Département de chimie moléculaire

The domain of sol. metallopolymers (i.e., polymers spontaneously obtained from the self-assembly of metal ions and polytopic bridging ligands) is promising for the construction of novel materials with perspectives in magnetic, redox, optical, electrochromic, or mech. properties. We report the prepn. and characterization of metallo-supramol. gels based on a multitopic cyclam bis-terpyridine platform (CHTT) that are representative of a second generation of mol. gels exhibiting "intelligent" properties. The systems were characterized by UV-visible spectroscopy, cyclic voltammetry, viscometry, rheol., and small-angle neutron scattering (SANS). A basic anal. of the viscosity taking into account the interplay of hydrodynamic vs. Brownian motions of 1D species is proposed. SANS data demonstrate the formation of rod-like species whose radius R and aspect ratio f = L/R were extd. Rheol. features are typical of weak gels having storage moduli of more than 1 order of magnitude weaker than for ordinary mol. organogels. These new mol. materials exhibit interesting properties: (i) chemosensitivity, with the gelation being dependent on the type of metal, stoichiometry M/CHTT, solvent, and counterion; (ii) electrosensitivity: the Co(II)/CHTT system can be electrochem. and reversibly commuted between the gel (red) and liq. (green) states; and (iii) mech. sensitivity, with the system being able to cycle from weakly to highly viscous states upon fast application/suppression of a shearing stress. [on SciFinder(R)]