Department of Chemistry, National Taiwan University, Taipei 106, Taiwan.
Inorg Chem. 2010 Feb 15;49(4):1372-83. doi: 10.1021/ic9011313.
A series of charge-neutral mononuclear Pt(II) complexes Pt(fpbpy)(pz) (3a), Pt(fpbpy)(dmpz) (4a), Pt(fpbpy)(dbpz) (5a), and Pt(fpbpy)(dtfpz) (6a), fpbpyH = 6-(5-trifluoromethyl-pyrazol-3-yl)-2,2'-bipyridine, pzH = pyrazole, dmpzH = 3,5-dimethylpyrazole, dbpzH = 3,5-di-tert-butylpyrazole, and dtfpzH = 3,5-bis(trifluoromethyl)pyrazole, and the cationic Pt(II) dimer {Pt(fpbpy)}(2)(mu-pz) (3b), {Pt(fpbpy)}(2)(mu-dmpz) (4b), and {Pt(fpbpy)}(2)(mu-dbpz) (5b) were synthesized. Series a mononuclear complexes reveal two distinctive ligand arrangements. As unveiled by X-ray crystallography, 3a exhibits a nearly perfect planar geometry, while structural determination on 6a shows a perpendicular arrangement of dbpz ligand due to steric congestion. In sharp contrast, the dinuclear complexes, exemplified by 4b and 5b, display an intramolecular Pt...Pt separation of 3.601 and 3.403 A, respectively. As for photophysical properties, the structural variation leads to a salient difference in emission features between 3a (580 nm) and 6a (510 nm). The results are rationalized by the contribution of ligand-to-ligand charge transfer and intraligand pi-pi* transition for 3a and 6a in the lowest-lying excited state, respectively. On the other hand, dinuclear complexes 3b and 4b reveal dual phosphorescence (denoted as P(1) and P(2) bands), for which the short wavelength emission (the P(1) band) is akin to that observed for the intraligand pi-pi* transition of 6a, while the much red-shifted, broad emission (the P(2) band) is attributed to the formation of intramolecular ligand-metal-to-metal charge transfer excimer transition. Further studies of relaxation dynamics on both 3b and 4b showed fast excited-state equilibrium between the P(1) and P(2) bands. In contrast, only the P(2) emission band was resolved for 5b, indicating its exergonic excimer formation. Supplementary support of the excited-state thermodynamics is also provided by time-dependent density functional theory calculations, incorporating both geometry optimized S(0) and T(1) states.
一系列中性单核 Pt(II)配合物 Pt(fpbpy)(pz) (3a)、Pt(fpbpy)(dmpz) (4a)、Pt(fpbpy)(dbpz) (5a) 和 Pt(fpbpy)(dtfpz) (6a)、fpbpyH = 6-(5-三氟甲基-吡唑-3-基)-2,2'-联吡啶、pzH = 吡唑、dmpzH = 3,5-二甲基吡唑、dbpzH = 3,5-二-叔丁基吡唑和 dtfpzH = 3,5-双(三氟甲基)吡唑以及阳离子 Pt(II)二聚体 [{Pt(fpbpy)}(2)(mu-pz)]+(3b)、[{Pt(fpbpy)}(2)(mu-dmpz)]+(4b)和[{Pt(fpbpy)}(2)(mu-dbpz)]+(5b)被合成。a 系列单核配合物显示出两种独特的配体排列。正如 X 射线晶体学所揭示的那样，3a 表现出几乎完美的平面几何形状，而 6a 的结构测定表明由于空间位阻，dbpz 配体呈垂直排列。相比之下，二聚体配合物，以 4b 和 5b 为例，显示出 3.601 和 3.403 Å 分别的分子内 Pt...Pt 分离。至于光物理性质，结构变化导致 3a(580nm)和 6a(510nm)之间的发射特征明显不同。结果通过配体-配体电荷转移和 3a 和 6a 中最低激发态的内配体 pi-pi跃迁对各自的贡献来合理化。另一方面，二聚体配合物 3b 和 4b 显示出双重磷光(分别表示为 P(1)和 P(2)带)，其中短波长发射(P(1)带)类似于观察到的 6a 中内配体 pi-pi跃迁，而波长更大的宽带发射(P(2)带)归因于分子内配体-金属-金属电荷转移激基复合物跃迁的形成。对 3b 和 4b 的弛豫动力学的进一步研究表明，P(1)和 P(2)带之间存在快速的激发态平衡。相比之下，仅为 5b 分辨出 P(2)发射带，表明其有利的激基复合物形成。时变密度泛函理论计算也提供了对激发态热力学的补充支持，包括几何优化的 S(0)和 T(1)态。
