4CN-Trp to monitor protease activity was demonstrated. We synthesize Nα-Boc-4-dicyanovinyltryptophan OMe (4DCV-Trp) and characterize its photophysical properties in different solvents. We find that the maximum absorption wavelength of 4DCV-Trp is at ca. 430 nm in water, and that its fluorescence spectrum exhibits a large Stokes shift (e.g., ca. 150 nm in water). Furthermore, solvent-dependent studies reveal a positive, linear correlation between the frequency of 4DCV-Trp’s fluorescence maximum and the solvent polarity index, suggesting that 4DCV-Trp could serve as a polarity reporter of proteins. In addition, we synthesize 4-nitrotryptophan and validate its utility as a fluorescence quencher of a blue fluorescent amino acid, 4-cyanotryptophan.