Mukhopadhyay Arindam, Jana Kanyashree, Hossen Tousif, Sahu Kalyanasis, Moorthy Jarugu Narasimha
Department of Chemistry , Indian Institute of Technology , Kanpur 208016 , India.
Department of Chemistry , Indian Institute of Technology , Guwahati 781039 , India.
J Org Chem. 2019 Sep 6;84(17):10658-10668. doi: 10.1021/acs.joc.9b01126. Epub 2019 Aug 22.
Two regioisomeric pairs of heptahelical mono- and biscoumarins that are differentiated by "" and "" disposition of the pyran-2-one moiety have been synthesized and investigated to understand the influence of helicity on excited-state and chiroptical properties. A slight variation in the helicities is found to manifest in contrasting excited-state properties of coumarin-annelated heptahelicenes; in addition to the intramolecular charge transfer, structural relaxation in the excited state is shown from theoretical calculations to cause decrease in the fluorescence quantum yield for a system with higher helicity. The optically pure enantiomers of heptahelical coumarins exhibit helicity-dependent chiroptical properties, namely, specific rotations, molar ellipticities, Cotton effects, and anisotropic dissymmetry factors. Theoretical calculations point to factors that are not readily explicable.
