The Role of Fiber Agglomeration in Formation of Perylene-Based Fiber Networks

The agglomeration of self-assembled fibers of π-conjugated molecules is crucial to the formation of low-molecular-weight supramolecular gels. However, identification of the in situ spectroscopic signatures of fiber agglomeration has remained a challenging endeavor. Here, we use a combination of chiroptical techniques, namely circular dichroism (CD), magnetic circular dichroism (MCD), and fluorescence-detected circular dichroism (FDCD), to investigate the agglomeration of self-assembled fibers of a chiral low-molecular-weight gelator, l-alanine-substituted perylene imide bis(n-butyl) ester (PIBE). Surprisingly, we find that agglomerated PIBE fibers exhibit an opposite CD signature in comparison to the isolated PIBE fibers. In contrast, the MCD and FDCD responses do not change during the agglomeration process, revealing that the local structure in the individual fibers is unperturbed. Using Brownian dynamics simulations, we conclude that the effective charge on the fibers dictates the agglomeration process and that the final geometry of the agglomerated fibers is marked by crossed nodes.