A series of 3,2-polymethylene-2-phenylbenzo[b]-1,10-phenanthrolines was reacted with Ru(tpy)Cl3 to afford two ruthenium (Ru) complexes, a pentaaza-coordinated (N5Cl) complex [Ru(tpy)(L)Cl]+ and a hexa-coordinated (N5C) complex [Ru(tpy)(L)]+. The ratio of these two complexes was found to be highly dependent on the length of the polymethylene bridge between terminal phenyl and central pyridine rings. The reaction between the dimethylene-bridged ligand and Ru(tpy)Cl3 afforded a hexa-coordinated (N5C) complex as an only isolatable product in 83% yield, while the others afforded pentaaza-coordinated products and hexa-coordinated products in ratios of 1:1.6-3.5 with 80-90% overall yields. The UV spectra of pentaaza-coordinated complexes (N5Cl) and hexa-coordinated (N5C) cycloruthenated complexes were similar to show absorbances at 253-255, 276-286, 312-324, 360-373, and 490-532 nm. All of these complexes showed greenish blue light emissions in the range 450-460 nm upon excitation in the range 368-382 nm, while excitation at 500-532 nm resulted in green light emissions at 570 nm for pentaaza-coordinated complexes and 577-579 nm for hexaaza-coordinated species. Irradiation of the plasmid (100 μM) in the presence of 8c (λirr > 395 nm, 10 min) in air resulted in single-strand cleavage leading to the production of nicked plasmid (Form II), probably via intercalation.
Keywords: 2,2′;6′,2″-terpyridine; 3,2′-polymethylene-2-phenylbenzo-[b]-1,10-phenanthroline; Chiral ruthenium complex; DNA cleavage; Green light emission; N,N,C-polydentate; Pentaaza-coordinated complex.