Unsymmetrically bi-functionalized 1,1′-ferrocenyl bi-hydrazone and hydrazone-cyanovinyl molecules as fluorescent “on–off” sensor: Synthesis, cytotoxicity and cancer cell imaging behavior

Abstract

Unsymmetrically bi-functionalized ferrocenyl compounds are significant class of multifunctional molecule having unique structural features, varied conformational orientations, tunable electrochemical behavior and wide functional prospects. Strategic design of these unsymmetrical derivatives involving multifunctional components containing sandwich based electroactive fragment, heterocyclic moieties and a highly emissive photo-responsive unit can create flexible, biocompatible fluorescent single molecule - probe for sensor and signaling based molecular devices. Therefore, synthesis of fluorophoric 1,1′-unsymmetrical bi-functionalized ferrocenyl molecular receptor have been carried out using two different types of solid supported condensation reactions, one using Schiff base condensation reaction to link hydrazone based heterocyclic moieties and the other involving a Knoevenagel condensation to link cyano-vinyl based donor–acceptor system, to obtain 1,1′-ferrocenyl rhodaminyl-pyridyl hydrazones and 1,1′-ferrocenyl hydrazone-cyanovinylester derivatives. The unsymmetrical nature of the molecules has been established by single crystal diffraction study and explored for their fluorescence and electrochemical based signaling and sensing behavior of metal cations in solution and subcellular level. The study showed significant intracellular metal recognition and imaging characteristics for their potential in applications related to bioimaging of heavy metal ions. DFT study revealed distinct interaction of the metal ion leading to a change in structural conformation due to the rotational flexibility within the ferrocenyl axis. Molecules were also explored for their cytotoxic behavior and protein binding interaction to understand their biological potential.