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Circularly polarized luminescence (CPL) and Raman optical activity (ROA) were observed in a single spectroscopic experiment for a purely organic molecule, an event that had so far been limited to lanthanide‐based complexes. The present observation was achieved for [16]cycloparaphenylene lemniscate, a double macrocycle constrained by a rigid 9,9′‐bicarbazole subunit, which introduces a chirality source and allows the molecule to be resolved into two configurationally stable enantiomers. Distortion of oligophenylene loops in this lemniscular structure produces a large magnetic transition dipole moment while maintaining the π‐conjugation‐induced enhancement of the Raman signal, causing the appearance of the CPL/ROA couple. A two‐photon mechanism is proposed to explain the population of the lowest‐energy excited electronic state prior to the simultaneous emission‐scattering event. [ABSTRACT FROM AUTHOR]

Poly(phenylacetylene)s are a family of helical polymers constituted by conjugated double bonds. Raman spectra of these polymers show a structural fingerprint of the polyene backbone which, in combination with its helical orientation, makes them good candidates to be studied by Raman optical activity (ROA). Four different well‐known poly(phenylacetylene)s adopting different scaffolds and ten different helical senses have been prepared. Raman and ROA spectra were recorded and allowed to establish ROA‐spectrum/helical‐sense relationships: a left/right‐handed orientation of the polyene backbone (Mhelix/Phelix) produces a triplet of positive/negative ROA bands. Raman and ROA spectra of each polymer exhibited the same profile, and the sign of the ROA spectrum was opposite to the lowest‐energy electronic circular dichroism (ECD) band, indicating a resonance effect. Resonance ROA appears then as an indicator of the helical sense of poly(phenylacetylene)s, especially for those with an extra Cotton band in the ECD spectrum, where a wrong helical sense is assigned based on ECD, while ROA alerts of this misassignment. [ABSTRACT FROM AUTHOR]

Oligo‐S,S‐dioxothienylenevinylenes have been prepared by transferring oxygen atoms to the sulfur atoms using the HOF⋅CH3CN complex. Their photophysical properties are presented in comparison with their thiophenevinylene congeners. Together with their vibrational properties and molecular force fields, this study allows for the interpretation of the alteration of aromaticity and inter‐ring exocyclic π‐conjugation in this series. Selective oxidation of the sulfur atoms of oligothiophene vinylene oligomers, which leaves the surrounding electron‐rich olefins intact, promotes the enhancement of inter‐ring/ exocyclic π‐conjugation such as demonstrated by the analysis of the molecular force fields (i.e., force constants) associated to the C=C and C−C bonds. [ABSTRACT FROM AUTHOR]

Introducing one or two alkynyl–iron moieties onto a carbo[6]helicene results in organometallic helicenes (2 a,b) that display strong chiroptical activity combined with efficient redox‐triggered switching. The neutral and oxidized forms have been studied in detail by electronic and vibrational circular dichroism, as well as by Raman optical activity (ROA) spectroscopy. The experimental results were analyzed and spectra were assigned with the help of first‐principles calculations. In particular, a recently developed method for ROA calculations under resonance conditions has been used to study the intricate resonance effects on the ROA spectrum of mono‐iron ethynylhelicene 2 a. Ironing in kinks: Introducing one or two alkynyl–iron moieties onto a carbo[6]helicene results in organometallic helicenes that display strong chiroptical activity combined with efficient redox‐triggered switching (see figure). The chiroptical properties and redox‐switching activity of iron alkynylhelicenes determined experimentally and theoretically are reported. [ABSTRACT FROM AUTHOR]

The chiroptical features of supramolecular polymers formed from N-heterotriangulenes 1- 3 have been investigated by circular dichroism (ECD) and vibrational circular dichroism (VCD) techniques. In solution, the CD spectra demonstrate that the helicity of the aggregates depends on only the stereogenic centres located at the peripheral chains. In the gel state, the chiroptical features are conditioned by the point chirality of the stereogenic centres and by the achiral solvent utilised. Sonication of the gels formed in CCl4 reveals both kinetic and thermodynamic phases. These findings reveal the presence of pathway complexity in the gel state triggered by sonication. The described solvent-induced helical stereomutation demonstrates that the gel state can be utilised as an outstanding benchmark for investigating uncommon chiroptical effects and to explore the rules of chirality transmission. [ABSTRACT FROM AUTHOR]

