Colorimetric and fluorescence turn-on sensor for biologically important anions based on carbazole derivative

A colorimetric and fluorescent anion chemosensor containing carbazole group has been designed and synthesized based on photoinduced electron transfer (PET). The strong basic anions such as F−, AcO− and H2PO4− resulted in significant red-shift in absorption band and enhancement in fluorescent emission intensity of the compound 1, synchronously accompanied by a “naked eye” color change from light yellow to orange-yellow in organic medium. The determination limit of sensor 1 toward H2PO4− is 1.0 × 10− 6 mol·L− 1. 1H NMR titration experiments shed light on the nature of the interaction between 1 and the anions. Theoretical investigation further illustrated the possible binding mode of host–guest and the roles of molecular frontier orbitals in anion binding.