Boron- and Oxygen-Doped π-Extended Nanographene: An Emitting Material for Organic Light-Emitting Diodes

Expanding the molecular framework of hexabenzo[a,c,fg,j,l,op]tetracene (HBT) via heteroatom incorporation and topological edge control is crucial for achieving desired photophysical properties. However, synthesizing heteroatom-doped HBT derivatives remains highly challenging, and effective molecular design strategies have not yet been established. Herein, the synthesis of boron (B)- and oxygen (O)-doped expanded HBT (BO-HBT) is carried using a sequential Scholl cyclization strategy. This work is the first example of a B/O-expanded HBT molecule, demonstrating that heteroatom incorporation and peripheral alkyl group modifications enable accurate tuning of its electronic structure and photonic properties. Consequently, BO-HBT exhibits a reduced bandgap (2.55 eV), robust electrochemical stability, a horizontal emitting dipole orientation ratio of 88%, and a high photoluminescence quantum yield of 62.8% in toluene. Density functional theory calculations further elucidate its fluorescence mechanism, revealing that all the frontier orbitals of BO-HBT are predominantly localized in the central pyrene and boron-containing parts and the peripheral biphenyl moieties play a minor role. Hence, the redox and photoluminescence properties of BO-HBT closely resemble those of BO-BPP, a structurally related B/O-fused pyrene system. Notably, BO-HBT demonstrated promising performance as an emitting dopant material in organic light-emitting diodes (OLEDs), achieving an external quantum efficiency of up to 6.2% in the pure green visible region and exceeding 10% in hyperfluorescent devices. These results represent the first successful demonstration of an HBT derivative as an emissive dopant in OLEDs and underscore BO-HBT's potential for advanced optoelectronic applications.