T. Rajendran

Steric effects in the photoinduced electron transfer reactions of ruthenium(II)-polypyridine complexes with 2,6-disubstituted phenolate ions

The rate constants (kq) for the photoinduced electron transfer reactions of Ru(II)-polypyridyl complexes (Ru(NN)32+) with 2,6-disubstituted phenolate ions in aqueous acetonitrile are highly sensitive to change in the bulkiness of the ligand in Ru(NN)32+ as well as the phenolate ion. The decrease in kq value with the increase in the size of the ligand in Ru(NN)32+ and the phenolate ion is ascribed to the decrease in the electronic coupling matrix element, ∣HDA ∣, between the donor and acceptor with the increase in the electron transfer distance. The hydrophobic interaction or possible π–π stacking between the pyridine rings of Ru(NN)32+ and the aryl moiety of ArO− leads to less steric effect.

Micellar effect on the photoinducedelectron-transfer reactions ofruthenium(II)–polypyridyl complexes with phenolateions. Effect of cetyltrimethylammoniumchloride

Although the emission spectra and excited-state lifetime of Ru(bpy) 3 2+ (bpy=2,2′-bipyridine), Ru(dmbpy) 3 2+ (dmbpy=4,4′- dimethyl-2,2′-bipyridine) and Ru(phen) 3 2+ (phen=1,10-phenanthroline) are little affected by the addition of the cationic surfactant cetyltrimethylammonium chloride (CTAC), an appreciable shift in λ max em , emission intensity and emission lifetime are observed for Ru(dtbpy) 3 2+ (dtbpy=4,4′-di-tert-butyl-2,2′-bipyri dine) and Ru(dpphen) 3 2+ (dpphen=4,7-diphenyl-1,10-phenanthroline). These results point out the importance of hydrophobic interactions over the coulombic repulsion thereby bringing the ruthenium(II) complexes close to the cationic micelles. The rate of luminescence quenching of five *Ru(NN) 3 2+ complexes, with alkyl-substituted phenolate ions in the presence of CTAC, follows different trends depending on the nature of the ligand in Ru(NN) 3 2+ as well as the quencher. The micellar inhibition is explained by considering ArO - being strongly associated with CTAC leaving Ru(NN) 3 2+ in the aqueous phase. The micellar catalysis at high [CTAC] with Ru(dtbpy) 3 2+ and Ru(dpphen) 3 2+ may be due to the operation of predominant hydrophobic interaction over the electrostatic repulsion.

Novel one-pot synthesis of luminescent neutral rhenium-based molecular rectangles

The one-pot synthesis of soluble, neutral, luminescent rectangular supramolecules in high yields by solvothermal methods and fine tuning of the molecular architecture in one dimension from ∼7 A to a nanometer scale, ∼21 A, have been achieved.

Self-assembly of tetrametallic square [Re4(CO)12Br4(μ-pz)4] (pz = pyrazine) from [Re(CO)4Br(pz)]. A mechanistic approach

Self-assembly of the tetranuclear square [Re4(CO)12Br4(μ-pz)4] (pz = pyrazine) from the monometallic complex [Re(CO)4Br(pz)] in acetone at room temperature has been investigated. The mechanistic pathway is examined and proved by both in-situ1H NMR and ES-MS studies. Both techniques are helpful to identify three species, Re2(CO)8Br2(μ-pz), Re(CO)3Br(pz)2 and Re2(CO)7Br2(μ-pz)(pz), as intermediates. The other intermediates, Re3(CO)11Br3(μ-pz)2, Re3(CO)10Br3(μ-pz)2(pz), Re4(CO)14Br4(μ-pz)3 and Re4(CO)13Br4(μ-pz)3(pz), detected by electrospray mass spectral techniques also support the proposed mechanistic pathway.