Tri(4-iodo-2,3,5,6-tetrachlorophenyl)methane ( 2) is reported as a general building block for the synthesis of various π-conjugated polychlorotriphenylmethyl (PTM) radicals. Three push-pull-type triphenylamine-substituted PTM radicals with different substitution patterns were prepared and all exhibited intense inter-valence charge-transfer bands and large two-photon absorption (TPA) cross sections. Moreover, increase of solvent polarity also resulted in improved TPA response. The charge-transfer character of the relevant excited states provoked the efficient photo-generation of charges, anions in the PTM and cations in the amine arms, driven by the amphoteric redox character and the small coupling between donor and acceptor. [ABSTRACT FROM AUTHOR]

The combination of a bis-alkynyl-helicene moiety with two iron centers leads to novel electroactive species displaying unprecedented redox-triggered chiroptical switching. Upon oxidation, strong changes of vibrational modes (either local or extended coupled modes) are detected by vibrational circular dichroism and Raman optical activity. Remarkably, the sign of the optical rotation at 1.54 mm (that is, at wavelengths typically used for telecommunications) changes upon oxidation while the topology and stereochemistry of the helicene remain unchanged. [ABSTRACT FROM AUTHOR]

The combination of a bis-alkynyl-helicene moiety with two iron centers leads to novel electroactive species displaying unprecedented redox-triggered chiroptical switching. Upon oxidation, strong changes of vibrational modes (either local or extended coupled modes) are detected by vibrational circular dichroism and Raman optical activity. Remarkably, the sign of the optical rotation at 1.54 μm (that is, at wavelengths typically used for telecommunications) changes upon oxidation while the topology and stereochemistry of the helicene remain unchanged. [ABSTRACT FROM AUTHOR]

The helical organization of oligo- p-phenylene-based organogelators has been investigated by atomic force microscopy, circular and vibrational circular dichroism, and Raman techniques. Whilst OPPs with more than two phenyl rings in the core self-assemble into left-handed helices, that with a biphenyl core shows an inversion of the supramolecular helicity depending on the formation conditions through the atropisomerism of the biphenyl central unit. The results presented herein outline a new example of kinetically controlled modulation of supramolecular helicity. [ABSTRACT FROM AUTHOR]

The article discusses research which aims to analyze the Raman vibrational spectra of dianionic tetracyanoethylene (TCNE) dimers. It reports experimental details including information on TCNE multicenter bonds, strength estimation of multicenter C--C bonds, and stretching force constant identification. It describes vibrational normal modes related to relevant Raman bands. It also evaluated temperature dependence of low-frequency bands in the Raman spectra.

A chiral bisurea-based superhydrogelator that is capable of forming supramolecular hydrogels at concentrations as low as 0.2 m M is reported. This soft material has been characterized by thermal studies, rheology, X-ray diffraction analysis, transmission electron microscopy (TEM), and by various spectroscopic techniques (electronic and vibrational circular dichroism and by FTIR and Raman spectroscopy). The expression of chirality on the molecular and supramolecular levels has been studied and a clear amplification of its chirality into the achiral analogue has been observed. Furthermore, thermal analysis showed that the hydrogelation of compound 1 has a high response to temperature, which corresponds to an enthalpy-driven self-assembly process. These particular thermal characteristics make these materials easy to handle for soft-application technologies. [ABSTRACT FROM AUTHOR]

Making more electron‐deficient oligothiophene vinylenes (OTVs) by selective oxidation of the sulfur atoms converts them into significantly more π‐conjugated molecules, with enhanced inter‐ring/exocyclic π‐conjugation and, concomitantly, with enhanced optical features. This unique oxidation of OTVs leaves the surrounding electron‐rich olefins intact. A comparison of these [all]‐S,S‐dioxide oligothienylene‐vinylenes with their parent oligothienylene‐vinylenes and also with oligothiophenes has been carried out. More information can be found in the Communication by J. Casado, F. Langa, S. Rozen, et al. on page 464. [ABSTRACT FROM AUTHOR]