λ5-Phospha[7]helicenes: Synthesis, Properties, and Columnar Aggregation with One-Way Chirality
✍ Scribed by Dr. Koji Nakano; Hiromi Oyama; Yoshio Nishimura; Satoshi Nakasako; Prof. Dr. Kyoko Nozaki
- Publisher
- John Wiley and Sons
- Year
- 2011
- Tongue
- English
- Weight
- 771 KB
- Volume
- 51
- Category
- Article
- ISSN
- 0044-8249
No coin nor oath required. For personal study only.
✦ Synopsis
Helical extension of p-conjugated systems is of great interest for the production of novel molecules and materials with unusual properties and applications. A typical example is helical polyacetylenes, in which continuous p conjugation is achieved through covalent bonds. 2] Another example is the assembly of short helical fragments, such as helicenes. 4] For instance, helicenebisquinone derivatives were reported to form one-dimensional columnar aggregates with the aid of long alkyl side chains. [5] Unique optical properties, such as high nonlinear optical susceptibility [5c,f] and circularly polarized luminescence, were reported for these aggregates. [5e, 6] Single crystals would also be suitable for creating such architectures if the p-conjugated helical molecules are appropriately stacked. Nevertheless, our analysis of the Cambridge Crystallographic Database revealed that structures with one-dimensional columnar helicene packing that is driven by p-p stacking interactions are rather uncommon, [7] and in the majority of structures with helicene packing, the packing is noncolumnar and mostly driven by CH-p interactions. We hypothesized that the use of dipole-dipole interactions in addition to inherent p-p stacking interactions might produce a one-dimensional columnar arrangement of helicenes. Dipole-dipole interactions have been used as part of systems that contain cooperative interactions for the formation of one-dimensional molecular arrangements. [8] Theoretical studies on the corannulene dimer have also demonstrated that dipole-dipole interactions should be a significant part of the binding energy of bowl-shaped molecules. Previously, we have reported the synthesis of oxa-and aza[7]helicenes 3 and 4 by using palladium-catalyzed reactions. These helicenes do not possess dipole-moment vectors that are parallel to their helical axes, and no onedimentional columnar stack was formed. Herein, we report the preparation of l 5 -phospha[7]helicenes 1 and 2 as a new