(Chemical Equation Presented) The functionalized, enantiomerically pure helicene 1 derived from bis(benzodithiophene) functionalized with four heptyl groups is prepared from 1,8-dibromo-4,5-diheptylbenzo[1,2-b:4,3-b′] dithiophene building block 2. Such helicene structure, functionalized with bromines at the terminal positions of the helicene inner rim and multiple solubilizing alkyl groups, is an attractive building block for long [n]helicenes and oligohelicenes. Chirooptical properties and the degree of electron delocalization are determined and compared to those of analogous carbon-sulfur helicene and helicenes derived from benzodithiophene to provide a correlation between chirooptical properties and the degree of electron delocalization. Helicene 1 possesses amoderately increased electron delocalization, but its chirooptical properties are similar to those for analogous helicenes with relatively lower electron delocalization, indicating that chirooptical properties are not significantly affected by electron delocalization for this series of helicenes. Molecular structures of racemic helicene 1 and its benzodithiophene building block 2 are confirmed by single-crystal X-ray analysis. Crystals of 2 are chiral and adopt the shape of long, flexible, flat needles that can be readily bent.
ASJC Scopus subject areas
- Organic Chemistry