Novel Thiophene-Derived Schiff Base as a Fluorescent Sensor for the Highly Sensitive and Selective Relay Recognition of Zn²⁺ and Fe²⁺ ions

Abstract:

Chemosensors based on Schiff bases are pivotal in environmental and biological applications, serving to identify specific metal ions at trace levels. Despite the distinctive importance of thiophene-based molecules in medicinal contexts, the number of reported chemosensors utilizing these moieties remains limited.

In this study, we present the synthesis and characterization of a novel Schiff base sensor (TBH), derived from thiophene-2-carboxaldehyde and benzil. We investigate its application as a selective relay probe for the detection of Zn²⁺ and Fe²⁺ ions.

The introduction of Zn²⁺ to TBH resulted in a significant enhancement in fluorescent intensity, attributed to the formation of a 1:1 TBH–Zn²⁺ complex, with no response observed for other cations, including Mg²⁺, Ba²⁺, Cd²⁺, Cu²⁺, Co²⁺, Mn²⁺, Cr³⁺, Hg²⁺, Sn²⁺, La³⁺, Ca²⁺, Na⁺, K⁺, and particularly Fe²⁺. Furthermore, Fe²⁺ induced fluorescence quenching in the TBH–Zn²⁺ system, forming a 1:1 MY–Fe²⁺ complex. The TBH-Zn²⁺ complex demonstrates potential as a secondary sensor for Fe²⁺ ions. The sensor's signal change is based on the chelation-enhanced fluorescence (CHEF) effect of TBH–Zn²⁺, coupled with the inhibition of photoinduced electron transfer (PET).

Moreover, the rapid and selective features of the proposed sensor make it promising for the precise monitoring of Zn²⁺and Fe²⁺ in biological and environmental research.