## 1 Introduction  
Great effort has been spent for decades to develop new luminescent organic semiconductors for organic light-emitting diodes (OLEDs) [1; 2; 3; 4; 5; 6; 7; 8; 9; 10]. The OLED field requires organic fluorophores with highly efficient emission that can act as hole-transporting electron donors or as electron-transporting electron acceptors [11; 12; 13; 14; 15; 16; 17; 18; 19; 20]. Useful organic semiconductors for OLEDs also possess a number of other qualities including solution processability, charge carrier mobility, thermal stability, and well-defined molecular energy levels. A disproportionate amount of research has focused on the development of red and green emitting devices while highly efficient blue emitting devices receive less attention. The large molecular energy gap necessary for blue emission often results in materials with low electron affinities that act as poor charge transporters and limit an OLED's efficiency. In addition, research has also concentrated on the development of electron donor materials, which has restricted many of the most widely-used electron acceptor materials to expensive options that are difficult to synthesize or process. These problems can be addressed with highly-polar heterocycle benzimidazoles. Many materials containing benzimidazole are suitable for both emissive and charge transport layers in OLEDs. Among benzimidazole materials, one of the most useful and extensively utilized is 1,3,5-tris(N-phenylbenzimidazole-2-yl)benzene (TPBI) (Figure 1a) [21; 22; 23; 24]. TPBI has a unique aromatic polycyclic core and ring structure features, which result in high thermal stability, chemical stability, and resistance to oxidation. TPBI and similar materials are commonly used as electron transporting, hole blocking layers within OLED devices [23; 24]. In many cases, TPBI is also employed as part of an OLED's emissive layer as an electron transporting host material for fluorescent or phosphorescent dye molecules. The high electron mobility and hole blocking properties of TPBI allow the formation of excitons in the OLED emissive layer directly adjacent to a device's hole transporting layer. This avoidsexciton formation at the interface of the emissive layer and the electron transporting layer which can reduce or quench emission. TPBI's strong performance in OLED devices derives from three distinct 1-phenyl-benzimidazole components. We sought to bolster the optical and electronic properties of TPBI by developing materials that combine three benzimidazole moieties into the highly electron-deficient, rigid aromatic structure of benzo [1,2-\(d\):3,4-\(d\):5,6-\(d\)''] trimidazole. We report here the synthesis and characterization of a family of molecules with a benzotriimidazole core and phenyl rings as pendants at the 1 and 2 position of each imidazole ring. A variety of substituents on the phenyl pendants at the 2 position on each imidazole ring were compared to observe the overall effect on optical and electronic properties caused by slight changes to the electron density of the benzotriimidazole core. Additionally, the phenyl pendants add to the 3D structure of each molecule, increasing bulkiness and limiting molecular packing density to suppress exciton quenching of photoluminescence. These benzotriimidazole-based materials possess strong blue fluorescence and they are the first of their kind to be reported for potential OLED applications. The closest existing, previously-reported material to the benzotriimidazoles described in this work are a group of tris(aroyleneimidazole)s synthesized by [PERSON] et al. [25] for use as electron-transporting materials for organic photovoltaic applications. The tris(aroyleneimidazole)s are large planar molecules that promote self-assembly and they are structurally distinct from the family of benzotriimidazoles reported here, and do not possess their strong fluorescence.