Electronic and Photophysical Properties of Platinum(II) Biphenyl Complexes Containing 2,2′-Bipyridine and 1,10-Phenanthroline Ligands

Pt­(bph)­(bpy) and Pt­(bph)­(phen), where bph is the 2,2′-biphenyl dianion, bpy is 2,2′-bipyridine, and phen is 1,10-phenanthroline, crystallize in the space groups I41/a and P21/c, respectively, in two different configurations as X-shaped and bowed (B). The distance between Pt centers is 3.5 Å indicative of π–π stacking. The complexes are optically active, absorb light at 440 nm, and emit in the solid state at room temperature and in the solid glass phase at 77 K. The emission maxima for both in the glass occur near 581 nm but are red-shifted to ∼700 nm in the solid state. Both complexes exhibit solvatochromism in nitrile-based solvents with the Pt­(bph)­(phen) complex showing greater excited state dipole character compared to the Pt­(bph)­(bpy) derivative. Frontier orbitals for the HOMO determined by DFT calculations contain electronic contributions from the biphenyl ligand and the platinum center. The LUMO orbitals primarily reside on the diimine ligands. TDDFT calculations indicate the low-energy transitions occur from the metal/bph combination to the diimine ligand.

Pt(bph)(bpy)与Pt(bph)(phen)两种配合物，其中bph（2,2′-biphenyl dianion）为2,2'-联苯二阴离子，bpy（2,2′-bipyridine）为2,2'-联吡啶，phen（1,10-phenanthroline）为1,10-邻菲啰啉。二者分别以X形与弯曲形（构型B）两种不同构型结晶，对应的空间群依次为I4₁/a与P2₁/c。Pt中心间距为3.5 Å，表明存在π-π堆积相互作用。该类配合物具有光学活性，在440 nm波长处有特征光吸收，且可在室温固态以及77 K的固态玻璃态下产生荧光发射。两种配合物在玻璃态中的发射峰最大值均靠近581 nm，但在固态中红移至约700 nm。二者在腈类溶剂中均表现出溶剂变色效应，其中Pt(bph)(phen)配合物相较于Pt(bph)(bpy)衍生物，展现出更强的激发态偶极特性。经密度泛函理论（DFT, Density Functional Theory）计算得到的最高占据分子轨道（HOMO, Highest Occupied Molecular Orbital），其电子云贡献主要来自联苯配体与铂中心；最低未占据分子轨道（LUMO, Lowest Unoccupied Molecular Orbital）则主要分布于二亚胺配体之上。含时密度泛函理论（TDDFT, Time-Dependent Density Functional Theory）计算结果表明，低能跃迁主要由金属/联苯配体单元向二亚胺配体发生。