Liquid-crystalline self-organization of isocyanide-containing dendrimers induced by coordination to gold(I) fragments.

Dendritic polyisocyanides can be considered as promising polytopic ligands to generate a great diversity of metallodendrimers due to the ability of the isocyanide moiety to bind to various transition metals. Here, new isocyanide-containing dendrimers and their corresponding polynuclear gold complexes have been prepared, [G(i)(NC)(Z)] and [G(i)(NCAuR)(Z)], respectively, where G(i) is a poly(phenyl ether) dendrimer, i is the generation number (i = 0, 1, or 2), Z is the number of peripheral groups (Z = 3 x 2(i)), and AuR are the surface groups ([R = Cl, C[triple bond]C-C(6)H(4)-OC(12)H(25), C[triple bond]CC(6)H(2)(OC(12)H(25))(3)]. The compounds are derived from a highly flexible phenyl ether-based dendritic core, G(i), having the general formula G(0) = C(6)H(3)(OC(11)H(22)OC(6)H(4)-)(3), G(1) = C(6)H(3)OC(11)H(22)OC(6)H(3)(OC(11)H(22)OC(6)H(4)-)(2), G(2) = C(6)H(3)OC(11)H(22)OC(6)H(3){OC(11)H(22)OC(6)H(3)(OC(11)H(22)OC(6)H(4)-)(2)}(2)), growing from the trivalent phloroglucinol and with undecylene aliphatic spacers between each branching benzene ring and end-functionalized by isocyanide groups. As in their monomeric model counterparts, stable liquid-crystalline phases are induced upon complexation of the AuR gold moieties at the branch termini. The nature of the anionic ligand R promotes the appearance of smectic or columnar mesophases, the formation of which are governed by steric and dipolar interactions. Based on X-ray diffraction experiments, models describing the supramolecular organization of these metallodendrimers into smectic and columnar mesophases are proposed: columnar phases result from the one-dimensional stacking of molecular disks made of self-assembled supermolecules in oblate cylindrical conformation, while the smectic phases form by the lateral two-dimensional registry of the supermolecules in antiparallel head-to-head prolate conformation.