Helicenes: synthesis and applications.

Two-dimensionally extended, polycyclic heteroaromatic molecules (heterocyclic nanographenes) are a highly versatile class of organic materials, applicable as functional chromophores and organic semiconductors. In this Review, we discuss the rich chemistry of large heteroaromatics, focusing on their synthesis, electronic properties, and applications in materials science. This Review summarizes the historical development and current state of the art in this rapidly expanding field of research, which has become one of the key exploration areas of modern heterocyclic chemistry.

Heterocyclic Nanographenes and Other Polycyclic Heteroaromatic Compounds: Synthetic Routes, Properties, and Applications

In this review, we discuss the rich chemistry of helicenes and helicenoids containing main-group elements. Enantioenriched helicenic derivatives containing main-group elements B, Si, N, and P, either incorporated within the helical backbone or grafted to it, will be thoroughly presented. We will describe their synthesis, resolution, and asymmetric synthesis, their structural features, electronic and chiroptical properties, and emission, together with other photochemical properties and applications.

/pdf/enantioenriched-helicenes-and-helicenoids-containing-main-2dk3dhah9a.pdf

Enantioenriched Helicenes and Helicenoids Containing Main-Group Elements (B, Si, N, P).

Chiral helicene, a fully conjugated system without stereogenic carbon, can filter spins effectively at room temperature, a consequence of the chiral-induced spin-selectivity effect. The chirality dictates the spin of the electrons transferred through helicene, and magnetoresistance devices based on these molecules show antisymmetric magnetoresistance versus H plots.

Helicenes—A New Class of Organic Spin Filter

We have prepared gold nanoparticles covered with N-isobutyryl-l-cysteine and N-isobutyryl-d-cysteine, respectively. These particles with a mean particle size smaller than 2 nm are highly soluble in water and are amenable to chiroptical techniques such as vibrational circular dichroism (VCD) and circular dichroism (CD) spectroscopy. Density functional theory shows that the VCD spectra are sensitive toward the conformation of the adsorbed thiol. Based on the comparison between the experimental VCD spectrum and the calculated VCD spectra for different conformers, a preferential conformation of the thiol adsorbed on the gold particles can be proposed. In this conformation the carboxylate group interacts with the gold particle in addition to the sulfur. The particles could furthermore be separated according to their charge and size into well-defined compounds. The optical absorption spectra revealed a well-quantized electronic structure and a systematic red-shift of the absorption onset with increasing gold core size, which was manifested in a color change with particle size. Some compounds showed basically identical absorption spectra as analogous gold particles protected with l-glutathione. This shows that these particles have identical core sizes (10-12, 15 and 18 gold atoms, respectively) and indicates that the number and arrangement of the adsorbed thiol are the same, independent of the two thiols, which have largely different sizes. Some separated compounds show strong optical activity with opposite sign when covered with the d- and l-enantiomer, respectively, of N-isobutyryl-cysteine. The origin of the optical activity in the metal-based transitions is discussed. The observations are consistent with a mechanism based on a chiral footprint on the metal core imparted by the adsorbed thiol.

/pdf/chiral-n-isobutyryl-cysteine-protected-gold-nanoparticles-41moe222z9.pdf

Chiral N-isobutyryl-cysteine protected gold nanoparticles: preparation, size selection, and optical activity in the UV-vis and infrared.

Ein konfigurationsstabiles Heterohelicen: Uber die diastereomeren Salze mit dem phosphorhaltigen Anion binphat gelang die Trennung der Enantiomere eines [4](Hetero)heliceniumkations (siehe Bild: N=violett, O=rot). Die absoluten Konfigurationen wurde durch Messung des Schwingungscirculardichroismus bestimmt. Die Energiebarriere fur die Enantiomerisierung der Verbindung ist deutlich groser als beim [6]Helicen.

/pdf/a-highly-configurationally-stable-4-heterohelicenium-cation-3ve3n5r8kk.pdf

A Highly Configurationally Stable [4]Heterohelicenium Cation†

https://doc.rero.ch/record/5855/files/Bas_Delphine_-_Vibrational_and_Electronic_Circular_Dichronism_20060726.pdf

Vibrational and electronic circular dichroism of Δ-TRISPHAT [tris(tetrachlorobenzenediolato) - phosphate(V)] anion

We report on the first stage of our theoretical study of the quino[2,3,4-kl]acridinium,1,13-dimethoxy-5,9-dipropyl-cation. This molecule, involved in the synthesis of novel triazaangulenium dyes of high chemical stability, is a chiral [4]-helicenium. The structure and the IR spectrum of the quino[2,3,4-kl]acridinium,1,13-dimethoxy-5,9-dimethyl-cation derived from theoretical calculations which use various density functional theory methods, are compared with the geometry derived from X-ray diffraction measurements and the experimental IR spectrum. Our study shows that the chosen variant of DFT methods (Becke88 for exchange, P86 for correlation, 3-21G** basis set) reproduces the experimental geometry within 0.004 A and the IR frequencies within 15 cm−1.

Density Functional Study of a Helical Organic Cation

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A Highly Configurationally Stable [4]Heterohelicenium Cation†

Vibrational and electronic circular dichroism of Δ-TRISPHAT [tris(tetrachlorobenzenediolato) - phosphate(V)] anion

Density Functional Study of a Helical Organic Cation