Peripheral Fusion of Carbon‐Based Aromatic Rings to B4N4‐Heteropentalene Leading to Close π‐Stacking in the Solid State

• Published in: Chemistry : a European journal 2024-12, Vol.30 (68), p.e202402862-n/a
• Main Authors: Kashida, Junki, Shoji, Yoshiaki, Taka, Hideo, Ishiwari, Fumitaka, Saeki, Akinori, Fukushima, Takanori
• Format: Article
• Language: English
• Subjects: Amorphous materials; Aromatic compounds; Boron; Carbon; Chemical synthesis; Crystallization; Density functional calculations; Heterocycles; Luminescence; Main group elements; Phosphorescence; Quantum efficiency; Vacuum deposition
• ISSN: 0947-6539; 1521-3765; 1521-3765
• DOI: 10.1002/chem.202402862

π‐Electronic molecules with a BN‐heterocyclic and carbon‐based aromatic hybrid ring system (h‐CBN) are interesting in that they potentially exhibit synergistic properties arising from the two different π‐systems. Here we report the synthesis and properties of a h‐CBN‐type molecule (1) having a bicyclic B4N4‐heteropentalene core fused with extended aromatic rings. This molecule exhibits excellent chemical stability despite the absence of bulky substituents for kinetic protection, which in turn provides effective stacking of the π‐system upon crystallization. Depending on the crystallization solvent, 1 forms two polymorphs, i. e., the α‐ and β‐phases. While both phases have one‐dimensional columnar structures, the π‐stacking geometries associated with the transfer integrals of the frontier orbitals are different, resulting in a twofold difference in the electrical conducting properties. We also found that upon thermal vacuum deposition, 1 gives an amorphous film, which serves as a host material for a red phosphorescent OLED device (maximum external quantum efficiency: 15.5 and 13.3 % at 0.1 and 2.5 mA, respectively). A π‐conjugated molecule containing a hybrid system, in which aromatic rings are fused to the periphery of B4N4‐heteropentalene, crystallizes into two polymorphs, both of which have one‐dimensional π‐stacked columns, while exhibiting different photoconductive properties depending on the stacking geometries. Upon thermal vacuum deposition, this molecule forms an amorphous film that can serve as a host material for red phosphorescent OLEDs.