Synthesis of luminescent naphthalene diimide based nano Co/Zn organic frameworks: Cell imaging, sensing studies of explosive compound and pesticide

Abstract

The solvothermal reaction of cobalt nitrate/zinc nitrate with 2,7-di(4H-1,2,4-triazol-4-yl)benzo[lmn]-[3,8]phenanthroline-1,3,6,8(2H,7H)-tetraone (L1) ligand and 1,3,5-tricarboxylic acid (TCA)/5-sulphoisophthalic acid (5-SIA) resulted in the formation of Co(II)/Zn(II) organic frameworks. The synthesised MOFs were structurally characterised by single crystal X-ray diffraction studies including IR and NMR techniques. The approximate particle size of the MOFs was calculated by Debye-Scherrer formula using the powder X-ray diffraction (PXRD) technique, which came out to be 40 nm for Co-MOF and 62 nm for Zn-MOF. The particle size encouraged us to investigate these as imaging probes for human colon cancer cell line (HCT-15). Cytotoxicity assay studies show that the MOFs are non-toxic to the cells and show good cellular internalisation. The emission properties of MOFs were further utilised for the sensing of 2,6-dichloro-4-nitroaniline (DCN) and 2,4,6-trinitophenol (TNP) as sensitive and selective detection of pesticide DCN and explosive TNP. Co/Zn-MOFs show good quenching response to the analytes with low limit of detection (LOD). The quenching efficiency of Zn-MOF is more than that of Co-MOF which may be attributed to the interaction of co-ligands with the analyte. The quenching mechanism was further encountered and it was found out that electron and energy transfer is responsible for the quenching of emission of the MOFs. The LUMO and HOMO energy levels were evaluated by density function theory (DFT) calculations.