Synthesis, Structure and Photophysical Properties of Pyrene–based [5]Helicenes: an Experimental and Theoretical Study

• Published in: ChemistrySelect (Weinheim) 2017-02, Vol.2 (4), p.1436-1441
• Main Authors: Wang, Chuan‐Zeng, Kihara, Rie, Feng, Xing, Thuéry, Pierre, Redshaw, Carl, Yamato, Takehiko
• Format: Article
• Language: English
• Subjects: Chemical Sciences; DFT calculations; Material chemistry; Optical properties; Photocyclization; Pyrene-cored helicenes; π−π interactions
• ISSN: 2365-6549; 2365-6549
• DOI: 10.1002/slct.201601327

Pyrene‐cored [5]helicenes were prepared by a facile, efficient Wittig reaction and an intramolecular photocyclization reaction utilising 2,7‐di‐tert‐butylpyrene‐4‐carbaldehyde and naphthalene/pyrene‐based phosphorus ylides. Optical properties based on UV−vis absorption and fluorescence spectra were investigated. X‐ray crystallography revealed that the pyrene‐based [5]helicenes exhibited strong face‐to‐face π−π interactions and edge‐to‐face π−π interactions. HOMO and LUMO energies and molecular orbitals were also studied by density functional theory (DFT) calculations. This study has revealed that the torsion angle of the helical structure plays a role in determining the π−π interactions and the frontier molecular orbital energy levels. Thus, pyrene‐based helicenes need to be considered when one designs new highly efficient organic light‐emitting diodes and organic semiconductor materials. This work presents a facile, efficient, general strategy for the synthesis of pyrene‐based [5]helicenes. Optical properties of those helical compounds based on UV−vis and fluorescence spectra were investigated. It is expected that this work will generate an upsurge of interest in helicene molecules for applications as high‐performance organic photonics materials, such as highly efficient OLED devices, and new organic semiconductors.