Marked Differences in Light-Switch Behavior of Ru(II) Complexes Possessing a Tridentate DNA Intercalating Ligand

Abstract

The tridentate ligand 3-(pyrid-2'-yl)dipyrido[3,2-a:2',3'-c]phenazine (pydppz) has been prepared in two steps by elaboration of 2-(pyrid-2'-yl)-1,10-phenanthroline. Both homoleptic [Ru(pydppz)(2)](2+) and heteroleptic [Ru(tpy)(pydppz)](2+) (tpy = 2,2';6',2' '-terpyridine) complexes have been prepared and characterized by (1)H NMR. The absorption and emission spectra are consistent with low-lying MLCT excited states, which are typical of Ru(II) complexes. Femtosecond transient absorption measurements show that that the (3)MLCT excited state of the heteroleptic complex [Ru(tpy)(pydppz)](2+) (tau approximately 5 ns) is longer-lived than that of the homoleptic complex [Ru(pydppz)(2)](2+) (tau = 2.4 ns) and that these lifetimes are significantly longer than that of the (3)MLCT state of the parent complex [Ru(tpy)(2)](2+) (tau = 120 ps). These differences are explained by the lower-energy (3)MLCT excited state present in [Ru(tpy)(pydppz)](2+) and [Ru(pydppz)(2)](2+) compared to [Ru(tpy)(2)](2+), resulting in less deactivation of the former through the ligand-field state(s). DFT and TDDFT calculations are consistent with this explanation. [Ru(tpy)(pydppz)](2+) and [Ru(pydppz)(2)](2+) bind to DNA through the intercalation of the pydppz ligand; however, only the heteroleptic complex exhibits luminescence enhancement in the presence of DNA. The difference in the photophysical behavior of the complexes is explained by the inability of [Ru(pydppz)(2)](2+) to intercalate both pydppz ligands, such that one pydppz always remains exposed to the solvent. DNA photocleavage is observed for [Ru(tpy)(pydppz)](2+) in air, but not for [Ru(pydppz)(2)](2+). The DNA damage likely proceeds through the production of small amounts of (1)O(2) by the longer-lived complex. Although both complexes possess the intercalating pydppz ligand, they exhibit different photophysical properties in the presence of DNA.

Synthesis, GC selective DNA binding and topoisomerase II inhibition activities of ruthenium(II) polypyridyl complex containing 11-aminopteridino[6,7-f][1,10]phenanthrolin-13(12H)-one

“…Considering the structure of the complex, the most possible binding mode is the hydrogen bonds formed between the guanine residue on the intercalative ligand appo and GC base pairs of DNA. [53,[56][57][58].…”

Synthesis, DNA-binding and photocleavage studies of ruthenium complexes [Ru(bpy)2(mitatp)]2+ and [Ru(bpy)2(nitatp)]2+

“…However, due to its short lifetime of triplet excited state (75, 259 ns in the presence of DNA) and relative low excited redox potential (0.97 V) [10,11], the quantum yields of 1 O 2 of [Ru(bpy) 2 (dppz)] 2+ is very low, resulting its inefficacy in cleaving DNA. Although some Ru(II) dipyridophenazine complexes with photoreactive groups or polyazaaromatic units have been recently reported to exhibit effective DNA photocleavage properties [6,[12][13][14][15], complexes that exhibit considerable DNA-binding affinity and specificity in cleavage are yet to be found.…”

Single oxygen-mediated DNA photocleavage of a di-bithiazolyl ruthenium(II) complex [Ru(btz)2(dppz)]2+

“…However, it is noticed that [Ru(bpy) 2 (dppz)] 2+ (bpy = 2,2 0 -bipyridine, dppz = dipyrido[3,2-a:2 0 ,3 0 -c]phenazine), although binding to DNA with the highest affinity (K b > 10 6 M À1 ) [3], is difficult to cleave DNA directly due to its short lifetime and low oxidizing ability in excited states [4]. Until to now, the improvements for the DNA photocleavage properties of the [Ru II (dppz)] system are primarily focused on the modifications of the intercalating ligand dppz with photoreactive groups or polyazaaromatic unit [5][6][7][8][9][10], the influence of ancillary ligands has attracted much less attention [11].…”