Helical Sense-Responsive and Substituent-Sensitive Features in Vibrational and electronic Circular Dichroism, in Circularly Polarized Luminescence and in Raman Spectra of Some Simple Optically Active Hexahelicenes

Four different hexahelicenes, 5-aza-hexahelicene
(1), hexahelicene (2), 2-methyl-hexahelicene (3), and
2-bromo-hexahelicene (4), were prepared and their enantiomers,
which are stable at r.t., were separated. Vibrational
circular dichroism (VCD) spectra were measured for
compound 1; for all the compounds, electronic circular
dichroism (ECD) and circularly polarized luminescence
(CPL) spectra were recorded. Each type of experimental
spectrum was compared with the corresponding theoretical
spectrum, determined via Density Functional Theory (DFT).
Following the recent papers by Nakai et al., this comparison
allowed to identify some features related to the helicity and some other features typical of the substituent groups on the helical
backbone. The Raman spectrum of compound 1 is also examined from this point of view.