Mechanistic Multiscale Simulations and Charge Transport Properties of Amorphous and Crystalline α‐NPD Molecular Conformations: Insights From Molecule to Material Level

ABSTRACT The optoelectronic and charge transfer integral properties of N,N′‐di(1‐naphthyl)‐N,N′‐diphenyl‐4,4′‐diamine (α‐NPD) organic light‐emitting diode (OLED) in amorphous and crystalline structures is studied based on the Marcus–Levitch–Jortner theory and quantum chemistry calculations. The charge transfer integral simulations have been investigated through hole‐hopping regime from molecule‐to‐molecule in dimers molecules and are determined by HOMO→LUMO$$ \mathrm{HOMO}\to \mathrm{LUMO} $$ frontier molecular orbitals (FMOs) for hole and electron transport. Quantum approaches with TD/DFT and DFT have been used to describe the most relevant electronic transitions of α‐NPD, which present π→π*$$ \pi \to {\pi}^{\ast } $$ character in harmony with the solvent states. Furthermore, the obtained results reveal that geometric deformations have been relied to naphthalene form and benzene rings in α‐NPD structures, and the charge transfer integral in amorphous state shows thole=4.46meV$$ {t}_{\mathrm{hole}}=4.46\ \mathrm{meV} $$ and telec=3.18meV$$ {t}_{\mathrm{elec}}=3.18\ \mathrm{meV} $$, and in the crystalline state, it shows thole=4.25meV$$ {t}_{\mathrm{hole}}=4.25\ \mathrm{meV} $$ and telec=3.95meV$$ {t}_{\mathrm{elec}}=3.95\ \mathrm{meV} $$. Comparing the transfer integrals average of hole/electron in the both amorphous and crystalline states, a higher value of hole transfer is explored in the amorphous form. The charge transfer transition obtained from FMO states and density of states (DOS), as well as reorganization energies values, indicates that α‐NPD would be an effective organic electronic hole transport material. The optoelectronic and charge transfer integral of α‐NPD in both amorphous and crystalline structures were investigated using the Marcus–Levich–Jortner theory. Charge transfer integrals were examined in the hopping regime through HOMO→LUMO$$ \mathrm{HOMO}\to \mathrm{LUMO} $$transitions. Time‐dependent density functional theory (TD/DFT) and density functional theory (DFT) were used to describe the electronic transitions, particularly focusing on the π→π*$$ \pi \to {\pi}^{\ast } $$ character. The charge transfer integral for holes was found to be thole=4.46 meV, and for electrons, telec=3.18 meV. In the crystalline state, the values for holes and electrons are thole=4.25 meV and telec=3.95 meV, respectively. These charge transfer integral transition values indicate that α‐NPD is an effective hole transporter.