A Molecular Chameleon: Chromophoric Sensing by a Self-Complexing Molecular Assembly

Abstract

A color change from purple to green takes place on addition of tetrathiafulvalene (TTF) to the macrobicyclic receptor 1 , which is composed of a cyclobis(paraquat-p-phenylene) tetracation that shares one of its paraphenylene rings with a 1,5-naphthoparaphenylene-[36]crown-10 macrocycle. The TTF molecule forces the macrobicycle to turn inside out (see schematic drawing below) and displaces the self-complexed 1,5-dioxynaphthalene ring system from the center of the tetracationic cyclophane.

Mechanically selflocked chiral gemini-catenanes

“…In mechanically selflocked bicyclic structures, one of the incorporated macrocycles is often de-threaded from another macrocycle by aromatic ring tumbling 23 24 . If such de-threading took place in our molecules, the proton signals of the octamethylene chain would coalesce in 1 H NMR spectra.…”

“…In contrast, the covalently linked single-component locked molecules, which may be called mechanically selflocked molecules (MSMs) 19 , have sporadically been reported. Typical examples of MSMs include pseudo[1]rotaxane 20 21 22 , pseudo[1]catenane 23 24 , pretzelane 25 26 , double-lasso rotamacrocycle 27 28 and molecular figure-of-eight 29 . Compared with the well-established MIMs, however, the construction of higher-order MSM systems still remains a challenge, mainly due to the lack of a convenient general synthetic route and the tremendous obstacles in both synthesis and characterization.…”

Advancements and strategic approaches in catenane synthesis

“…So far, the efficacy of π–π interaction templates was magnificently demonstrated by the synthesis of a constellation of donor–acceptor catenanes based on CBPQT 4+ with variations in their topologies under kinetic or thermodynamic control. Typical representative catenated structures included linear catenanes, with a representative example of Olympiadane 105 , 118 composed of a linear arrangement of five interlocked macrocycles; pseudo[1]catenanes 106 , 119 wherein the interpenetrated polyether ring and CBPQT 4+ were covalently linked via a shared phenylene unit; handcuff catenanes 107 , 120 with the illustrated instance relying upon the attractions between the π-donating tetrathiafulvalene-bridging bis-macrocycle and a π-accepting ring (Fig. 37).…”

The Story of the Little Blue Box: A Tribute to Siegfried Hünig

“…A diverse family of topologically distinct donor-acceptor MIMs comprised of CBPQT 4 + has been made (Figure 9) by employing either kinetic or thermodynamic approaches, including a) rotacatenanes, [137] with the illustrated example consisting [138] of a fused pillar [5]arene/naphtho [36]crown-10 macrobicyclic core and an imidazolium-based dumbbell, b) [3]pseudocatenanes or handcuff catenanes, [139] comprising πdonating macrocyclic polyethers fused to a central TTF core, c) side-chain poly [2]catenanes, [140] with the illustrated example consisting of polyurethane as the backbone, d) bis [2]catenanes, comprising two CBPQT 4 + rings fused to a flexible linker [141] or a central phenylene unit, [142] e) a cyclic bis [2]catenane, with two catenanes connected together by a covalent linker, [143] f) a side-chain poly [2]rotaxane with polyacrylate as the backbone, [144] g) tripodal [4]rotaxanes, reminiscent of G1 dendrimers, [116,145] h) branched catenanes possessing a combination of linear and radial links, [99,146] i) a [3]catenane, which comprises a fused triple-torus polyether catenated by two CBPQT 4 + rings, [147] j) a pseudo [1]catenane, where the interlocked polyether macrocycle is fused to a phenylene unit in CBPQT 4 + , [148] k) [1]rotaxanes, [149] in which the rods that thread through CBPQT 4 + are fused to the encircling rings, l) a molecular figure-of-eight, in which the rod is anchored to opposite ends of an encircling ring, [150] and m) oligorotaxanes [151] in which CBPQT 4 + rings thread onto polyether-bridged DN oligomers, causing the thread to fold into an extended stack of alternating π-donors and πacceptors. Many other donor-acceptor MIMs, such as pretzelanes, [152] polyrotaxanes, [153] and poly [2]catenanes [154] are not dis...…”