N,N-Diphenylanilino-heterocyclic aldehyde-based chemosensors for UV-vis/NIR and fluorescence Cu(ii) detection

Abstract

Herein, three N,N-diphenylanilino-heterocyclic aldehyde probes (5, 6 and 7) are synthesized, characterized and their sensing behaviour against metal cations tested. Acetonitrile solutions of the three probes show an intramolecular charge-transfer band in the 360–420 nm range due to the presence of an electron donor N,N-diphenylanilino group and an electron acceptor aldehyde moiety. Besides, all three probes are moderately emissive with bands in the 540–580 nm range in acetronitrile. The chromo-fluorogenic behaviour of the three probes in acetonitrile in the presence of selected metal cations is assessed. Of all the metal cations tested only Cu(II) induces marked colour and emission changes. In this respect, addition of Cu(II) cations to solutions of the probes induces the appearance of NIR absorptions at 756 nm for 5, at 852 nm for 6 and at 527, 625 and 1072 nm for 7. Besides, Cu(II) induces a marked quenching of the emission of the three probes. The observed spectral changes are ascribed to the formation of 1 : 1 probe-Cu(II) complexes in which the metal cation interacts with the acceptor part of the chemosensors. In addition, the limits of detection determined using UV-visible and fluorescence titrations are in the 0.21–5.12 μM range, which are values lower than the minimum concentration prescribed by the World Health Organization (WHO) guideline for drinking water for copper (30 mM). Besides, probe 7 is used for the detection of Cu(II) in aqueous environments using SDS anionic surfactant.