Ortho-hydroxyl-oriented tandem-responsive diacylhydrazones with super sensitivity for Al3+ and subsequent potential recognition of Cu2+.

Structure is a crucial factor to decide the selectivity and sensitivity of chemosensors. In this work, a diacylhydrazone 2a and its congeneric derivatives 2b-2d were synthesized and their applications for Al 3+ detection were investigated. Except 2d , all the other compounds exhibit notable turn-on fluorescence toward Al 3+ over 15 other metal ions and the sensitivities of 2b and 2c are even higher after modification, illustrating ortho -OH indispensability in their structures for sensing. Reversibility investigation shows that the sensors all have regeneration ability. Meanwhile, the sensor-Al 3+ systems show selective fluorescence turn-off for Cu 2+ , providing a potential platform for tandem recognition of Al 3+ and Cu 2+ . 2a as a standard, shows a 1:2 molar ratio to Al 3+ confirmed by Job’s plot, 1 H NMR spectra and mass spectra, and its detection limit for Al 3+ is 7.63 nM in ethanol. It has relevant sensitivity over pH 3-9, with the highest sensitivity at around pH 4. Apart from Al 3+ detection, anion selectivity was also explored and it shows that 2a , 2b and 2c all have selectivity toward CN − evidenced by UV-vis spectra. [ABSTRACT FROM AUTHOR]