Department of Chemistry, University of Durham, Durham DH1 3LE, UK.
Inorg Chem. 2010 Jan 18;49(2):476-87. doi: 10.1021/ic9016323.
Platinum(II) complexes of the form PtL(n)Cl are reported, containing the N--N--N-coordinating ligands 2,6-di(8-quinolyl)pyridine (L(1)), 2,6-di(8-quinolyl)-4-methoxypyridine (L(2)), or 2,6-di(7-aza-indolyl)-pyridine (L(3)). Metathesis of the chloride co-ligand in PtL(1)Cl can be accomplished under mild conditions, as exemplified by the formation of the complexes PtL(1)OMe and PtL(1)(C[triple bond]C-tfp), in which L(1) remains bound as a terdentate ligand {HC[triple bond]C-tfp = 3,5-bis(trifluoromethyl)-phenylacetylene}. An N--C--N-coordinated, cyclometalated analogue of PtL(1)Cl has also been prepared, namely, PtL(4)Cl where HL(4) is 1,3-di(8-quinolyl)benzene. The common feature among the six new complexes described here is that they contain 6-membered chelate rings, rather than the usual 5-membered rings that form when more common N--N--N ligands, such as 2,2':6',2''-terpyridine (tpy), bind to Pt(II). All the quinolyl-based complexes are phosphorescent in solution at room temperature, with quantum yields up to 4%. This contrasts with the well-established lack of emission from Pt(tpy)Cl under these conditions. Density functional theory calculations suggest that the improvement may stem, at least in part, from the relief of ring strain associated with the larger chelate ring size, leading to a more optimal bite angle at the metal, close to 180 degrees , and hence to a stronger ligand field. Consideration of the luminescence parameters, including data at 77 K, together with absorption and electrochemical data and the results of TD-DFT calculations, suggests that the lowest-lying singlet states have metal-to-ligand charge-transfer (MLCT) character, but that the triplet state from which emission occurs has more predominant ligand-centered character. The azaindolyl complex PtL(3)Cl is not emissive at room temperature, apparently owing to a particularly small radiative rate constant. The cyclometalated complex PtL(4)Cl emits at lower energy than PtL(1)Cl but, in this case, the luminescence quantum yield is inferior to related complexes with 5-membered chelate rings.
报告了一种形式为 PtL(n)Cl 的铂(II)配合物，其中包含 N--N--N 配位的配体 2,6-二(8-喹啉基)吡啶 (L(1))、2,6-二(8-喹啉基)-4-甲氧基吡啶 (L(2)) 或 2,6-二(7-氮杂吲哚基)吡啶 (L(3))。PtL(1)Cl 中氯配体的交换可以在温和条件下完成，例如形成配合物 PtL(1)OMe 和 PtL(1)(C[三键]C-tfp)，其中 L(1) 仍然作为三齿配体{HC[三键]C-tfp = 3,5-双(三氟甲基)苯基乙炔}结合。还制备了 PtL(1)Cl 的 N--C--N 配位的环金属化类似物，即 PtL(4)Cl，其中 HL(4) 是 1,3-二(8-喹啉基)苯。这里描述的六个新配合物的共同特征是它们都含有 6 元螯合环，而不是当更常见的 N--N--N 配体（如 2,2':6',2''-三联吡啶（tpy））与 Pt(II) 结合时形成的通常的 5 元环。所有基于喹啉的配合物在室温下在溶液中都是磷光的，量子产率高达 4%。这与在这些条件下 Pt(tpy)Cl 缺乏发射的既定事实形成对比。密度泛函理论计算表明，这种改进至少部分源于与较大螯合环尺寸相关的环应变的缓解，导致金属处更接近 180 度的最佳咬合角，从而导致更强的配体场。对发光参数的考虑，包括 77 K 下的数据，以及吸收和电化学数据以及 TD-DFT 计算的结果，表明最低的单重态具有金属-配体电荷转移（MLCT）特性，但发射来自三重态具有更主要的配体中心特征。氮杂吲哚配合物 PtL(3)Cl 在室温下不发光，显然是由于辐射速率常数特别小。环金属化配合物 PtL(4)Cl 发射的能量低于 PtL(1)Cl，但在这种情况下，发光量子产率不如具有 5 元螯合环的相关配合物好。
