Linear and star-shaped benzimidazolyl derivatives: syntheses, photophysical properties and use as highly efficient electron transport materials in OLEDs

Five benzimidazolyl functionalized linear and star-shaped molecules have been synthesized using Ullmann condensation methods. These molecules all possess deep LUMO energy levels and large HOMO–LUMO energy gaps ranging from 3.55 to 3.95 eV. All five compounds are fluorescent with emission in the UV region, and display high thermal and morphological stability. One of these star-shaped molecules, 2,4,5-tris(benzimidazolyl)-1,3,5-triazine, has been demonstrated to be a highly effective electron transport/hole blocking material in organic light emitting devices (OLEDs) with performance comparable to the commonly used electron transport material Alq₃ (q = 8-hydroxyquinolinate). In addition, metal ion titrations have established that these ligands show a distinct fluorescent response to the addition of Ag(I) or Zn(II) in solution.