Emission pathway switching by solvent polarity: Facile synthesis of benzofuran-bipyridine derivatives and turn-on fluorescence probe for zinc ions

Bipyridine attached benzofuran derivatives were prepared by the cyclization of alkyne ortho-substituted phenols. Electronically different substituents, N,N-dibutylamino vs tert-butyl group, were attached on benzofuran rings. Depending on the polarity and pH of solvent environment, N,N-dialkylamino group participates in two distinctively different roles in emissive properties, i.e., ICT-type and PET-type behaviors. Upon capturing lone-pair electrons of N,N-dialkylamino groups by protonation, ratiometric blue-shift and complete turn-on behaviors were observed in THF and MeCN solution, respectively. Such peculiar behavior was further utilized to show turn-on sensing of zinc ions.