A selective fluorescent probe for relay recognition of Al3+ and Cu2+ through fluorescence off-on-off functionality

A new 3-hydroxylflavone-based fluorescent probe N'-(3-(3-hydroxy-4-oxo-4H-chromen-2-yl)benzylidene)picolinohydrazide (1) with two different binding sites, 3-hydroxy-4-keto (site 1) and 2-picolinyl hydrazide (site 2), has been designed and synthesized. It shows highly selective relay recognition of Al3+ and Cu2+ via a fluorescence off-on-off mechanism. In DMSO-H2O (1:9, v/v) solution, probe 1 displays highly selective response to Al3+ with remarkable emission enhancement through its binding of Al3+ to site 1. Moreover, the in situ system generated from the sensing of Al3+ demonstrates eminent relay recognition of Cu2+ via a fluorescence quenching through its binding of Cu2+ to site 2. These proposed binding modes are also proved by H-1 NMR titration. The detection limits for Al3+ and Cu2+ are calculated to be 21.7 mu M and 0.95 mu M, respectively. (C) 2015 Elsevier B.V. All rights reserved.