Exerting control of self-assembly pathways via morphological switching and patterning in amino-acid-based benzene-1,3,5-tricarboxamide conjugates

Small structural changes to benzene-1,3,5-tricarboxamide (BTA) dictate its self-assembly behavior and morphological outcome. Functionalization with an α-amino acid close to the BTA core, which also possesses a terminal terpyridine (tpy) unit, led to a robust gel in the case of glycine, whereas monodisperse, solid microspheres formed in the case of alanine, phenylalanine, and leucine. The self-assembly pathways of the chiral and achiral BTAs are orthogonal and both microspheres and gel fibers independently assemble in the same medium. Further hierarchical self-assembly results upon addition of lanthanide ions (i.e., Eu(III) and Tb(III) that emit at long wavelengths with long excited-state lifetimes) that crosslink the microspheres through coordination, whereas coordination within the gel led to a change in morphology toward microspheres, as well as the formation of hierarchical superstructures. The chirality of the BTA influences helicity of the assembly and the resulting enantiomeric conformation around the lanthanides, evidenced by circularly polarized luminescence.