Search

Molecular platforms are essential components of various surface‐mounted molecular devices. Here, we document the synthesis of two universal triptycene‐based tripodal pedestals featuring terminal alkynes in the axial position. We showcase their versatility by incorporating them into the structures of diverse functional molecules such as unidirectional light‐driven molecular motors, photoswitches, and Brownian molecular rotors using standard cross‐coupling reactions. We also present their fundamental physical properties, including acidity constants, data from differential scanning calorimetry, and crystallographic analysis of two parent and five derived structures. Finally, and importantly, we demonstrate that the photochemical properties of selected photoswitch representatives remain uncompromised when fused with tripods. [ABSTRACT FROM AUTHOR]

2,9‐ and 2,10‐diphenylpentacene were synthesized by direct C−H borylation of ketal‐protected pentacene, followed by halodeboronation, resolution of the dihalo isomers, Suzuki arylation, cleavage of the ketals and decarbonylation in the solid state. They were studied as main active components in organic field effect transistors (OFETs). Diphenyl substitution of pentacene affects the unit cell dimensions only slightly, preserving a face to edge molecular packing in the first layers of thin films evaporated on SiO2 substrates. Both isomers self‐assemble into nanoribbons during the thin film growth upon vapor deposition. The similarity between the surface induced phases of the 2,9‐isomer and unsubstituted pentacene leads to similar 4‐probe hole mobilities, i. e. 0.13 cm2 V−1 s−1 for the former. Whereas 2,9‐disubstitution thus does essentially preserve the thin film characteristics of unsubstituted pentacene, 2,10‐disubstitution is detrimental to the molecular ordering in the thin films and therefore to the field effect mobility which is only 0.07 cm2 V−1 s−1. The known strong enhancement of field effect mobility observed upon diphenyl substitution of anthracene can thus not be emulated analogously with pentacene. [ABSTRACT FROM AUTHOR]

This article discusses the synthesis of triptycene-based tripodal molecular platforms, which are important for surface-mounted molecular devices. These molecular tripods have been shown to be versatile by being integrated into various functional molecules, such as molecular motors, photoswitches, and molecular rotors. The researchers achieved this by using standard cross-coupling reactions. For more information, readers can refer to the research article by J. Kaleta and co-workers. [Extracted from the article]

A series of inherently chiral (di)thiahelicenes/dithiophenohelicenes containing 5, 6, 9 or 11 (hetero)cycles in their helical backbone with thiophene subunit(s) embedded in it or annulated to its periphery were uniformly synthesized by intramolecular alkyne [2+2+2] cycloisomerization. Their structural, chemical and physicochemical properties such as crystal packing, oxidation, barrier to racemization, spontaneous thin film transformation or electrochemical behavior were studied and compared with the respective properties of the parent all‐carbon helicenes and dibenzohelicenes. [ABSTRACT FROM AUTHOR]

The tetraene 7,7‐dimethoxy‐2,3,5,6‐tetramethylenebicyclo[2.2.1]heptane is a key compound for the preparation of a large variety of acenes protected by a carbonyl bridge. We report herein a medium scale preparation in seven steps of this valuable starting material. Diels–Alder addition between 6,6‐dimethtyl fulvene and maleic anhydride, followed by carboxylation, ozonolysis of the double bond, reduction of the four ester groups, then chlorination of the alcohol groups and dehydrochlorination give the target compound in 17 % overall yield. [ABSTRACT FROM AUTHOR]

Racemic and highly enantioenriched 3‐methoxycarbonyl, 3‐carboxy, and 3‐hydroxymethyl derivatives of dibenzo[6]helicene were prepared. The Langmuir layers of these helicenes were formed at the air–water interface and transferred onto solid substrates to afford Langmuir–Blodgett films, which were then studied by ambient atomic force microscopy and (chir)optical spectroscopy. Significant differences were found in the behaviour of the Langmuir layers as well as in the morphology, UV/Vis, electronic circular dichroism (ECD), and fluorescence spectra of the Langmuir–Blodgett thin films depending on the molecular chirality and nature of the polar group. The experimental results were supported by molecular dynamics simulations. [ABSTRACT FROM AUTHOR]

