Md. Delwar Hossain

Ionic conductivity of Ni(II)-based metallo-supramolecular polymers: effects of ligand modification

Ni(II)-based metallo-supramolecular polymers (polyNiL1-4) were synthesized via complexation of Ni(II) ions with bis(1,10-phenanthroline) ligands bearing a different spacer and/or substituents. The ionic conductivity of the polymer films was greatly enhanced with increasing relative humidity. It was also found that the polymer without a hydrophobic spacer (polyNiL3) showed about 500 times as high ionic conductivity as the polymer with a spacer. The ionic conductivity of the polyNiL3 film reached 0.75 × 10−3 S cm−1 at 98%RH.

Platinum(II)-Based Metallo-Supramolecular Polymer with Controlled Unidirectional Dipoles for Tunable Rectification.

A platinum(II)-based, luminescent, metallo-supramolecular polymer (PolyPtL1) having an inherent dipole moment was synthesized via complexation of Pt(II) ions with an asymmetric ligand L1, containing terpyridyl and pyridyl moieties. The synthesized ligand and polymer were well characterized by various NMR techniques, optical spectroscopy, and cyclic voltammetry studies. The morphological study by atomic force microscopy revealed the individual and assembled polymer chains of 1-4 nm height. The polymer was specifically attached on Au-electrodes to produce two types of film (films 1 and 2) in which the polymer chains were aligned with their dipoles in opposite directions. The Au-surface bounded films were characterized by UV-vis, Raman spectroscopy, cyclic voltammetry, and atomic force microscopy study. The quantum mechanical calculation determined the average dipole moment for each monomer unit in PolyPtL1 to be about 5.8 D. The precise surface derivatization permitted effective tuning of the direction dipole moment, as well as the direction of rectification of the resulting polymer-attached molecular diodes. Film 1 was more conductive in positive bias region with an average rectification ratio (RR = I(+4 V)/I(-4 V)) ≈ 20, whereas film 2 was more conducting in negative bias with an average rectification ratio (RR = I(-4 V)/I(+4 V)) ≈ 18.

Real-time humidity-sensing properties of ionically conductive Ni(II)-based metallo-supramolecular polymers

Metallo-supramolecular polymers composed of Ni(II) ions and bis(2,9-dimethyl-1,10-phenanthroline) showed ionic conductivity, which enhanced by about four orders of magnitude with increasing relative humidity from 30 to 98% RH, in the film state. Four Ni(II)-based polymers with different counter anions were synthesized to investigate the ionic conduction mechanism. The highest ionic conductivity (5 × 10−2 S cm−1) at 98% RH was observed in the polymer with chloride ions as the counter anion. The Grotthuss-type proton transfer mechanism was indicated by the low activation energy (0.21 eV) for the ionic conduction. The polymer film prepared on an interdigitated electrode showed dynamic humidity-sensing properties based on the quick and large current-response to humidity change.

Effect of a three-dimensional hyperbranched structure on the ionic conduction of metallo-supramolecular polymers

Fe(II)-, Co(II)- and Ni(II)-based metallo-supramolecular polymers with three-dimensional (3D) hyperbranched structures (3D-polyFe, 3D-polyCo and 3D-polyNi) showed highly humidity-responsive ionic conductivity. The 3D polymers exhibited 10–100 times higher ionic conductivity than their 1D linear equivalents due to the improved ion conduction pathway in the amorphous 3D structure.

Nano molar detection of Cd(II) ions by luminescent metallo-supramolecular polymer formation

A Cd(II)-based metallo-supramolecular polymer (polyCd) was formed via the 1 : 1 complexation of Cd(II) ions with bis(1,10-phenanthroline) bearing a fluorine moiety as a luminescent spacer. The stepwise complexation was observed in UV-vis spectral titration. Selective sensing of Cd(II) ions based on the luminescent polymer formation was successfully achieved with sensitivity down to 8 nM concentration.

Effect of metal–metal distance in Ni(II)-based metallo-supramolecular polymers: DNA binding and cytotoxicity

Two Ni(II)-based metallo-supramolecular polymers (polyNiL1 and polyNiL2) with different metal–metal distances were synthesized via (1 : 1) complexation between the Ni salts with bis(1,10-phenanthroline)s and their DNA binding properties and cytotoxicity were revealed. Short metal–metal distances (1.35 nm) in polyNiL2 showed ∼7 times stronger DNA binding properties and remarkably higher cytotoxicity to Hela-Fucci cells than long metal–metal distances (1.95 nm) in polyNiL1. Enhancement of Ni polymer-induced cell killing has been observed in a cell cycle study.