The photoreactivity of 2,6-difluoro-4-nitroanisole in the presence of nucleophiles suggests that 2,6-difluoro-4-nitrophenyl ethers can constitute improved biochemicalphotoprobes for use in photoaffinity labeling reagents, specially for proteins where a number of good nucleophiles are present. Almost no photoreduction processes are observed, and one of the fluorine atoms is never replaced. This would