Juliá Fabio, García-Legaz María-Dulce, Bautista Delia, González-Herrero Pablo
Departamento de Química Inorgánica, Facultad de Química and ‡SAI, Universidad de Murcia , Apdo. 4021, 30071 Murcia, Spain.
Inorg Chem. 2016 Aug 1;55(15):7647-60. doi: 10.1021/acs.inorgchem.6b01100. Epub 2016 Jul 20.
The synthesis, characterization, and photophysical properties of a wide variety of bis-cyclometalated Pt(IV) complexes featuring a C2-symmetrical or unsymmetrical {Pt(ppy)2} unit (sym or unsym complexes, respectively; ppy = C-deprotonated 2-phenylpyridine) and different ancillary ligands are reported. Complexes sym-[Pt(ppy)2X2] (X = OTf(-), OAc(-)) were obtained by chloride abstraction from sym-[Pt(ppy)2Cl2] using the corresponding AgX salts, and the triflate derivative was employed to obtain homologous complexes with X = F(-), Br(-), I(-), trifluoroacetate (TFA(-)). Complexes unsym-[Pt(ppy)2(Me)X] (X = OTf(-), F(-)) were prepared by reacting unsym-[Pt(ppy)2(Me)Cl] with AgOTf or AgF, respectively, and the triflate derivative was employed as precursor for the synthesis of the homologues with X = Br(-), I(-), or TFA(-) through its reaction with the appropriate anionic ligands. The previously reported complexes unsym-[Pt(ppy)2X2] (X = Cl(-), Br(-), OAc(-), TFA(-)) are included in the photophysical study to assess the influence of the arrangement of the cyclometalated ligands. Density functional theory (DFT) and time-dependent DFT calculations on selected derivatives were performed for a better interpretation of the observed excited-state properties. Complexes sym-[Pt(ppy)2X2] (except X = I(-)) exhibit phosphorescent emissions in fluid solutions at 298 K arising from essentially (3)LC(ppy) excited states, which are very similar in shape and energy. However, their efficiencies are heavily dependent on the nature of the ancillary ligands, which affect the energy of deactivating ligand-to-ligand charge transfer (LLCT) or ligand-to-metal charge transfer (LMCT) states. The fluoride derivative sym-[Pt(ppy)2F2] shows the highest quantum yield of this series (Φ = 0.398), mainly because the relatively high metal-to-ligand charge transfer admixture in its emitting state leads to a high radiative rate constant. Complexes unsym-[Pt(ppy)2X2] emit from (3)LC(ppy) states in frozen matrices at 77 K, but their emissions are totally quenched in fluid solution at 298 K because of the presence of low-lying, dissociative LMCT excited states, which also cause photoisomerization reactions. Complexes unsym-[Pt(ppy)2(Me)X] (X = F(-), Cl(-), Br(-), TFA(-)) show strong emissions in fluid solutions at 298 K (Φ = 0.52-0.63) because deactivating LMCT states lie at high energies. However, derivative unsym-[Pt(ppy)2(Me)I] is only weakly emissive at 298 K because of the presence of low-lying LLCT [p(I) → π*(ppy)] states.
报道了多种具有C2对称或不对称{Pt(ppy)2}单元（分别为对称或不对称配合物；ppy = C-去质子化的2-苯基吡啶）以及不同辅助配体的双环金属化Pt(IV)配合物的合成、表征和光物理性质。通过使用相应的AgX盐从sym-[Pt(ppy)2Cl2]中提取氯离子获得配合物sym-[Pt(ppy)2X2]（X = OTf(-)，OAc(-)），并使用三氟甲磺酸盐衍生物获得X = F(-)、Br(-)、I(-)、三氟乙酸盐（TFA(-)）的同系配合物。配合物unsym-[Pt(ppy)2(Me)X]（X = OTf(-)，F(-)）分别通过使unsym-[Pt(ppy)2(Me)Cl]与AgOTf或AgF反应制备，并且三氟甲磺酸盐衍生物用作通过其与适当的阴离子配体反应合成X = Br(-)、I(-)或TFA(-)的同系物的前体。先前报道的配合物unsym-[Pt(ppy)2X2]（X = Cl(-)、Br(-)、OAc(-)、TFA(-)）包含在光物理研究中，以评估环金属化配体排列的影响。对选定的衍生物进行了密度泛函理论（DFT）和含时DFT计算，以便更好地解释观察到的激发态性质。配合物sym-[Pt(ppy)2X2]（X = I(-)除外）在298 K的流体溶液中表现出磷光发射，其源于基本上是(3)LC(ppy)激发态，其形状和能量非常相似。然而，它们的效率在很大程度上取决于辅助配体的性质，辅助配体影响失活的配体-配体电荷转移（LLCT）或配体-金属电荷转移（LMCT）态的能量。氟化物衍生物sym-[Pt(ppy)2F2]显示出该系列中最高的量子产率（Φ = 0.398），主要是因为其发射态中相对较高的金属-配体电荷转移混合导致了高辐射速率常数。配合物unsym-[Pt(ppy)2X2]在77 K的冷冻基质中从(3)LC(ppy)态发射，但由于存在低位解离的LMCT激发态，它们在298 K的流体溶液中的发射完全猝灭，这些激发态也会引起光异构化反应。配合物unsym-[Pt(ppy)2(Me)X]（X = F(-)、Cl(-)、Br(-)、TFA(-)）在298 K的流体溶液中表现出强发射（Φ = 0.52 - 0.63），因为失活的LMCT态处于高能级。然而，衍生物unsym-[Pt(ppy)2(Me)I]在298 K时仅微弱发光，因为存在低位的LLCT [p(I) → π*(ppy)]态。
