Liu Yao, Hammitt Richard, Lutterman Daniel A, Thummel Randolph P, Turro Claudia
Department of Chemistry, The Ohio State University, Columbus, Ohio 43210, USA.
Inorg Chem. 2007 Jul 23;46(15):6011-21. doi: 10.1021/ic700484j. Epub 2007 Jun 14.
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) and heteroleptic Ru(tpy)(pydppz) (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) (tau approximately 5 ns) is longer-lived than that of the homoleptic complex Ru(pydppz)(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) (tau = 120 ps). These differences are explained by the lower-energy (3)MLCT excited state present in Ru(tpy)(pydppz) and Ru(pydppz)(2) compared to Ru(tpy)(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) and Ru(pydppz)(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) to intercalate both pydppz ligands, such that one pydppz always remains exposed to the solvent. DNA photocleavage is observed for Ru(tpy)(pydppz) in air, but not for Ru(pydppz)(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.
通过对2-(吡啶-2'-基)-1,10-菲咯啉进行两步合成制备了三齿配体3-(吡啶-2'-基)二吡啶并[3,2-a:2',3'-c]吩嗪(pydppz)。制备了同配体[Ru(pydppz)₂]²⁺和异配体[Ru(tpy)(pydppz)]²⁺(tpy = 2,2';6',2''-三联吡啶)配合物，并通过¹H NMR进行了表征。吸收光谱和发射光谱与低能级的金属-配体电荷转移(MLCT)激发态一致，这是Ru(II)配合物的典型特征。飞秒瞬态吸收测量表明，异配体配合物[Ru(tpy)(pydppz)]²⁺的³MLCT激发态寿命(tau约为5 ns)比同配体配合物[Ru(pydppz)₂]²⁺的³MLCT激发态寿命(tau = 2.4 ns)长，且这些寿命明显长于母体配合物[Ru(tpy)₂]²⁺的³MLCT激发态寿命(tau = 120 ps)。这些差异可以解释为，与[Ru(tpy)₂]²⁺相比，[Ru(tpy)(pydppz)]²⁺和[Ru(pydppz)₂]²⁺中存在能量较低的³MLCT激发态，导致前者通过配体场态的失活较少。密度泛函理论(DFT)和含时密度泛函理论(TDDFT)计算结果与该解释一致。[Ru(tpy)(pydppz)]²⁺和[Ru(pydppz)₂]²⁺通过pydppz配体的插入与DNA结合；然而，只有异配体配合物在DNA存在时表现出发光增强。配合物光物理行为上的差异可以解释为[Ru(pydppz)₂]²⁺无法插入两个pydppz配体，使得总有一个pydppz暴露在溶剂中。在空气中观察到[Ru(tpy)(pydppz)]²⁺能进行DNA光裂解，而[Ru(pydppz)₂]²⁺则不能。DNA损伤可能是由寿命较长的配合物产生少量单线态氧(¹O₂)所致。尽管两种配合物都含有插入性的pydppz配体，但它们在DNA存在时表现出不同的光物理性质。
