A combined experimental and theoretical study of the conformation of N,N′-diphenyl-N,N′-di(m-tolyl)benzidine using solid-state 15N NMR and DFT calculations

The conformation of N,N′-diphenyl-N,N′-di(m-tolyl)benzidine (TPD) is studied by solid-state 15N NMR and density functional theory (DFT) calculations. The results of the 15N NMR for amorphous TPD agree with those of the DFT calculations, confirming that the DFT-optimized TPD single molecule reflects the structure in the condensed amorphous state. Various stable conformers are considered to exist in the amorphous state. Torsion angles change the shape of molecules and the state of the electron clouds around the nitrogens, and therefore significantly affect the intermolecular electron coupling. It suggests that the torsion angle is a crucial factor for the carrier transport properties.