Blue Luminescent 2-(2‘-Pyridyl)benzimidazole Derivative Ligands and Their Orange Luminescent Mononuclear and Polynuclear Organoplatinum(II) Complexes

Five new 2-(2‘-pyridyl)benzimidazole derivative ligands, 1,4-bis[2-(2‘-pyridyl)benzimidazolyl]benzene (1,4-bmb), 4,4‘-bis[2-(2‘-pyridyl)benzimidazolyl]biphenyl (bmbp), 1-bromo-4-[2-(2‘-pyridyl)benzimidazolyl]benzene (Brmb), 1,3-bis[2-(2‘-pyridyl)benzimidazolyl]benzene (1,3-bmb), and 1,3,5-tris[2-(2‘-pyridyl)benzimidazolyl]benzene (tmb), have been
synthesized by Ullmann condensation methods. The corresponding mononuclear and polynuclear PtII complexes,
Pt2(1,4-bmb)Ph4 (1), Pt2(bmbp)Ph4 (2), Pt(Brmb)Ph2 (3), Pt2(1,3-bmb)Ph4 (4), and Pt3(tmb)Ph6 (5), have been obtained
by the reaction of the appropriate ligand with [PtPh2(SMe2)]n. The structures of the free ligands 1,4-bmb, bmbp,
and tmb, as well as the complexes 1−3, were determined by single-crystal X-ray diffraction. All ligands display
fluorescent emissions in the purple/blue region of the spectrum at ambient temperature and phosphorescent emissions
in the blue/green region at 77 K, which are attributable to ligand-centered π → π* transition. No ligand-based
emission was observed for the PtII complexes 1−5. All PtII complexes display orange/red emissions at 77 K in a
frozen solution or in the solid state, attributable to metal-to-ligand charge transfers (MLCT). Variable-temperature
1H NMR experiments establish that complexes 1, 4, and 5 exist in isomeric forms in solution at ambient temperature
due to the hindered rotation of the square PtC2N2 planes in the complexes.

本研究通过乌尔曼缩合（Ullmann condensation）法合成了5种新型2-(2'-吡啶基)苯并咪唑类配体：1,4-二[2-(2'-吡啶基)苯并咪唑基]苯（1,4-bmb）、4,4'-二[2-(2'-吡啶基)苯并咪唑基]联苯（bmbp）、1-溴-4-[2-(2'-吡啶基)苯并咪唑基]苯（Brmb）、1,3-二[2-(2'-吡啶基)苯并咪唑基]苯（1,3-bmb）以及1,3,5-三[2-(2'-吡啶基)苯并咪唑基]苯（tmb）。通过上述配体与[PtPh2(SMe2)]n的反应，得到了对应的单核及多核二价铂（Pt(II)）配合物：Pt2(1,4-bmb)Ph4（1）、Pt2(bmbp)Ph4（2）、Pt(Brmb)Ph2（3）、Pt2(1,3-bmb)Ph4（4）以及Pt3(tmb)Ph6（5）。采用单晶X射线衍射（single-crystal X-ray diffraction）法解析了游离配体1,4-bmb、bmbp、tmb以及配合物1~3的晶体结构。所有配体在室温下均展现出紫/蓝色波段的荧光发射，在77 K时则展现出蓝/绿色波段的磷光发射，该发光源于配体中心π→π*跃迁（ligand-centered π → π* transition）。二价铂配合物1~5均未观测到基于配体的发光。所有二价铂配合物在77 K的冷冻溶液或固态下均展现出橙/红色发射，该发光源于金属-配体电荷转移（metal-to-ligand charge transfer, MLCT）。变温核磁共振氢谱（variable-temperature 1H NMR）实验表明，由于配合物中方形PtC2N2平面的旋转受阻，配合物1、4和5在室温溶液中以异构体形式存在。