Vapochromism and Its Structural Basis in a Luminescent Pt(II) Terpyridine−Nicotinamide Complex

A novel Pt(II) terpyridine complex that has a nicotinamide moiety linked to the terpyridyl ligand
has been synthesized in good yield and studied structurally and spectroscopically. The complex, [Pt(Nttpy)Cl](PF6)2 where Nttpy = 4‘-(p-nicotinamide-N-methylphenyl)-2,2‘:6‘,2‘ ‘-terpyridine, is observed to be brightly
luminescent in the solid state at room temperature and at 77 K. The complex exhibits reversible vapochromic
behavior and crystallographic change in the presence of several volatile organic solvents. Upon exposure
to methanol vapors, the complex changes color from red to orange, and a shift to higher energy is observed
in the emission maximum with an increase in excited-state lifetime and emission intensity. The crystal and
molecular structures of the orange and red forms, determined by single-crystal X-ray diffraction on the
same single crystal, were found to be equivalent in the molecular sense and only modestly different in
terms of packing. In both forms, the cationic Pt(II) complexes possess distorted square planar geometries.
Analysis of the orange form's crystal packing reveals the presence of solvent molecules in lattice voids,
Pt···Pt separations averaging 3.75 Å and a zigzag arrangement between nearest neighbor Pt atoms,
whereas the red form is devoid of solvent within the crystal lattice and contains complexes stacked with a
nearly linear arrangement of Pt(II) ions having an average distance of 3.33 Å. On the basis of the
crystallographic data, it is evident that sorption of methanol vapor induces a change in intermolecular contacts
and Pt···Pt interactions in going from red to orange. Disruption of the d8-d8 metallophilic interactions
consequently alters the emitting state from 3[(d)σ*−π*(terpyridine)] that is formally a metal−metal-to-ligand
charge transfer (MMLCT) state in the red form to one in which the HOMO corresponds to a more localized
Pt(d) orbital in the red form (3MLCT).

一种将烟酰胺基团连接于三联吡啶配体上的新型二价铂（Pt(II)）三联吡啶配合物已被高产率合成，并完成了结构与光谱学表征。该配合物[Pt(Nttpy)Cl](PF6)2（其中Nttpy代表4'-(对烟酰胺-N-甲基苯基)-2,2':6',2''-三联吡啶）在室温及77 K的固态下均表现出强发光性能。该配合物在多种挥发性有机溶剂氛围下可表现出可逆的汽相变色行为与晶体结构变化。当暴露于甲醇蒸汽中时，该配合物的颜色会从红色转变为橙色，其发射峰最大值向高能量方向移动（蓝移），同时激发态寿命与发射强度均有所提升。通过同一单晶的单晶X射线衍射分析，可确定橙色与红色两种晶型的晶体及分子结构：其分子层面的结构完全一致，仅在分子堆积方式上存在小幅差异。两种晶型中的阳离子型二价铂配合物均呈现扭曲的平面四方形配位几何构型。对橙色晶型的晶体堆积分析显示，其晶格空隙中存在溶剂分子，铂-铂（Pt···Pt）平均间距为3.75 Å，相邻铂原子间呈锯齿状排列；而红色晶型的晶格中不含溶剂分子，配合物以近乎直线的方式堆叠，其中二价铂离子的平均间距为3.33 Å。基于晶体学数据可知，甲醇蒸汽的吸附会使配合物从红色晶型转变为橙色晶型的过程中，分子间接触与铂-铂相互作用发生改变。d8-d8亲金属相互作用的破坏，使得发光态从红色晶型中形式上属于金属-金属到配体电荷转移（MMLCT）的3[(d)σ*−π*(三联吡啶)]态，转变为最高占据分子轨道（HOMO）更定域于Pt(d)轨道的3MLCT态。