Construction of a Supramolecular Fluorescence Sensor from Water‐soluble Pillar[5]arene and 1‐Naphthol for Recognition of Metal Ions

Abstract

A new fluorescent chemosensor comprised of a pyridine functionalized pillar[5]arene (PyP5) and 1‐naphthol has been designed and utilized for the recognition of metal cations. The 1‐naphthol was encapsulated by the PyP5 cavity and formed a 1 : 1 host ‐ guest inclusion complex. Whilst free 1‐naphthol is known to be strongly fluorescent, this strong fluorescence was quenched in the inclusion complex 1‐naphthol@PyP5. Using the 1‐naphthol@PyP5 inclusion complex as a fluorescent probe, various metal cations have been detected. The experimental results revealed that the probe responded to both Ag+ and Fe3+, via an obvious fluorescence quenching or an incomplete quenching of fluorescence, respectively. As a result, a fluorescence method for the detection of two metal cations using a single system has been developed. On the other hand, 1‐naphthol is an important intermediate of fine chemicals, which is widely used in the synthesis and production of dyes, spices, oils, medicines and pesticides.[50–52] The oxygen atom of 1‐naphthol is sp2 hybridized and can form extensive π bonds, and can exhibit strong fluorescence. The successful preparation of water‐soluble pillar[5]arene can provide new opportunities for chemists working in the field of host–guest chemistry and the recognition of metal ions. Therefore, more and more research has centered on the synthesis of water‐soluble pillar[5]arenes.[53–56] On this basis, we have synthesized a pyridine functionalized pillar[5]arene. Pyridine functionalized pillar[5]arenes are extremely soluble in water and strongly bind 1‐naphthol in water, which is mainly driven by hydrophobic and electrostatic interactions. The probe system is constructed by encapsulating one equivalent of 1‐naphthol, which possess strong intrinsic fluorescence, into the hydrophobic cavity of PyP5. To this inclusion complex, namely 1‐naphthol@PyP5, were added metal ions. The addition of Ag+ led to incomplete quenching of fluorescence, whilst Fe3+ led to complete quenching of fluorescence. Based on the linear relationship between the fluorescence intensity and the concentration of Ag+ and Fe3+, a simple fluorescent probe method for the analysis of Ag+ and Fe3+ was constructed. The observed visual signals indicate the potential of this probe system in rapid assay applications.