Supramolecular structural diversity among first-generation hybrid dendrimers and twin dendrons

Hybrid dendrimers, obtained by complete monofunctionalization of the peripheral amines of a zero-generation polyethyleneimine dendrimer, provide structurally diverse lamellar, columnar, and cubic self-organized lattices that are less readily available from other modified dendritic structures. The reaction of tris(2-amino-ethyl)amine (TREN) with 4-dodecyloxybenzimidazolide provides only the corresponding zero-generation TREN dendrimer. From the mixture of tri- and disubstituted TREN derivatives obtained from first-generation self-assembling dendritic imidazolides, the hybrid dendrimer and a twin dendron could be separated, purified, and characterized. The hybrid dendrimers display smectic, columnar hexagonal (Phi(h)), and cubic (Pm (3) over barn) lattices. The TREN twin dendrons, on which only two peripheral amines have been acylated, exhibit centered-rectangular columnar (Phi(r-c)), Phi(h), and Pm (3) over barn lattices. The existence of a thermoreversible Phi(h)-to-Pm (3) over barn phase transition in the first-generation hybrid dendrimers and twin dendrons is exploited to elucidate an epitaxial relationship between the two mesophases. We postulate a mechanism by which the transition proceeds. The thermoreversible Phi(h)-to-Pm (3) over barn phase change is accompanied by optical property changes that are suitable for rudimentary signaling or logic functions. This structural diversity reflects the quasiequivalence of flat-taper and conical self-assembling dendrons and the ability of flexible dendrimers to accommodate concomitant conformational and shape changes.