Sun Yi, Wang Suning
Department of Chemistry, Queen's University, Kingston, Ontario K7L 3N6, Canada.
Inorg Chem. 2009 Apr 20;48(8):3755-67. doi: 10.1021/ic9000335.
To investigate the impact of metal-chelation on intraligand charge transfer emission involving a triarylboron group, three 2,2'-bipyridine derivative molecules, 5,5'-bis(BMes(2))-2,2'-bipy (B2bpy), 5-(BMes(2))-5'-(NPh(2))-2,2'-bipy (BNbpy), and 5,5'-bis(NPh(2))-2,2'-bipy (N2bpy) have been synthesized, which can be described as donor-only, donor-acceptor, and acceptor-only systems. Each of these molecules displays distinctive electrochemical and photophysical properties with BNbpy and N2bpy being bright emitters and B2bpy being a strong electron acceptor. In addition, BNbpy displays a "turn-on" fluorescent response while B2bpy has a "turn-off" response upon binding with fluoride ions. These molecules can readily chelate to a PtPh(2) or a PtCl(2) group, producing square planar complexes Pt(B2bpy)Ph(2) (Pt-1), Pt(B2bpy)Cl(2) (Pt-1a), Pt(BNbpy)Ph(2) (Pt-2), Pt(BNbpy)Cl(2) (Pt-2a), and Pt(N2bpy)Ph(2) (Pt-3) that have significantly altered electrochemical and photophysical properties from those of the free ligands. Metal chelation has been found to greatly enhance the electron accepting ability of the three ligands, especially B2bpy and BNbpy. The Ph and Cl auxiliary ligands have also been found to have a significant impact on the electrochemical and photophysical properties of the complexes. B2bpy complexes Pt-1 and Pt-1a are not luminescent at ambient temperature while BNbpy complexes Pt-2 and Pt-2a display room temperature phosphorescence in solution under air that has a similar "turn-on" response toward fluoride ions as the free BNbpy does but with a much more dramatic color switch (orange or red to blue-green). The persistent intraligand N-->B charge transfer transition in the BNbpy complexes is believed to play a key role in their unique phosphorescent response toward fluorides. The complex Pt-3 displays a bright blue-green phosphorescence in solution at ambient temperature. Density functional theory computations established that the lowest electronic transition in the Pt(II) complex is from the Pt(II) d orbital and the auxiliary ligand to the pi* orbital of the 2,2'-bipy derivative ligand.
为了研究金属螯合对涉及三芳基硼基团的配体内电荷转移发射的影响，合成了三种2,2'-联吡啶衍生物分子，5,5'-双（二甲基苯基硼）-2,2'-联吡啶（B2bpy）、5-（二甲基苯基硼）-5'-（二苯基膦氮）-2,2'-联吡啶（BNbpy）和5,5'-双（二苯基膦氮）-2,2'-联吡啶（N2bpy），它们可分别描述为仅含供体、供体-受体和仅含受体的体系。这些分子各自展现出独特的电化学和光物理性质，其中BNbpy和N2bpy是明亮的发光体，而B2bpy是强电子受体。此外，BNbpy与氟离子结合时显示“开启”荧光响应，而B2bpy则有“关闭”响应。这些分子能够轻松地与二苯基铂（PtPh₂）或二氯铂（PtCl₂）基团螯合，生成平面正方形配合物Pt（B2bpy）Ph₂（Pt-1）、Pt（B2bpy）Cl₂（Pt-1a）、Pt（BNbpy）Ph₂（Pt-2）、Pt（BNbpy）Cl₂（Pt-2a）和Pt（N2bpy）Ph₂（Pt-3），它们的电化学和光物理性质与游离配体相比有显著改变。已发现金属螯合极大地增强了这三种配体的电子接受能力，尤其是B2bpy和BNbpy。还发现苯基和氯辅助配体对配合物的电化学和光物理性质有显著影响。B2bpy配合物Pt-1和Pt-1a在室温下不发光，而BNbpy配合物Pt-2和Pt-2a在空气中的溶液中显示室温磷光，对氟离子具有与游离BNbpy类似的“开启”响应，但颜色变化更为显著（从橙色或红色变为蓝绿色）。据信BNbpy配合物中持续的配体内氮→硼电荷转移跃迁在其对氟化物的独特磷光响应中起关键作用。配合物Pt-3在室温下的溶液中显示亮蓝绿色磷光。密度泛函理论计算表明，Pt（II）配合物中的最低电子跃迁是从Pt（II）d轨道和辅助配体到2,2'-联吡啶衍生物配体的π*轨道。
