Bromine atom introduction improves the F - sensing ability of an indolo[3,2- b ]carbazole-salicylaldehyde-based fluorescence turn-on sensor.

The heavy-atom effect usually quenches fluorescence, but scarcely enhances it. Herein, fluorescence turn-on sensors without or with a bromine atom for F - detection are presented, achieving fast response time within 1 min, and the LODs of 1.9 × 10 -7 and 8.5 × 10 -8 M, reflecting that halogen atom introduction is beneficial for F - detection ability improvement. The sensing mechanism of -OH unit deprotonation is confirmed based on the results of a 1 : 2 stoichiometric ratio, 1 H NMR titration and TD-DFT calculation. The water environment F - detection and spiked recovery experiments demonstrate their potential for real sample detection.