Cooperative CH...pi Interactions in the Crystal Structure of 2,5-Di(3-biphenyl)-l,l-dimethyl-3,4-diphenyl-silole and Its Effect on Its Electronic Properties

摘要

In order to develop a fundamental understanding for the effect of molecular packing on the carrier transport properties of organic semiconductors, single crystals of 2,5-di-(3-biphenyl)-l,l-dimefhyl-3,4-diphenylsilacy-clopentadiene (PPSPP) were prepared using the physical vapor transport technique and characterized by X-ray crystallography. There is no evidence of pi-pi stacking in the PPSPP single-crystal because of the nearly orthogonal arrangements of the phenyl rings in the biphenyl moieties. Although the PPSPP molecules do not have any -NH or -OH groups that would provide donors for normal hydrogen bonds, the crystal structure reveals the presence of several CH groups that act as donors for CH...pi interactions with nearby phenyl groups in an edge-to-face motif. It is proposed that the cooperativity between several weak CH...pi bonds enhances their effects and gives rise to a tighter molecular packing than what would be observed for a typical molecular crystal where van der Waals forces dominate. Theoretical electronic-structure calculations indicate that there is a decoupling between the CH...pi interactions that stabilize the crystal structure and the electronic interactions that give the largest electronic couplings defining the preferred electron hopping directions. However, the dense molecular packing between adjacent PPSPP molecules may influence its electron transport properties in the solid state.