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

Moussa, Mehdi El Sayed; Srebro, Monika; Anger, Emmanuel; Vanthuyne, Nicolas; Roussel, Christian; Lescop, Christophe; Autschbach, Jochen; Crassous, Jeanne

doi:10.1002/chir.22201

Cited by 36 publications

(18 citation statements)

References 67 publications

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“…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 ).…”

Section: B Results and Discussionmentioning

confidence: 79%

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

et al. 2014

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Enantiopure mono-cycloplatinated-[8]helicene and bis-cycloplatinated-[6]helicene derivatives were prepared through column chromatography combined with crystallization of diastereomeric complexes using a chiral ancillary sulfoxide ligand. The UV-visible spectra, circular dichroism, molar rotations, and (circularly polarized) luminescence activity of these new helical complexes have been examined in detail and analysed with the help of first-principles quantum-chemical calculations.

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Section: B Results and Discussionmentioning

confidence: 79%

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

et al. 2014

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“…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.…”

Section: Resultsmentioning

confidence: 99%

Ruthenium‐Grafted Vinylhelicenes: Chiroptical Properties and Redox Switching

Srebro

Anger

Moore

et al. 2015

Chemistry A European J

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The properties of mono- and bis-Ru-vinyl[6]helicene complexes (2 a and 2 b, respectively), recently synthesized by using molecular engineering of helicenes based on the grafting of lateral organometallic substituents on the π-helical backbone through a vinyl bridge, are presented. These helicene derivatives are thoroughly characterized, with special attention given to their chiroptical properties and redox switching activity. The UV/Vis and electronic circular dichroism (ECD) spectra of P and M enantiopure species, both in the neutral and oxidized states ([2 a](·+), [2 b](·+), and [2 b](2+)), are analyzed with the aid of quantum-chemical calculations. The extended π-conjugation facilitated by the vinyl moiety, clearly visible in the electronic structures of 2 a,b, introduces new active bands in the ECD spectra that consequently lead to a significant increase in optical rotation of Ru-vinylhelicenes compared with the organic precursors. The vibrational circular dichroism (VCD) spectra were measured and calculated for both the organic and organometallic species and constitute the first examples of VCD for metal-based helicene derivatives. Finally, the redox-triggered chiroptical switching activity of 2 a,b is examined in detail by using ECD spectroscopy. The modifications of the ECD spectra in the UV/Vis and NIR region are well reproduced and rationalized by calculations.

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“…[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.…”

Section: Methodsmentioning

confidence: 99%

“…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.…”

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

et al. 2015

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Herein we report on the theoretical-experimental analysis of the one-and two-photon absorption and circular dichroism spectra of two intrinsically chiral aromatic molecules -hexahelicene derivatives -with helical chirality and intramolecular charge transfer (ICT). The primary outcomes of our investigation demonstrate that the TPA cross-section and the amplitude of the TPCD signal of this type of helicenes are strongly affected by the strength of the ICT and the nature of the extension of the electronic delocalization, i.e. beyond (EXO-ICT) or within (ENDO-ICT) the helicene core. These results were corroborated through the comparative theoretical analysis of the corresponding contributions of the magnetic dipole transition moment and the electric quadrupole transition moment to the TPA rotatory strength on a series of five similar helicene derivatives with different molecular electron delocalization disposition.Two-photon absorption (TPA) and two-photon circular dichroism (TPCD) spectra were obtained using the double L-scan technique over a broad spectral range (400 nm -900 nm) using 90 fs pulses at a low repetition rate (2-50 Hz) produced by an amplified femtosecond system.The theoretical simulations were performed using modern analytical response theory within the Time-Dependent Density Functional Theory (TD-DFT) approach using B3LYP and CAM-B3LYP, and the aug-cc-pVDZ and 6-311++G(d,p) basis sets.

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

Cited by 36 publications

References 67 publications

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

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

Ruthenium‐Grafted Vinylhelicenes: Chiroptical Properties and Redox Switching

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

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