Induction of Chirality on Nanographenes

Abstract

Chirality induction is an important topic in studies of nanographenes (NGs). We report chirality enhancements of NGs through postsynthetic chemical modifications of NGs with pyrene and m-terphenyl groups. These substituents were installed into N-(p-bromophenylethyl)imides on the edges of the NGs with Pd-catalyzed cross-coupling reactions. Circular dichroism (CD) spectra demonstrated that these bulky substituents improved the induced CD signal of the NGs compared to those previously reported and suggested that they induced the opposite chirality. Density functional theory calculations indicated possible edge structures for the NGs and indicated that π/π and CH/π interactions among the neighboring substituents influenced the orientations of the imides. These imides distorted the edges, and the distorted edges eventually generated the chiral environments of the NGs. The interactions among the substituents are, therefore, likely to allow detection of the CD signals in the visible region and induction of the opposite chirality.