Impact of peripheral alkyl chain length on mesocrystal assemblies of G2 dendrons

Unique sphere-packing mesophases such as Frank-Kasper (FK) phases have emerged from the viable design of intermolecular interactions in supramolecular assemblies. Herein, a series of C-n-G2-CONH2 dendrons possessing an identical core wedge are investigated to elucidate the impact of peripheral alkyl chain lengths (C-n) on the formation of the close-packed structures. The C-18 and C-14 dendrons, of which the contour lengths of the periphery L-p are longer than the wedge length L-w, assemble into a uniform sphere-packing phase such as body-centred cubic (BCC), whereas the C-8 dendron with short (L-p < L-w) corona environment forms the FK A15 phase. Particularly in the intermediate C-12 and C-10 dendrons (L-p approximate to L-w), cooling the samples from an isotropic state leads to cooling-rate-dependent phase behaviours. The C-12 dendron produces two structures of hexagonal columnar and sphere-packing phases (BCC and A15), while the C-10 dendron generates the A15 and sigma phases by the fast- and slow-cooling processes, respectively. Our results show the impact of peripheral alkyl chain lengths on the formation of mesocrystal phases, where the energy landscape of the dendrons at L-p/L-w approximate to 1 must be more complex and delicate than those with either longer or shorter peripheral alkyl chains.