Chiroptical properties of the ground and excited states of two thia-bridged triarylamine heterohelicenes

Two thia-heterohelicenes of different length, namely a hetero [4]-helicene (1), and a hetero [6]-helicene (2) are studied by electronic circular dichroism (ECD), circularly polarized luminescence (CPL), vibrational circular dichroism (VCD) and optical rotation (OR). It is found that the ECD and VCD spectra are characteristically different from the corresponding spectra of the parent helicene molecules, indicative of the presence of hetero atoms. CPL spectra are discussed on the basis of DFT calculation results. The sign of the OR is different for the two thiaheterohelicenes and is correctly predicted by DFT calculations.