MD/QC Simulation of the Structure and Spectroscopic Properties of α-NPD-BAlq Exciplexes at an α-NPD/BAlq Interface in OLEDs

The structure and spectroscopic properties of exciplexes formed at an interface between a hole-transporting layer of N,N′-di(naphthalen-2-yl)-N,N′-diphenyl-benzidine (α-NPD) and an electron transporting layer of bis(2-methyl-8-quinolinato)(4-phenylphenolato)-aluminum (BAlq) in an OLED are investigated by multiscale (molecular dynamics, MD, and quantum chemistry, QC) simulations. Four α-NPD–BAlq pairs with different orientations of components are selected from the central 5-nm slab with the interface for subsequent QC calculations. Calculations for these pairs are performed within DFT/PBE0 and DFT/BHandHLYP approaches for the ground state and TDDFT/PBE0 and TDDFT/BHandHLYP approaches for the excited state with inclusion of D3BJ dispersion corrections. The calculated binding energies of the complexes are in the range from –19.0 to –24.7 kcal/mol in the ground state and from –21.9 to –34.1 kcal/mol in the excited state. The calculated S1 excited states are characterized by strong intermolecular charge transfer, and the corresponding S1→S0 transition energies are in good agreement with the available experimental data.