INTERCALATION INTO CALF THYMUS DNA OF -(4-ARYLPHENYL)IMIDAZO[4,5-F]-[1,10]PHENANTHROLINE (ARYL = -OME, -NME2 OR -NO2) IN ITS BIPYRIDYL RUTHENIUM(II) COMPLEX

New ligands, 2-(4-methoxyphenyl)imidazo [4,5-f][1,10] phenanthroline ( MOP) and 2-(4-dimethylaminophenyl)imidazo[4,5-f] [1,10]phenanthroline (DMNP) and their (bpy)(2)Ru2+ complexes (bpy=2,2'-bipyridine), have be en synthesized. Single crystal X-ray diffraction reveals that MOP is a planar molecule. The binding of the above two complexes, Ru(bpy)(2)NO P2+ and (NOP=2-(4-nitrophenyl) imidazo [4,5-f] [ 1,10] phenanthroline) to calf thymus DNA is investigated using various photophysical method s. Considerable absorption, hypo- and bathochromicity, as well as enan tiomeric selectivity demonstrate that the complexes bind to DNA throug h intercalation of MOP, DMNP or NOP into the base pairs. The absorptio n change, regarding the DMNP or NOP localized transition, provides a u nique 'direct' criterion. Steady-state emission enhancement, reduced a ccessibility to ferrocyanide quencher, and an excited-state Lifetime i ncrease are also observed for Ru(bpy)(2)MOP2+ and Ru(bpy)(2)DMNP2+ onc e bound to DNA. The monoexponential emission-decay profiles infer that the perpendicular intercalation might be the sole binding mode. Owing to a relatively low sensitivity to collision-quenching by neighboring molecules, the emission change of Ru(bpy)(2)DMNP2+ is lower than that of Ru(bpy)(2)MOP2+.No emission is observed for Ru(bpy)(2)NOP2+ due to intramolecular electron transfer caused by -NO2, which is unaffected by DNA. (C) 1998 Elsevier Science S.A. All rights reserved.