Expanded [2,1][n]Carbohelicenes with 15- and 17-Benzene Rings

Abstract

Expanded carbohelicenes with structures fused to 15- and 17-benzene were successfully synthesized. Establishing a new synthetic strategy is crucial to realize the development of longer expanded [2,1][n]helicenes with a kekulene-like projection drawing structure. This article describes the sequential integration of the π-elongating Wittig reaction of functionalized phenanthrene units and ring-fusing Yamamoto coupling for the synthesis of [2,1][15]helicenes and [2,1][17]helicenes. X-ray crystallographic structures, photophysical properties, and density functional theory (DFT) calculations revealed the unique characteristics of the synthesized expanded helicenes. Furthermore, because of the high enantiomerization barrier derived from a wide-range intrahelix π–π interaction, the optical resolution of [2,1][17]helicene was successfully achieved, and chiroptical properties such as circular dichroism and circularly polarized luminescence were elucidated for the first time as enantiomers of pristine [2,1][n]helicene core.

Can Magnetic Dipole Transition Moment Be Engineered?

“…In that way, m could be engineered for a selected transition, in principle, with no limits. This suggestive idea is supported by previous observations of our group [20] and strengthened by the observations of a similar behavior in other helical structures by Matsuda, Don Tilley, Isobe, Wu and Itami groups [21–26] …”

“…This suggestive idea is supported by previous observations of our group [20] and strengthened by the observations of a similar behavior in other helical structures by Matsuda, Don Tilley, Isobe, Wu and Itami groups. [21][22][23][24][25][26] Herein, we have analyzed such appealing possibility in three different families of organic helical structures (simple carbo[n]helicenes and ortho-oligophenylethynylenes, o-OPEs) and a chiral molecular circuit based on paraphenylethynylene-linked paracyclophanes recently reported by Morisaki. [27] First, we need to identify the best transitions in terms of j m j for each compound.…”

π-Extended Helical Multilayer Nanographenes with Layer-Dependent Chiroptical Properties

“…Circularly polarized luminescence (CPL) materials have garnered significant interest due to their wide range of potential applications in fields like biological science, CPL lasers, spintronics, and more. − Within this context, helical nanographenes (NGs) emerge as a captivating class, distinguished by their inherent chirality, distinct dynamic characteristics, and exceptional chiroptical properties. − With the incorporation of [ n ]­helicene units into NGs, a variety of helical NGs with diverse topologies have been reported and considered to be the impetus for the development of novel tailor-made chiroptical materials with high CPL brightness. − Among them, helical NGs extended along the perpendicular direction to the helical axis are garnering increased attention in recent years due to the extended π-electron delocalization, enhanced chirality stability, and upgraded photoluminescence. − …”

X-ray and Optical Circular Dichroism as Local and Global Ultrafast Chiral Probes of [12]Helicene Racemization

“…Helicene chemistry is a rapidly growing field − with applications to asymmetric catalysis, nonlinear optics, spin filters, switches and sensors, and the design of molecular machines . They can be synthesized with different sizes and are usually referred to as [ n ]­helicenes, where n denotes the number of benzene rings.…”