“Cascade recognition” of Cu2+ and H2PO4− with high sensitivity and selectivity in aqueous media based on the effect of ESIPT

Abstract

Organic molecular sensors have the advantage of being used through easy, fast, economical and reliable optical methods for detecting toxic metal ions in the environment. In the present work, a simple but specific organic ligand N,N-(3,3′-dimethyl biphenyl)-bis(4-diethylaminosalicyladimine) (Q2) was designed and synthesized according to the excited state intramolecular proton transfer (ESIPT). Q2 can be regarded as a colorimetric and fluorescent sensor for relay recognition of Cu2+ and H2PO4− in DMSO/H2O (8:2, v/v) HEPES buffer solutions. Moreover, sensor Q2 showed a highly sensitive and selective response towards Cu2+ and H2PO4− over other metal ions and anions. Particularly, the fluorescence “ON–OFF–ON” responding circle could be repeated over 4 times by the sequential addition of Cu2+ and H2PO4−. Notably, the actual usage of sensor Q2 was further demonstrated by test kits and silica gel plates. The fluorescence changes of Q2 upon the addition of Cu2+ and H2PO4− were utilized as an INHIBIT logic gate at the molecular level, using Cu2+ and H2PO4− as chemical inputs and the fluorescence intensity signal as the output.