Chiroptical Properties of Carbo[6]Helicene Derivatives Bearing Extended π‐Conjugated Cyano Substituents

Abstract

New carbo[6]helicene derivatives grafted with π-conjugated cyano-phenyl arms were synthesized in enantiopure forms and their π-conjugation examined by UV-vis spectroscopy. The influence of the π-conjugation on the circular dichroism spectra and molar rotations is discussed based on comparing experimental data with results from quantum-chemical calculations. The results highlight the fact that increasing the spatial extension of the π-system in a helicene molecule is an efficient way of increasing its molar rotation.

Straightforward access to mono- and bis-cycloplatinated helicenes displaying circularly polarized phosphorescence by using crystallization resolution methods

“…A strong over-estimation relative to the measured value (16406 vs. 8290 degree cm 2 /dmol) was calculated for the 2-pyridyl-[6]helicene ligand 1a . As shown in references 15, pristine and substituted helicenes can reveal a pronounced dependence of the optical rotations on their molecular structure. Inclusion of van der Waals (dispersive) forces in the geometry optimizations may be needed to improve the calculated chiroptical properties of 1a ( vide supra ).…”

Ruthenium‐Grafted Vinylhelicenes: Chiroptical Properties and Redox Switching

“…4a The comparison of chiroptical properties of the ethynyl‐capped [6]helicene with the parent carbo[6]helicene indicates that introducing one ethynyl moiety onto a [6]helicene core has indeed a slight effect on its chiroptical properties (compare with Table 2). 10a,b The experimental ECD spectrum of P ‐ 2 a (Figure 3 a, top) displays 1) an intense negative band at 250 nm, 2) a strong positive one at 335 nm that appears to originate from the helicene’s π–π* excitation number (no.) 6 calculated at 325 nm and displaying the strongest calculated rotatory strength, and 3) new low‐energy positive bands of moderate magnitude (380–460 nm), which are not present in the spectrum of 1 a and correspond to excitation nos.…”

Two-photon absorption and two-photon circular dichroism of hexahelicene derivatives: a study of the effect of the nature of intramolecular charge transfer

“…[6]helicene (Figure 1.b) were obtained from racemic 2-ethynyl- [6]carbohelicene and commercially available 4-bromobenzonitrile through a Sonogashira coupling reaction followed by chiral HPLC separation. 41 Although both the P and M enantiomers were obtained for this derivative, only the M enantiomer (henceforth CN6) was used for the spectroscopic measurements due to impurities that could not be removed from the solution containing the P enantiomer.…”

“…Similar evidences have already been reported by Rizzo and co-workers in other molecular systems 29,33,45,68 and, are in accordance with previous calculations performed in CN6. 41 Next, one should highlight the fact that the amplitudes of the OPA and ECD signals in both molecules are virtually identical, though there is an obvious difference in ICT between the two. This observation shall be explained more in detail after completing the theoreticalexperimental analysis of the nonlinear spectra of A6 and CN6 presented next.…”