Light-Responsive Oligothiophenes Incorporating Photochromic Torsional Switches (PTS)

We present a quaterthiophene and sexithiophene that can reversibly change their effective π-conjugation length via photoexcitation. The reported compounds make use of light-responsive molecular actuators consisting of an azobenzene attached to a bithiophene unit by both direct and linker-assisted bonding. Upon exposure to 350 nm light the azobenzene undergoes trans -to- cis isomerization mechanically inducing the oligothiophene to assume a planar conformations (extended π-conjugation). Exposure to 254 nm wavelenght promotes azobenzene cis -to- trans isomerization, forcing the thiophenic backbones to twist out of planarity (confined π-conjugation). Twisted conformations are also reached by cis -to- trans thermal relaxation with rate that increases proportionally with the conjugation length of the oligothiophene moiety. The molecular conformations of quaterthiophene and sexithiophene were characterized using steady-state UV-vis, X-ray crystallography and quantum-chemical modelling. Finally, we tested the proposed light-responsive oligothiophenes into field-effect transistors to probe the photo-induced tuning of their electronic properties

rac-4,8-Divinyl­bicyclo­[3.3.1]nonane-2,6-dione

The title compound, C13H16O2, is a chiral bicyclic structure composed of two fused cyclo­hexa­ne rings possessing both boat and chair conformations. The mol­ecules are packed in enantio­pure columns which are pairwise linked forming an overall racemic solid; within the column pairs the packing is governed by weak dipole–dipole inter­actions stemming from stacked carbonyl functionalities (COcentroid–COcentroid distance = 3.290 Å)

A tautoleptic approach to chiral hydrogen-bonded supramolecular tubular polymers with large cavity

A new strategy towards tubular hydrogen‐bonded polymers based on the self‐assembly of isocytosine tautomers in orthogonal directions is proposed and experimentally verified, including by 1H fast magic‐angle spinning (MAS) solid‐state NMR. The molecular tubes obtained possess large internal diameter and tailor‐made outer functionalities rendering them potential candidates for a number of applications

Stereoselective Self-Sorting on Surfaces: Transcription of Chiral Information

Templated self-sorting on surfaces has been introduced recently as a new approach to construct multicomponent architectures directly on solid oxide surfaces. In this process, two-dimensional information placed on the surface is transcribed into three-dimensional architectures with up to 97% intrinsic templation efficiency. Previously, we have shown that isosteric partners of different color do neither self-sort nor respond to templation during self-organizing surface-initiated copolymerization (co-SOSIP). To evaluate the importance of chirality in this process, co-SOSIP with mixtures of pseudo-enantiomers of isosteric partners is explored. The composition of the obtained SOSIP architectures is independent of the composition of the initiator mixtures on the surface. This absence of templation from the surface rules out the occurrence of uniform self-sorting of pseudo-enantiomeric isosters, a process similar to chiral resolution in conglomerates. Alternate self-sorting, the complementary process comparable with racemic crystallization, is indistinguishable from random mixing in structural studies. However, different photocurrent generation by pseudo-racemic compared with pseudo-homochiral photosystems support, on the functional level, that alternate self-sorting occurs with pseudo-enantiomeric partners. These results support that chirality is important for the transcription of two-dimensional information into three-dimensional architectures and suggest that alternate self-sorting dominates over uniform self-sorting as racemic crystallization dominates over chiral resolution

Chemoselective Deprotection of Sulfonamides Under Acidic Conditions: Scope, Sulfonyl Group Migration, and Synthetic Applications

Chemoselective acidic hydrolysis of sulfonamides with trifluoromethanesulfonic acid has been evaluated as a deprotection method and further extended to more complex synthetic applications. In contrast to conventional troublesome sulfonamide hydrolysis, a near-stoichiometric amount of acid was found to be sufficient to bring about efficient deprotection of various neutral or electron-deficient <i>N</i>-arylsulfonamides, whereas electron-rich substrates provided sulfonyl group migration products. The deprotection method developed is fully selective for <i>N</i>-arylsulfonamides, and the possibility to discriminate among various different sulfonamides is demonstrated

Directional stack exchange along oriented oligothiophene stacks

Directional growth of π-basic oligothiophene stacks on solid substrates is achieved by self-organizing, surface-initiated disulfide exchange polymerization. Successful addition of co-axial π-acidic stacks by templated hydrazone exchange provides general access to multicomponent architectures of unique complexity

Baker's Yeast for Sweet Dough Enables Large-Scale Synthesis of Enantiomerically Pure Bicyclo[3.3.1]nonane-2,6-dione

An improved synthetic procedure of racemic bicyclo[3.3.1]nonane-2,6-dione has been developed. Employing Baker's yeast for sweet dough made it possible to kinetically resolve the racemic compound and to isolate enantiomerically pure (+)-bicyclo[3.3.1]nonane-2,6-dione on a large scale. Furthermore, the developed procedure made it possible to produce (-)-bicyclo[3.3.1]nonane-2,6-dione with an enantiomeric excess of 75%

Chirality, a never-ending source of confusion

In this Discussion a few points of confusion concerning chirality are clarified. The term chirodescriptive is proposed for such space groups that lack inversion centres, reflection planes, glide planes or rotary-inversion axes and thus can contain enantiopure, chiral objects. It is pointed out that chiral compounds can (and often do) crystallise in non-chirodescriptive space group when they occur as racemates and in such cases there is no incompatibility between chirality and mirror planes or centres of inversions. We also propose the term raceomorphism to describe the relationship between a conglomerate and a collection of racemic crystals of the same compound