A highly lipophilic terpyridine ligand as an efficient fluorescent probe for the selective detection of zinc(ii) ions under biological conditions†

The present work describes the synthesis of new terpyridine (tpy) molecules possessing functionalized long alkyl chains at the 4′-position associated with a planar structure with considerable delocalization. Out of the three synthesized tpy derivatives (L₁, L₂, and L₃), L₂ containing an ester group at the end of the alkyl chain emerged as an excellent probe for the selective detection of Zn²⁺. The detection of Zn²⁺ ions under biological conditions was achieved by the introduction of a distinct aliphatic undecanoic ester chain at the 4′-position of the core terpyridine ring, thereby making it more lipophilic. The increased lipophilicity aids in the probe performance by enabling precise Zn²⁺ detection and bioimaging. The bioimaging capability of the probe L₂ for Zn²⁺ ions was demonstrated in ICG cell lines. The RGB method was integrated into the detection process, making it portable and low-cost. The LODs were determined to be 106 and 115 nM, respectively, for the solution-phase and test paper strips. The probe L₂ was successfully utilized to determine Zn²⁺ levels in pharmaceutical and water samples.