Electrochemically Controlled Formation/Dissociation of Phosphonate‐Cavitand/Methylpyridinium Complexes

Abstract

The phosphorus-bridged cavitand 1 self-assembles very efficiently in CH2Cl2 with either the monopyridinium guest 2+ or the bispyridinium guest 3(2+). In the first case a 1:1 complex is obtained, whereas in the second case both 1:1 and 2:1 host-guest complexes are observed. The association between 1 and either one of the guests causes the quenching of the cavitand fluorescence; in the case of the adduct between 1 and 3(2+), the fluorescence of the latter is also quenched. Cavitand complexation is found to affect the reduction potential values of the electroactive guests. Voltammetric and spectroelectrochemical measurements show that upon one-electron reduction both guests are released from the cavity of 1. Owing to the chemical reversibility of such redox processes, the supramolecular complexes can be re-assembled upon removal of the extra electron from the guest. Systems of this kind are promising for the construction of switchable nanoscale devices and self-assembling supramolecular materials, the structure and properties of which can be reversibly controlled by electrochemical stimuli.

Molecular Recognition with Ditopic Cavitand Re Complexes

“…The same conclusion was derived in the related case of the complexation of methyl viologen by two monotopic tetraphosphonate cavitands. [17] Similar results were obtained when the monotopic guest 8 was used in a titration with the ditopic Re complex 6 ( Figure 3). As expected, a Job's plot analysis of the system revealed a 1:2 host/guest stoichiometry, and the fluorescence titration in CH 2 Cl 2 gave a K ass value of Scheme 4.…”

“…[16] In the case of methyl viologen, the binding of the first tetraphosphonate cavitand to the ditopic guest does not hamper the association of the second one and the two association constant values obtained for each of the N-CH 3 binding sites are close to that reported for the complexation of the monotopic guest. [17] In this paper we report the synthesis of a whole series of cavitands bearing increasing numbers of phosphonate moieties at their upper rims, as well as the corresponding Re-based ditopic complexes. Their complexation properties towards both the monotopic and the ditopic N-methylpyridinium salts illustrated below have been explored.…”

Polymerization with Ditopic Cavitand Monomers

“…As a first step in this direction, we demonstrated hierarchical self-assembly on silicon with cavitands, amenable to polymeric scale-up [48]. The second is embedding cavitand monomers into covalent polymers to induce specific properties such as molecular level miscibility of immiscible polymers [49] or trigger phase segregation upon specific external stimuli [50].…”

Host–Guest‐Driven Copolymerization of Tetraphosphonate Cavitands

“…The corresponding homopolymers featured guest-triggered reversibility, template-driven conversion from linear to star-branched forms and responsiveness to electrochemical stimuli. [16] Herein we introduce cavitand-based supramolecular copolymers in which the host and guest functionalities are present on two different species: 1) ditopic hosts (AA) with two tetraphosphonate cavitands covalently attached at their lower rim, and 2) ditopic guests (BB), in which flexible ethylene oxide chains of different length are functionalized with two N-methylpyridinium end groups (Scheme 1). The formation of linear and cyclic supramolecular species with an AABB copolymerization motif was investigated by using different techniques: the influence of the monomers structures on the thermodynamic parameters of polymerization was analyzed by isothermal titration calorimetry (ITC); the linear polymer structure and relative chain length were determined by using X-ray analysis and viscosity measurements, respectively.…”

“…The designed monomers were cavitands bearing four inward‐facing PO groups at the upper rim and a single N ‐methylpyridinium unit at the lower rim. The corresponding homopolymers featured guest‐triggered reversibility, template‐driven conversion from linear to star‐branched forms and responsiveness to electrochemical stimuli 16…”