Molecular dynamics study of N,N'-di-n-alkyl-3,4,9,10-perylenetetracarboxylic diimide (PTCDI)/rubrene interface: Why the charge transfer at the interface is optimized depending on the alkyl chain length of PTCDI.

Molecular dynamics simulations were performed to investigate the interfacial structure of the N,N'-di-n-alkyl-3,4,9,10-perylenetetracarboxylic diimide (PTCDI)/rubrene interface, which represents the donor/acceptor interface in new types of organic light-emission diodes. In particular, the interfacial structure was examined for different alkyl chain lengths of PTCDI (Cn-PTCDI) at n = 4, 8, and 13, in order to elucidate the observed maximum charge transfer efficiency at the C8-PTCDI/rubrene interface in a recent experiment. The results revealed that the molecular conformation of the acceptor (Cn-PTCDI) molecules at the interface undergoes changes depending on the alkyl chain length when interacting with the rubrene molecule. It was found that the closest complex between Cn-PTCDI and rubrene is formed at n = 8, consistent with the experimental observation. In addition, the interfacial structures of Cn-PTCDI/air and rubrene/air were examined and compared to gain insights into the inherent stability associated with the intermolecular interactions at the interface.