Abstract: Helical chirality is a novel enantioselectivity‐inducing property in transition‐metal‐catalyzed transformations. The principle is illustrated herein for the example of asymmetric olefin metathesis. This work reports the synthesis of the first helically chiral Ru‐NHC alkylidene complex from an aminohelicene‐derived imidazolium salt, which was ligated to the first generation Hoveyda–Grubbs catalyst. Kinetic data were acquired for benchmark test reactions and compared to an achiral catalyst. The helically chiral Ru‐catalyst was evaluated in asymmetric ring‐closing metathesis (RCM) and ring‐opening metathesis–cross‐metathesis (ROM/CM) reactions, which proceeded with promising levels of enantioselectivity. Extensive NMR‐spectroscopic investigations and a DFT geometry optimization were performed. These results led to a topographic steric map and calculation of percent‐buried‐volume values for each quadrant around the metal center. [ABSTRACT FROM AUTHOR]

A series of oxahelicenes composed of ortho/ meta-annulated benzene/pyridine and 2 H-pyran rings were synthesized on the basis of the cobalt(I)-mediated (or rhodium(I)- or nickel(0)-mediated) double, triple, or quadruple [2+2+2] cycloisomerization of branched aromatic hexa-, nona-, or dodecaynes, thus allowing the construction of 6, 9, or 12 rings in a single operation. The use of a flow reactor was found to be beneficial for the multicyclization reactions. The stereogenic centers present in some of the oligoynes steered the helical folding in such a way that the final oxa[9]-, [13]-, [17]- and [19]helicenes were obtained in both enantiomerically and diastereomerically pure form. Specifically, the oxa[19]helicenes beat the current record in the length of a helicene backbone. Single-molecule conductivity was studied by the mechanically controllable break-junction method with a pyridooxa[9]helicene. [ABSTRACT FROM AUTHOR]

Chimerical pyrene-based dibenzo[7]helicene rac- 1 and 2 H-pyran[7]helicene ( M, R, R)-(−)- 2, in which two pyrene subunits are fused to the [7]helicene/[7]heterohelicene scaffold, were synthesised by means of Ni0- or CoI-mediated [2+2+2] cycloisomerisation of dipyrenyl-acetylene-derived triynes. Pyrene-based dibenzo[7]helicene 1 was obtained in enantioenriched form by enantioselective cycloisomerisation under Ni0/QUINAP catalysis (57 % ee) or in enantiopure form by racemate resolution by liquid chromatography on a chiral column. 1,3-Allylic-type strain-controlled diastereoselective cycloisomerisation was employed in the synthesis of enantiopure ( M, R, R)-(−)- 2. Physicochemical properties of 1 and 2 encompassing the helicity assignment, stability to racemisation, X-ray crystal structure, UV/Vis, experimental/calculated electronic circular dichroism and fluorescence spectra were studied. Accordingly, comparison of the X-ray crystal structure of ( M, R, R)-(−)- 2 with calculated structures (DFT: B3LYP/cc-pVDZ, B97D/cc-pVDZ) indicated that its helical backbone is slightly over-flattened owing to intramolecular dispersion forces between tert-butylated pyrene subunits. Both 1 and 2 are fluorescent (with quantum yields in dichloromethane of ΦF=0.10 and 0.17, respectively) and are suggested to form intramolecular excimer states upon excitation, which are remarkably stabilised and exhibit large Stokes shifts (296 and 203 nm, respectively). [ABSTRACT FROM AUTHOR]

A cobalt-mediated [2+2+2] cycloisomerisation of ynedinitriles to helical pyridazines in good to high yields was developed. The construction of the pyridazine nucleus from one alkyne and two nitrile units is proposed to follow either a conventional organometallic mechanism or to be triggered by a single-electron transfer from a CoII species. Various [5]-, [6]- and [7]helicene pyridazines were prepared. [ABSTRACT FROM AUTHOR]

The article discusses the rapid access and functionalized derivatives of dibenzohelicenes. It states that the dibenzohelicenes' construction relies on the pivotal Sonogashira and Suzuki-Miyaura couplings for the assembly of key aromatic triynes with a subsequent alkyne cycloisomerization for the formation of helical backbones. It says that the dibenzohelicenes have an advantage over helicenes due to the simplicity of its non-photochemical preparation.

Both experiments and molecular dynamics simulations point to the fact that racemic assemblies are more stable than enantiopure ones. B Helicene rafts on water b : Amphiphilic derivatives of dibenzo[6]helicene form stable Langmuir layers at the air-water interface. Both experiments and molecular dynamics simulations point to the fact that racemic assemblies are more stable than enantiopure ones. [Extracted from the article]