Synthesis and TD-DFT investigation on optoelectronic properties of bis-boron/nitrogen-doped azaullazines as organic light-emitting diodes (OLEDs)

Abstract

This study explores the synthesis and the optoelectronic, electrochemical, and charge transport properties of dual Boron/Nitrogen-doped azaullazine (ZAU) derivatives using time dependent-density functional theory (TD-DFT). These derivatives are being developed for next-generation organic electronics. Quantum chemical simulations indicate that this change lowers LUMO level, reducing the electronic bandgap from 4.42 eV in ZAU1 to 4.05 eV in ZAU3. While HOMO remains in the central rigid core for both molecules, ZAU3’s LUMO shifts to the ester arms, significantly altering the spatial structure. This reduces the electron exchange integral, establishing conditions for a small singlet-triplet energy gap in thermally activated delayed fluorescence (TADF) host architectures. However, this change decreases the vertical transition probability (f = 0.0653; LHE = 14.0%) compared to ZAU1 (f = 0.1095; LHE = 22.3%). Analysis using Marcus electron-transfer theory shows that ZAU3 achieves better charge-transport kinetics in the solid-state, with low hole and electron reorganization energies by limiting structural relaxation. Moreover, ester functionalization alters the adiabatic ionization potential (IP_a = 5.86 eV) and electron affinity (EA_a = 1.79 eV), reducing interfacial injection barriers. Molecular electrostatic potential (MEP) surfaces reveal a substantial increase in ZAU3’s permanent dipole moment (3.87 D vs. 1.62 D for ZAU1). Additionally, 2D Reduced Density Gradient (RDG) and Non-Covalent Interaction (NCI) plots verify that the extended molecular structures are stabilized by widespread weak van der Waals interactions. This intricate balance between spatial orbital separation and internal reorganization is crucial, positioning ZAU1 as ideal for emissive layers or light harvesting. At the same time, ZAU3 is suitable as a high-mobility charge-transport matrix or ambipolar interlayer and a potential TADF host. This research provides valuable insights into the design principles of heteroatom-doped luminescent materials and makes a significant contribution to the development of OLED materials.