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Enhancing the selectivity of prolinamide organocatalysts using the mechanical bond in [2]rotaxanes.
Chem Sci
March 2020
Departamento de Química Orgánica, Facultad de Química, Regional Campus of International Excellence "Campus Mare Nostrum", Universidad de Murcia E-30100 Murcia Spain
The synthesis of a pair of switchable interlocked prolinamides and their use as organocatalysts in three different enamine-activated processes are reported. A diacylaminopyridine moiety was incorporated into the thread for directing [2]rotaxane formation further allowing the association of complementary small molecules. The rotaxane-based systems were tested as organocatalysts in asymmetric enamine-mediated processes, revealing a significantly improved catalytic ability if compared with the non-interlocked thread.
View Article and Find Full Text PDFPhotoinduced Electron Transfer Involving a Naphthalimide Chromophore in Switchable and Flexible [2]Rotaxanes.
Chemistry
January 2020
Istituto ISOF-CNR, via P. Gobetti 101, 40129, Bologna, Italy.
The interlocking of ring and axle molecular components in rotaxanes provides a way to combine chromophoric, electron-donor and electron-acceptor moieties in the same molecular entity, in order to reproduce the features of photosynthetic reaction centers. To this aim, the photoinduced electron transfer processes involving a 1,8-naphthalimide chromophore, embedded in several rotaxane-based dyads, were investigated by steady-state and time-resolved absorption and luminescence spectroscopic experiments in the 300 fs-10 ns time window. Different rotaxanes built around the dialkylammonium/ dibenzo[24]crown-8 ether supramolecular motif were designed and synthesized to decipher the relevance of key structural factors, such as the chemical deactivation of the ammonium-crown ether recognition, the presence of a secondary site for the ring along the axle, and the covalent functionalization of the macrocycle with a phenothiazine electron donor.
View Article and Find Full Text PDFRotaxane-Based Mechanophores Enable Polymers with Mechanically Switchable White Photoluminescence.
ACS Cent Sci
May 2019
Adolphe Merkle Institute, University of Fribourg, Chemin des Verdiers 4, CH-1700 Fribourg, Switzerland.
Three mechanoresponsive polyurethane elastomers whose blue, green, and orange photoluminescence can be reversibly turned on by mechanical force were prepared and combined to create a blend that exhibits deformation-induced white photoluminescence. The three polyurethanes contain rotaxane-based supramolecular mechanoluminophores based on π-extended pyrene, anthracene, or 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4-pyran (DCM) luminophores, respectively, and 1,4,5,8-naphthalenetetracarboxylic diimide as an electronically matched quencher. Each polymer shows instantly reversible, strain-dependent switching of its photoluminescence intensity when stretched and relaxed, as deformation leads to a spatial separation of the luminophore and quencher.
View Article and Find Full Text PDFA Phosphine Oxide Functional Group Based [2]Rotaxane That Operates as a Multistable Molecular Shuttle.
Chemphyschem
June 2016
Key Laboratory of Mesoscopic Chemistry of MOE, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing, 210023, China.
A switchable [2]rotaxane based on a pyridinediamide crown ether macrocycle and a thread bearing phosphine oxide, urea, and dibenzylammonium functional groups was successfully developed and characterized by (1) H NMR and 2D NMR spectroscopy, mass spectrometry, and single-crystal analysis. The three recognition sites in the [2]rotaxane were sorted from strong to weak, according to their bonding abilities, so that the macrocycle could move along the thread from one side to the other in a directional way, operating as a multistable molecular shuttle.
View Article and Find Full Text PDFSelecting reactions and reactants using a switchable rotaxane organocatalyst with two different active sites.
Chem Sci
January 2015
School of Chemistry , University of Manchester, Oxford Road , Manchester , M13 9PL , UK . Email: ; http://www.catenane.net.
The activation mode of a rotaxane-based organocatalyst with both secondary amine and squaramide catalytic units can be switched with acid or base. The macrocycle blocks whichever of the catalytic sites it is positioned over. The switchable rotaxane catalyst generates different products from a mixture of three building blocks according to the location of the macrocyclic ring in the rotaxane.
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