Thiophene/selenophene-based windmill-shaped triple [6]helicenes

Abstract

The construction of multiple helicenes, one of the important branches of curved polyaromatic hydrocarbons (PAHs), is a fundamental goal in both helicene chemistry and supramolecular chemistry. Here, we demonstrate the facile and efficient construction of four thiophene/selenophene-based windmill-shaped triple [6]helicenes. The key step involved was the oxidative photocyclization of four 1,3,5-tris(2-(5-(trimethylsilyl)dithieno/diseleno[2,3-b:3′,2′-d]thiophen/selenophen-2-yl)vinyl)benzenes in the presence of iodine in dry toluene. The windmill-shaped molecular structures of triple [6]helicenes were confirmed by X-ray crystallographic analysis. With the replacement of S with Se in molecular skeletons, the racemic triple [6]helicenes exhibited different crystal-packing patterns based on multiple intermolecular interactions. The novel capsule structures of the racemic triple [6]helicenes were formed by two enantiomers based on the intermolecular interactions. The chiral resolution of the third racemic triple [6]helicene was carried out via chiral HPLC, and the chiroptical properties such as the CD spectra and optical rotations of the enantiomers were investigated. Furthermore, the spectroscopic and physicochemical behaviors of the racemic triple [6]helicenes showed that the heteroatom replacement of S with Se could precisely modulate their emission properties and molecular energy levels.