Dinesh Maity

Synthesis, structural characterization, solvatochromism, and ion-binding studies of a ditopic receptor based on 2-(4-[2,2′: 6′,2′′]terpyridin-4′-yl-phenyl)-1H-phenanthro[9,10-d] imidazole (tpy-HImzphen) unit

A terpyridyl-imidazole based ditopic receptor 2-(4-[2,2′:6′,2′′]terpyridin-4′-yl-phenyl)-1H-phenanthro[9,10-d]imidazole (tpy-HImzphen) has been synthesized and characterized using standard analytical and spectroscopic techniques and also by single crystal X-ray crystallography. The receptor shows multi-channel sensing ability towards F− and Fe2+ ions. Both the anion and cation binding properties of the receptor were thoroughly investigated in dimethylformamide–acetonitrile (1 : 9) solution using absorption, emission, and 1H NMR spectral studies. In the presence of excess of F− ions, deprotonation of the imidazole N–H fragment occurs, an event which is signalled by the development of bright yellow color visible with the naked eye. Anion-induced lifetime enhancing makes the receptor a suitable lifetime-based sensor for F− ions. The absorption and emission titration of the receptor with Fe2+ ion indicates that single conversion of free tpy-HImzphen (colorless) to Fe2+ complex (deep violet color) of 2 tpy-HImzphen : 1 Fe2+ stoichiometry. The influence of different solvents on the absorption and emission spectral behavior and on the lifetime of the receptor and its Zn(II) complex have also been investigated in detail.

A two-pocket Schiff-base molecule as a chemosensor for Al3+

4,4′-Sulfonylbis(2-(-2-hydroxybenzylideneamino)phenol) (H4L) was synthesized by the reaction between bis-(3-amino-4-hydroxy phenyl)sulphone and salicylaldehyde (1 : 2 ratio) and has been characterized by standard methods. H4L shows a weak emission peak at 485 nm in 10 mM HEPES buffer in water : DMSO (1 : 9, v/v) (pH = 6.7) at room temperature. There is a significant enhancement in the emission intensity at 485 nm only in the presence of Al3+. Other relevant metal ions could not considerably alter its emission spectrum, indicating that H4L is a selective fluorescent probe for Al3+. H4L forms a complex with Al3+ in a 1 : 2 ratio, as is evident from Jobs analysis and mass spectral data. There is a significant increase in the quantum yield and lifetime of the probe upon complex formation with aluminum. The limit of detection has been determined and shows moderate sensitivity towards the metal ion. A pH dependent study indicated that the emission intensity of H4L increases sharply when the pH of the medium is more than 7. The emission intensity of H4L in the presence of one equivalent of Al3+ starts increasing when the pH is ∼5.0. Thus, all the spectral studies were performed at pH 6.7. Some theoretical calculations were performed to investigate the spectral transitions. H4L was used for the identification of Al3+ using sea water.

Demonstration of intramolecular energy transfer in asymmetric bimetallic ruthenium(II) complexes

A new family of bimetallic Ru(ii) complexes derived from an asymmetric bridging ligand (tpy-Hbzim-dipy) consisting of both bipyridine and terpyridine chelating sites covalently connected via phenyl-imidazole spacer were designed in this work to demonstrate intramolecular energy transfer from one component to the other in asymmetric dyads. To fine tune the photo-redox properties, both bidentate and tridentate terminal ligands in the complexes were varied systematically. Both steady state and time-resolved luminescence spectral results indicated photo-induced intramolecular energy transfer from the excited MLCT state of the [(bpy/phen)2RuII(dipy-Hbzim-tpy)] component to the MLCT state of the tpy-containing unit [(dipy-Hbzim-tpy)RuII(tpy-PhCH3/H2pbbzim)] in dyads with rate constant values on the order of 106-107 s-1. Temperature-dependent luminescence studies indicated an enhancement in the luminescence intensity and excited state lifetimes upon decreasing the temperature.