Rotaxane-Encapsulation Enhances the Stability of an Azo Dye, in Solution and when Bonded to Cellulose

Abstract

The groups of Cram and Warmuth have shown that exotic high-energy intermediates such as cyclobutadiene, orthobenzyne, and cycloheptatetraene can be stabilized by encapsulation inside calixarene-based cages. [1] These results inspired us to attempt to encapsulate and stabilize more mundane species such as dyes [2] and conjugated polymers [3] by synthesizing rotaxanes [4] in which the reactive p system of the dye or polymer is protected inside the cavity of a macrocycle. We have previously reported the synthesis of azo dye rotaxanes; [2a±c, 5] however, two key questions remained unanswered: a) Does encapsulation improve the longevity of the azo chromophore? b) Does encapsulation detrimentally prevent the dye from binding to surfaces? Here we address these issues by reporting an efficient synthesis of a Figure 4. A TEM photograph and an SAED pattern of a cross section of a layer overgrown on a sodalite {111} substrate. a) The substrate is sodalite {111} prepared by mechanical polishing. The cancrinite crystals grow perpendicular to the sodalite {111} substrate. b) An SAED pattern recorded along the sodalite [12 Å 5 Å ] zone axis. Spots due to cancrinite and sodalite are observed and indexed. c) A composite electron-diffraction simulation along the sodalite [12 Å 5 Å ]/cancrinite [2 Å 112] zone axis. The spots resulting from superposition of diffracted beams from sodalite and cancrinite crystal planes are circled.

Strategies for the Synthesis of Enantiopure Mechanically Chiral Molecules

“…69 Anderson and co-workers later reported the formation of a CD-based [2]rotaxane as a single mechanical epimer. 70 Moving beyond static stereogenic units, Anderson and co-workers reported the stereoselective synthesis of co-conformationally chiral [3]rotaxane 15 and [2]rotaxane 16 (Figure 4A, iii). 71 Stoppering of the host-guest complexes formed between a bis-diazonium salt and a-CD produced rotaxanes 15 and 16, both of which contain a centrosymmetric axle and so express co-conformational mechanical planar chirality.…”

Ring‐to‐Thread Chirality Transfer in [2]Rotaxanes for the Synthesis of Enantioenriched Lactams

“… Schematic representations of: A) a pair of mechanically planar rotaxanes ( enantiomers ) and one example of a mechanically planar ligand used in Au I catalysis; [11] B) two orientational mechanostereoisomers and an example of a α‐CD‐based orientational isomer having multiple stereocenters at the ring; [15] C) orientational mechanostereoisomers with a single stereogenic center, and a general representation of an isomer having just one stereogenic center at the ring ( this work ).…”

Ring‐to‐Thread Chirality Transfer in [2]Rotaxanes for the Synthesis of Enantioenriched Lactams

“…Although such MIMs are probably contemplated as orientational isomers, due to the cone shape of its ring component, they are better qualified as mechanically planar chiral diastereoisomers. Thus, cyclodextrins have been extensively employed for the selective assembly of chiral oriented rotaxanes [15–21] or as nanoreactors for performing asymmetric processes in their cavity [22–26] . Having these precedents in mind, we envisaged that polyamide macrocycles, quite habitual ring components of [2]rotaxanes, incorporating a chiral carbon atom, could also be used to develop synthetically useful chirotopic environments (Figure 1C).…”