Two fluorescent anion sensors bearing phenol, carbazole-NH and -NO 2 group were designed and synthesized. They both exhibited highly binding ability for , respectively. Theoretical investigation indicated it was the highest HOMO to induce the red-shift phenomena of two sensors.

Three fluorescent turn‐on probes containing 3,6‐dichloro‐9H‐carbazole as carbazyl part have been designed and synthesized. Among studied anions F−, AcO−, H2PO$\rm{{_{4}^{-}}}$, Cl−, Br− and I−, AcO− showed the strongest binding ability with all probes. The strong basic anions, such as AcO−, H2PO$\rm{{_{4}^{-}}}$, and F−, induced a significant red‐shift in absorption and a concomitant increase in fluorescent emission of the probes caused by photoinduced electron transfer (PET). The determination limit of probe 3 (Scheme 1) toward AcO− is 3.0×10−7 M. 1H‐NMR Titration experiments shed light on the nature of the interaction between the probes and the anions. Theoretical investigation further illustrated the possible binding mode in these hostguest interactions and the roles of molecular frontier orbitals in molecular interplay.

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