Diketopyrrolopyrrole-derived Schiff base as colorimetric and fluoromertic probe for sequential detection of HSO4− and Fe3+ with “off-on-off” response

Anion to cation relay recognition was designed and realized for the first time with sequence specificity (HSO4− → Fe3+) by use of a novel diketopyrrolopyrrole-derived Schiff base (1) via a fluorescence “off-on-off” mechanism. 1 served as a chemodosimeter for HSO4−via hydrolysis process with 10.6 fold fluorescence enhancement as well as color changing from red to orange. The in situ system generated from 1 + HSO4− showed good relay recognition ability for Fe3+via fast fluorescence quenching by the formation of a 1:1 complex with color change from orange to faint yellow. Moreover, other anions or metal ions failed to generate distinct response, which indicated that 1 had desirable selectivity for relay recognition of HSO4− and Fe3+. 1 also functioned when supported by silica, indicating that probe 1 had the potential for working as optical solid sensors.